EE245 Homework 2
Due 9/13/00
First Name:
Last Name:
Here is a
paper
written by Kirt Williams and Richard Muller on etch rates for micromachining processes.
What is the actual composition (by weight) of "concentrated HF"?
49%(by weight)HF+51%water
"5:1 BHF"?
Made by 5 parts of NH4F(40%) and 1 part of HF(49%), i.e. 33%NH4F+8.3%HF+58.7%water
Is phosphoric acid a solid, liquid, or gas at room temperature?
solid
At what temperature do we typically etch with it?
160
o
C
What two pieces of equipment were used to measure the etch rates?
NanoSpec AFT interferometer and Alphastep 200 profiler
Find two MEMS-related journal and give their names here:
JMEMS, Sensor and Actuator, and so on
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?
11inch*8.5inch = 279mm*215.9mm ======> 0.17inch*0.22inch = 5588um*4318um
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?)
Check the etch table, if we use 5:1 BHF, annealed PSG's etching speed is 4400A/min=0.44um/min.
We need to etch 2um's film and plus 50% overetch, then it gives us a time of
2um/(0.44um/min)*1.5 = 6.82mins = 410sec
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?)
Cl2 + He (180:400 sccm), Lam Rainbow 4420, etch rate 3200A/min, so the time is
2um/(0.32um/min)*1.5 = 9.375mins = 563secs
Note: For both masks, the area outside of box is considered to be transparent.
After release, it will curl up.
Draw a cross-section of the same process as in question 2, but assume that positive resist is used for both lithography steps.