Study on feature profile evolution for chlorine etching of silicon in an RF biased sheath

Ion-enhanced plasma etching has been widely used in Micro-Electro-Mechanical Systems (MEMS) and semiconductor manufacture. Especially, the pattern transfer in the production of micro-electronic devices requires high anisotropy etch to achieve deep and vertical trench profiles. Usually, a bias power will be applied on the substrate to form a sheath from which ions gain their kinetic energies, which is key for the ion assisted etching yield. In this work, we simulated a 2D profile evolution progress for chlorine etching of silicon. In addition to a DC bias investigation, we also consider a radio frequency (RF) biased sheath. In the method, first, a sheath model is used to get the ion energy distributions (IEDs) and ion angular distributions (IADs) of ions entering into the trench region after passing through the sheath. Then, ion motions in trench and flux distributions at the trench surface are calculated by tracing ion trajectories in the local electric field. Finally, considering the ion assisted etch yield of silicon in chlorine plasma, the cell removal algorithm is simulated to achieve evolution progress of the trench. Influences of different aspects such as the ion reflection, the bias voltage, the charging of the mask sidewalls, and the discharge pressure on the profile evolution are studied. Results show that ion reflections on sidewalls and local electric field in the trench cause the trenching, a large voltage can cause tapering, and the application of RF bias will reduce the trenching and achieve a larger etch rate. The gas pressure is also key in the trench formation. We can achieve more ideal trench topography by adjusting these discharge parameters.