Patent Number: 053902289
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of stabilizing shapes of optical elements and an optical apparatus employing the same. More particularly, the present invention relates to a method of stabilizing shapes of optical elements which prevents shape changes caused by local temperature changes and which is intended for use with synchrotron radiation light or high-intensity light beams which are widely used for physics and chemistry research, analysis apparatuses, manufacturing apparatuses or the like, and to an optical apparatus employing the same. 2. Description of the Related Art In recent years, a light source which emits synchrotron radiation (SR) light or high-intensity light beams, such as excimer laser beams, has been developed. Optical apparatuses using such a light source for physics and chemistry research, analysis apparatuses, manufacturing apparatuses or the like have lately attracted attention, and a lot of research and development of these apparatuses has been performed. Generally, optical apparatuses require various types of optical elements for the purposes of reflection, transmission, light condensation, diffraction, spectrophotometry, polarization, image formation or the like. Since the intensity of light beams used is high in these optical apparatuses, which use, in particular, a high-intensity light source, phenomena such as deformation, performance deterioration, irradiation damage, or destruction of optical elements occur. An example of such high intensity light beams concerns the SR light technology field, where the radiation power from a light source has recently reached the order of kilowatts as the result of advancements made in the technology regarding what is commonly called insertion type light sources, such as multi-pole wigglers or undulators. Radiation ranging from X-rays to electromagnetic waves in vacuum ultraviolet rays are often used regarding radiation lengths from a light source. To prevent attenuation in the atmosphere, in most cases, the optical elements are installed in a vacuum vessel or a vacuum beam line. As a result, heat radiation by conduction or convection to the atmosphere does not occur in optical elements placed in a vacuum. Thus, there is a tendency for the temperature of optical elements to increase much more than when they are placed in the atmosphere. To be specific, in a semiconductor exposure apparatus which uses synchrotron radiation light or high-intensity illumination light from an excimer laser or the like, heat strain caused by temperature changes or temperature distribution changes of mirrors or lenses which reflect, converge, and enlarge illumination light, or caused by reticles or masks, becomes a major obstacle to the improvement of accuracy of the semiconductor exposure apparatus. In particular, when electromagnetic waves, such as synchrotron radiation light or vacuum ultraviolet rays, are used, optical systems, such as mirrors or lenses, and masks are generally placed in a vacuum chamber or a pressure reduction chamber in order to prevent the attenuation of the energy of illumination light. If members to be illuminated, such as mirrors, lens, or masks, are heated by illumination light, the temperature increases considerably because there is hardly any conduction by atmosphere gas or heat radiation by convection. Heat strain caused by temperature changes or changes in temperature distribution considerably changes the distribution of intensity of illumination light, causing exposure irregularities. For this reason, various methods for cooling the above-mentioned members to be illuminated by using a water cooling jacket or the like have been developed. An example thereof is described in "Rev. Sci. Instrum. 60, 1493 (1989), T. Oversluizen, et al.". However, in an optical apparatus using a light source which emits high-intensity light beams, even if optical elements are cooled, the temperature of the surfaces of the optical elements continues to vary usually by several to several tens of degrees. As a result, the shapes of the optical elements slightly change their forms, and there are some cases in which the optical performance of the optical apparatuses deteriorates. For example, in a projection exposure apparatus for transferring fine patterns for use in the manufacturing of semiconductor devices, it is required that temperature variations of optical elements, such as mirrors, be controlled to approximately 1/100.degree. C. However, in the prior art, the cooling of optical elements alone is not sufficient to control the temperature variations of the optical elements to approximately 1/100.degree. C. SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus which is capable of effectively correcting temperature variations of optical elements when a light source which emits high-intensity light beams is used, preventing the deformation of optical elements due to heat strain, and easily preventing the deterioration of optical performance. Another object of the present invention is to provide a method of manufacturing highly integrated semiconductor devices. In accordance with one aspect of the invention, a method of stabilizing shapes of objects comprises the steps of measuring a temperature distribution of an object being irradiated with radiation energy, and causing the temperature of a part of the object to be changed on the basis of the measurement to control the change of the shape of the object. In accordance with another aspect of the invention, a method of stabilizing shapes of objects comprises the steps of determining a temperature distribution of a mask in a thermally stable state, and controlling the temperature distribution of the mask being irradiated with radiation energy to be the same as the temperature distribution in the thermally stable state. In accordance with still another aspect of the invention, an optical apparatus comprises an optical element, means for irradiating the optical element with radiation energy, measuring means for measuring the temperature distribution of the irradiated optical element, and temperature control means for changing the temperature of a part of the optical element based on a measurement by the measuring means. In accordance with another aspect of the invention, an exposure apparatus comprises transfer means for exposing and transferring an exposure pattern to an object to be exposed by irradiating exposure energy onto a mask having an exposure pattern formed thereon, measuring means for measuring the temperature distribution of the mask, and temperature control means for changing the temperature of part of the mask on the basis of the measurement by the measuring means. In accordance with yet another aspect of the invention, a method of manufacturing semiconductor devices and semiconductor devices made by the steps of preparing a reflection type mask having a circuit pattern formed thereon, measuring the temperature distribution of the mask, changing the temperature to obtain a substantially uniform temperature distribution of the mask, and exposing and transferring a circuit pattern of the mask onto a wafer by irradiating the mask with exposure energy. In accordance with another aspect of the invention, a method of manufacturing semiconductor devices and semiconductor devices made by the steps of preparing a reflection type mask having a circuit pattern formed thereon, determining a temperature distribution of the mask in a thermally stable state when the mask is being irradiated before the mask is irradiated with exposure energy, and exposing and transferring a circuit pattern of the mask onto a wafer by irradiating the mask with exposure energy. Objectives and advantages in addition to those discussed above shall be apparent to those skilled in the art from the description of the preferred embodiments of the invention which follow. In the description, reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention. Such examples, however, are not exhaustive of the various embodiments of the invention, and therefore reference is made to the appended claims for determining the scope of the invention.