Computer visualisation and proximity effect correction for submicron electron beam lithography

摘要

The resolution of the electron beam lithography is limited by a natural phenomena called the proximity effect. The proximity effect is the process whereby scattering of the electrons travelling through the resist results in non-uniformity of the absorbed energy distribution. Therefore, for exposures of submicron pattern features, the detrimental effects of the proximity effect must be corrected. This thesis describes a Monte Carlo simulation model which was used to determine the radial energy distribution (RED) in the resist for a point source exposure. The conventional MC models were found to be inadequate for low energy electrons and high atomic number (Z) substrates. Therefore, Mott scattering cross section for elastic collisions was used which takes quantum-mechanical effects into account. The inelastic collisions were simulated using Moller cross section and Gryzinski cross section for free and bound electrons respectively. The generation of secondary and tertiary electrons were also included in the model. This thesis also describes the development of a tool to simulate the exposures of submicron pattern features including the resist development process, using the RED data. The extent of the proximity effect was examined for different exposure conditions. A proximity effect checking tool was also developed to automatically identify the proximity effect critical areas. With these tools, a fully interactive visualisation CAD package, XPROX, was developed with 3D colour graphics and a MOTIF X window interface. Using this CAD package, quantitative evaluations of different proximity correction techniques were carried out. It was also used to visualise and correct the proximity effect interactively by examining the proximity effect critical areas. Therefore, this package provided a sophisticated set of facilities to visualise and correct the proximity effect in exposures of submicron pattern features.