The image-forming limit of x-ray lithography is said to be ∼70 nm using existing devices and technologies. This article presents methods to extend the limit to 25 nm or even below. Preparatory to the study, a light source was designed to improve x-ray beam toward shorter wavelength. In addition, a simulation code has been developed to evaluate the methods. The first method is to use a mask with a larger period and pattern than deigned images. The mask forms the designed images with an enlarged period. Two-dimensional, 25 nm width images can be formed using a 100 nm period pattern mask at 8 μm gap. The second method is to use a mask with interference slits. Since the image pattern is sharply focused, ⩽25 nm images can be formed at 8–12 μm gaps. Multiple exposures are applied to both methods in order to fill in the clearances of the images. Simulation results are shown in both methods for typical patterns.
We have developed a short beamline with high brightness for x-ray lithography. The beamline contains a single, a scanning toroidal mirror and a vacuum-protection system with an acoustic delay line. The practical exposure intensity on a wafer was approximately 50 mW/cm 2 at stored electron current of 500 mA. Dose uniformity of Ϯ2.8% was achieved in a 26 mmϫ26 mm exposure area by optimizing the scan speed. Minimum resolution of 80 nm was obtained with a 15 m gap. The optimum dose for TDUR-N908 ͑Tokyo Ohka͒ was 1300 mA s, which corresponds to exposure time of 2.6 s when the stored electron current is 500 mA. Since the sensitivity of TDUR-N908 is 110 mJ/cm 2 , the beam intensity in our beamline is estimated to be 43 mW/cm 2 . By reducing the exposure field, a beam intensity of more than 50 mW/cm 2 can be achieved.
Articles you may be interested inExtreme expansion of proximity gap by double exposures using enlarged pattern masks for line and space pattern formation in x-ray lithography (evolution of exposure method to symmetric illumination)
In this paper is presented an optical design of high-performance beam lines for synchrotron-radiation-based X-ray lithography. The optical system is composed of a single toroidal scanning mirror and a movable beryllium window whose motions are synchronized. The use of a toroidal scanning mirror is thought to cause excessive deformation of beam shape during scanning and to suppress the light-condensing capacity. This problem has been solved by placing the rotating center of the mirror near the light source point. Thus, intense illumination power can be obtained. A beam reflected by the toroidal mirror forms an arc-shaped section, which causes nonuniformity in the exposure intensity. A beryllium window foil with a specific curvature can compensate the nonuniformity. A series of analytical studies and computer simulations have proven the performance of the optical design.
We propose here a new method in X-ray nanolithography. Using this method, two-dimensional patterns with a linewidth of 25 nm can be formed. A conventional proximity X-ray lithography system is applicable to the method with a practical gap of approximately 8 µm. A 2X mask is used in the method instead of a 1X mask, changing the mask-wafer position (not gap) during exposure. The mask forms multispot images on the wafer; thus the traces of the relative change of the mask-wafer position during exposure ('dynamic exposure') produce a periodic pattern. The image formability and operational productivity for three kinds of 2X masks proposed for application to this method are described.
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