| AVS 55th International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuP |
| Session: | Plasma Science Poster Session |
| Presenter: | M. Wang, Iowa State University |
| Authors: | M. Wang, Iowa State University M.J. Kushner, Iowa State University |
| Correspondent: | Click to Email |
During plasma etching of via-like structures having high aspect ratios (HAR > 10), twisting is sporadically observed. This is where an otherwise straight feature will turn from the vertical. Twisting may occur in only a few percent of features among other features that have unaltered profiles. The effect is most frequent when feature size openings to the plasma are only tens of nm. Twisting in plasma etching of SiO2 has been computationally investigated using the Hybrid Plasma Equipment Model to obtain the energy and angle distribution of ions and neutrals; and the Monte Carlo Feature Profile Model to predict profiles. The basic operating conditions are a capacitively coupled plasma sustained in Ar/C4F8/O2 = 80/15/5 (1 kW, 10 MHz, 40 mTorr, 300 sccm). Parametric investigations were made while varying aspect ratio (10-40), height of the photoresist mask, power deposition and reaction probabilities (e.g., angular dependence of scattering). When including charging, features should be resolved with atomic-scale resolution to eliminate numerical effects. We found that as the feature size decreases, the flux entering the feature becomes more stochastic in nature. This randomness in the flux can then lead to variations in both the total etch rate on a feature-to-feature basis as well as on the profile. For example, preferential polymer buildup on one side of the feature may produce asymmetric etching. These effects are magnified when including charging as the stochastic nature of the flux produces errant local electric fields that deflect ion trajectories. The height and character of the mask material potentially has an important role in twisting. The photoresist height contributes to the effective aspect ratio; and its electron and ion scattering characteristics contribute to deliver of charge deeper into the feature.
*Work supported by the Semiconductor Research Corp., Micron Inc. and Tokyo Electron Ltd.