Process optimization of APEX-E

Abstract

Excimer laser lithography combined with chemically amplified resists offers aviable approach to lithography at 0.5prn and below. APEX-E, a positive tonedeep-uv resist used in conjunction with a 0.44NA excimer laser stepper iscapable of 0.35pin resolution. To improve the process window for this resistwhile reducing the performance variability, the Taguchi method of qualitycontrol was employed. The baseline process for APEX-E was characterized, thensubsequently used as a comparison to the optimized process as suggested by theTaguchi experiments. Using the baseline process for this photoresist, theexposure latitude was 29% for 0.Spxn lines and spaces. This was increased to 40%after process optimization was completed. At 0.35pin dimensions, the exposurelatitude increased from 15% to 23%. Improved linewidth control was alsoverified during the confirmation experiment. The standard deviation for 0.Sprnlines and spaces decreased from 0.0216 using the baseline process to 0.0081with the optimized process. Thin film interference effects resulted in a0.ll4prn linewidth change from the minimum to the maximum on the swing curve for0.5iim lines and spaces. This was reduced to 0.O44prn using an appropriate ARCOR.Linewidths were linear down to 0.4pm for both the baseline and optimizedprocess. Linearity was further extended to 0.35psn with the addition of theARCOR process.