Improved reflectivity control of APEX-E positive tone deep-UV photoresist

Abstract

A study optimizing the actinic absorbance of APEX-E positive deep UV photoresist was performed using a variety of dye additives. The selection of a dye and the optimization of dye content for APEX-E positive photoresist has led to substantial process enhancements in reduction of reflective notching and of thin film interference effects. The usual side effects as found in dyed I-line resists such as significant loss of photospeed, decreased focus latitude and sidewall angle decrease were not apparent with selected conjugated aromatic dyes. The benefit of added absorbance has allowed the direct use of dyed APEX-E to counteract the step interference (notching) problems over the severe topography of CMOS gate level and eliminate the reflective notching of surface strap level in the fabrication of 16 Mb devices. In addition, the depth of focus window was enhanced and process latitude was maintained. Geometries of 250nm were printed, with dyed APEX-E for optical densities ranging from 0.4 to 0.8 per micron with a DUV optical scanner.