JP2012178453A - GaN-BASED LED ELEMENT - Google Patents

Abstract

An element structure for reducing loss due to light absorption of a metal film formed as an electrode in a GaN-based LED element having a roughened surface formed in a GaN-based semiconductor film is provided.
A first-type conductive layer having a roughened upper surface, a light-emitting layer arranged on the lower surface side of the first-type conductive layer, and the first-type conductive layer sandwich the light-emitting layer. The planarization region 123B is formed by removing at least a part of the first-type conductive layer in the GaN-based semiconductor film including the stacked portion 120 including the second-type conductive layer 121 disposed in A translucent electrode 140 made of a film is provided so as to be continuous from the flattened region to the laminated portion, and an electrode metal film connected to the translucent electrode is provided above the flattened region. 150 and a reflective metal film 130 having a higher reflectance than the electrode metal film with respect to the light generated in the light emitting layer are disposed so as to face each other with the translucent electrode interposed therebetween.
[Selection] Figure 1

Description

  The present invention relates to a GaN-based LED (light-emitting diode) element having a textured surface on a GaN-based semiconductor film.

A GaN-based semiconductor is a compound semiconductor represented by the general formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), and is a group III nitride It is also called a semiconductor or a nitride semiconductor. A GaN-based LED element formed by using a GaN-based semiconductor to form a double hetero pn junction light-emitting structure composed of an n-type conductive layer, a p-type conductive layer, and a light-emitting layer sandwiched between these layers, Light in the near ultraviolet to green wavelength range can be generated. A white light emitting device configured by combining a GaN-based LED element and a phosphor has been put into practical use as a light source for a backlight unit of a liquid crystal display or a light source for indoor illumination.

  A general GaN-based LED element is manufactured through a process of epitaxially growing a GaN-based semiconductor film on a sapphire substrate by the MOVPE method. In this step, an n-type conductive layer is formed on the sapphire substrate via a buffer layer, and a light emitting layer and a p-type conductive layer are sequentially formed on the n-type conductive layer. When this p-type conductive layer is grown at a temperature of about 800 ° C., a textured surface having a large number of pits is formed (Non-patent Document 1).

  Non-Patent Document 2 discloses a GaN-based LED element having a transparent electrode made of ITO (indium tin oxide), which is a transparent conductive oxide (TCO), on a p-type conductive layer. Thus, it has been reported that when the roughened surface is formed on the p-type conductive layer, the output during flip-chip mounting is higher than when the upper surface of the p-type conductive layer is a mirror surface. This suggests that the light scattering action of the roughened surface has an effect of improving the light extraction efficiency. It is understood that the low transparency of the GaN-based semiconductor film having such a roughened surface is a manifestation of strong light scattering.

FIG. According to the electron microscope image shown in FIG. 1, the ITO film formed on the roughened surface of the GaN-based semiconductor grown at a low temperature has a non-uniform film thickness, and its surface smoothness is extremely poor.
Patent Document 1 discloses a method of partially planarizing a roughened surface formed on a GaN-based semiconductor film by low-temperature growth by an etch back method. In brief, the etch-back method is a method in which a rough semiconductor surface is covered with a mask layer that completely embeds the undulations on the surface, and the etching rate of the mask layer and the semiconductor is equal. In this planarization method, a flat semiconductor surface is exposed by etching until the mask layer is completely removed from the surface side of the mask layer.

JP 2006-196692 A International Publication WO2010 / 150809

L.W.Wu et al., Solid-State Electronics, 47, 2027 (2003) Chia-En Lee et al., IEEE Photonics Technology Letters, 20, 659 (2008) Yi-Jung Liu et al., Electrochemical and Solid-State Letters, 13, H406 (2010)

  In the GaN-based LED element disclosed in Non-Patent Document 2, an ITO film is formed on the roughened surface of the p-type conductive layer, and a metal bonding pad is formed on the surface of the ITO film. Since the back surface of this bonding pad reflects the surface shapes of the p-type conductive layer and ITO film which are the base, the smoothness is extremely poor and the reflectance is remarkably low. A metal surface with low reflectance absorbs a large part of incident light and converts it into heat, so that the luminous efficiency of the LED element is greatly reduced.

  In many attempts to provide a roughened surface on a GaN-based semiconductor film for the purpose of improving the light extraction efficiency, the electrode metal film is formed on the roughened surface. However, it seems that the light absorption of such a metal film has not been taken up as a problem. The present invention has been made in view of such circumstances, and in a GaN-based LED element having a roughened surface formed on a GaN-based semiconductor film by a method such as low-temperature growth, it absorbs light of a metal film formed as an electrode. The main object is to provide an element structure for reducing the loss based on the above.

According to the present invention, the following GaN-based LED elements are provided.
(1) The first-type conductive layer whose upper surface is roughened, the light-emitting layer disposed on the lower surface side of the first-type conductive layer, and the first-type conductive layer are disposed so as to sandwich the light-emitting layer. A planarization region is formed by removing at least a part of the first-type conductive layer in the GaN-based semiconductor film having a stacked portion including the second-type conductive layer, and a light-transmitting property including a TCO film An electrode is provided so as to be continuous from the flattened region to the stacked portion, and is formed above the flattened region by an electrode metal film connected to the light-transmitting electrode and the light emitting layer. A GaN-based LED element in which a reflective metal film having a higher reflectance than that of the electrode metal film is opposed to light with the translucent electrode interposed therebetween.
(2) The GaN-based LED element according to (1), wherein the orthogonal projection of the electrode metal film on the upper surface of the light emitting layer is included in the orthogonal projection of the reflective metal film on the upper surface.
(3) The GaN-based LED element according to (1) or (2), wherein the reflective metal film has a reflective surface made of aluminum or silver.
(4) The GaN-based LED element according to any one of (1) to (3), further including a dielectric reflective film sandwiched between the reflective metal film and the GaN-based semiconductor film.
(5) The GaN-based material according to any one of (1) to (4), wherein the translucent electrode has an opening, and the reflective metal film and the electrode metal film are in contact with each other through the opening. LED element.
(6) The GaN-based LED element according to any one of (1) to (5), wherein the planarized region is formed on a surface of the first type conductive layer.
(7) The GaN-based LED element according to any one of (1) to (6), wherein the first-type conductive layer is a p-type conductive layer and the second-type conductive layer is an n-type conductive layer.
(8) The GaN-based LED element according to any one of (1) to (6), wherein the first type conductive layer is an n-type conductive layer and the second type conductive layer is a p-type conductive layer.

  In each of the GaN-based LED elements according to the embodiment of the present invention, the light extraction efficiency is good due to the action of the roughened upper surface of the first-type conductive layer, and the reflectance for the light generated in the light emitting layer is high. A reflective metal film higher than the electrode metal film is formed on the planarization region formed by removing at least a part of the first conductivity type layer, and the electrode metal film disposed above the reflective metal film is formed. Since the incidence of the light is prevented, the loss due to the light absorption of the electrode metal film is reduced.

The structure of the GaN-type LED element which concerns on embodiment is shown, Fig.1 (a) is a top view, FIG.1 (b) is sectional drawing in the position of the XX line of Fig.1 (a). It is a top view which displays only the electrode metal film contained in the GaN-type LED element shown in FIG. It is process sectional drawing for demonstrating the method to form a planarization area | region. It is process sectional drawing for demonstrating the method to form a planarization area | region. It is a figure for demonstrating the relationship between the orthogonal projection of the reflective metal film with respect to the upper surface of a light emitting layer, and the orthogonal projection of an electrode metal film in suitable embodiment. It is sectional drawing of the GaN-type LED element which concerns on embodiment. It is sectional drawing of a reflective metal film. It is sectional drawing of the GaN-type LED element which concerns on embodiment. It is sectional drawing of the GaN-type LED element which concerns on embodiment. It is sectional drawing of the GaN-type LED element which concerns on embodiment.

  The structure of the GaN-based LED element 100 according to the embodiment is shown in FIG. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line XX in FIG. The GaN-based LED element 100 has a GaN-based semiconductor film stacked on a light-transmitting substrate 110. The GaN-based semiconductor film includes a stacked portion 120 in which an n-type conductive layer 121, a light-emitting layer 122, and a p-type conductive layer 123 are sequentially stacked from the translucent substrate 110 side. On the upper surface of the p-type conductive layer 123 provided at the uppermost part of the stacked portion 120, a roughened region 123A and a planarized region 123B formed by removing a part of the p-type conductive layer 123 are provided. Is provided. In FIG. 1A, the outer edge of the flattened region 123B is indicated by a broken line. In the roughened region 123 </ b> A, as shown in the enlarged view in FIG. 1, pits having a V-shaped cross section are formed at a high density on the surface of the p-type conductive layer 123.

  On the stacked portion 120, a translucent electrode 140 made of a TCO film is formed with a reflective metal film 130 formed in the planarization region 123B of the p-type conductive layer 123 interposed therebetween. An electrode metal film 150 is formed on a part of the translucent electrode 140 so as to face the reflective metal film 130 with the translucent electrode 140 interposed therebetween. Since the reflective metal film 130 is formed on the planarization region 123B, the back surface thereof is relatively flat. The material of the reflective metal film 130 is selected so that the reflectance with respect to the light generated in the light emitting layer 122 is higher than that of the electrode metal film 150. Since the reflective metal film 130 and the electrode metal film 150 are disposed so as to face each other, the reflective metal film 130 effectively prevents light generated in the light emitting layer 122 from entering the back surface of the electrode metal film 150. .

  An n-side electrode forming surface 121 </ b> A that is an exposed surface of the n-type conductive layer 121 is provided adjacent to the stacked unit 120. An n-side electrode 160 is formed on the n-side electrode formation surface 121A. The n-side electrode 160 may be composed only of a metal film, or may be a laminate composed of a TCO film that is in ohmic contact with the n-type conductive layer 121 and a metal film laminated thereon. Considering that a phenomenon (droop phenomenon) in which light emission efficiency decreases with an increase in injection current inevitably occurs in a GaN-based LED element, the area of the n-side electrode forming surface 121A is the minimum necessary for forming the n-side electrode 160. It is preferable to increase the area of the stacked portion 120, which is a portion including the light emitting structure, as much as possible.

In the peripheral region of the element, a groove bottom 121B that is an exposed surface of the n-type conductive layer 121 that is continuous with the n-side electrode formation surface 121A is provided so as to surround the stacked portion 120. The groove bottom 121B corresponds to the bottom surface of a groove formed in the GaN-based semiconductor film for element isolation in the process of manufacturing the GaN-based semiconductor device 100 using a wafer-sized substrate. The configuration in which the n-side electrode forming surface 121A and the groove bottom 121B are continuous is not essential, and they may be separated.

  FIG. 2 is a top view showing only the electrode metal film 150 extracted. The electrode metal film 150 includes a bonding pad portion 151 and an extension portion 152 extending from the bonding pad portion. The bonding pad 151 is a part for bonding a bonding wire or a conductive bonding material. The conductive bonding material is used in the case of flip chip mounting. Specific examples of the conductive bonding material include solder, silver paste, and metal bumps. The extension 152 is provided to efficiently spread the current in a direction parallel to the light emitting layer 122, and has an elongated shape so as not to absorb or shield light generated in the light emitting layer 122 as much as possible. As shown in FIG. 1A, in the GaN-based LED element 100, the n-side electrode 160 also has a bonding pad portion and an extension portion. The planar shape of the bonding pad provided on the electrode metal film 150 or the n-side electrode 160 is not limited to a rectangle, and may be a circle, an ellipse, or the like.

  The configuration in which the bonding pad portion and the extension portion are provided on the electrode metal film and / or the n-side electrode is particularly useful in a GaN-based LED element having a large size. Depending on the shape and size of the GaN-based LED element and the arrangement of the bonding pad portions, the number of extensions extending from one bonding pad portion can be one, or three or more. Also, a configuration in which the extension portion branches in the middle, a configuration in which the extension portions extending from different bonding pad portions are connected, and the like can be appropriately employed. Note that both the electrode metal film and the n-side electrode have a bonding pad portion, but it is not essential to have an extension portion.

The GaN-based LED element 100 can be manufactured by the procedure described below.
First, a translucent substrate 110 having a wafer size (for example, 2 inches in diameter) that can be used for epitaxial growth of a GaN-based semiconductor is prepared. For example, a single crystal substrate made of sapphire, spinel, silicon carbide, zinc oxide, magnesium oxide, GaN, AlGaN, AlN, NGO (NdGaO ₃ ), LGO (LiGaO ₂ ), LAO (LaAlO ₃ ), or the like can be used. A sapphire substrate is one of the preferred translucent substrates. Among them, a PSS (Patterned Sapphire Substrate) in which convex portions or concave portions for generating light scattering are formed by etching on the surface on which a GaN-based semiconductor is to be grown. Is particularly preferred. Particularly suitable among the PSSs are those having convex portions formed in a conical or hemispherical shape.

  Next, the n-type conductive layer 121, the light emitting layer 122, and the p-type conductive layer 123 are sequentially grown on the prepared translucent substrate 110 by vapor phase epitaxial growth. As the epitaxial growth method, a MOVPE method, an HVPE method, an MBE method, a sputtering method, a reactive sputtering method, and other known methods can be appropriately used. When a translucent substrate having a large lattice constant difference from the GaN-based semiconductor, such as a sapphire substrate, is used, the n-type conductive layer 121 is grown after forming a buffer layer on the translucent substrate 110.

For the types of impurities that can be added to impart n-type conductivity or p-type conductivity to the GaN-based semiconductor, known techniques can be referred to. The n-type conductive layer 121 is preferably Al _x Ga _1-x N (0 ≦ x ≦ 0.05) to which Si (silicon) is added at a concentration of 3 × 10 ^{18 to} 5 × 10 ¹⁹ cm ⁻³ . It is formed to a thickness of 2 to 6 μm. The light emitting layer 122 is preferably a multiple quantum well layer in which In _x Ga _1-x N (0 <x) well layers and In _y Ga _1-y N (0 ≦ y <x) barrier layers are alternately stacked. To do. For the types and concentrations of impurities that can be added to each of the well layer and the barrier layer, known techniques can be referred to. The p-type conductive layer 123 is preferably Al _x Ga _1-x N (0 ≦ x ≦ 0.05) to which Mg (magnesium) is added at a concentration of 5 × 10 ¹⁹ to 1 × 10 ²¹ cm ⁻³ . 0.3-2μ
It is formed to a thickness of m. If the thickness of the p-type conductive layer is too small, care must be taken because sufficient light scattering action cannot be generated even if the upper surface is roughened.

  Various functions are known between the light-transmitting substrate 110 and the n-type conductive layer 121, between the n-type conductive layer 121 and the light-emitting layer 122, and between the light-emitting layer 122 and the p-type conductive layer 123 with reference to known techniques. It is possible to insert a GaN-based semiconductor layer having For example, a defect reduction layer, a strain relaxation layer, a carrier block layer, and the like. The GaN-based semiconductor layer to be inserted may have a multilayer structure such as a superlattice.

A method for roughening the upper surface of the p-type conductive layer 123 is not particularly limited. When the MOVPE method is used, pits can be generated on the upper surface by setting the growth temperature of the p-type conductive layer 123 to 700 to 900 ° C. The film thickness and growth conditions of the p-type conductive layer 123 are set so that pits having a depth of 0.3 μm or more, more preferably 0.4 μm or more are formed. Since threading dislocations are involved in the generation of pits, threading dislocations are generated at a density of about 10 ⁸ / cm ³ in order to generate pits having a preferable size on the upper surface of the p-type conductive layer 123 at a high density. Thus, it is preferable to use a translucent substrate having a certain lattice constant difference with a GaN-based semiconductor such as a sapphire substrate. When a nitride semiconductor substrate such as a GaN substrate is used, a layer having a function of increasing threading dislocation density is preferably provided between the substrate and the p-type conductive layer. Patent Document 2 can be referred to for a layer having such a function.
After forming the p-type conductive layer 123 so that the upper surface becomes flat at a growth temperature of 1000 ° C. or higher, the upper surface can be roughened by etching using a nanomask. For such techniques, publicly known documents can be referred to as appropriate.

Next, a part of the surface layer portion is removed from the p-type conductive layer 123 by dry etching, thereby forming a planarized region 123B on the upper surface thereof. In this step, the aforementioned etch back method is used. Specifically, first, as shown in FIG. 3A, a protective film P is formed on the entire roughened upper surface of the p-type conductive layer 123. Protective film P may be formed of an oxide such as a metal or SiO _2. Next, using an ordinary photolithography technique, an opening corresponding to the shape of the planarized region to be formed is formed in the protective film P as shown in FIG. After forming the opening, as shown in FIG. 3C, the upper surface of the wafer is covered with a mask layer Q in which the undulations are embedded flat. The mask layer Q can be formed using a photoresist.

  Next, the wafer is dry-etched from above the mask layer Q. At this time, dry etching is performed so that the etching rate of the protective film P is smaller than the etching rate of the mask layer Q, and the etching rate of the mask layer Q and the GaN-based semiconductor (p-type conductive layer 123) is equal. Etching conditions are set. When such a condition is used, as shown in FIG. 4D, in the region where the protective film P is formed, etching stops when the protective film P is exposed. On the other hand, in the region where the opening is formed in the protective film P, the mask layer Q and the p-type conductive layer 123 are etched at the same rate. As a result, as shown in FIG. When removed, the exposed surface of the p-type conductive layer 123 becomes flat. Thereafter, as shown in FIG. 4F, the protective film P is removed using an appropriate etchant. Through the above procedure, the planarized region 123B can be formed in a desired planar shape.

  After the formation of the planarization region 123B, a reflective metal film 130 is formed on the planarization region. The thickness of the reflective metal film 130 can be 50 nm to 1 μm. It is important to form the reflective metal film 130 so as not to protrude from the planarization region 123B. This is because when the reflective metal film 130 protrudes over the roughened region 123A, the reflectance is remarkably reduced in the protruding portion due to the deterioration of the smoothness of the reflection surface.

  The reflective metal film 130 is formed of a metal having a high reflectivity with respect to the light generated in the light emitting layer 122, which reflects light incident on the back surface side (p-type conductive layer 123 side). Since the typical emission wavelength of the GaN-based LED element is 360 to 500 nm, preferable metals include Al (aluminum), Ag (silver), Rh (rhodium), Pt (platinum), Pd (palladium), and the like. Illustrated. Of these, Al and Ag are particularly preferable. The reflective surface made of Al can be formed using Al alone, and in order to improve heat resistance and the like, Ti, Nd (neodymium), Si (silicon), Cu (copper), Mg (magnesium), It can be formed using an Al alloy to which an element such as Mn (manganese) or Cr is added. The reflecting surface made of Ag can be formed by using Ag alone, and in order to improve heat resistance, chemical stability, etc. and to prevent migration, Cu, Au (gold), Pd, Nd, Si, Ir , Ni, W, Zn (zinc), Ga (gallium), Ti, Mg, Y (yttrium), In (indium), Sn (tin), and the like, and can be formed using an Ag alloy.

  After the reflective metal film 130 is formed, a translucent electrode 140 that covers substantially the entire surface of the p-type conductive layer 123 is formed with the reflective metal film interposed therebetween. The material of the transparent electrode 140 includes indium oxide-based TCO such as ITO and IZO (indium zinc oxide), zinc oxide-based TCO such as AZO (aluminum zinc oxide) and GZO (gallium zinc oxide), A tin oxide-based TCO such as FTO (fluorine-doped tin oxide) can be preferably used. There is no limitation on the method of forming the translucent electrode 140, sputtering method, reactive sputtering method, vacuum deposition method, ion beam assisted deposition method, ion plating method, laser ablation method, CVD method, spray method, spin coating method, A known method such as a dip method can be used as appropriate. When the vapor phase method is used, the film formation conditions and the deposition time are set so that the film thickness when the film is formed on a flat surface is 0.1 to 0.5 μm, preferably 0.15 to 0.25 μm. Can be set. A TCO film formed on a roughened surface by a vapor phase method tends to have a large thickness non-uniformity.

  The translucent electrode 141 may be patterned by either a subtractive method or an additive method (lift-off method). By performing heat treatment before or after patterning, the electrical characteristics, contact resistance, transparency, and the like of the light-transmitting electrode 141 may be improved. Although the mechanism is not clear, when the translucent electrode 141 is formed of ITO, GaN-based heat treatment is performed in a nitrogen atmosphere at 500 to 600 ° C. (preferably 540 to 580 ° C.) for 10 to 20 minutes. The output of the LED element 100 can be improved.

  After forming the translucent electrode 140, an electrode metal film 150 is formed. The thickness of the electrode metal film 150 can be set to 0.2 to 2 μm. The electrode metal film 150 is preferably formed with a metal having good adhesion to the TCO at a portion in contact with the translucent electrode 140. Examples of such metals include simple substances such as Cr (chromium), Ti (titanium), Ni (nickel), W (tungsten), Zr (zirconium), and alloys containing these metal elements. Cr, Ti, Ni, W, and Zr have low reflectivity with respect to light with a wavelength of 360 to 500 nm emitted from the GaN-based LED element 100, but the light is incident on the back surface of the electrode metal film 150 by the reflective metal film 140. Therefore, the decrease in luminous efficiency due to the use of these metals for the electrode metal film 150 is small. The surface layer portion of the electrode metal film 150 can be formed of Au, Pt, or the like, or can be formed using a metal contained as a component in solder that is scheduled to be used for bonding.

The planar shape and the area of the reflective metal film 130 and the electrode metal film 150 may be the same, but in that case, the effect of the reflective metal film 130 is significantly reduced if the planar arrangement of both is slightly shifted in the manufacturing process. Therefore, as shown in FIG. 5, the area of the reflective metal film 130 is larger than that of the electrode metal film 142 so that the orthogonal projection of the reflective metal film 130 on the upper surface of the light emitting layer 122 includes the orthogonal projection of the electrode metal film 150. A slightly larger size is desirable. For example, the area of the reflective metal film 130 can be 120 to 150% of the area of the electrode metal film 150.

  Next, the p-type conductive layer 123 and the light emitting layer 122 are partially removed from the GaN-based semiconductor film by dry etching, thereby forming the n-side electrode formation surface 121A. By using the above-described etch back method in this step, the entire region of the n-side electrode formation surface 121A can be made flat. When the etch back method is not used, the n-side electrode formation surface 121A exhibits a surface shape similar to the roughened region 123A of the p-type conductive layer.

  The n-side electrode 160 provided on the n-side electrode formation surface 121A is formed of a material that forms good ohmic contact with the n-type GaN-based semiconductor at least at a portion in contact with the n-type conductive layer 121. As such a material, Al (aluminum), Ti (titanium), W (tungsten), Ni (nickel), Cr (chromium) or V (vanadium) alone, or an alloy containing one or more metals selected from these. Is mentioned. Among these, Al and Al alloys are particularly preferable materials because of their high reflectance in the wavelength region of 350 to 500 nm. Examples of the Al alloy include those containing additive elements such as Ti, Nd (neodymium), Si (silicon), Cu (copper), Mg (magnesium), Mn (manganese), and Cr. The n-side electrode 130 has a TCO film, that is, a translucent film made of indium oxide, ITO, IZO, zinc oxide, AZO, GZO, tin oxide, FTO, or the like, at a portion in contact with the n-type conductive layer 121. Also good.

  The surface layer portion of the n-side electrode 130 is made of metal. In order to increase the bondability of an Au wire frequently used as a bonding wire, it is preferable to form the surface layer portion of the n-side electrode 130 with Au. When the surface layer portion is formed of a metal that is difficult to oxidize, such as Au or Pt, the wettability by solder is good. The surface layer portion may be formed using a metal contained as a component in solder that is scheduled to be used for bonding. A barrier layer made of a refractory metal is provided between the metal layer used for the surface layer portion and the metal layer provided therebelow so as not to cause an undesirable alloying reaction between these layers. be able to.

  Usually, each element on the wafer is electrically separated before a dicing process in which the wafer is divided to make the GaN-based LED element 100 into a chip (also referred to as a die). Specifically, an element isolation groove reaching the n-type conductive layer 121 is formed in the GaN-based semiconductor film by etching so that the stacked portion 120 included in each LED element is electrically isolated. In the dicing process, the wafer is divided at the position of the element isolation groove. As a result, the GaN-based LED element 100 formed into a chip has a groove bottom 121B that is the bottom of the element isolation groove at the peripheral edge. . The step of forming the element isolation trench may be simultaneous with the step of forming the n-side electrode formation surface 121A or may be a separate step. In a preferred example, the n-side electrode formation surface 121A can be formed flat using an etch back method, and the element isolation groove can be formed in a separate process so that the groove bottom 121B becomes a rough surface. By making the groove bottom 121B rough, the light extraction efficiency of the GaN-based LED element 100 is improved.

  Before the dicing process, the surface of the electrode metal film 150 and the n-side electrode 160 is removed to protect the end face of the light emitting layer 122 exposed in the element isolation process and the surface of the translucent electrode 140 made of a thin TCO film. It is preferable to form a passivation film that covers the surface of the wafer. The passivation film can be formed using silicon oxide, silicon nitride, silicon oxynitride, PSG (phospho-silicate-glass), BPSG (boro-phospho-silicate-glass), spin-on glass, or the like.

In the dicing process, before the wafer is divided, the back surface of the light-transmitting substrate 110 may be subjected to a grinding process or a lapping process to reduce the film thickness. The LED chip may be cut out from the wafer using a dicer equipped with a dicing blade, or
A scribe line may be formed on the wafer surface with a diamond pen, and the wafer may be divided into chips by using the scribe line as a starting point. Instead of the scribe line, the wafer can be divided starting from a groove formed on the wafer surface by laser processing or a modified region formed inside the wafer.

  When mounting the GaN-based LED element 100 obtained by the above procedure, the LED chip may be fixed to the member to which the LED chip is fixed so that the surface of the translucent substrate 110 is directed, Conversely, the LED chip may be fixed to the member to which the LED chip is to be fixed so that the surface of the GaN-based semiconductor film is directed (flip chip mounting). In the case of flip chip mounting, after the LED chip is fixed to the fixing member, the translucent substrate 110 can be separated from the GaN-based semiconductor film by using a laser lift-off technique.

  The manufacturing procedure of the GaN-based LED element 100 described above is an example, and the order of some processes can be changed. For example, the step of forming the n-side electrode formation surface 121A may be performed before the step of forming the planarization region 123B. Further, when the lowermost layer of the n-side electrode 160 is formed of a TCO film, the TCO film and the translucent electrode 140 can be simultaneously formed using the same material. Alternatively, the electrode metal film 150 and the metal layer included in the n-side electrode 160 can be formed simultaneously using the same material.

Next, a modified example will be described.
In one example, as shown in FIG. 6, a dielectric reflection film 170 can be provided between the reflection metal film 130 and the p-type conductive layer 123. Since the loss due to reflection on the metal surface is generally larger than the reflection loss of the dielectric mirror, it is desirable to reflect as much light as possible by the dielectric reflection film 170 before reaching the reflection metal film 130.

  An example of the dielectric reflection film 170 is a low refractive index film that generates total reflection at the interface with the p-type conductive layer 123. This low refractive index film is a dielectric having a refractive index lower than that of the p-type conductive layer 123, for example, a metal fluoride such as magnesium fluoride or lithium fluoride, silicon oxide, magnesium oxide, spinel, aluminum oxide, zirconium oxide. It can be formed using a glass-based material such as a metal oxide such as PSG, BPSG, or spin-on glass. Preferably, the film thickness of the low refractive index film is such that a high reflection condition is established for vertically incident light, that is, (2n-1) / 4 times the wavelength of light generated in the light emitting layer 122 (n is a natural number). Set to be.

  Another example of the dielectric reflection film 170 is a Bragg reflection film. This reflection film is also called DBR, dielectric multilayer mirror, etc., and can reflect normal incident light of a specific wavelength with a reflectance close to 100%. As is well known, the specific wavelength can be adjusted to the wavelength of light generated in the light emitting layer 122 by appropriately designing the thickness of each layer constituting the multilayer film. The dielectric reflecting film 170 can also be constituted by a low refractive index film formed immediately above the p-type conductive layer 123 and a Bragg reflecting film laminated thereon. In this case, light incident at a large incident angle is totally reflected by the low refractive index film, and light incident at a small incident angle is reflected by the Bragg reflection film.

  The dielectric reflective film 170 also has a function of reliably insulating between the p-type conductive layer 123 and the reflective metal film 130. By reliably insulating between the p-type conductive layer 123 and the reflective metal film 130, light emission in the light emitting layer 122 immediately below the reflective metal film 130 can be reliably suppressed. Light generated directly below the reflective metal film 130 is strongly shielded or absorbed by the reflective metal film 130 as compared to light generated in other regions, so that the light emission of the GaN-based LED element 100 is less likely to occur. It is preferable for increasing the efficiency.

  In order to prevent an undesired chemical reaction between the reflective metal film 130 and the translucent electrode 140 and thus the reflectivity of the reflective metal film 130 decreases, as shown in FIG. A laminated film including the reflective surface forming layer 131 and the barrier layer 132 can be formed. Here, the reflective surface forming layer 131 is preferably formed of Al, Ag, or the like. The barrier layer 132 is a layer formed on the translucent electrode 140 side with respect to the reflective surface forming layer 131, and can be formed using a single substance or alloy such as Cr, Ti, Ni, W, Zr. For the same purpose, a thin film made of an inert oxide such as silica may be inserted between the reflective metal film 130 and the translucent electrode 140.

  As described above, the electrode metal film 150 has a bonding pad portion. The electrode metal film 150 must be firmly fixed to the p-type conductive layer 123 so as to withstand strong stress applied when a bonding wire is bonded to the portion. When the GaN-based LED element 100 is flip-chip mounted, a bonding material (for example, solder) that is a mechanical holding member at the same time as the conductive material is bonded to the electrode metal film 150. Again, the bond between the p-type conductive layer 123 and the electrode metal film 150 must be strong.

Therefore, in one example, as shown in FIG. 8, a through hole is provided in the translucent electrode 140 on the reflective metal film 130, and the reflective metal film 130 and the electrode metal film 150 are directly bonded through the through hole. As a result, the number of interfaces between different materials existing between the p-type conductive layer 123 and the electrode metal film 150 is reduced, so that the bonding strength between the two is improved.
In the example shown in FIG. 9, the planarization exposed surface 121 </ b> B is formed on the n-type conductive layer 121 by using the etch back method, and the reflective metal film 130 and the electrode metal film 150 are formed on the transparent electrode 140. The structure which opposes on both sides of is formed. Dielectric reflection film 170 is formed so as to be continuous from the planarization exposed surface 121B to the end surface of the stacked portion 120, whereby the end surfaces of the n-type conductive layer 121 and the light emitting layer 122 facing the planarization exposed surface 121B. And the translucent electrode 140 are insulated. According to this structure, since the light emitting layer 122 does not exist below the reflective metal film 130, the light emission efficiency is improved.

  In the GaN-based LED element 200 shown in FIG. 10, the GaN-based semiconductor film including the stacked portion 220 in which the p-type conductive layer 223, the light-emitting layer 222, and the n-type conductive layer 221 are sequentially stacked is the light-emitting layer of the n-type conductive layer 221. A roughened region 221A and a flattened region 221B are provided on the surface opposite to the 222 side. On the stacked portion 220, a translucent electrode 240 made of a TCO film is formed with a reflective metal film 230 formed in the planarized region 221B of the n-type conductive layer 221 interposed therebetween. An electrode metal film 250 is formed on a part of the translucent electrode film 240 so as to face the reflective metal film 230 with the translucent electrode 240 interposed therebetween. Since the reflective metal film 230 is formed on the planarization region 221B, the back surface thereof is relatively flat. The material of the reflective metal film 230 is selected so that the reflectance with respect to the light generated in the light emitting layer 222 is higher than that of the electrode metal film 250. Since the reflective metal film 230 and the electrode metal film 250 are disposed so as to face each other, the reflective metal film 230 effectively prevents light generated in the light emitting layer 222 from entering the back surface of the electrode metal film 250. .

100 GaN-based LED element 110 Translucent substrate 120 Laminated body 121 n-type conductive layer 121A n-side electrode forming surface 121B groove bottom 122 light-emitting layer 123 p-type conductive layer 130 n-side electrode 131 reflecting surface forming layer 132 barrier layer 140 light-transmitting Electrode 150 metal electrode 151 bonding pad 152 extension 160 n-side electrode 170 dielectric reflection film P protective film Q mask layer

Claims (8)

  A first-type conductive layer having a roughened upper surface, a light-emitting layer disposed on the lower surface side of the first-type conductive layer, and a second layer disposed so as to sandwich the light-emitting layer between the first-type conductive layer A planarized region is formed by removing at least a part of the first-type conductive layer in the GaN-based semiconductor film including a stacked portion including the conductive layer, and the translucent electrode made of a TCO film is formed on the GaN-based semiconductor film. It is provided so as to continue from the flattened region to the laminated portion. Above the flattened region, an electrode metal film connected to the translucent electrode and the light generated in the light emitting layer are provided. A GaN-based LED element in which a reflective metal film having a higher reflectance than the electrode metal film is disposed so as to face each other with the translucent electrode interposed therebetween.   2. The GaN-based LED element according to claim 1, wherein the orthogonal projection of the electrode metal film on the upper surface of the light emitting layer is included in the orthogonal projection of the reflective metal film on the upper surface.   The GaN-based LED element according to claim 1, wherein the reflective metal film has a reflective surface made of aluminum or silver.   The GaN-based LED element according to any one of claims 1 to 3, further comprising a dielectric reflective film sandwiched between the reflective metal film and the GaN-based semiconductor film.   The GaN-based LED element according to claim 1, wherein the translucent electrode has an opening, and the reflective metal film and the electrode metal film are in contact with each other through the opening.   The GaN-based LED element according to claim 1, wherein the planarization region is formed on a surface of the first type conductive layer.   The GaN-based LED element according to any one of claims 1 to 6, wherein the first-type conductive layer is a p-type conductive layer and the second-type conductive layer is an n-type conductive layer.   The GaN-based LED element according to any one of claims 1 to 6, wherein the first-type conductive layer is an n-type conductive layer and the second-type conductive layer is a p-type conductive layer.

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