SURFACE TE NSION DRIVEN FABRI CATION OF THREEessay.utwente.nl/69504/1/MSc. report J....

Author: JDate: 28 Versie: 3.

M.Sc. The Group: TCommitteIng J.W. BReferencPeriod: N

SURFA

anarthanan Saugust 2010 .0

esis University

Transducer Scee: Prof.Dr.irBerenschot, De: Nov. 2009 – au

ACE TE

undaram

y of Twente

cience and Tecr. M. ElwensDr. J. Snoeijer.

ugust 2010

NSION

DI

chnology Grospoek, Dr.ir.

DRIVEN

IMENSI

up L. Abelmann

N FABRI

ONAL M

n, Dr.ir. N.R.

CATION

MICROS

Tas, Dr.ir. J

N OF TH

STRUCT

J.W. van Ho

HREE‐TURES

onschoten,

Surface tension driven fabrication of three‐dimensional microstructures

TABLE OF CONTENT 1 Introduction.................................................................................................................................................... 3

1.1 motivation ............................................................................................................................................. 3

1.2 Outline of this project ............................................................................................................................ 4

2 Theory ............................................................................................................................................................ 5

2.1 Capillary forces ...................................................................................................................................... 5

2.1.1 Folding with capillary forces .............................................................................................................. 6

2.1.2 Effects of different contact angles .................................................................................................. 12

2.1.3 Varying the structural dimension .................................................................................................... 14

3 Folding templates ......................................................................................................................................... 15

3.1 Method ................................................................................................................................................ 15

3.1.1 Design of the templates .................................................................................................................. 15

3.1.2 Cleanroom processes ...................................................................................................................... 17

3.1.3 Experimental setup ......................................................................................................................... 18

3.2 Results ................................................................................................................................................. 19

3.2.1 First results folding structures with more the 2 flaps. .................................................................... 19

3.2.2 Results of folding of prism ............................................................................................................... 19

4 Folding with different contact angle ............................................................................................................ 22

4.1 method ................................................................................................................................................ 22

4.1.1 white light measurement using lateral scanning interferometry ................................................... 22

4.2 Results ................................................................................................................................................. 24

5 Varying design of the prisms ........................................................................................................................ 25

5.1 Problem definition ............................................................................................................................... 25

5.1.1 Torsion in folding ............................................................................................................................. 25

5.1.2 Folding without symmetry .............................................................................................................. 26

5.1.3 Varying contact area ....................................................................................................................... 28

5.1.4 Lifting objects out of the plane ....................................................................................................... 28

5.2 Results ................................................................................................................................................. 29

5.2.1 Torsion in folding ............................................................................................................................. 30

5.2.2 Folding without symmetry .............................................................................................................. 30

5.2.3 Varying contact area ....................................................................................................................... 32

5.2.4 Lifting objects out of the plane ....................................................................................................... 34

6 Conclusion .................................................................................................................................................... 36

6.1 Recommendation ................................................................................................................................ 37

7 Bibliography ................................................................................................................................................. 38

8 Appendix – process documents ................................................................................................................... 39

Surface te

1 INT

1.1 M

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scale of t

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same tec

the figure

will be dr

FIGURE 1 S

IN SIZE FRO

In this re

nitride lik

folding m

of water

We all kn

surface te

an silicon

ension driven

TRODUCTI

MOTIVATION

ntion of the t

r. Even more,

e capacity tha

r, but also by

con chip. This

s technology i

gy creates sm

these mechan

hones, which

chnology as co

e. This planar

ramatically inc

SCANNING ELECT

OM 0.5 MM TO 1

eport we will d

ke the ancient

method has to

drops to fold

now the smal

ension of the

n nitride temp

fabrication o

ON

transistor led

everyone can

an a supercom

the invention

s technology is

is Micro Elect

mall mechanic

nical devices.

h react to mo

omputer chip

r disposition o

creased if the

TRON MICROSCO

MM. (1)

discuss a met

t Japanese tec

be as such th

the structure

ll insects that

water. This sa

plate into a str

of three‐dimen

to a revoluti

n have a comp

mputer of the

n of the whole

s now mature

ro Mechanica

cal systems w

These system

vement, or h

s, all the com

of the structu

re was a way

OPE IMAGE OF A

thod to create

chnique called

hat a small str

s. This is beca

t walk on the

ame force can

ructure like a p

nsional micros

on which ma

puter in his po

e 70’s. This a

e process that

e and is being

al Systems, als

which interact

ms are used in

have a compa

mponents lay

ures limits the

to create ME

SPIDER MITE ON

e three dime

d origami. The

ructure can be

ause capillary

e water, this i

n be used to fo

pyramid.

structures

de possible t

ocket nowada

all was possib

t was needed

used to deve

so called MEM

electrically.

n sensors and

ss function. T

planar on the

e possibilities

MS devices th

N A POLYSILICON

nsional struct

e structures a

e folded. The

forces becom

s possible du

old structures

hat almost ev

ays, the conte

ble not only b

to make mill

lop new types

MS. As the na

Figure 1 gives

can also be f

These structu

e surface. Also

of this techn

hat stood up fr

N MEMS GEAR‐T

tures by foldin

re of course o

method we u

me dominant a

e the capillar

s. One single d

very househo

emporary mob

by the inventi

lions of transi

s of technolog

me already im

s an impressi

found in cont

ures are made

o this can bee

nology. The po

rom the surfa

TRAIN. SPIDER M

ng flat pieces

on a micro sca

use is the capi

at smaller scal

ry force also

drop is enoug

ld owns a

bile phone

ion of the

stors on a

gies.

mplies this

ion of the

temporary

e with the

en seen in

ossibilities

ace.

MITES RANGE

s of silicon

ale, so the

llary force

es.

called the

h to fold a


1.2 OUTLINE OF THIS PROJECT

In this project we are going to fold a template made in silicon nitride using standard IC technology and fold this

into three dimensional structures. Folding will be done by using the capillary forces of water drops. At first we

will determine the theoretical forces working on these structures when a drop of water is placed on them, and

assess whether these structures can be made to fold. And if they fold, will these structures stay folded? We will

determine the folding rate and how different surface parameters will influence this rate. The structures and

theoretical model are already created and determined.

The folding of the structures led to new effects which we will investigate experimentally. Effects that posed

new questions were that of the structures stayed folded after folding and that the structures kept folding

seamlessly every single time. We will look at the stiffness of hinges, the geometry, the manner in which we

dispense water and the surface characteristics of the structures. Getting a clear picture of the forces that play

role.

All these experiments will give enough data to give an understanding on the folding of silicon nitride structures.

In addition to all this we will try to lift the logo of the university out of the plane, and try dispense a drop of

water through a channel, instead of dispensing water off hollow fiber used in the experiments

We will discuss the created model of folding in chapter 2. In this chapter the theory behind capillary folding and

how this force can be harnessed for folding structures. The setup and the method how we did these

experiments are elaborated in chapter 3.1. Different experiments are spread out over different chapters and

have sub results. This is the chronological order in which the experiments were done. Results of the Simple

folding experiments can be found in chapter3.2, experiments with variation of the structure parameters can be

found in chapters 4.2 and 5.2. This is followed by an overall conclusion and recommendations.

Surface te

2 TH

2.1 CA

The force

capillarie

regardles

everywhe

water str

that wet

with a for

This all ca

the same

in the flu

their sha

minimiza

FIGURE 2 LI

Every liqu

where th

liquid air

give an a

factor. Th

example

walk on w

inner wal

ension driven

HEORY

APILLARY FO

e we use to

s. When thes

ss of gravity.

ere in their sy

riders to walk

glasses stick t

rce of 10N, so

an be explain

e liquid. Molec

uid as illustrat

pes to minim

tion of the int

IQUID AIR INTER

uid is specific

he liquid react

interface. The

ngle to the sh

hese forces be

of this scaling

water. Or if w

ll of the straw

Air

Liquid

fabrication o

ORCES

fold structure

e tubes are p

This phenom

stem. But the

k on water. Sa

to flat surface

o hold a glass p

ed by the fac

cules on the s

ted in Figure

mize the expos

terface manif

FACE, TOP MOLE

how it reacts

ts to the solid

ese interface

hape of the dr

ecome domin

g is a small in

we would look

w, and if we loo

of three‐dimen

es is the sam

placed in a bat

menon is use

e same force c

ame force is r

es. A drop of w

plate of 1 kg

ct that molecu

surface will ha

2. This is an

sed surface. T

ests in formin

ECULE IS NOT HA

to the solid s

d is called to s

forces depen

roplet on a so

ant when we

nsect that can

k at a straw w

ok at a shorel

nsional micros

me force that

th of water, t

ed by plants

can be witness

responsible fo

water with a

ules in liquids

ave half less m

unfavorable e

The exposed s

ng of droplets.

APPY BECAUSE IT

surfaces. This

solid liquid in

d on the liqui

lid plane. This

scale down, a

n walk on wat

with water we

ine we will no

structures

can be seen

the water will

to get wate

sed as surface

or sticky hair

radius of 1 cm

want to be s

molecules surr

energy state.

surface is also

.

IS NOT SURROU

has a lot to do

terface, and

id. A contact a

s angle relates

and thus beco

ter using surfa

will see that

ot see this effe

in really nar

tend to flow

er with nutri

e tension, this

when coming

m can hold tw

urrounded by

rounding them

This is the re

o called the li

NDED BY SAME K

o with surface

how the liqui

angle measure

s directly to th

ome favorable

ace tension, b

the water sta

ect. As shown

rrow tubes, a

into the tube

ients from th

s phenomena

g out of the s

wo glass plates

y other molec

m than other

eason that flu

iquid air inter

KIND OF MOLEC

e tension. The

d reacts to ai

ement of the

he solid liquid

e In this appli

but an elepha

ands higher a

n in Figure 3.

also called

e upwards

he soil to

is used by

shower or

s together

cules from

molecules

uids adjust

rface. This

ULES

e interface

ir is called

liquid will

d interface

cation. An

ant cannot

gainst the


FIGURE 3 DIFFERENCE BETWEEN WATER IN A TUBE AND LARGE WATER BODIES. THERE IS A CLEAR EFFECT ON THE EDGE OF THE TUBE

BUT THERE NONE ON THE EDGE OF A SHORELINE

When drop is placed on a surface the drop can form a thin film or become a drop. This depends on the surface

and liquid characteristics. This is quantified by the contact angle θc.

When a drop tends to become a thin film on a surface we call this fully wetting. When considering water it will

fully wet a SiN surface. This is the material our templates are made of. Other liquids will react differently to this

surface and may form a droplet. In this case the contact angle of the drop with the surface can be measured by

viewing the drop.

2.1.1 FOLDING WITH CAPILLARY FORCES It was proven recently (2) that when a drop of water is put on a thin sheet of polymer, the polymer would

spontaneously wrap. This is due to that the drop will try to minimize the water air interface, the capillary force

will fold the polymer sheet as shown in Figure 4. As you can see in the figure the sheet of plastic is on a

millimeter scale. After folding the water will totally evaporate. As already explained in the previous chapter this

effect should become larger when we scale down to micrometers.

Water between shorelines

Water in a vertically

placed capillary

millimeters

meters

Surface te

FIGURE 4 W

FOLDING O

There wa

solder. Pl

(3). This w

hinges. F

using wat

By using

in Figure

productio

the prod

object as

most righ

same size

ension driven

WRAPPING OF D

ON A MILIMETER

as a demons

lacing solid so

was scaled do

or folding it w

ter.

water on tem

5(a) to (d). T

on by convent

uction proces

s shown in Fig

ht top templat

e, namely 50µ

fabrication o

ROP OF WATER

SCALE.

tration of as

older on the h

own to scale o

would be gre

mplates the TS

The design of

tional lithogra

sses can be f

gure 5(b). The

te results in th

µm.

of three‐dimen

WITH SQUARE A

sembling mil

hinges and me

of 100nm. Pro

at if we could

ST group alrea

the template

aphic process

found in chap

e top center t

he cube as sh

nsional micros

AND TRIANGULA

limeter sized

elting the sold

oblem with th

d combine th

ady folded var

es are shown

es, and there

pter 3.1. Fold

template resu

own in Figure

structures

R SHEETS OF PDM

structures u

der made the

his technique

e scale of the

rious structure

in Figure 5(a

efore it is desi

ing the long

ults in the sha

e 5 (d). The bla

MS (POLYDIMETH

using capillary

e structures st

is that the so

e last techniq

es (4) with the

). These temp

gned in plana

structure res

pe as shown

ack bar in the

HYLSILOXANE ) E

y effects usin

tand up from

older will be l

que and the b

e use of wate

plates are des

ar manner. M

sults in a pris

in Figure 5 (c

ese figures are

EXAMPLE OF

ng molten

the plane

eft on the

benefits of

er. As seen

signed for

ore about

m shaped

c) and the

e all of the

Surface te

FIGURE 5 (A

ZOOM IN O

The prism

made. Be

just take

and the v

figure the

thickness

and then

transition

different

shown in

We will m

structure

progressi

model wh

angle tha

circle. Th

the hinge

ension driven

A) DESIGN TEMP

ON THE HINGES (D

m structure is

ecause a prism

the front view

volume of wa

e flaps are be

s. Structures c

opens, or the

ns are shown

angles and t

Figure 9 is sh

make the follo

e is fully wett

ion of folding

here we again

at flaps make

e angle of thi

e, t is the thick

fabrication o

PLATES (B) FOLDE

D)

s specially de

m structure is

w. By doing th

ter on the str

nt slightly. Th

can behave in

e hinges are l

n in figure 8

he water men

hown in Figure

owing assump

ting and the

we need to d

n take the fro

when folding

s piece of this

kness of the h

of three‐dimen

ED PRISM (C) OP

signed to ver

much longer

his simplificat

ructure. A fron

e hinge is dep

two manners

loose enough

and Figure 9

niscus is show

e 5 (b). An arti

tions, the edg

drop covers t

define the follo

ont view of a p

g. The curvatu

s circle is θ. F

inge; if we tak

nsional micros

EN AND FOLDED

rify the two d

than that it is

tion the variab

nt view of the

picted as a th

s, either the h

so that the s

9. In these fig

wn as a thin l

ist impression

ges of the dro

the whole su

owing dimens

prism to simp

ure of the men

Figure 6 shows

ke l0 as a part

structures

D HALF A DODECA

dimensional t

s wide, we can

bles we can d

e template of

inner line, l0 i

hinges are too

structure can

gures the flap

line. The end

n of the folded

oplet is pinned

urface of the

sions as show

plify the mode

niscus on the

s the bending

of a circle the

AEDER (C) FOLDE

heoretical mo

n neglect long

istinguish are

a prism is sh

s the length o

o stiff and the

fold complete

ps are shown

result of the

d prism is show

d down on the

structure. To

wn in Figure 10

el. W is the w

structure can

g of a hinge, w

en R is the rad

ED AND OPENED

odel the grou

gitudinal dime

e the angles o

own in Figure

of the hinge a

e structure fol

ely. These tw

n schematical

folding prog

wn in Figure 7

e edges of the

o form a mod

0. This figure s

width of the fla

n be seen as a

where l0 is the

dius of this cir

D CUBE WITH

up already

ension and

f the flaps

e 6, in this

nd t is the

ds al little

o types of

ly making

ression as

7.

e flap. The

del of the

shows the

aps, φ the

a part of a

e length of

rcle.

Surface te

FIGURE 6 B

FIGURE 7 A

ension driven

ENDING A THE H

ARTISTS IMPRESS

R

fabrication o

HINGE, WHERE l0

ION OF A FOLDE

t

l0

of three‐dimen

IS THE LENGTH O

D PRISM

nsional micros

OF THE HINGE, T

structures

THE THICKNESS A

AND φ THE ANGGLE THAT THE HIN

NGE MAKES


figure 8 schematic overview of the front view of a prism while Folding and opening progresses

Figure 9 schematic overview of the front view of a prism while Folding progresses

Surface te

FIGURE 10

THE MENIS

THE MENIS

A droplet

bending t

interface

the bend

results in

written a

Where

volume a

with:

FIGURE 11

If we min

how the

w

ension driven

THE VARIABLES

SCUS AS A PART O

CUS WHEN ENOU

t placed on t

the flaps. The

of the drople

ding stiffness.

a bending en

s

is the

and in our sim

PHASE DIAGRAM

nimize the ene

equilibrium a

w

θ

fabrication o

FOR THE MODEL

OF A CIRCLE THE

UGH WATER IS E

the surface w

e total energy

et. The bendin

E is the Youn

nergy per unit

. If we n

balance betw

mplification th

M OF THE EVOLUT

ergy in resp

angle change

φ w

of three‐dimen

L, w IS THE WIDT

N θ IS THE ANGL

VAPORATED AN

will tend to m

of the system

ng energy of

ng’s modulus

t length as:

normalize this

ween mechan

he surface S a

sin 2

TION OF EQUILIB

ect to resu

depends on t

w

nsional micros

TH OF A FLAP, φ

LE OF THE TIP OF

D THE STRUCTUR

minimize the

m consists of

a curved plat

and υ the Po

. Th

per unit leng

nical bending f

as constant, t

and

BRIUM STATES A

lting in an equ

the stiffness p

w

θ

structures

φ IS THE ANGLE T

F THIS PART. RIGH

RE DID NOT FOLD

liquid air inte

the elastic en

e can be writ

oisson’s ratio.

he surface ene

th:

forces and ca

the relation o

is the norm

S FUNCTION OF V

uilibrium angl

parameter .

φw

THAT THE FLAP T

HT FIGURE SHOW

D COMPLETELY

erface and de

nergy in the h

ten as and

Bending the

ergy of the liq

pillary forces.

of the angles

malized cross s

VOLUME

e of . As w

For a certain

TAKES, WHEN CO

WS THE CONCAV

eform the str

inges and the

d where

flaps over th

uid air interfa

. When taking

and can

section.

we can see in

stiffness of t

ONSIDERING.

E SHAPE OF.

ructure by

e liquid‐air

is

he angle φ

ace can be

g the total

be found

Figure 11,

the hinges


the flaps bend due to evaporation of the droplet to a certain angle and then open again after attaining the

equilibrium angle , this is shown in Figure 11 as the line where . For a certain lesser stiffness the

flaps fold completely into a prism. The in this case is reached when completely folded. This is depicted as

the line . The stiffness is the threshold stiffness value where we get the transition from folding and

opening into folding completely. For angles smaller then 2 3 the flaps will not close completely and will

open again after reaching this angle. At the angle =2 3 the flaps close completely this corresponds

to √3. Reducing any further will result in a not larger than 1.39 rad, leading to a discontinuous

transition in the diagram. This means that the structure will abruptly reopen again.

In Figure 11 we see that for the interface shape transitions from a convex in to a concave shape. On the

transition point the angle of the interface will be zero ( 0), from this we can find . has a minimum for

=2 3 and this results in √3. Note that there is a gap between after that =2 3 . According to

this model after the gap the structure should fold open.

2.1.2 EFFECTS OF DIFFERENT CONTACT ANGLES Previous experiments we used the fully wetting surfaces. This means that the contact angle of the water with

the surface of the structures is pinned down at the edges and the angle that the water makes with the edge is

totally dependent on the volume of water.

For not fully wetting surface the curvature of the meniscus is dependent on the contact angle this is shown in

Figure 12. Looking at this figure one might observe that there is an dependency between θ and θc. This

dependence is clearly illustrated in Figure 13. We can deduce from this figure that α=180o‐90o‐φ‐½ θ and

α=90o‐θc, this results in ½ θ=θc – φ. Substituting this in the energy function formulated in the previous chapter

will result in

. This means that now the energy is not dependent on θ but

dependent on θc.

FIGURE 12 SCHEMATIC OVERVIEW OF THE MODEL AND VARIABLES WHEN THE LIQUID IS NOT FULLY WETTING . θC IS THE CONTACT

ANGLE, W IS THE WIDTH OF A FLAP, φ IS THE ANGLE THAT THE FLAP TAKES, WHEN CONSIDERING THE MENISCUS AS A PART OF A CIRCLE

THEN θ IS THE ANGLE OF THE TIP OF THIS PART. RIGHT FIGURE SHOWS THE CONCAVE SHAPE OF THE MENISCUS WHEN ENOUGH WATER

IS EVAPORATED AND THE STRUCTURE DID NOT FOLD COMPLETELY.

φ w

w

w

θ

φw

w

w

θ

θc

θc

Surface te

It was alr

fixed con

the maxim

then see

previous

FIGURE 13

FIGURE 14

ension driven

ready proven

ntact angle it

mum point of

how this ma

model the qu

HOW CONTACT A

MAXIMUM EQU

φeq,ma

φ

fabrication o

that folding s

is not necess

f the progress

ximum equili

uestion arises

ANGLE IS RELATE

ILIBRIUM ANGLE

½ θ

θc

w

½ w

ax1

φeq,max2

φeq,max3

of three‐dimen

structures are

ary to perfor

sion lies, the m

brium angle c

whether the e

ED TO θ

ES FOR DIFFEREN

φ

α

nsional micros

e following th

m all the ang

maximum equ

changes for d

experimental

NT CONTACT ANG

structures

e theoretical

gle measurem

uilibrium angle

ifferent conta

results will fo

GLES

model, so to

ents. We nee

e φeq , as show

act angles θc.

ollow this mod

see the effec

ed to determ

wn in figure 1

in Figure 15.

del.

ct of the a

ine where

4. We can

As in the

Surface te

FIGURE 15

2.1.3 VExperime

folded. S

fact that

we need

FIGURE 16 G

Another

end up se

effect to

design in

a view on

ension driven

HOW THE MAXIM

VARYING THEents done rev

EM picture sh

structures sta

change the ar

GLUING RESIDU

effect is that

eamless over

the limit by i

such a way t

n the force tha

fabrication o

MUM ANGLE CHA

E STRUCTURA

veal new phe

how that ther

ay folded. To

re over which

IN THE SEAM OF

the structure

nanometers.

ntroducing ne

hat an additio

at play a role

of three‐dimen

ANGES DUE TO T

L DIMENSION

nomena whic

e are some m

get a better i

the flaps are

F A FOLDED CUBE

e fold seamle

This is a huge

ew designs wh

onal torsion fo

in this folding

nsional micros

THE CHANGE OF C

N ch need to b

material on the

dea about th

glued togeth

E

essly every sin

e accuracy tha

hich will test

orce is neede

g mechanism.

structures

CONTACT ANGLE

be examined

e edge of the

e amount of f

er.

ngle time. The

at is created b

different kind

d to fold seam

E

more. The st

fold. This mig

force that is h

e flaps move

y the capillary

ds of distortio

mlessly. This e

ructures that

ght be the ca

holding the fla

over microm

y force. We pu

ons. We will c

extra hurdle w

t fold stay

use of the

aps folded

meters and

ushed this

hange the

will give us


3 FOLDING TEMPLATES

3.1 METHOD

3.1.1 DESIGN OF THE TEMPLATES Now we have explained the theoretical model we need to design and construct the templates to verify the

model. Design of the templates were done in CleWin and are depicted in Figure 17 and Figure 18. There were

different sets of structures with different hinge types. We varied the hinges so that we can experiment with

different stiffness’s. There are two types of hinges, one type is the solid version, this is a hinge made out of

150nm of SiN. The second type of hinge is also made of 150nm SiN but they are not solid, 8 small hinges

connect the flap with a length of 10µm. Both these designs are shown in Figure 18. Also the width of these

hinges are varied. Every single type of hinge will result in a different . The varieties of this set is listed in Table

1.

The of the perforated hinges are proportional to length of the hinges holding the flaps together divided by

the total length of structure. So how bigger the holes in the length, how smaller the factor .

Typeofhinge Hingewidth(µm) Flapwidth(µm) ß

Solid 3 80 5,08

Solid 5 80 3,05

Solid 8 80 1,90

Solid 15 80 1,02

Solid 5 50 4,88

Solid 8 50 3,05

Solid 12 50 0,20

10µmhinges 10 80 0,24

10µmhinges 20 80 0,12

10µmhinges 6 80 0,27

10µmhinges,5µmgap 25 80 0,07 TABLE 1 TYPES OF DIFFERENT HINGES USED FOR DIFFERENT SETS OF STRUCTURES

Surface te

FIGURE 17

PYRAMID

FIGURE 18

ension driven

DIFFERENT STRU

DESIGN PRISM S

fabrication o

UCTURE TEMPLAT

TRUCTURE (A) SO

of three‐dimen

TES, FIRST ONE I

OLID HINGE (B) H

nsional micros

IS A CUBE, THREE

HINGE WITH HOL

structures

E SIDED PYRAMI

LES

D, HALF A DODEECAEDER AND A

FOUR SIDED


3.1.2 CLEANROOM PROCESSES As already discussed the templates are created using contemporary cleanroom processes. The process

document for creating these structures can be found in the appendix. Here we can see that the following takes

place. On a silicon wafer a SiN layer of 1µm is deposited and etched away by plasma etching, leaving grooves

for the hinges on the surface of the Silicon wafer. On top of this another SiN layer is deposited of 100 nm. This

layer is also deposited between the flaps forming the hinge. Everything but the templates are ethed away,

leaving a SiN template on the surface of the silicon wafer. The total structure is then isotropically underetched,

the left over Silicon form the pillar on which the template rest. Simplified step by step overview is given in

Figure 19.

Blank Silicon wafer

Adding SiN layer

Etching away the hinges

Adding SiN layer

Etching away everything but the template

underetching

FIGURE 19 SIMPLIFIED STEP BY STEP OVERVIEW OF THE PROCESS NEEDED TO CREATE TEMPLATES

Surface te

3.1.3 To get th

just abou

created t

couple of

50µm and

big strong

The setup

relation t

probe m

structure

FIGURE 20

Using thi

that take

measured

three tim

were com

the mode

ension driven

EXPERIMENTA

e structure to

ut 300µm in w

that can dispe

f hundreds of

d a larger one

g fiber, to form

p consists furt

to the table. P

akes it possi

e. On the micr

PHOTO OF THE S

s setup we w

es place. We m

d frame by fr

mes the angle,

mpensated fo

el as discussed

fabrication o

AL SETUP o fold, one mu

width, and th

ense small am

f micrometers

e with an inne

m the nozzle.

ther of a tabl

Previously me

ble to move

oscope a ccd

SETUP WITH THE

will add a drop

measured the

rame by hand

, the average

r the viewing

d in the previo

of three‐dimen

ust get a drop

e drop must

mount of wate

s in diameter.

er diameter of

The big fiber

e with a micr

entioned fiber

the fiber m

camera is plac

IMPORTANT CO

p of water on

angles that t

d using a com

was taken of

angle and pl

ous chapter u

nsional micros

p of water on t

not be much

er through a n

To do so we

f 50µm, the b

is then conne

oscope. This

r is fixed on a

icrometers a

ced, the feed

OMPONENTS HIG

the set of str

the flaps make

mputer softwa

f these three

lotted in a gra

sing these exp

structures

the template.

bigger than

nozzle which i

uses hollow

igger one is st

ected to a pum

microscope is

a probe and fe

t a time and

is recorded o

HLIGHTED

ructures and c

e with the ba

are. For every

measuremen

aph. The ques

perimental re

As explained

that. Therefo

s small enoug

fibers, on wit

tronger. The t

mp.

s placed at an

ed by a pump

d maneuver t

n the comput

create a set o

se of the stru

y flap on ever

nts as the actu

stion is wheth

sults.

d before the te

ore the setup

gh to generate

th an outer di

thin fiber is sli

n angle of 60 d

p with demi w

the tip just a

ter.

of movies of t

ucture. The an

ry frame we

ual angle. The

her we can re

emplate is

has to be

e drops of

ameter of

id into the

degrees in

water. This

above the

he folding

ngles were

measured

ese angles

econstruct

Surface te

3.2 R

3.2.1 First expe

not repro

remarkab

Some str

Confirmin

other wa

structure

puddle do

their orig

held its fo

If water i

the flaps

bounce b

FIGURE 21 T

3.2.2 Initial fold

heat of th

folded co

movies ta

shown in

flap is me

measurem

structure

We did s

well. This

edges we

ension driven

ESULTS

FIRST RESULTeriments on t

oducible in th

ble.

uctures had s

ng that the fo

y around. Wh

e floated on th

ownward. So

ginal position.

orm even whe

is added to th

will fold dow

back to their o

TRIANGLE PYRAM

RESULTS OF Fding of prisms

he lights mad

ompletely. The

aken showed

Figure 22. Th

easured. The

ments were t

e folded fully.

see some phe

s happened e

ere pulled tog

fabrication o

TS FOLDING ST

these were no

he amount of

stiff hinges du

olding angle w

hen administe

he surface of t

we had down

This last obs

en the water w

he cavity the f

wn as shown

original state.

MID WITH WATE

FOLDING OF P

s was a succe

e the drop ev

e set with the

that the ang

he measureme

measuremen

taken per fla

enomena wort

every time. Th

ether by the c

of three‐dimen

TRUCTURES W

ot that succes

time I took t

ue to design a

would increase

ering an amou

this puddle. W

nward folding

ervation cont

was evaporate

flaps will floa

in Figure 21.

ER IN CAVITY, (B)

PRISM ss. It is fairly e

vaporate it wa

e array of 10µ

gle of the flap

ent is done at

ts are compe

p and averag

th mentioning

he meniscus o

capillary force

nsional micros

WITH MORE TH

ssful. Although

to do the exp

and didn’t fold

e when the h

unt of water in

When this pud

. After all the

tradicts the ob

ed. See Figure

t on the surfa

. After all the

THE WATER IN T

easy to place

as clear that t

m hinges fold

ps increased

t both flaps, a

ensated for th

ged. Table 2 i

g, the structu

of water guid

es, and the str

structures

HE 2 FLAPS.h the group h

periment. The

d into the full

hinges are less

nto the cavity

ddle dried up

water had ev

bservation of

e 5d.

ace of the wa

e water is eva

THE CAVITY IS PU

a drop on the

he flaps bend

ded all comple

until they clo

and the angle

e angle of the

is similar to T

ures that folde

ed both edge

ructure folds s

had successful

ere were som

structures bu

s stiff. Folding

below the st

the flaps follo

aporated the

the cube that

ater and when

aporated in th

ULLING THE FLAP

e structure wit

ded and at som

etely. Frame b

osed seamless

of the flaps in

e microscope

Table 1 but w

ed completely

es of the flaps

seamlessly.

lly folded a cu

me phenomen

ut they bende

g action also

ructure the fl

owed the surf

flaps jumped

t was folded.

n the water e

he cavity the

PS OF THE TEMPL

th the setup.

me type of hi

by frame analy

sly. Measurem

n relation to t

. On every fra

we added wh

y, folded seam

s to each oth

ube it was

a that are

ed a little.

works the

aps of the

face of the

d back into

This cube

vaporates

flaps will

LATE DOWN

While the

nges even

ysis of the

ments are

the center

ame three

hether the

mlessly as

er. So the

Surface te

FIGURE 22

Other hi

measurem

structure

FIGURE 23

2

4

6

8

10

12

14

16an

gles in degrees

0

5

10

15

20

25

30

35

angles in degrees

ension driven

MEASUREMENT

nges which

ment done o

e behave in wh

MEASUREMENT

0

20

40

60

80

00

20

40

60

0

0

5

0

5

0

5

0

5

20 25 3

fabrication o

OF FULLY FOLDIN

were solid a

n a structure

hich manner.

OF FOLDING AN

20

30 35 40 45

of three‐dimen

NG, TAKEN FROM

nd were nar

e that doesn’t

In this case a

D OPENING, TAK

40

frame

5 50 55 60

frame

nsional micros

M A MOVIE THAT

rrow were to

t fold comple

maximum an

KEN FROM A MO

60

es

65 70 75

es

structures

T PROGRESSED 5

oo stiff for f

etely. The tab

gle of 32 degr

VIE THAT PROGR

80

80 85 90 9

FRAMES PER SEC

fully folding.

le beneath th

rees is achieve

RESSED 5 FRAME

100

95

COND.

Figure 23 s

his figure sho

ed by both fla

ES PER SECOND

angle ri

angle le

angle

angle

hows the

ows which

aps.

ght flap

eft flap

rightflap

left flap


Typeofhinge Hingewidth Flapwidth(µm) ß foldingSolid 3 80 5,08

Solid 5 80 3,05

Solid 8 80 1,90

Solid 15 80 1,02 Fully

Solid 5 50 4,88

Solid 8 50 3,05

Solid 12 50 0,20 Fully

10µmhinges 10 80 0,24 Fully



10µmhinges,5µmgap

25 80 0,07 Fully

TABLE 2 FOLDING OF DIFFERENT STRUCTURES

We can convert the measurements done frame by frame, a time progression, in to a measurement done on

variation of the water volume. This is exactly how we setup the theoretical model and these measurements will

give the measurement point for constructing the graph shown in Figure 24.

FIGURE 24 MEASURED PHASE DIAGRAM OF THE EVOLUTION OF EQUILIBRIUM STATES AS FUNCTION OF VOLUME (4)

It is striking that the simplification of the model has so little influence that the actually measured values

correspond almost exactly to the model. Simplifications like totally ignoring a whole dimension do not make

the theoretical model deviate from the measured values.

0 0.5 1 1.5 2 2.50

0.5

1

1.5

2

normalised volume

eq (

rad

)

= 1.8

= 1.5

= 0.07 = 0.8


4 FOLDING WITH DIFFERENT CONTACT ANGLE

4.1 METHOD

To determine the effects of a defined contact on the folding of the structure we need to use liquids that have a

defined contact angle on SiN. Or we need to change the surface of the SiN so that water has a contact angle on

the this surface. After drafting a list of liquids with different contact angles we came to a conclusion that not all

liquids were appropriate to use in my setup due to safety reasons.

Changing the property of a surface can be done by depositing a layer of Fluor Carbon. Fluor Carbon is

hydrophobic and the thickness of the layer determines the amount of hydrophobeness and thus the contact

angle of the liquid on this surface. A layer of FC can be deposited by using a Reactive Ion Etching chamber (RIE)

(5).

The results of some reference experiments done on an empty silicon en SiN surface are depicted in Figure 25.

We decided to do the folding measurements by putting the samples in the RIE chamber between 0 and 10

minutes.

FIGURE 25 VARYING OF CONTACT ANGLE DUE TO TIME OF FC DEPOSITION

Changing the surface into hydrophobic means that the drop of water coming from the fiber might cling to the

fiber and not want to stick to the surface. To overcome this we have coated the fiber also with FC, this is done

by submersing the fiber into liquid FC. The fiber did not clog by this layer of FC.

4.1.1 WHITE LIGHT MEASUREMENT USING LATERAL SCANNING INTERFEROMETRY To change the contact angle we chose to deposit a FC layer onto the structures. The question rised whether the

flaps on the structure would bend to the extra force asserted by the elasticity of the FC layer. To measure

whether this is the case, whitelight measurements using lateral scanning interferometry were conducted on

the structures. This will give a clear indication of the orientation of the flaps. The interferometer measures the

horizontal distance of the surface.

0

20

40

60

80

100

120

60 30 10

Angle (degrees)

Time (minutes)

Si : Contact angle water

SiN : Contact angle water

Surface te

FIGURE 26

Figure 26

angle of t

not addit

ension driven

INTERFEROMETE

6 shows one o

the flaps of 0

tionally increa

fabrication o

ER MEASUREMEN

of the actual m

.06 degrees. T

ase the angle o

of three‐dimen

NT OF THE FLAPS

measurement

This we concl

of the flaps.

nsional micros

S

t done on the

luded as negl

structures

structures. T

ectable. This

here was an a

means that a

average incre

adding a layer

ase of the

of FC will


4.2 RESULTS

We did the same folding experiments as in the previous experiments, and this time we looked only to the

maximum of each set. We got similar results as shown in Figure 22 and Figure 23, and from these results we

looked at the maximum angle attained. We managed to do this experiment for two different hinge stiffness’s.

The results of the measurement are depicted In Figure 27. The solid line is the theoretical and expected

progression of to variation of the contact angle . The crosses are the measured points.

FIGURE 27 MAXIMUM ANGLE FOR DIFFERENT CONTACT ANGLES (4)

Again it is striking that we get measurements that fit the model despite of the simplifications. We actually

conclude that capillary properties doe follow the model, and thus this process is predictable and useful for

fabrication of three dimensional structures on this scale.

0 0.5 1 1.5 20

0.1

0.2

0.3

0.4

0.5

0.6

c (rad)

max

(ra

d)

Surface te

5 VA

5.1 P

5.1.1 TWe have

hurdles. O

lateral di

shown in

structure

rear whe

folding p

close sea

FIGURE 28 S

ension driven

ARYING DE

ROBLEM DE

TORSION IN Fseen that ev

One of these

rection. In ot

Figure 28 wil

e would close

re the structu

rocess Other

mlessly, and m

STRUCTURE WIT

D1

D2

fabrication o

SIGN OF T

EFINITION

FOLDING very time the

hurdles is to

her words if

l the structur

seamlessly, a

ure was D1 in

scenario for

may open aga

TH DECREASING F

of three‐dimen

THE PRISM

prism fold th

see whether

we design fla

e fold seamle

at the front w

width, the h

this design is

ain.

FLAP WIDTHS

nsional micros

MS

e fold seamle

the capillary

aps of the pris

ssly. This wou

where the wid

inge would b

s that the hin

structures

essly. To put t

forces will ov

sm with decre

uld result in a

dth is D2 the h

e pressed dow

nge would no

this to the tes

vercome the r

easing flap wi

folding like sh

hinges would

wnwards. add

ot give way an

st we have m

rotational for

idth over the

hown in Figur

stretch out a

ding extra stra

nd the struct

ade some

rces in the

length as

e 29 if the

and at the

ain on the

ure won’t

Surface te

FIGURE 29

The diffe

not be an

5.1.2 Next set

shown in

And if th

meet hal

same, in t

ension driven

DISTORTION OF

rence betwee

ny influence o

FOLDING WIT

of structures

Figure 30, th

ey do they ca

fway of the o

the second ca

Rear vie

Fro

fabrication o

THE HINGES

en D1 and D2

f other effect

THOUT SYMM

have flaps of

he width D2 is

an fold in two

other flap as s

ase the angles

ew

ont view

of three‐dimen

are not more

s other than t

ETRY different wid

s larger than D

o ways, the e

shown in Figu

s will be differ

nsional micros

e than the hin

the bending a

dth, the left fla

D1. Again we

nds of the fla

ure 31. In the

rent, ɸ1 is not

structures

ge width of 5

and stretching

ap will have a

will test whe

aps meet each

first case bot

t equal to ɸ2.

µm. This is ch

g of hinges.

a smaller widt

ther these fla

ht other, or o

th the angles

hosen so that

th then the rig

aps will fold se

one end of th

of the flaps w

there will

ght one as

eamlessly.

e flap will

will be the

Surface te

FIGURE 30 S

FIGURE 32 (

FIGURE 31

ension driven

STRUCTURE WIT

(A) STANDARD 4

POSSIBLE OUTCO

D1 D

fabrication o

TH DIFFERENT FLA

45 ANGLE EDGE (B

Option

OME FOR FOLDIN

D2

of three‐dimen

AP WIDTHS

B) FLEXIBLE EDGE

n 1

NG A STRUCTURE

nsional micros

E

E WITH DIFFEREN

structures

NT FLAP WIDTHS

optiion 2

Surface te

5.1.3 VThird typ

structure

the conta

hinge stif

structure

structure

We will c

is varied f

FIGURE 33 S

FIGURE 34 S

5.1.4

d

d

ension driven

VARYING CONpe of structur

es tend to stay

act surface of

ffness and co

es folding and

es together.

create three se

from 20 µm to

STRUCTURE WIT

STRUCTURE WIT

LIFTING OBJE

fabrication o

NTACT AREA res will have

y folded desp

f the flaps and

ontact area co

d opening aga

ets of three d

o the full 390µ

TH VARYING CON

TH VARYING CON

ECTS OUT OF T

d

d

of three‐dimen

a varying co

pite of the ela

d we will vary

ombination w

ain. This will g

different conta

µm.

NTACT SURFACE

NTACT SURFACE F

THE PLANE

d

d

nsional micros

ntact surface

astic forces in

y the elasticit

will be on the

give us inform

act angles. Ev

FOLDED

structures

e. Previous ex

the hinges. T

ty of the hing

transition of

mation of the

very set consis

d

d

d

d

xperiments ha

To test this ph

es . We will t

structures al

e quantity of t

sts of twenty v

ave shown th

henomena we

try to determ

ways staying

the forces ke

variations of d

d

d

hat folded

e will vary

mine which

folded to

eeping the

d where d

Surface te

Last but n

created s

from the

will be et

This desig

to perfor

etching n

the etcha

underetc

FIGURE 35 S

FIGURE 36 W

5.2 R

ension driven

not least we w

structures wit

plane and we

tched free fro

gn has a smal

rm well. With

not to free the

ant to reach i

hing. This stru

STRUCTURE WIT

WHERE IT CAN G

ESULTS

fabrication o

will try to lift

h the letters o

e will have a m

m the underly

ll hole in the e

hout the hole

e right flap fro

n the center

ucture suppor

TH A LETTER

GO WRONG WITH

of three‐dimen

a structure o

of the univers

micro billboar

ying silicon, an

extension tha

the addition

om the cente

of the arm. I

rts the flaps th

H UNDERETCHING

nsional micros

of the surface

sity on the fla

rd. In the sam

nd thus hang

at is holding t

to the struct

r flap as show

n this figure t

hat lay on top

G

structures

using this fol

ps. When the

e time that th

freely like the

he letter. This

ture which ho

wn in Figure 3

the white sha

p.

lding action. F

e flaps fold the

he flaps are u

e flaps.

s hole is made

olds the lette

36. The hole w

ape is the stru

For this exper

ese letters wi

nder etched t

e for the und

er can cause t

will make it po

ucture that is

riment we

ll be lifted

the letters

er etching

the under

ossible for

s left after


5.2.1 TORSION IN FOLDING Folding experiments confirm seamless folding. This means that the hinges stretch and fold where needed to

facilitate this. We can conclude that the capillary forces are large enough to force the hinges.

5.2.2 FOLDING WITHOUT SYMMETRY Folding with flaps of different widths resulted in some remarkable results. As already stated in the previous

chapter the folding could have gone in two ways. From the measurements of the optical microscope it looked

like that the folding occurs in the manner as depicted as option 2 in Figure 32b. Further experiments revealed

the full extent of the mechanics in this folding.

In the very first measurements we saw that the flaps will take a maximum angle and fold back when the hinges

were stiff enough. This is due the torque on the flaps. We have determined that the capillary effect administers

a force on the flaps, the folding occurs not when the this force is larger than the counter acting elastic force of

the hinges, but when the width of the flaps times the capillary force is larger than the elastic force. This means

a fully folding structure won’t fully fold when the flaps are made less wide. This is shown in Figure 37.

Another way to explain this is by using the model we used in the previous chapter. We have a factor which is

dependant on the width of the flaps w: . This means that when we change the w we change the

folding property of the flap. In this case in such a way that it will not bend through to close.

FIGURE 37 CAPILARY FORCE VS ELASTICITY FORCE, THIS SIMPLIFIED MODEL SHOWS HOW TORQUE IS RELATED TO THE LENGTH OF THE

FLAP.

We have witnessed that a smaller flap takes a maximum angle, while the normal and larger flap keeps folding

and then crashing into the flap with the maximum angle. The larger flap doesn’t have the width to fold

seamlessly over the a flap that would stop the folding. This shown in frames taken from a measurement in

Figure 38. Here you can see that the right flap stays on the same angle while the left flap keeps on folding, in

the end it will collapse and not stay folded.

T=Fcapilary∙L1

L1

L2

T=Felastic∙L2

Central flap

Folding flap

Surface te

FIGURE 38 A

Although

which ap

previous

maximum

FIGURE 39 S

ension driven

ASYMETRIC FOLD

the width dif

pear to fold n

example, und

m angle, this is

SEM PICTURE OF

fabrication o

DING, RIGHT FLA

fference betw

normally (Figu

der a SEM the

s shown in Fig

F ASYMETRIC FOL

of three‐dimen

AP REACHES A MA

ween flaps in t

ure 39), where

it is clear tha

gure 40.

LDED STRUCTUR

nsional micros

AXIMUM ANGLE

his figure is d

e the differen

at the left flap

E

structures

AND STOPS FOL

ramatic, this p

ce in width ar

crashed into

DING

phenomena o

re not that dr

the right flap

occurs also in

ramatic as sho

p that stood st

structures

own in the

teady on a

Surface te

FIGURE 40

FLAP.

5.2.3 VThis expe

contact a

stayed fo

solid hing

µm2. Onl

structure

µm2 the l

area of 7

used in th

This mea

Where

µm this i

µm leads

and gives

SEM pict

middle th

ension driven

CRASHING PHEN

VARYING CONeriment consis

area and every

olded for all c

ge resulted in

ly three type

es revealed tha

ast 7 structur

720 µm2 and w

he calculation

n that for the

is an equilibri

s to 4.4∙10‐5 J

s us a measure

ures of folded

he flaps will no

fabrication o

NOMENA, RIGHT

NTACT AREA sted of three

y variation wa

ontact areas.

n all structure

es of structur

at due to the

res open at 68

we assume th

ns.

energy

10 and w

um point, this

J/m2 . This is t

e for the force

d structure w

ot stay closed

of three‐dimen

T FLAP REACHED

sets, with thre

as repeated te

So we can co

es opening fo

res fell in thi

manufacturin

80 µm2. Becau

hat the deviat

with θ = 2/3

s means that

the minimum

es that the glu

with reduced c

.

nsional micros

A MAXIMUM A

ee different h

en times in te

onclude that t

or all contact

is category. R

ng process the

use the majori

tion is due to

12

π ≈2 we get

a structure th

m energy per s

uing substanc

contact area

structures

ANGLE AND THE

hinge types. Ev

n rows. The h

the hinges we

area’s except

Repeating thi

ere is a deviat

ity of the stru

production p

Ub=4∙10‐5 J/m

hat folds seam

square area n

e has to asser

is shown in F

LEFT FLAP CLOSE

very set had t

hinges with ho

eren’t stiff en

t for contact

s experiment

ion. The first t

cture only sta

process we wi

m2. For a conta

mlessly over t

eeded to kee

rt.

Figure 41. For

ED INTO THE ST

twenty variati

oles in them f

nough. The se

area’s larger

t for the ten

three rows op

ay closed with

ill take this va

act area of 72

he whole leng

ep the structu

r any larger h

EADY RIGHT

ons of the

folded and

t with the

than 720

n identical

pen at 720

h a contact

alue to be

20 µm x 1

gth of 800

ure folded,

ole in the

Surface te

FIGURE 41

There wa

middle of

need a la

FIGURE 42

We made

Where w

length) .

height wh

The disto

requiring

expressio

the lengt

dimensio

the same

ension driven

FOLDED STRUCT

as an unexpec

f the folded f

rge force.

BENDING IN THE

e an estimatio

w(x) describes

E is the Youn

hen taking the

ortion is appr

g 0 0,

on for

h of the flaps

. We meas

ons we get 602

e of the whole

fabrication o

URE WITH SMAL

cted effect wh

flaps for very

E MIDDLE OF FOL

on by taking u

the deformat

g’s modulus

e crosssection

roximated by

s. Figure 43 sh

sure a maxim

2 N/m for q. T

e width. If yo

of three‐dimen

LLER CONTACT AR

hile doing the

large gaps. A

LDED STRUCTURE

sing the Euler

tion along the

and I is the s

n of a flap, 1 µ

a 4th order p

0,

. Here u is t

hows the w(x)

mum distortio

This model ass

u look carefu

nsional micros

REA

ese experimen

A SiN flap of 8

ES

r‐Bernoulli eq

e x direction o

second mome

µm and b is th

polynomial:

0, 0 0

the distortion

) when the va

on of 2.4µm

sumes that th

lly you might

structures

nts. As shown

0 by 725 µm

uation:

of the flap, q is

ent of area. In

e width of the

0,

n, L is the leng

alues are filled

m from Figure

e whole flap b

see that in F

in Figure 42

is very rigid.

s the distribut

this case

e flap: 80µm.

. Solvi

,

gth of the flap

d in. Now that

e 42. Filling

bends as a wh

igure 42 the b

there is bend

To deform th

ted load (forc

, wher

ing this funct

, we

ps and x the p

t w(x) is know

in the value

hole, and the

bending on th

ding in the

his flap we

ce per unit

re h is the

tion when

acquire

osition on

wn we find

es for the

bending is

he edge is

Surface te

larger tha

flaps. We

resulting

510,5 N/

really larg

FIGURE 43 A

1572 N/m

We need

related to

look at th

the flap,

using the

whole len

µm2) we

If we com

constant

seperatio

1572 N/m

5.2.4 As you m

letter wit

images of

Figure 44

underetc

ension driven

an the bendin

e redo the cal

in a q of 419

m Multiplying

ge for such sm

APPROXIMATION

m2. This is a m

to keep into

o the distance

he torque on

510.5 N/m w

e formula for

ngth of 800µm

get 0.83∙107N

mpare this fo

which is bet

on is the rough

m2. This is a m

LIFTING OBJEmight have see

th the same e

f the lifted let

4b shows the

hing through

fabrication o

ng on the hin

culation for t

9N/m. We tak

g this with th

mall device.

N OF THE DISTOR

uch smalle th

account the t

e over the fla

the right loca

we get a force

energy Ub , w

m and then d

N/m2 for the ad

orce with van

tween 10‐19 a

hness betwee

uch smalle th

ECTS OUT OF T

en on the cov

experimental

tters.

hole we mad

this hole can

of three‐dimen

ge side. This

he amount be

ke the average

he length of t

RTION

han the adhesi

torque that is

ap. So when w

ation of the st

of 36.5 N/m

where ∙eviding by th

dhesive force

der Waals fo

and 1020, and

en to plates an

han the adhesi

THE PLANE er and in Figu

setup as used

e in the desig

also be seen i

nsional micros

is to be expe

ending as it is

e value as go

he structure

ion force, and

asserted on t

we compare t

tructure. If we

at L2. To calcu

∙ . So this g

e minimal su

needed to ke

orce, which is

d h is the sur

nd in our case

ion force, and

ure 44b, this e

d in the whole

gn so that und

in this figure a

structures

ected because

s on the hinge

od estimation

of 720 µm re

d we must con

the structure.

two different

e take the fac

ulate the torq

gets us a F of

rface that nee

eep the flaps t

s given as

rface seperati

e we will assu

d we must con

experiment w

e project we m

deretching wo

as I have high

e on this side

e side of the f

n of the force

esults in a for

nclude that ot

Figure 37 sho

forces on this

tor times t

que we need t

7.5 N/m . W

ed to keep th

together.

(6), wh

ion between

me it 15nm. T

nclude that ot

as a success a

made Scannin

ould free the

lighted it with

the hinges p

flaps, which i

e asserted on

rce of 0.37 N

ther forces pla

ows how mom

s structure w

he force at th

to calculate t

When taking th

he flaps toget

here A is the

to plates. Th

This results in

ther forces pla

as well. After

ng Electron M

arm. The effe

h a white circl

ull on the

s 1.67µm,

the flaps:

. Which is

ay a role.

mentum is

we need to

he edge of

he energy

his for the

her(720x1

Hamaker

he surface

a force of

ay a role.

lifting the

Microscope

ect of this

e.

Surface te

FIGURE 44 (

If lifting f

pull the le

FIGURE 45 (

FIGURE 46 T

ension driven

(A) HOLE IN THE

fails the struct

etter to the fl

(A) LIFTING OF LE

TOP VIEW OF LIF

fabrication o

ARM WAS NEED

ture won’t ret

oor of the cav

ETTER FAILED (B)

FTER LETTERS

of three‐dimen

DED FOR ETCHING

turn to its orig

vity, and gluin

) LIFTED LETTER O

nsional micros

G FREE THE ARM

ginal position

ng the letter to

O

structures

M WITH THE LETT

because wate

o the floor. Re

ER (B) LIFTED 'LE

er will come u

esults of this is

ETTER ‘TWENTE’

under the stru

s shown in Fig

ucture and

gure 45a.


6 CONCLUSION In earlier work it was already proven that folding with capillary forces is a easy and predictive way to create

three dimensional micro structures. But these works were with liquids that solidified and were left behind in

the structure. The decision was made to overcome this by using demi water for folding. Which would

evaporate totally and leave nothing behind. A theoretical model was made for predicting the folding behavior

of the structures.

From experiments it was clear that the folding mechanism followed the theoretical model almost to the letter.

Experiments done with variation of the contact angle by changing the surface characteristics of the structures

revealed the folding progression followed the deviations as expected in the theoretical model. Experiments

with varying contact angles revealed that the capillary force is 70 times larger than the force asserted by the

hinges. Making them ideal for folding.

The choice for using water was made because in theory nothing will be left behind in the structures because

the water evaporates. In our experiments it became clear that a residue is left in the seam of the structures.

Further experiments revealed that this residue has an adhesive force of 0.83∙107 N/m2. Which is much larger

than the van der Waals power, which is 1571 N/m2. So we can conclude that other forces play a role in this

adhesion.

We need to determine what this consists of. One might think of a combination of adhesive forces of the

material with for example electrostatic forces. Further experimentation is needed.

Experiment with contact area variation resulted also in an unexpected bending of the flaps. As shown in Figure

42. We estimated the force needed to bend a flap as 0.37 N. Illustrating once again that the capillary forces are

really large.

When the structures fold completely, every single time the flaps of the structure folds seamlessly. To test this

further new structures where created with varying flap widths over the length. Still the flaps folded seamlessly,

meaning that the hinges were stretched out on one end and folded on the other end. Concluding once again

that the capillary forces are really large.

Experiments were done trying to lift added structures to the normal folding structure. It was no problem to lift

this added structure from the plane. We made a micro billboard for “University Twente” and lifted this out of

the plane. This opens new opportunities we could try create more elaborate self‐assembling structures which

work on this principle.

Surface te

6.1 R

There are

the struc

keeping t

together.

any other

der Waal

We have

every sing

nozzle lik

the midd

experime

FIGURE 47 T

FIGURE 48 T

Close up

created h

of water

the drop

channel s

ension driven

ECOMMEND

e still some un

cture from fol

this structure

. Folding expe

r forces keepi

s interaction.

to consider n

gle template

ke that of an i

dle of the str

ents. Figure 48

TEMPLATE OF A

TOPVIEW OF STR

p images mad

have a diamet

on the chann

of water to

so that gravity

fabrication o

DATION

nanswered qu

ding back. W

es from foldin

eriments with

ng these stru

new ways of d

is not a good

nkjet printer.

ructure. For t

8 and Figure 4

CUBE WITH A CH

RUCTURES WITH

e by a SEM s

ter of 34µm. I

nel did not res

get through

y will generate

of three‐dimen

uestions. Like w

We have to an

ng back. It is

hout this subs

cture togethe

elivering wate

method for m

Or delivering

his last solut

49 are SEM ph

HANNEL (TOPVIEW

CHANNELS

how us the ri

nitial experim

sult in the wa

the channel,

e enough pres

nsional micros

what is the su

alyze this sub

probable th

stance need t

er. One can th

er droplets to

mass producti

g water from

tion the grou

hotos showing

W LEFT OPTICAL

idges created

ments by holdi

ater flowing t

a suggestion

ssure to get th

structures

ubstance that

bstance to ge

at more than

o be perform

ink of electro

the structure

on. We could

the bottom o

p has already

g the structure

L MICROSCOPE, S

by this proce

ing this struct

hrough the ch

n would be to

he water thro

is left on the

t a clear idea

n just the glu

med to determ

static forces,

e. Positioning

consider deli

of the structur

y made some

es from differe

SIDE VIEW ELECTR

ess is shown

ture upside do

hannel. The p

o create a co

ugh the chann

seam, which

a of the force

ue is keeping

mine whether

hydrogen bon

a fiber from t

ivering water

re through a c

e samples to

rent angles.

RON MICROSCOP

in Figure 49.

own and putt

pressure is too

olumn of wat

nels.

is keeping

s that are

the flaps

there are

nds or van

the top for

through a

channel in

do initial

PE)

The holes

ing a drop

o large for

ter on the

Surface te

FIGURE 49 C

7 BIB1. www.m

2. Capilla

Lionel Do

3. MEMS

4. Elastoc

Ondarçuh

5. Applica

1994, Sen

6. Casimi

L. Klimch

7. MATER

8. Surface

Yeatman

systems,

9. Pierre

Science+B

10. Critica

s.l. : Ame

ension driven

CHANNEL

BLIOGRAP

mems.sandia

ary Origami: S

oppler, Jose´ B

. R.R.A. Syms

capillary fabri

hu, R. G. P. Sa

ations of fluo

nsors and Act

ir and van der

hitskaya, U. M

RIALS ANALYS

e Tension‐Pow

, Victor M. B

2003.

e‐Gille de Ge

Business Med

al Review: Ad

erican Vacuum

fabrication o

HY .gov, Sandia N

Spontaneous

Bico, Benoıˆt

, E.M. Yeatma

ication of thre

anders, J. Sun

orocarbon pol

uators, Vol. 19

r Waals forces

Mohideen and

IS OF FLUORO

wered Self‐Ass

Bright and Ge

nnes, Fançoi

dia, Inc., 2003.

dhesion in surf

m Society, 199

of three‐dimen

National Labo

Wrapping of

Roman, and C

an, V.M. BRig

ee‐dimensiona

daram, M. Elw

lymers in mic

994, pp. 136‐1

s between two

V. M. Mostep

OCARBON FILM

sembly of Mic

orge M. Whit

se Brochard‐

.

face micromec

7. S0734‐211X

nsional micros

oratories SUM

f a Droplet wi

Charles N. Ba

ght, and G.M.

al microstruct

wenspoek, an

cromechanics

140.

o plates or a s

panenko. 200

MS. J. Elders,

crostructures—

tesides. Vol.

‐Wyart. Capil

chanical struc

X(97)02301‐9

structures

MMiT(TM) Tec

ith an Elastic

roud. 156103

Whitesides. 1

tures. J. W. va

nd N. R. Tas. 9

and microma

sphere lens ab

00, PHYSICAL R

H. V. Jansert

—The State‐of

12 No. 4, s.l.

llarity and W

ctures. Mabou

9.

chnologies.

Sheet. Charlo

3, s.l. : Physica

12,4, 2003.

an Honschote

97, 2010, APP

achining. Jans

bove a plate m

REVIEW A.

and M. Elwen

f‐the‐Art. Rich

: Journal of M

Wetting Pheno

udian, Roya a

otte Py, Paul

al Review Lette

en, J. W. Bere

PLIED PHYSICS

sen, H.V., et

made of real m

nspoek.

hard R. A. Sym

Microelectrom

omena. Paris

and Howe, Ro

Reverdy,

ers, 2007.

nschot, T.

LETTERS.

al., et al.

metals. G.

ms, Eric M.

mechanical

: Springer

oger T. 15,


8 APPENDIX – PROCESS DOCUMENTS

Projectnr. : Number Revision : 01Page : 1 of 23

Project : Project Rev. by : J.Sundaram : 2010‐05‐05 Author : J.Sundaram File :procesdocument approach 3.doc

Capillary origami. Approach 3. Silicon nitride structure on a silicon support with flap deviations 1. Introduction 1.1 Design description 1.2 Explanation of typical process steps 1.3 Masks 2. Mask layout (overview) 3. Process outline wafer 4. Specific design parameters 5. Procesparameters 5.1 Wafer selection 5.2 Top wafer processing 5.3 Bottom wafer processing 5.4 Anodic bonding 6. Processdata form

Projec

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1

1.1 This Hons The are ftheylengttheroverhingrelat

Figure

ctnr. : Number

ct : Project or : J.Sunda

Introduc

Design d

structure is dschoten.

flaps in thesefive differenty tend to foldth. You can e might be torcome this toe on one endtively relaxed

e 1 structure w

D1

D2

r

aram

ction

descriptio

developed o

e structures t type of strud seamlessly. see this in Fiorsion in theoroidal force d of the strucd.

with decreasing

2

on

n the structu

are shaped ductures. One So this strucgure 1 where hinges. Queor will therecture will be

flap widths

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Rev. byFile

ure defined i

differently totype of struccture is madee the width Destion is whete be a seam. Istretched ou

: 01Page

: J.Sundaram:procesdocum

n the proces

o assess diffecture will tese of flaps thaD1 is larger tther these flaIf they wouldut while the

mment approach

s document

rent aspectst torsion. What decrease inhan D2.Wheaps will closed close seamhinge on the

: 2 of 23: 2010‐0

3.doc

of J.W. van

s of folding. Then the flapsn width overen these flapse seamlessly lessly then the other end w

3

05‐05

There s fold, the s fold and he will be



Next type of structures have flaps of different width, the left flap will have a smaller width then the right one as shown in Figure 3, the width D2 is larger than D1. Again we will test whether these flaps will fold seamlessly. And if they do they can fold in two ways, the ends of the flaps meet eacht other, or one end of the flap will meet halfway of the other flap as shown in Figure 4. In the first case both the angles of the flaps will be the same, in the second case the angles will be different, ɸ1 is not equal to ɸ2.

Rear view

Front view

Figure 2 distortion of the hinges

Projec

ProjecAutho

Figure

Thirdthat phenhing

Figure

ctnr. : Number


e 3 structure w

d type of strufolded strucnomena we wes to see wh

e 4 possible ou

D1

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aram

with different fla

uctures will hctures tend towill vary the hat kind of ef

tcome for foldi

D2

ap widths

have a varyino stay foldedcontact surfaffect these va

ing a structure

Revision

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ng contact sud despite of tace of the flaariables have

with different f

: 01Page


rface. Previohe elastic foaps and we we.

flap widths

mment approach

ous experimerces in the hwill vary the e

: 4 of 23: 2010‐0

3.doc

ents have shoinges. To teselasticity of t

3

05‐05

own st this the

Projec

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Figure

The flapsfoldeedgeoverprop

ctnr. : Number


e 5 structure w

edges of thes (Figure 6 a)ed the stay foes as shown ircome unaligperly.

d

d

r

aram

with varying con

e flaps make c. This is beneolded. To tesin Figure 6 b gment and er

d

d

ntact surface

contact realleficial for thest how this pand Figure 7rrors in proce

d

d

d

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y well due toe adhesive prroperty varie7. The edges essing. Small

: 01Page


o the 45 degrroperties of tes we devisehave to be aer form facto

d

d

mment approach

rees slope onthese structud a structureat least 5µm ors will not b

d

d

: 5 of 23: 2010‐0

3.doc

n the edges oures. Ones the with flexiblin width duebe produces

3

05‐05

of the hey are e e to

d

d

Projec

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Figure

Figur

ctnr. : Number


e 7 structures w

re 6 (a) standard

r

aram

with flexible ed

d 45 angle edge

dges

e (b) flexible ed

Revision

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dge

: 01Page


mment approach

: 6 of 23: 2010‐0

3.doc

3

05‐05

Projec

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Last expefold timeand This undethe uwill m

Figure

ctnr. : Number


but not leasteriment we cthese letterse that the flapthus hang fre

design has aer etching tounder etchinmake it poss

e 8 structure w

r

aram

t we will try created strucs will be liftedps are undereely like the

a small hole i perform weg not to freeible for the e

with a letter

to lift a strucctures with thd from the pr etched the lflaps.

n the ‘arm’ tell. The additie the right flaetchant to re

Revision

Rev. byFile

cture of the she letters of tplane and weletters will be

hat is holdinion to the strap from the ceach in the ce

: 01Page


surface usingthe universit will have a me etched free

g the letter. ructure whiccenter flap asenter of the a

mment approach

g this folding ty on the flapmicro billboae from the u

This hole is mh holds the ls shown in Fiarm.

: 7 of 23: 2010‐0

3.doc

action. For tps. When theard. In the sanderlying sili

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3

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Figure

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1.3 Exam ThreFOLDGEOUND

ctnr. : Number


e 9 where it can

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lready statednecessary torrupted.

Masks

mple:

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n go wrong wit

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ma etching byhis etching teof the free sttely removed

d in the prev make a hole

needed: : Defin: Defin

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th underetching

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ious paragrae in the arm s

nition of foldnition of finanition of spac

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g

ess steps

d ) is chosen es not affect tctures by adhma underetc

ph, when usso that the u

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: 01Page


as process sthe silicon nihesion due toch under the

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tep for the uitride structuo capillary fo folding flaps

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tures deretched

: 8 of 23: 2010‐0

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underetchingure. We are aorces, since ths.

e arm and leon’t get

UN GE FO

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ctnr. : Number


Mask lay

name: maske

re above: paple = UND)

tion de

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erview)

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wafer

description

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structures (re

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green = FOLD

inside whi

Inside whiInside blacInside whi

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D;

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3. LPCVD SiRN ‐ low‐depostion rate (#depo002)

4. Lithography ‐ Olin 907‐17 (#lith057) Lithography ‐ Postbake standard (#lith009) Plasma etching SiN (Etske) (#etch004)

5. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017) Cleaning Standard (#clean003) Etching HF (1%) user made (#etch028)


7. Lithography ‐ Olin 907‐17 (#lith057) Lithography ‐ Postbake standard (#lith009) Plasma etching SiN (Etske) (#Etch 072)

8. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017) Cleaning Standard (#clean003)

9. Lithography ‐ Olin 907‐17 (#lith057) Lithography ‐ Postbake standard (#lith009) Etching HF (1%) user made (#etch028) Plasma etching of Silicon ‐ standard (Oxford) (#etch013)

10. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017)

Projec

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4

ctnr. : Number


Specific

75µ

r

aram

c design

µm

paramet

Revision

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ers

75µm

: 01Page


mment approach

75µm

: 12 of 2: 2010‐0

3.doc

23

05‐05



5 Process parameters Top wafer: p‐type, <100> oriented, DSP

5.1 Wafer selection (only a top wafer)

Step Process Process parameters Design related parameters and Remarks

1. Substrate selection ‐ Silicon <100> OSP (#subs001)

CR112B / Wafer Storage Cupboard Supplier: Orientation: <100> Diameter: 100mm Thickness: 525µm +/‐ 25µm Polished: Single side Resistivity: 5‐10Ωcm Type: p

silicon wafer

2. Cleaning Standard (#clean003)

CR112B / Wet‐Bench 131 HNO3 (100%) Selectipur: MERCK HNO3 (69%) VLSI: MERCK • Beaker 1: fumic HNO3 (100%), 5min • Beaker 2: fumic HNO3 (100%), 5min • Quick Dump Rinse <0.1µS • Beaker 3: boiling (95°C) HNO3 (69%), 10min • Quick Dump Rinse <0.1µS • Spin drying

wet chemical cleaning of the wafer

3. Etching HF (1%) user made (#etch028)

CR116B / Wet‐Bench 2 HF (1%) VLSI: MERCK 112629.500 • Quick Dump Rinse <0.1µS • Spin drying


CR125C / Tempress LPCVD new system 2007

program: SiRN01/N2 Tube: G3 • Use 5‐8 boat fillers in front and back of the boat to achieve specifications • SiH2Cl2 flow: 77.5 sccm • NH3 flow: 20 sccm

Thickness SiRN: 1000 nm



• temperature: 820/850/870°C• pressure: 150 mTorr • deposition rate: ± 4 nm/min • Nf: ± 2.18 • Stress (range): 200‐280 Mpa • Boat position 12: 200 MPa (centre of the boat) •Boat position 1: 280 MPa (front of the boat) • Uniformity/wafer: <2% • Uniformity over the boat: (20 wafers): < 8%

5. Lithography ‐ Olin 907‐17 (#lith057)

CR112B / Suss Micro Tech Spinner (Delta 20) Hotplate 120 °C: • Dehydration bake (120°C): 5min HexaMethylDiSilazane (HMDS): • Spin program: 4 (4000rpm, 20sec) Olin 907‐17: • Spin program: 4 (4000rpm, 20sec) Hotplate 95 °C: • Prebake (95°C): 90s CR117B / EVG 620 Electronic Vision Group 620 Mask Aligner: • Hg‐lamp: 12 mW/cm 2 • Exposure Time: 4sec CR112B / Wet‐Bench 11 Hotplate 120°C (CR112B or CR117B): • After Exposure Bake (120°C): 60sec Developer OPD4262: • Time: 30sec in Beaker 1 • Time: 15‐30sec in Beaker 2 • Quick Dump Rinse <0.1µS • Spin drying

Mask FOLD

6. Lithography ‐ Postbake standard (#lith009)

CR112B / Hotplate 120°C • Time: 30min

7. Plasma etching SiN (Etske) (#etch004)

CR102A / Elektrotech PF310/340 Dirty chamber Styros electrode • Electrode temp.: 10°C • CHF3 flow: 25sccm



• O2 flow: 5sccm • pressure: 10mTorr • power: 75W Etchrate SiN = 50nm/min (for VDC=‐460V) Etchrate SiN = 75 nm/min (for VDC = ‐580V) Etchrate Olin resist = 95nm/min If DC‐Bias < 375V apply chamber clean (#etch003)


CR102A / Tepla 300EBarrel Etcher (2.45 GHz) Multipurpose sytem • O2 flow: 200sccm (50%) • Power: 500W • Pressure: 1.2 mbar • Time: 10 min for 1‐3 wafers, 400 nm/min • Time: 20 min for 4‐10 wafers • End point detection by visual inspection of the plasma color. • Blue color means still photoresist on the wafer, purple means clean.


CR112B / Wet‐Bench 131 HNO3 (100%) Selectipur: MERCK HNO3 (69%) VLSI: MERCK • Beaker 1: fumic HNO3 (100%), 5min • Beaker 2: fumic HNO3 (100%), 5min • Quick Dump Rinse <0.1µS • Beaker 3: boiling (95°C) HNO3 (69%), 10min • Quick Dump Rinse <0.1µS • Spin drying

10. Etching HF (1%) user made (#etch028)

CR116B / Wet‐Bench 2 HF (1%) VLSI: MERCK 112629.500 • Quick Dump Rinse <0.1µS • Spin drying


CR125C / Tempress LPCVD new system 2007

program: SiRN01/N2 Tube: G3 • Use 5‐8 boat fillers in front and back of the boat to achieve specifications • SiH2Cl2 flow: 77.5 sccm • NH3 flow: 20 sccm

200 nm thickness SiRN (to be varied for different wafers) Note: in the first run, the thickness was 100 nm



• temperature: 820/850/870°C • pressure: 150 mTorr • deposition rate: ± 4 nm/min • Nf: ± 2.18 • Stress (range): 200‐280 Mpa • Boat position 12: 200 MPa (centre of the boat) •Boat position 1: 280 MPa (front of the boat) • Uniformity/wafer: <2% • Uniformity over the boat: (20 wafers): < 8%


CR112B / Suss Micro Tech Spinner (Delta 20) Hotplate 120 °C: • Dehydration bake (120°C): 5min HexaMethylDiSilazane (HMDS): • Spin program: 4 (4000rpm, 20sec) Olin 908‐35: • Spin program: 4 (4000rpm, 20sec) Hotplate 95 °C: • Prebake (95°C): 120s CR117B / EVG 620 Electronic Vision Group 620 Mask Aligner: • Hg‐lamp: 12 mW/cm 2 • Exposure Time: 9sec CR112B / Wet‐Bench 11 Hotplate 120°C (CR112B or CR117B): • After Exposure Bake (120°C): 60sec Developer OPD4262: • Time: 30sec in Beaker 1 • Time: 15‐30sec in Beaker 2 • Quick Dump Rinse <0.1µS • Spin drying


CR112B / Hotplate 120°C • Time: 30min

14. Plasma etching SiN (Etske) (#Etch 072)

CR102/ Electrotech PF310/340 Application: roughening of SiRN for Pt adhesion remarks: If Silicon surface is exposed to plasma us a short etch time

Mask GEOM



Sputter directly after etching step Pt layer (maximum delay time 10 min) Dirty chamber Styros electrode • Electrode : 10 °C • SF6: 30 sccm • O2: 5 sccm • pressure: 40 mTorr • Power: 60 Watt • Time: 30 sec


CR102A / Tepla 300EBarrel Etcher (2.45 GHz) Multipurpose sytem • O2 flow: 200sccm (50%) • Power: 500W • Pressure: 1.2 mbar • Time: 10 min for 1‐3 wafers, 400 nm/min • Time: 20 min for 4‐10 wafers • End point detection by visual inspection of the plasma color. • Blue color means still photoresist on the wafer, purple means clean.


CR112B / Wet‐Bench 131HNO3 (100%) Selectipur: MERCK HNO3 (69%) VLSI: MERCK • Beaker 1: fumic HNO3 (100%), 5min • Beaker 2: fumic HNO3 (100%), 5min • Quick Dump Rinse <0.1µS • Beaker 3: boiling (95°C) HNO3 (69%), 10min • Quick Dump Rinse <0.1µS • Spin drying


CR112B / Suss Micro Tech Spinner (Delta 20) Hotplate 120 °C: • Dehydration bake (120°C): 5min HexaMethylDiSilazane (HMDS): • Spin program: 4 (4000rpm, 20sec) Olin 908‐35: • Spin program: 4 (4000rpm, 20sec) Hotplate 95 °C: • Prebake (95°C): 120s CR117B / EVG 620 Electronic Vision Group 620 Mask Aligner: • Hg‐lamp: 12 mW/cm 2 • Exposure Time: 9sec

Mask UND



CR112B / Wet‐Bench 11 Hotplate 120°C (CR112B or CR117B): • After Exposure Bake (120°C): 60sec Developer OPD4262: • Time: 30sec in Beaker 1 • Time: 15‐30sec in Beaker 2 • Quick Dump Rinse <0.1µS • Spin drying


CR112B / Hotplate 120°C• Time: 30min

19. Plasma etching of Silicon ‐ release (Oxford) (#etch070)

CR102A / Oxford Plasmalab 100 ICPApplication: release of membranes and cantilever SLE = poly‐silicon • Temp.: 20°C • SF6 flow: 120sccm • CM pressure: 10mTorr • ICP power: 600W • He pressure: 20mbar Cleaning step: Optional • CCP power: 7.5W • VDC: ‐40‐55V • Time: 1min SLE etching: xx min

Etchrate SiRN: 5 nm/min

(Mask UND) Procedure of Isotropic etching step:

take quarter piece. Use scotch tape to mount it on a 4” SiN wafer (thickness SiN ~ 1000nm) etchrate measured: Sample wafer 282 ‐ Right‐bottom t =60 min 48 micron underetch t=140 min 120 micron underetch (RO_01) t=160 min 140 micron underetch (RO_02) , this one is OK, so 140 micron


CR102A / Tepla 300E Barrel Etcher (2.45 GHz) Multipurpose sytem • O2 flow: 200sccm (50%) • Power: 500W • Pressure: 1.2 mbar • Time: 10 min for 1‐3 wafers, 400



nm/min • Time: 20 min for 4‐10 wafers • End point detection by visual inspection of the plasma color. • Blue color means still photoresist on the wafer, purple means clean.



5.2 Wafer processing The actual cooking of the wafer processing can be performed online using the TST Technology website, which can be found on: http://tst‐server1/tst/



Remarks and results (Erwin): (the required changes in the process document and in the mask have been made) ‐masks: 1) Put names on the masks (names have been added, JvH ) 2) dimension of the hinges to critical for specific designs (changes have been made, JvH ). 3) if we want to do the isotropic etching on waferscale mask 3 should be uniform 4) now 2 times thick nitride etching is it possible to do it in one run? 5) for metal hinges design should be in such a way that there is only metal on places where the

hinges are. Process: Step 11) thickness of the second SiN layer was ~ 100nm: see the note (JvH) in step 11

12) step coverage problem: next time we should use thicker resist (908‐35) because of the large step in the SiN (1 micron) 17) see step 12) use 908‐35 After step 18) is the usual HF etching not necessary because step 19) is started with a 1 min directional etch. (see opticonal cleaning step.) 19) Oxford system is used: see recipe below: #etch 070

Plasma etching of Silicon ‐ release (Oxford) (#etch070)

CR102A / Oxford Plasmalab 100 ICP Application: release of membranes and cantilever SLE = poly‐silicon • Temp.: 20°C • SF6 flow: 120sccm • CM pressure: 10mTorr • ICP power: 600W • He pressure: 20mbar Cleaning step: Optional • CCP power: 7.5W • VDC: ‐40‐55V • Time: 1min SLE etching: xx min

Etchrate SiRN: 5 nm/min

For the isotropic dry etching of single crystalline silicon: Maskmaterial:



Olin 908/35 Load: only a few % of the silicon is etched away Procedure of Isotropic etching step:

- take quarter piece. Use scotch tape to mount it on a 4” SiN wafer (thickness SiN ~

1000nm) - etchrate measured: Sample wafer 282 ‐ Right‐bottom t =60 min 48 micron underetch

t=140 min 120 micron underetch (RO_01) t=160 min 140 micron underetch (RO_02) , this one is OK, so 140 micron

underetch is needed to free the whole structure

- After 90 min of etching the photoresist is not shiny anymore: temperature problem!

This will cause not a serious problem. After stripping the resist the structures are shiny again, see picture below. When we do this isotropic etching step on waferscale, the temperature will be constant due to good Helium backside contact and this problem will not occur. Another option to avoid this effect when using quarter pieces: use fomblin oil to make a good thermal contact with the dummy wafer.



SEM images:

Overview of the mask:

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