Nucleation and Growth of Silicon Thin Film Microstructures by Localized Laser Chemical Vapor Deposition.

Localized laser chemical vapor deposition (LLCVD) has become an important process for the direct generation of thin film microstructures, and is finding novel applications in microelectronics processing. Understanding the fundamental dynamics associated with thin film growth by LLCVD is necessary to control interface and thin film properties, and maintain reproducibility of deposit formation. In this dissertation, the nucleation and initial stages of silicon thin film growth by LLCVD from low pressure (<10 Torr) silane (SiH_4) on surfaces of c-Si and amorphous Si_{rm x}N_{rm y} are investigated. The nucleation stage of thin film growth is modeled via a real time Monte Carlo simulation. This model includes the effects of laser-substrate heating, transport of parent molecules to the surface and reaction products away from the surface, heterogeneous pyrolytic decomposition of the parent molecule on the laser-heated region of the surface, and adatom migration and desorption dynamics. The first predictions of the initial thin film morphology and its temporal evolution during static laser-heating of micron -dimensional regions of the surface are obtained. The nucleation phase of thin film growth is shown to influence the initial thin film morphology strongly. Silicon thin films are grown by LLCVD from silane on well prepared surfaces of c-Si and Si_ {rm x}N_{rm y} using a focused (2.3 μm diameter FWHM), visible (2.4 eV) laser. The thin film growth characteristics are subsequently determined by scanning electron microscopy and stylus profilometry, and compared to model predictions. For silicon thin films grown on the Si(100) surface, the experimentally measured overall growth rate, incubation period prior to nucleation, and the deposit morphology deviate sharply vis a vis model predictions. The first experiments of silicon thin film growth by hybrid-heating deposition, in which both thermal conduction heating and laser-heating are used simultaneously, are conducted to resolve these discrepancies. In summary, for deposition on Si surfaces, suppressed silicon growth and an altered morphology are observed within the laser -irradiated region, strongly indicating that a nonthermal, nonCVD growth mechanism is important in silicon thin film growth by LLCVD. This nonthermal effect is attributed to an interaction between silicon adatoms and the large concentration of photon-induced electron-hole pairs at the silicon surface. This is the first reported observation of a nonthermal growth mechanism in LLCVD under these conditions, and this effect is shown to be responsible for the deviations between the LLCVD experimental results and model predictions.