TRAVIT: Dry Etch Simulation Software

Microloading and macroloading effects in dry etch contribute significantly to variations in critical dimensions across a photomask. Microloading is a pattern dependent effect, while macroloading depends on long scale pattern density, as well as the distribution of plasma and reactants 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 the 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 corrections or modifications are needed. When the CD-variation due to dry etch is known, corrective measures can be taken.

Simulating dry etching processes is a complex problem that requires 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 currently available in 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 the simulation of CDs and CD variations, which 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 the input, an initial resist profile and the etch parameters are given by the user, and the software outputs profiles for all the layers as a function of time. The simulation can handle isotropic etch, anisotropic etch, and a combination of the two. Using the etched profiles found by the software, the CD's and calculates CD-variations are extracted. Our goal has been to develop a software tool 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 the processes involved. The process engineer does not need to have a detailed knowledge and understanding of plasma physics, chemistry, or kinetics to run the simulation.

See examples or references.