System and method for generating comparable areas of lithographic masks

Abstract

Embodiments of the present disclosure provide methods for generating intra-die references for inter-die defect detection techniques. An inspection method using intra-die references includes finding similar tiles of a lithographic mask, the similar tiles defined by similar CAD information. A comparison distance is selected based on (i) areas of the similar tiles and (ii) spatial relationships between the similar tiles. Based on the comparison distance, the similar tiles are aggregated to provide a plurality of aggregated areas; and comparable areas of the lithographic mask are defined based on the plurality of aggregated tiles. An image of at least some of the comparable areas of the lithographic mask is acquired using an inspection module. The acquired images are compared.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to US 16 / 752,353, filed January 24, 2020. The disclosure of this application is incorporated herein by reference in its entirety and for all purposes. Background Technology

[0003] A lithographic printing mask is exposed to radiation during the lithographic printing process, thereby forming a pattern on the wafer.

[0004] Errors in lithographic printing masking can result in a large number of defective wafers. Different masking errors may be associated with different costs.

[0005] Due to the high costs associated with some lithographic mask errors, lithographic masks need to be rigorously inspected.

[0006] Lithographic printing masks include multi-die lithographic printing masks and single-die lithographic printing masks. A multi-die mask can form multiple dies once exposed during the lithographic printing process. A single-die mask can form multiple dies once exposed sequentially during the lithographic printing process.

[0007] Multi-die lithographic printing masks can be inspected using die-to-die comparisons.

[0008] Single-core lithographic printing masks cannot be inspected using inter-core comparisons.

[0009] There is a growing need for accurate and rapid methods to inspect lithographic printing masks without using inter-die comparisons. Summary of the Invention

[0010] This disclosure relates to aspects and implementations of inspecting lithographic printing masks using an in-die reference for inter-die defect detection technology. The disclosed method comprises the following steps: identifying similar blocks of the lithographic printing mask; defining the similar blocks by similarity CAD information; selecting a comparison distance based on (i) the regions of the similar blocks and (ii) the spatial relationships between the similar blocks; aggregating the similar blocks based on the comparison distance to provide multiple aggregated regions; and defining a comparable region of the lithographic printing mask based on the multiple aggregated blocks. Additional steps may include: acquiring images of at least some of the comparable regions; and comparing the images of at least some of the comparable regions to provide inspection results.

[0011] In some implementations, defining comparable regions may include at least one of the following: (i) ignoring aggregated regions that fail to pass the size criterion; and (ii) adding strip-shaped aggregated regions to each other.

[0012] In certain implementations, selecting the comparison distance can include computing, for each distance in the set of distances, an aggregated area of similar patches spaced apart by the distance, thereby providing a set of aggregated areas. Alternatively, selecting the comparison distance can include finding a highest aggregated area in the set of aggregated areas; and defining the distance associated with the highest aggregated area as the comparison distance.

[0013] In certain implementations, the set of distances is selected prior to providing the set of aggregated areas. Selecting the set of distances can include disregarding distances below a distance threshold. The method can include repeating providing the set of aggregated areas for different sets of distances.

[0014] In certain implementations, aggregating similar patches can include defining consecutive strips, where each of the consecutive strips has a width equal to the comparison distance; finding, within each pair of adjacent strips in the consecutive strips, similar patches spaced apart by the comparison distance; and disregarding patches within each pair of adjacent strips that fail to have similar patches spaced apart by the comparison distance.

[0015] In certain implementations, the method can include repeating the steps of: selecting a comparison distance; aggregating similar patches; and defining a comparable area for each of a plurality of directions oriented to one another.

[0016] The disclosed systems include computer systems that implement any one or more of the methods described herein. In certain implementations, the computer systems are connected to or integrated with an inspection system. The inspection system includes a mechanical stage for carrying a lithographic mask to be inspected and an image acquisition module for acquiring an image of a portion or all of the lithographic mask.

[0017] In certain implementations, the systems include a non-transitory computer-readable storage medium having stored thereon instructions encoding any one or more of the methods described herein. BRIEF DESCRIPTION OF DRAWINGS

[0018] The subject matter of the present application is particularly pointed out and distinctly claimed in the concluding portion of the specification. The application, however, both as to organization and method of operation, together with objects, features, and advantages thereof, can best be understood by reference to the following detailed description when read with the accompanying drawings in which: Figure One The present application can best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0019] Figure 1 、 Figure 3 and Figure 4 depicts a flow diagram of a method for producing intra-die references in accordance with one or more aspects of the present disclosure;

[0020] Figure 2 depicts a flow diagram of a method for inspecting a lithographic mask in accordance with one or more aspects of the present disclosure;

[0021] Figure 5 A block diagram of an illustrative inspection system operating in accordance with examples of the present application is depicted;

[0022] Figures 6 to 18 An area of a lithographic printing mask illustrating aspects of the present disclosure is schematically depicted.

[0023] It will be appreciated that, for simplicity and clarity, the drawing figures illustrate the elements using only a few of the many possible elements that can be present in a typical implementation. The purpose of this drawing is to provide a conceptual description of the illustrative implementations, and not to limit the scope of the disclosure. In the drawings: DETAILED DESCRIPTION

[0024] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the application. However, it will be understood by those skilled in the art that the present application can be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present application.

[0025] The subject matter of the present application is particularly pointed out and distinctly claimed in the concluding portion of the specification. The application, however, both as to organization and method of operation, together with objects, features, and advantages thereof, can best be understood by reference to the following detailed description when read with the accompanying drawings in which: Figure One The present application can best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings in which:

[0026] It will be appreciated that, for simplicity and clarity, the drawing figures illustrate the elements using only a few of the many possible elements that can be present in a typical implementation. The purpose of this drawing is to provide a conceptual description of the illustrative implementations, and not to limit the scope of the disclosure. In the drawings:

[0027] Because the illustrated embodiments of the present application can be implemented using electronic components and circuits known to those skilled in the art, further details as to specific programming code (which will differ at some level no matter how detailed the specification) and computer architecture are not provided in this description. For the most part, the illustrative code and the computer architecture can be omitted inasmuch as applied those skilled in the art will be able to construct appropriate software and computer architecture using the description herein as a guide. However, a general purpose computer also can interact with a human user through a keyboard and a display, and can process information stored on a computer readable medium.

[0028] Any reference in this specification to method claims should be regarded as applying to both method claims and system claims, and vice versa.

[0029] Any reference in this specification to system claims should be regarded as applying to method claims and system claims, and vice versa.

[0030] Any reference in this specification to an "application" should be read as a reference to the system as a whole, and not to the individual components thereof.

[0031] It is well known to detect defects on masks and wafers using inter-die defect detection techniques: comparing measured images of dies to images of reference dies; analyzing differences between die images to detect defects. The reference dies can be another die on the same mask or wafer.

[0032] Defect free manufacturing of single-die masks poses a challenge to using inter-die techniques. For example, when inspecting a single-die mask, there is no reference die.

[0033] According to embodiments of the present invention, a method for generating intra-die references for inter-die defect detection techniques is provided. The references are generated by defining comparable areas in a die based on analyzing die design data, and by imaging these comparable areas by an inspection tool. A dedicated imaging plan can be generated for the inspection tool with respect to the comparable areas. The comparable areas can be defined such that the dedicated imaging plan will be optimized with respect to operational considerations related to the operation of the inspection tool. For example, scanning the comparable areas can require less changes in the mechanical stage direction of the inspection tool.

[0034] Once available, the images of the comparable areas can be used for defect detection using known inter-die defect detection techniques.

[0035] Figure 1 A method 700 according to embodiments of the present invention is shown.

[0036] The method 700 is for generating comparable areas using computer aided design information.

[0037] The method 700 can start at step 710: finding similar tiles of a lithographic mask. The term "tile" as used herein relates to a portion of an area of a lithographic mask die. Each tile of a lithographic mask is defined by computer aided design information. Alternatively, the tiles can be defined using "design intent" information of the mask. Post-OPC information can also be used. The present invention is not limited to the specific technique used for finding similar tiles, and known techniques for similarity analysis can be used.

[0038] A block can be defined to correspond to a functional criterion, e.g. a CPU core, a memory area, etc. A block can be defined based on a size criterion: a block can be defined as a mask area large enough so that image registration inaccuracies, edge imaging effects, yield impact and other imaging factors and operational considerations will not degrade the efficiency and completeness of the inspection and detection. According to embodiments of the application, blocks are defined automatically based on design information and by employing a similarity criterion. Alternatively, blocks and / or block sizes can be predefined, or can be set empirically based on trials and error testing during a preliminary setup phase.

[0039] To illustrate, given a lithographic mask of a 10 cm X 10 cm area and a typical pixel size of a few nanometers (e.g. 30 nm X 30 nm or less), a block size (minimum comparable area size) can be defined to be of the order of: a few hundred nanometers, e.g. 100 nm X 100 nm; a few hundred microns, e.g. 100 μ X 100 μ; a few hundred millimeters, e.g. 100 mm X 100 mm and larger. According to embodiments of the application, a minimum block size can be set. The application is not limited to the shape of the blocks and comparable areas, and the examples listed above relate to square shapes for simplicity.

[0040] Similar blocks are defined by similar computer aided design information.

[0041] According to known techniques for evaluating similarity, the term "similar" means identical up to an allowed deviation. The allowed deviation can refer to an allowed number of different patterns, an allowed number of block segments that differ from each other.

[0042] The allowed deviation can be a predefined value, a value defined by the lithographic mask manufacturer, mask vendor, programmer or inspection tool user.

[0043] A non-limiting example of an allowed deviation between two blocks, when comparing the two blocks, is having corresponding block segments that differ from each other by one, two, three, four percent, of five percent (or even more). The corresponding block segments are located at the same position within the block pair.

[0044] According to another embodiment (not illustrated in Figure 4 Step 710 is replaced with the following steps: receiving similar blocks of the lithographic mask. For example, the die layout information can be provided from another system or by a user.

[0045] After finding similar blocks, it is necessary to find repeating combinations of similar blocks.

[0046] A repeating combination can be determined with respect to a comparison distance - a characteristic of a repeating period of the repeating combination corresponding to similar blocks.

[0047] Step 710 can be followed by step 720: selecting comparison distances based on (i) areas of similar tiles of the lithography mask of the object and (ii) spatial relationships between the similar tiles; wherein the similar tiles are defined by similar CAD information.

[0048] The spatial relationships can comprise distances between the similar tiles.

[0049] It can be desirable to provide a comparable area comprising a plurality of similar tiles. Inspecting a lithography mask can benefit from a comparable area comprising a plurality of similar tiles. (higher signal-to-noise ratio, higher robustness)

[0050] Step 720 can be followed by step 730: aggregating the similar tiles based on the comparison distances to provide a plurality of aggregated areas.

[0051] Step 730 can be followed by step 740: defining comparable areas of the lithography mask based on the plurality of aggregated tiles.

[0052] The comparable areas define areas of the lithography mask that should be compared to each other when inspecting the lithography mask. The comparable areas can be included in an inspection recipe. For example, locations of the comparable areas can be used to set up an image acquisition plan of an inspection tool.

[0053] The comparable areas can be stored, sent to another system, used for inspecting the lithography mask, etc.

[0054] Figure 2 A method 701 according to an embodiment of the application is shown.

[0055] The method 701 is for inspecting a lithography mask. The inspection uses comparable areas.

[0056] The method 701 can start with a sequence of steps comprising steps 710, 720 and 730.

[0057] Step 740 can be followed by step 810: acquiring images of at least some of the comparable areas.

[0058] Step 810 can comprise acquiring images of two, some or all of the comparable areas found during step 740.

[0059] Step 810 can comprise acquiring the images by an inspection system or any other system that illuminates the lithography mask (or at least illuminates at least some of the comparable areas) with radiation and senses the radiation resulting from the illumination.

[0060] Alternatively, step 810 can comprise acquiring images of at least some of the comparable areas without generating the images. For example, the step can comprise retrieving the images from a memory unit, an inspection system, etc.

[0061] Step 810 can be followed by step 820: comparing images of at least some of the comparable regions to provide an inspection result.

[0062] An inspection method can be provided that can begin with receiving information about comparable regions. Receiving can be followed by steps 810 and 820.

[0063] According to embodiments of the invention, spatial relationships between similar blocks and in particular distances between similar blocks can be responsive to multiple directions. The multiple directions can include directions that are oriented at ninety degrees or any other angular deviation from one another.

[0064] For example, assume that the multiple directions include an X-axis and a Y-axis. In this case, generating comparable regions includes defining X-axis comparable blocks and defining Y-axis comparable regions.

[0065] Defining X-axis comparable blocks can include selecting X-axis comparison distances based on spatial relationships along the X-axis, aggregating similar blocks, and defining X-axis comparable regions.

[0066] Defining Y-axis comparable blocks can include selecting comparison distances, can include selecting Y-axis comparison distances based on spatial relationships along the Y-axis, aggregating similar blocks, and defining Y-axis comparable regions.

[0067] Figure 3 Method 702 according to embodiments of the invention is shown.

[0068] Method 702 can begin with step 708: selecting a new direction (e.g. X-axis or Y-axis).

[0069] Step 708 can be followed by steps 710, 720, 730, and 740.

[0070] Step 740 can be followed by jumping to step 708.

[0071] When the directions are X-axis and Y-axis, then two iterations of steps 710, 720, 730, and 740 are performed.

[0072] After completing all iterations of steps 710, 720, 730, and 740, then the comparable regions for the multiple directions are found.

[0073] Comparable blocks for one or more directions can be used when inspecting lithographic printing masks.

[0074] Thus, step 740 can be followed by steps 810 and 820.

[0075] Figure 4 Method 703 according to embodiments of the invention is shown.

[0076] Figure 4 Some steps that can be included in steps 720, 730 and 740 are illustrated.

[0077] Step 720 can include steps 721, 722 and 723. Step 722 is after step 721 and before step 723.

[0078] Step 721 can include selecting a set of distances. The set of distances can include a plurality of different distances. The comparison distance is selected from the set of distances.

[0079] The minimum and / or maximum distance threshold can be selected and can remain fixed during the execution of the method 703 or can vary over time.

[0080] For example, Figure 9 Four distances VI, V2, V3 and V4 are illustrated that are defined between different similar blocks, said blocks belonging to two regions 200 and 300 of a lithographic mask.

[0081] Step 721 can be followed by step 722: for each distance of the set of distances, compute the aggregated area of similar blocks that are spaced apart by said distance, thereby providing a set of aggregated areas.

[0082] For example, see Figure 9 Table 333.

[0083] Table 333 includes a row for each distance of VI, V2, V3 and V4. Table 333 has three rows: one row indicates the distance, another row ("relevant similar blocks") lists the blocks with similar blocks that are spaced apart from the block by a distance, and a third row indicates the aggregated size of all similar blocks (Area (VI), Area (V2), Area (V3) and Area (V4)).

[0084] For distance VI, the relevant similar blocks include blocks 203-210, 215, 216, 218, 303-306, 311-318, and its aggregated size is indicated as Area (VI).

[0085] For distance V2, the relevant similar blocks include blocks 203-206, 303-305, 311-314, and its aggregated size is indicated as Area (V2).

[0086] For distance V3, the relevant similar blocks include blocks 201, 202, 203-214, 215-219, and its aggregated size is indicated as Area (V3).

[0087] For distance V4, the relevant similar blocks include blocks 203, 207-210, 215-218, and its aggregated size is indicated as Area (V4).

[0088] Step 722 can be followed by step 723: finding the highest aggregation region in the set of aggregation regions; and defining the comparison distance as the distance associated with the highest aggregation region.

[0089] For example, referring to Figure 9 the example and assuming that region (V1) is greater than each of regions (V2), (V3) and (V4), then V1 is the comparison distance.

[0090] Step 730 can comprise steps 731, 732 and 733. Step 731 can be followed by steps 732 and 733.

[0091] Step 731 can comprise defining consecutive strips, wherein the width of each of the consecutive strips is equal to the comparison distance.

[0092] Step 732 can comprise finding, within each pair of adjacent strips in the consecutive strips, similar tiles spaced apart by the comparison distance.

[0093] Step 733 can comprise ignoring tiles that fail to have similar tiles spaced apart by the comparison distance within each pair of adjacent strips.

[0094] Steps 731, 732 and 733 can be performed multiple times for different comparison distances.

[0095] Step 740 can comprise step 741.

[0096] Step 741 can comprise at least one of (i) ignoring aggregation regions that fail the size criterion, e.g., the width and / or height of the aggregated tiles can be too small (below a predefined threshold), and (ii) adding strip-shaped aggregation regions to each other.

[0097] Figure 5 A lithographic mask 1990 and an inspection system 1900 according to an embodiment of the application are shown.

[0098] The inspection system 1900 can comprise a processor 1920, a mechanical stage 1940 and an image acquisition module 1910. The image acquisition module 1910 can comprise optics 1914 and a controller 1912 for controlling the optics 1914.

[0099] The mechanical stage 1940 is configured to support and move the lithographic mask 1990 with respect to the image acquisition module 1910.

[0100] The optics 1914 are configured (under control of the controller 1912) to illuminate the lithography mask 1990 (or at least a comparable area of the lithography mask 1990) with one or more beams of any type of radiation (visible, ultraviolet, deep ultraviolet, extreme ultraviolet, electrons, ions) for detecting radiation caused by the illumination and generating an image of the lithography mask 1990 (or the illuminated comparable area).

[0101] The optics 1914 are configured (under control of the controller 1912) to illuminate the lithography mask 1990 (or at least a comparable area of the lithography mask 1990) with one or more beams of any type of radiation (visible, ultraviolet, deep ultraviolet, extreme ultraviolet, electrons, ions) for detecting radiation caused by the illumination and generating an image of the lithography mask 1990 (or the illuminated comparable area).

[0102] The image acquisition module 1910 can detect photons, electrons and / or ions.

[0103] The optics 1914 can detect transmitted radiation (that passes through the lithography mask 1990), scattered particles and / or photons, reflected particles and / or photons, etc.

[0104] The inspection system 1900 can or can not be an aerial inspection system

[0105] The processor 1920 can be configured to calculate the comparable area and, additionally or alternatively, to process the detection signals from the image acquisition module 1910 to provide an inspection result.

[0106] In some cases, due to the size of the zones, there is no need to aggregate the zones. Even in such cases, it is not important which areas are selected to form the comparable area, and a trade-off between yield and accuracy should be made.

[0107] Figure 6 Various areas of a lithography mask 100 according to embodiments of the application are shown.

[0108] The various areas include first level areas Al 101 and A2 102, second level areas B 110, Bl 111 and B2 112, second level areas C 120, Cl 121, C2 122 and C3 123, fourth level area D 130, fifth level area E 131, sixth level area F 132, seventh level areas G 140, Gl 141, G2 142 and G3 143, eighth level area H 133, ninth level areas I1 135 and I2 136, and tenth level area T 134.

[0109] The first level area Al 101 includes the second level area Bl 111, the third level area Cl 121 and the seventh level area Gl 141.

[0110] The first hierarchical area A2 102 comprises a second hierarchical area B2 112, a third hierarchical area C2 122 and a seventh hierarchical area G2 142.

[0111] The first hierarchical areas A1 101 and A2 102 are similar to each other. Assuming that the first hierarchical areas A1 101 and A2 102 are defined as comparable areas, the question remains whether the second hierarchical areas B1 111 and B2 112 are defined as comparable areas.

[0112] Since the second hierarchical areas B1 111 and B2 112 are already comprised in the comparable areas (the first hierarchical areas A1 101 and A2 102), the comparison of the second hierarchical areas B1 111 and B2 112 seems redundant.

[0113] On the other hand, if the second hierarchical areas B1 111 and B2 112 are not defined as comparable areas, the second hierarchical area B 110 (which is located outside the first hierarchical areas A1 101 and A2 102) cannot be evaluated, because the second hierarchical area 110 does not have a comparable area to be compared.

[0114] The same considerations can apply to the definition of the third hierarchical areas C1 121 and C2 122 as comparable areas.

[0115] The same considerations can apply to the definition of the seventh hierarchical areas G1 141 and G2 142 as comparable areas. Although there are two seventh hierarchical areas (G 140 and G3 143) outside the first hierarchical areas A1 101 and A2 102, it is easier not to define the seventh hierarchical areas G1 141 and G2 142 as comparable areas.

[0116] According to embodiments, a predefined number of areas should be selected from a certain number of the highest hierarchical areas. The predefined number and the certain number can be defined by a user of the inspection tool, a manufacturer of the lithographic mask, a mask vendor, etc.

[0117] Figure 7 Various areas 200 and 300 of a lithographic mask according to embodiments of the application are shown.

[0118] The areas 200 and 300 comprise a plurality of similar blocks of different types.

[0119] Figure 8 Various areas 200 and 300 of a lithographic mask according to embodiments of the application and similar blocks 201-219 and 301-322 of the various areas are shown.

[0120] The blocks 201-219 belong to the area 200 and the blocks 301-322 belong to the area 300.

[0121] The tiles 201 and 301 are similar to each other.

[0122] The tiles 202 and 302 are similar to each other.

[0123] The tiles 203-214 and 303-310 are similar to each other.

[0124] The tiles 215-219 and 311-322 are similar to each other.

[0125] Figure 10 Regions 410, 420, 430, and 440 of a lithographic mask according to an embodiment of the application are shown.

[0126] The regions 410, 420, 430, and 440 form a sequence of four consecutive strips. The regions 410, 420, 430, and 440 are substantially identical to each other and comprise similar tiles, such as (i) tiles 441, 442, 443, and 444, which are similar to each other, (ii) tiles 462, 463, and 464, which are similar to each other, (iii) tiles 472, 473, and 474, which are similar to each other, (iv) tiles 481, 482, 482, and 484, which are similar to each other, and (v) tiles 491, 492, 493, and 494, which are similar to each other.

[0127] The tiles 441, 481, and 491 belong to the region 410.

[0128] The tiles 442, 462, 472, 482, and 492 belong to the region 420.

[0129] The tiles 443, 463, 473, 483, and 493 belong to the region 430.

[0130] The tiles 444, 464, 474, 484, and 494 belong to the region 440.

[0131] The tile 461 belongs to the region 410 and is different from the corresponding tiles 462, 463, and 464.

[0132] The tile 471 belongs to the region 410 and is different from the corresponding tiles 472, 473, and 474.

[0133] Figure 11 Regions 410, 420, 430, and 440 of a lithographic mask according to an embodiment of the application are shown.

[0134] Figure 11 The comparison distance V is shown to be equal to the width of the region 410.

[0135] Figure 11A region of the lithographic mask is shown after a first iteration of aggregating similar regions based on comparing distances. In Figure 11 The first region 410 is defined as the distance between (i) the leftmost region 4101 that owns a left border with an X-axis value X L 451 and (ii) a right border with an X-axis value X L +V 452.

[0136] Figure 12 Regions 410, 420, 430, and 440 of a lithographic mask are shown according to an embodiment of the invention.

[0137] Figure 12 A region 4102 that extends beyond the left border is shown truncated.

[0138] The regions of the region 410 (after truncating the region 4102) should be compared with the regions of the region 420.

[0139] Figure 13 A region of the lithographic mask is shown after a second iteration of aggregating similar regions based on comparing distances. In Figure 12 The second region 420 is defined as the distance between (i) the leftmost region 4201 that owns a left border with an X-axis value X L +V 452 and (ii) a right border with an X-axis value X L +2V 453.

[0140] Figure 14 A region of the lithographic mask is shown after a third iteration of aggregating similar regions based on comparing distances. In Figure 13 The third region 430 is defined as the distance between (i) the leftmost region 4301 that owns a left border with an X-axis value X L +3V 453 and (ii) a right border with an X-axis value X L +3V 454.

[0141] The regions of the third region 430 are compared with the regions of the fourth region 440.

[0142] The result of aggregating the regions of the regions 410, 420, 430, and 440 can result in defining each of the regions 410, 420, 430, and 440 as an aggregated region. Alternatively, the result of aggregating the regions of the regions 410, 420, 430, and 440 can result in defining a combination of the regions 410 and 420 as one aggregated region and a combination of the regions 430 and 440 as another aggregated region.

[0143] If the lithographic mask comprises another example of regions 410, 420, 430 and 440, then the combination of regions 410, 420, 430 and 440 can be considered as a single aggregated region.

[0144] Figure 15 Regions 511-514, 521-524 of a lithographic mask according to an embodiment of the application, aggregated regions 531-534, and segments 535 and 536 are shown.

[0145] Regions 511, 512, 513, 514, 521, 522, 523 and 524 are similar to each other and are arranged in two sequences of regions. The first sequence of regions comprises regions 511-514. The second sequence of regions comprises regions 524-524.

[0146] The first sequence of regions is positioned above the second sequence of regions. The first sequence of regions is shifted to the left compared to the second sequence of regions.

[0147] Figure 15 Four comparable regions 531, 532, 533 and 534 are also shown.

[0148] Comparable region 531 has a rectangular shape and comprises a portion of region 511 and region 521. Comparable region 532 has a rectangular shape and comprises region 512 and region 522. Comparable region 533 has a rectangular shape and comprises region 513 and region 523. Comparable region 534 has a rectangular shape and comprises region 514 and a portion of region 524.

[0149] Because of the left shift between the first and second sequences of regions, comparable region 531 comprises segment 535.

[0150] Because of the left shift between the first and second sequences of regions, segment 536 is outside of comparable region 534.

[0151] Void 535 and certain portions 536 do not compare with any corresponding portion. Thereby, the definition of comparable regions is flawed.

[0152] Figure 16 Regions 511-514, 521-524 of a lithographic mask according to an embodiment of the application, aggregated regions 541-544 and aggregated regions 551-554 are shown.

[0153] Aggregated region 541 comprises region 511, aggregated region 542 comprises region 512, aggregated region 543 comprises region 513 and aggregated region 544 comprises region 514.

[0154] Aggregation region 552 includes region 521, aggregation region 552 includes region 522, aggregation region 553 includes region 523 and aggregation region 554 includes region 524.

[0155] Note that one aggregation region can include a combination of regions 511 and 512, and another aggregation region can include a combination of regions 513 and 514.

[0156] Note that one aggregation region can include a combination of regions 521 and 522, and another aggregation region can include a combination of regions 523 and 524.

[0157] Note also that one aggregation region can include a combination of regions 521-524, and another aggregation region can include a combination of regions 511-514.

[0158] Figure 17 Region 600 is shown including a plurality of zones according to an embodiment of the application.

[0159] Region 600 includes individual zones. Zone 601 is similar to individual zones such as zone 602, 603 and 604. The distance between zone 601 and zone 602 is VI, the distance between zone 601 and zone 603 is V2 and the distance between zone 601 and zone 604 is V3. V2 exceeds VI and is less than V3.

[0160] Figure 16 Searching for comparison distances (and in particular selecting a set of distances from which to select comparison distances) can involve starting from distances no less than V3, ignoring distances below a distance threshold equal to V3.

[0161] After applying this restriction and defining aggregation regions, other aggregation regions can be searched for by allowing comparison distances to be less than V3 - reducing the distance threshold. The distance threshold can be reduced to V2, and after defining aggregation regions using V2, the distance threshold can be further reduced to VI. Alternatively, the distance threshold can be reduced from V3 to VI or any other value below V3.

[0162] It has been found that the process of aggregating zones can be an iterative process that can involve varying the restriction on comparison distances. The variation can include reducing the restriction on comparison distances.

[0163] Aggregating from a higher restriction on comparison distances can result in larger aggregation regions.

[0164] Each next iteration of aggregation can involve reducing the restriction on minimum comparison distances until a pre-defined threshold is reached.

[0165] When aggregated along a certain direction, the aggregated regions can have a strip shape, the strip being wider along a certain direction. One or more strip-shaped aggregated regions can be added to each other to provide a comparable region.

[0166] Figure 18 Comparable regions 920 and 930 according to embodiments of the application are shown, X-axis aggregated regions 921, 922 and 923, and Y-axis aggregated regions 931, 932 and 933.

[0167] X-axis aggregated regions 921, 922 and 923 are strip-shaped regions and combine to provide comparable region 920.

[0168] Y-axis aggregated regions 931, 932 and 933 are strip-shaped regions and combine to provide comparable region 930.

[0169] Any reference to Figures 11 to 18 The proposed aggregated regions can be comparable regions.

[0170] Embodiments of the application described herein are intended to be

[0171] In the above specification, the application has been described with reference to specific examples of embodiments of the application. It is evident, however, that various modifications and changes can be made thereto without departing from the broader spirit and scope of the application as set forth in the appended claims.

[0172] Furthermore, the terms "front", "back", "top", "bottom", "over", "under", and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are capable of operation in other orientations than described or otherwise shown in the figures.

[0173] The connections as discussed herein can be any type of connection suitable to transfer signals from or to the respective nodes, units, or elements, for example via intermediate elements. Accordingly, unless implied or explicitly specified otherwise, the connections can be direct connections or indirect connections. References only to the connections can be made also only to the direct connections. However, embodiments could alter the implementation of the connections. For example, separate unidirectional connections could be used instead of bidirectional connections and the like. The connections could also be implemented directly between the associated nodes, units, or elements without intermediate elements. Similarly, several connections between the same nodes, units, or elements could be substituted with a single connection that carries multiple signals. Also, where multiple signals are transmitted over the same connection, the signals could be separated by multiplexing techniques and / or by using discrete carriers. Therefore, many options exist for transferring signals.

[0174] Although specific conductivity types or potential polarities have been described in examples, it should be appreciated that the conductivity types and potential polarities can be reversed.

[0175] Each signal described herein can be designed as positive or negative logic. In the case of a negative logic signal, the signal is active low where a logic true state corresponds to a logic level of zero. In the case of a positive logic signal, the signal is active high where a logic true state corresponds to a logic level of one. It should be noted that any of the signals described herein can be designed as either negative or positive logic signals. Accordingly, those signals described as positive logic signals in alternative embodiments can be implemented as negative logic signals and those signals described as negative logic signals can be implemented as positive logic signals.

[0176] Furthermore, when referring to a signal, state bit, or similar device being presented in its logic true or logic false state, respectively, the terms "asserted" or "set" and "negated" (or "de-asserted" or "cleared") are used herein. If the logic true state is a logic level of one, then the logic false state is a logic level of zero. And if the logic true state is a logic level of zero, then the logic false state is a logic level of one.

[0177] Those skilled in the art will recognize that boundaries between the logic blocks are merely illustrative and that alternative embodiments can merge logic blocks or circuit elements or impose an alternate decomposition of various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely examples, and that actual implementations can include many other architectures.

[0178] Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermediate components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.

[0179] Also for example, embodiments can be found that include a plurality of means for performing each of the operations described above. And various embodiments can include multiple instances of a particular

[0180] Also for example, in one embodiment, the illustrated examples can be implemented as circuitry located within the same physical hardware, such as within a single integrated circuit chip. Alternatively, the examples can be implemented as any number of separate integrated circuit chips.

[0181] However, other modifications, changes and substitutes are possible. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive sense.

[0182] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of elements or steps other than those listed in a claim. Further, the word 'a' or 'an' preceding an element does not exclude the presence of a plurality of such elements. Further, the usage of the words first, second and third, if any, does not limit the scope and does not require these words to indicate different temporal or chronological sequence of elements. The mere fact that measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[0183] While certain features of the application have been illustrated and described, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the application.

Claims

1. A method of generating comparable areas of a lithographic mask, the method comprising: finding similar tiles of the lithographic mask; the similar tiles being defined by similar CAD information; selecting a comparison distance based on (i) areas of the similar tiles and (ii) spatial relationships between the similar tiles; based on the comparison distance, aggregating the similar tiles to provide a plurality of aggregated areas; and defining the comparable areas of the lithographic mask based on the plurality of aggregated areas, wherein selecting the comparison distance comprises: calculating, for each distance in a set of distances, an aggregated area of similar tiles spaced apart by the distance, thereby providing a set of aggregated areas; finding a highest aggregated area in the set of aggregated areas; and defining the distance associated with the highest aggregated area as the comparison distance, wherein aggregating the similar tiles comprises: defining consecutive strips, wherein a width of each of the consecutive strips is equal to the comparison distance; finding, within each pair of adjacent strips in the consecutive strips, similar tiles spaced apart by the comparison distance; and ignoring tiles that fail to have similar tiles spaced apart by the comparison distance within each pair of the adjacent strips, and wherein defining the comparable areas comprises at least one of (i) ignoring aggregated areas that fail a size criterion; and (ii) adding strip-shaped aggregated areas to each other.

2. The method of claim 1, comprising acquiring images of at least some of the comparable areas; and comparing the images of the at least some of the comparable areas to provide an inspection result.

3. The method of claim 1, wherein the set of distances is selected prior to providing the set of aggregated areas; and wherein selecting the set of distances comprises ignoring distances below a distance threshold.

4. The method of claim 3, comprising repeating providing the set of aggregated areas for different sets of distances.

5. The method of claim 1, comprising repeating the steps of selecting the comparison distance, aggregating the similar tiles, and defining the comparable areas for each of a plurality of directions oriented to each other.

6. A non-transitory computer readable medium comprising instructions which, when executed by a processor, cause the processor to perform operations comprising: finding similar tiles of a lithographic mask; the similar tiles being defined by similar CAD information; selecting a comparison distance based on (i) areas of the similar tiles and (ii) spatial relationships between the similar tiles; based on the comparison distance, aggregating the similar tiles to provide a plurality of aggregated areas; and defining comparable areas of the lithographic mask based on the plurality of aggregated areas, wherein selecting the comparison distance comprises: calculating, for each distance in a set of distances, an aggregated area of similar tiles spaced apart by the distance, thereby providing a set of aggregated areas; finding a highest aggregated area in the set of aggregated areas; and defining the distance associated with the highest aggregated area as the comparison distance, wherein aggregating the similar tiles comprises: defining consecutive bands, wherein each of the consecutive bands has a width equal to the comparison distance; finding within each pair of adjacent bands of the consecutive bands similar blocks spaced apart by the comparison distance; and ignoring blocks within each pair of the adjacent bands that fail to have similar blocks spaced apart by the comparison distance, and wherein defining the comparable regions comprises at least one of (i) ignoring aggregated regions that fail a size criterion; and (ii) adding band-shaped aggregated regions to each other.

7. A system for generating comparable regions of a lithographic mask, the system comprising: a memory; and a processor operably coupled with the memory for: finding similar blocks of the lithographic mask; the similar blocks being defined by similar CAD information; selecting a comparison distance based on (i) areas of the similar blocks and (ii) spatial relationships between the similar blocks; aggregating the similar blocks based on the comparison distance to provide a plurality of aggregated regions; and defining the comparable regions of the lithographic mask based on the plurality of aggregated regions, wherein to select, the processor is further for: for each distance of a set of distances, computing aggregated regions of similar blocks spaced apart by the distance, thereby providing a set of aggregated regions; finding a highest aggregated region of the set of aggregated regions; and defining the distance associated with the highest aggregated region as the comparison distance, wherein to aggregate the similar blocks, the processor is further for: defining consecutive bands, wherein each of the consecutive bands has a width equal to the comparison distance; and finding within each pair of adjacent bands of the consecutive bands similar blocks spaced apart by the comparison distance; and ignoring blocks within each pair of the adjacent bands that fail to have similar blocks spaced apart by the comparison distance, wherein to define the comparable regions, the processor is further for (i) ignoring aggregated regions that fail a size criterion; and / or (ii) adding band-shaped aggregated regions to each other.

8. The system of claim 7, wherein the system is connected to or integrated with an inspection system, the inspection system being capable of inspecting a lithographic mask; and wherein the processor is further for: acquiring images of at least some of the comparable regions; and comparing the images of the at least some of the comparable regions to provide an inspection result.

9. The system of claim 7, wherein the processor is further for: prior to providing the set of aggregated regions, selecting a set of distances by ignoring distances below a distance threshold.

10. The system of claim 9, wherein the processor is further for: repeating providing the set of aggregated regions for different sets of distances.

11. The system of claim 7, wherein the processor is further for: repeating the steps of selecting the comparison distance, aggregating the similar blocks, and defining the comparable regions for each of a plurality of directions oriented to each other.

Images