1. Briefly answer the following questions. You may use diagrams if necessary. a. In modern thin film deposition systems, the substrates are placed on a rotating platen. What is the purpose of the rotation? b. Consider deposition of 2 different thin films, film A with an activation energy (EA) of 1.5e V and film B with an activation energy of 2 ev. Each growth is in separate reactors. We know that both the films can be grown at 400 " C. If both the reactors are set at 400 "C, which film will have a higher growth rate? State your reasoning. c. The critical radius of nucleus of material C is composed of 100 atoms and material D critical nucleus radius is reached with 1000 atoms. If both the materials are grown under identical conditions, which film will grow first? State your reason. d. Why is it difficult to dope amorphous Si (a-Si) but easier to dope hydrogenated amorphous Si (a-Si:H)? e. If you were given 3 wafers, all with a 1 um thick silicon film and told that one wafer had an amorphous film, another had polycrystalline film, and the third had an epitaxial film. How would you identify each film if you had all the necessary tools available? f. Consider a horizontal reactor with a Si wafer placed flat on it, as sketched below. Start here (i) (ii) Gas flow Sketch the boundary layer profile over the wafer under the following conditions: i. At gas flow rates of 50 seem and 200 scem, assuming the same pressure in the reactor in both cases. Sketch both profiles in figure (i) above. ii. At reactor pressures of 1 Torr and 50 Torrs in figure marked (ii) above, assuming same flow rates in both cases. Briefly explain what you considered when sketching these profiles. g. When growing epitaxial silicon on sapphire substrates to produce SOS wafers, the source of silicon is silane, which decomposes at relatively low temperatures compared to other Si sources. i. State why silane is the source chosen. ii. What the purpose of SOS wafers? Why not use regular silicon wafers, which would be much cheaper? h. What is the difference between a partially depleted SOI (PDSOI) and a fully deleted SOI (FDSOI) device? Which one would have superior performance?ii. One can increase the speed of MDSFETs either by straining their channels or using 301 1wafers [er berth]. What are the mechanisms in each case that lead tc increased speed? j. 1|Il'lp'rhere weuld you use a highk dielectric and state why?r Where would you use a Icrwk dielectric and state why