Investigation of single sideband optical lithography using oblique incidence illumination

We propose a new method for enhancing the image contrast in oblique illumination lithography. In this article, we analyze the modulation transfer function to clarify the cause of poor contrast in oblique illumination systems. A unique optimization procedure is also proposed. It is carried out for the oblique illumination systems, including single sideband optical lithography. It is found that the contrast enhancing method and optimization can improve the resolution for annular source and four-point-type sources. These improvements open up the possibility of 0.25-μm resolution with i-line lithography.