Strain Relaxation at Semiconductor Surface Revealed by Extremely Asymmetric X-Ray Diffraction.

Abstract

Extremely asymmetric X-ray diffraction is a noble method to evaluate strain fields near crystal surfaces or interfaces. This method is sensitive to crystal structure near surface region because a glancing angle of X-ray is set near a critical angle of total reflection. A minute strain fields (≥ 0.1%) at surface brings a variation of intensity and width of rocking curves. Therefore we can evaluate strain near surfaces by analyzing curve-shape or integrated intensity of the curves. We show two examples of experimental strain evaluation. One is Si reconstructed surfaces. We quantitatively evaluated intrinsic strain fields near Si reconstructed surfaces, i.e., Si(111)-(7×7), Si(111)-(√3×√3)-Al, and Si(111)-(√3×√3)-Ag surfaces. From the fitting of the experimental rocking curves with calculated curves, we found that all reconstructed surfaces bring a contraction of the (111) spacing due to surface lattice relaxation, and such strain extends to some ten nm under the surfaces. Another example is silicide surface. We evaluated a strain evolution near hydrogen-terminated Si(111) surface due to nickel deposition. We found that a compressive strain gradually introduces into the substrate accompany with a growth of “Ni diffusion layer” near the hydrogen-terminated surface.