Electron cyclotron resonance hydrogen plasma has been found effective in cleaning Si surfaces in a matter of minutes, with no substrate heating. Deep level transient spectroscopy measurements showed only a broad defect peak with relatively low concentration immediately after the plasma exposure. Subsequent thermal anneals reveal emergence of strong new defects that have apparently been latent until the thermal anneal treatment. After annealing at temperatures above 450 degrees C, several well-defined defect peaks with concentrations above 1X10(13) cm(-3) appear near the Si surface. These defect concentrations reach their maximum at an anneal temperature of 500 degrees C and reduce to negligible levels at 750 degrees C. Experiments on wafers of different oxygen concentrations show that these defects are unrelated to the presence of oxygen in Si.