High Rate Deposition of Microcrystalline Silicon Using Resonance Plasma Source (HELIX) – Plasma Properties and Deposition Results

Abstract

AbstractMicrocrystalline silicon layers have been deposited by PECVD using a resonance plasma source (Helix) operating at frequencies of 46, 68, 113 and 163 MHz. The plasma discharges in hydrogen and various hydrogen/silane mixtures were investigated by optical emission spectroscopy (OES) and mass spectroscopy (MS). Growth rate, crystalline fraction and hydrogen content of the layers were studied for different gas compositions, excitation frequencies and plasma powers.Plasma monitoring revealed preferably the formation of positive ions. The density of positive hydrogen ions increased steadily 15 times by raising the frequency from 46 MHz to 163 MHz, whereas the ion energy was reduced from 75 eV to 23 eV and the radiation from hydrogen decreased to 50 %. Growth rates up to 1.5 μm/h have been achieved for microcrystalline layers at 230 °C deposition temperature. The content of hydrogen was below 15 at.%. Raman spectroscopy measurements reveal that 20 to 70 % of the silicon was crystalline depending on the silane concentration.