Effect of heavy boron doping on the lattice strain around platelet oxide precipitates in Czochralski silicon wafers

The effect of heavy boron doping on local lattice strain around platelet oxide precipitates in Czochralski silicon wafers was investigated quantitatively by convergent beam electron diffraction (CBED). Lightly boron doped (p^-) polished wafers, including platelet precipitates with density of about 5X10⁹/cm³ and with an edge length of about 500 nm, were prepared with an isothermal annealing at 800°C for 700 h. Heavy boron doped (p/p⁺) epitaxial wafers, including an almost equal precipitate density and length to p^- wafers, were also prepared with an isothermal annealing at 800°C for 200 h. It was found by strain analysis from high-order Laue zone patterns in the CBED disk that (i) the type of lattice strain was coincident in p^- and p/p⁺ wafers: the strain along the normal direction of the platelet precipitate was compressive, while the strain along the parallel direction of the platelet was tensile; (ii) the strain in p/p⁺ wafers was smaller than that in p^- wafers; and (iii) the punched-out dislocations were generated by platelets only in p^- wafers. The results of (ii) and (iii) indicate that the strain around the platelets is relaxed due to the heavy boron doping.