A Simple Optical System Parameter Optimization Method by Comparing the Critical Dimension

Abstract

Resolution enhancement technology will play a crucial role in the future of optical lithography. The only question is how much the resolution limit can be extended. The better critical dimension (CD) uniformity is demanded as pattern size is decreased. In our previous work, we had made a simulation tool which can find the optimum illumination system such as numerical aperture, wavelength, and illumination shape for best CD control. In order to improve better CD control, the mask size, assist feature size and placement are modified by the simulated annealing (SA) algorithm. However, in this method, the effects of post exposure bake or development process are not considered to predict the real CD, since the results are obtained only with the aerial image which can be precisely calculated. To consider these elements that affect CD profile, threshold energy resist model (TERM) model was suggested previously. However, TERM model still has a weak point in extracting necessary parameters for the transfer function. Therefore, we made a simulation tool using Monte Carlo method that extracts the necessary parameters with the experimental data. The experimental data include the exposure energy, measured line CD on a mask, wafer line CD after development. Finally, the predicted line CDs are compared to the empirical data under a different optical system condition to verify the extracted parameters. The simulation results matching the actual process can be obtained by using these methods.