A multi-step deposited AlN films in a DC pulsed sputtering and film characteristics classification with principal component analysis of OES data

In this work, a unique approach in experiments was carried out by a pulsed DC sputtering for the 60/30-min process in one-step and multi-step (two- and four-step) deposition to obtain trends of residual stress and film properties of aluminum nitride (AlN). Film characteristics comparison between one-step and multi-step deposition was used to study the correlation among film crystallite orientation, residual stress, and film features. The thickness, microstructure, residual stress, and crystallite status of AlN films were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The results show that the films have different stress characteristics in different microstructures when processed at the same amount of time in different deposition intervals. The increase in the degree of ion bombardment and induced substrate temperature raised leads to the interpretation of different microstructural changes in films. In this investigation, the film with thickness about 1300 nm for one-step deposition has a surface roughness of 2.67 nm, the grain size of 65.1 nm, and residual stress of 1575 MPa. In the four-step deposition, these values were reduced to 2.46 nm, 51.4 nm, and 841 MPa, respectively. In situ optical emission spectroscopy (OES) data were collected during plasma deposition of selected dominant wavelengths of N₂ (315 and 336 nm) and Al (394 and 396 nm) for large-scale data analysis. Based on a cross-validation test executed from OES data preprocessing, the methodology with the principal component analysis (PCA) and value of microstructure characteristics (VMC) algorithm demonstrated that this unique multi-step deposition technique can provide a good stress gradient control from microstructural analysis and can effectively classify film characteristics in AlN film deposition.