PHOTOELECTRON SPECTROSCOPIC INVESTIGATION OF THE BIAS-ENHANCED NUCLEATION OF POLYCRYSTALLINE DIAMOND FILMS

In the present work we describe an investigation of the nucleation mec hanism of polycrystalline diamond films if the bias-enhanced-nucleatio n (BEN) method is used. Photoelectron spectroscopy with excitation ene rgies in the ultraviolet [ultraviolet photoelectron spectroscopy (UPS) ] and x-ray regime (x-ray photoelectron spectroscopy) as well as elect ron energy loss spectroscopy are employed to monitor the nucleation pr ocess and the subsequent diamond film growth. The deposition is perfor med in situ, thus avoiding surface contamination with oxygen or hydroc arbons. The observation of the temporal evolution of composition and s tructure of the deposited film and its interface with the underlying s ilicon substrate allow us to develop a qualitative model, which descri bes the nucleation process. The BEN pretreatment leads, through the ir radiation with low-energy ions, to the codeposition of an amorphous ca rbon phase and the crystalline diamond phase. The presence of both pha ses is readily apparent in the UPS analysis, which will prove to be an indispensible tool in the structural characterization of the carbon p hase present at the surface. There is no indication for the presence o f graphite or large graphitic clusters. A deconvolution of the C 1s an d Si 2p core-level peaks does confirm the presence of two carbon phase s and the formation of a silicon carbide interface. With increasing de position time the contribution of diamond to the carbon film increases and upon switching to diamond growth conditions the amorphous carbon phase is rapidly etched and only the diamond crystals remain and conti nue to grow. This removal of the amorphous phase leads to a decrease i n the overall carbon concentration at the surface by 18-30% during the first 30 sec of the diamond growth period and was observed for a vari ety of pretreatment conditions. A silicon carbide interfacial layer is formed early on during the BEN pretreatment and its thickness is redu ced considerably by etching during the diamond growth period. These re sults are summarized and discussed in the framework of a qualitative m odel for the nucleation process.