Annealing behaviors of open spaces and gas desorption in chemical vapor deposited SiO2 studied with monoenergetic positron beams

The annealing properties of open spaces in 90-nm-thick SiO2 deposited from tetraethylorthosilicate (TEOS) using plasma-enhanced chemical vapor deposition (PECVD) were studied with monoenergetic positron beams. From the lifetime of positronium (Ps) and an empirical model assuming a spherical open space, the mean diameter of open spaces was estimated to be 0.45 nm for PECVD-SiO2 before annealing. In the annealing temperature range below 350 °C, the size of the open spaces and their concentration increased as the temperature increased. Because initial water desorption from PECVD-SiO2 occurred in this temperature range, the observed increases in the size and concentration of spaces were attributed to the detrapping of water from such regions. Above 400 °C annealing, Ps formation was suppressed due to carrier traps introduced by the desorption of gas incorporated during TEOS decomposition. The size of the open spaces reached its maximum value (0.61 nm) after 800 °C annealing and started to decrease above 900 °C. After 1000 °C annealing, although the size of the spaces was close to that in thermally grown SiO2, their concentration remained low, which was attributed to residual impurities in the SiO2 network.