Solutions for Assignment-6

Transcription

1 Solutions for Assignment-6 Q1. What is the aim of thin film deposition? [1] (a) To maintain surface uniformity (b) To reduce the amount (or mass) of light absorbing materials (c) To decrease the weight and bulkiness of the materials (d) All of these The main motives of thin film deposition are: To maintain surface uniformity To reduce the amount (or mass) of light absorbing materials To decrease the weight and bulkiness of the materials Q2. Which of the following does not include in liquid phase thin film deposition technique? [1] (a) Electroplating (b) Spin coating (c) Chemical vapor deposition (d) Spray pyrolysis Q3. Which of the following statement is correct in context to DC sputtering? [1] (a) A conductive target is used for the transfer of plasma from cathode to anode (b) An insulative target is used for the transfer of plasma from cathode to anode (c) A conductive inter-layer is used for the transfer of plasma from cathode to anode (d) A electrolytic solution is used for the transfer of plasma from cathode to anode

2 Q4. What is the range of incident angle (from normal) for sputtering technique? [1] (a) (b) (c) (d) The maximum sputter yield occurs when the incident angle is from normal. Q5. How much kinetic energy is required in evaporation technique used for thin film preparation? [1] (a) 0.5 ev (b) 3 ev (c) 2 ev (d) 4 ev

3 In evaporation technique, the deposited material condenses onto the substrate with very little kinetic energy (i.e. Kinetic energy ~ 0.5 ev). Q6. Which of the following statement is true for evaporation technique? [1] (a) Mean free path of atoms in the vapor is greater than the distance between source and substrate (b) Mean free path of atoms in the vapor is smaller than the distance between source and substrate (c) Mean free path of atoms in the vapor is equal to the distance between source and substrate (d) Mean free path of atoms in the vapor is independent of the distance between source and substrate The generated atoms can reach from the source to substrate only, if the mean free path of generated atoms will be greater than the distance between the two. Q7. At what temperature range is thermal oxidation of silicon usually performed? [1] (a) 400 C 600 C (b) 600 C 800 C (c) 800 C 1200 C (d) 1200 C 1400 C Thermal oxidation of silicon is usually performed at a temperature between 800 C 1200 C, resulting in so called High Temperature Oxide layer (HTO). Q8. Which of the following equations represents a correct relation between diffusion flux of reactant species to the wafer and mass transfer coefficient? [1] (a) F 1 = h G (C S C G ) (b) F 1 = h G (C G C S ) (c) F 1 = C G (C S h G ) (d) F 1 = C G (h G C S ) The derived flux equation from Fick s law is represented as,

4 F 1 = h G (C G C S ) where, F 1 is diffusion flux of reactant species to the wafer through the boundary layer (also known as mass transfer flux), h G is the mass transfer coefficient (cm/sec), C G is the reactant concentration at bulk of gas and C S is the reactant concentration at substrate surface. Q9. What is the full name of SILAR method? [1] (a) Simultaneous induced layer adsorption and reaction (b) Simple ionic layer absorption and reaction (c) Successive ionic layer adsorption and reaction (d) Successive induced layer absorption and reaction The full form of SILAR is Successive Ionic Layer Adsorption and Reaction. Q10. Which type of material is used for anode in electroplating technique? [1] (a) Metal (b) Ceramic (c) Insulators (d) Semiconductors A metallic coating is electrodeposited on the cathode of an electrolytic cell consisting of a positive electrode (anode), a negative electrode (cathode), and an electrolyte solution (containing the metal ions) through which electric current flows. Q11. Match the techniques given in SectionA on the basis of methodology given in SectionB. [2] Section A Section B 1. Electroplating (i) A liquid precursor is deposited onto the substrate due to centrifugal force. 2. Spin coating (ii) A thin film deposition process where temperature and relative vapor pressure plays a crucial role. 3. Spray pyrolysis (iii) A solution is used for the transfer of electrons from the

5 deposition 4. Dip coating anode to the cathode. (iv) Thin film is deposited due to the formation of a chemical compound. (a) 1-(iii), 2-(i), 3-(iv), 4-(ii) (b) 1-(i), 2-(iii), 3-(iv), 4-(ii) (c) 1-(iii), 2-(i), 3-(ii), 4-(iv) (d) 1-(iii), 2-(iv), 3-(i), 4-(ii) Electroplating: An electrochemical process is one in which metal ions are transferred from a solution and are deposited as a thin layer onto the surface of a cathode. Spin coating: Spin casting uses a liquid precursor deposited onto a smooth and flat substrate which is subsequently spun at a high speed to centrifugally spread the solution over the substrate. Spray pyrolysis deposition: It is a process in which a thin film is deposited by spraying a solution on a heated surface where the constituents react to form a chemical compound. Dip coating: It is a process where the substrate to be coated is immersed in a liquid and then withdrawn with speed under controlled temperature and atmospheric conditions. Q12. What will be the sputter yield if the incident angle is 90? [2] (a) 1 (b) 0.5 (c) 0 (d) 0.4 It can be clearly observed from the graph given below that sputtering yield is zero when the incident angle 90.

6 Q13. Calculate the mean free path of atoms in the vapor, if particle density and interaction cross section are 10 m -3 and 0.5 m 2, respectively? [2] (a) 5 m -1 (b) 0.2 m (c) 0.05 m 5 (d) 20 m -5 Given, particle density and interaction cross section are 10 m -3 and 0.5 m 2, respectively. As we know that, mean free path of atoms in the vapor is given by, λ mfp = 1 nσ λ mfp = λ mfp = 0.2 m Q14. Compute the diffusion coefficient for copper in nickel at 650 ºC. Taking temperatureindependent pre-exponential (entropic pre-factor) as m 2 /s, diffusion activation energy as 256 kj/mol and gas constant as 8.31 J/mol-K. [2] (a) m 2 /s (b) m 2 /s (c) m 2 /s (d) m 2 /s The diffusion coefficient may be determined by applying:

7 D = D o exp E D RT Temperature-independent pre-exponential, D o = m 2 /s Activation energy, E D = 256 kj/mol Gas constant, R = 8.31 J/mol-K Temperature, T = 650 ºC = ( ) K = 923 K Substituting the values in the above equation; D = m 2 s exp J mol 8.31 J mol K 923 K D = m 2 Q15. Which of these techniques require an external current source for the deposition of metallic ions on the substrate? [2] (a) Electroless plating (b) Chemical bath deposition (c) Electroplating (d) Dip Coating Electroplating is the technique in which an external current source, through which electric current flows, is necessary for the transfer of metallic ions from the anode to the cathode. s