Continuous bump height measurement metrology

Abstract

A method can include performing a first measurement of a height difference between a bump and a corresponding area by illuminating the bump and the corresponding area with first radiation; wherein the first measurement is subject to a first measurement error caused by a first illumination virtual penetration into a layer; wherein each bump has a corresponding area adjacent to the bump; performing a second measurement of a thickness of the layer at the corresponding area; wherein at least some of the first measurements are performed in parallel with the performance of at least some of the second measurements; determining the first measurement error from the second measurement; and determining the height difference between the bump and the corresponding area from the first measurement and the first measurement error.

Description

[0001] Cross-references

[0002] This application claims priority to U.S. Provisional Patent No. 62 / 705,731, filed June 13, 2020, and U.S. Provisional Patent No. 62 / 705,730, filed June 13, 2020. Both provisional patents are incorporated herein by reference. Background Technology

[0003] Bumps can be formed on the base layer or on intermediate elements on the base layer.

[0004] The top layer can be manufactured on the base layer. The upper part of the bump extends above the top layer. The lower part of the bump is surrounded by the top layer.

[0005] The top layer can be made of light-definable polyimide (PI) and / or polybenzoxazole (PBO).

[0006] Top layers made of PI and / or PBO have been widely used as dielectrics for wafer-level redistribution layers.

[0007] The top layer made of PI and / or PBO is partially transparent to primary radiation such as visible light.

[0008] Visible light-based triangulation can scan bumps and top layers to provide height measurements.

[0009] It may be necessary to measure the height difference between (a) the top of the bump and (b) the top surface of the top layer.

[0010] Due to the partial transparency of the top layer—visible light-based triangulation does not measure the height of the top surface of the top layer—but rather the height of a virtual plane within the top layer. This virtual plane represents a virtual reflective plane within the top layer. Because of the difference between the refractive index of air and the refractive index of the top layer, light changes its propagation angle as it enters the top layer. When light is reflected by the top surface of the base layer—the virtual plane represents the virtual reflective plane in the case where the propagation angle remains unchanged within the top layer.

[0011] The distance between the top surface of the top layer and the virtual plane is called the virtual penetration depth and is unknown—visible light-based triangulation does not provide a reliable measurement of bump characteristics.

[0012] There is an increasing need to provide a reliable system and method for estimating the height difference between the top of the bump and the upper surface of the top layer. Summary of the Invention

[0013] The present invention provides a system, a non-transitory computer-readable medium, and a method for estimating the height difference between the top surface of a bump and the upper surface of a top layer.

[0014] A method for measuring height differences between tops of a plurality of bumps and respective areas of an upper surface of a layer can be provided, the method can comprise performing first measurements of height differences between the bumps and the respective areas by illuminating the bumps and the respective areas with first radiation; wherein the first measurements are affected by first measurement errors caused by a virtual penetration of the first illumination into the layer; wherein each bump has a respective area proximal to the bump; performing second measurements of a thickness of the layer at the respective areas; wherein at least some of the first measurements are performed in parallel to at least some of the second measurements; determining the first measurement errors from the second measurements; and determining the height differences between the bumps and the respective areas from the first measurements and the first measurement errors.

[0015] The first measurement errors can represent a virtual penetration depth of the first radiation into the respective areas.

[0016] The determination of the first measurement errors can be based on the second measurements and a refractive index of the layer.

[0017] The first radiation can be white light.

[0018] The layer can comprise at least one of a photo-definable polyimide and a polybenzoxazole.

[0019] The bumps can comprise a majority of bumps of a wafer.

[0020] The method can comprise performing the first measurements before or after performing the second measurements.

[0021] The performing of the first measurements can comprise performing white light triangulation.

[0022] The performing of the second measurements can comprise performing reflectometry.

[0023] The performing of the second measurements can comprise performing chromatic confocal measurements.

[0024] A measurement system for measuring height differences between tops of a plurality of bumps and respective areas of an upper surface of a layer can be provided, the system can comprise one or more measurement units and at least one processing unit configured to: perform first measurements of height differences between the bumps and the respective areas by illuminating the bumps and the respective areas with first radiation; wherein the first measurements are affected by first measurement errors caused by a virtual penetration of the first illumination into the layer; wherein each bump has a respective area proximal to the bump; perform second measurements of a thickness of the layer at the respective areas; wherein at least some of the first measurements are performed in parallel to at least some of the second measurements; determine the first measurement errors from the second measurements; and determine the height differences between the bumps and the respective areas from the first measurements and the first measurement errors.

[0025] The first measurement error represents a virtual penetration depth of the first radiation into the respective area.

[0026] The determination of the first measurement error can be based on the second measurement and a refractive index of the layer.

[0027] The first radiation can be white light.

[0028] The layer can comprise at least one of a photo-definable polyimide and a polybenzoxazole.

[0029] The bumps can comprise a majority of bumps of the wafer.

[0030] The execution of the first measurement can comprise performing a white light triangulation.

[0031] The second measurement unit can be a reflectometer.

[0032] The second measurement unit can comprise a chromatic confocal measurement unit.

[0033] A non-transitory computer readable medium for measuring height differences between a plurality of bump tops and respective areas of an upper surface of a layer can be provided, the non-transitory computer readable medium can store instructions for: performing a first measurement of a height difference between a bump and a respective area by illuminating the bump and the respective area with a first radiation; wherein the first measurement is affected by a first measurement error resulting from a virtual penetration of the first illumination into the layer; wherein each bump has a respective area that is proximal to the bump; performing a second measurement of a thickness of the layer at the respective area; wherein at least some of the first measurements are performed in parallel to the performance of at least some of the second measurements; determining the first measurement error from the second measurement; and determining the height difference between the bump and the respective area from the first measurement and the first measurement error.

[0034] The first measurement error can represent a virtual penetration depth of the first radiation into the respective area.

[0035] The determination of the first measurement error can be based on the second measurement and a refractive index of the layer.

[0036] The first radiation can be white light.

[0037] The layer can comprise at least one of a photo-definable polyimide and a polybenzoxazole.

[0038] The bumps can comprise a majority of bumps of the wafer.

[0039] The non-transitory computer readable medium can store instructions for performing the first measurement before or after performing the second measurement.

[0040] The execution of the first measurement can comprise performing a white light triangulation.

[0041] The performance of the second measurement can comprise performing reflectometry.

[0042] The performance of the second measurement can comprise performing chromatic confocal measurement. BRIEF DESCRIPTION OF DRAWINGS

[0043] The present application will be more fully understood and appreciated by

[0044] Figure 1 a first stage of the process is illustrated;

[0045] Figure 2 a second stage of the process is illustrated;

[0046] Figure 3 a third stage of the process is illustrated; and

[0047] Figure 4 a wafer and bump are illustrated;

[0048] Figure 5 an example of a system is illustrated; and

[0049] Figure 6 an example of a method is illustrated. DETAILED DESCRIPTION

[0050] Because the apparatus embodying the present application is largely composed of electronic components and circuitry known to those skilled in the art, circuit details will not be explained to any greater extent than is deemed necessary to understand and appreciate the underlying concepts of the present application, so as not to obscure or distract from the teachings of the present application.

[0051] Any reference in the specification to a method should be considered as a reference to a system configured to perform the method, and to a non-transitory computer program product storing instructions which, when executed by a computer, will cause the method to be performed, mutatis mutandis. The non-transitory computer program product can be a chip, a memory unit, a disk, an optical disk, a nonvolatile memory, a volatile memory, a magnetic storage unit, a memristor, an optical storage unit, etc.

[0052] Any reference in the specification to a system should be considered as a reference to a method that can be performed by the system, mutatis mutandis, and to a non-transitory computer program product storing instructions which, when executed by a computer, will cause the method to be performed.

[0053] Any reference in the specification of a non- transitory computer program product shall be applicable to a method that can be performed when applying instructions stored in the non-transitory computer program product, and to a system capable of executing instructions stored in the non-transitory computer program product, mutatis mutandis.

[0054] The term "comprising" is synonymous with "including," "containing," or "having," is inclusive and open-ended and does not exclude additional, unrecited elements or method steps.

[0055] The term "consisting" is closed and excludes any additional, unrecited elements or method steps.

[0056] The term "consisting essentially of limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s).

[0057] In the claims and specification, any reference to the term "comprising" (or "including" or "containing") shall be applicable mutatis mutandis to the term "consisting of and to the phrase "consisting essentially of.

[0058] In the claims and specification, any reference to the term "consisting of shall be applicable mutatis mutandis to the term "comprising" and to the phrase "consisting essentially of.

[0059] In the claims and specification, any reference to the phrase "consisting essentially of shall be applicable mutatis mutandis to the term "comprising" and to the term "consisting of.

[0060] In the following description, the application will be described with reference to specific examples of embodiments of the application. It is to be understood that various modifications and changes can be made to the application as described without departing from the spirit and scope thereof as set forth in the appended claims.

[0061] A system and method for calculating the height difference between the top of the bump and the upper surface of the top layer, which is at least partially transparent to radiation such as white light, is provided. The top layer can be made of PI and BPO.

[0062] With reference to Figure 1 It can be necessary to measure the height difference between (a) the top of the bump 11 (11') and (b) the upper surface of the top layer 12. The height of the top of the bump is denoted bump top height 21. The height of the upper surface of the top layer is denoted upper surface height 22.

[0063] The visible light beam 71 is shown propagating at a first angle 91 until reaching the top layer, then changing its propagation angle to a second propagation angle 92 and proceeding within the top layer (see 72) until impinging on the top of the base layer 13 to provide a reflected light beam 73, which propagates within the top layer until reaching air, changes its propagation angle, and continues propagating in air to provide a detected light beam 74. Figure 1 The angle a is also shown, and the first angle is equal to (90° - a).

[0064] Assuming the refractive index of the top layer is denoted n, and the thickness of the top layer is denoted b, then the virtual penetration depth is equal to the square root of (1 - sin 2 a) / (n 2 - sin 2 a) times b.

[0065] The virtual plane 18 is a virtual reflection plane that virtually continues the proceeding of the illuminating light beam 71 in the top layer, which has the first angle 91 maintained in the top layer (see virtual propagation line 81), and virtually coincides with the detected light beam 74 (see arrow 82).

[0066] The height of the top of the bump is denoted bump top height 21. The height of the upper surface of the top layer is denoted upper surface height 22.

[0067] The position of the inner portion corresponds to the virtual penetration depth. The virtual penetration depth of the visible light in the top layer is denoted penetration depth 24.

[0068] Therefore, the measured height can be equal to the upper surface height - the penetration depth.

[0069] Therefore, the height difference measured by the visible light based triangulation is equal to: measured height difference 23 = (bump top height + penetration depth) - upper surface height.

[0070] Figure 1 A first stage is illustrated, during which the visible light based triangulation is applied to provide a measured height difference 23, which is an example of a first measurement of a height difference.

[0071] The upper surface height is the height of the upper surface of the top layer 12. The top layer 12 is located above the base layer 13. Figure 1 An intermediate element 19 is also shown, which is formed on the base layer 13. The bump 11 is formed on the intermediate element 19.

[0072] The bump top height 21 is the measured height of the top (11') of the bump 11.

[0073] The penetration depth 24 is a virtual penetration depth of the first radiation within the top layer 12. This virtual penetration introduces a first measurement error - because the first measurement actually measures the height of the virtual penetration - which is equal to (top surface height - penetration depth).

[0074] (top surface height - penetration depth) is measured in the vicinity of the bump - at a point which can be considered to correspond to the area of the bump.

[0075] The first measurement of the height difference (e.g. the measurement height difference 23) is equal to the bump top height minus (top surface height - penetration depth).

[0076] The measurement height difference is (bump top height + penetration depth) - top surface height.

[0077] The measurement height difference is done by measuring (top surface height - penetration depth) in the vicinity of each bump to be measured.

[0078] This stage is applied to a group of bumps - e.g. all the bumps in a wafer.

[0079] Figure 2 A second stage is illustrated during which the thickness of the top layer is measured (top layer thickness 27) using a thickness sensor. Examples of such sensors include reflectometer sensors and chromatic confocal sensors.

[0080] The thickness can be measured in the vicinity of each bump of the group of bumps - or can be measured in the vicinity of some bumps and estimated in any way in the vicinity of other bumps.

[0081] The first and second stages can be performed simultaneously in a partially overlapping manner or in a fully overlapping manner.

[0082] The thickness sensor can be different from the sensor used during the visible light based triangulation.

[0083] The first and second stages are followed by a third stage, namely estimating a virtual penetration depth to provide an estimated penetration depth 24'.

[0084] The estimated penetration depth =

[0085] The third stage is followed by a fourth stage (see Figure 3 ), namely correcting the measurement height difference by subtracting the estimated penetration depth 24' from the measurement height difference 23 to provide an estimated height difference 26 (see Figure 4 ) - namely the estimated difference between the bump top and the top surface of the top layer.

[0086] Figure 5 is an example of a measurement system 200.

[0087] The measurement system 200 is configured to measure the height difference between the top of a plurality of bumps and corresponding areas on the upper surface of the layer.

[0088] The measurement system 200 may include one or more measurement units and at least one processing unit, which is configured to:

[0089] a. A first measurement of the height difference between a bump and a corresponding region is performed by irradiating the bump and the corresponding region with a first radiation; wherein the first measurement is affected by a first measurement error caused by the first illumination virtually penetrating into the layer; wherein each bump has a corresponding region adjacent to the bump.

[0090] b. Perform a second measurement on the thickness of the layer located in the corresponding region.

[0091] c. Determine the first measurement error based on the second measurement.

[0092] d. Determine the height difference between the bump and the corresponding area based on the first measurement and the first measurement error.

[0093] One or more measurement units may include a first measurement unit for performing a first measurement and a second measurement unit for performing a second measurement.

[0094] exist Figure 5 In this design, the first measuring unit is a triangulation unit 210, which can be a white light triangulation sensor. See, for example, US Patent 8363229.

[0095] exist Figure 5 In this design, the second measuring unit is a thickness sensor 230. Examples of such sensors include reflectometer sensors and color confocal sensors.

[0096] exist Figure 5 In the diagram, chip 280 is supported by chuck 290 and processing unit 240 is also shown.

[0097] The determination of the first measurement error and / or the height difference can be performed by at least one processing unit. At least one processing unit may or may not belong to one or more measurement units.

[0098] The processing unit can be a server, desktop computer, hardware accelerator, etc.

[0099] The measuring system may include other parts and / or components, such as a mechanical table.

[0100] Figure 6 An example of a method 300 for measuring the height difference between the top of multiple bumps and a corresponding area on the upper surface of a layer is illustrated.

[0101] Each bump has a respective area, which is an area proximate to the bump. Proximate can be within a millimeter distance (e.g. less than a centimeter or a fraction of a centimeter). The respective area can be closer to the bump relative to the other bump. The respective area can contact the bump and / or surround the bump. The respective area can be any shape or size - e.g. can be on the order of millimeters. The respective area can be equal to (or can be slightly larger than) the size of the radiation spot (of the first radiation and / or of the second radiation). Alternatively, the respective area can be much larger than the size of the radiation spot.

[0102] The method 300 can comprise steps 310 and 320.

[0103] Each of steps 310 and 320 can be performed on all bumps of the wafer, or on a substantial majority (e.g. at least 60%, 70%, 80%) of such bumps.

[0104] Almost all bumps are measured in step 310 and are also measured in step 320.

[0105] Step 310 can comprise performing a first measurement of a height difference between the bump and the respective area by illuminating the bump and the respective area with the first radiation. The first measurement is affected by a first measurement error, which is caused by the first illumination virtually penetrating into the layer.

[0106] Step 320 can comprise performing a second measurement of a thickness of the layer at the respective area.

[0107] Step 310 can be performed at least partially in parallel with step 320. Thus, at least some of the first measurements can be performed in parallel with at least some of the second measurements.

[0108] Such temporal overlap can be obtained when one measurement does not interfere with the other measurement.

[0109] The first radiation can be white light.

[0110] The layer can comprise at least one of photo-definable polyimide and polybenzoxazole.

[0111] Step 310 can comprise performing a white light triangulation. See, e.g., US patent 8363229.

[0112] Step 320 can comprise performing the measurement using a thickness sensor. Examples of such sensors include a reflectometer sensor and a chromatic confocal sensor.

[0113] Step 310 and 320 can be followed by step 330 of determining the first measurement error based on the second measurement.

[0114] For example, step 330 can comprise calculating the following equation

[0115] Estimate penetration depth = 1.5 * (1.5 * 0.5) = 1.125 mm

[0116] Step 330 can be followed by step 340 of determining the height difference between the bump and the respective area based on the first and second measurement errors.

[0117] In the foregoing specification, the application has been described with reference to specific examples of embodiments of the application. It is evident, however, that various modifications and changes can be made thereto without departing from the broader spirit and scope of the application as set forth in the appended claims.

[0118] Those skilled in the art will recognize that boundaries between the functionality of the above described operations merely illustrative. The functionality of multiple operations can be combined into a single operation, and / or the functionality of a single operation can be distributed in additional operations. Moreover, optional embodiments can include multiple instances of a particular operation, and the order of operations can be altered in various other embodiments.

[0119] Therefore, it is to be understood that the architectures depicted herein are merely illustrative, and that consistent with the present disclosure, a host of other architectures can be implemented to achieve the same functionality. In an abstract, but still definite sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermediate components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.

[0120] 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.

[0121] The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. It is understood that where the description above refers to embodiments of the application, it is also implicitly referring to the exact, but for variations in form, the same embodiments of the application. Thus, where a particular feature is described, it will be understood that this feature is not a prerequisite. Where the specification states that a particular element of the applications has a particular property, it is understood that this property is not a prerequisite.

[0122] Furthermore, the term "a" or "an" as used herein is defined as one or more unless otherwise indicated. Moreover, in the claims the use of introductory phrases such as "at least one" and "one or more" should not be construed to imply that the inclusion of one or more of elements introduces a limitation on the compositions or methods of the claim as opposed to the exclusion of any of the listed non- encompassed elements. Lastly, the use of terms such as "first" and "second" are used to arbitrarily distinguish one element from another unless otherwise indicated.

[0123] Accordingly, these terms are not intended to signify time or other prioritization of the elements. The fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be advantageous.

Claims

1. A method for measuring height differences between tops of a plurality of bumps and respective areas of an upper surface of a layer, the method comprising: performing a first measurement of height differences between the bumps and the respective areas by illuminating the bumps and the respective areas with a first radiation at an angle a with respect to a perpendicular direction to the layer; wherein the first measurement is affected by a first measurement error resulting from a virtual penetration of the first radiation into the layer, wherein each bump has a respective area adjacent to the bump; performing a second measurement of a thickness of the layer at the respective areas, wherein at least some of the first measurements are performed in parallel with at least some of the second measurements; determining the first measurement error from the thickness b of the layer measured by the second measurement, the angle a and a refractive index n of the layer; and determining the height differences between the bumps and the respective areas from the first measurements and the first measurement error.

2. The method of claim 1, wherein, The first measurement error represents a virtual penetration depth of the first radiation into the respective areas.

3. The method of claim 1, wherein, The first radiation is white light.

4. The method of claim 1, wherein, The layer comprises at least one of photo-definable polyimide and polybenzoxazole.

5. The method of claim 1, wherein, The bumps comprise a majority of bumps of a wafer.

6. The method of claim 1, wherein, The performing of the first measurement comprises performing white light triangulation.

7. The method of claim 1, wherein, The performing of the second measurement comprises performing reflectometry.

8. The method of claim 1, wherein, The performing of the second measurement comprises performing chromatic confocal measurement.

9. The method of claim 1, wherein, The first measurement error is calculated according to the formula .

10. A measurement system for measuring height differences between tops of a plurality of bumps and respective areas of an upper surface of a layer, the system comprising: one or more measurement units and at least one processing unit configured to: perform a first measurement of height differences between the bumps and the respective areas by illuminating the bumps and the respective areas with a first radiation at an angle a with respect to a perpendicular direction to the layer, wherein the first measurement is affected by a first measurement error resulting from a virtual penetration of the first radiation into the layer; wherein each bump has a respective area adjacent to the bump; perform a second measurement of a thickness of the layer at the respective areas, wherein at least some of the first measurements are performed in parallel with at least some of the second measurements; determine the first measurement error from the thickness b of the layer measured by the second measurement, the angle a and a refractive index n of the layer; and determine the height differences between the bumps and the respective areas from the first measurements and the first measurement error.

11. The measurement system of claim 10, wherein, The first measurement error represents a virtual penetration depth of the first radiation into the respective areas.

12. The measurement system of claim 10, wherein, The first radiation is white light.

13. The measurement system of claim 10, wherein, The layer comprises at least one of photo-definable polyimide and polybenzoxazole.

14. The measurement system of claim 10, wherein, The bumps comprise a majority of bumps of a wafer.

15. The measurement system of claim 10, wherein, The first measurement unit is a white light triangulation unit.

16. The measurement system of claim 10, wherein, The second measurement unit is a reflectometer.

17. The measurement system of claim 10, wherein, The second measurement unit is a chromatic confocal measurement unit.

18. The measurement system of claim 10, wherein, The first measurement error is calculated according to the formula .

19. A non-transitory computer readable medium for measuring height differences between tops of a plurality of bumps and respective areas of an upper surface of a layer, the non-transitory computer readable medium storing instructions for: performing a first measurement of a height difference between the bump and the corresponding area by illuminating the bump and the corresponding area with a first radiation at an angle a with respect to a perpendicular to the layer; wherein the first measurement is affected by a first measurement error, the first measurement error being caused by the first radiation virtually penetrating into the layer, and wherein each bump has a corresponding area adjacent to the bump; performing a second measurement of a thickness of the layer at the corresponding area; wherein at least some of the first measurements are performed in parallel with at least some of the second measurements; determining a first measurement error from the thickness b of the layer measured by the second measurement, the angle a and a refractive index n of the layer; and determining the height difference between the bump and the corresponding area from the first measurement and the first measurement error.

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