Effects of pulse parameters on the pulsed-DC reactive sputtering of AlN thin films

A series of studies on the pulsed-DC reactive sputtering of highly (002)-textured aluminum nitride (AlN) thin films was conducted with systematically adjusted pulse parameters including reverse voltage, pulse frequency, and pulse duration. The film quality was evaluated by the full width at half maximum (FWHM) of the (002) rocking curve as well as the (002) peak intensity. In the asymmetric bipolar mode, the FWHM increases while the peak intensity decreases with reverse voltage, implying a detrimental effect of reverse voltage on the quality of AlN film. Whereas in the unipolar mode, the film quality improves with pulse frequency as evidenced by the decreasing FWHM and increasing peak intensity. It is also found that there is a critical pulse duration of about 500 μs, beyond which the FWHM starts to increase while the peak intensity starts to decrease due to target poisoning. Typical measurements on thus-optimized AlN film show a roughness of 1.7 nm and a (002) FWHM of less than 1.9°.