The Preparation Of Cubic Boron Nitride Thin Films By ECR CVD System And Study Of Their Properties

Cubic boron nitride (c-BN) thin films have significant and potential technological application prospect in machinery, electronic and optical devices etc. Because c-BN possesses excellent physical and chemical properties, such as ultrahigh hardness only inferior to diamond, inertness against oxidation at high temperature, uneasy react with iron group metal, the possibility of using as n-type and p-type doped semiconductors, as well as the translucent property in the region of infrared and visible spectra. With wide bandgap, c-BN thin films have unpredictable prospect in the high temperature, high frequency and high power devices. The preparation and property research of c-BN thin film have been one of difficult and attractive fields in the scientific world. This paper focuses on the preparation of c-BN thin films, growth mechanism of c-BN thin films, and the mechanism of phase transition from hexagonal boron nitride (h-BN) to c-BN by annealing technique.ECR CVD system is a new technology for thin film deposition. It can form plasma with high density and high ionization at low temperature and low pressure, which will provide conditions for gases easy to react and deposit films. The structure of thin films deposited in this preparation system is related to the gases that take part in reaction. Recently, the gas of BF₃ was introduced into CVD technique, and high quality c-BN of micro thickness can be deposited with it. It may be realized the preparation of c-BN thin film at low substrate bias. In this work, the preparation of c-BN thin film using ECR CVD system by introducing BF₃ gas was studied. We detected and analyzed structural characteristics of c-BN thin film with FTIR spectra, Raman scattering spectra and XRD spectra. Then we calculated the content of c-BN in BN thin film by FTIR spectra and the optical bandgap by UV spectra.We prepared BN thin film by ECR CVD system and most of the BN thin films were mainly h-BN phase. We studied the gas systems of BF₃-Ar-N₂-H₂ and BF₃-Ar-He-N₂ on the preparation of c-BN thin film respectively, and studied the characteristics of BN thin films as functions of hydrogen gas (H₂), nitrogen gas (N₂), voltage of hot wire, microwave power, ratio of different gas, deposition pressure, substrate bias and multi-steps deposition technique. We deposited h-BN thin films by layer by layer (LBL) techniques using ECR CVD system, and the c-axial of h-BN was vertical comparing with substrate surface. We simply discussed the deposition mechanism of c-BN thin film prepared by ECR CVD system and there exist physical mechanism besides the chemical route. The content of c-BN in BN films were more than 50% when substrate biases were -80V and -90 V.We studied the mechanism of phase transition from h-BN to c-BN by traditional furnace annealing technique. BN thin films prepared by ECR CVD system included E-BN phase, and the transition from h-BN to c-BN might be through the way of h-BN→w-BN→c-BN. The structures of samples depended on preparation processes, and decided the degree of defects in the samples. The native defects of films prompted the phase transition from h-BN to c-BN.