31. What kind of substrate is provided above the barrier to dopants?
A. insulating
B. conducting
C. silicon
D. semiconducting
Answer: A
Above a layer of silicon dioxide which acts as a barrier, an insulating layer is provided upon which other layers may be deposited and patterned.
32. The photoresist layer is exposed to ____________
A. Visible light
B. Ultraviolet light
C. Infrared light
D. LED
Answer: B
The photoresist layer is exposed to ultraviolet light to mark the regions where diffusion is to take place.
33. In nMOS device, gate material could be ____________
A. silicon
B. polysilicon
C. boron
D. phosphorus
Answer: B
In an nMOS device, the gate material could be metal or polysilicon. This polysilicon layer has heavily doped polysilicon deposited by CVD.
34. Which is the commonly used bulk substrate in nMOS fabrication?
A. silicon crystal
B. silicon-on-sapphire
C. phosphorus
D. silicon-di-oxide
Answer: C
In nMOS fabrication, the bulk substrate used can be either bulk silicon or silicon-on-sapphire.
35. In nMOS fabrication, etching is done using ____________
A. plasma
B. hydrochloric acid
C. sulphuric acid
D. sodium chloride
Answer: A
In nMOS fabrication, etching is done using hydrofluoric acid or plasma. Etching is a process used to remove layers from the surface.
36. Heavily doped polysilicon is deposited using ____________
A. chemical vapor decomposition
B. chemical vapor deposition
C. chemical deposition
D. dry deposition
Answer: B
The polysilicon layer consists of heavily doped polysilicon deposited by chemical vapour deposition.
37. In diffusion process ______ impurity is desired.
A. n-type
B. p-type
C. np type
D. none of the mentioned
Answer: A
Diffusion is carried out by heating the wafer to a high temperature and passing a gas containing the desired n-type impurity.
38. Contact cuts are made in ____________
A. source
B. drain
C. metal layer
D. diffusion layer
Answer: A
Contact cuts are made in the desired polysilicon area, source, and gate. COntact cuts are those places where a connection has to be made.
39. Interconnection pattern is made on ____________
A. polysilicon layer
B. silicon-di-oxide layer
C. metal layer
D. diffusion layer
Answer: C
The metal layer is masked and etched to form an interconnection pattern. The metal layer was formed using aluminum deposited over the formed surface.
40. SIlicon-di-oxide is a good insulator.
A. true
B. false
Answer: A
SIlicon-di-oxide is a very good insulator so a very thin layer is required in the fabrication of MOS transistor.
