Transfer wafer and LED element transfer method

Abstract

To correct warpage caused in a wafer more easily during transfer of LED elements.SOLUTION: A transfer wafer has a support substrate with a modified layer internally provided in a predetermined two-dimensional pattern, and a plurality of LED elements provided in a predetermined array on one main surface of the support substrate.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a transfer wafer and a method for transferring LED elements. [Background technology]

[0002] In recent years, micro LED (Light Emitting Diode) displays have been attracting attention as a new display technology. A micro LED display is a display device in which miniaturized LED elements are arranged in an array on the display surface as pixels. By individually controlling the light emission of the LED elements of each pixel, a micro LED display can display images with high contrast and high response speed.

[0003] An LED element is constructed by, for example, forming a heterojunction of epitaxially grown compound semiconductors on a substrate. However, the substrate on which the LED element is formed may warp due to the difference in lattice constant or thermal expansion coefficient between the substrate and the epitaxially grown compound semiconductor.

[0004] Here, when manufacturing a micro LED display, a method is being considered in which a plurality of LED elements formed on a growth substrate are pressed against a circuit substrate to transfer the plurality of LED elements to the circuit substrate at once. In such a case, warping of the growth substrate on which the LED elements are formed makes it difficult to uniformly transfer the LED elements to the circuit substrate. Therefore, there is a demand for suppressing warping of the growth substrate or for correcting warping of the growth substrate when transferring the LED elements.

[0005] For example, Patent Document 1 listed below discloses a technique for suppressing warpage that occurs in a sapphire substrate by forming grooves on both main surfaces of the sapphire substrate when crystals of a compound semiconductor are grown on the sapphire substrate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2000-174335 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the technology disclosed in the above Patent Document 1, stress concentration occurs due to the grooves provided on both main surfaces of the substrate when transferring the LED elements, making it difficult to uniformly press the sapphire substrate, which is the growth substrate.

[0008] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a new and improved transfer wafer and a method for transferring LED elements, which can more easily correct warping that occurs in the wafer when transferring LED elements. [Means for solving the problem]

[0009] In order to solve the above problem, according to one aspect of the present invention, a transfer wafer is provided, comprising a support substrate having a modified layer formed therein in a predetermined two-dimensional pattern, and a plurality of LED elements arranged in a predetermined array on one main surface of the support substrate.

[0010] In addition, in order to solve the above problem, according to another aspect of the present invention, there is provided a method for transferring LED elements, comprising the steps of forming a plurality of LED elements in a predetermined arrangement on one main surface of a support substrate having a modified layer provided therein in a predetermined two-dimensional pattern, and transferring the plurality of LED elements collectively onto a circuit substrate. Effect of the Invention

[0011] As described above, according to the present invention, warpage occurring in a wafer can be easily corrected when transferring LED elements. [Brief description of the drawings]

[0012] [Figure 1] FIG. 10 is an explanatory diagram showing the flow of a transfer process of an LED element. [Diagram 2] 1 is an explanatory diagram illustrating warping that occurs in a support substrate on which an LED element is formed. FIG. [Diagram 3] FIG. 2 is a schematic explanatory diagram showing a configuration of a transfer wafer according to an embodiment of the present invention. [Figure 4] 1A to 1C are explanatory diagrams illustrating a method for forming a modified layer using laser light. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and duplicated explanations will be omitted.

[0014] <1. Transfer of LED elements> First, the transfer of an LED element according to one embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram showing the flow of a transfer process of an LED element 110.

[0015] As shown in FIG. 1, the LED element 110 formed on one main surface (front surface) of the support substrate 100 is transferred to the circuit board 200 through steps (a) to (d).

[0016] First, in step (a), the LED elements 110 are formed in a matrix on one main surface (front surface) of the support substrate 100. The support substrate 100 is, for example, a sapphire substrate. The support substrate 100 may be a disk-shaped wafer, or may be a rectangular wafer obtained by dicing a part of a disk-shaped wafer. The LED element 110 is, for example, composed of a pn junction of a p-type semiconductor and an n-type semiconductor provided on one main surface of the support substrate 100, and emits light when a forward voltage is applied. The LED element 110 may be, for example, composed of a pn junction of a compound semiconductor such as InGaN, GaN, or AlGaN. The constituent material of the LED element 110 is appropriately selected according to the wavelength of the light emitted from the LED element 110.

[0017] Next, in step (b), the support substrate 100 on which the LED elements 110 are formed is disposed so as to face the circuit substrate 200 onto which the LED elements 110 are transferred. The circuit substrate 200 is provided with a drive circuit for individually driving each of the transferred LED elements 110 and a control circuit for controlling the drive of each of the LED elements 110. The circuit substrate 200 may be, for example, a glass substrate, a glass epoxy substrate, an epoxy substrate, a polyimide substrate, or a (meth)acrylic substrate, or may be a flexible substrate made of polyester, polyethersulfone, or the like.

[0018] Furthermore, bumps 210 having a convex shape such as a cone shape, a cylinder shape, or a tapered shape are provided on one main surface (front surface) of the circuit board 200. At least the surface of the bumps 210 is made of metal, and functions as connection terminals that electrically connect the drive circuit and control circuit provided on the circuit board 200 to the LED elements 110. The bumps 210 may be made of, for example, a single metal or multiple metals, or may be made by coating the surface of a resin with a metal.

[0019] Next, in step (c), the support substrate 100 and the circuit substrate 200 are pressed against each other while the LED element 110 and the bump 210 face each other. Specifically, the support substrate 100 and the circuit substrate 200 are pressed against each other while the front surface of the support substrate 100 and the front surface of the circuit substrate 200 face each other so that the electrodes of the LED element 110 and the bump 210 come into contact with each other. The LED element 110, the bump 210, and the circuit substrate 200 may be bonded to each other by, for example, an adhesive layer (not shown) provided between the support substrate 100 and the circuit substrate 200.

[0020] Furthermore, in step (d), the LED element 110 is peeled off from the support substrate 100 by laser lift-off, and the LED element 110 is transferred to the circuit board 200.

[0021] Laser lift-off is a technique for irradiating the LED element 110 formed on the front surface of the support substrate 100 with laser light from the back surface side opposite to the front surface of the support substrate 100, thereby peeling the LED element 110 from the support substrate 100. Specifically, in laser lift-off, a laser light is focused on and irradiated onto the interface region between the LED element 110 to be peeled and the support substrate 100, and nitrogen and the like in the GaN in the interface region are vaporized (ablated) by the laser light. As a result, the LED element 110 is peeled off from the support substrate 100 at the interface region.

[0022] After the laser lift-off is performed, the support substrate 100 is lifted up, thereby peeling the support substrate 100 from the circuit substrate 200, the bumps 210, and the LED elements 110. Through the above steps (a) to (d), the LED elements 110 formed on the front surface of the support substrate 100 are transferred to the circuit substrate 200.

[0023] Here, warping occurring in the support substrate 100 will be described with reference to Fig. 2. Fig. 2 is an explanatory diagram for explaining warping occurring in the support substrate 100 on which the LED elements 110 are formed.

[0024] 2, the support substrate 100 on which the LED elements 110 are formed may warp due to a difference in lattice constant or thermal expansion coefficient between the LED elements 110 and the support substrate 100. For example, the support substrate 100 may warp such that the front surface side on which the LED elements 110 are formed expands due to tensile stress from the LED elements 110. In addition, depending on other layers formed on the support substrate 100 or the configuration of the support substrate 100, the support substrate 100 may warp such that the back surface side opposite to the front surface on which the LED elements 110 are formed expands.

[0025] Therefore, it has been considered to correct the warpage of the support substrate 100 by pressing the entire back surface of the warped support substrate 100 with a pressing member 300 when pressing against the circuit substrate 200. In addition, although not shown, it has been considered to correct the warpage of the support substrate 100 by attaching a flat correction substrate to the back surface of the warped support substrate 100.

[0026] However, if the warp occurring in the support substrate 100 is not completely corrected, the LED elements 110 may not be transferred uniformly from the support substrate 100 to the circuit substrate 200.

[0027] The present invention has been conceived in view of the above circumstances. A transfer wafer according to one embodiment of the present invention includes a support substrate 100 and LED elements 110, and is a wafer for transferring the LED elements 110 to a circuit board 200 by the above process.

[0028] In the transfer wafer according to this embodiment, a modified layer in which bonds are chemically cut is provided in a predetermined two-dimensional pattern inside the support substrate 100 on which the LED elements 110 are formed. This allows the transfer wafer according to this embodiment to further reduce the elasticity of the support substrate 100 in the thickness direction, so that it is possible to more easily correct the warp that occurs in the support substrate 100 when pressed against the circuit substrate 200. In addition, the transfer wafer according to this embodiment can flatten the back surface of the support substrate 100 by forming a modified layer inside the support substrate 100, so that it is possible to press the support substrate 100 uniformly without generating stress concentration when pressed against the circuit substrate 200.

[0029] The transfer wafer according to this embodiment will be described in more detail below with reference to Fig. 3 and Fig. 4. Fig. 3 is a schematic explanatory diagram showing the configuration of the transfer wafer according to this embodiment. Fig. 4 is an explanatory diagram explaining a method for forming a modified layer using a laser beam.

[0030] As shown in FIG. 3, in the transfer wafer according to this embodiment, a modified layer 105 is provided in a predetermined two-dimensional pattern inside a support substrate 100 on which LED elements 110 are formed.

[0031] Specifically, the modified layer 105 may be provided in a linear pattern extending between the LED elements 110. In other words, the modified layer 105 may be provided in a two-dimensional pattern extending in a lattice pattern between the LED elements 110 arranged in a matrix.

[0032] The modified layer 105 is a layer in which the bonds of the support substrate 100 are chemically cut. The modified layer 105 may be a recrystallized layer, a void, or a crack formed inside the support substrate 100.

[0033] 4, the modified layer 105 includes voids 105A and recrystallized layers 105B formed by focusing pulsed laser light Ls inside the support substrate 100 with a lens CL and locally melting and resolidifying the support substrate 100. The modified layer 105 may be formed continuously in spike shapes at predetermined intervals in the scanning direction D of the laser light Ls.

[0034] Specifically, at the focal point of the laser light Ls on the support substrate 100, the energy given to the support substrate 100 by the laser light Ls exceeds a threshold value, and the single crystal constituting the support substrate 100 (for example, a sapphire substrate) melts. The support substrate 100 has a smaller volume per unit substance amount in a molten state than in a single crystal state. Therefore, the volume of the support substrate 100 locally shrinks due to melting, and a void 105A is formed below the focal point. Thereafter, the energy is diffused by thermal diffusion, and the molten single crystal is recrystallized, forming a recrystallized layer 105B above the focal point of the laser light Ls.

[0035] The modified layer 105 can cut the crystal structure inside the support substrate 100 by the voids 105A and the recrystallized layer 105B, and can therefore reduce the elasticity in the thickness direction of the support substrate 100. Such a modified layer 105 can be formed by, for example, stealth dicing (registered trademark).

[0036] The modified layer 105 formed on the support substrate 100 in this embodiment is not intended for cutting (dicing) the support substrate 100. Therefore, the modified layer 105 is preferably formed on the support substrate 100 in a manner that does not cut the support substrate 100. For example, the number of modified layers 105 formed on the support substrate 100 is preferably less than the number formed by normal stealth dicing. In addition, the position of the modified layer 105 formed on the support substrate 100 is preferably near the center in the thickness direction of the support substrate 100. Furthermore, the shape of the modified layer 105 formed on the support substrate 100 is preferably an ellipse rather than an acute-angled wedge shape.

[0037] The modified layer 105 is formed continuously at a predetermined interval in the scanning direction D of the laser light Ls to form a linear processed region. The linear processed region of the modified layer 105 may be provided extending between the LED elements 110 as described above.

[0038] This is because the modified layer 105 scatters the incident laser light due to the voids 105A and the recrystallized layer 105B. Specifically, in the transfer wafer according to this embodiment, the LED elements 110 formed on the support substrate 100 are pressed against the circuit substrate 200, and then the support substrate 100 and the LED elements 110 are peeled off by laser lift-off. At this time, if the modified layer 105 exists directly under the LED elements 110, the laser light of the laser lift-off irradiated from the back surface of the support substrate 100 may be scattered by the modified layer 105, making it difficult to peel off the support substrate 100 and the LED elements 110. Therefore, in order to reliably perform the laser lift-off of the LED elements 110, it is preferable that the modified layer 105 is provided between the LED elements 110.

[0039] The modified layer 105 may be provided in a plurality between the LED elements 110 so as to form a double line or triple line, or may be thinned out for each group of the LED elements 110 and provided between the LED elements 110. The two-dimensional pattern of the modified layer 105 formed on the support substrate 100 can be appropriately deformed according to the elasticity of the support substrate 100 required to correct the warpage of the support substrate 100. However, the modified layer 105 is preferably formed periodically over the entire surface of the support substrate 100 in order to uniformly reduce the elasticity of the support substrate 100 in the thickness direction.

[0040] As described above, according to the transfer wafer of this embodiment, the elasticity of the support substrate 100 in the thickness direction can be further reduced, so that it is possible to more easily correct the warpage that occurs in the support substrate 100 when it is pressed against the circuit substrate 200. Furthermore, the transfer wafer of this embodiment can flatten the back surface of the support substrate 100 by forming the modified layer 105 inside the support substrate 100, so that it is possible to press the support substrate 100 uniformly without generating stress concentration when it is pressed against the circuit substrate 200.

[0041] Although the preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such an example. It is clear that a person having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Explanation of symbols]

[0042] Reference Signs List 100: Support substrate, 105: Modified layer, 110: LED element, 200: Circuit board, 210: Bump, 300: Pressing member, 105A: Gap, 105B: Recrystallized layer, Ls: Laser light

Claims

1. A supporting substrate having a modified layer formed therein in a predetermined two-dimensional pattern; A plurality of LED elements provided in a predetermined arrangement on one main surface of the support substrate; A transfer wafer comprising:

2. The transfer wafer according to claim 1 , wherein the modified layer is a layer in which bonds to the support substrate are chemically cut.

3. The transfer wafer according to claim 1 , wherein the other main surface of the support substrate opposite to the one main surface is flat.

4. The transfer wafer according to claim 1 , wherein the modified layer is provided between the LED elements.

5. The transfer wafer according to claim 1 , wherein the support substrate is a sapphire substrate.

6. The transfer wafer according to claim 1 , which is used for collectively transferring a plurality of the LED elements onto a circuit board.

7. forming a plurality of LED elements in a predetermined arrangement on one main surface of a support substrate having a modified layer formed therein in a predetermined two-dimensional pattern; transferring a plurality of the LED elements to a circuit board at once; A method for transferring an LED element, comprising:

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