Measuring apparatus, exposure apparatus and method, and device manufacturing method

A measuring apparatus includes a pinhole mask, located on an object plane of an optical system to be measured, and having a plurality of pinholes for generating a spherical wave from a measuring light beam, and a diffraction grating for splitting the measuring light beam that has passed the pinhole mask and the optical system, in which Lg=m·Pg2/λ is met, where Pg is a grating pitch of the diffraction grating, λ is a wavelength of the measuring light beam, m is an integer other than zero, and Lg is a distance between the diffraction grating and an image plane of the optical system. The measuring apparatus detects an interferogram formed by interference between a plurality of the measuring light beams split by the diffraction grating. The plurality of measuring light beams includes an aberration of the optical system.

This application is a U.S. national stage application of PCT International Application No. PCT/JP2006/309063, filed Apr. 24, 2006, and which claims priority from Japanese patent application numbers 2005-125977, filed Apr. 25, 2005, and 2006-009879, filed Jan. 18, 2006, both of which are hereby incorporated by reference herein in their entirety as if fully set forth herein.

TECHNICAL FIELD

The present invention generally relates to a measuring apparatus, and more particularly, to a measuring apparatus that measures an aberration of an optical system to be measured (“tested optical system” hereafter), such as a projection optical system that projects a pattern of a reticle (mask) onto a plate to be exposed. The inventive measuring apparatus is suitable, for example, for measuring a wavefront aberration of a projection optical system in an exposure apparatus that employs, e.g., extreme ultraviolet (“EUV”) light.

BACKGROUND ART

When photolithography is used to manufacture a semiconductor device, and the like, a projection exposure apparatus has, so far, been used to expose a pattern of a reticle onto a plate via a projection optical system. A growing demand for a finer semiconductor device promotes a reduction to practice of a projection exposure apparatus that uses EUV light having a wavelength (such as 5 nm to 20 nm) shorter than that of ultraviolet light.

For precise transfer of a mask pattern onto a plate with a desired magnification, a projection optical system requires a high imaging performance that maintains aberration to be as low as possible. Particularly, a growing demand for a finer semiconductor device causes the transfer performance to be sensitive to an aberration of the projection optical system. Therefore, a requirement is to measure a wavefront aberration of the projection optical system with high precision.

A lateral shearing interferometer (“LSI”) is one known apparatus that highly, precisely, measures the wavefront aberration of a projection optical system for EUV light without extremely accurate alignment of a pinhole, unlike a point diffraction interferometer (“PDI”). In general, the LSI arranges a pinhole mask that has one pinhole on an object plate of the tested optical system. The image of the pinhole is projected on an image plane, while being influenced by aberration of the projection optical system. A diffraction grating is located between the image plane and the tested optical system, and the light beams transmitted through the tested optical system slightly laterally shift according to their diffraction order. As a result, the transmitted light beams slightly laterally shift on an observation plane subsequent to the image plane, and overlap and interfere with each other, generating an interferogram (interference pattern). The interferogram gives a laterally differential wavefront of the original wavefront, which is reconstructed to the original wavefront through integration.

To extract from the pinhole a light beam with enough intensity to measure a wavefront, it is necessary to use a bright light source and to condense the light from this light source to the pinhole. One conceivable bright light source is an undulator light source that is inserted into an electron storage ring, but this requires large-scale facilities, incurring a high cost. A small light source, particularly one which also serves as an exposure light source, is preferable for wavefront measurements used in an assembly process or at an installation place of an exposure apparatus.

On the other hand, a light beam from an exposure light source, such as laser produced plasma (“LPP”) light and discharged produced plasma (“DPP”) light, has such a low directivity that it is very difficult to condense the light to the pinhole. When this exposure light source is used for wavefront measurements, an amount of the light that passes the pinhole is too small to produce a sufficiently intense interference image on the observation plane for wavefront measurements.

One proposed scheme arranges many reflection dots on the object plane of the tested optical system to improve the light use efficiency. See, for example, Japanese Patent Application, Publication No. 2004-219423. This reference also discusses arranging a diffraction grating on an image plane position of the tested optical system. The diffraction grating laterally shifts diffracted light beams with different orders and causes interference. A phase shift method finds a differential wavefront between the laterally shifted diffracted light beams, and calculates the wavefront of the tested optical system.

In general, a lateral shearing interferometer (LSI) using the phase shift method needs to take multiple interference images while shifting, by a specific quantity, a phase difference between diffracted light beams with respective orders, and to similarly take multiple interference images while changing the above lateral shifting direction. Accordingly, this type of LSI should take two pairs of interference images, requiring a long period of time for measurements. A problem of measurement error occurs unless an optical component, such as a diffraction grating, is maintained extremely stable in its height direction when moved, while these interference images are being taken.

DISCLOSURE OF THE INVENTION

A measuring apparatus according to one aspect of the present invention includes a pinhole mask, located on an object plane of an optical system to be measured, and having a plurality of pinholes for generating a spherical wave from a measuring light, and a diffraction grating for splitting the measuring light that has passed the pinhole mask and the optical system, wherein Lg=m·Pg2/λ is met, where Pg is a grating pitch of the diffraction grating, λ is a wavelength of the measuring light, m is an integer other than zero, and Lg is a distance between the diffraction grating and an image plane of the optical system, and wherein the measuring apparatus calculates a wavefront aberration of the optical system from an interferogram formed by causing interference of the measuring light split by the diffraction grating.

An exposure apparatus according to another aspect of the present invention for exposing a pattern of a reticle onto a plate using light from a light source includes a projection optical system for projecting the pattern onto the plate, and the measuring apparatus using the light to detect a wavefront aberration of the projection optical system as an interferogram.

An exposure method according to still another aspect of the present invention includes the steps of calculating a wavefront aberration of a projection optical system as an optical system to be measured by using the measuring apparatus, adjusting the projection optical system based on a calculated wavefront aberration of the projection optical system, and exposing a plate by using an adjusted projection optical system.

A device manufacturing method, as still another aspect of the present invention, includes the steps of exposing a plate using the above exposure apparatus, and developing the plate that has been exposed. Claims for a device fabrication method for performing operations similar to those of the above exposure apparatus cover devices as intermediate and final products. Such devices include semiconductor chips, such as an LSI and VLSI, CCDs, LCDs, magnetic sensors, thin film magnetic heads, and the like.

A further object and other characteristics of the present invention will be made clear by the preferred embodiments described below by referring to the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the accompanying drawings, a description will be given below according to the preferred embodiments of the present invention.

First Embodiment

FIG. 1is a schematic sectional view showing a basic arrangement of a measuring apparatus according to one embodiment of the present invention, and schematic plan views of a pinhole mask10and a diffraction grating plate14, when viewed from the top. The measuring apparatus1is one that measures an optical characteristic (a wavefront aberration in particular) of a tested optical system12. The measuring apparatus1includes the pinhole mask10, the diffraction grating plate14, a detector20, and a controller30.

The pinhole mask10is located on an object plane of the tested optical system12, and has plural pinholes10afor generating spherical waves from the measuring light. The pinhole mask10should effectively shield the EUV light, and is made of Ni, for example. The pinhole mask10should be 150 nm thick or greater when Ni is used.

The pinhole10ahas a diameter equal to or less than the diffraction limit. For an EUV exposure optical system with a numerical aperture (“NA”)=0.26 and a magnification=¼, the NA of its incidence side is 0.065, and a diameter of the pinhole10afor covering diffraction angles in this range by an approximately aplanatic diffracted light is 13.5/(2×0.065)=104 nm. As described later, the pinhole10amay be of a reflection type and of a transmission type. The plural pinholes10a(or pinhole array) are arranged apart from each other by an interval of a spatial coherence length of an illumination light or longer.

The reflection pinhole mask10has, for example, a reflective film made of a multilayer film of molybdenum and silicon on a silicon or glass substrate, a chrome or another absorbing layer above it, and a hole in the absorbing layer penetrating through the reflection layer. The transmission pinhole mask10has a through hole in a self-supporting film made of, e.g., metal, such as nickel.

An interferogram generated by the light that has transmitted through or is reflected on the pinhole10a, which is distant from a wavefront-aberration measuring point on a transfer area of the tested optical system12, gradually changes shape according to a wavefront aberration characteristic of the tested optical system12as the distance increases. The area of the light transmitting or reflecting pinholes10ashould be limited to an area in which the aberration of the tested optical system12is regarded to be substantially the same. This embodiment sets an area size A of the pinhole array to an area having a diameter of 0.1 mm to 1 mm or so, in which the aberration of the tested optical system12is regarded to be the same. Even if the area size A of the pinhole array is made larger than the above area, a limited illumination area IA provides the same effect.

The diffraction grating plate14has a two-dimensional diffraction grating15. The two-dimensional diffracting grating15is a diffraction grating that splits the light from the tested optical system12into many diffracted lights, and forms multiple light condensing points on an image plane IS.FIG. 1omits diffracted lights other than the 0-th order generated by the two-dimensional diffraction grating15. Equation 1 below provides a Talbot effect and a high contrast interferogram, where Lg is a distance Lg between the two-dimensional diffraction grating15and the image plane IS, Pg is a grating pitch of the diffraction grating, λ is a wavelength of the measuring light, and m is an integer other than zero. The condition “other than zero” is to generate a fine interferogram called a carrier in the interferogram, and to provide a wavefront reconstruction through a so-called Fourier transformation method, which Fourier-transforms an interferogram and obtains a wavefront from the phase information of the carrier component.
Lg=m·Pg2/λ  (1)

The thus obtained interferogram is a maximum or a minimum (although it is maximum inFIG. 1), as understood from the symmetry of the light intensity at a point on the alternate long and short dash that connects a center of the aperture part of the diffraction grating14to the condensing point of the 0-th order diffracted light.

The detector20is a detector or a camera, such as a backside illumination type CCD, which serves as an observing means for observing an interferogram.

When the interval between plural pinholes is made longer than the spatial coherence length of the illumination light, lights passing the pinholes do not interfere with each other. On the detector20, many interferograms generated from the lights from the pinholes10acan be simply superimposed in terms of the intensity, and provide a sufficient light intensity on the detector20even if the illumination light intensity to respective pinholes10ais low. When the bright and dark positions of the light intensity of the interferogram agree with each other, a sufficiently intense interferogram for measurements can be obtained without a contrast degradation of the interferogram.

Since the brightness and darkness of the interferogram agree on the line that connects the center of the aperture part of the diffraction grating plate14to the condensing point of the 0-th order diffracted light of the transmission light from each pinhole10a, these straight lines cross each other at one point on the image plane of the detector20in order not to degrade the contrast. As is apparent fromFIG. 1, Equation 2 below satisfies this condition, where Pg is the pitch of the grating, Pi is a cycle of a pinhole image, and Lc is a distance from the image plane IS of the tested optical system12to the detector20:
Pi=Pg·Lc/(Lg+Lc).  (2)

Equation 3 below is met, where Pp is a cycle of the pinhole array, and β is a magnification of the tested optical system12:
Pp=Pi/β.(3)

The cycle Pp that satisfies Equation 4 below provides accordance between the bright and dark positions of the light intensity of the interferogram resulting from the reflecting or transmitting light from any pinhole10aon the detector20without a contrast degradation:
Pp=(Pg/β)·(Lc/(Lg+Lc)).  (4)

WhileFIG. 1arranges the two-dimensional diffraction grating15above the image plane IS, the diffracting grating15may be located below the image plane IS, although Lg becomes a negative value in this case.

When the detector20is sufficiently distant from the image plane IS, Equation 5 below may be made by approximating (Lg+Lc) to 1:
Pp=Pg/β.(5)

The controller30acquires and analyzes an interferogram detected by the detector20, and calculates a wavefront aberration of the tested optical system12.

In operation, an illumination optical system (not shown) illuminates plural pinholes10ain the pinhole mask10simultaneously, generating many spherical waves. The diffracted lights that have passed the pinholes10ailluminate the tested optical system12, are influenced by the aberration of the tested optical system12, and form an image on the image plane IS via the diffraction grating plate14. The detector20observes a sufficiently intense interferogram. This embodiment does not require observing two sets of interferograms, and avoids time-consuming measurements.

The controller30processes the thus obtained interferogram and reconstructs the wavefront of the tested optical system. One illustrative reconstruction method is a method that includes the steps of first obtaining differential wavefronts of the diffraction grating plate14in two orthogonal directions, then integrating these respective differential wavefronts in the two directions, and finally, synthesizing them.

Second Embodiment

FIG. 10is a schematic plan view showing a structure of a pinhole mask11according to another embodiment of the measuring apparatus1. The measuring apparatus1can replace the pinhole mask10with the pinhole mask11. Similar to the pinhole mask10, the pinhole mask11can be of a transmission type or of a reflection type. The location of the pinhole mask11in the measuring apparatus1is the same as that of the pinhole mask10.

As shown inFIG. 10, the pinhole mask11has a pinhole unit11bhaving pinholes11ain each pinhole10aof the pinhole mask10. The pinhole mask11has many more pinholes11athan the pinhole mask10, improves its light use efficiency, and can measure the wavefront with a smaller amount of illumination light.

A smaller interval L between the pinholes11acan increase the number of pinholes, and improve the light use efficiency. However, an excessively small interval L between the pinholes11acauses interference between transmitting or reflected lights from adjacent pinholes, the deformed wavefront, and measurement errors. Restrained interference from adjacent pinholes and a smaller interval are preferable. For reduced interference between adjacent pinholes, the interval L of the pinhole11ashould be made such a distance that the coherence factor of the illumination light of the pinhole11abecomes zero. The shortest interval for the coherence factor of zero is 0.61×λ/NAi, where NAi is the NA of the illumination light of the pinhole11a, and its wavelength is λ.

FIG. 11is a graph showing a relationship between an absolute value of the coherence factor and a distance between two pinholes11ain the pinhole mask11. Referring toFIG. 11, a distance for the coherence factor of zero appears to be 0.16 μm. A regular triangle arrangement of the pinholes11a, as shown inFIG. 10, maximize the number of the pinholes11a, and thus, the light use efficiency.

FIG. 12is a random arrangement illustration of the pinholes11a. The regular arrangement shown inFIG. 10enables the pinhole unit11bto serve as a diffraction grating, and the illumination light to be discretely diffracted. As a result, when the incident-side NA of the tested optical system12is greater than the diffraction angle and the NA of the illumination light, the sufficiently intense incident light may not cover the entire incident pupil of the tested optical system12. In that case, the randomly arranged pinholes11ado not cause discrete diffractions of the illumination light, and the light incident upon the tested optical system12can cover the whole area of the incident pupil.

A larger diameter Dw of each pinhole unit11bprovides a wavefront measurement with a smaller amount of illumination light, but simultaneously deteriorates the contrast of an interferogram observed by the detector20. Accordingly, the diameter Dw of the pinhole unit11bshould be determined by taking into account the intensity and contrast of the interferogram. One suitable example of a diameter Dw of the pinhole unit11bis shown. The contrast of the interferogram will be deteriorated to 60% of the first embodiment where the interval Pp of a pinhole unit11bis 3.5 μm, and the diameter Dw of the pinhole unit11bis 0.6 times that of the interval Pp. On the other hand, the above interval of 0.16 μm of the pinhole11aenables the pinhole unit11bto include about one hundred sixty pinholes11a, and provides an interference image that is about one hundred sixty times as intense as that of the first embodiment.

Third Embodiment

Referring toFIG. 2, a description will be given below of an exposure apparatus100according to one aspect of the present invention.FIG. 2is a schematic block diagram showing a configuration of the exposure apparatus100. The exposure apparatus100uses the EUV light as exposure light. However, the present invention does not limit the exposure apparatus100to use the EUV light as the exposure light. The exposure apparatus100includes an EUV light source section110, an illumination optical system120, a mask stage142that supports and drives a mask140, a projection optical system150, a wafer stage162that supports and drives a wafer160, and a wafer-side unit170.

The exposure apparatus100is a projection exposure apparatus (scanner) that uses the EUV light (with a wavelength of, e.g., a step-and-scan method onto the wafer160. Such an exposure apparatus is suitable for the photolithography process on a sub-micron or a quarter-micron order or less. Since the transmittance of the EUV light is low in the atmosphere, the illumination optical system120, and the like, are housed in a vacuum chamber102.

The EUV light source110is a light source that oscillates the EUV light, using a DPP EUV light source that generates EUV light by turning Xe gas, Sn steam, and the like, into plasma through discharge. The EUV light source110may use an LPP EUV light source that condenses and irradiates a high-output laser to Xe and Sn, to generate the plasma. The DPP light source ejects a gas around an electrode in a vacuum, applies a pulse voltage to the electrode, and causes discharge, thus generating the high-temperature plasma. The EUV light with a wavelength of 13.5 nm or so is emitted from the plasma and utilized. The target material may use a metallic thin-film, an inert gas, a liquid droplet, and the like. In order to enhance an average intensity of EUV light to be emitted, a higher repetitive frequency of the pulse laser is preferably, such as, typically, several kHz. The measuring apparatus1uses the exposure light source, and becomes smaller and less expensive than that using an undulator light source.

The illumination optical system120is an optical system that propagates EUV light to illuminate the mask140. In this embodiment, the illumination optical system120has a collimator optical system, an integrator123, an aperture stop124, an arcing optical system, a planar mirror127, a planar mirror130, and a switching mechanism132.

The collimator optical system serves to receive and substantially collimate the EUV light from the EUV light source110, and includes a concave mirror121, a convex mirror122, and a plane mirror. The integrator123has multiple cylindrical reflective surfaces, a fly-eye, a fish-scale shaped fly-eye, and the like, thus uniformly illuminating the mask140with a predetermined NA. The integrator123is switched to the plane mirror130through the switching mechanism132, and is located on the optical path during exposure. On the reflective surface of the integrator123, the aperture stop124is located whose aperture surface is arranged almost perpendicular to the reflective surface. The aperture stop124regulates the distribution shape of the effective light source, and controls the angular distribution of light that illuminates each point on the mask40as an illuminated surface. The arcing optical system serves to condense light from the integrator123into an arcuate shape, and includes a convex mirror125and a concave mirror126. The plane mirror127deflects the image-side light of the arcing optical system toward the mask140at a predetermined angle. This embodiment sets an incident angle of the plane mirror127to about 6° in measuring a wavefront of the projection optical system150as the tested optical system, which is equal to an angle between a corresponding principal light upon the object side of the projection optical system150and a normal of the mask plane.

The plane mirror130is switched to the integrator123and arranged on the optical path by the switching mechanism132during measurements of the wavefront of the projection optical system150. The light that has reflected on the plane mirror130is reflected on the arcing optical system, and is condensed on the object plane of the projection optical system130.

The mask140is a reflection type mask, on which a circuit pattern (or an image) to be transferred is formed, and is supported and driven by the mask stage142. The diffracted light emitted from the mask140is reflected on the projection optical system150, and is projected onto the wafer160. The mask140and the wafer160are located in an optically conjugate relationship. Since the exposure apparatus100of this embodiment is a scanner, the mask140and the wafer160are scanned at the speed ratio of the reduction ratio, thus transferring the pattern on the mask140to the wafer160.

In measuring the wavefront of the projection optical system150, the pinhole mask10or11is located in place of the mask140. The pinhole mask10or11is located on a dedicated stage for wavefront aberration measurement or the mask stage142. This embodiment uses the pinhole mask10and the catoptric plural pinholes10a. The light that has been reflected on the pinhole mask10passes the projection optical system150, and forms an image on the image plane IS.

The projection optical system150serves to project the mask pattern onto the wafer160, and is a tested optical system for the measuring apparatus1. The projection optical system150is a coaxial optical system that includes multiple multilayer mirrors, and is designed to maintain a non-telecentric condition at its object side and a telecentric condition at its image side. The smaller number of multilayer mirrors in the projection optical system150increases the use efficiency of the EUV light, but the aberration correction becomes difficult. Four to six multilayer mirrors are necessary for aberration corrections. The multilayer mirror has a spherical or an aspheric reflective surface that is a convex surface or a concave surface. Their NAs range between 0.1 and 0.3.

The projection optical system150applied to the EUV light is quite sensitive to the positional accuracy and thermal deformation, and it is necessary that a wavefront aberration be measured during an exposure interval, and the mirror position be adjusted based on the measurement result for feedback. Impurities may adhere to the top of the multilayer mirror causing a chemical change, i.e., a so-called phase change, due to contamination that may arise. It is necessary to measure the wavefront aberration of the projection optical system150using an exposure wavelength on the exposure apparatus body, and the exposure apparatus100, installed with measuring apparatus1, meets this requirement.

The wafer160is a plate to be exposed, and covers a wide range of plates, such as a liquid crystal plate and other substrates. A photoresist is applied on the wafer160.

The wafer stage162supports and drives the wafer160. The wafer stage162may apply any structures known in the art, and thus, a detailed description of the structure and operations will be omitted.

The wafer-side unit170is provided on the image plane of the measuring apparatus1. The wafer-side unit170is located on the wafer stage162, and includes, as shown inFIG. 3, the diffraction grating plate14and the detector20. Here,FIG. 3is a schematic sectional view showing the wafer-side unit170. The wafer-side unit170can be moved by the wafer stage162in a direction perpendicular to the optical axis. The light beams diffracted by the diffraction grating plate14generate an interferogram, while diffracted light beams with different orders on the detector20shift laterally and overlap each other. The interferogram can be analyzed by an LSI method to measure the wavefront aberration of the projection optical system150.

In measuring the wavefront of the projection optical system150, the switching mechanism132switches the integrator123to the plane mirror130. This will enable the enlarged arc-shaped light on the object plane of the projection optical system150to be condensed as an image of the intermediate condensing point of the EUV light source110. The pinhole mask11would also provide a similar effect.

The illumination optical system120illuminates the pinhole mask10, and spherical wavefronts emitting from the plural pinholes10aare diffracted in two orthogonal directions on the diffraction grating14via the projection optical system150. These diffracted lights overlap each other while being laterally shifted, generating an interferogram on the detector20. The controller30calculates differential wavefronts in two orthogonal directions from the interferogram obtained by the detector20, and integrates them to reconstruct the original wavefronts. The method of obtaining the differential wavefront from the interferogram uses the Fourier transform method. The interferogram has information about differential wavefronts in two orthogonal directions, and the original wavefront can be reconstructed from one interference image.

The wafer stage162or other means moves the diffraction grating plate14to similarly measure aberrations at several points over the field of the projection optical system150, and an aberration characteristic is measured over the field of the projection optical system150. A light condensing spot is moved to an arbitrary object point with an arc field of the projection optical system150to measure a wavefront aberration. For this purpose, the plane mirror130is rotated around an axis that is parallel to the paper plane and plane mirror130(shown by a dotted line inFIG. 2), and the deflecting mirror127is rotated around an axis that is perpendicular to the paper plane. A rotation of the plane mirror127moves the light condensing spot in the lateral direction on the paper plane ofFIG. 2. The reticle stage142and the wafer stage162move the pinhole10aand the wafer-side unit170to the measurement positions in the transfer region.

The third embodiment switches the integrator123to the plane mirror130, but an alternate embodiment uses multiple integrators and switches all the integrators to the plane mirrors, thus illuminating the pinhole masks10or11with high intensity.

Fourth Embodiment

Referring toFIG. 4, a description will be given of an exposure apparatus100a. Here,FIG. 4is a schematic block diagram showing the configuration of the exposure apparatus100A. The exposure apparatus100A is different from the exposure apparatus100in that the pinhole10aof the pinhole mask10is changed to a transmission type pinhole to facilitate its manufacture. For a transmission type pinhole, the light beams need to be deflected from above the pinhole mask10. The exposure apparatus100A of this embodiment thus has a mask-side unit144. The exposure apparatus100acan have a similar effect even with the pinhole mask11. Those elements inFIG. 4, which are the same as corresponding elements inFIG. 2, are designated by the same reference numerals, and a description thereof will be omitted.

The mask-side unit144may be located on a dedicated test reticle or may be located on the mask stage142.FIG. 5is a schematic sectional view showing the structure of the mask-side unit144. InFIG. 5, the light angle of the mask-side unit144is drawn as a large angle for description purposes. The mask-side unit144has the pinhole mask10having the pinholes10a, and the deflecting mirror9. The deflecting mirror9deflects the EUV light toward the pinhole mask10.

Referring toFIG. 6, a description will be given of an interval of the deflecting mirror9and the pinhole mask10, and of the light shielding. The object-side NA is 0.0625, the principal ray angle is 6°, and the interval between the deflecting mirror9and the pinhole mask10is z0. The principal ray is a straight line of y=ax (a=tan(90°-60°)), and the end lights are y=bx and y=cx, respectively.

The EUV light from the illumination optical system120is reflected on the deflecting mirror9of the mask-side unit144, and condensed on the pattern plane of the pinhole mask10where the transmission type pinhole10ais located. The condensing point on the pattern plane of the pinhole mask10and the light from the illumination optical system120should be sufficiently separated. In other words, the straight line of y=cx and the condensing point must be spatially separated. A graph inFIG. 7shows a relationship between the light separation distance Δ when the transmission type pinhole10ais located at the distance z0with respect to the reflection surface. Referring toFIG. 7, even if the image-side NA of the projection optical system150is 0.25 (the object-side NA is 0.0625), the light beams are separated by 1 mm or longer if the deflecting mirror9and the pinhole10aare separated by 10 mm or so.

Fifth Embodiment

In the third embodiment, the distance from the arcing optical system to the object plane of the projection optical system150becomes longer by a deflection length of the deflecting mirror9in the mask-side unit144ofFIG. 5. Thus, the light from the illumination optical system120forms an image of an intermediate condensing point before the pinhole mask10, and lowers the light intensity on the pinhole mask10. This embodiment solves this problem by using a convex mirror having a negative power instead of the plane mirror130. This will extend the distance up to the condensing point, and even if the mask-side unit144uses the deflecting mirror9, the light can be condensed into the pinhole mask10.

Sixth Embodiment

A description will now be given of the exposure method of the present invention (aberration correction followed by exposure). In the exposure apparatus100, multiple optical elements (not shown) composing the projection optical system150are installed to be movable in an optical axial direction and/or in a direction orthogonal to the optical axis. A driving system (not shown) for aberration adjustment drives one or more optical systems based on aberration information obtained by this embodiment to correct or to optimize one or more aberration values (especially, Seidel's five aberrations). The adjusting means of the aberration of the projection optical system150may use, in addition to movable lenses, various known techniques, such as a movable mirror (when the optical system is a catadioptric system and a catoptric system), a tilting plane-parallel plate, a pressure-controllable space, and an actuator-aided surface correction.

In exposure, the EUV light emitted from the EUV light source110arc-illuminates the reticle140uniformly. The EUV light is reflected on the reticle140, carries a circuit pattern, and is imaged onto the wafer160via the projection optical system150.

Seventh Embodiment

Referring now toFIGS. 8 and 9, a description will be given of an embodiment of a device manufacturing method using the above exposure apparatus.FIG. 9is a flowchart for explaining a fabrication of devices (for example, semiconductor chips, such as ICs and LSIs, LCDs, CCDs, etc.). Here, a description will be given of fabrication of a semiconductor chip as an example. Step1(circuit design) designs a device circuit. Step2(mask fabrication) forms a mask having a designed circuit pattern. Step3(wafer preparation) manufactures a wafer using materials such as silicon. Step4(wafer process), which is referred to as a pretreatment, forms actual circuitry on the wafer through a lithography technique using the mask and the wafer. Step5(assembly), which is also referred to as a post-treatment, forms into a semiconductor chip, the wafer formed in Step4, and includes an assembly step (e.g., dicing, bonding), a packaging step (chip sealing), and the like. Step6(inspection) performs various tests for the semiconductor device made in Step5, such as a validity test and a durability test. Through these steps, a semiconductor device is finished and shipped (Step7).

FIG. 9is a detailed flowchart of the wafer process shown in Step4inFIG. 8. Step11(oxidation) oxidizes the surface of the wafer. Step12(CVD) forms an insulating film on the surface of the wafer. Step13(electrode formation) forms electrodes on the wafer by vapor disposition, and the like. Step14(ion implantation) implants ions into the wafer. Step15(resist process) applies a photosensitive material onto the wafer. Step16(exposure) uses the exposure apparatus to expose a circuit pattern of the mask onto the wafer. Step17(development) develops the exposed wafer. Step18(etching) etches parts other than a developed resist image. Step19(resist stripping) removes unused resist after etching. These steps are repeated, and multilayer circuit patterns are formed on the wafer. The manufacturing method of this embodiment uses a projection optical system adjusted based on highly precisely measured aberrations, which enables high-precision semiconductor devices to be manufactured, which have been so far difficult to accomplish. 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 present invention is also applicable to a step-and-repeat exposure apparatus.