1.
A boron-doped crystal is measured at its seed end with a four-point probe of spacing 1
mm.The (V/I) reading is 10 ohms. What is the seed end doping and the expected reading at
0.95 fraction solidified?
2. What is depth of Focus?
3. What is lithography field?
4. What is misalignment in lithography?
5. What is selectivity in an etching process?
6. In an older MOSFET technology, the field oxide is a 1-μthick thermal oxide.Would you
grow it in a dry or wet ambient? Why?
7. For etching a small feature with faithful replication of the resist pattern, is dry or wet
etching technique preferred? Why?
8. If you want to deposit oxide at the lowest possible temperature, what processing
technology would you use?
9. Calculate the final thickness of the silicon dioxide on a wafer that initially has 0.2μm after
an additional 3 h of 1,000°C dry oxidation (A=0.165μm and B= 0.0117μm²/h at 1,000°C dry
oxidation).
10. What are the advantages of CVD over PVD
11. What is the need for LPCVD? Explain with reference to APCVD
12. Describe atmospheric pressure CVD process. How is uniform deposition achieved in
APCVD?
13. What is rapid thermal annealing?
14. Describe in detail the methods to minimize channeling
15. If the gap between the wafer and the mask is kept 40μ and the resist is exposed to an X-
ray of 4.4Å wavelength. Calculate the theoretical resolution
16. compare the depth of Focus of 100X optical lens and an ebeam at 15kV
17. Why X-ray lithography is not popular
18.Silicon is oxidised and a 1+/- 0.2μm thick dioxide is grown on the silicon wafer. If the
oxide etch rate is 1000Å/mins in the HF then determine the total time including the over etch
time?
19. The etch rate is faster in bigger geometry than small geometry patters. Why?
20. Difference between plasma etching and wet etching
21. If 1x1019 atoms per cm-3 boron is doped into a silicon wafer and the wafer is kept in a high
temperature furnace. Find the temperature at which the semiconductor becomes intrinsic
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22. What are isotropic and anisotropic etching process
23. what are oxidation induced defects in semiconductor
24. Describe ion implantation mechanism
25. Gold is diffused into a silicon wafer using a constant source diffusion with a
surface concentration of 1018cm-3. How long does it take the gold to diffuse
completely through a silicon wafer 400μm thick with a background concentration of
1016cm-3 at a temperature of 1000°C
26. A disk drive's MTBF number may be 1,200,000 hours and the disk drive may be running
24 hours a day, seven days a week. One year has 8,760 hours. Calculate the percentage
failure?
27. A disk drive's MTBF number may be 700,000 hours and the disk drive may be running
2400 hours a year. Calculate the percentage failure ? ( Ans-0.34%)
28.Define the following terms: Failure Rate; Cumulative distribution function; Density
function; Mean time between failure.
29. Define the relationship between cumulative distribution function (cdf) F(t) and the
density function f(t).
30. 10% of metal lines fail due to electromigration failures in 200 hours at 175 C, in 32 hours at 200 C
and in 4 hours at 250 C. Find the activation energy and pre exponential term, Ro
1.Calculate the voltage that corresponds to breakdown electric field for 150 Å SiO2 gate oxide
Breakdown Voltage = VX - VR
32. What is the definition of the FIT?
33.What is burn-in
Burn-in is a technique to cause failure of parts that would fail early in its life prior to shipping the
parts to the customer.
34. What is critical dimension in Lithography
Critical dimension : Absolute size of a minimum feature in an IC (line width/ spacing / contact
dimension)
35. Contact lithography
Advantages of contact lithography Fast: capable of exposing the entire wafer at once Inexpensive:
Mature technology
Disadvantages Lowest resolution Pattern defects Mask wear due to physical contact between mask
and substrate
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36. What is shadow printing
Contact and proximity mask printing together is called shadow printing
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