KR20170049405A - Method of forming led substrate - Google Patents

Abstract

The present invention is to provide a method for forming an LED substrate capable of forming an LED substrate at low cost by a simple operation. The method for forming an LED substrate includes a buffer layer forming step of forming a buffer layer on the surface of a silicon substrate; a light emitting layer forming step of forming a light emitting layer on the surface of the buffer layer; a ring-shaped reinforcing part forming step of forming a ring-shaped reinforcing part by grinding a central part while leaving the outer peripheral part of the back surface of the silicon substrate; a reflective film forming step of forming a reflective film on the back surface of the silicon substrate; an electrode forming step of forming an electrode on the reflective film; and a division step of dividing the silicon substrate into chips along a division-planned line.

Description

[0001] METHOD OF FORMING LED SUBSTRATE [0002]

The present invention relates to a method of forming an LED substrate.

Conventionally, an LED (Light Emitting Diode) substrate is formed by laminating a light emitting layer composed of an n-GaN layer, an active layer and a p-GaN layer on a sapphire substrate. As an LED substrate, there is known a horizontal LED substrate in which an n-type electrode is disposed beside a p-type electrode without separating a sapphire substrate having an insulating property (see, for example, Patent Document 1). In the LED substrate of the horizontal structure, the side of the p-GaN layer is etched to partially expose the n-GaN layer, and the p-type electrode and the n-type electrode are disposed on the surface of the p-GaN layer and the surface of the n- . there is a possibility that the current is concentrated when the p-type electrode is directed to the n-type electrode, and the durability of the LED substrate is lowered.

As the LED substrate, there is known an LED substrate having a vertical structure in which a sapphire substrate having an insulating property is separated and a p-type electrode and an n-type electrode are vertically arranged (for example, see Patent Document 2). The sapphire substrate is separated from the n-GaN layer by laser lift off (LLO), and the p-type electrode and the n-GaN layer are formed on the surface of the p-GaN layer and the back surface of the n- Type electrodes are supported by the support substrate. Therefore, unlike the LED substrate having a horizontal structure, the current does not concentrate from the p-type electrode toward the n-type electrode, and the durability of the LED is improved.

Recently, a technique (GaN on Silicon technology) for forming an LED substrate by laminating a light emitting layer on a silicon substrate via a buffer layer instead of a sapphire substrate has also been developed (see Patent Documents 3 and 4, for example). Compared with a sapphire substrate, a silicon substrate is inexpensive as an epitaxial substrate, and it is possible to greatly reduce the cost of manufacturing an LED substrate.

Japanese Laid-Open Patent Publication No. 09-116192 Japanese Patent No. 5653327 Japanese Laid-Open Patent Publication No. 2012-243807 Japanese Patent No. 5752855

However, since the lattice mismatch is large in the silicon substrate and GaN, it is necessary to form a buffer layer on the silicon substrate in order to laminate the GaN layer. In the case of forming a vertically-structured LED substrate, it is difficult to separate the silicon substrate from the LED substrate using the above-described laser lift-off. Even if the silicon substrate is separated from the LED substrate and can be replaced from the silicon substrate to the support substrate, there is a problem that the work becomes troublesome as much as the replacement operation occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of forming an LED substrate capable of forming an LED substrate at a low cost by a simple operation.

A method for forming an LED substrate according to the present invention is a method for forming an LED substrate comprising a buffer layer forming step of forming a buffer layer on one surface of a silicon substrate, a light emitting layer forming step of forming a light emitting layer on the surface of the buffer layer formed in the buffer layer forming step, A step of forming an annular reinforcing portion on the outer side of the concave portion by grinding the center of the other surface of the silicon substrate to form a concave portion; and a step of forming, on the concave portion after the step of forming the annular reinforcing portion, An electrode forming step of forming an electrode on the surface of the reflective film formed in the reflective film forming step; and a dividing step of dividing the substrate into chips along a line to be divided after the electrode forming step.

According to this configuration, the central portion of the other surface of the silicon substrate is ground, and the annular reinforcing portion is formed around the central portion. Since the rigidity of the silicon substrate is ensured by the annular reinforcing portion, there is no occurrence of warp even if the center portion of the silicon substrate is thin. Therefore, there is no case where the substrate replacement operation from the silicon substrate to the support substrate occurs. In addition, since the central portion of the silicon substrate is thin, the light emitted from the back surface of the light emitting layer is transmitted through the silicon substrate and reflected by the reflection film, thereby improving the light emitting efficiency. In addition, by using the silicon substrate as the epitaxial substrate, the cost can be greatly reduced.

According to the present invention, the central portion of the other surface of the silicon substrate is ground, whereby the annular reinforcing portion is formed around the central portion. As a result, the inexpensive silicon substrate can be used as an epitaxial substrate, and the replacement of the light emitting layer from the silicon substrate to the support substrate does not occur. In addition, by thinly grinding the silicon substrate, light from the back surface of the light emitting layer can be transmitted through the silicon substrate, reflected by the reflection film, and transmitted through the silicon substrate again, thereby improving the brightness.

1 is an explanatory diagram of an LED structure of a comparative example.
2 is a diagram showing an example of the buffer layer forming step of the present embodiment.
Fig. 3 is a view showing an example of a light-emitting layer forming step of this embodiment.
Fig. 4 is a view showing an example of a ring-shaped reinforcement forming step of the present embodiment.
5 is a view showing an example of the reflective film forming process of this embodiment.
6 is a diagram showing an example of the electrode forming process of the present embodiment.
Fig. 7 is a diagram showing an example of a dividing step of the present embodiment.
8 is a view showing an example of the electrode forming step of the first modification.
9 is a view showing an example of an electrode forming step of the second modification.
10 is a view showing another example of the dividing step of the present embodiment.

Before describing the present embodiment, the LED structure of the comparative example will be briefly described. 1 is an explanatory diagram of an LED structure of a comparative example. In the LED structure of the comparative example, the same reference numerals as in the present embodiment are used for the convenience of explanation.

1A, a buffer layer 20 is formed on a silicon substrate 10 and an n-GaN layer 31, an active layer 32, and a p-GaN layer 33 are formed on the buffer layer 20, A light emitting layer (LED light emitting layer) 30 is formed. The silicon substrate 10 is larger in diameter than the sapphire substrate, and is less expensive than the sapphire substrate as the epitaxial substrate. A buffer layer 20 is formed between the silicon substrate 10 and the n-GaN layer 31 in order to absorb the difference in lattice mismatch between silicon and GaN. In this structure, it is difficult to separate the silicon substrate 10 from the light emitting layer 30 using a laser lift-off, and to form an LED substrate having a vertical structure.

Usually, the laser lift off is used for a sapphire substrate having a light emitting layer laminated thereon, and a sapphire substrate is separated from the light emitting layer by condensing a laser beam on the n-GaN layer. In this structure, the laser beam can not be directly focused on the n-GaN layer 31, and it is difficult to separate the silicon substrate 10 from the light emitting layer 30. [ In this case, it is also conceivable to use the silicon substrate 10 as a support substrate without separating the silicon substrate 10 from the n-GaN layer 31. However, if the silicon substrate 10 remains thick, the light emitted from the back surface of the light emitting layer 30 is absorbed by the silicon substrate 10 and the light emitting efficiency is lowered .

On the other hand, as shown in Fig. 1B, it is also conceivable that the back surface of the silicon substrate 10 is ground to be thinned. As a result, the absorption amount of light by the silicon substrate 10 is reduced. However, there is a problem that the silicon substrate 10 is heated by the heating of the silicon and the GaN during the deposition of the electrodes 51 and 52, and the thinly grounded silicon substrate 10 is cracked.

Therefore, in this embodiment, attention is paid to the fact that the silicon substrate 10 is easily grinded as compared with the sapphire substrate, and the rigidity of the silicon substrate 10 is secured by grinding only the central portion while leaving the periphery of the silicon substrate 10 . Thus, the amount of light absorbed from the light emitting layer 30 by the silicon substrate 10 is suppressed while the cracks of the silicon substrate 10 are suppressed. Further, a reflecting film is formed on the back surface of the silicon substrate 10, and the light transmitted through the thin silicon substrate 10 is reflected by the reflecting film.

Hereinafter, with reference to the accompanying drawings, a method of forming the LED substrate of the present embodiment will be described in detail. Fig. 2 shows a buffer layer forming step, Fig. 3 shows a light emitting layer forming step, Fig. 4 shows a ring strengthening part forming step, Fig. 5 shows a reflection film forming step, Fig. 6 shows an electrode forming step and Fig.

As shown in Fig. 2, a buffer layer forming step is performed first. In the buffer layer forming step, the buffer layer 20 is formed on one surface (surface) of the silicon substrate 10. As a method for forming the buffer layer 20, a base layer film forming method such as MOCVD (Metal Organic Chemical Vapor Deposition) method, MBE (Molecular Beam Epitaxy) method, CVD (Chemical Vapor Deposition) method or sputtering method can be used. Further, the buffer layer 20 is preferably formed in a multi-layer structure to prevent cracks generated during cooling after GaN formation.

As shown in Fig. 3, a light emitting layer forming step is performed after the buffer layer forming step. In the light emitting layer forming step, the light emitting layer 30 is formed on the surface of the buffer layer 20. The light emitting layer 30 is formed by laminating an n-GaN layer 31, an active layer 32, and a p-GaN layer 33 on the surface of the buffer layer 20 in this order. As the method for forming the light emitting layer 30, for example, the MOVCD method or the MBE method described above can be used. As described above, the light emitting layer 30 is laminated on one surface of the silicon substrate 10 with the buffer layer 20 interposed therebetween, thereby suppressing cracks arising from lattice mismatching between silicon and GaN. The laminating sequence of the light emitting layer (Epi layer) may be the p-GaN layer 33, the active layer 32, and the n-GaN layer 31 on the surface of the buffer layer 20.

As shown in Fig. 4, after the luminescent layer forming step, a ring-shaped reinforcing portion forming step is performed. In the process of forming the annular reinforcing portion, the center of the other surface (back surface) of the silicon substrate 10 is ground to form the concave portion 11, and the annular reinforcing portion 12 is formed outside the concave portion 11 . 4A, the protective tape T1 is attached to the light emitting layer 30 laminated on the silicon substrate 10, and the silicon substrate 10 to which the protective tape T1 is attached is bonded to the light emitting layer 30, Is brought into the grinding apparatus (not shown). In the grinding apparatus, the silicon substrate 10 is sucked and held on the chuck table 61 via the protective tape T 1 with the other surface of the silicon substrate 10 facing upward.

4B, the grinding wheel 63 of the grinding unit 62 rotates to approach the chuck table 61, and the other surface of the grinding wheel 63 and the silicon substrate 10 are in rotational contact with each other, The substrate 10 is ground. At this time, only the central portion of the other surface of the silicon substrate 10, which is finally used as the LED device, is ground by using the grinding wheel 63 having a smaller diameter than the radius of the silicon substrate 10. As a result, the circular recess 11 is formed on the other surface of the silicon substrate 10, and the annular reinforcing portion 12 is formed on the outer peripheral portion of the silicon substrate 10.

4C, in the silicon substrate 10, the central portion is thinned by the recess 11, and the rigidity is ensured by the annular reinforcing portion 12 surrounding the recess 11. As shown in Fig. Since the central portion of the silicon substrate 10 used as the LED device is thinned, the amount of light absorption at the central portion of the silicon is suppressed. It is preferable that the central portion of the silicon substrate 10 is ground until the thickness becomes 1 [占 퐉] - 40 [占 퐉] in order to transmit the light. Since the rigidity of the silicon substrate 10 is secured by the annular reinforcing portion 12, warpage of the silicon substrate 10 is suppressed, and breakage or the like at the time of forming the electrode by vapor deposition is prevented .

As shown in Fig. 5, a process of forming a reflective film is performed after the process of forming the annular reinforced portion. In the reflective film forming process, the reflective film 40 is formed on the bottom surface of the concave portion 11 formed on the other surface of the silicon substrate 10. Thereby, the light emitted from the rear surface of the light emitting layer 30 is transmitted through the silicon substrate 10 and is reflected by the reflection film 40. The reflected light is again transmitted through the silicon substrate 10 and emitted from the surface side of the light emitting layer 30 The luminous efficiency is improved. As a method for forming the reflective film 40, a sputtering method, a vapor deposition method, or the like can be used. Although the reflective film 40 is formed of a metal film, it may be formed of another material as long as it can reflect the light transmitted through the silicon substrate 10.

As shown in Fig. 6, an electrode forming step is performed after the reflective film forming step. In the electrode forming step, the n-type electrode 51 is formed on the surface of the reflective film 40. After the n-type electrode 51 is formed on the surface of the reflective film 40, the protective tape T 1 (see Fig. 5) is peeled off from the surface of the light emitting layer 30, (52) are formed. the n-type electrode 51 and the p-type electrode 52 are formed by the vapor deposition method. However, since the rigidity of the silicon substrate 10 is secured by the annular reinforcing portion 12, even if the thermal expansion coefficient of silicon and GaN is different, The silicon substrate 10 is not warped by the heat of the silicon substrate 10. Therefore, even if the silicon substrate 10 is made thin, no warpage occurs, so that the electrode can be easily formed.

In this embodiment, the p-type electrode 52 is formed on the surface of the light emitting layer 30 after the protection tape T1 (see Fig. 5) is peeled from the surface of the light emitting layer 30. However, But is not limited to the configuration. The p-type electrode 52 may be formed on the surface of the light emitting layer 30 before the protective tape T1 is adhered to the surface of the light emitting layer 30. [ That is, the p-type electrode 52 may be formed on the surface of the light emitting layer 30 between the light emitting layer forming step and the annular reinforcing part forming step. The method of forming the n-type electrode 51 and the p-type electrode 52 is not limited to the vapor deposition method, and sputtering or the like may be used.

As shown in Fig. 7, the dividing step is performed after the electrode forming step. In the dividing step, the silicon substrate 10 is divided into chips C (LED substrates) along the line to be divided (not shown). 7A, the surface of the light emitting layer 30 is adhered to the dicing tape T2 covering the opening of the ring frame (not shown), and the silicon substrate 10 supported by the ring frame is bonded to the cutting device (Not shown). In the cutting apparatus, the silicon substrate 10 is placed on the chuck table 71 via the dicing tape T2 while the other surface of the silicon substrate 10, that is, the n-type electrode 51 is directed upward Suction is maintained. In this case, a transparent chuck table 71 is used to confirm the line to be divided and is aligned below the chuck table 71.

The cutting blade 72 is aligned with the line to be divided of the silicon substrate 10 so that the cutting blade 72 can be inserted to the middle of the dicing tape T2 on the outer side in the radial direction of the silicon substrate 10 The cutting blade 72 is lowered. Then, the chuck table 71 is cut and transferred with respect to the cutting blade 72 rotating at a high speed, so that the silicon substrate 10 and the light emitting layer 30 are cut along the line to be divided. When the silicon substrate 10 and the light emitting layer 30 are fully cut along one scheduled line to be divided, the cutting blade 72 is aligned with the line to be divided on the side, Is cut.

By repeating this cutting operation, the silicon substrate 10 and the light emitting layer 30 are fully cut along the lines to be divided. As a result, the silicon substrate 10 is divided into chips C along the line to be divided. In the dividing step, the silicon substrate 10 may be divided into chips (C). For example, the silicon substrate 10 may be divided along the planned dividing line by ablation by a laser beam You can. Alternatively, a modified layer along a line to be divided may be formed in the silicon substrate 10 by a laser beam, and an external force may be given to the silicon substrate 10 using the modified layer as a dividing point.

When the reflective film 40 is cut and held on the chuck table 71 with the reflective film 40 facing upwardly, since the line to be divided can not be confirmed in the reflective film 40, the transparent chuck table 71 is used Alignment from the chuck table 71 side is required. Therefore, as shown in Figs. 10A and 10B, the surface of the silicon substrate 10 held in suction by the chuck table 71 may be reversed. In this case, the surface of the reflection film 40 (electrode) is attached to the dicing tape T2 covering the opening of the ring frame, and the surface of the silicon substrate 10 supported by the ring frame, that is, The silicon substrate 10 is sucked and held on the chuck table 71 via the dicing tape T2. As described above, the silicon substrate 10 may be aligned and cut from above.

Alternatively, after the annular reinforcing portion 12 is firstly removed, the silicon substrate 10 may be adhered to the dicing tape T2 covering the opening portion of the ring frame. The annular reinforcing portion 12 may be removed by grinding the inner peripheral surface of the annular reinforcing portion 12 with a cutting blade so that the inner peripheral surface of the annular reinforcing portion 12 is cut by a laser beam The concave portion 11 and the annular reinforcing portion 12 may be separated from each other.

As described above, the LED substrate forming method of the present embodiment uses the silicon substrate 10 as a support substrate, thereby eliminating the replacement work from the silicon substrate 10 to the support substrate, thereby enhancing the work efficiency. Further, only the central portion is left while leaving the outer circumferential portion of the silicon substrate 10, so that the rigidity of the silicon substrate 10 is secured while being thinned. Therefore, the rigidity of the support substrate is not lowered even though the silicon substrate 10 at the point necessary for the LED device is thinned. The reflective film 40 is formed on the other surface of the silicon substrate 10 so that the light transmitted through the thinned silicon substrate 10 is reflected forward in the reflective film 40 to improve the luminous efficiency. In addition, by using the silicon substrate 10 as an epitaxial substrate, the cost can be reduced as compared with a configuration using a sapphire substrate as an epitaxial substrate.

Further, the present invention is not limited to the above-described embodiment, and various modifications can be made. In the above-described embodiment, the size, shape and the like shown in the accompanying drawings are not limited to this, but can be suitably changed within the range of the effect of the present invention. In addition, as long as the scope of the object of the present invention is not deviated, it is possible to appropriately change and carry out the present invention.

For example, the n-type electrode on the other surface of the silicon substrate may be connected to the n-GaN layer through an Si-through electrode (TSV: Through-Silicon Via). Hereinafter, a method of forming the LED substrate of the first modification will be described with reference to FIG. 8 is a view showing an example of an electrode forming step of the first modification. The first modified example differs from the present embodiment only in the electrode forming step. Therefore, only the electrode forming step will be described briefly.

8, in the electrode formation step of the first modification, the through hole 15 is formed which is etched from the reflective film 40 side to reach the n-GaN layer 31 from the reflective film 40. The through hole 15 is filled with a conductive material such as a metal to form the Si through electrode 53 and the n type electrode 51 connected to the Si through electrode 53 is formed. Thereby, the n-type electrode 51 and the n-GaN layer 31 are directly connected, and the resistance between the n-type electrode 51 and the n-GaN layer 31 can be reduced. Therefore, the brightness of the LED substrate can be improved with low power consumption.

Alternatively, an n-type electrode and a p-type electrode may be formed on the other surface of the silicon substrate, and they may be connected to the n-GaN layer and the p-GaN layer by Si-penetrating electrodes, respectively. Hereinafter, a method of forming the LED substrate of the second modification will be described with reference to FIG. 9 is a view showing an example of an electrode forming step of the second modification. The second modification is different from the present embodiment only in the electrode formation process. Therefore, only the electrode forming step will be described briefly.

9, in the electrode forming step of the second modification, a through hole 15 which is etched from the reflective film 40 side to reach the n-GaN layer 31 from the reflective film 40, ) To reach the p-GaN layer 33 is formed. The n-type electrode 51 connected to the Si through electrodes 53 and 54 and the p-type electrode 51 connected to the n-type through holes 53 and 54 are formed by filling the through holes 15 and 16 with a conductive material such as metal. (52) are formed. Thereby, the n-type electrode 51 and the n-GaN layer 31 are directly connected and the p-type electrode 52 and the p-GaN layer 33 are directly connected. Therefore, the resistance between the n-type electrode 51 and the n-GaN layer 31 and the resistance between the p-type electrode 51 and the p-GaN layer 33 can be reduced and the power consumption of the LED substrate can be reduced. In addition, the light emission by the surface of the light emitting layer 30 is not blocked by the p-type electrode 52, and the light emitting area of the light emitting layer 30 can be increased. Therefore, the luminance of the LED substrate can be further improved as compared with the first modified example.

In the above embodiment, the protective tape T1 is replaced with the dicing tape T2. However, the present invention is not limited to this configuration. When the p-type electrode 52 is formed on the surface of the light emitting layer 30 before the protective tape T1 is adhered, the dicing tape T2 is adhered to the surface of the protective tape T1 without removing the protective tape T1. .

INDUSTRIAL APPLICABILITY As described above, the present invention has an effect of forming an LED substrate at low cost by a simple operation, and is particularly useful for a method of forming an LED substrate in which a light emitting layer is formed using a silicon substrate as an epitaxial substrate.

10: silicon substrate
11:
12:
20: buffer layer
30: light emitting layer
31: n-GaN layer
32:
33: p-GaN layer
40:
51: n-type electrode (electrode)
52: p-type electrode (electrode)
C: Chip

Claims (1)

A buffer layer forming step of forming a buffer layer on one surface of the silicon substrate;
A light emitting layer forming step of forming a light emitting layer on the surface of the buffer layer formed in the buffer layer forming step,
An annular reinforcing portion forming step of forming a ring-shaped reinforcing portion on the outside of the concave portion by grinding the center of the other surface of the silicon substrate after the light emitting layer forming step to form a concave portion;
A reflective film forming step of forming a reflective film on the concave portion after the step of forming the annular reinforcing portion;
An electrode forming step of forming an electrode on a surface of the reflective film formed in the reflective film forming step;
And a dividing step of dividing the light emitting element into chips along a line to be divided after the electrode forming step.

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