Effect of Rapid Thermal Annealing on Oxygen Precipitation Behavior in Silicon Wafers

Abstract

The effect of rapid thermal annealing (RTA) on oxygen precipitation behavior in Czochralski silicon wafers was investigated with an emphasis on the RTA ambient, temperature and cooling rate. It was found that (i) anomalous oxygen precipitation (AOP) was observed in the case of RTA temperature at ≧1240°C with cooling rates of ≧25°C/s in Ar and in the case of RTA temperature at ≧1200°C with cooling rates of ≧5°C/s in N2, while AOP was not observed in O2, (ii) an M-like depth profile of precipitate density appeared for the cooling rates of ≧50°C/s in Ar, and ≧25°C/s in N2, and (iii) the width of the precipitate denuded zone was larger than the width of outdiffused oxygen in the case of RTA in Ar. The relationships of thermal equilibrium concentrations C J * and diffusion constants D J were estimated to be C I *<C V * and D I>D V (I: interstitial, V: vacancy) from the experimental results of RTA in Ar and the calculated results using the Voronkov model.

Vacancy self-trapping during rapid thermal annealing of silicon wafers

“…1 ͑filled symbols͒ are the vacancy profiles following the same RTA steps as before but now with vacancy aggregation included explicitly. Interestingly, m-like profiles are now observed in close agreement with experimental observations, 8 whereby the region with the highest residual vacancy concentration following recombination with self-interstitials exhibits the earliest onset of aggregation during cooling and therefore the lowest final vacancy concentration after the RTA treatment. The parametric constraints derived in our previous work 7,9 notwithstanding the present predictions are quite robust with respect to the point defect properties in Eqs.…”

“…5,7 Recently, RTA experiments under certain annealing protocols, namely, high temperatures and cooling rates, demonstrated unusual BMD density distributions in which the maximum BMD density is observed to lie somewhere in between the wafer edge and the center, leading to a so-called m-like profile. 8 Given the importance of BMD density distributions in silicon technology, we specifically address this density variation here by applying a recently developed model for defect diffusion and aggregation. 9 The approach taken in this work is to first consider the predictions from a point defect-only model and then analyze the effects of including vacancy aggregation.…”

“…On the other hand, a previous study has demonstrated that some combinations of point defect diffusion and equilibrium concentration parameters do, in fact, produce m-like vacancy profiles in which the maximum is not located at the wafer center. 8 However, in order to achieve this, the point defect equilibrium concentrations were chosen to have almost identical activation energies and preexponential coefficients, leading to the unlikely constraint that the equilibrium concentrations of self-interstitials and vacancies are within a few percent of each other across several decades.…”

“…Note that in both cases, the noid density is of the same order as the experimentally measured BMD density. 8 In summary, a mechanism is presented for the formation of spatial variations in the BMD distribution in silicon wafers following RTA treatment. It is proposed that these variations arise from the formation of very small voids, which unfortunately are difficult to observe directly.…”

Impact of Rapid Thermal Oxidation at Ultrahigh-Temperatures on Oxygen Precipitation Behavior in Czochralski-Silicon Crystals II

“…11,14 Therefore, to obtain a good understanding of the oxygen precipitate behavior in this RTO experiment, a C v − C i depth profile was estimated by numerical simulation using the same technique as in references 11, 15, and 16 for the conditions used in this study. The calculated C v − C i depth profiles are shown in Fig.…”