Induced Convective Effects on Intrawafer Uniformity in LPCVD

The hot wall multiple wafer in tube LPCVD reactor is extensively employed in the manufacture of solid-state devices. With the current trend toward larger wafers, a fundamental understanding of the operation of these reactors, and more specifically their effect on intrawafer deposition profiles, has become imperative to the industry. We investigate the intrawafer uniformity problem, identify two conditions that guarantee uniformity, and discuss their predictions for scaleup to larger wafers. In addition we address a phenomenon which is often ignored in CVD, i.e., convection induced via the stoichiometry of the deposition reaction. Here the prediction of intrawafer profiles involves a novel example of a flow field solely induced via reaction. The steady-state deposition rate on a wafer's surface results from a balance between the diffusional resistance of the reactant gas to the surface and the convective resistance due to the net flow of product gases away from the wafer's surface. Accounting for this convective resistance allows reasonable prediction of the deposition profile to be made and introduces an additional dimensionless group which is shown to be important.