Low-pressure chemical vapor deposition of polycrystalline silicon : analysis of nonuniform growth in an industrial-scale reactor

The performance of an industrial-scale low-pressure chemical vapor deposition reactor is simulated for the deposition of undoped polycrystalline silicon from silane at 25 Pa and 900 K using a one-dimensional, two-zone model with independently obtained rate equations. The radial growth rate nonuniformity across a wafer is completely determined by the radial variations in the growth rates from silylene and disilane. The shape of the concentration profiles of these species can be adequately described in terms of a (modified) Thiele modulus based on the kinetics of their most important formation and disappearance reactions. With increasing reactor tube radius the radial growth rate nonuniformity increases significantly due to higher concentration levels of silylene and disilane in the annular zone. A smaller reactor tube radius promotes radial uniformity across the wafers but is detrimental for the axial uniformity along the length of the wafer load. The effect of interwafer spacing on radial growth rate nonuniformity is less pronounced. Moreover, an improvement in radial uniformity by an increase in interwafer spacing is achieved at the cost of wafer packing density. A quantification of these opposing effects is possible with the model presented