High-rate reactive sputtering of yttria-stabilized zirconia using pulsed d.c. power

Polycrystalline yttria-stabilized zirconia (YSZ) thin films were deposited by reactive magnetron sputtering of a Zr-Y alloy target in an Ar-O₂ atmosphere. Using a combination of pulsed d.c. power at a frequency of 70 kHz at both the target and substrate, and partial pressure control of the O₂ gas, arcing was controlled and a stable process was obtained. Fully-oxidized cubic (Y₂O₃)_0.10(ZrO₂)_0.90 films were deposited at rates as high as 210 nm/min, or ∼60% of the metal alloy deposition rate. For films deposited onto electrically-conducting substrates, the structure and hardness of the films were affected by the negative substrate bias V_s. With V_s = floating (34 V), X-ray diffraction scans showed a strong (200) texture, which switched to a strong (111) texture for V_s = 80-150 V. Scanning electron microscopy showed a porous structure with no substrate bias and a dense structure with a bias of V_s = 80 V. The film hardness measured using nanoindentation was ≈ 4 GPa for V_s = 34 V, and reached a maximum of 17 GPa, comparable to bulk YSZ, at V_s = 80-100 V. For films deposited onto glass substrates, the pulsed d.c. substrate bias had no effect, such that porous, low-hardness YSZ was obtained. This was due to the very short time constant for charging the thick glass substrate, compared with the d.c. pulse period.