The phase and microstructure of CrAlN films deposited by pulsed dc magnetron sputtering with synchronous and asynchronous bipolar pulses

CrAlN films have been deposited from a Cr target and an Al target using pulsed dc magnetron sputtering. The Cr and Al targets were pulsed in asynchronous and synchronous pulsing modes at different pulsing frequencies and duty cycles. The ion energy distributions of the plasma were characterized by a Hiden mass spectrometer. The pulsed plasma contains a wide range of energetic ions. The ion energies depend on the pulsing parameters and the pulsing mode of the two targets. The ion energy and ion flux increased as the pulsing frequency was increased. The plasma exhibited higher ion energies and ion fluxes in the synchronous pulsing mode than those in the asynchronous pulsing mode for the same pulsing frequency and duty cycle. A decrease in the N content and an increase in the Al/(Cr + Al) ratio were observed as the pulsing frequency was increased in both pulsing modes. When the pulsing frequency was increased to 350 kHz, the films deposited in the asynchronous pulsing mode exhibited a NaCl cubic structure, whereas a mixture of the cubic and hexagonal phases was formed in the films deposited in the synchronous pulsing mode. The hardness of the films increased with an increase in the pulsing frequency in the asynchronous pulsing mode. In contrast, a decrease in the hardness was found in the synchronously deposited films as the pulsing frequency was increased due to the formation of hexagonal AlN phase and the stress relaxation in the films.