Growth kinetics of micrometer-size silicon lines produced by decomposition of silane using a laser direct-writing technique

Abstract

Polycrystalline Gaussian shape silicon lines as small as 1 μm in width were deposited by pyrolysis of silane (SiH4) on polysilicon/silicon-dioxide/monosilicon substrates. As a heat source, a cw argon-ion laser operating in the 488–514 nm range was used. The growth kinetics and morphology of the silicon lines were investigated at various scanning speeds of the laser spot, laser beam powers, and reactant gas pressures. The scanning speed was varied between 1 and 100 μm/s and the SiH4 pressure was taken in the 5–250 mbar range. From the deposition kinetics, the vertical deposition rate of silicon was calculated. According to the SiH4 pressure and laser output power values, three successive kinetic regimes were observed. At low SiH4 pressures, the deposition rate of Si lines was proportional to the reactant gas pressure. At intermediate SiH4 pressures, the deposition rate was independent of the reactant gas pressure and complied with the Arrhenius law; the apparent activation energy was found to be 25 kcal mol−1. At relatively high SiH4 pressures, the deposition rate increased again with increasing SiH4 pressure. The structure of the deposited lines was analyzed through electron microdiffraction. The morphology of the deposited Si lines, investigated using an optical microscope and an atomic force microscope, was found to be very regular and uniform. The effect of the laser beam on the quality of the interfaces underlying the deposited lines was analyzed by means of a transmission electron microscope. On the basis of the experimental results, a reaction mechanism involving surface decomposition steps of ‘‘cold’’ SiH4 molecules is proposed and discussed in this article.