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Abstract
A hollow cathode magnetron (HCM) has been developed by surrounding a DC planar sputtering magnetron (PSM) cathode with a hollow cathode structure (HCS), which was at the same electrical potential as the cathode. A HCM can be operated at substantially lower pressure than a PSM. The usual lowest pressure for a PSM is 1-2 mTorr. Ar HCM discharges were operated stably at 0.3 mTorr and a current I = 300 mA using a Cu cathode and a cylindrical HCS of length L = 8.0 cm and inner diameter D = 9.8 cm. Sub-mT operation were also possible for a HCM using other gases and cathodes. At pressures less than a few mT, experiments showed substantially improved utilization of cathode material for a HCM over a PSM. Transition from a PSM to a HCM depends on L. Sub-mT operation is possible only when $L > L\sb0$, a critical length. $L\sb0$ = 6.9 $\pm$ 1.2 cm were found experimentally for D = 9.8 cm. $L\sb0$ = 3.5 $\pm$ 1.0 cm for D = 6.6 cm. New features of HCM are due to hollow cathode effects of the HCS, which can' improve utilization of electron energy, efficiency using ions and photons. Empirical fittings to HCM I-V, V-p relations are discussed. A 0-D analytic discharge model was developed based on ion density balance and power balance.
Molecular ion $(N\sbsp{2}{+})$-surface interaction were studied on HCMs using optical emission spectroscopy (OES). Nitrogen atom velocity distribution were obtained from its Doppler-shifted characteristic line (NI 8216.3 A) emission. NI 8216.3 A was used because it is well separated from nitrogen molecular bands and more intense than other visible nitrogen atom lines. Jansson's nonlinear method was used to improve the spectrometer resolution. Detector cooling and quartic polynomial data smoothing were used to increase signal-to-noise ratio. A minimization of $\chi\sbsp{w}{2}$ criterion was used to obtain the optimal Jansson-deconvolved spectra. Spectra or velocity distribution of nitrogen atom for different cathode materials, cathode bias and discharge pressure were obtained.
Based on the results of the thesis, HCMs have potential to become useful plasma processing devices. For plasmas with electron temperature of a few eV and ionization fraction up to a few percent, energetic nitrogen atoms are generated from dissociated $N\sbsp{2}{+}$ ions that are reflected from the cathode surface and become neutralized.
