Boron-Induced Microstrains in Dislocation-Free Silicon Crystals

Dislocation-free silicon crystals, Czochralski-grown and solution-doped with boron, have been investigated by x-ray diffraction microscopy. The x-ray measurements indicate that the perfection of dislocation-free crystals can be less than that of crystals of finite dislocation density. Microstrains were found to be the dominating imperfection. Large-area topographs show diffraction contrast which is strongly reflection dependent. The topographs clearly show the presence of inhomogeneous strains confined to localized lines and planes but extending over the whole crystal cross section. The x-ray measurements suggest that boron-doped silicon contains numerous precipitates which act as strain centers. The precipitates lie on {111} planes and produce a strong warping and bending of the lattice planes.