WO2010008993A1 - Adaptive fly-eye and other mirrors for extreme ultraviolet and other optical systems - Google Patents

Abstract

Segmented mirrors and adaptive mirrors are disclosed, along with methods involving use of same. An exemplary segmented mirror (150, 150b) includes an array of multiple mirror elements and a monitoring device (160a-166a). The mirror elements have respective reflective surfaces and are respectively movable. The elements reflect respective portions of a beam of utility light incident on the array. The monitoring device is situated relative to the array and includes a source of sensor light (160a) and a Shack-Hartmann sensor (164a). The source is situated to direct the sensor light onto at least some of the elements, and the Shack-Hartmann sensor (164a) is situated to receive sensor light reflected from the elements. The sensor can determine, from detected locations of focal spots of sensor light produced by the sensor, information concerning an optical result desirably being obtained by use of the segmented mirror.

Description

ADAPTIVE FLY-EYE AND OTHER MIRRORS FOR EXTREME ULTRAVIOLET AND OTHER OPTICAL SYSTEMS

Cross Reference to Related Application This application claims priority to and the benefit of U.S. Provisional Patent

Application No. 61/081,672 filed on July 17, 2008, which is incorporated herein by reference in its entirety.

Field This disclosure pertains to, inter alia, optical systems that employ fly-eye mirrors as, for example, optical integrators. Exemplary optical systems of this nature are used with extreme ultraviolet (EUV) radiation, such as illumination- optical systems used in EUV lithography (EUVL) systems. The disclosure also pertains to adaptive fly-eye and types of adaptive mirrors used in optical systems, particularly adaptive mirrors whose performance is optically monitored.

Background

Fly-eye (also called "fly's-eye") optics are often used in illumination-optical systems as "optical integrators" for producing an illumination-light beam having substantially uniform illumination intensity across an illumination field. Fly-eye optics encompass fly-eye lenses and fly-eye mirrors. A typical fly-eye lens comprises an array of multiple lenslets. When the array is placed optically downstream of a light source, the lenslets image respective portions of the light source over the illumination field. A typical fly-eye mirror comprises an array of multiple mirror segments that image respective portions of the light source. A fly- eye lens is usable if the lenslets have reasonable transparency and refractivity to the particular wavelength(s) of light with which the lens is used. Otherwise, a fly-eye mirror may be usable in situations in which a fly-eye lens is impractical or unusable. Extreme ultraviolet (EUV) is an example of a wavelength range {e.g., λ = 1- 50 nm) of electromagnetic radiation to which substantially no practical materials are known to be refractive. This is especially the case with EUV radiation in the range of λ = 10-15 nm. Consequently, EUV optical systems operating in this wavelength range are catoptric, comprising only reflective optical elements (generally called "mirrors"). The range λ = 10-15 nm is the range used in EUVL systems currently under development.

A representative EUVL system includes an illumination-optical system and a projection-optical system. Both optical systems are catoptric (fully reflective). The illumination-optical system is situated upstream of a pattern-defining body called herein a "reticle," and the projection-optical system is situated between the reticle and a lithographic substrate (e.g., a "wafer"). The illumination-optical system provides at least one illumination beam for illuminating a selected region on the reticle, which is also reflective. The projection-optical system receives a patterned beam as reflected from the reticle and forms an image of the pattern on an exposure- sensitive surface of the substrate.

Several types of mirrors are used in EUV optical systems, including glancing-incidence mirrors and multilayer-film mirrors. Glancing-incidence mirrors reflect EUV light incident to the mirror at large incidence angles (e.g., 80 to 90 degrees). At incidence angles less than glancing, no single mirror-making material is known that exhibits satisfactory reflectivity to incident EUV light, so multilayer- film mirrors are used. The multilayer film is a surficial film comprising multiple "layer pairs" each comprising at least a respective layer of a first material and a respective layer of a second material. The layer pairs are formed so that, depthwise, successive layers of the first and second material are in alternating order. The multilayer film produces constructive interference of EUV light reflected at various depths from different layers of the multilayer film. Currently, the greatest reflectivity of EUV light achievable with a multilayer-film mirror is approximately 70%. The choice of first and second materials for forming the layers, their relative thicknesses, and the period length (thickness of a layer pair) are selected based upon the particular wavelength of EUV light to be reflected from the multilayer- film mirror. For example, a wavelength of 13.5 nm is reflected from a multilayer- film mirror of which the first material is molybdenum (Mo) and the second material is silicon (Si).

Fly-eye mirrors used in EUV illumination-optical systems are multilayer- film mirrors, usually used at relatively small angles of incidence, i.e., at angles close to normal incidence. Two fly-eye mirrors are typically used, with the second fly-eye mirror being located downstream of the first. The first fly-eye mirror is arranged to receive substantially collimated light from a collimating mirror located between the EUV source and the first fly-eye mirror. The first fly-eye mirror is conjugate to the reticle, and the second fly-eye mirror is conjugate to the pupil in the projection- optical system.

Conventional fly-eye mirrors used in EUVL systems are segmented mirrors, by which is meant that these mirrors each comprise a respective array of multiple (e.g., several hundred) segments or "elements." The elements are typically stationary. Exemplary first and second fly-eye mirrors for use in an EUV illumination-optical system are shown in FIGS. 2(A) and 2(B), respectively. Each element 112e in the first fly-eye mirror 112 is arc-shaped, and each element 114e in the second fly-eye mirror 114 is substantially rectangular. As shown in FIG. 2(C), the elements 112e of the first fly-eye mirror 112 direct respective rays 116 (respective portions of the illumination beam) to respective elements 114e of the second fly-eye mirror 114. The elements 114e of the second fly-eye mirror 114 reflect their respective rays through an illumination-field mask (e.g., arc-shaped field) to the reticle. The illumination field on the reticle is illuminated substantially uniformly due to the integration of the rays from the fly-eye mirror elements, even if the illumination light produced by the source has an uneven distribution of intensity. See, for example, Komatsuda, "Novel Illumination System for EUVL," Proc. SPIE 3997:765-776, 2000; and U.S. Patent No. 6,195,201 to Koch et al, both incorporated herein by reference. Fabrication of segmented fly-eye mirrors is discussed in Takino et al , "Fabrication of a Fly-Eye Mirror for an Extreme Ultraviolet Lithography Illumination System, Proc. SPIE 4343:576-584, 2001; Takino et al, "Fabrication of a Fly-Eye Mirror for an Extreme Ultraviolet Lithography Illumination System by Arranging Silicon Mirror Elements," Proc. SPIE 4688:648-655, 2002; Takino et al, "Fabrication and Testing of a Complex- Shaped Mirror Constructed with Silicon Mirror Elements," Optical Eng. 46(4):043401-l to 043401-5, April 2007; and Takino et al, "5-Axis Control Ultra- Precision Machining of Complex-Shaped Mirrors for Extreme Ultraviolet Lithography System," CIRP Annals - Manufacturing Technology 56: 123-126, 2007, all incorporated herein by reference to the extent allowed by law.

Certain EUV illumination-optical systems are adjustable to produce EUV illumination light appropriate for different illumination conditions (σ). The illumination condition may change if, for example, a different pattern is to be exposed, compared to a previously exposed pattern. An example illumination condition is the width of the illumination beam of EUV light at the pupil of the projection-optical system. This condition is called the "pupil-fill" condition. The conventional manner of changing pupil-fill in these systems is by using a variable aperture diaphragm, usually located just upstream of the second fly-eye mirror, that blocks a selected range of off-axis EUV light. See FIG. 2(D), showing an aperture diaphragm 118 providing an exemplary opening 120 with respect to the second fly- eye mirror 114. Pupil fill is reduced by stopping down the diaphragm 118, thereby decreasing the diameter of the aperture 120. Stopping-down results in a decreased area of the second fly-eye mirror 114 receiving EUV light passing through the aperture 120, as the diaphragm 118 blocks outlying portions of the illumination beam. Increasing the aperture diameter 120 may result in a beam having greater width than of a beam actually reflectable by the second fly-eye mirror 114.

Adjusting pupil fill using an aperture diaphragm can result in discarding some otherwise useful illumination light because outlying light is blocked (either by the second fly-eye mirror or by the diaphragm) and thus not used for exposure. In these situations, throughput of the lithographic system is compromised. Another problem with this technique is that EUV light blocked by the diaphragm tends to be absorbed by the diaphragm, causing excessive heating of the diaphragm and nearby components. Finally, reducing pupil fill with an aperture diaphragm also reduces the number of fly-eye elements contributing to the homogenization of the incident radiation. Thus, some dose uniformity may be sacrificed.

Methods have been proposed for changing the characteristic of EUV illumination light using adaptive optics. See, for example, U.S. Patent No. 6,803,994 to Margeson and U.S. Patent No. 6,989,922 to Phillips et al. Certain aspects of mirrors with deformable surfaces and actuators for controlling deformation of the surfaces are discussed in Hardy, "Active Optics; A New Technology for the Control of Light," IEEE Proc. 60(6), 1978, and U.S. Patent No. 5,037,184 to Ealey, and an adaptive fly-eye mirror having adjustable (configurable) elements is discussed in U.S. Patent No. 6,977,718 to LaFontaine. Individual segments of the mirror are moved using respective piezoelectric "pushers." However, providing each mirror element with a dedicated pusher may be impractical due to spatial constraints. Also, there is no effective way as yet of monitoring the performance of the adjustable fly-eye mirror.

Summary Shortcomings of conventional technology summarized above are addressed by one or more aspects of the invention disclosed herein.

One aspect is directed to segmented mirrors, of which an embodiment comprises an array of multiple mirror elements and a monitoring device. The mirror elements have respective reflective surfaces and are respectively movable, based on data produced by the monitoring device. The elements reflect respective portions of a beam of utility light incident on the array. The monitoring device is situated relative to the array and includes a source of sensor light and a Shack-Hartmann sensor. The source is situated to direct the sensor light onto at least some of the elements, and the Shack-Hartmann sensor is situated to receive sensor light reflected from the elements. The individual elements create beamlets of reflected sensor light, and the Shack-Hartmann sensor receives the beamlets and converges them to form an array of respective focal spots on a planar detector such as a CCD array. The positions of the focal spots relative to reference data reveal data concerning the optical alignment of the mirror elements. A particularly useful segmented mirror is a segmented fly-eye mirror.

However, the principles described herein can be applied to any of various other configurations of segmented mirrors, including (but not limited to) planar mirrors, convex mirrors, and concave mirrors. The mirrors can be configured for use with any desired wavelength or range of wavelengths of "utility light" {e.g., illumination light used for making lithographic exposures). Example segmented fly-eye mirrors are those used with EUV light as the utility light, such as in an illumination-optical system of an EUV lithography (EUVL) system. The elements of fly-eye mirrors for use with EUV light include a multilayer-film that is reflective to incident EUV light. With fly-eye mirrors (as well as other types of mirrors), the utility light desirably is incident thereon at a different angle of incidence (e.g., lower angle of incidence) than the sensor light. For use as "adaptive" mirrors, the segmented mirrors include respective positioning devices coupled to the elements of the mirror. The positioning devices are operable to change positions and/or orientations of the respective elements to achieve the desired alignment of the elements. The positioning devices can be "active" devices that include respective integral actuators such as, but not limited to, piezoelectric actuators. Alternatively, the positioning devices can be "passive" and rely upon engagement with at least one extraneous actuator that moves into position to engage a positioning device and operate the positioning device to move the respective element.

Certain embodiments of adaptive segmented mirrors comprise an array of movable elements each comprising a respective surface that is reflective to incident utility light. Each such mirror also includes means for directing a beam of sensor light onto the array of elements such that the sensor light illuminates at least a subset of the elements. An example of such means is a source of sensor light and a lens or the like, situated between the source and the segmented mirror, that conditions (e.g., collimates) the beam of sensor light for incidence on at least some of the elements. Each element that receives the sensor light produces a respective beamlet of reflected sensor light. The embodiment also includes means for receiving and individually converging the beamlets of sensor light reflected from the elements and for producing an array of respective focal spots from the received beamlets. The embodiment also includes means for detecting positions of the focal spots and for ascertaining, from the detected positions, respective positions of the respective elements. The means for receiving and converging can comprise an array of lenslets situated between the means for detecting and the array of elements. As the beamlets of reflected sensor light pass through the lenslets, the lenslets converge each beamlet to a respective focal spot. Although some focal spots may overlap others, most of the focal spots tend to have their own respective positions, which facilitates their detection and evaluation. The means for detecting and means for receiving and converging desirably are embodied in a Shack-Hartmann sensor, which typically comprises an array of lenslets and a planar light detector such as a CCD array.

Again, particularly advantageous configurations of such adaptive segmented mirrors are fly-eye mirrors that are reflective to EUV light. These fly-eye mirrors have particular utility in illumination-optical systems of EUVL systems.

Segmented mirrors, as summarized above, that are "adaptive" also comprise means for moving the elements. These means can be configured as positioning devices, at least one per element. The elements can be moved simultaneously (e.g., by simultaneous actuation of all the positioning devices) or in a sequential or other ordered manner, such as serially. The adaptive segmented mirror desirably includes controlling means that receives and evaluates data from the detecting means (e.g., from a Shack-Hartmann sensor). Based on an optics model or other suitable program, the controlling means activates the moving means to change position of one or more elements. These changes of position are achieved by moving and/or tilting the elements, which can be performed simultaneously or in a sequential or other ordered manner. The controlling means can be configured to evaluate data and activate the moving means in real time. In certain embodiments, the mirror elements are arranged in multiple subsets, wherein directing the sensor light, detection of reflected sensor light, and moving respective elements are performed serially from one subset to the next.

According to another aspect, optical integrators are provided. An exemplary optical integrator comprises first and second fly-eye mirrors. The first fly-eye mirror is situated to receive utility light such as, but not limited to, EUV illumination light used for making a lithographic exposure. The second fly-eye mirror is located downstream of the first fly-eye mirror to receive utility light reflected from the first fly-eye mirror. The second fly-eye mirror reflects the utility light further downstream. At least one of the fly-eye mirrors is segmented and comprises an array of multiple reflective elements having respective reflective surfaces and respective positioning devices. The elements reflect respective portions of the utility light. The optical integrator includes a monitoring device that includes a source of sensor light and a Shack-Hartmann sensor. The source is situated to direct the sensor light onto at least some of the mirror elements, and the Shack-Hartmann sensor is situated to receive sensor light reflected from the illuminated elements. In certain embodiments it is desirable that both fly-eye mirrors have these features.

The optical integrator desirably includes a controller connected to the positioning devices and to the Shack-Hartmann sensor. The controller operates under an optics model or other suitable program to impart an attitudinal change to at least one positioning device based on data received by the controller from the Shack-Hartmann sensor.

Other aspects of the invention are directed to, inter alia, catoptric illumination-optical systems comprising one or more segmented mirrors as summarized above, and to EUVL systems comprising same.

Yet another aspect is directed to methods for determining optical performance of a segmented mirror. In an embodiment of such a method a beam of sensor light is directed at multiple elements of a segmented mirror to produce respective beamlets of reflected sensor light. The beamlets are converged as respective focal points onto a two-dimensional sensor array. Relative positions of the focal spots are determined, wherein the positions correspond to a parameter of optical performance of the mirror. The steps of converging and determining desirably are performed using a Shack-Hartmann sensor, which includes both an array of lenslets for converging and a CCD array for detecting. Methods are also provided for controlling optical performance of a segmented mirror. A beam of sensor light is directed at multiple elements of the segmented mirror to produce respective beamlets of reflected sensor light. The beamlets are converged as respective focal spots onto a two-dimensional sensor array. The respective positions of the focal spots are determined, wherein the positions correspond to a parameter of optical performance of the mirror. Based on the determined positions of the focal spots, respective positions of the elements are controlled and changed as necessary. An example optical characteristic is a desired pupil-fill condition. Various embodiments providing ways to change the pupil-fill condition obviate the conventional use of a diaphragm aperture for this purpose. It is noted that the step of directing the beam of sensor light can be performed by "distributed illumination" of selected groups of elements at different respective times. Other features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

Brief Description of the Drawings

FIG. l(A) is a schematic diagram of a first example illumination-optical system for an EUV lithography (EUVL) system.

FIG. l(B) is a schematic diagram of a second example illumination-optical system for an EUVL system. FIG. l(C) is a schematic diagram of a third example illumination-optical system for an EUVL system.

FIG. 2(A) is a plan view of a first fly-eye mirror for use in an EUV illumination-optical system.

FIG. 2(B) is a plan view of a second fly-eye mirror for use in an EUV illumination-optical system.

FIG. 2(C) shows the manner in which individual elements of the first fly-eye mirror direct respective rays (respective portions of the illumination beam) to respective elements of the second fly-eye mirror.

FIG. 2(D) is a plan view of the second fly-eye mirror and an aperture diaphragm providing an exemplary opening with respect to the second fly-eye mirror.

FIG. 3 is a schematic drawing showing a general situation of the first and second fly-eye mirrors in a representative embodiment of an illumination-optical system, including monitors for each of the fly-eye mirrors. FIG. 4 is an elevational section of one element of a fly-eye mirror according to an embodiment, the element including a positioning device that, when activated appropriately, moves the element in the z, θ_x, and θ_y directions.

FIG. 5 depicts five elements similar to that shown in FIG. 4, each including a respective positioning device. Also shown are the source, lens, and sensor for monitoring the elements, as well as a movable screw-actuator module engaged with the screws of one of the positioning devices to move the respective element. FIG. 6 shows example ray traces from an array of mirror elements through the lenslet array and onto a single CCD detector of a downstream Shack-Hartmann sensor.

FIG. 7 is similar to FIG. 6, except that FIG. 7 shows an alternative embodiment in which two CCD detectors, rather than one as in FIG. 6, are used in the Shack-Hartmann sensor.

FIG. 8 is similar to FIG. 6, except that FIG.8 shows an alternative embodiment in which two illuminator beams, rather than one as in FIG. 6, are used in the Shack-Hartmann sensor. FIG. 9(A) depicts an exemplary distributed illumination conducted on arcuate elements of the first fly-eye mirror, wherein every fourth element is illuminated at any instant in time.

FIG. 9(B) depicts an exemplary distributed illumination conducted on arcuate elements of the first fly-eye mirror, wherein every eighth element is illuminated at any instant in time.

FIG. 10 depicts an exemplary distributed illumination conducted on rectangular elements of the second fly-eye mirror, wherein every fourth element is illuminated at any instant in time.

FIG. 11 is an embodiment of an "open-loop" control scheme for monitoring the elements of a fly-eye mirror.

FIG. 12 is an elevational view of an embodiment of an element of a fly-eye mirror including an integral positioning device for the element.

FIG. 13 is an elevational view of a portion of an embodiment of a fly-eye mirror including multiple elements, configured as shown in FIG. 12, each having a respective integral positioning device. Also shown is the sensor used for monitoring the elements.

FIG. 14 is a schematic diagram of an embodiment of an EUVL system comprising monitored segmented fly-eye mirrors as described herein.

FIG. 15 is a flow-chart of an embodiment of a method for manufacturing semiconductor devices, as exemplary microdevices.

FIG. 16 is a flow-chart of an embodiment of a lithographic method performed using the system of FIG. 14. FIG. 17 is a flow-chart of an embodiment of a lithographic method, performed using the system of FIG. 14, for manufacturing liquid-crystal-display devices, as exemplary microdevices.

Detailed Description

The invention is described below in the context of representative embodiments that are not intended to be limiting in any way.

General Considerations These general considerations apply generally to all embodiments.

In the following description, certain terms may be used such as "up," "down," "upper," "lower," "horizontal," "vertical," "left," "right," and the like. These terms are used, where applicable, to provide some clarity of description when dealing with relative relationships. But, these terms are not intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an "upper" surface can become a "lower" surface simply by turning the object over. Nevertheless, it is still the same object.

An example illumination-optical system 33 for an EUVL system is shown in FIG. l(A). The system includes an EUV source 31. For EUV micro lithography, the source 31 is usually a "point source" that generates an EUV-producing plasma from laser irradiation of or electrical discharge involving a target material. The depicted rays denote the illumination beam 32 produced by the source 31. The depicted system includes a collector mirror 30, a collimator mirror 34, a first fly-eye mirror 35 a, and a second fly-eye mirror 35b. The fly-eye mirrors 35 a, 35b constitute a fly- eye mirror group 35. The collector mirror 30 collects divergent EUV radiation from the source, especially if the source is a point source. The collimator mirror 34 converts the illumination beam 32 to a substantially parallel bundle of rays for delivery to the first fly-eye mirror 35a. In this particular system the second fly-eye mirror 35b gently converges the illumination beam 32. The illumination beam 32 from the second fly-eye mirror 35b is condensed onto the surface of a reticle, mask, or other pattern-defining device (generally called a "reticle" M herein). The reticle

M is mounted on a reticle stage 38. A turning mirror 36 between the second fly-eye mirror 35b and the reticle M directs the illumination beam 32 for incidence on the reticle at a low angle of incidence. Patterned light 39 reflected from the reticle M propagates to a downstream projection system (not shown).

Another illumination-optical system 40 for an EUVL system is shown in FIG. l(B). The system 40 is similar to that shown in FIG. l(A), but also includes a condenser mirror 42 located downstream of the second fly-eye mirror 44b. The illumination beam 46 propagating from the second fly-eye mirror 44b to the condenser mirror 42 is substantially parallel, wherein the condenser mirror rather than the second fly-eye mirror converges the beam. The illumination beam 46 from the condenser mirror 42 is condensed onto the surface of the reticle R. A turning mirror 48 between the condenser mirror 42 and the reticle R directs the illumination beam 46 for incidence on the reticle at a low angle of incidence. Also shown are a first fly-eye mirror 44a (in a fly-eye group 44 with the second fly-eye mirror 44b). Upstream of the first fly-eye mirror 44a is a collimating mirror 50 that receives illumination light 46 from a source 52 comprising a collector mirror 54. The collector mirror 54 collects EUV light produced at a point source 56 at which a beam produced by a laser 57 and condensed by a lens 58 impinges on a target material delivered by a conduit 60. Downstream of the reticle R is a projection- optical system 62 that conditions and directs patterned light 65 from the reticle to a wafer or other lithographic substrate 64.

Yet another illumination-optical system 80 is depicted in FIG. l(C), also depicting a source 82, a reticle M, a projection-optical system PL, and a wafer W or other lithographic substrate. The source 82 is a point source comprising a collector mirror 84 that collects EUV light produced at a point source 86 at which a beam produced by a laser 87 and condensed by a lens 88 impinges on a target material delivered by a conduit 90. Downstream of the collector mirror 84 is a collimating mirror 92 and a fly-eye group 94 comprising a first fly-eye mirror 94a and second fly-eye mirror 94b. These mirrors receive and reflect EUV illumination light 96 from the source 82. The second fly-eye mirror 94b imparts a slight convergence to illumination light 96 reflected therefrom to a convex mirror 98. Downstream of the convex mirror 98 is a concave mirror 100 and glancing-incidence planar mirror 102 that converge the illumination light 96 onto the surface of the reticle M. EUV illumination-optical systems as exemplified by FIGS. 1(A)-I(C) can benefit from appropriate changes being made to the pupil-fill condition to satisfy particular illumination circumstances. Fortunately, the pupil-fill condition only needs to be changed occasionally, such as during initial setup of the EUVL system, when changing the pattern, when preparing the system for use with a different-sized reticle, and/or when projecting images onto a different- sized die on the lithographic substrate than previously.

As discussed, the illumination-optical systems in FIGS. 1(A)-I(C) comprise first and second fly-eye mirrors. The first fly-eye mirror is located conjugate to the reticle plane, and the second fly-eye mirror is located conjugate to a pupil plane located in the projection-optical system. Exemplary first and second fly-eye mirrors 112, 114 are shown in FIGS. 2(A) and 2(B), respectively. The fly-eye mirrors 112, 114 need not be the same size. For example, the second fly-eye mirror 114 can be larger than the first fly-eye mirror 112.

Representative Embodiments

In these embodiments, an EUV illumination-optical system comprises first and second fly-eye mirrors as generally described above. Both fly-eye mirrors are segmented, each comprising multiple (e.g., several hundred) elements. At least some of the elements are individually movable or adjustable with respect to at least tip and tilt (θ_x and θ_y motions) and possibly other motions such as Z-direction motion. Both fly-eye mirrors are adaptive in these embodiments, being capable of providing variable pupil-fill conditions without having to aperture part of the illumination beam. This results in more energy of the illumination beam being used for making lithographic exposures, which improves lithographic throughput.

A general situation drawing of the first and second fly-eye mirrors is shown in FIG. 3, in which the first and second fly-eye mirrors 150a, 150b, respectively, have multiple elements that are individually adjustable. Substantially collimated rays 152 of EUV light (as an example "utility light"), propagating from an upstream collimated source or collimating mirror (not shown) are incident on the first fly-eye mirror 150a, which reflects respective rays of EUV light 154 from its elements. The rays 154 propagate to respective elements of the second fly-eye mirror 150b, which reflect the rays (see FIG. 2(C)). The rays 156 of EUV light reflected from the second fly-eye mirror 150b propagate to the reticle (not shown). The EUV light 152, 154 is incident on the fly-eye mirrors 150a, 150b at low angles of incidence.

In this embodiment, the fly-eye mirrors 150a, 150b have associated monitoring systems 158a, 158b that monitor tilt and tip (and other changes in position) of the respective segments of the mirrors. (In an alternative configuration, only one of the fly-eye mirrors has a monitoring system while the other fly-eye mirror does not, in which configuration the monitoring system can be associated with either of the mirrors.) Each monitoring system 158a, 158b includes a source 160a, 160b of "sensor light," a lens 162a, 162b (or other collimating element), and a sensor 164a, 164b, respectively. The sources 160a, 160b produce respective beams of sensor light 166a, 166b that are incident on the respective fly-eye mirrors 150a, 150b, preferably at higher angles of incidence than the EUV light 152, 154. Thus, the sensor light 166a, 166b does not disrupt the functions of the fly-eye mirrors 150a, 150b with respect to the "utility light" (EUV illumination light). The lenses 162a, 162b desirably are collimating lenses. The sensor light 166a, 166b reflects from the elements of the respective fly-eye mirrors 150a, 150b and propagates to the respective sensors 164a, 164b.

The sensor light desirably has a wavelength that corresponds to a high reflectivity of the light from the multilayer film covering the elements. The wavelength can generally be selected from the range of approximately 248 nm to 1000 nm. Useful factors to consider when selecting a wavelength include the following: reflectivity from the multilayer film and sensitivity of the imaging sensor to that wavelength of sensor light. As noted, the angle of incidence of sensor light desirably is greater than the angle of incidence of EUV light on the fly-eye mirror. An exemplary range for the angle of incidence of the sensor light on the fly-eye mirror is 5° to 30°.

Each sensor 164a, 164b desirably is a Shack-Hartmann sensor but alternatively can be a tilt/tip sensor or other suitable sensor. A Shack-Hartmann sensor comprises an array of lenslets and a CCD array (or analogous detector array) located downstream of the lenslets. To obtain this lenslet function, the lenslets must be refractive to the wavelength of sensor light; this is a factor affecting the selection of sensor- light wavelength. The lenslet array provides a corresponding array of sub- apertures that break up an incident wavefront into a respective number of raylets. Each lenslet converges its respective raylet on a respective focal "spot" on the CCD array. Each lenslet has an associated region on the CCD in which its respective focal spot can be located, depending upon the slope of the respective portion of the wavefront (relative to a plane parallel to the CCD array) entering the lenslet. The CCD array is connected to electronics that record the focal-spot positions and compare the recorded positions against a reference. The resulting determinations of respective local wavefront slope for all the lenslets are integrated to produce a map of the wavefront surface entering the Shack-Hartmann sensor from the segmented fly-eye mirror.

In other words, if the raylets are produced by a substantially aberration- free, planar wavefront entering the Shaft-Hartmann sensor, they are incident on the CCD array in their reference or calibrated focal-spot positions. Raylets produced by a respective aberrated portions of the wavefront are not incident on the CCD array in their reference focal-spot positions. The degrees and directions of focal-spot displacement provide measurements of the aberrated wavefront of incoming utility light, compared to an aberration-free wavefront. Since the Shack-Hartmann sensor provides data for all its detected focal spots simultaneously, all the data needed to map the wavefront can be obtained in a single frame of the CCD array. Also, modern CCD arrays and associated electronics allow sampling and detecting of sensor light to be performed very quickly.

Although Shack-Hartmann sensors are conventionally used for obtaining measurements of aberrated wavefronts of light, their use for monitoring adaptive optics, especially a segmented mirror, is believed to be novel.

In this embodiment, the fly-eye mirrors are segmented, and the elements thereof are individually movable. Exemplary specifications for numbers of elements and their degrees of tip/tilt are as follows ("FEl" denotes the first, or upstream, fly- eye mirror, and "FE2" denotes the second, or downstream, fly-eye mirror):

FEl : number of elements: 200 (arcuate) tip/tilt: ±5° (tolerance ±2') FE2: number of elements: >200 (rectangular) tip/tilt: ±5° (tolerance ±25")

It is assumed that any wavefront aberration associated with the mirror elements are known and can be corrected for, or are small compared to the angular tolerances stated above.

For moving the individual segments, respective positioning devices are used. The positioning devices can have integral actuators or rely upon extraneous actuators being brought into engagement with the positioning devices. The positioning devices of a particular fly-eye mirror need not all have the same configurations.

An embodiment of a positioning device 180 capable of moving a respective element 182 in the z, θ_x, and θ_y directions is shown in FIG. 4. The element 182 includes a multilayer film 184 and metal layers 186a, 186b. The multilayer film 184 provides reflectivity to incident EUV radiation. The metal layers 186a, 186b provide a substrate for the multilayer film 184. The under- surface 188 of the element 182 is in thermal contact with the positioning device 180. The positioning device 180 comprises a thermal conductor 190, a cooling plate 192 (or analogous base member), and adjustment screws 194 situated at the corners of the cooling plate 192. The thermal conductor 190 contacts the under-surface 188 of the element 182 and conducts heat from the under-surface and thus from the element. The thermal conductor 190 can be, for example, a heat pipe, a volume of thermally conductive liquid, an array of weak, thermally conductive springs, or other suitable configuration providing a combination of thermal conductivity and compliance. The thermal conductor's compliance allows the thermal conductor 190 to accommodate motions (e.g., z, θ_x, and/or θ_y motions, relative to the cooling plate 192) imparted to the element 182 by the positioning device 180, while maintaining full contact with the under-surface 188 and cooling plate 192. In this embodiment the cooling plate 192 includes a conduit 196 for passage of a liquid coolant for maintaining a desired temperature of the cooling plate as the cooling plate absorbs heat from the thermal conductor 190. Surrounding the thermal conductor 190 is a bellows 198 or analogous component for achieving a vacuum seal. If the thermal conductor 190 is a liquid, an axially compliant wall 200 can be situated between the thermal conductor and the bellows 198 to contain the liquid. For example, the axially compliant wall 200 can be a second bellows distinct from the bellows 198.

The screws 194 extend along their respective longitudinal axes from the cooling plate 192 to the under- surface of the element 182. The screws 194 desirably are tipped with respective springs 202 to provide compliance between the screws and the element 182. The screws 194 are used for moving the element 182 relative to the cooling plate 192. Appropriate turnings of the screws 194 about their longitudinal axes yield corresponding adjustments in position and/or attitude (e.g., z, θ_x, and θ_y motions) of the element 182 relative to the cooling plate 192. For example, turning all the screws 194 an equal amount moves the segment 182 in the z-direction. Certain differential turnings of the screws 194 produce θ_x and θ_y motions of the element 182. Normally, these motions are very slight. These turnings of the screws are made by a screw-actuator module (discussed below), which is configured and operated essentially as a robotic screw-driver.

In an alternative configuration, not shown, the screws 194 are replaced with respective shafts that are displaceable in their respective longitudinal axial directions to produce corresponding adjustments of position and/or attitude of the element 182. The shafts can be displaceable using, for example, piezoelectric pushers or other, analogous actuators. Each shaft can have an associated locking device engaged therewith to maintain the positions of the shafts without having to maintain continuous energization of the actuators. See, e.g., columns 8-12 and associated drawings in U.S. Patent No. 6,989,922 to Phillips et ah, incorporated herein by reference.

The cooling plate 192 provides a thermal mass for receiving heat conducted from the element 182 via the thermal conductor 190. Thus, the temperature of the element 182 is maintained substantially constant at a desired level during use. Turning now to FIG. 5, five representative elements 182 are shown with their respective positioning devices 180. Also shown are the source sensor-lightlβO, lens

162, and sensor 164 for monitoring the elements 182. (Optics, not shown, can be situated between the elements 182 and the sensor 164, if desired, to facilitate placement of the sensor relative to the elements, for example.) The figure also depicts a screw-actuator module 210 engaged with the screws 194 of one of the positioning devices 180. The number of screw-actuator modules 210 used with the adjustable elements 182 of a fly-eye mirror 112, 114 can be as few as one per mirror (and used for adjusting the mirror's actuator devices 180 individually, one-by-one) or as many as at least one per element 182 (that can be used individually or simultaneously). The screw-actuator module 210 engaging a positioning device 180 turns at least one respective screw 194 as appropriate for achieving the desired motion of the element 182. Unless a respective screw-actuator module 210 is provided for each positioning device 180 of the fly-eye mirror, at least some of the screw-actuator modules are mobile from one element 182 to another of the mirror. In the figure, the screw-actuator module 210 is engaged with the middle positioning device 180. After adjusting the screw(s) 194 of the middle positioning device 180, the screw-actuator module 210 moves or is moved into engagement with another (e.g., the next) positioning device requiring adjustment.

Appropriate adjustments of the respective elements 182 of the fly-eye mirrors 112, 114 configure the fly-eye mirrors, and thus the illumination-optical system, for achieving a desired pupil-fill or other optical performance characteristic. The elements 182 of each fly-eye mirror need not be adjusted exactly the same way to achieve this result.

At least during the making of the adjustments, the sensors 164 provide realtime monitoring of the fly-eye mirrors 112, 114 themselves, including during actual use of the fly-eye mirrors with utility light such as exposure light. In view of the large angular range over which the elements 182 can be adjusted, a beam 166 of sensor light reflected from a particular element and entering the sensor 164 can be directed over multiple lenslets of the sensor rather than being confined substantially to the field of only one lenslet of the sensor as in conventional uses of Shack- Hartmann sensors. However, the beamlet may illuminate several adjacent lenslets simultaneously because of its size. The intensities of the beamlets may vary with the respective angles of the mirror elements 182 from which the beamlets are produced, and considerable overlap may exist from nearby beamlets. Beamlets can even change their relative ordering at the CCD detector of the Shack-Hartmann sensor.

These phenomena are shown in FIG. 6, in which multiple representative mirror elements 182 are arrayed vertically on the left, and the right-hand portion of the figure shows a corresponding portion of a Shack-Hartmann sensor 164. The sensor 164 includes a vertical array 230 of lenslets and a CCD detector 232 (or other image sensor). The lenslets 230 and CCD detector 232 are respective parallel planes. In various embodiments the relatively large angular range of tilt of an element 182 can sweep its respective beamlet over multiple lenslets of the sensor 164. Also, there can be substantial overlap from adjacent or nearby beamlets, and beamlets can switch their order at the CCD array. For example, in the figure, the second and third elements 182b, 182c from the top direct their respective beamlets to the same two lenslets 230a, 230b that produce substantial superposition of raylet focal spots 234a, 234b, 234c on the CCD array 232. A similar phenomenon occurs with the second, third, and fourth elements 182i, 182h, 182g from the bottom, which produce substantial superposition of raylet focal spots on the CCD array 232. Note also the fourth and fifth elements 182d, 182e from the top produce respective beamlets that overlap before being incident on the lenslets.

In FIG. 7, relay optics, if any, between the elements 182 and sensor 164 are not shown, for clarity. If, for example, a demagnifying relay-optical system were present in such a location (to fit all the mirror-element images on one CCD array), the ranges of mirror-element angles would be larger than shown.

Normally, the elements of a fly-eye mirror have curved reflective surfaces (e.g., each surface is a respective portion of a sphere). The degree of curvature of the elements dictates the focal lengths of the fly-eye mirrors and thus establishes the location of respective image planes of the mirrors. If the focal length is of appropriate magnitude, it may be possible to use the CCD array of the sensor 164 without having to use an upstream array of lenslets, in which event focal spots are produced without having to use a lenslet array. Normally, one CCD array is adequate. For example, for a fly-eye mirror having a 10^χ20 array of elements (total = 200 elements), and assuming no overlap, a total of 2Ox 144 = 2880 CCD pixels would be required. This is based on the specifications for the first and second fly-eye mirrors provided above and on the following: Assuming the dynamic range for elements of the first fly-eye mirror is 1440 and the dynamic range for elements of the second fly-eye mirror is 300, then the number of pixels needed per element of the first fly-eye mirror is 144, and the number of pixels needed per element of the second fly-eye mirror is 30. Modern CCD arrays have pixel arrays of greater than 10^3χ10³, which would cover all the mirror elements without difficulty.

Alternatively, multiple CCD arrays can be used. Use of multiple CCD arrays is shown in FIG. 7, depicting ten elements 182 and a lenslet array 230 as in FIG. 6. The beamlets from the lenslets propagate to a first CCD array (CCDl, 232a) and/or to a second CCD array (CCD2, 232b).

Further alternatively, instead of a single beam 166 (FIG. 5) of sensor light, multiple beams of sensor light (produced by respective sources 160) can be used to scan different respective subsets of the mirror elements into a single CCD array. An example is shown in FIG. 8, in which are shown the lenslet array 230 and CCD array. Sensor light ("illuminator 1" and "illuminator 2") from two sources is used. In the group 236a are the mirror elements collected with illuminator 1, and in the group 236b are the mirror elements collected with illuminator 2. Beamlets from both groups of elements propagate to the lenslets 230 and CCD array 232. Compared to conventional uses of Shack-Hartmann sensors, in this and other embodiments the displacement of focal spots on the CCD detector is potentially much greater, with possible extensive overlap and switching of order of the respective focal spots relative to the order of elements for sensing purposes. This can cause confusion in tracking the positions of individual mirror elements to clearly identify the particular focal spot(s) being produced by a particular element. One way to prevent confusion is to adjust a fraction of the mirror elements at a time, spread out over the array of elements. This technique can include dithering the adjusted mirror elements. Another way in which to prevent confusion is to illuminate a fraction of the mirror elements at a time, spread out over the array of elements. This latter method is termed "distributed illumination."

FIGS. 9(A) and 9(B) depict exemplary distributed illuminations conducted on the arcuate elements of the first fly-eye mirror. In FIG. 9(A) four illumination steps are conducted to illuminate all the elements. In each illumination step, a respective one-fourth of the elements are illuminated. The illuminated elements desirably are spaced apart from one another to reduce the probability of raylet overlap at the CCD array. In the figure, the illuminated element in each group of four elements is depicted as shaded for clarity, wherein at the instant of time shown in the figure, the elements denoted "1" are illuminated. In the next illumination step, the elements denoted "2" are illuminated, and so on. FIG. 9(B) depicts a distributed illumination cycle involving eight illumination steps.

FIG. 10 depicts an exemplary distributed illumination conducted on the rectangular elements of the second fly-eye mirror. Four illumination steps are conducted to illuminate all the elements. In each illumination step, a respective one- fourth of the elements are illuminated. In the figure, the illuminated element in each group of four elements is depicted as shaded for clarity, wherein at the instant of time shown in the figure, the elements denoted " 1 " are illuminated. In the next illumination step, the elements denoted "2" are illuminated, and so on.

In the various distributed illumination schemes, any of various approaches can be used for selectively illuminating the desired elements at each respective moment in time. One approach is to use a mask interposed between the source 160 and the mirror surface, wherein the mask defines apertures of defined shape and spacing from one another to correspond with the particular elements to be illuminated. A different mask can be used during each illumination step or the same mask can be positionally shifted between each illumination step to allow illumination of a different group of elements. Another approach is to use a smaller illumination beam 166 and scan the beam over the desired elements. Yet another approach is to dither only the elements actually being illuminated.

FIG. 11 shows an exemplary open-loop control diagram for various embodiments utilizing a Shack-Hartmann sensor. Shown is a fly-eye mirror 250 on which EUV utility light is incident at a low angle of incidence. EUV light reflected from the elements of the fly-eye mirror 250 propagates to an optical system 252, to a pupil plane 254, and then used for making a lithographic exposure. Included in the optical system 252 are the other components of the reticle illumination system, the reticle, and the projection optics. Also shown are the source 256 of utility light and the Shack-Hartmann sensor 258. Data from the Shack-Hartmann sensor 258 are routed to a controller 260 programmed with a desired optics model 262. The controller 260 is connected to the actuators 264 that move the elements of the fly- eye mirror 250. This control scheme is open-loop, compared to conventional closed-loop control schemes. In this scheme shown in FIG. 11 the actual wavefront at the pupil plane 254 is not what is being monitored by the Shack-Hartmann sensor. Rather, the elements of the fly-eye mirror 250 itself are being monitored by the Shack-Hartmann sensor 258, and the results are used for controlling the actuators 264.

Second Embodiment

This embodiment shares many of the features of the first embodiment, but each of the respective elements of the fly-eye mirror(s) being monitored has a respective at least one integral positioning device, thereby minimizing or eliminating the need for a screw-actuator module or the like. An example embodiment of a segment 280 is shown in FIG. 12, which depicts one element 282. For reflectivity to EUV utility light, the element 282 includes a multilayer film 284 and metal layers 286a, 286b. The under-surface 288 of the element 282 is in thermal contact with a thermal conductor 390, which in turn is in thermal contact with a cooling plate 292 or analogous base. The cooling plate 292 includes a coolant conduit 296. These components are similar to corresponding components shown in FIG. 4. Extending from the cooling plate 292 to the under-surface 288 is at least one actuator 294, such as a piezoelectric actuator. Desirably, each element 282 has multiple actuators (e.g., three) for producing motions of the element 282 in the z, θ_x, and θ_y directions relative to the cooling plate 292. The actuators 294 include at least one flexure 302 coupling them to the under-surface 288. Flexures 303 also can be used for coupling the actuators 294 to the cooling plate 292. The flexures 302, 303 are provided and arranged to achieve desired degree(s) of constraint of the elements combined with desired degree(s) of freedom of motion of the elements relative to the cooling plate 292.

Referring now to FIG. 13, multiple segments 280, as shown in FIG. 12, are shown. Each segment includes a respective element 282 mounted to the cooling plate 292 or other rigid substrate by multiple actuators 294 and respective flexures 302, 303. The actuators 294 are connected to a controller 310 operating under the commands of an optical model 321. The controller 310 is connected to receive data from a Shack-Hartmann sensor 314 that receives sensor light produced by a source 316, collimated by a lens 318, and reflected from the elements 282. Note the relatively large angle of incidence of the sensor light 320 and relatively low angle of incidence of the EUV utility light 322.

Although many of the embodiments described herein concern a first fly-eye mirror having arc-shaped elements and a second fly-eye mirror having rectangular elements, this is not intended to be limiting. The elements of the fly-eye mirrors alternatively can have any of various other suitable shapes such as, but not limited to, polygonal, round, elliptical, and slit-like. Also, the elements need not have curved reflective surfaces (they can be planar, for example), and need not have only spherically curved surfaces (they can have aspherically curved surfaces). Although the optical systems described above have adaptive fly-eye mirrors that are monitored, this is not intended to be limiting. In other embodiments the monitored adaptive mirror(s) is an adaptive planar mirror, condensing mirror, collimating mirror, expanding mirror, or the like. Also, the range of embodiments is not limited to optical systems having two fly-eye mirrors or other segmented mirrors; the subject optical systems can have more than two segmented mirrors or as few as one segmented mirror, wherein at least one of the segmented mirrors is monitored.

Although the embodiments described above are in the context of reflective optical systems comprising pairs of adaptive fly-eye mirrors, each pair comprising an upstream fly-eye mirror and a downstream fly-eye mirror, this is not intended to be limiting. The reflective optical systems can include optical systems in which only one adaptive mirror is used, and are not limited to illumination-optical systems. Also, the range of embodiments is not limited to systems comprising adaptive fly- eye mirrors. Alternative embodiments include adaptive mirrors other than fly-eye mirrors.

From the foregoing, the following differences of the subject embodiments from conventional adaptive optics are manifest: (1) each sensor monitors the respective adaptive mirror itself (situated inside an optical system), rather than monitoring an aberrated wave-front (exiting an optical system) as in conventional systems; (2) the slopes of wave-fronts entering the sensor can be large and discontinuous, rather than being only small and continuous as in conventional systems; (3) beamlet overlaps in the sensor are common rather than rare as in conventional systems; and (4) the adaptive mirror is adjusted only occasionally, rather than continuously as in conventional systems.

An embodiment of an EUV micro lithography system 400 incorporating fly- eye mirrors as described herein is shown in FIG. 14. In the figure and following description, an XYZ orthogonal coordinate system is used, and the positional relationships of components are described with reference to the XYZ orthogonal coordinate system. The XYZ orthogonal coordinate system is arranged such that the X-axis and the Y-axis are in a plane parallel to a wafer P (sensitive lithographic substrate), and the Z-axis is orthogonal to the X-Y plane (and thus orthogonal to the wafer P). In the figure the XYZ orthogonal coordinate system is arranged such that the X-Y plane is parallel to a horizontal plane, and the Z-axis is in the vertical direction. In this embodiment, the scanning-motion direction of the wafer P is the X-direction.

The microlithography system 400 includes an EUV light source 402 that emits EUV illumination light 404. The illumination light 404 is produced by irradiation of a target material (supplied by a conduit 406 into the source 402) by a laser beam 408 produced by a laser 410. The laser beam 408 is converged on the target material by a lens 412. The laser 410 is connected to a controller 422. By thus controlling the operation of the laser 410, the light intensity of the illumination light 404 emitted from the EUV light source 402 may be varied. Note that the EUV light source 402 is contained in a chamber 418.

The illumination light 404 is collected by a mirror 414, which directs the illumination light to a collimating mirror 416. The collimating mirror 416 directs the illumination light 404 to an optical integrator comprising a first (entrance) fly- eye mirror IR₁ and a second (exit) fly-eye mirror IR₂. The incident surface of the entrance fly-eye mirror IR₁ is located at a position that is optically conjugate to the surface of the reticle M and to the surface of the wafer P (or at least conjugate to respective locations in the vicinity of these surfaces). The illumination light 404 reflected from the entrance fly-eye mirror IR₁ has a divided wavefront as a result of reflection from the multiple elements of the entrance fly-eye mirror IR₁. The illumination light 404 incident on the entrance fly-eye mirror IR₁ is reflected thereby to the exit fly-eye mirror IR₂. The incidence surface of the exit fly-eye mirror IR₂ is optically conjugate to the pupil of the projection-optical system PL, described below (or at least conjugate to a location in the vicinity of the pupil).

The fly-eye mirrors IR₁, IR₂ are segmented as described above. At least one of the fly-eye mirrors comprises a sensor assembly as described above for monitoring the elements of the mirror. The respective portions of the illumination light 404 reflected by the elements of the entrance fly-eye mirror IR₁ are incident to respective elements of the exit fly-eye mirror IR₂. Accordingly, multiple light- convergence points are produced at the irradiation side of the exit fly-eye mirror IR₂, or in the vicinity thereof, according to the number of elemental mirrors of the exit fly-eye mirror IR₂. The convergence points collectively serve as a secondary light source. The second fly-eye mirror IR₂ directs the EUV light to a condensing mirror IR₃, from which the light is directed by a bending mirror IR₄ to the reflective reticle M. At least the mirrors IR₁-IR₄ constitute the illumination-optical system IL of EUVL system 400. Although not shown, just upstream of the reticle M is a field- stop that defines an arcuate slit-like opening. Light passing through the arcuate opening forms a correspondingly arcuate illuminated area on the reticle M. The reticle M defines a pattern and is mounted on a movable reticle stage 420. The reticle stage 420 comprises actuators and position sensors that are connected to a controller 422. The reticle stage 420 desirably is movable in the X-axis, Y-axis, and Z-axis directions as well as rotatable in the θ_x, θ_y, θ_z directions.

As illumination light reflects from the reticle M, the light becomes patterned by the corresponding pattern in the illuminated region of the reticle. This patterned EUV light EL is shaped by the projection-optical system PL to form an image of the pattern on the sensitive surface of the wafer P. The projection-optical system PL comprises multiple mirrors PR₁, PR₂, PR₃, PR₄. (The depicted projection-optical system PL in this embodiment has four mirrors; other embodiments have projection- optical systems with fewer or more mirrors (e.g., two or six). The wafer P is held on a movable substrate stage 426. The substrate stage 426 comprises actuators and position sensors that are connected to the controller 422. The substrate stage 426 holds the wafer P for exposure, and desirably is movable in the X-axis, Y-axis, and Z-axis directions as well as rotatable in the θ_x, θ_y, θ_z directions. The substrate stage 426 is situated in a chamber 424 that is situated in a larger vacuum chamber VC that houses the projection-optical system PL, the illumination-optical system IL, and the reticle stage 420. Also situated in the vacuum chamber VC is the chamber 418.

The position-measuring devices of the reticle stage 420 and substrate stage 426 typically comprise interferometers (not detailed). The interferometers output their position-measurement data to the controller 422. The controller 422 outputs respective driving signals to the reticle stage 420 and substrate stage 424. Actuators, such as linear motors or pneumatic actuators, move the reticle stage 420 and the substrate stage 424, based on the driving signals output from the controller 422. The EUVL system described above uses EUV light as the exposure light.

This is not intended to be limiting, especially because fly-eye mirrors are not limited strictly to EUVL systems. Systems comprising at least one monitored, segmented fly-eye mirror as described herein encompass systems usable with any of various wavelengths, including wavelengths outside the EUV range. For example, exposure light can be laser light produced by a KrF excimer laser, an ArF excimer laser, or an F₂ laser.

Although the embodiments were described above in the context of mirrors and mirror elements being planar, spherically concave, or spherically convex, it will be understood that, for example, a segmented mirror may have aspherical segments and/or at least one mirror of an optical system may have an aspherical surface. Furthermore, the mirrors in an optical system need all be concave or all convex. Alternatively, an optical system may have both types of mirrors and/or at least one planar mirror.

Although the embodiments were described above in the context of adaptive fly-eye mirrors having adjustable segments, this is not intended to be limiting. A subject mirror having adjustable segments that are monitored need not be a fly-eye mirror. Rather, the segmented mirror can have any of various functions, including functions not of a fly-eye mirror.

Semiconductor devices and other micro-devices can be fabricated using a system as described above, using a process shown generally in FIG. 15. In step 501 the function and performance characteristics of the micro-device are established and designed. In step 502 a mask (reticle) defining a pattern is created according to the previous design step 501. In a parallel step 503 a substrate (e.g., semiconductor wafer) is manufactured from an appropriate material (e.g., silicon). In step 504 (substrate processing) the reticle pattern created in step 502 is exposed onto the substrate from step 503 using an EUVL system such as one of the systems described above. In step 505 the semiconductor device is assembled by executing a dicing step, a bonding step, and a packaging step, for example. The completed device is inspected in step 506.

FIG. 16 depicts a flow-chart of an exemplary method for manufacturing semiconductor devices (as exemplary microdevices). The method includes forming a prescribed circuit pattern on a wafer or similar as a photosensitive substrate using an exposure apparatus such as the embodiment described above. In step S301 a metal film is applied (e.g., by vacuum-evaporation) to a lot of wafers. In step S302 a photoresist is deposited onto the metal film on the lot of wafers. In step S303 an exposure system (such as the EUVL embodiment described above) is used to perform lithographic exposures, by which images of the pattern defined on the mask are formed successively in each shot area of the lot of wafers, using the projection- optical system. After developing the photoresist on the lot of wafers in step S304, the lot of wafers is etched (step S305), using the photoresist pattern as a mask, so that a circuit pattern corresponding to the mask pattern is formed in each shot area on each wafer.

The EUVL system described above also can be used for printing a prescribed pattern (circuit pattern, electrode pattern, or the like) on a plate (e.g., glass substrate) so as to imprint a layer of a liquid-crystal-display device (a type of microdevice). An example of such a method is depicted in the flow-chart of FIG. 17. In FIG. 17 a lithography process is performed in the pattern-formation step S401, in which the pattern of a mask is transferred (exposed) onto a photosensitive substrate (glass substrate or the like onto which a photoresist has been deposited) using the exposure apparatus. Thus, a prescribed pattern containing numerous electrodes or the like is formed on the photosensitive substrate. The exposed substrate is subjected to a development step, an etching step, a resist-stripping step, and optionally other steps to form the prescribed pattern on the substrate. These steps can be followed by a color-filter-formation step S402.

In the co lor- filter- formation step S402, multiple groups of three dots corresponding to R (red), G (green), and B (blue) are arranged in a matrix. Alternatively, multiple groups of three R, G, B stripes are arranged in a horizontal scan-line direction, to form a color filter. After the color- filter-formation step S402 a cell-assembly step S403 is executed, in which a substrate having the prescribed pattern formed in step S401, a color filter formed in step S402, and optionally other structures, are assembled into a liquid-crystal panel (comprising multiple liquid- crystal cells). In the cell-assembly step S403, for example, liquid-crystal material is injected into gaps between the substrate (having a prescribed pattern formed in the pattern-formation step S401) and the color filter formed in the color- filter-formation step S402, to fabricate cells of a liquid-crystal panel.

In the module-assembly step S404 electronic circuits required for operating the cells of the liquid-crystal panel, a backlight, and other components are installed, to complete fabrication of the liquid-crystal-display device. By means of the above- described method of manufacture of a liquid-crystal-display device, because exposure is performed using the particular embodiment of exposure apparatus as described above, declines in resolution, contrast, and the like on the photosensitive substrate surface are avoided, and display devices having detailed circuit patterns are produced with high throughput.

As far as is permitted by the law, the disclosures in all references cited above are incorporated herein by reference.

Whereas the invention has been described in connection with representative embodiments, it will be understood that it is not limited to those embodiments. On the contrary, the invention is intended to encompass all modifications, alternatives, and equivalents as may be included within the spirit and scope of the invention, as defined by the appended claims.

Claims

What is claimed is:

1. A segmented mirror, comprising: an array of multiple mirror elements having respective reflective surfaces and being respectively movable, the elements reflecting respective portions of a beam of utility light incident on the array; and a monitoring device situated relative to the array, the monitoring device comprising a source of sensor light and a Shack-Hartmann sensor, the source being situated to direct the sensor light onto at least some of the elements, and the Shack- Hartmann sensor being situated to receive sensor light reflected from the elements.

2. The mirror of claim 1 , configured as a fly-eye mirror.

3. The mirror of claim 1 or claim 2, wherein: the utility light is a beam of EUV light; and each element comprises a multilayer-film reflective to incident EUV light.

4. The mirror of any one of claims 1 - 3, wherein: the elements reflect utility light incident thereon at a relatively low angle of incidence; and the elements reflect sensor light incident thereon at a relatively high angle of incidence.

5. The mirror of any one of claims 1 - 4, further comprising respective positioning devices coupled to the elements, the positioning devices being operable to change orientations of the respective elements.

6. The mirror of claim 5, wherein the positioning devices comprise respective integral actuators.

7. The mirror of claim 5, further comprising at least one extraneous actuator movable to engage a positioning device and operate the positioning device to move the respective element.

8. An adaptive segmented mirror, comprising: an array of elements each comprising a respective surface that is reflective to incident utility light and each being respectively movable; means for directing a beam of sensor light onto the array of elements such that the sensor light illuminates at least a subset of the elements, each element that receives sensor light producing a respective beamlet of reflected sensor light; means for receiving and individually converging the beamlets of sensor light reflected from the elements and for producing an array of respective focal spots from the received beamlets; and means for detecting positions of the focal spots and for ascertaining, from the detected positions, respective positions of the respective elements.

9. The mirror of claim 8, configured as a fly-eye mirror.

10. The mirror of claim 9, wherein: the utility light is EUV light; and the fly-eye mirror is reflective to EUV light.

11. The mirror of any one of claims 8 - 10, wherein the means for detecting comprises at least one CCD array.

12. The mirror of any one of claims 8 - 11, wherein the means for receiving and converging comprises an array of lenslets situated between the means for detecting and the array of elements.

13. The mirror of any one of claims 8 - 12, wherein the means for detecting and means for receiving and converging collectively comprise a Shack-

Hartmann sensor.

14. The mirror of any one of claims 8 - 13, further comprising means for moving the elements.

15. The mirror of claim 14, wherein the means for moving moves the elements serially.

16. The mirror of claim 14, wherein the means for moving moves at least some of the elements simultaneously.

17. The mirror of any one of claims 14 - 16, further comprising controlling means, wherein: the controlling means receives data from the means for detecting; and based on an optics model, the controlling means activates the means for moving to change position of at least one element.

18. The mirror of any one of claims 8 - 17, wherein: the elements are arranged in multiple subsets; and the means for directing produces serial illumination of the subsets.

19. An optical integrator, comprising: a first fly-eye mirror situated to receive utility light: a second fly-eye mirror located downstream of the first fly-eye mirror to receive utility light reflected from the first fly-eye mirror and reflect the utility light downstream; at least one of the fly-eye mirrors being segmented and comprising an array of multiple reflective elements having respective reflective surfaces and respective positioning devices, the elements reflecting respective portions of the utility light incident on the array; and a monitoring device situated relative to the array, the monitoring device comprising a source of sensor light and a Shack-Hartmann sensor, the light source being situated to direct the sensor light onto at least some of the elements, and the Shack-Hartmann sensor being situated to receive sensor light reflected from the elements.

20. The optical integrator of claim 19, further comprising a controller connected to the positioning devices and to the Shack-Hartmann sensor, the controller operating under an optics model to impart an attitudinal change to at least one positioning device based on data received by the controller from the Shack- Hartmann sensor.

21. The optical integrator of claim 19 or claim 20, wherein the reflective elements comprise multilayer films reflective to EUV utility light.

22. The optical integrator of any one of claims 19 - 21, wherein the positioning devices comprise respective integral actuators.

23. The optical integrator of any one of claims 19 - 22, wherein the positioning devices comprise at least one extraneous actuator movable about from one positioning device to another.

24. The optical integrator of any one of claims 19 - 23, wherein both fly- eye mirrors are segmented and have respective monitoring devices.

25. A catoptric illumination-optical system, comprising: a first mirror that receives a beam of utility light and reflects the beam; an optical integrator located downstream of the first mirror and comprising a first fly-eye mirror and a second fly-eye mirror, the fly-eye mirrors being segmented and comprising multiple reflective elements, the reflective elements of at least one of the fly-eye mirrors comprising respective positioning devices rendering the elements movable; and a monitoring device situated relative to the fly-eye mirror having movable reflective elements, the monitoring device comprising a source of sensor light and a sensor, the light source being situated to direct the sensor light onto the elements, and the sensor being situated to receive sensor light reflected from the elements, the sensor comprising a device that breaks received sensor light into multiple raylets and a device that detects raylets as respective focus spots on a detector array.

26. The system of claim 25, wherein the monitoring device comprises a

Shack-Hartmann sensor.

27. The system of claim 25 or claim 26, wherein the first mirror is a collimating mirror.

28. The system of any one of claims 25 - 27, further comprising a controller connected to the monitoring device and to the positioning devices, the controller, operating under an optics model, receiving data from the monitoring device concerning respective positions of the focus spots, and actuating the positioning devices to change the respective positions of the focus spots.

29. An EUV lithography system, comprising: a reticle stage; an EUV source; and an illumination-optical system situated between the EUV source and the reticle stage, the illumination-optical system comprising (a) a first mirror that receives a beam of EUV light from the EUV source and reflects the beam, (b) an optical integrator located downstream of the first mirror and comprising a first fly- eye mirror and a second fly-eye mirror, the fly-eye mirrors being segmented and comprising multiple reflective elements, the reflective elements of at least one of the fly-eye mirrors comprising respective positioning devices rendering the elements movable, and (c) a monitoring device situated relative to the fly-eye mirror having movable reflective elements, the monitoring device comprising a source of sensor light and a sensor, the light source being situated to direct the sensor light onto the elements, and the sensor being situated to receive sensor light reflected from the elements, the sensor comprising a device that breaks received sensor light into multiple raylets and a device that detects raylets as respective focus spots on a detector array.

30. The system of claim 29, wherein the monitoring device comprises a Shack-Hartmann sensor.

31. The system of claim 29 or claim 30, wherein the first mirror is a collimating mirror.

32. The system of any one of claims 29 - 31 , further comprising a controller connected to the monitoring device and to the positioning devices, the controller, operating under an optics model, receiving data from the monitoring device concerning respective positions of the focus spots, and actuating the positioning devices to change the respective positions of the focus spots.

33. A method for determining optical performance of a segmented mirror, comprising: directing a beam of sensor light at multiple elements of the segmented mirror to produce respective beamlets of reflected sensor light; converging the beamlets as respective focal spots onto a two-dimensional sensor array; and determining respective positions of the focal spots, the positions corresponding to a parameter of optical performance of the mirror.

34. The method of claim 33, wherein the segmented mirror is a fly-eye mirror reflective to EUV light.

35. The method of claim 33 or claim 34, wherein the steps of converging and determining are performed using a Shack-Hartmann sensor placed to receive the beamlets.

36. A method for controlling optical performance of a segmented mirror, comprising: directing a beam of sensor light at multiple elements of the segmented mirror to produce respective beamlets of reflected sensor light; converging the beamlets as respective focal spots onto a two-dimensional sensor array; determining relative positions of the focal spots, the positions corresponding to a parameter of optical performance of the mirror; and based on the determined positions of the focal spots, controlling respective positions of the elements .

37. The method of claim 36, performed in real time.

38. The method of claim 36 or claim 37, wherein the optical characteristic is a desired pupil-fill condition.

39. The method of any one of claims 36 - 38, wherein the directing step is performed by distributed illumination of selected groups of elements at different respective times.

40. In an EUV lithography system, a method for controlling a parameter of optical performance of an illumination-optical system having an optical integrator including first and second segmented fly-eye mirrors, the method comprising: with respect to at least one of the fly-eye mirrors, directing a beam of sensor light at multiple elements of the mirror to produce respective beamlets of reflected sensor light; converging the beamlets as respective focal spots onto a two-dimensional sensor array; determining respective positions of the focal spots, the positions corresponding to a parameter of optical performance of the mirror; and based on the determined positions of the focal spots, controlling respective positions of the elements to achieve the desired parameter of optical performance.

41. The method of claim 40, wherein the desired parameter is a desired pupil fill condition.

42. The method of claim 40 or claim 41 , wherein the directing, converging, determining, and controlling steps are performed on both fly-eye mirrors.