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

Superresolution reflection near-field scanning optical microscopy (NSOM) of ultra-large-scale integrated circuits (ULSI) that have been subjected to c hemical mechanical polishing (CMP) ave 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 h as a resolution close to 0.2 mum. Evert though there is a significant thick ness of oxide between the tip and the layer being imaged, the data recorded with visible light clearly exhibits higher resolution than those ultraviol et confocal images that have undergone computer deconvolution. The AFM imag es exhibit no topography representing circuit features because the CMP oper ation that these static random access memory chips (SRAMs) have been subjec ted to produces flat topographic free surfaces. In terms of NSOM imaging, t his is most interesting since the contribution of topography is totally rem oved and index of refraction variations ave 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 a s capacitance and resistance are presented on these SRAMs. This demonstrate s the ability of NSOM to act as a tool that provocatively integrates the be st of far-field, optical imaging on the one hand with the most advanced sca nned probe electrical imaging of circuit function on the other.