Reflecting mirror and exposure apparatus using the same

A mirror apparatus including a reflecting mirror reflecting light, partition walls, the walls and the reflecting mirror defining a plurality of air chambers, and a regulator regulating air pressure in at least one of the air chambers. With this configuration, the front surface of the reflecting mirror is deformed into a smooth shape so as to correct optical aberration.

BACKGROUNG OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflecting mirror adapted to be approprietly used as part of an optical projection system incorporated in a projection exposure apparatus.

2. Description of the Related Art

Heretofore, a photolithographic process for manufacturing a semiconductor element, utilizes an optical projection unit for projecting a pattern formed on a mask (or a reticle) onto a photosensitive substrate such as a wafer by way of an optical projection system in order to expose the substrate with the pattern. There has been used, as the projection exposure apparatus, an exposure apparatus of a static expousure type, such as a step-and-repeat type optical reduction exposure apparatus (a so-called stepper) or an exposure apparatus of a scanning expsoure type such as a slit scanning type exposure apparatus.

Conventionally, in the above-mentioned exposure apparatus, g-ray (having a wavelength of 436 nm), i-ray (having a wavelength of 365 mn) or the like has been used as exposure light. In recent years, Kr Excimer laser light (having a wave length of 248 mn), ArF Excimer light (having a wave length of 193 nm) or the like are being used. In order to carry out exposure with the use of exposure light in the above-mentioned wavebands, by using a cata-diptoric optical system as the optical projection system, satifactory scale efficiency can be obtained, and accordingly, there has been exhibited such an advantage that the optical projection system can be miniaturized.

The above-mentioned cate-dioptric optical projection system includes various kinds of reflecting optical elements (optical projection elements) such as plane mirrors and reflecting mirrors.

By the way, various factors detrioate the optical performance of the exposure apparatus. For example, optical abberation is caused by errors in manufacture and assembly of optical projection elements and thermal deformantion caused by heat induced by exposure light during the operation of the unit, and accordingly, the image quality on the photosenstive substrate (wafer) is deteriorated. As a result, the abberation should be corrected by changing the surface shape of the reflecting mirror.

For example, as disclosed in Japanese Patent Laid-Open No. 2004-64076 (corresponding to U.S. Pat. No. 6,842,277) (Refer toFIG. 9), force actuators54are provided to a reflecting mirror52on the side remote from the reflecting surface thereof in order to transmit defromation forces to the rear surface of the reflecting mirror from the force actuators54through the intermediary of mechanical links51(Refer toFIG. 10A) connecting between the force actutors and the rear surface of the reflecting mirror. As a result, the front surface of the reflecting mirror is deformed into a desired shape in order to correct the optical abberation. Further, as disclosed in WO 02/12948 (corresponding to U.S. Pat. No. 6,393,373), air cylinders are incorporated as the actuators, and accordingly, derormatin forces F are transmitted to the rear surface of the reflecting mirror from the actuators through the intermediary of mechanical links connected to the rear surface of the reflecting mirror. As a result, the front surface of the reflecting mirror is deformed into a desired shape in order to correct optical abberation.

However, in the above-mentioned example, it is necessary to arrange several actuators at the rear surace of the reflecting mirror, and accordingly, the configuration becomes complicated. Further, so many actuators have to be controlled, and accordingly, a control system therefor is complicated. Further, as shown inFIG. 10a, should a mechanical link be used to push and pull the rear surace of the reflecting mirror to which the mechanical links are connected, sectional shapes of parts where the links and the rear surface of the reflecting mirror are connected would be indeed visible at the front surface of the reflecting mirror as shown inFIG. 10b.As a result, in addition to form errors such as mirror surface form errors and deformation errors, error components having high spatial frequencies would be created. In particular, with a configuration including seveal actuators, since several error components would be presented, additional optical abberations having high spatial frequencies would be created, and as a result, an image quality on a light sensitive substrate (wafer) is deteriorated.

SUMMARY OF THE INVENTION

The present invention is directed to a mirror apparatus in which a rear surface of a reflecting mirror is deformed into a smooth shape in order to correct optical abberation.

According to one aspect of the present invetion, a mirror apparatus includes a reflecting mirror reflecting light, partition walls, wherein the partition walls and the mirror define a plurality of air chambers, and a regulator regulating air pressure in at least one of the plurality of air chambers.

Further, according to one aspect of the present invetion, an exposure apparatus includes the above-mentioned mirror apparatus as a part of an optical projection system.

According to the present invention, the front surface of the reflecting mirror can be deformed into a smooth shape in order to correct optical abberation. Further, with the use of the above-mentioned mirror apparatus in an optical projection system in an exposure apparatus, the optical performance of the exposure apparatus can be enhanced, thereby it is possible to manufacture semiconducotr devices with a high quality.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

FIG. 1Ais a view illustrating a schematic configuration of a mirror apparatus100in a first embodiment of the present invention, andFIG. 1Bis a sectional view along line A-A′ inFIG. 1A. The mirror apparatus100can be installed in an exposure apparatus so as to reflect exposure light within an effective diameter range on its reflecting surface, which is deformed into a desired shape at that time in order to correct optical abberation.

The mirror apparatus100incorporates therein a concave reflecting mirror8, partition walls5to7for defining, together with the reflecting mirror8, a plurality of air chambers1to4which are substantially sealed up. The partition walls5to7include side walls5with which the air chambers are defined through partition thereby, an outer peripheral wall6surrounding the plurality of air chambers, and a bottom wall7opposed to the reflecting mirror8. The reflecting mirror and the partition walls can be made of a material having a low thermal expansion rate, such as invar, low theraml expansion glass or low thermal expansion ceramics. Further, the plurarity of air chambers are arranged on the side of the reflecting mirror8remote from a reflecting surface11. It is noted here that the wording “sealed up” stated above concerns substantial sealing of such a degree that an enough force can be applied to the reflecting mirror by the air pressure.

The outer peripheral wall6is formed therein with air communication holes9through which the air chambers communicate with pressure gauges12and an air feed pump13by way of a tube10. The air feed pump13feeds air into the air chambers. A servo valve14is connected between each of the air chambers and the air feed pump13, and accordingly, the flow rate of the air fed into each of the air chambers is controlled by the servo valve14. By controlling the flow rate of air fed into each of the air chambers, the pressure in the air chamber can be controlled. Further, the pressures in the air chambers1to4are controlled, independent from one another.

The pressure gauges12and the servo valves14can be directly attached to the partition walls5. However, should the partition walls be deformed by the dead weights of the pressure gauges12and the servo valves14, the thus caused deformation would be transmitted to the reflecting mirror8which would therefore be deformed. In order to prevent occurrence of the deformation, the pressure gauges12and the servo valves14are connected to the air chambers through the intermediary of the tubes10having a low stiffness, and accordingly, their dead weights are born by separate support members (which are not shown). In the case of directly attaching the pressure gauges12and the servo valves14to the partition walls, the thickness of the partition walls can be increased in parts where they are attached, in order to increase the stiffness thereof.

Further, in order to prevent the reflecting mirror8from being deformed by heat generated from the pressure gauges12and the servo valves14, it is effective to connect them to the air chambers through the intermediary of the tubes10having a low stiffness so as to isolate the reflecting mirror8from the heat sources. Alternatively, it is effective to arrange a cooling unit (which is not shown) around the pressure gauges12and the servo valves14in order to cool them.

Air pressure (which will be hereinbelow denoted P0) outside of the air chambers is measured by a pressure gauge which is not shown. A controller15computes air pressures P1to P4which are required for deformation of the reflecting mirror8, from the air pressure P0and a desired deformation value of the reflecting mirror, and delivers instructions to the servo valves. For this computation, there may be used a correlation between desired deformation values and air pressures which has been stored in the controller15in the form of a function. Alternatively, there can be used a correlation between desired deformation values and air pressures, which has been obtained through experimentation and simulations and which has been stored in the controller15in the form of a table. The servo valves regulate air quantities fed into the air chambers and air quantities discharged from the air chambers in order to change air pressures in the respective air chambers. The air pressures in the respective air chambers P1to P4which are measured by the pressure gauges12are fed back to the controller15. Thus, the air pressures in the respective air chambers15are controlled. It is noted here that if an exhaust pump (which is not shown) is used together with the air feed pump13, the pressures P1to P4may be set to be higher or lower than the pressure P0. As a result, the reflecting mirror may be deformed. Any of various kinds of regulators which can adjust the air pressure in the air chamber may be appropriately used. Explanation will be hereinbelow made of the deformation of the reflecting mirror.

It is estimated that the air pressures P1to P4are effected in the air chambers with the air pressure P0outside the air chambers. In this embodiment, differential pressure P1-P, P2-P0, P3-P0, P4-P0between the respective air chambers and outside of the chambers are controlled as deformation forces for the reflecting mirror8. That is, the air pressures are regulated in order to deform the shape of the reflecting mirror.

FIG. 2is a view illustrating an example of a deformed shape of the mirror within the effective diameter range of the reflecting mirror8, which shows a distribution of deformation values at several positions (X- and Y-directions) after the deformation thereof with respect to an initial position0. For example, if the air pressures P1, P2are set to be higher than P0while the pressures P3, P4are set to be lower than P0, the reflecting mirror is deformed into a convex shape in the parts located within the air chambers1,2but into a concave shape in the parts located within the air chambers3,4.FIG. 2shows the reflecting surface at this time, that is, it is convexly deformed at two positions but is concavely deformed at two positions. Thus, by controlling the air pressures in the air chambers as stated above, the reflecting mirror may be locally deformed, and further, the degree of deformation may also be controlled.

The rear surface of the reflecting mirror8substantially defines a surface (pressure receiving surface) for receiving the air pressures within its effective diameter range. Variations in the air pressures in the respective air chambers are received by this overall pressure receiving surface, and accordingly, deformation forces applied to the reflecting mirror may be uniformly received by the overall pressure receiving surface. Namely, no deformation forces applied to the rear surface of the reflecting mirror are locally concentrated, and accordingly, the reflecting surface may be deformed in a smooth shape. A stage unit17is located between the reflecting mirror8and a reference base16. An intermediate ring18having high stiffness supports the air chambers at three positions through the intermediary of coupling members19which are located in the parts having relatively high stiffness in the partition walls, that is, for example, the outer peripheral wall6or the bottom plate7. Further, actuators20interposed between the intermediate ring18and the reference base16are operated while the position of the reflecting mirror8or the positions of the air chambers are measured by means of a laser interferometer21so as to change the representative positions of the reflecting mirror8and degrees of inclination (tilts) thereof.

The mirror apparatus100in this embodiment can accept correction for various optical aberrations by changing the shape of the reflecting mirror8or those of the air chambers1-4as well as positions thereof. For example, although the thickness of the reflecting mirror8shown inFIG. 1is uniform, the thickness of the reflecting mirror can be changed as shown inFIGS. 3A to 3C. In the case of changing the thickness, displacements on the reflecting surface which are deformed by the air pressures cause concavities and convexities to be formed in radial directions within the effective diameter range.

It is noted that the number of the air chambers arranged on the rear side of the reflecting mirror8is not limited to four. For example., with the provision of three air chambers at angular intervals of 120 deg., displacements on the reflecting surface may cause convexities to be formed at angular intervals of 120 deg., as shown inFIG. 4.

Further, the reflecting mirror8and the side walls5can be arranged in a noncontact manner with a fine gap therebetween. In this arrangement, it is required to design such a configuration so that air is prevented from passing through the gap between the reflecting mirror8and the side walls5by a large quantity. For example, the gap is as small as possible or a seal member having low stiffness is provided. With the provision of the noncontact configuration, the reflecting mirror and the side walls may be isolated from each other in view of mechanical stiffness, and accordingly, the reflecting surface may be deformed into a smooth shape in the vicinity of the side walls.

Further, if the side walls5are displaceable, the locations of the respective air chambers can be changed. As a result, it is possible to accept various deformation of the front surface of the reflecting mirror8. That is, it is possible to accept correction for various aberrations.

Further, if the corner parts between the reflecting mirror8and the side walls5and between the reflecting mirror8and the outer peripheral wall6are rounded (having a smooth surface with curvature), the reflecting surface can be deformed into a spatially smooth shape in the vicinity thereof.

It is noted that although the pressure gauges12are used as control sensors in this embodiment, displacement gauges may also be used. For example, the displacement of the reflecting surface outside of the effective diameter range is measured above the air chambers1-4, and thus, control can be made with the use of the relationship between the thus obtained local displacements and the shape of the reflecting surface, which has been previously obtained.

The mirror apparatus100in this embodiment can cope with correction for various optical aberrations by changing the shape of the reflecting mirror8or those of the air chamber1-4or changing the position of the air chambers. As a result, the mirror apparatus can correct optical aberrations due to errors in manufacture and assembly of optical projection elements, and due to thermal deformation caused by heat of exposure light during operation of an exposure apparatus.

In comparison with a process of deforming a reflecting mirror with actuators, according to this embodiment, the reflecting mirror surface can be deformed into a smooth shape so as to correct optical aberration. Further, since no complicated mechanism is required, it is advantageous in view of the costs thereof.

Second Embodiment

FIG. 5ais a view illustrating a schematic configuration of a mirror apparatus100in a second embodiment of the present invention, andFIG. 5bis a sectional view along line B-B′. Explanation will be mainly made of arrangements different from those in the first embodiment while explanation of the arrangements the same as that of the first embodiment will be omitted. The mirror apparatus100reflects exposure light in its effective diameter range on the reflecting surface thereof, and deforms the reflecting surface into a desired shape at that time so as to correct optical aberration.

The reflecting mirror incorporates therein a concave reflecting mirror8, support portions23having high stiffness, for supporting the mirror, and partition walls defining a plurality of air chambers1to4which are substantially sealed, together with the reflecting mirror. The partition walls includes side walls5having low stiffness and a base level block16. The reflecting mirror8, the base level block16and the support portions23can be made of materials having a small thermal expansion coefficient, such as, invar, glass having a low expansion coefficient or ceramics having a low expansion coeffcient.

The base level block16is formed therein with communication ports9, and accordingly, the air chambers are connected to pressure gauges12and an air feed pump13by way of the communication ports9and tubes10. Servo valves14are provided between the air chambers and the air feed pump13so as to control the flow rate of air fed to the air chambers. By controlling the flow rate of air fed into the air chambers, pressures in the air chambers may be controlled. As a regulator for regulating the air pressure, there can be used any of various kinds of units capable of regulating air pressures in the air chambers. Further, the air pressures in the air chambers can be controlled, independent from one another.

A stage unit17is arranged between the reflecting mirror8and the reference level block16so as to enable the reflecting mirror8to change its representative positions and degrees of inclination (tilts), similar to the first embodiment.

The deformation of the reflecting mirror8is similar to that in the first embodiment, and accordingly, the explanation thereof will be omitted.

The mirror apparatus100in the embodiment of the present invention can accept correction for various optical aberration by changing the shapes and positions of the reflecting mirror8and the air chambers1-4, similar to the first embodiment. As a result, the reflection mirror apparatus can correct and/or reduce optical aberrations due to errors in manufacture and assembly of optical projection elements, and also due to thermal deformation caused by heat of exposure light during operation of the exposure apparatus.

According to this embodiment, in comparison with a method in which a reflecting mirror8is deformed by actuators, the reflecting mirror surface may be deformed in a smooth shape so as to correct optical aberration. Further, no complicated mechanism is required, thereby it is advantageous in view of its costs.

Third Embodiment

Explanation will be made of an exposure apparatus in an exemplified form, which is applied thereto with the mirror apparatus according to the present invention. Referring toFIG. 6, the exposure apparatus includes an illumination system101, a reticle stage102mounted thereon with a reticle, a projection optical system103, and a wafer stage104mounting a wafer thereon. The exposure apparatus is adapted to project a circuit pattern formed on the reticle onto the wafer which is therefore exposed thereto, and can be of a step-and-repeat projection exposure type or a step-and-scan projection exposure type.

The illumination system104illuminates the reticle on which the circuit pattern is formed, and includes a light source portion and an illumination optical system. The light source portion can utilize, as a light source, for example, laser such as ArF excimer laser having a wavelength of about 193 nm, KrF excimer laser having a wavelength of about 248 nm or F2excimer laser of about 153 nm. However, the kind of laser is not limited to excimer lasers alone, but YAG lasers can be also used. The number of laser sources are not limited to a specific one. In the case of using laser as the light source, there can be used a light beam shaping optical system for shaping a parallel ray light beam emitted from the laser source into a desired beam shape, and an incoherent optical system for converting a coherent light beam into an incoherent light beam. Further, the light source portion is not limited to laser, but there can be used one or more of lamps such as a mercury lamp or an xenon lamp.

The illumination optical system is an optical system for illuminating a mask, and includes lenses, mirrors, a light integrator and a diaphragm.

As the optical projection system103, there can be used an optical system (cata-dioptric optical system) having at least one concave mirror, an all mirror type optical system or the like. The mirror apparatus100in the first or second embodiment is used as at least a part of this optical projection system. The reticle stage102and the wafer stage104can be displaced by, for example, linear motors. In the case of the step-and-scan projection exposure type, the respective stages are displaced, in synchronization with each other. Further, an additional actuator is incorporated to at least either one of the wafer stage and the reticle stage in order to align the pattern on the reticle with the wafer.

The above-mentioned exposure apparatus is adapted to be used for a manufacture of a device formed therein with a micro pattern, for example, a semiconductor device such as a semiconductor integrated circuit, a micro machine or a thin film magnetic head.

With the use of the mirror apparatus100in at lease a part of the optical projection system, there can be corrected and/or reduced optical aberration due to errors in manufacture and assembly of optical projection elements, and also due to thermal deformation caused by heat of exposure light during operation of the exposure apparatus, and thereby it is possible to carry out exposure with a high degree of accuracy.

Next, an explanation will be made of an embodiment of a device manufacture method utilizing the above-mentioned exposure apparatus with reference toFIGS. 7 and 8.FIG. 7is a flow-chart for explaining a manufacture of a device (a semiconductor chip such as IC or LSI, LCD, CCD and the like). In this embodiment, a method of manufacturing a semiconductor chip as an example, will be explained.

At step S1(circuit design), a circuit of the semiconductor device is designed. At step S2(manufacture of a mask), a mask is manufactured based upon the designed circuit pattern. At step S3(manufacture of a wafer), a wafer is made from silicon. At step S4(wafer process), that is, the so-called preprocess, with the use of the mask and the wafer, an actual circuit is formed on the wafer through lithography by the above-mentioned exposure apparatus. At step S5(assembly), that is, the so-called post process, a semiconductor chip is formed from the wafer manufactured at step S4. Step S5includes process steps such an assembly step (dicing, bonding) and a package step (enclosing a chip). At step S6(inspection), an operation confirming test and an endurance test for the semiconductor device manufactured at step S5are carried out. The semiconductor device is completed through the above-mentioned steps, and at step S7, shipping thereof is carried out.

FIG. 8is a flow chart for explaining the wafer process step S4in detail. At step S11(oxidation), the front surface of the wafer is oxidized. At step S12(CVD), an insulation film is formed on the front surface of the wafer. At step S13is formation of an electrode. At step S14(ion plantation), ions are planted into the wafer. At step S15(resist process), the wafer is coated thereover with a photosensitive material. At step S16(exposure), the circuit pattern on the mask is projected onto the wafer which is therefore exposed by the exposure apparatus. At step S17(development), the thus exposed wafer is developed. At step18(etching), the photosensitive material is scraped in the part other than a resist image. At step S19(resist removal), the resist which becomes unnecessary after completion of the etching is removed. With the repetitions of the steps as stated above, circuit patterns are formed on the wafer in multi-layers.

This application claims the benefit of Japanese Patent Laid-Open No. 2005-131834, filed Apr. 28, 2005, which is hereby incorporated by reference herein in its entirety.