Development of Silicon Carbide Atomic Layer Etching Technology

Abstract

Silicon carbide (SiC) is an emerging material for applications in ultra-precision devices and space optics due to its low thermal expansion characteristics (3.8×10−6/℃) and light density (3g/cm³). However, machining and polishing of SiC are challenging because of its hardness and stiffness. Further, the conventional mechanical processing methods could result in micro-cracks on the surface of SiC, which consequently degrade the lifetime of the device under harsh conditions. We find that very smooth polishing of SiC without any surface damage is possible using plasma atomic layer etching, an emerging technology in the field of semiconductor manufacturing. In the present study, we conducted experiments to identify the mechanism of plasma atomic layer etching for bi-atomic materials and elucidated the optimized processing conditions to minimize the surface roughness of the etched SiC. By using process gases, such as SF6, H2, and O2, the etch rate could be controlled and the increase in the surface roughness could be minimized. We identified three main reasons for the increase in the surface roughness. The first is different etching speed of the silicon and carbon by fluorine active species. The second is the masking effect of C-H-F films produced during process. The last is the selective etching of silicon oxide and the other layers by fluorine active species. Due to the low etching property of silicon oxides, the surface roughness may increase at a faster rate under rich oxygen condition. Conversely, it is possible to minimize the surface roughness by adjusting the ratio of process gases. Under the optimum conditions of SF6 and O2 gas ratio (0.8), the etch rate of 1 layer/cycle and the roughness increment of 0.1 nm were obtained