Detection of Arc Hazards Related to Wafers

Abstract

A method, a non-transitory computer-readable medium, and a detection system for detecting an arc hazard related to a wafer. The detection system may include a measurement unit, an electrode, and a processing unit. The measurement unit may be configured to provide a measurement result by measuring an electrical parameter of the electrode during a test period when the wafer is movable relative to the electrode and when a specific electric field can be formed between the electrode and the wafer; wherein the specific electric field causes a separated end portion of a partially separated conductive element of the wafer to move away from the wafer. The processing unit may be configured to determine the presence of the arc hazard based on the measurement result.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of U.S. Non - Provisional Application No. 16 / 560,625, filed on September 4, 2019, the entire content of which is incorporated herein by reference for all purposes. Background Art

[0003] Wafers, such as semiconductor wafers, undergo multiple mechanical and chemical processes, which may cause various types of defects. One type of defect is the formation of partially separable elements. Non - limiting examples of partially separable elements are conductive whiskers.

[0004] A charged - particle evaluation system, such as a scanning electron microscope (SEM), evaluates a wafer while introducing a very high voltage difference (e.g., more than one thousand volts) between the wafer and an electrode of the charged - particle evaluation system. The electrode may be part of an electron optical device and, for example, may be an objective lens of the charged - particle evaluation system.

[0005] An arc is an electrical breakdown of a gas that results in a long - duration discharge. A leakage current through a normally non - conductive medium, such as air, generates a plasma, and the plasma can produce visible light. (www.wikipedia.org).

[0006] Under high - voltage conditions, a partially separable element can be pulled towards the electrode of the charged - particle evaluation system, and even if the partially separable element does not contact the electrode, it can trigger the formation of an arc.

[0007] The formation of an arc in a charged - particle evaluation system can cause wafer damage and can severely damage the charged - particle evaluation system. The deterioration starting from (i) the state where a leakage current begins between the charged - particle evaluation system and the wafer and (ii) the formation of an arc is very fast. In many cases, the deterioration is too fast, and once started, the formation of an arc cannot be stopped.

[0008] Therefore, partially separable elements are considered arc hazards.

[0009] When high - voltage conditions are not applied, the partially separable elements are not pulled away from the wafer and are difficult to detect.

[0010] There is an increasing need to provide an accurate and efficient way to detect arc hazards before an actual arc is formed. Summary of the Invention

[0011] Some embodiments of the present disclosure relate to a method, a non-transitory computer-readable medium, and a detection system for detecting an arc hazard related to a wafer. The detection system may include a measurement unit, an electrode, and a processing unit. The measurement unit may be configured to provide a measurement result by measuring an electrical parameter of the electrode during a test period when the wafer is movable relative to the electrode and when a specific electric field is formed between the electrode and the wafer; wherein the specific electric field causes a separated end of a partially separated conductive element of the wafer to move away from the wafer. The processing unit may be configured to determine the presence of the arc hazard based on the measurement result. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The subject matter regarded as the embodiments of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both as to organization and method of operation, together with objects, features, and advantages thereof, the embodiments of the present disclosure may best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, in which:

[0013] Figure 1 An example of a part of the detection system is shown;

[0014] Figure 2 An example of a part of the detection system is shown;

[0015] Figure 3 Examples of two versions of the detection system are shown;

[0016] Figure 4 A part of the detection system embedded in a charged particle evaluation system is shown;

[0017] Figure 5 Examples of the electrode and an additional electrode are shown;

[0018] Figure 6 An example of the leakage current measured by the measurement unit during a plurality of test periods; and

[0019] Figure 7 An example of the method is shown. DETAILED DESCRIPTION

[0020] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure.

[0021] However, those skilled in the art will understand that the current 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 current embodiments of the present disclosure.

[0022] The subject matter regarded as embodiments of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both as to organization and method of operation, together with objects, features, and advantages thereof, the embodiments of the present disclosure may best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings.

[0023] It will be appreciated that, for the sake of simplicity and clarity of illustration, the elements shown in the drawings are not necessarily drawn to scale. For example, the dimensions of some elements may be exaggerated relative to other elements for clarity. Additionally, it is considered appropriate that reference numerals may be repeated among the drawings to indicate corresponding or analogous elements.

[0024] Since most of the illustrated embodiments of the present disclosure can be implemented using electronic components and circuits known to those of ordinary skill in the art, details are not explained to any greater extent than necessary as shown above in order to understand and appreciate the underlying concepts of the current embodiments of the present disclosure and in order not to obscure or render ambiguous the teachings of the current embodiments of the present disclosure.

[0025] Any reference in this specification to a method should be modified as necessary to apply to a system capable of performing the method and should be modified as necessary to apply to a non-transitory computer-readable medium storing instructions for performing the method.

[0026] Any reference in this specification to a system should be modified as necessary to apply to a method executable by the system and should be modified as necessary to apply to a non-transitory computer-readable medium storing instructions executable by the system.

[0027] Any reference in this specification to a non-transitory computer-readable medium should be modified as necessary to apply to a method applicable when instructions stored in the computer-readable medium are executed and should be modified as necessary to apply to a system configured to execute the instructions stored in the computer-readable medium.

[0028] The term “and / or” means additionally or alternatively.

[0029] It has been found that an arc hazard can be detected by a detection system that can (i) cause a separating end of a partially separable element to be pulled away from a wafer and (ii) detect the separating end of the partially separable element.

[0030] The detection can be performed prior to the evaluation of the wafer by a charged particle evaluation system and can prevent the formation of an arc within the charged particle evaluation system.

[0031] The detection system can be configured to detect arc hazards related to a wafer. The detection system can include a supply unit or can be configured to be coupled to a supply unit. The detection system can include a wafer support unit but can be configured to receive a wafer (supported and moved by the wafer support unit) during a test period.

[0032] Figure 1 An example of part 101 of the detection system is shown. The detection system can include a measurement unit (represented as 201 in Figure 3 ), an electrode 30, and a processing unit (represented as 210 in Figure 3 ). The processing unit can include at least one processing circuit. The processing circuit can include one or more hardware processors, such as one or more general-purpose units, one or more graphics processing units, one or more hardware accelerators, one or more neural network chips, one or more field-programmable gate arrays, etc.

[0033] The measurement unit 201 is configured to provide measurement results by measuring the electrical parameters of the electrode during a test period. During the test period, the wafer 10 moves relative to the electrode 30, and a specific electric field is formed between the electrode 30 and the wafer 10. The specific electric field can be formed by introducing a voltage difference between the electrode 30 and the wafer 10 by one or more supply units (such as Figure 3 supply unit 202). The specific electric field can be a fixed value during the test period or can vary during the test period. The specific electric field causes the separated ends of the partially separable conductive elements of the wafer to move away from the wafer towards the electrode 30.

[0034] During the evaluation of the wafer by the charged particle evaluation system, the specific electric field can mimic or approximate the electric field applied to the wafer by the charged particle evaluation system.

[0035] If the charged particle evaluation system anticipates that the wafer will be subjected to different electric field values, the specific electric field can be determined based on one, some, or all of these different values. For example, the wafer can undergo multiple different test iterations to test different values of the specific electric field. The results of the different test iterations can indicate which values of the electric field can be safely applied by the charged particle evaluation system during the evaluation of the wafer.

[0036] The specific electric field can be at least a pre-defined safety gap higher than the highest electric field applied to the wafer by the charged particle evaluation system. The safety gap can further reduce the risk of forming an arc and can prevent undesired electric field deviations within the charged particle evaluation system and / or can compensate for the inaccuracy of the detection system in detecting arc hazards.

[0037] While considering any differences between the detection system and the charged particle evaluation system, a specific value of the electric field can be set. For example, during the evaluation of the wafer by the charged particle evaluation system, the wafer is flattened by the chuck that supports the wafer. During the evaluation of the wafer by the charged particle evaluation system, a first distance can be maintained between the wafer and the electrode of the charged particle evaluation system. On the other hand, when tested by the detection system, the wafer may not be flattened. The detection system can receive the warped wafer and thus can position the electrode of the detection system at a second distance from the wafer. The second distance can exceed the first distance to compensate for the packaging of the packaged wafer.

[0038] Introducing a second distance that exceeds the first distance may require the detection system to apply a greater voltage difference to obtain the same electric field.

[0039] For another example, when the wafer is evaluated by the charged particle evaluation system, the wafer is maintained under high vacuum conditions (e.g., below 10 -8 mbar). On the other hand, the detection system can detect the partially separable element in a non-vacuum environment. Any differences in any environmental parameters can be considered.

[0040] The processing unit 210 can be configured to determine the presence of an arc hazard based on the measurement results. The processing unit 210 can generate or receive a mapping between the value of the measurement results and the value of the electric field that will cause the formation of an arc once applied by the charged particle evaluation system.

[0041] Based on the mapping, the processing unit can determine the range of safe values of the electric field that can be (by the charged particle evaluation system) applied to the wafer without the formation of an arc.

[0042] The processing unit 210 can determine whether the wafer can be tested by the charged particle evaluation system, and if the wafer can be tested by the charged particle evaluation system, determine under what conditions the wafer is tested by the charged particle evaluation system. For example, the processing unit can determine the allowable range of the electric field to be applied to the wafer during the charged particle beam evaluation of the wafer.

[0043] The mapping can be determined by testing the wafer, by simulating the electric field formed by the detection system, and by the charged particle evaluation system, etc.

[0044] The conditions that can be applied during the evaluation of the wafer by the charged particle evaluation system can be determined based on the amount of risk that the customer can tolerate.

[0045] As Figures 1 to 3 shown, the wafer support unit 12 is used to support the wafer and to move the wafer relative to the electrode during the test period. The goal of moving the wafer is to check whether the area of the wafer moving near the electrode includes a partially separable element. The wafer can be moved without contacting the electrode with the main body of the wafer.

[0046] Figure 1 Shows an electrode 30 supported by a support element 24 and a base 22. The electrode 30 and the base 22 form an opening. The entire wafer 10 can move inside and outside the opening 26 so as to scan the entire top side of the wafer. Moving only a part of the wafer 10 inside the opening 26 will only scan the partially separable elements for a part of the wafer. The opening can have a rectangular shape or any other shape.

[0047] The electrode 30 and the base 22 are shown as parallel plates, but can have other shapes. Other spatial relationships can exist between the wafer 10, the electrode 30 and the base 22. The electrode 30 can be made of ceramic, plastic or other partially conductive materials. Alternatively, the electrode can be made of a conductive material such as metal.

[0048] The electrode can include a conductive region and a non-conductive region. The electrode can include a partially conductive region and other regions. The electrode can be replaced by more than one single electrode electrically coupled to each other.

[0049] Figure 1 A support element 32 is also shown, which can connect the base 22 to the frame of the evaluation device or any other support structure of any other system. During the test period, the detection device can measure any leakage current between the electrode 30 and the wafer 10.

[0050] Figure 2 Shows an electrode 30 supported by a support element 24 and a base 22. The electrode 30 and the base 22 form an opening. Figure 2 Additional electrodes 42, 43 and 44 supported by a support element 45 are also shown. The additional electrodes are below the electrode 30 and enclose a circular space larger than the size of the wafer.

[0051] Once the wafer 10 descends into the circular space, the wafer is surrounded by the additional electrodes 42, 43 and 44, and the edge of the wafer faces the additional electrodes 42, 43 and 44 without the main body of the wafer contacting the additional electrodes 42, 43 and 44. The additional electrodes 42, 43 and 44 can detect the partially separable elements present on the edge of the wafer. It should be noted that the detection system can include the additional electrodes but not the electrode 30.

[0052] Figure 3 Two versions of the detection system are shown. One version of the detection system includes Figure 1 part 101. The other version of the detection system includes Figure 2 part 102. In both cases, these parts are electrically coupled to a measurement unit 201 and a supply unit 202 (collectively denoted as 200) coupled to a processing unit 210.

[0053] Figure 4Shows part 102 of the detection system embedded in the charged particle evaluation system 250. The wafer support unit can be part of a robot that is used to load and unload wafers from a cassette and move wafers to or from a load lock. Any other location can be provided. The detection system can be located outside the charged particle evaluation system.

[0054] Figure 5 Shows electrode 30 and additional electrodes 42, 43, and 44 coupled in series with each other via high voltage conductor 49, which is also coupled to a supply unit and / or a measurement unit. Electrode 30 and the additional electrodes can be independently coupled to the supply unit and / or the measurement unit.

[0055] Figure 6 Shows an example of the leakage current measured by the measurement unit during a plurality of test periods. Curve 71 shows a negligible current through electrode 30 when the wafer moves inward into the opening formed between electrode 30 and the base.

[0056] Peak 61 represents the leakage current, which can be caused by a partially separable element that is partially separated from the upper side of the wafer and can pose an arc hazard. Curve 72 shows a negligible current through electrode 30 when the wafer descends into the circular space surrounded by additional electrodes 42, 43, and 44.

[0057] Peak 62 represents the leakage current, which can be caused by a partially separable element that is partially separated from the edge of the wafer and can pose an arc hazard.

[0058] Curve 73 shows a negligible current through electrode 30 when the wafer moves outward away from the detection system.

[0059] Peak 63 represents the leakage current, which can be caused by a partially separable element that is partially separated from the edge of the wafer and can pose an arc hazard.

[0060] Figure 6 Also shows current threshold 74. Peaks 61, 62, and 63 exceed the threshold and thus indicate the presence of an arc hazard. Curves 71, 72, and 73 are below the threshold and indicate the absence of an arc hazard.

[0061] It should be noted that measurement results such as the measured current through the electrode can be processed by threshold processing (as Figure 6 shown), but other methods of processing the measurement results can be applied.

[0062] Figure 7Shows an example of method 700. Method 700 may be executed by detection system 100. Method 700 may include at least some of steps 705, 710, 720, 730, and 740.

[0063] Figure 7 Shows a sequence of steps 705, 710, 720, 730, and 740. Step 705 may include generating or receiving a mapping between values of measurement results (obtained by the detection system) and values of an electric field that, once applied by a charged particle evaluation system, will cause the formation of an arc. Step 705 may include determining the mapping by testing a wafer or by simulating the electric field formed by the detection system and by the charged particle evaluation system, etc.

[0064] Step 710 may include forming a specific electric field between an electrode and a wafer. The specific electric field causes a separated end of a partially separable conductive element of the wafer to move away from the wafer. The specific electric field is maintained during a test period in which the wafer is tested. During the evaluation of the wafer by the charged particle evaluation system, the specific electric field may mimic or approximate the electric field applied to the wafer by the charged particle evaluation system.

[0065] If the wafer is expected by the charged particle evaluation system to be subjected to different electric field values, the specific electric field may be determined based on one, some, or all of these different values. For example, the wafer may undergo multiple different test iterations to test different values of the specific electric field. The results of the different test iterations may indicate which values of the electric field may be applied by the charged particle evaluation system during the evaluation of the wafer.

[0066] The specific electric field may be at least a pre-defined safety gap higher than the highest electric field applied to the wafer by the charged particle evaluation system. The safety gap may further reduce the risk of arcing and may prevent undesired electric field deviations within the charged particle evaluation system and / or may compensate for inaccuracies of the detection system in detecting arc hazards.

[0067] The value of the specific electric field may be set while taking into account any differences between the detection system and the charged particle evaluation system.

[0068] For example, during the evaluation of the wafer by the charged particle evaluation system, the wafer is flattened by a chuck supporting the wafer, and a first distance may be introduced between the wafer and the electrode of the charged particle evaluation system. On the other hand, when tested by the detection system, the wafer may not be flattened. The detection system may receive a warped wafer and may thus position the electrode of the detection system at a second distance from the wafer. The second distance exceeds the first distance to compensate for the packaged wafer.

[0069] Introducing a second distance that exceeds the first distance may require the detection system to apply a greater voltage difference to obtain the same electric field.

[0070] For example, when a wafer is evaluated by a charged particle evaluation system under high vacuum conditions (e.g., below 10 -8 bar), the detection system can detect a partially separable component in a non-vacuum environment. Any environmental parameter can be considered.

[0071] Step 720 may include measuring the leakage current from the electrode to the wafer during a test period. The wafer may be electrically coupled to a wafer support unit that can be grounded or biased to another voltage level.

[0072] Step 730 may include, when the wafer is moved relative to the electrode and when a specific electric field is formed between the electrode and the wafer, providing a measurement result by the measurement unit and by measuring the electrical parameters of the electrode during the test period.

[0073] There may be more than one single electrode, and step 730 may include moving the wafer relative to the electrode and one or more additional electrodes during one or more portions of the test period and obtaining measurement results related to the leakage current between the wafer and at least one of the electrodes.

[0074] Step 740 may include determining the presence of an arc hazard by the processing unit based on the measurement results.

[0075] Step 740 may include at least one of the following:

[0076] Based on a mapping, determining a range of safe values of the electric field that can be applied (by the charged particle evaluation system) to the wafer without forming an arc.

[0077] Determining whether the wafer can be tested by the charged particle evaluation system and, if the wafer can be tested by the charged particle evaluation system, determining under what conditions the wafer can be tested by the charged particle evaluation system. For example, determining the allowable range of the electric field to be applied to the wafer during the charged particle beam evaluation of the wafer.

[0078] Based on the amount of risk that the customer may tolerate, determining the electric field that can be applied during the evaluation of the wafer by the charged particle evaluation system.

[0079] To determine the allowable region of the voltage applied to the wafer by the charged particle evaluation system, steps 710, 720, 730, and 740 can be repeated multiple times at different values of the electric field.

[0080] Any of the relationships mentioned above can be learned in any way. For example, a reference structural element with a groove of a known size can be illuminated to provide measurement results associated with the known size of the groove. Additionally or alternatively, the relationship can be learned by simulating the electron images obtained when scanning the structural element.

[0081] In the foregoing description, embodiments of the present disclosure have been described with reference to specific examples of embodiments of the present disclosure. However, it will be apparent that various modifications and changes can be made therein without departing from the broader spirit and scope of the embodiments of the present disclosure as set forth in the appended claims.

[0082] In addition, the terms "front", "back", "top", "bottom", "above", "below", etc. (if any) in the specification and claims are used for descriptive purposes and not necessarily for describing a permanent relative position. It will be understood that such terms are interchangeable under appropriate circumstances, such that the embodiments of the present disclosure described herein can, for example, be operated in orientations other than those shown or otherwise described herein.

[0083] As discussed herein, a connection can be any type of connection suitable for transmitting signals, for example, from or to a corresponding node, unit, or device via an intermediate device. Thus, unless otherwise implied or stated, a connection can be, for example, a direct connection or an indirect connection. A connection can be shown or described as a single connection, multiple connections, a unidirectional connection, or a bidirectional connection. However, different embodiments can vary the implementation of the connection. For example, separate unidirectional connections can be used instead of a bidirectional connection, and vice versa. Also, multiple connections can be replaced by a single connection that transmits multiple signals serially or in a time-division multiplexed manner. Similarly, a single connection carrying multiple signals can be separated into various different connections carrying subsets of those signals. Thus, there are many options for transmitting signals.

[0084] Any arrangement of components that achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components combined herein to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "operably connected" or "operably coupled" to each other to achieve the desired functionality.

[0085] In addition, those skilled in the art will recognize that the boundaries between the operations described above are merely illustrative. Multiple operations can be combined into a single operation, a single operation can be distributed over additional operations, and operations can be performed at least partially overlapping in time. Moreover, alternative embodiments can include multiple instances of a particular operation, and in various other embodiments, the order of operations can be changed.

[0086] Moreover, for example, in one embodiment, the example shown can be implemented as circuitry located on a single integrated circuit or within the same device. Alternatively, the example can be implemented as any number of separate integrated circuits or separate devices interconnected in a suitable manner.

[0087] However, other modifications, variations and alternatives are also possible. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

[0088] In a claim, any reference signs placed 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 listed in a claim. Further, the terms "a" or "an" as used herein are defined as one or more than one. Also, the use of introductory phrases such as "at least one" and "one or more" in a claim shall not be construed to imply that the introduction of another claim element by the indefinite article "a" or "an" limits any particular claim containing such introduced claim element to embodiments of the disclosure having only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and the indefinite article (such as "a" or "an"). The same holds for the use of definite articles. Terms such as "first" and "second" are used arbitrarily to distinguish between elements so described. Thus, these terms are not necessarily intended to indicate a temporal or other precedence of such elements. The fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[0089] Although certain features of embodiments of the present disclosure have been shown and described herein, many modifications, substitutions, changes and equivalents will now occur to those of ordinary skill in the art. Accordingly, it is to be 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. A detection system for detecting arc hazards related to a wafer, the detection system comprising: an electrode; a wafer support unit configured to support the wafer and move the wafer relative to the electrode during a test period; a supply unit electrically coupled to the electrode and the wafer and configured to maintain a specific electric field between the electrode and the wafer; a measurement unit configured to provide a measurement result by measuring an electrical parameter of the electrode during the test period when the wafer moves relative to the electrode and when the specific electric field is formed between the electrode and the wafer, the specific electric field causing a separated end of a partially separated conductive element of the wafer to move away from the wafer; and a processing unit configured to determine the presence of the arc hazard based on the measurement result.

2. The detection system according to claim 1, wherein, the wafer support unit is configured to support the wafer without flattening the wafer.

3. The detection system according to claim 1, wherein, the measurement unit is a galvanometer configured to measure a leakage current from the electrode to the wafer during the test period.

4. The detection system according to claim 3, wherein, the measurement unit is configured to measure a leakage current from the electrode to the wafer during the test period when the main bodies of the electrode and the wafer are spaced apart from each other.

5. The detection system according to claim 1, wherein, the electrode is supported by a support unit and positioned above the path of the wafer during the test period.

6. The detection system according to claim 1, wherein, the electrode is supported by a support unit and configured to surround the wafer during the test period.

7. The detection system according to any one of claims 1 to 6, further comprising at least one additional electrode; wherein the electrode is supported by a support unit and positioned above the path of the wafer during a first part of the test period; and wherein the at least one additional electrode is supported by at least one additional support unit and configured to surround the wafer during a second part of the test period.

8. The detection system according to claim 7, wherein, the height of the electrode is higher than the height of the at least one additional electrode.

9. The detection system according to claim 1, wherein, the processing unit is configured to determine an allowable electric field range to be applied to the wafer during an evaluation of charged particle beams on the wafer.

10. A method for detecting arc hazards related to a wafer using the detection system according to claim 1, the method comprising: forming a specific electric field between the electrode and the wafer; When the wafer moves relative to the electrode, and when the specific electric field is formed between the electrode and the wafer, a measurement result is provided by a measurement unit by measuring an electrical parameter of the electrode during a test period, wherein the specific electric field causes a separated end portion of a partially separated conductive element of the wafer to move away from the wafer; and determining the presence of the arc hazard by a processing unit based on the measurement result.

11. The method according to claim 10, further comprising measuring a leakage current from the electrode to the wafer during the test period.

12. A non-transitory computer-readable medium, the non-transitory computer-readable medium comprising computer-readable instructions that, when executed by a computerized evaluation system, cause the computerized evaluation system to perform a process using the detection system as claimed in claim 1, the process comprising: forming a specific electric field between an electrode and a wafer; when the wafer moves relative to the electrode, and when the specific electric field is formed between the electrode and the wafer, providing a measurement result by measuring an electrical parameter of the electrode during a test period, wherein the specific electric field causes a separated end portion of a partially separated conductive element of the wafer to move away from the wafer; and determining the presence of the arc hazard by a processing unit based on the measurement result.

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