Change in the microscopic diffusion mechanisms of boron implanted into silicon with increase in the annealing temperature

TL;DR

This paper develops a two-stream model to simulate boron diffusion in silicon during annealing, revealing temperature-dependent mechanisms and quantifying diffusion enhancement, which aids in improving microcircuit fabrication processes.

Contribution

The paper introduces a novel two-stream diffusion model that distinguishes between mechanisms at different annealing temperatures, enhancing understanding of boron redistribution in silicon.

Findings

At 800°C, boron diffuses mainly via long-range migration of interstitials.

At 900°C, pair diffusion dominates, causing significant transient enhanced diffusion.

The diffusion enhancement at 900°C is approximately 44 times compared to normal diffusion.

Abstract

A two stream model of boron diffusion in silicon has been developed. The model is intended for simulation of transient enhanced diffusion including redistribution of ion-implanted boron during low temperature annealing. The following mechanisms of boron diffusion were proposed, namely: the mechanism of a long-range migration of nonequilibrium boron interstitials and the mechanism due to the formation, migration, and dissolution of the "impurity atom - silicon self-interstitial" pairs. Based on the model, simulation of the redistribution of boron implanted into silicon substrates for annealing temperatures of 800 and 900 Celsius degrees was carried out. The calculated boron concentration profiles agree well with the experimental data. It was shown that for a temperature of 800 Celsius degrees the transport of impurity atoms occurred due to the long-range migration of nonequilibrium boron interstitials generated during cluster transformation or dissolution. On the other hand, it was found that at a temperature of 900 Celsius degrees the pair diffusion mechanism played a main role in the significant transient enhanced diffusion. A number of parameters describing the transport of nonequilibrium boron interstitials and transient enhanced diffusion of substitutionally dissolved boron atoms were determined. For example, it was found that at a temperature of 900 Celsius degrees the time-average enhancement of boron diffusion was approximately equal to 44 times. The results obtained are important for the development of methods of transient enhanced diffusion suppression keeping in mind the scaling of the dimensions of silicon integrated microcircuits.