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Mat. Res. Soc. Symp. Proc. Vol. 585 © 2000 Materials Research Society

Two different techniques were used to produce carbon nitride: (1) direct ion beam deposition using a gas mixture of (CH 4/N2), and (2) direct nitrogen ion (N+/N2+) sputtering of a graphite target. The effects of RF power, gas composition, and ion energy on the chemical and physical properties of the as-deposited carbon nitride films were investigated. The chemical composition of the CNx films was determined by Rutherford backscattering (RBS) and hydrogen forward scattering (HFS) methods. Optical characterization of the carbon nitride films was done by ellipsometric measurements, and adsorption in the UV and visible regions. The refractive indices of the carbon nitride films were measured ellipsometrically with a Rudolph AutoEL-HI instrument which was fitted with a HeNe laser emitting at 632.8 nm. The deposition rate of the DLC films was determined from step profilometer (Techor Inc.) measurements. The chemical bonding information was obtained from Fourier Transform Infrared (FTIR) measurements. RESULTS AND DISCUSSION Direct Ion Beam Deposition from Gas Mixture of N 2 /CH4 The parameters manipulated for depositing carbon nitride films were: N 2/CI-I 4 ratio (0.20.67), RF power (99-600 W), and ion energy (200-1750 eV). The films produced were amorphous, optical smooth and brown in color. Ion Beam Composition A typical mass spectrum of CH4/N 2 (16/8) at an RF power of 199W is shown in Figure 1. The major ions are: CH 3 + (m/e =15), N2+ (m/e = 28), N+/CH 2+ (m/e = 14). NH3+ (m/e = 17), N114+ (m/e = 16), CHN4 /C 2H3+ (m/e = 27), N 2I+/C2H5+ (ni/e = 29), N2H 2+ (m/e = 30), CH+ (m/e = 13) and C+ (ni/e = 12). The relative ion concentrations varied with RF power and the N 2/CH 4 ratio in the plasma.

2.E-7

co)

t42+/C 2H4+

C.) I.E-7

J

N2+H2

0

n/e Figure 1.

Mass Spectra of RF Discharge of CH4N 2 Mixture

246

Film Composition The elemental chemical composition of carbon nitride films produced by various plasma parameters is tabulated in Table 1. The as-deposited films produced using a direct ion beam gas mixture of N 2/CH 4 contained a significant amount of hydrogen (30 at. %). Zorman et al [4] reported that 22-33 at.% of H was incorporated in the as-deposited A-C:N:H films using a Kaufman ion source with an unspecified gas ratio of N 2/CH 4 . At a constant ion energy of 500 eV, the nitrogen incorporated into the film linearly increased with the amount of nitrogen in the plasma as shown in Fig. 2. The N/C ratio increased from 0.17 to 0.27 and remained constant as the N/C ratio in the plasma varied from 0.4 to 1.0. However, increasing the N/C ratio in the plasma does not further increase the amount of nitrogen incorporated in the film. At a fixed N/C ratio of 1 in the plasma, the N/C ratio in the film was found to vary from 0.26 to 0.28 as the ion energy increased from 200 eV to 700 eV. Zorman et al [4] also reported that the N/C ratio in the films varied from 0.23 to 0.30 as the ion energy increased from 100 eV to 600 eV. Table 1. Effect of Proce