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.
The effect of heavy boron doping on oxygen precipitation in Czochralski silicon substrates of epitaxial wafers has been studied with transmission electron microscopy observations and a preferential etching method. Prolonged isothermal annealing between 700 and 1000ЊC for up to 700 h was performed on p/pϩ (5-20 m⍀ cm) and p/pϪ (10 ⍀ cm) wafers. It was found that, with an increase in boron concentration, (i) the precipitate density increased, and (ii) the precipitates could nucleate at a higher temperature. The growth process of platelet precipitates was also investigated and compared with the process in polished pϪ wafers. It was confirmed that (i) precipitate growth rate in p/pϩ wafers was higher than that in pϪ wafers, and (ii) precipitate nucleation in p/pϪ wafers was delayed compared with p/pϩ wafers. The precipitate growth in p/p+ wafers was determined to be reaction-limited, which differed from the diffusion-limited growth in pϪ wafers.
Dependence of mechanical strength of Czochralski silicon (CZ‐Si) wafers on the temperature of oxygen precipitation annealing has been studied both experimentally and theoretically. Thermal stress was applied to CZ‐Si wafers after oxygen precipitation annealing at 1100°C or 1000°C after preannealing at 800°C. The warpages and the densities of slip dislocations in the wafers annealed at 1100°C are much higher than those in the wafers annealed at 1000°C, nevertheless each precipitate density is almost equal. Transmission electron microscopy observations of the 1100°C samples showed that both platelet and polyhedral precipitates were generated, but very few of these precipitates actually generated punched‐out dislocations. In contrast, in the 1000°C samples, only platelet precipitates were generated, many of which generated punched‐out dislocations. Further studies showed that slip dislocations formed only from platelets which did not punch out dislocations, i.e., slip dislocations formed only in the 1100°C samples. The mechanism of the generation of slip dislocation by oxide precipitates is discussed with calculated results of the system energy change due to slip dislocation generation.
A computer simulation model for oxygen precipitation during crystal growth and wafer annealing of Czochralski silicon is constructed. In this model, the precipitate morphology is determined by minimizing the excess free energy. This model is connected with the formation models of grown-in defects, such as crystal-originated particles ͑COPs͒ in the vacancy-rich region or extrinsic stacking faults in the self-interstitials rich region. That is, the simulation of oxygen precipitation starts at 1000 or 900°C with the input data of residual point defect concentrations after COP or stacking-fault formation. The model well simulates oxygen precipitation behavior. For example, the simulated results of isothermal annealing at 700 and 800°C show that (i) the precipitate morphology is initially spherical, then changes to oblate spheroidal with an increase in annealing time, and (ii) the aspect ratio  is almost constant at (2.0-6.0) ϫ 10 Ϫ2 for longer than 200 h. The simulated  agrees approximately with experimentally determined  ϭ (0.8-2.5) ϫ 10 Ϫ2 of platelet precipitates reported in the literature. The values of both the density and the growth rate of precipitates agree for the simulations and experiments. The model also shows that oxygen precipitation during crystal growth strongly depends on the residual point defect concentrations after grown-in defect formation.Further advances in device processing require double side polished silicon wafers to achieve higher flatness and low particle generation. For such wafers, implementation of external gettering at the back surface ͑e.g., poly or sandblasting͒ is difficult to realize. Therefore, all candidates for 300 mm diam wafers, such as crystaloriginated particles ͑COPs͒ less polished wafers, high temperature annealed wafers, and epitaxial ͑epi͒ wafers require internal gettering ͑IG͒ by oxide precipitates. Because oxygen precipitation behavior depends not only on oxygen concentration but on the thermal history of the crystal ͑i.e., the pulling rate of the crystal, the crystal portion, etc.͒, the control of oxygen precipitation becomes far more difficult in comparison with that of 200 mm diam wafers.A computer simulation technique of oxygen precipitation behavior is a powerful tool applicable to various Czochralski ͑CZ͒ silicon wafers which undergo various device fabrication processes. 1-7 Hartzell et al. first reported the model, which describes the kinetics of oxygen precipitation by rate equations associated by a FokkerPlanck equation. 2 The continuity equations for point defect distribution and the strain relief by the emission of self-interstitials were incorporated in the model by Schrems 3 and Esfandyari et al. 4 Senkader et al. expanded the model to deal with oxygen precipitation associated with the formation of stacking faults. 5 However, the first model that included the nucleation process and took into account the effects of point defects was reported by Kobayashi. 6 The model showed that the precipitate nucleation occurs in a growing crystal in a temperature ran...
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