Shigeo Moriyama

Mechanically Ruled Stigmatic Concave Gratings

Concave gratings that form stigmatic images in normal incidence spectrographs are analyzed and a new method of ruling stigmatic concave gratings has been developed. The ruling engine is numerically controlled for varying the groove spacings and is capable of ruling both straight and curved grooves. Three types of concave gratings, one conventional and two stigmatic have been ruled and the imaging properties of them are examined. From the results of the examination, the possibility of producing mechanically ruled stigmatic concave gratings with the freedom of choosing stigmatic wavelengths is proved.

Laser scanning system using a rotationally asymmetric aspheric surface.

In recent laser beam printers, higher resolution and a more compact system design are always desired. In this study, a rotationally asymmetric aspheric surface is introduced to achieve these purposes. This surface can completely eliminate field curvature aberration caused by the oblique incidence of the laser beam to the scanning optics, achieving high resolution over a wide scanning range.

Development Of A Precision Diamond Cutting Machine For Fabrication Of Asymmetrical Aspheric Mirrors

A high-precision, numerically controlled, diamond cutting machine has been developed for fabrication of asymmetrical aspheric mirrors, such as toroidal mirrors used in SOR optics. In this machine, a work-piece is securely fixed to a machine base, and its side face is cut by a flying single-point diamond tool. A tool spindle is laid on an X-Y slide, and its position is numerically controlled by using a laser interferometer. It is possible to fabricate a cylindrical surface by having the spindle-axis rotate slightly about an axis perpendicular to the X-Y slide. Furthermore, while the spindle is rotating, cutting-depth can be dynamically controlled by utilizing a piezo-actuator fixed to the diamond tool. The cutting-depth control is synchronized to the current rotation angle of the spindle, and cutting-depth data are numerically programmed as function of X-Y slide position. A suitable combination of these programmable figure parameters allows fabrication of asymmetrical aspheric mirrors. In order to achieve high figure accuracy, accurate straight motion is required with the X-Y slide. Therefore, straightness error compensation control is adopted, which incorporates a ZERODURE straightedge of 1m length and three optical-fiber gap sensors. The machine accepts a work-piece with maximum dimensions of 600mm length and 100mm width. A figure accuracy of 0.1 μm and surface roughness of 0.03μmRmax have been achieved.

Novel alignment technique for 0.1-μm lithography using the wafer rear surface and canceling tilt effect

A new wafer rear surface alignment (RSA) technique using a rear surface and canceling tilt effect (RECT) for wafer steppers is proposed. RECT alignment can provide the alignment accuracies of less than 0.03 μm (3σ) that are required for 0.1-μm lithography. The accuracy is almost the same as the resolution limit in the alignment sensor; therefore, position detection errors, which are caused by multi-interference in resist films and the asymmetric profile of marks deformed during manufacturing processes, must be decreased until they can be neglected. The concept of wafer RSA has provided a breakthrough to obtain higher overlay accuracy by fabricating alignment marks on the wafer rear surface. RSA, however, has the disadvantage of a position detection error e caused by a thickness between the wafer surface and the rear surface, which strongly depends on the wafer tilt. To overcome this problem, RECT consists of two-beam-illumination optics to cancel the error e. The diffracted beams that are reflected from two separate points on the grating mark include information on both mark positions and light-path difference due to wafer tilt. Thus, the wafer-tilt-induced error can be automatically canceled by processing this information. In an experiment using a six-axis fine positioning stage, it was proven that alignment accuracy can be minimized to as small as 0.015 μm (3σ) for a wafer-tilt angle range of ±50 μrad.

Fabrication Of Nonaxisymmetric Aspheric Lenses For Laser Printers

A new fabrication technique for nonaxissymmetric aspheric glass lenses is developed. In a laser printer, a combination lens system consisting of spherical lenses and a long cylindrical lens is used for the F-e conversion system. However, the conventional F-e lens system has a large aberration characteristic In its wide beam scanning. Aberration-free characteristics can be achieved using a nonaxissymmetric aspheric surface on a normal toroidal lens. This configuration results in a surface similar to a toroidal figure, but with the short radius gradually varied along the main axis. However, this type of nonaxissymmetric lens is difficult to produce with the conventiona lapping method. To overcome this problem, a new numerically controlled aspheric surface generator is constructed. Pairs of glass blanks are set around a turntable that rotates continuously at about 4 rpm. The surfaces of the blanks are machined with a grinding wheel, while the grinding spindle swings to generate the short radius of a basic toroidal figure. Furthermore, the grinding depth is dynamically controlled by actuating the turntable position through linkage with the rotation angle of the turntable. With this figure-generating principle, pairs of lenses with arbitrary surfaces can be machined at the same time. A 115 mm x 16 mm modified toroidal lens with an aspheric length of 80 Am is machined. Machining time for a lens is 45 minutes, and a figure accuracy of ± 0. 2 P.M and a surface roughness of 0.05 (Lm Rmax are achieved.

Alignment technique using wafer rear surface

A new wafer Rear Surface Alignment (RSA) technique for wafer stepper is proposed. Lithography systems such as wafer steppers are necessary to improve the overlay accuracy corresponding to resolution. For 0.1 ?m lithography, 0.03 ?m (3?) overlay accuracy is required. The RSA has the potential to obtain an overlay accuracy of more than 0.03 ?m (3?), because it is not affected in theory by resist film and asymmetric profile of patterns deformed by various device manufacturing processes. The RSA system, however, is affected by the thickness and tilt of a wafer; the process has been expanded to include the patterning of target marks on the wafer rear surface. These problems arise because the RSA system has not been widely applied to lithography systems. The new RSA called RECT alignment (using REar surface and Canceling Tilt effect) is independent of wafer tilt and dose not require any optics to detect wafer tilt or numerical compensator. The purpose of this paper is to propose the above RSA technique and to validate the RECT alignment optics. Experimental results are as follow: detecting error caused by wafer tilt of 50 ?rad is approximately less than 0.010 ?m. When the conventional sensor is used, on the other hand, the detecting error caused by wafer tilt is more than 0.03 ?m

10-mm-thick head mechanism for a stacked optical disk system

A 10-mm-thick head mechanism for a 30 GB, multi-head type stacked optical disk system has been developed. A pair of linear brushless motors are utilized as the coarse actuator, and a 2D motion lens actuator is utilized as the fine one. The average access time is 150 ms. The track following characteristics are tested. The tracking error is 0.03 micrometers in amplitude with a 3600 rpm, 254 mm diameter disk.

Overlay error estimation of wafer rear surface alignment for 0.1-μm lithography

This paper proposes using the wafer rear surface alignment (RSA) method in a lithography system in order to achieve 0.1-µm lithography. To evaluate alignment limitations, the error due to processed layers, which induces degradation of mark visibility, is measured with two conventional sensors. One is a heterodyne sensor that is stable for grained aluminum samples. The other is a broad-band sensor effective for reducing the multiple interference effect in resist films. With these sensors, the estimated limitation is 0.053 µm (M±3σ), obtained in both experiments and in simulations. The RSA method is effective in overcoming this limitation, because there are no disturbance marks due to resist film or grained aluminum film. The RSA is shown to improve the alignment limitation from 0.053 µm to 0.031 µm (M±3σ).

Precision Aspheric Generators for Off-axis X-ray Mirrors and Asymmetric Aspheric Lenses

This paper describes two types of newly developed precision aspheric generators. One is a fly cutting type machine for fabricating off-axis X-Ray metal mirrors. While the cutting spindle is rotating, the cutting depth can be dynamically controlled according to programmed data synchronized with the current rotation angle of the spindle. A figure accuracy of 0. 1 μ m and a surface roughness of 0.03 μ m Rmax are achieved. Aspheric mirrors fabricated using this machine were built in an X-ray microscope, and demonstrated a 2 μ m resolution. The other newly developed aspheric generator is for fabricating nonaxissymmetric aspheric glass lenses used in laser beam printers. Pairs of glass blanks are set around a turntable which rotates at about 4 rpm. The surfaces of the blanks are machined with a grinding wheel, where the grinding depth is dynamically controlled. The typical machining time for a lens is 30 minutes. A figure accuracy of 0. 2 μ m and a surface roughness of 0.05 μ m Rmax are achieved.

Reflection Coefficient Correction Technique for an Optical Fiber Displacement Sensor

This paper presents a novel reflection coefficient correction technique for an optical fiber displacement sensor. The new technique uses conventional fiber prove, however, displacement signal and reflection coefficient signal are simultaneously detected with it, where illumination fiber functions for both irradiating a target plane and detecting reflection light from the target. An experimental setup consists of commercially available fiber prove and a laser diode was bulit, and it was found that measuring error was less than 0.05 μm even in case of target reflection coefficient changing from 40% to 95%. In this paper, measuring principle and design method for the optical system are described, also, some experimental results are discussed.