a) You developed a lithography process based on KrF excimer laser source. You de
ID: 1837380 • Letter: A
Question
a) You developed a lithography process based on KrF excimer laser source. You developed a
mask set for this lithographic tool. A friend of yours thinks he could obtain better results if he
uses the mask-set in an identical tool that uses an X-ray source instead of the KrF excimer
laser. Is this an excellent idea? Explain why.
b) Briefly explain the main types of photoresist and compare their performance. Would you
prefer a low or high contrast photoresist?
c) Give two main shortcomings of the e-beam lithography. Why do every semiconductor fab still
need e-beam lithography tool despite these shortcomings?
Explanation / Answer
a) It is an excellent idea since it will increase the efficiency of the process because of the coherent nature of X-rays.
b) The main types of photoresist are: 1) positive resist, which is a type of photoresist in which the part that is exposed to light becomes soluble in the photoresist developer while the part of the photoresist that is unexposed remains insoluble. 2) Negative resist, which is a type in which the part that is exposed to light is insoluble in the photoresist developer while the part of the photoresist that is unexposed can be dissolved.
I do prefer a high contrast photoresist, for better resolution.
c) 1) Blanking or deflection errors which occur when the deflection of electron beam is not proper.
2) shaping errors which occur in variable-shaped beam systems when the sample is being projected by the wrongly shaped beam.
Despite all these draw backs, e-beam lithography tool is widely used in semiconductor industry because of its high resolution and low throughput.
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