Threshold behavior in the formation of nanoscale silicon particles prepared by sputtering

DC magnetron sputtering of silicon was carried out at 175 watts in argon gas at pressures from 100 mtorr to 900 mtorr. Sputter deposits were collected on an array of transmission electron microscopy (TEM) grids placed between the sputter source and a cold-finger located 10.5 cm above the sputter source. The resulting deposits were analyzed by TEM, and the morphologies were found to include granular films, well-defined particles 5–13 nm in diameter, and transition morphologies between that of particles and granular films. The resulting morphology map, as a function of sputtering pressure and TEM-grid location, indicated that particles were more likely to form at higher pressures and locations farther from the source. In addition, results obtained by varying the cold-finger temperature and the sputter-source/cold-finger distance indicated that the temperature of the cold-finger can play a significant role in particle formation at small sputter-source/cold-finger separations. Deposits with granular-film morphologies were amorphous under most conditions. However, deposits containing particles exhibited the diamond-cubic crystalline phase under some conditions as well as the amorphous phase.