Mass Spectrometry, Optical Emission Spectroscopy, and Atomic Force Microscopy Studies of Si Etch Characteristics in a Cl2 Plasma Generated by an Electron Cyclotron Resonance Source

Etching of Si with a Cl2 plasma generated by a multipolar electron cyclotron resonance source has been studied using mass spectrometry, optical emission spectroscopy (OES), and atomic force microscopy (AFM). It is found that the Si etch rate can be related to the SiCl63 intensity measured using mass spectrometry and the Si emission intensity at 634.6 nm using OES. At higher microwave or rf power, the Si etch rate, SiCl63 intensity, and Si emission intensity increase but the selectivity of Si over SiO2 decreases. Selectivity >80 is obtained with 30% O2 addition in Cl2. The induction time for Si etching is monitored by mass spectrometry and it decreases with microwave or rf power. Surface roughness is measured by AFM and it increases slightly with microwave or rf power. The optimized condition for Si etching was applied to the etching of polysilicon gate down to the thin gate oxide. A two-step etch process was developed for the etching of 0.35 µ m polysilicon gate with vertical profile, smooth morphology, and high selectivity to the underlying gate oxide. Only 0.5 nm of the gate oxide was removed with 100% overetch. End point for polysilicon gate etching was clearly monitored using mass spectrometry or OES.