A new two-step growth method was proposed to fabricate microcrystalline silicon (mu c-Si:H) thin films by an electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD). An ultra thin Si film was first deposited and followed by H(2) plasma treatment for few minutes, and then the mu c-Si:H film was deposited on it. High-resolution transmission electron microscope (HRTEM) and Raman spectrometer were used to study the microstructures and the crystalline volume fraction of mu c-Si:H films. The HRTEM results show that the amorphous silicon thin film with a thickness of 15 nm can be crystallized by H(2) plasma treatment in 2 min, and then it serves as the seed layer for the subsequent growth of mu c-Si:H films. By optimizing the deposition parameters, the mu c-Si:H film without amorphous incubation layer can be fabricated by this new two-step method and a proper crystalline volume fraction of 50.6% can be obtained. (C) 2011 Elsevier B.V. All rights reserved.