Effects of aluminum sputtering target surface grain relief and crystallographic orientation on sputtering <i>I</i>–<i>V</i> characteristics

The effects of Al sputtering target surface grain relief and crystallographic orientation on magnetron sputtering target I–V characteristics have been investigated to reveal the nature of I–V characteristic deviations. Eight aluminum single crystals, three polycrystalline Al-1 wt % Si targets with different degrees of (100), (110), and (111) crystallographic orientations and three polycrystalline Al-1 wt % Cu targets with grain sizes of 0.25, 0.95, and 5.5 mm were used. Square grid patterns were machined into the sputtering surface of five of the (110) and one of the (111) single crystals to simulate the surface grain relief and the (110) or (111) preferred crystallographic orientations of polycrystalline targets. These patterns consisted of intersecting grooves with dimensions comparable to target grain sizes and plasma sheath thicknesses. Groove depth to width aspect ratios ranging from 0.067 (20/3000 μm) to 0.33 (100/300 μm) were used. I–V measurements with patterned and nonpatterned single crystals showed that both crystallographic orientation and surface relief affect the I–V characteristics. (110) single crystal targets decreased the target bias voltage when compared with (111) single crystal targets. A minimum in target voltage was found at intermediate values of aspect ratio. For polycrystalline Al-1 wt % Si and Al-1 wt % Cu targets minimum target voltage was obtained using targets with the smallest degree of (111) crystallographic orientation and 0.95 mm grain size.