Residual stress classification of pulsed DC reactive sputtered aluminum nitride film via large-scale data analysis of optical emission spectroscopy

The amount of residual stress generated during the growth process of aluminum nitride (AlN) thin films prepared by pulsed DC reactive magnetron sputtering was investigated. The evaluated process parameters were pulsed DC frequency, DC power and flow gas ratio. AlN film may crack or peel from the substrate due to significant film residual stress. Therefore, the control of residual stress in films is very important for the synthesis of mechanically stable AlN films. A correlation between the residual stress and the crystal orientation of the films was studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM) and scanning electron microscopy (SEM) were used to measure the residual stress, crystal structure and thickness in AlN films. The results show that AlN film has a different structure and stress characteristic under different deposition conditions. The film residual stress correlates well with the film thickness. Besides, in situ optical emission spectroscopy (OES) big data were analyzed using principal component analysis (PCA) in this study. The PC1-DEV (standard deviation in the first principal component direction) was used to calculate the value residual stress (VRS) to accurately predict and classify the stress state of the deposited film, i.e., compression stress or tensile stress. The Box–Behnken experimental design was applied, a mathematical design of experiment (DOE) model was established based on the response surface method (RSM), and the optimum conditions for generating the minimum residual stress were determined.