This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Electrochemical Etching – 12”.
1. Metal-assisted chemical etching approach is widely used to produce pSi structures with precisely defined geometric features.
a) True
b) False
View Answer
Explanation: Metal-assisted chemical etching of silicon is considered a simple and cost-competitive alternative to conventional electrochemical methods. This approach has been used to produce pSi structures with precisely defined geometric features and characteristics not achievable by other fabrication approaches.
2. _____ can be controlled in metal-assisted etching.
a) Etching rate
b) Etching direction
c) Etching area
d) Etching temperature
View Answer
Explanation: The etching direction in metal-assisted etching can be controlled on silicon (100) and non-(100) directions to produce pSi structures with slanted growth directions. 100, 110, 111, etc. are miller indices for the orientation of the Si structure.
3. Metal-assisted etching can produce pSi structures with high surface-to-volume ratio.
a) True
b) False
View Answer
Explanation: Metal-assisted etching enables the fabrication of pSi structures with high surface-to-volume ratio, high crystalline quality and low level of defects.
4. It can be said that metal-assisted etching of silicon is an alternative approach to conventional electrochemical etching methods.
a) True
b) False
View Answer
Explanation: Metal-assisted etching can produce pSi structures with high surface-to-volume ratio high crystalline quality and low level of defects. In addition, metal-assisted etching makes it possible to produce pSi structures within a broad range of feature sizes, which can range from 5 nm to > 1 μm. For these reasons, metal-assisted etching of silicon has become an alternative approach to conventional electrochemical etching methods.
5. Etching rate is affected by _____
a) temperature
b) pressure
c) coating on Si surface
d) material thickness
View Answer
Explanation: When a silicon substrate is partly covered by a noble metal and it is immersed in an etchant solution composed of an oxidative agent (e.g. hydrogen peroxide) and HF, the silicon beneath the noble metal is etched at a faster rate than that of the uncovered silicon.
6. Geometric features of the pSi structure are determined by noble metal mask.
a) True
b) False
View Answer
Explanation: Basically, the geometric features of the resulting pSi structures are established by the noble metal mask. The noble metal sinks into the silicon substrate, producing pores or pillars depending on the etching conditions and the metal features.
7. In metal-assisted etching of pSi, chemical reactions occur between _____
a) noble metal and etching agent
b) silicon and etching agent
c) noble metal and silicon
d) no such reactions occur in metal-assisted etching
View Answer
Explanation: As far as the mechanisms and reactions involved in the formation of pSi structures produced by metal-assisted etching is concerned, it is well-known that chemical and electrochemical reactions occur near the interface between the noble metal and the silicon substrate when the system is immersed in an etchant composed of HF and H2O2.
8. In metal-assisted etching of pSi, the noble metal works as a cathode.
a) True
b) False
View Answer
Explanation: In this system, the noble metal works as a cathode, where hydrogen peroxide is reduced at the metal surface following these electrochemical reactions while the silicon works as the anode:
H2O2 + 2H+ -> 2H2O + 2H+
2H+ -> H2 + 2 protons.
9. In the above mentioned method, charge transfer between noble metal and silicon occurs for the oxidation.
a) True
b) False
View Answer
Explanation: In analogy with chemical etching of silicon, it is accepted that charge transfer between noble metal and silicon occurs for the oxidation and dissolution of the latter by hole injection mechanism.
10. In hole injection mechanism, holes are created in the noble metal.
a) True
b) False
View Answer
Explanation: In that system, the noble metal plays the role of cathode, where the reduction of the oxidant takes place. Holes generated in the noble metal are then injected into the silicon substrate, oxidising silicon atoms, which subsequently are dissolved by reacting with HF.
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