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

实验计划将传统的表面分析技术与新的基于激光的方法相结合，以检查半导体薄膜的化学气相沉积（CVD）中的表面化学，特别是砷化镓。这些激光技术包括光反射（PR）和表面二次谐波产生（SHG）。它们将被用来研究吸附、表面扩散和解吸在整个沉积机制中的各个步骤。表面键能、表面扩散系数和吸附质相互作用将被测量。CVD的表面化学性质实际上仍然是未知的。这种理解的缺乏可能是由于气体和半导体之间相互作用的薄弱造成的。通常需要大于10-4托的环境压力来诱导显著的化学反应，但在这些压力下，大多数传统的表面分析工具（使用带电粒子）都失败了。PR和SHG尚未被广泛使用，但在这种压力下是有效的。此外，高空间分辨率（~0.5微米）使这些技术特别适合测量表面扩散。尽管表面扩散在许多沉积反应中被认为是限速的，但目前半导体领域还没有这样的数据。表面化学控制杂质掺入、缺陷形成、低温生长速率和许多其他沉积现象，这些现象对半导体薄膜的制造至关重要。可靠的表面反应速率和机理是智能CVD反应器设计的关键。对于砷化镓来说尤其如此，目前的薄膜生长试验方法只产生了好坏参半的结果；砷化镓在高速电路和光电子通信器件中的潜在应用，需要对表面生长现象的理解做出重大努力。

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.