Measurement of periodicity and strain in arrays of single crystal silicon and pseudomorphic Si1−xGex/Si fin structures using x-ray reciprocal space maps

Characterization of the periodicity and strain state of an array of lithographically patterned silicon and silicon-germanium alloy on silicon fins using reciprocal space mapping of Bragg diffraction peaks is presented. Various patterned structures with different pitch values of 90 nm, 65 nm, and 42 nm have been studied and data for the 42 nm pitch sample is discussed in this paper. Diffraction from fin arrays is treated kinematically analogous to periodic surface grating structures. Diffraction from the symmetric 004 planes is used to calculate pitch and analyze the pitch walking pattern which appears as harmonic peaks on either side of the fin peaks. Pitch walking refers to the presence of two periodicities in the array due to the lithographic process. Longitudinal scans are evaluated at the fin peak positions to probe into the shape of the fin structure. Nonrectangular fin shapes resulted in peak splitting of the longitudinal scans of higher order fin peaks indicating a finite sidewall slope. Asymmetric 224 planes were analyzed to study the quality and strain-relaxation of the fin structures both parallel and perpendicular to the fin length using reciprocal space mapping techniques.