EE245 Homework 2

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1. Here is a paper written by Kirt Williams and Richard Muller on etch rates for micromachining processes.
1. What is the actual composition (by weight) of "concentrated HF"?  "5:1 BHF"?
2. Is phosphoric acid a solid, liquid, or gas at room temperature? At what temperature do we typically etch with it?
3. What two pieces of equipment were used to measure the etch rates? 
   
2. Find two MEMS-related journal and give their names here:
   
   
3. 20# Xerox paper (letter size) is about 100 microns thick. If you were to scale a sheet of Xerox paper down to 2 microns thick how big would it be?
   
   
4. Draw the cross-section of the following process flow, along the dash-line direction in the picture. Assume a bare {100} silicon starting substrate. If I release theis cantilever, how will it curl?
       1. LPCVD PSG, 2 micron
       2. spin negative photoresist, expose using mask1, develop
       3. timed HF etch with 50% overetch (how long will this take?)
       4. strip resist in acetone
       5. LPCVD polysilicon, 2 microns, anneal at 900C for 30 minutes
       6. spin positive resist, expose using mask 2, develop
       7. plasma poly etch, 50% overetch (what machine should I use? how long will this take?)
   
       Note: For both masks, the area outside of box is considered to be transparent.
   
5. Draw a cross-section of the same process as in question 2, but assume that positive resist is used for both lithography steps.