Correlation of impedance matching and optical emission spectroscopy during plasma-enhanced chemical vapor deposition of nanocrystalline silicon thin films

In this paper, the correlation of impedance matching and optical emission spectroscopy during plasma-enhanced chemical vapor deposition (PECVD) was systematically investigated in SiH ₄ plasma diluted by various hydrogen dilution ratios. At the onset of nanocrystallinity in SiH _4- depleted plasma condition, the SiH ⁺ radical reached a threshold value as the dominant radical, such that a-Si to nc-Si transition was obtained. Furthermore, the experimental data of impedance analysis showed that matching behavior can be greatly influenced by variable plasma parameters due to the change of various hydrogen dilution ratios, which is consistent with the recorded optical emission spectra (OES) of Hα* radicals. Quadruple mass spectrometry (QMS) and transmission electron microscopy (TEM) were employed as associated diagnostic and characterization tools to confirm the phase transformation and existence of silicon nanocrystals.