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

Abstract

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.

Oxygen transport in Czochralski silicon investigated by dislocation locking experiments

“…In work by Sueoka et al, a high boron concentration was found to cause enhanced oxygen precipitation in the 700-1000 • C temperature range [14]. It is likely that this effect is due to enhanced oxygen transport, which has been found in this present work.…”

“…The measured activation energies for oxygen transport in low boron doped p-type Cz-Si and high boron doped p-type Cz-Si, given in Eqs. (12) and (14), respectively, are the same within experimental error. Therefore, the experimentally measured effective diffusion coefficients vary significantly in their pre-factors.…”

“…[13] However, there is indirect evidence for oxygen transport being enhanced in highly boron doped material. Sueoka et al have found that oxygen precipitation, a process limited by oxygen transport, is enhanced in highly boron doped Cz-Si [14]. Additionally, a SIMS investigation by Heck et al shows that oxygen transport is enhanced in Cz-Si into which boron had been diffused [15].…”

Diffusion-driven precipitate growth and ripening of oxygen precipitates in boron doped silicon by dynamical x-ray diffraction

“…The BF and DF images taken under two beam condition for (004) show pronounced strain contrast making it difficult to unambiguously determine the shape of the precipitate. In contrast, the images taken under two beam condition for (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) clearly reveal that the precipitate has a plate-like character and lies on the (001) plane. From the smallest width of the contrast, the thickness of the precipitates can be roughly estimated.…”

“…In highly doped material with dopant concentrations exceeding the O concentration by about one order of magnitude, the precipitation behavior changes again as function of the dopant, the dopant concentration, and the temperature. For highly boron (B) doped (pþ) material, the nucleation rate is found to be enhanced, [13][14][15][16] whereas the growth kinetics is reported to be unaffected at 1050 C. 15 The high density can be explained by several approaches like an enhancement of the density of nucleation sites in pþ material due to the presence of, e.g., B 2 O 3 complexes. 14,17 Alternatively, the O diffusivity in pþ material might even be further enhanced in the low temperature nucleation regime.…”