Study On Oxygen Impurity In Cubic Boron Nitride Thin Films

Cubic boron nitride (cBN) is a synthetic wide band-gapâ…¢-â…¤semiconductor material, and cBN thin films have significant and potential technological application prospect in cutting tools, electronic and optical devices,etc., because cBN possesses excellent physical and chemical properties, such as ultrahigh hardness only inferior to diamond, inertness against oxidation at high temperature, uneasy reaction with iron group metal, as well as the possibility of using as n-and p-type doped semiconductors. These extensive potential applications have led to the intensive investigation of cubic boron nitride thin films.In other to apply cBN thin films to high temperature electronic devices, high purity cBN thin films are needed before controlled doping. Meanwhile, cBN thin films are more prepared by vapor deposition methods, so the detection and control of oxygen impurities in cBN films become especially important.In this paper, cBN thin films were prepared by inductively-coupled plasma-enhanced chemical vapor deposition (PECVD) method. The influences of base pressure and oxygen concentration during film deposition on the content of oxygen impurity were investigated. Our results suggest that the decrease of base pressure up to 10-5Pa still cannot eliminate the oxygen impurity in cubic boron nitride films, and the introduction of O2 into the deposition system suppresses both cubic boron nitride nucleation and growth. At a B2H6 concentration of 2.5% during film deposition, the critical O2 concentration allowing the nucleation of cubic boron nitride is found to be less than 1.4%, while that allowing the growth of cubic boron nitride is higher than 2.1%.Moreover, a new infrared absorption peak near 1230cm-1, which could be attributed to the antisymmetric B-O stretching vibration of the trigonal BO3 group was detected, and the intensity of this IR peak increased almost linearly with oxygen concentration from 3-12atom% in BN thin films. Therefore, the oxygen impurity content in cubic boron nitride films can be evaluated quasi-quantitatively by this new IR absorption peak.