W1−xSix/Simultilayers (MLs) (x⩽0.66) were deposited onto oxidized Si substrates, heat treated by rapid thermal (RTA) and standard furnace annealing up to 1000 °C for 30 s and 25 min, respectively, and analyzed by various x-ray techniques and Rutherford backscattering spectrometry.W1−xSix/SiMLs are more stable the higher the value ofxbecause the driving force for interdiffusion is suppressed by the doping; the temperature for complete interdiffusion increases from 500 to 850 °C asxincreases from 0 to 0.66. The as-deposited MLs were amorphous. Their thermal stability increases with increasingx. The interface roughness is independent ofxbut increases with increasing RTA temperature. The reflectivity ofW1−xSix/SiMLs is lower than that of W/Si because of lower optical contrast. ©1997 American Institute of Physics.