Behavior of hydrogen atoms in plasma enhanced chemical vapor deposition of microcrystalline silicon film

Microcrystalline silicon ($\mu $c-Si) thin film grown by low temperature plasma enhanced chemical vapor deposition (PECVD) is an attractive material for applications in large area electronics and optoelectronics especially on flexible plastic substrates. In the PECVD processes for the ${\rm g}\mu $c-Si film formation, conditions with high pressure (1 Torr $\sim )$ and high H$_{2}$-dilution of SiH$_{4}$ are widely appropriated. Hence, the role of H atoms is very important to fabricate highly crystallized $\mu $c-Si film, however their behavior in the gas phase has not been clarified yet. In this study, we measured the absolute density and translational temperature of H atoms in a very high frequency capacitilvely coupled plasma (VHF-CCP) source at high pressure by using vacuum ultraviolet laser absorption spectroscopy (VUVLAS). The VHF power and the flow rate of SiH$_{4}$/H$_{2}$ gas were fixed at 500 W and 5/495 sccm, respectively. The pressure was varied from 0.5 Torr to 7 Torr. The absolute density increased 4.1 $\times$ 10$^{12}$ cm$^{-3}$ to 9.0 $\times$ 10$^{12}$ cm$^{-3}$ and translational temperature increased from 500 to 1600 K with increasing pressure.