NL2023285A - Apparatus for imaging an object at multiple positions - Google Patents

Abstract

Disclosed is a system for imaging an object which is at any one of a number of positions, the system including one or more beam splitters each of which splits the light from the object into an imaging beam and a continuing beam, and optics for each beam splitter which receives 5 the imaging beam and images the object when the object is a respective position.

Description

FIELD [0001] The present disclosure relates optical systems such as may be used in to semiconductor photolithography alignment systems.

BACKGROUND [0002] A lithographic apparatus applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that application, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (including part of one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.

[0003] Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and socalled scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During lithography, a reticle is used to transfer a desired pattern onto a substrate, such as a wafer. Reticles may be formed of material(s) transparent to the lithographic wavelength used, for example glass in the case of visible light. In addition, reticles can also be formed of material(s) that reflect the lithographic wavelength chosen for the specific system in which it is used. An illumination source (e.g., exposure optics located within a lithographic apparatus) illuminates the reticle, which is disposed on a reticle stage. This illumination exposes an image onto the substrate that is disposed on a substrate stage. The image exposed onto the substrate corresponds to the image printed on the reticle. While exposure optics are used in the case of photolithography, a different type of exposure apparatus may be used depending on the particular application. For example, x-ray, ion, electron, or photon lithographies each may require a different exposure apparatus, as is known to those skilled in the art. The particular example of photolithography is discussed here for illustrative purposes only.

[0005] Tire reticle is generally located between a semiconductor chip and a light source. A loading process is required for loading the reticle onto a reticle exposure stage. The reticle must be very precisely aligned at a predetermined position. Any error in the alignment must be within a correctable range of compliance. Conventionally, an alignment mark formed in the reticle is used to align the reticle by locating the alignment mark. Alignment operations are performed by detecting the alignment mark of the reticle.

[0006] To decrease reticle exchange time and thereby increase throughput of the lithography system, pre-alignment, that is, alignment of the reticle at an off-line alignment station is desirable. Once the reticle is placed on the platen the reticle pre-alignment marks are used to position the reticle in the approximately correct location. The stage is moved to position special alignment marks attached to the stage in the correct position to do the reticle fine alignment. The marks are illuminated, for example, with a HeNe laser. The reticle is then moved to give the best alignment position and held in that position until removed from the stepper/scanner.

[0007] Conventionally reticle pre-alignment systems are capable only of imaging a reticle at a predetermined single working elevation. It may be advantageous, however, to have the flexibility of being able to image the reticle not at just one elevation but at additional elevations as well. There is therefore a need for a system that can image the reticle at any one of multiple possible working elevations.

SUMMARY [0008] The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments and is not intended to identify key or critical elements of all embodiments nor set limits on the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

[0009] According to one aspect of an embodiment there is disclosed system for imaging an object which is at a first position or a second position, the system including a beam splitter to split the light from the object into a first beam and a second beam, and optics which receives the first beam and images the object when the object is at the first position and other optics which receives the second beam and images the object when the object is at the second position.

[0010] According to another aspect of an embodiment there is disclosed an apparatus for imaging an object at one of a first position and a second position, the apparatus comprising a beam splitter arranged to receive light from the object and for splitting the light into a first beam and a second beam, a first optical element arranged to receive the first beam, and an arrangement comprising a folding mirror and a second optical element arranged to receive the second beam. The apparatus may further comprise a third optical element arranged optically between the beam splitter and the first optical element and a fourth optical element arranged optically between the folding mirror and the second optical element. The apparatus may further comprise a third optical element arranged optically between the object and the beam splitter.

[0011] According to another aspect of an embodiment there is disclosed an apparatus for imaging an object at one of a first position and a second position, the apparatus comprising a beam splitter arranged to receive light from the object and for splitting the light into a first beam traversing a first arm and a second beam, the first arm comprising a first optical element arranged to receive the first beam and a second optical element arranged to receive the first beam from the first optical element, a folding mirror arranged to receive the second beam and to reflect the second beam into a second arm, the second aim comprising a third optical element arranged to receive the reflected second beam and a fourth optical element arranged to receive the second beam from the third optical element.

[0012] According to another aspect of an embodiment there is disclosed an apparatus for imaging an object at one of a first position and a second position, the apparatus comprising a first optical element arranged to receive light from the object, a beam splitter arranged to receive light from first optical element and for splitting the light into a first beam traversing a first arm and a second beam, the first arm comprising a second optical element arranged to receive the first beam, and an arrangement comprising a folding mirror and a third optical element arranged to receive the second beam.

[0013] According to another aspect of an embodiment there is disclosed an apparatus for imaging an object which is at one of a first position and a second position, the apparatus comprising a beam splitter arranged to split light from the object into a first beam and a second beam, a first optical system arranged to receive the first beam and to image the object when the object is at the first position, and a second optical system arranged to receive the second beam and image the object when the object is at the second position. The first optical system may comprise a first optical element and a second optical element and wherein the second optical system comprises a folding mirror, a third optical element, and a fourth optical element. The apparatus may further comprise a first optical element arranged optically between the object and the beam splitter and the first optical system may comprise a second optical element and the second optical system may comprise a folding mirror and a third optical element.

[0014] According to another aspect of an embodiment there is disclosed an apparatus for imaging an object which is at a first position or a second position, the apparatus comprising a beam splitter arranged to split the light from the object travelling a first optical path into a first beam and a second beam, a first optical module arranged to receive the first beam and to image the object when the object is at the first position, and a second optical module arranged to receive the second beam and to image the object when the object is at the second position.

[0015] According to another aspect of an embodiment there is disclosed an apparatus for imaging an object at one of a first position and a second position, the apparatus comprising a first optical element arranged to receive light from the object at a first working distance WD1 from the first position and at a second distance WD2 from the second position, a beam splitter arranged to receive light from first optical element and for splitting the light into a first beam traversing a first arm and a second beam, the first arm comprising a first arm lens group having a focal length Fl ’ arranged to receive the first beam, and a second beam traversing a second arm lens group having a focal length F2' and comprising a first lens and a second lens separated by a distance d; WD1, WD2, F2’, and Fl’ satisfying the relationship

WD2F2' ,

--7~ k WD1 Fl' where k is a coefficient in the range of about 1 to about 4.

[0016] According to another aspect of an embodiment there is disclosed an apparatus for imaging an object at any one of a plurality of positions, the apparatus comprising a first optical bifurcation module comprising a first beam splitter arranged to receive light from the object and for splitting the light into a first beam and a second beam and a first imaging module arranged to receive the second beam and for imaging the object when the object is at a furthest one of the plurality of positions, at least one additional optical bifurcation module comprising an additional beam splitter arranged to receive light from the first beam and for splitting the light into an imaging beam and a continuing beam and an additional imaging module arranged to receive the imaging beam and for imaging the object when the object is at another one of the plurality of positions, the continuing beam propagating to one of a next additional optical bifurcation module and a final optical module arranged to receive light from the continuing beam and comprising a folding mirror and a final optical imaging module arranged to receive the second beam and for imaging the object when the object is at a nearest one of the plurality of positions.

[0017] Further embodiments, features, and advantages of the subject matter of the present disclosure, as well as the structure and operation of the various embodiments are described in detail below with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING [0018] FIG. 1 depicts a lithographic apparatus in accordance with an aspect of an embodiment of the invention.

[0019] FIG. 2 illustrates a pre-alignment system configured to pre-align a reticle, according to an aspect of an embodiment of the invention.

[0020] FIG. 3 is a diagram of an optical system for imaging a reticle at a single position.

[0021] FIG. 4A is a diagram of an optical system for imaging a reticle at a two positions as an example of multiple positions according to an aspect of embodiment of the invention.

[0022] FIG. 4B is a diagram of an optical system for imaging a reticle at a multiple positions according to an aspect of embodiment of the invention.

[0023] FIG. 5 is a diagram of an optical system for imaging a reticle at a multiple positions according to an aspect of an embodiment of the invention..

[0024] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art based on the teachings contained herein.

DETAILED DESCRIPTION [0025] Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to promote a thorough understanding of one or more embodiments. It may be evident in some or all instances, however, that any embodiment described below can be practiced without adopting the specific design details described below. . In the description that follows and in the clauses the terms “up,” “down,” “top,” “bottom,” “vertical,” “horizontal,” and like terms may be employed. These terms are intended to show relative orientation only and not any orientation with respect to gravity unless otherwise indicated.

[0026] FIG. 1 schematically depicts a lithographic apparatus 100 according to an embodiment of the invention. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or EUV radiation); a support structure or support or pattern support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W.

[0027] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[0028] The support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” [0029] Tire term “patterning device” as used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its crosssection such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[0030] Tire patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.

[0031] The term “projection system” as used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system.” [0032] The support structure and the substrate table may also be hereinafter referred to as an article support. An article includes but is not limited to a patterning device, such as a reticle, and a substrate, such as a wafer.

[0033] As herein depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask).

[0034] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

[0035] The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e. g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0036] Referring to FIG. 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system if required, may be referred to as a radiation system.

[0037] The illuminator IL may include an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator and a condenser. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

[0038] The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. After being reflected by the patterning device (e.g. mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure (e.g. mask table) MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure (e.g. mask table) MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device (e.g. mask) MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device (e.g. mask) MA, the mask alignment marks may be located between the dies.

[0039] FIG. 2 illustrates a system 200 configured to pre-align a reticle 202, according to an embodiment of the invention. System 200 comprises illumination sources 208 and prealignment system 206, which may include multiple optics 212, optical detectors 214, and controllers 216.

[0040] Illumination sources 208 are configured to illuminate reticle 202 with light of a pre-determined wavelength used for reticle pre-alignment. In an embodiment, light generated by illumination sources 208 is in a near-infrared region of 650 nm to 1000 nm. In another embodiment, light of a wavelength of 880 nm is used. It is to be appreciated that the wavelength of light generated by illumination sources 208 for reticle alignment is a design choice, as understood by a skilled artisan. In the present embodiment, illumination source 208 comprises dual light sources 208 a-b. In alternate embodiments, illumination source 208 may include a single light source or more than two light sources. It is to be appreciated that the number of light sources is a design choice, as understood by a skilled artisan. Illumination source 208 generates beams of radiation 209 a-b, which are used to illuminate alignment targets 204 a-b of reticle 202. Interaction of beams 209 a-b with alignment targets 204 generates imaging beams 210 a-b, which are directed into pre-alignment system 206. Imaging beams 210 a-b are directed by optics 212 either onto optical detectors 214 controlled by controllers 216. Controllers 216 generate a control signal 218, which is used to pre-align reticle 202 based on imaging beams 210 a-b. According to one aspect of an embodiment, reticle 202 is a reflective patterning device used for Extreme Ultraviolet Lithography (EUV). According to one aspect of an embodiment, reticle 202 is reticle MA and alignment targets 204 a-b are alignment targets Ml and M2, as shown in FIG. 1. Similar systems can be utilized for transmissive patterning devices with illuminators 209a and 209b placed above reticle 202.

[0041] FIG. 3 is a diagram of a system for imaging an object (e.g., a reticle) at a single object position 300. The system of FIG. 3 is telecentric in which the chief rays are collimated and parallel to the optical axis in image and/or object space. A key characteristic of telecentricity is constant magnification regardless of image and/or object location. The light from the object a partially focused by a first optical system (lens group) 310 and then the light path is folded by a folding mirror 320. The light in the folded light path is then additionally focused by a second optical system (lens group) 330 and is imaged at an image plane 340.

[0042] The system of FIG. 3 is useful for imaging an object which may be positioned only at a single elevation with respect to the optical system. As mentioned, however, it is advantageous to minimize the time necessary for pre-alignment by possibly shortening or eliminating steps in the pre-alignment procedure. One technique for this minimization involves increasing the elevation (working distance) for a conventional reticle pre-alignment system and adding a second reticle position at a second working distance. To meet this requirement according to one aspect of an embodiment a multichannel optical arrangement is used. The multichannel optical arrangement involves multiple optical branches partially sharing optical paths.

[0043] According to one aspect of an embodiment, in one arrangement, referred to herein as the stacked arrangement, passive elements such as a beam-splitter and folding mirrors are in object space and there is no shared active optical element (e.g., lens group) in the shared object space. The stacked version of the system involves the use of two identical branches or arms sharing common object space. In another arrangement, referred to herein as the bifurcated arrangement, some active optical elements reside in the shared (common) portions of the paths and so are shared. This has the advantage that the design can be made more compact and uses fewer lenses.

[0044] FIG. 4A is a diagram of a stacked system for imaging an object (e.g., a reticle) at multiple positions, either an object high position 400 or at an object low position 410. The system of FIG. 4 is telecentric in which the chief rays are collimated and parallel to the optical axis in image and/or object space. The light from the object is split by a beam splitter 420, e.g., a 50%/50% split mirror, which splits the light beam into an upper arm and a lower arm. Along a upper arm there is a first upper arm lens group 430 and a second upper arm lens group 440, which together image the object when the object is in the high position 400 at an image plane 450. The lower arm is folded by a folding mirror 460 which redirects the light to a first lower arm lens group 470 and a second lower arm lens group 480, which together image the object when the object is in the low position 410 at an image plane 490.

[0045] If necessary, in general, the number of branches can be more than two for both the stacked and bifurcate (multifurcate) arrangements. Also, different magnifications can be formed by different branches. FIG. 4B is a diagram of a stacked system for imaging an object (e.g., a reticle) at multiple positions, either an object high position 400, at an intermediate position 400’, at an object low position 410, or at other positions indicated by the solid circles in the top of the figure. The system of FIG. 4B is telecentric in which the chief rays are collimated and parallel to the optical axis in image and/or object space. The light from the object is split by a beam splitter 420, e.g., a 50%/50% split mirror, which splits the light beam into an upper arm and a lower arm. Along the upper arm there is a first upper arm lens group 430 and a second upper arm lens group 440, which together image the object when the object is in the high position 400 at an image plane 450. The light from the object is split again by a beam splitter 420’, e.g., a 50%/50% split mirror, which splits the light beam into an intermediate arm and continuing arm. Along the intermediate arm there is a first intermediate arm lens group 430’ and a second intermediate arm lens group 440’, which together image the object when the object is in the intermediate position 400’ at an image plane 450’. The lower arm is folded by a folding mirror 460 which redirects the light to a first lower arm lens group 470 and a second lower arm lens group 480, which together image the object when the object is in the low position 410 at an image plane 490. The solid circles in the lower portion of the diagram are intended to indicate that additional arms for imaging the object at additional positions can also be included.

[0046] FIG. 5 is a diagram of a bifurcated system for imaging an object (e.g., a reticle) at either an object high position 500 or at an object low position 510. The system of FIG. 5 is telecentric in which the chief rays are collimated and parallel to the optical axis in image and/or object space. The light from the object is received by a front shared lens group 520 and is then split by a beam splitter 530, e.g., a 50%/50% split mirror, which splits the light beam into an upper arm and a lower arm. Along a upper arm there is an upper arm back lens group 540 which images the object when the object is in the high position 500 at an image plane 550. The lower arm is folded by a folding mirror 560 which redirects the light to a lower arm lens group 570 which images the object when the object is in the low position 510 at an image plane 580.

[0047] In this arrangement, the front lens group 520 is common for the different working distances WD1 and WD2. The difference in these working distances, AWD=WD1WD2, is selected to be greater than the depth of the field and may be greater than WD2.

[0048] The relationship between the focal lengths of the back lens groups 540 and 570 and the working distances WD1 and WD2 can be defined by the equation:

WD2 F2' ,

--- — K

WD1 Fl^f where F2' is the focal length of the back lens group 570 of the short pass WD2, F1' is the focal length of the back lens group 540 of the long pass WD1, and k is a coefficient which depends on AWD and the distance d between two components in back lens group 570 and is in the range of about 1 to about 4.

[0049] As an example for AWD>WD2, let WDl=75.5mm and WD2=35.5mm. In this case, the above formula gives:

35.5 F2'=-30mm

--;------------~ 1.1 /

75.5 Fi--12mm [0050] As another example, let WDl=66mm and WD2=26mm. In this case, the above formula gives:

F2'--90mm g^

66Fl'=-12mm [0051] In this case note that the change in focal length F2', the focal length of the back lens group 570 of the short pass WD2, because the distance between components in back lens group 570 has been changed.

[0052] It will be apparent to one of ordinary skill in the art that the above principles can also be applied to systems that image an object at more than two positions. Also, although the above description is in terms of an optical system for semiconductor photolithography as an example, it will be apparent to one of ordinary skill in the art that the disclosed systems can be used in other applications where it is desired to image an object which may be at any one of a multiple number of positions.

[0053] The present disclosure is made with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. For example, the metrology module functions can be divided among several systems or performed at least in part by an overall control system.

[0054] The above description includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended clauses. Furthermore, to the extent that the term “includes” is used in either the detailed description or the clauses, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is construed when employed as a transitional word in a clause. Furthermore, although elements of the described aspects and/or embodiments may be described or appear in clauses in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and/or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise. Other aspects of the invention are set out as in the following numbered clauses.

1. Apparatus for imaging an object at one of a first position and a second position, the apparatus comprising:

a beam splitter arranged to receive light from the object and for splitting the light into a first beam and a second beam;

a first optical element arranged to receive the first beam;

an arrangement comprising a folding mirror and a second optical element arranged to receive the second beam.

2. Apparatus of clause 1 further comprising a third optical element arranged optically between the beam splitter and the first optical element and a fourth optical element arranged optically between the folding mirror and the second optical element.

3. Apparatus of clause 1 further comprising a third optical element arranged optically between the object and the beam splitter.

4. Apparatus for imaging an object at one of a first position and a second position, the apparatus comprising:

a beam splitter arranged to receive light from the object and for splitting the light into a first beam traversing a first arm and a second beam, the first arm comprising a first optical element arranged to receive the first beam and a second optical element arranged to receive the first beam from the first optical element:

a folding mirror arranged to receive the second beam and to reflect the second beam into a second arm, the second arm comprising a third optical element arranged to receive the reflected second beam and a fourth optical element arranged to receive the second beam from the third optical element.

5. Apparatus for imaging an object at one of a first position and a second position, the apparatus comprising:

a first optical element arranged to receive light from the object;

a beam splitter arranged to receive light from first optical element and for splitting the light into a first beam traversing a first arm and a second beam, the first arm comprising a second optical element arranged to receive the first beam; and an arrangement comprising a folding mirror and a third optical element arranged to receive the second beam.

6. Apparatus for imaging an object which is at one of a first position and a second position, the apparatus comprising:

a beam splitter arranged to split light from the object into a first beam and a second beam;

a first optical system arranged to receive the first beam and to image the object when the object is at the first position; and a second optical system arranged to receive the second beam and image the object when the object is at the second position.

7. Apparatus of clause 6 wherein the first optical system comprises a first optical element and a second optical element and wherein the second optical system comprises a folding mirror, a third optical element, and a fourth optical element.

8. Apparatus of clause 6 further comprising a first optical element arranged optically between the object and the beam splitter and wherein the first optical system comprises a second optical element and the second optical system comprises a folding mirror and a third optical element.

9. Apparatus for imaging an object which is at a first position or a second position, the apparatus comprising:

a beam splitter arranged to split the light from the object travelling a first optical path into a first beam and a second beam;

a first optical module arranged to receive the first beam and to image the object when the object is at the first position; and a second optical module arranged to receive the second beam and to image the object when the object is at the second position.

10. Apparatus for imaging an object at one of a first position and a second position, the apparatus comprising:

a first optical element arranged to receive light from the object at a first working distance WD1 from the first position and at a second distance WD2 from the second position:

a beam splitter arranged to receive light from first optical element and for splitting the light into a first beam traversing a first arm and a second beam, the first arm comprising a first arm lens group having a focal length Fl ’ arranged to receive the first beam, and a second beam traversing a second arm lens group having a focal length F2’ and comprising a first lens and a second lens separated by a distance d; WD1, WD2, F2’, and Fl ’ satisfying the relationship

--; = k WD1 Fl’ where k is a coefficient in the range of about 1 to about 4.

11. Apparatus for imaging an object at any one of a plurality of positions, the apparatus comprising:

a first optical bifurcation module comprising a first beam splitter arranged to receive light from the object and for splitting the light into a first beam and a second beam and a first imaging module arranged to receive the second beam and for imaging the object when the object is at a furthest one of the plurality of positions;

at least one additional optical bifurcation module comprising an additional beam splitter arranged to receive light from the first beam and for splitting the light into an imaging beam and a continuing beam and an additional imaging module arranged to receive the imaging beam and for imaging the object when the object is at another one of the plurality of positions, the continuing beam propagating to one of a next additional optical bifurcation module and a final optical module arranged to receive light from the continuing beam and comprising a folding mirror and a final optical imaging module arranged to receive the second beam and for imaging the object when the object is at a nearest one of the plurality of positions.

Claims (1)

CONCLUSION A device adapted to illuminate a substrate. 1/6 200 3/6 320 4/6 FIG. 4A 5/6 47ö FiG. 5