**Problem 1: (Laser Micromachining – 25 pts)**

Assume that we want to machine very accurate features on the surface of a wafer by laser micromachining, using a 193nm Excimer laser. The material we wish to ablate has a threshold fluence of 10J/cm². Assume that we are using a focusing lens with a certain magnification, and that typical numerical aperture values for focusing lenses are NA=0.1 for a 4x lens, NA=0.25 for 10x lens, and 0.65 for 40x lens. Your task is to answer the following questions, and to provide your own discussion and interpretation of the results:

a) What is the minimum laser spot size achievable for the 3 different focusing lenses?

b) In all cases, calculate the maximum peak to valley roughness of a wafer that must be machined using the minimum spot size. Assume that the wafer can be scanned in a perfectly perpendicular plane to the laser beam.

c) In all 3 cases, calculate the peak power of a 10ns pulsed Excimer laser that would be required to machine the corresponding minimum spot features.

Subject | Science |

Due By (Pacific Time) | 07/27/2015 04:00 pm |

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