CRYSTALLOGRAPHIC CONTROL OF MICROCRYSTALLINE SILICON FILMS IN A SiF4/SiH4/H2 PLASMA BY VHF-PECVD

摘要

The effects upon ihc crystallographic properties of silicon films prepared from SiF_4/SiH_4/H_2 gas mixtures by varying the flow rale of SiF_4, input power, and the distance between parallel plate electrodes of capacitively coupled very high frequency plasma enhanced (VHF-I'l-CVD) reactor are systematically studied. The results show that at low powers an appropriate electrode distance for best crystallinity is about 15 mm. The appropriate power for best crystallinity with a highest Bragg reflection peak of Si (220) is about 60 W. The SiF4 addition suppresses the formation of crystallographic texture (111). Noticeably, the addition of SiF_4 significantly effects upon (311) oriented texture as the peak-intensity ratio of (311)/(1H) is directly proportional to SiF_4 flow rate. Increasingly added SiF_4 causes the increased internal strain, grain size, and crystallinity evidenced by the results of apparent grain sizes and the D-spacing.