立方氮化硼薄膜沉积过程的相变研究

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

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.

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.