Die attach system and method for integrated accuracy verification and calibration using such system

Abstract

A die attachment system is provided. A die attachment system includes a verification substrate configured to receive a plurality of dies, the verification substrate including a plurality of substrate reference marks. The die attachment system also includes an imaging system for determining alignment of the plurality of dies with the validation substrate by imaging each die of the plurality of dies with a respective substrate reference mark of the plurality of substrate reference marks.

Description

[0001] This divisional application of the invention patent application is a divisional application of Chinese invention patent application CN201980058090.0 (International Application No. PCT / EP2019 / 073766) with the invention title of "Die Attachment System and Method for Integrating Precision Verification and Calibration Using This System" filed on September 5, 2019.

[0002] Cross - reference to related applications

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 727,447, filed on September 5, 2018, the content of which is incorporated herein by reference. Technical field

[0004] The present invention relates to systems and methods for attaching dies to substrates, and more particularly, to improved systems and methods for precision verification and calibration of die attachment systems. Background art

[0005] Regarding the placement of dies on substrates (e.g., semiconductor dies on substrates), many conventional applications utilize "pick - and - place" operations. In such operations, a die is "picked up" from a semiconductor wafer or other die supply source, and then the die is moved to (and "placed" on) a target substrate. Such operations may also utilize one or more transfers between a "pick - up" tool and a "place - ment" tool.

[0006] Some die attachment applications do not utilize pick - and - place operations. For example, a die supply source (e.g., a wafer including multiple dies) can be placed between a bonding tool and a substrate. A die included in the die supply source can be attached to a film or the like. After aligning the bonding tool, the die to be attached, and the placement position of the substrate, the bonding tool presses the die against the placement position of the substrate.

[0007] After the operation is completed, it is often the case that a device separate from the die attachment system is used to perform the precision of the die attachment operation. Such precision determination is often time - consuming and expensive. Therefore, it is desirable to provide improved systems and methods for verifying the precision of die attachment operations and similar processes. Summary of the invention

[0008] According to an exemplary embodiment of the present invention, a die attachment system is provided. The die attachment system includes a verification substrate configured to receive a plurality of dies, the verification substrate including a plurality of substrate reference marks. The die attachment system further includes an imaging system for determining the alignment of the plurality of dies with the verification substrate by imaging each of the plurality of dies with a corresponding substrate reference mark among the plurality of substrate reference marks.

[0009] According to another exemplary embodiment of the present invention, a method of operating a die attachment system is provided. The method includes the steps of: providing a verification substrate configured to receive a plurality of dies, the verification substrate including a plurality of substrate reference marks; and imaging each die of the plurality of dies with a corresponding substrate reference mark of the plurality of substrate reference marks using an imaging system of the die attachment system to determine alignment of the plurality of dies with the verification substrate.

[0010] According to yet another exemplary embodiment of the present invention, another die attachment system is provided. The die attachment system includes: a die supply source that holds a die supply form / configuration including a first plurality of reference marks; a first motion system for moving the die supply source; a bonding head that includes a bonding tool and an imaging system; a second motion system for moving the bonding head; a substrate that includes a second plurality of reference marks; and wherein the imaging system is configured to image a reference mark of the first plurality of reference marks and a reference mark of the second plurality of reference marks in a single field of view.

[0011] According to yet another exemplary embodiment of the present invention, a method of calibrating a die bonder is provided. The method includes the steps of: providing a calibration die supply form including a calibration die supply that includes a first plurality of reference marks; providing a bonding head that includes a bonding tool and an imaging system; providing a substrate that includes a second plurality of reference marks; and imaging a reference mark of the first plurality of reference marks and a reference mark of the second plurality of reference marks in a single field of view using an imaging system of the die bonder. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention may be best understood from the following detailed description when read in connection with the accompanying drawings. It is to be emphasized that, in accordance with the usual practice, the various features of the drawings are not drawn to scale. On the contrary, the dimensions of the various features are arbitrarily enlarged or reduced for clarity.

[0013] Figure 1A is a top view block diagram of elements of a die attachment system according to an exemplary embodiment of the present invention;

[0014] Figure 1B is Figure 1A a side view of elements of the die attachment system;

[0015] Figure 2 is a top view of a verification substrate according to an exemplary embodiment of the present invention;

[0016] Figure 3 is according to an exemplary embodiment of the present invention Figure 2 a top view of a portion of the substrate, indicating an ideal die attachment position;

[0017] Figures 4 to 6 is a top view of a verification substrate used in combination with a die placement accuracy process according to an exemplary embodiment of the present invention;

[0018] Figures 7A to 7B is a top view of a calibration operation according to an exemplary embodiment of the present invention;

[0019] Figures 8A to 8B is a top view showing a pre - bonding inspection operation according to an exemplary embodiment of the present invention; and

[0020] Figures 9A to 9B is a top view showing a calibration operation according to an exemplary embodiment of the present invention. Detailed Description

[0021] As used herein, the term "die" is intended to refer to any structure that includes (or is configured to include in subsequent steps) a semiconductor chip or die. Exemplary "die" elements include bare semiconductor dies (e.g., bare LED semiconductor dies), semiconductor dies on substrates (e.g., lead frames, PCBs, carriers, semiconductor chips, semiconductor wafers, BGA substrates, semiconductor components, etc.), packaged semiconductor devices, flip - chip semiconductor devices, embedded substrate dies, etc.

[0022] As described above, certain die attachment applications do not utilize pick - and - place operations. For example, a die supply source (e.g., a wafer including multiple dies, such as an LED die or other sources of LED wafers) can be positioned between the bonding tool and the substrate. The die supply source can include multiple dies (e.g., LED dies) attached to a film or the like. A variety of processes can be used to effect the transfer of the die from the die supply source to the substrate. Two exemplary processes are described below.

[0023] According to a first exemplary process, after the placement positions of the bonding tool, the die to be attached, and the substrate are aligned, the bonding tool presses the die against the placement position of the substrate. An adhesive is provided on the lower surface of the die (and / or on the placement position of the substrate) such that the die is now fixed to the substrate. Such a bonding tool can include needles, multiple pins (e.g., separately actuatable pins), etc. for contacting the die associated with the transfer from the die supply source to the substrate.

[0024] According to a second exemplary process, after the placement positions of the bonding tool, the die to be attached, and the substrate are aligned, a laser or other light source (e.g., where the laser can be carried by the bonding head) is used to transfer the die from the die supply source to the substrate. An adhesive is provided on the lower surface of the die (and / or on the placement position of the substrate) such that the die is now fixed to the substrate.

[0025] Although two exemplary processes are described above, it should be understood that other transfer processes are contemplated. Regardless of the transfer process, aspects of the present invention can be used to improve related die attachment systems and related processes.

[0026] In accordance with certain exemplary embodiments of the present invention, accuracy verification can be integrated into a die attachment system, for example, using a camera of the die attachment system. A conventional substrate or a dedicated substrate can be used for die attachment. The dedicated substrate has a high local reference relative accuracy with respect to an overall substrate alignment reference. Exemplary dedicated substrates include prior art glass substrates having lithographically applied reference marks, or metal substrates having laser engraved references. A camera (or other imaging system) of the die attachment system can be used to register the x, y, and θ deviations of the attached die with respect to its corresponding substrate reference. By imaging both the substrate reference and the die in the same camera image field of view, measurement errors can be minimized and typically depend only on the quality of the camera and the relative accuracy of the substrate reference marks.

[0027] Thus, aspects of the present invention can relate to obtaining x, y, and θ deviation data. Such deviation data can be used for, for example: (i) integrating an accuracy report regarding the die attachment system; (ii) determining system deviations and feeding them back into the system to improve die attachment accuracy; and (iii) deriving diagnostic information to investigate the root cause of accuracy-related uncertainties.

[0028] This is different from conventional systems, for example, in that verification and calibration related to die attachment accuracy are integrated with the system used to attach the die.

[0029] This is a significant improvement compared to conventional systems and methods, for example, because no additional measurement equipment (and associated management) is required to obtain accuracy data. Since it is integrated with the die attachment system itself, shorter calibration / verification cycles can be provided.

[0030] Now referring to the drawings, Figure 1AThe bare die attachment system 100 is shown. The bare die attachment system 100 includes a support structure 110 for supporting a substrate 112; a bare die supply source 108 including a plurality of bare dies 108a (wherein the plurality of bare dies 108a are disposed on a film / foil 108b included as part of the bare die supply source 108), the plurality of bare dies 108a being configured to be attached to the substrate 112; and a bonding head 104 including a bonding tool 104b for contacting the bare die 108a during transfer of the bare die 108a from the bare die supply source 108 to the substrate 112. The bare die attachment system 100 further includes a bonding head support 102 and a supply support 106. The bonding head support 102 and the supply support 106 are each mounted on a machine structure 150 such that the bonding head support 102 and the supply support 106 are movable independently relative to the machine structure 150. The bonding head support 102 supports the movable bonding head 104. The bonding head support 102 includes a motion system (e.g., a robot) for moving the bonding head 104 in the x, y directions. The bonding head 104 includes a camera 104a (and other vision system components) used in alignment and / or inspection operations. The bare die supply source 108 is movably mounted on the supply support 106. The supply support 106 includes a motion system (e.g., a robot) for moving the bare die supply source 108 in the x, y directions. In Figure 1A (and Figure 1B ) In an exemplary embodiment of the present invention as shown, during the bare die attachment operation, the bare die supply source 108 is positioned between the bonding tool 104b and the substrate 112 supported by the support structure 110.

[0031] Compared with Figure 1A The side view (partial cross-section) of Figure 1B shows the bonding head 104 (including the camera 104a and the bonding tool 104b) that has moved to a position above the bare die 108a, which in turn is located above the substrate 112. Two "post-bonded" bare dies 108a' have been attached to the substrate 112 at respective bonding positions and the bonding tool 104b is shown engaging another bare die 108a above a third respective bonding position on the substrate 112. The bonding tool 104b (e.g., including needles, multiple pins, etc.) presses the bare die 108a against the third bonding position on the substrate 112 to complete another transfer.

[0032] Although Figures 1A - 1B shows the bonding tool 104b for completing the transfer of the bare die from the film 108b to the substrate 112 among the plurality of bare dies 108a, other types of transfers (e.g., the above-mentioned laser transfer) are conceivable.

[0033] Figures 1A - 1BA substrate 112 is shown, which is a substrate used in conjunction with a typical die attachment process. Aspects of the present invention utilize a verification substrate used in conjunction with operations such as (i) die attachment accuracy verification, (ii) pre-bond alignment, (iii) calibration operations, etc. An exemplary verification substrate is labeled herein with the reference numeral "112a". In an exemplary embodiment of the present invention, the verification substrate 112a is used in conjunction with a die bonder (e.g., Figures 1A - 1B the die bonder 100 shown in Figures 1A - 1B . Instead of

[0034] Figure 2 the substrate 112, the verification substrate 112a will be located on the support structure 110 of the die attachment system 100. Figure 2 A verification substrate 112a is shown. The verification substrate 112a includes a plurality of local substrate reference marks 112a1 and a plurality of global alignment reference marks 112a2. The verification substrate 112a can be a glass substrate, a metal substrate, etc. The reference marks 112a1, 112a2 can be lithographically applied reference marks, laser engraved reference marks, and other types of reference marks. The accuracy performance (e.g., in the x, y, and θ dimensions) of a die attachment system (e.g., the die attachment system 100) can be provided relative to the verification substrate 112a. The verification substrate 112a can be used to transform relative measurements made by a camera of the die attachment system (e.g., the camera 104a of the die attachment system 100). Such measurements can also involve the reference coordinate system 200 shown in

[0035] Figure 3 where the reference coordinate system is the xy coordinate system of the die attachment system (e.g., the die attachment system 100).

[0035] Figure 3 An exemplary die 108a is shown at the die attachment position attached to the verification substrate 112a. More specifically, the die 108a is attached between four (4) local substrate reference marks 112a1 on the verification substrate 112a. In Figure 3 , the die 108a is shown in the ideal position. Figure 3 The die center 108a1 is shown centered within the theoretical ideal position 108a2 with respect to the die center 108a1 (where, in the example shown in Figure 3 , the ideal position 108a2 is at the center of the substrate reference mark 112a1).

[0036] Figures 4 to 6 Steps of a method for determining (and / or verifying) the accuracy of a die attachment operation are shown. Figure 4 A plurality of dies 108a are shown attached to the bonding position (target position) of the verification substrate 112a. For example, Figures 1A - 1BThe die bonder 100 shown (e.g., using the bonding tool 104b) attaches a plurality of dies 108a to the verification substrate 112a. The die attachment process can be accomplished by imaging one or more of the plurality of global alignment reference marks 112a2 prior to bonding. The relative positions of the local substrate reference mark 112a1 and the global alignment reference mark 112a2 are precisely known (e.g., through prior measurements or precise fabrication).

[0037] Figure 5 A field of view 500 including a measurement axis 500a is shown (e.g., captured by a camera of a die attachment system such as the die attachment system 100). After attaching a plurality of dies 108a to the verification substrate 112a (as Figure 4 shown), an image of each bonded die 108a and its corresponding local substrate reference mark 112a1 is captured in a single field of view, as Figure 5 shown. This imaging (using the field of view 500) results in an initial measurement obtained in the camera measurement coordinate system. And although Figure 5 shown is a single field of view measurement of a single die 108a bonded to a portion of the verification substrate 112a, it should be understood that multiple images of multiple bonded dies 108a can be captured.

[0038] After Figure 5 the imaging, the position of the die 108a relative to the local substrate reference system (including the local substrate reference mark 112a1, the center point 112a1a) is determined. As Figure 6 shown, the measurement results after conversion to the substrate reference frame are shown, which typically involves de-rotation of the camera angle relative to the substrate. This makes the measurement results invariant to accidental camera orientation and position. As Figure 6 shown, in addition to the angular θ deviation (about the Figure 6 θ axis shown), an x offset and a y offset are also determined.

[0039] Although Figures 4 to 6 shown is a method for determining the accuracy of die placement on the substrate (which can be used as feedback for correction in future die placement operations), other improvements can be provided according to the inventive systems and methods described herein. Figures 7A - 7B Shown is a method for determining (and correcting) system biases in die attachment operations. Such system errors are typically obtained as the average or median of measured die offsets. Figure 7A Shown are a plurality of dies 108a bonded to the verification substrate 112a (wherein the die bonding is performed on a die bonder, such as the die bonder 100 including the bonding tool 104b). As seen from Figure 7AAs can be seen, each of the multiple bare dies 108a is offset from the desired bonding position between adjacent local substrate reference marks 112a1 (the systematic error is illustrated as an offset from the cross at the bottom of Figure 7A as shown eccentric to Figure 7A ).

[0040] After determining (and / or applying) the systematic error (e.g., by correcting the average or median die offset), another bonding operation can be completed. Figure 7B Illustrated are multiple bare dies 108a bonded to substrate 112 after feedback from the systematic error determination (e.g., see Figure 1A substrate 112 shown). In Figure 7B , since the local substrate reference mark 112a1' may not be on substrate 112 (since it is on verification substrate 112a), the local substrate reference mark 112a1' is shown in a "ghost" format. Nevertheless, as Figure 7B shown, this feedback results in improved bonding, where the bonded die 108a is placed more precisely between adjacent local substrate reference marks 112a1' (the systematic error is illustrated as corrected in Figure 7B where the "dot" is centered on the cross at the bottom of Figure 7B ). Of course, it should be understood that feedback can be achieved by bonding die 108a to another verification substrate 112a to confirm the improved accuracy (as opposed to Figure 7B substrate 112 shown).

[0041] In addition to Figures 4 to 6 die attachment accuracy verification and Figures 7A - 7B systematic error determination and correction shown in Figures 8A - 8B consider other embodiments of the present invention. For example, certain accuracy-related diagnostics can be performed within the scope of the present invention. Figure 8A Illustrated is an example of such a diagnostic technique incorporating a pre-accuracy check. Figure 8A is a block diagram of a die attachment system 100 where camera 104a images die 108a still attached to film 108b. That is, imaging is performed before the die attachment operation is completed. Multiple dies 108a are still located on film 108b of die supply source 108. This film is typically transparent (or translucent or semi-transmissive) such that the marks on the substrate below the film are clearly visible and can be accurately measured. In Figures 8A - 8BIn [description], the verification substrate 112a is positioned below the die supply source 108 (where multiple dies 108a are still on the film 108b). More specifically, the die supply source 108 (and / or the verification substrate 112a) is moved such that at least one die among the multiple dies is positioned above the corresponding bonding position of the verification substrate 112a (i.e., between the respective local substrate reference marks 112a1). In this orientation, the field of view of the camera is imaged to show the relative position of the die 108a with respect to the respective local substrate reference marks 112a1. Figure 8B A single die 108a in such a field of view is shown. Using the image obtained from this field of view, accuracy data can be obtained before the die attachment process occurs. This image data can be used as feedback to correct any accuracy issues.

[0042] In another exemplary method of the present invention, Figures 9A - 9B A calibration operation (e.g., robot platform calibration) is shown. The principle of relative mark offset measurement can be applied to robot platform calibration (where the robot platform is a part of the die bonder that is moved by a motion system, e.g., the bonding head 104 moved by a motion system or the die supply source 108 moved by another motion system). In conjunction with such robot platform calibration, the typical non-linear deviation of the robot axis is measured according to the x, y positions in the working area of the robot platform. For a robot platform with a downward-looking camera (e.g., the bonding head 104 moved by the motion system of the bonding head support 102), the substrate mark measurement can be directly used to create a so-called error map of the robot platform. For a robot platform without a downward-looking camera (e.g., the die supply source 108 moved by the motion system of the supply support 106), a camera of another platform (e.g., the camera 104a) can be used as a measuring device to obtain a similar error map. For this purpose, a calibration die supply form is inserted to replace the actual die supply source, where an exemplary calibration die supply form includes a lithographically manufactured glass plate with marks (the so-called "calibration wafer"). The deviation of the calibration die supply form is obtained by measuring the relative offset of the supply form marks with respect to the substrate reference marks. This can be done at various positions covering the working area of the robot platform. Thus, two robot platforms can be calibrated to the same calibration reference simultaneously. Generally, multiple marks in one field of view are used for this purpose (both on the substrate and on the supply form), thereby creating a more accurate and reliable position and angle offset measurement capability.

[0043] Referring to Figures 9A - 9BThe specific example shown provides a calibrated die supply form 108’ in place of the die supply source 108 in the other figures provided herein. The calibrated die supply form 108’ remains to include a calibrated die supply 108c with a supply form mark 108c1. Although these supply form marks are square (similar to the shape of die 108a in the previous figures), any type of supply form mark shape can be contemplated. A substrate 112a (including substrate reference marks 112a1, 112a2) is positioned below the calibrated die supply form 108’. In this configuration, a camera 104a can be used to measure the relative offset of the supply form mark 108c1 with respect to the substrate reference marks 112a1 and / or 112a2. The relative offset amount can be used in conjunction with the robot platform calibration of each robot platform as described above (e.g., the bonding head 104 moved by the motion system of the head support 102 and the die supply source 108 moved by the motion system of the supply source 106).

[0044] Although the present invention has been described and illustrated primarily with respect to die attachment operations without “pickup” operations, the present invention is not limited thereto. The present invention has broad applicability in the semiconductor bonding industry including die attach machines (sometimes referred to as die bonding machines) or other packaging machines (e.g., flip chip machines / operations, advanced packaging operations, etc.).

[0045] Although exemplary embodiments of the present invention have been illustrated and described with respect to marks having specific shapes (e.g., cross-shaped marks, circular marks, rectangular marks, etc.) and a specific number of marks relative to a single die (e.g., four substrate reference marks 112a1 around each die), details of these types are exemplary in nature and do not constitute a limitation on the scope of the present invention.

[0046] Although the present invention has been described and illustrated with respect to exemplary embodiments of the present invention, those skilled in the art should understand that various foregoing and other changes, omissions, and additions can be made thereto and thereon without departing from the spirit and scope of the present invention. Rather, various modifications to the details can be made within the scope of equivalent forms of the present invention without departing from the present invention.

Claims

1. A die attachment system, comprising: A verification substrate configured to receive a plurality of dies, the verification substrate including a plurality of substrate reference marks; And An imaging system for determining the alignment of the plurality of dies with the verification substrate by imaging each die of the plurality of dies with a corresponding substrate reference mark of the plurality of substrate reference marks.

2. The die attachment system according to claim 1, wherein, The imaging system includes a camera.

3. The die attachment system according to claim 1, wherein, Using image data from the imaging system to determine the positional deviation between each die of the plurality of dies and the corresponding substrate reference mark of the plurality of substrate reference marks.

4. The die attachment system according to claim 3, wherein, The positional deviation includes deviation components along the x-axis, along the y-axis, and around the θ-axis.

5. The die attachment system according to claim 1, wherein, In a single field of view of the camera of the imaging system, each die of the plurality of dies and the corresponding substrate reference mark of the plurality of substrate reference marks are imaged together.

6. The die attach system according to claim 1, wherein, The verification substrate is a precision verification substrate, and the alignment determined using the imaging system is the placement accuracy after each die of the plurality of dies is placed on the verification substrate.

7. The die attachment system according to claim 1, wherein, The verification substrate is a glass substrate.

8. The die attachment system according to claim 1, wherein, The verification substrate is a precision verification substrate, and the alignment determined using the imaging system is a pre-bonding alignment determined before each die of the plurality of dies is bonded to a substrate. During the pre-bonding alignment determination, each die of the plurality of dies is positioned above the verification substrate.

9. The die attachment system according to claim 8, wherein, During the pre-bonding alignment determination, each die of the plurality of dies is adhered to a film of a die supply source.

10. The bare die attachment system according to claim 1, wherein, The imaging system is configured to image each die of the plurality of dies and the corresponding substrate reference mark of the plurality of substrate reference marks in a single field of view.

11. The die attachment system according to claim 1, further comprising a light source for transferring the plurality of dies from a die supply source to the verification substrate during transfer.

12. The die attachment system according to claim 11, wherein, The light source is a laser.

13. The die attachment system according to claim 11, wherein, The light source is carried by a bonding head of the die attachment system.

14. A die attachment system, comprising: A calibrated die supply form including a calibrated die supply, the calibrated die supply including a first plurality of reference marks; A first motion system for moving the calibrated die supply form; A bonding head including (i) a light source for transferring a die from a die supply source, and (ii) an imaging system; A second motion system for moving the bonding head; A substrate including a second plurality of reference marks; And Wherein the imaging system is configured to image a reference mark of the first plurality of reference marks and a reference mark of the second plurality of reference marks in a single field of view.

15. The die attachment system according to claim 14, wherein, Images from the imaging system are subsequently used in combination with the calibration of at least one of the calibrated die supply form and the bonding head during a bonding operation.

16. The bare die attachment system according to claim 14, wherein, The calibrated die supply form is a die supply source of the die attachment system, and the die supply source is configured to carry a plurality of dies fixed to a film during a die attachment operation.

17. The die attachment system according to claim 14, wherein, During imaging of the imaging system, a calibration die supply form including a calibration die supply source in place of the die attachment system is included, and wherein, during a subsequent bonding operation, the die supply source is replaced into the die attachment system.

18. A method of calibrating a die bonder, the method comprising the steps of: Providing a calibration die supply form including a calibration die supply, the calibration die supply including a first plurality of reference marks; Providing a bonding head including (i) a light source for transferring a die from a die supply source, and (ii) an imaging system; Providing a substrate including a second plurality of reference marks; And Using the imaging system of the die bonder to image a reference mark among the first plurality of reference marks and a reference mark among the second plurality of reference marks in a single field of view.

19. The method according to claim 18 further comprises the following steps: During a subsequent bonding operation, using an image from the imaging system to calibrate a position of at least one of the calibration die supply form and the bonding head.

Images