Etching and deposition of materials are critical steps in the manufacturing of integrated circuits and flat panel displays. Both etching and deposition may have isotropic and anistropic components, due to directional sputtering and redeposition of materials. Previous attempts at modeling profile evolution haveused so-called "string theory" to simulate the moving solid-gas interface between the semiconductor and the plasma. One complication of this method is that extensive de-looping schemes are required at the profile corners. Our profile evolution model avoids such complications by using a level set simulation to track the plasma-substrate interface over time. By embedding the location of the interface in a field variable, the need for de-looping schemes is eliminated and profile corners are more accurately modeled. This simulation of profile evolution using level sets (or SPELS) calculates both isotropic and anisotropic etch rates of a substrate in low pressure (10s mTorr) plasmas, considering the incident ion energy angular distribution functions and neutral fluxes. We have coupled SPELS to plasma reactor models such as SEMS (developed in our IPT) to use calculated species fluxes. We are investigating etching profiles of different substrate materials (Si, SiO2) in various gas mixtures (Cl2, HBr, C4F8). Comparisons to experimentally obtained profile shapes from industry are underway.
To view an article on Helen's research, please see the NAS website:
http://www.nas.nasa.gov/Main/Features/2000/
Fall/plasma.html
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