Geon Lim

High-speed plasmonic nanolithography with a solid immersion lens-based plasmonic optical head

This letter describes the use of a plasmonic optical head to achieve high-speed nanopatterning. A plasmonic optical head employs both a sharp-ridged nanoaperture and a nanogap control to maintain the nanogap required for near-field nanolithography. The nanogap control uses a gap error signal produced by evanescent coupling through the air-gap. We demonstrate that a plasmonic optical head achieves a patterning resolution of 70 nm and a patterning speed of 100 mm/s. The proposed combination of a surface plasmon nanoaperture and a nanogap servo system is one of the strategies used to achieve high-speed, high-resolution nanolithography.

Mechanochemical Synthesis of Nano-Sized CeO2 and its Application for CMP Slurry

Nano-crystalline CeO2 was synthesized by the mechanical milling and subsequent heat-treatment from the mixture of Ce(OH)4 as precursor, and NaCl as diluent. The diluent provided diffusion barrier during milling and heat-treatment, which was easily dissolved out by deionized water. The size of crystallite and the strain variance of CeO2 were depended on the temperature and heat-treatment time: increased with the temperature (400~700oC) and time (1~24 hours) increasing, and saturated near at 20nm in size owing to the densification of diluent. The synthesized nano-crystalline CeO2 powder was applied as an abrasive in CMP (Chemical Mechanical Planarization) slurry. When blanket-type SiO2 and Si3N4 wafers were polished with the slurries, the removal rates (RR) of SiO2 and Si3N4 wafers and selectivities (RRSiO2/RRSi3N4) were influenced by synthetic condition of abrasive, the suspension stability and the pHs of slurries.

Experimental demonstration of line-width modulation in plasmonic lithography using a solid immersion lens-based active nano-gap control

Plasmonic lithography has been used in nanofabrication because of its utility beyond the diffraction limit. The resolution of plasmonic lithography depends on the nano-gap between the nanoaperture and the photoresist surface—changing the gap distance can modulate the line-width of the pattern. In this letter, we demonstrate solid-immersion lens based active non-contact plasmonic lithography, applying a range of gap conditions to modulate the line-width of the pattern. Using a solid-immersion lens-based near-field control system, the nano-gap between the exit surface of the nanoaperture and the media can be actively modulated and maintained to within a few nanometers. The line-widths of the recorded patterns using 15- and 5-nm gaps were 47 and 19.5 nm, respectively, which matched closely the calculated full-width at half-maximum. From these results, we conclude that changing the nano-gap within a solid-immersion lens-based plasmonic head results in varying line-width patterns.

Improved Nanogap Servo System Using an Error-Based Disturbance Observer for High-Speed in Solid Immersion Lens-Based Plasmonic Lithography

We proposed an advanced nanogap servo system using the error-based disturbance observer (EDOB) system. To achieve the feedback control over the nanogap based on the gap error signal (GES) in the near-field region, a precise gap-curve was obtained experimentally between a solid immersion lens and a photoresist-coated wafer using a piezo nanoposition actuator. With an accurate nanogap servo system, the EDOB was designed with a low-pass filter of 2.0 kHz bandwidth. Due to the powerful properties of the EDOB, which include stable robustness and disturbance rejection, a high-speed nanogap servo was achieved with up to 400 and 300 mm/s at the desired gaps of 20 and 15 nm, respectively. The disturbance rejection performance was evaluated from the GES, and the maximum deviation value was reduced by approximately 40% over that of the servo system without the EDOB.

Investigation on improvement of lateral resolution of continuous wave STED microscopy by standing wave illumination

In this paper, we report the enhancement of resolution of continuous wave (CW) stimulated emission depletion (STED) microscopy by a novel method of structured illumination of an excitation beam. Illumination by multiple excitation beams through the specific pupil apertures with high in-plane wave vectors leads to interference of diffracted light flux near the focal plane, resulting in the contraction of the point spread function (PSF) of the excitation. Light spot reduction by the suggested standing wave (SW) illumination method contributes to make up much lower depletion efficiency of the CW STED microscopy than that of the pulsed STED method. First, theoretical analysis showed that the full width at half maximum (FWHM) of the effective PSF on the detection plane is expected to be smaller than 25% of that of conventional CW STED. Second, through the simulation, it was elucidated that both the donut-shaped PSF of the depletion beam and the confocal optics suppress undesired contribution of sidelobes of the PSF by the SW illumination to the effective PSF of the STED system. Finally, through the imaging experiment on 40-nm fluorescent beads with the developed SW-CW STED microscopy system, we obtained the result which follows the overall tendency from the simulation in the aspects of resolution improvement and reduction of sidelobes. Based on the obtained result, we expect that the proposed method can become one of the strategies to enhance the resolution of the CW STED microscopy.

Investigation on achieving super-resolution by solid immersion lens based STED microscopy

The feasibility of stimulated emission depletion (STED) microscopy using a solid immersion lens was investigated. First, the theoretical feasibility of the considered system is discussed based on a vectorial field algorithm that uses a stratified medium composed of a SIL air-gap and test sample. Using the simulation, we verified that evanescent waves with much higher spatial frequencies corresponding to the high numerical aperture in the air-gap can be utilized to achieve a higher resolution than a confocal fluorescent image without a depletion beam. The simulated expectation was supported by actual imaging on two types of samples: fluorescent beads with a 20 nm diameter and an actin sample with a filamentous structure. The lateral resolution of the system was determined to be 34 nm via the imaging results on the nano-beads. The system was quite promising for achieving nano-scale surface imaging of biological samples; an even higher resolution was achieved by adjusting the wavelength and the intensity of the depletion beam.

SIL-STED microscopy technique enhancing super-resolution of fluorescence microscopy

We have characterized a new type STED microscope which combines a high numerical aperture (NA) optical head with a solid immersion lens (SIL), and we call it as SIL-STED microscope. The advantage of a SIL-STED microscope is that its high NA of the SIL makes it superior to a general STED microscope in lateral resolution, thus overcoming the optical diffraction limit at the macromolecular level and enabling advanced super-resolution imaging of cell surface or cell membrane structure and function Do. This study presents the first implementation of higher NA illumination in a STED microscope limiting the fluorescence lateral resolution to about 40 nm. The refractive index of the SIL which is made of material KTaO3 is about 2.23 and 2.20 at a wavelength of 633 nm and 780 nm which are used for excitation and depletion in STED imaging, respectively. Based on the vector diffraction theory, the electric field focused by the SILSTED microscope is numerically calculated so that the numerical results of the point dispersion function of the microscope and the expected resolution could be analyzed. For further investigation, fluorescence imaging of nano size fluorescent beads is fulfilled to show improved performance of the technique.

Low-cost strategy for time delay adjustment of STED microscopy using digital oscilloscope

There has been much research about STED microscopy to reduce cost. In that microscopy, it is necessary to synchronize the pulsed lights which is just for initial setup. However, there has not been researched in order to reduce this expense until now. So, in this paper, we propose the low-cost strategy to measure the time delay in STED microscopy. To achieve that, we utilized TCSPC principle with a general digital oscilloscope. As a result, we attained successful measurement and adjustment about two pulsed lights with 180-ps delay in STED system.

Three dimensional measurement of micro-optical components using digital holography and pattern recognition

This paper proposes a method for inspecting transparent micro-optical components that combines digital holography and pattern recognition. As many micro-optical components have array structures with numerous elements, the uniformity of each element is important. Consequently, an effective inspection requires simultaneous measurement of these elements. Pattern recognition is used to solve this issue and can be adopted effectively using the unique characteristics of digital holography to obtain both amplitude and phase information on the object. To verify this approach, an experimental demonstration was performed with a micro-lens array using a circle-detection algorithm based on the Hough Transform. As an experimental results 30 micro-lenses are detected and measured simultaneously by using proposed inspection method.

Improving nano gap control using frequency adaptive peak filter in Solid Immersion Lens-based plasmonic lithography

Plasmonic lithography is the latest technique to overcome diffraction limit of previous optical lithography. In the plasmonic lithography, the nano gap between nano metal wave guide and photoresist should be in sub-wavelength region. SIL-based plasmonic lithography is the one of the solutions to maintain small air gap. However, the nano gap control is so sensitive that a little disturbance is able to have a large effect on the nano gap control. So, we analyzed the characteristics of disturbance, and then modified the previous controller to suppress the disturbance. We applied two peak filters which were fixed one and adaptively changeable one. We experimentally confirmed the improvement of the nano gap control, which reduced nano gap error by 30 %. The proposed control will improve the quality of lithography pattern.