Small defects in Czochralski silicon substrates are responsible for defect generation in oxide layers grown thermally on the substrates. The relationship between the defect density D and the thickness t(ox) of as-grown oxides is shown to be D = A . t(ox) . exp (-B . t(ox)), where A and B are constants. Good agreement is obtained between these equations and experimental data. We show that the implantation of ions straight through the oxide layers eliminates oxide defects at implantation doses above 10(14) cm-2. This suggests that oxide defects are associated with structures that are destroyed by the ion implantation, during which their constituent atoms are randomly displaced. In addition, we show that pouring deionized water on a rotating wafer with an oxide layer eliminates oxide defects. Electrostatic measurement reveals that negative charges are produced during the rotation. We propose a model in which electrons produced through friction between the water and the SiO2 surface induce a high electric field, and an oxide defect is selectively subjected to excessive electron conduction followed by local joule-heating, which changes the chemical state of the defect.