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Correcting device, exposure apparatus, device production method, and device produced by the device production methodCorrecting device, exposure apparatus, device production method, and device produced by the device production method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060077363, Correcting device, exposure apparatus, device production method, and device produced by the device production method. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] In general, the present invention relates to an exposure apparatus. More particularly, the present invention relates to an exposure apparatus used to expose a material to be processed, such as a monocrystalline substrate for a semiconductor wafer or a glass substrate for a liquid crystal display (LCD), a correcting device that corrects deformation of a mask or a reticle (hereafter, these terms are used interchangeably in the application) used in the exposure apparatus, a device production method using the material to be processed, and a device that is produced from the material to be processed. The present invention is, for example, suitable for application to an exposure apparatus which exposes a monocrystalline substrate for a semiconductor wafer by the step-and-scan projection method, the scan projection method, or the step-and-repeat projection method in a photolithography process. [0003] Here, the step-and-scan projection method is a projection exposure method in which a wafer is continuously scanned in synchronism with a scanning movement of a mask or a reticle in order to project a pattern of the mask onto the wafer by exposure, after which, after completion of an exposure of one shot, the wafer is moved stepwise in order to move the next shot to an exposure area. The scan projection method is a projection exposure method in which a portion of the mask pattern is projected onto the wafer by a projection optical system and the mask and a material to be processed are scanned in synchronism with each other with respect to the projection optical system in order to project the whole mask pattern onto the wafer by exposure. The step-and-repeat projection method is a projection exposure method in which the wafer is moved stepwise with each full exposure of a shot of the wafer in order to move the next shot to the exposure area. [0004] 2. Description of the Related Art [0005] In recent years, the demand for smaller and thinner electronic devices has caused an increasing demand for finer semiconductor devices installed in the electronic devices. For example, it is expected that design rules of a mask pattern will become increasingly smaller in the future as a result of an attempt to realize a line and space (L & S) of 130 nm in a mass production line. L & S refers to an image projected onto a wafer during exposure with the widths of the lines and spaces being equal, so that it is a measure of exposure resolution. In the exposure, resolution, overlay accuracy, and throughput are three important parameters. Resolution is defined as the smallest dimension that can be precisely transferred. Overlay accuracy is defined as the accuracy with which several patterns are overlaid on a material to be processed. Throughput is the number of materials that are processed per unit time. [0006] There are basically two types of exposure methods, a 1.times. magnification transfer method and a projection method. The 1.times. magnification transfer method includes a method in which a mask and a material to be processed are brought into contact with each other and a method in which they are separated slightly. However, in the former method, although a high resolution can be obtained, the mask gets damaged and the material to be processed gets scratched or defective due to dust or pieces of silicon being pressed into the mask. In the latter method, the problem that exists in the former method is initially solved, but, when the separation between the mask and the material to be processed becomes smaller than the maximum size of dust particles, damage to the mask similarly occurs. [0007] To overcome the problem that the mask and the material to be processed become damaged, a projection method in which the mask and the material to be processed are further separated has been proposed. Of the different types of projection methods, the projection method that uses a scanning projection exposure apparatus is in dominant use in recent years in order to improve resolution and to increase the size of an exposure area. In this projection method, the mask is exposed a portion at a time, and the mask and the wafer are caused to be in synchronism with each other. By scanning the wafer either continuously or intermittently, the entire mask pattern is projected onto the wafer by exposure. [0008] In general, a projection exposure apparatus comprises an illumination optical system that illuminates a mask and a projection optical system, disposed between the mask and a material to be processed, which projects a circuit pattern of the mask that has been illuminated onto the material to be processed. In the illumination optical system, in order to obtain a uniform illumination area, light beams from a light source are made to enter a light integrator comprising, for example, fly's eye lenses that are provided using a plurality of rod lenses. With a light-exiting surface of the light integrator being used as a secondary light source surface, these light beams that have entered the light integrator are used to subject a mask surface to Koehler illumination through a condenser lens. [0009] However, when the optical axis substantially coincides with the direction of gravitational force, the center portion of the mask is flexed by an amount on the order of a few microns in the direction of the gravitational force due to its own weight, resulting in a problem that overlay accuracy is reduced during the exposure. More specifically, the following problems arise: (1) Distortion of a projected image of the pattern changes as a result of distortion of the mask pattern, and (2) focal depth, which is the focal range that allows a certain image-formation performance to be maintained, is reduced by curvature of field. In particular, it is expected that due to the recent demand for finer patterns, even a slight variation in the pattern must be increasingly taken into account in the future. [0010] To overcome such problems, Japanese Patent Laid-Open No. 10-214780 proposes, in a first embodiment, to enclose a mask in order to apply static pressure to a hermetically sealed space through a pressure control device. However, when the mask is enclosed, heat produced by exposure causes the mask to be distorted, so that this method is not a preferable method. In addition, the same document proposes, in a second embodiment, to correct the distortion of the mask through a piezoelectric device disposed around the mask. However, the use of the piezoelectric device around the mask is not necessarily effective in removing flexure of the center portion of the mask caused by its own weight. [0011] Japanese Patent Laid-Open No. 6-176408 proposes to supply gas having a predetermined pressure to a mask from a direction opposite to the direction in which the mask flexes. However, it is difficult to uniformly apply pressure to the mask. In addition, it is difficult to dispose gas blowing means while maintaining an exposure optical system. SUMMARY OF THE INVENTION [0012] In general, it is an object of the present invention to provide a novel, useful correcting device, exposure apparatus, device production method, and device produced by the production method, which make it possible to overcome these conventional problems. [0013] More specifically, it is an object of the present invention to provide, for illustrative purposes, a correcting device that properly maintains the flatness of a mask, and an exposure apparatus and a device production method, which make it possible to increase overlay accuracy by making use of the correcting device. [0014] It is another object of the present invention to provide, as for different illustrative purposes, devices, such as a high-quality semiconductor, a liquid crystal device (LCD), a charge-coupled device (CCD), and a thin-film magnetic head, which are produced by the device production method. [0015] To overcome the above-described problems, according to a first aspect, the present invention provides a correcting device comprising a gas flow path including a first area and a second area, the first area being formed above a reticle having formed thereon a pattern that is projected onto a material to be processed in order to form an image of the pattern on the material to be processed, and the second area being connected to the first area, having a cross-sectional area that is different from that of the first area, and not being disposed in line with the reticle; and a blowing section that blows gas to the gas flow path. [0016] According to this correcting device, by blowing gas (e.g., air or nitrogen) to a gas flow path having two continuously formed areas, such as a first area and a second area, having different cross-sectional areas, a difference in pressure between the first area and the second area can be produced by making use of Bernoulli's theorem. By properly making use of the pressure difference, the correcting device can correct distortion caused by factors other than the self-weight of the reticle. In addition, the correcting device can restrict a rise in temperature of the reticle caused by exposure heat by cooling the reticle as a result of blowing air onto it. [0017] When a third area is provided upstream from the first area in terms of the gas that is blown, and when the cross-sectional area of the third area is greater than the cross-sectional area of the first area, it is possible to reduce the temperature of the gas in the first area, so that the rise in temperature of the reticle caused by the exposure heat can be more efficiently reduced. [0018] When the structure of the first aspect is used, the correcting device may further comprise a smoothing section, disposed between the first and second areas, for smoothing movement of the gas between the first and second areas. Accordingly, the smoothing section can prevent the gas from deviating from Bernoulli's theorem caused by the gas swirling between the first and second areas. The gas flow path may be provided opposite to the material to be processed with regard to the reticle. In general, since a pellicle film is provided at the side of the material to be processed, by providing the gas flow path opposite to the material to be processed with regard to the reticle, it is possible to prevent deformation of and damage to the pellicle film caused by air blowing across or onto the pellicle film. [0019] When the structure of the first aspect is used, the correcting device may further comprise a control section that controls the blowing section so that, when the density of the gas is .rho., the weight of the reticle is G, the area of projection of the reticle is A.sub.R, the cross-sectional area of the first area is A.sub.1, the pressure of the gas in the first area is P.sub.1, the velocity is V.sub.1, the cross-sectional area of the second area is A.sub.2, and the pressure of the gas in the second area is P.sub.2, the following formula is satisfied: P.sub.1-P.sub.2=0.5.rho.V.sub.1.sup.2{(A.sub.1/A.sub.2).sup.2-1}=-G/A.sub- .R. By virtue of this structure, the correcting device can correct the distortion caused by the self-weight of the reticle. P.sub.2 may be set at atmospheric pressure. When the second area is set at atmospheric pressure and the space around the reticle is open, as disclosed in the first embodiment illustrated in Japanese Patent Laid-Open No. 10-214780, the exposure heat is no longer confined in the area around the recticle, so that the temperature rise of the reticle can be restricted. [0020] According to a second aspect, the present invention provides a correcting device comprising a blowing section that blows gas onto a reticle having formed thereon a pattern to be projected onto a material to be processed in order to form an image of the pattern on the material to be processed; a detecting section that detects pressure at front and back surfaces of the reticle and produces a detection result; and a control section that controls the blowing section so that a difference between the pressures is maintained to be a predetermined value, after receiving the detection result provided by the detecting section. The correcting device can correct the distortion of the reticle because the pressure difference at the front and back surfaces of the reticle is controlled by the control section so that it becomes a predetermined value (for example, a value that cancels the deformation caused by the weight of the reticle due to gravitational force). [0021] According to a third aspect, the present invention provides a correcting device comprising a blowing section that blows gas onto a reticle having formed thereon a pattern to be projected onto a material to be processed in order to form an image of the pattern on the material to be projected; a detecting section that detects a flexure amount of the reticle and produces a detection result; and a control section that controls the blowing section so that the flexure amount is zero after receiving the detection result provided by the detecting section. The correcting device can correct the distortion of the reticle because feedback is controlled by the control section so that the flexure amount of the reticle is zero. [0022] The control sections of these correcting devices can, for example, control the gas speed and the temperature of the gas at the blowing section. 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