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

在用NF3对碳化硅进行反应离子刻蚀(RIE)时，当NF3压力为3pA时，刻蚀速率最小。在1PaNF3压力和100W射频功率条件下，RIE处理的抛光碳化硅样品表面在30min内保持在纳米量级的光滑，而在60min后表面变得粗糙，达到20 nm量级。相反，在高于3PaNF3压力下，由于F自由基与表面硅的反应，RIE使表面富碳，表面富碳部分作为微掩膜在其上形成尖峰。用光学发射光谱观察到NF3等离子体中含有N_2~+、N_2、F等自由基。在较低的NF3压力下，N22+离子优先进行物理刻蚀，在较高的NF3压力下，优先进行F自由基的化学刻蚀。因此认为，在射频功率为100W、NF3气压为0.5pA的条件下，刻蚀速度可达87 nm/μ，刻蚀深度为2 mm，刻蚀深度为2 mm，表面光滑，尺寸为nm。对多晶硅和碳化硅(111)样品在RIE处理过程中的尖峰形成机制的分析表明，尖峰的生长方向与碳化硅表面的临界面和晶界无关。在顺流刻蚀过程中，多晶硅表面(311)和(220)晶面的刻蚀速率比(111)、(200)和(222)晶面的刻蚀速率小。而用Ar~(++)离子溅射时，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.