Three-stage full-wave simulation architecture for in-depth analysis of microspheres in microscopy

Superresolution based on coherent thermal radiation with selective information

We reexamine superresolution methods that may have been overlooked by previous optical microscopy techniques. For a one-dimensional (1D) system, we show that maximizing the information capacity of an imaging system is not a necessary condition for surpassing the Abbe diffraction limit. Specifically, the spatial resolution of two coherent emitters can go beyond the Abbe diffraction limit if an appropriate information zone, but not the full information zone, is selected for far-field imaging. Based on this principle, we show that λ/2.6 superresolution can be easily achieved for two coherent thermal radiative sources with a sufficiently large phase difference. Similar effects can be found for a 1D array of thermal radiative sources coupled by surface phonon polaritons. Introducing a dielectric microsphere into the system can further enhance the phase difference among the radiative sources, achieving superresolution better than λ/4. The concept and method presented here can be implemented to enhance the spatial resolution of thermal imaging.

Microspheres give improved resolution in nondestructive examination of semiconductor devices

The minimum spatial resolution of typical optical inspection systems used in the microelectronics industry is generally governed by the classical relations of Ernst Abbe. Kwon et al. show in a new Light: Science and Applications article that using an additional glass microsphere in the optical path can improve the resolution significantly.

Microsphere-assisted, nanospot, non-destructive metrology for semiconductor devices

As smaller structures are being increasingly adopted in the semiconductor industry, the performance of memory and logic devices is being continuously improved with innovative 3D integration schemes as well as shrinking and stacking strategies. Owing to the increasing complexity of the design architectures, optical metrology techniques including spectroscopic ellipsometry (SE) and reflectometry have been widely used for efficient process development and yield ramp-up due to the capability of 3D structure measurements. However, there has been an increasing demand for a significant reduction in the physical spot diameter used in the SE technique; the spot diameter should be at least 10 times smaller than the cell dimension (~30 × 40 μm²) of typical dynamic random-access memory to be able to measure in-cell critical dimension (CD) variations. To this end, this study demonstrates a novel spectrum measurement system that utilizes the microsphere-assisted super-resolution effect, achieving extremely small spot spectral metrology by reducing the spot diameter to ~210 nm, while maintaining a sufficiently high signal-to-noise ratio. In addition, a geometric model is introduced for the microsphere-based spectral metrology system that can calculate the virtual image plane magnification and depth of focus, providing the optimal distance between the objective lens, microsphere, and sample to achieve the best possible imaging quality. The proof of concept was fully verified through both simulations and experiments for various samples. Thus, owing to its ultra-small spot metrology capability, this technique has great potential for solving the current metrology challenge of monitoring in-cell CD variations in advanced logic and memory devices.

Overcoming refractive index limit of mesoscale light focusing by means of specular-reflection photonic nanojet

The physical origin of subwavelength photonic nanojet in specular-reflection mode (s-PNJ) is theoretically considered. This specific type of photonic nanojet (PNJ) emerges upon double focusing of a plane optical wave by a transparent dielectric microparticle located near a flat mirror. For the first time, to the best of our knowledge, we report a unique property of s-PNJ for increasing its focal length and intensity using circular-shaped microparticles with a refractive index ratio exceeding the known limiting value that fundamentally distinguishes s-PNJ from regular PNJ behavior. This may drastically increase the trapping potential of PNJ-based optical tweezers.