Estimation of Optimum Electron-Beam Projection Lithography Mask Biases Taking Coulomb Beam Blur into Consideration

In electron-beam projection lithography, a large field is exposed by one dose, and the mask biasing has been proven to be one of the most suitable methods for proximity effect correction. In this study, we obtained the exposure intensity distribution (EID) function through an exposure experiment with a 100 kV point beam exposure tool and expressed it as the sum of seven Gaussian functions. We calculated the exposure dose distribution in the line-and-space and isolated-line patterns as convolutions of the 7-Gaussian EID function and mask patterns, and the predicted line widths agreed well with the experimental results. The range of mask biases determined using the 7-Gaussian EID function for the gate and metal interconnect layers of 65-nm-node ASIC devices were ±22 nm and ±43 nm, respectively.