Intrafield CD variation by stray light from neighboring field

Abstract

The main object of this paper is to investigate the root cause of CD change by neighboring field observed in KrF scanner (max. 0.70NA) and to measure the amount of stray light from neighboring field precisely. Line widths of gate pattern are measured at the isolated and surrounded field and the amount of CD change by neighboring field is found to be proportional to the clear ratio of mask. By exposing with special configuration, it is found that the line width is linearly decreased as the dose of neighboring field increases. From this linear dependency on doses of neighboring field, it is clear that non-negligible amount of light is scattered out into the adjacent field. The amount of this stray light level coming from neighboring field is obtained quantitatively by synthetic analysis of above result and double exposure to mimic background DC light by flare. About 1.2% of stray light from outside of the field is observed at the slit position close to the boundary of neighboring field. Disappearing pad test is also performed to measure the flare from exposure of field itself. Finally, it is obtained the distribution of total stray light - nominal flare plus flare from adjacent field - and it is found to be existed around 0.7% deviation of stray light across the slit.