Effect of Heavy Carbon, Nitrogen and Boron Doping on Oxygen Precipitation Behavior in Silicon Epitaxial Wafers

摘要

The effect of heavy carbon (C), nitrogen (N) and boron (B) doping on oxygen precipitation behavior in silicon epitaxial (epi) wafers was studied with transmission electron microscopy observations and a preferential etching method. Prolonged isothermal annealing was performed on C, N and B doped epi wafers between 700 ℃ and 1000 ℃ up to 700h. It was found that, with an increase in the concentration of C in p/p- and B in p/p+ epi wafers, (i) the density of nucleated precipitates increased, and (ii) the precipitates could nucleate at a higher temperature; up to 850 ℃ by C doping and 900 ℃ by D doping. On the other hand, the nucleation behavior in p/p-epi wafers was not affected by N doping; the nucleation temperature was lower than 800 ℃. The growth of platelet precipitates was investigated and compared with the growth in p- polished wafers. It was confirmed that the growth rate in B doped p/p+ epi wafers was higher than that in C, N doped p/p- epi and p- polished wafers. This enhanced growth in B doped p/p+ epi wafers was caused by the enhanced oxygen diffusion, which was confirmed with the out-diffusion profile of oxygen by secondary ion mass spectroscopy. The lattice strain around the platelet precipitates was also investigated by using convergent beam electron diffraction. It was found that the strain in C doped p/p- epi wafers was as large as that in B doped p/p+ epi wafers, and far relaxed compared with N doped p/p- epi wafers was as large as that in B doped p/p+ epi wafers, and far relaxed compared with N doped p/p- epi and p- polished wafers. The possible mechanism of strain relaxation is the function of C and B atoms as the effective sinks of silicon interstitials emitted by oxide precipitates.