Control of the Surface Reactivity of the Si(100) Surface

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CONTROL OF THE SURFACE REACTIVITY OF THE Si(1O0)

SURFACE

JOHN T. YATES, JR.*, M. J. BOZACK*, L.MUEHLHOFF*, AND W. J. CHOYKE** * Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 **Department of Physics, University of Pittsburgh and Westinghouse Research and Development Center, Pittsburgh, Pennsylvania 15235 ABSTRACT We have used molecular beam methods and temperature programmed desorption to probe the reaction of several hydrocarbons with the Si(100) surface at cryogenic temperatures. It has been found that the kinetics of the surface reaction with the C=C bond can be strongly influenced by the production of active surface sites using prebombardment with Ar ions. The chemistry of the adsorbate is also influenced by electron bombardment of the adsorbed layer. Conversely, capping of active sites with atomic hydroThis work forms a first gen retards the kinetics of the surface reaction. step in using the methods of surface kinetics and spectroscopy to probe the details of the elementary steps at work in chemical vapor deposition and plasma vapor deposition, leading to the production of SiC films. A.

Introduction

The complexity of surface reactions used in chemical and plasma deposition processes on silicon surfaces provides a challenge to surface chemists and physicists. At the present time very little systematic research directed at the understanding of organic surface chemistry on silicon has been published. Klimesch et al.[1] have reported that ethylene adsorption occurs on Si(111),

and that about 20-30 % of the layer desorbs without

decomposition. Stroscio, Bare, and Ho [2] have studied methanol adsorption on Si(111), finding that methoxy species are produced along with Si-H surface species. In the work to be reviewed here, we show how the reactivity of hydrocarbon molecules with a Si(l00) surface can be measured using molecular beam methods, and how the basic surface chemistry can be controlled by treatment of the surface either prior to adsorption or after the formation of adsorbed species. Although vibrational spectroscopic information about the surface species themselves is currently not available, we offer plausible surface bonding models to explain our observations. B.

Experimental Methods

The experimental methods and results reported in this review are more thoroughly discussed elsewhere [3-7]. We employ a basic ultrahigh vacuum system shown in Figure 1. A Si(l00) single crystal is mounted so that it may be heated by electrical conduction or by the use of a focused lamp. The crystal may be cleaned by heating and Ar ion bombardment, and the surface condition checked by AES and LEED methods. A molecular beam doser is arranged to supply incident adsorbate molecules to the clean crystal, and the reaction may be followed by study of the reflected flux of reactant molecules using the quadrupole mass spectrometer (QMS). Also, temperature programmed desorption is employed to study the liberation of species from the Si(O0) surface following controlled ad