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

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.

Modeling of the transient interstitial diffusion of implanted atoms during low-temperature annealing of silicon substrates

“…A primary Cross-sectional TEM (XTEM) was also performed to analyze the extent of amorphization and the Ge-PAI induced EOR defects. The simulation of boron redistribution carried out for these conditions in 35 , has shown good agreement with the experimental data for the average migration length of boron interstitials l AI = 11 nm. Also it was supposed that approximately 8.6% of the implanted boron atoms occupied interstitial positions.…”

“…Therefore, it was proposed in 53 to determine the microscopic mechanism of impurity transport by means of a change in the form of the impurity profile with increase in annealing duration. It is worth noting that the calculations which were carried out in 34,35,48,49,54 show that the "tail" representing a straight line is formed by the long-range migration of impurity interstitials not only in the case of initial distribution in the form of δ-function, but also for a generation rate of nonequilibrium interstitials described by the Gaussian distribution or any other distribution. Besides, the average migration length of impurity interstitials can be comparable with the characteristic size of the initial doped region, or even less than this size.…”

“…However, the transient enhanced diffusion is observed as before, although it has another character and a smaller intensity. In the papers 34,35 a qualitative difference of the form of boron profiles produced by annealing at temperatures of 800 • C and below was pointed out in comparison with the annealing at 900 • C and higher temperatures. Really, at low annealing temperatures an extended "tail" is observed in the low-concentration re-gion of the impurity profile and the shape of this "tail" is a straight line if the axis of concentration is logarithmic.…”