Conformality of SiO₂ films from tetraethoxysilane-sourced remote microwave plasma-enhanced chemical vapor deposition

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:TE0S 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.