The optical proximity effects are becoming a significant consideration to the linewidth control in sub-micron optical litho-graphy, as the lithographic tools are being operated closer to the resolution limits. Proximity effect was first used to discribe pattern distortion caused by electron scattering in E-beam lithography. The term was described as a similar phenomenon of pattern distortion in optical lithography. Optical proximity effects seen on wafers arise from non-linear interactions between nearby regions of the aerial image. There are various forms of proximity effects, line width error, line end shortening, cornor rounding, etc, and the optical proximity behavior depends on the exposure wavelength, the partial coherence, and the numerical aperture of the printer. With parameter, the term is calculated from the image of mask with various patterns. The aerial image was calculated using Hopkins transmission cross coefficient, TCC, formulation and rapid integral evaluation technique using Simpson method without aberration and 16-point Gausian quadruture method with defocus. Various type of mask, conventional mask, alternating type PSM, attenuated type PSM and tri-phase type PSM, which the term was calculated with was used. Each mask have 0.18㎛ or 0.25㎛ minimum feature size which will be used in 1GB DRAM or 256MB DRAM. Of these mask, tri-phase type PSM which have two 120˚ phase-shifters desigend in a study. Sum of overlaped wave-vectors which are diffracted from each shifter is zero. So this mask has good contrast.
From the obtained data, in the conventional masks with 0.25㎛ pattern the maximum of proximity effect and its variation are smallest at σ= 0.6, and its variation rate in NA= 0.4~0.5 is 30% at σ= 0.4, 80% at σ= 0.6 and 10% at σ= 0.8. In the pattern of group 3 or 4, the variation rate of proximity effect in a tri-phase PSM which in NA = 0.4~0.5 is 8% ±1 is smaller then in conventional mask or attenuated type.
