Graded TiAlN layers deposited by electron cyclotron resonance-assisted reactive sputtering

Abstract

Graded TiAlN layers were deposited by plasma reactive sputtering assisted by electron cyclotron resonance (ECR). For reactive sputtering, dual cathode radio-frequency magnetron targets, Ti and Al, were used. The layers were deposited using various combinations of variables such as power input, bias substrate voltage, and gas feed composition. The deposition process was monitored by optical emission spectroscopy (OES). The OES results indicate that microwave excitation added to radio-frequency plasma has contrasting effects on the Ti and Al concentration in the gas phase, enhancing titanium and quenching aluminum species reaching the deposited substrate. Thus, by the regulation of the ECR power and the ratio of nitrogen to argon flow, formation of graded layers is possible. The layers formed in this way were characterized with regard to structure, composition, and mechanical properties using an x-ray diffractometer, an Auger electron spectroscopy microscope, and a Vickers microhardness and scratch tester (for adhesion). It was observed that layers deposited at a low ECR power (⩽100 W) yielded an oriented (111) crystalline structure with good adhesion (failure load >70 N). These layers displayed a higher microhardness (∼25 GPa) at substrate bias voltage (∼50 VDC) than that of a grounded substrate (10–15 GPa). However, layers deposited at an ECR power higher than 100 W showed a random or amorphous structure with an intermediate adhesion range (failure load of 30–50 N). The relationship between the processing parameters, the structure, and the properties of the layers formed are presented and discussed.