Mechanisms of carbon and oxygen incorporation into thin metal films grown by laser photolysis of carbonyls

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Abstract
We report the results of a series of experiments studying metal film growth by low-power UV-laser photolysis of metal carbonyls. Small-area Mo, W, and Cr films were grown on Si substrates by photolysis in a background pressure of 0.1–0.2 Torr of the carbonyl. The different metals exhibited vastly different deposit morphologies. Elemental depth profiling by Auger electron spectroscopy (AES) revealed the presence of large amounts of carbon and oxygen in the films. Ultrahigh vacuum studies of the interaction of 257- and 514-nm radiation with multilayer coverages of Mo(CO)6 and W(CO)6 adsorbed on Si(111)7×7 using high-resolution electron energy-loss spectroscopy, laser-induced desorption, and AES were performed to clarify the mechanisms of adsorbed metal carbonyl decomposition and impurity incorporation into the films. Decomposition of both the adsorbed and gas-phase carbonyls proceeds through direct electronic excitation of the molecule by absorption of the 257-nm radiation; however, the photodecomposition products of the adsorbed carbonyls are different from the gas-phase decomposition products. The evidence suggests that both the surface and the previously deposited photofragments stabilize the partially photolyzed carbonyls, preventing removal of all the CO ligands from the adsorbed species.