Composition and Structure of SiC x :H Films Formed by Plasma Immersion ION Implantation From A Methane Plasma
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COMPOSITION AND STRUCTURE OF SiCx:H FILMS FORMED BY PLASMA IMMERSION ION IMPLANTATION FROM A METHANE PLASMA K. Volz, Ch. Klatt*, W. Ensinger Materials Science Center, Philipps-University, 35032 Marburg, Germany; [email protected] *Max-Planck Institute for Nuclear Physics, 69120 Heidelberg, Germany ABSTRACT Hydrocarbon ions are implanted into silicon by pulse biasing Si to a high voltage of -45 kV in a methane plasma. The resulting SiCx:H films are examined with respect to their composition and chemical binding by RBS, NRA and IR spectroscopy. The process may yield all C/Si ratios, up to pure C films. The H depth profile is shown to be strongly governed by the C depth profile. Silicon carbide bonding as well as C – H bonds can be proven in the implanted region. INTRODUCTION During plasma immersion ion implantation (PIII) a substrate is pulse biased to a high negative voltage in a plasma, which contains ions of the species to be implanted [1,2]. Using this technique, three-dimensional coating of workpieces with e.g. oxides and nitrides is possible. If carbides or carbon films are to be formed, hydrocarbon plasmas can be used. From these plasmas a considerable amount of hydrogen is also implanted. The attention in the present paper is mainly put on the hydrogen incorporation and binding in the SiCx:H films formed by PIII, as the incorporation of H is important for e.g. semiconductor applications of SiC. EXPERIMENTAL The PIII apparatus consists of a cylindrical process chamber with a volume of 40 l. On top, a RF matching box is situated. It is connected to a RF generator with an excitation frequency of 13.65 MHz at a maximum electrical power of 1250 W. The sample holder is connected to a high voltage pulse generator with a maximum voltage of -60 kV. The apparatus has been described in detail elsewhere [3]. (100) silicon wafers have been pulse biased to -45 kV in a methane plasma. The RF power has been chosen in that way that the ion density at the sample position was 109/cm3. The base pressure was below 10-4 Pa, the working pressure in the range of 2x10-2 Pa. The pulse repetition rate was 600 Hz in all cases, but the number of pulses, the samples have been treated with have been varied up to 2.1x106. The implantation temperature, achieved by beam heating, did not exceed 150 °C in all cases. Rutherford Backscattering Spectrometry (RBS) with 3.6 MeV He ions has been used to gain information on the composition of the films. Carbon and silicon depth profiles have been obtained from the RBS spectra by applying the computer code RUMP [4]. In order to convert the areal atomic density scale from RBS into a quantitative depth scale, the atomic density of silicon has been used. The density of this material is lower than the one of silicon carbide but in the range of the one of graphite so that the depth scale is overestimated in those regions, where a high silicon carbide fraction is present.
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The 15N resonant reaction 1H(15N;αγ)12C at 6.385 MeV is used for depth profiling hydrogen [5]. Crystalline silicon has b
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