TWI544661B - Light emitting diode chip having distributed bragg reflector and method of fabricating the same - Google Patents

Description

Light-emitting diode chip with distributed Bragg mirror and manufacturing method thereof

An exemplary embodiment of the present invention relates to a light emitting diode wafer and a method of fabricating the same, and more particularly to a light emitting diode wafer having a distributed Bragg mirror and a method of fabricating the same.

Gallium nitride-based LED chips that emit light at blue or ultraviolet wavelengths can be used in a variety of different applications. In particular, various types of light emitting diode packages (light emitting diodes) are commercially available that emit mixed color light (such as white light required for backlight devices, general illumination, or other similar illumination). Package).

Since the light outputted from the light-emitting diode package can be determined depending on the light-emitting efficiency of the light-emitting diode wafer, research for improving the light-emitting efficiency of the light-emitting diode wafer has continued. In particular, attempts to improve the luminous efficiency of light-emitting diode wafers are already underway. For example, techniques for forming a metal mirror or a distributed Bragg reflector (DBR) on the bottom surface of a transparent substrate such as a sapphire substrate have been studied.

Figure 1 shows the reflectivity measured by forming an aluminum layer on the bottom surface of a sapphire substrate according to the related art.

As can be seen from Fig. 1, when the aluminum layer is not formed on the sapphire substrate, the reflectance is about 20%, but when the aluminum layer is formed on the sapphire substrate, the reflectance in the visible wavelength range is about 80%.

Figure 2 shows the reflectance measured by periodically applying TiO ₂ /SiO ₂ to the bottom surface of a sapphire substrate to form a DBR according to the related art.

As shown in FIG. 2, when a DBR is formed to reflect light emitted from a light emitting diode wafer, for example, light having a peak wavelength of 460 nm is emitted. Figure 2 shows that the reflectance in a light-emitting diode using DBR can reach about 100% in the blue wavelength range (e.g., in the wavelength range of 400 nm to 500 nm).

However, DBR can only increase the reflectivity of a portion of the visible range.

Therefore, the reflectance for other ranges is much lower than the reflectance for the wavelength range of 400 nm to 500 nm as shown in Fig. 2. That is, as shown in FIG. 2, when most of the reflectance is less than 50% at a wavelength of 550 nm or more, the reflectance at a wavelength of about 520 nm or more suddenly decreases.

Therefore, when a light-emitting diode chip using DBR is mounted in a light-emitting diode package to emit white light, DBR exhibits high reflectance for light in a blue wavelength range emitted from the light-emitting diode wafer, but For light emitted in the green and/or red wavelength range, DBR does not exhibit effective reflection characteristics. Therefore, there is a limitation in improving the luminous efficiency of the light-emitting diode.

An exemplary embodiment of the present invention provides a light emitting diode wafer and a method of fabricating the same that can increase the light emitting efficiency of a light emitting diode package that provides mixed color light (for example, white light).

Exemplary embodiments of the present invention also provide a DBR having high reflectance over a wide range of wavelengths and a light emitting diode wafer having the DBR.

Additional features of the invention will be set forth in the description in the description.

An exemplary embodiment of the present invention discloses a light emitting diode wafer including: a substrate having a first surface and a second surface; a light emitting structure disposed on the first surface of the substrate, the light emitting structure including being disposed at the first conductive An active layer between the semiconductor layer and the second conductive semiconductor layer; a distributed Bragg mirror disposed on the second surface of the substrate, the distributed Bragg mirror reflecting light emitted by the light emitting structure; and being disposed therein Metal layer on a Bragg mirror. The distributed Bragg mirror has at least 90% reflection for light of a first wavelength in the blue wavelength range, light of a second wavelength in the green wavelength range, and light of a third wavelength in the red wavelength range rate.

An exemplary embodiment of the present invention also discloses a method of fabricating a light emitting diode wafer, the method comprising: forming a light emitting structure on a first surface of the substrate; removing a portion of the substrate by grinding the second surface of the substrate; Thereafter, the surface roughness of the second surface of the substrate is reduced by lapping the substrate; and a distributed Bragg mirror is formed on the second surface of the substrate. The light emitting structure includes a first conductive type semiconductor layer, a second conductive type semiconductor layer, and an active layer disposed between the first conductive type semiconductor layer and the second conductive type semiconductor layer.

It is to be understood that the foregoing general description

The above described features and advantages of the present invention will be more apparent from the following description.

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which FIG. However, the invention may be embodied in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough, and the scope of the invention will be fully disclosed. In these figures, the dimensions of layers and regions may be exaggerated to make the drawings clear. Like numbers in the drawings indicate like elements.

3 is a cross-sectional view of a light emitting diode 20 having a distributed Bragg mirror 45, and FIG. 4 is an enlarged cross-sectional view of the distributed Bragg mirror 45 of FIG. 3, in accordance with an exemplary embodiment of the present invention.

Referring to FIG. 3, the light emitting diode chip 20 includes a substrate 21, a light emitting structure 30, and a distributed Bragg mirror 45. In addition, the LED wafer 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 a transparent substrate such as sapphire or tantalum carbide (SiC), but is not particularly limited thereto. The upper surface (i.e., the front surface of the substrate 21) may have a predetermined pattern, such as a patterned sapphire substrate (PSS). At the same time, the extent of the substrate 21 determines the overall wafer area. In an exemplary embodiment of the present invention, when the wafer area of the light emitting diode wafer is relatively increased, the reflection effect is increased. Therefore, the substrate 21 may have a range of 90,000 μm ² or more. In some embodiments, it can be 1 mm ² or greater.

A light emitting structure 30 is placed on the substrate 21. The light emitting structure 30 includes a first conductive type semiconductor layer 25, a second conductive type semiconductor layer 29, and an active layer 27 disposed between the first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 29. In this configuration, the first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 29 have conductivity types opposite to each other. The first conductivity type may be an n-type and the second conductivity type may be a p-type and vice versa.

The first conductive type semiconductor layer 25, the active layer 27, and the second conductive type semiconductor layer 29 may be made of a gallium nitride-based compound (i.e., (Al, In, Ga) N) material. The constituent elements and composition of the active layer 27 are determined to emit light of a desired wavelength, such as ultraviolet light or blue light. The first conductive type semiconductor layer 25 and/or the second conductive type semiconductor layer 29 may be formed in a single layer structure as shown in the drawing, or may be formed in a multilayer structure. Additionally, the active layer 27 can be formed as a single quantum well structure or a multiple quantum well structure. In addition, the buffer layer 23 may be interposed between the substrate 21 and the first conductive type semiconductor layer 25.

The semiconductor layers 25, 27 and 29 can be formed by metal-organic chemical vapor deposition (MOCVD) technology or molecular beam epitaxy (MBE) technology, and can be lithographically and etched. The region of the process patterning the first conductive type semiconductor layer 25 is partially exposed.

Meanwhile, the transparent electrode layer 31 may be formed on the second conductive type semiconductor layer 29 by, for example, indium tin oxide (ITO) or nickel/gold (Ni/Au). The transparent electrode layer 31 is used to spread current because it has a lower specific resistance than the second conductive type semiconductor layer 29. A p-electrode pad 33 is formed on the transparent electrode layer 31, and an n-electrode pad 35 is formed on the first conductive type semiconductor layer 25. As shown, the p-electrode pad 33 is electrically connected to the second conductive semiconductor layer 29 through the transparent electrode layer 31.

At the same time, a distributed Bragg mirror 45 is placed on the lower portion (i.e., the back side of the substrate 21). The distributed Bragg mirror 45 includes a first distributed Bragg mirror 40 and a second distributed Bragg mirror 50.

Referring to FIG. 4, the first distributed Bragg mirror 40 is formed by repeating a plurality of pairs of the first material layer 40a and the second material layer 40b, and the second distributed Bragg mirror 50 repeats the plurality of pairs of the third material layers 50a. Formed with the fourth material layer 50b. The plurality of pairs of first material layer 40a and second material layer 40b have a relatively higher reflectance for light in the red wavelength range (for example, 550 nm or 630 nm) than for light in the blue wavelength range, and the second distributed Prague Mirror 50 has a relatively high reflectivity for light in the blue wavelength range (eg, 460 nm light) versus for light in the red or green wavelength range. In this case, the optical thickness of the material layer 40a and the material layer 40b in the first distributed Bragg mirror 40 is thicker than the optical thickness of the material layer 50a and the material layer 50b in the second distributed Bragg mirror 50, or The reverse is also true, but is not limited to this.

The first material layer 40a may be the same material as the third material layer 50a, that is, have the same refractive index (n) (refractive index (n)), and the second material layer 40b may be the same material as the fourth material layer 50b. , that is, have the same refractive index (n). For example, the first material layer 40a and the third material layer 50a may be made of titanium oxide (TiO ₂ ) (n is approximately equal to 2.5), and the second material layer 40b and the fourth material layer 50b may be made of cerium oxide (SiO ₂ ). Made (n is approximately equal to 1.5).

Meanwhile, the optical thickness (refractive index x thickness) of the first material layer 40a may substantially have an integral multiple relationship with the optical thickness of the second material layer 40b, and the optical thicknesses thereof may be substantially identical to each other. Furthermore, the optical thickness of the third material layer 50a may be substantially an integral multiple of the optical thickness of the fourth material layer 50b, while the optical thicknesses thereof may be substantially identical to each other.

Further, the optical thickness of the first material layer 40a may be thicker than the optical thickness of the third material layer 50a, and the optical thickness of the second material layer 40b may be thicker than the optical thickness of the fourth material layer 50b. The optical thicknesses of the first material layer 40a, the second material layer 40b, the third material layer 50a, and the fourth material layer 50b can be controlled by controlling the reflection coefficient and/or thickness of each material layer.

Referring back to FIG. 3, a reflective metal layer 51 made of aluminum (Al), silver (Ag) or rhodium (Rh) or the like may be formed on the lower portion of the Bragg mirror 45 to protect the Bragg mirror 45. A protective layer 53 may be formed thereon. The protective layer 53 may be made of any metal layer such as titanium (Ti), chromium (Cr), nickel (Ni), platinum (Pt), tantalum (Ta), and gold (Au) or an alloy thereof. The reflective metal layer 51 or the protective layer 53 protects the Bragg mirror 45 from external impact or contamination. For example, when the light emitting diode wafer is mounted in a light emitting diode package, the reflective metal layer 51 or the protective layer 53 prevents the distributed Bragg mirror 45 from being deformed from a material such as an adhesive. Further, the reflective metal layer 51 can reflect the light transmitted through the distributed Bragg reflector 45. Therefore, the thickness of the distributed Bragg mirror 45 can be relatively reduced. The distributed Bragg mirror 45 exhibits a relatively high reflectivity, but can transmit visible light of a long wavelength range with a large angle of incidence. Therefore, the reflective metal layer 51 can be disposed at a lower portion of the distributed Bragg mirror 45 to reflect light transmitted through the distributed Bragg mirror 45, thereby improving luminous efficiency.

According to the present exemplary embodiment, there is provided a first distributed Bragg mirror 40 including high reflectance for relatively long wavelength visible light and a second distributed Bragg mirror 50 having high reflectivity for relatively short wavelength visible light. A Bragg mirror 45 in which the first distributed Bragg mirror 40 and the second distributed Bragg mirror 50 are stacked to form a distributed Bragg mirror 45. By combining the first distributed Bragg mirror 40 and the second distributed Bragg mirror 50, the distributed Bragg mirror 45 can increase the reflectivity of light over most of the visible range.

A distributed Bragg mirror according to the related art has high reflectance for light of a specific wavelength range, but has relatively low reflectance for light of different wavelength ranges, so that luminous efficiency in a white-emitting light-emitting diode package is improved There are restrictions. However, according to the present exemplary embodiment, the distributed Bragg mirror 45 may have high reflectance for light of a blue wavelength range, and high reflectance for light of a green wavelength range and light of a red wavelength range, This makes it possible to improve the luminous efficiency of the light-emitting diode package.

Furthermore, compared to the case where the configuration of the second distributed Bragg mirror 50 is closer to the substrate 21 than the first distributed Bragg mirror 40, the configuration of the first distributed Bragg mirror 40 is smaller than that of the second distributed Bragg mirror With 50 closer to the substrate, the loss of light in the distributed Bragg reflector 45 can be further reduced.

Although the present exemplary embodiment illustrates two types of mirrors, namely, a first distributed Bragg mirror 40 and a second distributed Bragg mirror 50, more types of mirrors can be used. In this case, a mirror having a relatively high reflectance for a long wavelength can be placed relatively close to the light emitting structure 30.

Further, in the present exemplary embodiment, the thicknesses of the first material layers 40a in the first distributed Bragg mirror 40 may be different from each other. Furthermore, the thicknesses of the second material layers 40b may be different from each other. In addition, the thicknesses of the third material layers 50a in the second distributed Bragg mirror 50 may be different from each other. Further, the thicknesses of the fourth material layers 40b may be different from each other.

The present exemplary embodiment illustrates that the material layer 40a, the material layer 40b, the material layer 50a, and the material layer 50b are made of cerium oxide (SiO ₂ ) or titanium oxide (TiO ₂ ), but are not limited thereto. Therefore, they can be made of other materials such as tantalum nitride (Si ₃ N ₄ ), compound semiconductors or the like. 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 may be at least 0.5.

Furthermore, the more the number of pairs of the first material layer 40a and the second material layer 40b in the first distributed Bragg mirror 40 and the third material layer 50a and the fourth material layer in the second distributed Bragg mirror 50 The more the logarithm of 50b, the higher the reflectivity will become. The total number of logs can be 20 or more.

The surface roughness of the back surface of the substrate 21 can be controlled before the distributed Bragg mirror 45 is formed. When the surface roughness of the back surface of the substrate 21 is relatively large, it may be difficult to obtain high reflectance by the distributed Bragg mirror 45 in a wide wavelength range. When the interface between the distributed Bragg reflector 45 and the substrate 21 is defective, the distributed Bragg mirror 45 is easily deformed. Even when a light-emitting diode process is applied to, for example, a light-emitting diode package, a slight thermal process is applied, which may cause a problem of a decrease in the refractive index of the distributed Bragg mirror 45. The surface roughness of the back surface of the substrate 21 can be controlled to have a root-mean-square (RMS) value of 3 nm or less. Alternatively, the surface roughness of the back surface of the substrate 21 may have an RMS value of 2 nm or less. In some embodiments, it can have an RMS value of 1 nm or less.

A method of manufacturing a distributed Bragg mirror 45 and a light emitting diode wafer will now be described.

First, the surface roughness of the substrate 21 is controlled before the distributed Bragg mirror 45 is formed. For example, the back surface of the substrate 21 on which the light emitting structure is formed is first ground to remove a portion of the substrate 21. In this case, the back surface of the substrate 21 is scratched by grinding to make it relatively rough. Thereafter, the surface of the substrate 21 is subjected to lapping with a slurry having small particles. In the buffing process, the depth of the groove (such as scratches in the surface of the substrate 21, etc.) is reduced, thereby reducing the surface roughness. In this case, the surface roughness of the back surface of the substrate 21 can be controlled to be smaller at 3 μm by controlling the particle size of the diamond slurry used in the polishing process and the surface plate. However, in general, it is difficult to control the surface roughness using only a buffing process using surface plates and abrasive particles. Therefore, after the surface roughness is reduced by the buffing process, the back surface of the substrate 21 can be polished by a chemical mechanical polishing (CMP) process. The surface roughness of the back surface of the substrate 21 can be controlled to 1 nm or less by the CMP process control.

Then, the material layer (e.g., TiO _2, SiO ₂ and Si ₃ N ₄ or the like) having different refractive indices are alternately deposited on the surface of the substrate 21. The deposition of these material layers can be carried out by various methods such as sputtering, electron beam deposition, plasma enhanced chemical vapor deposition (PECVD), and the like. In particular, ion assisted deposition can be used. Ion-assisted deposition forms a layer of material having a suitable thickness by measuring the reflectivity of a layer of material deposited on substrate 21, making it suitable for forming a layer of material for a distributed Bragg mirror.

After forming a distributed Bragg mirror, the metal layer can be formed on a distributed Bragg mirror. Thereafter, the substrate is diced to complete the individual light-emitting diode wafers.

FIG. 5 shows a cross-sectional view of a distributed Bragg mirror 55 in accordance with another exemplary embodiment of the present invention. The light emitting diode wafer according to the present exemplary embodiment is substantially similar to the light emitting diode wafer described with reference to FIGS. 3 and 4. 3 and 4 show and illustrate that the distributed Bragg mirror 45 has a stacked structure of a first distributed Bragg mirror 40 and a second distributed Bragg mirror 50. On the other hand, in the distributed Bragg mirror 55 according to the present exemplary embodiment, a plurality of pairs of the first material layer 40a and the second material layer 40b and the plurality of pairs of the third material layer 50a and the fourth material layer 50b are mixed. In other words, at least a pair of the third material layer 50a and the fourth material layer 50b are placed between the plurality of pairs of the first material layer 40a and the second material layer 40b. Further, at least a pair of the first material layer 40a and the first material layer 40b are placed between the plurality of pairs of the third material layer 50a and the fourth material layer 50b. In this configuration, the optical thicknesses of the first material layer 40a, the second material layer 40b, the third material layer 50a, and the fourth material layer 50b are controlled to have high reflectance for light in a wide range of visible light. Therefore, the optical thicknesses of each of the material layers constituting the distributed Bragg mirror may be different from each other.

FIG. 6 is a cross-sectional view of a light emitting diode wafer 20a having a plurality of light emitting units, according to another exemplary embodiment of the present invention.

Referring to FIG. 6, the light emitting diode wafer 20a includes a plurality of light emitting units on the substrate 21. Further, the light emitting diode chip 20a may include a distributed Bragg mirror 45 and a metal layer 51 and/or a protective layer 53.

The substrate 21 and the distributed Bragg mirror 45 are similar to the distributed Bragg mirror described with reference to FIGS. 3, 4, and 5, and thus detailed description thereof will be omitted. However, the substrate 21 may be an insulator that is electrically insulated from the plurality of light emitting units. For example, substrate 21 can be a patterned sapphire substrate.

At the same time, a plurality of mutually isolated light-emitting units 30 are placed. Each of the plurality of light emitting units 30 is the same as the light emitting structure 30 with reference to FIG. 3, and thus detailed description thereof will be omitted. In addition, the buffer layer 23 can be interposed between the light emitting unit 30 and the substrate 21, and the buffer layer 23 can also be isolated from each other.

The first insulating layer 37 covers the front surface of the light emitting unit 30. The first insulating layer 37 has an opening on the first conductive type semiconductor layer 25 and an opening on the second conductive type semiconductor layer 29. The side wall of the light emitting unit 30 is covered by the first insulating layer 37. The first insulating layer 37 also covers the substrate 21 in the region between the light emitting units 30. The first insulating layer 37 may be formed of a cerium oxide (SiO ₂ ) layer or a silicon nitride layer, and may be a layer formed by plasma chemical vapor deposition in a temperature range of 200 ° C to 300 ° C. . In this case, the first insulating layer 37 may be formed to have 4500 To a thickness of 1 μm. When forming the first insulating layer and having less than 4500 At the thickness of the first insulating layer having a relatively small thickness due to a step coverage characteristic on the bottom side of the light emitting unit, and possibly wiring and light emission formed on the first insulating layer An electrical short circuit occurs between the units. Meanwhile, when the thickness of the first insulating layer becomes larger, an electrical short circuit can be prevented, but the transmittance of light may be deteriorated to reduce the luminous efficiency. Therefore, it is preferable to form the first insulating layer having a thickness of not more than 1 μm.

At the same time, a wiring 39 is formed on the first insulating layer 37. The wiring 39 is electrically connected to the first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 29 through the opening. The transparent electrode layer 31 may be disposed on the second conductive type semiconductor layer 29, and the wiring may be connected to the transparent electrode layer 31. In addition, the wires 39 are electrically connected to the first conductive type semiconductor layer 25 to the second conductive type semiconductor layer 29 of the adjacent light emitting units 30, respectively, so that a series array of the light emitting units 30 can be formed. Multiple series arrays can be formed and each connected in anti-parallel such that they can be connected to an alternating current (AC) power source. In addition, a series of bridge rectifiers (not shown) connected to the light unit can be connected, and the light unit can be driven with the bridge rectifier under an alternating current source. This bridge rectifier can be connected by a light-emitting unit having the same structure (such as the light-emitting unit 30 using the wiring 29).

On the other hand, the wiring may connect the first conductive type semiconductor layers 25 of the adjacent light emitting units to each other or the second conductive type semiconductor layers 29 of the adjacent light emitting units to each other. Therefore, a plurality of light emitting units connected in series and in parallel can be provided.

Wiring 39 can be made of a conductive material such as a doped semiconductor material such as polysilicon or a metal. In particular, the wires 39 may be formed in a multilayer structure, such as a lower layer of chromium or titanium and an upper layer of chromium or titanium. In addition, a metal layer of gold, gold/nickel or gold/aluminum may be interposed 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 unit 30 from being damaged by an external impact.

The second insulating layer 41 may be formed of the same material as the first insulating layer 37 and the yttria layer or a tantalum nitride layer. The second insulating layer 41 may be a layer formed using plasma chemical vapor deposition (PECVD) in a temperature range of 200 ° C to 300 ° C, similar to the first insulating layer. Further, when the first insulating layer is formed by using a PECVD method, the second insulating layer may be deposited in a temperature range of -20% to +20% of a deposition temperature of the first insulating layer, or may be the same Deposition at the deposition temperature.

Meanwhile, the second insulating layer 41 may be relatively thin compared to the first insulating layer 37, and may have 500 Or greater thickness. The second insulating layer 41 is thinner than the first insulating layer 37, and the second insulating layer can be prevented from peeling off from the first insulating layer. In addition, when the second insulation layer is 2500 When thin, it may be difficult to protect the wiring and the light unit from external impact or moisture penetration.

At the same time, the phosphor layer 43 can be placed on the light emitting diode chip 20a. The phosphor layer 43 may be a layer in which a resin is dispersed in a phosphor or a layer deposited by an electrophoresis method. The phosphor layer 43 covers the second insulating layer 41, thereby converting the wavelength of light emitted from the light emitting unit 30.

FIG. 7 is a cross-sectional view for explaining a light emitting diode wafer 20b having a plurality of light emitting units, according to another exemplary embodiment of the present invention.

Referring to FIG. 7, the light-emitting diode wafer 20b according to the present exemplary embodiment is substantially similar to the aforementioned light-emitting diode wafer 20a, but they are in the shape of the light-emitting unit 30 and the first conductive type semiconductor to which the wiring 39 is connected. Aspects of portions of layer 25 are not identical.

That is, the light emitting unit 30 of the light emitting diode wafer 20a has the exposed upper surface of the first conductive type semiconductor layer 25, and the wiring 39 is connected to the upper surface of the first conductive type semiconductor layer 25. Unlike the light emitting diode wafer 20a, the light emitting unit 30 of the light emitting diode wafer 20b according to the present exemplary embodiment is formed to have an inclined side surface to expose the inclined side surface of the first conductive type semiconductor layer 25, and The wiring 39 is connected to the inclined side surface of the first conductive type semiconductor layer 25.

Therefore, according to the present exemplary embodiment, in addition to the process of separating the light emitting cells, a separate process of exposing the upper surface of the first conductive type semiconductor layer 25 is not required, whereby the process can be simplified. In addition, it is not necessary to expose the upper surface of the first conductive type semiconductor layer 25, whereby the area reduction of the active layer 27 can be avoided. Further, since the wirings 39 are connected along the inclined side surfaces of the first conductive type semiconductor layer 25, the current dispersion performance of the light emitting unit 30 can be improved, and therefore, the forward voltage can be reduced, and the light emission can be improved. The reliability of the polar body chip 20b.

Experimental example

Figure 8 is a simulation diagram showing the change in reflectance of a distributed Bragg mirror according to an incident angle. In this case, the distributed Bragg mirror is made by alternately stacking 40 layers of SiO ₂ and TiO ₂ on a glass substrate. The thickness of each layer is individually controlled so that the entire region of 400 nm to 700 nm having an incident angle of 0° has a reflectance of 99% or more. Therefore, the distributed Bragg mirror has an overall thickness of 2.908 μm. Meanwhile, in the case of a substantially used light-emitting diode wafer, light incident at an incident angle of about 60 or more will be totally reflected due to the sapphire substrate (n is approximately equal to 1.78) and SiO ₂ ( The difference in refractive index between n is approximately equal to 1.48), and therefore, the simulation of the angle of incidence of 60 or more is omitted. Meanwhile, the graph of FIG. 8 shows the entire visible region of the portion at 100% reflectance (which is similar to the graph shown in FIG. 9).

As can be understood from the graph of Fig. 8, the 40-layer distributed Bragg mirror exhibits an ultra-high reflectance of 99% or higher with respect to an incident angle of 0° in the entire visible region. However, when the incident angle of light incident on the distributed Bragg mirror is increased, it is understood that the reflectance of the long-wavelength visible light is attenuated. When the incident angle exceeds 30°, the reflectance for light at 700 nm is reduced to 99% or lower.

9A and 9B respectively show an example of improving the reflectance of long-wavelength incident light with incident angles of 50° and 60° by increasing the number of stacked Bragg mirrors.

Referring to FIGS. 9A and 9B, as illustrated in FIG. 8, in the case where the distributed Bragg mirror has 40 layers (40 L) and the total thickness is 2.908 μm, the reflectance for an incident angle of 50° (40 L - 50°) And the reflectance (40L-60°) for the incident angle of 60° is much reduced compared to the reflectance (40L-0°) for the incident angle of 0° in the visible region of the long wavelength. In addition, refractive index decay occurs in a portion of the intermediate region of the visible region (eg, adjacent to 510 nm to 520 nm).

However, when the number of layers of the distributed Bragg mirror is increased to 48 layers (total thickness: 3.829 μm) or 52 layers (total thickness: 4.367 μm), even if the incident angle is large, it is possible to obtain substantially in a wide wavelength region. Uniform high reflectivity.

Therefore, increasing the number of stacked Bragg mirrors can improve the reflectance and maintain high reflectance for incident light at a large incident angle. However, increasing the number of stacked Bragg mirrors results in an increase in process time and may cause cracks in distributed Bragg mirrors.

10A and 10B are plan views showing distributed Bragg mirrors after performing a dicing process, respectively. In this case, the case shown in Fig. 10A is a distributed Bragg mirror in which 40 layers are stacked by ion assisted deposition, and Fig. 10B is a distributed Bragg mirror in which 48 layers are stacked by ion assisted deposition.

When 40 layers were stacked (Fig. 10A), cracks did not occur in the distributed Bragg mirror, and when 48 layers were stacked (Fig. 10B), cracks appeared in the cloth Bragg mirror. When 52 layers are stacked (not shown), cracks also occur.

The reason for cracks in distributed Bragg mirrors is not clear, but is believed to be related to ion assisted deposition. That is, since the high-density layer is deposited by ion collision, the pressure is accumulated in the distributed Bragg mirror, and thus cracks may occur in the distributed Bragg mirror during the cutting of the substrate. Therefore, it may not be suitable to mass-produce a light-emitting diode wafer only by increasing the number of stacks.

In connection with this understanding, as illustrated in Figure 3, a reflective metal layer can be formed in a distributed Bragg mirror such that a relatively high reflectivity for light having a large angle of incidence can be maintained.

Table 1 shows the number of stacked Bragg mirrors, an epoxide, and relative luminous efficiency in the state of a white light-emitting diode package depending on whether a reflective metal layer (Al) is applied or not. In these experimental examples, other conditions (such as the type of the light-emitting diode and the type of the package) were the same except for the types of the distributed Bragg reflector, the reflective metal layer, and the epoxide. The number of stacked layers of the distributed Bragg mirror is 40, and the luminous efficiency of the light emitting diode package (sample No. 1) of the light emitting diode chip to which the Al reflective metal layer (indicated by "X") is not applied is Percentage (%) is indicated.

Comparing Sample 1 with Sample 2, Sample 5, and Sample 6, when the Al reflective metal layer was not applied, it was found that the luminous efficiency differs depending on the type of epoxide used as the adhesive. That is, the sample using the transparent epoxy resin showed higher luminous efficiency than the sample using the silver paste. This shows that the reflectivity of the distributed Bragg mirror is affected by the adhesive in the absence of the Al reflective metal layer.

Meanwhile, when the same kind of adhesive is used, the sample to which the Al reflective metal layer is applied (indicated by "O") shows higher luminous efficiency than the other samples. For example, comparing Sample 1 with Sample 3, Sample 2 and Sample 4, and Sample 5 and Sample 7, it is understood that when an Al reflective metal layer is applied, the luminous efficiency is improved.

Meanwhile, comparing Sample 1 with Sample 5 and Sample 2 and Sample 6, when the same adhesive was used without applying the Al reflective metal layer, it was found that the luminous efficiency was improved according to the increase in the number of stacks. It will be appreciated that an increase in the number of distributed Bragg mirror stacks may improve the reflectivity of the distributed Bragg mirror over a wide range of incident angles, thereby resulting in improved luminous efficiency.

However, comparing Sample 3 with Sample 7, when the Al reflective metal layer and the silver paste were applied, although the number of stacks was increased, there was no difference in luminous efficiency. A relatively high reflectance is maintained for long-wavelength visible light having a large incident angle by the Al reflective metal layer. Therefore, when a distributed Bragg mirror and a reflective metal layer are applied, it is known that when the number of stacked Bragg mirrors is reduced, good luminous efficiency can be achieved at a package level. Furthermore, the reduced number of stacks of distributed Bragg mirrors prevents cracks in the distributed Bragg mirrors.

At the same time, when an Al reflective metal layer is applied to the distributed Bragg mirror, a decrease in the reflectance of the distributed Bragg mirror at the chip level can be observed. This phenomenon is considered to be closely related to the surface roughness of the substrate. Hereinafter, the influence of the surface roughness of the substrate on the reflectance of the wafer level to the distributed Bragg mirror will be explained.

Figure 11 is a graph showing the reflectance of a distributed Bragg mirror according to whether or not CMP is performed after a sapphire substrate polishing process using a copper surface plate.

First, after the back surface of the sapphire substrate was ground, a polishing process using a copper surface plate was performed by using a diamond slurry having particles of 3 μm. After performing the buffing process using the copper surface plate, the surface roughness of the back surface of the sapphire substrate showed a root mean square value (RMS) of about 5.12 nm in a region of 5 μm × 5 μm.

Thereafter, after the sapphire substrate is subjected to a CMP process, the first distributed Bragg mirror and the second distributed Bragg mirror mentioned above are formed by controlling the thickness of TiO ₂ and SiO ₂ to fabricate a sample (example) 1). On the other hand, the comparative example was similar to Example 1 in that a distributed Bragg mirror was directly formed without performing a CMP process to fabricate a sample. The CMP process was carried out using a 20 kg amount of SiO ₂ slurry, and after the CMP process, the surface roughness of the sapphire substrate showed an RMS value of about 0.25 nm in a region of 5 μm × 5 μm.

In the case of the comparative example, as shown in FIG. 10, the distributed Bragg mirror exhibits a reflectance of about 90% or more in the visible light range, but the reflectance according to the wavelength is irregular, and 90 is displayed adjacent to 550 nm. % or smaller value. On the other hand, in the case of Example 1, in the broad wavelength range of visible light, most of the reflectance of the distributed Bragg mirror shows a value close to 100%.

Fig. 12 is a graph showing the reflectance after deposition of an aluminum layer of about 500 nm on a sample fabricated in the same manner as the example of Fig. 11 and the comparative example.

In the case of the comparative example, it has been confirmed that the reflectance is considerably reduced after the deposition of Al. On the other hand, in the case of the example, the high reflectance is maintained even after the deposition of Al, and there is no case where the reflectance is reduced.

In the comparative example, it is considered that the phenomenon of the decrease in reflectance is exhibited after the deposition of Al because the distribution of the rough surface is formed on the sapphire substrate according to the comparative example when depositing Al using the electron beam deposition technique. The Bragg mirror is deformed due to interface defects. In the case of Example 1, since the surface roughness of the sapphire substrate was good, it was confirmed that when Al was deposited, the distributed Bragg mirror was not deformed and the reflectance was maintained.

Figures 13, 14 and 15 are graphs showing reflectance according to the size of the slurry particles during the buffing process using a tin surface platform.

In this configuration, the size of the slurry contained in the diamond particles is 3 μm, 4 μm and 6 μm, respectively. After polishing using a tin surface platform, the surface roughness of the sapphire substrate shows an RMS value of about 2.40 nm, 3.35 nm, and 4.18 nm, depending on the diamond particle size.

After the buffing process was performed by the tin surface platform and the Al of 500 nm in the example of FIG. 8 was deposited, the same distributed Bragg mirror as in Example 1 was formed.

As can be understood from the drawings, after using a 3 μm slurry and a tin surface platform for the buffing process, the distributed Bragg mirror has a reflectance of 90% or more in a wide wavelength range of the visible light range. However, when Al is deposited, the reflectance at approximately 550 nm is slightly reduced.

In contrast, as shown in Figures 14 and 15, after using a 4 μm or 6 μm slurry and a tin surface platform for the buffing process, the reflectivity of the distributed Bragg reflector is less than 90% at 550 nm. And after depositing Al, the reflectance is reduced to 80% or less.

It can be understood from the above experimental examples that the surface roughness of the sapphire substrate has an influence on the reflectance of the distributed Bragg mirror before the formation of the distributed Bragg mirror. Further, when the surface roughness of the sapphire substrate is controlled so as to have an RMS value of 3 nm or less, the reflection characteristics are relatively improved. Further, when the surface roughness of the sapphire substrate is 1 nm or less, it is expected that the reflectance does not decrease even after deposition of Al.

As is apparent from the above description, according to an exemplary embodiment of the present invention, a distributed Bragg mirror having a high reflectance over a wide wavelength range can be provided to improve the implementation of a mixed color light (e.g., white light). The luminous efficiency of the polar body package. Furthermore, the reflectivity of the distributed Bragg mirror can also be ensured by controlling the surface roughness of the substrate on which the distributed Bragg mirror is formed.

The invention may be modified or modified differently without departing from the spirit and scope of the invention. Therefore, it is intended that the present invention cover the modifications of the invention and the scope of the appended claims.

20, 20a, 20b. . . Light-emitting diode chip

twenty one. . . Base

twenty three. . . The buffer layer

25. . . Semiconductor layer

27. . . Active layer

29. . . Semiconductor layer

30. . . Light-emitting structure (lighting unit)

31. . . Transparent electrode layer

33, 35. . . Electrode pad

37. . . First insulating layer

39. . . wiring

40. . . First distributed Bragg mirror

40a. . . First material layer

40b. . . Second material layer

41. . . Second insulating layer

43. . . Phosphor layer

45, 55. . . Distributed Bragg mirror

50. . . Second distributed Bragg mirror

50a. . . Third material layer

50b. . . Fourth material layer

51. . . Metal layer

53. . . The protective layer

The accompanying drawings, which are incorporated in and in the

1 is a graph showing the reflectance of aluminum formed on a sapphire substrate according to the related art.

2 is a reflectance diagram of a distributed Bragg mirror on a sapphire substrate in accordance with the related art.

3 is a cross-sectional view of a light emitting diode wafer having a distributed Bragg mirror, in accordance with an exemplary embodiment of the present invention.

4 is an enlarged cross-sectional view of the distributed Bragg mirror of FIG. 3.

FIG. 5 is a cross-sectional view of a distributed Bragg mirror in accordance with another exemplary embodiment of the present invention.

FIG. 6 is a cross-sectional view of a light emitting diode wafer having a plurality of light emitting units, in accordance with another exemplary embodiment of the present invention.

FIG. 7 is a cross-sectional view of a light emitting diode wafer having a plurality of light emitting units, in accordance with another exemplary embodiment of the present invention.

Figure 8 is a simulation of the change in reflectivity of a distributed Bragg mirror based on the angle of incidence.

9A and 9B respectively show an example of improving the reflectance of long-wavelength incident light with incident angles of 50° and 60° by increasing the number of stacked Bragg mirrors.

10A and 10B are plan views showing distributed Bragg mirrors after performing a cutting process, respectively.

Figure 11 is a graph showing the reflectance of a distributed Bragg mirror according to the presence or absence of chemical mechanical polishing (CMP) after a sapphire substrate polishing process using a copper surface plate.

Figure 12 is a graph showing the reflectance after deposition of an aluminum reflective metal layer on a distributed Bragg mirror fabricated in a manner similar to that of Figure 11.

Figures 13, 14 and 15 are graphs showing the reflectance according to the particle size of the slurry during the buffing process using a tin surface platform.

20. . . Light-emitting diode chip

twenty one. . . Base

twenty three. . . The buffer layer

25. . . Semiconductor layer

27. . . Active layer

29. . . Semiconductor layer

30. . . Light-emitting structure (lighting unit)

31. . . Transparent electrode layer

33, 35. . . Electrode pad

40. . . First distributed Bragg mirror

45. . . Distributed Bragg mirror

50. . . Second distributed Bragg mirror

51. . . Metal layer

53. . . The protective layer

Claims (18)

A light emitting diode wafer comprising: a substrate comprising a first surface and a second surface; a light emitting structure disposed on the first surface of the substrate, the light emitting structure comprising an active layer, the active layer being disposed in Between the first conductive semiconductor layer and the second conductive semiconductor layer; a distributed Bragg mirror disposed on the second surface of the substrate, the distributed Bragg mirror comprising an insulating material, the distributed a Bragg mirror reflects light emitted by the light emitting structure; and a metal layer disposed on the distributed Bragg mirror, wherein the distributed Bragg mirror includes light for a first wavelength in a blue wavelength range, The second wavelength of light in the green wavelength range and the third wavelength in the red wavelength range have a reflectivity of at least 90%, wherein the distributed Bragg mirror comprises: a first distributed Bragg mirror Included, for the green wavelength range of light or the red wavelength range of light, a higher reflectance for the blue wavelength range of light; and second a Bragg mirror comprising a higher reflectance for the blue wavelength range than for the red wavelength range, wherein the first distributed Bragg mirror and the second distributed Bragg reflection The mirrors are in contact with each other. The light-emitting diode wafer of claim 1, wherein the metal layer comprises a reflective metal layer. The light-emitting diode wafer of claim 2, wherein the reflective metal layer comprises aluminum. The light-emitting diode wafer of claim 1, wherein the second surface of the substrate comprises a surface roughness comprising a root mean square value of 3 nm or less. The light-emitting diode wafer of claim 4, wherein the second surface of the substrate is surface-treated and includes a surface roughness comprising a root mean square value of 1 nm or less. The light-emitting diode chip according to claim 1, further comprising a plurality of light-emitting units disposed on the substrate. The light-emitting diode chip of claim 6, further comprising at least one light-emitting unit array, wherein a part of the plurality of light-emitting units are connected in series. The illuminating diode chip according to claim 6, further comprising a wiring connecting the adjacent illuminating units in series, wherein the plurality of illuminating units comprise inclined side surfaces, and the wiring is connected to An inclined side surface of the first conductive type semiconductor layer of one of the adjacent light emitting units. The light-emitting diode wafer according to claim 1, wherein the distributed Bragg mirror comprises a structure in which layers including different refractive indexes are alternately stacked, and the optical thicknesses of each of the alternating layers are not mutually different. the same. The light emitting diode chip of claim 1, wherein the distributed Bragg mirror comprises for a range of 400 nm to 700 Light of all wavelengths in the nm range has a reflectance of 98% or higher at an incident angle of 0°. The light-emitting diode wafer of claim 1, wherein the distributed Bragg mirror comprises a reflectance of 95% or higher at an incident angle of 50° for light of 700 nm. A method of fabricating a light emitting diode wafer, comprising: forming a light emitting structure on a first surface of a substrate, the light emitting structure comprising: a first conductive type semiconductor layer; a second conductive type semiconductor layer; and an active layer disposed at the Between the first conductive semiconductor layer and the second conductive semiconductor layer; removing a portion of the substrate by grinding the second surface of the substrate; after the grinding, polishing the substrate And reducing a surface roughness of the second surface of the substrate; and forming a distributed Bragg mirror on the second surface of the substrate, wherein the substrate is formed prior to forming the distributed Bragg mirror The surface roughness of the second surface includes a root mean square value of 3 nm or less. The method of manufacturing a light-emitting diode wafer according to claim 12, further comprising forming a reflective metal layer or a protective layer on the distributed Bragg mirror. Manufacturing a light-emitting diode as described in claim 12 a method of wafer, wherein the distributed Bragg mirror includes light for a first wavelength in a blue wavelength range, light of a second wavelength in a green wavelength range, and a third wavelength in a red wavelength range Light has a reflectivity of at least 90%. The method of manufacturing a light-emitting diode wafer according to claim 12, wherein the surface roughness of the second surface of the substrate comprises 1 nm or more before forming the distributed Bragg mirror A small root mean square value. The method of manufacturing a light-emitting diode wafer according to claim 12, further comprising grinding the second surface of the substrate by a chemical mechanical polishing process after performing the polishing. The method of manufacturing a light-emitting diode wafer according to claim 15, further comprising grinding the second surface of the substrate using a chemical mechanical polishing process. A method of fabricating a light emitting diode wafer according to claim 12, wherein forming the distributed Bragg mirror comprises using ion assisted deposition.