This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Electrochemical Etching – 4”.
1. In reactive ion etching, argon gas is ionized by bombarding with electrons.
Explanation: Ar gas is introduced into the vacuum chamber where they are ionized by bombarding with electrons. These ions are then directed on to the wafer where they remove material by physical bombardment.
2. In deposition process, material is added unlike etching where material is removed.
Explanation: The deposition process is the opposite of etching. Here, material is added to the wafer surface. The layers different from grown layers like oxide and nitride, where the underlying Si is consumed during a high temperature furnace process.
3. Which of the following does not hold true?
a) In epitaxial layers, poly Si is grown using deposition
b) For making trench capacitors deposited films are used
c) Deposited layers can also be used as passivation layers
d) Deposition is same as etching
Explanation: Some of the layers, where deposited films are used, are
(1) Epitaxial layers – usually poly Si is grown for use as a gate.
(2) Dielectric layers – intermetallics (high k capacitors)
(3) Trench capacitors
(4) Intermetal conducting plugs
(5) Metal layers – conductors
(6) Passivation layers.
4. In deposition, the Si from the wafer is consumed.
Explanation: In deposition, the Si from the wafer is not consumed and the wafer can be maintained at room temperature or at elevated temperatures.
5. How many deposition techniques are there?
Explanation: There are two main growth techniques-
(1) Physical deposition
(2) Chemical deposition
Depending upon few parameters, the deposition method is selected.
6. Which of the following has no role in selecting the type of growth technique?
a) Thickness of the film
b) Stress on the film
c) Temperature of the film
d) Purity of the film
Explanation: There are some important _lm parameters, which need to be controlled and these decide the type of growth technique that is adopted.
(1) Thickness and uniformity
(3) Composition control
(6) Film integrity.
7. In case of deep holes/grooves the choice of technique plays an important role.
Explanation: In most cases, the underlying substrate is not at. The choice of technique becomes especially important when depositing in deep trenches/holes, with a high aspect ratio (depth/width) that needs to be maintained.
8. For which of the following physical deposition technique is not suitable?
a) Deep trenches
b) Flat surfaces
c) Wafer of very reactive material
d) Rough surfaces
Explanation: In case of deep trenches/holes, aspect ratio (depth/width) needs to be maintained. In such cases, physical deposition techniques will not work since they will cover the hole before filling it.
9. In chemical vapour deposition, chemicals containing the desired film/layer are used.
Explanation: the basic principle is that chemicals containing the desired film/layer are introduced into a reactor (where the wafer is held at high temperature) in the form of a vapour. These chemicals react on the wafer surface to form the film on the wafer.
10. Low pressure chemical vapour deposition (LPCVD) is used to_____
a) increase the purity of the film
b) to reduce the roughness of the film
c) to form thick films
d) to reduce stress on the film
Explanation: CVD process can be in atmospheric conditions or under low pressure (LPCVD). LPCVD is usually used for growing silicon nitride, to reduce the comprehensive stress on the film. For growing atomically thin films, a layer by layer growth process, called atomic layer deposition (ALD), is used.
Sanfoundry Global Education & Learning Series – Manufacturing Processes.
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