Thermal-cyclic etching of SiGe with selective removal over Ge using fluorocarbon-based plasma and infrared heating

Self-limiting thermal-cyclic etching of SiGe films demonstrating etch selectivity over Ge was achieved using alternating exposure to radicals generated in CHF3/N2/O2 plasma and infrared heating. Si, Ge, and SiGe with Ge contents from 25% to 70% were used as sample materials. In situ x-ray photoelectron spectroscopy revealed a N 1s peak attributed to N-H bonds after radical exposure to SiGe and Ge. The peak disappeared upon heating to 100 °C, indicating removal of the surface-modified layer. Cyclic etching of SiGe and Ge using a dry chemical removal tool shows thickness reduction with increasing cycles. The etch per cycle (EPC) for SiGe ranged from 3 to 7 nm, while that for Ge was 1–2 nm. Si was continuously etched. Saturation behavior with respect to radical exposure time was observed for both SiGe and Ge. Enhanced EPC of SiGe over Ge is attributed to the selective formation of the modified layer on SiGe surfaces.