Comparative study of film quality on c axis oriented AlN deposited by pulsed DC and RF reactive sputtering with optical emission spectroscopy big data analysis

This study compares the quality of aluminum nitride (AlN) thin films deposited on Si substrates using 350 kHz pulsed DC and 13.56 MHz RF reactive sputtering techniques under identical process conditions with varied source power. Our focus was on evaluating the differences in film properties such as crystallinity, surface morphology, and thickness uniformity. Our results indicated that, although scanning electron microscopy cross-sectional images showed a lower deposition rate for RF sputtering, the produced films exhibited better crystallinity, as evidenced by sharper and more intense XRD peaks, particularly the ⟨002⟩ peak. Calculations derived from XRD spectra of c axis oriented AlN thin films, utilizing RF source power at 700 W, revealed that the optimal c axis lattice constant is 4.8706 Å, and the texture coefficient in the ⟨002⟩ (TC₀₀₂) direction is 1.99. Both values surpass those obtained at the same power level in pulse DC power source. Additionally, atomic force microscopy measurements indicate that the surface roughness of films deposited by both pulsed DC and RF sputtering slightly increased with the sputtering power. In the in situ optical emission spectroscopy (OES) plasma spectrum, the higher spectral intensities observed in RF sputtering, particularly the emission characteristic of ionized nitrogen (N₂⁺) at around 390.93 nm, suggest that RF plasma provides energy conditions conducive to the formation of high-quality AlN films. Additionally, we applied the principal component analysis algorithm for big data analysis to reduce dimensionality and visualize the clustering results of OES data recorded during the deposition of thin films using two different power sources. It is evident from the analysis that there are distinct clustering effects for both power sources, and thus, substantiating the presence of diverse characteristics between the two sources is essential.