KR20120086241A - Manufacturing method of led chip - Google Patents

Abstract

PURPOSE: A method for manufacturing an LED chip is provided to reduce the number of processes by omitting a process for removing a reflection film along a division line. CONSTITUTION: An LED body(2) is formed on the rear of a mother board(1). A reflection film(3) is formed on the rear of the mother board. The reflection film selectively reflects light from the LED body. A laser source(4) emits laser beams. The laser beams pass through the reflection film and reach a focus location of the mother board.

Description

Manufacturing Method of LED Chip {MANUFACTURING METHOD OF LED CHIP}

The present invention is characterized in that an LED element body for generating luminescent light is formed on one main surface (referred to as the surface side) of the light-transmissive substrate, and the emitted light is reflected on the other main surface (referred to as the back side). The manufacturing method of the LED chip which has a structure in which the reflecting film was formed.

The LED chip of the structure which formed the LED element main body which consists of group III nitride type semiconductor on the chip-shaped sapphire board | substrate is commercialized as a blue light emitting diode (LED), for example.

Recently, in order to increase the extraction efficiency of the light emitted from the LED chip, a metal reflective film is formed on the back side of the light transmissive substrate (such as a sapphire substrate) through which the emitted light can pass, and together with the light emitted directly from the LED element body, An LED chip has been used that effectively uses the emitted light that has once entered the substrate and is reflected by the metal reflective film on the back side and then passed through the substrate again (see Patent Document 1).

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

On the first main surface (surface) of the sapphire substrate 10, a GaN buffer layer 12, an n-type GaN layer 13, an n-type AlGaN layer 14, a light emitting layer 15 made of GaInN, and a p-type AlGaN layer 16 ) And the p-type GaN layer 17, the n-type AlGaN layer 14, the light emitting layer 15, and the p-type AlGaN layer 16 until a portion of the n-type GaN layer 13 is exposed. , a semiconductor laminated structure having a region in which part of the p-type GaN layer 17 is removed by etching is formed. On the outer circumferential surface of the semiconductor laminate structure, except for the electrode forming portion, a SiO ₂ film 18 is formed as an insulating protective film. On the p-type GaN layer 17, a light-transmissive p-type electrode 19 (Au thin film) and an n-type GaN layer 13 are formed with an n-type electrode 20 (Ti / Al / Au film), respectively.

The reflective film 11 is formed on the 2nd main surface (back surface side) of the sapphire substrate 10. As the reflective film 11, a material having excellent reflection characteristics with respect to the wavelength of the light emitted from the light emitting layer 15 is used. Specifically, for example, a single layer Au film is formed, whereby the light emitted from the back surface is emitted. The reflection is made toward the sapphire substrate 10 side.

In addition to the Au film, an Al film or a dielectric multilayer film is used as the material of the reflecting film for the reflecting film 11 in consideration of the light emission characteristics and the material cost of the LED element. That is, since the light emission wavelength region (light emission spectrum) is different depending on the type and the film thickness of the semiconductor material of the LED element body, a material having excellent reflection characteristics with respect to the light emission wavelength is selected and used according to the device and the LED (product). For example, when using fluorescent light by the fluorescent material applied to the periphery of an element, a material is selected also considering this effect. Specifically, if the white LED (white LED consisting of a fluorescent material and a blue LED, or a white LED consisting of an RGB three-wave fluorescent material and a purple light source), a dielectric having excellent reflectance in a wavelength region of about 350 nm to 800 nm, which is a visible light wavelength. A multilayer film may be used in some cases. On the other hand, when the material cost is given priority, an Al film is used.

The LED chip in which the reflecting film was formed in the back surface side is manufactured by going through the following manufacturing processes. That is, a wafer-shaped sapphire substrate is used as the mother substrate, first the LED element body is formed in a lattice pattern on the first main surface (surface) of the mother substrate, and then the back surface is polished to the required thickness, and then A reflective film is formed on the second main surface (rear surface) (element formation step). Then, in order to divide into individual LED element main bodies, a sapphire substrate is divided | segmented into chip shape, and it takes out as an LED chip (product) (chip dividing process).

Here, the chip | dividing process which divides into an individual LED chip from a mother board | substrate is demonstrated. In general, also in the manufacturing process of the LED chip, similarly to other semiconductor products, when dividing the mother substrate by chip, mechanical processing using a dicing blade (dicer), diamond scriber or the like, or a laser for irradiating a laser beam The division by any one of the processes is performed.

Among these, when the mother substrate is divided by mechanical scribing using a processing tool such as a dicing blade or a diamond scriber, the sapphire is a much harder brittle material than glass and the like, so that the processing tool is easily worn and processed. In addition to the desired crack, chipping that causes product defects is likely to occur on the divided surface.

On the other hand, when dividing a mother substrate by laser processing using a high output pulse laser (pulse width 10 ^-9 to 10 ^-7 second), such as a YAG laser, division by a laser ablation or multiphoton absorption which is a well-known technique is performed. That is, laser light is condensed in the vicinity of the substrate surface or inside the substrate, and an abrasion is generated in the vicinity of the substrate surface to form grooves, or by processing multi-photons to form a processing deterioration portion in the substrate. It is set as the starting point for dividing (refer patent document 2, patent document 3).

However, when processing sapphire which is a brittle material with a laser, it is necessary to raise irradiation energy compared with the processing with glass etc. in both abrasion and multiphoton absorption. As a result, in the case of the process by abrasion, the groove width formed will become wider. Also in the case of forming a processing deterioration part inside the substrate by multiphoton absorption, the deterioration part becomes wider and the surface roughness of the divided surface formed on the deterioration part becomes rough, so that the divided part of the desired precision is not necessarily obtained.

Accordingly, a new laser processing method using the pulse width (hereinafter referred to as a pulse width of 10 ^-10 seconds or less of the pulsed laser "ultra-short pulse laser") of 10 ^-10 seconds ultra-short pulse laser (in the following, the specification (Also referred to as BI method) has been proposed (see Patent Document 4). According to this, an ultra-short pulse laser having an extremely short pulse width and high power density is injected using a Nd: YAG laser (wavelength 1064 nm) by focusing so as to be focused near the surface of the sapphire substrate. At this time, the laser light is not absorbed by the substrate material (sapphire) except at the vicinity of the condensing point, but multi-photon absorption is caused at the condensing point, causing instantaneous and local melting and sublimation (local microablation). . And microcracks are formed in the range from the surface layer part of a board | substrate to a surface. That is, in the conventional ablation, almost all of the energy from the irradiated laser beam is consumed for melting and evaporating the substrate material and used for the formation of a wider ablation hole (a hole diameter of about 8 mu m). In the BI method), the energy of the irradiation laser is partially consumed in the formation of minute melting traces (small holes having a pore diameter of about 1 μm), and the remaining energy is consumed as an impact force for forming minute cracks. As described above, the dissolution traces are discretely formed along the division scheduled line like a perforation line, so that an easy separation region in which adjacent dissolution traces are connected by minute cracks is formed, and the substrate can be divided along this region.

Japanese Patent Application Laid-open No. Hei 10-308532 Japanese Patent Application Laid-open No. Hei 11-177137 Japanese Patent Application Laid-open No. 2004-268309 Japanese Patent Application Publication No. 2005-271563

The chip division process in LED manufacturing demonstrated that laser ablation processing, laser processing by multiphoton absorption, and new laser processing by ultra-short pulsed laser (BI method) were applied.

However, in the case of dividing the mother chip having the reflective film formed on the rear surface side to cut the LED chip, if the division is to be performed by the laser processing as described above, the laser beam is reflected by the reflective film due to the presence of the reflective film on the rear surface side. This reflection or absorption becomes a processing problem.

As one of the division methods by laser irradiation, it is possible to irradiate the laser irradiation from the surface side on which the LED element body is formed, not from the back side side, but the light emission of the irradiated laser beam also affects the LED element body, and the LED element itself. Since a problem of lowering the luminous efficiency of the light emitting device occurs, it is preferable to perform laser irradiation from the back side from the viewpoint of maintaining the luminous efficiency.

In the LED manufacturing process so far, an Al film is used for the reflective film from a practical point of view of material cost, and from the viewpoint of focusing on the extraction efficiency of the emitted light rather than the material cost, the Au film is superior to the light emission wavelength than the Al film. Although the use of materials, such as a dielectric multilayer film, is considered, from the viewpoint of a chip | tip division process, what kind of film is preferable as a reflecting film was not considered at all.

Therefore, when a mother substrate having a structure in which a reflective film such as an Al film is formed on the rear surface side is formed by laser irradiation from the rear surface side, first, the reflective film is removed in a band shape along the division scheduled line (peeling). The mother substrate was exposed, and the laser light was subsequently irradiated toward the exposed portion from the back side of the mother substrate.

In that case, laser ablation for removing the reflective film is performed under irradiation conditions (different from laser irradiation for forming a split starting point, described later) to remove the reflective film or to remove the reflective film along the division scheduled line. In the end, a step of removing (peeling) the reflective film in a lattice shape along the dividing scheduled line is required, which is a factor that increases the number of processing steps.

Therefore, this invention provides the manufacturing method of LED which does not need to remove the reflection film along a predetermined | prescribed division line previously, when forming a division origin by laser-irradiating the mother substrate in which the reflection film is formed in the back surface from the back surface side. It aims to do it.

In the method for manufacturing the LED chip of the present invention made to achieve the above object, a plurality of LED element bodies are patterned on the front side of the light transmissive substrate, and a mother film is formed on the back side including the division scheduled line. It is a manufacturing method of the LED chip which includes the process of forming the dividing origin for dividing | segmenting for every LED element main body by irradiating a laser beam along a dividing line to a board | substrate, and is provided with the following structures.

That is, it has a property of reflecting the wavelength range (preferably, also the wavelength range of the fluorescent light from a fluorescent material) which the LED element main body emits as a reflecting film, and transmitting the wavelength light of the laser beam irradiated to a division scheduled line. The reflective film is formed on the back surface side, and the laser beam is transmitted through the reflective film from the back surface side to directly irradiate the back surface of the substrate, thereby laser processing the substrate.

Here, the light transmissive substrate may be a sapphire substrate.

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

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

Moreover, what is necessary is just to irradiate the pulse laser of 1064 nm by Nd: YAG laser as a laser beam.

In addition, as the pulse laser, an ultrashort pulsed laser whose pulse width is shorter than 10 ^-10 seconds may be irradiated discretely along the division scheduled line to form a division origin.

Here, the term "discrete irradiation" means that a small melting trace (small hole having a pore diameter of about 1 µm) is obtained by discretely irradiating with a new laser processing method (BI method) at a distance. Although formed at intervals, it is irradiation of the interval which the micro cracks formed between adjacent molten traces connect. In other words, the molten trace and the microcracks are formed so as to be continuous, so that the process of inducing the cracks to be advanced is performed.

In this way, by forming the dissolution traces discretely along the predetermine line like a cut line, a separation facilitating region in which adjacent dissolution traces are connected by minute cracks is formed, and the substrate can be divided along this region.

According to the LED chip manufacturing method of the present invention, as the optical characteristic of the reflective film formed on the back side of the transparent substrate that transmits the light emitted by the LED element, the LED element body and the wavelength region of the fluorescent material can be reflected, By having the property of transmitting the wavelength light of the laser beam irradiated to the dividing scheduled line, when performing laser irradiation along the dividing scheduled line, if it irradiates from the back surface side, it will permeate a reflection film and a laser beam will be irradiated directly to a board | substrate.

In other words, the laser beam is irradiated onto the substrate by removing the reflective film in advance, but the laser beam reaches the back of the substrate even when the laser irradiation is performed while the reflective film is formed on the rear surface side, and the reflective film is substantially absent. The same laser processing as is possible.

Thereby, in manufacture of an LED chip provided with a back surface reflecting film, the process of removing a reflecting film along a division planned line becomes unnecessary, and the number of process steps can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the state which formed the LED element main body in the surface side of a mother substrate.
FIG. 2 is a view showing a state in which a reflective film is formed on the rear surface side of a mother substrate on which an LED element body is formed.
3 is a diagram showing an ideal reflection spectrum as a reflection film.
It is a figure which shows the processing state at the time of dividing a mother board into individual LED chips by laser irradiation.
FIG. 5 is a diagram illustrating a state in which a brake process is performed along the division starting point.
6 is a cross-sectional view showing an example of the structure of the LED element body.

Hereinafter, the manufacturing process of the LED chip of this invention is demonstrated in detail based on a sequential drawing, taking the LED chip using group III nitride type semiconductor as an example. The manufacturing method of the LED chip which concerns on this invention mainly consists of two processes, an element formation process and a chip | tip dividing process.

(Element formation step)

In the element formation step, a plurality of LED element bodies are patterned on the front side (first main surface side) of the mother substrate, and a reflective film is formed on the back side (second main surface side).

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the state which formed the LED element main body in the surface side of a mother substrate, FIG. 1 (a) is a top view (top view of a surface side), and FIG. 1 (b) is a front view. The mother board | substrate 1 consists of a wafer-shaped sapphire board | substrate, and many LED element main bodies 2 which are regularly arranged longitudinally and horizontally to form a square grating are pattern-formed on the surface 1a (1st main surface). . Each LED element main body 2 has the element structure shown in FIG. 6, and is formed by the well-known semiconductor manufacturing process.

Moreover, the gap which becomes a division | segmentation schedule line at the time of dividing | segmented by LED element main body is formed between the adjacent element main bodies 2.

Sapphire used as the mother board | substrate 1 is a material which has light transmittance with respect to the wavelength range (350 nm-800 nm) which the LED element main body 2 emits light. In addition, as long as it is a material which has light transmittance with respect to the light emission wavelength range of the LED element main body 2, you may use other than a sapphire substrate as a board | substrate. When the LED element main body 2 is a monochromatic light emitting diode instead of a white light emitting diode, it is sufficient to have a light transmittance with respect to the emission wavelength of the corresponding monochromatic light instead of the whole visible region.

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

As the reflective film 3, a material having a property of selectively reflecting the light emitted from the LED element main body 2 and transmitting the wavelength light of the laser beam irradiated to the division scheduled line is used. Since an infrared laser (YAG laser, YVO laser, etc.) which is wavelength light of 900 nm or more is normally used for a laser beam, the reflecting material which permeates the infrared wavelength range of 900 nm or more is used.

Specifically, for example, it is preferable to use a reflecting film that reflects a wavelength region of 400 nm to 700 nm with a reflectance of 90% or more, and transmits wavelength light (1064 nm) of a Nd: YAG laser with a transmittance of 50% or more. .

3 is a diagram showing an ideal reflection spectrum as the reflective film 3.

A reflective film close to such characteristics can be formed by a dielectric multilayer film.

(Chip dividing process)

Next, the mother substrate in which the LED element main body 2 and the reflecting film 3 were formed is divided into individual LED chips.

It is a figure which shows the processing state at the time of dividing a mother board into individual LED chips by laser irradiation.

Using a Nd: YAG pulse laser as the laser 4, the wavelength was 1064 nm, the pulse width was 20 picoseconds, the pulse energy was 0.1 µJ to 50 µJ, the repetition frequency was 10 Hz to 200 Hz, and the scanning speed was 50 mm / in the direction of the division scheduled line. Under the conditions of seconds to 3000 mm / second, the ultra-short laser beam is irradiated from the back surface 1b side. In addition, the scanning speed causes the interval (irradiation pitch) of the previous irradiation position to be 3 µm to 20 µm, in order to balance the repetition frequency.

Then, in the lens optical system (not shown) incorporated in the laser 4, the focus is adjusted so that the focus position in the depth direction is focused at the position A (divided starting point) which is slightly inside the substrate from the substrate back side 1b.

When the laser is irradiated in this way, the laser beam L is transmitted through the reflective film 3 to reach the focal position of the mother substrate 1 and acts directly. Discrete small holes are formed at intervals of 20 mu m, and minute cracks are formed between the adjacent holes and the holes, thereby forming a processing line (scribe line) that becomes the starting point of division. The same process is repeated along all the grid lines to be divided, and the division origin for dividing by the LED element bodies is formed.

FIG. 5: is a figure which shows the state which performs a brake process with respect to the mother substrate 1 in which the division origin was formed.

The brake bar 5 is applied to the position P1 on the surface side opposite to the position where the division origin A is formed, and the support bars 6a and 6b are placed at the positions P2 and P3 spaced apart from the division origin A to the left and right sides on the rear surface side. , By applying a bending moment in a three-point supporting state, the brake is performed along the division scheduled line. Then, the same brake process can be performed for every LED chip by executing the same break point along all the division origins.

Therefore, according to the present invention, after forming the reflecting film 3, the mother substrate itself can be laser-processed immediately without peeling off the reflecting film 3 along the division scheduled line.

In the said embodiment, although chip | tip division by irradiation of an ultrashort pulse laser was performed, you may apply conventional abrasion processing or the process by multiphoton absorption. Also in these cases, laser processing can be performed immediately, without peeling the reflective film formed in the back surface side along the dividing scheduled line.

This invention is used for manufacture of the LED chip in which the reflection film was formed in the back surface of a board | substrate.

A: Focus position (divided starting point)
L: laser beam
1: light transmissive substrate (sapphire substrate)
1a: surface side
1b: back side
2: LED element body
3: reflecting film
4: laser (Nd: YAG laser)
5: brake bar
6a, 6b: support bar

Claims (6)

A plurality of LED element bodies are patterned on the front side of the light transmissive substrate, and the LED element main body is irradiated with a laser beam along the dividing due line to the mother substrate on which the reflective film is formed including the upper part of the dividing due line. It is a manufacturing method of an LED chip comprising a step of forming a split starting point for dividing into stars,
As the reflecting film, a reflecting film having a property of reflecting the wavelength range of the emitted light emitted by the LED element main body and transmitting the wavelength light of the laser beam irradiated to the division scheduled line is formed on the back surface side,
A method of manufacturing an LED chip, characterized in that the laser beam is transmitted through a reflective film from the back side to directly irradiate the back side of the substrate. The method for manufacturing an LED chip according to claim 1, wherein the light transmissive substrate is a sapphire substrate. The said reflecting film is a manufacturing method of the LED chip of Claim 1 or 2 whose reflectance of the visible light region of 400 nm-700 nm is 90% or more, and the transmittance | permeability of the infrared region of 900 nm or more is 50% or more. The method of claim 3, wherein the reflective film is formed of a dielectric multilayer film. The manufacturing method of the LED chip as described in any one of Claims 1-4 which irradiates the pulse laser of 1064 nm by a Nd: YAG laser as a laser beam. 6. The method of claim 5, wherein the production of a pulsed laser, LED chips for a short ultra-short pulse laser than 10 ^-10 sec pulse width, to investigate discretely along the division planned line.

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