Potential of phase-shifted optical proximity correction for 65 nm T-shaped pattern in high numerical aperture lithography

Optical proximity correction (OPC) has been employed as a key enabling resolution enhancement technique required to meet image size control requirements imposed by state-of-the-art integrated circuit product programs. However, at the sub- 65-nm node, the line end shortening effect for T-shaped pattern becomes pronounced and it is hard to correct using OPC due to the small gap size. Phase shift masks (PSMs) can improve lithography resolution and will be used at 65 nm node. However, phase conflicts occur when imaging a T-shaped pattern with PSM. Hence, it is becoming increasingly more challenging to print T-shaped patterns for sub- 65-nm nodes. A new OPC method, phase-shifted optical proximity correction (PSOPC), has been proposed to improve the imaging fidelity for T-shaped pattern and avoid the phase conflict caused by the use of PSM. A PSOPC mask has phase-shifted segments that can simultaneously modify the intensity and phase of the incident light. PROLITH 9.0 and in-house-software microcruiser were applied to demonstrate the new approach of PSOPC. The authors' results show that the line end shortening can be reduced to 4.6 nm and the depth of focus can be improved to over 200 nm. These results showed that PSOPC has significant potential as a new resolution enhancement technology for 65 nm T-shaped pattern lithography.