3D-RID The application of micro- machining to radiation imaging detectors.

3D-RID

The application of micro-machining to radiation imaging

detectors

3D-RID Val O’Shea Como 9/10/’03

3D-RID -- a detector development project funded bythe European Commission

Partners: Applied Scintillation Technologies (UK)Czech Technical University (CZ)Metorex Oy (FI)Mid Sweden University (SE)Royal Institute of Technology (SE)Surface Technology Systems (UK)University of Freiburg (DE)University of Glasgow (UK)


Outline of talk:

Motivation for 3d -- what is it?

Simulation

Processing -- micromachining

Devices

Conclusion


3D type detectorsX-rayphoton

Legend:BC = Back contactROIC = Read out circuit

1. Scintillator 2. Scintillator 3. Neutron absorber 4. Direct pn-junctionlight guiding to CCD pn-junction detection pn -junction detection detection

pp+-+--+-++-+-

E E

n

de

pth

Si CCD

CsI

Si pitch

X-rayphoton

Si

ROIC

CsI+ -

+ -

BC

Neutrons

Si

ROIC

LiF+ -

+ -

BC

ROIC

Particles

+ -

+ -

BClow doped Si

N

N

P

PSilicon orGaAs

ROIC

BC

+ -

+ -

de

pth

pitch


The electrodes are cylindrical and are biased to create an electrical field that sweeps the charge carriers horizontally through the bulk. The electrons and holes are then collected at oppositely biased electrodes.

Traversing ionising radiation creates electron-hole pairs in proportion to the energy deposited in the material. The free charges then drift through the device under the influence of an applied electric field. Proposed by S.Parker et al, Nucl. Instr. And Meth. A 395 pp. 328-

343(1997).

Equal detector thickness

W2D>>W3D

Equal detector thickness

W2D>>W3D

h+

e -

+ v e+ v e -v e

x

W

ionising radiation

E

h+

e-E

-ve

+ve

n

n+

p+

-ve -ve

W2D

x2D

3D

3D

3D Geometry


ISE SimulationElectric Potential Distribution

50m pitch 300m thick silicon doping: 1x1019 /cm3

10 m pore diameter 50 x 90 m pitch 300 m thick silicon


ISE SimulationElectric field Distribution

• 50V bias


ISE Simulation


2D MEDICI software package

Si material parameters.Schottky barrier height= 0.65eV.SRH statistics +impact ionisation.No charge trapping or surface current.Sidewall damage caused by reactive ion etching, ND=1017atm./cm3.

-160 -140 -120 -100 -80 -60 -40 -20 0-1.6x10

-3

-1.4x10-3

-1.2x10-3

-1.0x10-3

-8.0x10-4

-6.0x10-4

-4.0x10-4

-2.0x10-4

0.0

MEDICI simulation MEDICI simulation with dry etching defects cathode-biased (experimental)

Cu

rren

t(A

)

Bias(V) Simulated cell Defect distribution

MediciSimulation


3D- Detector Structure

Unit cell

Pixel

n+

p+

50

m

50 m

35 m

p+

p+

n+

n+

35

m

50 m


Simulated Depletion Voltages

Si

ND [cm-3] 1012 1013 1012 1013 1012 1013

Pixel size [m]

50 50 100 100 150 150

Vdepl. [V] 1.7 15 6.5 70 20 190


–Connection from the readout & detector die combination to the communication / utility

circuitry

Basic image cell : vertical hybridisation of detector, read-out electronics & Interface circuitry & connector

3D-Stacked Imaging Tiles

Courtesy Eric Beyne IMEC


Tiling of 3D-image stacks

• Tiling on frame :

– flexible design,

– high accuracy alignment

Courtesy Eric Beyne IMEC


Preamp

DiscL

Double Disc logic

Vth Low

Vth High

13-bits

Shift Register

Input

Ctest

Testbit

Test Input

Maskbit

3 bits Threshold Adjust

3 bits Threshold Adjust

Shutter

Mux

Mux

ClockOut

Previous Pixel

Next Pixel

Conf

8 bits configuration

Polarity

Analog Digital

DiscH

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

195 200 205 210 215 220 225

THL DAC

Su

m o

f T

ota

l Co

un

ts

Cd109 Data

2 Peak Gaussian Fit

22KeV Gaussian Fit

24.9KeV Gaussian Fit

Charge Sharing and Photon Counting

Medipix2 Schematic

Courtesy Xavi Llopart and the Medipix Collaboration


Conventional ICP Source

Gas Inlet

Plasma Chamber

Ceramic Process Chamber

Process Height

Wafer/Sample

MESC CompatibleIsolation Valve

Temperature ControlledBellows Sealed Electrode

Helium CoolingGas Inlet

Weighted Clamp(Optional)

Pumping Port

13.56 MHzRF Matching Unit

~

13.56 MHzRF Matching Unit

~


Process Results - Si

10m diameter pore50m pitch8m thick PR mask<1% exposed area

Results: • 182µm depth• 40:1 selectivity to PR• 2.0µm/min


Process Results - Si

10m diameter hole50m pitch7-8m thick remant PR mask<1% exposed area

SF6 / C4F8 ProcessASE-HRM Source


Process Results - Advanced GaAs Etch (AGE) Process in ICP

Cl2 / SiCl4 + CH4 Switched ProcessProfile Angle =89.6°, Etch Rate = 1.25m/min, Selectivity=6.7:1,Depth = 37m


Process Results - GaAs

•Scallops visible in walls

•Anisotropic profile


TOPS:The Strathclyde Electron and Terahertz to Optical Pulse SourceStrathclyde University..

• 3mJ laser pulses.• 40fs pulse duration.• 1kHz pulse repetition rate.• 400nm wavelength.

Ti:Sapphire laser

Femtosecond laser

Cold processing.Low shockwave damage.

Tapering.Repeatability.Surface debris.

Advantages:

Disadvantages:

Laser drilling


diameter :•entrance hole:10m.•exit hole: 6m.

depth: 200m.

Laser drilling


Electrochemical Etching• Chemical reactions between Si atoms, HF solution and “h+” (positive charge carriers)

• HF concentration• Current density• Applied bias• Light intensity• Temperature• Silicon properties (type, orientation, resistivity)

Setup - ParametersP la tin u mE lec tro d e

n S i

V

I

E lectro ly te (H F so lu tio n )

h +


Macropore formation: Principle

• SCR (electric field) in silicon

• h+ directed towards the pore tips

Anisotropic etching

• Passivation of the pore walls is due to the SCR (Lehmann’s model)

Importance of the silicon resistivity !

• Condition for stable pore formation

J at the pore tip = Jps

Possibility to control the diameter

V

I

S C R

H F so lu tio n


Preprocessing for electrochemical etching

Front side: Inverted pyramids focus the current lines (h+)at the top of the pyramids

Back side: Formation of an Al grid uniform back side contact(especially for high resistivity sample)

Al

Si

Photolithography + KOH etching

Al deposition + photolithography + Al etching


Formation of pores by EE: Large pores

Spacing = 30-45 um; Depth = 230-260 um; Wall thickness 4 um; Active area > 80%.

S i

Electroly te

300 WH alogen Lam p

A l g rid

Pt E

lect

rode

P ow er Supp ly

IV

M eta llic ring


Images of the samples D32 and D41 ( = 2-5 kcm)

Demonstrators - Thindrill

Depth 200 mdia: 10-12

Depth 360 mdia: 10-16


Formation of pores by EE: Thindrill

I n m 1 2 3 4

Spacing 50 50 50 30

Depth 220 320 260 145

Diameter 12 18 12-20 12

1 2

3

4


Large pitch (45 or 30 µm) High resistivity ( = 2-5 kcm)

Depth: 380 µm, wall: 4 µm, Pitch: 30 µm, aspect

ratio 100!

Large pores - Sloped Walls

Depth: 180 µm, pitch: 30 µm, diameter from 6 to 18 µm. A linear function was applied to

the current.

i (mA

)

dep

th

2 63


Diffusion 1: 1150ºC, 1h45’

Profile along A

A

5 µm

AFM

SSRMThickness at the pore bottoms: 3 m.

Thickness on a planar wafer (SIMS): 6 m.

Transport of boron down to the pore bottom may be limited.

Formation of pn junctions: Results from diffusion


Diffusion 1: SIMS profiles at different positions along the pore depth:

- No B in the substrate (profiles c, g). Walls fully doped.

n - ty p e s u b s tra te

b o ro n d o p e d re g io n

c , g : su b s t ra te

d , i : b o tto m

e : m id d le

f , h : to p

boro

n do

ped

regi

on

0 1 2 3 4 5 61E15

1E16

1E17

1E18

1E19

1E20dei f

h

gcB

oron

con

cent

ratio

n (c

m-3)

Depth (microns)

Substrate: c g

Pore bottoms: i d

Pore middle: e

Pore tops: f h



Diffusion 2: 1050ºC, 1h10’. SIMS profiles at different positions along the depth:

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.01015

1016

1017

1018

1019

1020

Bor

on

con

cent

ratio

n (c

m-3)

Depth (microns)

Pore tops: m p

Pore middles: n o

Pore bottoms: k l

Substrate: j n - ty p e su b s tra te

j : su b s t ra te

k , l : b o tto m

n , o : m id d le

m , p : to p

b o ro n d o p e d la y e rs

- [B] in pores [B] in a planar sample; no significant variation along pore depth.

- Boron atmosphere in the pores maybe more uniform at 1050ºC than at 1150ºC.

- Boron layers on each side of the walls.



SCM at a pore bottom of a DRIE matrix after deposition: typical signature of a pn junction

SCM AFM

A

Profile along A

PN Junction Formation: Results from LPCVD


n - s ilico n

C s I:T l

p + s i lic o n

X - ra y

n -

CsI

:Tl

E c

E v

B u lk c o n ta c t

p + c o n ta c ts

p +

Why: concept of x-ray imaging detector below

Formation of pn junctions on walls of pores

Process steps: 1. Formation of pore arrays 2. Formation of pn junctions in pore walls

3. Filling pores with a scintillator, CsI(Tl)4. Contacts and bump-bonding to the ROC


Making ElectrodesMetal evaporation:

Ti (33nm)Pd (33nm)Au (150nm)

Tracks of Al (150nm)

Wire bonding (25µm wire)


3D GaAs Performance

241Am

Readout by DASH-E(P.Sellar – RAL)

Bias 10V

Run at –30 C as thereis no leakage currentcompensation


Conclusion

•Much more to do

•Si diode arrays 256X256 and 55 um pitch are being made

•Charge integrating chip for this array is designed -- Analogue Medipix

•Testing of and characterisation of bumped assemblies

•Improvement of filling uniformity – other fillings

3D-RID The application of micro- machining to radiation imaging detectors.

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Transcript of 3D-RID The application of micro- machining to radiation imaging detectors.