The hydrogen reaction on a hydrogenated silicon film is in two phases. This is manifested in slowing down of the hydrogen loss at the growing film. The slow down occurs in phases and both the processes have exponential character. The first phase consists of hydrogen incorporation into the layer and this occurs within the first 50 s. The second phase is of etching. This is confirmed by the similarity between the rate of hydrogen loss in the second phase and the rate of production of silyl species. (c) 2006 Elsevier B.V. All rights reserved.