The dependences of silicon dioxide step coverage in micron-scale trenches on substrate temperature, total pressure, absorbed microwave power, and O2:tetraethoxysilane (TEOS) flow ratio were investigated in a remote plasma configuration in which oxygen is excited upstream of the deposition chamber in a microwave glow discharge. Of the independent parameters investigated, temperature has the strongest effect on conformality. Conformality degrades modestly with decreasing pressure and increasing O2:TEOS flow ratio, but is nearly independent of absorbed microwave power. Step coverage degrades significantly with increasing temperature; for example, step coverage in a long rectangular trench of aspect ratio 2 is greater than 90% at 250 °C, but less than 40% at 400 °C at otherwise fixed conditions. We attribute this behavior to a thermally activated oxygen–atom recombination reaction on the growing silicon dioxide surface, that consumes reactive oxygen and leads to larger gradients in oxygen atom flux in the feature as temperature is increased.
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Raupp et al. (1995) studied this question.