Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/544—Marks applied to semiconductor devices or parts, e.g. registration marks, alignment structures, wafer maps
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/70605—Workpiece metrology
  • G03F7/70616—Monitoring the printed patterns
  • G03F7/70633—Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/70605—Workpiece metrology
  • G03F7/70681—Metrology strategies
  • G03F7/70683—Mark designs
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/70605—Workpiece metrology
  • G03F7/706843—Metrology apparatus
  • G03F7/706845—Calibration, e.g. tool-to-tool calibration, beam alignment, spot position or focus
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
  • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
  • G03F9/7073—Alignment marks and their environment
  • G03F9/7076—Mark details, e.g. phase grating mark, temporary mark
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
  • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
  • G03F9/7088—Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
  • H01L21/0271—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers
  • H01L21/0273—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers characterised by the treatment of photoresist layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
  • H01L21/68—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for positioning, orientation or alignment
  • H01L21/681—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for positioning, orientation or alignment using optical controlling means
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2223/00—Details relating to semiconductor or other solid state devices covered by the group H01L23/00
  • H01L2223/544—Marks applied to semiconductor devices or parts
  • H01L2223/54426—Marks applied to semiconductor devices or parts for alignment

Definitions

• the present invention generally relates to an overlay target used for overlay metrology, and more particularly to a multi-layer target and complimentary metrology systems.
• semiconductor- based devices may be produced by fabricating a series of layers on a substrate, some or all of the layers including various structures.
• the relative position of these structures both within a single layer and with respect to structures in other layers is critical to the performance of the devices.
• the misalignment between various structures is known as overlay error.
• overlay error is one of the most critical process control techniques used in the manufacturing of integrated circuits and devices.
• Overlay accuracy generally pertains to the determination of how accurately a first patterned layer aligns with respect to a second patterned layer disposed above or below it and to the determination of how accurately a first pattern aligns with respect to a second pattern disposed on the same layer.
• overlay measurements are performed via test patterns that are printed together with layers of the wafer. The images of these test patterns are captured via an imaging tool and an analysis algorithm is used to calculate the relative displacement of the patterns from the captured images.
• Such overlay metrology targets generally comprise features formed in two layers, the features configured to enable measurement of spatial displacement between features of the layers (i.e., the overlay or displacement between layers).
• FIGS. 1A through 2B illustrate typical overlay targets of the prior art.
• FIGS. 1A and 1 B illustrate overlay targets having 180 degree and 90 degree rotational symmetry, respectively, about a center of symmetry.
• the target structures of FIG. 1A and 1 B include pattern elements (e.g., 102a through 108b), which are individually invariant to 90 degree rotation. Due to the 90 degree invariance of the individual pattern elements the pattern elements of targets 100 and 101 of FIGS. 1A and 1 B are suitable for both X-overlay and Y-overlay measurements.
• FIGS. 2A and 2B illustrate targets 200 and 201 which display invariance to a 90 degree and 180 degree rotation, respectively.
• the pattern elements e.g., 202a through 208d
• the pattern elements display only 180 degree rotational symmetry.
• at least two separate orthogonally oriented pattern elements must be used in order to measure overlay in both the X- and Y-direction.
• the pattern elements 202a, 204a, 202d, and 204d may be used to measure overlay in a first direction
• elements 202b, 204b, 204c, and 202c may be used to measure overlay in a second direction orthogonal to the first direction.
• the multidirectional overlay mark may include, but is not limited to, a plurality of target structures including three or more target structures, each target structure including a set of two or more pattern elements, wherein the target structures are configured to share a common center of symmetry upon alignment of the target structures, each target structure being invariant to N degree rotation about the common center of symmetry, wherein N is equal to or greater than 180 degrees, wherein each of the two or more pattern elements has an individual center of symmetry, wherein each of the two or more pattern elements of each target structure is invariant to M degree rotation about the individual center of symmetry, wherein M is equal to or greater than 180 degrees.
• multi-layer overlay target for use in imaging based metrology may include, but is not limited to, a plurality of target structures including three or more target structures, wherein each target structure includes a set of two or more pattern elements, wherein the target structures are configured to share a common center of symmetry upon alignment of the target structures, wherein each target structure is invariant to a 90 degree rotation about the common center of symmetry, wherein each of the two or more pattern elements has an individual center of symmetry, wherein each of the two or more pattern elements of each target structure is invariant to M degree rotation about the individual center of symmetry, wherein M is equal to or greater than 180 degrees.
• the apparatus may include, but is not limited to, an illumination source; a first polarizer configured to polarize at least a portion of light emanating from the illumination source; a beam splitter configured to direct a first portion of light processed by the first polarizer along an object path to a surface of one or more specimens and a second portion of light processed by the first polarizer along a reference path; a detector disposed along a primary optical axis, wherein the detector is configured to collect a portion of light reflected from the surface of the one or more specimens; and a second polarizer configured to analyze at least a portion of light reflected from the surface of the one or more specimens prior to the light impinging on the image plane of the detector, wherein the first polarizer and the second polarizer are arranged to minimize the amount of light reflected from unpattern portions of the one or more specimens reaching the detector.
• the apparatus may include, but is not limited to, an illumination source; a detector disposed along a primary optical axis, wherein the detector is configured to collect a portion of light reflected from a surface of the one or more specimens; an aperture positioned at a pupil plane of an illumination path, wherein the aperture is configured to select an illumination angle of illumination emanating from the illumination source, wherein the illumination angle is suitable for achieving a selected contrast level at an imaging plane of the detector; and a first beam splitter configured to direct a first portion of light transmitted through the aperture along an object path to a surface of one or more specimens and a second portion of light transmitted through the aperture along a reference path.
• FIG. 1A is a top plan view of an overlay target.
• FIG. 1 B is a top plan view of an overlay target.
• FIG. 2A is a top plan view of an overlay target.
• FIG. 2B is a top plan view of an overlay target.
• FIG. 3 is a top plan view of a multi-layer overlay target, in accordance with one embodiment of the present invention.
• FIG. 4 is a top plan view of a multi-layer overlay target, in accordance with one embodiment of the present invention.
• FIG. 5A is a top plan view of a multi-layer overlay target, in accordance with one embodiment of the present invention.
• FIG. 5B is a top plan view of a multi-layer overlay target, in accordance with one embodiment of the present invention.
• FIG. 6 is a top plan view of a multi-layer overlay target, in accordance with one embodiment of the present invention.
• FIG. 7 is a top plan view of a multi-layer overlay target, in accordance with one embodiment of the present invention.
• FIG. 8 is a top plan view of a multi-layer overlay target printed in the presence of dummy fill, in accordance with one embodiment of the present invention.
• FIG. 9 is a top plan view of a multi-layer overlay target printed in the presence of dummy fill, in accordance with one embodiment of the present invention.
• FIG. 10 is a top plan view of a multi-layer overlay target printed in the presence of dummy fill, in accordance with one embodiment of the present invention.
• FIG. 11 is a block diagram view of a system suitable contrast enhancement of a multi- layer overlay metrology target.
• FIG. 12 is a block diagram view of a system suitable contrast enhancement of a multi-layer overlay metrology target.
• FIG. 13A is a schematic view of an illumination pupil structure suitable for contrast enhancement, in accordance with one embodiment of the present invention.
• FIG. 13B is a schematic view of an illumination pupil structure suitable for contrast enhancement, in accordance with one embodiment of the present invention.
• FIG. 13C is a schematic view of an illumination pupil structure suitable for contrast enhancement, in accordance with one embodiment of the present invention.
• an overlay target suitable for imaging based overlay metrology is described in accordance with the present disclosure.
• the overlay targets of the present invention may be used to determine overlay error between two successive process layers of a semiconductor wafer.
• an overlay target may be utilized to measure the alignment of a first semiconductor layer with respect to a second semiconductor layer, where the second layer and the first layer are disposed successively.
• an overlay target may be used to determine alignment error between two structures formed on a common semiconductor layer via two or more different processes (e.g., lithographic exposures).
• an overlay target may be utilized to measure the alignment of a first pattern with respect to a second pattern, where the first pattern and the second pattern are successive patterns formed on the same semiconductor layer.
• an overlay target may be printed at a specific location on a first wafer layer and a second wafer layer, so that when the first and second layers are properly aligned the pattern elements of the first structure and second structure of the overlay target also align.
• first and second layers are 'mis- registered,' however, a relative shift between the pattern elements of the first structure 102 and the second structure 104 of a given thin overlay mark 100 exists, a shift that can be measured through a variety of techniques.
• the structures and pattern elements described herein may be fabricated using any process known in the art suitable for semiconductor wafer processing, such as, but not limited to, photolithographic, etching, and deposition techniques. Methods for printing overlay targets and their contained structures, pattern elements, and pattern sub-elements are described generally in U.S. application Ser. No. 11 /179,819 filed on Feb. 23, 2006, and is incorporated herein by reference.
• FIG. 3 illustrates a top plan view of a six- layer overlay target 300 suitable for imaging based metrology, in accordance with an exemplary embodiment of the present invention.
• the overlay target 300 may include three or more target structures.
• each of the target structures of the overlay target 300 includes two or more pattern elements.
• texture patterns in FIG.2 are used to represent the different target structures of a target, wherein pattern elements belonging to the same target structure have the same texture.
• the texture patterns displayed in the various figures of the present disclosure should not be interpreted as limiting as the selected texture pattern is not representative of a structural aspect of the associated pattern element, but is merely utilized to represent pattern elements of the same target structure.
• the target 300 may include six target structures (each structure illustrated with a unique texture). Further, each of the six target structures of target 300 may include two pattern elements. For instance, as shown in FIG. 3, a first structure may include pattern elements 302a and 302b, a second structure may contain pattern elements 304a and 304b, a third structure may include pattern elements 306a and 306b, a fourth structure may include pattern elements 308a and 308b, a fifth structure may include pattern elements 310a and 310b, and a sixth structure may include pattern elements 312a and 312b. More generally, a given structure of target 300 (i.e., first, second, third, or up to an Nth structure) may contain from two pattern elements up to and including an Nth pattern element.
• each of the target structures of target 300 are designed such that each is invariant to a 180 degree rotation about a common center of symmetry 110.
• a 180 degree rotation about a common center of symmetry 110.
• the top view image of the structures remains identical to the top view image of the structures prior to rotation.
• the overall target consisting of the multiple individual structures, is invariant to a 180 degree rotation about the common center of symmetry 110 when properly aligned.
• the two pattern elements of each structure may be oriented at positions diagonally opposed to one another, resulting in 180 degree rotational symmetry for the overlay target as a whole.
• overlay metrology measurements may be performed utilizing any pair of the six target structures present in overlay target 300.
• overlay metrology measurements may be acquired from all six structures in a single image grab.
• each pattern element of each structure of the target 300 possesses an individual center of symmetry.
• the pattern elements of 300 are designed such that each pattern element (e.g., 302a -302b, 304a-304b and etc.) are invariant to a 90° rotation about the center of symmetry of the individual pattern element.
• X-overlay and Y-overlay measurements may be performed utilizing the same pattern element.
• a rectangular target region as depicted in FIG. 3, is not a limitation and that generally a variety of mark region shapes (e.g., square, trapezoid, parallelogram, or ellipse) may be used to characterize the perimeter of an overlay target boundary.
• mark region shapes e.g., square, trapezoid, parallelogram, or ellipse
• a set of structures of a given target may be arranged such that their outermost edges form an ellipsoidal or circular shaped target region.
• the two dimensional shapes of the various pattern elements of the first structure and the second structure are not limited.
• the square shape of the pattern elements as depicted in FIG. 3, should not be interpreted as a limitation but merely an illustration. It is recognized that a variety of pattern element shapes exist that may produce the 90 degree rotational invariance as required of the pattern elements (e.g., 302a through 312b) of target structure 300.
• the pattern elements of target structure 300 may include pattern elements having a square shape, a cross shape, or a diamond shape, among others.
• the pattern elements of the first structure may be identical to the pattern elements of the second structure.
• all of the pattern elements of target structure 300 may have a square shape.
• the pattern elements of the various structures of the target structure 300 may be different.
• the pattern elements 302a and 302b of the first structure may be different from the pattern elements 304a and 304b of the second structure.
• the pattern elements 302a and 302b of the first structure may have a square shape
• the pattern elements 304a and 304b of the second structure may have a 'cross' shape (not shown).
• the shapes of the pattern elements within a single target structure may be uniform. More specifically, the pattern elements within a given structure may have an identical shape. For example, the pattern elements 306a and 306b of the third target structure may both have a square shape.
• the shapes of the pattern elements within a given structure may be non-uniform (not shown). More specifically, a given structure may contain more than one pattern element shape.
• the fourth structure may include pattern element 308a having a 'cross' shape (not shown) and a pattern element 308b having a square shape. It should be recognized that there is no generalized limitation on the shape of the pattern elements of the target structures of overlay target 300, provided the shapes of the pattern elements and the orientation of the pattern elements results in the target structures having 180 degree rotational invariance about their common center of symmetry and each pattern element of each target structure having 90 degree rotational invariance about its individual center of symmetry.
• the pattern elements of the structures of overlay target 300 may be arranged according to various sets of spatial positions.
• the pattern elements 302a and 302b of the first structure, the pattern elements 304a and 304b of the second structure, the pattern elements 306a and 306b of the third structure, the pattern elements 308a and 308b of the fourth structure, the pattern elements 310a and 310b of the fifth structure, and the pattern elements 312a and 312b of the sixth structure may be arranged such that they form a periodic or non-periodic pattern.
• the two-dimensional arrangement of the pattern elements 302a through 312b forms a two-dimensional periodic array. It is contemplated herein that a variety of arrangements may be suitable for creating the 180 degree rotational invariance of the target 300.
• FIG. 4 illustrates a top plan view of an overlay target 400, in accordance with an alternate embodiment of the present invention. Applicant notes that unless otherwise noted the descriptive material provided above with respect to target 300 should be interpreted to apply to the remainder of the instant disclosure.
• the multilayer overlay target 400 may include three or more target structures, with each target structure including two or more pattern elements.
• the overlay target 400 may include six target structures, with each target structure containing four pattern elements.
• a first structure may include pattern elements 402a, 402b, 402c and 402d
• a second structure may contain pattern elements 404a, 404b, 404c, and 404d
• a third structure may contain pattern elements 406a, 406b, 406c, and 406d, and so on.
• a given structure of target 400 i.e., first, second, third, or up to an Nth structure
• each of the target structures of target 400 are designed such that each is invariant to a 180 degree rotation about a common center of symmetry 110, resulting target 400 also being invariant to a 180 degree rotation.
• the pattern elements 402a and 402b of the first structure of target 400 are oriented diagonally from the pattern elements 402c and 402d and arranged such that the first target structure is invariant to 180 degree rotation about its center of symmetry 110. It is noted, however, that the target structures of target 400 are not invariant to a 90 degree rotation
• target 400 may also be utilized in overlay metrology between more than two layers. Resultantly, overlay metrology measurements may be performed utilizing any pair of the six target structures present in overlay target 400. Moreover, due to the collocation of the center of symmetries 110 of each structure of target 400, overlay metrology measurements may be acquired from all six structures in a single image grab.
• the center of symmetry for the set of pattern elements utilized for X-overlay measurements (e.g., 402a and 402d) is collocated with the set of pattern elements utilized for Y-overlay measurements (e.g., 402b and 402c).
• a design such as this allows for the simultaneous acquisition of X-overlay and Y-overlay data in a single "image grab.” As such, the move- acquire-measurement time as compared to traditional overlay targets is greatly reduced.
• the design depicted in FIG. 4 may allow for compatibility with presently existing metrology tool procedures and architectures.
• the individual pattern elements of target 400 are designed such that each pattern element (e.g., 402a -402b, 404a-404b and etc.) is invariant to a 180° rotation about the center of symmetry 112 of the individual pattern element.
• each pattern element e.g., 402a -402b, 404a-404b and etc.
• the individual pattern elements of target 400 are not invariant to a 90° rotation about the center of symmetry 112 of the individual pattern element.
• a single pattern element e.g., 402a
• each individual pattern element may be utilized to measure either X-overlay or Y-overlay.
• the target structures of target 400 include pairs of pattern elements, one designated for X-overlay and one designated for Y-overlay.
• the shapes of the pattern elements depicted in FIG. 4 do not represent a limitation as it should be recognized that there exist a number of other pattern elements shapes having 180 degree rotational symmetry (but not 90 degree rotational symmetry) which are suitable for implementation in the present invention.
• any pattern element and target structure scheme which produces 180 degree rotational symmetry (without producing 90 degree rotational symmetry) for the target structures about the common center of symmetry 110, while producing 180 degree rotational symmetry (without producing 90 degree rotational symmetry) for the individual pattern elements (e.g., 402a through 412d) about each pattern element center of symmetry 112, may be suitable for implementation in the present invention.
• the target structure and pattern element scheme depicted in FIG. 4 should be interpreted merely as illustrative and should not be considered limiting.
• FIG. 5A illustrates a top plan view of an overlay target 500, in accordance with an alternate embodiment of the present invention.
• the multilayer target 500 may include three or more target structures, with each target structure including two or more pattern elements.
• the overlay target 500 may include six target structures, with each target structure containing four pattern elements.
• a first structure may include pattern elements 502a, 502b, 502c and 502d
• a second structure may contain pattern elements 504a, 504b, 504c, and 504d, and so on.
• a given structure of target 500 i.e., first, second, third, or up to an Nth structure
• each of the target structures of target 500 are designed such that each is invariant to a 90 degree rotation about a common center of symmetry 110, resulting in target 500 also being invariant to a 90 degree rotation.
• the pattern elements 512a, 512b, 512c, and 512d of the sixth target structure of target 500 are arranged such that the sixth target structure is invariant to 90 degree rotation about its center of symmetry 110.
• the individual pattern elements of target 500 are designed such that each pattern element (e.g., 502a -502d, 504a-504d and etc.) is invariant to a 180° rotation about the center of symmetry of the individual pattern element 112. Again, the pattern elements of 500 are not invariant to a 90° rotation about the center of symmetry of the individual pattern element 112. Therefore, as in target 400, a single pattern element (e.g., 502a) cannot be utilized to measure both X-overlay and Y-overlay. As such, each individual pattern element may be utilized to measure either X-overlay or Y-overlay.
• each pattern element may be utilized to measure either X-overlay or Y-overlay.
• the target structures of target 500 include two pairs of pattern elements, one pair (502a and 502c) designated for X-overlay measurement and one pair (502b and 502d) designated for Y-overlay measurement.
• the shapes of the pattern elements depicted in FIG. 5 do not represent a limitation as it should be recognized that there exist a number of other pattern elements shapes having 180 degree rotational symmetry (without producing 90 degree rotational symmetry) about an individual center of symmetry of the pattern element which are suitable for implementation in the present invention.
• any pattern element and target structure scheme which produces 90 degree rotational symmetry for the target structures about the common center of symmetry 110, while producing 180 degree rotational symmetry (without producing 90 degree rotational symmetry) for the individual pattern elements (e.g., 502a through 512d) about each pattern element center of symmetry 112, may be suitable for implementation in the present invention.
• the target structure and pattern element scheme depicted in FIG. 5 should be interpreted merely as illustrative and should not be considered limiting.
• FIG. 5B illustrates a top plan view of an overlay target 501 , in accordance with an alternate embodiment of the present invention.
• the multilayer target 501 may include three or more target structures, with each target structure including two or more pattern elements.
• the overlay target 501 may include six target structures, with each target structure containing four pattern elements.
• a first structure may include pattern elements 514a, 514b, 514c and 514d
• a second structure may contain pattern elements 516a, 516b, 516c, and 516d
• a third structure may contain pattern elements 518a, 518b, 518c, and 518d, and so on.
• a given structure of target 501 i.e., first, second, third, or up to an Nth structure
• the overlay target 501 is designed to be invariant to 180 degrees, but not invariant to 90 degrees.
• each of the target structures of target 501 are designed such that each is at least invariant to 180 degree rotation about a common center of symmetry 110, resulting in target 501 also being invariant to a 180 degree rotation.
• the pattern elements 524a, 524b, 524c, and 524d of the sixth target structure of target 501 are arranged such that the sixth target structure is invariant to 180 degree rotation (but not 90 degree rotation) about its center of symmetry 110.
• each constituent target structure of overlay target 501 need not be limited to 180 degree rotational symmetry.
• the arrangement of pattern elements 518a, 518b, 518c, and 518d form a 90 degree rotationally invariant target structure.
• the combination of the six target structures form an overlay target 501 which lacks 90 degree rotational symmetry but possesses 180 degree rotational symmetry since the remaining target structures lack 90 degree rotational symmetry.
• any pattern element and target structure scheme which produces 180 degree rotational symmetry for the target structures about the common center of symmetry 110, while producing 180 degree rotational symmetry for the individual pattern elements (e.g., 514a through 524d) about each pattern element center of symmetry 112, may be suitable for implementation in the present invention.
• the target structure and pattern element scheme depicted in FIG. 5B should be interpreted merely as illustrative and should not be considered limiting.
• FIG. 6 illustrates a top plan view of overlay target 600, in accordance with alternate embodiment of the present invention.
• one or more target structures of the various embodiments of the overlay targets described previously herein may lack sufficient contrast suitable for implementation in an overlay metrology measurement process.
• one or more target structures of a given overlay target 600 may be enhanced by increasing the overall target structure surface area, thereby increasing the information content of the enhanced target structure.
• the number of pattern elements included in a given target structure may be determined by the level of contrast of the given target structure.
• the first structure of target 600 may have lower contrast levels than desirable.
• the designer of the target may enhance the contrast by including additional pattern elements to the target structure.
• the first target structure of target 600 includes four overall pattern elements 602a, 602b, 602c, and 602d, as opposed to the only two pattern elements in the remaining targets structures of the target 600.
• the additional pattern elements utilized to increase contrast of a given target structure should be designed to adhere to the overall set of design rules for the given target. As such, the additional pattern elements should adhere to the symmetry requirements placed on the overall target structure and individual pattern elements in a manner consistent with the above described targets 300, 400, 500, and 501.
• the pattern elements 602a, 602b, 602c, and 602d maintain 180 degree rotational symmetry about the center of symmetry 110 of the overall target 600. Resultantly, the target 600 will maintain 180 degree rotational symmetry about the center of symmetry 110 in a manner similar to targets 300, 400, and 501 described previously herein. Furthermore, also as illustrated in FIG. 6, the pattern elements 602a, 602b, 602c, and 602d maintain 90 degree rotational symmetry about the center of symmetry of the individual pattern elements in a manner consistent with target 200 described previously herein.
• FIG. 7 illustrates a top plan view of overlay target 700, in accordance with an alternate embodiment of the present invention.
• each target structure of target 700 may include the number of pattern elements necessary to achieve adequate levels of information content (i.e., contrast).
• the information content of one or more target structures may be satisfied by increasing the overall target structure area of target structures lacking in contrast.
• the first structure, second structure, third structure and fourth structure of target 700 may have varying degrees of information deficiencies. As such, the designer may tailor the number of pattern elements of each target structure to make up for this deficiency.
• the first structure having the lowest level of contrast, may include twelve pattern elements 702a, 702b, 702c, 702d, 702e, 702f, 702g, 702h, 702i, 702j, 702k, and 7021.
• the second and third structures may have a similar level of contrast needs, each including eight overall pattern elements.
• the second structure includes 704a, 704b, 704c, 704d, 704e, 704f, 704g, and 704h, while the third structure includes 706a, 706b, 706c, and 706d.
• the fourth target structure of target 700 may require little contrast enhancement or may have surplus information content.
• the fourth target structure may include only 4 target pattern elements 708a, 708b, 708c, and 708d.
• the additional pattern elements utilized to increase contrast of the target structures of overlay target 700 should be designed to adhere to the overall set of design rules for the given target. As such, the additional pattern elements should adhere to the symmetry requirements placed on the overall target structure and individual pattern elements in a manner consistent with the above described targets 400, 500, and 501.
• the pattern elements 704a. . .704h of the second target structure maintain 90 degree rotational symmetry about the center of symmetry 110 of the overall target 700, while pattern elements 708a . . . 708d of the fourth target structure possess 180 degree rotational symmetry about the center of symmetry 110.
• the target 700 will maintain at least 180 degree rotational symmetry about the center of symmetry 110 in a manner similar to targets 400 and 501 described previously herein. It is further recognized that the above described utilization of additional pattern elements may also be implemented such that the overlay target possesses 90 degree rotational symmetry similar to target 500 illustrated in FIG. 5A.
• the individual pattern elements 702a . . . 7021, 704a . . . 704h, 706a . . . 706h, and 708a . . . 708d each are 180 degree rotationally symmetric about the center of symmetry of each individual pattern element in a manner consistent with target 400, 500, and 501 described previously herein.
• FIG. 8 illustrates a top plan view of overlay target 800 in the presence of dummy fill 801 , in accordance with an alternate embodiment of the present invention.
• the overlay targets 400, 500, and 501 wherein X-overlay and Y-overlay measurements are performed utilizing different pattern elements, allow for overlay metrology measurement processes in the presence of dummy fill 801.
• FIG. 8 depicts an overlay target 800 implemented in the presence of dummy fill 801.
• overlay target 800 includes six target structures, with each target structure including four pattern elements. In this manner, the first structure includes pattern elements 802a . . . 802d, the second structure includes pattern elements 804a . . .
• the third structure includes pattern elements 806a . . . 806d
• the fourth structure includes pattern elements 808a . . . 808d
• the fifth structure includes pattern elements 810a . . . 81 Od
• the sixth structure includes pattern elements 812a . . . 812d.
• two of the pattern elements of each structure are designated for X-overlay measurement (e.g., 802a, 806a, or 810a), while the remaining two pattern elements of each target structure are designated for Y- overlay measurement (e.g., 812d, 808d, or 804d).
• the pattern elements (e.g., 802a . . . 812d) of target 800 each include a plurality of sub-elements 803.
• each pattern element (e.g., 802a . . . 812d) may include three parallel thin rectangular shaped and periodically spaced sub-elements 803. It should be noted that the shape and arrangement of the sub-elements 803 depicted in FIG. 8 does not represent a limitation but rather should be interpreted as illustrative.
• the dummy fill 801 may consist of a periodic grating structure printed above or below the overlay target 800 as illustrated by the FIG. 8.
• each pattern element e.g., 802a . . . 812d
• the lines of the dummy fill 801 run perpendicularly to the lines of the sub-element 803 structure.
• aligning the sub-elements 803 of the pattern elements e.g., 802a . . . 812d
• aligning the sub-elements 803 of the pattern elements mitigates the risk of contamination of the metrology signal of a given overlay target with information from the underlying dummy fill structure 801.
• the overlay target 800 possesses 180 degree rotational symmetry about the common center of symmetry of the constituent target structures of the target, while the individual pattern elements (e.g., 802a . . . 812d) of the target 800 possess 180 degree rotational symmetric about the center of symmetry of each individual pattern element.
• the periodicity of the sub-elements 803 of the pattern elements (e.g., 802a . . . 812d), the dummy fill structure 801 , or both may consist of a resolution below that which is suitable for the implementing metrology system.
• the 1 st and -1 st diffraction orders may fall outside the aperture of the objective of the imaging system of the metrology system. It is recognized herein that this feature is particularly advantageous in the case of the dummy fill structure as it further mitigates the risk of contamination of the metrology signal of the target 800 with a signal from the dummy fill pattern 801.
• Target 900 illustrates a top plan view of overlay target 900 in the presence of dummy fill 801 , in accordance with an alternate embodiment of the present invention.
• Target 900 is similar to target 800 in that it possesses identical symmetry requirements as well as orthogonal pattern element and dummy fill alignment.
• Target 900 illustrates a square dimensioned target suitable for implementation in a metrology process.
• FIG. 10 illustrates a top plan view of overlay target 1000 in the presence of dummy fill 801 , in accordance with an alternate embodiment of the present invention.
• Target 1000 is similar to target 800 in that it possesses identical symmetry requirements as well as orthogonal pattern element and dummy fill alignment.
• Target 1000 illustrates the implementation of contrast enhancement as described previously herein with respect to FIGS. 6 and 7.
• FIG. 10 illustrates an acquisition mark 1001 located at the center of the overlay target 1000.
• the acquisition mark 1001 may be utilized to identify the approximate position of the center of the target in order to position the target in the center of the field of view (FOV) of the given metrology tool.
• FOV field of view
• systems 1100 and 1200 suitable for contrast enhancement are described in accordance with the present invention. It is contemplated herein that systems 1100 and 1200 of the present invention may enable the implementation of the various multi-layer targets described previously herein.
• One limitation associated with the multilayer targets of the present invention includes the potential for lack of information content (i.e., contrast level) associated with their small measurement structures.
• the systems 1100 and 1200 are directed at providing enhanced contrast levels to counteract the presence of low contrast in one or more target structures of the various multi-layer targets of the present invention.
• the system 1100 is directed at the utilization of structured illumination in order to enhance the contrast level associated with one or more measurement structures associated with the target structures of the multi- layer targets of the present invention.
• the system 1200 is directed at the utilization of cross-polarization in order to enhance the contrast level associated with one or more measurement structures associated with the target structures of the multi-layer targets of the present invention.
• the systems 1100 and 1200 of the present invention may consist (but not required to consist) of adapting or reconfiguring presently existing optical metrology systems.
• the present invention may consist of adapting the KLA-Tencor Archer 100 overlay control system.
• a first linear polarizer may be inserted into an illumination path of a traditional system (e.g., Archer 100 system), while a second linear polarizer is placed within the imaging path of the traditional system.
• an aperture may be inserted at a pupil plane of an illumination path of a traditional system (e.g., Archer 100 system).
• the present invention is not limited to an adaptation of an Archer 100 system, but rather the description above should be interpreted merely as an illustration. It is anticipated that the present invention may be extended to a wide variety of microscopy and overlay metrology systems.
• the system 1100 suitable for contrast enhancement of a multi-layer overlay metrology target may include an illumination source 1102, an aperture 1104, a beam splitter 1108, and a detector 1110 configured to receive light reflected from one or more specimens 1114 (e.g., one or more wafers of a wafer lot).
• an illumination source 1102 an aperture 1104, a beam splitter 1108, and a detector 1110 configured to receive light reflected from one or more specimens 1114 (e.g., one or more wafers of a wafer lot).
• the illumination source 1102 of the system 1100 may include any illumination source known in the art.
• the illumination source 1102 may include a broadband light source (e.g., white light source).
• the illumination source 1102 may include, but is not limited to, a halogen light source (HLS).
• the halogen light source may include, but is not limited to, a tungsten based halogen lamp.
• the illumination source 1102 may include a Xenon arc lamp.
• the beam splitter 1108 of the system 1100 may split the light beam emanating from an illumination source 1102, after passing through the aperture, into two paths: an object path 1112 and a reference path 1113.
• the object path 1112 and the reference path 113 of the system 100 may form a portion of a two beam interference optical system.
• the beam splitter 1108 may direct a first portion of the beam of light from the illumination path 1115 along the object path 1112, while allowing a second portion of the beam of light from the illumination path 115 to be transmitted along the reference path 1113.
• the beam splitter 108 may direct a portion of the light emanating from the illumination source 1102, after passing through the aperture 1104, to the surface of the specimen 1114 (e.g., via object path 1112) disposed on the specimen stage 1118.
• the beam splitter 1108 may transmit a second portion of the light emanating from the illumination source 1102 to the components of the reference path 1113.
• the beam splitter 1108 may transmit a portion of light from the illumination path 1115 along the reference path 1113 to a reference mirror (not shown). It should be recognized by those skilled in the art that any beam splitter known in the art is suitable for implementation as the 1 beam splitter 1108 of the present invention.
• the reference path 1113 may include, but is not limited to, a reference mirror, a reference objective, and a shutter configured to selectively block the reference path 1113.
• a two-beam interference optical system may be configured as a Linnik interferometer. Linnik interferometry is described generally in U.S. Patent No. 4,818,110, issued on April 4, 1989, and U.S. Patent No. 6,172,349, issued on January 9, 2001 , which are incorporated herein by reference.
• the system 1100 may include a main objective lens 1109.
• the main objective lens 1109 may aid in directing light along the object path 1112 to the surface of the specimen 1114 disposed on the specimen stage 1118.
• the beam splitter 1108 may direct a portion of the light beam 1115 emanating from the illumination source 1102, after passing through the aperture 1104, along the object path 1112.
• the main objective lens 1109 may focus light from the object path 1112, which is collinear with the primary optical axis 1107, onto the surface of the specimen 1114.
• any objective lens known in the art may be suitable for implementation as the main objective lens 1109 of the present invention.
• a portion of the light impinging on the surface of the specimen 1114 may be reflected by the specimen 1114 and directed along the primary optical axis 1107 via the objective 1109 and the beam splitter 1108 toward the detector 1110.
• intermediate optics devices such as intermediate lenses, additional beam splitters (e.g., a beam splitter configured to split off a portion of light to a focusing system), and imaging lenses 1106 may be placed between the objective 1109 and the imaging plane of the detector 1110.
• the detector 1110 of the system 100 may be disposed along the primary optical axis 1107 of the system 1100.
• the camera 1110 may be arranged to collect imagery data from the surface of the specimen 1114.
• the detector 1110 may include a charge coupled device (CCD) based camera system.
• the detector 1110 may include a time delay integration (TDI)-CCD based camera system.
• the detector 1110 may be communicatively coupled with a computer system (not shown).
• digitized imagery data may be transmitted from the detector 1110 to the computer system via a signal, such as a wireline signal (e.g., copper line, fiber optic cable, and the like) or a wireless signal (e.g., wireless RF signal).
• a signal such as a wireline signal (e.g., copper line, fiber optic cable, and the like) or a wireless signal (e.g., wireless RF signal).
• the detector 110 may reside along an additional optical axis of the system 1100.
• one or more additional beam splitters may be utilized to divert a portion of light reflected from the surface of the specimen 1114 and traveling along the object path 1 112 onto an additional optical axis, which non-parallel to the object path 1112.
• the camera 1110 may be arranged such that light traveling along the additional optical axis impinges the image plane of the camera 1110.
• the aperture 1104 may be position at a pupil plane of the illumination path 1115.
• the aperture 1104 may be configured to have a well-defined shape in order to select an predetermined illumination angle of the illumination emanating from the illumination source 1102. The illumination angle is selected so as to achieve a selected contrast level at an imaging plane of the detector 1110.
• the aperture may have a geometric shape or a combination of geometric shapes.
• the aperture may have an 'X' shape or a 'cross' shape.
• the aperture may have a ring shape. It is further recognized herein that these shapes may be achieved via diffractive optical elements.
• the illumination path may include a plurality of apertures.
• one of the plurality of apertures may be selected during recipe training in order to optimize the contrast level for a specific stack and target design. It is recognized herein that this may be done utilizing a trial and error method.
• the aperture 1104 may include a tunable aperture.
• the aperture 1104 may consist of a tunable aperture that may be programmed by a user in order to produce a plurality of selectable illumination structures.
• a programmed tunable aperture may be tuned in a manner to optimize the contrast for a specific stack or target design.
• the tunable aperture may include, but is not limited to, a micro mirror array.
• the system 1200 suitable for contrast enhancement of a multi-layer overlay metrology target may include an illumination source 1202, a first polarizer 1204, a beam splitter 1206, a second polarizer 1208 and a detector 1210 configured to receive light reflected from one or more specimens 1212 (e.g., one or more wafers of a wafer lot).
• an illumination source 1202 a first polarizer 1204, a beam splitter 1206, a second polarizer 1208 and a detector 1210 configured to receive light reflected from one or more specimens 1212 (e.g., one or more wafers of a wafer lot).
• the illumination source 1202, the beam splitter 1206, the detector of 1210, the specimen stage 1214, and the reference path 1216 are similar to the illumination source 1102, the beam splitter 1108, the detector of 1110, the specimen stage 1118, and the reference path of 1113 of system 1100.
• the description of system 1100 should be interpreted to extend to system 1200 except where otherwise noted.
• the first polarizer 1204 is arranged to polarize light emanating from the illumination source 1202.
• the first 1204 may be disposed along an illumination path 1205 such that light emanating from the illumination source 1202 may be polarized by the first polarizer 1204.
• the second polarizer 1208 may be arranged to serve as an analyzer for light reflected from the specimen 1202.
• the first polarizer 1204 and the second polarizer 1208 may configured be such that the amount of light reflected from unpatterned parts of the specimen 1212 or from periodic unresolved patterns of the specimen 1212 that reaches the imaging plane of the detector 1210 is minimized.
• the first polarizer 1204 and the second polarizer 1208 may both include linear polarizers. In the case of linear polarizers, the first polarizer 1204 and the second polarizer 1208 may be arranged such that their polarizing axes are substantially perpendicular to one another.
• the first polarizer 1204 may include a polarizer configured to transmit only radially polarized light, while the second polarizer is configured to transmit only azimuthally polarized light.
• the signal from unpatterned portions of the specimen 1212 may be minimized in a variety of other manners.
• a combination of wave-plates and polarizers may be implemented to achieve the results illustrated above.
• a first polarizer 1204 and first quarter-wave plate (not shown) oriented at 45 degrees with respect to the first polarizer may be positioned in the illumination path 1205, while a second polarizer 1208 and a second quarter- wave plate (not shown) oriented at 45 degree with respect to the second polarizer may be positioned along the imaging path 1209.
• any combination of polarizers and wave- plates e.g., half-wave plate which creates the cross-polarization effect as described above may be suitable for implementation in the present invention.
• the systems 1100 and 1200 may be utilized in combination to improve the level of contrast.
• the present invention may be utilized to ensure a low level of intensity at a point of symmetry of the target.
• the combination of structured illumination and cross-polarization aspects of the present invention may be implemented utilizing the illumination pupils illustrated in FIG. 13.
• a suitable illumination pupil may have a cross-shape 1302, a vertical line shape 1304 (e.g., Y-direction), or a horizontal line shape 1306 (e.g., X- direction).
• the illumination pupils 1302, 1304, and 1306 may be implemented in combination with an illumination polarizer and an imaging polarizer.
• the pupils 1302-1306 may be implemented in concert with a X-polarizer disposed within the illumination path (e.g., 1115 or 1205) of the system and a Y-polarizer disposed within the imaging path (e.g., 1107 or 1207) of the system.
• the pupils 1302-1306 may be implement in concert with a Y-polarizer disposed within the illumination path of the system and a X-polarizer disposed within the imaging path of the system.
• All of the system and methods described herein may include storing results of one or more steps of the method embodiments in a storage medium.
• the results may include any of the results described herein and may be stored in any manner known in the art.
• the storage medium may include any storage medium described herein or any other suitable storage medium known in the art.
• the results can be accessed in the storage medium and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc.
• the results may be stored "permanently,” “semi-permanently,” temporarily, or for some period of time.
• the storage medium may be random access memory (RAM), and the results may not necessarily persist indefinitely in the storage medium.
• a typical data processing system generally includes one or more of a system unit housing, a video display device, a memory such as volatile and non-volatile memory, processors such as microprocessors and digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices, such as a touch pad or screen, and/or control systems including feedback loops and control motors (e.g. , feedback for sensing position and/or velocity; control motors for moving and/or adjusting components and/or quantities).
• a typical data processing system may be implemented utilizing any suitable commercially available components, such as those typically found in data computing/communication and/or network computing/communication systems.
• any two components so associated can also be viewed as being “connected”, or “coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “couplable”, to each other to achieve the desired functionality.
• Specific examples of couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

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