Resolution enhancement method using an apodized mask

Abstract

Optical super-resolution techniques, such as the phase shift mask, off axis illumination, and the pupil filter method, are strong candidates for mass production of next-generation ultra-large-scale integrated circuits. Although we can greatly improve the resolution and the depth of focus by using these techniques, there are some drawbacks. They depend on the patterns, as well as the pattern orientation. We suggest an apodized mask technique as a new super-resolution technique, which can improve resolution independent of the pattern type and the orientation. The linewidth and the secondary maxima can be greatly reduced by using a transmittance-controlled apodized mask. The resolution obtained by using triangular, exponential, and Gaussian types of apodized masks is better than that obtained by using a conventional rectangular-type mask. We also suggest several chrome mask etching methods for the apodized mask.