Improvement of the focus exposure latitude using optimized illumination and mask design

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Abstract
The performance of off-axis illumination techniques in comparison to conventional illumination has been investigated for features in the 0.5*((lambda) /NA) range. Conventional masks, chromium masks with assistant features, and halftone phase-shifting masks have been used in combination with these techniques. The analysis includes dense and isolated test features as well as real design features of a random logic IC. Advanced positive tone i-line resists and a 0.48 NA wafer stepper have been applied. Focus and exposure latitudes, linearity, cd proximity effects, and feature deformations caused by the applied techniques are considered. The analysis is done experimentally and theoretically based on cd calculations of developed resist features using Depict-3. The advantages and drawbacks of these techniques are discussed. An ultimate resolution of dense IC features down to 0.30 micrometers for a 0.48 NA i-line wafer stepper is achieved using annular illumination with halftone phase-shifting masks. For 0.5*((lambda) /NA) features practically usable latitudes are demonstrated.

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