32. Which component is added to the p-type material in order to get the impurity concentration in epitaxial films?
A. Bi-borane (B2H2)
B. Phosphine (PH3)
C. Boron chloride (BCl3)
D. Phosphorous pentoxide (P2O5)
Answer: A
Bi-Borane is used for doping p-type materials and Phosphine is used for doping n-type materials whereas Boron chloride and Phosphorous pentoxide are used for doping during the diffusion process.
33. Where are the silicon wafers placed in the reaction chamber for the epitaxial growth process?
A. Cup
B. Boats
C. Ingots
D. Crucible
Answer: B
The silicon rods are not directly placed in the reaction chamber instead they are placed on a rectangular graphite rod called boats and then it is heated to 1200°c.
34. Which of the following is used to obtain silicon crystal structure while fabricating Integrating Circuits?
A. Oxidation
B. Epitaxial growth
C. Photolithography
D. Silicon wafer preparations
Answer: B
Epitaxial growth is the arranging of atoms in a single-crystal fashion upon a single crystal substrate so that the resulting layer is an extension of the substrate crystal structure.
35. Why oxidation process is required?
A. To protect against contamination
B. To use it for fabrication of various components
C. To prevent diffusion of impurities
D. All of the mentioned
Answer: D
Oxidation provides an extremely hard protective coating, thus protecting against contamination, and by selective etching, it can be made to fabricate components.
36. Mention the chemical reaction for oxidation process
A. Si + 2H2O –> SiO2 + 2H2
B. Si + O2 –> SiO2
C. 2Si + 2H2O –> 2SiO2 + 2H2
D. 2Si + 2H2O + 2O2 –> 2SiO2 + 2H2 + O2
Answer: A
For the oxidation process, silicon wafers are heated to a high temperature, and simultaneously they are exposed to a gas containing H2O or O2 or both.
37. At what temperature should the oxidation process be carried out to get an oxide film of thickness 0.02 to 2µm?
A. 0-105oc
B. 950-1115oc
C. 200-850oc
D. 350-900oc
Answer: B
Silicon wafers are raised to a high temperature in the range 950-1115oc and are exposed to the gas. The thickness of the layer is governed by time, temperature, and moisture content.
38. Oxidation process in silicon planar technology is also called as
A. Photooxidation
B. Silicon oxidation
C. Vapour oxidation
D. Thermal oxidation
Answer: D
The oxidation process is called the thermal oxidation process because high temperature is used to grow the oxide layer.
39. In the Crzochralski crystal growth process, the materials are heated up to
A. 950oc
B. 1000 oc
C. 1420oc
D. 1200oc
Answer: C
In the Crzochralski crystal growth process, the materials are heated up to 1420oc.
The materials are heated above 1420oc which is greater than the silicon melting point.
40. How to obtain silicon ingots of 10-15cm diameter?
A. By crystal pulling process
B. By crystal melting process
C. By crystal growing process
D. All of the mentioned
Answer: A
During the crystal pulling process, the seed crystal and the crucible rotate in opposite directions, in order to produce ingots of circular cross-section (diameter of 10/15cm normally obtained.
41. If the thickness of the wafer after all polishing steps in silicon wafer preparation is 23-40 mils. Find its raw cut slice thickness?
A. 16-32 mils
B. 23-40 mils
C. 8-12 mils
D. None of the mentioned
Answer: A
Usually, the silicon wafer obtained has a very rough surface due to the slicing operation. So, these wafers undergo a number of polishing steps to produce a flat and smooth polished surface. Therefore, the thickness of wafers will be reduced from its raw cut slice.
