Yasuhito Myoi

Photolithography system using annular illumination

Photolithography is a leading technique in LSI device fabrication. The LSI pattern size has approached the exposure wavelength such as the g or i-line of a Hg lamp. This fact indicates that the shorter wavelength or some novel technique will be needed in order to cope with finer patterns. It is known that annular illumination can improve the depth of focus and resolution. We applied the annular illumination method to the step and repeat exposure system. Experiments and simulations using annular illumination were carried out and subhalf-micron patterns were produced. The process latitudes of the annular illumination method are evaluated.

Photolithography System Using Modified Illumination

Since the LSI pattern size has approached the exposure wavelength, various methods have been developed to overcome limitations in photolithography. This fact indicates that a shorter wavelength or some novel techniques will be needed in order to cope with finer patterns. The modified illumination method was proposed in order to improve the depth of focus and resolution limit. We applied the modified illumination method to the step-and-repeat exposure system. Experiments using modified illumination were carried out and sub-half-micron patterns were produced. The process latitudes of the modified illumination method are evaluated.

CW 20-kW SAGE CO/sub 2/ laser for industrial use

A CW CO/sub 2/ laser with power output of more than 20 kW is described. The laser consists of a discharge excitation system named SAGE (Silent-discharge Assisted Glow discharge Excitation) and a ZnSe or KCl transmissive window for extracting high-quality beams with axisymmetric intensity profile from a confocal positive-branch unstable resonator. SAGE is effective in forming a uniformly distributed and stable discharge in a large-volume, high-pressure gas excitation medium. Together with appropriate high-pressure gas conditions and a properly selected zeolite to adsorb water vapor in the laser chamber, the transmissive windows enable gas-sealed operations. The structure of the 20-kW SAGE laser and its performance characteristics are described. The maximum CW power of 26.5 kW with an efficiency of 16.5% is attained with the ZnSe window, and a 20.3-kW power output is extracted through the KCl window. Long-term gas-sealed operation at a CW power level of 20 kW has been demonstrated for a period of 65 h. >

Photolithographic system using modified illumination

A modified annular illumination method known as PHOENEX (Photolithography enhanced by modified exposure) is discussed. Compared with annular illumination, the modified illumination effectively cuts off the background element, which does not contribute to the imaging. In this study, the process latitudes of the modified illumination are evaluated using experiments and simulations. The DOF limit is doubled compared to the conventional method. The optical contrast is improved by the shifter-shade-type phase shift mask. The resolution limit is also improved by the modified illumination.<<ETX>>

Photolithography system using a combination of modified illumination and phase shift mask

Various methods have been developed to overcome the limitations in photolithography. Modified illumination and phase shift mask technologies have been developed in order to improve the depth of focus and resolution limit. We have combined these two methods and applied them to the step and repeat exposure system. Experiments using the modified illumination were carried out and subhalf-micron patterns were produced. The process latitude of 64M dynamic random access memory (DRAM) is doubled by this combination process.

Proposal of a Next-Generation Super Resolution Technique

A super resolution technique has been developed in order to support next-generation devices. We found that the super resolution technique was effective for smaller patterns but not for larger ones, leading to the restriction of its applicability. In order to obtain wider applicability, we propose a new optical system which has been improved and is applicable to all kinds of mask patterns. According to the proposed optical system, the mask pattern produces a specific source shape preferable for the mask pattern itself. Then the mask pattern is illuminated by this self-optimized illumination source. Thus optimal improvements can be obtained under the same illumination conditions, even if conventional patterns and phase-shift patterns of spatial frequency modulation types and diffracted amplitude modulation types are on the same photomask. Consequently, the super resolution technique will be brought into full use by this optical system.

Energy-efficient optical system for excimer laser ablation apparatus

To improve the capabilities of excimer laser ablation processing apparatus, we have been developing an innovative Multiple Irradiation Optical System (multiple irradiator). In this system, we placed a reflector opposite the mask, and used a mask with a highly reflective coating. The laser beams therefore irradiate the mask repeatedly, and we can use the laser energy more efficiently than conventional optical systems. The experimental results show that our system is 12 times more energy efficient than the conventional optical systems. Also, we have made a prototype excimer laser material processing apparatus with the multiple irradiator, which is suitable for drilling viaholes of less than 100 micrometers diameters such as viaholes of print circuit boards. The processing speed is less than 1 minute when the material is 100 mm X 100 mm wide and 25 micrometers thicknesses polyimide film, and the laser energy is 40 mJ/shot with 600 Hz frequency.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

New type of LCD projector with separately processed low-frequency chrominance and wideband luminance signals

We have developed an LCD projector based on a new concept utilizing human vision characteristics. It is known that human vision has high spatial resolution for monochrome images and low spatial resolution for color images. The new projector generates a wide-band frequency luminance signal, and low-frequency color signals from input signals. The present system uses an LCD panel of high definition for high resolution luminance image and three panels of low definition for low resolution color image. Use of low definition LCD panels, which are available at low cost, permits reduction in the cost of the system. In the developed projector, all the LCD panels have 640 X 480 pixels, but the number of pixels is electrically limited to 320 X 480 for the color panel. Light from a lamp is split by a polarizing beam splitter into two linearly polarized beams, one of which irradiates the luminance panel and the other of which irradiates the color panels, and thus both the polarized beams are utilized unlike conventional projectors where only one polarized component is utilized and the other component is lost away as heat. The projected NTSC (National Television System Committee) images were substantially of the same quality as the images which are obtained using three panels of 640 X 480 pixels. The projected VGA images had a picture quality sufficient for presentations at conferences.

Optical proximity correction for super-resolution technique

In order to support next generation ULSI devices, some super resolution techniques are developed. The super resolution technique is effective for smaller pattern but not for larger pattern. This is because the optimum dose is changed, due to the pattern characteristic. However, the z-image profile has sufficient focus latitude. To overcome this problem, the optical proximity correction (OPC) is effective. This phenomenon is observed in the conventional illumination as well as the other super resolution technique. Thus, we developed the OPC system. Using the parallel processing system, we can correct the memory device data in about 2 days. The active region reduction due to the optical diffraction was preferably compensated by the OPC system. Therefore, the OPC system can be applied to the practical use. The OPC system is applicable to the super resolution. Consequently, the applicability of the super resolution technique is significantly enhanced.

The application of an unstable resonator to a high-pressure CW CO2 laser

Abstract Unstable resonators provide high quality beams of high output power needed for material processing. We have developed a CO2 laser of over 5 kW for material processing with an unstable resonator of positive confocal configuration under high-pressure, sealed condition. High quality beams with high extraction efficiency of the power were obtained and deep pentration was attained in welding tests.