Homework for Chapter 5: Lithography and Etching
Questions:
1. Describe the process modules of photolithography.
2. What is the purpose of softbake? What will happen if excessive bake or
insufficient bake? Please describe the equipments for soft-bake.
3. How many printing methods for exposure? Please compare them.
4. What will affect resolution and DOF of exposure? How to improve them?
5. Please describe in detail different kinds of resist removal.
6. Please describe at least two kind of advanced lithography techniques.
7. Please describe wet etch and dry etch briefly.
8. Please compare wet etch with dry etch for oxide etch.
9. Please compare wet etch with dry etch for nitride etch.
Problems:
3) A 2 m layer of silicon dioxide on a Si substrate needs to be etched down to
the Si. There is a 5% variation in the oxide thickness and a 5% variation in
the oxide etch rate.
a) How much overetch (in % time) is necessary to ensure complete removal of
the oxide layer?
b) Assuming that the overetch in (i) has been carried out, what selectivity of the
oxide etch rate to the Si etch rate is required so that no more than 5 nm of Si
is being etched?