Step-by-step HF etching on Si (0001) and C (000-1) crystal faces of 4H-SiC with OH or F-OH terminations: A first-principles study of the atomic-scale etching mechanism

Abstract

Etching is a crucial step in the process of integrated circuits (ICs). This study investigates the sequential HF etching behavior of the Si (0001) and C (000-1) crystal faces of 4H-SiC with OH or F-OH terminations using first-principles density functional theory (DFT). Our research highlights significant differences between the C and Si faces in energetically favorable and etching efficiency. The C face shows more favorable etching energetics, with more negative and smoother relative energy variations near zero. In contrast, the Si face exhibits larger energy fluctuations and higher energy barriers, indicating a more difficult etching process. We also observed that the F-rich F-OH co-termination requires fewer HF molecules to etch a complete C-Si unit compared to the OH termination. Notably, the F-OH co-terminated C face exhibits more favorable reaction energetics and kinetics with a lower energy barrier of 2.77 eV. Additionally, the final etching products are highly consistent regardless of the C or Si face and termination type, with Si and C atoms removed as SiF4 and CHF3 gas molecules, respectively. Therefore, the termination mainly influences the energetics and kinetics of the etching process, with minimal impact on the etching products. Meanwhile, the etching process is accompanied by proton transfer and the formation of structures such as H3O⁺ and -C-O-Si-. These results provide key insights into etching mechanisms, which reveal the origin of the kinetic limitations and, by identifying these rate-limiting steps, provide a direction for future optimization of 4H-SiC etching processes.