JP2012174730A - GaN-BASED LED ELEMENT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide 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 on a GaN-based semiconductor film by a method such as low temperature growth.SOLUTION: From a GaN-based semiconductor film of a laminate structure including a p-type conductive layer whose upper surface is roughened, a luminescent layer disposed on the lower surface side of the p-type conductor layer, and an n-type conductive layer disposed to hold the luminescent layer between itself and the p-type conductive layer, at least some of the p-type conductive layer and the luminescent layer are removed to obtain a GaN-based LED element having a structure in which a laminate section including the p-type conductive layer, the luminescent layer and the n-type conductive layer, and a flat exposed surface of the n-type conductive layer are adjacent to each other. In the GaN-based LED element, an n-side electrode including a first electrode metal film is formed on the exposed surface, and a translucent electrode composed of a TCO film is formed on the upper surface of the p-type conductive layer.

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.

Also, FIG. 1, the surface on which the n-side electrode (bonding pad) is formed (exposed surface of the n-type conductive layer) is drawn flat, but this surface is obtained by dry etching the roughened surface of the p-type conductive layer. If it is formed, it is actually a roughened surface similar to the surface of the p-type conductive layer. Therefore, it is considered that the back surface of the n-side electrode formed on this surface has poor smoothness and low reflectance.

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) A p-type conductive layer having a roughened upper surface, a light-emitting layer disposed on the lower surface side of the p-type conductive layer, and an n-type disposed so as to sandwich the light-emitting layer between the p-type conductive layer The p-type conductive layer, the light-emitting layer, and the n-type conductive layer are removed by removing at least a part of the p-type conductive layer and the light-emitting layer from the laminated GaN-based semiconductor film including the conductive layer. And a n-side electrode including a first electrode metal film is formed on the exposed surface, and the p-type conductive layer is formed on the exposed surface. A GaN-based LED element in which a translucent electrode made of a TCO film is formed on the upper surface of the conductive layer.
(2) The GaN-based LED element according to (1), wherein the p-type conductive layer has pits formed by low-temperature growth on an upper surface.
(3) The GaN-based LED element according to (1) or (2), wherein at least a part of the first electrode metal film is in contact with a flat exposed surface of the n-type conductive layer.
(4) The GaN-based LED element according to (3), wherein the first electrode metal film has an Al layer in a portion in contact with a flat exposed surface of the n-type conductive layer.
(5) In the above (1) or (2), the n-side electrode has a TCO film in a portion in contact with the flat exposed surface of the n-type conductive layer, and has the first metal film on the TCO film. GaN-type LED element of description.
(6) The GaN-based LED element according to any one of (1) to (5), wherein the first electrode metal film has a bonding pad portion and an extension extending from the bonding pad portion.
(7) A second electrode metal film is formed on a part of the translucent electrode, and a dielectric film that insulates the translucent electrode and the p-type conductive layer immediately below the second electrode metal film. The GaN-based LED element according to any one of (1) to (6).
(8) The GaN-based LED element according to (7), wherein the second electrode metal film has a bonding pad portion and an extension extending from the bonding pad portion.
(9) The GaN-based LED element according to (7) or (8), wherein the dielectric film has better surface smoothness than the p-type conductive layer.
(10) The dielectric film according to (9), wherein the dielectric film has an extension extending from directly below the second electrode metal film between the p-type conductive layer and the translucent electrode. GaN-based LED element.
(11) The n-type conductive layer is formed by removing at least a part of the p-type conductive layer and the light-emitting layer from the GaN-based semiconductor film at a site different from the flat exposed surface of the n-type conductive layer. The GaN-based LED element according to any one of (1) to (10), which has a rough exposed surface of a type conductive layer.
(12) The GaN system according to (11), wherein the rough exposed surface of the n-type conductive layer has a ring shape and surrounds the flat exposed surface of the stacked portion and the n-type conductive layer when viewed in plan. LED element.

Each of the GaN-based LED elements (1) to (12) according to the embodiment of the present invention is excellent in light extraction efficiency due to the action of the roughened upper surface of the p-type conductive layer, while being formed as an n-side electrode forming surface. Since the exposed surface of the n-type conductive layer is flat, a decrease in light emission efficiency due to light absorption of the metal film included in the n-side electrode is suppressed.

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 n side electrode contained in the GaN-type LED element shown in FIG. It is process sectional drawing for demonstrating the method of forming an n side electrode formation surface. It is process sectional drawing for demonstrating the method of forming an n side electrode formation surface. FIG. 5A is a top view showing only a dielectric film, FIG. 5A is a top view of a dielectric film included in the GaN-based LED element shown in FIG. 1, and FIG. 5B is a diagram of a dielectric film according to a modification. It is a top view. It is a figure for demonstrating the relationship between the orthogonal projection of the electrode metal film with respect to the upper surface of a light emitting layer, and the orthogonal projection of a dielectric film in suitable 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. As shown in the enlarged view of FIG. 1B, pits having a V-shaped cross section are formed at a high density on the upper surface of the p-type conductive layer 123 provided at the uppermost portion of the stacked portion 120. . That is, the upper surface of the p-type conductive layer 123 is roughened.

An n-side electrode forming surface 121 </ b> A that is an exposed surface of the flat n-type conductive layer 121 is provided adjacent to the stacked unit 120. An n-side electrode 130 is formed on the n-side electrode formation surface 121A. The n-side electrode 130 may be composed of only 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 the light emission efficiency decreases with an increase in injection current inevitably occurs in the GaN-based LED element, the area of the n-side electrode formation surface 121A is the minimum necessary for forming the n-side electrode 130. 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.

A p-side electrode 140 including a translucent electrode 141 made of a TCO film and an electrode metal film 142 formed on a part thereof is formed on the stacked portion 120. A dielectric film 150 that insulates the p-type conductive layer 123 from the translucent electrode 141 is formed immediately below the electrode metal film 142. In the peripheral region of the element, a groove bottom 121B that is an exposed surface of the rough n-type conductive layer 121 is provided so as to surround the stacked portion 120 and the n-side electrode formation surface 121A. The groove bottom 121B is a 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.

FIG. 2 is a top view showing only the n-side electrode 130 extracted. The n-side electrode 130 has a bonding pad portion 131 and an extension portion 132 extending from the bonding pad portion. The bonding pad 131 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 132 is provided in order to efficiently spread 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 electrode metal film 142 included in the p-side electrode 140 also has a bonding pad portion and an extension portion. The planar shape of the bonding pad portion provided on the n-side electrode 130 or the electrode metal film 142 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 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. In both the n-side electrode and the p-side electrode, it is essential that the electrode metal film has at least a portion that can be used as a bonding pad, but it is not essential to have an extension.

Since the electrode metal film 142 is formed on the roughened surface of the p-type conductive layer 123 via the translucent electrode 141, the reflectance of the back surface thereof is extremely low. Therefore, when light emission is allowed immediately below, the light is absorbed by the electrode metal film 142 with a high probability, resulting in a large loss. Therefore, the dielectric film 150 is formed in order to suppress light emission directly under the electrode metal film 142 and reduce loss. Since the current is not sufficiently diffused in the direction parallel to the layer inside the p-type conductive layer 123 having a large sheet resistance, if the dielectric film 150 prevents the current injection from the translucent electrode 141 to the p-type conductive layer 123. In addition, current injection into the light emitting layer 122 immediately below the dielectric film 150, that is, immediately below the electrode metal film 142 is substantially prevented.

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, an n-type conductive layer 121, a light emitting layer 122, and a p-type conductive layer 123 are sequentially grown on the prepared translucent substrate 110 by an epitaxial growth method. 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 . It is formed to a thickness of 0.3-2 μm. 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, 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. In this step, the n-type conductive layer 121 is exposed flat using the etch back method described above. Specifically, first, as shown in FIG. 3A, a protective film P is formed on the entire top 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 n-side electrode formation surface 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, the etching rate of the protective film P is lower than the etching rate of the mask layer Q, and the mask layer Q and the GaN-based semiconductor (p-type conductive layer 123, light-emitting layer 122, n-type conductive layer 121) Dry etching conditions are set so that the etching rates are equal. 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. By continuing the etching, a flat n-side electrode formation surface 121A is formed over the entire area as shown in FIG. Thereafter, as shown in FIG. 4G, the protective film P is removed using an appropriate etchant.

After the formation of the n-side electrode formation surface 121A, a dielectric film 150 is partially formed on the p-type conductive layer 123. The material of the dielectric film 150 is not particularly limited, and magnesium fluoride, lithium fluoride, silicon oxide, magnesium oxide, spinel, aluminum oxide, zirconium oxide, tantalum oxide, niobium oxide, titanium oxide, silicon nitride, silicon oxynitride, etc. Various metal fluorides, oxides, nitrides, and oxynitrides can be used. Moreover, glass-type materials, such as PSG (Phospho-Silicate-Glass), BPSG (Boro-Phospho-Silicate-Glass), spin-on glass, can also be used. The planar shape and size of the dielectric film 150 can be made substantially the same as the electrode metal film 142 formed thereabove as shown in FIG. However, when the shape and the size are completely the same, the effect of the dielectric film 150 is significantly reduced only by slightly shifting the planar positions of the dielectric film 150 and the electrode metal film 142 in the manufacturing process. Therefore, as shown in FIG. 6, the area of the dielectric film 150 is slightly larger than that of the electrode metal film 142 so that the orthogonal projection of the dielectric film 150 on the upper surface of the light emitting layer includes the orthogonal projection of the electrode metal film 142. It is desirable to enlarge it. For example, the area of the dielectric film 150 is 120 to 150% of the electrode metal film 142.

When the dielectric film 150 is formed of a glass-based material, the surface flatness of the dielectric film 150 can be made better than that of the p-type conductive layer 123 by reflow. In such a case, the TCO film formed on the surface of the dielectric film 150 has a lower sheet resistance because the in-plane film thickness variation is smaller than that of the TCO film formed on the surface of the p-type conductive layer 123. It becomes. Accordingly, as shown in FIG. 5B, when an extension 150A extending from a region immediately below the electrode metal film 142 to a region not directly below is formed in the dielectric film, a sheet of the translucent electrode 141 is formed on the extension 150A. A region where the resistance is partially lowered is formed. At this time, the current diffusing in the translucent electrode 141 is easily diffused particularly along the longitudinal direction of the extension 150A. This means that the current flowing through the translucent electrode 141 can be easily diffused in a desired direction by appropriately providing the extension 150A.

After the formation of the dielectric film 150, a translucent electrode 141 made of a TCO film is formed on the p-type conductive layer 123. 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), oxidation such as FTO (fluorine doped tin oxide) Tin-based TCO can be preferably used. There is no limitation on the method for forming the translucent electrode 141, and sputtering, reactive sputtering, vacuum deposition, ion beam assisted deposition, ion plating, laser ablation, CVD, spraying, spin coating, A known method such as a dip method can be used as appropriate. The translucent electrode 141 may be patterned by either a subtractive method or an additive method (lift-off method).

Any of the n-side electrode 130 and the electrode metal film 142 may be formed first. Moreover, it can also form simultaneously. In the case of simultaneous formation, the n-side electrode 130 and the electrode metal film 142 have substantially the same thickness (in the case of a multilayer structure, the thickness of each layer).

The n-side electrode 130 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 preferred materials because of their high reflectance in the near ultraviolet to blue wavelength region. 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. This TCO film can be formed simultaneously with the translucent electrode 142 provided on the p-type conductive layer 123.

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 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.

The electrode metal film 142 may be formed of a metal having high reflectivity such as Al, Ag, or a platinum group (Pt, Pt, Pd, Rh, Ru, Ir) at a portion in contact with the translucent electrode 141. Alternatively, it may be formed of a metal that adheres strongly to TCO, such as Cr, Ni (nickel), Ti (titanium), Zr (zirconium), or W (tungsten). The surface layer portion of the electrode metal film 142 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.

As described above, the electrode metal film 142 has at least a portion that can be used as a bonding pad. When the GaN-based LED element 100 is mounted, a bonding wire or a conductive bonding material is bonded to the portion. The electrode metal film 142 must be firmly fixed to the p-type conductive layer 123 so that it can withstand the strong stress that is applied when the bonding wire is bonded by applying ultrasonic waves. Alternatively, in order for the flip-chip mounted GaN-based LED element 100 to be securely fixed to the mounting surface, the bond between the electrode metal film 142 and the p-type conductive layer 123 must be strong.

Therefore, as an example, as shown in FIG. 7, a through hole may be provided in the TCO film 141 on the dielectric film 150, and the dielectric film 150 and the electrode metal film 142 may be directly bonded through the through hole. As a result, the number of interfaces between the materials existing between the p-type conductive layer 123 and the electrode metal film 142 is reduced, so that the bonding strength between the two is improved.

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 layer 121 is formed in the GaN-based semiconductor film by etching so that each LED element has an isolated stacked portion 120. 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 groove bottom 121B is preferably rough (not flattened) so as not to reflect light incident on the groove bottom 121B from the inside of the GaN-based semiconductor film. Therefore, it is preferable that the etching process for forming the element isolation trench is a separate process from the etching process for forming the n-side electrode formation surface 121A.

In one example, in order to improve the light extraction efficiency, a hole or a groove having the exposed surface of the rough n-type layer 121 as a bottom surface can be formed in the GaN-based semiconductor film even in a region other than the peripheral portion of the element.

Before the dicing process, in order to protect the end surface of the light emitting layer 122 exposed by the formation of the n-side electrode formation surface 121A and the element isolation groove and the surface of the translucent electrode 141 made of a thin TCO film, It is preferable to form a passivation film that covers the surface of the wafer except the surface. The passivation film can be formed of silicon oxide, silicon nitride, silicon oxynitride, PSG, BPSG, 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 from 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 a member to which the LED chip is to be fixed so that the surface on which the n-side electrode 130 and the p-side electrode 140 are formed faces (flip chip mounting). In the case of flip chip mounting, after fixing the LED chip to the fixing member, the GaN-based semiconductor film and the translucent substrate 110 can be separated using a laser lift-off technique.

100 GaN-based LED element 110 Translucent substrate 120 Laminated portion 121 n-type conductive layer 121A n-side electrode formation surface 121B groove bottom 122 light-emitting layer 123 p-type conductive layer 130 n-side electrode 131 bonding portion 132 extension portion 140 p-side electrode 141 Translucent electrode 142 Electrode metal film 150 Dielectric film 150A Extension P Protective film Q Mask layer

Claims (12)

A p-type conductive layer having a roughened upper surface, a light-emitting layer disposed on the lower surface side of the p-type conductive layer, and an n-type conductive layer disposed so as to sandwich the light-emitting layer between the p-type conductive layer, A laminate including the p-type conductive layer, the light-emitting layer, and the n-type conductive layer by removing at least a part of the p-type conductive layer and the light-emitting layer from a GaN-based semiconductor film having a multilayer structure including And a flat exposed surface of the n-type conductive layer are formed adjacent to each other, an n-side electrode including a first electrode metal film is formed on the exposed surface, and the p-type conductive layer A GaN-based LED element in which a translucent electrode made of a TCO film is formed on the upper surface. The GaN-based LED element according to claim 1, wherein the p-type conductive layer has pits formed on the upper surface by low-temperature growth. The GaN-based LED element according to claim 1 or 2, wherein at least a part of the first electrode metal film is in contact with a flat exposed surface of the n-type conductive layer. 4. The GaN-based LED element according to claim 3, wherein the first electrode metal film has an Al layer in a portion in contact with a flat exposed surface of the n-type conductive layer. 3. The GaN-based LED element according to claim 1, wherein the n-side electrode has a TCO film in a portion in contact with a flat exposed surface of the n-type conductive layer, and has the first metal film on the TCO film. . The GaN-based LED element according to claim 1, wherein the first electrode metal film has a bonding pad part and an extension part extending from the bonding pad part. A second electrode metal film is formed on a part of the translucent electrode, and a dielectric film is provided immediately below the second electrode metal film to insulate the translucent electrode from the p-type conductive layer. Item 7. The GaN-based LED element according to any one of Items 1 to 6. The GaN-based LED element according to claim 7, wherein the second electrode metal film has a bonding pad portion and an extension extending from the bonding pad portion. The GaN-based LED element according to claim 7 or 8, wherein the dielectric film has better surface smoothness than the p-type conductive layer. 10. The GaN-based LED element according to claim 9, wherein the dielectric film has an extended portion extending from directly below the second electrode metal film between the p-type conductive layer and the translucent electrode. . The n-type conductive layer formed by removing at least a part of the p-type conductive layer and the light emitting layer from the GaN-based semiconductor film at a site different from the flat exposed surface of the n-type conductive layer. The GaN-based LED element according to claim 1, which has a rough exposed surface. 12. The GaN-based LED element according to claim 11, wherein when viewed in a plan view, a rough exposed surface of the n-type conductive layer has an annular shape and surrounds the laminated portion and a flat exposed surface of the n-type conductive layer.

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