WO2013032949A1

WO2013032949A1 - Test object for testing an array of beams

Info

Publication number: WO2013032949A1
Application number: PCT/US2012/052385
Authority: WO
Inventors: Zvika Rosenberg; Nissim Elmaliach; Dirk Zeidler; Thomas Kemen
Original assignee: Applied Materials Israel, Ltd.; Applied Materials, Inc.; Carl Zeiss Smt Gmbh
Priority date: 2011-08-26
Filing date: 2012-08-24
Publication date: 2013-03-07
Also published as: GB201114846D0; GB2494118A

Abstract

A test object for testing a multiple beam system is provided. The test object includes multiple regions, each made up of multiple fields, each of which includes multiple sub-fields, each of which includes multiple structural elements. The location and number of sub-fields of at least one field corresponds to the number of beams of an array of beams of the multiple beam system and to an expected spatial relationship between the beams of the array of beams. Various scanning patterns can be applied in order to allow the array of beams to scan the entire field. Images of the subfields obtained using the multiple beam system are used to evaluate spatial or optical characteristics thereof.

Description

TEST OBJECT FOR TESTING AN ARRAY OF BEAMS

RELATED APPLICATIONS

[001] This application claims the priority benefit of U.S. Provisional Application 61/527,707, filed 26 August 2011, and GB Patent application No. 1114846.7, filed 28 August 2011.

FIELD OF THE INVENTION

[002] The present invention relates to a test object for use in testing a multi-beam inspection system.

BACKGROUND

[003] Multi-beam systems acquire images by illuminating a sample with an array of beams. US patents 7554094 and 7244949 of Knippelmeyer et al. describe a multiple beam system.

[004] When using an array of beams, the characteristics of each beam (focus, aberrations, location errors) have to be substantially the same.

[005] There is a growing need to evaluate the beam characteristics of beams of a multiple beam system.

SUMMARY OF THE INVENTION

[006] A test object, for testing a multiple beam system, includes multiple regions, each region including multiple fields and each field including multiple sub-fields, wherein each sub-field includes multiple patterned structural elements, and a location and number of sub- fields of at least one field correspond to a number of beams in an array of beams of the multiple beam system and to an expected spatial relationship between the beams of the array of beams. The size of each field of the test object may correspond to a field of view (FOV) of the multiple beam system.

[007] In some instances, sub-fields that belong to the same field may be identical to each other at least in areal portions. Sub-fields that belong to different fields may differ from each other by at least one spatial characteristic of patterns that belong to the different fields. Each sub-field may include a border that includes border patterns, multiple patterns and textual information about the sub-field. Different sub-fields may differ from each other by spacing between features, a size of features, or a shape of features. The test object may include multiple groups of sub-fields and different groups of sub-fields may differ from each other by size and/or shape; said difference in size or shape may correspond to a difference in a spatial relationship between the beams of the array of beams.

[008] A method for evaluating a multiple beam system includes obtaining images of sub- fields of a field of a test object by scanning the sub-fields by an array of beams. The test object may include multiple regions, each region including multiple fields, and each field including multiple sub-fields. Each sub-field may include multiple structural elements and a location and number of sub-fields of at least one field may correspond to a number of an array of beams of the multiple beam system and to an expected spatial relationship between the array of beams. The multiple beam system is evaluated by evaluating at least one spatial or optical characteristic of the array of beams based on the images of the sub-fields of the test object.

BRIEF DESCRIPTION OF THE DRAWINGS

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

[0010] Figure 1 illustrates a test object according to an embodiment of the invention;

[0011] Figure 2 illustrates multiple fields of a region of the test object of figure 1, according to an embodiment of the invention;

[0012] Figures 3-6 and 10 illustrate sub-fields of a field of the test object of figure 1, according to various embodiments of the invention;

[0013] Figure 7 illustrates a sub-field according to an embodiment of the invention;

[0014] Figure 8 illustrates a sub-field according to an embodiment of the invention;

[0015] Figure 9 illustrates a sub-field according to an embodiment of the invention;

[0016] Figure 11 illustrates a sub-field according to an embodiment of the invention;

[0017] Figure 12 illustrates a sub-field according to an embodiment of the invention;

[0018] Figure 13 illustrates a sub-field according to an embodiment of the invention; and

[0019] Figure 14 illustrates a method according to an embodiment of the invention.

[0020] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION

[0021] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may 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 invention.

[0022] The figures can be out of scale.

[0023] A test object for testing a multiple beam system is provided. The test object includes multiple regions. Each region includes multiple fields. Each field includes multiple sub-fields. Each sub-field may include multiple structural elements. A location and number of sub-fields of at least one field correspond to a number of beams of an array of beams of the multiple beam system and to an expected spatial relationship between the beams of the array of beams. For example, the sub-fields of a single field can be scanned by the array of beams while introducing substantially the same movement between the array of beams and the test object. Additionally or alternatively, the sub-fields of the single field can be scanned by the array of beams while introducing substantially the same deflection to the array of beams. Once illuminated by the array of beams each beam may impinge on a different sub-field. Various scanning patterns can be applied in order to allow the array of beams to scan the entire field.

[0024] The size of each field may correspond to the field of view (FOV) of the multiple beam system. Thus, the entire field can be scanned by the array of beams without changing the FOV of the array of beams.

[0025] The sub-fields that belong to the same field may be ideally identical to each other. According to an embodiment of the invention at least two sub-fields of the same field can differ from each other.

[0026] Sub-fields that belong to different fields may differ from each other by at least one spatial characteristic of patterns that belong to the different fields.

[0027] Each sub-field may include a border that comprises border patterns, multiple patterns and textual information about the sub-field. The textual information may include a unique code to identifying the sub-field. By the aid of this code it is possible also to verify that each beam in the array of beams impinges on the intended sub-field. [0028] Different sub-fields may differ from each other by at least one out of spacing between features, a size of features, and shape of features.

[0029] The test object can be arranged to test an array of beams that differ from each other by pitch, number of beams or any other spatial characteristic. Different fields of the test object can be sized to comply with different arrays of beams.

[0030] The test object can be made of silicon and include silicon patterns. It may be made by any lithography process that can manufacture highly accurate patterns in the nanometer region.

[0031] Figure 1 illustrates a test object according to an embodiment of the invention. The test object 10 may include multiple regions (such as region 20) that are illustrated in figure 1 as having a rectangular shape. The regions can differ from each other by size, shape and, additionally or alternatively, patterns included in the regions. Alternatively, the regions can be ideally identical to each other.

[0032] Figure 2 illustrates multiple fields 30 of a region 20 of the test object 10 of figure 1, according to an embodiment of the invention. The fields can be of the same size, shape or may differ from each other. Different fields usually include different patterns or differ from each other by at least one spatial parameter such as the distance between patterns, shape of patterns, size of patterns, type of patterns, and the like. Figure 2 illustrates a rectangular array that includes twenty rows and twenty columns denoted A1..T20, wherein each column is associated with a letter (A..T). The fields of each column are further associated with numbers ranging from 1 (upmost row) till 20 (lowest row). The fields of figure 2 may have the same size. For example, the size of each field can be about 200 microns by 200 microns and adjacent fields can be spaced apart by 5-100 microns. For example, the size of each field can be about 199 microns by 222 microns.

[0033] According to an embodiment of the invention the region can exhibit the following characteristics:

a. Region size - 4000-5000 micron by 4000-500 micron.

b. Every region is divided into 300-500 fields.

c. Each field can be divided into sub-fields; the number of subfields is equal or larger than the number of beams in the array of beams. d. There can be 4 groups of sub-fields according to their pitch - that may range between few microns to 15 and even 40 microns.

e. There can be structures with pitch periods 1 :1, 1 :2, 1 :6 and Isolated for each Critical Dimension (CD) size f. There can be structures with arrays of lines (approximately 12μιη length, sub die dimension) with CD sizes (line widths) of 20, 30, 40, 50, 70, 100, 200, 400, 800, lOOOnm

g. There can be structures with arrays of patterns with sizes of 60, 70, 80,

90, 100, 200, 400, 600, 800, lOOOnm

h. There can be structures with CD & Pitch and feature for pattern recognition next to array of lines.

[0034] The sub-fields of fields A1-A10 of the first row of fields may exhibit the following characteristics:

a. Al - - Horizontal lines, 20 nm, line /space - -1:1

b. A2- Horizontal lines, 30 nm, line /space - 1:1

c. A3 - Horizontal lines, 40 nm, line /space - 1:1

d. A4- Horizontal lines, 50 nm, line /space - 1:1

e. A5 - Horizontal lines, 70 nm, line /space - 1:1

f A6- Horizontal lines, 100 nm, line /space -1:1

g- A7- Horizontal lines, 200 nm, line /space -1:1

h. A8- Horizontal lines, 400 nm, line /space -1:1

i. A9- Horizontal lines, 800 nm, line /space -1:1

j- A10 - Horizontal lines, 1000 nm, line /space -1:1

[0035] The sub-fields of fields B1-B10 of the second row of fields may exhibit the following characteristics:

a. Bl- - Horizontal lines, 20 nm, line /space - -1:2

b. B2- Horizontal lines, 30 nm, line /space - 1:2

c. B3- Horizontal lines, 40 nm, line /space - 1:2

d. B4- Horizontal lines, 50 nm, line /space - 1:2

e. B5- Horizontal lines, 70 nm, line /space - 1:2

f B6- Horizontal lines, 100 nm, line /space -1:2

g- B7- Horizontal lines, 200 nm, line /space -1:2

h. B8- Horizontal lines, 400 nm, line /space -1:2

i. B9- Horizontal lines, 800 nm, line /space -1:2

j- B10 - Horizontal lines,1000 nm, line /space -1 :2

[0036] The sub-fields of fields CI -CIO of the third row of fields may exhibit the following characteristics:

a. CI - Horizontal lines, 20 nm, line /space - 1 :6 b. C2 - Horizontal lines, 30 nm, line /space -1:6

c. C3 - Horizontal lines, 40 nm, line /space - 1 :6

d. C4 - Horizontal lines, 50 nm, line /space - 1 :6

e. C5 - Horizontal lines, 70 nm, line /space - 1 :6

f. C6 - Horizontal lines, 100 nm, line /space -1:6

g. C7 - Horizontal lines, 200 nm, line /space - 1 :6

h. C8 - Horizontal lines, 400 nm, line /space - 1 :6

i. C9 - Horizontal lines, 800 nm, line /space - 1 :6

j. CIO - Horizontal lines,1000 nm, line /space -1 :6

[0037] The sub-fields of fields D1-D10 of the fourth row of fields may exhibit the following characteristics:

a. Dl - - Vertical lines, 20 nm, line /space - 1:1

b. D2- Vertical lines, 30 nm, line /space - 1:1

c. D3 - Vertical lines, 40 nm, line /space - 1:1

d. D4- Vertical lines, 50 nm, line /space - 1:1

e. D5 - Vertical lines, 70 nm, line /space - 1:1

f. D6- Vertical lines, 100 nm, line /space - 1:1

g- D7- Vertical lines, 200 nm, line /space - 1:1

h. D8- Vertical lines, 400 nm, line /space - 1:1

i. D9- Vertical lines, 800 nm, line /space - 1:1

j- D10 - Vertical lines, 1000 nm, line /space -1:1

[0038] The sub-fields of fields E1-E10 of the fifth row of fields may exhibit the following characteristics:

a. El- - Vertical lines, 20 nm, line /space - 1:2

b. E2- Vertical lines, 30 nm, line /space - 1:2

c. E3- Vertical lines, 40 nm, line /space - 1:2

d. E4- Vertical lines, 50 nm, line /space - 1:2

e. E5- Vertical lines, 70 nm, line /space - 1:2

f E6- Vertical lines, 100 nm, line /space -1:2

g- E7- Vertical lines, 200 nm, line /space -1:2

h. E8- Vertical lines, 400 nm, line /space - 1:2

i. E9- Vertical lines, 800 nm, line /space -1:2

j- E10 - Vertical lines, 1000 nm, line /space -1 :2 [0039] The sub-fields of fields F1-F10 of the sixth row of fields may exhibit the following characteristics

a. Fl - - Vertical lines, 20 nm, line /space - 1 :6

b. F2 - Vertical lines, 30 nm, line /space - 1 :6

c. F3 - Vertical lines, 40 nm, line /space - 1 :6

d. F4 - Vertical lines, 50 nm, line /space - 1 :6

e. F5 - Vertical lines, 70 nm, line /space - 1 :6

f. F6 - Vertical lines, 100 nm, line /space - 1 :6

g- F7 - Vertical lines, 200 nm, line /space - 1 :6

h. F8 - Vertical lines, 400 nm, line /space - 1 :6

i. F9 - Vertical lines, 800 nm, line /space - 1 :6

j- F10 - Vertical lines, 1000 nm, line /space -1 :6

[0040] The sub-fields of fields G1-G10 of the seventh row of fields may exhibit the following characteristics:

a. Gl -Isolated Horizontal lines, 20 nm, line /space - 1 :50

b. G2 - Isolated Horizontal lines, 30 nm, line /space - 1 :30

c. G3 - Isolated Horizontal lines, 40 nm, line /space - 1 :25

d. G4 - Isolated Horizontal lines , 50 nm, line /space - - 1 :20

e. G5 - Isolated Horizontal lines, 70 nm, line /space - 1 :20

f. G6 - Isolated Horizontal lines, 100 nm, line /space -1 :20

g- G7 - Isolated Horizontal lines, 200 nm, line /space -1 :20

h. G8 - Isolated Horizontal lines, 400 nm, line /space - 1 :5

i. G9 - Isolated Horizontal lines, 800 nm, line /space - 1 :5

j- GlO-Isolated Horizontal lines, 1000 nm, line /space -1 :3

[0041] The sub-fields of fields H1-H10 of the eighth row of fields may exhibit the following characteristics :

a. HI -Isolated Vertical lines, 20 nm, line /space - 1 :50

b. H2 - Isolated Vertical lines, 30 nm, line /space - 1 :30

c. H3 - Isolated Vertical lines, 40 nm, line /space - 1 :25

d. H4 - Isolated Vertical lines, 50 nm, line /space - 1 :20

e. H5 - Isolated Vertical lines, 70 nm, line /space - 1 :20

f. H6 - Isolated Vertical lines, 100 nm, line /space -1 :20

g. H7 - Isolated Vertical lines, 200 nm, line /space -1 :20

h. H8 - Isolated Vertical lines, 400 nm, line /space - 1 :5 i. H9 - Isolated Vertical lines, 800 nm, line /space - 1 :5

j. H10- Isolated Vertical lines, 1000 nm, line /space -1 :3

[0042] The sub-fields of fields 11-110 of the ninth row of fields may exhibit the following characteristics :

a. 11 -Contact holes, 60 nm, line /space - 1 :2

b. 12 - Contact holes, 70 nm, line /space - 1 :2

c. 13 - Contact holes, 80 nm, line /space - 1 :2

d. 14 - Contact holes, 90 nm, line /space - 1 :2

e. 15 - Contact holes, 100 nm, line /space - 1 2

f 16 - Contact holes, 200 nm, line /space - 1 2

g- 17 - Contact holes, 400 nm, line /space - 1 2

h. 18 - Contact holes, 600 nm, line /space - 1 2

i. 19 - Contact holes, 800 nm, line /space - 1 2

j- 110- Contact holes, 1000 nm, line /space - 1 :2

[0043] Sub-fields of fields A1-A10, B1-B10, C1-C10, D1-D10, E1-E10, F1-F10, G1-G10, Hl- H10 and 11-110 can be sized according to an array of beams in which the beams are spaced apart by a pitch of 10 microns. In the above description for the Sub-fields of fields A1-A10, Bl- B10, C1-C10, D1-D10, E1-E10, F1-F10, G1-G10, H1-H10 and 11-110 the numbers given in nm describe the distances between two neighbored structures, the ratios "line / space" define the ratios between the width of the structure and the distance between two neighbored structures, "horizontal" means a particularly selected direction, "vertical" means a direction is perpendicular to the "horizontal" direction and "contact holes" means structures which have similar or equal dimensions in two perpendicular directions .

[0044] Sub-fields of fields A11-A20, B11-B20, C11-C20, D11-D20, E11-E20, F11-F20, G11-G20, H11-H20 and 111-120 can be equivalent to sub-fields of fields A1-A10, B1-B10, C1-C10, D1-D10, E1-E10, F1-F10, G1-G10, H1-H10 and 11-110 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 11 microns.

[0045] Sub-fields of fields J1-J10, K1-K10, L1-L10, M1-M10, N1-N10, Ol-OlO, P1-P10, Ql- Q10, R1-R10 and SI -SI 0 can be equivalent to sub-fields of fields A1-A10, B1-B10, CI -CIO, Dl- D10, E1-E10, F1-F10, G1-G10, H1-H10 and 11-110 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 12 microns.

[0046] Sub-fields of fields J11-J20, K11-K20, L11-L20, M11-M20, N11-N20, 011-020, Pl l- P20, Q11-Q20, R11-R20 and S11-S20 can be equivalent to sub-fields of fields A1-A10, B1-B10, C1-C10, D1-D10, E1-E10, F1-F10, G1-G10, H1-H10 and 11-110 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 13 microns.

[0047] Sub-fields of fields Jl 1 and J12 are like sub-fields of fields Jl, J2 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 11 microns.

[0048] Sub-field of fields Tl and T2 are like sub-field of fields Jl, J2 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 12 microns.

[0049] Sub-field of fields Ti l and T12 are like sub-field of fields Jl, J2 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 13 microns.

[0050] Sub-field of fields J13-J20 are like sub-field of fields J3-J10 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 11 microns.

[0051] Sub-field of fields T3-T10 are like sub-field of fields J3-J10 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 12 microns.

[0052] Sub-field of fields T13-T20 are like sub-field of fields J3-J10 but are sized according to an array of beams in which the beams are spaced apart by a pitch of 13 microns.

[0053] However also other sizes of the sub-fields are possible especially if the pitch between the individual beams in the beam array is different.

[0054] Figures 3-6 and 10 illustrate sub-fields of a field of the test object of figure 1, according to various embodiments of the invention. Figures 3-6 illustrate a sub-field of fields that include 127 identical sub-fields. This corresponds to an array of beams that includes 127 beams that are spaced apart by a pitch of 10 microns. For each beam in the array of beams one sub-field is provided. The position of each sub-field in the field and the distances between the sub-fields in the fields corresponds to the positions and distances of the individual beam in the array of beams in the object plane of the multi-beam system. The array of beams may be shaped as honeycomb or as a hexagon. It is noted that the array of beams may be of any shape (including for example non-hexagon shapes) and the sub-fields can be of any shape - especially of a shape that corresponds to the shape of the array of beams. Non-limiting examples of the array of the sub- fields may include a rectangular array, a square, a triangle or any other shape. The shapes of the array of sub-fields and the array of beams may differ from each other.

[0055] Figure 7 illustrates a sub-field of field A2 70 according to an embodiment of the invention. It includes: (a) border elements such a dashed line and triangular shapes 75, (b) patterns (structural elements) such as horizontal lines 76, (c) pitch 71, (d) pattern recognition targets 72, (e) line - space ratio indication 73, (f) line size 74, and (g) sub-field number (for example 1 till 127).

[0056] It is noted that the array can be rectangular. [0057] Figure 7 illustrates a sub-field 70 that is 13 urn by 11.39μηι and has lines of width of 30 nm, line space ration of 1 :2.

[0058] The border lines can be 0.5 micron wide. The triangles can provide an indication about errors in the vertical and horizontal directions. The triangles can be spaced apart by 3 microns and have a width of 1 micron. The sub-field can include five different pattern recognition patterns.

[0059] Figure 8 illustrates a sub-field of a field according to an embodiment of the invention. It includes an array of circles or holes.

[0060] Figure 9 illustrates a sub-field of field Jl 90 according to an embodiment of the invention. It includes four arrays of rectangles. Each array of rectangles includes multiple co- centered rectangles.

[0061] Figure 10 illustrates a sub-field of field J2 100 according to an embodiment of the invention. All the sub-fields of field J2 except the central sub-field are flat and do not have a feature. The central sub-field (denoted 1/1) has holes. The diameter of the holes is 100 nm, the pitch between holes is 300nm and the depth of each hole is 2000nm.

[0062] Figure 11 illustrates a sub-field of fields J3, J4 and J5 according to an embodiment of the invention. Each sub-field has multiple horizontal lines. The lines of sub-fields J3, J4 and J5 can differ by each other by the pitch between the horizontal line, by the width of the horizontal lines or by both.

[0063] Figure 12 illustrates a sub-field of fields J6, J7 and J8 according to an embodiment of the invention. Each sub-field has multiple vertical lines. The lines of sub-fields J6, J7 and J8 can differ by each other by the pitch between the vertical line, by the width of the vertical lines or by both.

[0064] Figure 13 illustrates a sub-field of fields J9 and J10 according to an embodiment of the invention. Each sub-field has a mesh of lines oriented at 45 degrees and 135 degrees in relation to the horizontal direction as defined above. The lines of sub-fields J9 and J10 can differ by each other by the pitch between the vertical line, by the width of the vertical lines or by both.

[0065] Figure 14 illustrates a method 140 according to an embodiment of the invention.

[0066] Method 140 may include stage 142 of obtaining images of sub-fields of a field of a test object by scanning the sub-fields by an array of beams; wherein the test object comprises multiple regions, wherein each region comprises multiple fields; wherein each field comprises multiple sub-fields; wherein each sub-field comprises multiple structural elements; wherein a location and number of sub-fields of a same field correspond to a number of an array of beams of the multiple beam system and to an expected spatial relationship between the array of beams. Stage 142 may be followed by stage 144 of evaluating at least one spatial or optical characteristic of the array of beams based on the images of the sub-fields. The evaluation can include comparing the images obtained by each beam of the array to expected images to be obtained.

[0067] Method 140 can be applied on the above-mentioned test object.

[0068] While certain features of the invention have been illustrated and described herein, 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 invention.

Claims

CLAIMS What is claimed is:

1. A test object for testing a multiple beam system, the test object comprises multiple regions, wherein each region comprises multiple fields; wherein each field comprises multiple sub-fields; wherein each sub-field comprises multiple patterned structural elements; wherein a location and number of sub-fields of at least one field correspond to a number of beams in an array of beams of the multiple beam system and to an expected spatial relationship between the beams of the array of beams.

2. The test object according to claim 1, wherein the size of each field corresponds to the field of view (FOV) of the multiple beam system.

3. The test object according to claim 1, wherein the sub-fields that belong to a same field are identical to each other at least in areal portions.

4. The test object according to claim 1, wherein sub-fields that belong to different fields differ from each other by at least one spatial characteristic of patterns that belong to the different fields.

5. The test object according to claim 1, wherein each sub-field comprises a border that comprises border patterns, multiple patterns and textual information about the sub-field.

6. The test object according to claim 1, wherein sub-fields differ from each other by at least one out of spacing between features, a size of features, a shape of features.

7. The test object according to claim 1, wherein the sub-fields are grouped into multiple groups and different ones of the groups of sub-fields differ from each other by at least one of size and shape; wherein a difference in the size or shape corresponds to a difference in a spatial relationship between the beams of the array of beams.

8. A method for evaluating a multiple beam system, the method comprising:

obtaining images of sub-fields of a field of a test object by scanning the sub-fields by an array of beams; wherein the test object comprises multiple regions, wherein each region comprises multiple fields; wherein each field comprises multiple sub-fields; wherein each sub-field comprises multiple structural elements; wherein a location and number of sub-fields of at least one field correspond to a number of an array of beams of the multiple beam system and to an expected spatial relationship between the array of beams; and

evaluating at least one spatial or optical characteristic of the array of beams based on the images of the sub-fields.