Review of advances in cubic boron nitride film synthesis

TLDR: A review of recent developments in BN film synthesis and characterization can be found in this paper, where the key experimental parameters controlling cBN film formation and synthesis techniques are discussed and the proposed mechanisms of cBN formation and the observed mechanical and electrical properties of CBN films are analyzed.

Abstract: Cubic boron nitride (cBN) has a number of highly desirable mechanical, thermal, electrical, and optical properties. Because of this, there has been an extensive worldwide effort to synthesize thin films of cBN. Film synthesis is difficult in that without significant levels of ion bombardment during growth, only sp2-bonded BN forms, not sp3-bonded cBN. Recently there has been considerable progress in improving the deposition techniques and cBN film quality. In addition, progress has been made in understanding how energetic deposition conditions can lead to cBN formation. However, unanswered questions remain and process improvements are still needed. In this paper we critically and comprehensively review recent developments in cBN film synthesis and characterization. First, the structures and stability of the BN phases and characterization techniques are described. Next, the key experimental parameters controlling cBN film formation and synthesis techniques are discussed. Following a review of microstructure, the proposed mechanisms of cBN formation and the observed mechanical and electrical properties of cBN films are analyzed. We conclude by highlighting the current impediments to the practical realization of cBN-film technology.

Figures

Fig. 7. Formation of BN phases as a function of ion/boron flux and ion energy as compiled by Reinke et al. [I 131. cBN forms only between the upper solid line and either the lower solid line or the dotted line. For insufficient relative ion flux (below lower solid line or dotted line), only tBN forms. For too high of an ion flux (above upper solid line), no film growth occurs because of ion sputtering. Note that the tBN/cBN boundary in the lower solid line is fixed at F= J/ ag = 1 above 500 eV, and is therefore independent of ion energy. Reinke et al. [ 1131 attributed this to the stoichiometry requirement of having sufficient nitrogen ions to react with the evaporated boron atoms to form BN. In contrast, the dotted line represents the data of Mirkarimi et al. [ 1081. In their technique (ion-assisted pulsed laser deposition), nitrogen comes from the ablation target as well as the ion source. Their results show an E’” scaling for cBN formation between 500 and 1200 eV.