P. Thévenin

Optical properties of boron nitride thin films deposited by microwave PECVD

Abstract Hexagonal boron nitride thin films (h-BN) were deposited by microwave PECVD on various substrates (silicon, quartz, glass…), and were analysed by infrared, UV visible and microraman spectroscopies. The interpretation of the IR spectra recorded at oblique incidence allowed us to determine the preferential orientation of the c -axis of the h-BN films. The influence of the deposition conditions on the orientation is studied as a function of the plasma power. The optical constants in the infrared are also given by the Kramers–Kronig method.

Formation and characterisation of c-BN thin films deposited by microwave PECVD

Abstract Boron nitride thin films were deposited on silicon substrates at low temperature by plasma-enhanced chemical vapour deposition (PECVD), with a microwave surfatron launcher. An organometallic compound, borane-dimethylamine, was used as the boron precursor. To promote the growth of the cubic phase, a negative self-bias was applied to the sample holder by means of a 13.56-MHz RF signal. A very high fraction of c-BN was achieved as revealed by infrared spectrometry. The assignation of the characteristic TO absorption band was ascertained by the observation of its LO associated mode by performing the IR transmission spectra at non-normal incidence. The deposited films are well adherent and do not delaminate even after 6 months in the atmosphere, and they exhibit a very low roughness, as observed by atomic force microscopy.

Influence of annealing treatment on the physical properties of c-BN films deposited by IBAD technique

Boron nitride films prepared by ion beam assisted deposition (IBAD) have been studied. The presence of the cubic phase was checked by HRTEM microscopy. The adhesion of the films was very poor and without a thin boron sublayer, the films delaminated just after deposition. In an attempt to improve the adhesion, post deposition annealing was performed. The structure and the stress of the films were followed by infrared spectroscopy (FTIR). Annealing carried out on c-BN films shows a thermal threshold of stability around 950 °C. These effects are discussed according to the proportion of the cubic phase present in the film.

Electrical properties of MIS structures with BN insulating layer

Abstract Electrical properties of MIS structures with a BN insulating layer on InP substrate are investigated by means of capacitance-voltage characteristics. These characteristics show the conventional shape for MIS structures. The BN:1nP interface is studied by deep-level transient spectroscopy using the DLS-82E spectrometer. The measured spectra exhibit non-conventional behavior, with the gradual increase of the filling pulse duration and the filling pulse amplitude, which can be explained by means of dipolar relaxation effects.

Synthesis of cubic boron nitride thin films by microwave PECVD

Boron nitride can be synthesised in two major crystalline polytypes, the hexagonal (h-BN) and the cubic one (c-BN), related respectively to the sp2 and the sp3 hybridation of the chemical bondings of both atomic species. The cubic form is very attractive, due to its extreme properties, similar to those of diamond in term of hardness, thermal conductivity, chemical inertness and optical transparency, It is even more stable against oxidation up to higher temperature, and can be doped whether P or N type, making it a candidate for applications in power electronics. Classically, c-BN can be synthesised under high pressure and high temperature, but more recently PVD and CVD have been successfully employed to obtain thin films. In these later cases, the growth process requires bombardment with energetic particles, and general ways the structure is left in compressive stress after deposition and delamination or cracking of the film can occur. We have deposited boron nitride thin films on silicon substrates at low temperature (below 300/spl deg/C) in a microwave plasma enhanced chemical vapor deposition (PECVD) apparatus, An organometallic compound, borane dimethyl amine, was used as boron precursor. To promote the growth of the cubic phase a negative self bias was applied to the sample holder by mean of a 13.56 MHz RF signal. Characterisation of the samples involve infra red and Raman spectrometries, and atomic force microscopy. Films containing a fraction of c-BN, as high as 98%, have been obtained, as can be seen on the infra red spectra. The ratio has been determined according to the relative intensity of the active IR mode of the cubic and the hexagonal phases. At normal incidence only the transversal optical (TO) modes are observed, whereas at oblique incidence the longitudinal optical (LO) modes are also evidenced, according to the Berreman effect. The c-BN TO absorption band is observed at 1071 cm/sup -1/ and its associated LO mode is located at 1267 cm/sup -1/. The films exhibit a very low roughness, as observe by atomic force microscopy, and contain nanocrystals of about 10 nm averaged size, as deduced from the Raman measurements. These deposits are very adherent and do not delaminate even after more than one year. Also, PECVD seems to be a promising method for the synthesis of c-BN layers.