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HW2 Fall 2009

# HW2 Fall 2009 - b Compute the thickness of each of the...

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EEL5225 Principles of MEMS Transducers HW2 Fall 2009 Semester Assigned: Wednesday, 9/2 Due: Wednesday, 9/9 1. A 1600 angstrom thick oxide is required as a dielectric layer for a MEMS device. The oxidation time must be longer than 10 minutes in order to have adequate process control but shorter than 3 hours to have adequate throughput. Use the Deal-Grove model for a bare (100) silicon wafer. a. Using the data on slide 19 in handout 3, determine which temperatures can be used for dry oxidation to meet these criteria. b. Similarly, determine which temperatures can be used for wet oxidation to meet these criteria. 2. To achieve a 1600 angstrom thick oxide at 920C in a shorter amount of time while maintaining a high- quality dielectric, we use a dry/wet/dry oxide where the initial and final dry steps are 30 min each. a. Compute the time required for the wet step to achieve a 1600 angstrom total thickness.
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Unformatted text preview: b. Compute the thickness of each of the three layers. Sketch and label the layers. c. Discuss how much longer the dry/wet/dry process takes compared to a pure wet oxidation, but how much time is saved compared to a pure dry oxidation. 3. Explain why some silicon is consumed during thermal oxidation, and derive the equation x Si consumed = 0.46 x ox . 4. Explain whether the residual stress in thermally grown oxide is compressive or tensile and give reasons why. Research typical stresses in thermally grown oxide and give references. 5. A device fabrication involves depositions of Al, Cr, Si 3 N 4 , and SiO 2 . For each material, choose a deposition process (PVD or CVD). For PVD, specify Evaporation or Sputtering; for CVD, specify LPCVD or PECVD. Explain each of your choices. Hint: Temperature and quality....
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