Design of a contact probe with high positioning accuracy for plasmonic lithography.

Plasmonic lithography with a contact probe records nano-meter scale features and has high-throughput owing to its capability to scan in contact mode. The probe is commonly based on a micrometer-scale cantilever, which leads to the tip-positioning problem due to force-deflection that induces lateral tip displacement. We propose a geometrically modified probe to achieve high positioning accuracy. Contrary to a conventional cantilever-tip probe, we designed a "circular probe" with arc-shaped arms that hold the tip in the center. The mechanism is based on the "fixed-fixed beam" concept in material mechanics. To confirm its positioning accuracy, we used a finite element method (FEM) to calculate the tip displacement for a circular probe and compared the results with those using a conventional cantilever-tip probe. The probe was designed considering a silicon-based micro-fabrication process. The designed probe has a square outline boundary with a length of 50 µm, four arms, and a pyramidal tip with a height of 5 µm. The ratio of the lateral tip displacement to the vertical deflection was evaluated to indicate the accuracy of the probe. The probe has higher positioning accuracy by a factor of 10(3) and 10 in its approach mode and scan mode, respectively, compared with a cantilever-tip probe. We expect that the probe is suitable for the applications that require high positioning accuracy, such as nanolithography in contact mode and applications based on multiple-probe arrays.

Modeling of three-dimensional photoresist profiles exposed by localized fields of high-transmission nano-apertures.

Using a simple theoretical model, we calculate three-dimensional profiles of photoresist exposed by arbitrarily shaped localized fields of high-transmission metal nano-apertures. We apply the finite difference time domain (FDTD) method to obtain the localized field distributions, which are generated by excitation of localized surface plasmon polaritons underneath a C-shaped or a bow-tie-shaped aperture. Incorporating the results of FDTD simulations with the theoretical model, we visualize three-dimensional exposure profiles of the photoresist as a function of the exposure dose and the gap distance between the aperture and the photoresist. It is found that the three-dimensional exposure profiles provide useful information for choosing process parameters for nanopatterning by plasmonic lithography using the aperture.

Wavefront error measurement of high-numerical-aperture optics with a Shack-Hartmann sensor and a point source.

We developed a new, to the best of our knowledge, test method to measure the wavefront error of the high-NA optics that is used to read the information on the high-capacity optical data storage devices. The main components are a pinhole point source and a Shack-Hartmann sensor. A pinhole generates the high-NA reference spherical wave, and a Shack-Hartmann sensor constructs the wavefront error of the target optics. Due to simplicity of the setup, it is easy to use several different wavelengths without significant changes of the optical elements in the test setup. To reduce the systematic errors in the system, a simple calibration method was developed. In this manner, we could measure the wavefront error of the NA 0.9 objective with the repeatability of 0.003 lambda rms (lambda = 632.8 nm) and the accuracy of 0.01 lambda rms.

Spatiospectral transmission of a plane-mirror Fabry-Perot interferometer with nonuniform finite-size diffraction beam illuminations.

The transmission of a plane-mirror Fabry-Perot (PFP) interferometer is theoretically modeled and investigated by treating the spatial and spectral features in a unified manner. A spatiospectral transfer function is formulated and utilized to describe the beam propagation and the multiple-beam interference occurring in an ideal one-dimensional strip PFP interferometer with no diffraction loss. The spatial-frequency filtration of a finite-size beam input not only determines the transmitted spatial beam profile but also plays a crucial role in affecting the overall spectral transmittance. The inherent deviations of the spectral transmittance from what we know as the standard Airy's formula are revealed in diverse aspects, including the less-than-unity peak transmittance, the displacement of a resonance peak frequency, and the asymmetric detuning profile. Our theoretical analysis extends to the misaligned PFP interferometers, such as the cases in which non-normal-incidence beams or wedge-aligned mirrors are used that could severely degrade the effective interferometer finesse.