Effect of Heavy Boron Doping on Oxygen Precipitation in Czochralski Silicon Substrates of Epitaxial Wafers

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 1000°C for up to 700 h was performed on p/p+ (5-20 mΩ cm) and p/p- (10 Ω 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 p- wafers. It was confirmed that (i) precipitate growth rate in p/p+ wafers was higher than that in p- wafers, and (ii) precipitate nucleation in p/p- wafers was delayed compared with p/p+ wafers. The precipitate growth in p/p+ wafers was determined to be reaction-limited, which differed from the diffusion-limited growth in p- wafers.