Subject: MEMS (micro-Electro-Mechanical System) Midterm Date:5/13 (Wen.)
Problem 1 (5%)
(a) Which are the three orientations of silicon wafers
most commonly employed in micromachining?
Please draw them by using the Miller indices. (2%)
(b) When etching a 100-oriented single-crystal Silicon (Si)
wafer with KOH, we obtain grooves with sidewalls
that have a very precisely defined angle (approximately
54.7 degrees slope). Calculate this angle with at least
3 decimal digits of accuracy (or, in other words, quantitatively
explain why this angle is observed).(3%)
Problem 2 (10%)
Briefly draw a flow chart to describe the photolithography process
sequence and then state the purpose for each step.
z
<111>
y
<100>
x
Problem 3 (20%)
(a) What is the difference when we compared the positive photoresist with negative one for the
photolithography process? (5%)
(b) What is a sacrificial layer? (5%)
(c) What is the lift-off process? (5%)
(d) What is LIGA (5%)
((a), (b) and (c) Please draw some figures to describe these processes of microfabrication.)
Problem 4 (5%)
In the isotropic etching diagram for silicon, the isotropic HNA silicon etching was well characterized.
Please answer the following question:
(a) If HF:HNO3:HC2H3O2=70:10:20, what is the etching rate? (1%)
(b) At this point, which components controls the etch rate? (2%)
(c) If we use water(10%) instead of HC2H3O2 (10%) as our diluent, the etching rate will be more
sensitive to which components? (2%)
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