Abstract Sparse image reconstruction techniques have been used to recover high frequency information lost during the acquisition process in different imaging domains, such as ultrasound, synthetic aperture radar, optical microscopy, and astronomical and microscopic imaging. In this work, a signal processing framework is proposed to estimate the Point Spread Function (PSF) of the dark-field subsurface microscopy system from observation data. This PSF is incorporated into an image reconstruction framework, which can be formulated with two different image reconstruction techniques, regularized image reconstruction and dictionary-based image reconstruction. It is observed that both techniques provide at least 12% resolution improvement; lines with 224 nm spacing were localized after resolution improvement while lines with 252 nm spacing are at the limit of localization in experimental data. However, dictionary-based image reconstruction provides higher edge resolution and maintains the homogeneity of the intensity within the structures.

Abstract The demand for high resolution has raised interest for the use of aplanatic solid immersion lenses (aSIL) for backside optical inspection and failure analysis of integrated circuits due to its high numerical aperture capability. This work investigates the performance of aSIL microscopy in imaging of fully depleted silicon on insulator (SOI) chips and explores the effect of the buried oxide (BOx) thickness on the spatial resolution and photon collection efficiency. Three different cases, namely, bulk silicon, SOI with an ultrathin BOx of 10 nm, and SOI with a standard BOx thickness of 145 nm, are studied. It is observed that there is a 15% drop in the collection efficiency for ultra-thin BOx compared to bulk silicon and up to 80% decrease in the collection efficiency and 30% increase in the spot-size for standard Box.

Abstract Aplanatic solid immersion lens (SIL) microscopy is required to achieve the highest possible resolution for next generation silicon IC backside inspection and failure analysis. However, aplanatic SILs are susceptible to spherical aberration introduced by substrate thickness mismatch. We have developed a wavefront precompensation technique using a MEMS deformable mirror and demonstrated an increase in substrate thickness tolerance in aplanatic SIL imaging. Good agreement between theory and experiment is achieved and spot intensity increases by at least a factor of two to three are demonstrated for thicknesses deviating several percent from ideal. This technique is also capable of fixing aberrations due to SIL fabrication, off-axis imaging and refractive index mismatch.

Abstract This paper demonstrates a differential dual-phase interferometric imaging method in which the reflected probe beam modulated weakly by the charge carriers is mixed separately with two reference beams with a known phase shift in between. Performing a balanced detection scheme on these two channels, the common-mode-noise associated with strong DC background and its noise can be significantly reduced. The performance of the interferometric technique is systematically compared with the conventional mapping method through investigating inverter chains on two test chips of 180nm bulk silicon technology and 32nm SOI technology. The future work will focus on adapting the method for GHz frequency regime and time-domain implementation of the method. The method will find applications in failure analysis and testing of advanced technology IC chips for which the high sensitivity in modulation mapping is required.

Abstract As feature sizes in integrated circuits (ICs) become smaller, higher-resolution defect detection and failure analysis techniques are required. The introduction of solid immersion lenses (SIL) has been an enabling technology for highresolution backside IC imaging. High Numerical Aperture (NA) SIL imaging introduces properties of focused light which cannot be predicted by scalar beam optics. For example, spatial resolution can be manipulated in selected directions by modification of the polarization direction in linearly polarized light. In this work, we propose a unified framework combining multiple SIL microscopy images collected using polarizations at different directions in order to improve image reconstruction performance and ultimately resolution and defect localization. We show improvement in reconstruction quality by combining data taken using light with multiple polarizations. We demonstrate the effectiveness of our framework on experimental data.

Abstract We present a method for correcting spherical aberrations in solid immersion microscopy through the use of a deformable mirror. Aberrations in solid immersion imaging for failure analysis can be induced through off-axis imaging, errors in lens fabrication or mismatch of design and substrate wafer thickness. RMS wavefront error correction of 30% is demonstrated in the case of substrate wafer thickness error.

Abstract We investigate a complementary objective lens design for correcting chromatic aberration in the use of a silicon aplanatic solid immersion lens for back-side photon emission microscopy of metal-oxide-semiconductor circuits. Our simulations demonstrate that the chromatic aberration due to material dispersion of aplanatic silicon solid immersion lenses can be reduced by more than an order of magnitude in the spectral window 1.5µm-2.1µm, providing new diffraction limited performance. On-axis and off-axis imaging performance of the proposed optical design is evaluated.

Abstract As the feature size in integrated circuits (ICs) become smaller, the techniques we use to localize defects must also progress to the level that they can resolve potential errors. Additionally, because most errors cannot be identified by visual inspection alone, it is necessary to develop techniques, such as thermography, with the capability of localizing failures to the specific component or defect at fault. This paper will review the theory and application of an advanced subsurface (through the substrate) analytical technique for IC failure analysis – solid immersion lens thermal emission microscopy.