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

Abstract

Formation of tantalum silicides has been investigated by cosputtering tantalum and silicon on polycrystalline silicon and oxidized silicon wafers. Alloys with as‐deposited Si/Ta atomic ratios of 0.6 to 3 are sintered in hydrogen or argon ambient in the temperature range 400–1000 °C. It is found that for alloys with Si/Ta?1.0 and sintered at temperatures 5Si₃ is formed. At higher temperatures and in presence of polycrystalline silicon TaSi₂ is formed. In the absence of polycrystalline silicon (i.e., on oxide) only Ta₅Si₃ is formed at all temperatures. For alloys with Si/Ta ratios ?2 only TaSi₂ is formed. In all cases the resistivity decreases as a result of sintering, ending up in a value as a low as ∼50 μΩ cm after 1000 °C/30 min sintering. The stress in the silicided films is found to be nearly 1×10¹⁰ dyn/cm², tensile. The results have been explained on the basis of the fact that in cosputtered films interaction occurs locally which leads to smaller grain size, higher resistivities, lower stress, and smoother surface.