等离子体增强化学气相沉积法制备立方氮化硼薄膜过程中的表面生长机理

Surface growth mechanism of cubic boron nitride thin films prepared by plasma-enhanced chemical vapor deposition

利用感应耦合等离子体增强化学气相沉积法以Ar,He,N2和B2H6为反应气体制备了高纯立方氮化硼薄膜.用四极质谱仪对等离子体状况进行了系统的分析,发现B2H6完全被电离而N2只是部分被电离.H2和过量的N2在等离子体中生成大量中性的H原子和活化的N2,它们与表面的相互作用严重地阻碍了立方氮化硼的成核与生长.同时,H2等离子体和Ar等离子体并不能对sp2杂化氮化硼进行有效的选择性化学刻蚀和溅射.对在超薄硅片边上生长的立方氮化硼薄膜用高分辨电子显微镜进行直接观察,发现最优化条件下生长的立方氮化硼薄膜表面是纯立方相{111}晶面结构,不存在sp2杂化氮化硼表面薄层.研究结果表明,在等离子体增强化学气相沉积法制备立方氮化硼薄膜过程中,立方氮化硼是在表面上成核并生长的.

Chemical species in the low-pressure inductively coupled plasma for cubic boron nitride （cBN） film deposition using B2 I-I6, N2, He and Ar as reactant gases were investigated by quadrupole mass spectrometry. B2 I-I6 was found to be ionized totally, while N2 was only partially ionized. The species in plasma were Ar, He, N2 molecules and Ar^＋ , He^＋ , N^＋ , N2^＋ , B^＋ , BxHy^＋ , H^＋ and H2^＋ ions, no H and N radical was detected by appearance potential mass spectrometry. The introduction of H2 and N2 gases into the deposition system was found to produce a large mount of H radicals and excited N2^＋ molecules, which suppressed the cBN formation by reacting with the growth surface. The etching and sputtering of cBN and turbostraotic boron nitrde （tBN） by H2 and Ar plasmas were also evaluated, and we did not find that the tBN is selectively etched or sputtered. Moreover, highresolution transmission electron microscopy of as-deposited cBN on the edge of uhrathin silicon flake substrate showed that the surface of as-deposited cBN film was composed of cBN {111} nanofacets, and no thin sp^2-bonded boron nitride surface layer was observed. Our results suggest that cBN nucleates and then grows on the top surface in chemical vapor deposition systems, and the processes of cBN surface nucleation and growth in the present system was also discussed simply.