Q1:
Explain the difference between wet isotropic and anisotropic etching. What are
three factors that can affect etch rates of a wet etching process?
Sol:
Isotropic etching uses wet etchants that have a uniform etch rate in all directions.
Anisotropic etching uses wet etchants that are orientation dependent. These etchants will
etch in different directions at different rates.
Temperature, Etchant concentration and apparent atomic density
Q2:
Suppose you wanted to etch a V into a <100> Si wafer with an angle of 54.74 degrees
with respect to the <100> plane. First, how deep would the etching need to be?
Secondly, how long would it take?
You may assume :
• That you are using 30% KOH Solution at 60°C
o Hint: Determine approx. etch rates from graph in slides
• The gap in between the mask is 5µm wide
Solution:
Tan(54.74) = y/2.5 µm
y = 3.536 µm
The etch rate is 25 microns/hour
25 microns/hr = .416 microns/min
3.536 microns / .416 microns/min = 8.5 min
Q3:
A solution contains two parts of 69.51% HNO3, six parts of 49.23% HF, and two
parts of acetic acid (HC2H3O2). Find the etch rate of silicon in this solution. Label
the intersection point on the etch-curve provided and submit with homework.
Solution:
Q4:
What is the anisotrophy of solution on silicon with a lateral etch rate of 5 µm/min
and a vertical etch rate of 10 µm/min?
Solution:
A
= 1 – RL/Rv
= 1 – (5 µm/min)/( 10 µm/min) = 0.5