Presidential Young Investigators Award: Surface Chemistry In Semiconductor Thin Film Deposition

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Experiments are planned that will combine conventional surface analytical techniques with new laser-based methods to examine surface chemistry in the chemical vapor deposition (CVD) of thin semiconductor films, particularly of gallium arsinide. These laser techniques include photoreflectance (PR) and surface second harmonic generation (SHG). They will be used to examine the individual steps of adsorption, surface diffusion, and desorption in the overall deposition mechanism. Surface bond energies, surface diffusion coefficients, and adsorbate interactions will be measured. The surface chemistry of CVD remains virtually uncharted. This lack of understanding may result from the weakness of the interactions between gases and semiconductors. Ambient pressures greater than 10-4 Torr are often required to induce significant chemistry, but at these pressures most conventional surface analytical tools (which employ charged particles) fail. PR and SHG have not been widely employed but are effective at such pressures. Furthermore, high spatial resolution (~0.5 micron) makes these techniques particularly suited for measurements of surface diffusion. Such data are currently nonexistent for semiconductors, even though surface diffusion is expected to be rate-limiting in many deposition reactions. Surface chemistry controls impurity incorporation, defect formation, low-temperature growth rates, and many other deposition phenomena that are vitally important to the manufacture of thin semiconductor films. Reliable surface reaction rates and mechanisms are crucial for intelligent CVD reactor design. This is particularly true for gallium arsinide, for which the current trial-and-error approach to film growth has yielded only mixed results; the potential application of gallium arsinide to high-speed circuits and to optoelectronic devices for communications warrants a major effort toward the understanding of surface growth phenomena.