Nanocrystalline silicon layers have been deposited by electron cyclotron resonance chemical vapor deposition from silane as precursor. Although hydrogen was not deliberately introduced in the plasma it was incorporated in the grown layers as evidenced by the presence of a main infrared absorption band around 2100 cm(-1) with a shoulder at 2000 cm(-1). This suggests that most of the hydrogen is bonded to internal surfaces of microcavities instead of isolated Si-H bonds. In the first few hundreds, similar to 500 Angstrom, of deposited layers, the estimated hydrogen concentration is rather low, below 5 atom So, and increases strongly for larger thicknesses. Solid phase crystallization at similar to 1100 degrees C occurs in thin layers close to the substrates in which the hydrogen concentration is below a certain critical value of similar to 5 atom %.