Fast growth of amorphous silicon layers by amplitude modulation PECVD

Abstract

ABSTRACTHydrogenated amorphous silicon has been deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) with a square wave amplitude modulated rf signal of 50 MHz. We studied the dependence of the deposition rate on the modulation frequency, using optical emission spectroscopy and plasma modeling. We observed an enhancement in deposition rate by modulating the plasma. This behavior is explained by the characteristics of the electronenergy distribution during the periodical onset of the plasma. According to a one-dimensional fluid model, high-energy electrons cause a large production of radicals at the onset. The heating occurs over the whole plasma volume, leading to an increase of the homogeneity of the layers. The discharge structure is changed completely. A comparison is made between results obtained at 13.56 MHz and at 50 MHz deposition voltages.