Analysis on pressure dependence of microcrystalline silicon by optical emission spectroscopy

Hydrogenated microcrystalline silicon films were prepared by very high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) at 180 °C. The optical emission spectroscopy (OES) was used to monitor the plasma during the deposition process. When the pressure was enhanced from 50 to 80 Pa, the intensities of SiH*, Hα* and Hβ* increase at first and then decrease for the pressures higher than 80 Pa. The transition from microcrystalline to amorphous phase occurs when increasing the pressure at silane concentration of 5%. It was found that the intensity ratio of IHα*/ISiH* affects the growth of microcrystalline silicon. With the increase of IHα*/ISiH* the crystallnity of films was improved. There are no direct relations between the SiH* intensity and the deposition rate. The deposition rate and dark conductivity are also discussed.