Fluorination of SiC with NF_3 by Plasma Assisted Reaction and Thermally Chemical Reaction

用NF_3反应离子刻蚀SiC时，当NF_3气压为3 Pa时，刻蚀速率最小。在NF_3气压为1 Pa、射频功率为100 W的条件下，经过RIE处理的抛光SiC样品，在30 min内表面仍保持nm量级的光滑，而在60 min内表面变得粗糙，粗糙度为20 nm。当NF_3压力高于3 Pa时，SiC表面由于F自由基与Si反应而变得富碳，富碳部分充当了微掩模，在SiC表面形成了尖峰，发射光谱观察到N_2^+、N_2和F自由基等物种。在较低的NF_3气压下，N_22^+离子优先进行物理刻蚀;在较高的NF_3气压下，F自由基优先进行化学刻蚀。在NF_3气压为0.5Pa、射频功率为100 W时，刻蚀速率可达87 nm/min，刻蚀深度为2 μm，刻蚀后的SiC表面为纳米级光滑。分析了反应离子刻蚀（RIE）过程中多晶SiC和SiC（111）样品尖峰的形成机理，发现尖峰的生长方向与SiC表面的临界面和晶界无关。在向下流动蚀刻（DFE）期间，多晶SiC表面上诸如（311）和（220）的晶格平面的蚀刻速率与（111）、（200）和（222）晶格平面的蚀刻速率相比小。另一方面，Ar^+离子溅射对上述各晶面的刻蚀速率几乎相等。

In the reactive ion etching (RIE) of SiC with NF_3, the etching rate was minimum at NF_3 pressure of 3 Pa. The surface of polished SiC specimen with treatment by RIE under conditions such as NF_3 pressure of 1 Pa and RF power of 100 W remained smooth in the scale of nm within 30 minutes, whereas it became rough in scale of 20 nm over 60 minutes. In contrast, the SiC surface became carbon-rich by RIE under NF_3 pressures higher than 3 Pa, because of the reaction of F radicals with Si on the SiC surface, and the carbon-rich part of SiC surface acted as a micromask to form spikes on it. The species such as N_2^+, N_2, and F radicals were observed in NF_3 plasma by optical emission spectroscopy. The physical etching by N_22^+ ion under lower NF_3 pressures and the chemical etching by F radicals under higher NF_3 pressures were preferentially occurred, respectively. Therefore, it is considered that the etching rate of 87 nm/min was obtained at NF_3 pressure of 0.5 Pa with RF power of 100 W, and that the depth of 2 μm was etched anisotropically with the smooth SiC surface in scale of nm. Analysis on the spike formation mechanism on the poly-SiC and SiC(111) specimens during RIE treatment revealed that the growth orientation of spike was independent of the critical face and the grain boundery on the SiC surface. The etching rates of the lattice planes such as (311) and (220) on the poly-SiC surface during Down Flow Etching (DFE) were small compared with those of (111), (200), and (222) lattice planes. On the other hand, the each etching rate for lattice planes mentioned above by sputtering with Ar^+ ion was almost equal to each other.