Projection Lens System Research Articles

Measurement and correction of TEM image distortion using arbitrary samples.

We have developed a method to quantitatively measure image distortion, one of the five Seidel aberrations, in transmission electron microscopes without using a standard sample with a known structure. Displacements of small local segments in an image due to image distortion of the intermediate and projection lens system are first measured by comparing images taken before and after a given shift at the first image plane of the objective lens. Then, the sum of the second partial derivatives, or the Laplacian, of the displacement field is measured, and the radial and azimuthal distortion parameters are determined from the measured results. We confirmed using numerically distorted images that the proposed method can measure the image distortion within a relative error ratio of 0.04 for a wide range of distortion amount from 0.1% to 5.0%. The distortion measurement and correction were confirmed to work correctly by using the experimental images, and the iterative measurement and correction procedure could reduce the distortion to a level where the average image displacement was < 0.05 pixels.

Design of Refractive/Diffractive Hybrid Projection Lens for DMD-Based Maskless Lithography

The projection lens is the core component of DMD-based maskless lithography and its imaging quality directly affects the transferal of exposure pattern. Based on the traditional projection lens system, we have designed diffractive optical element (DOE) and aspheric surfaces to optimize the refractive/diffractive hybrid projection lens system to improve its imaging quality. We found that the best effect is obtained when DOE is very close to the front lens group before the diaphragm of the hybrid system. Compared with the traditional projection lens system, this hybrid projection lens system has lower wave aberration with the help of DOE, and higher image quality owing to the modulation transfer function (MTF) value being improved. Finally, a hybrid projection lens system with working distance of 29.07 mm, image Space NA of 0.45, and total length of 196.97 mm is designed. We found that the maximum distortion and field curvature are 1.36 × 10−5% and 0.91 μm, respectively.

Maskless lithography based on oblique scanning of point array with digital distortion correction

The oblique scanning of a rectangular array of ultraviolet (UV) spots provides a feasible means of realizing maskless lithography with well-controlled UV exposure. In such a method, the UV light is modulated by a digital micromirror device (DMD), collected by a microlens/pinhole array, and then projected onto a photoresist (PR) layer for UV patterning. However, the strict requirements imposed on the optical distortion of the image projection system pose a significant technical challenge. Accordingly, the present study proposes a method for improving the UV patterning accuracy by using an empirically-derived distortion model to adjust the working DMD images. The patterning errors caused by optical distortion are then further reduced by adjusting the tilt angle of the oblique scanning process. The experimental results show that the proposed method yields a significant reduction in the UV patterning error. Consequently, it provides a practical solution for performing maskless lithography without the need for a high-quality image projection lens system.

Design of large aperture zoom projection lens

In order to obtain a large aperture zoom projection lens after optimizing a large aperture fixed focal length projection lens as the initial structure, a reasonable initial structure of fixed focal length lens was selected.According to DMD diagonal size, the dimension mapping of initial structure was done using AUTOCAD, the material of each lens was initially selected, and 5 zoom components were programmed in this system. The design was carried out by limiting the basic parameters and dimensions of lens with various operations, and 2 aspheric surfaces were used reasonably. After the optimization by using the optical design software ZEMAX and CODE V, a zoom projection lens system in visible light band was obtained. The system has a short focal length of 14.61 mm with 60° field of view(FOV) and 1.5 F number, while it has a long focal length of 29.31 mm with 30° FOV and 1.6 F number. The design results show that the modulation transfer function (MTF) of each FOV at each focal length is not less than 0.46 at the cut-off frequency 60 lp/mm. The dispersion angle at each focal length is not more than 1.6'. The projection lens achieves high quality of image. This lens system consists of 11 pieces of lenses and 1 piece of parallel plate, and the lens 2 uses aspheric surface. The system has less chips of lenses with low refractive index, and the material of each lens is easy to choose.

Multiple Patterning with Process Optimization Method for Maskless DMD-Based Grayscale Lithography

We report a multiple patterning approach utilizing digital-micromirror-device (DMD)-based grayscale lithography, providing a solution to improve fabrication accuracy for entire target three-dimensional structure. Because DMD-based lithography system consists a projection lens system, better resolution can be obtained around focal position comparing to the outer region of depth of focus. Thus, for thick-film resist micro structuring, exposing with multiple focal positions with separate grayscale masks leads to improvement of fabrication accuracy. In order to find the best combination of the multiple focal positions and their grayscale masks, the computational optimization is combined to the multiple patterning approach. Through a several experiments, effectiveness of the proposed approach was successfully demonstrated.

Effect of a diffuser on distortion reduction for a virtual image projector

Distortion aberration of a virtual image generated by a projection lens system isreduced by a diffuser. This technique is implemented by putting a diffuser onthe intermediate image plane in the imaging system. Theoretical simulation andexperimental imaging results of the proposed technique are analyzed and demonstrated.

Optical System with 4 ㎛ Resolution for Maskless Lithography Using Digital Micromirror Device

In the present study, an optical system is proposed for maskless lithography using a digital micromirror device (DMD). The system consists of an illumination optical system, a DMD, and a projection lens system. The illumination optical system, developed for 95% uniformity, is composed of fly's eye lens plates, a 405 nm narrow band pass filter (NBPF), condensing lenses, a field lens and a 250W halogen lamp. The projection lens system, composed of 8 optical elements, is developed for 4 <TEX>${\mu}m$</TEX> resolution. The proposed system plays a role of an optical engine for PCB and/or FPD maskless lithography. Furthermore, many problems arising from the presence of masks in a conventional lithography system, such as expense and time in fabricating the masks, contamination by masks, disposal of masks, and the alignment of masks, may be solved by the proposed system. The proposed system is verified by lithography experiments which produce a line pattern with the resolution of 4 <TEX>${\mu}m$</TEX> line width.

High efficiency pocket-size projector with a compact projection lens and a light emitting diode-based light source system

We present a light emitting diode (LED)-based ultramini digital micromirror device projector with a size of 75 mm x 67 mm x 42 mm and a weight of 338 g. The LED illuminator inside this projector makes it possible to achieve a volume of 18 cm(3) by using a dichroic filter and a collimating lens. The illumination system consists of high uniformity of 93% through a microlens array as a homogenizer. A total internal reflection prism is also used to reduce the size of both the illumination system and the telecentric projection lens. A projection lens system with an ultrasmall track of 42 mm, including a high modulation transfer function value of 0.4 at 46.2 line pairs/mm, an optical distortion of only 0.25 %, and a television distortion of 0.01%, is designed. Through the above superior specification, we can produce a 20 in. (51 cm) color display comparable in brightness to a laptop with a contrast of 3700:1. The device is compact and suitable for personal use.

마이크로 디스플레이를 이용한 프로젝션 TV용 광학계 설계

This paper discusses the optical system design for projection TV using LCOS type micro display, which provides the high resolution, slim depth, and a large screen of more than 60 inches. We analyzed the relationship between the illumination system, projection lens, color separation & recombination system, and micro display. From this quantitative analysis, the starting data for the optimum light engine was defined, and all optical systems were designed by an optimization process. Three RGB panels were proposed for a high luminence system, and the four prisms symmetrically located make equal optical path lengths for the RGB rays. This color separation & recombination system enables the a compact illumination system. Also, in order to the slim light engine with high resolution, the folded projection lens system was designed by inserting a mirror between projection lenses.

Optical Properties of LSI Mask Using Cover Substrate

In order to investigate the optical properties of an LSI mask that uses a cover substrate, we have designed a high-numerical aperture (NA), very low aberration reduction projection lens system. On the basis of this design, it was found that the wavefront aberration of the LSI mask that uses a cover substrate between the mask and projection lens is reduced by optimizing of the mask position and imaging position. A phase-shift mask (PSM) using a cover substrate was formed for the experiments. We measured the intensity profiles of this PSM by Zeiss aerial image measurement system (AIMS). It was found that the intensity profiles of this PSM are better than those of the conventional PSM. We have also found that an LSI mask using a cover substrate of specific thickness is able to achieve better image formation using the projection lens system.

Hollow Beam Electron Gun for Electron Beam Reducing Image Projection System: Computer Simulation

A new hollow beam electron gun with an annular emission area is described. A cathode image is focused at the contrast aperture of the projection lens system, and the mask is irradiated by a uniform intensity electron beam which is conjugate to a flattop region near the crossover. The emittance is 7.8 mm mrad for a beam energy of 100 keV. Brightness can be varied from 8×102 to 4.5×103 A/cm2sr by changing only the cathode temperature. The gun crossover, the flattop area and the cathode image axial positions can also be varied widely, without changing gun brightness and emittance, by changing the gun control anode potential. The emission current can be reduced by reducing the “ratio (emission area radial width/maximum emission area radius) of the cathode surface” without changing the emittance and with little brightness change. Using this simulated electron gun, the basic electron optics of an electron beam projection lithography system with a hollow beam is designed.

Monochromatic Projection Optical System for ArF Excimer Laser Lithography

We have developed an ArF excimer laser exposure system that combines a monochromatic quartz projection lens system and a spectrally-narrowed ArF excimer laser. The bandwidth of the laser was narrowed to 0.7 pm by using three prisms and an etalon. We delineated 0.2 µm lines-and-spaces using a chemically amplified resist and 0.16 µm lines-and-spaces using a top surface imaging resist.

Extending scalar aerial image calculations to higher numerical apertures

The usual formula for the scalar aerial image of an isolated object due to a projection lens system has been generalized beyond the paraxial approximation in an attempt to extend scalar diffraction theory to include numerical aperture (NA) values up to about 0.6. Beyond this regime, or certainly beyond NA=0.7, polarization effects need to be included, thereby demanding a full vector treatment and invalidating the present scalar formulation. A key point to the present scalar result without the paraxial approximation is the predicted functional dependence of the aerial image on magnification as NA increases. A second key point is that the usual scaling of λ/NA for the object dimensions and λ/NA2 for defocus become invalid for high NA systems. Numerical results of illustrative test cases are shown.

Reciprocal Space Imaging of Photoelectron Distributions

We present details of a display type photoelectron spectrometer, based on the principal of mirror-electron-microscopy employing an electrostatic projection lens system, which is capable of imaging photoelectrons as a linear function of their parallel wavevector throughout the entire Brillouin zone. The photocurrent is amplified onto a phosphor screen via a channel electron multiplier array. The very low light levels are then picked up with a specially developed CCD camera so that the digitized image can be both position and energy analysed. The system has the advantage over existing display type analysers in that the image is a rectilinear mapping of k||-space independent of both photon energy used or binding energy of the electronic states selected. It is possible to energy select various states at or below the Fermi energy with a retarding field analyser to a resolution of 0.3 eV.The performance of this electrostatic lens system is demonstrated by imaging the photoelectron distribution from the valence band states of a clean Cu(001) surface. Analysis of the results shows good agreement with the energy band diagram of copper and with results obtained by conventional angle-resolved photoelectron spectroscopy.

A projection lens system for oscilloscopes

A projection lens system for oscilloscopes

Camera Timing Marker with Dual Spark and Neon Light Sources

Efficient camera timing marker blocks with dual light sources, one spark and one neon lamp, for installation in 16 and 35mm high-speed cameras have been designed and produced. These timing-light sources can be operated continuously in short bursts or pulsed at cycling times of 1,000 to 50,000 cps. They are positioned to produce intense timing marks with sharp leading edges outside and between the perforations on either side of 16mm and 35mm film. They are designed with small dimensions for fitting into most high-speed cameras. — The rear source consists of a small spark-gap assembly designed to fire from a 5,000- to 10,000-v d-c pulse. This spark gap produces an intense spot of light at pulse frequencies of from 1,000 to 10,000 cps with the pulse duration of 12 to 30μsec. The resulting high-contrast image is readily observable and measurable on medium-speed black-and-white and color films, with the cameras operating at at 16mm frame rates of 8,000 frames/sec (200 ft/sec) and higher. — The neon source utilizes the NE2J or BA1C neon lamps which, when pulsed with short-duration pulses at input voltages of 200 to 300 v, produce bright images at frequencies of 1,000 to 50,000 cps. Extremely sharp edges and light intensities of an order of magnitude over conventional systems are obtained with a special f/1.3 illuminating and projection lens system designed to collect the light from the neon electrode and produce a bright image of a slit on the film.