Etching-induced physical damage at the bottom of ultrahigh-aspect-ratio contact holes was investigated by transmission electron microscopy, and a characteristic hemispherical lattice disorder was discovered in the Si substrate. Depth profiles of impurities in this disordered region were analyzed by secondary ion mass spectrometry, and it was found that this phenomenon is characteristic only for hydrogen-containing plasma. The mechanism of such damage formation is explained by proton (H+) channeling into the substrate at the ultrahigh-aspect-ratio contact hole bottom.