Water-induced room-temperature oxidation of Si–H and –Si–Si– bonds in silicon oxide

Hydrogenated amorphous silicon oxide (a-SiOx:H) films have been fabricated by plasma-enhanced chemical vapor deposition at temperature ranging from 15 to 150 °C. It is found that once these films are taken out from the reaction chamber and immersed into water or exposed to the atmosphere, the Si–H and –Si–Si– bonds in the films start to oxidize. After immersing the films into deionized water, many small gas bubbles are formed upon the films’ surface and these bubbles were collected into sealed tubes and identified as hydrogen gas (H2(g)) using gas chromatography technique. By using infrared absorption spectroscopy and monitoring these oxidation processes at various times, it is clear that at room temperature water (H2O) molecules react with Si–H bonds and –Si–Si– bonds and form more chemically stabilized Si–O–Si, Si–O–H, H–O–H bonds, and H2(g). Study of the Si–H decreasing rates reveals that second-order reaction occurs at the initial stage of oxidation, which is consistent with two adjacent Si–H bonds oxidizing together with one attacking H2O molecule. A model of porous structure, which is probably inherent at low temperature deposition, is proposed to explain why H2O molecules can percolate through the films and eventually fully oxidize these films.