Abstract
Near-stoichiometric SiO2 films, with little H incorporation and wet etch rates 1.5–3 times that of thermal oxide, have been deposited in a low pressure oxygen/silane helicon diffusion plasma, which has been pulsed with a 50% duty cycle at frequencies from 0.005 Hz to 1 kHz. At low pulse frequencies, the deposition rate is about 50% of the continuous rate, but as the pulse frequency increases from 0.1 to 100 Hz, the deposition rate increases and equals that for a continuous plasma. A likely explanation is that deposition from silane radicals and oxygen continues to take place in the afterglow after the plasma has extinguished. A simple model gives a time constant for this process of about 200 ms.