Nitrogen Implantation Effects on the Chemical Bonding and Hardness of Boron and Boron Nitride Coatings
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Mat. Res. Soc. Symp. Proc. Vol. 555 ©1999 Materials Research Society
substrates are positioned laterally from the center of the 6.3cm diameter target. A substrate using a BoralectricTM heater. A 0.23Pa sputter gas pressure is temperature of 300tC is achieved maintained using a 28 cm 3 min' total flow rate. Deposition rates of 0.019 nm s- and 0.025 nm s-1 are produced using the Ar and Ar-25%N 2 sputter gases, respectively. The as-deposited coating thickness (t.) is measured using a Dektak II contact profilometer. The as-deposited samples are modified by nitrogen implantation. A tantalum shadow mask exposes the center of each coated wafer to the implanted species. Two sets of implants are performed that accentuate the effects of the per nitrogen implant energy and current density. The nitrogen implantations are achieved with a cryogenically pumped Varian 3000 system using a Freeman source. In the first set, the variable is implant energy. A two-pocket shadow mask is used for samples no. 417a and 417b. The terminal potential is set at 90 or 180 keV. A selection at the analyzer magnet of 14 atomic mass units (amu) is used for N' ions. These conditions yield 90 or 180 keV per incident2 nitrogen atom. A 24kA focused beam is rastered across a surface that covers the hard-masked substrates. This exposure condition area in excess of 100 cm produces a 5.Ox 104 cm-2 s-' flux of nitrogen atoms, i.e. an equivalent "nitrogen atom" beam current density (PN) of 81 gtA cm 2. The total dose of nitrogen atoms at either 90 or 180 keV is Ixl017 cm-2. In the second implantation set, the variable is current density with respect to the first implant set. For this implant, a four-pocket shadow mask is used for samples no. 814 and 819. The terminal potential is set at 200 keV. A selection at the analyzer magnet of 28 amu is atom. A 15itA used for N 2+ ions. These conditions yield 100 keV per incident nitrogen defocused beam is rastered across a surface area in excess of 100 cm 2 that covers the hardmasked substrates. This exposure condition produces a 1.9x l0'4 cm-2 S- flux of nitrogen atoms, i.e. an equivalent PN of 31 gA cm 2 . The total dose of nitrogen atoms at 100 keV is 2x1017 cm-2. Note that before this implant, the samples received a small 1.4x 1016 cm 2 dose of 200 keV (Ni) nitrogen atoms as 14 amu was inadvertantly selected for the implant condition. The change in thickness (At) found in the implanted region is measured using a Dektak II contact profilometer. A summary of the implant conditions is listed in Table 1 for each sample wherein a suffix is added to each sample no. indicating the implantation energy per nitrogen atom. For example, the 90 keV implanted BN sample no. 417a is designated as 417-90. Near-edge x-ray absorption fine structure (NEXAFS) spectroscopy provides information about the elemental composition and bonding character of the B and BN samples.[ 71 NEXAFS spectroscopy is based on the availability of x-ray radiation of tunable wavelength that is produced by a synchrotron. Measurements are taken on beamline 8.0
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