Anodic oxidation of Si in oxygen/chlorine plasma

By adding a few percent of chlorine to oxygen plasma, the anodization rate of Si was enhanced; for example, the rate was doubled for oxygen containing 3-percent chlorine. With a chlorine concentration of 1.5 percent, the density of trap states at the Si-SiO
2
interface was reduced from 7×10
¹¹
/cm
²
.eV to 5×10
¹¹
/cm
²
.eV at the midgap of Si; after annealing at 800°C in argon for 60 min, it was reduced to 8 × 10
¹⁰
/cm
²
.eV, and did not return to the original value after heating the specimen to 800°C. The density and capture cross section of traps in plasma-anodic oxide were also measured using the constant-current avalanche-injection method. The number of electron traps with small cross sections in plasmaanodic SiO
2
films was reduced by annealing them at 800°C in argon, but SiO
2
films which were anodized in oxygen/chlorine plasma showed an increase of trap density under the same annealing condition.