This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Nanofabrication”.
1. What is the main difference between physical and chemical vapour deposition?
a) They employ different processes
b) They are used to create a thin film
c) They have different area of application
d) They produce high quality coatings
View Answer
Explanation: PVD is a physical process which does not indulge in chemical reactions. On the contrary, CVD uses thermal decomposition or reaction of gas phase species in order to deposit a coating on to the substrate.
2. Choose the correct top down process from the given set of options.
a) PVD
b) CVD
c) MBE
d) Ball milling
View Answer
Explanation: Ball milling is a typical process of crushing and reducing the size of coarse grain materials. This is brought by carbide or hard steel balls that crush mechanically in rotating drums under controlled conditions.
3. Choose the correct option with respect to molecular beam epitaxy.
a) Very costly and simple process
b) Very costly as well as complicated system
c) No control on doping
d) Only enables growth of matched lattice structures
View Answer
Explanation: MBE has lot of advantages. It has precise control of doping, enables growth of lattice mismatched structures and has a controlled growth rate. But this process is quite expensive and uses very sophisticated machinery.
4. Which of the following step is not involved in optical lithography?
a) Surface preparation
b) Resist coating
c) Etching
d) Surface greasing
View Answer
Explanation: Optical lithography, also known as photo lithography, involves the basic procedures of surface cleaning or substrate preparation, resist coating, exposure, development and pattern transfer (etching). Standard grease is in fact removed from the substrate during its cleaning.
5. Which among the following is not a key ingredient of Wet Etching process?
a) Oxidizer
b) Acid or Base
c) Neutralizer
d) Diluent media
View Answer
Explanation: Wet Etching process is carried out using oxidizer (e.g. H2O2, HNO3), acid or base to dissolve the oxidized surface (e.g. H2SO4, NH4OH) and a diluent media to transport the products (e.g. H2O).
6. What is the major difference between photolithography and electron beam lithography?
a) Resists
b) Photomasks
c) High speed
d) Top down approach
View Answer
Explanation: Optical lithography, also known as photolithography, uses photomasks to project the patterns on substrate. Electron beam lithography, on the other hand does not need any mask to engrave the patterns.
7. Which of the following is not involved in a CVD (Chemical Vapour deposition) process?
a) Reaction of gases
b) Thermal decomposition of gases
c) Formation of structures of patterns from pre-existing parts
d) Employment of catalysts in certain chemical reactions
View Answer
Explanation: CVD is a process in which reaction or thermal decomposition of gaseous species occurs at elevated temperatures, followed by their deposition on a substrate. Several CVD processes employ catalysts to improve the rate of chemical reactions.
8. Find out the class of a clean room which is required in modern lithographic processes.
a) In the range 1 to 10
b) In the range 1 to 5
c) In the range 5 to 10
d) In the range 10 or more
View Answer
Explanation: A class X clean room can be defined as one that has a dust count of X particles (having diameter of 0.5μm or larger) per cubic foot. For a modern lithographic process, a class 10 or better clean room is needed.
9. Which factor is not responsible for the thickness of the film in spin coating process?
a) Viscosity of resist fluid
b) Spin speed
c) Wafer size
d) Percent solid content indigenous to the resist.
View Answer
Explanation: The thickness of the film in spin coating process is directly proportional to the viscosity of the liquid resist as well as the percent solid content indigenous to the resist. It also varies inversely with the spin speed.
10. Which among the following options is not a bottom up process?
a) Optical lithography
b) Sol-gel method
c) Self-assembly
d) Molecular beam epitaxy
View Answer
Explanation: Optical lithography is a top down process. This method uses light to transfer geometric patterns from a photo mask to a thin layer of radiation sensitive material (photoresist), covering the substrate.
11. PVD coatings have many advantages, which among the following is not one of them?
a) They can be deposited with improved properties compared to substrate materials
b) Process demands complex machineries to operate at high temperature and vacuum, requiring skilled operators
c) Some kind of organic as well as inorganic material can be used
d) Process is more environment friendly than many other processes
View Answer
Explanation: PVD requires the vaporization of the material at a very high temperature and vacuum. This is then condensed onto the substrate to generate films. Since it operates at such extreme conditions, complex machineries are need. These machines are expensive with high maintenance rendering the process uneconomical. Moreover, skilled labours are required to operate such machineries. They in turn need to be highly paid.
12. Find out from the following options a typical precursor material for chemical vapour deposition.
a) WFl4
b) SiO2
c) WF6
d) TiCl3
View Answer
Explanation: Precursors, used in CVD, are deposited as films or coatings on the substrate in the gaseous phase. They include metal hydrides, halides, carbonyls, alkyls etc. WF6 is one such metal halide that is used as precursor material in CVD.
13. Choose the correct option which corresponds to the advantage of electron beam lithography.
a) Requirement of vacuum
b) High resolution but often constrained by aberrations in electron optics
c) Maskless lithography
d) Slow throughput
View Answer
Explanation: Electron beam lithography (EBL) is often known as maskless lithography. Unlike optical lithography, which uses photomasks to project the patterns, EBL does not need masks anymore to perform its tasks.
14. What type of process forms engraved patterns that are reverse of the masks patterns?
a) Optical lithography using positive resists
b) Molecular beam epitaxy
c) Self – assembly
d) Optical lithography using negative resists
View Answer
Explanation: Optical lithography uses two types of photo resists, Positive and negative resists. While the positive resists result in patterns same as that on the mask, the negative resists engrave reverse patterns. For negative resists the exposed regions becomes less soluble.
15. Choose the correct option indicating the sequential order of spin coating process.
a) Rotation of wafer ➔ Deposition of solvent solution ➔ Evaporation of the solvent from the film ➔ Thinning of coating
b) Deposition of solvent solution ➔ Thinning of coating ➔ Rotation of wafer ➔ Evaporation of the solvent from the film
c) Deposition of solvent solution ➔ Rotation of wafer ➔ Thinning of coating ➔ Evaporation of the solvent from film layer
d) Deposition of solvent solution ➔ Evaporation of the solvent from the film ➔ Rotation of wafer ➔ Thinning of coating
View Answer
Explanation: Spin coating can be done using four major steps. First, the liquid resist is applied on the substrate. Second, the substrate is spun with final radial velocity. Third, the thinning of coating takes place which mainly depends on spin speed. Fourth, evaporation of the solvent occurs from the film, resulting in further thinning.
More MCQs on Nanofabrication:
Sanfoundry Global Education & Learning Series – Nanotechnology.
To practice all areas of Nanotechnology, here is complete set of 1000+ Multiple Choice Questions and Answers.
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