Selective release and transfer of microdevices

Abstract

A method of selectively transferring microdevices from a donor substrate to contact pads on a receiver substrate is disclosed. The method can include providing a donor substrate including a plurality of microdevices, transferring the plurality of microdevices to an intermediate substrate, aligning a selected set of microdevices on the intermediate substrate proximate to a system substrate, providing a photosensitive layer between the selected set of microdevices and the system receiver, activating the selected set of microdevices to cure the photosensitive layer between the selected set of microdevices and the system substrate with light emitted by the selected set of microdevices, and bonding the selected set of microdevices to corresponding contact pads on the system substrate.

Description

[0001] Cross-reference of related applications

[0002] This application claims the benefit and priority of U.S. Patent Application No. 62 / 852,555, filed May 24, 2019, which is hereby incorporated herein by reference in its entirety.

[0003] Background Technology and Technical Field

[0004] The present invention relates to integrating microdevices into a system substrate, and more particularly, to structures and methods for transferring and bonding selective microdevices from an donor substrate to a receiver substrate.

[0005] Typically, numerous microdevices, including light-emitting diodes (LEDs), organic LEDs, sensors, solid-state devices, integrated circuits, MEMS (microelectromechanical systems), and other electronic components, are often mass-produced on planar substrates. To form an operational system, microdevices from at least one donor substrate need to be selectively transferred to a receiver substrate.

[0006] Various methods have been employed to transfer microdevices from donor substrates to receiver substrates. In one approach, receiver forces are selectively generated to improve selectivity during microdevice transfer. Receiver forces can be generated using mechanical, thermal, or electrostatic techniques; however, these techniques present problems. They typically require complex mechanical structures for the transfer. In another method, which is very difficult to perform physically, localized heating can be selectively activated to locally increase the temperature.

[0007] In another transfer method, localized epoxy photocuring can be used to photocur the microdevice from the donor substrate to the receiver substrate. However, limitations and difficulties arise in controlling the spot size of the external light source and in eliminating astigmatism. This results in undesirable curing and transfer of adjacent microdevices within close proximity. In these alternative methods, the technology is limited in miniaturizing device size and increasing the density of microdevices on the substrate.

[0008] Therefore, there is a need for improved methods and systems for efficiently releasing microdevices (specifically, microLEDs) from the donor substrate and transferring them to the receiver substrate. Summary of the Invention

[0009] One objective of the present invention is to provide a method and structure for transferring and bonding selective microdevices from an donor substrate to a receiver substrate.

[0010] Another objective of the present invention is to provide a transfer method in which a cartridge substrate has a bonding material that releases a microdevice to a receiver substrate in the presence of light, while simultaneously bonding the same photocurable device to the receiver substrate.

[0011] According to one embodiment, a method for integrating a plurality of microdevices on a system substrate may be provided. The method may include: providing an donor substrate comprising a plurality of microdevices; transferring the plurality of microdevices to an intermediate substrate; aligning a selected set of microdevices on the intermediate substrate close to a system substrate; providing a photosensitive layer between the selected set of microdevices and a system receiver; curing the photosensitive layer between the selected set of microdevices and the system substrate by light emitted by the selected microdevices; and bonding the selected set of microdevices to corresponding contact pads on the system substrate.

[0012] In one embodiment, the photosensitive layer may comprise a visible light-curable transparent epoxy resin or a photoresist layer. In another embodiment, the photosensitive layer may comprise an adhesive.

[0013] According to another embodiment, transferring the set of selected microdevices to the corresponding contact pads on the system substrate may include: coating at least a portion of the system substrate with the photosensitive layer, aligning and pressing the intermediate substrate against the system substrate such that each of the selected microdevices is aligned with the corresponding contact pad on the system substrate, activating the set of selected microdevices; and curing the photosensitive layer.

[0014] According to yet another embodiment, the microdevice is fabricated on the donor substrate.

[0015] According to one embodiment, a sidewall reflector may be provided on or above the microdevice on the substrate to reflect light back toward the microdevice.

[0016] According to some other embodiments, a sacrificial release layer may be conformally coated on or over the microdevice on the donor substrate. The sacrificial layer may be a photoresist layer.

[0017] According to one aspect of the invention, light can be reflected from the sidewall reflector.

[0018] According to another embodiment, a transparent planarization layer can be provided for the final device structure on a backplane substrate.

[0019] According to one aspect of the invention, controlled communication capabilities are provided for microdevices on an donor substrate.

[0020] According to another aspect of the invention, self-emission curing can be provided by locally focusing the light of a microdevice.

[0021] According to one aspect of the present invention, a method for selectively transferring at least one microLED can be provided.

[0022] According to another aspect of the invention, the method of the invention typically requires a simple mechanical structure for transfer.

[0023] According to another aspect of the invention, the method of the present invention typically requires light to cure the photosensitive layer, compared to heat and pressure in other conventional methods.

[0024] The foregoing and additional aspects of the invention, as well as the embodiments, will be apparent to those skilled in the art from the various embodiments and / or aspects made with reference to the drawings (a brief description of which is provided below). Attached Figure Description

[0025] The foregoing content and other advantages of the present invention will immediately become apparent after reading the following embodiments and referring to the drawings.

[0026] Figure 1 The illustration shows a cross-sectional view of an donor substrate with microdevices according to all embodiments of the present invention.

[0027] Figure 2 The illustration shows a cross-sectional view of a temporary substrate integrated with a circuit of an integrated microdevice according to an embodiment of the present invention.

[0028] Figure 3 The illustration shows a cross-sectional view of the removal of the donor substrate according to an embodiment of the present invention.

[0029] Figure 4 The illustration shows a cross-sectional view of selectively removing the sacrificial layer according to an embodiment of the present invention.

[0030] Figure 5 The illustration shows a cross-sectional view of a microdevice integrated into a backplane using a visible light-curable photoresist / epoxy resin according to an embodiment of the present invention.

[0031] Figure 6 The illustration shows a cross-sectional view illustrating the use of a temporary substrate to transfer other sets of microdevices according to an embodiment of the present invention.

[0032] Figure 7 The illustration shows a cross-sectional view of a transparent planarization layer on a backplate substrate according to an embodiment of the present invention.

[0033] Figure 8A The illustration shows a cross-sectional view of the top side of a metal reflector according to an embodiment of the present invention.

[0034] Figure 8B The illustration shows a cross-sectional view of a metal reflector used for back-side emission according to an embodiment of the present invention.

[0035] Figure 8C The illustration shows a cross-sectional view of top-side emission via a distributed Bragg reflector according to an embodiment of the present invention.

[0036] Figure 8D The illustration shows a cross-sectional view of back-side emission via a distributed Bragg reflector according to an embodiment of the present invention.

[0037] Figure 9 This invention illustrates a series of steps for transferring and bonding a microdevice to a backplane according to an embodiment of the invention.

[0038] Using the same reference number in different drawings indicates similar or identical elements.

[0039] The foregoing and additional aspects of the invention, as well as the embodiments, will be apparent to those skilled in the art from the various embodiments and / or aspects described with reference to the drawings (a brief description of the drawings is provided below). Detailed Implementation

[0040] While the invention is readily adaptable to various modifications and alternatives, specific embodiments or implementations are illustrated by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the specific forms disclosed. Rather, the invention encompasses all modifications, equivalents, and alternatives falling within the spirit of the invention as defined by the appended claims.

[0041] In this specification, the terms "system substrate," "receiver substrate," and "display substrate" are used interchangeably. However, it will be apparent to those skilled in the art that the embodiments described herein are independent of substrate type.

[0042] In this specification, the terms "donor substrate" and "carrier substrate" are used interchangeably. However, it will be apparent to those skilled in the art that the embodiments described herein are independent of substrate type.

[0043] In this specification, the terms "temporary substrate," "intermediate substrate," and "cassette substrate" are used interchangeably. However, it will be apparent to those skilled in the art that the embodiments described herein are independent of substrate type.

[0044] In this specification, the terms "wafer" and "substrate" are used interchangeably. However, it will be apparent to those skilled in the art that the embodiments described herein are independent of substrate type.

[0045] Furthermore, these embodiments illustrate four micro-light-emitting devices, but the invention is not limited thereto. The number of micro-light-emitting devices can be changed according to actual needs.

[0046] Figure 1 The illustration shows a cross-sectional view of an donor substrate having microdevices according to an embodiment of the present invention.

[0047] Here, microdevices (e.g., GaN LEDs) are fabricated by depositing material stacks on a sapphire substrate. The microdevice structure can take the form of one of the following: cylindrical structure, mesa structure, hip chip structure, or vertical structure.

[0048] GaN LED device 102 includes a donor substrate 100 (e.g., sapphire), an n-type GaN layer or buffer layer 106 (e.g., undoped GaN) formed on the substrate 100, an active layer (e.g., multiple quantum well (MQW)) layer, and a p-type GaN layer. A transparent conductive layer (e.g., Ni / Au or ITO) is typically formed on the p-doped GaN layer for better lateral current conduction. The donor substrate can be a growth substrate or a carrier substrate. Typically, p-type metal contacts 112-p, such as Pd / Au, Pt, or Ni / Au, are then formed on the transparent conductive layer. Since the substrate (sapphire) is an insulator, the n-type GaN is exposed to contact this layer. This step is typically accomplished using a dry etching process to expose the n-type GaN and then depositing appropriate metal contacts, such as n-type metal contacts 112-n.

[0049] In some embodiments, a sidewall reflector 108 may be deposited over the microdevice on the donor substrate to reflect light back toward the sidewall of the microdevice. In one case, the reflector may be made of a metal (e.g., Ag, Al, Au). In another case, the reflector may be made of a distributed Bragg reflector.

[0050] In either case, these sidewall reflectors should be optimized to have high reflectivity for the emission spectrum of the specific microLED. For example, a red LED may have a different reflector than a blue LED, based on which one is more efficient at reflecting at the stated wavelength (color).

[0051] In one embodiment, the microdevice may be conformally coated with a sacrificial release layer 110, which may consist of a photoresist layer, a metal layer, or a conformal dielectric layer. However, the composition of the sacrificial layer is not limited to the materials listed above. In one case, the sacrificial release layer 110 must be selectively etched with respect to the sidewall reflector 108.

[0052] In another embodiment, a passivation layer may be provided around the microdevice on the donor substrate. In one case, the passivation layer may be a dielectric layer to isolate the sidewalls of the microLED. In another case, the passivation layer may be polyimide.

[0053] Then, for example, the dielectric layer and sidewall reflector 108 can be patterned by using photolithography patterning and etching to partially expose the top surface of the microLED.

[0054] Figure 2The illustration shows a cross-sectional view illustrating the integration of a temporary substrate with an donor substrate having integrated microdevices according to all embodiments of the present invention. (Reference) Figure 2 Embodiments of the present invention include a substrate 100, a microdevice 102, and a driving circuit layer 120. A buffer layer 106 may be deposited between the substrate 100 and the microdevice 102. The buffer layer (or layer) may serve as a release layer and for separating the fully integrated system from the substrate 100. A planarization layer 116 is developed over and around the microdevice 102. The planarization layer 116 may consist of several different layers and materials. An opening / via 118 is then formed (e.g., etched) into the planarization layer 116, down to the photoresist layer. In one case, the via is formed by depositing a conductive material, such as a metal, or a transparent conductive oxide into a trench. In one example, the via is formed by sputtering metal into a trench. The photoresist may be removed from localized areas.

[0055] The temporary substrate 114 can then be bonded to the microdevice by placing the driving circuit layer 120 in the opening, thereby allowing the driving circuit layer to be patterned for individual microdevices. The driving circuit layer 120 may be a thin-film transistor (TFT), a CMOS chiplet, or other type of integrated circuit. In one case, the temporary substrate 114 may be a glass substrate or a sapphire substrate.

[0056] Figure 3 The diagram illustrates a cross-sectional view illustrating the removal of the donor substrate according to an embodiment of the invention. In one embodiment, the donor substrate 100 can be removed after the temporary substrate 114 is installed. The donor substrate 100 can be removed from the lateral functional device. In one case, laser stripping can be used to remove the donor substrate. The donor substrate can be irradiated with a laser to peel the microdevice from the donor substrate and transfer it to the temporary substrate. In another case, particularly in the case of red microdevices, chemical stripping can be used to remove the donor substrate. Chemical stripping may be a preferred option for removing the donor substrate when the red LED is made of GaAs on a GaAs donor substrate. However, chemical stripping can be used on any other type of microdevice made of GaN on a sapphire substrate, such as blue and green microdevices.

[0057] According to one embodiment, the microdevice on the donor substrate may have different anchors, which hold the device to the donor substrate after it has been peeled off. The anchors may also be connected to the donor substrate directly or indirectly through other layers.

[0058] In the next step, the GaN buffer layer 122 and passivation layer on each side of the microdevice can be etched back. ICP etching can be used to etch the GaN and passivation layer to ~1µm to 2µm for optical focusing.

[0059] Figure 4The illustration shows a cross-sectional view illustrating the selective removal of a sacrificial layer according to an embodiment of the present invention. In one embodiment, a sacrificial layer 110 coated above a microLED can be removed. In one example, the microdevice may be covered by a sacrificial layer that can be debonded from a temporary substrate by chemical, optical, thermal, or mechanical force. The debonding method can be selective or global. The sacrificial layer can be removed by solution treatment (e.g., solvent stripping or acid etching). Removing the sacrificial layer facilitates the release process of the microdevice.

[0060] In one scenario, the planarization layer 126 can be etched back or plasma etched.

[0061] The process of transferring a microdevice from the cartridge to the receiver substrate can be based on different mechanisms.

[0062] Figure 5 The illustration shows a cross-sectional view of microdevices integrated into a backplane using a visible-light-curable photoresist / epoxy resin according to an embodiment of the present invention. After removing the sacrificial layer, the next step may be to bond the microdevices to the receiver substrate. Reference Figure 5 The receiver substrate may have contact pads for coupling or connecting microdevices. Microdevices can be coupled or connected to a driving circuitry system 134 on the receiver substrate via the contact pads. The driving circuitry system may be a thin-film transistor (TFT), CMOS chiplet, or other type of integrated circuit formed on the receiver substrate. Here, the receiver substrate 128 may be fabricated separately. A temporary substrate may be aligned with the receiver substrate such that the selected microdevice is aligned with the corresponding contact pad. The temporary substrate and the receiver substrate may be moved together until the selected microdevice is positioned at a defined distance from the contact pad. This defined distance may correspond to full or partial contact, but is not limited to this. In other words, it may not be absolutely necessary for the selected microdevice to actually touch the corresponding contact pad, but it must be close enough that the forces described below can be manipulated.

[0063] In one embodiment, a thin layer / film of photosensitive layer / visible light 130 (e.g., a red light-curable photoresist or epoxy resin) may be selectively or globally applied / coated over receiver substrate 128. The layer / film should not be cured until the microLED emits light into the film, at which point the light cures the film. This causes the microLED to bond to the backplane. The adhesive force of the bond is stronger than the force holding the microLED to the cartridge. When the cartridge is lifted, the anchor will break and the microLED will be transferred to the backplane.

[0064] In one aspect, a temporary substrate can be aligned and pressed against a backplane / system substrate such that each of the selected microdevices aligns with a contact pad on the system substrate. The selected microdevices can actually touch the corresponding contact pads on the receiver pads. Microdevice 132 can be activated. A group of selective microdevices or all microdevices can be activated. Light can be reflected from a sidewall reflector. Since the reflector is actually embedded in a visible light-curable photoresist / epoxy resin, light leakage and curing are minimized in close proximity to the device. The visible light-curable epoxy resin can be cured. In one case, the epoxy resin is cured with light. In another case, it can be cured with heat or pressure. A group of selected microdevices can be transferred to corresponding contact pads on the system substrate.

[0065] This method can be applied multiple times to the same receiver substrate using different or the same intermediate substrates.

[0066] In one scenario, after all devices have been transferred, the uncured photosensitive layer (where no device exists) can be removed using a developer solution.

[0067] Figure 6 The illustration depicts a cross-sectional view illustrating the use of a temporary substrate for transferring other sets of microdevices according to an embodiment of the present invention. The temporary substrate is moved apart from the receiver substrate, thereby attaching the selected microdevice to the corresponding contact pad, such as... Figure 6 As shown in the image.

[0068] Once the temporary substrate is separated from the receiver substrate, further processing steps can be performed. For example, the temporary substrate 136 can be realigned with the receiver substrate 128, and the steps can be repeated to transfer a different set of microdevices to a different set of contact pads until the temporary substrate is empty.

[0069] If the receiver substrate is filled, it can be moved to the next step. If the receiver substrate requires further filling, further transfer steps from one or more additional cartridge substrates can be performed. Before a new transfer cycle, if the cartridge does not have enough devices, the cycle begins from the first step. If the cartridge substrate has enough microdevices, the cartridge substrate is offset (or moved and aligned) to a new area of ​​the receiver substrate in a subsequent step.

[0070] In one example, a second photocurable layer may be provided between a second set of selected microdevices and a second set of contact pads, the second set of selected microdevices being different from the selected microdevices and the second set of contact pads being different from the selected contact pads on the receiver substrate. The intermediate substrate 136 and the receiver substrate 128 may then be realigned such that each of the second set of selected microdevices is aligned with the second set of contact pads on the receiver substrate. The donor substrate and the receiver substrate may be moved together until each of the second set of selected microdevices is in contact with or near the second set of contact pads and the second photocurable layer on the receiver substrate.

[0071] Figure 7 The diagram illustrates a cross-sectional view of a transparent planarization layer on a backplane substrate according to an embodiment of the present invention. Further processing steps can be performed once the temporary substrate is separated from the receiver substrate. In one aspect, a transparent planarization layer 138 may be provided for the final device structure on the backplane substrate. This planarization layer may be etched down to metal contacts on the microLED. Through-holes may be formed in the planarization layer to control the LED.

[0072] Figure 8A The illustration shows a cross-sectional view of top-side emission using a metal reflector according to an embodiment of the present invention. Here, the common top contact can be a patterned electrode system 140, through which microdevices can be connected to a backplane via openings / vias 142 in a planarized layer. The common top electrode 140 can be composed of a transparent conductive oxide (e.g., ITO) deposited by physical vapor deposition. However, the common top electrode is not limited to these materials. The metal reflector can be composed of reflective conductors such as Au, Ag, Cr, etc., and deposited by physical vapor deposition. However, the metal reflector is not limited to these materials. The backplane can control and communicate with at least one microLED at any given time.

[0073] Figure 8B The diagram illustrates a cross-sectional view of back-side emission using a metal reflector according to an embodiment of the present invention. Here, the drive circuit layer 144 can be patterned for individual microdevices. It can be passive or optimized for release.

[0074] Figure 8C The illustration shows a cross-sectional view of top-side emission via a distributed Bragg reflector according to an embodiment of the present invention. (Reference) Figure 8C Instead of using metallic reflectors on the sidewalls of the microdevice, distributed Bragg reflectors 148 can be used. These are highly reflective structures made of alternating dielectric layers with different reflectivities. Examples of Bragg reflectors consist of alternating layers of Si and Mo or TiO2 and SiN. However, the composition of Bragg reflectors is not limited to these materials. The materials can be deposited using physical vapor deposition.

[0075] Figure 8D The diagram illustrates a cross-sectional view of back-side emission via a distributed Bragg reflector according to an embodiment of the present invention. Here, the drive circuit layer 144 can be patterned for individual microdevices. It can be passive or optimized for release.

[0076] Figure 9 A flowchart illustrating a method 900 for transferring and bonding microdevices to a backplane according to an embodiment of the present invention is provided. In step 902, a plurality of microdevices are provided on an donor substrate. In step 904, the plurality of microdevices are transferred to an intermediate substrate. Then, in step 906, the microdevices are aligned close to a system substrate. In step 908, a photosensitive layer is provided between a selected set of microdevices and the system substrate. Then, in step 910, the selected set of microdevices is turned on, and the photosensitive layer between the selected set of microdevices and the system substrate can be cured by light emitted by the selected microdevices. In step 912, the selected microdevices are bonded to corresponding contact pads on the system substrate.

[0077] According to one embodiment, a method for integrating a plurality of microdevices on a system substrate may be provided. The method may include: providing an donor substrate comprising a plurality of microdevices; transferring the plurality of microdevices to an intermediate substrate; aligning a selected set of microdevices on the intermediate substrate in proximity to the system substrate; providing a photosensitive layer between the selected set of microdevices and a system receiver; and transferring the selected set of microdevices to corresponding contact pads on the system substrate.

[0078] According to another embodiment, the photosensitive layer may include a visible light curable transparent epoxy resin or a photoresist layer or an adhesive.

[0079] According to another embodiment, transferring the selected set of microdevices to corresponding contact pads on a system substrate may include: coating at least a portion of the system substrate with a photosensitive layer; aligning and pressing an intermediate substrate against the system substrate such that each of the selected microdevices is aligned with a corresponding contact pad on the system substrate; activating the selected set of microdevices; and curing the photosensitive layer. The photosensitive layer is cured by applying light.

[0080] According to some other embodiments, the method may further include removing an intermediate substrate.

[0081] According to some embodiments, the step of providing an donor substrate including a microdevice includes: fabricating a microdevice on the donor substrate; mounting a reflector on a sidewall of the microdevice on the donor substrate; conformally depositing a sacrificial layer on or above the microdevice; and providing a planarization layer on or above the microdevice.

[0082] According to another embodiment, the planarization layer may be patterned to form an opening on the top of the microdevice for connection to an intermediate substrate.

[0083] According to another embodiment, the sacrificial layer may include one of the following: a photoresist layer, a metal layer, or a conformal dielectric layer. The sacrificial layer may be removed before aligning the microdevices on the intermediate substrate close to the system substrate. Etching or photolithography may be used to pattern the sidewall reflectors to expose the top surface of the microdevices.

[0084] According to one embodiment, a microdevice can be fabricated on an donor substrate, the microdevice comprising one of the following: a cylindrical structure, a mesa structure, a flip-chip structure, or a vertical structure.

[0085] According to another embodiment, the step of transferring multiple microdevices to an intermediate substrate may include: providing an anchor for holding each microdevice to the donor substrate; and removing the donor substrate. The donor substrate is removed by one of the following: laser lift-off or chemical etching.

[0086] According to some embodiments, removing the intermediate substrate may include breaking the anchor of the selected set of microdevices. The intermediate substrate may include a patterned driving circuit layer. The patterned driving layer may include a TFT. The system substrate is one of a sapphire substrate or a glass substrate.

[0087] According to another embodiment, the method may further include: aligning a second set of selected microdevices on an intermediate substrate a second time near the system substrate; providing a second photosensitive layer between the second set of selected microdevices and the system substrate; moving the intermediate substrate to the system substrate such that each of the second set of selected microdevices is aligned with a corresponding second selected contact pad on the system substrate; activating the second set of selected microdevices; curing the photosensitive layer between the second set of selected microdevices and the system substrate; and bonding the second set of selected microdevices to a corresponding second contact pad on the system substrate.

[0088] According to another embodiment, the photosensitive layer can be applied globally or selectively.

[0089] According to one embodiment, the method may further include providing a transparent planarization layer over the system substrate after removing the intermediate substrate and removing the uncured photosensitive layer with a developer solution.

[0090] In summary, methods and structures for transferring and bonding microdevices from donor substrates to receiver substrates are provided.

[0091] The foregoing description of one or more embodiments of the invention has been presented for illustrative and descriptive purposes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible based on the teachings herein. The scope of the invention is not intended to be limited by this embodiment, but rather by the appended claims.

Claims

1. A method of integrating a plurality of micro devices on a system substrate, comprising: providing a donor substrate comprising the plurality of micro devices; transferring the plurality of micro devices to an intermediate substrate; aligning a set of selected micro devices on the intermediate substrate proximate to the system substrate; moving the intermediate substrate to the system substrate such that each of the selected micro devices is aligned with a corresponding contact pad on the system substrate; providing a photosensitive layer between the set of selected micro devices and the system substrate; switching on the selected micro devices; curing the photosensitive layer between the set of selected micro devices and the system substrate by light emitted by the selected micro devices; and bonding the set of selected micro devices to the corresponding contact pads on the system substrate; wherein the providing a donor substrate comprising the plurality of micro devices comprises: fabricating the micro devices on the donor substrate; mounting sidewall reflectors on sidewalls of the micro devices on the donor substrate, the sidewall reflectors being etched into a visible light curable epoxy or photoresist; conformally depositing a sacrificial layer on or over the micro devices; and providing a planarization layer on and over the micro devices.

2. The method of claim 1, wherein the photosensitive layer comprises a visible light curable transparent epoxy or photoresist.

3. The method of claim 1, wherein the photosensitive layer is applied globally or selectively.

4. The method of claim 1, further comprising: removing uncured photosensitive layer by a developer solution.

5. The method of claim 1, further comprising: removing the intermediate substrate.

6. The method of claim 1, wherein the planarization layer is patterned to form openings on top of the micro devices for connection to the intermediate substrate.

7. The method of claim 1, wherein the sacrificial layer comprises one of: a photoresist layer, a metal layer, or a conformal dielectric layer.

8. The method of claim 1, wherein the sacrificial layer is removed prior to aligning the micro devices on the intermediate substrate proximate to the system substrate.

9. The method of claim 1, wherein the sidewall reflectors are patterned using etching or lithography to expose top surfaces of the micro devices.

10. The method of claim 1, wherein the micro devices fabricated on the donor substrate comprise one of: a cylindrical structure, a mesa structure, a flip chip structure, or a vertical structure.

11. The method of claim 1, wherein the transferring the plurality of micro devices to an intermediate substrate comprises: providing an anchor for holding each micro device to the donor substrate; and removing the donor substrate.

12. The method of claim 11, wherein the donor substrate is removed by one of: laser lift-off or chemical etching.

13. The method of claim 11, wherein removing the intermediate substrate comprises breaking the anchors of the set of selected micro devices.

14. The method of claim 1, wherein the intermediate substrate comprises a patterned drive circuit layer. ​ 15. The method of claim 14, wherein the patterned drive circuit layer comprises TFTs.

16. The method of claim 1, wherein the system substrate is one of: a sapphire substrate or a glass substrate.

17. The method of claim 1, further comprising: second time aligning a second set of selected micro devices on the intermediate substrate proximate to the system substrate; providing a second photo-sensitive layer between the second set of selected micro devices and the system substrate; moving the intermediate substrate to the system substrate such that each of the second set of selected micro devices is aligned with a corresponding second selected contact pad on the system substrate; switching on the second set of selected micro devices; curing the photo-sensitive layer between the second set of selected micro devices and the system substrate; and bonding the second set of selected micro devices to the corresponding second contact pad on the system substrate.

18. The method of claim 4, further comprising: providing a transparent planarization layer over the system substrate after removing the intermediate substrate.

19. The method of claim 3, further comprising: removing uncured photo-sensitive layer by a developer solution. ​

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