COMPOSITIONAL VARIATIONS IN TI-W FILMS SPUTTERED OVER TOPOGRAPHICAL FEATURES

To study compositional variations in Ti-W films sputtered from Ti-W al loy targets and deposited over topographical features, the sticking co efficients and angular distributions of sputtered flux arriving at the substrate for titanium (Ti) and tungsten (W) atoms have been investig ated by an overhang structure, pinhole experiment, and simulation pack age. The simulation involves the combination of a vapor transport mode l which is able to model the angular distributions for the respective materials, and a film growth model which is able to predict the compos itional variation of the deposited Ti-W films over topographical featu res. Experimentally, it was found that the sticking coefficients of Ti and W are both very close to unity for the conditions considered. How ever, the angular distributions of these two materials are quite diffe rent due to their different transport properties through the sputter g as. For the Ti-W films, the compositional variations calculated using the simulated angular distributions agreed well with the ones measured experimentally. This result clearly demonstrates that the differences between the angular distributions of Ti and W atoms cause the composi tional variations in the films. In the case of Ti-W films deposited ov er vias or trenches, the films on the sidewalls are Ti enriched, but o n the bottom are Ti deficient. The good agreement between the simulati on and experimental results indicates that the model will be very usef ul for predicting and optimizing the properties of films deposited by alloy targets.