An excimer-laser, gas-assisted deposition technique has been developed for depositing thin films of crystalline and amorphous Si and of Cu by UV-laser evaporation of target materials. A clean Si wafer is mounted inside a cryogenic vacuum chamber, cooled to 15 K, and then coated with Ar or another inert gas. The coated target is irradiated by the focused, 248-nm output of an excimer laser at fluences ranging from 2.0 to 20 J/cm2. Si evaporates on absorbing the laser radiation and condenses to create a Si film upon the laser-beam entrance window. Scanning-electron microscopy, transmission-electron microscopy, and Raman backscattering spectroscopy analyses indicate that the film is uniform and consists of a mixture of both crystalline and amorphous Si. The operational threshold laser fluence required for Si evaporation is 2.5 J/cm2 with an Ar coating and 4.0 J/cm2 without any coating. At higher fluences, the evaporation rate, and hence the deposition rate, is three times higher with the Ar coating than without. It has been determined that the gas coating functions as an antireflective layer on Si; thus the Si reflectance (R) at 248 nm decreases from 67% without the Ar coating to 28% with the coating. The reduced reflectance leads to an increased coupling of the incident laser energy into the Si target and produces the observed enhancement in the evaporation process. Other nonreactive gases that have given comparable results are N2, Kr, and Xe.
© 1986 Optical Society of AmericaFull Article | PDF Article
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