Plasma Technology for Advanced Devices
Silicon Etching Mechanisms with HBr and Cl2
The effects of exposing a single crystalline silicon surface to a halogen plasma can be studied with spectroscopic ellipsometry (SE). The measurements show that the surface layer is partially amorphized after plasma exposure. In addition, the existance of a halogen containing layer can be shown (slide 1).
Similar information can be obtained by XPS. The thickness of the amorphized layer is derived from the FHWM of the Si-Si peak (slide 2).
Slide 3 compares the thicknesses of the brominated top layer as measured by SE and XPS. Similarity between etch rate and halogen coverage suggests that the etch rate is limited by the ability of halogenated products at the surface to form volatile species. Halogen coverage can be limited by: thermal flux of neutrals, ion flux, steric hindrance. At etch rate saturation (20 As-1), the silicon atom removal rate is 1016 cm-2 s-1, thermal flux of HBr at 2 mTorr is higher than 1017 cm-2 s-1.
From the studies, the following conclusions can be drawn (slide 4):