Phosphorus Diffusion in Partially Crystallized Films of SiO[sub 2]

Abstract

The diffusion of phosphorus into thin SiO2 films on Si was studied to assess the significance of an anomalous, rapid diffusion mode. Diffusions were performed over a wide range of temperature and time using neutron‐activated, red phosphorus diffusion sources. It was found that diffusion anneals in P vapors catalyzed a localized amorphous‐to‐crystalline transformation in the initially amorphous films, creating rapid diffusion paths at the interfaces between the crystalline islands and the surrounding amorphous matrix. The shape of the penetration profiles confirmed that interfaces contributed to the flux of P through the film. Both rapid and normal diffusion coefficients were determined and are discussed. Crystallization with subsequent rapid diffusion may be a contributing factor to the failure of SiO2 diffusion masks.

Diffusion of phosphorus doped silica for active optical fibers

“…5. Coefficients of phosphorus diffusion in amorphous SiO 2 according to [10][11][12][13][14][15], in comparison with the present study for 10, 2 and 0 mol% P 2 O 5 .…”

“…The investigation on MCVD fibers [15] yields an activation energy which is the smallest value reported [10][11][12][13][14][15], and by no means comparable with our results. In detail, three sets of experiments have been carried out, which are displayed in Fig.…”

“…Diffusion coefficients of phosphorus in amorphous SiO 2 have been determined several times at temperatures between 700 and 1200°C in thin layers oxidized on silicon with respect to the importance of phosphorus as semiconductor dopant in thin film device technology [10][11][12][13][14]. One investigation was reported at higher temperatures up to 1900°C, using gas phase deposited material similar to in our case, in the shape of fibers of diameters between 100 and 300 lm [15].…”

“…The latter paper yields also a review of the literature which shows a great scatter of the data both concerning the absolute magnitude of D and the activation energy, ranging between 420 and 110 kJ mol À1 K À1 . Reasons for this variation might be affects of impurities or admixtures, or nucleation and crystal growth in connection with increased interface diffusion [14]. Above all, not any of the past investigations has considered the concentration dependence of the diffusion coefficient, neither for the determination nor for the presentation of the results.…”

“…Two of them show relatively good agreement with our results if we take into account the concentration profiles given in [15] with maximum concentration of 14 and 12 mol% P 2 O 5 before and after heat treatment at 1175°C, respectively. The third experiment at about 1900°C would Table 1 Extrapolation of diffusion coefficients to lower and higher temperatures lg (D cm 2 s À1 ) According to (6) According to (12) } (a) Sah [10] (b) Allen [11] (c) Barry [12] (d) Thurstone [13] (e) Campbell [14] (f) Fleming [15] Fig. 5.…”