立方氮化硼薄膜沉积过程的相变研究

从能量和结构两个角度分析了BN四种相的转变过程，以及杂质和缺陷对立方氮化硼(c-BN)薄膜制备的影响.研究了从六角氮化硼(h-BN)到c-BN转变的一个可能的过程，即h-BN→菱形氮化硼(r-BN)→c-BN过程.对纯的h-BN到r-BN的转变需要克服一个很高的能量势垒，在实验室条件下很难能够提供能量来越过这个势垒.而从r-BN到c-BN的转变只需要克服一个很低的能量势垒.这个能量势垒要低于从h-BN到纤锌矿氮化硼(w-BN)转变所需要克服的能量势垒.c-BN薄膜的制备过程中，薄膜在高能粒子轰击下，会产生大量的缺陷，这些缺陷对立方相的形成起到了重要的作用，缺陷和杂质的存在大大降低了从h-BN到r-BN转变的能量势垒.根据这个理论模型，在两步法制备c-BN薄膜的基础上，调整实验参数，形成三步法制备高质量c-BN薄膜.主要研究了三步法中第一步的时间和衬底负偏压对c-BN薄膜制备的影响，找到合适的沉积时间和衬底负偏压分别为5min和-180V.采用三步法制备薄膜，可以重复得到高立方相体积分数(立方相体积分数超过80%)的BN薄膜，并且实验重复性达到70%以上. 关键词： 立方氮化硼 能量势垒 缺陷 衬底偏压

Phase transformation in process of deposition of cubic boron nitride thin films

Phase transitions between the polytypes of boron nitride and the influence of defect and impurity on preparation of c-BN thin film are studied from energy and structure aspects. A pathway from h-BN to c-BN is analysed, namely: h-BN→r-BN→c-BN. The transformation from h-BN to c-BN is more difficult than that from r-BN to c-BN. The energy barrier is very high in direct transformation from h-BN to c-BN, but it is very low from r-BN to c-BN. In fact, defects and impurities in c-BN thin films may favorably drive the transformation from h-BN to c-BN. Defects and impurities can reduce the energy barrier for the transformation sufficiently enough for it to proceed under conditions obtainable in common laboratories. Based on the theoreticd model, we developed a new method to prepare c-BN thin film (three-step method). The effect of time and substrate bias voltage on the first step of preparation of c-BN thin film is investigated. The study proves that 5 min and -180V is very favorable. The c-BN thin film that content with cubic phase exceeding 80% can be repeatedly prepared using the three-step method. Results of experiments accord with the theoreticat model very well.