The interactions between alpha-Ta films and SiO2 after being annealed in the temperature range of 650-850 degreesC in Ar ambient have been studied using X-ray diffraction (XRD) and sheet resistance measurements. The thermal-induced products are dependent on the annealing temperatures. Under low temperature annealing, the alpha-Ta films are oxidized at the top and the bottom with increasing sheet resistance, and the oxygen source mainly comes from the annealing ambient and some which dissolved in alpha-Ta films. Free oxygen and silicon atoms released from SiO2 substrate enhance the formation of Ta oxide and generate Ta silicides under higher temperature annealing. The formation of two kinds of Ta silicides depends on the quantities of Ta atoms and free Si atoms from SiO2 at the interface. These interfacial reactions result in the increasing sheet resistance till the formation of dominate TaSi2. The oxidized Ta(N) interlayer could play an additional barrier on the diffusion of Ta and released Si atoms to improve the thermal stability of alpha-Ta films. (C) 2004 Elsevier B.V. All rights reserved.