Growth of BN film on Si substrate by carbothermic reduction of boric acid in nitrogen glow discharge plasma

摘要

The quest for boron nitride is driven by the fact that its properties are similar and, in some cases, superior to those of diamond [1]. In the cubic phase (c-BN) it is characterized by low density, extreme hardness, large thermal conductivity, wide band gap, trans-parency over a large region of the electromagnetic spectrum and high electrical resistivity. Cubic boron nitride, as a substitute for diamond, has potential applications in hard coatings, heat sinks for elec-tronic devices, optical coatings etc. It is also specu-lated that c-BN may be better suited than diamond for electronic device applications because c-BN can be easily doped as n- and p-type, whereas ?-type diamond has proven difficulty to grow [2]. The importance of growing c-BN thin films on substrates like Si is prompted by the demand from the electronic industry. Although a wide variety of chemical vapour deposition (CVD) [3-5], physical vapour deposition [6, 7], ion assisted techniques [8], ion implantation, RF sputtering, magnetron sputter-ing [9] and electron cyclotron resonance plasma enhanced CVD techniques [10] have been reported to grow BN films, most of the results mention the growth of a mixture of hexogonal and cubic phase. So far, ion beam techniques have the edge over other methods in depositing c-BN films [2,11-13] but the processes are quite expensive. Cheaper methods such as plasma-assisted CVD, tried by a few researchers, [14-16], do not give satisfactory results in respect of adhesion and single phase growth. In our search for alternate methods of BN film growth, a new technique of carbothermic reduction of boric acid in an RF glow discharge plasma (nitrogen) has been developed and the structural characterization of the films by X-ray diffraction (XRD) and scanning electron microscope (SEM) are reported here.