阅读说明：本技术 具有倾斜周期性结构的计量目标及方法 (Metrology targets with tilted periodic structures and methods ) 是由 F·约埃尔 M·吉诺乌克 A·斯维泽尔 V·莱温斯基 I·塔尔西斯-沙皮尔 于 2018-11-29 设计创作，主要内容包括：本发明揭示计量目标、其设计方法及测量方法,所述目标具备相对于光刻工具的正交产生轴X及Y倾斜的周期性结构,从而实现具有对角线(倾斜(oblique/tilted))元件的装置(例如DRAM装置)的更准确叠加测量。一或多个倾斜周期性结构可用于提供关于一或多个层的一维或二维信号,从而可能提供针对应用到一个层的多个步骤的叠加测量。所述倾斜周期性结构可用于修改当前计量目标设计(例如,成像目标及/或散射测量目标)或设计新的目标,且可分别调整测量算法以从所述倾斜周期性结构导出信号及/或提供其预处理图像。所揭示的目标是过程兼容的且更准确地反映关于各种过程步骤的装置叠加。(Metrology targets, design methods thereof, and measurement methods are disclosed that are provided with periodic structures that are tilted with respect to orthogonal generation axes X and Y of a lithography tool, enabling more accurate overlay measurements of devices having diagonal (tilted) elements, such as DRAM devices. One or more tilted periodic structures may be used to provide one or two dimensional signals with respect to one or more layers, possibly providing a superposition measurement for multiple steps applied to one layer. The tilted periodic structure may be used to modify a current metrology target design (e.g., an imaging target and/or a scatterometry target) or to design a new target, and the measurement algorithm may be adjusted to derive a signal from the tilted periodic structure and/or provide a pre-processed image thereof, respectively. The disclosed objective is process compatible and more accurately reflects device overlays on various process steps.)

1. A metrology target comprising a plurality of periodic structures and produced by a lithographic tool having orthogonal production axes X and Y, wherein at least one of the periodic structures is tilted with respect to axes X and Y.

2. The metrology target of claim 1, configured as an imaging target and having the periodic structure of at least one target layer configured to be tilted with respect to axes X and Y and in two non-parallel directions.

3. The metrology target of claim 1, configured as a moire effect based target.

4. The metrology target of claim 3, having the periodic structure of at least one target layer configured to be tilted with respect to axes X and Y and in two non-parallel directions.

5. The metrology target of any one of claims 2-4, comprising at least three layers, wherein a tilted periodic structure is in one of the layers.

6. The metrology target of any one of claims 1-5, tilting one measurement direction relative to the X-axis of the lithographic tool, wherein the tilted periodic structures have two types that differ in pitch and/or CD (critical dimension).

7. The metrology target of any one of claims 1-6, wherein the tilted periodic structures are arranged to fill rectangles having sides along the X and Y axes.

8. The metrology target of any one of claims 1-7, wherein the tilted periodic structures are configured to fill a specified space designed according to available wafer area.

9. The metrology target of any one of claims 1-8, wherein the tilted periodic structures are arranged to fill a convex quadrilateral designed according to available wafer area.

10. The metrology target of claim 1, configured as a SEM (scanning electron microscope) target having two partially overlapping, alternating periodic structures, both of which are tilted with respect to the X-axis.

11. The metrology target of any one of claims 1-10, wherein elements of the periodic structure are segmented.

12. The metrology target of claim 11, wherein the segmentation of the elements is two-dimensional.

13. The metrology target of claim 11, wherein a pitch of the segments is one-fifth or less of a pitch of the corresponding periodic structures.

14. The metrology target of claim 11, wherein the segments are rectangular.

15. The metrology target of any one of claims 1-14, wherein the tilted periodic structures form an angle between 20 ° and 70 ° with respect to corresponding axes X and Y.

16. The metrology target of any one of claims 1-14, wherein the target further comprises at least one intermediate layer having assist features between two of the periodic structures.

17. The metrology target of claim 16, wherein the assist features are tilted with respect to axes X and Y.

18. The metrology target of any one of claims 1-17, wherein at least two of the periodic structures are placed side-by-side.

19. A target design file for the metrology target of any one of claims 1 to 18.

20. A metrology measurement of the metrology target of any one of claims 1-18.

21. A metrology measurement method of a metrology target according to any one of claims 1 to 18, wherein a given metrology measurement algorithm is adjusted by image processing and/or signal modelling to derive a corresponding signal from the tilted periodic structure.

22. A target design method includes configuring at least one periodic structure of a metrology target produced by a lithographic tool having orthogonal production axes X and Y to be tilted with respect to the axes X and Y.

23. The target design method of claim 22, further comprising: tilted structures relative to the axes X and Y are identified in a device design, and the at least one tilted periodic structure of the metrology target at the same layer and at the same angle relative to the axes X and Y is designed as the identified tilted structure.

Technical Field

The present invention relates to the field of metrology, and more particularly, to metrology target design.

Background

United states patent No. 6,921,916, the entire contents of which are incorporated herein by reference, discloses overlay marks for determining the relative position between two or more successive layers of a substrate or between two or more separately generated patterns on a single layer of a substrate; and united states patent publication No. 2007/0008533, which is incorporated herein by reference in its entirety, discloses overlay targets having flexible symmetry properties and metrology techniques for measuring overlay error between two or more successive layers of such targets.

Disclosure of Invention

The following presents a simplified summary of the invention in order to provide a basic understanding of the invention. The summary does not necessarily identify key elements nor limit the scope of the invention, but merely serves as an introduction to the following description.

One aspect of the invention provides a metrology target comprising a plurality of periodic structures and generated by a lithographic tool having orthogonal generation axes X and Y, wherein at least one of the periodic structures is tilted with respect to the axes X and Y.

These, additional and/or other aspects and/or advantages of the present invention are set forth in the following description; may be derivable from the embodiments; and/or may be learned by practice of the invention.

Drawings

For a better understanding of embodiments of the present invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings, in which corresponding elements or sections are designated by the same numeral throughout.

In the drawings:

fig. 1A through 1E are high-level schematic diagrams of one layer of the device (fig. 1A) and a prior art method for providing overlay metrology targets to measure the overlay between different layers or features of the device 80 (fig. 1B through 1E).

Fig. 2A, 2B, and 3-5 are high-level schematic diagrams of metrology targets, periodic structures, and elements thereof, according to some embodiments of the invention.

FIG. 6B is a high level schematic of metrology targets according to some embodiments of the present invention compared to the prior art target schematically illustrated in FIG. 6A.

Fig. 7A, 7B and 7C are high-level schematic diagrams of segment edge configurations according to some embodiments of the invention.

Fig. 8 is a high-level flow diagram illustrating a method according to some embodiments of the invention.

Detailed Description

In the following description, various aspects of the present invention are described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details presented herein. In addition, well-known features may have been omitted or simplified in order not to obscure the present invention. With specific reference to the drawings, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments and combinations of the disclosed embodiments, which may be practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing," "computing," "calculating," "determining," "enhancing," "deriving," or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices. In a particular embodiment, the illumination technique may include electromagnetic radiation in a range (e.g., infrared range, visible range, ultraviolet or even shorter wave radiation (e.g., x-rays) and possibly even particle beams).

Embodiments of the present invention provide efficient and economical methods and mechanisms for measuring process-compatible designs of tilted semiconductor devices, and thereby provide improvements in the art of metrology and semiconductor production. New overlay mark designs and algorithmic methods of process compatible design are provided for reducing overlay measurement inaccuracies.

In a particular embodiment, the metrology targets, their design methods, and measurement methods are provided with periodic structures that are tilted with respect to orthogonal generation axes X and Y of the lithography tool, enabling more accurate overlay measurements of devices having diagonal (tilted) elements, such as DRAM devices. One or more tilted periodic structures may be used to provide one or two dimensional signals with respect to one or more layers, possibly providing a superposition measurement for multiple steps applied to one layer. The tilted periodic structure may be used to modify a current metrology target design (e.g., an imaging target and/or a scatterometry target) or to design a new target, and the measurement algorithm may be adjusted to derive a signal from the tilted periodic structure and/or provide a pre-processed image thereof, respectively. The disclosed objective is process compatible and more accurately reflects device overlays on various process steps.

Fig. 1A through 1E are high-level schematic diagrams of one layer of the device 80 (fig. 1A) and a prior art method for providing an overlay metrology target 90 to measure the overlay between different layers or features of the device 80 (fig. 1B through 1E).

Fig. 1A schematically illustrates structural characteristics of many contemporary semiconductor devices, such as DRAM (dynamic random access memory) devices, i.e., having at least one layer aligned at a specified tilt to the regular cartesian coordinates of a lithography tool, such as a scanner having X and Y axes, e.g., having a 22 ° tilt relative to X.

Optical Overlay (OVL) based metrology on the device is not feasible at this time, as the design rule pitch cannot be resolved by contemporary optical techniques of both imaging and SCOL (scatterometry based) OVL tools. Instead, OVL measurements are performed on specially designed "proxy" metrology targets having a typical scale (pitch) greater than one hundred nanometers, as opposed to typical device pitches of several 10nm or less. In addition, the standard target is aligned only in the X-Y direction.

Fig. 1B-1E demonstrate a prior art method to measure the mismatch of device layers with tilted structures using a standard XY alignment target, such as designing the XY alignment target with device-like segments schematically illustrated in fig. 1B (e.g., a periodic target with a periodic structure having tilted segmented elements, possibly at a minimum design rule pitch), or designing the segmented target not similar to a tilted device (possibly at a minimum design rule pitch), schematically illustrated in fig. 1C-1E, e.g., fig. 1C schematically illustrates the segmentation of elements perpendicular to the periodic structure and along the periodic structure measurement direction, fig. 1D schematically illustrates the segmentation of elements parallel to the periodic structure and perpendicular to the periodic structure measurement direction, and fig. 1E schematically illustrates a segmented two-dimensional two-layer imaging target. Note that the prior art target 90, as well as the targets disclosed below, are schematically illustrated, showing partial sections of the target that are otherwise adequately designed with respect to the size and extent of the periodic structure.

However, the main difficulties are that none of the prior art target designs are process compatible (or even well printed), are asymmetric, and have no device-like behavior (especially with respect to tilted structures). For example, target 90 designed according to the principles illustrated in FIGS. 1B, 1C, and 1D typically results in an overlay value that does not reflect well the overlay of the device and has severe printability issues (target 90 illustrated in FIGS. 1B and 1C has poorer printability than target 90 illustrated in FIG. 1D). Similar difficulties arise using the extended design schematically illustrated in fig. 1E, which may be composed of the elements illustrated in fig. 1B-1D. The segmented two-dimensional bi-layer imaging target 90 may include inner X and inner Y periodic structures 95X and 95Y, outer X and outer Y periodic structures 95X 'and 95Y' (collectively represented as periodic structures 95). In particular, such structures are generally defined by the constraints of (i) the outer X periodic structure 95X 'being orthogonal to the outer Y periodic structure 95Y'; (ii) inner X periodic structure 95X is orthogonal to inner Y periodic structure 95Y; (iii) the outer X periodic structure 95X' is parallel to the inner X periodic structure 95X; and (i) the outer Y periodic structures 95Y' are parallel to the inner Y periodic structures 95Y.

In contrast to the prior art, the following discloses a target 100 and method 200 that address difficulties associated with scalability and process compatibility of the prior art targets, and also reflects the offset (misregistration) encountered by devices with tilted structures. The following methods provide modifications that can be applied to both imaging and scatterometry overlay target designs, and the presented examples are illustrative and non-limiting. In the disclosed target 100, the at least one periodic structure and/or the at least one layer are not aligned along the X and Y directions and may be applied to any of: (i) measuring only one direction (schematically illustrated as direction M in fig. 4 and 5), which is independent of the scanner X or tool X direction, and which may reflect the inclination of the device structure, in which direction the outer and inner structures are parallel (outer M is parallel to inner M); or to measure the vectors of the superposition between layers (possibly, a layer may result from two successive processes, as a line in one direction and a cut into the other direction), requiring two directions, denoted as directions M and N in fig. 2A and 2B, and requiring only that the corresponding outer periodic structures are not parallel to each other and that the corresponding inner periodic structures are not parallel to each other (schematically represented in fig. 2A as outer M (first pair of gratings) are not parallel to outer N (second pair of gratings) and inner M '(first pair of gratings) are not parallel to inner N' (second pair of gratings)). Note that while some non-parallel associations are illustrated as being perpendicular, this choice of angles is presented for purposes of explanation only, and is not limiting. Note that the above description provides non-limiting examples, and may be implemented along similar lines for different target types, such as multi-layer targets, targets with assist features on the same and other layers, and targets that generate measurement signals using various methods, such as direct imaging, moire effect (moire effect) imaging, scatterometry, and so forth.

Note that the disclosed target design principles may be applied to targets based on moire effects, for example, as disclosed in U.S. patent No. 10,101,592, which is incorporated herein by reference in its entirety.

Fig. 2A, 2B, and 3-5 are high-level schematic diagrams of a metrology target 100, a periodic structure 110, and elements 120 thereof, according to some embodiments of the invention. Although in fig. 2A, 2B, and 3-5, some elements 120 of periodic structure 100 (and elements 97 of periodic structure 95) are illustrated as complete strips, in various embodiments, elements 120 (and 97) may be segmented in various directions (e.g., along or across respective measurement directions, or tilted, see, e.g., fig. 7A-7C below). Although in fig. 2A, 2B, and 3-5, some elements 120 of periodic structure 100 (and elements 97 of periodic structure 95) are illustrated as complete strips, in various embodiments, elements 120 (and 97) may be unsegmented or segmented in different directions.

The metrology target 100 may comprise a plurality of periodic structures 110, each having a repetitive element 120 (explicitly illustrated in FIG. 2A) and generated by a lithography tool (e.g., a scanner, not shown) having orthogonal generation axes X and Y. At least one of the periodic structures is tilted (diagonal) with respect to the axes X and Y. For example, in FIG. 2A, periodic structures 95X, 95Y corresponding to the inner X and inner Y periodic structures of imaging target 90 illustrated in FIG. 1E are also part of metrology target 100, while outer X and outer Y periodic structures 95X ', 95Y' of imaging target 90 illustrated in FIG. 1E are replaced by tilted periodic structures 110X, 110Y at angles α and β, respectively, relative to the X-axis (which may correspond to the angle of a semiconductor device produced by a lithography tool). In a particular embodiment, the periodic structures 110X, 110Y may be orthogonal to one another (e.g., β -90 °), e.g., oblique to the axes X and Y and periodic along two non-parallel directions (e.g., orthogonal directions). The tilted periodic structures 110X, 110Y are collectively represented as a tilted periodic structure 110. Note that in various embodiments, at least two of the periodic structures may be placed side-by-side.

In a particular embodiment, the tilted periodic structures 110 may form an angle between 20 ° and 70 ° with respect to the corresponding axes X and Y (and/or tilt axes X 'and Y' in the case where the target 110 is tilted as in fig. 2B).

The metrology target 100 may include two, three, or more layers, and the tilted periodic structures 110 may be designed in one or more layers. The metrology target 100 may include one, two, or possibly more measurement directions, and the tilted periodic structure 110 may be designed in one or more measurement directions. In a particular embodiment, the different tilted periodic structures 110 may be of one, two, or more types, e.g., different in pitch and/or CD (critical dimension). For example, fig. 2A and 2B schematically illustrate a metrology target 100 having differently tilted periodic structures 110X, 110Y along two measurement directions in one layer, and fig. 4 and 5 schematically illustrate a metrology target 100 having differently tilted periodic structures 110A, 110B along one measurement direction in two layers. Various embodiments include the same and/or different tilted periodic structures 110 in any combination of measurement directions and layers, e.g., depending on the corresponding device design. The tilted periodic structures 110A, 110B are collectively represented as tilted periodic structures 110.

With respect to the periodic structures schematically illustrated in fig. 3, note that such structures may be applied as any portion of any fully designed object 100, emphasizing that any of the disclosed periodic structures may be printed in a non-rectangular shape (possibly with any number of sides), possibly in relation to the available area (real estate). The two corresponding periodic structures may be rotationally symmetric (rotated 180 °) with respect to each other, e.g. to allow TIS (tool induced offset) error measurement and reduction.

As illustrated in fig. 2A and 2B, metrology target 100 may be tilted with respect to the X and Y axes of the lithography tool, e.g., to design along the X 'and Y' axes. Note that while prior art 90 as illustrated, for example, in FIG. 1E may be tilted as a complete target, the disclosed metrology target 100 also includes tilted periodic structures 110 relative to tilt axes X 'and Y' and having a direction (along which the respective pitch is measured) that is also tilted periodic relative to the tilt axis. In a particular embodiment, the disclosed metrology target 100 may have at least two non-orthogonal measurement directions (e.g., one corresponding to the periodic structure 95 and another corresponding to the periodic structure 110).

In a particular embodiment, the tilted periodic structures 110 may be disposed to fill rectangles having sides along the X and Y axes, relative to any of the target types, as illustrated, for example, in fig. 2A and 4. In a particular embodiment, the tilted periodic structures 110 may be configured to fill rectangles having sides along the tilted X 'and Y' axes, as illustrated, for example, in fig. 2B.

In a particular embodiment, the tilted periodic structures 110 may be disposed to fill a convex quadrilateral 115 (or possibly a shape with more than four sides) designed according to the available wafer area, relative to any of the target types, as illustrated, for example, in fig. 3 and 5.

In a particular embodiment, the tilted periodic structures 110 may be configured to fill any specified space designed according to the available wafer area, relative to any of the target types.

In a particular embodiment, the target 100 may include a single periodic structure 110 per measurement direction and per layer rather than the pair of periodic structures 110 per measurement direction and per layer illustrated above, for example, if rotational symmetry is not required.

In various embodiments, the target 100 may include at least one intermediate layer having assist features between two periodic structures. The assist features may be inclined with respect to the axes X and Y.

FIG. 6B is a high-level schematic diagram of metrology targets 100 according to some embodiments of the present invention compared to the prior art target 90 schematically illustrated in FIG. 6A. In a particular embodiment, the metrology target 100 may be configured as an SEM (scanning electron microscope) target (e.g., a CDSEM (critical dimension scanning electron microscope) target) and/or an imaging target having two partially overlapping, alternating periodic structures 110A, 110B (collectively indicated as tilted periodic structures 110), both of which are tilted (by an angle indicated as α) with respect to the X-axis.

Fig. 7A through 7C are high-level schematic diagrams of a segment edge configuration according to some embodiments of the invention. Note that the segmentation illustrated in FIG. 7B may cause printability problems, which can be solved by the segmentation illustrated in FIG. 7C and FIG. 7A.

In a particular embodiment, the tilted periodic structure 110 can be segmented, as schematically illustrated in fig. 7A-7C, wherein the elements 120 of the periodic structure 110 are segmented into sub-elements 130 at a smaller pitch (represented as "segment pitch" in fig. 7A-7C) (e.g., closer to or similar to the device pitch). For example, the pitch of the segments may be, for example, one fifth or less of the pitch of the corresponding periodic structure 110 (represented as "pitch" in fig. 7A-7C).

In a particular embodiment, the segmentation may be two-dimensional.

Fig. 7A-7C schematically illustrate an initial design of a segment tilting element 120 in a tilted periodic structure 110, for example, as indicated using customer design rules and performed using, for example, segmented customer design rules to ensure printability, where the tilted periodic structure 110 has a desired pitch, for example, for imaging measurements. Note that in any of the disclosed designs, the space on the mask may be filled using parallel SARF (sub-resolution assist features), which are not shown herein to maintain simplicity, and which improve printability of target design 100.

Note that the terms "line" and "space" (on the wafer or on the photolithographic mask) are used for ease of explanation and do not limit the scope of the present invention. In particular, elements indicated herein as lines and spaces may be constructed of various types of structures that may fill the respective lines and/or spaces (similarly or in different manners across the object). For example, the spaces between different gratings that are periodic structures may be filled differently than the spaces within the gratings (using different types of elements).

In a particular embodiment, sub-element 130 (a segment of element 120) is optimized for specified lighting conditions to avoid or minimize printability issues. For example, the edges may be optimized by standard techniques, such as OPC (optical proximity correction), CMP (chemical mechanical planarization) assistance, and the like. Specifically, in the case of tilted dipole illumination, segments designed according to the principles illustrated in fig. 7A and 7C are expected to cause less printability problems than the segments illustrated in fig. 7B.

Note that while the precise configuration of the edges of the device structures is less critical in semiconductor device design, the metrology measurement of the disclosed metrology target 100 is sensitive to the details of the segment edges and may be degraded by non-uniform generation of segment edges. Thus, the inventors propose to design symmetric edges (as illustrated with respect to the major axis of the ellipse 135) rather than asymmetric edges (as illustrated with respect to the major axis of the ellipse 93).

In various embodiments, a series of measurement algorithms may be used to extract metrology measurements, such as the algorithms described in U.S. patent No. 6,921,916 and U.S. patent publication No. 2007/0008533, which are incorporated by reference herein, and modifications thereof, as well as other algorithms (e.g., 2D fitting, correlation, etc.) to find the desired offset.

For example, the following non-limiting measurement algorithm may be used to measure a target 100 configured as an imaging target. First, image processing may be used to rotate the captured image of the target 100 (possibly using additional re-pixelation) such that each pair of periodic structures 110 (e.g., inner left and inner right) is parallel to the X or Y direction of the original target (e.g., corresponding to X and Y of a lithography tool or to tilted X 'and Y', see fig. 2A and 2B, respectively). The centers of symmetry for each pair of periodic structures 110 can be derived from the images, from which the X and Y centers of symmetry for the inner and outer structures can be calculated, and the vectors between the centers of symmetry for the inner and outer structures provide the superposition. It will be apparent that any one-dimensional or two-dimensional measurement algorithm may be modified accordingly to provide metrology measurements of the disclosed target 100.

In various embodiments, other algorithms may be used (e.g., the following non-limiting examples). Taking the example periodic structures 110 illustrated in fig. 3 (e.g., as part of the extended target 100) as an example, an image (or partial image) of each periodic structure 110 in the target 100 may be captured, the periodic model (function class) in the corresponding direction M may be selected as the sum of the cosine and sine in the direction M with the period P, 2P, 3P, …, nP (P is the pitch), and selected to be constant in the orthogonal direction N. The number of periods n may be chosen such that the n +1 th harmonic is independent of the optical system or empirically known to be less than the noise level (including higher harmonics above n + 1). One-dimensional signals may be derived by projecting a selected periodic model into the M-direction to produce a one-dimensional signal, which may then be processed in a canonical superposition algorithm using the one-dimensional signals per periodic structure (as described, for example, in U.S. patent No. 6,921,916 and U.S. patent publication No. 2007/0008533, and other sources, which are incorporated herein by reference).

In a particular embodiment, the number of periodic structures 110 may be designed in one layer, e.g., representing multiple process steps applied to the layer (e.g., a generation step and a cutting step, possibly one or both tilted with respect to an axis (X, Y) of a lithography tool). For example, the produced layers may be regular (along the X or Y axis), while the cut layers may be diagonal, requiring the tilted periodic structures 110 to provide their metrology measurements.

It is emphasized that the disclosed target 100 may be of any type, and that the disclosed target design principles may be applied to a wide range of metrology targets 100. Further note that the present invention is not limited to a particular metrology tool, technique, or target type. For example, the target 100 may be any form or type of one-or two-dimensional target, imaging target, scatterometry target of any type, or moire-based target, possessing a tilted periodic structure as part of its design.

Fig. 8 is a high-level flow diagram illustrating a method 200 according to some embodiments of the invention. Method stages may be performed with respect to metrology target 100 described above, which may optionally be configured to implement method 200. The method 200 may be implemented at least in part by, for example, at least one computer processor in a metering module. Particular embodiments include a computer program product comprising a computer-readable storage medium having a computer-readable program embodied therewith and configured to implement the relevant stages of the method 200. Particular embodiments include a target design file for respective targets designed by an embodiment of method 200. The method 200 may include the following stages, regardless of their order.

Particular embodiments include a target design method 200, comprising: tilted structures relative to axes X and Y are identified in the device design (stage 205) and at least one tilted periodic structure of the metrology target at the same layer and at the same angle relative to axes X and Y is designed as the identified tilted structure (stage 210).

Particular embodiments include a target design method 200 that includes configuring at least one periodic structure of a metrology target produced by a lithography tool having orthogonal production axes X and Y to be tilted with respect to the axes X and Y (step 220).

In a particular embodiment, method 200 may further include segmenting elements of the periodic structure to approach or reach a minimum design rule pitch (stage 230) and possibly designing the segments to be rectangular, with vertical edges (stage 235).

In a particular embodiment, the method 200 may further include designing any of the imaging, SEM (scanning electron microscope), and/or scatterometry targets accordingly (stage 240) and adjusting the respective measurement algorithms to take advantage of the tilted periodic structure (stage 250). For example, in a particular embodiment, the method 200 may include applying image processing and possibly re-pixelation to prepare an image of a target having a tilted periodic structure for analysis by a corresponding metrology algorithm (stage 255) and/or applying a corresponding model projected in a tilted measurement direction to derive a one-dimensional signal of the corresponding periodic structure and using it for overlay derivation (stage 257).

Note that the disclosed methods may be applied to any type of metrology target and may be implemented using any metrology tool technology. For example, the method 200 may be applied to integrate the tilted periodic structure as part of a design in any of the following: one or one dimensional targets, imaging targets, scatterometry targets of any type, and/or targets based on moire effects.

Advantageously, the disclosed target 100 and method 200 provide overlay measurements that accurately represent device overlay, e.g., Pattern Placement Error (PPE) and Etch Placement Error (EPE) for target 100 that provide errors very close to the minimum design rule-dense device features. Further, the disclosed target 100 and method 200 enable measurement of diagonal (tilted) periodic structures, such as one-dimensional or two-dimensional structures of a target structure having non-orthogonal periodic structures in one or more layers, each of the previous and current layers may include one or more tilted periodic structures 110. The disclosed goal is process compatible and closely corresponds to device production performance. Adjustment of the segment edges of the segmented elements of the tilted periodic structure 110 can further enhance measurement accuracy, possibly relative to the illumination used (e.g., dipole illumination, optionally rotated).

Aspects of the present invention are described above with reference to flowchart illustrations and/or partial diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each part of the flowchart illustrations and/or part of the figures, and combinations of parts in the flowchart illustrations and/or part of the figures, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or partial diagram or portions thereof.

These computer program instructions may also be stored in a computer-readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer-readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or partial diagram or portion thereof.

The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or partial diagram or portion thereof.

The foregoing flowcharts and formulas illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each portion of the flowchart or partial diagram may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the section may occur out of the order noted in the figures. For example, in fact, two portions shown in succession may, depending upon the functionality involved, be executed substantially concurrently or the portions may sometimes be executed in the reverse order. It will also be noted that each portion of the flowchart and/or block diagram illustrations, and combinations of portions in the flowchart and/or block diagram illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

In the foregoing description, embodiments are examples or implementations of the invention. The various appearances of "one embodiment," "an embodiment," "a particular embodiment," or "some embodiments" are not necessarily all referring to the same embodiments. Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention is described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. Particular embodiments of the invention may include features from different embodiments disclosed above, and particular embodiments may incorporate elements from other embodiments disclosed above. The disclosure of elements of the invention in the context of particular embodiments is not to be taken as limiting their use in particular embodiments alone. Further, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in specific embodiments other than those outlined in the description above.

The invention is not limited to the drawings or the corresponding description. For example, flow need not move through each illustrated block or state, or need not move in exactly the same order as illustrated and described. Unless defined otherwise, the meanings of technical and scientific terms used herein are to be commonly understood by one of ordinary skill in the art to which this invention belongs. While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the present invention should not be limited by what has been described so far, but by the appended claims and their legal equivalents.