Probing Strain Fields About Thin Film Structures Using X-Ray Microdiffraction
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PROBING STRAIN FIELDS ABOUT THIN FILM STRUCTURES USING X-RAY MICRODIFFRACTION C.E. Murray*, I.C. Noyan*, P.M. Mooney*, B. Lai+, Z. Cai+ *
I.B.M. T.J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598 Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439
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ABSTRACT The transfer of strain between thin film features and the underlying substrate represents an important factor in the performance and reliability of semiconductor devices, particularly as the distances between these structures decrease. In order to characterize the interaction regions produced in the substrate due to strained thin film structures, we employed synchrotron-based xray diffraction techniques to map the enhanced diffracted intensity of the single-crystal Si substrate at sub-micron resolution. The dynamic-to-kinematic transition observed in the scattering of x-rays from deformed crystals makes this technique extremely sensitive to the amount of substrate deformation as a function of position. Measurements were conducted on 1 µm thick Ni dots evaporated onto Si (111) substrates and 0.24 µm thick, heteroepitaxially grown SiGe strips of various widths on Si (001). The interaction field resolved by the enhanced Si diffracted intensity in the substrate extended up to 100 times the thickness of these features. Although the boundary of the interaction field varied as a function of feature width, a characteristic curve was generated to describe the decay rate of enhanced Si diffracted intensity when the distance from the feature edge is normalized by a mean interaction distance (MID). The rate of decay of the strain fields predicted by traditional treatments of the mechanical interaction between the thin film and substrate did not correspond to the measured decay rates. INTRODUCTION The fabrication procedures used to produce ultra-large scale integration (ULSI) technology can impart significant stresses within the constituent features and underlying substrate. The resulting stress distributions, which can be highly dependent on feature geometry and density, can differ significantly among and within microelectronic structures. A precise knowledge of the values of stress is critical to ensuring the reliability of back-end of line (BEOL) features, that are susceptible to stress-voiding and electromigration, and the performance of front-end features such as transistors based on strained silicon. As device dimensions diminish, the ability to measure the strain within these structures becomes increasingly difficult. Conventional x-ray stress measurements, performed with the use of a relatively large beam (0.1 to 10 mm), can assess the volume-averaged stress within arrays of features but cannot localize the stress distribution within features. The use of x-ray diffraction to detect strain fields in single crystal substrates began over four decades ago with transmission-based x-ray techniques1. The loss or gain of intensity caused by the transition from a dynamic diffraction condition to a kinematic condition in a defor
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