X-ray topography and diffraction studies of misfit dislocation nucleation in Si-based structures

Abstract

The combination of different X–ray topography techniques and reciprocal space mapping is used to monitor the early stages of relaxation in silicon–based heterostructures. For lightly doped silicon layers grown on heavily boron–doped 150 mm substrates, Lang transmission topography demonstrates that an orthogonal array of 60°; misfits nucleates only at the wafer periphery. The length of the individual misfit segment depends on the epitaxial layer thickness and on the presence of the orthogonal blocking misfit segments. Double–crystal X–ray topography, with better strain and tilt resolution, allows one to distinguish between the different tilt components of parallel misfit dislocations. Relaxation is quantified using triple–axis X–ray diffraction. Reciprocal space maps around both the (004) and (224) reflections show that the misfits relieve about 38% of the strain. The combination of these X–ray techniques offers insight into the means to reduce dislocation formation and into the fundamental nature of the dislocations themselves.