Pulse synchronized substrate bias for the High Power Pulsed Magnetron Sputtering deposition of CrAlN

In a high power pulsed magnetron sputtering (HPPMS) process a substrate bias is applied to affect the ions in the coating chamber and therefore the coating properties. For this reason the present experiments on an industrial scale coating unit are focusing on the identification of correlations between plasma and coating properties for a CrAlN process while using a pulsed substrate bias. The measurements regarding the plasma properties were carried out on the substrate side for a better understanding of the interaction of plasma and coating properties. These investigations should point out the significant potential of plasma diagnostics for measuring plasma properties to contribute to improved coating processes using pulsed substrate bias U-B,U-p. For this purpose a substrate bias synchronized to the HPPMS pulse is used since the pulsed bias can influence ions of a specific species. It was found that the even low values of a pulsed substrate bias lead to high values of the Debye sheath thickness and thus to a shielding of opposite surfaces. For complex shaped substrates like cemented carbide cutting inserts a better coatability for pulsed substrate bias up to U-B,U-p = -150 V was reached. Also increased values of the mean ion energy and the ion flux density were found compared to the use of a continuous substrate bias. Regarding the chemical composition a significant higher nitrogen content of the coatings was found when using a pulsed substrate bias compared to the use of a continuous substrate bias. Comparing the indentation hardness of a process using a pulsed substrate bias increased hardness values were found compared to the use of a continuous substrate bias. Generally, a significant change of both, plasma and coating properties was found when changing the mode of substrate bias.