JP2008066557A - Semiconductor light emitting device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device in which a heavy current can be passed and a resistance to distortion caused by a temperature is high, since a bump electrode is provided. <P>SOLUTION: A semiconductor light emitting device forms a bump 25 between a semiconductor light emitting element using a thick substrate 11 and a sub mount. After making the semiconductor light emitting device, the substrate 11 is cured with filler and then ground. After the substrate 11 is ground in a desired thickness, fine irregular structures 18 are formed on a front surface. Thereby, the semiconductor light emitting device is obtained whose thin substrate has fine irregular structures at an optical projection side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor light-emitting device and a method for manufacturing the semiconductor light-emitting device in which the light extraction efficiency is increased by reducing the thickness of the substrate serving as the light extraction surface and reducing the amount of light leaked from the side surface of the substrate.

  Semiconductor light emitting devices such as light emitting diodes and laser diodes are attracting attention because of their high light conversion efficiency. Light extraction efficiency is raised as one of the problems in such a light emitting device.

  Currently, there are III-V semiconductors as light-emitting elements used in high-luminance semiconductor light-emitting devices. Since these semiconductors have an internal refractive index higher than that of air, total reflection occurs at the interface with air, and the efficiency of light that can be extracted from the light-emitting element decreases. Therefore, attempts to improve the light extraction efficiency have been proposed.

  One is an attempt to provide a layer having a lower refractive index with air (see Patent Document 1). The semiconductor light emitting device has a high internal refractive index. Therefore, the light extraction efficiency is improved by providing a layer having a higher refractive index than air and a lower refractive index than the inside of the semiconductor light emitting device. Specifically, particles having a high refractive index are arranged in a resin layer arranged around the semiconductor light emitting element, and the refractive index of the resin layer lower than that of the semiconductor light emitting element is increased to improve the light extraction efficiency (Patent Document 1). 19th stage).

  There is also an attempt to improve light extraction efficiency by directly forming a fine concavo-convex structure on a light emitting layer or a transparent crystal substrate (see Patent Document 2). In order to avoid total reflection that occurs at the interface of the semiconductor light emitting device, the surface of the light emitting device is made to have a concavo-convex structure, thereby suppressing interference due to multiple reflection and improving light extraction efficiency. Specifically, a silicon-based organic solvent is applied to a transparent crystal substrate, a mold having a fine concavo-convex structure is pressed onto the transparent crystal substrate, the concavo-convex structure is transferred, and a fine concavo-convex structure is created by dry etching (such as the 11th stage of Patent Document 2). ).

  FIG. 6 shows a schematic diagram of this semiconductor light emitting device. A semiconductor light emitting element is connected to the extraction electrodes 122 and 123 on the submount 121 by bumps 124 and 125. A minute concavo-convex structure 118 is provided on the upper surface of the substrate 111 of the semiconductor light emitting device to prevent total reflection. Since the semiconductor light emitting element is bonded to the submount by the bumps, the substrate has a certain thickness or more so that it can withstand ultrasonic welding during the bonding.

In particular, products having a high emission luminance on the front surface have been realized in which the surface is made uneven, and the thickness of the transparent substrate is reduced to reduce the amount of light leaked from the side surface. FIG. 7 shows an overview thereof. A p-side electrode 116 is joined to the p-side extraction electrode 160 on the submount 121 via a solder 150, and the n-side electrode 115 is formed on a surface opposite to the p-side electrode with respect to the substrate 112. A current supply line 190 is connected to the n-side electrode by wire bonding.
JP 2004-15063 A JP 2006-1000068 A

  In the method of improving the light extraction efficiency by providing a layer having a small refractive index around the semiconductor light emitting element, a loss of light emission occurs. Therefore, it can be said that providing a concavo-convex structure on the surface of the transparent substrate is an effective method. In addition, the light emitted from the side surface of the semiconductor light emitting element is conventionally used efficiently by using a reflecting mirror or the like, but is basically difficult to handle. Therefore, the configuration shown in FIG. 7 is effective from the viewpoint of reducing the ratio of the light emitted from the side surface by reducing the thickness of the substrate itself.

  In order to achieve such a configuration, it is conceivable that a semiconductor light emitting device is formed by creating a semiconductor light emitting element using a thin substrate and mounting it on a submount.

  By the way, especially in the case of a semiconductor light emitting device for high brightness, the temperature of the semiconductor light emitting element itself during use becomes considerably high, and the thermal stress is repeatedly applied between the wire bonding 190 and the n-side electrode 115. As a result, there is a problem in the durability of this connection portion. Therefore, it is preferable to use the bump method shown in FIG. 6 for taking out the electrode. However, in the bump method, the connection portion between the semiconductor light emitting element and the submount is welded by ultrasonic vibration and is not so mechanically strong. For the transparent substrate, a strong material such as sapphire can be used, but a material having a cleavage property such as gallium nitride (GaN) is often used in order to increase the light emission efficiency. Then, the transparent substrate must be thick to some extent in order to withstand high-frequency vibration when forming bumps.

  Under these circumstances, in order to produce a semiconductor light-emitting device having a thin transparent substrate and a bump electrode, the bump electrode is constituted by a thick transparent substrate, and then the transparent substrate is ground, and the transparent substrate is thinned. An uneven structure must be formed on the surface of the substrate.

  However, the bump electrode is not so strong in mechanical strength, and there is a problem that it cannot withstand the stress during grinding of the transparent substrate.

  In order to solve the above-described problems, the present invention provides a bump electrode formed between a thick transparent substrate on which a semiconductor light emitting element is formed and a submount, and the semiconductor light emitting element including the submount and the transparent substrate is filled with a filler. The transparent substrate is then ground to a predetermined thickness after being in a state that can withstand the processing. Then, the manufacturing method which forms an uneven structure on the surface of a transparent substrate is provided.

  According to the manufacturing method of the present invention, it is possible to obtain a semiconductor light emitting device that is formed on a thin transparent substrate having a concavo-convex structure on the surface and is bonded to a submount with a bump electrode.

  The semiconductor light-emitting device obtained by the manufacturing method of the present invention can have a very small side surface with respect to the front surface from which light is mainly emitted, and the front surface is subjected to total reflection prevention treatment. Very few. In addition, since the bump electrode is provided, a semiconductor light emitting device that can flow a large current and has high resistance to strain due to temperature can be obtained.

  FIG. 1 shows a semiconductor light emitting device 1 obtained by the method for manufacturing a semiconductor light emitting device of the present invention. The semiconductor light emitting device 1 includes a support portion 20 including lead electrodes 22 and 23 and bumps 24 and 25 formed on a submount 21, a substrate 11, an n-type layer 12, an active layer 13, a p-type layer 14, and an electrode 15. , 16 is included.

  The submount 21 supports the semiconductor light emitting element 10 and facilitates attachment to a housing or a lead frame. For the submount 21, a silicon Zener diode, a silicon diode, silicon, aluminum nitride, alumina, other ceramics, or the like can be used. Further, the submount 21 may be provided with a through hole 28. The through hole is a through hole formed in the submount and includes a conductive material such as copper, aluminum, and gold inside.

  The extraction electrode is a terminal for supplying an external current to the semiconductor light emitting element 10. Therefore, it consists of an n-side extraction electrode 22 and a p-side extraction electrode 23. For the extraction electrode, a conductive material such as copper, aluminum, gold, or silver is used. Since the extraction electrode can be formed with a larger area than the semiconductor light emitting element 10, it can be joined to an external current supply line (not shown) by soldering, etc., by applying a large current. It can withstand repeated heat shocks. When the submount has a through hole, it is not necessary to solder an external current supply line to the extraction electrode. This is because it can be connected to a current supply line such as an external electrode or a lead frame through the through hole. However, the through hole and the extraction electrode need to be in an electrically conductive state.

  The bumps serve to fix the semiconductor light emitting element 10 on the submount 21 and to electrically couple the lead electrodes 22 and 23 to each other. There are n-pole bumps 24 and p-pole bumps 25 corresponding to the lead electrodes 22 and 23. Further, since the bumps are provided according to the electrodes provided on the semiconductor light emitting element 10, there may be a plurality of bumps.

  The contact area between the bump and the electrode of the semiconductor light emitting element is 20 on one surface of the semiconductor light emitting element 10 on which the n-side electrode 15 and the p-side electrode 16 are formed in order to promote heat dissipation from the semiconductor light emitting element to the submount. % Or more is desirable, and preferably 50% or more.

  As the material, gold, gold-tin, solder, indium alloy, conductive polymer, or the like can be used, but a material mainly containing gold or gold is particularly preferable. Using these materials, it can be formed using a plating method, a vacuum deposition method, a screen printing method, a droplet injection method, a wire bump method, or the like.

  For example, a gold wire is prepared by a wire bump method, and one end of the gold wire is bonded to a lead electrode on a submount with a bonder, and then the wire is cut to form a gold bump. In addition, a liquid in which fine nanoparticles such as gold are dispersed in a volatile solvent is printed by the same method as ink jet printing, and the solvent is volatilized and removed to form bumps as an aggregate of nanoparticles. You can also.

  A state in which the extraction electrode and the bump are formed on the submount is referred to as a support portion 20. The support portion 20 may have a through hole as apparent from the above description.

  The substrate 11 has a role of holding a portion that emits light. As a material, insulating sapphire can be used. However, since the light emission efficiency and the light emitting part are based on a gallium nitride compound semiconductor, in order to reduce reflection of light at the light emitting layer, more specifically, at the interface between the n-type layer 12 and the substrate 11. It is preferable to use GaN, SiC, AlGaN, AlN, or ZnO having a refractive index equivalent to that of the light emitting layer. These substrates are easily lattice-matched with the gallium nitride-based compound semiconductor, and the crystallinity of the light emitting layer can be improved.

  The n-type layer 12, the active layer 13, and the p-type layer 14 that are light emitting layers are sequentially stacked on the substrate 11. The material is not particularly limited but is preferably a gallium nitride compound. Specifically, the n-type layer 12 of GaN, the active layer 13 of InGaN, and the p-type layer 14 of GaN, respectively. As the n-type layer 12 and the p-type layer 14, AlGaN or InGaN may be used, or a buffer layer made of GaN or InGaN may be used between the n-type layer 12 and the substrate 11. It is. For example, the active layer 13 may have a multilayer structure (quantum well structure) in which InGaN and GaN are alternately stacked.

  Thus, the active layer 13 and the p-type layer 14 are removed from a part of the n-type layer 12, the active layer 13 and the p-type layer 14 laminated on the substrate 11, and the n-type layer 12 is exposed. An n-side electrode 15 is formed on the exposed n-type layer 12. Similarly, a p-side electrode 16 is formed on the p-type layer 14. That is, by removing the active layer 13 and the p-type layer 14 and exposing the n-type layer 12, the light emitting layer, the p-side electrode, and the n-side electrode can be formed on the same side of the substrate.

  The p-side electrode 16 uses a first electrode made of Ag, Al, Rh or the like having high reflectivity in order to reflect the light emitted from the light emitting layer to the substrate 11 side. In order to reduce the ohmic contact resistance between the p-type layer 14 and the p-side electrode 16, it is desirable to use a second electrode such as Pt, Ni, Co, or ITO between the p-type layer 14 and the first electrode. The n-side electrode 15 can use Al, Ti, or the like. It is desirable to use Au or Al on the surfaces of the p-side electrode 16 and the n-side electrode 15 in order to increase the adhesive strength with the bumps. These electrodes can be formed by vacuum deposition, sputtering, or the like.

  The size of the semiconductor light-emitting element 10 is not particularly limited, but it is desirable that one side is 400 μm or more in order to more effectively improve the light extraction efficiency from the front surface.

  FIG. 2 shows a method for manufacturing the semiconductor light emitting device 1 of the present invention. As described above, the support portion 20 in which the extraction electrode and the bump are formed on the submount is prepared. As the submount, a surface having a larger area than that of the semiconductor light emitting device by polishing the surface of a predetermined material is used. This is to increase productivity.

  Further, the semiconductor light emitting device 10 in which the n-type layer, the active layer, the p-type layer and the n-side electrode, and the p-side electrode are formed is placed on the substrate and welded by ultrasonic vibration. Welding is performed by fixing the support portion 20 or the semiconductor light emitting element 10 side, fixing the other with a chuck of an ultrasonic welding apparatus, and applying ultrasonic vibration. At this time, the bump, the n-side electrode 15 and the p-side electrode 16 can be welded by heating from the support portion 20 or the semiconductor light emitting element 10 side with a lower ultrasonic output as compared with the case of not heating. Damage to the light emitting element 10 can be reduced. The heating temperature is preferably 100 to 400 ° C.

  FIG. 2A shows a state in which the bump, the n-side electrode, and the p-side electrode are welded. At this time, the substrate has a thickness of about 0.3 mm to 1 mm. It can withstand vibration due to ultrasonic welding up to a thickness of about 200 μm, but if it is about 150 μm, the GaN substrate may be cracked.

  Next, this is filled with the filler 3. This state is shown in FIG. As the filler, photoresist, epoxy, silicon, and various waxes can be used. This filler is for reinforcing adhesion between the n-side electrode or p-side electrode and the bump or between the bump and the extraction electrode when the substrate is ground. Since the substrate may be removed after grinding, it is preferable that a removable remover (removal solution) or a removal method can be prepared.

  Grinding from above is performed in such a state reinforced with the filler. FIG. 2C shows a state after grinding. For grinding, various polishing machines can be used. Specifically, an apparatus such as a grinding machine or a lapping machine can be used. The thickness of the substrate after grinding is desirably 150 μm or less. This is because if a substrate thicker than 150 μm is sufficient, bumps can be formed without grinding. A thinner substrate is preferable because the ratio of light emitted from the side surface is reduced. The preferred thickness of the substrate varies depending on the product specifications and the material used, but it is desirable that it is at least 1/10 or less of the longer one of the vertical and horizontal lengths of the substrate.

  Since the substrate thickness is ground from 1 mm to several μm, the grinding is preferably performed in a plurality of steps. That is, while the amount of grinding up to the target thickness is large, a grinding method with a high grinding rate is performed, and when approaching the target thickness, grinding is performed with a grinding method with a low grinding rate. For example, in a grinding machine or lapping machine, the grinding rate can be changed by changing the grain size of the grindstone.

  After the substrate is ground to the target thickness, a concavo-convex structure is formed on the substrate surface as a total reflection preventing process. There is no particular limitation on the pattern of the concavo-convex structure. If microfabrication using nanoimprint technology is used, it is possible to form a fine pattern of the same size as the wavelength of light or a smaller scale depending on the wavelength of light used. In addition, various patterns such as a groove shape, a weight shape, and a semi-spherical shape can be formed. Note that the surface on which nanoimprinting is performed needs to be flat, but the ground surface formed of the semiconductor light emitting element 10 and the filler 3 is formed very flat, so that a fine pattern can be formed with high accuracy.

  The formation of the concavo-convex shape on the surface by etching is simple and improves the light extraction effect. However, it is difficult to accurately control the uneven shape, and the same uneven shape cannot be formed on many substrate surfaces.

  In addition, by adjusting the grain size of the grindstone used at the end of the grinding step, it is possible to finish the surface roughness within a certain range in a state where the grinding is finished, thereby obtaining a concavo-convex structure on the substrate surface.

  In addition, a concavo-convex structure can be formed on the substrate surface by an ink jet printing method. Since this method does not include a step of etching the substrate, it can be easily performed. The light extraction effect can be obtained by adjusting the refractive index of the concavo-convex structure itself to be created.

  FIG. 3 illustrates a case where the concavo-convex structure 18 is formed on the substrate surface by the nanoimprint technique.

  After solidifying with a filler and grinding the substrate to a predetermined thickness (as shown in FIG. 2C), a resist is applied to the surface. As the resist, a polymer resist such as PMMA (polymethyl methacrylate), a silicon organic solvent, or the like can be used. After these are applied to the substrate surface, the resist is cured by pre-baking, and then a mold having a pattern formed thereon is pressed to transfer the fine uneven pattern formed on the mold surface to the resist.

  The uneven structure pattern may be a dot pattern or a groove pattern, but is not particularly limited. Also, the upper surface of the substrate may not be the same pattern. The size of the pattern depends on the wavelength of the light used, but a submicron size pattern of 1 μm or less is preferable. For example, a groove pattern having a width of submicron is used.

  Since a large force is applied to the transfer of the mold, the filler is made strong, or a resist that can transfer the pattern even if the force is not so large is selected. FIG. 3D shows a state in which the fine pattern 40 is formed.

  Next, this is etched. Etching can be used by either wet etching or dry etching. In dry etching, there are an ion milling method and a chlorine gas method. In wet etching, etching can be performed using an etchant mainly composed of acid.

  FIG. 3E shows a state after etching. Since the resist and the filler are also removed by etching, there is a portion where the filler is lost.

  FIG. 3F shows a state where the filler is removed thereafter. In the example of FIG. 3 (F), the filler is removed to expose the extraction electrode. However, if the through-hole is provided in the submount and the extraction electrode is not used for connection to the external current line, the filling is performed. It is not necessary to remove the material.

  FIG. 3G shows a process of cutting out each semiconductor light emitting device after removing the filler. Semiconductor light-emitting devices that already have a thin substrate and have a concavo-convex structure on the surface and are supplied with current by bumps are already formed on the submount, and are cut one by one. This is preferably cut out by using a micro slicer or the like, but is not limited to this method. In addition, when a plurality of semiconductor light emitting devices are prepared in advance on one submount, a plurality of semiconductor light emitting devices may be cut out together.

  The case where a concavo-convex structure is formed by wet etching will be described with reference to FIG. The state up to the state of FIG. 2C is the same as described above. In the state of FIG. 2C, since the surface of the substrate is exposed, it is immersed in an aqueous solution of potassium hydroxide (KOH) as it is. If conditions such as potassium hydroxide concentration, temperature, and erosion time are appropriately determined, a concavo-convex structure having a size of submicron to several μ can be formed on the substrate surface. FIG. 4D shows a state in which the concavo-convex structure 42 is formed by etching with potassium hydroxide. Note that the side surface and the electrode formation surface of the semiconductor light emitting element 10 can be protected from being eroded by the filler 3 during wet etching.

  As shown in FIGS. 4E and 4F, the filler is then removed and cut in the same manner as in FIGS. 3F and 3G.

  FIG. 5 shows a method of forming the concavo-convex structure 44 by the ink jet printing method. FIG. 5D shows a state in which the filler is removed in a state where the thickness of the substrate is cut as shown in FIG. Here, the resin is printed in a predetermined pattern by an ink jet printing method. Examples of the pattern include a dot pattern, a groove pattern, and a mixed pattern of dots and grooves, but are not particularly limited. In the ink jet printing method, printing is performed on the substrate surface while ejecting sub-micron ink, so that the groove pattern is also formed as a continuous dot.

  In addition, by mixing nanoparticles in the resin, the refractive index of the concavo-convex structure can be set equal to or lower than that of the substrate. The nanoparticles may be mixed with a phosphor. By mixing phosphors, the color of light emitted from the front surface of the substrate can be changed. After the concavo-convex structure is formed, it is dried and cured.

The phosphor preferably has a submicron diameter. This is because the uneven structure itself may be formed on a submicron scale. The phosphor is not particularly limited. For example, when the light emitted from the semiconductor light emitting element 10 is blue, a yellow phosphor that absorbs blue light and emits yellow light after being excited is exemplified. . As such a yellow phosphor, a rare earth-doped nitride-based or rare earth-doped oxide-based phosphor is preferable. Specifically, rare earth doped alkaline earth metal sulfide, (Y · Sm) ₃ (Al · Ga) ₅ O ₁₂ : Ce and (Y _0.39 Gd _0.57 Ce _0.03 Sm _0.01 ) ₃ Al ₅ O _{12 of} rare earth doped garnet. Rare earth doped alkaline earth metal orthosilicate, rare earth doped thiogallate, rare earth doped aluminate and the like can be suitably used.

A glass material prepared by a sol-gel method can be used instead of the resin. Specifically, it is a compound represented by the general formula Si (X) _n (R) _4-n (n = 1 to 3). Here, R is an alkyl group, and X is selected from halogen (Cl, F, Br, I), a hydroxy group (—OH), and an alkoxy group (—OR). A phosphor or an alkoxide whose general formula is represented by M (OR) n can also be added to this glass material. The refractive index of the concavo-convex structure can be changed by adding an alkoxide.

  Some of these glass materials have a curing reaction temperature of about 200 degrees Celsius, and can be said to be suitable materials considering the heat resistance of materials used for bumps and electrode portions.

  The present invention can be used for a semiconductor light emitting device, particularly a semiconductor light emitting device for high luminance output.

The figure showing the structure of the semiconductor light-emitting device of this invention The figure which shows the process until grinding in the manufacturing method of the semiconductor light-emitting device of this invention. The figure which shows the process of creating uneven structure on the upper surface of the semiconductor light-emitting device of this invention by the nanoimprint construction method The figure which shows the process of creating uneven structure on the upper surface of the semiconductor light-emitting device of this invention by the wet etching method The figure which shows the process of creating uneven structure on the upper surface of the semiconductor light-emitting device of this invention by an inkjet printing method The figure which shows the structure of the conventional semiconductor light-emitting device The figure which shows the structure of the conventional semiconductor light-emitting device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor light-emitting device 3 Filler 10 Semiconductor light-emitting element 11, 111 Substrate 12, 112 n-type layer 13, 113 Active layer 14, 114 p-type layer 15, 115 n-side electrode 16, 116 p-side electrode 18, 118 Surface uneven structure 20 support part 21, 121 submount 22, 122 n-side lead electrode 23, 123, 160 p-side lead electrode 24, 124 n-pole bump 25, 125 p-pole bump 150 solder 190 current supply line

Claims (10)

A submount on which an extraction electrode is formed;
A substrate that has undergone total antireflection treatment on at least one surface;
A light-emitting layer made of a gallium nitride compound semiconductor formed on a surface opposite to the surface subjected to the total antireflection treatment of the substrate;
A p-side electrode and an n-side electrode formed on the same surface side on which the light emitting layer is formed with respect to the substrate;
A semiconductor light emitting device having the p-side electrode or n-side electrode and a bump for joining the extraction electrode. The semiconductor light emitting device according to claim 1, wherein a thickness of the substrate is smaller than at least 1/10 of a longer side in the vertical and horizontal directions of the substrate. The semiconductor light emitting device according to claim 2, wherein the substrate is a material having a cleavage property. 3. The semiconductor light emitting device according to claim 2, wherein the substrate is any one of GaN, SiC, AlGaN, AlN, and ZnO. The semiconductor light emitting device according to claim 1, wherein the submount has a through hole filled with a conductor. Forming a phosphor layer made of a gallium nitride compound semiconductor on a substrate;
Processing the phosphor layer to form an electrode to create a semiconductor phosphor element;
Welding the light emitter element to a submount to create a semiconductor light emitting device;
Filling a filler between the submount and the light emitting element;
Grinding the surface of the substrate opposite to the surface on which the phosphor layer is formed;
And a step of subjecting the ground surface to a total antireflection treatment. The total antireflection treatment includes a step of creating a submicron-width groove by nanoimprinting;
The method of manufacturing a semiconductor light emitting device according to claim 6, further comprising a step of etching the substrate along the groove. The method of manufacturing a semiconductor light emitting device according to claim 6, wherein the total reflection preventing process includes a step of chemically treating the substrate. The method of manufacturing a semiconductor light emitting device according to claim 6, wherein the grinding step includes a plurality of grinding steps with different grinding speeds. The method of manufacturing a semiconductor light emitting device according to claim 6, wherein the total reflection preventing treatment is performed by forming dots of submicron size on the ground substrate surface by ink jet printing.

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