Lattice Strain around Platelet Oxide Precipitates in C- And N-Doped Silicon Epitaxial Wafers

The effect of heavy C and N doping on local lattice strain around platelet oxide precipitates in Czochralski silicon substrates of p/p- epitaxial (epi) wafers was investigated quantitatively using convergent beam electron diffraction (CBED). C- and N-doped p/p- epi wafers, including platelet precipitates with an edge length of approximately 500 nm, were prepared with an isothermal annealing at 800°C for 700 h. The results of strain analysis were compared with the reported results of p^- polished wafers and heavily B-doped p/p⁺ epi wafers, including an almost equal platelet density and length to C- and N-doped p/p^- epi wafers. It was found, with strain analysis from high order Laue zone patterns in the CBED disk, that (i) the type of lattice strain in C- and N-doped p/p^- epi wafers was coincided to p^- polished and B-doped p/p⁺ epi waters. The strain along the normal direction to the flat plane of the platelet precipitate was compressive, while the strain along the parallel direction to the flat plane of the platelet was tensile; (ii) 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 and p^- polished wafers. Since the substitutional carbon concentration did not change during the isothermal annealing, the strain relaxation in C-doped p/p⁺ epi wafers was caused by the availability of effective sinks in the matrix for silicon interstitials emitted by the precipitates.