Abstract: Resolution enhancement techniques have been explored extensively in the last few years in attempts to reliably extend optical lithography to smaller features. Off-axis illumination has shown remarkable success improving the depth of focus for dense lines and spaces. However, the depth of focus for isolated lines is degraded. This paper shows experimental results of 0.22 $mu@m lines at varying pitch printed with a rim phase-shifting mask on a GCA DUV stepper with 0.53 NA and annular illumination of 0.6 - 0.7 $sigma@. Although the results demonstrate a depth of focus of greater than 1.0 $mu@m, there are severe proximity effects which cause a 60 nm difference between the dimension of dense versus isolated lines. We hypothesize that this proximity effect is caused by three physical phenomena, the aerial image itself, reflections from the silicon substrate, and acid diffusion in the APEX-E (IBM) resist. Simulation results are presented which show that of the 60 nm linewidth difference, 10 nm is due to the image, 10 nm is caused by substrate reflections, and 40 nm is the result of acid diffusion in the resist. !11
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