TWI447964B - LED wafer manufacturing method - Google Patents

Description

LED chip manufacturing method

The present invention relates to a method of manufacturing an LED chip having a structure in which an LED element that emits light is formed on a main surface (as a surface side) on one side of a light-transmitting substrate, and on the other main surface A reflective film having the property of reflecting the emitted light is formed on the back side.

The LED chip in which the LED element main body including the group III nitride-based semiconductor is formed on the wafer-shaped sapphire substrate can be produced, for example, in the form of a blue light-emitting diode (LED).

Recently, in order to improve the light-emitting efficiency of the LED chip, a metal reflective film is formed on the back side of a light-transmissive light-transmissive substrate (such as a sapphire substrate), which is not only effective in utilizing the self-LED. The emitted light that is directly emitted from the element body is used, and the emitted light that is once incident on the substrate and reflected by the metal reflective film on the back side and then passed through the substrate again is used (see Patent Document 1).

6 is a cross-sectional structural view showing a GaN-based LED which is a typical example of an LED wafer in which a reflective film is formed on the back side of a light-transmitting substrate.

A semiconductor laminate structure is formed on the first main surface (surface) of the sapphire substrate 10, and the semiconductor laminate structure includes two regions: a GaN buffer layer 12, an n-type GaN layer 13, and an n-type AlGaN layer are sequentially laminated in one region. 14. A light-emitting layer 15, a p-type AlGaN layer 16, and a p-type GaN layer 17 including GaInN; and a portion of the n-type AlGaN layer 14, the light-emitting layer 15, the p-type AlGaN layer 16, and the p-type GaN layer 17 in another region It is removed by etching until one portion of the n-type GaN layer 13 is exposed. On the outer peripheral surface of the semiconductor laminate structure, an SiO ₂ film 18 is formed as an insulating protective film in addition to the electrode forming portion. Further, a translucent p-type electrode 19 (Au thin film) is formed on the p-type GaN layer 17, and an n-type electrode 20 (Ti/Al/Au film) is formed on the n-type GaN layer 13.

A reflective film 11 is formed on the second main surface (back side) of the sapphire substrate 10. The reflective film 11 is made of a material having good reflection characteristics with respect to the wavelength of light emitted from the light-emitting layer 15, and specifically, for example, a layer of Au film is formed, whereby light emitted from the back surface is emitted toward the sapphire substrate 10 Side reflection.

Further, in the reflective film 11, in consideration of the light-emitting characteristics and material cost of the LED element, in addition to the Au film, an Al film or a dielectric multilayer film may be used as the material of the reflective film. In other words, depending on the type and thickness of the semiconductor material of the LED element body, the light-emitting wavelength region (light-emitting spectrum) is different. Therefore, it is possible to selectively use the reflection characteristics for the light-emitting wavelength in accordance with the device and the LED (product). material. For example, when a fluorescent light beam applied to a fluorescent material around the element is used, the material is also selected in consideration of the influence. Specifically, in the case of a white LED (a white LED including a fluorescent material and a blue LED, or a white LED including an RGB 3 wavelength fluorescent material and a violet light source), a wavelength of visible light, that is, a wavelength of about 350 nm to 800 nm may be used. A dielectric multilayer film having excellent reflectance in a region. On the other hand, when the material cost is prioritized, the A1 film can be used.

The LED wafer on which the reflective film is formed on the back side is manufactured through the following manufacturing steps. That is, the wafer-shaped sapphire substrate is used as a mother board, and first, the LED elements are formed in a lattice pattern on the first main surface (surface) of the mother board. The main body, then, after grinding the back surface to a desired thickness, a reflective film is formed on the second main surface (back surface) of the mother board (element forming step). Thereafter, in order to divide into individual LED element bodies, the sapphire substrate is divided into wafers and taken out as LED chips (products) (wafer dividing step).

Here, the wafer dividing process in which the mother board is divided into individual LED chips will be described. In general, in the manufacturing process of the LED chip, similarly to other semiconductor products, when the mother board is divided into individual wafers, a cutter (dicer), a diamond scriber, etc. are used. Machining or performing segmentation by any laser processing using an irradiated laser beam.

Among them, when the mother board is divided by mechanical scribing using a processing tool such as a dicing blade or a diamond scriber, since the sapphire is a much harder brittle material than glass, the processing tool is easily worn and processed. In addition to the required crack, the split surface is prone to chipping which causes defective products.

On the other hand, when using a laser output such as a YAG laser with a high output pulsed laser (pulse width of 10 ^-9 to 10 ^-7 seconds) to divide the mother board, a well-known technique, that is, laser ablation (Laser) is used. Ablation) or multiphoton absorption for segmentation. That is, the laser beam is concentrated near the surface of the substrate or inside the substrate to cause ablation near the surface of the substrate to form a groove, or a multi-photon absorption is used to form a processed metamorphic portion inside the substrate, thereby making the processed portion useful. The starting point of the division at the break (see Patent Document 2 and Patent Document 3).

However, when using a laser to process a hard and brittle material, sapphire, it is necessary to make any of ablation and multiphoton absorption. The irradiation energy is higher than the irradiation energy when processing glass or the like. As a result, when the processing is performed by ablation, the groove width formed is widened. When the processed metamorphic portion inside the substrate is provided by multiphoton absorption, the modified portion is also widened, and the surface roughness of the divided surface formed by the modified portion becomes thick, and it is not always possible to obtain a divided surface having good precision.

Therefore, the proposed use of a pulse width of ^10-10 seconds of ultrashort pulse laser (pulse width will be ^10-10 seconds of pulsed lasers known as "ultra-short pulse laser") of the new laser processing method (The following is also referred to as the BI method in this specification) (refer to Patent Document 4). Therefore, using a Nd:YAG laser (wavelength 1064 nm), the focus is adjusted to be emitted so that ultrashort pulsed lasers having extremely short pulse widths and high power densities are concentrated near the surface of the sapphire substrate. At this time, the laser beam is not absorbed by the substrate material (sapphire) except for the vicinity of the condensed spot, but causes multiphoton absorption at the condensed spot, thereby instantaneously and locally generating melting and sublimation (small local ablation). Further, micro cracks are formed in the range from the surface layer portion to the surface of the substrate. That is, in the previous ablation, almost all the energy generated by the irradiated laser beam is consumed by the melting and transpiration of the substrate material, and is used to form a large ablation hole (the aperture is about 8 μm), and the new mine In the injection processing method (BI method), only a part of the energy for irradiating the laser is consumed by the formation of minute molten traces (a small hole having a pore diameter of about 1 μm), and the rest of the energy is consumed as an impact force for forming a microcrack. The above-described dissolution marks are formed in a dispersed manner along a predetermined dividing line as a perforation, whereby an easy-separation region in which adjacent dissolution marks are connected by minute cracks is formed, and the substrate can be divided along the region.

[Advanced technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 10-308532

[Patent Document 2] Japanese Patent Laid-Open No. Hei 11-177137

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2004-268309

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2005-271563

In the wafer dividing step in LED manufacturing, laser ablation processing, laser processing using multiphoton absorption, and new laser processing (BI method) using ultrashort pulse laser can be used. Description.

However, when the mother board in which the reflective film is formed on the back side is divided and the LED chip is cut out, if the laser processing is to be used for the division by the above-described laser processing, the laser beam may be caused on the back side, so that the laser beam is caused. It is reflected or absorbed, which becomes a barrier to processing.

As one of the division methods using laser irradiation, laser irradiation can be performed from the surface side on which the LED element main body is formed instead of the back side, but the illumination of the irradiated laser beam also affects the LED element main body, resulting in the LED element Since the luminous efficiency of the self is lowered, it is desirable to perform laser irradiation from the back side from the viewpoint of maintaining luminous efficiency.

Further, in the current LED manufacturing step, from the viewpoint of the practicality of the material cost, the reflective film uses an Al film, and since the material cost is more important than the material cost, it has been The use of materials such as Au films or dielectric multilayer films which are more excellent in reflectance characteristics than the Al film, but not from the viewpoint of the wafer dividing step, has been studied. It is preferable which film is preferably a reflective film.

Therefore, when a mother board which is formed with a reflection film such as an Al film on the back side is subjected to laser irradiation from the back side to form a division start point, first, the reflection film is removed (stripped) in a strip shape along a predetermined division line. The mother board is exposed, and then the exposed light beam is irradiated from the back side of the mother board toward the exposed portion.

In this case, it is necessary to perform peeling using a pattern formed by photolithography along a predetermined dividing line, or irradiation conditions for removing the reflecting film (unlike laser irradiation for forming a dividing starting point described later) In order to perform laser ablation for removing the reflective film, in either case, the step of removing (peeling) the reflective film in a lattice shape along a predetermined dividing line is required, which is a factor causing an increase in processing time.

In view of the above, an object of the present invention is to provide a method for producing an LED, which is not required to be additionally removed along a predetermined dividing line in the case where a mother substrate on which a reflecting film is formed on the back surface is subjected to laser irradiation from the back side to form a dividing starting point. Reflective film.

In order to achieve the above object, a method of manufacturing an LED chip of the present invention comprises the steps of irradiating a laser beam along a predetermined dividing line with respect to a mother board to form a dividing starting point for dividing into individual LED element bodies, in the mother board, A plurality of LED element main bodies are formed in a pattern on the surface side of the light-transmitting substrate, and a reflective film is formed on a portion including a predetermined dividing line on the back surface side, and the above-described manufacturing method includes the following configuration.

That is, as the reflective film, a reflective film having the following properties is formed on the back side, and the laser beam is directly irradiated through the reflective film from the back side. Performing laser processing on the substrate in the manner of the back surface of the substrate; the properties of the reflective film are: reflecting the wavelength range of the emitted light emitted from the main body of the LED element (more preferably, the wavelength range of the fluorescent light beam from the fluorescent material), and illuminating The wavelength of the laser beam to the predetermined dividing line is transmitted.

Here, the light-transmitting substrate may be a sapphire substrate.

Further, the reflective film may have a reflectance of 90% or more in a visible light region of 400 nm to 700 nm, and a transmittance of 50% or more in an infrared region of 900 nm or more.

Specifically, the reflective film may also be formed of a dielectric multilayer film.

Further, as the laser beam, a 1064 nm pulsed laser using a Nd:YAG laser can be irradiated.

Further, as the pulse laser, an ultrashort pulse laser having a pulse width shorter than 10 ^{- 10} seconds may be scatteredly irradiated along a predetermined dividing line to form a dividing starting point.

Here, the term "dispersively irradiated" means that the irradiation is performed at intervals as described below, that is, by a novel laser processing method (BI method), the irradiation is dispersed with a distance therebetween, thereby forming a minute interval therebetween. The melt marks (apertures having a pore diameter of about 1 μm), but the minute cracks formed between the adjacent melt marks are connected to each other. In other words, since the melt marks and the micro cracks are connected to each other, they are processed by induction so that the cracks progress.

As described above, the above-described dissolution marks are formed dispersedly along a predetermined dividing line such as a perforation, whereby an easily separated region in which adjacent dissolution marks are connected by minute cracks is formed, whereby the substrate can be divided along the region.

A method of manufacturing an LED chip according to the present invention is formed as an LED The optical characteristics of the reflective film on the back side of the transparent substrate through which the light emitted by the element has a property of reflecting light of a wavelength region of the LED element main body and the fluorescent material, and causing a thunder to be irradiated onto a predetermined dividing line When the wavelength light of the light beam is transmitted, when the laser beam is irradiated along the predetermined dividing line, if the light is irradiated from the back side, the laser beam is directly transmitted to the substrate through the reflecting film.

In other words, the laser beam is irradiated onto the substrate by removing the reflection film in advance, but when the laser beam is irradiated in a state where the reflection film is provided on the back side, the laser beam can reach the back surface of the substrate. The same laser processing as in the case of substantially no reflection film is performed.

Thereby, in the manufacture of the LED wafer having the back surface reflective film, the step of removing the reflective film along the predetermined dividing line is not required, and the number of processing steps can be reduced.

Hereinafter, an LED chip using a group III nitride-based semiconductor will be exemplified, and a manufacturing procedure of the LED wafer of the present invention will be sequentially described in detail based on the drawings. The method for manufacturing an LED wafer of the present invention mainly comprises two steps of an element forming step and a wafer dividing step.

(component forming step)

In the element forming step, a plurality of LED element bodies are formed in a pattern on the surface side (first main surface side) of the mother board, and a reflective film is formed on the back side (second main surface side).

Fig. 1 is a view showing a state in which an LED element body is formed on the surface side of a mother board, and Fig. 1(a) is a plan view (a plan view on the front side), and Fig. 1(b) is a front view. The mother board 1 is composed of a wafer-shaped sapphire substrate on the surface 1a (the first On one main surface, a plurality of LED element bodies 2 arranged in a vertical and horizontal direction are formed in a pattern so as to form a square lattice. Each of the LED element bodies 2 has the element structure shown in FIG. 6, and is formed by a well-known semiconductor manufacturing process.

Further, a gap is provided between the adjacent element bodies 2, and the gap is a predetermined dividing line when the main body of each LED element is divided.

The sapphire used as the mother board 1 is a material having a light transmissive property in a wavelength region (350 nm to 800 nm) in which the LED element main body 2 emits light. Further, as long as it is a material having light transmissivity in the light-emitting wavelength region of the LED element body 2, a material other than the sapphire substrate may be used as the substrate. When the LED element body 2 is not a white light emitting diode but a monochromatic light emitting diode, it may be light transmissive for the light emission wavelength of the corresponding monochromatic light and not for the entire visible light region.

2 is a view showing a state in which a reflective film is formed on the back side of the mother substrate 1 on which the LED element body 2 is formed, and FIG. 2(a) is a bottom view (a plan view on the back side), and FIG. 2(b) is a front view. Figure. A reflective film 3 is formed on the entire back side 1b of the mother board 1.

As the reflective film 3, a material having a property of selectively reflecting the emitted light of the LED element main body 2 and transmitting the wavelength light of the laser beam irradiated onto the predetermined dividing line can be used. As the laser beam, an infrared laser (YAG laser, YVO laser, or the like) having a wavelength of 900 nm or more is generally used. Therefore, a reflective material that transmits an infrared wavelength region of 900 nm or more can be used.

Specifically, it is preferable to use a reflection film in which light of a wavelength region of 400 nm to 700 nm is reflected by a reflectance of 90% or more, and light of a wavelength of Nd:YAG laser (1064 nm) is 50% or more. Transmitted through.

FIG. 3 is a view showing an ideal reflection spectrum of the reflective film 3.

A reflective film close to the above characteristics may be formed of a dielectric multilayer film.

(wafer dividing step)

Next, the mother board on which the LED element body 2 and the reflection film 3 are formed is divided into individual LED wafers.

Fig. 4 is a view showing a state of processing when a mother board is divided into individual LED chips by laser irradiation.

As the laser 4, the Nd:YAG pulse laser is used at a wavelength of 1064 nm, a pulse width of 20 picoseconds, a pulse energy of 0.1 μJ to 50 μJ, a repetition frequency of 10 kHz to 200 kHz, and a scanning speed of 50 mm/sec to 3000 mm/sec in a predetermined dividing line direction. Under the condition, the ultrashort laser beam is irradiated from the side of the back surface 1b. Further, as the scanning speed, the repetition frequency is used, and the interval from the previous irradiation position (irradiation pitch) is 3 μm to 20 μm.

Further, the focus is adjusted by a lens optical system (not shown) built in the laser 4 so that the focus position in the depth direction is concentrated at a position A (divided starting point) slightly closer to the inner side of the substrate than the substrate back side 1b.

When the laser beam is irradiated in the above manner, the laser beam L is directly transmitted to the focal position of the mother board 1 through the reflection film 3, and the mother board 1 is moved on the one hand, and can be processed at intervals of 3 μm to 20 μm. A small hole is formed in a dispersed manner, and a micro crack is formed between the adjacent hole and the hole, thereby forming a processing line (scribe line) as a starting point of the division. The same processing is repeated along all of the grid-shaped predetermined dividing lines to form a dividing starting point for dividing into individual LED element bodies.

Fig. 5 is a view showing the disconnection process of the mother board 1 on which the division starting point is formed. The schema of the state.

The break bar 5 is aligned with the position P1 on the surface side facing the position where the split start point A is formed, and the support bars 6a, 6b are aligned on the back side with respect to the split start point A at the position P2 on the left and right sides thereof. And P3, thereby applying a bending moment in a state of being supported at three points, thereby being disconnected along a predetermined dividing line. Then, the same disconnection process is performed along all the division start points, whereby it can be divided into each LED wafer.

Therefore, according to the present invention, after the reflective film 3 is formed, the reflective film 3 may not be peeled off along the predetermined dividing line, but the mother plate itself may be subjected to laser processing immediately.

In the above embodiment, wafer division is performed by irradiating an ultrashort pulse laser, but it is also possible to use a previous ablation process or a process using multiphoton absorption. In these cases, the reflection film formed on the back side may be peeled off along the predetermined dividing line, and the laser processing may be performed immediately.

[Industrial availability]

The present invention can be used to manufacture an LED wafer in which a reflective film is formed on the back surface of a substrate.

1‧‧‧Transparent substrate (sapphire substrate)

1a‧‧‧Surface side

1b‧‧‧back side

2‧‧‧LED component body

3‧‧‧Reflective film

4‧‧ ‧ laser (Nd: YAG laser)

5‧‧‧Disconnect bar

6a, 6b‧‧‧ support rod

A‧‧‧Focus position (segment starting point)

L‧‧‧Laser beam

FIGS. 1(a) and 1(b) are views showing a state in which an LED element body is formed on the surface side of the mother board.

(a) and (b) of FIG. 2 show a state in which a reflective film is formed on the back side of the mother board on which the LED element main body is formed.

Fig. 3 is a view showing an ideal reflection spectrum of a reflective film.

Fig. 4 is a view showing a state of processing when a mother board is divided into individual LED chips by laser irradiation.

Fig. 5 is a view showing a state in which the disconnection processing is performed along the division start point.

Fig. 6 is a cross-sectional view showing an example of a structure of an LED element main body.

1‧‧‧Transparent substrate (sapphire substrate)

2‧‧‧LED component body

3‧‧‧Reflective film

4‧‧ ‧ laser (Nd: YAG laser)

A‧‧‧Focus position (segment starting point)

L‧‧‧Laser beam

Claims (8)

A method of manufacturing an LED chip, comprising: a step of irradiating a laser beam along a predetermined dividing line with respect to a mother board to form a dividing starting point for dividing into individual LED element bodies, wherein the mother board is transparent a plurality of LED element main bodies are formed in a pattern on the surface side of the substrate, and a reflective film is formed on the back surface side including a portion on the predetermined dividing line; and as the reflective film, a reflective film having the following properties is formed on the back surface side: the LED is formed The wavelength range of the emitted light emitted from the element body is reflected, and the wavelength light of the laser beam irradiated to the predetermined dividing line is transmitted; and the laser beam is directly transmitted to the back surface of the substrate by transmitting the laser beam from the back side to the reflecting film. The substrate is subjected to laser processing. The method of manufacturing an LED wafer according to claim 1, wherein the light-transmitting substrate is a sapphire substrate. The method for producing an LED wafer according to claim 1, wherein the reflective film has a reflectance of 90% or more in a visible light region of 400 nm to 700 nm, and a transmittance of an infrared region of 900 nm or more is 50% or more. The method for producing an LED chip according to claim 2, wherein the reflective film has a reflectance of 90% or more in a visible light region of 400 nm to 700 nm, and a transmittance of an infrared region of 900 nm or more is 50% or more. The method of manufacturing the LED wafer of claim 3, wherein the reflective film is formed of a dielectric multilayer film. A method of manufacturing an LED wafer according to claim 4, wherein said reflective film is formed of a dielectric multilayer film. A method of manufacturing an LED chip according to any one of claims 1 to 6, wherein The laser beam is irradiated with a 1064 nm pulsed laser using a Nd:YAG laser. A method of manufacturing an LED chip according to claim 7, wherein as the pulsed laser, an ultrashort pulse laser having a pulse width shorter than 10 ^{- 10} seconds is dispersedly irradiated along a predetermined dividing line.