Effect of humidity, residual solvent, and adventitious clean-room contaminants on the performance of AZ-PN

Abstract

E-beam/x-ray resist AZ-PN is relatively insensitive to process delay times of up to 24 h within the experimental error. Beyond this, deviation from the designed pattern size occurs due to delay times especially between exposure and post exposure bake. In the present paper an attempt has been made to evaluate the influence of humidity, prebake conditions, and overcoat materials on the sensitivity of AZ-PN to identify the reasons for the delay time (exposure - PEB) effect on the image transfer. Acidic overcoat material was used to eliminate the scavenging effect of basic impurities present in the clean room environment and prebake conditions were varied to change the residual solvent content of the resist film. It was observed that among the factors studied, humidity or moisture played a significant role. For instance, when the wafers were stored at 86% humidity the sensitivity (at 50% normalized film thickness) decreased from 7 (mu) C/cm2 to 13 and 19 (mu) C/cm2 for 48 and 96 h, respectively, while the decrease was only from 7 (mu) C/cm2 to 9 (mu) C/cm2 at 46% humidity for a delay time of 48 h. Under identical delay times, the higher the humidity, the higher the decrease in sensitivity. Use of overcoat materials decreased the overall sensitivity of the resist but did not influence the delay time behavior. Similarly, an increase in the prebake temperature from 80 to 100 degree(s)C or performing the prebake under vacuum at 90 degree(s)C for 30 minutes had no effect on the contrast curves. It was inferred from the results that if humidity is controlled, process delay time latitude of AZ-PN can be further improved.