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TRAVIT: Dry Etch Simulation Software

Microloading and macroloading effects in dry etch contribute significantly to variation of critical dimension across the photomask. Microloading is a pattern dependent effect, while macroloading depends on long scale pattern density and also on distribution of plasma and reagents across the mask. Hence, when a process is established for a given system, the CD variation depends on the pattern under etch. The contribution of dry etch to CD variation for high end masks should not exceed a few nanometers all over the mask. Therefore, it would be highly desirable to simulate a pattern via mathematical modeling to predict CD-variation due to dry etch and then decide if the predicted variation remains within the prescribed tolerance, or if additional correction or some modifications are needed. When the CD-variation due to dry etch is known, corrective measures can be taken.

Simulating a dry etching process is a complex problem that requires a detailed knowledge of plasma physics, the interaction of plasmas with solids, plasma chemistry, kinetics, etc. Because of this complexity, there is no commercial software tool available to the industry. The first dry etch simulator, TRAVIT, was recently introduced. It was developed primarily for photomask fabrication.

TRAVIT is a software tool that is focused on simulation of CDs and CD variations; these are not being addressed by currently known models. An analytic model is used to simulate the dynamics of etch profiles. A GDSII pattern is taken as an input, an initial resist profile and etch parameters are given by the user; the software comes up with profiles for all layers as a function of time. The simulation can handle isotropic etch, anisotropic etch, and a combination of the two. Using etched profiles found by the software, it then extracts CD’s and calculates CD-variation. Our goal has been to develop software for process engineers, rather than for research scientists. The only inputs the simulation software needs are about the type of pattern to be etched and process involved. The process engineer does not need a detailed knowledge and understanding of plasma physics, chemistry, or kinetics to run simulation.