You have to deposit four layers on top of each other.

• The first layer is an n-type, highly doped Si crystalline film. Choose the appropriate method, the suitable temperature and the dopant used. Show the main chemical reactions and the main steps of the process. Calculate the segregation factor. What kind of substrate should be used to avoid stress and defects? Explain why.
• The second layer is the natural oxide of the first layer. How do you fabricate 25 nm of thin layer with excellent properties? Explain your choice. What kind of temperature and gases are required? Explain how the thickness will vary in time for this situation.
• The third layer is a metal. Choose a deposition method with high deposition rate and good uniformity. Explain why is this method better than the others in obtaining the desired properties. Compare the chosen method with evaporation, by calculating the film thickness variation over a 10-inch wafer if the evaporation source is at 20-inch distance from the layer. Give other differences between the chosen method and evaporation. Explain how a high deposition rate is obtained. If a structure needs to be planarised, give three completely different metal deposition methods that can be used for this purpose. Show how it is done in each case.
• The last layer is a dielectric deposited on top of the metal. Indicate what type of deposition may be used in this case. Explain how a plasma is created and the reactions take place. Choose the method that can deliver the best layers in terms of step coverage and explain what happens in this case in the reactor. What is the rate limiting step for this method, considering that high flows are used? Explain why. What is the problem in obtaining good step coverage layers with this method? How can this be controlled?