Bare die attach system and method for integrated accuracy verification and calibration using the system

Abstract

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

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 727,447, filed September 5, 2018, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to systems and methods for attaching a die to a substrate, and more particularly, to improved systems and methods for accuracy verification and calibration of a die / die attach system. Background Art

[0004] Many conventional applications related to the placement of a die on a substrate (e.g., placement of a semiconductor die on a substrate) utilize a "pick and place" operation. In such an operation, a die is "picked up" from a semiconductor wafer or other die supply source, and then moved to (and "placed" on) a target substrate. Such an operation may also utilize one or more transfers between a "pick up" tool and a "placement" tool.

[0005] Some die attach applications do not utilize pick and place operations. For example, a die supply (e.g., a wafer including multiple die) may be placed between a bonding tool and a substrate. Dies included in the die supply may be attached to a membrane or the like. After alignment between the bonding tool, the die to be attached, and the placement location of the substrate, the bonding tool presses the die against the placement location of the substrate.

[0006] The accuracy of the die attach operation tends to be performed using equipment separate from the die attach system after the operation is completed. Such accuracy determination is often time consuming and expensive. Therefore, it is desirable to provide improved systems and methods for verifying the accuracy of die attach operations and similar processes. Summary of the invention

[0007] According to an exemplary embodiment of the present invention, a bare die attach system is provided. The bare die attach system includes a verification substrate configured to receive a plurality of bare dies, the verification substrate including a plurality of substrate reference marks. The bare die attach system also includes an imaging system for determining alignment of the plurality of bare dies with the verification substrate by imaging each bare die in the plurality of bare dies with a corresponding substrate reference mark in the plurality of substrate reference marks.

[0008] According to another exemplary embodiment of the present invention, a method of operating a die attach system is provided. The method includes the following steps: providing a verification substrate configured to receive a plurality of die, the verification substrate including a plurality of substrate reference marks; and using an imaging system of the die attach system to image each of the plurality of die with a corresponding substrate reference mark of the plurality of substrate reference marks to determine alignment of the plurality of die with the verification substrate.

[0009] According to another exemplary embodiment of the present invention, another die attach system is provided. The die attach system includes: a die supply source that maintains a die supply form including a first plurality of reference marks; and 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 in the first plurality of reference marks and a reference mark in the second plurality of reference marks in a single field of view.

[0010] According to another exemplary embodiment of the present invention, a method of calibrating a die attach machine is provided. The method includes the following steps: 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 a bonding tool and an imaging system; providing a substrate including a second plurality of reference marks; and imaging a reference mark in the first plurality of reference marks and a reference mark in the second plurality of reference marks in a single field of view using an imaging system of the die attach machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention can be best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not drawn to scale. On the contrary, the sizes of the various features are arbitrarily expanded or reduced for clarity.

[0012] Figure 1A is a block diagram top view of elements of a die attach system according to an exemplary embodiment of the present invention;

[0013] Figure 1B yes Figure 1A A side view of a component of a die attach system;

[0014] Figure 2 is a top view of a verification substrate according to an exemplary embodiment of the present invention;

[0015] Figure 3 According to an exemplary embodiment of the present invention Figure 2 a top view of a portion of a substrate indicating an ideal die attach location;

[0016] Figures 4 to 6 is a top view of a verification substrate used in conjunction with a die placement accuracy process according to an exemplary embodiment of the present invention;

[0017] FIG. 7A to FIG. 7B is a top view of a calibration operation according to an exemplary embodiment of the present invention;

[0018] FIG. 8A to FIG. 8Bis a top view illustrating a pre-bonding inspection operation according to an exemplary embodiment of the present invention; and

[0019] FIG. 9A to FIG. 9B is a top view illustrating a calibration operation according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0020] As used herein, the term "bare die" is intended to refer to any structure that includes (or is configured to include in a subsequent step) a semiconductor chip or die. Exemplary "bare die" components include bare semiconductor die (e.g., bare LED semiconductor die), semiconductor die on a substrate (e.g., lead frame, PCB, carrier, semiconductor chip, semiconductor wafer, BGA substrate, semiconductor element, etc.), packaged semiconductor device, flip chip semiconductor device, embedded substrate die, etc.

[0021] As described above, some die attach applications do not utilize pick and place operations. For example, a die supply source (e.g., a wafer including multiple die, such as an LED wafer from other sources of LED die) can be positioned between a bonding tool and a substrate. The die supply source can include multiple die (e.g., LED die) attached to a membrane or the like. A variety of processes can be used to achieve the transfer of die from the die supply source to the substrate. Two exemplary processes are described below.

[0022] According to a first exemplary process, after the placement locations of the bonding tool, the die to be attached, and the substrate are aligned, the bonding tool presses the die against the placement location of the substrate. An adhesive is provided on the lower surface of the die (and / or on the placement location of the substrate) so that the die is now fixed to the substrate. Such a bonding tool may include a needle, a plurality of pins (e.g., separately actuatable pins), etc. for contacting the die associated with the transfer from the die supply source to the substrate.

[0023] According to a second exemplary process, after the bonding tool, the die to be attached, and the placement position of the substrate are aligned, a laser or other light source (e.g., where the laser can be carried by a 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) so that the die is now fixed to the substrate.

[0024] 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 may be used to improve related die attach systems and related processes.

[0025] According to certain exemplary embodiments of the present invention, accuracy verification can be integrated into a die attach system, for example using a camera of the die attach system. Conventional substrates or specialized substrates can be used for die attach. Specialized substrates have high local reference relative accuracy relative to an overall substrate alignment reference. Exemplary specialized substrates include prior art glass substrates with photolithographically applied reference marks, or metal substrates with laser engraved references. The camera (or other imaging system) of the die attach system can be used to register the x, y, and theta deviations of an attached die relative 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 only depend on the quality of the camera and the relative accuracy of the substrate reference marks.

[0026] Thus, aspects of the present invention may involve obtaining x, y, and theta deviation data. Such deviation data may be used, for example, to: (i) consolidate accuracy reports on die attach systems; (ii) determine system deviations and feed back into the system to improve die attach accuracy; and (iii) derive diagnostic information to investigate root causes of accuracy-related uncertainties.

[0027] This differs from conventional systems, for example, in that verification and calibration related to die attach accuracy is integrated with the system used to attach the die.

[0028] This is a significant improvement over conventional systems and methods, for example, because no additional measurement equipment (and associated management) is required to obtain accuracy data.Because of the integration with the die attach system itself, a shorter calibration / validation cycle can be provided.

[0029] Now referring to the accompanying drawings, Figure 1AA die attach system 100 is shown. The die attach system 100 includes a support structure 110 for supporting a substrate 112; a die supply source 108 including a plurality of die 108a (wherein the plurality of die 108a are disposed on a film / foil 108b included as part of the die supply source 108), the plurality of die 108a being configured to be attached to the substrate 112; and a bond head 104 including a bonding tool 104b for contacting the die 108a during transfer of the die 108a from the die supply source 108 to the substrate 112. The die attach system 100 also includes a bond head support 102 and a supply support 106. The bond head support 102 and the supply support 106 are each mounted on a machine structure 150 such that the bond head support 102 and the supply support 106 are independently movable relative to the machine structure 150. The bond head support 102 supports the movable bond head 104. The bond head support 102 includes a motion system (e.g., a robot) for moving the bond head 104 in the x and y directions. The bond head 104 includes a camera 104a (and other vision system components) used in conjunction with alignment and / or inspection operations. The 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 die supply source 108 in the x and y directions. Figure 1A (and Figure 1B ), during a die attach operation, a die supply source 108 is positioned between a bonding tool 104b and a substrate 112 supported by a support structure 110.

[0030] and Figure 1A compared to, Figure 1B 1 shows the bond head 104 (including the camera 104a and the bonding tool 104b) having moved to a position over the die 108a, which in turn is located over the substrate 112. Two "bonded" dies 108a' have been attached to the substrate 112 at respective bonding locations and the bonding tool 104b is shown engaging another die 108a over a third respective bonding location on the substrate 112. The bonding tool 104b (e.g., including a needle, a plurality of pins, etc.) presses the die 108a against the third bonding location on the substrate 112 to complete another transfer.

[0031] Although Figure 1A-1B 1. A bonding tool 104b is shown for completing the transfer of a die in the plurality of dies 108a from the film 108b to the substrate 112, although other types of transfer are contemplated (eg, laser transfer as described above).

[0032] Figure 1A-1BA substrate 112 is shown, which is a substrate used in conjunction with a typical die attach process. Various aspects of the present invention utilize a verification substrate used in conjunction with operations such as (i) die attach accuracy verification, (ii) pre-bond alignment, (iii) calibration operations, etc. An exemplary verification substrate is labeled herein with reference numeral "112a". In an exemplary embodiment of the present invention, verification substrate 112a is used in conjunction with a die attach machine (e.g., Figure 1A-1B In conjunction with certain exemplary methods described herein, the verification substrate 112a will be located on the support structure 110 of the die attach system 100 (instead of the die attach system 100). Figure 1A-1B substrate 112).

[0033] 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 overall alignment reference marks 112a2. The verification substrate 112a may be a glass substrate, a metal substrate, or the like. The reference marks 112a1, 112a2 may be photolithographically 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 attach system (e.g., die attach system 100) may be provided relative to the verification substrate 112a. The verification substrate 112a may be used to convert relative measurements made by a camera of the die attach system (e.g., camera 104a of die attach system 100). Such measurements may also involve also Figure 2 2 , where the reference coordinate system is an xy coordinate system of a die attach system (eg, die attach system 100 ).

[0034] Figure 3 An exemplary die 108a is shown at a die attach location attached to a verification substrate 112a. More specifically, the die 108a is attached between four (4) local substrate reference marks 112a1 on the verification substrate 112a. Figure 3 , die 108a is shown in an ideal position. Figure 3 The die center 108a1 is shown as being centered within the theoretical ideal position 108a2 (wherein Figure 3 In the example shown, the ideal position 108a2 is at the center of the substrate reference mark 112a1).

[0035] Figures 4 to 6 Steps of a method of determining (and / or verifying) the accuracy of a die attach operation are shown. Figure 4 A plurality of die 108a are shown attached to a bonding location (target location) of a verification substrate 112a. For example, a Figure 1A-1BThe die attach machine 100 shown attaches a plurality of dies 108a to a verification substrate 112a (e.g., using a bonding tool 104b). The die attach process can be accomplished by imaging one or more of a plurality of global alignment reference marks 112a2 prior to bonding. The relative positions of the local substrate reference marks 112a1 and the global alignment reference marks 112a2 are precisely known (e.g., by prior measurement or precise manufacturing).

[0036] Figure 5 A field of view 500 including a measurement axis 500a is shown (eg, as captured by a camera of a die attach system such as die attach system 100). After attaching a plurality of die 108a to a verification substrate 112a (eg, Figure 4 As shown), an image of each bonded bare die 108a and its corresponding local substrate reference mark 112a1 is captured in a single field of view, such as Figure 5 This imaging (using field of view 500) results in initial measurements being obtained in the camera measurement coordinate system. Figure 5 A single field of view measurement of a single die 108a bonded to a portion of a verification substrate 112a is shown, but it should be understood that multiple images of multiple bonded dies 108a may be taken.

[0037] exist Figure 5 After imaging, the position of the bare die 108a relative to the local substrate reference system (including the local substrate reference mark 112a1 and the center point 112a1a) is determined. Figure 6 As shown, the measurements are shown after conversion to the base reference frame, which typically involves a de-rotation of the camera angle relative to the base. This makes the measurements invariant to accidental camera orientation and position. Figure 6 As shown, except for the angle θ deviation (around Figure 6 In addition to the θ axis shown, an x-offset and a y-offset are also determined.

[0038] although Figures 4 to 6 A method of determining the accuracy of die placement on a substrate (which may be used as feedback for corrections in future die placement operations) is shown, but other improvements may be provided in accordance with the inventive systems and methods described herein. Figure 7A-7B A method of determining (and correcting for) systematic deviations in a die attach operation is shown. Such systematic errors are usually obtained as the average or median of the measured die offsets. Fig. 7A A plurality of dies 108a are shown bonded to a verification substrate 112a (where the dies are bonded on a die attach machine, such as die attach machine 100 including bonding tool 104b). Fig. 7AAs can be seen in FIG. 1 , each of the plurality of bare die 108 a is offset from the desired bonding position between adjacent local substrate reference marks 112 a 1 (system error is in Fig. 7A The middle figure shows the eccentric Fig. 7A The offset of the cross at the bottom of the ).

[0039] After determining (and / or applying) the systematic error (eg, by correcting for the mean or median die offset), another bonding operation may be completed. Figure 7B 1 is shown bonded to substrate 112 after feedback from system error determination (see, e.g., Figure 1A The substrate 112 shown in FIG. Figure 7B , since local substrate reference mark 112a1' may not be on substrate 112 (since it is on verification substrate 112a), local substrate reference mark 112a1' is shown in a "ghost" format. Figure 7B As shown, this feedback results in improved bonding, wherein the bonded die 108a is more accurately placed between adjacent local substrate reference marks 112a1' (in Figure 7B The systematic error is shown as corrected in , where the "point" is centered at Figure 7B Of course, it should be understood that the improved accuracy (with Figure 7B The substrate 112 shown is opposite) to achieve feedback.

[0040] Apart from Figures 4 to 6 Die attach accuracy verification and Figure 7A-7B In addition to the illustrated systematic error determination and correction, other embodiments of the present invention are contemplated. For example, certain accuracy-related diagnostics may be performed within the scope of the present invention. Figures 8A-8B An example of this diagnostic technique combined with a preliminary accuracy check is shown. Fig. 8A 1 is a block diagram of a die attach system 100 in which a camera 104a images a die 108a while still attached to a film 108b. That is, the imaging is performed before the die attach operation is completed. A plurality of die 108a are still located on the film 108b of the die supply 108. The film is typically transparent (or translucent or translucent) so that markings on the substrate beneath the film are clearly visible and can be accurately measured. Figures 8A-8BIn the embodiment, the verification substrate 112a is positioned below the die supply source 108 (where the plurality of die 108a are still on the film 108b). More specifically, the die supply source 108 (and / or the verification substrate 112a) is moved so that at least one of the plurality of die is located above a corresponding bonding position of the verification substrate 112a (i.e., between the corresponding 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 corresponding local substrate reference marks 112a1. Figure 8B A single die 108a is shown in such a field of view. Using images obtained from this field of view, accuracy data can be obtained before the die attach process occurs. This image data can be used as feedback to correct any accuracy issues.

[0041] In another exemplary method of the present invention, Figures 9A-9B A calibration operation (e.g., a 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 a die attach machine that is moved by a motion system, such as a bonding head 104 moved by a motion system or a die supply source 108 moved by another motion system). In conjunction with such a robot platform calibration, typical nonlinear deviations of the robot axes are measured based on the x, y positions in the working area of ​​the robot platform. For a robot platform with a downward-looking camera (e.g., a bonding head 104 moved by a motion system of a bonding head support 102), the substrate mark measurement can be used directly to create a so-called error map of the robot platform. For a robot platform without a downward-looking camera (e.g., a die supply source 108 moved by a motion system of a supply support 106), a camera of another platform (e.g., 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 in place of the actual die supply source, wherein an exemplary calibration die supply form includes a lithography manufacturing glass plate with a mark (a so-called "calibration wafer"). The deviation of the calibrated bare 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 locations covering the working area of ​​the robot platform. Therefore, both robot platforms can be calibrated to the same calibration reference at the same time. Typically, multiple marks in one field of view are used for this purpose (both on the substrate and on the supply form), creating a more accurate and reliable position and angular offset measurement capability.

[0042] Reference Figures 9A-9BIn the specific example shown, a calibration die supply form 108' is provided in place of the die supply source 108 in the other figures provided herein. The calibration die supply form 108' maintains a calibration die supply 108c including a supply form mark 108c1. Although these supply form marks are square (similar to the shape of the die 108a in the previous figures), any type of supply form mark shape is conceivable. The substrate 112a (including substrate reference marks 112a1, 112a2) is positioned below the calibration die supply form 108'. In this configuration, the camera 104a can be used to measure the relative offset of the supply form mark 108c1 relative to the substrate reference marks 112a1 and / or 112a2. The relative offset can be used in conjunction with the robot platform calibration of each robot platform as described above (e.g., the bond head 104 moved by the motion system of the bond head support 102 and the die supply source 108 moved by the motion system of the supply source 106).

[0043] Although the present invention has been described and illustrated primarily with respect to a die attach operation without a "pick-up" operation, 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.).

[0044] Although exemplary embodiments of the present invention are illustrated and described with respect to marks having specific shapes (e.g., cross marks, circular marks, rectangular marks, etc.) and specific numbers of marks relative to a single die (e.g., four substrate reference marks 112a1 surrounding each die), these types of details are exemplary in nature and do not constitute a limitation on the scope of the present invention.

[0045] Although the present invention has been described and illustrated with respect to exemplary embodiments of the present invention, it will be appreciated by those skilled in the art that the foregoing and various other changes, omissions and additions may be made thereto and thereto without departing from the spirit and scope of the present invention. Rather, various modifications may be made to the details within the scope of equivalent forms of the present invention without departing from the present invention.

Claims

1. A die attach system, comprising: a verification substrate configured to receive a plurality of dies, the verification substrate comprising a plurality of substrate reference marks; as well as an imaging system for determining alignment of the plurality of die with the verification substrate by imaging each of the plurality of die with a corresponding substrate reference mark of the plurality of substrate reference marks in a single field of view; a bonding tool for contacting each of the plurality of dies during transfer from a die supply source to the verification substrate; as well as A supply support for supporting the die supply, the die supply being positioned between the bonding tool and the verification substrate.

2. The die attach system of claim 1 , wherein: The imaging system includes a camera.

3. The die attach system of claim 1 , wherein: The imaging system is configured to obtain image data used to determine a positional deviation between each die in the plurality of dies and a corresponding substrate reference mark in the plurality of substrate reference marks using image data from the imaging system.

4. The die attach system of claim 3, wherein: The position deviation includes deviation components along the x-axis, along the y-axis, and around the θ-axis.

5. The die attach system of claim 1 , wherein: Each die of the plurality of dies is imaged together with a corresponding substrate reference mark of the plurality of substrate reference marks in a single field of view of a camera of the imaging system.

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

7. The die attach system of claim 1, wherein: The verification substrate is a glass substrate.

8. The die attach system of 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 prior to bonding each of the plurality of dies to a substrate, wherein each of the plurality of dies is positioned over the verification substrate during the pre-bonding alignment determination.

9. The die attach system of 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. A method of operating a die attach system, the method comprising the steps of: providing a verification substrate configured to receive a plurality of dies, the verification substrate comprising a plurality of substrate reference marks; An imaging system of the die attach system is used to image each of the plurality of die with a corresponding substrate reference mark among the plurality of substrate reference marks for determining alignment of the plurality of die with the verification substrate, wherein each of the plurality of die is imaged together with a corresponding substrate reference mark among the plurality of substrate reference marks in a single field of view of a camera of the imaging system.

11. The method according to claim 10, wherein: The imaging system includes a camera.

12. The method according to claim 10, wherein: With respect to alignment determination, image data from the imaging system is used to determine a positional deviation between each die in the plurality of dies and a corresponding substrate reference mark in the plurality of substrate reference marks.

13. The method according to claim 12, wherein: The position deviation includes deviation components along the x-axis, along the y-axis, and around the θ-axis.

14. The method according to claim 10, wherein: The verification substrate is an accuracy verification substrate, and the alignment determined using the imaging system is a placement accuracy of each die in the plurality of dies after being placed on the verification substrate.

15. The method according to claim 10, wherein: The verification substrate is a glass substrate.

16. The method according to claim 10, wherein: The verification substrate is a precision verification substrate, and the alignment determined using the imaging system is a pre-bonding alignment determined prior to bonding each of the plurality of dies to a substrate, wherein each of the plurality of dies is positioned over the verification substrate during the pre-bonding alignment determination.

17. The method according to claim 16, wherein: During the pre-bonding alignment determination, each die of the plurality of dies is adhered to a film of a die supply source.

18. A die attach system comprising: a calibration die supply format, comprising a calibration die supply, the calibration die supply comprising a first plurality of reference markings; a first motion system for moving the calibration die supply form; a bonding head including a bonding tool and an imaging system; a second motion system for moving the bonding head; a substrate comprising a second plurality of reference marks; as well as Wherein the imaging system is configured to image reference markers of the first plurality of reference markers and reference markers of the second plurality of reference markers in a single field of view.

19. The die attach system of claim 18, wherein: Images from the imaging system are used in conjunction with calibration of at least one of the calibration die supply form and the bond head during a subsequent bonding operation.

20. The die attach system of claim 18, wherein: The calibration die supply form is a die supply source of the die attach system, the die supply source being configured to carry a plurality of dies secured to a film during a die attach operation.

21. The die attach system of claim 18, wherein: During imaging by the imaging system, a die supply form is calibrated to replace a die supply source of the die attach system, and wherein the die supply source is replaced into the die attach system during a subsequent bonding operation.

22. A method of calibrating a die attach machine, the method comprising the steps of: providing a calibration die supply format including a calibration die supply, the calibration die supply including a first plurality of reference markings; providing a bonding head including a bonding tool and an imaging system; providing a substrate including a second plurality of reference markings; as well as Reference marks in the first plurality of reference marks and reference marks in the second plurality of reference marks are imaged in a single field of view using an imaging system of a die attach machine.

23. The method according to claim 22, further comprising the steps of: During a subsequent bonding operation, the image from the imaging system is used to calibrate the position of at least one of the calibration die supply form and the bond head.

Images