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

The combination of different X-ray topography techniques and reciprocal spa ce mapping is used to monitor the early stages of relaxation in silicon-bas ed heterostructures. For lightly doped silicon layers grown on heavily boro n-doped 150 mm substrates, Lang transmission topography demonstrates that a n orthogonal array of 60 degrees misfits nucleates only at the wafer periph ery. The length of the individual misfit segment depends on the epitaxial l ayer thickness and on the presence of the orthogonal blocking misfit segmen ts. Double-crystal X-ray topography, with better strain and tilt resolution , allows one to distinguish between the different tilt components of parall el misfit dislocations. Relaxation is quantified using triple-axis X-ray di ffraction.. Reciprocal space maps around both the (004) and (224) reflectio ns show that the misfits relieve about 38% of the strain. The combination o f these X-ray techniques offers insight into the means to reduce dislocatio n formation and into the fundamental nature of the dislocations themselves.