KR20070041147A - High power light emitting diode fabricating method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a light emitting device, wherein a scratch is formed on a portion of an upper portion of a p-semiconductor layer, and a portion of the n-semiconductor layer is formed in a portion of the p-semiconductor layer including the scratch. A method of manufacturing a high power light emitting device in which the scratch shape formed on the p-semiconductor layer is etched and transferred to the n-semiconductor layer as it is.

In addition, according to the manufacturing method of the present invention, it is possible to effectively reduce the total internal reflection of the light generated due to the existing flat n-semiconductor layer surface, it is possible to manufacture a high output light emitting device that can maximize the light output.

Gallium Nitride, Light Emitting Diode, Horizontal, CMP, Light Output

Description

High Power Light Emitting Diode Fabricating Method

1 is a cross-sectional view of a horizontal light emitting device according to the prior art.

FIG. 2 is a schematic diagram illustrating aspects of transmission and total reflection of light in a portion A including the flat n-GaN layer surface of FIG. 1. FIG.

3A to 3F are cross-sectional views for explaining a preferred embodiment of the method of manufacturing a high output light emitting device according to the present invention.

FIG. 4 is a schematic diagram illustrating a transmission pattern of light in a portion B including the scratched n-GaN layer surface of FIG. 3F; FIG.

5 is an enlarged photograph of a scratch formed on a surface of an n-GaN layer of a high output light emitting device according to the present invention;

<Description of main parts of drawing>

100. Substrate 110. Buffer layer

120. n-semiconductor layer 130. active layer

140.p-semiconductor layer 151.first mask

152. Second Mask 160. Scratch

170. Transparent electrode 180a. N-electrode pad

180b. P-electrode pad

The present invention relates to a method of manufacturing a light emitting device, and in particular, to minimize the total internal reflection of the light generated on the surface of the n-semiconductor layer of the horizontal gallium nitride-based light emitting device, high output light emission that can maximize the light output of the light emitting device It relates to a method for manufacturing a device.

Recently, in order to increase external quantum efficiency or light output of a horizontal light emitting device, a method of maximizing internal quantum efficiency and a method of improving light extraction efficiency to the outside of the light emitting device have been attempted.

Specifically, a method of maximizing the internal quantum efficiency is a method of reducing the light loss due to the current diffusion layer, and a method of improving the light extraction efficiency to the outside of the light emitting device, which is generated at the interface between the inside and the outside of the light emitting device. There is a way to reduce the amount of light loss due to total reflection.

For reference, the quantum efficiency refers to the ratio of photons or electrons in the material to photons or electrons of other energy, and in particular, when converted to photons, it is also referred to as luminous efficiency.

Hereinafter, a structure and a problem thereof according to the prior art horizontal light emitting device according to the drawings will be described.

1 shows a schematic structure of a horizontal gallium nitride (GaN) -based light emitting device according to the prior art.

As shown in the figure, a horizontal gallium nitride (GaN) based light emitting device includes a sapphire substrate 10, a buffer layer 11, an n-GaN layer 12, an active layer 13, a p-GaN layer 14, And a current diffusion layer 15, an N-electrode pad 16, and a P-electrode pad 17.

The sapphire (Al ₂ O ₃ ) substrate is known to be most suitable for growing gallium nitride crystals among various substrates, and is commonly used as a substrate for manufacturing a gallium nitride-based light emitting device.

The buffer layer 11 is formed on the sapphire substrate 10 in order to reduce lattice defects between the gallium nitride semiconductor layer and the sapphire substrate and to maintain better gallium nitride (GaN) crystalline.

The n-GaN layer 12 is a semiconductor layer formed by adding n-type impurities to gallium nitride (GaN) so that a plurality of carriers become electrons. The n-GaN layer 12 is positioned below the active layer 13 to supply electrons to the active layer. Do it.

The active layer 13 converts excess energy into light when electrons and holes are recombined.

The p-GaN layer 14 is a semiconductor layer formed by adding a p-type impurity to gallium nitride (GaN) so that a plurality of carriers become holes. The p-GaN layer 14 is positioned above the active layer 13 to provide holes to the active layer. Supply it.

The current diffusion layer 15 and the N-electrode pad 16 are formed on the p-GaN layer 14 and the n-GaN layer 12, respectively.

At this time, the current diffusion layer 15 is formed to increase the transmittance of light on the p-GaN layer 14 and to spread the current flowing through the P-electrode pad 17 evenly over the entire surface of the p-GaN layer. Indium tin oxide (ITO) is widely used.

The P-electrode pad 17 is formed on the current spreading layer 15.

The N-electrode pad 16 and the P-electrode pad 17 serve to stably supply power from the outside of the light emitting device to the internal semiconductor layer.

FIG. 2 is a schematic diagram illustrating an aspect of transmission and total reflection of light in a portion A including the flat n-GaN layer surface of FIG. 1.

As mentioned above, the light emitting device generates light through recombination of electrons and holes in the active layer 13 positioned between the n-GaN layer 12 and the p-GaN layer 14.

Although the light generated in this way travels in all directions, only a part of the light traveling to the upper surface of the n-GaN layer 12 is illustrated as an example.

This is because the portion of the light emitting device of the present invention that wants to improve light extraction efficiency is the n-GaN layer 12 upper surface.

On the other hand, the advancing light refracts at the interface between the materials having different refractive indices according to the law of refraction or Snell's Law.

Here, Snell's Law is a law that holds for all general waves, including light. When the wave enters and refracts from an isotropic medium to another isotropic medium, The plane containing the normal of the direction and the interface) and the refracting plane (the plane containing the normal of the direction of the refractive wave and the interface) are in the same plane, and sinθ ₁ / sinθ ₂ when the incident angle is θ ₁ and the refractive angle is θ ₂ . = n (scheduled) relationship must be established.

In addition, n is there also expressed by n2 / n1 as the refraction relative refractive index on the side of the medium on the incident side medium, summarized by applying the right-hand side of the equation noted above, n1sinθ ₁ = n2sinθ can derive the _second of equations .

However, if the incident angle θ _{1 of} light directed to the flat n-GaN layer 12 upper interface is greater than or equal to the critical angle θ _c , it will not penetrate the interface and will be totally reflected inside.

In other words, in the structure of a horizontal light emitting device having a flat upper surface of an n-GaN layer, light below a critical angle is well transmitted, but light above the critical angle is not transmitted, and it is easily totally reflected.

Of course, the totally reflected light may totally reflect at the lower interface of the n-GaN layer and accidentally reach the upper interface of the n-GaN layer, but since the incident angle at the time of re-incidence is also likely to be larger than the critical angle, the total incident light is eventually totally reflected. Is likely to be.

And this total internal reflection leads to light loss and becomes a factor of lowering light output.

In order to solve this problem, the present invention is to provide a manufacturing method for processing the n-GaN layer surface to be uneven to reduce the total reflection on the exposed n-GaN layer surface and improve the light output. The purpose.

As described above, the manufacturing method of the high output light emitting device according to the present invention for processing the surface of the n-GaN layer not flat is performed by performing a mesa etching process to expose the n-semiconductor layer when manufacturing the conventional horizontal light emitting device. Before, a scratch shape is formed in a portion of the upper portion of the p-GaN layer through a chemical-mechanical polishing (CMP) process, and mesa etching is performed from a portion of the upper portion of the p-GaN layer including the scratch to a portion of the n-GaN layer. And the scratch shape of the p-GaN layer is transferred to the n-GaN layer as it is.

Specifically, the method of manufacturing a high output light emitting device according to the present invention includes the steps of sequentially growing an n-semiconductor layer, an active layer, a p-semiconductor layer on the substrate; forming a first mask and a second mask spaced apart from each other on the p-semiconductor layer; Forming a scratch on the exposed area over the p-semiconductor layer where the first mask and the second mask are not formed; Removing the first mask; Mesa etching from the p-semiconductor layer to a portion of the n-semiconductor layer through the second mask to form the scratch on the exposed n-semiconductor layer; removing the second mask remaining on top of the p-semiconductor layer; and forming electrode pads in the region where the first mask was located on the n-semiconductor layer and in some regions above the p-semiconductor layer; Is done.

Hereinafter, a method of manufacturing a high output light emitting device according to the present invention will be described in detail with reference to the drawings.

3A to 3F are cross-sectional views for describing a preferred embodiment of the method of manufacturing a high output light emitting device according to the present invention.

3A illustrates a step of sequentially growing the buffer layer 110, the n-semiconductor layer 120, the active layer 130, and the p-semiconductor layer 140 on the substrate 100.

In general, the substrate 100 is preferably a gallium nitride (GaN) substrate which does not need to form a buffer layer.

However, the case where the substrate 100 is a sapphire (Al ₂ O ₃ ) substrate will be described as an example.

In order to manufacture the light emitting device using the sapphire substrate, it is preferable to grow the buffer layer 110 first before growing the n-semiconductor layer 120 as shown in the drawing.

The n-semiconductor layer 120 or the p-semiconductor layer 140 may be a gallium nitride (GaN) semiconductor layer.

3B illustrates a step of forming the first mask 151 and the second mask 152 spaced apart from each other on the p-semiconductor layer 140.

Specifically, forming the first mask 151 and the second mask 152 on the p-semiconductor layer 140, the step of forming the second mask on the entire surface of the p-semiconductor layer, Exposing a portion of the p-semiconductor layer by removing a portion of the second mask formed on the entire surface of the upper portion of the p-semiconductor layer, and applying the first mask to a central region of the part of the exposed p-semiconductor layer. It is preferable that it consists of the step of forming.

Here, the first mask 151 and the second mask 152 serve as a mask for forming a scratch, but the second mask 152 is not etched in the p-semiconductor layer during a mesa etching process. It also serves as a mask for areas that do not.

In addition, the first mask 151 and the second mask 152 are preferably made of different materials.

In addition, the first mask 151 and the second mask 152 may be made of chromium (Cr) and oxide (SiO ₂ ), respectively.

3C shows that the scratch 160 is formed on the exposed region of the p-semiconductor layer 140 on which the first mask 151 and the second mask 152 are not formed, and the first mask 151 is removed. Indicates.

In this case, the scratch 160 is preferably formed through a chemical-mechanical polishing (CMP) process, and the shape of the scratch may be optimized and formed as required through control of various variables in the CMP process.

In addition, the depth of the scratch 160 depends on the size of the diamond slurry (Diamond Slurry) used in the CMP process and the overall process time, etc. In the CMP process according to an embodiment of the present invention, the size of 0.1 μm to 10 μm Preference is given to using diamond slurries.

For reference, the diamond slurry is one of special lubricants that are frequently used in the CMP process, and is particularly suitable for finishing polishing.

On the other hand, the deeper the scratch is formed through the CMP process, the deeper the surface area through which light can pass, the light extraction efficiency through the n-semiconductor layer can be increased.

However, forming the scratch deeply is not always good.

Because, in order to form a deep scratch, the thickness of the p-semiconductor layer which will primarily form a scratch must be thick, and similarly, the thickness of the n-semiconductor layer that will ultimately transfer the scratch must also be thick. There is a disadvantage that the size of the overall becomes large.

In addition, if the thickness of the semiconductor layer is increased in this way, there is a possibility that the resistance may be increased electrically. Therefore, the scratch depth is preferably formed so as not to be too deep or too shallow.

In consideration of these various conditions, the thickness of the p-semiconductor layer, which can maximize the light extraction efficiency of the n-semiconductor layer, is most preferably formed to be 0.5 μm to 1 μm.

After such a CMP process, the first mask chromium metal mask is removed through a chromium etchant, in which case the chromium etchant has no effect on the oxide mask (SiO ₂ ). Does not give.

FIG. 3D illustrates a Mesa etch from the p-semiconductor layer 140 to a portion of the n-semiconductor layer 120 through the second mask 152, so that the scratch 160 is exposed on the exposed n-semiconductor layer 120. ) Is formed and the second mask 152 remaining on the p-semiconductor layer 140 is removed.

As shown in the figure, when the scratch shape formed on the surface of the P-semiconductor layer through Mesa etching through the CMP process, the scratch shape is transferred to the n-semiconductor layer as it is.

This is because the Mesa etching process is performed by a dry etching method which is vertically etched to the same depth.

3E illustrates a step of forming the transparent electrode 170 on the p-semiconductor layer 140.

The transparent electrode 170 generally refers to an electrode material having high transmittance. In recent years, indium tin oxide (ITO) has been widely used.

FIG. 3F illustrates the steps of forming the N-electrode pad 180a and the P-electrode pad 180b in the region where the first mask is located on the n-semiconductor layer 120 and the partial region on the transparent electrode 170, respectively. Indicates.

Each of the electrode pads 180a and 180b may be formed to be ohmic contact in order to overcome a current-voltage characteristic difference generated when the semiconductor layer and the metal are bonded.

As such, when the process of forming the electrode pad is finished, the high output light emitting device according to the present invention is completed.

For reference, the total reflection phenomenon occurring on the surface of the p-GaN layer is determined by the refractive index relationship in each layer.

However, the high output light emitting device according to the manufacturing method of the present invention has the effect of varying the reflection angles of the light totally reflected inside the light emitting device through the irregularly formed scratch.

Therefore, the high output light emitting device according to the present invention has the effect of reducing the total reflection phenomenon in the p-GaN layer as well as the n-GaN layer, it can be expected to improve the overall light output efficiency of the light emitting device.

FIG. 4 is a schematic diagram illustrating a transmission pattern of light in a portion B including the scratched n-GaN layer surface of FIG. 3F.

As shown in the figure, in the high output light emitting device according to the exemplary embodiment of the present invention, an irregular and various angled interface is formed on the n-GaN layer due to the scratch.

In such a structure, even if any light is totally reflected at any interface at an angle of incidence larger than the critical angle as shown in the drawing, the possibility of encountering the obliquely opposite side interface again increases, so that the light of the n-GaN layer There are many opportunities to penetrate the exposed interface.

5 is an enlarged photograph of a scratch formed on the surface of the n-GaN layer of the high output light emitting device according to the present invention.

As can be seen in the picture, the scratches are not uniform in direction, depth, width, etc., and are formed irregularly.

In summary, the high-powered light emitting device having such a scratch according to the manufacturing method of the present invention has a light loss due to total reflection at the interface of the n-GaN layer, as compared to a conventional horizontal light emitting device having a flat n-GaN layer surface. It can reduce and improve the light output.

While the configuration of the invention according to the embodiment of the present invention has been described in detail, the present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention.

According to the method of manufacturing the high output light emitting device of the present invention as described above, since the interface facing at an angle increases due to the scratches formed on the exposed surface of the n-GaN layer, even if light is totally reflected, it meets another interface again and transmits the interface. It is effective to increase the chance to do.

Therefore, the high output light emitting device including the scratched n-GaN layer according to the manufacturing method of the present invention has the effect of minimizing light loss due to total internal reflection, thereby improving light output efficiency.

On the other hand, the total reflection phenomenon occurring on the surface of the p-GaN layer is determined by the refractive index relationship in each layer, the high output light emitting device according to the manufacturing method of the present invention diversify the reflection angle of the totally internally reflected light through the irregularly formed scratch As a result, the total reflection phenomenon occurring in the p-GaN layer is also reduced, and the light output efficiency is also improved.

Claims (11)

Sequentially growing an n-semiconductor layer, an active layer, and a p-semiconductor layer on the substrate; Forming a first mask and a second mask on the p-semiconductor layer so as to be spaced apart from each other; Forming a scratch on the exposed region over the p-semiconductor layer where the first mask and the second mask are not formed; Removing the first mask; Mesa etching from the p-semiconductor layer to a portion of the n-semiconductor layer through the second mask to form the scratch on the exposed n-semiconductor layer; Removing the second mask remaining on top of the p-semiconductor layer; and And forming an electrode pad in a region where the first mask is on the n-semiconductor layer and a portion of the p-semiconductor layer. The method of claim 1, Forming a first mask and a second mask on the p-semiconductor layer, Forming a second mask on the entire surface of the p-semiconductor layer; Exposing a portion of the p-semiconductor layer by removing a portion of the second mask formed on the entire surface of the upper portion of the p-semiconductor layer; and And forming a first mask in a central region of a part of the exposed surface of the p-semiconductor layer. The method of claim 1, The substrate, A method of manufacturing a high power light emitting device, characterized in that the gallium nitride (GaN) substrate. The method of claim 1, The n-semiconductor layer or p-semiconductor layer, A method of manufacturing a high power light emitting device, characterized in that the gallium nitride (GaN) semiconductor layer. The method of claim 1, The thickness of the p-semiconductor layer is A high output light emitting device manufacturing method characterized in that 0.5 ㎛ ~ 1 ㎛. The method of claim 1, The first mask and the second mask, A high output light emitting device manufacturing method, characterized in that each made of a different material. The method of claim 1, The first mask, Method of manufacturing a high output light emitting device, characterized in that made of chromium (Cr). The method of claim 1, The second mask, Method of manufacturing a high power light emitting device, characterized in that consisting of oxide (SiO ₂ ). The method of claim 1, The scratch, A method of manufacturing a high power light emitting device, characterized in that formed through a chemical-mechanical polishing (CMP) process. The method of claim 8, The CMP process, Method of manufacturing a high power light emitting device, characterized in that using a diamond slurry (Diamond Slurry) having a size of 0.1 ㎛ ~ 10 ㎛. The method of claim 1, Between the p-semiconductor layer and the electrode, A method of manufacturing a high output light emitting device, characterized in that it further forms a transparent electrode (Transfarent Metal).

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