HW_2 - ECE 432 Introduction to MEMS Homework 2(Due in class...

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ECE 432 Introduction to MEMS Sunil Bhave Homework 2 (Due in class on Monday, 9/10/2007) Fall 2007 1. Silicon Crystal a. Show that the angles between the {110} and {111} planes of a silicon (100) wafer are 35.26, 90 and 144.74º b. With KOH, the etch selectivity between the {100} and {111} planes is 400:1, not infinite.Therefore, the sidewalls of a pit etched in a (100) wafer will be very close to the {111} planes but not exactly parallel to them. (a) What angle do they really make? (b) What etch ratio would be needed to make 45° sidewalls? 2. Deep Reactive Ion Etching (DRIE) Explain what you see in the scanning electron micrographs (SEMs) below and why these effects occur: 3. Bulk Etching The Si {100} wafer shown below has a patterned silicon nitride mask on its top surface, and an unpatterned nitride layer on the bottom surface. With TMAH, the etch selectivity between the {100} and {111} planes is 35:1, and the {100} etch rate is 1 μm/min. Assuming that the nitride layer and all other Si crystal planes are not etched, sketch the wafer cross section after 400 minutes of etching on the drawing at the bottom of the page.
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  • Fall '07
  • Bhave
  • Crystalline silicon, Etching, Sunil Bhave, etch selectivity, Si etch depth

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