Method for focusing an electron beam on a wafer having a transparent substrate - Patents.com

Abstract

A method, non-transitory computer readable medium and system for focusing an electron beam. The method can include focusing an electron beam onto at least one evaluated area of ​​a wafer based on a height parameter of each of the at least one evaluated area. The wafer includes a transparent substrate. The height parameter of each of the at least one evaluated area is determined based on a detection signal generated as a result of irradiating one or more height measurement areas of the wafer with a photon beam. The irradiation is performed while the one or more supported areas of the wafer are in contact with one or more support elements of a chuck and while each height measurement area of ​​the one or more height measurement areas is spaced from the chuck by a distance greater than a depth of field of an optical component associated with the photon beam.

Description

[Technical field]

[0001] cross reference This application claims priority to U.S. Patent Application No. 17 / 164,803, filed February 1, 2021, the disclosure of which is incorporated herein by reference in its entirety for all purposes. [Background technology]

[0002] A scanning electron microscope is a high-resolution system that evaluates samples, such as wafers, by scanning an evaluated area of ​​the wafer with an electron beam. A review scanning electron microscope scans the evaluated area that contains suspected defects. A metrology scanning electron microscope scans the evaluated area that contains the features to be measured.

[0003] When scanning the area under evaluation, the electron beam should be focused on the area under evaluation, for example, the area under evaluation should be in the focal plane of the objective lens of the scanning electron microscope.

[0004] Focusing is usually performed based on a height map of the sample. The height map is created using a height measurement unit that illuminates different areas of the wafer (called height-measured areas) to provide height parameters for the height-measured areas. The height-measured areas usually cover only a small part of the wafer. To provide the height map, the height parameters of the areas that are not height-measured areas are calculated by extrapolation or interpolation.

[0005] Some wafers have a transparent substrate supported by a chuck that is in contact with the entire substrate.

[0006] A height parameter of the height-measured area is measured by illuminating the height-measured area with a light beam while the height-measured area is supported by and in contact with the chuck.

[0007] In some cases, especially when the area being height measured is transparent, the light beam may be reflected off the chuck, which may introduce height measurement errors since the height measurement may reflect the height of the chuck rather than the height of the area being height measured.

[0008] Such height measurement errors can cause the electron beam to focus on the backside of the wafer, or at some other point other than the top surface of the wafer.

[0009] There is an increasing demand to provide an accurate solution for height parameter measurement. Summary of the Invention

[0010] A method for focusing an electron beam, a non-transitory computer readable medium and a detection system may be provided.

[0011] The subject matter which is regarded as embodiments of the present disclosure is particularly shown and distinctly claimed in the concluding portion of this specification, however, the embodiments of the present disclosure, both as to organization and method of operation, together with its objects, features, and advantages, can best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 illustrates an example of a method. [Diagram 2] FIG. 2 illustrates an example of a wafer and a chuck. [Diagram 3] FIG. 2 illustrates an example of a wafer and a chuck. [Figure 4] 11A to 11C are diagrams showing examples of an evaluation area, an area to be subjected to height measurement, height parameters, and a height map. [Diagram 5] FIG. 13 is a diagram showing an example of an evaluation area. [Figure 6] FIG. 1 illustrates an example of an electron beam system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure.

[0014] However, it will be understood by those skilled in the art that embodiments of the present disclosure 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 embodiments of the present disclosure.

[0015] The subject matter which is regarded as embodiments of the present disclosure is particularly shown and distinctly claimed in the concluding portion of this specification, however, the embodiments of the present disclosure, both as to organization and method of operation, together with its objects, features, and advantages, can best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings.

[0016] It will be understood 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 accompanying figures to indicate corresponding or analogous elements.

[0017] Because the illustrated embodiments of the present disclosure can, for the most part, be implemented using electronic components and electronic circuits known to those skilled in the art, as set forth above, details will not be described in more detail than is deemed necessary for an understanding and appreciation of the ideas underlying the embodiments of the present disclosure, so as not to obscure or distract from the teachings of the embodiments of the present disclosure.

[0018] Any reference in this specification to a method should, mutatis mutandis, apply to a system capable of carrying out that method, and should, mutatis mutandis, apply to a non-transitory computer readable medium storing instructions for carrying out that method.

[0019] Any reference in this specification to a system should be applied, mutatis mutandis, to the manner in which that system may be performed, and should be applied, mutatis mutandis, to a non-transitory computer readable medium storing instructions executable by that system.

[0020] Any reference herein to a non-transitory computer readable medium should be applied, mutatis mutandis, to methods that may be applied in executing instructions stored on the computer readable medium, and should be applied, mutatis mutandis, to a system configured to execute instructions stored on the computer readable medium.

[0021] The term "and / or" means in addition to or instead.

[0022] An "area to be evaluated" is an area to be evaluated. This evaluation can include defect review, metrology, etc.

[0023] The "height measured area" is the area whose height parameter is measured.

[0024] The term "height parameter" of an area may be a parameter relating to the entire area or just a portion (one or more points) of the area, may relate to the absolute height of the area, may be a parameter relating to the relative height of the area, may be the height of the area, may be the distance from the area to a reference point (e.g. to the objective lens of an electron beam system), may be the elevation difference between the area and a reference point on the wafer, and the like. For simplicity of explanation, the various examples given below relate to the height parameter as the height of the area.

[0025] The term "electron beam system" refers to a system capable of generating one or more electron beams and scanning or otherwise irradiating a sample (or an area of ​​a sample) with the one or more electron beams. A scanning electron microscope is a non-limiting example of an electron beam system.

[0026] A method, system, and non-transitory computer readable medium are provided for accurately measuring height parameters of height-measured areas of a wafer while the height-measured areas are sufficiently far from the chuck (even when the supported areas of the wafer are supported by the chuck), where the distance between each height-measured area and the chuck is sufficiently large to prevent the chuck from affecting the height measurements of the height-measured areas.

[0027] This accurate height parameter measurement can be processed (e.g., by creating a height map) to provide height parameters for areas of the wafer different from the area being measured for height, including height parameters for each area being evaluated.

[0028] The height parameter of the evaluation area is used to focus the electron beam on the evaluation area, e.g., the height parameter can be used as a starting point for an autofocus unit or for focusing the electron beam, etc.

[0029] The area to be evaluated may be the area to be measured for height. The area to be evaluated may be different from the area to be measured for height. The area to be evaluated may partially overlap with the area to be measured for height. The area to be evaluated may not overlap with the area to be measured for height.

[0030] The height parameter of the evaluated area may be determined based on the height parameters of one or more height measured areas.

[0031] For example, if the area being evaluated is different from one or more height-measured areas, the height parameters of the one or more height-measured areas can be used by applying a function (e.g., interpolation, extrapolation, weighted averaging, averaging, machine learning functions, non-machine learning functions, or other functions) to the height parameters of the one or more height-measured areas.

[0032] The height of the evaluated area can be calculated by a processor or height measurement unit of the electron beam system based on the height of the height measurement area, the height of the evaluated area can also be calculated by other components or units of the electron beam system, or it can be calculated by a computerized unit external to the electron beam system.

[0033] FIG. 1 illustrates a method 100 for focusing an electron beam.

[0034] The method 100 may begin at step 110 with obtaining height parameters of one or more height assessed areas of the wafer.

[0035] Step 110 may include generating height parameters for one or more height-assessed areas or receiving height parameters for one or more height-assessed areas.

[0036] The generating may include irradiating one or more height measurement areas of the wafer with a photon beam, generating (by one or more sensors) a detection signal generated as a result of the irradiation, and processing the detection signal to provide height parameters of the one or more height evaluation areas.

[0037] This irradiation is performed while one or more supported areas of the wafer are in contact with one or more support elements of the chuck, and while each of the one or more height measurement areas is spaced from the chuck a distance sufficient to prevent reflections from the chuck (if any) from affecting the height parameters.

[0038] For example, each height measurement area of ​​the one or more height measurement areas may be spaced from the chuck by a distance greater than the depth of field of an optical component associated with the photon beam, which may or may not belong to the height measurement unit.

[0039] This distance may be, for example, greater than 1, 5, 10, 20, 30, 40, 50 millimeters, etc.

[0040] The shape and size of the supported area of ​​the wafer is defined by the shape and size of the corresponding support elements of the chuck, for example, an annular support element may be positioned to support the edge of the wafer or other annular supported area of ​​the wafer.

[0041] The support element of the chuck may be stationary or may be movable, eg, capable of being lowered, raised or otherwise moved.

[0042] The supported area or areas can be located anywhere on the wafer, and the supported area or areas can have any shape and / or size.

[0043] One supported area may have the same shape and size as another supported area.

[0044] One supported area may have a different shape and / or a different size than another supported area.

[0045] For example, the one or more supported areas of the wafer may be the edge area of ​​the wafer or may be an area different from the edge area of ​​the wafer.

[0046] The chuck may be configured to support one or more sizes of wafers.

[0047] A wafer of a first size may be supported by one or more support elements of the chuck, and a wafer of another size may be supported by one or more other support elements of the chuck.

[0048] The one or more support elements supporting the larger wafer can be taller than the one or more support elements supporting the smaller wafer, and the one or more support elements supporting the larger wafer can at least partially surround the smaller wafer.

[0049] Following step 110, step 120 may be performed in which the electron beam system focuses the electron beam onto at least one evaluated area of ​​the wafer based on (in response to) a height parameter of each of the at least one evaluated area.

[0050] A height parameter of each of the at least one evaluated area may be calculated based on height parameters of one or more height evaluation areas of the wafer.

[0051] This calculation can be performed during step 110, during step 120 or during a dedicated step of calculating the height parameters of each of the at least one evaluated area based on the height parameters of one or more height evaluation areas of the wafer.

[0052] When there are multiple assessed areas, the calculation of height parameters for all the multiple assessed areas may be performed at once, per assessed area, per set of two or more assessed areas, etc. For example, the height parameters for an assessed area may be calculated after evaluating another assessed area or before evaluating other assessed areas.

[0053] This calculation of the height parameter and / or obtaining the height parameter of one or more height evaluation areas of the wafer may be performed, at least in part, during or after an alignment process of the wafer, etc. The alignment process may include illuminating one or more height measurement areas of the wafer, generating detection signals resulting from the illumination, and determining an initial height parameter for the wafer.

[0054] During scanning of the area to be evaluated, the focus can be maintained or changed, for example by performing an autofocus.

[0055] The method 100 may include a step 130 of evaluating at least one evaluated area.

[0056] Step 130 may be performed after step 120, in parallel with step 120, or overlapping with the performance of step 120.

[0057] Steps 110, 120 and 130 may be repeated for multiple wafers.

[0058] The chuck may only support wafers of the same size.

[0059] Alternatively, the chuck may support one or more wafers of different sizes, which may be supported by different support elements of the chuck or which may share at least one support element of the chuck.

[0060] The chuck may be coated with a photon absorbing material, for example, the chuck may be coated with a black coating material.

[0061] 2 shows an example of a wafer 10, a supported area 11, a height measurement area 13, an evaluation area 14, a chuck 20, a support element 21 of the chuck (which may be ring-shaped or have a round cross section), a distance 31 between the unsupported area of ​​the wafer and a bottom 22 of the chuck 20, and a focal depth 32 of an optical component (e.g., a height measurement unit) related to the photon beam. The wafer 10 has a transparent substrate. The transparent substrate may be the entire wafer or a large portion of the wafer. For simplicity of explanation, it is assumed that the entire element designated 10 is the transparent substrate of the wafer.

[0062] The distance 31 is greater than the depth of focus 32 so that when measuring the height of the height measured area 13, reflections from the chuck (particularly the bottom 22 of the chuck 20) ​​do not affect the measurement of the height parameter.

[0063] FIG. 2 further illustrates that the height measurement area 13 is spaced apart from the supported area 11, while the evaluation area 14 may at least partially overlap the supported area 11.

[0064] 3 shows an example of a wafer 10 supported by a support element 21 of a chuck 20, another wafer 10' (smaller than wafer 10) supported by another support element 21' having the shape of a ring. The distance 33 between the bottom and the other wafer 10' is also greater than the depth of focus 32.

[0065] FIG. 3 further illustrates another example of three pins 21 ″ that function as support elements for a wafer smaller than wafer 10 .

[0066] FIG. 4 shows an example of a first plurality (N) of height measurement areas 13(1) to 13(N), a second plurality (M) of evaluated areas 14(1) to 14(M), height parameters HP(13,1) to HP(13,N) of the height measurement areas 13(1) to 13(N), and height parameters HP(14,1) to HP(14,M) of the evaluated areas 14(1) to 14(M).

[0067] During step 110 of the method 100, the height parameters HP(13,1) to HP(13,N) of the height measurement areas 13(1) to 13(N) may be processed to provide height parameters HP(14,1) to HP(14,M) of the evaluated areas 14(1) to 14(M).

[0068] 4 also illustrates the generation of a wafer height parameter HP(10) across the wafer. The height parameter HP(10) can, for example, reflect an average height of different areas of the wafer. Calculation of the wafer height parameter is optional.

[0069] 5 shows the evaluated area 14, a scan pattern 72 followed by the electron beam 61 as it scans the evaluated area 14, and a starting point 71 of the scan pattern 72. Height parameters for the evaluated area 14 may include, for example, a function of the height of the starting point 71, or the height of other points in the evaluated area 14, or the height of one or more points in the evaluated area.

[0070] 6 shows an electron beam system 40, which includes a vacuum chamber 41, a chuck 20, an electron beam column 43, a height measurement unit 42, a processor 45, a memory unit 46, and a controller 47. The controller 47 is configured to control the electron beam system 40.

[0071] The wafer 10 is supported by a chuck 20 and is disposed within a vacuum chamber 41 .

[0072] The height measurement unit 42 may be configured to determine a height parameter of the height-assessed area of ​​the wafer by irradiating the area with a photon beam 62 (or multiple photon beams).

[0073] Electron beam column 43 may be configured to scan electron beam 61 (or multiple electron beams) over one or more areas to be evaluated.

[0074] The electron beam system 40 may be configured to perform the method 100 .

[0075] FIG. 6 further shows an example of a height measurement unit 42 which may be a laser focusing system.

[0076] The height measurement unit 42 may include a laser source 51 , a two-way mirror 52 , a first lens 53 , a one-way mirror 54 , a second lens 55 , a prism 57 , a first sensor 58 and a second sensor 59 .

[0077] A light beam from a laser source 51 passes through a two-way mirror 52 and a first lens 53, and strikes a one-way mirror .

[0078] The one-way mirror 54 directs the light beam towards a second lens 55. The second lens 55 focuses the light beam and directs it towards the area to be measured for height.

[0079] The light beam is then reflected from the area being height measured towards a one-way mirror 54 .

[0080] When the light beam is focused on the area to be height measured, the reflected light beam passes through the second lens 55, strikes the center of the one-way mirror 54, and is directed towards the first lens 53. The reflected light beam passes through the first lens 53 and is reflected by the two-way mirror 52 towards a first location (e.g., the center) of the prism 57. The prism 57 splits the reflected light beam evenly between the first sensor 58 and the second sensor 59.

[0081] If the light beam is not focused on the area to be height measured, the reflected light beam passes through the second lens 55, strikes an off-center location on the one-way mirror 54, and is directed towards the first lens 53. The reflected light beam passes through the first lens 53 and is reflected by the two-way mirror 52 towards a second location (e.g., an off-center location) of the prism 57. The prism 57 splits the reflected light beam unequally between the first sensor 58 and the second sensor 59.

[0082] Thus, the relationship between the light detected by the first sensor 58 and the light detected by the second sensor 59 indicates whether the light beam is focused or unfocused, and provides an indication as to the amount of unfocusedness.

[0083] Other height measurement units may be provided.

[0084] It should be noted that the method 100 can be performed by a system that does not include electron beam optics.

[0085] In the foregoing specification, embodiments of the present disclosure have been described with reference to specific examples of the embodiments of the present disclosure, however, it will be apparent that various modifications and changes can be made thereto without departing from the broader spirit and scope of the embodiments of the present disclosure as set forth in the appended claims.

[0086] Furthermore, when terms such as "front," "back," "top," "bottom," "upper," "lower," and the like are used in this description and in the claims, they are used for purposes of explanation and not necessarily to describe permanent relative positions, and it is understood that these terms, as so used, are interchangeable such that, under appropriate circumstances, the embodiments of the disclosure described herein can operate in orientations other than those illustrated or otherwise described herein, for example.

[0087] The connections discussed herein may be any type of connection suitable for transferring signals from the respective corresponding nodes, units or devices, e.g., via an intermediate device, or any type of connection suitable for transferring signals to the respective corresponding nodes, units or devices, e.g., via an intermediate device. Thus, unless otherwise implied or stated, the connections may be, e.g., direct or indirect connections. The connections may be illustrated or described as being single, multiple, unidirectional or bidirectional connections. However, the implementation of the connections may differ in different embodiments. For example, separate unidirectional connections may be used instead of bidirectional connections, and vice versa. Furthermore, instead of multiple connections, a single connection may be used that transfers multiple signals sequentially or in a time division multiplexed manner. Similarly, a single connection carrying multiple signals may be split into different connections that carry subsets of these signals. Thus, there are many options for transferring signals.

[0088] Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components herein that are combined to achieve a particular functionality can be viewed as "associated" with one another such that the desired functionality is achieved, regardless of architecture or intervening components. Similarly, any two components so associated can also be viewed as "operably connected" or "operably coupled" with one another such that the desired functionality is achieved.

[0089] Moreover, those skilled in the art will recognize that the boundaries between operations described above are merely examples. Multiple operations may be combined into a single operation, a single operation may be divided into multiple additional operations, and operations may be performed in a manner that at least partially overlaps in time. Additionally, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be changed in various other embodiments.

[0090] Further, for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within the same device, or the examples may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in any suitable manner.

[0091] However, other modifications, variations and alternatives are also possible. Accordingly, the specification and drawings are to be regarded in an illustrative sense and not in a restrictive sense.

[0092] In the claims, reference signs in parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of other elements or steps than those recited in the claim. Furthermore, as used herein, the terms "a" or "an" are defined as one or more than one. Furthermore, the use of introductory phrases such as "at least one" and "one or more" in the claims should not be construed as implying that the introduction of another claim element by the indefinite article "a" or "an" limits a particular claim containing such introduced claim element to an embodiment of the present disclosure containing only one such element. This is true even when the same claim contains the introductory phrase "one or more" or "at least one" and an indefinite article such as "a" or "an". The same is true with respect to the use of definite articles. Unless otherwise stated, terms such as "first" and "second" are used to arbitrarily distinguish between the elements that such terms describe. Thus, these terms are not necessarily intended to indicate a temporal or other priority of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[0093] While certain features of the embodiments of the present disclosure have been illustrated and described herein, many modifications, substitutions, changes and equivalents will occur to those skilled in the art, and it is therefore understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the embodiments of the present disclosure.

Claims

1. 1. A method of focusing an electron beam, the method comprising: focusing, by an electron beam system, the electron beam onto at least one evaluated area of ​​the wafer based on an evaluation area height parameter of each of the at least one evaluated area. Including, the wafer comprises a transparent substrate; the height parameter of each of the at least one evaluated area is determined based on a detection signal generated as a result of irradiating one or more height measurement areas of the wafer with a photon beam; the irradiating is performed while one or more supported areas of the wafer are in contact with one or more support elements of a chuck and while each height measurement area of ​​the one or more height measurement areas is spaced from the chuck a distance greater than a depth of field of an optical component associated with the photon beam. method.

2. The method of claim 1 , wherein the distance is greater than 10 millimeters.

3. The method of claim 1 , wherein the one or more supported areas of the wafer are edge areas of the wafer.

4. The method of claim 3 , wherein the one or more supported areas of the wafer are in contact with an annular area of ​​the chuck.

5. 2. The method of claim 1, wherein an alignment process is performed prior to focusing the electron beam on the at least one evaluated area of ​​the wafer, the alignment process including irradiating the one or more height measurement areas of the wafer, generating the detection signal, and determining an initial height parameter for the wafer.

6. The method of claim 1 , further comprising the step of focusing the electron beam on an evaluation area of ​​the at least one evaluation area of ​​the wafer and then scanning the evaluation area with the electron beam.

7. 7. The method of claim 6, wherein the at least one evaluated area includes a first evaluated area, a second evaluated area, and a third evaluated area, the method further comprising determining a height parameter of the second evaluated area after scanning the first evaluated area with the electron beam and before scanning the third evaluated area with the electron beam.

8. The method of claim 1 , wherein an evaluated area of ​​the at least one evaluated area at least partially overlaps a height measured area of ​​the one or more height measured areas.

9. The method of claim 1 , wherein an evaluated area of ​​the at least one evaluated area is spaced apart from a respective height measured area of ​​the one or more height measured areas.

10. the wafer being a first wafer, the method further comprising: focusing the electron beam onto at least one other evaluated area of ​​a second wafer based on a respective evaluated area height parameter of the at least one other evaluated area. Including, the second wafer is a different size than the first wafer; the second wafer includes a transparent substrate; the height parameter of each of the at least one other evaluated area is determined based on a detection signal generated as a result of irradiating one or more other height measurement areas of the second wafer with the photon beam; the irradiating is performed while one or more other supported areas of the second wafer are in contact with one or more other areas of the chuck and while each height measurement area of ​​the one or more other height measurement areas is spaced from the chuck a distance greater than the depth of field of the optical component associated with the photon beam; the one or more other areas of the chuck are spaced apart from the one or more support elements of the chuck. The method of claim 1.

11. The method of claim 10 , wherein the one or more other areas of the chuck are surrounded by the one or more support elements of the chuck.

12. The method of claim 1 , wherein the chuck is coated with a photon absorbing material.

13. 1. An electron beam system comprising: A height measuring unit; a chuck comprising one or more support elements configured to support one or more supported areas of the wafer while each of the one or more height measurement areas of the wafer is spaced from the chuck by a distance greater than a depth of field of an optical component of the height measurement unit; Equipped with the wafer comprises a transparent substrate; the height measurement unit is configured to measure heights of the one or more height measurement areas by irradiating the one or more height measurement areas with a photon beam while the wafer is supported by the chuck; the electron beam system further comprising: an electron beam column configured to focus an electron beam onto at least one evaluated area of ​​the wafer based on an evaluation area height parameter of each of the at least one evaluated area. Equipped with the electron beam system is configured to determine the height parameter of each of the at least one evaluated area based on the height of the one or more height measurement areas. Electron beam system.

14. The electron beam system of claim 13 , wherein the distance is greater than 10 millimeters.

15. 1. A method of scanning an area of ​​a wafer, the method comprising: measuring a height of each of the areas by irradiating the areas with a photon beam, the measuring being performed while the wafer is supported by a chuck and the areas are spaced from the chuck by at least 10 millimeters; and evaluating each of the areas by scanning the area with an electron beam focused on the area, the focusing of the electron beam being responsive to the height of the area. The method includes:

16. The method of claim 15 , wherein the measuring of the height of the respective areas is performed during an alignment process that is performed prior to the evaluation of the areas.

17. The method of claim 15 , wherein the measurement of the height of one of the areas is performed after evaluating at least one other of the areas.

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