Structural Disorder in Hard Amorphous Carbon Films Implanted with Nitrogen Ions
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several applications, especially as protective coatings. fulfill Up to now, the studies on a-C:H films were mostly aimed to characterize, modify and optimize their structure and properties under a wide range of deposition parameters. In the last few years, the study of dopant incorporation into a-C:H films has received special attention, especially as an attempt to improve their electronic properties. The introduction of dopants into either obtained by principle, be can, in a-C:H films incorporation during film growth, i.e. growing the film in the or by post-growth implantation of presence of dopant atoms, the use of dopantConcerning nitrogen doping, dopant ions. has been deposition the film gases during containing successfully exploited to produce intentionally doped films by [2,3]. In general, ion implantation Plasma Enhanced-CVD (PECVD) is scarcely used to dope a-C:H films. In fact, both structural rearrangement (surface layer graphitization) and hydrogen loss are the dominant effects with respect to the electrical and In nitrogen optical properties of the implanted material [4]. implanted a-C:H films, these modifications were correlated with the total deposited energy by incident atoms in either elastic and inelastic collisions [5]. 227 Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society
Among the different techniques used to study the structural implantation, positron annihilation disorder caused by ion spectroscopy (PAS) is one of the most sensitive to the presence of point defects. It is well suited for the analysis of defect Till now only distribution in crystalline semiconductors [6]. few PAS studies on disordered carbon films have been done [7-9]. In fact, the interpretation of PAS results from amorphous not well established as it is for crystalline compounds is materials. In this paper, we report on the results of investigation of defects and structural depth distribution of ion-induced disorder in nitrogen implanted a-C:H films. PAS was used to gain mechanisms of ion beam induced some insights on the modifications and their influence on the positron annihilation parameters. SIMS and Raman results are also presented and discussed. EXPERIMENTAL PROCEDURES a-C:H films, 350 nm thick, were deposited onto p-type Si (100) substrates mounted over a water-cooled stainless steel cathode (13.56 MHz)-diode sputtering system. They were of a Varian r.f. obtained by plasma decomposition of methane at a total pressure of 8 Pa and self-bias voltage Vb, of -370 V. Their chemical composition was: 86.1 atom % of C and 13.9 atom % of H (density= 2.1 g/cm3). After deposition the samples were implanted at room temperature with 70 keV nitrogen ions at fluences between 2 and 9x10 16 N/cm 2. The incident energy was selected so that the projected range plus range straggling of implanted ions (Rp+ARp= 150 nm) falls within the film thickness, as given by the Monte Carlo-based code Transport of Ions in Matter (TRIM) [10]. The positron annihilation measurements we
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