ECE 1406, Homework #4, Due April 29, 2003
1. 2.3, Text. For part a, draw the profile for an etch to completion, and for a 50% overetch. In each case, what is the width of the exposed silicon area completely cleared of oxide. Assume an ideal isotropic etch with no mask undercut.
2. a. Discuss briefly the mechanisms leading to anisotropy in dry plasma etching. (From notes or references.)
b. What are two drawbacks of plasma etching relative to wet etching?
3. Discuss the advantages and disadvantages of being in the reaction-rate-limited or mass-transfer-limited portions of the growth rate (as a function of temperature) curve for a CVD process.
4. You have two steppers that produce more or less fuzzy images for 0.1 micron lithography.
Assume that the light intensity for the less fuzzy image is given by 15(1+sin(kx)) mJ/cm2, where k=p/(100nm).
Assume that the light intensity for the more fuzzy image is given by 15(1+0.2sin(kx)) mJ/cm2, where k=p/(100nm).
a. What sensitivity is required to give a photoresist linewidth of 100 nm (at zero thickness)?
b. What contrast is required in each case to ensure that the photoresist reaches full thickness in the center of the 100 nm line?
c. If the photoresist sensitivity changes by 10%, what is the change in linewidth in each case (at zero thickness)?
The idea here is to see the photoresist processing difficulties that are seen when blurrier images (smaller k1 values) are used.