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Basic IC Fabrication
07/03/2014
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Concepts to be covered in this session
silicon substrate
silicon dioxide
oxide
field oxide gate oxide
polysilicon
silicon nitride
metal ion implant
photoresist
photo mask
exposure etch
resist strip deposition
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Wafer Fabrication Oxidation
eposition
!ithography
"tching
iffusion
Ion Implantation
Process #teps
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silicon substrate
source drain
gateoxide oxide
top nitride
metal connection
to source
metal connection to gate
metal connection
to drain
polysilicon gatedoped silicon
field oxide
gate oxide
Fabrication process of a simple $etal Oxide
#emiconductor %$O#& transistor
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The manufacture of a single $O# transistor begins
'ith a silicon substrate
#ilicon #ubstrate
silicon substrate
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Fabrication of a silicon single crystal
#liced into thin disks called 'afers
Wafers are finely round( mirror)smooth and clean
Clean)*oom environment is re+uired
Wafer Fabrication
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silicon substrate
oxide
field oxide
Field Oxide ,ro'th
- layer of silicon dioxide %field oxide& serves as
isolation bet'een material bet'een devicesmanufactured on the same substrate.
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Oxidation
-t atmospheric pressure
-t .//0C to 12//0C
Temperature accuracy of
gro'th of oxide layers is
reproducible
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silicon substrate
oxidephotoresist
eposition of Photoresist
Photoresist provides the means for transferring the
image of a mask onto the top surface of the 'afer
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Physical vapor deposition%P3&%#putter deposition&
Chemical vapor deposition
%C3&
Perfect conformity
#putter deposition
eposition
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#hado' onphotoresist
photoresist
"xposed area of
photoresist
Chrome plated
glass mask
4ltraviolet !ight
silicon substrate
oxide
$ask #tep
4ltraviolet light exposes photoresist through 'indo's in a photomask
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!ithography
Transferring geometric shapes# "5g5 gate electrodes( contact 'indo's
or metal interconnections
Optical lithography is the prevailing
method at present
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4nexposed area
of photoresist
silicon substrate
"xposed area of photoresist
oxide
photoresist
#ilicon #ubstrate
"xposed photoresist becomes soluble and can be easily
removed by the develop chemical
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silicon substrate
oxide
photoresistphotoresist
"tch of photoresist
4nexposed photoresist remains on surface of oxide to
serve as a temporary protective mask for areas of the
oxide that are not to be etched
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"tching
4sed to partly remove material
to create patterns
Chemical %wet& etching
*eactive ion %dry& etching
Combination of both
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silicon substrate
oxide oxide
silicon substrate
photoresist
Oxide "tch
-reas of oxide protected by photoresist remain on the
silicon substrate 'hile exposed oxide is removed bythe etching process
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silicon substrate
oxide oxide
silicon substrate
field oxide
*emoval of Photoresist
The photoresist is stripped off )) revealing the pattern
of the field oxide
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silicon substrate
oxide oxide
gate oxide
thin oxide layer
,ate Oxide gro'th
- thin layer of oxide is gro'n on the silicon and 'ill
later serve as the gate oxide insulator for the transistorbeing constructed
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silicon substrate
oxide oxide
gate oxide
,ate oxide etch
The gate insulator area is defined by patterning the
gate oxide 'ith a masking and etching process
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silicon substrate
oxide oxide
gate oxide
polysilicon
gate oxide
Polysilicon deposition
Polysilicon is deposited and 'ill serve as the building
material for the gate of the transistor
P l h
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silicon substrate
oxide oxidegate
ultra)thingate oxide
polysilicon
gate
Poly gate etch
The shape of the gate is defined by a masking and
etching step
I i l t ti f 6d i
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opant ions are selectively implanted through
'indo's in the photoresist mask
silicon substrate
oxide oxidegate
source drain
photoresist
#canning directionof ion beam
implanted ions in activeregion of transistors
Implanted ions inphotoresist to beremoved during
resist strip5
ion beam
Ion implantation for source6drain
I I l t ti
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Ion Implantation
-toms are ioni7ed( acceleratedand
implanted
3ariety of combinations of
target material ose can vary bet'een 1/11
and 1/1.6cm2
-cceleration energie bet'eenseveral
ke3 and severalhundredke3
- li
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silicon substrate
oxide oxidegate
source drain
doped silicon
-nnealing
The source and drain regions of the transistor are
made conductive by implanting dopant atoms intoselected areas of the substrate
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iffusion
Important for electrical
characteristics
forms source( drain and channel
regions
ope polysilicon in $O# prcessing
#ili 8it id d iti
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silicon substrate
oxide oxidegate
source drain
top nitride
#ilicon 8itride deposition
- layer of silicon nitride is deposited on top of the
completed transistor to protect it from theenvironment
"t h C t t h l
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silicon substrate
source drain
gate
contact holes
"tch Contact holes
9oles are etched into selected parts of the top nitride
'here metal contacts 'ill be formed
$ t l iti
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silicon substrate
source drain
gateoxide oxide
silicon substrate
source drain
gateoxide oxide
metal contacts
$etal eposition
$etal is deposited and selectively etched to provide
electrical contacts to the three active parts of thetransistor
Process flo'
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Process flo'
silicon substratesilicon substrate
oxide oxide
silicon substrate
field oxide
silicon substrate
oxide oxide
silicon substrate
oxide oxidegate
ultra)thingate oxide
polysilicongate
silicon substrate
oxide oxidegatesource drain
silicon substrate
source drain
gate
contact holes
C l t t t f $O#
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silicon substrate
source drain
gateoxide oxide
top nitride
metal connection
to source
metal connection to gate
metal connection
to drain
polysilicon gatedoped silicon
field oxide
gate oxide
Complete structure of $O#
Completed #tructure of a #imple $O# Transistor
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#ilicon s'itches: the 8$O#
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Above silicon:
Thin oxide (SiO2) under the gate areas; Thick oxide everywhere else;
Above silicon:
Thin oxide (SiO2) under the gate areas; Thick oxide everywhere else;
#ilicon s'itches: the 8$O#
#ilicon s'itches: the P$O#
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#ilicon s'itches: the P$O#
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