Etch Control and SiGe Surface Composition Modulation by Low Temperature Plasma Process for Si/SiGe Dual Channel Fin Application

In this study, we discuss Si-SiGe etch characteristics as well as SiGe surface composition modification. It is required to etch Si and SiGe simultaneously for Si/SiGe dual channel Fin-FETs. Therefore, etch control of these two materials is desired. However, not only halogen chemistries but also physical sputtering etch SiGe selective to Si. We found that Si can be etched faster than SiGe by hydrogen plasma. Our analysis presents that hydrogen bonds selectively with Si rather than Ge, which leads to Si selective removal. As for SiGe surface modification, realizing Si-rich surface in SiGe is known to improve SiGe/high-k interface quality in advanced CMOS. It is also presented that the low-temperature hydrogen plasma induces Si-surface segregation (i.e., Si-rich surface) in SiGe, which is confined near the top-surface region. We proposed this may be caused by ion-energy-driven surface reaction. Our study also shows that Ge/Si ratio increases with plasma exposure time, which has correlation with surface roughness. Using the hydrogen plasma and conventional halogen plasma, we successfully demonstrate to etch Si/SiGe dual channel fins with depth and CD value control.