Photostabilization of i-line Photoresist and ARC Layer

Abstract

Stabilization after the lithography process is crucial in order to prevent deformation of photoresist patterns by other thermal processes used in semiconductor production. UV hardening is capable of minimizing negative effects of thermal processes such as rounded shaped lines; line width widening or shrinkage and CD shift. The amount of UV energy absorbed and final process temperature are important process parameters; which effect directly the degree of cross-linking. So, this paper examines optimization of process parameters such as the ramp rate, which is the tangent of the temperature-time curve (°C/sec) and the final temperature. Also the ramp rate indicates the time; that wafer is exposed to the high degree of UV energy. Process parameters are optimised with respect to the improvement of etch selectivity, decrease of the CD shift. Profile photos have been taken with Scanning Electron Microscope. In the experiments, the novolak based i-line photoresist and ICON-7 as anti reflecting coating are used for the lithography process. Many variables have been taken into consideration while determining optimum process parameters. These are resist thickness, type of the surface layer of wafer, magnitude of the critical dimension (>1 μm & < 1 μm ) and the size of the open area on the reticle used during exposure.