semiconductors assingment

1. (a) Name the three major groups of contamination and briefly describe

their physical characteristics.

(b) Where do the above contamination types come from? Give one

example of each.

2. Name two processes metrics which would be worsened by poor

cleanroom practices in a semiconductor cleanroom. Describe briefly what

is meant by each term.

3. (a) What sizes of particles would cause problems for the following

processes:

• 5 µm bipolar • 4.5 µm NMOS • 1.1 µm CMOS • 0.9 µm BICMOS • 0.3 µm CMOS?

(b) What effect is illustrated by the above?

(c) What additional particle related issue affects smaller feature size

processes?

4. FIGURE 1 shows a system which is to be assessed for particles. The

maximum specification limit on the system is +100 particles of >0.5 µm.

(a) A CWC is run by processing a test wafer through the entire sequence

(process module 1 and module 2) and it reveals that 350 particles of

>0.5 µm have been added. Comment on this finding.

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(b) A second CWC is run with the wafer being processed only through

module 1 and it reveals that 334 particles of >0.5 µm have been added. Comment on this finding.

(c) A third CWC is run with the wafer being processed through module

2 and it reveals that 328 particles of >0.5 µm have been added. Comment on this finding.

(d) Suggest where the particles may be coming from and suggest ways to

isolate the sources of particles.

FIG. 1

5. The approximate number, N, of square chips of area A that can be formed

on a wafer of diameter D is given by the equation:

A VLSI chip is to be fabricated on a 300 mm wafer and uses 6 lithography

processes. It is reckoned that on average there will be 2 defects per wafer

for each lithographic process. Assume the defects fall on different chips.

N A

D A� π 4

2 –( )

Process 2

Process 1

Wafer transport

mechanism

Wafer receive cassette

Top view

Wafer send

cassette

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Calculate the cumulative percentage yield of the lithography processes if

the chip has an area of:

(a) 0.5 cm2

(b) 1 cm2

(c) 2 cm2

(d) 4 cm2.

Comment on the results.

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