a) A micro-fabrication expert evaluates two new lithographic systems with different light sources and numerical aperatures (NA), where the resolution (R) is given as R=k/NA. The lithographic system A uses KrF excimer laser source (248 nm) while the lithographic system B uses the I-line of a Hg lamp (365 nm) as the photon source. The lithographic tool constants k1=0.6 and k2 = 0.5. The lens diameter is 8 cm (6cm) and its focal length is 5 cm (4cm) in the system A (B). Determine the corresponding minimum feature size and depth of focus that could be defined by the two lithographic systems.
b) 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.
c) Briefly explain the main types of photoresist and compare their performance. Would you prefer a low or high contrast photoresist?
d) Give two main shortcomings of the e-beam lithography. Why do every semiconductor fab still need e-beam lithography tool despite these shortcomings?