Theoretical analysis of 157-nm hard pellicle system purification via a cyclic purge/fill process

Abstract

Optical lithography with 157-nm light is expected to bridge the gap between 193-nm technology and next-generation lithography. One important practical difficulty facing the implementation of 157-nm tech- nology is gas absorption of 157-nm light. The exposure process for 193-nm technology is carried out in an air environment, but oxygen gas and water vapor severely attenuate 157-nm radiation. However, 157-nm exposure can be carried out in a nitrogen environment, which can be achieved by purging. A challenging aspect of the nitrogen purging pro- cess is the evacuation of the volume delineated by the pellicle frame, and the 800-mm-thick hard pellicle plate, which can fracture when sub- jected to an excessive pressure difference. A technique for pellicle puri- fication via a cyclic purging and filling process is investigated. A theoret- ical analysis of the gas flow and pressure variation in the system is presented. The maximum stress induced in the hard pellicle during the process is predicted using finite element modeling. The minimum time for purification without causing excessive stress in the pellicle plate is estimated for a nominal set of conditions. Finally, a parametric analysis of important geometric variables including the size and number of purg- ing holes as well as the filter resistance is presented. © 2004 Society of