basic ic fabrication 1

7/25/2019 Basic IC Fabrication 1

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2014 Synopsys, Inc. All rights reserved. 1

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



silicon substrate

oxidephotoresist

eposition of Photoresist

Photoresist provides the means for transferring the

image of a mask onto the top surface of the 'afer



Physical vapor deposition%P3&%#putter deposition&

Chemical vapor deposition

%C3&

Perfect conformity

#putter deposition

eposition



#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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basic ic fabrication 1

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