Optimization of deposition processing of VN thin films using design of experiment and single-variable (nitrogen flow rate) methods

The purpose of this study was to find the optimum deposition conditions for vanadium nitride (VN) thin film using Taguchi design of experiment (DOE) method, and the attained parameters were further refined by conducting single-variable experiments, where the effect of the most sensitive processing parameter on the structure and properties of VN thin films was also investigated. VN thin films were deposited on Si (100) substrate by unbalanced magnetron sputtering (UBMS). Four major processing parameters, including substrate bias, nitrogen flow rate, substrate temperature and substrate rotational speed, were selected in the Taguchi DOE method to optimize the deposition process. Hardness and electrical resistivity of the VN thin films were chosen as the indexes of the property optimization. After deposition, the analysis of mean (ANOM) and analysis of variance (ANOVA) were carried out to assess the sensitive parameters and predict the optimum conditions. The results showed that electrical resistivity was a better index of property than hardness for the Taguchi experiment, and the sensitive parameters for electrical resistivity were nitrogen flow rate and substrate bias. From the Taguchi experiment, the optimum conditions for the minimum electrical resistivity of VN thin film were: substrate bias = −90 V, nitrogen flow rate = 3 sccm, substrate temperature = 300 °C, and substrate rotational speed = 20 rpm. The deposition process was further optimized by conducting a single-variable experiment with refining nitrogen flow rate based on the Taguchi optimum conditions. The results showed that the nitrogen flow rate could be adjusted to 2.5 sccm to reach better properties, where the VN film possessed an excellent combination of properties including high hardness, low electrical resistivity and low residual stress. The results of single-variable experiments indicated that defect density and minor β-V2N phase played important roles in hardness, residual stress, and electrical resistivity of the VN thin films.