Influence of a short reverse positive HPPMS pulse on the deposition of CrAlN

In conventional high power impulse magnetron sputtering processes (HPPMS) short pulses of a negative voltage are used to maintain the discharge. A new approach to accelerate ionized species towards the substrate position and subsequently improved coating properties is the use of a power supply, which generates a reverse positive pulse immediately after the negative pulse. In the present paper the influence of the frequency f and the pulse on time t(on) for a CrAlN process on the coating properties is investigated. All experiments were carried out on an industrial scale coating unit. In the present investigations coatings deposited by three different duty cycles are compared. For each duty cycle one coating was deposited using a conventional power supply and one coating using a power supply with a positive pulse. The positive pulse was clearly detected. It was found that the height of the positive pulse depends on the chosen pulse parameters. Furthermore, higher values of the peak power were found when using a power supply with a positive pulse, which should influence the ionization of the sputtered material. Regarding the chemical composition, a decreasing nitrogen content of the coatings was found when using a positive pulse. The investigations of the deposited coatings showed a denser morphology and increased values of the indentation hardness when using a power supply with a positive pulse compared to a conventional power supply. In addition to the higher indentation hardness, even the amount of plastic work showed increasing values for the power supply using a positive pulse compared to the conventional power supply. Furthermore, increased values of the roughness for coatings deposited on cemented carbide were found when using a positive pulse. The coatings deposited on cemented carbide showed a higher adhesion when using a positive pulse.