Measuring lattice parameter of iron silicides using x-ray Bragg-surface diffraction

We investigated the strain field of the β-FeSi2 semiconductor on a Si(001) substrate, where FeSi in a grain form coexists with β-FeSi2 during the growth of β-FeSi2. The lattice-parameter variations in silicon due to the presence of β-FeSi2, FeSi and the grain boundary between β-FeSi2 and FeSi were detected by using the x-ray three-beam, Si(002)/(1¯11), Bragg-surface diffraction, where (002) is a symmetric Bragg reflection and (1¯11) a surface diffraction. The diffraction images of (1¯11) reflection as a function of the azimuth rotation angle around the reciprocal lattice vector of (002) provide information of lattice-parameter variation in Si. The surface nature of the (1¯11) reflection makes the (1¯11) diffraction images extremely sensitive to the interfaces between Si, β-FeSi2 and FeSi. With the penetration (detection) depth calculated from the dynamical theory of x-ray diffraction, the strain field versus the depth in the Si substrate near the interfaces is determined with the resolution of 0.002 Å for lattice variation. The largest strain detected is about 0.4% up to 15–70 Å below the interfaces.