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    公开号:NL1036833A1
    申请号:NL1036833
    申请日:2009-04-08
    公开日:2009-10-19
    发明作者:Stanislav Y Smirnov；Eric Brian Cates；Adel Joobeur
    申请人:Asml Holding Nv；
    IPC主号:
    专利说明:

    HIGH NUMERICAL APERTURE CATADIOPTRIC OBJECTIVES WITHOUT OBSCURATION AND APPLICATIONS THEREOF
    CROSS REFERENCE TO RELATED APPLICATIONS
    This application clauses benefit under 35 U.S.C. § 119 (e) to U.S. Provisional Patent Application No. 61 / 045,125, entitled "High Numerical Aperture Objective Without Obscuration and Applications Thereof," to Smirnov et al., Filed April 15,2008, the whole of which is incorporated by reference as if fully set forth.
    BACKGROUND
    Field of the Invention
    The present invention is generally related to lithography, and more particularly to systems and methods for inspecting an object (such as a reticle or wafer) or a lithography system.
    Background Art
    Lithography is widely recognized as a key process in manufacturing and integrated circuit (IC) as well as other devices and / or structures. A lithographic apparatus is a machine used during lithography, which applies a desired pattern onto a substrate, such as onto a target portion of the substrate. During manufacture of ICs with a lithographic apparatus, a patterning device - which is alternatively referred to as a mask or a reticle - generates a circuit pattern to be formed on an individual layer in an IC. This pattern may be transferred onto the target portion (e.g., including part of, one, or several dies) on the substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate. In general, a single substrate contains a network or adjacent target portions that are successively patterned. Manufacturing different layers of the IC often requires imaging different patterns on different layers with different reticles. Therefore, reticles must be changed during the lithographic process.
    To ensure that the pattern is properly transferred to the target within appropriate tolerances, the reticle and / or the substrate (e.g., silicon wafer) on which the 1C is printed may be inspected for defects or other characteristics. An object (e.g., reticle or wafer) can be inspected by collecting light scattered off or transmitted through fine structures on the surface of the object. A specially designed objective typically directs the light toward the object and collects the scattered or transmitted light from the object. The amount of information about the fine structures on the object depends on the spectral bandwidth of the light and the numerical aperture (NA) or the objective. Increasing the spectral bandwidth of the light and the NA of the objective, increasing the amount of information that can be collected by the objective. Therefore, wide spectral bandwidth and high NA objectives are desired. From a manufacturing perspective, however, wide spectral bandwidth and high NA objectives are problematic because the objective should reduce chromatic aberrations (axial color) caused by the wide spectral bandwidth and reduce obscurations caused by the high NA.
    In general, three classes of objectives may be used to collect information about an object (e.g., reticle or wafer): (i) an all refractive objective; (ii) an all reflective objective; or (iii) a catadioptric objective. Although all refractive objectives may not have a central obscuration, these types of objectives typically do not adequately correct chromatic aberrations (axial color) caused by the wide spectral bandwidth at DUV wavelengths .. In addition, there is a limited number of refractive materials that can transmit high energy electromagnetic radiation (such as, deep ultraviolet (DUV)), further constraining the types of all refractive objectives that can be manufactured with desirable characteristics. All, refractive objectives are not desirable for object-inspection purposes.
    Unlike an all refractive objective, all reflective and catadioptric objectives can adequately correct chromatic aberrations (axial color). This is because reflective surfaces are apochromatic (i.e., reflective surfaces can reduce chromatic aberrations by combining three colors to a single focus). Unfortunately, conventional, rotationally-symmetric all reflective and catadioptric objectives typically have a central obscuration. Any obscuration is undesirable because it reduces the amount of collected light - and therefore the amount of information that can be collected about the fine structures of the object (e.g., reticle or wafer). Although it may be possible for an all reflective objective to be configured without a central obscuration, these types of all reflective objectives are typically not rotationally symmetrical, resulting in undesirable size and packaging constraints. More importantly these all reflective objectives will have high-NA limitations. Like, all refractive objectives, all reflective objectives are not desirable for object-inspection purposes.
    SUMMARY
    Given the foregoing, what is needed is a high NA catadioptric objective without a central obscuration, and applications thereof.
    Embodiments of the present invention are directed to a high NA catadioptric objective without a central obscuration, and applications thereof. Such an objective can operate through a wide spectral bandwidth of light, including deep ultraviolet (DUV) radiation. Importantly, refractive elements in the objective can be manufactured from a single type of material (such as, for example, CaF2 and / or fused silica). In addition, the elements of such an objective are rotationally symmetrical about an optical axis.
    An embodiment of the present invention provides an objective for inspecting a substrate using scattered radiation, including a first optical group, a second optical group, and a beam splitter. The first optical group reduces chromatic aberrations due to a spectral range of radiation and transforms the radiation of the first polarization into radiation or a second polarization. The second optical group increases a numerical aperture of the objective and the radiation of the second polarization onto the substrate. The beamsplitter provides radiation of the first polarization to the first optics group and radiation of the second polarization to the second optical group.
    Another embodiment of the present invention provides an objective for inspecting a substrate using scattered radiation, including a first optical group, a second optical group, and a folding mirror. The first optical group reduces chromatic aberrations due to a spectral range of radiation. The second optical group increases a numerical aperture of the objective and object radiation onto the substrate. The folding mirror provides off-axis radiation to the pupil of the objective.
    Further features and advantages of the invention, as well as the structure and operation of various various 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 specifically described described. Such others are presented for illustrative purposes only. Additional others will be apparent to persons skilled in the relevant art (s) based on the teachings contained.
    LETTER DESCRIPTION OF THE DRAWINGS / FIGURES
    The accompanying drawings, which are included and form part of the specification, illustrate the present invention, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art (s) to make and use the invention. FIGS. 1A and IB respectively depict reflective and transmissive lithographic apparatuses in accordance with the present of the present invention. FIG. 2 depicts an example objective that uses a polarized beam splitter in accordance with an embodiment of the present invention. FIG. 3 depicts an example modification to the objective of FIG. 2. FIG. 4 depicts another example objective that uses a polarized beam splitter in accordance with an embodiment of the present invention. FIG. 5 depicts an example modification to the objective of FIG. 4. FIG. 6-9 depict example objectives that use off-axis radiation in accordance with the present of the present invention.
    The features and advantages of the present invention will become more apparent from the detailed description set below when tasks in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit (s) in the corresponding reference number.
    DETAILED DESCRIPTION I. Introduction
    The present invention is directed to a high NA catadioptric objective without obscuration, and applications thereof. In the detailed description that follows, references to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every edition may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such a feature, structure, or characteristic in connection with other is what or not explicitly described. A high NA catadioptric objective in accordance with an embodiment of the present invention eliminates a central obscuration (which is present in conventional high NA all reflective objectives), while correcting for chromatic aberrations (which typically cannot be corrected using all refractive objectives in the DUV spectrum range). In one embodiment, the central obscuration is eliminated by using a polarized beam splitter that is configured to pass radiation or a first polarization (such as, parallel polarized (p-polarized) radiation) and reflect radiation or a second polarization (such as, sigma polarized (s-polarized) radiation). In another embodiment, central obscuration is eliminated by using one or more folding mirrors to direct off-axis radiation into the pupil of the objective.
    Before describing such objectives in detail, however, it is instructive to present an overview of, and terminology used to describe, a lithographic apparatus that may be used in accordance with an embodiment of the present invention. For example, an objective or an embodiment of the present invention may be used to inspect a recticle or, and / or a wafer patterned by, the lithographic apparatus. II. Overview and Terminology FIGS. 1A and IB schematically depict lithographic apparatus 100 and lithographic apparatus 100 ', respectively. Lithographic apparatus 100 and lithographic apparatus 100 each include: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., DUV or EUV radiation); a support structure (e g., a mask table) MT configured to support a patterning device (eg, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA ; and a substrate table (eg, a wafer table) WT configured to hold a substrate (eg, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatuses 100 and 100 'also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (eg, including one or more) C of the substrate W. In lithographic apparatus 100 the patterning device MA and the projection system PS is reflective, and in lithographic apparatus 100 the patterning device MA and the projection system PS is transmissive.
    The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination of, for directing, shaping, or controlling the radiation B. In some, for example, the illumination system IL may provide linearly polarized light, as described in more detail below.
    The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithographic apparatuses 100 and 100 ', and other conditions, such as for example whether or not the patterning device MA is hero in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be a frame or a table, for example, which may be fixed or movable, as required. The support structure MT may ensure that the patterning device is at a desired position, for example with respect to the projection system PS.
    The term "patterning device" MA should be broadly interpreted as referring to any device that may be used to transmit a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C, such as an integrated circuit.
    The patterning device MA may be transmissive (axis in lithographic apparatus 100 'or FIG. IB) or reflective (axis in lithographic apparatus 100 or FIG. 1A). Examples of patterning devices MA include reticles, masks, programmable minor 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 may be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B which is reflected by the mirror matrix.
    The term "projection system" PS may encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination of, 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. A vacuum environment may be used for EUV or electron beam radiation since other gases may absorb too much radiation or electrons. A vacuum environment may therefore be provided for the whole beam path with the aid of a vacuum wall and vacuum pumps.
    Lithographic apparatus 100 and / or lithographic apparatus 100 'may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables) WT. In such "multiple stage" machines the additional substrate tables WT may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other substrate tables are being used for exposure.
    Referring to FIGS. 1A and IB, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatuses 100, 100 may be separate entities, for example when the source SO is an excimer laser. In such cases, the source SO is not considered to be part of the lithographic apparatus 100 or 100 ', and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (FIG. IB) including, for example, suitable directing mirrors and / or a beam expander. In other cases, the source SO may be an integral part of the lithographic apparatus 100,100 '- for example when the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.
    The illuminator IL may comprise an adjuster AD (FIG. IB) 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) or the intensity distribution in a pupil IPU or the illuminator may be adjusted. In addition, the illuminator IL may include various other components (FIG. IB), such as an integrator IN and a condenser CO. The illuminator IL may be used to condition the radiation beam B, to have a desired uniformity and intensity distribution in its cross section.
    The projection system has a pupil PPU conjugate to the illumination system pupil IPU, where portions of radiation emanating from the intensity distribution at the illumination system pupil IPU and traversing a mask pattern without being affected by diffraction at a mask pattern create an image of the intensity distribution at the illumination system pupil IPU.
    Referring to FIG. 1A, the radiation beam B is incident on the patterning device (e.g., mask) MA, which is a hero on the support structure (eg, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., mask) MA. MA, the radiation beam B passing through the projection system PS, which radiation beam B onto a target portion C or the substrate W. With the aid of the second positioner PW and position sensor IF2 (eg, an interferometric device, linear encoder or capacitive sensor), the substrate table WT may be moved accurately, eg 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 may be used to accurately position the patterning device (eg, mask) MA with respect to the path of the radiation beam B. Patterning device (eg, mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.
    Referring to FIG. IB, the radiation beam B is an incident on the patterning device (e.g., mask MA), which is a hero on the support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which is the beam onto a target portion C or the substrate W. With the aid of the second positioner PW and position sensor IF (eg, an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, eg 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 (which is not explicitly depicted) in FIG. IB) can be used to accurately position the mask MA with respect to the path of the radiation beam B, eg, after mechanical retrieval from a mask library, or during a scan.
    In general, movement of the 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 mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate May be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one that is provided on the mask MA, the mask alignment marks may be located between the dies.
    The lithographic apparatuses 100 and 100 may be used in at least one of the following modes: 1. In step mode, the support structure (eg, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (/. e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion may be exposed. 2. In scan mode, the support structure (e.g., mask table) MT and the substrate table WT are scanned synchronously while a pattern beamed to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (eg, mask table) MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. 3. In another mode, the support structure (eg, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern is imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO may be employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation may be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array or a type as referred to.
    Combinations and / or variations on the described modes of use or entirely different modes of use may also be employed.
    Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms "wafer" or " those "may be considered as synonymous with the more general terms" substrate "or" target portion, "respectively. The substrate referred to may be processed, before or after exposure, in for example a track (a tool that typically applies to a layer of resist to a substrate and develops the exposed resist), a metrology tool and / or an inspection tool. Where applicable, the disclosure may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so the term substrate used may also refer to a substrate that already contains multiple processed layers.
    The terms "radiation" and "beam" used include and all types of electromagnetic radiation, including ultraviolet (UV) radiation (eg, having a wavelength of or about 365, 248, 193, 157 or 126 nm) or extreme ultraviolet radiation (eg , having a wavelength or 5nm or above).
    The term "lens," where the context allows, may refer to any one or combination of various types of optical components, including refractive and reflective optical components. III. Example Objectives Without Central Obscuration
    As set forth from above, according to the present invention are directed to a high NA catadioptric objective without central obscuration. Such an objective is very desirable in, for example, (i) IC metrology (reticle and / or wafer inspection), (ii) high-resolution imaging spectroscopy and scatterometry, and (iii) other applications requiring a combination of high NA, large field of view (FOV), and / or wide spectral bandwidth. Objectives in accordance with the present invention may be configured to (A) include a polarized beam splitter and / or (B) use off-axis radiation, as described in more detail below. A. Catadioptric Objectives That Include A Polarized Beam Splitter in accordance with the present of the present invention, a catadioptric objective includes a polarized beam splitter to eliminate a central obscuration while offering a high level of chromatic aberrations correction due to the reflective elements. The polarized beam splitter is configured to pass radiation or a first polarization (such as parallel polarized (p-polarized) radiation) and reflect radiation or a second polarization (such as sigma polarized (s-polarized) radiation).
    In such, the objective also includes a first optical group and a second optical group. The first optical group has a lens with negative optical power positioned close to a concave mirror. The concave mirror (in combination with the negative optical power lens) is configured to correct axial color and field curvature. The second optical group provides a high numerical aperture (NA) and object radiation onto an object (e.g., reticle or wafer) under inspection. Importantly, the second optical group typically includes refractive, not reflective, elements - avoiding a central obscuration typically included in conventional high NA systems with reflecting elements. FIGS. 2-5 respectively depict example objectives 200, 200 ', 200 ", and 200" that each include a polarized beam splitter 202 (for example, a beam splitter cube) in accordance with an embodiment of the present invention. In each configuration, the objective also includes a quarter-wave plate 204, negative power lenses 206, 210, a positive power lens 212, and a concave mirror 208. Positive power lens 212 is configured to provide the objective with a high NA. Concave mirror 208 is configured to correct field curvature and chromatic aberrations (axial color). Negative power lens 206 and 210 may also be configured to help correct field curvature and chromatic aberrations (axial color). In addition, negative power lens 210 is configured to increase the working distance between beam splitter 202 and object 214.
    For the objectives 200, 200 ', 200 ", and 200"' or FIGS. 2-5, the object plane is at infinity. The image plane coincides with an object (reticle, wafer, or sample) 214. The main difference between the figures shown in FIGS. 2 and 3 and the figures shown in FIGS. 4 and 5 is the order of reflection / refraction of light at beam splitter 202, as described in more detail below.
    Referring to objective 200 or FIG. 2, beam splitter 202 is configured to have high transmission for radiation or a first type of polarization (such as p-polarized radiation) and high reflection for radiation or a second type of polarization (such as s-polarized radiation), or vice versa, whether the first and second types of polarization are out of phase by 180 degrees. Objective 200 may be configured to collect scattered light from object 214 ("scattering embodiment") or to collect light transmitted through object 214 ("transmissive embodiment"). Each of these is described in more detail below.
    In a scattering embodiment, beam splitter 202 receives linearly polarized radiation or the first type from an illumination source (such as, for example, illumination source IL or FIG. 1A and / or IB). The linearly polarized radiation transmits through beam splitter 202, then quarter-wave plate 204, negative power lens (or lens group) 206, and reaches concave mirror 208.
    After reflection off concave mirror 208, the radiation again travels through negative power lens 206 and quarter-wave plate 204, and is incident on beam splitter 202. Because the radiation passes through quarter-wave plate 204 twice, the radiation is transformed from radiation of the first type of polarization into radiation or the second type of polarization (eg, from p-polarized radiation into s-polarized radiation). Consider, beam splitter 202 reflects the radiation toward negative power lens 210. The radiation then reaches object 214 (ie, the plane being investigated) after transmitting through negative power lens 210 and positive power lens 212. The alteration of negative refractive power lens 206, positive reflective power mirror 208, negative refractive power lens 210 then positive refractive power lens 212 is what gives the flexibility of the system to correct point aberrations, field aberrations, and chromatic aberrations. As mentioned above, the main function of concave mirror 208 and negative refractive power lens 206 is to correct axial colar.
    After incidence on object 214, the radiation is reflected (scattered) back through objective 200 in the reverse order or that described above. The reflected (scattered) radiation is collected and used to inspect / analyze structures on and / or object 214.
    In a transmissive embodiment, radiation is incident on object 214 from the opposite direction of objective 200, which is in the embodiment of FIG. 2 agreed to radiation impinging on object 214 from below. In this embodiment, the incident radiation transmits through object 214 and is directed toward beam splitter 202 by positive power lens 212 and negative power lens 210. Beam splitter 202 reflects radiation toward quarter-wave plate 204, negative power lens 206, and concave mirror 208 The radiation then reflects off concave mirror 208 and passes through negative power lens 206, quarter-wave plate 204, and beam splitter 202 and is collected for inspection / analysis of object 214 in a similar manner to that described above. FIG. 4 depicts an objective 200 "that is similar to objective 200 or FIG. 2. Unlike objective 200 or FIG. 2, however, in the example or FIG. 4 beam splitter 202 is configured to have high reflection for radiation or the first type of polarization and high transmission for radiation of the second type of polarization., radiation first reflects off beam splitter 202 and then goes through the beam splitter 202 after reflection off concave mirror 208. The configuration depicted in Fig. 4 also alters the position of quarter-wave plate 204, negative power lens 206, and concave mirror 208 relative to the image plane, which in turn alters the space occupied by the optical elements of objective 200 ". Objective 200 "may be used, for example, as an alternative to objective 200 depending on the packaging specifications or a given inspection system. FIGS. 3 and 5 respectively illustrate in which an additional lens 330 is included before beam splitter 202. Lens 330 helps to control the range of angles or incidence on the surface of beam splitter 202, which affects the efficiency of beam splitter 202. In addition, lens 330 is beneficial for correction of (chromatic) aberrations. With the exception of lens 330, objective 200 'or FIG 3 is substantially similar to objective 200 or FIG. 2, and objective 200 "or FIG. 5 is substantially similar to objective 200 "or FIG. 4.
    Although the objectives depicted in FIGS. 2-5 may have been described above in terms of radiation being reflected off object 214, it is appreciated that this is for illustrative purposes only, and not limitation. A person skilled in the relevant art (s) will appreciate those objectives can be used in those in which radiation is reflected off or transmitted through object 214. In transmissive, for example, radiation may enter objectives 200, 200 ', 200 " , and / or 200 '"via object 214, rather than directly from an illumination source as illustrated above for the reflective (scattering) exp. B. Catadioptric Objectives That Use Off-Axis Radiation
    In accordance with an embodiment of the present invention, a catadioptric objective uses off-axis radiation to eliminate a central obscuration (which is typically found in conventional high AFTER all reflective or catadiotric objectives), while correcting for chromatic aberrations (which is typically not corrected) for in all refractive objectives). In this embodiment, a concave mirror (included in a first optical group) corrects chromatic aberrations (axial color) and field curvature. One or more negative power lens are also included to assist in the correction of chromatic aberrations (axial color) and field curvature. The high NA is created by one or more all refractive elements in a second optical group. Importantly, the second optical group typically includes refractive, not reflective, elements. The combination of off axis illumination, intermediate image planes, and proper folding is what avoids a central obscuration typically included in conventional high NA all reflective or catadiotric objectives. FIGS. 6-9 depict various features of an objective that uses off-axis radiation to eliminate a central obscuration or typical high AFTER all reflective or catadiotric objectives, while correcting for chromatic aberrations (typically found in all refractive objectives). Each of these includes: positive power lenses 602,604,612 and 616; negative power lens 606; a concave mirror 608; and a folding mirror 610. The object plane is at infinity. The image plane coincides with an object (e.g., reticle or wafer).
    The objectives of FIGS. 6-9 may be used to collect radiation that is scattered off object 614 ("scattering exp") or to collect radiation that is transmitted through object 614 ("transmissive expire"). In scattering, radiation enters the objective through lens 602, is conditioned by the other elements of the objective, and then incident on object 614. The radiation is then scattered off object 614 and directed back through the objective in the reverse order from which it entered. In the transmissive, radiation is first transmitted through object 614 and then traverses through the objective in a similar manner to the radiation that is scattered off objective 614 in the scattering exp. For illustrative purposes, and not limitation, scattering are described in detail below. The operation of transmissive expiry will be apparent to persons or ordinary skill in the art based on the description provided.
    Referring generally to FIGS. 6-9, positive power lens 616 is configured to provide the objective with a high NA. Concave mirror 608 along with negative power lens 606 is configured to correct field curvature and chromatic aberrations (axial color). Positive power lens 602 is configured to provide a first intermediate image 603. In addition to their functionality described above, concave mirror 608 and negative power lens 606 also act as a 1-X optical relay to re-image the first intermediate image 603 as a second intermediate image 605. Folding mirror 610 provides the second intermediate image 605 to positive power lens 612 and positive power lens 616. Positive power lens 604 is configured to create an intermediate pupil on concave mirror 608.
    With specific reference to FIG. 6, an objective 600 includes folding mirror 610, concave mirror 608, and lenses 602, 604 (optional), 606, 612, and 616. Objective 600 provides two intermediate images 603 and 605. Lens 602 radiation to first intermediate image 603. Intermediate image 603 is reflected by folding mirror 610 and reimaged by a 1-X catadioptric relay including concave mirror 608 and lens 606 to create second intermediate image 605.
    Lens 604 can be placed after intermediate image 603 (as depicted in FIG. 6) or before intermediate image 603 (as depicted in FIG. 9). Lens 604 is located close to the intermediate image 603 and used to control the position of the intermediate pupil or objective 600. This pupil should coincide or be close to concave mirror 608.
    Intermediate image 605 is reimaged onto object 614 by a refractive relay including positive power lens 612 and 616.
    After incidence on object 214, the radiation is reflected (scattered) back through objective 600 in the reverse order or that described above. The reflected (scattered) radiation is collected and used to inspect / analyze structures on object 214.
    Objective 600 may be arranged in alternative configurations, as illustrated in FIG. 7 (using one folding mirror 610) and FIG. 8 (using two folding mirrors 610A and 610B). Different folding schematics may be used based on desired design characteristics.
    Concave mirror 608 and negative lens 606 correct axial color and field curvature aberrations. Chromatic correction can be achieved using one glass type - such as, for example, fused silica - in all refractive groups (e.g., lenses 602,604,606,612, and 616).
    The optical elements of objectives 600, 600 ', 600 ", and 600"' (except folding mirror 610) are rotationally symmetrical about the optical axis. Folding mirror 610 blocks radiation traveling parallel to the optical axis 631 (see FIGS. 6 and 9). Therefore, the useful area or field is located off-axis as shown in FIGS. 6-9. Importantly, the pupils of objectives 600, 600 ', 600 ", and 600" do not have a central obscuration as is typical in conventional high AFTER all reflective or catadiotric objectives.
    Although the objectives depicted in FIGS. 6-9 are described above in terms of radiation being reflected off object 614, it is appreciated that this is for illustrative purposes only, and not limitation. A person skilled in the relevant art (s) will appreciate those objectives can also be used in those in which radiation is transmitted through object 614. In such, for example, radiation may enter objectives 600, 600 ', 600 ", and / or 600 "'via object 614, rather than directly from an illumination source as illustratively described above. IV. Conclusion
    Described above are or of a high NA catadiotric objective without obscuration, and applications thereof. It is appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the clauses. The Summary and Abstract sections may set forth one or more but not all exemplary of the present invention as contemplated by the inventor (s), and thus, are not intended to limit the present invention and the appended clauses in any way.
    The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships. The boundaries of these functional building blocks have been arbitrarily defined for the convenience of the description. Alternate boundaries can be defined as long as the specified functions and relationships are appropriately performed.
    The foregoing description of the specific expired will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific expire, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed exponent, based on the teaching and guidance presented. It is understood that the phraseology or terminology is for the purpose of description and not of limitation, such that terminology or phraseology or the present specification is interpreted by the skilled artisan in light of the teachings and guidance.
    The breadth and scope of the present invention should not be limited by any of the above-described examples, but should be defined only in accordance with the following clauses and their equivalents. Other aspects of the invention are set out as in the following numbered clauses: 1. A catadioptric objective for inspecting a substrate using scattered radiation, including: a first optical group configured to transform radiation or a first polarization into radiation or a second polarization, the first optical group comprises a reflective element to reduce chromatic aberrations due to a spectral range of the radiation; a second optical group including a refractive element configured to increase a numerical aperture of the catadioptric objective; and a beamsplitter configured to provide radiation of the first polarization to the first optical group and radiation of the second polarization to the second optical group. 2. The objective of clause 1, where the beam splitter transmits radiation or the first polarization and reflects radiation or the second polarization. 3. The objective of clause 1, where the beam splitter reflects radiation of the first polarization and transmits radiation of the second polarization. 4. The objective of clause 1, further including: a lens configured to control a range of angles from which the beam splitter receives radiation. 5. The objective of clause 1, where the first optical group comprises a quarter-wave plate, a negative power lens, and a concave mirror. 6. The objective of clause 1, where the second optical group comprises a negative power lens and a positive power lens. 7. A catadioptric objective for inspecting a substrate using scattered radiation, including: a first optical group including a reflective element configured to reduce chromatic aberrations due to a spectral range of radiation; a folding mirror configured to provide off-axis radiation to a pupil of the objective; and a second optical group including a refractive element configured to increase a numerical aperture of the catadioptric objective. 8. The objective of clause 7, further including: a lens configured to control a position of the pupil of the objective. 9. The objective of clause 7, where the first optical group comprises a negative power lens and a concave mirror. 10. A method for inspecting a substrate using a catadioptric objective, including: transforming radiation or a first polarization into radiation or a second polarization using a first optical group of the catadioptric objective, the first optical group comprising a reflective element configured to reduce chromatic aberrations due to a spectral range of the radiation; increasing a numerical aperture of the catadioptric objective using a second optical group, the second optical group comprising a refractive element; and providing radiation of the first polarization to the first optical group and radiation of the second polarization to the second optical group. 11. The method of clause 10, providing the radiation of the first polarization to the first optical group and the radiation of the second optical group comprising: transmitting radiation of the first polarization; and reflecting radiation or the second polarization. 12. The method of clause 10, providing the radiation of the first polarization to the first optical group and the radiation of the second optical group comprising: reflecting radiation of the first polarization; and transmitting radiation or the second polarization. 13. The method of clause 10, further including: controlling a range of angles from which the beam splitter receives radiation. 14. The method of clause 10, further including using a quarter-wave plate, a negative power lens, and a concave mirror as the first optical group. 15. The method of clause 10, further including using a negative power lens and a positive power lens as the second optical group. 16. A method for inspecting a substrate using a catadioptric objective, including: reducing chromatic aberrations due to a spectral range of radiation by using a First optical group of the catadioptric objective; providing off-axis radiation to a pupil of the catadioptric objective by using a mirror; and increasing a numerical aperture of the catadioptric objective using a second optical group, the second optical group comprising a refractive element. 17. The method of clause 16, further including: controlling a position of the pupil of the catadioptric objective by using a lens. 18. The method of clause 16, further including using a negative power lens and a concave mirror as the first optical group.
    权利要求:
    Claims (1)
    [1]
    1, A lithography device comprising: an exposure device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.
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    法律状态:
    2009-12-01| AD1A| A request for search or an international type search has been filed|
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