A defect-free silicon epitaxial layer was deposited by in-situ electron cyclotron resonance (ECR) hydrogen plasma cleaning at room temperature (25 degrees C) in a multi-chamber chemical vapor deposition (MS-CVD) system with a load lock chamber. ECR hydrogen plasma was used and films were deposited thermally at low temperature (600 degrees C). Plain-view transmission electron microscopy (TEM), cross-sectional TEM, Rutherford backscattering spectroscopy, secondary ion mass spectrometry and in-situ emission-Fourier transform infrared spectroscopy results were presented to demonstrate the efficiency of room-temperature in-situ wafer cleaning processes. Process variables such as microwave power (and gas pressure), cleaning temperature and d.c. bias were investigated, and a d.c. bias turned out to play a crucial role in low-temperature in-situ cleaning processes. Also, the effect of the in-situ cleaning temperature on cleaning efficiency was investigated and discussed. The results were shown to help understand the mechanism of the low-temperature wafer cleaning process.