Abstract:
An apparatus for adjusting temperature of an object includes a heat radiation member, a deflection member to deflect heat radiation from the heat radiation member toward a region of the object, and an adjusting system to adjust temperature of the heat radiation member.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to a technique for adjusting temperature of an object, more particularly to a cooling apparatus for cooling an object such as an optical element in an exposure apparatus that exposes an object, such as a semiconductor wafer and a glass plate for a liquid crystal display (“LCD”), to light. The present invention is suitable, for example, for a cooling apparatus for cooling an object in an exposure apparatus that uses as exposure light ultraviolet (“UV”) light and extreme ultraviolet (“EUV”) light. 
   Reduction projection exposure apparatus have been conventionally employed which use a projection optical system to project a circuit pattern formed on a mask or a reticle onto a wafer, etc. to transfer the circuit pattern, in manufacturing such fine semiconductor devices as semiconductor memories and logic circuits in photolithography technology. 
   The minimum critical dimension (“CD”) to be transferred by the projection exposure apparatus or resolution is proportionate to a wavelength of light used for exposure, and inversely proportionate to the numerical aperture (“NA”) of the projection optical system. The shorter the wavelength is, the better the resolution is. Recent demands for finer semiconductor devices have promoted a shorter wavelength of ultraviolet light from an ultra-high pressure mercury lamp (i-line with a wavelength of approximately 365 nm) to KrF excimer laser (with a wavelength of approximately 248 nm) and ArF excimer laser (with a wavelength of approximately 193 nm). 
   However, the lithography using the ultraviolet light has the limit to satisfy the rapidly progressing fine processing of semiconductor devices, and an EUV exposure apparatus using EUV light with a wavelength of 10 to 15 nm shorter than that of the ultraviolet has been developed for efficient transfers of very fine circuit patterns. 
   In the wavelength range of the EUV light, an attenuation of energy by a gas is very large. Moreover, a carbon compound adheres to the optical element by a photochemical reaction of oxygen and impurities in the gas. Therefore, the exposure is executed in a vacuum environment. 
   On the other hand, since the EUV exposure apparatus is used to expose circuit patterns of 0.1 μm or smaller and required to meet very high critical dimension accuracy, only a deformation of about 0.1 nm or smaller is permissible on the optical element (in other words, the mirror surface). Deforms a shape of the optical element causes a deterioration of an optical performance, in particular, imaging performance. A mirror used for the EUV exposure apparatus does not reflect all the exposure light, but absorbs the exposure light of 30% or greater. Then, a temperature of the mirror rises gradually, and the surface shape of the mirror deforms. Therefore, it is necessary to cool the optical element. In other words, it is necessary to adjust the temperature of the optical element. However, because the EUV exposure apparatus exposes in the vacuum environment, the temperature adjustment is very difficult compared with the conventional. For example, the surface of the optical element can not be cooled by a convection in the vacuum environment. The temperature adjustment by supplying a cooling medium to a channel formed in the optical element generates a vibration, and a transfer position accuracy is deteriorated. 
   Then, it is thought to use a radiation (heat radiation) as cooling method of the optical element in the vacuum environment, in a non-contact manner. Concretely, a radiation board provides at a position opposite to a surface except an irradiation area irradiated to the exposure light on the optical element, and the heat is absorbed (radiation cooling) from the optical element through the radiation board. See, for example, Japanese Patent Applications, Publication Nos. 2004-80025 and 2004-29314. 
   When the radiation cooling is executed through the radiation board provided at the position opposite to the surface except the irradiation area on the optical element, the heat applied by the exposure light to the irradiation area moves to the surface of the optical element opposed to the radiation board, and is recovered. Therefore, a flow of the heat is generated in the optical element, and a temperature distribution is formed. The temperature distribution causes a heat distortion of the optical element and the deterioration of the optical performance. Especially, an exposure energy at unit time is enlarged to improve a throughput of the exposure apparatus, the temperature distribution is enlarged, and the optical performance is remarkably deteriorated. 
   If the radiation board provides at a position opposite to the irradiation area irradiated to the exposure light on the optical element, the irradiation area can be directly cooled, a heat quantity moved in the optical element decreases, and the temperature distribution generated in the optical element can be decreased. The irradiation area is located on an optical path of the exposure light, and the radiation board can not provide at the position opposite to the irradiation area. 
   BRIEF SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to a technique that adjusts a temperature of an object while suppressing nonuniformity of temperature distribution in the object. 
   An apparatus of one aspect according to the present invention for adjusting temperature of an object, said apparatus includes a heat radiation member, a deflection member to deflect heat radiation from said heat radiation member toward a region of the object, and an adjustment system to adjust temperature of said heat radiation member. 
   A method of manufacturing a device according to another aspect of the present invention includes the steps of exposing a substrate to a pattern of radiant energy using the above apparatus, developing the exposure substrate, and processing the developed substrate to manufacture the device. 
   Other objects and further features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic sectional view of a cooling apparatus of one aspect according to the present invention. 
       FIG. 2  is a partially enlarged sectional view of the cooling apparatus (a concave mirror and radiation cooling source) shown in  FIG. 1 . 
       FIG. 3  is a view for explaining a radiation energy radiated from arbitrary point in an irradiation area of an optical element shown in  FIG. 1 . 
       FIG. 4  is a schematic sectional view of one example of arrangement when one optical element is cooled by using plural cooling apparatus. 
       FIG. 5  is a schematic sectional view of a cooling apparatus of one aspect according to the present invention. 
       FIG. 6  is a schematic sectional view of a cooling apparatus as a variation of the cooling apparatus shown in  FIG. 1 . 
       FIG. 7  is a schematic sectional view of an exposure apparatus of one aspect according to the present invention. 
       FIG. 8  is a flowchart for explaining how to fabricate devices (such as semiconductor chips such as ICs, LCDs, CCDs, and the like). 
       FIG. 9  is a detailed flowchart of a wafer process in step  4  in  FIG. 8 . 
       FIG. 10  is a view for explaining an arrangement of a cooling apparatus to efficiently cool an optical element. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A description will now to be given of a cooling apparatus and exposure apparatus of one aspect according to the present invention. In each figure, the same reference numeral denotes the same element. Therefore, a duplicate description will be omitted. Here,  FIG. 1  is a schematic sectional view of a cooling apparatus  1 . 
   The cooling apparatus  1  is to cool an optical element OE in a vacuum or reduced pressure environment, in a non-contact manner. The optical element OE accommodates, for example, a chamber with the vacuum or reduced pressure environment. A vacuum pump (not shown) maintains the chamber to be high vacuum, for example, about 1×10 −6  [Pa] by so that a reaction between the residual gas component in the exposure optical path, such as polymer organic gas, and a light L may not contaminate the optical element OE&#39;s surface and lower its transmittance and reflectance. 
   The optical element OE includes an irradiation area IA irradiated to the light L, and images the light L using reflection, refraction, diffraction, etc. The optical element OE includes, for example, a mirror, a lens, a parallel plate glass, a prism, and a Fresnel zone plate, a kinoform, a binary optics, a hologram, and other diffraction optical elements. The instant embodiment describes the optical element OE as a mirror. 
   The cooling apparatus includes, as shown in  FIG. 1 , a concave mirror  10 , a radiation cooling source (radiation board or radiation member)  20 , a cooling mechanism  30 , and a temperature adjustment mechanism  40 . 
   The concave mirror  10  condenses a radiation energy (a kind of electromagnetic wave) from the irradiation area IA of the optical element OE. The radiation is a phenomenon that a part of an energy of material is discharged in the electromagnetic wave form or absorbs the electromagnetic wave and is excited. The radiation energy E discharged from the material of a black body with temperature of T is shown by E [W/m 2 ]=σT 4 , where σ is a Stefan-Boltzmann factor. 
   The concave mirror  10  has a surface shape of a paraboloid (the radiation cooling preferably provides at a focus position or the neighborhood, in other words, a position that a distance from the focus is 10% or less of focal length, for the paraboloid) or a spheroid (the radiation cooling source preferably provides at one focus position, and the irradiation area of the optical element preferably provides at the other focus position). The instant embodiment uses a paraboloid mirror as the concave mirror  10 . The paraboloid mirror is arranged so that a center IAC of the irradiation area IA of the optical element OE may exist on an extension line RL of the rotation axis. In other words, the concave mirror  10  is arranged as the rotation axis intersects with the center IAC of the irradiation area IA. However, the concave mirror  10  does not intercept the light L, in other words, is arranged at positions except the optical path of light L. 
   The concave mirror  10  is arranged on an opposite side of the irradiation area IA of the optical element OE for the radiation cooling source  20  described later as shown in  FIG. 1 , and has a visual angle θ of 160° or more to the concave mirror  10  from the radiation cooling source  20 . Here, the visual angle θ to the concave mirror  10  from the radiation cooling source  20  is defined. The center of the radiation cooling source  20  (a barycenter in the radiation cooling source is desirable) is considered to be a center of the angle (vertex). It thinks about a section of the concave mirror  10  in a plane surface including a straight line that connects the center IAC of the irradiation area IA of the optical element OE with the center of the radiation cooling source  20 . In the section, the center of the radiation cooling source  20  is considered to be the vertex of the angle, and the angle formed by one opening edge of the concave mirror  10 , the center of the radiation cooling source  20 , and the other opening edge of the concave mirror  10  is defined as the visual angle θ. A surface on the optical element OE side of the radiation cooling source  20  is given to processing to lower the radiation rate. On the other hands, a surface on the concave mirror  10  has higher radiation rate. Therefore, the concave mirror  10  side of the radiation cooling source  10  should cover with the concave mirror to prevent a thermal influence to a periphery environment. The higher radiation rate surface of the radiation cooling source  20  consists of a glass or ceramic. These insulators discharge a lot of radiation energy in a normal direction of the surface. On the other hand, considerably little radiation energy is discharged in a direction along the surface compared with the normal direction. Thereby, if the visual angle θ to the concave mirror  10  from the radiation cooling source  20  is 160° or more, the thermal influence that the surface on the concave mirror side of the radiation cooling source  20  exerts to the periphery environment can be decreased. 
   The concave mirror  10  has a surface  10   a  processed by mirror processing, and a mirror reflectivity for the radiation energy from the irradiation area IA of the optical element OE of 0.7 or more. A lot of radiation energy from the irradiation IA of the optical element OE can reach the radiation cooling source  20  by having higher mirror reflectivity. Therefore, a capacity to cool the irradiation area IA of the optical element OE increases. On the other hand, when an influence of a diffuse reflection of the concave mirror is large, the radiation energy from the irradiation area IA of the optical element OE diffuses by the concave mirror. Then, a ratio of the radiation energy that reaches the radiation cooling source becomes small, and a cooling amount becomes small. 
   The surface  10   a  of the concave mirror  10  is composed of a material with a low radiation rate such as gold, silver, and aluminum. The concave mirror  10  has an installation part  12  to install the cooling mechanism  30  (in the instant embodiment, a cryo-pumps head) described later in the vertex of the paraboloid. The installation part  12  B is composed as a penetration hole that cuts a part of the vertex neighborhood of the concave mirror  10 . 
   The radiation cooling source  20  is arranged at the focus of the concave mirror  10 , and cools the irradiation area IA of the optical element OE by the radiation. When there are a first member and a second member, the radiation energy (radiation heat) is transmitted to the first member from the second member, and he radiation energy is transmitted to the second member from the first member. As a result of the transfer, between such two members of the radiation energy, the radiation heat transfer is to be cooled one side while other member is heated as for the difference of two radiation energy (radiation heat transfer amount). In the instant embodiment, it is expressed that one side gives the other side the radiation energy (even heating and cooling) to easily express heating and cooling by the transfer of the radiation energy. The radiation cooling source  20  does not intercept the light L, in other words, is arranged at positions except the optical path of light L similar to the concave mirror  10 . 
   A surface of the radiation cooling source  20  is composed of a material with the radiation rate of 0.6 or more (for example, ceramic (alumina and SiC, etc.) and glass, etc., more preferably a material with the radiation rate of 0.7 or more). A surface  20   a  of the radiation cooling source  20  opposed to the optical element OE is composed of a material with a low radiation rate (the radiation rate is 0.2 or less, more preferably 0.15 or less), and has a board or film a metal (such as gold, silver, aluminum) on the surface. Moreover, a shielding board  22  composed of the material with a low radiation rate may be arranged at the surface  20   a  of the radiation cooling source  20  as shown in  FIG. 2 . The shielding board  22  uses gold, silver, aluminum etc. Here,  FIG. 2  is a partially enlarged sectional view of the cooling apparatus  10  (the concave mirror  10  and the radiation cooling source  20 ). 
   The cooling mechanism  30  cools the radiation cooling source  20 , and is a cryo-pumps in the instant embodiment. The cooling mechanism  30  cools the radiation cooling source  20  so that the temperature of the radiation cooling source  20  may become −100° C. or less. The cooling mechanism  30  may cool the radiation cooling source  20  by supplying the cooling medium such as a liquid nitrogen and liquid helium in the radiation cooling source  20 . However, in this case, it is necessary to give a heat insulation processing to a pipe that introduces the cooling medium to the radiation cooling source  20  or adjust the temperature to be the same temperature as an environmental temperature. 
   The temperature adjustment mechanism  40  is arranged at a back surface  10   b  of the concave mirror  10  as shown in  FIG. 2 , and adjusts the temperature of the concave mirror  10 . The temperature adjustment mechanism  40  prevents, in the instant embodiment, a temperature decrease of that originates in influence of radiation cooling source  20  by supplying a medium such as water, air, and nitrogen, and maintains the temperature of the concave mirror  10  to the same temperature as the environmental temperature. 
   Here, a description will be given of a flow of the radiation energy from the irradiation area IA of the optical element OE and an arrangement relationship between the concave mirror  10  and the radiation cooling source  20 . A ray from the center position of the radiation cooling source  20  is assumed, and a ray that reaches the concave mirror  10  is considered among these rays. 
   The majority of ray (electromagnetic wave) that reaches the concave mirror  10  from the radiation cooling source  20  mirror-reflects at the concave mirror  10 . In the mirror reflection, the normal at the reflection position becomes a bisector of the incident ray and reflected ray. Therefore, when the concave mirror  10  of the instant embodiment is used, the ray reflected from the concave mirror  10  is irradiated on the irradiation area IA of the optical element OE. As a result, the radiation cooling source  20  heat exchanges only the irradiation area IA through the concave mirror  10 . In other words, to cool the irradiation area IA of the optical element OE efficiently, it composes as shown in  FIG. 10 . A straight line that connects an arbitrary point on the irradiation area IA of the optical element OE with a predetermined point on the concave mirror  10  corresponding to the arbitrary point is considered. Moreover, a straight line that connects the predetermined point and the radiation cooling source  20  is considered. A bisector of an angle formed by two straight lines may be substantially corresponding to a normal of the concave mirror  10  in the predetermined point on the concave mirror  10 . Moreover, it is possible to reword as follows. A plane surface formed by the arbitrary point on the irradiation area IA of the optical element OE, the predetermined point on the concave mirror  10  corresponding to the arbitrary point, and the radiation cooling source  20  (a predetermined in the radiation cooling source  20 ) is considered. Moreover, in the plane surface, a straight line that connects the arbitrary point on the irradiation area IA of the optical element OE with the predetermined point on the reflection surface of the concave mirror  10  is considered. The concave mirror is composed so that an angle formed by the straight line and a normal in the predetermined point to the reflection surface of the concave mirror  10  and an angle formed by the predetermined point and the radiation cooling source  20  may substantially become the same. Here,  FIG. 10  is a view for explaining an arrangement of the cooling apparatus  1  to efficiently cool the optical element OE. 
   However, in the above description, the radiation cooling source  20  is considered to be a point, and when a surface area of the radiation cooling source  20  is 0, the radiation transfer heat amount becomes 0. Actually, as shown in  FIG. 3 , in the arbitrary point on the irradiation area IA of the optical element OE, the radiation energy radiated in a certain solid angle φ reflects at the concave mirror  10 , and reaches the radiation cooling source  20 . If the solid angle φ is considered as a form factor, the cooling capacity improves as the radiation cooling source  20  enlarges. However, even if the radiation cooling source  20  is arranged at the focus of the concave mirror  10 , the surface of the radiation cooling source  20  exists at a position apart from the focus of the concave mirror  10 . Therefore, in an optical expression, a cooled area becomes an unclear state, in other words, the cooled area is enlarged more than an ideality cooling state (the radiation cooling source  20  is considered to be the point). Thereby, the cooling capacity of the cooling apparatus  1  and a degree limited to the cooled area are relation ship of trade-off. Here,  FIG. 3  is a view for explaining the radiation energy radiated from arbitrary point in the irradiation area IA of the optical element OE. 
   If a size of the radiation cooling source  20  is 5% to 20% for a size of the opening part  14  of the concave mirror  10 , the cooled area can be limited, and the cooling capacity to achieve the effect of cooling the irradiation area IA of the optical element OE can be obtained. However, even if the size of the radiation cooling source  20  is 20% or more for the size of the opening part  14  of the concave mirror  10 , the cooled area can be limited to some degree. 
   Hereinbefore, the radiation energy reflected from the concave mirror  10  was considered. Hereafter, a radiation energy that directly reaches the radiation cooling source  20  among the radiation energy radiated from the plane including the irradiation area IA of the optical element OE is considered. An area NCA of the radiation cooling source  20  not covered with the concave mirror  10 , in other words, a plane  20   a  opposed to the irradiation area IA of the optical element OE can be seen from most positions of the plane including the irradiation area IA of the optical element OE. Therefore, as the above-mentioned, the area NCA of the radiation cooling source  20  not covered with the concave mirror  10  is composed of the material with a low radiation rate, or is covered with a cover with a low radiation rate. Therefore, the radiation energy that directly reaches the radiation cooling source  20  (in other words, a heat transfer amount to the radiation cooling source  20 ) among the radiation energy radiated from the plane including the irradiation area IA of the optical element OE decreases. Thereby, the cooling amounts in the area except the irradiation area IA can be decreased. 
   Thus, the cooling apparatus  1  can directly cool the irradiation area IA irradiated to the light L, in the non-contact manner. Moreover, the cooling apparatus  1  can improve the temperature distribution of the optical element OE that causes the deterioration of the imaging performance. In other words, the cooling apparatus  1  prevents a temperature gradient being formed on the optical element OE. Therefore, the optical element OE cooled by the cooling apparatus  1  can provide a superior optical performance. 
   Thus, the cooling capacity of the cooling apparatus  1  is limited. Then, one (irradiation area IA of) optical element OE may be cooled by using plural cooling apparatus  1 . Therefore, the cooling capacity can be increased. A large cooling amount can be obtained by using plural cooling apparatus  1 , and the temperature gradient on the optical element OE can be decreased. Here,  FIG. 4  is a schematic sectional view of one example of arrangement when one optical element OE is cooled by using plural cooling apparatus  1 . 
   The majority of a heat load given to the optical element OE is caused by the absorption of the light L. For example, in the present EUV exposure apparatus, the reflectivity of a reflection film to reflect the EUV light is 70% or less, and the mirror (optical element OE) absorbs about 30% of the irradiated EUV light. Before the EUV exposure apparatus operates (before the exposure), the EUV light is not irradiated to the mirror, and the heat load given to the mirror is 0. When the exposure is start, the EUV is irradiated to the mirror, and the heat load is given to the mirror. When the exposure of one wafer ends, the irradiation of the EUV light stops to exchange wafers. When the exchange of wafers ends, the EUV light is irradiated again, and the heat load is given to the mirror. 
   Therefore, the cooling apparatus should have an enough response for the heat load given to the mirror and execute the radiation cooling. This is because a temperature change of the mirror increases if the mirror is cooled when the light is not irradiated to the mirror (in other words, the heat load is not given to the mirror). However, the cooling apparatus  1  lowers the radiation cooling source  20  to a very low temperature, and can not make the radiation cooling follow the heat load given to the mirror (for example, cannot switch turning on and turning off of the radiation cooling at high speed). 
   Then, a shutter  50  that intercepts between the irradiation area IA of the optical element OE and the radiation cooling source  20  is arranged as shown in  FIG. 5 . The opening and shutting of the shutter  50  switches the execution of the radiation cooling and non-execution of the radiation cooling to the irradiation area IA. The shutter  50  has a size that can be covered at least the radiation cooling source  20 , and preferably has a size that can be covered the opening part  14  of the concave mirror  10 . Here,  FIG. 5  is a schematic sectional view of the cooling apparatus  1 . 
   The shutter  50  includes a driving control mechanism  60  that controls the opening and shutting (drive) of the shutter  50 . The driving control mechanism  60  opens the shutter  50  while the light L is irradiated to the optical element OE, and shuts the shutter  50  while the light L is not irradiated to the optical element OE. In other words, the driving control mechanism  60  controls the opening and shutting of the shutter  50  according to the irradiation and non-irradiation of the light L to the optical element OE. The driving control mechanism  60  is accessed to a computer that has an exposure data (an information of a timing that the irradiation and non-irradiation of the exposure light are switched) or has the exposure data. The driving control mechanism  60  controls the timing of the opening and shutting of the shutter  50  based on the exposure data. 
   The cooling apparatus  1  can make responded the radiation cooling follow according to the irradiation state of the light L to the optical element OE by the shutter  50  and driving control mechanism  60 . The cooling apparatus  1  switches, for example, on and off of the radiation cooling. Therefore, the temperature change of the optical element OE can be suppressed. 
   Referring to  FIG. 6 , a description will be given of a cooling apparatus  1 A as a variation of the cooling apparatus  1 . The cooling apparatus  1 A has a structure combined the cooling apparatus  1  and a cooling apparatus that is proposed by the instant assignee in Japanese Patent Application, Publication No. 2004-80025. Here,  FIG. 6  is a schematic sectional view of the cooling apparatus  1 A as a variation of the cooling apparatus  1 . 
   The cooling apparatus  1 A includes, as shown in  FIG. 6 , the radiation cooling source  20 , the cooling mechanism  30 , the temperature adjustment mechanism  40 , a radiation cooling mechanism  100 . 
   The radiation cooling mechanism  100  is provided at a position that dose not intercept the light L (in other words, except the optical path of light L) and apart from the optical element OE, and absorbs the heat from the optical element OE through the radiation. The radiation cooling mechanism  100  includes a radiation plate  110 , a Peltier element  120 , a heat release block  130 , a detector  140 , a controller  150 . 
   The radiation plate  110  is fixed apart by a predetermined interval from the optical element OE through a support member (not shown). The radiation plate  110  is cooled by a Peltier effect of the Peltier element  120  described later, and becoming at a low temperature to the optical element OE. In other words, the radiation plate  110  absorbs the heat from the optical element OE due to the temperature difference from the optical element OE. 
   The Peltier element  120  arranges, for example, a p-type semiconductor and a n-type semiconductor thermally parallel to each other. The Peltier element  120  is controlled by the controller  150  described later, and coupled with the radiation plate  110  to cool the radiation plate  110  using the Peltier effect. Concretely, a joint of a heat absorption surface  122  of the Peltier element  120  with the radiation plate  110  would absorb the heat from the radiation plate  110  and cool the radiation plate  110 . The heat value which the Peltier element  120  may absorb is adjustable by applied voltage. The heat release block  130  is coupled with the heat radiation surface  124  of the Peltier element  120 . 
   The heat release block  130  includes a channel (not shown) for the cooling medium to flow through. The channel is formed over the entire surface in the heat release block  130 , and enables the cooling medium to flow through the entire surface in the heat release  130 . The heat release block  130  collects the heat from the optical element OE absorbed via the radiation plate  110 , which is cooled by the cooling medium and exhausted from the heat radiation surface  124  of the Peltier element  120 . 
   The detector  140  is attached to the optical element OE outside the irradiation area IA, and detects the temperature of the optical element OE. The detector  140  includes a temperature sensor, such as a thermocouple, a resistor temperature sensor, and an infrared temperature sensor, and sends the detected temperature of the optical element OE to the controller  150 . 
   The controller  150  controls the radiation cooling mechanism  100  so that the temperature of the optical element OE detected by the detector  140  may have the constant value. More specifically, the controller  150  controls the temperature of the radiation plate  110  by changing the voltage applied to the Peltier element  120 . 
   The cooling apparatus  1  can make responded the radiation cooling follow according to the heat load given to the optical element OE by the shutter  50  and driving control mechanism  60 . However, the cooling apparatus  1  can not control the temperature of the optical element OE for small disturbance. Then, the cooling apparatus  1 A can decreases the temperature gradient of the entire optical element OE and maintains the temperature of the optical element OE to constant by applying the radiation cooling mechanism  100 . 
   Referring now to  FIG. 7 , a description will be given of an exemplary inventive exposure apparatus  500  that applies the cooling apparatus  1  or  1 A of the present invention. Here,  FIG. 7  is a schematic sectional view of the exposure apparatus  500  of the present invention. 
   The exposure apparatus  500  is a projection exposure apparatus that uses, as illumination light for exposure, EUV light EL (with a wavelength of, e.g., 13.4 nm). The exposure apparatus  500  exposes a circuit pattern formed on a mask  520  onto an object  540 . This exposure apparatus  500  is suitable for a lithography process less than submicron or quarter micron, and the present embodiment uses the step-and-scan exposure apparatus (also referred to as a “scanner”) as an example. The “step-and-scan manner”, as used herein, is an exposure method that exposes a mask pattern onto a wafer by continuously scanning the wafer relative to the mask, and by moving, after a shot of exposure, the wafer stepwise to the next exposure area to be shot. The “step-and-repeat manner” is another mode of exposure method that moves a wafer stepwise to an exposure area for the next shot every shot of cell projection onto the wafer. 
   Referring to  FIG. 7 , the exposure apparatus  500  includes an illumination apparatus  510 , a mask stage  525  that mounts the mask  520 , a projection optical system  530 , and a wafer stage  545  that mounts the object  540 . 
   A vacuum chamber VC is installed at least an optical path through which EUV light EL passes to maintain the vacuum environment as shown in  FIG. 7 . This is because the transmittance of the EUV light EL to the atmosphere is low, and the EUV light EL generates a contaminant through a reaction with residual gas, such as polymer organic gas. 
   The illumination apparatus  510  uses arc-shaped EUV light, for example, with a wavelength of 13.4 corresponding to an arc-shaped field of the projection optical system  530  to illuminate the mask  520 , and includes an EUV light source  512  and illumination optical system  514 . 
   The EUV light source  512  employs, for example, a laser plasma light source. It generates high temperature plasma by irradiating a pulsed laser beam with high intensity onto a target material in a vacuum chamber, and uses the EUV light, for example, with a wavelength of about 13 nm, which has been emitted from the plasma. The target material may use a metallic thin film, an inert gas, a liquid-drop, etc., and the target supply unit may use a gas jet and so on. The pulse laser is usually driven with a higher repetitive frequency, such as several kHz, for increased average intensity of radiated EUV light. 
   The illumination optical system  514  includes a condenser mirror  514   a , and an optical integrator  514   b . The condenser mirror  514   a  serves to collect the EUV light that is isotropically irradiated from the laser plasma. The optical integrator  514   b  serves to uniformly illuminate the mask  520  with a predetermined NA. The illumination optical system  514  further may include an aperture to limit the illumination area to an arc shape at a position conjugate with the mask  520 . An optical element in the illumination optical system  514  such as the condenser mirror  514   a  and optical integrator  514   b  may apply any one of the inventive cooling apparatuses  1  and  1 A. Therefore, the temperature distribution on the optical element improves, and the superior imaging performance can be provided. 
   The mask  520  is a reflection mask that forms a circuit pattern or image to be transferred, and supported and driven by the mask stage  525 . The diffracted light from the mask  520  is reflected by the projection optical system  530  and projected onto the object  540 . The mask  520  and the object  540  are arranged optically conjugate with each other. The exposure apparatus  500  is a step-and-scan exposure apparatus, and projects a reduced size of the pattern on the mask  520  on the object  540  by scanning the mask  520  and the object  540 . 
   The mask stage  525  supports the mask  520  and is connected to a moving mechanism (not shown). The mask stage  525  may use any structure known in the art. A moving mechanism (not shown) may include a linear motor etc., and drives the mask stage  525  at least in a direction X and moves the mask  520 . The exposure apparatus  500  assigns the direction X to scan the mask  520  or the object  540 , a direction Y perpendicular to the direction X, and a direction Z perpendicular to the mask  520  or the object  540 . 
   The projection optical system  530  uses plural multilayer mirrors  530   a  to project a reduced size of a pattern formed on the mask  520  onto the object  540 . The number of mirrors  530   a  is about four to six. For wide exposure area with the small number of mirrors, the mask  520  and object  540  are simultaneously scanned to transfer a wide area that is an arc-shaped area or ring field apart from the optical axis by a predetermined distance. The projection optical system  530  has a NA of about 0.2 to 0.3. An optical element in the projection optical system  530  such as the mirror  530   a  may apply any one of the inventive cooling apparatuses  1  and  1 A. Therefore, the temperature distribution on the optical element improves, and the superior imaging performance can be provided. 
   The instant embodiment uses a semiconductor wafer as the object to be exposed  540 , but it may include a spherical semiconductor and liquid crystal plate and a wide range of other objects to be exposed. Photoresist is applied onto the object  540 . 
   The object to be exposed  540  is held onto the wafer stage  545  by a wafer chuck. The wafer stage  545  moves the object  540 , for example, using a linear stage in XYZ directions. The mask  520  and the object  540  are synchronously scanned. The positions of the mask stage  525  and wafer stage  545  are monitored, for example, by a laser interferometer, and driven at a constant speed ratio. 
   In exposure, the EUV light EL emitted from the illumination apparatus  510  illuminates the mask  520 , and images a pattern formed on the mask  520  onto the object  540  surface. The instant embodiment uses an arc or ring shaped image plane, scans the mask  520  and object  540  at a speed ratio corresponding to a reduction ratio to transfer the entire pattern surface of the mask  520 . 
   As the optical performance is sensitive to a surface shape of the optical element in the projection optical system in the exposure apparatus, the inventive cooling apparatus  1  or  1 A preferably is used for an optical element in the projection optical system. In particular, the inventive cooling apparatus  1  or  1 A preferably uses for an optical element near the mask that receives much light intensity. Of course, it may be used for the illumination optical system. In particular, the optical element closest to a light source receives a large amount of light among the optical elements, and generates the large absorbed heat value inevitably. Then, the temperature gradient formed by the absorbed heat increases. The inventive cooling apparatus decreases the temperature rise by absorbing a large amount of the light and the temperature gradient formed on the optical element, and can decrease the heat distortion of the optical element. 
   Referring to  FIGS. 8 and 9 , a description will now be given of an embodiment of a device fabricating method using the above exposure apparatus  500 .  FIG. 8  is a flowchart for explaining a fabrication of devices (i.e., semiconductor chips such as IC and LSI, LCDs, CCDs, etc.). Here, a description will be given of a fabrication of a semiconductor chip as an example. Step  1  (circuit design) designs a semiconductor device circuit. Step  2  (mask fabrication) forms a mask having a designed circuit pattern. Step  3  (wafer preparation) manufactures a wafer using materials such as silicon. Step  4  (wafer process), which is referred to as a pretreatment, forms actual circuitry on the wafer through photolithography using the mask and wafer. Step  5  (assembly), which is also referred to as a posttreatment, forms into a semiconductor chip the wafer formed in Step  4  and includes an assembly step (e.g., dicing, bonding), a packaging step (chip sealing), and the like. Step  6  (inspection) performs various tests for the semiconductor device made in Step  5 , such as a validity test and a durability test. Through these steps, a semiconductor device is finished and shipped (Step  7 ). 
     FIG. 9  is a detailed flowchart of the wafer process in Step  4 . Step  11  (oxidation) oxidizes the wafer&#39;s surface. Step  12  (CVD) forms an insulating film on the wafer&#39;s surface. Step  13  (electrode formation) forms electrodes on the wafer by vapor disposition and the like. Step  14  (ion implantation) implants ion into the wafer. Step  15  (resist process) applies a photosensitive material onto the wafer. Step  16  (exposure) uses the exposure apparatus  500  to transfer a circuit pattern on the mask onto the wafer. Step  17  (development) develops the exposed wafer. Step  18  (etching) etches parts other than a developed resist image. Step  19  (resist stripping) removes disused resist after etching. These steps are repeated, and multilayer circuit patterns are formed on the wafer. The device fabrication method of this embodiment may manufacture higher quality devices than the conventional one. Thus, the device fabrication method using the exposure apparatus  500 , and the devices as finished goods also constitute one aspect of the present invention. 
   The above embodiment can directly cool the irradiation area irradiated to the light, and can avoid the temperature distribution (temperature gradient) of the optical element that causes the deterioration of the imaging performance. The above embodiment can provides the exposure apparatus and device fabrication method using such the effective cooling apparatus. 
   Further, the present invention is not limited to these preferred embodiments, and various variations and modifications may be made without departing from the scope of the present invention. For example, the inventive cooling apparatus is applicable to an optical element including a mask and a wafer, ultraviolet light with a wavelength of 200 nm or smaller, such as ArF excimer laser light and F 2  excimer laser light. 
   This application claims a foreign priority benefit based on Japanese Patent Applications No. 2004-257551, filed on Sep. 3, 2004, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.