Engineering Questions with Answers - Multiple Choice Questions
Manufacturing Processes – Electrochemical Etching – 15
1 - Question
Noble metal used in metal-assisted approach affects the formation of μpSi structures on the side walls of pores.
a) True
b) False
View Answer
Explanation: Another interesting phenomenon dependent on the noble metal is the formation of μpSi structures on the side walls of pores or wires during the etching process. A detailed explanation of the origin of these effects is yet to come although some scientists have pointed out towards the role of the noble metal type in the catalytic activity for the reduction of the oxidant.
2 - Question
Etching rate can be improved by_____
a) lowering the temperature
b) using less active oxidant and highly active etchant
c) increasing the number of electronic holes
d) reducing the surface area of the pores so that less time will be required for the etching
View Answer
Explanation: The more the injected electronic holes the faster the etching rate, resulting in a more efficient diffusion of electronic holes towards the side walls during the etching process and enabling the formation of μpSi structures on the side walls of pores or wires.
3 - Question
Noble metals affect the etching rate but not the geometric features of the resulting pSi.
a) True
b) False
View Answer
Explanation: The geometric features and morphology of the resulting pSi structures are mainly established by the shape of the noble metal deposited on the surface of the silicon wafer as a result of its catalytic effect, which results in a much faster etching rate at the interface noble metal-silicon.
4 - Question
Wire-like pSi structures are produced when the distance between noble metal particles is reduced.
a) True
b) False
View Answer
Explanation: Usually, well-defined and separated pores are produced from single particles distributed across the silicon surface. In contrast, when the distance between adjacent particles is reduced, wire-like or wall-like pSi structures are produced.
5 - Question
Pores produced by metal assisted etching feature _____ structure.
a) square-like
b) cylindrical
c) cone-like
d) needle-like
View Answer
Explanation: Typically, pores produced by metal assisted etching feature a cone-like structure with pore diameter decreasing with depth. This conical effect can be more or less pronounced, depending on the etching conditions.
6 - Question
The pore diameter at the pore mouth is always equal to that of the initial noble metal particle.
a) True
b) False
View Answer
Explanation: The conical effect in the pores formed by metal-assisted approach can be more or less pronounced, depending on the etching conditions, and the pore diameter at the pore mouth can be bigger or smaller than that of the initial noble metal particle.
7 - Question
The diameter of the pores can be said to be dependant on the diffusion of electronic holes injected from the noble metal-silicon interface.
a) True
b) False
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Explanation: The conical effect can be associated with the diffusion of electronic holes injected from the noble metal-silicon interface to the side walls, the partial dissolution of silicon by the etchant and the progressive dissolution and re-deposition of noble metal in the course of the etching process.
8 - Question
_____ is/are obtained when a homogeneous noble metal film is deposited on the surface of silicon.
a) Conical structure
b) Distorted and rough surfaces
c) Honey-comb structure
d) Wire-like structure
View Answer
Explanation: Silicon wires with well-defined geometry and shape are obtained when a homogeneous noble metal film featuring holes is deposited on the surface of a silicon substrate and subsequently etched in a suitable etchant solution.
9 - Question
Lithographic approach along with noble metal is used to produce highly ordered pores.
a) True
b) False
View Answer
Explanation: Silicon wires can be produced with highly ordered distribution and precisely controlled geometry if the surface of the silicon is patterned by lithographic approaches prior to the deposition of the noble metal film.
10 - Question
The morphology of the resulting pSi structures is dependent on the noble metal film.
a) True
b) False
View Answer
Explanation: The thickness of the noble metal film has a direct effect on the morphology of the resulting pSi structures as well. For instance, 3 and 5 nm thick films of gold lead to pores and wires, respectively. In the case of silver films, 5 nm thick films yield pores while films of 20–50 nm thickness result in silicon wires.