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

Abstract

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.