Chien-Kai Chung

Process of opto-mechanical design and assembly for reflective mirror subsystem of lithographic projection lens

Considering the system performance of the projection lens, not only surface quality of the optics shall be concerned, misalignment between each optics and the wavefront distortion contributed by the mounting stress and gravity are also the factors degraded the optical performance. This article introduces the opto-mechanical design and stress-free assembly process of the reflective mirror subsystem with 300 mm in outer diameter of an I-line lithographic projection lens. The flexure with mounting position pass through the center gravity of the mirror can be adopted as supporting mechanism to prevent the gravity distortion. The distortion due to temperature difference can be avoided by adopting CLERACREAM®-Z glass ceramic and INVAR for material of reflective mirror and supporting flexure respectively. The adjustment mechanism of the mirror subsystem integrates the concepts of Kinematic and exact constraint to provide six degrees of freedom (6DoF) of posture adjustment of the mirror. Furthermore, the assembly process of the flexure which minimizes the mounting stress on the mirror is presented. In the end of this article, interferometric performance test of the reflective mirror after opto-mechanical assembly compared with the measurement result in manufacturing stage is also presented. With the proposed opto-mechanical design and stress-free mounting process of the mirror, the surface distortion contributed by the amount of mounting stress and gravity effect is less than P-V 0.02 wave @632.8 nm.

The development of alignment turning system for precision len cells

In general, the drop-in and cell-mounted assembly are used for standard and high performance optical system respectively. The optical performance is limited by the residual centration error and position accuracy of the conventional assembly. Recently, the poker chip assembly with high precision lens barrels that can overcome the limitation of conventional assembly is widely applied to ultra-high performance optical system. ITRC also develops the poker chip assembly solution for high numerical aperture objective lenses and lithography projection lenses. In order to achieve high precision lens cell for poker chip assembly, an alignment turning system (ATS) is developed. The ATS includes measurement, alignment and turning modules. The measurement module including a non-contact displacement sensor and an autocollimator can measure centration errors of the top and the bottom surface of a lens respectively. The alignment module comprising tilt and translation stages can align the optical axis of the lens to the rotating axis of the vertical lathe. The key specifications of the ATS are maximum lens diameter, 400mm, and radial and axial runout of the rotary table < 2 μm. The cutting performances of the ATS are surface roughness Ra < 1 μm, flatness < 2 μm, and parallelism < 5 μm. After measurement, alignment and turning processes on our ATS, the centration error of a lens cell with 200mm in diameter can be controlled in 10 arcsec. This paper also presents the thermal expansion of the hydrostatic rotating table. A poker chip assembly lens cell with three sub-cells is accomplished with average transmission centration error in 12.45 arcsec by fresh technicians. The results show that ATS can achieve high assembly efficiency for precision optical systems.

Absolute measurement method for correction of low-spatial frequency surface figures of aspherics

Abstract. An absolute measurement method involving a computer-generated hologram to facilitate the identification of manufacturing form errors and mounting- and gravity-induced deformations of a 300-mm aspheric mirror is proposed. In this method, the frequency and magnitude of the curve graph plotted from each Zernike coefficient obtained by rotating the mirror with various orientations about optical axis were adopted to distinguish the nonrotationally symmetric aberration. In addition, the random ball test was used to calibrate the rotationally symmetric aberration (spherical aberration). The measured absolute surface figure revealed that a highly accurate aspheric surface with a peak-to-valley value of 1/8 wave at 632.8 nm was realized after the surface figure was corrected using the reconstructed error map.

Effects of UV laser milling parameters on the profile cutting of Gorilla glass substrates

The purposes of this study were to develop a high-speed milling system combined with an ablation path of the parallel lines and to investigate the cut quality on the glass substrates conducted by a nanosecond pulsed Nd:YVO4 laser (λ:355 nm). Experimental specimens were commercial Corning Gorilla glass with a thickness of 800 μm. Laser milling parameters including the laser fluence, number of milling pass, and scan speed of galvanometers along the processing path were adjusted for the profile cutting of the glass substrates. The laser milled depth, surface morphology, and surface roughness of the glass substrates after laser milling were measured by a 3D confocal laser scanning microscope. Experimental results showed that the milled depth outstandingly increased as increasing the laser fluence and the number of milling pass or decreasing the scan speed of galvanometers. The milled depths averagely increased from 38 μm to 107 μm when the scan speed of galvanometers decreased from 1500 mm/s to 300 mm/s with the laser fluence of 52 J/cm2 in a one-cycle milling process. Moreover, the milled depths averagely increased from 107 μm to 185 μm when the laser fluence decreased from 54 J/cm2 to 95 J/cm2 with the scan speed of galvanometers of 300 mm/s. When the number of milling pass increased to 5 with the laser fluences of 95 J/cm2 and scan speed of 300 mm/s, the Gorilla glass substrate was cut through a square hole. The edge of milled hollow square structures on the glass substrate had few of micro cracks, square angles, and steep and oblique walls around the milled boundaries as increasing the number of milling pass. In addition, the value of surface roughness increased with increasing the numbers of milling pass.

Parameters optimization of laser electrode patterning on ITO/glass using multi-performance characteristics analysis

The objective of this study was to obtain the optimal parameters for laser electrode patterning of indium-tinoxide (ITO) films coated on soda lime glass substrates; the parameters were determined through grey relational analysis. The electrode patterning parameters affecting the sheet resistance and optical transmittance of the film include the laser power, pulse repetition frequency, pulse duration, and focus point position. Multiple performance characteristics associated with the sheet resistance and optical transmittance were investigated by conducting experiments. An infrared (1064 nm) laser system was used to directly fabricate electrode patterns on ITO films, and the characteristics of the patterned films were systematically analyzed using an ultraviolet-visible-near-infrared spectrophotometer and a four-point probe instrument. The data obtained from the experiments were analyzed to optimize the laser patterning parameters correlated with multiple performance characteristics.

A novel absolute measurement for the low-frequency figure correction of aspheric surfaces

This study proposes an absolute measurement method with a computer-generated hologram (CGHs) to assist the identification of manufacturing form error, and gravity and mounting resulted distortions for a 300 mm aspherical mirror. This method adopts the frequency of peaks and valleys of each Zernike coefficient grabbed by the measurement with various orientations of the mirror in horizontal optical-axis configuration. In addition, the rotational-symmetric aberration (spherical aberration) is calibrated with random ball test method. According to the measured absolute surface figure, a high accuracy aspherical surface with peak to valley (P-V) value of 1/8 wave @ 632.8 nm was fabricated after surface figure correction with the reconstructed error map.