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
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '07
 Bhave
 Crystalline silicon, Etching, Sunil Bhave, etch selectivity, Si etch depth

Click to edit the document details