mse630 hw_2 solution

8/18/2019 MSE630 HW_2 Solution

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MSE 630 Homework Assignment #2 Solutions Fall, 2008

2.1 Sketch a process flow that would result in the structure shown in Figure 1-34 by

drawing a series of drawings similar to those in this chapter. You only need to

describe the flow up through the stage at which active device formation starts

since from that point on, the process is similar to that described in this chapter.

Answer:

The CMOS technology we need to realize is shown below, from Figure 1-3 in the

te!t"

PP

DGSDGS

P N

NWELL

P+

P-

P+ P+N+ N+

We can follow many of the process steps used in the CMOS process flow in

Chapter 2. The major differences are that an epi layer is needed, only one well (P

well) used, and the device structures are considerably simplified from those in the

text because there are no LDD regions etc.

P-

P+

The first ste# is to grow the blan$et e#i layer shown in the final cross-section" %

hea&ily do#ed '( substrate is chosen and a lightly do#ed boron e#ita!ial layer isgrown uniformly on its surface"


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P Implant

Boron Boron Boron

P-

P+

Mas$ )1 #atterns the #hotoresist" The Si3 * layer is remo&ed where it is not

#rotected by the #hotoresist by dry etching"Since the technology uses field im#lants

below the field o!ide, a boron im#lant is used to do#e these ' regions"

P P P

P-

P+

+uring the OCOS o!idation, the boron im#lanted regions diffuse ahead of the

growing o!ide #roducing the ' do#ed regions under the field o!ide" The Si 3 * is

stri##ed after the OCOS #rocess"


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P P P

P-

P+

N Implant

Phosphorus

Mask #2 is used to form the N well. Photoresist is used to mask the regions where

NMOS devices will be built. A phosphorus implant provides the doping for the N

wells for the PMOS devices

P P P

P-

P+

N well

A high temperature drive-in completes the formation of the N well.


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P P P

P-

P+

N well

P

Boron

%fter s#inning #hotoresist on the wafer, mas$ )3 is used to define the *MOS

transistors" % boron im#lant adusts the * channel .T/"

P P P

P-

P+

N well

P

Phosphorus

N

%fter s#inning #hotoresist on the wafer, mas$ ) is used to define the 'MOS

transistors" % #hos#horus or arsenic im#lant adusts the ' channel . T/" 0+e#endingon the * well do#ing, a boron im#lant might actually be needed at this #oint instead

of an * ty#e im#lant, to obtain the correct threshold &oltage"


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P P P

P-

P+

N well

P N

After etching back the thin oxide to bare silicon, the gate oxide is grown for the

MOS transistors.

P P P

P-

P+

N well

P N

% layer of #olysilicon is de#osited" 2on im#lantation of #hos#horus follows the

de#osition to hea&ily do#e the #oly"


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PP

P

P-

P+

N well

P N

'hotoresist is a##lied and mas$ ) is used to define the regions where MOS gatesare located" The #olysilicon layer is then etched using #lasma etching"

P P P

P-

P+

N well

P N

Arsenic

N+ N+

'hotoresist is a##lied and mas$ )4 is used to #rotect the 'MOS transistors" %n

arsenic im#lant then forms the *MOS source and drain regions"


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P P P

P-

P+

N well

P N

Boron

N+ N+ P+ P+

%fter a##lying #hotoresist, mas$ )5 is used to #rotect the *MOS transistors" % boron im#lant then forms the 'MOS source and drain regions"

%t this #oint we ha&e com#leted the formation of the acti&e de&ices, e!ce#t for afinal high tem#erature anneal to acti&ate the do#ants and dri&e in the unctions to

their final de#th" The rest of the #rocess flow would be similar to the CMOS flow in

the te!t"

mse630 hw_2 solution

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