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.

X-Ray topography is generally recognized as being a powerful tool for directly imaging defects in single crystals, semiconductor substrates and epitaxially grown layers. The timely identification of defects can lead to huge cost savings in wafer processing and increased yields. However, the primary limitation to its general usage within the semiconductor community has been the difficulty in system use and difficulty in integration into an in line analytical tool. To address the wider use of this powerful tool, Bede Scientific has developed a novel, high-speed digital x-ray topography concept (patent applied for) that can be implemented on an x-ray diffraction system equipped with a wafer stage and using the Microsource® x-ray tube. In this paper, we will present examples from work undertaken on a variety of materials, including: Si, SiC, Li 3 NbO 4 , InP and GaAs. Both reflection and transmission methods will be illustrated. All data was collected on a Bede D1 system using a Microsource®, a specially designed CCD detector, and an innovative software integration algorithm.

Different edge treatments were used during the processing of 150 mm diameter highly boron-doped silicon substrate wafers to create a variation of crystallographic damage around the wafer edges. We studied the wafer edge as misfit dislocation generation sites in epitaxial p/p ϩ silicon wafers. These strain-relaxing defects nucleate heterogeneously at the lattice-mismatched interface. We examined the effect of a variation of wafer edge treatments on misfit dislocation formation in p/p ϩ silicon test wafers. We determined that a lower microroughness of the wafer edge results in a decrease in the misfit dislocation density and length. We were able to show that a careful combination of edge treatments including damage removal steps helps significantly reduce misfit dislocations in strained layer epitaxy.

We determined that self implantation of pseudomorphically strained silicon epitaxial layers greatly attenuates strain relaxation. We employed highly boron doped 150 mm diameter silicon with a nominally un-doped, 2.5 μm thick epitaxial layer (p/p+). The compressively strained layer (mismatch ≈ 1.5 × 10−4) showed inhomogeneous relaxation after epitaxial growth, with misfits forming only near the wafer periphery. High temperature rapid thermal annealing was employed after ion implantation to study misfit dislocation nucleation and glide. Our results suggest that low dose ion implantation has a potential to reduce misfit dislocation propagation and nucleation in epitaxial thin films.

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