Nanoscale Imaging of Strain using X-Ray Bragg Projection Ptychography
(Top) Focused beam coherent X-ray nanodiffraction patterns collected from a SiGe-on-SOI prototype device edge and (middle and bottom) projected strain field reconstructed by ptychographic methods.
Users of the Center for Nanoscale Materials (CNM) from IBM exploited nanofocused X-ray Bragg projection ptychography to determine the lattice strain profile in an epitaxial SiGe stressor layer of a silicon prototype device. The theoretical and experimental framework of this new coherent diffraction strain imaging approach was developed by Argonne's Materials Science Division in collaboration with the CNM's X-Ray Microscopy Group to efficiently image strain fields with unperturbed boundary conditions in technologically and scientifically relevant energy systems.
This new technique is capable of imaging lattice distortions in thin films nondestructively at spatial resolutions of <20 nm using coherent nanofocused hard X-rays. This work marks a significant step forward in the development of nondestructive coherent X-ray diffraction imaging techniques for the study of nanoscale lattice features in real materials under real conditions. This study, in which structural subtleties were resolved in a device prototype arising from both intrinsic size effects and extrinsic boundary conditions, paves the way for nondestructive studies of structure in materials at nanometer length scales where prediction, measurement, and control of strain is difficult.
The data obtained by the IBM users measures strain from epitaxial lattice mismatches and device processing, which can be used to test continuum elastic modeling predictions of nanoscale strain distributions.
S. O. Hruszkewycz et al., "Quantitative nanoscale imaging of lattice distortions in epitaxial semiconductor heterostructures using nanofocused X-ray Bragg projection ptychography," Nano Letters, 12, 5148-5154, DOI: 10.1021/nl303201w (2012).