JP2011166146A - Light-emitting diode chip having distributed bragg reflector and method of fabricating the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting diode chip that has a distributed Bragg reflector having high reflectivity over a wide wavelength range and is improved in luminous efficiency. <P>SOLUTION: The light-emitting diode chip includes: a substrate having a top surface and a reverse surface; a light-emitting structure arranged on the top surface of the substrate and including an active layer arranged between a first conductive-type semiconductor layer and a second conductive-type semiconductor layer; a distributed Bragg reflector arranged on the reverse surface of the substrate, the distributed Bragg reflector reflecting light emitted from the light-emitting structure; and a metal layer arranged below the distributed Bragg reflector. The distributed Bragg reflector has a reflectivity of at least 90% for light of a first wavelength in a blue wavelength range, light of a second wavelength in a green wavelength range, and light of a third wavelength in a red wavelength range. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light emitting diode chip and a manufacturing method thereof, and more particularly, to a light emitting diode chip having a distributed Bragg reflector and a manufacturing method thereof.

  Gallium nitride series light emitting diode chips that emit blue wavelength light or ultraviolet light have been applied to various types, especially those that emit mixed light such as white light required for backlight units or general lighting fixtures. Various light emitting diode packages are commercially available.

  Since the light emitted from the light emitting diode package mainly depends on the light emission efficiency of the light emitting diode chip, research for improving the light emitting efficiency of the light emitting diode chip is continued. In particular, research for improving the light extraction efficiency of the light emitting diode chip has been continued. As one of such researches, a metal reflector or a distribution on a lower surface of a transparent substrate such as sapphire is used. A technique for forming a Bragg reflector is widely studied.

  FIG. 1 shows the reflectance measured by forming an aluminum layer on the lower surface of a conventional sapphire substrate. In FIG. 1, a graph 102 shows the reflectance of a sapphire substrate on which an aluminum layer is not formed, and a graph 104 shows the reflectance of a sapphire substrate on which an aluminum layer is formed on the lower surface.

  Referring to FIG. 1, a sapphire substrate not formed with an aluminum layer shows a reflectance of about 20% at a wavelength in the visible light region, but shows a reflectance of about 80% when an aluminum layer is formed. I understand that.

FIG. 2 shows reflectivity measured by forming a distributed Bragg reflector in which TiO ₂ / SiO ₂ is periodically laminated on the lower surface of a conventional sapphire substrate.

  When a distributed Bragg reflector (DBR) that reflects light having a peak wavelength of, for example, 460 nm emitted from the light emitting diode chip is provided instead of the aluminum layer, a blue wavelength of 400 to 500 nm as illustrated in FIG. It can be seen that the reflectance reaches almost 100% in the region.

  However, the DBR can only increase the reflectance for some of the visible light region, and the reflectance in other regions is very low compared to the wavelength region of 400 to 500 nm. That is, as shown in FIG. 2, the reflectivity sharply decreases for wavelengths of about 520 nm or more, and the reflectivity is almost less than 50% at 550 nm or more.

  Accordingly, when a light emitting diode chip having the DBR is mounted on a light emitting diode package for emitting white light, the DBR exhibits high reflectance with respect to light in the blue wavelength region emitted from the light emitting diode chip. The DBR does not exhibit effective reflection characteristics for light in the green and / or red wavelength region. For this reason, there is a limit to improving the light emission efficiency in the package.

  The present invention provides a light emitting diode chip that improves the light emission efficiency of a light emitting diode package that emits mixed color light such as white light, and a method of manufacturing the same.

  Moreover, this invention is providing the distributed Bragg reflector which has a high reflectance over a wide wavelength range, and a light emitting diode chip provided with the same.

  According to one embodiment of the present invention, a light emitting diode chip having a distributed Bragg reflector is disclosed. The light-emitting diode chip includes a substrate having a front surface and a back surface, and a light-emitting structure including an active layer located between the first conductive semiconductor layer and the second conductive semiconductor layer located on the front surface of the substrate. And a distributed Bragg reflector that is disposed on the back surface of the substrate and reflects the light emitted from the light emitting structure, and a metal layer located under the distributed Bragg reflector. Further, the distributed Bragg reflector has a reflectance of 90% or more with respect to the first wavelength light in the blue wavelength region, the second wavelength light in the green wavelength region, and the third wavelength light in the red wavelength region. .

  The metal layer may be a reflective metal layer or a protective layer. The reflective metal layer or the protective layer protects the distributed Bragg reflector when the light emitting diode chip is mounted on a package. Further, the reflective metal layer may reflect the light transmitted through the distributed Bragg reflector, and in particular, improves the light emission efficiency at the package level.

  Furthermore, the back surface of the substrate may have an RMS value with a surface roughness of 3 nm or less, preferably 2 nm or less, more preferably 1 nm or less. As the surface roughness decreases, the reflectivity of the distributed Bragg reflector improves.

  Further, by providing the light emitting diode chip with the distributed Bragg reflector, it is possible to effectively reflect mixed light such as white light, blue light, green light, and red light, and the light emitting diode package. The luminous efficiency of can be improved.

  The distributed Bragg reflector may be formed on the back surface of the substrate and contact the back surface of the substrate.

  The substrate may include a predetermined pattern on the front surface. For example, the substrate may be a patterned sapphire substrate.

Meanwhile, the substrate may have an area of 90,000 μm ² or more. For example, the substrate area may be 300 × 300 μm ² or more, or 1 × 1 mm ² or more. By forming a distributed Bragg reflector over a wide area in a light emitting diode chip having a relatively large area, the present invention is effective.

  The light emitting diode chip may include a plurality of light emitting cells on an upper front surface of the substrate. Furthermore, the light emitting diode chip may include at least one light emitting cell array in which the plurality of light emitting cells are connected in series. Further, the light emitting diode chip may further include a wiring for connecting adjacent light emitting cells in series. In an embodiment of the present invention, the plurality of light emitting cells have inclined side surfaces, and the wiring is connected to a side surface of the first conductive type semiconductor layer of one light emitting cell among the light emitting cells adjacent to each other. Good.

  In an embodiment of the present invention, the distributed Bragg reflector may include a first distributed Bragg reflector and a second distributed Bragg reflector. For example, the first distributed Bragg reflector has a higher reflectance with respect to light in the green wavelength region or the red wavelength region than light in the blue wavelength region, and the second distributed Bragg reflector has the green wavelength region or the red wavelength region. The reflectance with respect to light in the blue wavelength region may be higher than that of light.

  The first distributed Bragg reflector may be positioned closer to the substrate than the second distributed Bragg reflector.

  In an embodiment of the present invention, the distributed Bragg reflector includes a plurality of pairs of a first material layer having a first optical thickness and a second material layer having a second optical thickness. A plurality of pairs of a third material layer having a third optical thickness and a fourth material layer having a fourth optical thickness may be included. Here, the refractive index of the first material layer is different from the refractive index of the second material layer, and the refractive index of the third material layer is different from the refractive index of the fourth material layer.

  A plurality of pairs of the first material layer and the second material layer may be positioned closer to the light emitting structure than a plurality of pairs of the third material layer and the fourth material layer. Furthermore, the first material layer and the second material layer may have the same refractive index as the third material layer and the fourth material layer, respectively. The first optical film thickness may be thicker than the third optical film thickness, and the second optical film thickness may be thicker than the fourth optical film thickness.

  In an embodiment of the present invention, a plurality of pairs of the first material layer and the second material layer and a plurality of pairs of the third material layer and the fourth material layer may be mixed with each other.

  On the other hand, the first optical film thickness and the second optical film thickness may satisfy an integer multiple relationship, and the third optical film thickness and the fourth optical film thickness are An integer multiple relationship may be satisfied. In particular, the first optical film thickness and the second optical film thickness may be the same, and the third optical film thickness and the fourth optical film thickness may be the same. Unlike this, each layer of the distributed Bragg reflector can be individually adjusted to have a relatively high reflectivity for a wide range of wavelengths, so the thickness of each layer is different. Also good.

  According to another embodiment of the present invention, a method of manufacturing a light emitting diode chip having a distributed Bragg reflector is provided. In this method, a first conductive type semiconductor layer, a second conductive type semiconductor layer, and an active layer sandwiched between the first conductive type semiconductor layer and the second conductive type semiconductor layer are disposed on the front surface of the substrate. A light emitting structure including: a back surface of the substrate is ground to remove a part of the substrate; and the substrate is lapped to reduce a surface roughness of the back surface of the substrate; Forming a distributed Bragg reflector.

  Meanwhile, a reflective metal layer or a protective layer may be formed on the distributed Bragg reflector. The reflective metal layer or the protective layer protects the distributed Bragg reflector when the light emitting diode chip is mounted on the light emitting diode package.

  On the other hand, before forming the distributed Bragg reflector, the surface roughness of the back surface of the substrate may have an RMS value of 3 nm or less. In addition, the distributed Bragg reflector has a reflectance of 90% or more with respect to the first wavelength light in the blue wavelength region, the second wavelength light in the green wavelength region, and the third wavelength light in the red wavelength region.

  Preferably, before forming the distributed Bragg reflector, the surface roughness of the back surface of the substrate may have an RMS value of 1 nm or less. The method may further include a step of polishing the back surface of the substrate by a CMP process after the lapping. By the CMP process, the surface roughness of the back surface of the substrate can be polished to have an RMS value of 1 nm or less.

  In an embodiment of the present invention, the distributed Bragg reflector may be formed using, for example, an ion assisted deposition technique.

  According to an embodiment of the present invention, a distributed Bragg reflector having a high reflectance over a wide range of the visible light region is provided. Accordingly, the light emission efficiency of the light emitting diode package that emits mixed light such as white light can be improved. Furthermore, the reliability of the reflectance of the distributed Bragg reflector can be ensured by controlling the surface roughness of the back surface of the substrate on which the distributed Bragg reflector is formed.

It is a graph which shows the reflectance of aluminum on the sapphire substrate by a prior art. 6 is a graph showing reflectivity of a distributed Bragg reflector on a sapphire substrate according to the prior art. 1 is a cross-sectional view illustrating a light emitting diode chip having a distributed Bragg reflector according to an embodiment of the present invention. It is sectional drawing to which the distributed Bragg reflector of FIG. 3 was expanded. It is sectional drawing for demonstrating the distributed Bragg reflector by other embodiment of this invention. FIG. 6 is a cross-sectional view illustrating a light emitting diode chip having a plurality of light emitting cells according to still another embodiment of the present invention. 6 is a cross-sectional view illustrating a light emitting diode chip having a plurality of light emitting cells according to still another embodiment of the present invention. It is a simulation graph which shows the change of the reflectance according to the incident angle of a distributed Bragg reflector. This is an example in which the reflectance for long-wavelength incident light at an incident angle of 50 degrees is improved by increasing the number of stacked distributed Bragg reflectors. This is an example in which the reflectance for long-wavelength incident light at an incident angle of 60 degrees is improved by increasing the number of stacked distributed Bragg reflectors. (A) It is the top view which showed the distributed Bragg reflector after a dicing process was performed. (B) It is the top view which showed the distributed Bragg reflector after a dicing process was performed. It is a graph which shows the reflectance of the distributed Bragg reflector by the presence or absence of CMP after the lapping process of the sapphire substrate by a copper surface plate. It is a graph which shows the reflectance after forming an aluminum reflective metal layer further on the distributed Bragg reflector manufactured like the case of FIG. It is a graph which shows the reflectance of the distributed Bragg reflector according to the size of the slurry particle in the lapping process using a tin surface plate. It is a graph which shows the reflectance of the distributed Bragg reflector according to the size of the slurry particle in the lapping process using a tin surface plate. It is a graph which shows the reflectance of the distributed Bragg reflector according to the size of the slurry particle in the lapping process using a tin surface plate.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described in detail below are provided as examples in order to fully convey the concept of the present invention to those skilled in the art. Therefore, the present invention is not limited to the embodiments described below, and may be embodied in other forms. In the drawings, the width, length, thickness, and the like of components may be exaggerated for convenience. Throughout the specification, the same reference numbers basically indicate the same components.

  3 is a cross-sectional view illustrating a light emitting diode chip 20 having a distributed Bragg reflector 45 according to an embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view of the distributed Bragg reflector 45 of FIG. It is.

  Referring to FIG. 3, the light emitting diode chip 20 includes a substrate 21, a light emitting structure 30, and a distributed Bragg reflector 45. The light emitting diode chip 20 may include a buffer layer 23, a transparent electrode 31, a p-electrode pad 33, an n-electrode pad 35, a reflective metal layer 51, and a protective layer 53.

The substrate 21 is not particularly limited as long as it is a transparent substrate, and may be, for example, a sapphire or SiC substrate. The substrate 21 may also have a predetermined pattern on the upper surface, that is, the front surface, like a patterned sapphire substrate (PSS). On the other hand, the area of the substrate 21 determines the entire area of the chip. In the embodiment of the present invention, the reflective effect increases as the area of the light emitting diode chip is relatively large. Accordingly, the substrate 21 is preferably 90,000 μm ² or more, and more preferably 1 mm ² or more.

  The light emitting structure 30 is located on the substrate 21. The light emitting structure 30 includes a first conductivity type semiconductor layer 25, a second conductivity type semiconductor layer 29, and an active layer 27 disposed between the first and second conductivity type semiconductor layers 25 and 29. Here, the first conductivity type semiconductor layer 25 and the second conductivity type semiconductor layer 29 have opposite conductivity types, the first conductivity type may be n-type, and the second conductivity type is p-type. There may be, or vice versa.

  The first conductive semiconductor layer 25, the active layer 27, and the second conductive semiconductor layer 29 may be formed of a gallium nitride-based compound semiconductor material, that is, (Al, In, Ga) N. The active layer 27 has a composition element and a composition ratio so as to emit light having a desired wavelength, for example, ultraviolet light or blue light. The first conductive type semiconductor layer 25 and / or the second conductive type semiconductor layer 29 may be formed as a single layer as shown in the figure, but may be formed in a multilayer structure. The active layer 27 may be formed in a single quantum well structure or a multiple quantum well structure. Further, the buffer layer 23 may be disposed between the substrate 21 and the first conductivity type semiconductor layer 25.

  The semiconductor layers 25, 27, and 29 may be formed using MOCVD (Metal-Organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitaxy) technology, and the first conductivity type semiconductor layer 25 using photolithography and etching processes. Patterning may be performed so that a part of the region is exposed.

  On the other hand, the transparent electrode layer 31 may be formed of, for example, ITO or Ni / Au on the second conductivity type semiconductor layer 29. The transparent electrode layer 31 has a specific resistance lower than that of the second conductivity type semiconductor layer 29 and thus serves to disperse current. A p-electrode pad 33 is formed on the transparent electrode layer 31, and an n-electrode pad 35 is formed on the first conductivity type semiconductor layer 25. The p-electrode pad 33 may be electrically connected to the second conductivity type semiconductor layer 29 through the transparent electrode layer 31 as illustrated.

  On the other hand, a distributed Bragg reflector 45 is located below the substrate 21, that is, on the back surface. The distributed Bragg reflector 45 may include a first distributed Bragg reflector 40 and a second distributed Bragg reflector 50.

  Referring to FIG. 4, the first distributed Bragg reflector 40 includes a plurality of pairs of a first material layer 40a and a second material layer 40b, and the second distributed Bragg reflector 50 includes a third material layer. A plurality of pairs of 50a and the fourth material layer 50b are repeatedly formed. The plurality of pairs of the first material layer 40a and the second material layer 40b have a relatively high reflectance with respect to light in the red wavelength region, for example, light at 550 nm or 630 nm, compared to light in the blue wavelength region. The distributed Bragg reflector 50 may have a relatively high reflectance with respect to light in the blue wavelength region, for example, light at 460 nm, compared to light in the red or green wavelength region. At this time, the optical film thickness of the material layers 40a and 40b in the first distributed Bragg reflector 40 is thicker than the optical film thickness of the material layers 50a and 50b in the second distributed Bragg reflector 50, but the present invention is not limited thereto. The opposite is also possible.

The first material layer 40a may have the same material as the third material layer 50a, that is, the same refractive index, and the second material layer 40b may be the same material as the fourth material layer 50b, that is, the same refraction. You may have a rate. For example, the first material layer 40a and the third material layer 50a may be formed of TiO ₂ (n: about 2.5), and the second material layer 40b and the fourth material layer 50b are made of SiO ₂ (n: about 1). .5).

  On the other hand, the optical film thickness (refractive index × thickness) of the first material layer 40a has a substantially integral multiple relationship with the optical film thickness of the second material layer 40b. The film thickness may be substantially the same. Further, the optical film thickness of the third material layer 50a has a substantially integral relationship with the optical film thickness of the fourth material layer 50b. Preferably, these optical film thicknesses are substantially the same. It is good.

  Further, the optical film thickness of the first material layer 40a is made thicker than the optical film thickness of the third material layer 50a, and the optical film thickness of the second material layer 40b is made thicker than the optical film thickness of the fourth material layer 50b. May be. The optical film thickness of the first to fourth material layers 40a, 40b, 50a, 50b can be controlled by adjusting the refractive index and / or the actual thickness of each material layer.

  Further referring to FIG. 3, a reflective metal layer 51 such as Al, Ag, or Rh and a protective layer 53 for protecting the distributed Bragg reflector 45 may be formed below the distributed Bragg reflector 45. . The protective layer 53 may be formed of, for example, any one metal layer selected from Ti, Cr, Ni, Pt, Ta, and Au, or an alloy thereof. The reflective metal layer 51 or the protective layer 53 can protect the distributed Bragg reflector 45 from external impact and contamination. For example, the reflective metal layer 51 or the protective layer 53 can prevent the distributed Bragg reflector 45 from being deformed by a material such as an adhesive when the light emitting diode chip is mounted on the light emitting diode package. Further, since the reflective metal layer 51 can reflect the light transmitted through the distributed Bragg reflector 45, the thickness of the distributed Bragg reflector 45 can be relatively reduced. The distributed Bragg reflector 45 exhibits a relatively high reflectance, but may transmit visible light in a long wavelength region for light having a large incident angle. Therefore, by disposing the reflective metal layer 51 below the distributed Bragg reflector 45, the light transmitted through the distributed Bragg reflector 45 can be reflected, so that the light emission efficiency is improved.

  According to the present embodiment, the first distributed Bragg reflector 40 having a relatively high reflectance for visible light having a relatively long wavelength and the second distributed Bragg reflection having a relatively high reflectance for visible light having a relatively short wavelength. A distributed Bragg reflector 45 having a structure in which the reflector 50 is stacked is provided. With the combination of the first distributed Bragg reflector 40 and the second distributed Bragg reflector 50, the distributed Bragg reflector 45 can increase the reflectance with respect to light over most of the visible light region.

  The distributed Bragg reflector according to the prior art has a high reflectance with respect to light in a specific wavelength range, but has a relatively low reflectance with respect to light in other wavelength ranges, so that the luminous efficiency of a light emitting diode package that emits white light is low. There are limits to improvement. However, according to the present embodiment, the distributed Bragg reflector 45 has a high reflectance not only for light in the blue wavelength region but also for light in the green wavelength region and light in the red wavelength region. Luminous efficiency can be improved.

  Furthermore, by arranging the first distributed Bragg reflector 40 closer to the substrate 21 than the second distributed Bragg reflector 50, the optical loss in the distributed Bragg reflector 45 can be reduced as compared to the case where the first distributed Bragg reflector 40 is arranged in reverse. Can be reduced.

  In the present embodiment, the two reflectors of the first distributed Bragg reflector 40 and the second distributed Bragg reflector 50 have been described, but a larger number of reflectors may be used. In this case, it is preferable that a reflector having a relatively high reflectance with respect to a long wavelength is positioned relatively close to the light emitting structure 30.

  Moreover, in this embodiment, the thickness of the 1st material layer 40a in the 1st distributed Bragg reflector 40 may mutually differ. Further, the thicknesses of the second material layers 40b may be different from each other. Further, the thickness of the third material layer 50a in the second distributed Bragg reflector 50 may be different from each other. Further, the thickness of the fourth material layer 50b may be different from each other.

In the present embodiment, it has been described that the material layers 40a, 40b, 50a, and 50b are formed of SiO ₂ or TiO _2. However, the present invention is not limited to this, and other material layers such as Si ₃ N ₄ , compound semiconductors, etc. May be formed. However, the difference in refractive index between the first material layer 40a and the second material layer 40b and the difference in refractive index between the third material layer 50a and the fourth material layer 50b are preferably larger than 0.5.

  The number of pairs of the first material layer and the second material layer in the first distributed Bragg reflector 40 and the number of pairs of the third material layer and the fourth material layer in the second distributed Bragg reflector 50 are as follows. The greater the number, the higher the reflectance. The total number of these pairs may be 20 or more.

  Before the distributed Bragg reflector 45 is formed, the surface roughness of the back surface of the substrate 21 needs to be controlled. When the surface roughness of the back surface of the substrate 21 is relatively large, it becomes difficult for the distributed Bragg reflector 45 to obtain a high reflectance over a wide wavelength range. Moreover, when the interface between the distributed Bragg reflector 45 and the substrate 21 is defective, the distributed Bragg reflector 45 may be easily deformed. For example, when the light emitting diode chip is mounted on the light emitting diode package, the deformation causes a problem that the reflectance of the distributed Bragg reflector 45 is reduced even if it is applied even in a slight thermal process. there is a possibility. The back surface of the substrate 21 is controlled so that the surface roughness has an RMS (root-mean-square) value of 3 nm or less. Preferably, the back surface of the substrate 21 may have an RMS value with a surface roughness of 2 nm or less, more preferably 1 nm or less.

  Hereinafter, a method for manufacturing the distributed Bragg reflector 45 and the light emitting diode chip will be described.

  First, before the distributed Bragg reflector 45 is formed, the surface roughness of the substrate 21 is controlled. For example, first, a part of the substrate 21 is removed by grinding the back surface of the substrate 21 on which the light emitting structure is formed. At this time, the back surface of the substrate 21 is scratched by grinding and becomes a relatively very rough surface. Thereafter, the surface of the substrate 21 is lapped with a slurry of small particles. In the lapping process, the depth of grooves such as scratches in the surface of the substrate 21 is reduced, and the surface roughness is reduced. At this time, the surface roughness of the back surface of the substrate 21 may be controlled to be 3 μm or less by adjusting the size of the surface plate and diamond slurry particles used in the lapping step. However, in general, there is a limit to adjusting the surface roughness only by the lapping process using the surface plate and the slurry particles, and therefore chemical mechanical polishing (CMP) is performed after reducing the surface roughness in the lapping process. A back surface of the substrate 21 may be polished by performing a Chemical Mechanical Polishing process. By the CMP process, the surface roughness of the back surface of the substrate 21 can be controlled to 1 nm or less.

Next, material layers having different refractive indexes, such as TiO ₂ , SiO ₂ , and Si ₃ N _4, are repeatedly formed on the surface of the substrate 21. For the formation of the material layer, various known methods such as sputtering, electron beam vapor deposition, plasma enhanced chemical vapor deposition, and the like may be used. In particular, ion assisted deposition may be used. The ion-assisted vapor deposition method is particularly suitable for forming the material layer of the distributed Bragg reflector because the reflectivity of the material layer deposited on the substrate 21 is measured to form a material layer having an appropriate thickness.

  After the distributed Bragg reflector is formed, a metal layer may be formed on the distributed Bragg reflector. Thereafter, the substrate 21 is diced to complete an individual light emitting diode chip.

  FIG. 5 is a cross-sectional view illustrating a distributed Bragg reflector 55 according to another embodiment of the present invention. The light emitting diode chip according to the present embodiment is almost the same as the light emitting diode chip described with reference to FIGS. However, in FIGS. 3 and 4, the distributed Bragg reflector 45 is illustrated and described with respect to the laminated structure of the first distributed Bragg reflector 40 and the second distributed Bragg reflector 50. In the distributed Bragg reflector 55, a plurality of pairs of the first material layer 40a and the second material layer 40b and a plurality of pairs of the third material layer 50a and the fourth material layer 50b are mixed together. That is, at least a pair of the third material layer 50a and the fourth material layer 50b is located between a plurality of pairs of the first material layer 40a and the second material layer 40b, and the first material layer 40a and the second material layer 40b At least a pair of the two material layers 40b is located between a plurality of pairs of the third material layer 50a and the fourth material layer 50b. Here, the optical film thicknesses of the first to fourth material layers 40a, 40b, 50a, and 50b are controlled so as to have a high reflectance with respect to light over a wide range of the visible light region. Therefore, the optical film thickness of each material layer constituting the distributed Bragg reflector 55 may be different from each other.

  FIG. 6 is a cross-sectional view illustrating a light emitting diode chip 20a having a plurality of light emitting cells according to another embodiment of the present invention.

  Referring to FIG. 6, the light emitting diode chip 20 a may include a plurality of light emitting cells 30 formed on the substrate 21, a distributed Bragg reflector 45, and metal layers 51 and / or 53.

  The substrate 21 and the distributed Bragg reflector 45 are the same as the distributed Bragg reflector described with reference to FIGS. 3, 4, and 5, and detailed description thereof is omitted. However, the substrate 21 is preferably an insulator in order to electrically insulate a plurality of light emitting cells, and may be a patterned sapphire substrate, for example.

  Meanwhile, the plurality of light emitting cells 30 are spaced apart from each other. Since the plurality of light emitting cells 30 are the same as the light emitting structure 30 described with reference to FIG. 3, detailed description thereof is omitted. In addition, a buffer layer 23 may be disposed between the light emitting cell 30 and the substrate 21, and the buffer layers 23 are preferably spaced apart from each other.

The first insulating layer 37 covers the front surface of the light emitting cell 30 and has openings on the first conductive semiconductor layer 25 and the second conductive semiconductor layer 29. Further, the side wall of the light emitting cell 30 is covered by the first insulating layer 37, and the first insulating layer 37 covers the substrate 21 in a region between the light emitting cells 30. The first insulating layer 37 may be formed of a silicon oxide film (SiO ₂ ) or a silicon nitride film, and is a layer formed in a temperature range of 200 to 300 ° C. using plasma chemical vapor deposition (plasma CVD). There may be. At this time, the first insulating layer 37 is preferably formed to a thickness of 450 nm to 1 μm. If the first insulating layer is formed thinner than 450 nm, a first insulating layer having a relatively thin thickness is formed below the light emitting cell due to a step coverage characteristic. An electrical short circuit may occur during On the other hand, as the first insulating layer is thicker, an electrical short circuit can be prevented. However, in order to reduce the light transmittance and reduce the light emission efficiency, it is preferable not to exceed a thickness of 1 μm.

  On the other hand, the wiring 39 is formed on the first insulating layer 37. The wiring 39 is electrically connected to the first conductive semiconductor layer 25 and the second conductive semiconductor layer 29 through the opening. The transparent electrode layer 31 may be positioned on the second conductivity type semiconductor layer 29, and the wiring may be connected to the transparent electrode layer 31. Further, the wiring 39 may electrically connect the first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 29 of the adjacent light emitting cells 30 to form a series array of the light emitting cells 30. A plurality of such arrays may be formed, and the plurality of arrays may be connected to each other in anti-parallel and connected to an AC power source to be driven. Further, a bridge rectifier (not shown) connected to the series array of light emitting cells may be formed, and the light emitting cells may be driven under an AC power source by the bridge rectifier. The bridge rectifier can form a light emitting cell having the same structure as the light emitting cell 30 by using the wiring 39.

  In contrast, the wiring 39 may connect the first conductive semiconductor layers 25 of the adjacent light emitting cells to each other, and may connect the second conductive semiconductor layers 29 to each other. Thereby, a plurality of light emitting cells 30 connected in series and in parallel can be provided.

  The wiring 39 may be formed of a conductive material, for example, a doped semiconductor material (for example, polycrystalline silicon) or a metal. In particular, the wiring 39 may be formed in a multilayer structure, and may include, for example, a lower layer of Cr or Ti and an upper layer of Cr or Ti. Further, a metal layer of Au, Au / Ni or Au / Al may be disposed between the lower layer and the upper layer.

  The second insulating layer 41 may cover the wiring 39 and the first insulating layer 37. The second insulating layer 41 prevents the wiring 39 from being contaminated by moisture or the like, and prevents the wiring 39 and the light emitting cell 30 from being damaged by an external impact.

The second insulating layer 41 may be made of the same material as the first insulating layer 37 and may be formed of a silicon oxide film (SiO ₂ ) or a silicon nitride film. Similarly to the first insulating layer, the second insulating layer 41 may be a layer formed in a temperature range of 200 ° C. to 300 ° C. using plasma chemical vapor deposition. Further, when the first insulating layer 37 is a layer formed by plasma chemical vapor deposition, the second insulating layer 41 is within a temperature range within ± 20% with respect to the formation temperature of the first insulating layer 37. It is preferable that it is a layer formed at the same formation temperature, and it is more preferable that the layer is awakened at the same formation temperature.

  On the other hand, the second insulating layer 41 may be relatively thinner than the first insulating layer 37, and preferably has a thickness of 50 nm or more. Since the second insulating layer 41 is relatively thin compared to the first insulating layer 37, the second insulating layer 41 can be prevented from being peeled off from the first insulating layer 37. Further, when the second insulating layer 41 is thinner than 250 nm, it is difficult to protect the wiring and the light emitting cell from external impact or moisture penetration.

  On the other hand, the phosphor layer 43 may be positioned on the light emitting diode chip 20a. The phosphor layer 43 may be a layer in which a phosphor is dispersed in a resin or a layer formed by electrophoresis. The phosphor layer 43 covers the second insulating layer 41 and converts the wavelength of light emitted from the light emitting cell 30.

  FIG. 7 is a cross-sectional view illustrating a light emitting diode chip 20b having a plurality of light emitting cells according to another embodiment of the present invention.

  Referring to FIG. 7, the light-emitting diode chip 20b according to the present embodiment is almost the same as the light-emitting diode chip 20a described above, but the shape of the light-emitting cell 30 is different, whereby the first conductive type semiconductor to which the wiring 39 is connected. The part of the layer 25 is different.

  That is, in the light emitting cell 30 of the light emitting diode chip 20a, the upper surface of the first conductive semiconductor layer 25 is exposed, and the wiring 39 can be connected to the upper surface of the first conductive semiconductor layer 25. Unlike this, the light emitting cell 30 of the light emitting diode chip 20b according to the present embodiment is formed to have an inclined side surface, the inclined side surface of the first conductive type semiconductor layer 25 is exposed, and the wiring 39 is the first. The conductive semiconductor layer 25 is connected to the inclined side surface.

  Therefore, according to the present embodiment, it is not necessary to separately perform a process for exposing the upper surface of the first conductive type semiconductor layer 25 in addition to the process of isolating the light emitting cells, so that the process can be simplified. it can. Furthermore, since it is not necessary to expose the upper surface of the first conductivity type semiconductor layer 25, the area of the active layer 27 can be prevented from decreasing. In addition, since the wiring 39 is connected along the inclined surface of the first conductive type semiconductor layer 25, the current distribution performance of the light emitting cell 30 can be improved, thereby improving the forward voltage and reliability.

(Experimental example)
FIG. 8 is a simulation graph showing a change in reflectance according to the incident angle of the distributed Bragg reflector. Here, the distributed Bragg reflector is obtained by alternately laminating 40 layers of SiO ₂ and TiO ₂ on a glass substrate, and the thickness of each layer covers the entire region of 400 nm to 700 nm at an incident angle of 0 degree. And individually adjusted to have a reflectance of 99% or more. Thereby, the thickness of the whole distributed Bragg reflector was 2.908 μm. On the other hand, in the case of a light-emitting diode chip that is actually used, it is incident at an incident angle of about 60 degrees or more due to a difference in refractive index between the sapphire substrate (n: about 1.78) and SiO ₂ (n: about 1.48). Since light is totally reflected, a simulation for an incident angle of 60 degrees or more is omitted. On the other hand, in the graph of FIG. 8, the entire visible region is displayed at the reflectance of 100% (also displayed in the graph of FIG. 9).

  As can be seen from the graph in FIG. 8, the 40-layer distributed Bragg reflector showed an extremely high reflectance of 99% or more with respect to an incident angle of 0 degree in the entire visible light region. However, it can be seen that the greater the incident angle of light incident on the distributed Bragg reflector, the lower the reflectivity for long-wavelength visible light. When the incident angle exceeds 30 degrees, the reflectance for light having a wavelength of 700 nm decreases to 99% or less.

  FIGS. 9A and 9B show an example in which the reflectance for long-wavelength incident light at incident angles of 50 degrees and 60 degrees is improved by increasing the number of layers of the distributed Bragg reflector.

  Referring to FIGS. 9A and 9B, as described with reference to FIG. 8, in the case of the 2.908 μm reference distributed Bragg reflector 40L, the reflectance (40L-0 degrees) with respect to an incident angle of 0 degrees in the long wavelength visible light region. It can be seen that the reflectivity for an incident angle of 50 degrees (40L-50 degrees) and the reflectivity for an incident angle of 60 degrees (40L-60 degrees) are greatly reduced. Furthermore, a portion where the reflectance is reduced is generated in an intermediate region of the visible region, for example, in the vicinity of 510 nm to 520 nm.

  On the other hand, when the number of layers of the distributed Bragg reflector is increased to 48 layers (total thickness: 3.829 μm) or 52 layers (total thickness: 4.367 μm), a wide wavelength even when the incident angle is large. High reflectivity can be obtained almost uniformly over the region.

  Therefore, the reflectance can be improved by increasing the number of layers in which the distributed Bragg reflector is laminated, and a high reflectance can be maintained even for light incident at a large incident angle. However, an increase in the number of stacked distributed Bragg reflectors may increase process time and cause cracks in the distributed Bragg reflector.

  FIGS. 10A and 10B are plan views showing the distributed Bragg reflector after the dicing process is performed. Here, FIG. 10A shows a 40-layer distributed Bragg reflector laminated by ion-assisted deposition, and FIG. 10B shows a 48-layer distributed Bragg reflector laminated by ion-assisted deposition. .

  When 40 layers were stacked (FIG. 10 (a)), no cracks occurred in the distributed Bragg reflector, but when 48 layers were stacked (FIG. 10 (b)), cracks occurred in the distributed Bragg reflector. . When 52 layers were laminated, it was observed that cracks were similarly generated.

  The reason why cracks occur in the distributed Bragg reflector is not clear, but is expected to be due to ion-assisted deposition. That is, since ions are collided to form a high-density layer, stress is accumulated in the distributed Bragg reflector, and as a result, cracks may occur in the distributed Bragg reflector when the substrate is diced. Therefore, simply increasing the number of stacked layers is not suitable for providing a light-emitting diode chip having mass productivity.

  In this case, as described with reference to FIG. 3, by forming a reflective metal layer on the distributed Bragg reflector, a relatively high reflectance can be maintained even for light having a large incident angle.

  Table 1 shows the relative luminous efficiency in the white light emitting diode package state depending on the number of layers of the distributed Bragg reflector, the type of the epoxy resin, and whether or not the Al reflective metal layer is applied. In each experimental example, except for the types of the distributed Bragg reflector, the reflective metal layer, and the epoxy resin, the other conditions, for example, the type of the light emitting diode chip and the type of the package are all the same, and the number of layers of the distributed Bragg reflector is The relative luminous efficiency with respect to the luminous efficiency of the light emitting diode chip package (sample number 1) to which 40 layers are not applied and the Al reflective metal layer is not applied is shown in%.

  Comparing Samples 1 and 2 and Samples 5 and 6, it can be seen that when the Al reflective metal layer is not applied, a difference in luminous efficiency is shown depending on the type of epoxy resin used as the adhesive. That is, the sample using transparent epoxy shows higher luminous efficiency than the case using silver epoxy. This indicates that in the absence of the Al reflective metal layer, the reflectivity of the distributed Bragg reflector is affected by the adhesive.

  On the other hand, when the same type of adhesive is used, the sample to which the Al reflective metal layer is applied exhibits higher luminous efficiency than the sample that does not. For example, comparing Samples 1 and 3, Samples 2 and 4, and Samples 5 and 7, it can be seen that the luminous efficiency is improved when an Al reflective metal layer is applied.

  On the other hand, when samples 1 and 5 and samples 2 and 6 to which the Al reflective metal layer is not applied are compared using the same adhesive, it can be seen that the luminous efficiency improves as the number of layers increases. This is considered to be because the reflectance of the distributed Bragg reflector is improved in a wide incident angle range as the number of stacked layers of the distributed Bragg reflector is increased.

  However, when Sample 3 and Sample 7 to which an Al reflective metal layer and silver epoxy were applied were compared, there was no difference in luminous efficiency despite an increase in the number of layers. This is presumably because the Al reflective metal layer maintains a relatively high reflectivity even for visible light having a long incident angle and a long wavelength. Therefore, it can be seen that when the reflective metal layer is applied together with the distributed Bragg reflector, good luminous efficiency can be achieved at the package level while reducing the number of stacked distributed Bragg reflectors. Furthermore, a reduction in the number of stacked distributed Bragg reflectors can prevent cracks occurring in the distributed Bragg reflector.

  On the other hand, when the Al reflective metal layer is applied to the distributed Bragg reflector, it is observed that the reflectance of the distributed Bragg reflector decreases at the chip level, and this phenomenon is closely related to the surface roughness of the substrate. Conceivable. Hereinafter, the influence of the surface roughness of the substrate on the reflectance of the distributed Bragg reflector at the chip level will be described.

  FIG. 11 is a graph showing the reflectivity of the distributed Bragg reflector according to the presence or absence of CMP (chemical mechanical polishing) after the lapping process of the sapphire substrate with the copper surface plate.

  First, after grinding the back surface of the sapphire substrate, a lapping process was performed with a copper surface plate using a diamond slurry of 3 μm particles. The surface roughness of the back surface of the sapphire substrate after the lapping process using the copper surface plate showed an RMS value of about 5.12 nm in an area of 5 μm × 5 μm.

Next, after performing a chemical mechanical polishing (CMP) process on the back surface of the sapphire substrate, the thicknesses of TiO ₂ and SiO ₂ are controlled, and the first distributed Bragg reflector and the second distributed Bragg reflector described above are performed. A sample was formed (Example 1). As a comparative example for this, a sample was manufactured by forming a distributed Bragg reflector in the same manner as in Example 1 without performing the chemical mechanical polishing step. The chemical mechanical polishing process was performed using SiO ₂ slurry at a load of 20 kg, and the surface roughness of the sapphire substrate after the chemical mechanical polishing process showed an RMS value of about 0.25 nm in an area of 5 μm × 5 μm.

  In the case of the comparative example, as shown in FIG. 11, the reflectance of the distributed Bragg reflector shows a reflectance of approximately 90% or more in the visible light region, but the reflectance is irregular depending on the wavelength, and is around 550 nm. Shows a value of 90% or less. On the contrary, in the case of Example 1, the reflectance of the distributed Bragg reflector showed a value close to 100% over a wide wavelength range of visible light.

  FIG. 12 is a graph showing the reflectance after an Al layer of about 500 nm is formed on a sample manufactured in the same manner as the example and comparative example of FIG.

  In the case of the comparative example, it was confirmed that the reflectance after the formation of the Al layer was greatly reduced. On the other hand, in the case of the example, the reflectance did not decrease even after the Al layer was formed, and a high reflectance was maintained.

  The decrease in reflectivity after the Al layer is formed in the comparative example is that the distributed Bragg reflector of the comparative example formed on the sapphire substrate with a rough surface is deformed due to the interface failure while Al is deposited using the electron beam deposition technique. Therefore, it is thought that this phenomenon is shown. In the case of Example 1, since the surface roughness of the sapphire substrate is good, it is considered that the distributed Bragg reflector is not deformed during the deposition of Al, and the reflectance is maintained.

  FIGS. 13 to 15 are graphs showing the reflectance of the distributed Bragg reflector according to the size of the slurry particles in the lapping process using a tin surface plate.

  Here, the slurry contains diamond particles, and diamond particles having a size of 3 μm, 4 μm and 6 μm were used. The surface roughness of the sapphire substrate after the lapping process using a tin surface plate exhibited RMS values of about 2.40 nm, 3.35 nm and 4.18 nm depending on the size of the diamond particles.

  After performing the lapping process using a tin surface plate, the same distributed Bragg reflector as in Example 1 was formed, and an Al layer of about 500 nm was additionally formed as in the example of FIG.

  As can be seen from the drawing, the reflectivity of the distributed Bragg reflector after the lapping process using a 3 μm slurry and a tin surface plate was 90% or more over a wide wavelength range in the visible light region. However, after the formation of the Al layer, the reflectance slightly decreased near 550 nm.

  However, the reflectivity of the distributed Bragg reflector after the lapping process with 4 μm slurry and 6 μm slurry and a tin surface plate cannot reach 90% near 550 nm, and the reflectivity after forming Al is less than 80%. Diminished.

  As can be seen from the above experimental examples, it can be seen that the surface roughness of the sapphire substrate before forming the distributed Bragg reflector affects the reflectance of the distributed Bragg reflector. Moreover, it is necessary to control the surface roughness of the sapphire substrate to an RMS value of 3 nm or less. Further, when the surface roughness of the sapphire substrate is 1 nm or less, it is expected that the reflectance is not reduced even after the Al layer is formed.

Claims (12)

A substrate having a front surface and a back surface;
A light emitting structure including an active layer positioned on the front upper portion of the substrate and disposed between the first conductive semiconductor layer and the second conductive semiconductor layer;
A distributed Bragg reflector that is located on the back surface of the substrate and reflects light emitted from the light emitting structure;
A metal layer located under the distributed Bragg reflector,
The distributed Bragg reflector has a reflectance of 90% or more with respect to light having a first wavelength in a blue wavelength region, light having a second wavelength in a green wavelength region, and light having a third wavelength in a red wavelength region. Light emitting diode chip characterized by.   The light-emitting diode chip according to claim 1, wherein the metal layer is a reflective metal layer.   The light emitting diode chip according to claim 2, wherein the reflective metal layer is Al.   The light emitting diode chip according to claim 1, wherein the back surface of the substrate has an RMS value with a surface roughness of 3 nm or less.   5. The light emitting diode chip according to claim 4, wherein the back surface of the substrate is processed by chemical mechanical polishing and has an RMS value of a surface roughness of 1 nm or less.   The light emitting diode chip of claim 1, further comprising a plurality of light emitting cells on the substrate.   The light emitting diode chip according to claim 6, further comprising at least one light emitting cell array in which the plurality of light emitting cells are connected in series. The wiring further includes connecting the light emitting cells adjacent to each other in series,
The plurality of light emitting cells have inclined side surfaces;
The light emitting diode chip of claim 6, wherein the wiring is connected to a side surface of the first conductive semiconductor layer of one light emitting cell among the light emitting cells adjacent to each other. The distributed Bragg reflector is
A first distributed Bragg reflector having a higher reflectivity with respect to light in the green wavelength region or the red wavelength region than light in the blue wavelength region;
2. The light emitting diode chip according to claim 1, further comprising: a second distributed Bragg reflector having a higher reflectance with respect to light in the blue wavelength region than light in the green wavelength region or the red wavelength region.   The light emitting diode chip according to claim 1, wherein the distributed Bragg reflector has a structure in which layers having different refractive indexes are alternately stacked, and the optical film thicknesses of the layers are different from each other.   2. The light-emitting diode chip according to claim 1, wherein the distributed Bragg reflector has a reflectance of 98% or more at an incident angle of 0 degree with respect to light of all wavelengths within a range of 400 nm to 700 nm.   The light emitting diode chip according to claim 1, wherein the distributed Bragg reflector has a reflectance of 95% or more at an incident angle of 50 degrees with respect to 700 nm light.