Energy transferred to the substrate surface during reactive magnetron sputtering of aluminum in Ar/O₂ atmosphere

A study of the reactive sputtering of aluminum was carried out by coupling energy flux measurements at the substrate location with conventional diagnostics of the gas phase and analyses of the deposited films. The main purpose was to get some insight into the elementary mechanisms involved at the substrate surface during the film growth in the well known metal and oxide regimes and at the transitions from one to another. Measurements were carried out in front of a 10 cm Al target at a power of 400 W (i.e. 5 W/cm²) and a total pressure of 0.6 Pa. The flow rate ratio (O₂/O₂ + Ar) was varied in the range 0 to 50%. Different kinetics and values of energy transfer, denoting different involved mechanisms, were evidenced at metal-oxide (increasing flow rate) and oxide-metal (decreasing flow rate) transitions. The metal-oxide transition was found to be a progressive process, in agreement with optical emission spectroscopy and deposit analysis, characterized by an increase of the energy flux that could be due to the oxidation of the growing metal film. On the contrary, oxide-metal transition is abrupt, and a high energy is released at the beginning that could not be attributed to a chemical reaction. The possible effect of O⁻ ions at this step was discussed. - Highlights: • We use real-time energy flux measurements to study reactive magnetron sputtering. • At transitions rise of the energy flux transferred to the substrate is observed. • At the metal-oxide transition energy is released by oxidation of the Al growing film. • At the oxide-metal transition the energy transfer may be due to O⁻ born at the target. • Energy flux study gives some insight into mechanisms involved in the film growth