PATENT DOCUMENT

Publication Number: US-11820651-B2
Application Number: US-202117345266-A
Country: US
Kind Code: B2

Title: Mass transfer tool with high productivity

Abstract:
Mass transfer tools and methods for high density transfer of arrays of micro devices are described. In an embodiment, a mass transfer tool includes a plurality of articulating transfer head assemblies coupled with a main translation track, where each articulating transfer head assembly is translatable along the main translation track between a donor substrate stage and a receiving substrate stage.

Claims:
What is claimed is: 
     
       1. A mass transfer tool comprising:
 a receiving substrate stage; 
 a donor substrate stage; 
 a main translation track; 
 a plurality of articulating transfer head assemblies coupled with the main translation track, each articulating transfer head assembly translatable along the main translation track between the donor substrate stage and the receiving substrate stage, and 
 a review camera coupled with the main translation track, wherein the review camera is translatable along the main translation track over the receiving substrate independently of the plurality of articulating transfer head assemblies. 
 
     
     
       2. The mass transfer tool of  claim 1 , wherein each articulating transfer head assembly is adjustable in six degrees of motion. 
     
     
       3. The mass transfer tool of  claim 2 , wherein the plurality of articulating transfer head assemblies comprises a first set of articulating transfer head assemblies attached to a first carriage coupled to the main translation track, and a second set of articulating transfer head assemblies attached to a second carriage coupled to the main translation track. 
     
     
       4. The mass transfer tool of  claim 1 , further comprising a donor substrate stage translation track, wherein the donor substrate stage is translatable along the donor substrate stage translation track between an operable location directly overlapping the main translation track and an inoperable location away from the main translation track. 
     
     
       5. The mass transfer tool of  claim 4 , further comprising a second donor substrate stage translation track, wherein a second donor substrate stage is translatable along the second donor substrate stage translation track between a second operable location directly overlapping the main translation track and a second inoperable location away from the main translation track, and the second donor substrate stage is adjustable in at least two degrees of motion. 
     
     
       6. The mass transfer tool of  claim 5 , wherein one of the at least two degrees of motion is parallel to a longitudinal axis of the main translation track. 
     
     
       7. The mass transfer tool of  claim 4 , further comprising a cleaning station translation track, wherein a cleaning station is translatable along the cleaning station translation track between a cleaning location directly overlapping the main translation track and a non-cleaning location away from the main translation track. 
     
     
       8. The mass transfer tool of  claim 4 , further comprising a loading station translation track, wherein a micro pick up array (MPA) loading station is translatable along the loading station translation track between a loading location directly overlapping the main translation track and a non-loading location away from the main translation track. 
     
     
       9. The mass transfer tool of  claim 8 , wherein the MPA loading station includes a plurality of support structures that can be raised relative to a base structure of the MPA loading station. 
     
     
       10. The mass transfer tool of  claim 1 , further comprising a counter-weight, wherein the counter-weight is translatable parallel to a longitudinal axis of the main translation track over the receiving substrate state independently of the plurality of articulating transfer head assemblies and the review camera. 
     
     
       11. The mass transfer tool of  claim 10 , wherein the counter-weight is coupled with a counter translation track located adjacent to the main translation track. 
     
     
       12. The mass transfer tool of  claim 1 , further comprising an inspection station, wherein the plurality of articulating transfer head assemblies is translatable along the main translation track and directly over the inspection station. 
     
     
       13. A mass transfer tool assembly comprising:
 a plurality of subsystems including a donor substrate stage, pre-placement inspection station, a receiving substrate stage, and a post-placement inspection station; 
 an articulating transfer head assembly; and 
 a motion system to position the articulating transfer head assembly over the plurality of subsystems in a looped sequence; 
 wherein the articulating transfer head assembly is a part of a plurality of articulating transfer head assemblies that can be incremented over the plurality of subsystems in the looped sequence. 
 
     
     
       14. The mass transfer tool of  claim 13 , wherein each articulating transfer head assembly is adjustable in six degrees of motion. 
     
     
       15. The mass transfer tool of  claim 13 , wherein the motion system includes a plurality of arms, each arm including a corresponding articulating transfer head assembly. 
     
     
       16. The mass transfer tool of  claim 15 , wherein each arm includes a corresponding translation arm track to which the corresponding articulating transfer head assembly is attached. 
     
     
       17. The mass transfer tool of  claim 16 , further comprising a micro pick up array loading station adjacent the donor substrate stage, wherein the articulating transfer head assembly for each arm is translatable along the corresponding translation arm track between the donor substrate stage and the micro pick up array loading station. 
     
     
       18. The mass transfer tool of  claim 13 , wherein the plurality of subsystems includes a cleaning station. 
     
     
       19. The mass transfer tool of  claim 18 , wherein the cleaning station includes a substrate with a tacky coating or an electrostatic pattern. 
     
     
       20. A mass transfer tool comprising:
 a receiving substrate stage; 
 a donor substrate stage; 
 a main translation track; 
 a plurality of articulating transfer head assemblies coupled with the main translation track, each articulating transfer head assembly translatable along the main translation track between the donor substrate stage and the receiving substrate stage; and 
 a loading station translation track, wherein a micro pick up array (MPA) loading station is translatable along the loading station translation track between a loading location directly overlapping the main translation track and a non-loading location away from the main translation track. 
 
     
     
       21. The mass transfer tool of  claim 20 , further comprising a donor substrate stage translation track, wherein the donor substrate stage is translatable along the donor substrate stage translation track between an operable location directly overlapping the main translation track and an inoperable location away from the main translation track. 
     
     
       22. The mass transfer tool of  claim 20 , wherein the MPA loading station includes a plurality of support structures that can be raised relative to a base structure of the MPA loading station.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Application No. 63/109,752 filed Nov. 4, 2020, which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     Embodiments described herein relate to systems and methods for transferring micro devices. 
     Background Information 
     Integration and packaging issues are one of the main obstacles for the commercialization of micro devices such as radio frequency (RF) microelectromechanical systems (MEMS) microswitches, light-emitting diodes (LEDs), and MEMS or quartz-based oscillators. 
     Traditional technologies for transferring of devices such as “direct printing” and “transfer printing” include transfer by wafer bonding from a transfer wafer to a receiving wafer. In both traditional and variations of the direct printing and transfer printing technologies, the transfer wafer is de-bonded from a device after bonding the device to the receiving wafer. In addition, the entire transfer wafer with the array of devices is involved in the transfer process. 
     In one process variation a transfer tool including an array of electrostatic transfer heads is used to pick up and transfer an array of micro devices from a carrier (donor) substrate to a receiving substrate. In such an implementation, the transfer heads operate in accordance with principles of electrostatic grippers, using the attraction of opposite charges to pick up the micro devices. In a particular implementation it has been suggested to use an array of electrostatic transfer heads to populate a display backplane with an array of micro LED devices, in which sequential pick and place transfer operations are performed to populate the display backplane with a plurality of different color-emitting micro LEDs from different donor substrates. The cycle time for the tool is determined by the average time from one pick to the next pick, inclusive of any downtime for inspection, maintenance, etc. 
     SUMMARY 
     Mass transfer tools and methods for high density transfer of arrays of micro devices are described. In accordance with embodiments, tool throughput can be increased by incorporating various combinations of multiple articulating transfer head assemblies and multiple transfer lanes which can have a variety of configurations including linear, looped and combinations thereof. 
     In an embodiment, a mass transfer tool (MTT) includes a receiving substrate stage, a donor substrate stage, a main translation track, and a plurality of articulating transfer head assemblies coupled with the main translation track. Each articulating transfer head assembly may be translatable along the main translation track between the donor substrate stage and the receiving substrate stage. Various additional subsystems or stations can be located along the main translation track, or positionable thereto, such as a cleaning station, micro pick up array (MPA) loading station, inspection station, etc. 
     In an embodiment, an MTT includes a plurality of subsystems including a donor substrate stage, a pre-placement inspection station, a receiving substrate stage, and a post-placement inspection station. The MTT may additionally include one or more articulating transfer head assemblies, and a motion system to position the one or more articulating transfer head assemblies over the plurality of subsystems in a looped sequence. Likewise, additional subsystems can be integrated such as a cleaning station or MPA loading station. Various subsystems may also be combined into a single station. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 1 B  are schematic illustrations of a mass transfer tool assemblies in accordance with embodiments. 
         FIG.  2    is an isometric view illustration of a micro pick up array and pivot mount mounted onto an articulating transfer head assembly in accordance with an embodiment. 
         FIG.  3    is a schematic top view illustration of a mass transfer tool assembly in accordance with an embodiment. 
         FIG.  4 A  is a schematic top-down view illustration of a micro pick up array supported by an annular support structure of a micro pick up array loading station in accordance with an embodiment. 
         FIG.  4 B  is a schematic top-down view illustration of a micro pick up array supported by a plurality of support structures of a micro pick up array loading station in accordance with an embodiment. 
         FIG.  4 C  is a schematic cross-sectional side view illustration of a micro pick up array supported by one or more support structures in accordance with an embodiment. 
         FIG.  5    is a process flow for a sequence of transferring multiple groups of LEDs with multiple articulating transfer head assemblies in accordance with an embodiment. 
         FIGS.  6 A- 6 D  are schematic cross-sectional side view illustrations for a sequence of transferring multiple groups of LEDs with multiple articulating transfer head assemblies in accordance with an embodiment. 
         FIG.  7    is a graphical illustration showing the addition of multiple articulating transfer head assemblies and transfer lanes for increasing throughput in accordance with embodiments. 
         FIG.  8    is a schematic top view illustration of an MTT including a plurality of subsystems arranged in a loop architecture in accordance with an embodiment. 
         FIG.  9    is a schematic top view illustration of an MTT including a plurality of arms that are positionable over a plurality of subsystems arranged in a loop architecture in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe mass transfer tool (MTT) assemblies and methods of operation that enable picking up a high density of micro devices from one or more donor substrates with a plurality of articulating transfer head assemblies and placement of groups of the micro devices onto one or more receiving substrates. In accordance with embodiments, tool throughput can be increased by incorporating various combinations of multiple articulating transfer head assemblies and multiple transfer lanes. 
     In an embodiment, each articulating transfer head assembly carries a micro pick up array (MPA) that, depending upon size of the MPA and specifications for the receiving substrate, may include thousands of individual transfer heads. The transfer heads in accordance with embodiments can be designed for various modes of operation. For example, the transfer heads can include elastomeric contact surfaces for pick and place, include vacuum holes, or operate in accordance with electrostatic principles in order to generate higher gripping pressure and reduced size. The transfer heads can include mesa structures to provide localized contact points for the transfer heads. The electrostatic transfer heads may be monopolar, or multi-polar (e.g. bi-polar, etc.). For example, multi-polar transfer heads may be utilized to mitigate against residual charge buildup or provide a charge differential where the target substrate (e.g. donor, receiving, display) is not maintained at a reference voltage. 
     In the following description various embodiments are described with particular reference to tools and methods for transfer of micro light emitting diodes (LEDs). It is to be appreciated that the MTT and sequences can also be applied to other applications to increase throughput for the population of devices, and specifically micro devices. The terms “micro” device or “micro” LED as used herein may refer to the descriptive size of certain devices or structures in accordance with embodiments. As used herein, the term “micro” is meant to refer to the scale of 1 to 300 For example, each micro device may have a maximum length or width of 1 to 300 μm, 1 to 100 μm, or less. In some embodiments, the micro LEDs may have a maximum length and width of 20 μm, 10 μm, or 5 μm. However, it is to be appreciated that embodiments of the present invention are not necessarily so limited, and that certain aspects of the embodiments may be applicable to larger, and possibly smaller size scales. 
     In one aspect, embodiments describe an MTT in which multiple articulating transfer head assemblies are attached to the same main translation track or carriage at a fixed pitch that can be a multiple of the end product pitch on a mother substrate (e.g. display glass). In such an embodiment, articulating transfer head assemblies can pick sequentially from the same or different donor substrates (e.g. uLED donor), be scanned sequentially over an inspection station and placed either sequentially or simultaneously onto different regions of the mother substrate or different receiving substrates. This may increase the cycle time of the tool but will also increase the productivity of the tool by reducing total travel distance required to make multiple transfers. In another aspect, multiple donor substrate holders can be installed in the MTT. Each donor substrate holder may have the ability to move both in x, y and theta (rotational) directions. This will allow multiple articulating transfer head assemblies to pick up simultaneously, which may reduce the nonproductive time of the tool and reduce the cycle time of the tool. For example, the donor substrate stages may be adjustable for gross alignment of different donor substrates, while each articulating transfer head assembly is further adjustable in six degrees of motion for fine alignment. In an embodiment, a first set of articulating transfer head assemblies is attached to a first carriage coupled to the main translation track, and a second set of articulating transfer head assemblies attached to a second carriage coupled to the main translation track. Use of separate carriages may reduce a degree of freedom of movement needed for one of the donor substrate holders. A further extension to reduce cycle time and travel distance is to have the tool populate only half of the receiving substrate (the half closest to the donor substrate). Once the first half is completed, the receiving substrate can be rotated and brought back to the same or a different tool to process the other half. 
     In accordance with embodiments, one or more counter-weights can be installed that move in opposing motion to the articulating transfer head assemblies. The motion profiles can be matched so that the inertia from the counter-weight cancels out the inertia from the articulating transfer head assembly(s) (along with the attached holder, motor, and bearing, as well as any other moving subsystems such as a review camera). Such a configuration may reduce settling time (time is takes for the tool to reach position stability) and the overall cycle time. A further extension is to implement single pick multi place (SPMP) in conjunction, where each transfer head assembly will sequentially release a portion of the micro devices onto different locations of the receiving substrate, or onto different receiving substrates. 
     In another embodiment, the MTT subsystems may be arranged in a loop architecture (e.g. circular, elliptical, etc.). In a loop architecture a carousel with multiple articulating transfer head assemblies can rotate accurately. Each articulating transfer head assembly may by located over a specific station, for example, donor substrate (or MPA loading), pre-placement inspection station (e.g. upward facing inspection camera and/or line scan camera), receiving substrate (e.g. mother glass), post-placement inspection station (e.g. upward facing inspection camera and/or line scan camera), or cleaning station. The carousel may increment at every cycle. Thus, the cycle time of the MTT may include the motion time plus the longest step out of the various stations (e.g. placing operation on the receiving substrate). Such a tool architecture may have a much shorter cycle time compared to a linear system since all the station or subsystem operations are pipelined instead of being executed in series. Various extensions of the loop architecture include having two articulating transfer heads side-by-side on the carousel. Another extension is to include two carousels on opposite sides of the receiving substrate. 
     In various embodiments, description is made with reference to figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions and processes, etc., in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the embodiments. Reference throughout this specification to “one embodiment” means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
       FIGS.  1 A- 1 B  are schematic illustrations of mass transfer tools  100  in accordance with embodiments. Mass transfer tool  100  may include one or more articulating transfer head assemblies  200 , each for picking up an array of micro devices from a carrier (donor) substrate held by a donor substrate stage  104  and for transferring and releasing the array of micro devices onto a receiving substrate (e.g. mother glass) held by a receiving substrate stage  106 . In an embodiment, an inspection station  121  subsystem is located between the donor substrate stage  104  and the receiving substrate stage  106 . For example, this may include an upward facing inspection camera  120  and/or line scan camera  122 . In this manner, the underside of an articulating transfer head assembly  200  (e.g. a micro pick up array carrying a group of micro devices) may be inspected while the articulating transfer head assembly  200  moves between the donor substrate stage  104  and receiving substrate stage  106  to verify efficacy of the transfer operations. In an embodiment, the upward facing inspection camera  120  may be used to identify a fiducial (e.g. encoder) on the micro pick up array  103  (MPA, see  FIG.  2   ) or other part of the articulating transfer head assembly  200 , which can trigger the line scan camera  122  to stitch an image of the bottom surface of the MPA to identify the presence or absence of micro devices held by the MPA, as well as offset of the micro devices from the array of transfer heads. The MTT  100  may additionally include a cleaning station  116  and an MPA loading station  112 . For example, the cleaning station  116  may include a substrate for cleaning or removal of debris or micro devices from the MPA. Such a substrate may include a tacky coating, or alternatively an electrostatic pattern. The MPA loading station  112  may include a plurality of staging areas to supply or replace the MPAs. Operation of mass transfer tool  100  and articulating transfer head assembly  200  may be controlled at least in part by a computer  108 . 
     Referring now to  FIG.  2   , a perspective view of an articulating transfer head assembly  200  is shown in accordance with an embodiment. An articulating transfer head assembly  200  may be used in the mass transfer tool  100  to transfer micro devices to or from a substrate, e.g., receiving substrate or donor substrate, using micro pick up array (MPA)  103  which is supported by a pivot mount assembly  300 . The pivot mount assembly  300  may include a support structure (e.g. base)  302 , a pivot platform  304 , and plurality of spring arms  306 , and the MPA  103  supporting an array of electrostatic transfer heads  115  is mounted on the pivot platform  304 . In an embodiment, the pivot mount assembly  300  may include a flex circuit  308  to communicate with a printed circuit board (PCB) that is located nearby within the articulating transfer head assembly  200  to reduce signal degradation by limiting a distance that signals must travel. 
     In an embodiment, the MPA  103  includes an array of transfer heads  115 . In a particular embodiment, each transfer head operates in accordance with electrostatic principles to pick up and transfer a corresponding micro device. Alternatively, each transfer head may include an elastomeric surface to pick up and transfer a corresponding micro device using Van de Waals forces. In an embodiment each transfer head has a localized contact surface characterized by a maximum dimension of 1-300 μm in both the x- and y-dimensions. In an embodiment, each transfer head contact surface has a maximum lateral dimension of 1 to 100 μm or less. In some embodiments, each transfer head contact surface has a maximum length and width of 20 μm, 10 μm, or 5 μm. Similarly, each micro device, such as an LED or chip, may have a maximum lateral dimension of 1-300 μm or 1-100 μm, such as 20 μm, 10 μm, or 5 μm. The articulating transfer head assembly  200  can include features that allow for the exchange of the MPA at an MPA loading station, and for delivering voltage(s) to the transfer heads to facilitate pick up of a micro device using an electrostatic force and/or holding the MPA  103  onto the pivot platform  304  using electrostatic force. 
     Referring to  FIGS.  1 A- 1 B  and  FIG.  2   , computer  108  may control the operation of articulating transfer head assembly  200  of the MTT  100 . For example, articulating transfer head assembly  200  may include an actuator assembly for adjusting the MPA  103  retained by the transfer head assembly with at least six degrees of freedom, e.g., tipping, tilting, rotation, and movement in x, y, and z directions, based on feedback signals received from various sensors of the MTT  100 . Computer  108  may also control movement of the motor(s) and carriage(s)  202  for translating the articulating transfer head assembly(s)  200  along main translation track  110  (e.g. x direction) over the donor substrate stage  104  and receiving substrate stage  106  as well as the cleaning station  116  and MPA loading station  112 . In the particular embodiment illustrated in  FIG.  1 A  each articulating transfer head assembly  200  is attached to the same carriage  202  which can be driven by a motor. In the particular embodiment illustrated in  FIG.  1 B  sets of articulating transfer head assemblies  200  can be attached to corresponding carriages  202 , each being independently driven by a separate motor. Alternatively, each articulating transfer head assembly  200  can have its own corresponding carriage  202  and motor for independent movement. In an embodiment, the inspection station including the upward facing inspection camera  120  and/or line scan camera  122  may be located along the main translation track  110  between the donor substrate stage  104  and receiving substrate stage  106 . Additional actuators may be provided, e.g., between mass transfer tool  100  structural components and articulating transfer head assembly  200 , donor substrate stage  104 , receiving substrate stage  106 , cleaning station  116 , and MPA loading station  112  to provide movement in the x, y, or z direction for one or more of those sub-assemblies. For example, a gantry may support articulating transfer head assembly  200  and move articulating transfer head assembly  200  along an upper beam or side rails, e.g., in a direction parallel to an axis of motion of main translation track  110 . Thus, an array of transfer heads on MPA  103 , supported by transfer head assembly  200 , and a target substrate (e.g. supported by donor substrate stage  104  or receiving substrate stage  106 ) may be precisely moved relative to each other within all three spatial dimensions. 
     The articulating transfer head assembly  200  in accordance with embodiments may provide for negligible lateral or vertical parasitic motion for small movements of MPA  103 , e.g., motion less than about 5 mrad about a neutral position. In an embodiment, the articulating transfer head assembly includes a tip-tilt assembly  210  and a piezoelectric stage assembly  250  mounted underneath the tip-tilt assembly  210 . Together the tip-tilt assembly  210  and the piezoelectric stage assembly  250  may provide six degrees of motion. Specifically, the tip-tilt assembly  210  may provide tip (θx) and tilt (θy), where the piezoelectric stage assembly  250  provides z motion, x motion, y motion, and rotation (θz). In the particular embodiment illustrated a mounting plate  280  is secured underneath the piezoelectric stage assembly  250 . The pivot mount assembly  300  may be mounted onto the mounting plate  280  using a variety of manners such as using tabs or lips to press the pivot mount assembly against the transfer head assembly  200 , bonding, vacuum, electrostatic clamping, or pogo pin array board. The MPA  103  can be mounted on the pivot platform  304  of the pivot mount assembly  300  using suitable techniques such as electrostatic clamps, vacuum, or mechanical clips. In an embodiment, the MPA  103  is mounted onto the pivot platform  304  using electrostatic clamps to produce a strong holding force, which can be turned off for MPA replacement with the MPA loading station  112 . 
     Referring now to  FIG.  3    a schematic top view illustration is provided of an MTT  100  assembly in accordance with an embodiment. In particular, the MTT  100  is a linear assembly with various stations or sub-assemblies located adjacent to or along the main translation track  110 . As shown, the mass transfer tool  100  can include a receiving substrate stage  106 , which can hold one or more receiving substrates  150 , such as a mother glass for display application. The receiving substrate  150  may be patterned into a plurality of regions  152 , for example, which may correspond to separate end product areas (e.g. display panels) that can be scribed or peeled to form multiple products from the same receiving substrate  150 . The receiving substrate  150  may be secured to the receiving substrate stage  106  using a variety of techniques including gravity, clips, vacuum, etc. Similarly, a donor substrate can be secured to a donor substrate stage  104  using a variety of techniques including gravity, clips, vacuum, etc. 
     As shown in  FIG.  3   , the MTT  100  may include one or more donor substrate stages  104 . For micro LED transfer, the donor substrates may be patterned wafers including thousands of micro LEDs that have been processes to that they are poised for pick up and transfer to the receiving substrate with an articulating transfer head assembly  200 . Each donor substrate stage may optionally be moveable in any or all of x, y and/or theta directions. Alternatively, different donor substrate stages  104  may have different degrees of freedom. For example, where two donor substrate stages are included, at least one of them is movable in at least two degrees of motion, including a direction (e.g. x-direction) parallel to the longitudinal axis  135  of the main translation track  110 . This allows gross alignment of two adjacent donor substrate stages  104  with the articulating transfer head assemblies. Alternatively, the articulating transfer head assemblies  200  may be attached to different carriages  202 , or sets/groups of articulating transfer head assemblies  200  can be attached to different carriages  202  to remove a degree of freedom (e.g. x-direction) for both of the donor substrate stages  104 , thus simplifying the tool. Each donor substrate stage  104  may optionally be secured to a donor substrate stage translation track  105  that is translatable between an operable location directly overlapping the main translation track  110  and an inoperable location away from the main translation track  110 . In an exemplary implementation, each donor substrate stage translation track  105  is in a direction orthogonal to the longitudinal axis  135  (e.g. y-direction). Such y-motion may be in addition to, or part of the x, y and/or theta direction degrees of freedom of the donor substrate stage. Thus, the donor substrate stage may be movable in the y-direction in addition to being translatable along the donor substrate stage translation track  105  in the exemplary embodiment. Multiple donor substrate stages  104  may be included for a variety of reasons, such as loading a new donor substrate while another donor substrate is used in a transfer sequence, or a transfer sequence in which multiple articulating transfer head assemblies  200  can pick up from multiple donor substrates. 
     In the particular embodiment illustrated in  FIG.  3   , four articulating transfer head assemblies  200  are illustrated as being coupled with the main translation track  110  and translatable along the main translation track  110  between the donor substrate stage(s)  104  and the receiving substrate stage(s)  106 . While four articulating transfer head assemblies  200  are illustrated, this is exemplary, and embodiments are not limited to a specific amount. In an embodiment, the articulating transfer head assemblies  200  are coupled with the main translation track (e.g. on carriage  202 ) at a fixed pitch to one another. Also, the articulating transfer head assemblies  200  may be coupled with a carriage  202  at a fixed pitch, and where multiple carriages carry multiple articulating transfer head assemblies  202  the multiple carriages may be independently moveable. For example, this fixed pitch may correspond to a multiple of the regions  152  on the receiving substrate  150 , which may also correspond to an end product pitch. For example, each region  152  may correspond to a display panel that can be scribed or peeled from the receiving substrate  150  (e.g. mother glass). Alternatively, the articulating transfer head assemblies can be coupled with the translation track with different carriages  202 , or sets/groups of articulating transfer head assemblies can be attached to different carriages. 
     Referring again to  FIG.  1 B , in the illustrated embodiment two articulating transfer head assemblies  200  are attached to a corresponding carriage  202 . In an exemplary use, the first and third articulating transfer head assemblies can be positioned over the two donor substrate stages  104  of  FIG.  3    simultaneously. Furthermore, the corresponding carriage  202  position for the first and third articulating transfer head assemblies  202  can be independently adjusted. In this manner, this can free up a degree of freedom (e.g. x-translation) of one of the donor substrate stages  104 , further simplifying the tool. Once a pick operation is performed, the second and fourth articulating transfer head assemblies  200  can be independently positioned over the two donor substrate stages  104  for a second pick operation. 
     The MTT  100  in accordance with embodiments may optionally include a cleaning station  116 . The cleaning station  116  may optionally be translatable along a cleaning station translation track  117  between a cleaning location directly overlapping the main translation track  110  and a non-cleaning location away from the main translation track  110 . In this manner, the articulating transfer head assemblies  200  can be positioned over the cleaning station  116 . The cleaning station  116  may optionally be moveable in any or all of x, y and/or theta directions. The cleaning station  116  may include a cleaning substrate for cleaning or removal of debris or micro devices from the MPA. Such a cleaning substrate may include a tacky coating, or alternatively an electrostatic pattern. Similar to the donor substrate stage  104 , the cleaning station  116  may secure the cleaning substrate using a variety of techniques including gravity, clips, vacuum, etc. Inclusion of the cleaning station  116  can allow integration of a maintenance station directly into the transfer sequence path, and reduce downtime. While a straight cleaning station translation track  117  is illustrated, this is not required, and the cleaning station translation track  117  can be curved, etc. 
     In accordance with embodiments, one or more inspection stations  121  may be included in the MTT  100 . For example, an inspection station may include and upward facing inspection camera  120  and/or line scan camera  122 . In an embodiment, the plurality of articulating transfer head assemblies  200  is translatable along the main translation track  110  and directly over the inspection station  121 . The inspection station  121  may be in a fixed location, though it can also be translatable and/or moveable in any or all of x, y and/or theta directions. In operation, the upward facing inspection camera  120  may be used to identify a fiducial (e.g. encoder) on the micro pick up array  103  or other part of the articulating transfer head assembly  200 , which can trigger the line scan camera  122  to stitch an image of the bottom surface of the MPA  103 . After pick up from the donor substrate, the image may identify the presence or absence of micro devices held by the MPA  103 , as well as offset of the micro devices from the array of transfer heads. This information may be used to determine whether to proceed with the placement sequence, or to calculate a placement offset when positioning the articulating transfer head assemblies  200  over the receiving substrate. Alternatively, this information can be used to trigger a cleaning operation with the cleaning station  116  or interchange the MPA  103  with the MPA loading station  112 . Once placement has occurred, the articulating transfer head assemblies  200  can then be translated back toward the donor substrate stage(s)  104  for subsequent pick operations. During this translation, the articulating transfer head assembles  200  may then again track directly over the inspection station  121 , where the bottom surface of the MPA  103  is again scanned. Information from this can likewise be used to determine whether to proceed with the next pick operation, trigger a cleaning operation with the cleaning station  116 , or to interchange the MPA  103  with the MPA loading station  112 . 
     In accordance with embodiments, the MTT may include a counter-weight  140  that is translatable parallel to the longitudinal axis  135 . The counter-weight may include a single weight, or multiple weights. The counter-weight  140  can be coupled with the main translation track  110 , or with a separate counter translation track  142  located adjacent to the main translation track  110 . For example, the counter translation track  142  may be above, below, or on opposite sides of the main translation track  110  for weight balancing. In an embodiment, counter-weights are coupled to the counter translation track  142  on opposite sides of the main translation track  110 . In this configuration their center of mass may be coincident with the longitudinal axis  135 , and the plurality of articulating transfer head assemblies, etc. Arrangement along the counter translation track  142  may additionally help avoid collisions with other systems along the main translation track  110  and still allow the counter-weights to cancel out inertia from the articulating transfer head assembly(s) and review camera, and reduce settling time. The counter-weight may be independently translatable along the main translation track  110  or counter track  142 . Thus, the counter-weight  140  and plurality of articulating transfer head assemblies  200  may be connected to separate motors, and carriages attached to their respective translation tracks. Additionally, a review camera  130  can be coupled with the main translation track  110 , and likewise be independently translatable along the main translation track  110 , for example, with a separate motor and carriage. The counter-weight  140  may be installed to move in an opposing direction as the articulating transfer head assemblies  200 , as well as the review camera  130 , to cancel out inertia from the articulating transfer head assembly(s) and review camera  130 , and reduce settling time. The review camera  130  may be used to inspect the receiving substrate  150  before and/or after transfer of the micro devices. This information can be used to further validate the transfer sequence and detect errors, or misplaced or non-transferred micro devices. 
     Still referring to  FIG.  3   , the MPA loading station  112  may optionally be translatable along a loading station translation track  113  between a loading location directly overlapping the main translation track  110  and a non-loading location away from the main translation track  110 . In this manner, the articulating transfer head assemblies  200  can be positioned over the MPA loading station  112 . While a straight loading station translation track  113  is illustrated, this is not required, and the loading station translation track  113  can be curved, etc. The MPA loading station  112  may optionally be moveable in any or all of x, y and/or theta directions. In an embodiment, the MPA loading station  112  includes a plurality of support structures that can be raised above a base structure of the MPA loading station to either receive or donate an MPA  103 . The MPA loading station  112  may also be rotatable so as to position a specific MPA  103  or support structure underneath an articulating transfer head assembly  200 . 
     Referring now to  FIGS.  4 A- 4 C  schematic top-down and cross-sectional side view illustrations are provided of an MPA  103  supported by one or more support structures  118  of an MPA loading station  112 . In the embodiment illustrated in  FIG.  4 A , the MPA  103  may be supported by an annular support structure  118 . In the embodiment illustrated in  FIG.  4 B , the MPA  103  may be supported by a plurality of support structures  118 , which can be shaped as columns, walls, etc.  FIG.  4 C  is a schematic cross-sectional side view illustration taken along line C-C of either  FIG.  4 A  or  FIG.  4 B . As shown in  FIG.  4 C , the one or more support structures  118  can be raised relative to a base structure  109  of the MPA loading station  112 . For example, this may be accomplished with telescoping columns, walls, etc. that can be raised and lowered. In an embodiment, one or more vacuum channels  119  may optionally be formed in the support structure(s)  118  and optionally the base structure  109  to provide suction force to help secure the MPAs  103  on the support structures  118 . Being able to raise and lower the MPAs  103  with the support structure(s)  118  may allow the active surface of the MPAs  103  including the transfer heads  115  to remain protected from potential contamination. 
     It will be appreciated that transfer sequences in accordance with embodiments can be carried out in a variety of sequences, and using various combinations of stations or subsystems.  FIG.  5    is a process flow for a sequence of transferring multiple groups of LEDs with multiple articulating transfer head assemblies in accordance with an embodiment.  FIGS.  6 A- 6 D  are schematic cross-sectional side view illustrations for a sequence of transferring multiple groups of LEDs with multiple articulating transfer head assemblies in accordance with an embodiment. In interest of clarity and conciseness the following description of the process flow of  FIG.  5    is made with regard to the sequence illustrated in  FIGS.  6 A- 6 D . In particular, the processing sequences illustrated in  FIG.  5    and  FIGS.  6 A- 6 D  illustrate interoperability of a plurality of articulating transfer head assemblies  200  with a counter-weight  140  and review camera  130 . It is to be appreciated that the illustrated sequences are exemplary, and the MTT  100  can be operated in other complex sequences. Specifically, while sequential pick operations are described for each articulating transfer head assembly  200 , multiple articulating transfer head assemblies  200  can simultaneously pick up from multiple donor substrates as previously described with regard to  FIG.  3   . 
     Referring to  FIG.  6 A  at operation  5010  a first group of LEDs (or other micro devices) is picked up from a first donor substrate with a first articulating transfer head assembly  200 A. In this process sequence, the plurality of articulating transfer head assemblies  200  is labeled as  200 A,  200 B,  200 C,  200 D. This may include translating the donor substrate stage  104  underneath the main translation track  110 . The first articulating transfer head assembly  200 A then contacts the MPA  103  transfer heads  115  with the plurality of LEDs on a donor substrate to pick up a first group of LEDs from the donor substrate. Still referring to  FIG.  6 A  the motion of translating the first articulating transfer head assembly  200  over the donor substrate stage  104  may be accompanied by simultaneous movement of the review camera  130  over a region  152  on the receiving substrate  150  that will be receiving LEDs. In the particular embodiment illustrated, the review camera  130  is located over a region  152  which the fourth articulating transfer head assembly  200 D will transfer LEDs to. This may minimize total transfer distance of the review camera  130  after all LEDs have been picked up, though embodiments are not limited to this manner of operation. Additionally, the counter-weight  140  may be translated to a position along the main translation track  110  or counter translation track  142  to counter the movement of the articulating transfer head assembly(s)  200 A- 200 D, as well as the review camera  130 . In interest of clarity, the counter translation track  142  and longitudinal axis  135  are only illustrated in  FIG.  6 A , and are not included in  FIGS.  6 B- 6 D . 
     At operation  5020  a second articulating transfer head assembly  200 B is positioned over the same donor substrate and donor substrate stage  104 , and contacted with the donor substrate to pick up a second group of LEDs. As shown in  FIG.  6 B  this may be accompanied by positioning the review camera over a region  152  on the receiving substrate  150  that will be receiving the LEDs from the third articulating transfer head assembly  200 C. Additionally, the counter-weight  140  may be moved an equal but opposite distance along the main translation track  110  or counter translation track  142  as the articulating transfer head assembly(s)  200 A- 200 D. 
       FIG.  6 C  illustrates a continuance of this sequence where the third articulating transfer head assembly  200 C has already picked up a third group of LEDs, and now the fourth articulating transfer head assembly  200 D is picking up a fourth group of LEDs. Similarly, the review camera can now be positioned over a region  152  on the receiving substrate  150  that will be receiving the LEDs from the first articulating transfer head assembly  200 A. Additionally, the counter-weight  140  may be moved an equal but opposite distance along the main translation track  110  or counter translation track  142  as the articulating transfer head assembly(s)  200 A- 200 D. 
     Referring now to  FIG.  6 D , at operation  5030  the plurality of articulating transfer head assemblies  200 A,  200 B,  200 C,  200 D is translated along the main translation track  110  toward the receiving substrate  150 . During this translation, one or more, or all, of the articulating transfer head assemblies  200 A,  200 B,  200 C,  200 D can be translated over the inspection station  121 . It is also possible one or more of the articulating transfer head assemblies could have been translated over, and inspected by, the inspection station  121  during the previous operations of picking up the multiple groups of LEDs. For example, this is illustrated in  FIG.  6 C , which may further reduce total distance traveled along the main translation track  110 . 
     Still referring to  FIG.  6 D , at operation  5040  the plurality of articulating transfer head assemblies  200 A,  200 B,  200 C,  200 D can then be positioned over corresponding separate regions  152  of the receiving substrate  150 , and the different groups of LEDs can then be placed onto the different regions  152  of the receiving substrate  150  at operation  5050 . This placement may be performed sequentially, or simultaneously to increase throughput. 
     The processing sequence illustrated in  FIGS.  6 A- 6 D  can be modified in a number of ways. For example, the plurality of articulating transfer head assemblies can pick up from a plurality of different donor substrates held on corresponding donor substrate stages  104 . Picking up from the multiple donor substrate stages can be sequential, or simultaneous. In an embodiment, the first and third articulating transfer head assemblies  200 A,  200 C pick up from two different donor substrate stages  104  simultaneously, followed by translation, and picking up from the same donor substrate stages  104  with the second and fourth articulating transfer head assemblies  200 B,  200 D. Placement can also be performed sequentially or simultaneously. In an embodiment, one or more of the articulating transfer head assemblies has a single pick up operation, followed by multiple placement operations onto the same or different regions  152  of the receiving substrate  150 . 
     In accordance with embodiments, MTT  100  throughput can be increased by incorporating various combinations of multiple articulating transfer head assemblies  200  and multiple transfer lanes. This is schematically illustrated in  FIG.  7   , where the bottom left illustration is that of an MTT including a single donor substrate holder  104 , inspection station  121 , and articulating transfer head assembly  200 . As shown, throughput can be increased by addition of more articulating transfer head assemblies  200  or more transfer lanes. Transfer lanes can be added by either populating the receiving substrate stage  106  from different sides, and/or adding parallel transfer lanes (and hence main translation tracks) from the same side of the receiving substrate stage  106 . Accordingly, while the embodiments described and illustrated with regard to  FIGS.  1 A- 6 D  have been made with regard to a single transfer lane (and main translation track) from a single side of the receiving substrate stage  106 , the embodiments can also be applied in an MTT system with multiple transfer lanes, and different numbers of articulating transfer head assemblies located on one or more sides (e.g. opposite sides) of the receiving substrate stage  106 . 
     Referring now to  FIG.  8    a schematic top view illustration is provided of an MTT  100  assembly including a plurality of subsystems (or stations) arranged in a loop architecture in accordance with an embodiment. For example, the loop may be circular, oval, etc. where the one or more articulating transfer head assemblies  200  can be sequentially moved or rotated into position over different subsystems. In particular,  FIG.  8    illustrates an MTT including two groups of subsystems (or stations) arranged in a loop architecture. In an embodiment, an MTT  100  assembly includes a plurality of subsystems including a donor substrate stage  104 , a pre-placement inspection station  121 A, a receiving substrate stage  106 , and a post-placement inspection station  121 B. The MTT  100  additionally includes an articulating transfer head assembly  200 , and a motion system  225  to position the articulating transfer head assembly  200  over the plurality of subsystems in a looped sequence. For example, the motion system  225  may include a number of movable stages, arms, translation tracks, etc. The articulating transfer head assembly  200  may be part of a carousel  180  of a plurality of articulating transfer head assemblies that can be incremented over the plurality of subsystems in the looped sequence. Thus, multiple articulating transfer head assemblies  200  can be included so that each rotates over a specific subsystem, for example, donor substrate stage  104  (or MPA loading station  112 ), pre-placement inspection station  121 A (e.g. upward facing inspection camera  120  and/or line scan camera  122 ), receiving substrate stage  106  (e.g. to hold receiving substrate  150 ), post-placement inspection station  121 B (e.g. upward facing inspection camera  120  and/or line scan camera  122 ), or cleaning station  116 . While a circular looped architecture is illustrated, this is exemplary any other configurations are possible such as elliptical, oval, ovoid, etc. where an articulating transfer head assembly  200  can be returned to a starting location along a different path from which it leaves the starting location. In an embodiment, the motion system and upward facing inspection camera  120  and line scan camera  122  are arranged so that the multiple articulating transfer head assemblies  200  are scanned in the same order, for both pre-placement and post-placement. The carousel  180  may increment at every cycle. Thus, the cycle time of the MTT  100  may include the motion time plus the longest step out of the various stations (e.g. placing operation on the receiving substrate). In the particular embodiment illustrated in  FIG.  8    two carousels are located on opposite sides of the receiving substrate stage  106 . 
       FIG.  9    is a schematic top view illustration of an MTT  100  including a carousel  180  and separate arms  170  that are positionable over a plurality of subsystems arranged in a loop architecture in accordance with an embodiment. It is to be appreciated that while each arm  170  is illustrated as being a discrete piece, the MTT  100  may be more interconnected, and each arm  170  may also be a portion of an integrated system. In an embodiment each arm may include a corresponding articulating transfer head assembly  200 . Furthermore, each arm may include a corresponding translation arm track  111  to which the articulating transfer head assembly  200  is attached and translatable. For example, this may be a linear track along a length of the arm  170 . In an embodiment, an MPA loading station  112  may be located adjacent to the donor substrate stage  104  such that the articulating transfer head assembly  200  for each arm is translatable along the corresponding translation arm track  111  between the donor substrate stage  104  and the MPA loading station  112 . In this manner the MPA loading station  112  can be integrated into the same subsystem with the donor substrate stage  104  so that a separate increment is not necessary for every cycle, and instead an articulating transfer head assembly  200  can be moved to the MPA loading station  112  only when service is required. 
     In utilizing the various aspects of the embodiments, it would become apparent to one skilled in the art that combinations or variations of the above embodiments are possible for transferring an array of micro devices. Although the embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the appended claims are not necessarily limited to the specific features or acts described. The specific features and acts disclosed are instead to be understood as embodiments of the claims useful for illustration. In particular, while the above embodiments have been specifically described with regard to LEDs, and more particularly to micro LEDs, the MTT  100  and sequences can also be applied to other applications to increase throughput for the population of devices, and specifically micro devices. Accordingly, the above descriptions and illustrations of LEDs and display substrates are generically applicable to other micro device applications and receiving substrates that can be populated using the MTT  100  and transfer sequences described.

Metadata:
Filing Date: 20210611
Publication Date: 20231121
Grant Date: 20231121
Priority Date: 20201104
Inventors: MANENS, ANTOINE
Assignee: APPLE INC
CPC Classifications: [{"code": "B81C99/002", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L25/0753", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K13/0413", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K13/0812", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/67144", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L24/95", "inventive": true, "first": true, "tree": "[]"}, {"code": "B81C99/002", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L25/0753", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/95", "inventive": false, "first": false, "tree": "[]"}, {"code": "B81C99/002", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/67132", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/75", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/67144", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L25/0753", "inventive": true, "first": false, "tree": "[]"}, {"code": "B81C99/002", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K13/0812", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K13/0413", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/75821", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/75804", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/7501", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/759", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K13/0812", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K13/0413", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L25/0753", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 81379877