Reactive magnetron sputtering of tungsten target in krypton/trimethylboron atmosphere

Abstract

W-B-C films were deposited on Si(100) substrates held at elevated temperature by reactive sputtering from a W target in Kr/trimethylboron (TMB) plasmas. Quantitative analysis by X-ray photoelectron spectroscopy (XPS) shows that the films are W-rich between ~ 73 and ~ 93 at.% W. The highest metal content is detected in the film deposited with 1 sccm TMB. The C and B concentrations increase with increasing TMB flow to a maximum of ~18 and ~7 at.%, respectively, while the O content remains nearly constant at 2–3 at.%. Chemical bonding structure analysis performed after samples sputter-cleaning reveals CW and BW bonding and no detectable WO bonds. During film growth with 5 sccm TMB and 500 °C or with 10 sccm TMB and 300–600 °C thin film X-ray diffraction shows the formation of cubic 100-oriented WC1-x with a possible solid solution of B. Lower flows and lower growth temperatures favor growth of W and W2C, respectively. Depositions at 700 and 800 °C result in the formation of WSi2 due to a reaction with the substrate. At 900 °C, XPS analysis shows ~96 at.% Si in the film due to Si interdiffusion. Scanning electron microscopy images reveal a fine-grained microstructure for the deposited WC1-x films. Nanoindentation gives hardness values in the range from ~23 to ~31 GPa and reduced elastic moduli between ~220 and 280 GPa in the films deposited at temperatures lower than 600 °C. At higher growth temperatures, the hardness decreases by a factor of 3 to 4 following the formation of WSi2 at 700–800 °C and Si-rich surface at 900 °C.