SIMULATION OF MASK SCATTERING EFFECTS IN MASKED ION-BEAM LITHOGRAPHY

A new simulation program has been developed for modeling masked ion beam lithography and has been used to study the impact of mask scattering on resist profile shape. The model uses analytical calculations to find the energy deposition in the resist. The program output is the development contour in the resist for any specified time, mask, resist, or beam parameters. The program has been applied to a study of the mask membranes and absorber patterns used in masked ion beam lithography. The applications are to membrane support scattering, absorber layer scattering, tapered absorbers, and technological evaluation. The membrane scattering of the beam is found to have a minimum divergence of approximately 0. 3 degree . It is also possible to achieve inverse contrast in the ion beam mask, for thin absorbers. This same effect causes the effective bias of a tapered absorber to be approximately 75% of the taper width. Also, relatively high angled tapers can be tolerated for heavy absorbers within certain limitations. Finally, using optimistic assumptions, the channeling approach to masked ion beam lithography appears limited to a minimum feature size of about 0. 25 mu m.