DIFFUSION MECHANISM OF PHOSPHORUS FROM PHOSPHORUS VAPOR IN AMORPHOUS-SILICON DIOXIDE FILM PREPARED BY THERMAL-OXIDATION

The diffusion mechanism of phosphorus into thermally grown SiO2 films from phosphorus vapor has been investigated using secondary ion mass s pectrometry, wet-chemical spectrophotometric measurements, and x-ray p hotoelectron spectroscopy. The diffusion coefficients of phosphorus in SiO2 films were determined in the temperature range 1273 to 1373 K: D -p/cm(2) s(-1) = 3.79 x 10(-9) exp (-221000/RT) where R is 8.31 J K-1 mol(-1). The solubilities of phosphorus in SiO2 films at 1373 K ranged between 3.0 x 10(20) and 2.0 x 10(22) cm(-3) in the P-2 partial press ure range 0.001 to 0.22 atm and were approximately proportional to the first power of the P-2 partial pressure. The x-ray photoelectron spec tra revealed the presence of phosphorous pentoxide and atomic silicon in SiO2 films which underwent phosphorus diffusion. The mechanism for phosphorus diffusion in SiO2 films is as follows: after dissolving int o the interstitial site of SiO2 in the form of P-2, phosphorus is inco rporated into the network of SiO2 by exchanging its site with silicon in the lattice site and diffuses through the silicon lattice sites.