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 dep osition reactor is simulated for the deposition of undoped polycrystal line silicon from silane at 25 Pa and 900 K using a one-dimensional, t wo-zone model with independently obtained rate equations. The radial g rowth rate nonuniformity across a wafer is completely determined by th e radial variations in the growth rates from silylene and disilane. Th e shape of the concentration profiles of these species can be adequate ly described in terms of a (modified) Thiele modulus based on the kine tics of their most important formation and disappearance reactions. Wi th increasing reactor tube radius the radial growth rate nonuniformity increases significantly due to higher concentration levels of silylen e and disilane in the annular zone. A smaller reactor tube radius prom otes radial uniformity across the wafers but is detrimental for the ax ial uniformity along the length of the wafer load. The effect of inter wafer spacing on radial growth rate nonuniformity is less pronounced. Moreover, an improvement in radial uniformity by an increase in interw afer spacing is achieved at the cost of wafer packing density. A quant ification of these opposing effects is possible with the model present ed.