Preparation Of ZrW₂O₈/Cu Gradient Films By Radio Frequency Magnetron Sputtering And Properties Study

With the rapid development of integrated circuit, the radiation of heat from chips increases correspondingly, and it will challenge the adhesive performance between copper film interlink line and silicon substrate. In order to match the expansions of copper and silicon, which have different expansion coefficients, the excellent negative thermal expansion material ZrW₂O₈ was added into copper films to form gradient coextruded ones, which have higher adhesive force and good electrical conductibility.The experiment used two targets, pure copper target and the target of ZrO₂ and WO3 mixed with molar ratio 1:2. The as-deposited films were prepared on single crystal silicon substrate by radio frequency magnetron sputtering. The two targets worked simultaneously during the power of copper target increased and the power of oxide target decreased continuously. After heat treatment and deoxidization, ZrW₂O₈/Cu gradient films formed. The films' phases, morphologies and element distributions were examed and analyzed by X-ray diffraction, scanning electron microscope, atomic force microscope, X-ray photoelectron spectroscopy, et al. Scratch tester and electrical resistivity tester were individually used to test and compare the gradient films' adhesive performance and electrical conductibility with copper films'.The results show that, the as-deposited films are slick and flat coexistent ones consisting of copper oxide and amorphous zirconium tungstate, whose elements have gradient distributions. When the films are heat treated at different temperatures, the peaks of cubic zirconium tungstate in XRD spectra don't show up at 700℃, and gradually grow higher from 720℃to 760℃. Meanwhile, the peaks of copper oxide also grow higher. So the best crystallization temperature is 760℃. After deoxidization in hydrogen at 400℃, ZrW₂O₈/Cu gradient films form. The density of gradient film is high, but low of the copper film made in the same condition. And the monolayer homogeneous film ZrW₂O₈/Cu has small cracks. The gradient film shows superiority in quality.After the tests of performances, it is found that gradient films' adhesive force is much larger than that of copper films. The thermal expansion coefficient in the gradient film changes gradiently along the change of ratio of ZrW₂O₈ and Cu, then the thermal stress is eased up. Zirconium tungstate shows distinct improvement to the adhesive performance. But the insulating zirconium tungstate decreases gradient film's electrical conductivity compared with that of copper film. If preparing gradient films till sole copper target sputtering, the difference of electrical conductivities between gradient film and copper film will be much smaller.