High concentration diffusivity and clustering of arsenic and phosphorus in silicon

Abstract

The As diffusion coefficient as a function of its concentration was determined by Boltzmann–Matano analysis of the profiles of the dopant diffusing out of its conjugate phase precipitates during furnace annealing at 900 and 1050 °C of samples heavily doped by ion implantation. This method allowed to assure a constant diffusion source of As and to investigate a doping range attaining 3×1021 cm−3. Along the same lines, the diffusivity versus concentration of specimens heavily implanted with P was determined at 900 and 1000 °C. Dopant profiles were determined by secondary neutral mass spectroscopy. The diffusivity of both As and P increases with dopant content, attaining a maximum at a concentration which closely corresponds to the saturation value of the carrier density, ne, which we previously determined by equilibration annealing of specimens with excess dopant. This finding demonstrates that ne represents the limiting value of the concentration of unclustered dopant at the diffusion temperature. On the contrary, a diffusivity monotonically increasing with dopant concentration up to its solubility limit, was observed in the case of B and Sb, which do not cluster. Finally, we report the results of a simulation model which can accurately describe the evolution of the As profile upon annealing, by using our diffusivity data and taking into account both the precipitation and clustering phenomena.

Oxide precipitate nucleation at 300 °C in low resistivity n-type Czochralski Si

“…However, after thermal anneal to remove the ion implantation damage and to activate the As dopant, only about 10% of the implanted As is electrically active [25,26]. Positron annihilation studies of Ranki et al [27] on epitaxially grown Si layers with As concentrations above 10 20 cm…”

Direct observation of local atomic structure in arsenic implanted silicon

“…Thus, it can be stated that the implanted region is not amorphous, although vacancies exist in that region. In another investigation, we have verified the electrically active As þ concentration by the exponential dependence of the equilibrium carrier concentration on temperature [23][24][25]. The maximum value n e of electrically active As concentration is represented by n e ðAs þ Þ ¼ 2:2  10 22 expðÀ0:47=kTÞcm À3…”

Gettering Processes and the Role of Extended Defects

“…Finally, if phosphorus activity established by the diffusion source (e.g., POCl 3 ) exceeds the phosphorus solubility, c P > c (eq) P new phenomena occur such as the formation of SiP precipitates [97,98] and also electrically inactive mobile P species [99,100]. In this regime, metal silicide formation has been frequently observed by electron microscopy techniques [101][102][103][104] and also Mößbauer spectroscopy [105].…”