Kazuhiro Harada

Effects of Thermal History on the Formation of Oxidation-induced Stacking Fault Nuclei in Czochralski Silicon during Crystal Growth

The formation of oxidation induced stacking fault (OSF) nuclei during Czochralski silicon crystal growth was investigated using crystals subjected to in situ annealing for either 1 or 4 hours by halt of pulling during crystal growth. The effects of in situ annealing at temperatures from about 1160° C to 1030° C can be summarized as follows. In positions held at about 1090° C and 1030° C, the radial distributions of OSFs, LSTDs (light scattering tomography defects), and OPs (oxygen precipitates after annealing) changed greatly. In the position held at about 1090° C, large LSTDs were formed but the OSF-ring disappeared in the region where it should have been present if pulling was not halted. In the position held at about 1030° C, the defects in the OSF-ring grew, its width increased, and the OP density both inside and outside the OSF-ring decreased with holding time. However, the radial distribution of defects at the position held at about 1160° C was similar to that for a reference crystal which was not subjected to halt of pulling. These results indicate that these defects were not formed until 1160° C, the large LSTDs were formed at 1160–1090° C, the OSF nuclei were formed at 1090–1030° C, and the OP nuclei inside and outside the OSF-ring were formed below 1030° C. We discussed the influence of point defects upon the formation of OSF nuclei.

Defects in the Oxidation-Induced Stacking Fault Ring Region in Czochralski Silicon Crystal

We have examined the defects in the oxidation-induced stacking fault (OSF) ring region in the as-grown Czochralski silicon crystals subjected to in situ annealing by the halt of pulling during crystal growth using secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) in order to investigate the nature of OSF nuclei. Oxygen aggregates were observed in the ring region in the crystals held for 4 h and 16 h using SIMS. The aggregate density in the crystal held for 16 h corresponded to the density of the grown-in defects without a flow pattern revealed by non-agitated Secco etching. TEM observation indicated that one of the grown-in defects in the ring region in the crystal held for 4 h was oxygen precipitate with a dislocation loop. OSF density decreased with holding time and density of another defect which was not an OSF increased with holding time in the ring region held at temperatures below about 1060°C. We believe that the OSF nuclei were oxygen precipitates and the dislocation loop was appeared around the precipitate during the halt of pulling process, so that OSF nuclear density was decreased.

Computer simulation of point-defect fields and microdefect patterns in Czochralski-grown Si crystals

Computer simulation of the point-defect fields in Czochralski Si crystals is reported. Our model includes the following factors: for crystals, variable pull rate V(t), the lagging of crystallization rate \widetildeV behind V, crystal length increasing with time l(t), temperature field T(r,z) dependent on l or \widetildeV, and actual shape of the crystal–melt interface; for native point defects, transport with the moving crystal, Fickian diffusion and thermodiffusion, the vacancy–self-interstitial recombination, and annealing at the crystal surface. Temperature fields established during crystal growth are calculated using a global model of heat transfer in the system. Important cases of variable V and pulling halts are considered. Simulations successfully reproduce experimental data such as the shape and position of the interstitial and vacancy regions, including the R-OSF bands. The values of model constants, except for the critical point-defect concentrations, are the same as those obtained for pedestal Si crystals.