The microstructures and the thermal stability of Ni germanosilicide films on epi-Si1-xGex(x = 0.1,0.2)/Si substrates were studied for different silicidation temperatures. Ni films 25 nm thick were deposited by direct current magnetron sputtering and annealed at various temperatures to form Ni germanosilicide films using a rapid thermal processor. With the increase of the silicidation temperature (500 to 900 degrees C), the Ni germanosilicide formation and phase transition of Ni(Si1-yGey) to Ni(Si1-zGez)(2) were observed according to the sheet resistance measurement and X-ray diffraction analysis. Using various analytical electron microscope techniques, we investigated the microstructures and phases of Ni germanosilicide layers which were formed at 500 and 740 S C. With the increase of silicidation temperature and the initial Ge contents of epi-SiGe substrate, the severe agglomeration and the separation of Ni germanosilicide grains were observed, and Ge-rich SiGe grains reaching top surface of the sample were also formed between Ni germanosilicide grains. The formation of Ge-rich SiGe grains and the separation of Ni germanosilicide layer are believed to be the main causes for the increase of sheet resistance of the sample having higher Ge contents and annealed at high temperature. (c) 2006 The Electrochemical Society.