The formation of gold silicide in gold thin films deposited on Si has been studied by in situ X-ray diffraction (XRD) analysis during annealing up to 500degreesC. In addition, samples are prepared by rapid thermal annealing at 200degreesC for 10, 20, and 40 min, and analyzed by ex. situ grazing angle XRD, before and after annealing. The morphology is characterized by atomic force microscopy (AFM). The in situ XRD result shows that silicide has already been formed after the deposition of gold on silicon at room temperature. AFM micrographs reveal that silicon and gold are consumed through reacting near gold cluster interface and then silicide diffuses out and agglomerates to clusters again. The grazing angle XRD analysis shows also the evidence of phase transformation of gold silicide after annealing at 200degreesC from 20 to 40 min. These results are in good agreement with proposed kinetic model of silicide formation, in which silicon reacts with gold to form gold silicide and diffuses out along the silicon surface. (C) 2003 Elsevier Science B.V. All rights reserved.