Effects of target polycrystalline structure and surface gas coverage on magnetron <i>I</i>–<i>V</i> characteristics

The effects of Al target surface grain structure and surface gas coverage on sputtering magnetron I–V characteristics have been investigated to reveal the net effect of variations in the ion-induced electron emission yield (IIEEY) on I–V characteristics. One (110) single-crystal and three polycrystalline Al–1 wt % Cu targets with the similar (110) crystallographic orientations and grain sizes of 0.25, 0.95, and 5.5 mm were studied. The partial pressures were monitored before, during, and after sputtering. The direct IIEEY was measured under 600–900 eV Ar+ and He+ beam bombardment as a function of grain size and gas coverage at specimen temperatures of 19 and 74 °C. The IIEEY measurements demonstrated that both the surface grain structure and the gas coverage affect the electron emission. The direct IIEEY was highest in the small grain size and lowest in the large grain size specimens. An increase in specimen temperature raised the emission yield due to increased chemisorption of residual gas species. In contrast magnetron I–V characteristics suggested the highest IIEEY for medium grain size target. This difference is explained by the combined effect of residual gas adsorption and plasma sheath distortion around surface relief which results in IIEEY increase.