Reticle Purging Approaches by Nitrogen with Enhanced Efficiency

Abstract

The technology roadmap toward smaller structures and thinner layers in semiconductor manufacturing directs attention more and more toward yield-affecting influences from the air quality of manufacturing environment such as water vapor, O 2 , CO 2 etc. to absorb high-energy radiation and formation of haze form on reticle surfaces during microlithography processing. A useful method for reducing these yield-affecting influences is purging the reticle surface with nitrogen gas. The main issue is the difficulty in performing purge process in the space between the reticle and pellicle, which has a rather fragile geometry. Our study strives to find the optimized parameters by using computational fluid dynamic (CFD) simulation plus the corresponding inspection results of reticle exposed by 193 nm beam in the fab. Results show that Purging time is sensitive to both the number of purging holes and the purging flow rate. The required purging time can be reduced from 77 seconds to approximately 34 seconds by increasing the purging flow rate from 0.094 L/m to 0.376 L/m (corresponding to purging velocity of 1.0 m/s to 4.0 m/s). However, concerning the breaking of pellicle due to high velocity, the purging velocity was limited to 2.0 m/s (corresponding to its flow rate of 0.188 L/min). By doubling the number of purge/vent holes, with the same flow rate, the required purge time can be even reduced to 33 seconds.

Review—Airborne Molecular Contamination: Recent Developments in the Understanding and Minimization for Advanced Semiconductor Device Manufacturing

“…The efficiency of the purging process between the reticle and pellicle has a significant impact on the purge performance in reducing the product defects. 50 The purging time, the number of purge/vent holes, and purging flow rate are parameters that should be optimized to increase the purging performance. Hu et al conducted a series of parametrical studies on the purging of a FOUP designed for 300 mm wafers by N 2 .…”