立方氮化硼薄膜生长过程中的界面控制

Controlling the interfacial structure of cubic boron nitride thin film prepared by plasma-enhanced chemical vapor deposition

在立方氮化硼薄膜气相生长过程中生成的无定形初期层和乱层结构氮化硼中间层,一直是阻碍立方氮化硼薄膜外延生长的主要原因.系统地分析了硅衬底预处理对立方氮化硼薄膜中无定形初期层成分的影响,发现在等离子体化学气相生长法制备薄膜时,硅衬底上形成无定形初期层的可能原因有氧的存在、离子轰击以及高温下硅的氮化物的形成.在H2气氛中1200K热处理硅衬底可以有效地减少真空室中残留氧浓度,除去硅表面的自然氧化层,保持硅衬底表面晶体结构.控制衬底温度不超过900K,就能防止硅的氮化物的形成,成功地除去无定形初期层.对乱层结构氮化硼生长条件的系统研究发现,在接近溅射控制的衬底偏压附近有一个乱层结构氮化硼生长偏压区间.减小衬底偏压处于该乱层结构氮化硼生长区间的时间,能有效地抑制乱层结构氮化硼中间层的形成.并用高分辨电子显微镜成功地发现了立方氮化硼薄膜在硅衬底上直接成核与生长.本结果对立方氮化硼薄膜在大功率高温电子器件等方面的应用有重要意义.

The existence of an initial amorphous layer and a turbostratic boron nitride transition layer is one of the main hindrance to heteroepitaxial growth of cubic boron nitride on silicon susbtrate. In this paper, we systematically studied the effect of substrate pretreatment on the amorphous layer composition of cBN films prepared by plasma enhanced CVD, and found that the possible causes for the amorphous layer formation are the native silicon oxide, the oxygen remaining in the vacuum chamber, high energy ion bombardment, and the formation of silicon nitride at high substrate temperature. By 1200 K heating of silicon susbtrate in H2 atmosphere and by controlling the deposition temperature at below 900 K, the crystallinity of silicon susbtrate surface could be retained and the amorphous initial layer removed. Moreover, when the substrate bias is near the puttering effect dominated region, only pure turbostratic boron nitride film could be deposited. By reducing the time span of the substrate bias in puttering effect dominated region during the time dependent biasing technique, the turbostratic boron nitrde transition layer could be partitally eliminated. Nucleation of cubic boron nitride directly on silicon substrate was confirmed by high-resolution transmission electron microscopy. Our results may open up a possible route to cubic boron nitrde eptaxial growth on silicon substrate and lead to the potential high-temperature electronic applications of cubic boron nitride thin films.