Study of Diamond Nucleation on Silicon Using Direct Negative Carbon Ion Beam Source
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ABSTRACT The initial nucleation stages of sp3 bonded amorphous diamond on silicon substrates have been investigated. The energy of the incident carbon ions/atoms is understood as a key parameter for the vapor phase formation of amorphous diamond like carbon coatings. SKION's solid state carbon ion source is used for this study. The ion source is UHV compatible and capable of producing a controlled energy ion beam in the energy range of 5-300 eV. In the initial stage of the deposition, carbon is found to be deposited as a silicon carbide up to a thickness of about 180A at room temperature. Silicon is diffused to the surface and forms SiC. As the energy of the ion beam increases, the formation of silicon carbide becomes apparent. Further carbon ion bombardment then leads to the formation of an sp 3 bonded amorphous diamond film. Postannealing above 900'C leads to the formation of crystalline silicon resulting in a Si-rich SiC surface due to silicon out-diffusion. INTRODUCTION Ever since the low pressure formation of diamond and Diamond Like Carbon (DLC) thin films has been reported, numerous efforts have been conducted due to its unique properties such as high electrical resistivity, high hardness, chemical inertness,and high thermal conductivity[ 1,2]. There are two basic categories for the formation of DLC films which are Chemical Vapor Deposition (CVD) and vapor phase deposition. The CVD process is categorized as the process which uses a mixture of methane or other hydrocarbon gases and atomic hydrogen gases to form a film by chemical reaction on the surface at usually high substrate temperatures (900'C). Vapor phase deposition covers the technology which forms a film by direct deposition of energetic carbon atoms/ions at usually low substrate temperatures. Sputtering, laser ablation, carbon arc, and carbon ion beam deposition techniques fall into vapor phase techniques. Nucleation of the diamond phase in CVD process is enhanced by defects which are often prepared by scratching with diamond powders. Nucleation on diamond residual particles from the scratching process is also reported by providing seeds for diamond growth[3]. Very dense nucleation is achieved by ion beam induced defects in plasma enhanced CVD processes. Nucleation of the diamond phase in vapor phase deposition techniques is not well investigated. Very recently, people started to realize the importance of the energetic carbon ion deposition process in the formation of amorphous diamond like carbon films. The diamond like properties of the deposited film have a strong dependence on incident carbon energy [4-9]. At present, various efforts have been made in order to understand the growth and nucleation mechanism by the energetic carbon ion deposition[10-15]. In a conventional vapor phase deposition process, the energy of the carbon beams cannot be controlled because of the inability to control the energy of 221
Mat. Res. Soc. Symp. Proc. Vol. 396 01996 Materials Research Society
neutral vapors. It is well known that the energy of the incident carbo
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