Thin-film interactions in Si/SiO2/W-Ti/Al-1% Si system

Abstract

The thin‐film metal‐metal interactions in the Si/SiO₂/W‐Ti/Al‐1% Si system have been studied by transmission electron microscopy, glancing angle x‐ray diffraction, Rutherford backscattering spectrometry, and secondary ion mass spectrometry techniques. The reaction is predominantly controlled by the diffusion of tungsten into the Al–1% Si layer and the sequence of the compound formation follows the prediction of the binary Al‐W phase diagram. It was shown that Al₁₂W forms first after sintering for 30 min at 450 °C. The Al₁₂W phase then grows from the W‐Ti/Al‐1% Si interface into the Al layer. At a temperature somewhere between 500 and 520 °C the entire Al layer is transformed to Al₁₂W and then a more tungsten‐rich phase, Al₅W, starts to form at the W/Al₁₂W interface. As the sintering temperature is increased, the Al₅W phase grows into the Al₁₂W layer. The transformation of Al to Al₁₂W is accompanied by a significant deterioration of the top surface quality. The internal morphology of the Al‐W phase is highly twinned. Its formation is accompanied by a drastic increase in the sheet resistance. The Ti in the W‐Ti layer also out‐diffuses into the top Al layer. Titanium forms Al₃Ti particles which are dispersed inside as well as at the grain boundaries of the Al₁₂W grains. The differences in the compound formation between the present system and other systems, such as Si/W‐Ti/Al and Si/PtAl/W‐Ti/Al, are discussed.