Silicide formation in thin cosputtered (titanium + silicon) films on polycrystalline silicon and SiO2.

Abstract

Formation of the silicides of titanium has been investigated by cosputtering titanium and silicon on polycrystalline silicon and oxidized silicon wafers. Alloys with as-deposited Si/Ti atomic ratios of 0.5–8 were sintered in vacuum or hydrogen ambient in the temperature range 400–1000 °C. The Ti-Si interaction in such films was studied by the use of sheet resistance, x-ray diffraction, and stress measurements. It was found that in cases of silicon deficient alloys (e.g., the case of alloys sputtered on oxide with Si/Ti ratio <2) intermetallics Ti5Si3 and TiSi were formed. These intermetallics were stable up to 900 °C. In the presence of polycrystalline silicon and for alloys with Si/Ti ratio ?2, the only intermetallic formed was TiSi2. TiSi2 was responsible for very low resistivity (as low as ∼25 μΩcm) in the films. The volume change associated with silicide formation led to high tensile stresses in the films. It is suggested that in cosputtered films metallurgical interaction occurs locally which leads to small grain size, higher resistivities, and smoother surfaces. For films with excess silicon, up to 4 silicon atoms are accommodated within a unit cell of TiSi2. This suggests a range of solid solubility of silicon in TiSi2.