JP2010225767A - Nitride semiconductor light-emitting device, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a reliable nitride semiconductor light-emitting device which reduces contact resistance between an electrode formed on the backside of a substrate and the substrate while having the high reliability. <P>SOLUTION: The nitride semiconductor light-emitting device includes: a nitride semiconductor substrate 10; a nitride semiconductor layer which is formed on a first main face of the nitride semiconductor substrate 10, and has an active layer 13 generating a light; and an electrode 20 formed on a second main face of the nitride semiconductor substrate 10. Oxygen peak density at an interface portion between the nitride semiconductor substrate 10 and the electrode 20 is ≥29 atom%, and also carbon peak density is ≤11 atom%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor light emitting device and a method for manufacturing the same, and more particularly to a nitride semiconductor light emitting device in which an n-side electrode is provided on the back surface of a nitride semiconductor substrate.

  In recent years, various semiconductor laser elements have been widely used as light sources for optical disk devices. Among them, blue-violet semiconductor laser diodes (LD) using III-V (old IUPAC notation; 13-15 in the new IUPAC notation) nitride semiconductor such as gallium nitride (GaN) are in the red region (for DVD) Compared with light in the infrared region (for CD), light is emitted in a short wavelength region (400 nm band) that makes it possible to reduce the diameter of the focused spot on the optical disk. For this reason, the blue-violet semiconductor LD is effective for improving the reproduction and recording density of the optical disc, and is spreading as a light source for the next generation high-density optical disc (Blu-Ray-Disc), and has become indispensable. Yes.

In the blue-violet semiconductor LD, in recent years, a structure using a GaN substrate having an n-side electrode formed on the back side has become mainstream. When the n-side electrode is formed on the back surface of the GaN substrate, it is necessary to remove the altered layer formed by polishing the substrate by etching with a halogen gas and to perform a heat treatment at 400 ° C. or higher. In order to remove the deteriorated layer, Patent Document 1 discloses that after polishing the substrate, dry etching is performed with a mixed gas of chlorine and oxygen, an n electrode is formed, and a heat treatment at 350 ° C. to 390 ° C. is performed. Yes. By this method, the deteriorated layer and the nitrogen atoms exposed on the back surface of the GaN substrate are removed, and the contact resistance can be reduced.
JP 2005-347534 A

  However, in the above-described prior art, the etching process is performed using a mixed gas of chlorine and oxygen, so that the upper surface electrode and the like may be corroded by the mixed gas. It is necessary to attach a support substrate to the upper surface of the physical semiconductor layer. Forming the protective film on the upper surface of the substrate after the back surface polishing increases the number of processing steps when the substrate is thin, and thus increases the occurrence rate of cracks on the substrate. On the other hand, when a support substrate is affixed to a substrate (semiconductor light emitting element under fabrication), it is necessary to apply an adhesive material used for affixing to the entire top surface of the substrate in order to reliably cover the upper surface of the substrate. Thus, the adhesive material protrudes from the support substrate. When dry etching using chlorine gas or the like is performed in this state, the adhesive material is reattached to the polished back surface, and resistance increases or electrode peeling tends to occur after electrode formation. Moreover, since the heat treatment is performed at 350 to 390 ° C., the p-side electrode may be deteriorated by the heat treatment, and the contact resistance may be increased.

  In view of the above problems, an object of the present invention is to realize a highly reliable nitride semiconductor light emitting device while reducing the contact resistance between the electrode formed on the back surface of the substrate and the substrate.

  The nitride semiconductor light emitting device of the present invention is formed on a nitride semiconductor substrate having a first main surface and a second main surface facing each other, and on the first main surface of the nitride semiconductor substrate, A nitride semiconductor layer having an active layer for generating light; and an electrode formed on the second main surface of the nitride semiconductor substrate, wherein oxygen at an interface portion between the nitride semiconductor substrate and the electrode The peak concentration is 29 atomic% or more, and the carbon peak concentration is 11 atomic% or less.

  The contact resistance between the n-side electrode and the nitride semiconductor substrate can be reduced when the oxygen peak concentration at the interface portion between the two is high, and can be reduced when the carbon peak concentration at the interface portion is low. Therefore, the contact between the n-side electrode and the nitride semiconductor substrate is achieved by setting the oxygen peak concentration at the interface portion between the nitride semiconductor substrate and the electrode to 29 atomic% or more and the carbon peak concentration to 11 atomic% or less. The resistance can be greatly reduced.

  The electrode is composed of a plurality of layers, and the layer in contact with the nitride semiconductor substrate among the electrodes is composed of at least one metal selected from Ti, Ni, Al, Ta, Zr, and Mo. It is preferable to have a layer. The “metal” referred to here may be an alloy of two or more kinds of metals. Since these metals are easily bonded to oxygen on the second main surface of the nitride semiconductor substrate, an electrode structure with better adhesion can be realized.

  The electrode may be composed of a Ti film, a Pt film, and an Au film in the order closer to the nitride semiconductor substrate. Since the Pt film is provided, the solder material is prevented from diffusing into the nitride semiconductor substrate when the nitride semiconductor substrate is mounted on the submount or the like using solder.

  The film thickness of the Ti film may be 5 nm or more and 15 nm or less, and the film thickness of the Au film may be 100 nm or more. Thereby, it is possible to obtain an electrode having low resistance and stable to heat treatment.

  Of the electrodes, at least the Ti film may be formed on the entire surface of the second main surface. As a result, the contact area between the nitride semiconductor substrate and the electrode can be increased, and a good ohmic electrode can be formed.

  The oxygen peak concentration at the interface portion between the nitride semiconductor substrate and the electrode is particularly preferably 75 atomic% or less.

  The method for manufacturing a nitride semiconductor light emitting device of the present invention includes a step (a) of forming a nitride semiconductor layer including a plurality of layers including an active layer on a first main surface of a nitride semiconductor substrate; After the step (a), the nitride semiconductor substrate is polished from the second main surface side facing the first main surface to be thinned (b), and polished in the step (b). (C) performing an oxygen plasma treatment on the second main surface, removing carbon existing on the second main surface, and adsorbing oxygen on the second main surface; After the step (c), the method includes a step (d) of forming an electrode on the second main surface that has been subjected to the oxygen plasma treatment.

  According to this method, by performing oxygen plasma treatment in the step (c), carbon is removed from the second main surface, which is the polished surface of the nitride semiconductor substrate, and oxygen is adsorbed on the second main surface. . Therefore, the contact resistance value between the nitride semiconductor substrate and the electrode can be greatly reduced as compared with the conventional case. In addition, since it is not necessary to perform etching using chlorine gas, it is possible to prevent deterioration of the electrode provided on the first main surface side of the nitride semiconductor substrate and to manufacture a highly reliable nitride semiconductor light emitting device. It becomes possible.

  In the step (d), after the formation of the electrode, the oxygen peak concentration at the interface portion between the nitride semiconductor substrate and the electrode is preferably 29 atomic% or more and the carbon peak concentration is 11 atomic% or less. .

  As described above, in the step (c), the oxygen plasma treatment may be performed without etching the polished second main surface.

  After the step (b) and before the step (c), an adhesive material is used on the surface of the nitride semiconductor layer far from the nitride semiconductor substrate, and the adhesive material is viewed in plan view. In step (e), the method may further include a step (e) of fixing the support substrate so as to be within the outer shape of the nitride semiconductor substrate.

  According to the method of the present invention, before forming the electrode on the second main surface of the nitride semiconductor substrate, the contact resistance is kept low by treating the second main surface with oxygen plasma, and nitriding is performed. Good adhesion to the semiconductor substrate, and increase in contact resistance can be suppressed even by heat treatment, so high reliability even when heat is applied to melt the solder when mounting the chip-like nitride semiconductor light emitting device Sex can be secured. In addition, since the operating voltage is reduced even in high output operation, heat generation is suppressed, and a highly efficient and highly reliable nitride semiconductor light emitting device can be obtained.

  Hereinafter, each embodiment of the present invention will be described in detail as an example in which the configuration of the present invention is applied to a semiconductor laser device. In the following description, the surface on which the nitride semiconductor layer is provided among the main surfaces of the n-type GaN substrate is referred to as a “first main surface”, and the surface facing the first main surface is provided before and after the polishing step. This is called “second main surface”.

(First embodiment)
FIG. 1 is a cross-sectional view of a laser diode element (LD element) which is a nitride semiconductor light emitting element according to the first embodiment of the present invention. This figure shows a longitudinal section perpendicular to the direction of the optical resonator of the nitride semiconductor light emitting device.

  As shown in FIG. 1, the nitride semiconductor light emitting device of this embodiment includes a nitride semiconductor layer on an upper surface (first main surface) which is a Ga surface of an n-type GaN substrate 10. The nitride semiconductor layers are an n-type cladding layer 11, an n-type light guide layer 12, a multiple quantum well active layer 13, and a p-type light guide, each of which is made of a nitride semiconductor material in order from the side closer to the first main surface. The layer 14, the p-type cladding layer 15, and the p-type contact layer 16 are laminated. The n-type cladding layer 11 is made of, for example, AlGaN, the n-type light guide layer 12 is made of, for example, GaN, the multiple quantum well active layer 13 is made of InGaN, and the p-type light guide layer 14 is made of, for example, AlGaN. The p-type cladding layer 15 is made of, for example, AlGaN, and the p-type contact layer 16 is made of, for example, GaN. The light generated in the multiple quantum well active layer 13 is emitted from the cavity end face of the nitride semiconductor layer.

  Of the nitride semiconductor layer, a part (upper part) of the p-type cladding layer 15 and the p-type contact layer 16 extend along the resonator direction (the direction connecting the front side and the back side in FIG. 1) by etching. It is processed into a ridge stripe shape. The ridge stripe width is, for example, about 1.5 μm, the resonator length is, for example, 800 μm, and the chip width is, for example, 200 μm.

  A p-side contact electrode 18 is provided on the upper surface of the ridge stripe so as to be in contact with the p-type contact layer 16. A dielectric film 17 is provided on the side surface of the ridge stripe and on the upper surface of the p-type cladding layer 15 other than the ridge stripe portion. A p-side wiring electrode 19 is provided on the p-side contact electrode 18 and the dielectric film 17. The p-side contact electrode 18 is made of, for example, Pd or Ni, and the p-side wiring electrode 19 is made of, for example, a multilayer structure in which the uppermost layer is Au.

  On the other hand, an n-side electrode (Ti film / Pt film / Au film) 20 as a metal electrode is provided on the back surface (second main surface) which is the N surface of the GaN substrate 10.

  FIG. 2 is an enlarged cross-sectional view showing the vicinity of the back surface (second main surface) of the GaN substrate 10 in the nitride semiconductor light emitting device of this embodiment shown in FIG. As shown in the figure, the n-side electrode 20 includes a Ti film 21 as the first layer, a Pt film 22 as the second layer, and a third layer as viewed from the second main surface of the GaN substrate 10. It has a three-layer structure with an Au film 23. The Ti film 21 serves to reduce contact resistance with the GaN substrate 10, the Pt film 22 serves as a barrier metal that suppresses mutual diffusion of Au and Ga, and the Au film 23 serves as an external device such as solder bonding or wire bonding. It has the role of facilitating electrical and thermal bonding with the.

  Next, the film thickness of each layer in the n-side electrode 20 will be described. First, the Ti film 21 is preferably set thin because the thermal stability of the contact resistance is impaired when the film thickness is 20 nm or more. However, in consideration of the stability of film formation, the Ti film 21 is preferably 5 nm or more. When the film thickness is reduced and the controllability is impaired, the adhesion between the n-side electrode 20 and the GaN substrate 10 is also lowered. Therefore, the film thickness of the Ti film 21 is more preferably set to 5 nm or more and 15 nm or less.

  Since the Pt film 22 plays a role of barriering the diffusion of Au and Ga at a temperature (for example, 300 ° C. or higher) when the nitride semiconductor light emitting element is mounted on a submount or the like, the film thickness of the Pt film 22 is 10 nm or more. The thickness is preferably 100 nm or less, but if the film thickness is thick, the risk of film peeling due to stress increases, and more preferably 10 nm or more and 50 nm or less. The Au film 23 is preferably 100 nm or more in consideration of solder bonding and prevention of wire peeling.

  In addition, regarding the planar area of the n-side electrode 20, the Ti film 21 that is particularly responsible for contact formation is formed on the entire second main surface of the GaN substrate 10 in the chip-like nitride semiconductor light emitting device (LD chip). This is ideal in terms of electrical characteristics. This is because the contact resistance value between the n-side electrode 20 and the GaN substrate 10 can be made smaller as the area in contact with the GaN substrate 10 is larger. However, if the planar area of the Au film 23 is set to be approximately the same as the planar area of the second main surface of the GaN substrate 10 as with the Ti film 21, the Au film 23 is applied to the cleavage region in the chip formation process and cleaved. It may be difficult to divide the chip into pieces. Therefore, at least the planar shape of the Au film 23 is a shape obtained by removing the peripheral region from the planar shape of the GaN substrate 10, and the planar area of the Au film 23 is slightly smaller than the planar area of the second main surface of the GaN substrate 10. It is preferable to do this.

  In the nitride semiconductor light emitting device according to the present embodiment, the oxygen concentration and carbon in the interface portion with the Ti film 21 of the GaN substrate 10 are pre-processed on the second main surface of the GaN substrate 10 in the manufacturing process described later. By adjusting the concentration, the n-side electrode 20 and the GaN substrate 10 can make ohmic contact with low resistance. Here, “the interface portion of the GaN substrate 10 with the Ti film 21” refers to the distance from the interface between the GaN substrate 10 and the Ti film 21 (Ga: Ti concentration ratio is 1: 1). Means a portion within 10 nm.

  In addition, the stable n-side electrode 20 can be realized without increasing the contact resistance even when heat of 300 ° C. or higher is applied. At this time, the oxygen peak concentration at the interface portion is 29 atomic% or more, and the carbon peak concentration is 11 atomic% or less.

  In the n-side electrode 20 according to the present embodiment, the Ti film 21 is used as the first layer in contact with the second main surface of the GaN substrate 10, but instead, a metal that forms an oxide may be used. Absent. Examples of the metal constituting the first layer include, for example, at least one metal of Ti, Ni, Al, Ta, Zr, and Mo (including a case of an alloy of two or more metals).

  Next, a method for manufacturing the nitride semiconductor light emitting device of this embodiment will be described. 3A to 3D and FIGS. 4A to 4C are views showing a method for manufacturing the nitride semiconductor light emitting device of this embodiment. 3 (a) to 3 (d), 4 (b), and 4 (c) are longitudinal cross-sectional views perpendicular to the optical resonator direction of the nitride semiconductor light emitting device, and FIG. 4 (a) is a perspective view. FIG.

  First, as shown in FIG. 3A, a multilayer film structure composed of a nitride semiconductor layer is grown on the first main surface (Ga surface) of the GaN substrate 10 by metal organic chemical vapor deposition (MOCVD). . Here, the multilayer structure has an n-type cladding layer 11, an n-type light guide layer 12, a multiple quantum well active layer 13, a p-type light guide layer 14, a p-type clad layer 15, A mold contact layer 16 is provided. The multilayer film structure has, for example, a general double heterostructure.

  Next, as shown in FIG. 3B, after forming a ridge-shaped stripe portion, a dielectric film 17, a p-side contact electrode 18, and a p-side wiring electrode 19 are formed.

Specifically, a dielectric film made of SiO ₂ or the like is formed on the upper surface of the multilayer film structure by a CVD (Chemical Vapor Deposition) method, and then a striped resist mask pattern is formed by a photolithography method. By removing the film with hydrofluoric acid (HF) or the like, a striped SiO ₂ film is formed. Using this SiO ₂ film as a mask, dry etching using a chlorine-based gas is performed, and etching is performed to a desired depth in the middle of the p-type cladding layer 15 to form a ridge-shaped stripe portion. Thereafter, the dielectric film used as a mask is removed, and a dielectric film made of, for example, SiO ₂ is formed on the entire upper surface of the substrate (the nitride semiconductor light emitting element being fabricated) by the CVD method. Thereafter, only the ridge stripe portion is opened by a photolithography method, and the dielectric film is selectively removed with hydrofluoric acid (HF) or the like. Thereby, the dielectric film 17 as a current blocking layer is formed. Subsequently, after the p-side contact electrode 18 is formed by an electron beam (EB) vapor deposition method, the p-side contact electrode 18 is removed leaving a portion provided on the ridge stripe portion, whereby the p-side contact electrode 18 is formed on the ridge stripe portion. The side contact electrode 18 is formed. Subsequently, the p-side wiring electrode 19 is formed on the p-side contact electrode 18 and the dielectric film 17 by an electron beam (EB) vapor deposition method, and the configuration above the first main surface is formed. As a material of the p-side contact electrode 18, it is preferable to use Pd or Ni. The p-side wiring electrode 19 has a three-layer structure including, for example, a Ti film, a Pt film, and an Au film.

  Next, as shown in FIG. 3C, the GaN substrate 10 is polished from the back surface (second main surface) side by using a grinding machine or the like, and the GaN substrate 10 is thinned. The thickness after grinding is, for example, 80 μm. Examples of the polishing treatment method include a method of polishing a ground surface using diamond slurry.

  The purpose of thinning by polishing is to form a pair of optical resonator end faces during chip formation, and to form the optical resonator end faces by cleavage. That is, if the substrate is thick, it cannot be cleaved stably.

  Next, as shown in FIG. 3D, surface treatment is performed as preparation for forming the n-side electrode 20 on the polished surface (back surface; second main surface) of the GaN substrate 10. Specifically, oxygen plasma treatment is performed on the second main surface of the GaN substrate. By the oxygen plasma treatment, it is possible to remove carbon that is a contamination source on the back surface of the GaN substrate 10. Simultaneously with the removal of carbon, oxygen is adsorbed on the back surface (second main surface) of the GaN substrate 10 to form a bond between Ga and oxygen. The region where Ga and oxygen are bonded is considered to be within a depth range of about one to two crystal lattices from the back surface of the GaN substrate 10, but it can be further deepened by adjusting the conditions. It can also be formed.

  By combining Ga and oxygen, the barrier height at the interface between the GaN substrate 10 and the n-side electrode 20 is decreased, carrier tunneling is increased accordingly, and defects are introduced into the crystal structure. In addition, an effect of increasing the carrier concentration can be obtained. The conditions for the oxygen plasma treatment are, for example, a degree of vacuum (chamber pressure) of 20 Pa, a gas flow rate of 400 mL / min (sccm), and a plasma power of about 300 W. By the oxygen plasma treatment described above, the oxygen atom peak concentration in the back surface portion of the GaN substrate 10 (for example, the portion in the depth range of about 1 to 2 crystal lattices from the back surface) is 29 atomic% or more and carbon atoms The peak concentration is about 11 atomic% or less. The atomic concentrations of carbon and oxygen in the back surface portion of the GaN substrate 10 can be adjusted by changing the gas flow rate, plasma power, processing time, and the like.

  Next, as shown in FIG. 4A, the GaN substrate 10 is attached to the support substrate 24. Examples of the support substrate 24 include a silicon substrate and a quartz substrate, and examples of the adhesive material 25 for bonding the GaN substrate 10 and the support substrate 24 include organic wax and double-sided seal type tape. It is done. As a procedure for attaching to the support substrate 24, first, an adhesive material 25 is attached to the upper surface of the support substrate 24, the GaN substrate 10 (p-side wiring electrode 19) is brought into contact with the upper surface of the support substrate 24, and the GaN substrate 10 is attached. Fix it. At this time, the first main surface of the GaN substrate 10 is bonded to the support substrate 24 with the bonding surface facing.

  In this step, the GaN substrate 10 thinned by polishing is very easily broken, and it is difficult to withstand the photolithography process and the etching process necessary for forming the pattern of the support substrate 24. For this reason, adhesion to the support substrate 24 prevents frequent wafer cracks. Further, when the back surface of the GaN substrate 10 is contaminated with organic substances generated from the adhesive during the oxygen plasma treatment before the n-side electrode 20 is attached, the contact resistance increases. Therefore, this step is preferably performed immediately before the n-side electrode 20 is formed.

  Next, as shown in FIG. 4B, with the GaN substrate 10 attached to the support substrate 24, a Ti film 21, a Pt film 22, An Au film 23 is sequentially deposited. Thereby, the n-side electrode 20 having a three-layer structure of Ti film / Pt film / Au film can be formed on the back surface of the GaN substrate 10. The film thickness of the Ti film 21 is preferably about 5 nm or more and 15 nm or less, and is set to, for example, 10 nm in this embodiment. The thickness of the Ti film 21 will be described later using data.

  The Pt film 22 is provided to prevent the Ti film 21 and the Au film 23 from reacting during subsequent heat treatment and to prevent Ga diffusion from the GaN substrate 10. In order to obtain this effect, the thickness of the Pt film 22 is preferably about 10 nm to 50 nm. In the present embodiment, the thickness of the Pt film 22 is 35 nm.

  In addition, the Au film 23 is formed by joining a nitride semiconductor light emitting device (LD chip) divided into chips on the submount (the submount comes on the same side as the GaN substrate 10 when viewed from the multiple quantum well active layer 13). In the case of mounting in such a manner, the layer reacts with solder such as AuSn. The Au film 23 is wire-bonded when the LD chip is mounted on the submount by junction down (a method in which the submount comes to the opposite side of the GaN substrate 10 when viewed from the multiple quantum well active layer 13). It becomes the pad electrode for. In the former case, it is required to obtain good bonding without greatly changing the composition of solder (for example, AuSn). In the latter case, it is required to obtain a good bond with a wire (generally a gold wire). In the case of junction up, it is preferable that the film thickness of the Au film 23 is thin, so that the upper limit of the film thickness can be set. On the other hand, in the case of junction down, it is preferable that the film thickness of the Au film 23 is thick, so that the lower limit of the film thickness can be set. Therefore, it is preferable that the Au film 23 has a thickness of about 100 nm to 500 nm because both mounting methods can be supported. In this embodiment, the film thickness of the Au film 23 is 300 nm.

  Next, as shown in FIG. 4C, a resist 26 having a mask pattern formed on the n-side electrode 20 by photolithography is provided, and the n-side electrode 20 is etched using the resist 26 as a mask. 20 patterns are formed. Although FIG. 4C shows an example in which the Pt film 22 and the Ti film 21 are etched together with the Au film 23, only the uppermost Au film 23 may be etched. For the etching of the Au film 23, wet etching such as iodine solution or aqua regia or dry etching such as ion milling is used. Thereafter, the resist 26 is removed, and the pattern formation of the n-side electrode 20 is completed.

  In place of the above-described etching method, a resist having a predetermined pattern may be formed in advance before vapor deposition of the constituent material of the n-side electrode 20, and a method of peeling off after vapor deposition (lift-off method) may be performed. However, in the lift-off method, an organic component contained in the resist may adhere to the second main surface side, the carbon atom concentration at the interface portion between the n-side electrode 20 and the GaN substrate 10 increases, and the contact resistance is reduced. Since it may increase, it is more preferable to process by wet etching or ion milling than lift-off. Thereafter, although not shown, the wafer-like GaN substrate 10 is cleaved, the nitride semiconductor light emitting element is separated into LD chips, and the LD chip is mounted on the submount. When the LD chip is mounted on the submount, it is heated to a temperature necessary for melting the solder.

  Through the above steps, a predetermined n-side electrode structure is formed on the back surface of the GaN substrate 10, and a nitride semiconductor layer is formed on the upper surface (first main surface) of the GaN substrate 10, as shown in FIG. The nitride semiconductor light emitting device of the embodiment can be manufactured.

  FIG. 5 is a diagram showing a result of analyzing the interface portion (interface region portion) between the n-side electrode and the GaN substrate by Auger electron spectroscopy (AES) in the nitride semiconductor light emitting device according to this embodiment. FIG. 6 is a diagram illustrating a result of analyzing an interface portion (interface region portion) between an n-side electrode and a GaN substrate by an AES method in the nitride semiconductor light emitting device according to the comparative example. The nitride semiconductor light emitting device analyzed in FIG. 6 is manufactured by the same method as the nitride semiconductor light emitting device analyzed in FIG. 5 except that the oxygen plasma treatment is not performed before forming the n-side electrode. It is a semiconductor light emitting device. 5 and 6, the horizontal axis represents the depth, and the vertical axis represents the differential magnitude of the Auger electron count.

  From the comparison between FIG. 5 and FIG. 6, the oxygen and carbon peak intensities clearly change at the interface portion between the n-side electrode 20 and the second main surface of the GaN substrate 10 with and without oxygen plasma treatment. It can be confirmed. That is, it can be seen that the oxygen plasma treatment reduces the carbon concentration at the interface and increases the oxygen concentration.

  FIG. 7 is a diagram for explaining a method of calculating atomic concentrations of O (oxygen) and C (carbon) using the electron differential spectrum shown in FIG. The atomic concentrations of oxygen and carbon described in this specification are all calculated by the following method.

  First, a reference element concentration% is determined. In the electron differential spectrum, a value obtained by multiplying “Ga differential peak intensity” (i) in the GaN substrate by a sensitivity coefficient of Ga is “Ga atom concentration” (ii). The Ga atom concentration% in the GaN substrate is known and is 50 element%, and in this calculation method, the C and O atom concentrations are relatively represented on the basis of (ii).

  Next, the definition of O atom concentration% will be described. A value obtained by multiplying the maximum “O differential peak intensity” (iii) at the interface portion between the GaN substrate and the n-side electrode by the sensitivity coefficient of O is “O atom concentration” (iv). The O atom concentration% at the interface portion between the GaN substrate and the n-side electrode is expressed as O atom concentration% when (ii) is set (corrected) to 50 atom concentration, and this concentration is (50 / (ii) ) * (Iv).

  The same applies to C. “C differential peak intensity” that is maximum at the interface portion between the GaN substrate and the n-side electrode (v) multiplied by the sensitivity coefficient of C is “C atom concentration”. (Vi). The C atom concentration% at the interface portion between the GaN substrate and the n-side electrode is indicated by the C atom concentration when (ii) is set to 50 atom concentration%, and this concentration is (50 / (ii)) * (vi ).

  The C atom concentration% and the O atom concentration% in the nitride semiconductor light emitting device of this embodiment were determined using FIG. 5 and the atomic concentration determination method. The O atom concentration% was 29%, and the C atom concentration% was 11%.

  Next, the result of examining the relationship between the contact resistance between the n-side electrode 20 and the GaN substrate 10 and the atomic concentrations of C and O at the interface will be described.

  FIGS. 8A and 8B are diagrams illustrating a method for measuring contact resistance between the n-side electrode 20 and the GaN substrate 10. FIG. 8A schematically shows a planar shape of the n-side electrode 20, and FIG. 8B shows a cross section when the measuring element is cut in the vertical direction. Here, a pair of n-side electrodes 20 are formed on the back surface of the GaN substrate 10 so that the electrode spacing is 500 μm, and a voltage value when a current of 10 mA is passed between the n-side electrodes 20 is measured. Resistance was calculated. The planar shape of the n-side electrode 20 was a rectangular shape of 100 μm × 500 μm. All the contact resistance measurement data described later are obtained by this method.

FIG. 9 is a diagram showing the relationship between the contact resistance between the n-side electrode 20 and the GaN substrate 10 and the C atom concentration and O atom concentration at the interface portion. Here, the contact resistance is calculated using the measurement elements shown in FIGS. 8A and 8B, and the C atom concentration and the O atom concentration are calculated by the above-described method. The contact resistance value (Ω · cm ² ) shown on the vertical axis is an initial contact resistance value when the measurement element is not subjected to heat treatment.

  In the actual manufacturing process, a heat treatment for melting the solder is performed when the LD chip is mounted on the submount, but this level of heating hardly affects the state of atomic diffusion near the interface. Therefore, it is considered that the C atom concentration and the O atom concentration after heating are hardly changed from those before heating.

From FIG. 9, when the C atom concentration at the interface portion is 11% (in the figure: solid line), the contact resistance value is favorable at about 1 × 10 ⁻⁴ Ω · cm ² when the O atom concentration is 29% or more. It was found that the contact resistance value tends to increase rapidly when the O atom concentration is lower than 29%. Further, as the C atom concentration increases, there is a tendency that the contact resistance does not sufficiently decrease even if the O atom concentration is increased. When the C atom concentration is 31% (in the figure: dotted line), regardless of the O atom concentration. The contact resistance value was as high as about 1 × 10 ⁻² Ω · cm ² .

  In practice, the voltage value of the LD element needs to be about 4 to 5 V. In the nitride semiconductor light emitting device of this embodiment, the C atom concentration is 11% or less and the O atom concentration is 29% or more. Realization is possible with the obtained contact resistance. As described above, by using oxygen plasma treatment, carbon is removed at the interface between the n-side electrode 20 and the GaN substrate 10 and oxygen is adsorbed, so that the O atom concentration is specifically set to 29% or more and C atoms By setting the concentration to 11% or less, a low-resistance n-side electrode can be provided.

  FIG. 10 is a diagram showing the results of evaluating the thermal stability of the contact resistance between the n-side electrode and the GaN substrate in the nitride semiconductor light emitting device according to this embodiment. The horizontal axis represents the heat treatment temperature, and the vertical axis represents the contact resistance value. The conditions for the heat treatment were to hold the device at a set temperature for 30 seconds in a nitrogen atmosphere, and the temperature of the heat treatment was in the range of 25 ° C to 500 ° C. Since an actual LD chip is bonded to a heat sink material such as a submount via solder, the heat treatment temperature range was set assuming the solder melting temperature at that time.

  From FIG. 10, it can be confirmed that the contact resistance is maintained at a low value between the heat treatment temperatures of 25 ° C. and 500 ° C. From this result, in the nitride semiconductor light emitting device of the present embodiment, the contact resistance is lowered without heat treatment by optimizing the amounts of carbon and oxygen atoms at the interface between the GaN substrate and the n-side electrode. It can also be seen that the contact resistance can be maintained at a low value even when heat treatment is performed during mounting on a submount or the like.

  Next, the relationship between the carbon and oxygen atom concentration and the contact resistance, which the present inventors have found for the first time, will be discussed below.

  By reducing the carbon concentration at the interface between the back surface of the GaN substrate 10 and the n-side electrode 20, when the n-side electrode 20 is formed by vapor deposition or the like, the formation of carbide (carbide) of the electrode material at the interface is suppressed. Is done. As a result, an increase in barrier height between the GaN substrate 10 and the n-side electrode 20 due to the formation of carbide is suppressed, and as a result, a decrease in tunneling carriers due to the tunnel effect is suppressed. As a result, it is considered that the decrease in carriers on the second main surface of the GaN substrate 10 can be suppressed.

  On the other hand, since the carbide layer of the electrode has low adhesion to the GaN substrate 10, the effect of improving the adhesion between the GaN substrate 10 and the n-side electrode 20 can be expected by suppressing the formation thereof. Furthermore, by intentionally increasing the oxygen concentration at the interface between the back surface of the GaN substrate 10 and the n-side electrode 20, in the portion of the GaN substrate 10 near the interface with the n-side electrode 20, in addition to the combination of Ga and nitrogen, Ga And oxygen bond. Therefore, a stable metal oxide is formed between oxygen adsorbed on the second main surface of the GaN substrate 10 and the first layer (Ti film 21) of the n-side electrode 20, thereby improving adhesion. It is thought that you can.

In the present embodiment, an example in which the O atom concentration is 29% in the nitride semiconductor light emitting device has been shown. It has been confirmed that a good contact resistance value can be obtained in the temperature range of 500 ° C. or lower. The upper limit value of the O atom concentration is when oxygen is excessively introduced at the interface portion between the GaN substrate 10 and the n-side electrode 20 and a Ga ₂ O ₃ film is formed. Using the value of the calculation method, it is 75%. Accordingly, the O atom concentration is particularly preferably 29% or more and 75% or less.

  FIG. 11 is a diagram showing the results of evaluating the dependency of the contact resistance value on the heat treatment temperature in the nitride semiconductor light emitting device of this embodiment. In the figure, the horizontal axis represents the heat treatment temperature, and the vertical axis represents the contact resistance value between the GaN substrate and the n-side electrode. The heat treatment temperature was changed in the range of 25 ° C. to 400 ° C., and the thickness of the Ti film 21 in the n-side electrode was changed stepwise in the range of 5 to 100 nm.

From FIG. 11, when the Ti film thickness is 5 nm to 15 nm, the contact resistance value at 25 ° C. shows a good value of about 1 × 10 ⁻⁴ Ω · cm ² , and heat treatment is performed at a temperature up to 400 ° C. It was found that the contact resistance value can be kept low. On the other hand, when the Ti film thickness is 50 nm to 100 nm, the contact resistance value at 25 ° C. is remarkably increased as compared with the Ti film thickness being 5 to 15 nm. This is considered to be because when the Ti film is thick, the Ti oxide film is formed thick and this acts as a resistance layer. Furthermore, under the condition where the Ti film thickness is 50 nm to 100 nm, it has been confirmed that the contact resistance value rapidly increases as the heat treatment temperature is increased. From the above results, it can be seen that in the present embodiment, the thickness of the Ti film 21 is particularly preferably 5 nm or more and 10 nm or less.

  Therefore, according to the manufacturing method according to the present embodiment, after the GaN substrate is polished, an oxygen plasma treatment is performed on the polished surface of the GaN substrate, and then a Ti film, a Pt film, and an Au film are sequentially formed. Even if heat treatment is not performed, an n-side electrode structure with good adhesion and low resistance can be realized. Even if heat treatment is applied, the contact resistance between the GaN substrate and the n-side electrode can be kept low. For this reason, in the nitride semiconductor light emitting device of this embodiment, even if heat application accompanying solder melting is performed, the contact resistance does not increase and the operating voltage can be kept low, thereby realizing high output of laser light. Is possible.

  Further, according to the manufacturing method of the present embodiment, carbon generated on the back surface of the GaN substrate along with the polishing of the GaN substrate is removed by oxygen plasma treatment without using chlorine gas. Corrosion of the electrode 19 and the p-side contact electrode 18 does not occur.

  Moreover, in the n-side electrode of the nitride semiconductor light emitting device of the present embodiment, the example in which the Ti film is used as the first layer has been described, but a metal constituting the oxide may be used instead of the Ti film. Absent. Examples of the metal constituting the first layer of the n-side electrode include a layer formed of at least one metal or alloy of Ti, Ni, Al, Ta, Zr, and Mo. Since these metals are easily bonded to oxygen on the second main surface of the GaN substrate 10, an electrode structure with better adhesion can be realized.

  Although a laser device including a p-side wiring electrode and an n-side electrode has been described as an example of the nitride semiconductor light emitting device, the nitride semiconductor device is an LED (Light Emitting) including an n-side electrode on the back surface of a semiconductor substrate. Device).

(Second Embodiment)
In the method according to the first embodiment described above, after the GaN substrate is polished, the oxygen plasma treatment is performed only in the state of the GaN substrate, and then the step of attaching the GaN substrate to the support substrate is performed. It is not limited to such a case. As a second embodiment of the present invention, in a state where the GaN substrate is attached to the support substrate, oxygen plasma treatment, formation by deposition of the n-side electrode, and pattern formation for the n-side electrode are sequentially performed. A method for forming an n-side electrode with a low contact resistance will be described.

  The configuration of the nitride semiconductor light emitting device according to the second embodiment of the present invention is the same as that of the nitride semiconductor light emitting device according to the first embodiment shown in FIGS. Of the method for manufacturing a nitride semiconductor light emitting device according to this embodiment, processes different from those of the first embodiment will be described below.

  12A is a plan view schematically showing the arrangement of the support substrate 24, the adhesive material 25, and the GaN substrate 10, and FIG. 12B is a cross-sectional view of the nitride semiconductor light emitting device.

  First, an n-type GaN substrate 10 is prepared, a nitride semiconductor layer having a predetermined shape is formed on the upper surface (first main surface) of the GaN substrate 10, and then the GaN substrate 10 is ground and polished. The steps so far are the same manufacturing method as the method according to the first embodiment (see FIGS. 3A to 3C).

  Next, as shown in FIGS. 12A and 12B, after the grinding / polishing process, a step of attaching the GaN substrate 10 to the support substrate 24 is performed. For example, a silicon substrate, a quartz substrate, or the like is used as the support substrate 24, and examples of the adhesive material 25 for attaching the GaN substrate 10 and the support substrate 24 include organic wax and double-sided seal type tape. As an attaching procedure, first, an adhesive material is attached to the support substrate 24, and the support substrate 24 and the GaN substrate 10 are brought into contact with each other so that the first main surface of the GaN substrate 10 faces the support substrate 24. 10 is fixed on the support substrate 24.

  Here, after attaching the GaN substrate 10 to the support substrate 24, the adhesion area of the organic wax that is an adhesive material is smaller than the area of the GaN substrate, and the adhesive material does not protrude from the outer peripheral portion of the GaN substrate, It is preferable to be within the outer shape of the GaN substrate 10 in plan view. The shape of the adhesive material is preferably a circle similar to the shape of the general GaN substrate 10 and is preferably bonded and pasted so that the centers of the circular adhesive material and the GaN substrate are aligned. This is to prevent the back surface of the GaN substrate 10 from being contaminated by the organic matter generated from the adhesive material 25 during the pretreatment for forming the n-side electrode 20 in the next step. Therefore, the contact resistance between the GaN substrate 10 and the n-side electrode 20 can be kept low even if a pretreatment for forming the n-side electrode 20 with the GaN substrate 10 attached to the support substrate 24 is performed. Is possible. Further, by attaching the GaN substrate 10 before the pretreatment for forming the n-side electrode 20, it is possible to reduce cracking of the thinned wafer during the pretreatment for forming the n-side electrode 20 in the next step. An additional effect is also obtained. In the above description, the organic wax is used as an example of the adhesive material, but it may be in the form of a sheet.

  Subsequently, oxygen plasma treatment is performed as a pretreatment for forming the n-side electrode 20. Since this step is a manufacturing method similar to that of the first embodiment, description thereof is omitted.

FIG. 13 is a diagram showing the relationship between the contact resistance value and the ratio of the adhesive material area to the GaN substrate area (adhesive material area S _ad / GaN substrate area S _sub ) after the oxygen plasma treatment. In the figure, the horizontal axis represents the adhesive material area ratio, and the vertical axis represents the contact resistance value. The measurement was performed when the heat treatment temperature was 25 ° C. and when it was 300 ° C. The area of the adhesive material and the GaN substrate here means a planar area (see FIG. 12A).

As can be seen from FIG. 13, when the area ratio of the adhesive material area to the GaN substrate area (S _ad / S _sub ) is 100% or less, that is, the heat treatment temperature is 25 ° C. In this case, the contact resistance value was sufficiently low, and the contact resistance value was kept low even when the heat treatment temperature was 300 ° C. From this result, it can be said that even if organic matter is generated from the adhesive material 25, the back surface of the GaN substrate 10 does not travel and the back surface is not contaminated.

  On the other hand, when the area ratio of the adhesive material area to the GaN substrate area is larger than 100%, the contact resistance tends to increase at 25 ° C. due to contamination of the back surface of the GaN substrate 10 by the organic material of the adhesive material.

  From the above, in the method of the present embodiment, in order to prevent an increase in contact resistance and maintain a low contact resistance value by heat treatment, the area of the adhesive material is equal to or less than the area of the GaN substrate 10, and at the time of oxygen plasma treatment The adhesive material is preferably contained within the outer shape of the GaN substrate 10 in plan view.

  Next, an n-side electrode 20 composed of, for example, a Ti film 21, a Pt film 22, and an Au film 23 is formed on the back surface of the GaN substrate 10 by vapor deposition, and then the n-side electrode 20 is patterned. Since this is the same method as in the first embodiment, a description thereof will be omitted.

  By the manufacturing method described above, the n-side electrode structure of the present embodiment is formed on the back surface of the GaN substrate 10, and a nitride semiconductor light emitting device having the structure shown in FIG. 1 can be manufactured.

  As described above, according to the nitride semiconductor light emitting device and the method for manufacturing the same of the present embodiment, as in the first embodiment, the adhesion is good without performing the heat treatment, and the contact resistance with the GaN substrate 10 is improved. A low n-side electrode structure can be realized. Further, even if heat treatment is applied after the GaN substrate 10 is bonded to the support substrate 24, the contact resistance can be kept low. Further, since the handling of the GaN substrate 10 in a thin state can be avoided, the GaN substrate 10 can be prevented from being cracked or chipped.

  The present invention is useful, for example, as a short wavelength light source for electronic equipment.

1 is a cross-sectional view of a laser diode element (LD element) that is a nitride semiconductor light emitting element according to a first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing the vicinity of a back surface (second main surface) of a GaN substrate in the nitride semiconductor light emitting device according to the first embodiment shown in FIG. 1. (A)-(d) is a figure which shows the manufacturing method of the nitride semiconductor light-emitting device based on 1st Embodiment. (A)-(c) is a figure which shows the manufacturing method of the nitride semiconductor light-emitting device based on 1st Embodiment. In the nitride semiconductor light emitting element concerning a 1st embodiment, it is a figure showing the result of having analyzed the interface part of an n side electrode and a GaN substrate by Auger electron spectroscopy (AES) method. It is a figure which shows the result of having analyzed the interface part (interface area | region part) of an n side electrode and a GaN substrate by the AES method in the nitride semiconductor light-emitting device which concerns on a comparative example. It is a figure for demonstrating the calculation method of the atomic concentration of O (oxygen) and C (carbon) using the electron differential spectrum shown in FIG. (A), (b) is a figure which shows the measuring method of the contact resistance between an n side electrode and a GaN substrate. It is a figure which shows the relationship between the contact resistance between an n side electrode and a GaN substrate, and C atom concentration and O atom concentration in an interface part. In the nitride semiconductor light emitting element concerning a 1st embodiment, it is a figure showing the result of having evaluated the thermal stability of contact resistance between an n side electrode and a GaN substrate. In the nitride semiconductor light emitting element concerning a 1st embodiment, it is a figure showing the result of having evaluated the heat treatment temperature dependence of the contact resistance value. (A) is a top view which shows typically arrangement | positioning of a support substrate, an adhesive material, and a GaN board | substrate in the nitride semiconductor light-emitting device concerning 2nd Embodiment, (b) is a nitride semiconductor light-emitting device. It is sectional drawing. It is a figure which shows the relationship between the ratio (adhesive material area _Sad / GaN substrate area _Ssub ) with respect to the GaN substrate area of an adhesive material area, and contact resistance value after an oxygen plasma process.

10 GaN substrate 11 n-type cladding layer 12 n-type light guide layer 13 multiple quantum well active layer 14 p-type light guide layer 15 p-type cladding layer 16 p-type contact layer 17 dielectric film 18 p-side contact electrode 19 p-side wiring electrode 19 Wiring electrode 20 n side metal
21 Ti film 22 Pt film
23 Au film
24 Support substrate 25 Adhesive material
26 resist

Claims (10)

A nitride semiconductor substrate having a first main surface and a second main surface facing each other;
A nitride semiconductor layer formed on the first main surface of the nitride semiconductor substrate and having an active layer for generating light;
An electrode formed on the second main surface of the nitride semiconductor substrate,
A nitride semiconductor light emitting device having an oxygen peak concentration of 29 atomic% or more and a carbon peak concentration of 11 atomic% or less at an interface portion between the nitride semiconductor substrate and the electrode. The nitride semiconductor light emitting device according to claim 1,
The electrode is composed of a plurality of layers,
The nitride semiconductor light emitting element in which the layer in contact with the nitride semiconductor substrate among the electrodes has a layer composed of at least one kind of metal selected from Ti, Ni, Al, Ta, Zr, and Mo. The nitride semiconductor light emitting device according to claim 1,
The nitride semiconductor light emitting device, wherein the electrode is composed of a Ti film, a Pt film, and an Au film in order from the nitride semiconductor substrate. The nitride semiconductor light emitting device according to claim 3,
The nitride semiconductor light emitting device, wherein the Ti film has a thickness of 5 nm to 15 nm, and the Au film has a thickness of 100 nm or more. The nitride semiconductor light emitting device according to claim 4,
Of the electrodes, at least the Ti film is a nitride semiconductor light emitting element formed on the entire surface of the second main surface. In the nitride semiconductor light emitting device according to any one of claims 1 to 5,
The nitride semiconductor light emitting device, wherein an oxygen peak concentration at an interface portion between the nitride semiconductor substrate and the electrode is 75 atomic% or less. Forming a nitride semiconductor layer composed of a plurality of layers including an active layer on the first main surface of the nitride semiconductor substrate;
After the step (a), the nitride semiconductor substrate is thinned by polishing from the second main surface side facing the first main surface;
The second main surface polished in the step (b) is subjected to oxygen plasma treatment to remove carbon existing on the second main surface, and oxygen is adsorbed to the second main surface. Step (c);
A method for manufacturing a nitride semiconductor light emitting device, comprising the step (d) of forming an electrode on the second main surface that has been subjected to oxygen plasma treatment after the step (c). In the manufacturing method of the nitride semiconductor light emitting element according to claim 7,
In the step (d), after forming the electrode, a nitride semiconductor having an oxygen peak concentration of 29 atomic% or more and a carbon peak concentration of 11 atomic% or less at the interface portion between the nitride semiconductor substrate and the electrode Manufacturing method of light emitting element. In the manufacturing method of the nitride semiconductor light emitting element according to claim 7 or 8,
In the step (c), a method for manufacturing a nitride semiconductor light emitting element, wherein oxygen plasma treatment is performed without etching the polished second main surface. In the manufacturing method of the nitride semiconductor light emitting element according to any one of claims 7 to 9,
After the step (b) and before the step (c), an adhesive material is used on the surface of the nitride semiconductor layer far from the nitride semiconductor substrate, and the adhesive material is viewed in plan view. The method of manufacturing a nitride semiconductor light emitting device, further comprising a step (e) of fixing a support substrate so as to be within an outer shape of the nitride semiconductor substrate.

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