As the design rule of semiconductor microchips gets smaller, the distortion of a patterned image due to the optical proximity effect(OPE) becomes the limiting factor in the mass production. We developed an optical proximity correction (OPC) program that can be applied to a strong or attenuated phase shift mask (PSM) as well as to a binary mask. The OPC program named OPERA is based on a stochastic approach (Monte-Carlo) as other rule-free OPC programs, but it has two remarkable points. Firstly, proper cost function and optimization strategy enable us to achieve very closely clustered mask pattern that could be manufactured at a reasonable cost. Secondly, OPERA can carry out the optimization of illumination parameters for any modified illumination methods, such as, annular or quadrupole using the critical dimension information of mask patterns.

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We studied whether the critical layers of 0.12µm DRAM could be processed with optcal lithography techniques assuming ArF excimer laser as a light source. To enhance the aerial image fidelity and process margin, phase shift mask (PSM) patterns as well as binary mask patterns are corrected with in-house developed optical proximity correction (OPC) software.As the result, we found that the aerial image of the critical layers of a DRAM cell with 0.12µm design rule could not be reproduced with binary masks. But, if we use PSM or optical proximity corrected PSM, the fidelity of aerial image, resolution and process margin are so much enhanced that they could be processed with optical lithography.