Failure analysis of integrated circuits beyond the diffraction limit: contact mode near-field scanning optical microscopy with integrated resistance, capacitance, and UV confocal imaging

Abstract

Superresolution reflection near-field scanning optical microscopy (NSOM) of ultra-large-scale integrated circuits (ULSI) that have been subjected to chemical mechanical polishing (CMP) are presented. These NSOM images are rich in contrast, unlike simultaneously recorded atomic force microscopy (AFM) images. The NSOM data are compared to reflection confocal far-field optical microscopy using ultraviolet radiation with a wavelength of 248 nm, which has a resolution close to 0.2 /spl mu/m. Even though there is a significant thickness of oxide between the tip and the layer being imaged the data recorded with visible light clearly exhibits higher resolution than those ultraviolet confocal images that have undergone computer deconvolution. The AFM images exhibit no topography representing circuit features because the CMP operation that these static random access memory chips (SRAMs) have been subjected to produces flat topographic free surfaces. In terms of NSOM imaging, this is most interesting since the contribution of topography is totally removed and index of refraction variations are the only source for these rich NSOM images. Clearly, these NSOM images with cantilevered NSOM elements are free from topographic artifacts. Furthermore, simultaneous imaging of NSOM, normal force topography, and functional electrical characteristics such as capacitance and resistance are presented on these SRAMs. This demonstrates the ability of NSOM to act as a tool that provocatively integrates the best of far-field, optical imaging on the one hand with the most advanced scanned probe electrical imaging of circuit function on the other.