Anomalous Effect of Hydrogen Dilution on the Crystallinity of ICPCVD-Grown Silicon Thin Films at Very Low Temperature

The structural properties of Si thin films deposited by inductively coupled plasma chemical vapor deposition at 150°C and at different dilution ratios of H 2 to SiH 4 + H 2 were studied. The crystallinity and grain sizes of Si films decreased with increasing H dilution ratios and the onset of the transition from polycrystalline Si (poly-Si) to amorphous Si ( a -Si) was observed at a 98% H dilution ratio. This is an anomalous effect compared with the effect of H dilution on the morphology of Si films grown by conventional plasma- enhanced chemical vapor deposition processes. At a 99% H dilution ratio, the morphology completely changed to the amorphous state. The influence of radiofrequency (RF) power on crystallinity was also studied and the quality of poly-Si was improved by increasing the RF power.