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The growth of compound phases from thin film layers of Pd and Ti-Al deposited on Si is described in this work. The growth kinetics and composition of the compound phases were measured utilizing 2 MeV ⁴He backscattering. Crystalline structure and film texture effects of the compounds layers were measured by X-ray diffraction techniques. The Pd-Si system was first studied by depositing 1000 to 3000Å of Pd onto a Si substrate and heating to 200 to 700°C. A single phase of material with a composition Pd2Si developed when specimens were heated to a temperature of 200°C. The phase grows at a rate proportional to (time)1/2 indicating transport limited growth. The temperature dependence of the growth constant was found to be expressible as a single activation energy of approximately 1.5 eV over the 200 to 275°C temperature range where growth kinetics were measured. The X-ray diffraction data indicated that the Pd2Si phase which formed has the crystalline structure of Pd2Si known from metallurgical studies of bulk materials. The Pd2Si layers which formed from the thin film structures were found to be oriented with the hexagonal basal plane parallel to the substrate material. The degree of the preferred orientation of the Pd2Si depends on the Si substrate orientation. By far the highest degree of orientation was found when the Pd2Si was formed on -Si. The more complex Si-Ti-Al system is treated following the Pd-Si system. In this case a layer of Ti and then Al was evaporated on Si after which the specimens were heated to temperatures of 400° to 500°C. Backscattering of ⁴He ions was used to measure growth kinetics and composition of compound phases which develop. While the spectra are more complex the same basic analysis techniques developed for the Pd-Si system were applicable. While no measurable reaction of the Si and Ti was found in this temperature range, the Ti-Al reacts to form a phase of TiAl₃. The rate of formation of TiAl₃ was also found to be proportional to (time)1/2 indicating transport limited growth. The temperature dependence of the growth constant was found to be again expressible by a single activation energy over the temperature range measured. The value of activation energy was found to be approximately 1.85 eV. The X-ray diffraction analysis indicates that a single phase of TiAl3 forms until the entire Ti layer is consumed. At this point Si reacts with the system displacing most of the Al to form a Si-rich Ti-Al-Si ternary phase. The Ti-Al metal system is used to make contact to Si in integrated circuit applications. The TiAl₃ and subsequent Si-rich Ti-Al-Si ternary formation in this system can be directly related to severe erosion of metal -Si contact areas which result in failure of the integrated circuits. The measured rate of formation of TiAl₃ found from the backscattering measurements allows the thickness of Ti to be chosen large enough so that heat treatments following metal deposition will not cause contact failure. Thus, the rate kinetics of TiAl3 formation measured by 2 MeV ⁴He backscattering is found to have practical application in predicting and controlling a failure mechanism in an integrated circuit metallization scheme. |
