PATENT DOCUMENT

Publication Number: US-10804127-B2
Application Number: US-201615562738-A
Country: US
Kind Code: B2

Title: Electrostatic cleaning device

Abstract:
An electrostatic cleaning device, mass transfer tool, and method of operation are disclosed. In an embodiment an electrostatic cleaning device includes a cleaning electrode area including a first electrode pattern, a first trace line connected to the first electrode pattern, and a dielectric layer covering the cleaning electrode and the first trace line. In an embodiment, a mass transfer tool includes a translatable transfer head assembly that is translatable over a carrier substrate stage, a receiving substrate stage, and an electrostatic cleaning stage.

Claims:
What is claimed is: 
     
       1. An electrostatic cleaning device comprising:
 a cleaning electrode area including a first electrode pattern including a plurality of first fingers, and a second electrode pattern including a plurality of second fingers, wherein the plurality of first fingers are laterally parallel to and interdigitated with the plurality of second fingers; 
 a first trace line connected to the first electrode pattern; and 
 a dielectric layer covering the cleaning electrode area and the first trace line. 
 
     
     
       2. The electrostatic cleaning device of  claim 1 , wherein the first electrode pattern includes a comb configuration and the second electrode pattern includes a comb configuration. 
     
     
       3. The electrostatic cleaning device of  claim 1 , further comprising:
 a second trace line connected to the second electrode pattern; and 
 wherein the dielectric layer covers the cleaning electrode area, the first trace line and the second trace line. 
 
     
     
       4. The electrostatic cleaning device of  claim 3 , wherein the cleaning electrode area, the first trace line, and the second trace line are formed in a silicon layer. 
     
     
       5. The electrostatic cleaning device of  claim 4 , further comprising a base substrate, and an insulator layer between the silicon layer and the base substrate. 
     
     
       6. The electrostatic cleaning device of  claim 3 , further comprising a plurality of additional electrically separate cleaning electrode areas and a corresponding plurality of additional electrically separate first trace lines, and the dielectric layer covers each additional cleaning electrode area and each additional first trace line. 
     
     
       7. The electrostatic cleaning device of  claim 6 , wherein each additional cleaning electrode area includes an additional second electrode pattern interdigitated with an additional first electrode pattern, and further comprising a corresponding plurality of additional electrically separate second trace lines. 
     
     
       8. The electrostatic cleaning device of  claim 1 , further comprising a flex circuit coupled with the first trace line. 
     
     
       9. An electrostatic cleaning device comprising:
 a plurality of electrically separate cleaning electrode areas, each cleaning electrode area including a first electrode pattern and a second electrode pattern interdigitated with the first electrode pattern; 
 a corresponding plurality of electrically separate first trace lines, each first trace line connected to the first electrode pattern; 
 a corresponding plurality of electrically separate second trace lines, each second trace line connected to the second electrode pattern; 
 a dielectric layer covering each cleaning electrode area, each first trace line, and each econ trace line; 
 a first corresponding plurality of conductive contacts electrically coupled with the plurality of electrically separate first trace lines; and 
 a second corresponding plurality of conductive contacts electrically coupled with the plurality of electrically separate second trace lines. 
 
     
     
       10. The electrostatic cleaning device of  claim 9 , wherein the plurality of conductive contacts are electrically coupled with a plurality of via plugs. 
     
     
       11. The electrostatic cleaning device of  claim 9 , further comprising a conductive ground contact. 
     
     
       12. The electrostatic cleaning device of  claim 11 , further comprising a flex circuit coupled with the first corresponding plurality of conductive contacts, the second corresponding plurality of conductive contacts, and the conductive ground contact. 
     
     
       13. A mass transfer tool comprising:
 a carrier substrate stage; 
 a receiving substrate stage; 
 an electrostatic cleaning stage; 
 an electrostatic cleaning device that is detachably coupleable with the electrostatic cleaning stage, wherein the electrostatic cleaning device comprises:
 a cleaning electrode area including a first electrode pattern including a plurality of first fingers and a second electrode pattern including a plurality of second fingers, wherein the plurality of first fingers are laterally parallel to and interdigitated with the plurality of second fingers; 
 a first trace line connected to the first electrode pattern; and 
 a dielectric layer covering the cleaning electrode area and the first trace line; and 
 
 a translatable transfer head assembly that is translatable over the carrier substrate stage, the receiving substrate stage, and the electrostatic cleaning stage. 
 
     
     
       14. The mass transfer tool of  claim 13 , further comprising a translation track, wherein the translatable transfer head assembly is coupled with the translation track and the translatable transfer head assembly is movable along the translation track over the carrier substrate stage, the receiving substrate stage, and the electrostatic cleaning stage. 
     
     
       15. The mass transfer tool of  claim 13 , further comprising an upward facing inspection camera. 
     
     
       16. The mass transfer tool of  claim 13 , wherein the upward facing inspection camera is located between the receiving substrate stage and the carrier substrate stage. 
     
     
       17. The mass transfer tool of  claim 13 , further comprising a pair of voltage sources to supply separate operating voltages to the electrostatic cleaning device. 
     
     
       18. The mass transfer tool of  claim 13 , further comprising a micro pick up array including an array of bipolar electrostatic transfer heads that is detachably coupleable with the translatable transfer head assembly. 
     
     
       19. A micro device transfer and cleaning method comprising:
 picking up an array of micro devices with a micro pick up array; 
 placing the array of micro devices on a receiving substrate; 
 inspecting the micro pick up array to locate a micro device retained on the micro pick up array after placing the array of micro devices on the receiving substrate; and 
 cleaning the micro pick up array with an electrostatic cleaning device to remove the micro device from the micro pick up array; 
 wherein the electrostatic cleaning device comprises:
 a cleaning electrode area including a first electrode pattern including a plurality of first fingers and a second electrode pattern including a plurality of second fingers, wherein the plurality of first fingers are laterally parallel to and interdigitated with the plurality of second fingers; 
 a first trace line connected to the first electrode pattern; and 
 a dielectric layer covering the cleaning electrode area and the first trace line. 
 
 
     
     
       20. The method of  claim 19 , wherein cleaning the micro pick up array with the electrostatic cleaning device comprises:
 bringing the micro pick up array into close contact with the electrostatic cleaning device; 
 applying a voltage to the electrostatic cleaning device to build up charge on the electrostatic cleaning device; and 
 withdrawing the micro pick up array from the electrostatic cleaning device. 
 
     
     
       21. The method of  claim 19 , further comprising removing the voltage from the electrostatic cleaning device to remove the charge from the electrostatic cleaning device, and indexing the electrostatic cleaning device to a clean location.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/US2016/022383, filed Mar. 14, 2016, entitled ELECTROSTATIC CLEANING DEVICE, which claims priority to U.S. Provisional Patent Application No. 62/141,450, filed on Apr. 1, 2015, which are herein incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     Embodiments relate to an electrostatic cleaning device. More particularly, embodiments relate to a mass transfer tool with an integrated electrostatic cleaning device. 
     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 diode (LED) display systems, 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 described in U.S. Pat. No. 8,333,860 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 substrate to a receiving substrate. As described the transfer heads operate in accordance with principles of electrostatic grippers, using the attraction of opposite charges to pick up the micro devices. 
     SUMMARY 
     An electrostatic cleaning device, mass transfer tool, and methods of operation are described. In an embodiment an electrostatic cleaning device includes a cleaning electrode area including a first electrode pattern, a first trace line connected to the first electrode pattern, and a dielectric layer covering the cleaning electrode area and the first trace line. The cleaning area may additionally include a second electrode pattern that is interdigitated with the first electrode pattern. Additionally, a second trace line can be connected to the second electrode pattern, and the dielectric layer covers the first and second electrode patterns in the cleaning electrode area as well as the first and second trace lines. 
     In an embodiment, the cleaning electrode area and the one or more trace lines are formed in a silicon layer. For example, the electrostatic cleaning device may include a base substrate and an insulator layer between the silicon layer and the base substrate. Such a configuration may be formed form a silicon-on-insulator (SOI) substrate. 
     In an embodiment, the electrostatic cleaning device includes a plurality of separately operable cleaning electrode areas and a corresponding plurality of electrically separate first trace lines. The dielectric layer may additionally cover each cleaning electrode area and each first trace line. In such a configuration, each cleaning electrode area may additionally include a second electrode pattern interdigitated with the first electrode pattern. A corresponding plurality of electrically separate second trace lines may be connected to the second electrode patterns. 
     In an embodiment, a flex circuit is coupled with the first trace line. Were multiple electrode patterns and trace lines are included, the flex circuit may be coupled with the multiple trace lines. Furthermore, where multiple separately operable cleaning electrode areas are included, the flex circuit may be coupled with the one or more trace lines that correspond to the multiple separately operable cleaning electrode areas. In an embodiment, conductive contacts are electrically coupled with the trace lines. Conductive contacts can also be used to form conductive ground contacts. In a embodiment, a first plurality of conductive contacts are coupled with a plurality of electrically separate first trace lines, and a second corresponding plurality of conductive contacts are electrically coupled with a plurality of electrically separate second trace lines. A flex circuit may be coupled with the first corresponding plurality of conductive contacts, the second corresponding plurality of conductive contacts, and one or more conductive ground contacts. In an embodiment the conductive contacts may be coupled with a plurality of via plugs, for example, formed within the base substrate. 
     In an embodiment, a mass transfer tool includes a carrier substrate stage, a receiving substrate stage, an electrostatic cleaning stage, and a translatable transfer head assembly that is translatable over the carrier substrate stage, the receiving substrate stage, and the electrostatic cleaning stage. The translatable transfer head assembly may be coupled with a translation track, with the translatable transfer head assembly being moveable along the translation track over the carrier substrate stage, the receiving substrate stage, and the electrostatic cleaning stage. The mass transfer tool may additionally include an upward facing inspection camera. In an embodiment, the upward facing inspection camera is located between the receiving substrate stage and the carrier substrate stage. In this manner, a substrate or device carried by the translatable transfer head assembly, such as a micro pick up array, can be inspected between pick up and placement operations in order to determine whether a cleaning operation is to be performed. 
     In an embodiment, an electrostatic cleaning device is detachably coupleable with the electrostatic cleaning stage. The mass transfer tool may additionally include one or more voltage sources for operating or holding various components. For example, the mass transfer tool may include a pair of voltage sources to supply separate operating voltages to the electrostatic cleaning device. In an embodiment, a micro pick up array including an array of bipolar electrostatic transfer heads is detachably couplable with the translatable transfer head assembly. The mass transfer tool may additionally include another pair of voltage sources to supply separate operating voltages to the micro pick up array. 
     The electrostatic cleaning device may be used for cleaning purposes and may be used in conjunction with the mass transfer of micro devices. In an embodiment, a micro device transfer and cleaning method includes picking up an array micro devices with a micro pick up array, and placing placing the array of micro devices on a receiving substrate. The micro pick up array may then be inspected to locate any micro devices that may be retained on the micro pick up array after placing the array of micro devices on the receiving substrate. These may correspond to mis-transferred micro devices. In accordance with embodiments, the micro pick up array may then be cleaned with the electrostatic cleaning device to remove any mis-transferred micro devices from the micro pick up array. 
     In an embodiment, cleaning of a workpiece, such as the micro pick up array, with the electrostatic cleaning device includes bringing the micro pick up array into close contact with the electrostatic cleaning device, applying a voltage to the electrostatic cleaning device to build up charge on the electrostatic cleaning device, withdrawing the micro pick up array from the electrostatic cleaning device. In an embodiment, the voltage is then removed from the electrostatic cleaning device to remove the charge from the electrostatic cleaning device, and the electrostatic cleaning device is then indexed to a clean location to ready the electrostatic cleaning device for a subsequent cleaning operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic illustration of a mass transfer tool assembly in accordance with an embodiment. 
         FIG. 1B  is a perspective view illustration of a micro pick up array and pivot mount mounted onto a transfer head assembly in accordance with an embodiment. 
         FIG. 2A  is a schematic cross-sectional side view illustration of a micro pick up array positioned over a carrier substrate in accordance with an embodiment. 
         FIG. 2B  is a schematic cross-sectional side view illustration of a micro pick up array after picking up an array of micro devices from a carrier substrate in accordance with an embodiment. 
         FIG. 3A  is a schematic cross-sectional side view illustration of a micro pick up array positioned over a receiving substrate in accordance with an embodiment. 
         FIG. 3B  is a schematic cross-sectional side view illustration of a micro pick up array after placing an array of micro devices on a receiving substrate in accordance with an embodiment. 
         FIG. 4A  is a schematic cross-sectional side view illustration of a micro pick up array positioned over an electrostatic cleaning device in accordance with an embodiment. 
         FIG. 4B  is a schematic cross-sectional side view illustration of a micro pick up array into close contact with an electrostatic cleaning device in accordance with an embodiment. 
         FIG. 4C  is a schematic cross-sectional side view illustration of a micro pick up array after cleaning with an electrostatic cleaning device in accordance with an embodiment. 
         FIG. 5  is a process flow of a cleaning operation in accordance with an embodiment. 
         FIG. 6A  is a schematic top view illustration of an electrostatic cleaning device prior to cleaning a micro pick up array in accordance with an embodiment. 
         FIG. 6B  is a schematic top view illustration of an electrostatic cleaning device after cleaning a micro pick up array in accordance with an embodiment. 
         FIG. 7  is a process flow of a method of operating a mass transfer tool including inspection and cleaning in accordance with an embodiment. 
         FIG. 8  is a schematic illustration of a computer system in accordance with an embodiment. 
         FIGS. 9A-9E  are schematic top view illustrations of a method of forming an electrostatic cleaning device in accordance with an embodiment. 
         FIG. 9F  is a schematic top view illustration of Detail F in  FIG. 9D  in accordance with an embodiment. 
         FIGS. 10A-18C  are schematic cross-sectional side view illustrations taken along lines A-A, B-B, C-C, and D-D in  FIG. 9F  and schematic top view illustrations of a method of forming an electrostatic cleaning device in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe an electrostatic cleaning device, mass transfer tool, and methods of operation. In an embodiment, an electrostatic cleaning device includes a cleaning electrode area with a first electrode pattern, a first trace line connected to the first electrode pattern, and a dielectric layer covering the cleaning electrode area and the first trace. The cleaning electrode area may include a second electrode pattern interdigitated with the first electrode pattern and a second trace line connected to the first electrode pattern. In such a configuration the interdigitated electrodes patterns form an interdigitated bipolar electrode configuration. The electrostatic cleaning device may be integrated into a mass transfer tool for periodic cleaning of MEMS devices, such as a micro pick up array including an array of electrostatic transfer heads. In an embodiment, the mass transfer tool includes a translatable transfer head assembly, a carrier substrate stage, a receiving substrate stage, and an electrostatic cleaning stage to which the electrostatic cleaning device can be secured. In operation, the translatable transfer head assembly can be positioned over the carrier substrate stage, the receiving substrate stage, and the electrostatic cleaning stage, for example by moving along a translation track. In an embodiment, an upward facing inspection camera is located between the carrier substrate stage and the receiving substrate stage. 
     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” or “an 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” or “an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The terms “spanning”, “over”, “to”, “between” and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “spanning”, “over” or “on” another layer or bonded “to” or in “contact” with another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers. 
     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 μm. 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 electrostatic cleaning device for removing loose contamination from the surface of a microchip or a MEMS device. A variety of types of contamination may be removed, such as dust particles, wear particles, or other accumulated contamination. Contamination may additionally include non-transferred micro devices (e.g. micro chips, micro LEDs). The electrostatic cleaning device may also be used to clean a variety of microchips or MEMS devices, such as but not limited to a micro pick up array, pivot mount, and a released carrier substrate. 
     In accordance with embodiments, a mass transfer tool (MTT) and method of operation are described that enable in-situ inspection and cleaning. In an embodiment, the MTT carries a micro pick up array (MPA) that, depending upon size of the MPA, may include thousands of individual electrostatic transfer heads that correspond to a pixel density, e.g. pixels per inch (PPI) on a receiving substrate. Thus a pick and place operation may pick up thousands of closely arranged micro devices from a carrier substrate and place the micro devices on a receiving substrate. It has been observed that the presence of contamination (e.g. dust particles, wear particles, micro devices, etc.) on the MPA can have detrimental effects. For example, if contamination remains on the MPA after the placement operation on the receiving substrate, the contamination may interfere with a subsequent pick up operation from a carrier substrate. Such interference might possibly prohibit picking up a large number of micro devices. Furthermore, such contamination can possibly cause physical damage to the MPA or target substrate (e.g. carrier substrate or receiving substrate) during subsequent transfer operations. Likewise, contamination on the MPA after the pick up operation can interfere with the placement operation on the receiving substrate. 
     In another aspect, embodiments describe a structure and method of removing contamination using electrostatic attractive force. In accordance with embodiments, cleaning force is applied to the ECD quickly, for example, on the order of 10 milliseconds or less. The electrostatic cleaning force at the surface of the ECD is stronger than adhesion forces of the contamination on the device being cleaned. Furthermore, precise alignment of the microchip or MEMS device being cleaned and the ECD is not required. In accordance with embodiments, the speed of charge build up on the ECD is a determinant factor in the cleaning cycle time, with small operating capacitances resulting in faster cycle times. Accordingly, operating capacitances are related to the target contamination sizes. In an embodiment, rapid cleaning of contamination on the order of 0.25 μm to 25 μm, for example, may be achieved in a matter of milliseconds. Thus, embodiments describe a mass transfer tool and method of operation with integrated in-situ inspection and a rapid cleaning operation that does not require the precise alignment of the pick and place operations. As a result, transfer efficiency of the MTT can be increased with a reduced proportion of tool down time for cleaning to operating time, thereby increasing the availability of the MTT for production and reducing the total manufacturing cost of the display or lighting units being assembled. 
       FIG. 1A  is a schematic illustration of a mass transfer tool in accordance with an embodiment. Mass transfer tool  100  may include a transfer head assembly  200  for picking up an array of micro devices from a carrier substrate held by a carrier substrate stage  104  and for transferring and releasing the array of micro devices onto a receiving substrate held by a receiving substrate stage  106 . In an embodiment, an upward facing inspection camera  120  is located between the carrier substrate stage  104  and the receiving substrate stage  106 . In this manner, a device retained by the transfer head assembly  200  may be inspected by the inspection camera while the transfer head assembly  200  moves between the carrier substrate stage  104  and receiving substrate stage  106  to verify efficacy of the transfer operations. Operation of mass transfer tool  100  and transfer head assembly  200  may be controlled at least in part by a computer  108 . Computer  108  may control the operation of transfer head assembly  200  based on feedback signals received from various sensors, strain sensing elements, reference gages located on a pivot mount. For example, transfer head assembly  200  may include an actuator assembly for adjusting an associated micro pick up array (MPA)  103  retained by the transfer head assembly with at least three degrees of freedom, e.g., tipping, tilting, and movement in a z direction, based on feedback signals received from sensors associated with a pivot mount that carries MPA  103 . Computer  108  may also control movement of the transfer head assembly  200  along translation track  110  over the carrier substrate stage  104 , receiving substrate stage  106 , and cleaning stage  112  for holding an ECD. Additional actuators may be provided, e.g., between mass transfer tool  100  structural components and transfer head assembly  200 , cleaning stage  112 , carrier substrate stage  104 , or receiving substrate stage  106 , to provide movement in the x, y, or z direction for one or more of those sub-assemblies. For example, a gantry may support transfer head assembly  200  and move transfer head assembly  200  along an upper beam, e.g., in a direction parallel to an axis of motion of translation track  110 . Thus, in an embodiment an array of electrostatic transfer heads on MPA  103 , supported by transfer head assembly  200 , and a target substrate (e.g. supported by cleaning stage  112 , carrier substrate stage  104 , or receiving substrate stage  106 ) may be precisely moved relative to each other within all three spatial dimensions. 
     Referring to  FIG. 1B , a perspective view of a transfer head assembly  200  is shown in accordance with an embodiment. A transfer head assembly  200  may be used in combination with mass transfer tool  100  to transfer micro devices to or from a substrate, e.g., receiving substrate or carrier substrate, using micro pick up array (MPA)  103  which is supported by a pivot mount  300 . More particularly, transfer head assembly  200  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. Accordingly, transfer head assembly  200  may be incorporated in mass transfer tool  100  to adjust an MPA  103  relative to mass transfer tool  100 . Thus, transfer head assembly  200  may be fixed to a chassis of mass transfer tool  100 , e.g., at a location along translation track  110 . 
     As illustrated, the pivot mount  300  may include a base  302 , a pivot platform  304 , a plurality of primary spring arms  306 , and a plurality of secondary spring arms  307 , and the MPA  103  supporting a transfer head array  115  is mounted on the pivot platform  304 . In an embodiment, the transfer head array  115  is an electrostatic transfer head array  115 , where each transfer head operates in accordance with electrostatic principles to pick up and transfer a corresponding micro device. In an embodiment each electrostatic transfer head has a localized contact point characterized by a maximum dimension of 1-300 μm in both the x- and y-dimensions. In an embodiment, each electrostatic transfer head has a maximum dimension of 1 to 100 μm, or less. In some embodiments, each electrostatic transfer head has a maximum length and width of 20 μm, 10 μm, or 5 μm. 
     In an embodiment, the pivot mount  300  may communicate and send feedback signals to the mass transfer tool  100  through one or more electrical connections, such as a flex circuit  308 . Feedback may include analog signals from various sensors, strain sensing elements, reference gages that are used in a control loop to regulate actuation and spatial orientation of the transfer head assembly  200 . In an embodiment, the feedback signals are sent to a position sensing module located near the pivot mount  300  to reduce signal degradation by limiting a distance that analog signals must travel from a strain sensing element to the position sensing module. In an embodiment, the position sensing module is located within the transfer head assembly  200 . 
     Referring now to  FIG. 2A , a schematic cross-sectional side view illustration is provided of an MPA  103  positioned over a carrier substrate in accordance with an embodiment. As shown, the MPA  103  includes an electrostatic transfer head array  115  of electrostatic transfer heads  118 . The carrier substrate  114  is supported by the carrier substrate stage  104 . An array of micro devices  124  is supported by the carrier substrate  114 . Micro devices  124  may be a variety of devices, such as micro chips or micro LEDs. As shown, the micro pick array  103  is positioned over the carrier substrate  114 , with the electrostatic transfer heads  118  arranged such that each electrostatic transfer head  114  is positioned over a corresponding micro device  124 . In an embodiment, multiple transfer heads  118  may be positioned over a single micro device  124 . Referring now to  FIG. 2B , a schematic cross-sectional side view illustration is provided after the MPA has picked up an array of micro devices from the carrier substrate. Also illustrated is a contamination particle  126 . The contamination particle  126  may be attracted to the MPA  103  by the charged electrostatic transfer heads  118 , and interconnect or bus lines running through the MPA to supply the operating voltages to the electrostatic transfer heads  118 . Exemplary contamination particles  126  include dust particles, wear particles, and other contamination from the carrier substrate  114  that may accrue during fabrication and conditioning of the micro devices  124  for pick up from the carrier substrate  114 . 
     Referring now to  FIGS. 3A-3B  schematic cross-sectional side view illustrations are provided of an MPA prior to and after placing an array of micro devices on a receiving substrate  116  in accordance with an embodiment. In the particular embodiment illustrated, the MPA  103  holding the array of micro devices  124  and contamination particles  126  from  FIG. 2B  is moved over the receiving substrate  116 . The micro devices  124  are then brought into contact with contact pads  117  on the receiving substrate  116 , and bonded to the receiving substrate. For example, bonding may be accomplished by the transfer of energy, e.g. heat, from the transfer head assembly to the contact pads  117  to secure the micro devices  124  to the receiving substrate. In an embodiment, the transfer of heat may cause alloy bonding, eutectic bonding, or transient liquid phase bonding between conductive layers on the micro devices  124  and corresponding contact pads  117 . The micro devices  124  may then be released onto the receiving substrate  116 , for example, by changing the waveform of the operating voltage(s) of the electrostatic transfer heads  118 , turning off the operating voltages, and/or grounding. The MPA  103  is then moved vertically away from the receiving substrate  116 , leaving the placed micro devices  124  on the receiving substrate. 
     In the particular embodiment illustrated in  FIG. 3B , pre-existing contamination particles  126  that originated as described above with regard to  FIG. 2B  remain on the MPA  103 . As illustrated, additional contamination  126  is now shown on the MPA. The contamination particles  126  may be attracted to the MPA  103  by the charged electrostatic transfer heads  118 , and interconnect or bus lines running through the MPA to supply the operating voltages to the electrostatic transfer heads  118 . Exemplary contamination particles  126  include dust particles, wear particles, and other contamination from the receiving substrate  116 . Additionally, a non-transferred or mis-transferred micro device  124  remains on the MPA  103 . It is to be appreciated, that the particular embodiment illustrated in  FIG. 3B  is illustrative of an MPA  103  with an imperfect surface that may not be suitable for subsequent transfer operations, and that embodiments are not so limited. For example, other types of contamination may be present, or different configurations of non-transferred or mis-transferred micro devices may be present on the transfer surface. Accordingly, the particular embodiment illustrated is meant to be exemplary and not limiting. 
     Referring now to  FIGS. 4A-4C  schematic cross-sectional side view illustrations are provided of an MPA prior to, during, and after cleaning with an ECD in accordance with an embodiment. As shown, the MPA  103  is positioned over the ECD in  FIG. 4A , brought into close contact with the ECD in  FIG. 4B , and then vertically withdrawn away from the ECD in  FIG. 4C . In the particular embodiment illustrated, the contamination particles  126  and/or the non-transferred or mis-transferred micro devices from the MPA  103  illustrated in  FIG. 3B  are captured by and transferred from the MPA  103  to the electrodes  402  of the ECD  400  illustrated in  FIG. 4C . 
       FIG. 5  is a process flow of a cleaning operation in accordance with an embodiment. At operation  510  the transfer head assembly  200  (for example, holding the MPA  103  or another micro chip or MEMS device) is brought into close contact with the electrodes  402  of the ECD  400 , as also illustrated in  FIG. 4B . More specifically, any contamination particles  126  and/or micro devices  124  are brought into close contact with the electrodes  402  of the ECD  400 . For example, close contact may be 0-500 nm. At operation  520  a voltage is applied to the ECD  400 , and charge is allowed to build up on the electrodes  402  at operation  530 . For example, an exemplary operating voltage range may be between 50 V-500 V, or more specifically 100 V. Where a bipolar electrode is used, bipolar operating voltages are applied. Charge buildup may occur rapidly in accordance with embodiments in order to reduce time required for cleaning. For example, charge buildup may occur within approximately 10 milliseconds (ms) or less. The translatable transfer head assembly  200  is then withdrawn vertically away from the ECD  400  at operation  540 , resulting in a clean surface (e.g. clean MPA) where contamination previously on the device being cleaned is now retained on the ECD  400 . In an embodiment, the translatable transfer head assembly is withdrawn from the ECD  400  with a pure vertical motion. In such a manner, cleaning is accomplished electrostatically, without wiping, which may aid is preserving the mechanical integrity of both the ECD  400  and surface being cleaned (e.g. MPA  103 ). At operation  550  the voltage is removed from the ECD  400  and the electrodes  402  are discharged at operation  560 . At operation  570  the ECD  400  is moved to a different position relative to the transfer head assembly  200  aligning a still clean surface of the ECD  400  under the transfer head. In an embodiment the process flow in  FIG. 5  is repeated until the MPA  103  or other microchip is clean. 
       FIGS. 6A-6B  are schematic top view illustrations of an ECD prior to and after cleaning an MPA in accordance with an embodiment. The particular embodiment illustrated is a bipolar electrode configuration, though other electrode configurations are possible, including monopolar electrode and other multiple electrode configurations. As shown, cleaning electrode area  410  includes a first electrode pattern  405 A of first electrodes  402 A. In the embodiment illustrated, the first electrode pattern  405  is in a comb configuration and is interdigitated with a second electrode pattern  405 B of second electrodes  402 B also with a comb configuration, with each comb configuration including interdigitated fingers as electrodes  402 A,  402 B. A interconnect line  404 A is electrically connected with the first electrodes  402 A, and a second interconnect line  404 B is electrically connected with the second electrodes  402 B. In a bipolar configuration, opposite voltages may be applied to  402 A,  405 A,  404 A and  402 B,  405 B,  404 B. 
     Referring to  FIG. 6B , contamination particles  126  and micro devices  124  are retained by at least one electrode  402 A,  402 B, referred to generically as electrode  402 . In accordance with embodiments, precise alignment is not required for cleaning. For example, particle contamination may fall between the ECD  400  electrodes  402  or may be retained one or more electrodes  402 , or span across multiple electrodes  402 . In the context of micro device transfer and cleaning, the speed of charge build up on the ECD electrodes  402  is determinative of the cleaning cycle time, with small capacitances resulting in faster cycle times. In an embodiment, the ECD  400  is able to attract and retain particles ranging from 0.25 μm to 25 μm, minimum length or width, at an operating voltage of 50 V to 500 V. Size and spacing of the electrodes  402 , as well as distance to the particle contamination or micro device, contributes to the ECD pull force. In an embodiment, line width of the electrode  402  fingers is approximately 2 μm, with an approximately 1 μm gap separating adjacent electrode  402  fingers. These dimensions are exemplary, and represent adequate feature sizes that may be obtained using a stepper and lithographic patterning for electrodes  402  definition. 
       FIG. 7  is a process flow of a method of operating a mass transfer tool including inspection and cleaning operations in accordance with an embodiment. At operation  710  a translatable transfer head assembly is positioned over carrier substrate  104  and an array of micro devices  124  is picked up from the carrier substrate with a micro pick up array  103  retained by the translatable transfer head assembly. The translatable transfer head assembly  200  is then translated along the translation track  110  toward the receiving substrate  116 . During the translation, the bottom surface of the micro pick up array  103  is inspected by the upward facing inspection camera  120  at inspection operation  720 . At operation  730  it is determined whether a cleaning operation is necessary. For example, this may be determined with computer  108 . If a threshold amount of micro devices were not picked up or contamination particles are detected, then the MPA  103  is cleaned at operation  740 . Following the cleaning operation  740 , the ECD is indexed to a clean location at operation  780 . For example, the ECD can be indexed my moving the cleaning stage  112  in an x and/or y direction. The MPA  103  may then be moved over the carrier substrate to restart the pick and place procedure or the inspection operation  720  or cleaning operation  730  may optionally be repeated. If a cleaning operation was not necessary, then the micro devices picked up at operation  710  are placed on the receiving substrate at operation  750 . The translatable transfer head assembly  200  is then translated along the translation track  110  toward the carrier substrate  114 . During the translation, the bottom surface of the micro pick up array  103  is inspected by the upward facing inspection camera  120  at inspection operation  760 . At operation  770  it is determined whether a cleaning operation is necessary. For example, this may be determined with computer  108 . If any micro devices remain on the MPA  103  or a threshold amount of contamination is observed, then the MPA is cleaned at operation  740 . If a cleaning operation is not required, then the transfer head assembly is moved over the carrier substrate and the pick and place procedure can be repeated. 
     Referring to  FIG. 8 , a schematic illustration of a computer system is shown that may be used in accordance with an embodiment. Portions of embodiments are comprised of or controlled by non-transitory machine-readable and machine-executable instructions that reside, for example, in machine-usable media of a computer  108 . Computer  108  is exemplary, and embodiments may operate on or within, or be controlled by a number of different computer systems including general purpose networked computer systems, embedded computer systems, routers, switches, server devices, client devices, various intermediate devices/nodes, stand-alone computer systems, and the like. 
     Computer  108  of  FIG. 8  includes an address/data bus  802  for communicating information, and a central processor  804  coupled to bus  802  for processing information and instructions. Computer  108  also includes data storage features such as a computer usable volatile memory, e.g. random access memory (RAM)  806 , coupled to bus  802  for storing information and instructions for central processor  804 , computer usable non-volatile memory  808 , e.g. read only memory (ROM), coupled to bus  802  for storing static information and instructions for the central processor  804 , and a data storage device  810  (e.g., a magnetic or optical disk and disk drive) coupled to bus  802  for storing information and instructions. Computer  108  of the present embodiment also includes an optional alphanumeric input device  812  including alphanumeric and function keys coupled to bus  802  for communicating information and command selections to central processor  804 . Computer  108  also optionally includes an optional cursor control  814  device coupled to bus  802  for communicating user input information and command selections to central processor  804 . Computer  108  of the present embodiment also includes an optional display device  816  coupled to bus  802  for displaying information. 
     The data storage device  810  may include a non-transitory machine-readable storage medium  818  on which is stored one or more sets of instructions (e.g. software  820 ) embodying any one or more of the methodologies or operations described herein. For example, software  820  may include instructions, which when executed by processor  804 , cause computer  108  to control mass transfer tool  100  as described above for performing pick and place, inspection, and cleaning operations. Software  820  may also reside, completely or at least partially, within the volatile memory, non-volatile memory  808 , and/or within processor  804  during execution thereof by computer  108 , volatile memory  806 , non-volatile memory  808 , and processor  804  also constituting non-transitory machine-readable storage media. 
     Referring now to  FIGS. 9A-9E  schematic top view illustrations are provided of a method of forming an electrostatic cleaning device in accordance with an embodiment. As shown in  FIG. 9A , one or more cleaning electrode areas  410  are formed on or in substrate  401 . In an embodiment, a plurality of laterally separate cleaning electrode areas  410  are formed in the substrate  401 . For example, this may be accomplished by etching electrodes  402  into the substrate  401 . Following the formation of the one or more cleaning electrode areas  410 , interconnect lines  404  and trace lines  412  are formed. For example this may be accomplished by etching interconnects lines  404  and trace lines  412  into the substrate  401 . In an embodiment, each separate cleaning electrode area  410  includes separate corresponding trace lines  412 . A dielectric layer may then be formed over the substrate  401 , covering the cleaning electrode areas  410 , interconnect lines  404 , and trace lines  412 . Referring now to  FIG. 9C , electrode contact holes  420 , and optionally ground contact holes  422  are formed. For example, electrode contact holes  420  may be formed through the dielectric layer to expose the trace lines  412 , and the ground contact holes  422  may be formed into the substrate  401 . Conductive contacts  430 ,  432  may then be formed over the electrode contact holes  420  and ground contact holes  422  as illustrated in  FIG. 9D . A close up view of Detail F shown in  FIG. 9D  is described in further detail below with regard to  FIG. 9F . Referring now to  FIG. 9E , in an embodiment, a flex circuit  440  is coupled with the conductive contacts  430 ,  432  on the substrate  401 . For example, the flex circuit  440  can be used to connect the ECD  400  with operating voltage contacts, and optionally a ground on the cleaning stage  112 . In an embodiment, the flex circuit  440  includes or is coupled with a multiplexer in order to independently control each of the separate cleaning electrode areas  410  such that only a single cleaning electrode area  410  is charged at a time in the resultant ECD  400 . Inclusion of a flex circuit is not required, however. For example, in an embodiment, via plugs are formed in the substrate  401  for providing back side contacts. 
     Referring now to  FIG. 9F , a close up illustration of Detail F in  FIG. 9D  is provided in accordance with an embodiment. As illustrated, electrode trace line  412 A is coupled with interconnect line  404 A, which in turn is connected with the first electrode pattern  405 A (as described above), and electrode trace line  412 B is coupled with interconnect line  404 B, which in turn is connected with the second electrode pattern  405 B (as described above). In the embodiment illustrated, the first and second electrode patterns  405 A,  405 B form an interdigitated comb configuration, and the interconnect lines  404 A,  404 B are on opposite sides of the cleaning electrode area  410 . Also illustrated, the trace lines  412 A,  412 B are connected at midpoints of the interconnect lines  404 A,  404 B. 
       FIGS. 10A-18C  are schematic cross-sectional side view illustrations taken along lines A-A, B-B, C-C, and D-D in  FIG. 9F  and schematic top view illustrations of a method of forming an electrostatic cleaning device in accordance with an embodiment. Thus, it is to be appreciated that  FIGS. 10A-18C  are condensed schematic views combining structural features from various areas of the substrate used to form the ECD. Furthermore, in the following description a method and structure for forming an ECD are described, beginning with a silicon-on-insulator (SOI) substrate. The following description is exemplary of one method of forming an ECD, and embodiments are not so limited. For example, it is not required to use silicon, or an SOI substrate for the formation of an ECD, and other materials and substrates may be used. 
     Referring now to  FIGS. 10A-10B , in an embodiment, the substrate  401  includes a base substrate  404 , insulator layer  406 , and device layer  408 . For example, substrate  401  may be an SOI substrate including a silicon base substrate  404 , silicon device layer  408 , and buried oxide (e.g. SiO 2 ) layer  406 . In an embodiment, substrate  401  is an SOI substrate with (100) base Si substrate  404  with a thickness of approximately 500 μm, approximately 1 μm thick insulator layer  406 , and approximately 2 μm thick device layer  408 . In an embodiment, device layer  408  is doped. For example, device layer may be doped with boron for a resistivity of 0.01-0.1 ohm·cm. 
     Referring to  FIGS. 11A-11B , the cleaning electrode areas  410  may be etched into the device layer  408 . As shown, electrodes  402  (including  402 A,  402 B) are formed in the device layer  408  with gaps  403  separating adjacent electrode  402  lines. In an embodiment, electrode  402  lines are approximately 2 μm wide, and separated by a gap  403  of approximately 1 μm. In an embodiment, photoresist is patterned with a stepper, followed by dry reactive ion etching (DRIE) to etch the gaps  403  into the device layer  408 , stopping on the underlying insulator layer  406 . 
     A photoresist layer  422  may then be formed over the patterned device layer  408  as illustrated in  FIGS. 12A-12B , followed by the formation of openings  413  in the photoresist layer  422  as illustrated in  FIGS. 13A-13B . As show, the covered portions of the photoresist layer  422  will correspond to the interconnect lines  404 A,  404 B and trace lines  412 A,  412 B. Referring now to  FIGS. 14A-14B , the device layer  408  is then etched through openings  413 , stopping on the insulator layer  406  to form the interconnect lines  404 A,  404 B and trace lines  412 A,  412 B. 
     A dielectric layer  418  is then formed over the patterned device layer  408  as illustrated in  FIGS. 15A-15B . As shown, dielectric layer  418  may be formed over the cleaning electrode area  410  including electrodes  402 , interconnect lines  404 , and trace lines  412 . In an embodiment, the dielectric layer is SiO 2  or Al 2 O 3 . In an embodiment, the dielectric layer  418  is formed by atomic layer deposition (ALD). For example, the dielectric layer  418  may be approximately 0.5 μm thick ALD Al 2 O 3 . In other embodiments, alternative materials and thicknesses may be used to accomplish a specified capacitance of the ECD  400 . Dielectric layer  418  may also include multiple dielectric layers. 
     Referring now to  FIGS. 16A-17B , electrode contact holes  420 , and optionally ground contact holes  422  are formed. For example, electrode contact holes  420  may be formed through the dielectric layer  418  to expose the trace lines  412  using a suitable technique such as ion milling through the Al 2 O 3  layer, and the ground contact holes  422  may be formed through the device layer  408  and insulator layer  406  using a suitable technique such as reactive ion etching (RIE) to expose the base substrate  404 . Conductive contacts  430 ,  432  may then be formed over the electrode contact holes  420  and ground contact holes  422  as illustrated in  FIG. 18A-18B , with the conductive contacts  430  making electrical contact with the trace lines  412  and the conductive ground contacts  432  making electrical contact with the base substrate  404 . In an embodiment, the conductive contacts  430 ,  432  are formed of a TiW/Au metal layer stack. For example, the conductive contacts  430 ,  432  may be formed by blanket deposition followed by wet etching. 
       FIG. 18C  is a cross-sectional side view illustration of ECD including one or more via plugs  450  formed within a via opening  452  in the base substrate  404 . With such a configuration, the via plug  450  is electrically isolated from the base substrate  404 . As illustrated the conductive contact  430  is formed through the device layer  408  and insulator layer  406 , and on the via plug  450 . The conductive contact  430  makes electrical contact with the corresponding trace line  412  and via plug  450 . A back side contact  454  is formed on the bottom surface of the via plug to make a back side electrical connection with the ECD  400 . Back side contact  454  may be formed of a similar material as conductive contact  430 . 
     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 forming an ECD and MTT with integrated ECD. 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.

Metadata:
Filing Date: 20160314
Publication Date: 20201013
Grant Date: 20201013
Priority Date: 20150401
Inventors: BATHURST, Stephen P.
HIGGINSON, JOHN A.
GOLDA, DARIUSZ
KIM, HYEUN-SU
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L21/67028", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L21/6833", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/67028", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/67721", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L21/67288", "inventive": true, "first": false, "tree": "[]"}, {"code": "B08B6/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/67028", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/67288", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/67721", "inventive": true, "first": true, "tree": "[]"}, {"code": "B08B6/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/6833", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55640904