The changes of the crystallinity of muc-Si phase are studied in samples deposited with hydrogen dilution ratio, H-2/SiH4, from 9.0 to 19.0 by hot-wire CVD (Cat-CVD). In the samples deposited at filament temperature, T-f of 1850 degreesC, the crystalline fraction and the crystallite size of muc-Si phase increased with increasing the H-2/SiH4. The carbon content, C/(Si+C), was almost constant. In the XRD patterns, the intensity of Si(111) peak decreased and that of Si(220) peak increased with increasing the H-2/SiH4. In the samples deposited at T-f of 2100 degreesC with H-2/SiH4 over 11.4, the muc-Si phase was not formed and the C/(Si+C) increased. The growth mechanism of muc-Si in hetero-structured SiCx alloy films is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.