CALCULATION OF OPTICAL PARAMETERS
IN LASER ENGRAVING OF PHOTOMASKS    

Chen Yi Hong  &  Chen Wei Long
Gintic Institute of  Manufacturing Technology
Nanyang Technological University Nanyang Avenue, Singapore 2263  

Tam Siu Chung  
School of Electrical & Electronic Engineering
Nanyang Technological University Nanyang Avenue, Singapore 2263  

ABSTRACT
 
In laser engraving of photomasks, the line width is one of the critical characteristics  in determining the quality of masks and depends mainly upon the laser focus spot size. In this paper, a theoretical equation relating the laser focus spot size to the optical parameters of the laser system, including resonator parameters, beam expansion ratio and focal length of the focusing lens is derived. Confirmatory experiments using a Q-switched Nd:YAG laser system and photomasks with iron oxide coatings were carried out. The obtained actual spot sizes lay within 10% of the theoretical value.

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Reprinted from Proc. of 1995 Int. Conf. on Optoelectronics and Lasers, 365-368
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