Transfer wafer and transfer method for LED element

Abstract

The present invention addresses the problem of providing a transfer wafer and a method for transferring an LED element, wherein warpage generated in the wafer is more easily corrected during transfer of the LED element. A transfer wafer includes: a support substrate having a thickness of 100 [mu] m or more and 400 [mu] m or less; and a plurality of LED elements provided in a predetermined array on one main surface of the support substrate, the transfer wafer being used for transferring the plurality of LED elements to the entire circuit substrate.

Description

Technical Field

[0001] The invention relates to a transfer chip and a transfer method for LED components. Background Art

[0002] In recent years, micro-light emitting diode (LED) displays have attracted much attention as a new display technology. Micro-LED displays are display devices that use miniaturized LED elements as pixels and arrange them in an array on the display surface. Micro-LED displays can display images with high contrast and high response speed by individually controlling the light emission of the LED elements of each pixel.

[0003] LED elements are formed by heterojunction of epitaxially grown compound semiconductors on a substrate, for example. However, the substrate on which the LED element is formed may sometimes be warped due to a difference in lattice constant or thermal expansion coefficient between the substrate and the epitaxially grown compound semiconductors.

[0004] Here, the following research is conducted: When manufacturing a micro LED display, a plurality of LED elements formed on a growth substrate are pressed against a circuit substrate to transfer the plurality of LED elements as a whole to a circuit substrate. In this case, the 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, it is required to suppress the warping of the growth substrate or to correct the warping of the growth substrate when transferring the LED elements.

[0005] For example, Patent Document 1 listed below discloses a technique for suppressing warping of a sapphire substrate by providing grooves on both main surfaces of the sapphire substrate when a compound semiconductor crystal is grown on the sapphire substrate.

[0006] [Prior art literature]

[0007] [Patent Document]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2000-174335 Summary of the invention

[0009] [Problems to be solved by the invention]

[0010] However, in the technique disclosed in Patent Document 1, when transferring the LED element, stress concentration occurs due to the grooves provided on both main surfaces of the substrate, making it difficult to uniformly press the sapphire substrate as the growth substrate.

[0011] Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a novel and improved transfer wafer and a method for transferring LED elements, which can more easily correct the warpage generated in the wafer during the transfer of LED elements.

[0012] [Technical means to solve the problem]

[0013] In order to solve the above-mentioned problem, according to a certain aspect of the present invention, there is provided a transfer chip, comprising: a supporting substrate having a thickness of not less than 100 μm and not more than 400 μm; and a plurality of LED elements arranged in a prescribed arrangement on a main surface of the supporting substrate, wherein the transfer chip is used for transferring the plurality of LED elements onto a circuit substrate as a whole.

[0014] In addition, to solve the above-mentioned problem, according to another aspect of the present invention, a method for transferring LED elements is provided, comprising the following steps: forming a plurality of LED elements in a prescribed arrangement on a main surface of a supporting substrate having a thickness of greater than 100 μm and less than 400 μm; and transferring the plurality of LED elements as a whole to a circuit substrate.

[0015] [Effects of the Invention]

[0016] As described above, according to the present invention, it is possible to more easily correct the warpage of the wafer generated during the transfer of the LED elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 (a) to (d) are explanatory diagrams showing the flow of the transfer process of the LED element.

[0018] Figure 2 This is an explanatory diagram for explaining the warping that occurs in a supporting substrate on which an LED element is formed.

[0019] Figure 3 It is an explanatory diagram schematically showing the state of the sapphire substrate of Example 1 and Example 2.

[0020] [Explanation of Symbols]

[0021] 100: Support substrate

[0022] 110: LED components

[0023] 200: Circuit board

[0024] 210: Bump

[0025] 300: Pushing member DETAILED DESCRIPTION

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in the present specification and the drawings, components having substantially the same functional structure are denoted by the same reference numerals, and repeated description is omitted.

[0027] <1. Transfer of LED components>

[0028] First, refer to Figure 1 (a) to (d) illustrate the transfer of the LED element according to one embodiment of the present invention. Figure 1 (a) to (d) are explanatory diagrams showing the flow of the transfer process of the LED element 110.

[0029] like Figure 1 As shown in (a) to (d) of FIG. 1 , the LED element 110 formed on one main surface (surface) of the support substrate 100 is transferred to the circuit substrate 200 through the steps (a) to (d).

[0030] First, in step (a), LED elements 110 are formed in a matrix on the surface of a supporting substrate 100. The supporting substrate 100 is, for example, a sapphire substrate. The supporting substrate 100 may be a wafer in the shape of a circular plate, or a wafer in the shape of a rectangle obtained by cutting a portion of a wafer in the shape of a circular plate. The LED element 110 is, for example, composed of a pn junction of a p-type semiconductor and an n-type semiconductor disposed on one main surface of the supporting substrate 100, and emits light by applying a forward voltage. The LED element 110 may be 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 light emitted from the LED element 110.

[0031] Next, in step (b), the support substrate 100 formed with the LED element 110 is arranged to face the circuit substrate 200 to which the LED element 110 is to be transferred. The circuit substrate 200 is a substrate provided with a drive circuit and a control circuit, wherein the drive circuit drives each of the transferred LED elements 110 individually, and the control circuit controls 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 composed of polyester or polyethersulfone.

[0032] In addition, a bump 210 having a convex shape such as a conical shape, a cylindrical shape or a tapered shape is provided on one main surface (surface) of the circuit substrate 200. At least the surface of the bump 210 is made of metal, and the bump 210 functions as a connection terminal that electrically connects the drive circuit and the control circuit provided on the circuit substrate 200 to the LED element 110. The bump 210 may be made of, for example, a single metal or a plurality of metals, or may be formed by coating the surface of a resin with a metal.

[0033] Then, in step (c), the support substrate 100 and the circuit substrate 200 are pressed against each other in a state where 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 in a state where the surface of the support substrate 100 and the surface of the circuit substrate 200 face each other in a manner that the electrode of the LED element 110 and the bump 210 abut against each other. Thus, the LED element 110, the bump 210, and the circuit substrate 200 are bonded together by an adhesive layer (not shown) between the support substrate 100 and the circuit substrate 200.

[0034] Furthermore, in step (d), the LED element 110 is peeled off from the supporting substrate 100 by laser lift-off, and the LED element 110 is transferred to the circuit substrate 200 .

[0035] Laser lift-off is a method in which the LED element 110 formed on the surface of the support substrate 100 is irradiated with laser light from the back side of the support substrate 100 opposite to the surface, thereby removing the LED element 110 from the support substrate 100. Specifically, in laser lift-off, the laser light is focused on the interface region between the LED element 110 to be removed and the support substrate 100, so that nitrogen and the like of GaN in the interface region are vaporized (ablated) by the laser light. Thus, the LED element 110 is removed from the support substrate 100 at the interface region.

[0036] After laser lift-off, the support substrate 100 is lifted up to remove 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 surface of the support substrate 100 are transferred to the circuit substrate 200.

[0037] Here, refer to Figure 2 The warping of the support substrate 100 will be described. Figure 2 This is an explanatory diagram for explaining the warping that occurs in the support substrate 100 on which the LED element 110 is formed.

[0038] like Figure 2As shown, the support substrate 100 formed with the LED element 110 may be warped due to the difference in lattice constant or thermal expansion coefficient between the LED element 110 and the support substrate 100. For example, the support substrate 100 may be warped such that the surface side formed with the LED element 110 is widened due to the tensile stress from the LED element 110. In addition, depending on other layers formed on the support substrate 100 or the structure of the support substrate 100, the support substrate 100 may be warped such that the back side opposite to the surface formed with the LED element 110 is widened.

[0039] Therefore, the following study was conducted: the warping of the support substrate 100 was corrected by pressing the back side of the warped support substrate 100 with the pressing member 300 over the entire surface when pressing the circuit substrate 200. In addition, although not shown in the figure, the following study was conducted: the warping of the support substrate 100 was corrected by attaching a flat correction substrate to the back side of the warped support substrate 100.

[0040] However, if the correction of the warpage of the support substrate 100 is incomplete, the LED element 110 may not be uniformly transferred from the support substrate 100 to the circuit substrate 200 .

[0041] The present invention has been conceived in view of the above circumstances. A transfer wafer according to an embodiment of the present invention includes a support substrate 100 and an LED element 110 and is used to transfer the LED element 110 to the circuit substrate 200 through the above process.

[0042] In addition, in the transfer wafer of the present embodiment, the thickness of the support substrate 100 on which the LED element 110 is formed is 100 μm or more and 400 μm or less. Thus, the thickness of the support substrate 100 of the transfer wafer of the present embodiment becomes thinner, so that the elasticity in the thickness direction of the support substrate 100 can be further reduced, and thus, the warping generated in the support substrate 100 can be more easily corrected. For example, the support substrate 100 can be made to have a thickness of 100 μm or more and 400 μm or less by grinding the back surface opposite to the surface on which the LED element 110 is formed after the LED element 110 is formed.

[0043] When the thickness of the support substrate 100 is 400 μm or less, the elasticity in the thickness direction of the support substrate 100 becomes lower, and the warping of the support substrate 100 is easily corrected, which is preferred. On the other hand, when the thickness of the support substrate 100 is 100 μm or more, the strength for handling the support substrate 100 can be maintained, so the support substrate 100 is not easily broken, and the support substrate 100 is easily transported, which is preferred.

[0044] In addition, when the thickness of the support substrate 100 is 400 μm or less, the support substrate 100 can be cut in a shorter time. Therefore, the transfer wafer of this embodiment can transfer the LED element 110 as a whole to the circuit substrate 200 larger than the support substrate 100 by connecting a plurality of support substrates 100 cut into rectangular shapes in a tile shape. That is, the thickness of the support substrate 100 is preferably 400 μm or less so that it can be easily cut into any shape.

[0045] The thickness of the support substrate 100 is more preferably 100 μm to 200 μm. When the thickness of the support substrate 100 is 200 μm or less, the elasticity of the support substrate 100 in the thickness direction becomes lower, and thus the warping of the support substrate 100 can be corrected more easily.

[0046] As described above, the transfer wafer of the present embodiment can more easily correct the warpage generated in the support substrate 100 on which the LED element 110 is formed. Therefore, the transfer wafer of the present embodiment can more easily and uniformly transfer the LED element 110 formed on the support substrate 100 to the circuit substrate 200. In addition, since the transfer wafer of the present embodiment can maintain the strength for handling the support substrate 100, it is possible to make the transportation of the support substrate 100 easier and suppress the cracking of the support substrate 100 during transportation.

[0047] [Example]

[0048] The present invention will be described in more detail below by way of examples. The materials, steps and procedures described below are merely examples, and the scope of the present invention is not limited to the examples described below.

[0049] (Example 1 and Example 2)

[0050] First, a 4-inch-diameter circular plate-shaped sapphire substrate with a thickness of 600 μm was prepared. Next, GaN-based compound semiconductors were epitaxially grown on the sapphire substrate until the thickness reached 10 μm, thereby forming GaN-based LEDs arranged in a matrix at a predetermined pitch on the sapphire substrate. The arrangement pitch of the LEDs was set to 200 μm in the row direction and the column direction, respectively.

[0051] Then, after the surface of the sapphire substrate on which the LED is formed is protected by a resist, the back side of the sapphire substrate (the surface on the side opposite to the surface) is ground until the thickness of the sapphire substrate is 250 μm. Thereafter, the 4-inch circular plate-shaped sapphire substrate is cut into a 22 mm square rectangular shape. Next, the resist protecting the surface of the 22 mm square rectangular sapphire substrate is removed, and the warpage of the sapphire substrate is measured on the diagonal of the rectangular shape using a stylus step difference meter.

[0052] Furthermore, after the surface of the sapphire substrate was protected again with a resist, the back side of the sapphire substrate was polished until the thickness of the sapphire substrate was 150 μm. Thereafter, the resist protecting the surface of the sapphire substrate was removed, and the warpage of the sapphire substrate was measured on the diagonal line of the rectangular shape using a stylus step meter.

[0053] The shape of the sapphire substrate, the arrangement of the LEDs, and the direction in which the warpage is measured are shown in FIG. Figure 3 . Figure 3 It is an explanatory diagram schematically showing the state of the sapphire substrate of Example 1 and Example 2.

[0054] like Figure 3 As shown in the figure, LEDs are arranged in a matrix on a 22 mm square rectangular sapphire substrate. The surface shape on the diagonal line Cd of the rectangular shape of the sapphire substrate is measured using a stylus-type step difference meter, and the difference between the maximum and minimum values ​​of the measured surface shape is taken as the warpage of the sapphire substrate. Regarding the warpage of the sapphire substrate, two different sapphire substrates are respectively referred to as Example 1 and Example 2, and the sapphire substrates of Example 1 and Example 2 are measured with two types of thickness: 250 μm and 150 μm.

[0055] The measurement results of the warpage amounts of the sapphire substrates in Examples 1 and 2 are shown in Table 1 below.

[0056] [Table 1]

[0057] (Table 1)

[0058] Thickness: 250 μm Thickness: 150 μm Example 1 29.5μm 13.4μm Example 2 29.8μm 10.1μm

[0059] According to the results in Table 1, the sapphire substrates of Examples 1 and 2 can suppress the warping of the sapphire substrates because the thickness is 100 μm or more and 400 μm or less. Therefore, the sapphire substrates of Examples 1 and 2 can more easily correct the warping of the sapphire substrates.

[0060] In addition, it can be seen that the warping amount of the sapphire substrate in Examples 1 and 2 can be more suppressed when the thickness is 150 μm than when the thickness is 250 μm. Therefore, the warping amount of the sapphire substrate in Examples 1 and 2 can be more easily corrected by setting the thickness to be greater than 100 μm and less than 200 μm.

[0061] The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the examples described. It is obvious that anyone with common knowledge in the technical field to which the present invention belongs can think of various variations or modifications within the scope of the technical ideas described in the claims, and it should be understood that these also belong to the technical scope of the present invention.

Claims

1. A transfer wafer, comprising: A supporting substrate having a thickness of not less than 100 μm and not more than 400 μm; as well as A plurality of LED elements are arranged on one main surface of the support substrate in a predetermined arrangement. The transfer wafer is used for integrally transferring the plurality of LED elements to a circuit substrate.

2. The transfer wafer according to claim 1, wherein: The support substrate has a thickness of 100 μm or more and 200 μm or less.

3. The transfer wafer according to claim 1 or 2, wherein: The supporting substrate is in a rectangular shape.

4. The transfer wafer according to claim 1 or 2, wherein: The support substrate is a sapphire substrate.

5. A method for transferring an LED component, comprising the following steps: forming a plurality of LED elements in a predetermined arrangement on one main surface of a support substrate having a thickness of 100 μm or more and 400 μm or less; and The plurality of LED elements are integrally transferred to a circuit substrate.

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