In this study, atomic layer etching (ALE) of silicon nitride (SiN) using a cyclic process with monofluoromethane chemistry was investigated. Results show that an appropriate desorption time must be chosen at a specific adsorption time to achieve SiN ALE. The results also show that the infinite selectivity of SiN over Si can be achieved using the cycle process. To further understand this behavior, the adsorption and desorption effects were also studied. The results revealed a mechanism to obtain a high Si selectivity and a dominant factor that causes the Si loss. To further understand the ALE capability, we studied and compared the etched profiles and resulting surface roughness obtained by both a conventional process and an ALE process. The results show that the ALE process can achieve a high Si selectivity and a non-detectable level of Si surface damage, compared with a conventional continuous etching process.

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In Si/SiGe dual-channel FinFETs, it is necessary to simultaneously control the etched amounts of SiGe and Si. However, the SiGe etch rate is higher than the Si etch rate in not only halogen plasmas but also physical sputtering. In this study, we found that hydrogen plasma selectively etches Si over SiGe. The result shows that the selectivity of Si over SiGe can be up to 38 with increasing Ge concentration in SiGe. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results indicate that hydrogen selectively bonds with Si rather than with Ge in SiGe. During the etching, hydrogen-induced Si surface segregation is also observed. It is also observed that the difference in etched amount between SiGe and Si can be controlled from positive to negative values even in Si/SiGe dual-channel fin patterning while maintaining the vertical profiles. Furthermore, no plasma-induced lattice damage was observed by transmission electron microscopy for both Si and SiGe fin sidewalls.