JP2010135743A - GaN-BASED LED DEVICE AND MANUFACTURING METHOD THEREFOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN-based LED device employing a TCO film for a p-type electrode that achieves at least one of higher power and improved reliability. <P>SOLUTION: The GaN-based LED device includes: an active layer comprised of a GaN-based semiconductor and a p-type GaN-based semiconductor layer which are sequentially laminated on an n-type GaN-based semiconductor layer; a p-type electrode including the TCO film formed on the main surface opposite to the active layer side main surface of the p-type GaN-base semiconductor layer and a p-side bonding pad connected to the TCO film; a resistance control film that is formed on part of the main surface opposite to the p-type GaN-based semiconductor layer side of the TCO film; an resistance increase region which is formed on an interface between the p-type GaN-based semiconductor layer and the TCO film and reduces a current flowing in the active layer in a lower region of the resistance control film; and an n-side bonding pad connected to the n-type layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pn-junction type GaN-based LED element having a light-emitting element structure composed of p-type and n-type GaN-based semiconductors and a method for manufacturing the same, and more particularly to a TCO (Transparent Conductive Oxide) as a p-electrode. The present invention relates to a GaN-based LED element using a film and a manufacturing method thereof.

A GaN-based semiconductor is a compound semiconductor represented by the chemical formula Al _a In _b Ga _1-a-b N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), a group 3 nitride semiconductor, Also called a nitride-based semiconductor.
A GaN-based LED element that is currently popular has a double hetero pn junction type light-emitting element structure including an active layer having a quantum well structure as a basic structure. Typically, a GaN-based semiconductor is formed on a sapphire substrate. A structure in which an n-type layer, an active layer, and a p-type layer are sequentially formed and stacked, and a p-electrode and an n-electrode are formed on the surface of the p-type layer and the surface of the partially exposed n-type layer, respectively. have. The structure of this typical GaN-based LED element is called a horizontal electrode structure because current flows in the horizontal direction between two electrodes provided on the same surface of the element when the substrate plane is regarded as a horizontal plane. Sometimes.
A GaN-based LED element using InGaN as the material of the active layer can generate green to near-ultraviolet light and has high luminance, and thus has been put to practical use in applications such as traffic lights and display devices. However, it is said that further higher output is required for use in indoor and outdoor lighting and automobile headlamps.

  It is known that it is effective to form a p-electrode with a TCO film as a means for increasing the output of a GaN-based LED element (Patent Document 1).

JP 2001-210867 A JP 9-129922 A International Publication No. 98/4420 Pamphlet JP 2000-164928 A Japanese Patent Laid-Open No. 10-341038

  The GaN-based LED element disclosed in Patent Document 1 has a p-electrode structure in which a transparent electrode (ohmic electrode) made of a TCO film is provided so as to cover the p-type layer, and a metal wire is connected to a part of the transparent electrode. A p-side bonding pad is provided. In such a GaN-based LED element having a p-electrode structure, it has hitherto been regarded as a problem that the bonding pad shields light generated in the active layer. In order to solve this problem, it is only necessary to reduce the current flowing in the active layer in the region immediately below the bonding pad to suppress the light emission in the region. Therefore, as a means for this, contact between the p-type layer and the TCO film is performed. A configuration has been devised in which an insulating film for prevention is provided immediately below the bonding pad (for example, Patent Documents 2, 3, and 4).

  On the other hand, the present inventors have found that in a GaN-based LED element using a TCO film as a p-electrode, the current flowing in the active layer can be reduced in a specific region by means completely different from the prior art, It came to make this invention.

  A specific object of the present invention is to realize at least one of higher output and improved reliability of a GaN-based LED element using a TCO film as a p-electrode.

As embodiments of the present invention, the following GaN-based LED elements and methods for producing the same are provided.
(1) An active layer made of a GaN-based semiconductor and a p-type GaN-based semiconductor layer are sequentially stacked on the n-type GaN-based semiconductor layer,
A p-electrode including a TCO film formed on a main surface opposite to the main surface on the active layer side of the p-type GaN-based semiconductor layer, and a p-side bonding pad connected to the TCO film;
A resistance control film formed on a part of the main surface of the TCO film opposite to the p-type GaN-based semiconductor layer side;
A resistance increasing region formed at an interface between the p-type GaN-based semiconductor layer and the TCO film and reducing a current flowing through the active layer in a region below the resistance control film;
An n-side bonding pad connected to the n-type layer;
A GaN-based LED element having:
(2) The p-side bonding pad is formed on the TCO film, and at least a part of the resistance control film is inserted into a part between the p-side bonding pad and the TCO film. GaN-based LED element as described in 1).
(3) The n-side bonding pad is provided on a partly exposed surface of the n-type GaN-based semiconductor layer so that a horizontal electrode type element structure is formed, and the TCO film is formed on the p-side bonding pad and the n-type. (1) or (2), wherein an inter-pad region sandwiched between the side bonding pads is provided, and at least a part of the resistance control film is formed on the inter-pad region. GaN-based LED element.
(4) The GaN-based LED element according to (3), wherein the resistance control film is formed only inside the inter-pad region on the TCO film excluding the region covered with the p-side bonding pad. .
(5) The GaN-based LED element according to any one of (1) to (4), wherein the resistance control film is made of an insulating inorganic material.
(6) A stacked body in which an n-type GaN-based semiconductor layer, an active layer made of a GaN-based semiconductor, and a p-type GaN-based semiconductor layer are sequentially stacked on the substrate, and the active layer side of the p-type GaN-based semiconductor layer Preparing a semiconductor wafer having a TCO film formed on a main surface opposite to the main surface of
Forming a resistance control film on a part of the main surface of the TCO film opposite to the p-type GaN-based semiconductor layer side;
Forming a p-side bonding pad on the TCO film,
In the step of forming the resistance control film, the resistance control film is formed so that the resistance at the interface between the p-type GaN-based semiconductor layer and the TCO film is increased in a region corresponding to a portion where the resistance control film is formed. Forming the resistance control film by a sputtering method with the exposed surface of the TCO film excluding the region to be formed covered with a protective film;
A method for manufacturing a GaN-based LED element.
(7) A GaN-based LED element formed using the manufacturing method according to (6).

  According to the present invention, at least one of higher output and improved reliability is realized for a GaN-based LED element using a TCO film as a p-electrode.

It is sectional drawing which shows the structure of the GaN-type LED element which concerns on one Embodiment of this invention. It is a figure which shows the structure of the GaN-type LED element which concerns on one Embodiment of this invention, FIG.2 (a) is the top view which looked at the element from the electrode arrangement | positioning surface side, FIG.2 (b) is FIG.2 (a). It is sectional drawing in the position of XX. It is a figure for demonstrating the definition of "the area | region between pads." It is a figure which shows the structure of the GaN-type LED element which concerns on one Embodiment of this invention, Fig.4 (a) is the top view which looked at the element from the electrode arrangement surface side, FIG.4 (b) is FIG.4 (a). It is sectional drawing in the position of XX. It is a figure which shows the structure of the GaN-type LED element which concerns on one Embodiment of this invention, FIG.5 (a) is the top view which looked at the element from the electrode arrangement | positioning surface side, FIG.5 (b) is FIG.5 (a). It is sectional drawing in the position of XX. It is sectional drawing which shows the structure of the GaN-type LED element which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the GaN-type LED element which concerns on one Embodiment of this invention. It is the cathodoluminescence image of the surface of the epitaxial layer contained in the GaN-type LED chip which was produced using the method which concerns on a reference experiment example, and was lighted continuously under accelerated deterioration conditions. It is a cathodoluminescence image of the surface of the epitaxial layer contained in the GaN-type LED chip as produced using the method which concerns on a reference experiment example.

(Reference experiment example)
Using a normal MOVPE method, a 4 μm thick undoped GaN layer, a 4 μm thick n-type GaN contact layer made of Si-doped GaN, and an InGaN / GaN multiple layer on a c-plane sapphire substrate having a diameter of 2 inches via a buffer layer An epitaxial wafer is formed by sequentially stacking a quantum well active layer, a 170 nm thick p-type cladding layer made of Mg-doped Al0.1Ga0.9N, and a 40-nm thick p-type contact layer made of Mg-doped Al0.03Ga0.97N. Produced.

  Next, an ITO film for forming a p-side ohmic electrode was formed on the p-type contact layer of the epitaxial wafer to a thickness of about 0.2 μm by using an electron beam evaporation method. Then, the formed ITO film was subjected to a heat treatment at 500 ° C. for 20 minutes in an air atmosphere. After the heat treatment, this ITO film was formed into a predetermined shape by dissolving and removing unnecessary portions by hydrochloric acid etching.

  Next, a recess was formed by RIE (reactive ion etching) at a place where the n electrode of the epitaxial layer was to be formed, and the n-type contact layer was exposed at the bottom of the recess.

  Next, the lift-off method is used to simultaneously form an n-electrode (also used as a bonding pad) on the n-type contact layer surface exposed in the above process and a p-side bonding pad on the ITO film surface. It was.

The lift-off method is a technique for forming a desired thin film on a wafer surface in a desired pattern, and is a technique well known in the art.
(i) After forming a photoresist film on the wafer surface and providing a predetermined opening pattern in the photoresist film by photolithography;
(ii) forming a target thin film on the wafer;
(iii) Thereafter, the photoresist film is removed (at this time, a portion of the target thin film formed on the photoresist film is lifted off);
Through this step, the target thin film is formed in the same pattern as the opening pattern provided in the photoresist film in (i).

In this reference experimental example, an n-electrode and a p-side bonding pad were formed by a lift-off method using a photoresist film formed to a thickness of 6 μm. A naphthoquinonediazide-novolak resin-based positive photoresist (manufactured by AZ Electronic Materials, product name: AZ P4620) was used as the photoresist. The photoresist applied to the wafer surface was baked at 100 ° C. for 30 minutes, and then exposed and developed. The photoresist after development was not baked. The metal film for the electrode (bonding pad) was a two-layer structure film in which an Au film having a thickness of 500 nm was laminated on a TiW film having a thickness of 100 nm. Therefore, the film thickness of the photoresist film is 10 times that of the metal film. Both the TiW film and the Au film were formed by sputtering. When forming a TiW film, a Ti-W target having a Ti content of 10 wt% is used as a target, Ar (argon) is used as a sputtering gas, RF power is 200 W, and sputtering gas pressure is 1.0 × 10 ⁻¹ Pa. Sputtering was performed. After the formation of the metal film, the metal film was formed into a predetermined electrode shape by removing the photoresist film from the wafer using a remover solution.

  Next, a protective coating (passivation film) made of silicon oxide was formed on the wafer surface excluding the surfaces of the n-electrode and the p-side bonding pad by using an electron beam evaporation method. Thereafter, the back surface of the sapphire substrate was lapped to reduce the thickness of the wafer to 80 μm, and then the wafer was divided using a scriber to obtain a 350 μm square plate-like GaN-based LED chip. The forward voltage Vf (20 mA) of this chip was 3.3V.

  The LED chip produced by the above procedure was deteriorated under accelerated deterioration conditions. Specifically, the LED chip is flip-chip mounted on the stem via the submount, and continuously for 1000 hours under the conditions of an environmental temperature of 100 ° C. and a forward current of 114 mA so that the temperature of the pn junction is 230 ° C. Lighted up. After deteriorating in this way, the LED chip is removed from the submount, the protective coating and the ITO film are removed from the surface of the epitaxial layer using acid, and then the surface of the epitaxial layer (the surface of the p-type contact layer) is removed. A cathodoluminescence (CL) image was obtained. The acquired CL image is shown in FIG.

  As shown in FIG. 8, on the surface of the epitaxial layer included in the LED chip deteriorated by continuous lighting, a dark spot appearing in a portion where dislocation defects are present (because the efficiency of luminescence recombination is locally low). The density of the dark portion) was clearly different between the area immediately below the bonding pad and the surrounding area. That is, the density of dislocation defects was clearly lower in the region immediately below the p-side bonding pad than in the surrounding region.

  On the other hand, FIG. 9 shows a CL image of the surface of the epitaxial layer contained in the LED chip as it was obtained in the same manner. As is clear from FIG. 9, the distribution of transition defects on the surface of the epitaxial layer was uniform in the undegraded state.

  The present inventors measured the temperature of the pn junction when the LED chip was turned on under the above conditions by a method using a thermocouple, but a significant temperature was found between the area directly below the p-side bonding pad and the surrounding area. There was no difference. From this, the apparent difference in dislocation density between the area immediately below the bonding pad and the surrounding area, which is seen in the epitaxial layer of the chip deteriorated by continuous lighting, is not formed only by thermal action. The inventors concluded that there was not. The inventors believe that an electrical effect is involved in increasing the defect density associated with continuous lighting, and the density of carriers injected from the ITO film into the p-type layer is low immediately below the p-side bonding pad. Therefore, an increase in defect density is suppressed. The method of forming the bonding pad is related to the decrease in the injected carrier density immediately below the bonding pad. When the metal film constituting the bonding pad is formed by sputtering, the surface of the ITO film is protected by a thick photoresist film outside the region where the bonding pad is to be formed. On the other hand, the surface of the ITO film is exposed in the region where the bonding pad is to be formed. Therefore, when the bonding pad is formed, in this region, the surface of the p-type layer that is only covered with the thin ITO film is damaged by the impact of sputtered particles or high-energy particles. As a result, the resistance between the ITO film and the p-type layer is relatively high immediately below the bonding pad, and as a result, when a forward current is supplied to the LED chip, carriers from the ITO film to the p-type layer are obtained. Implantation is unlikely to occur directly below the bonding pad.

  The increase in resistance at the damaged part is explained as follows. That is, in the GaN-based semiconductor, nitrogen vacancies are formed at a high concentration in the damaged portion due to the high vapor pressure of nitrogen, which is a group V component. Since these nitrogen vacancies serve as donors, the p-type GaN-based semiconductor causes a decrease in p-type carrier concentration due to self-compensation. This increases the resistivity of the semiconductor and the contact resistance between the semiconductor and the electrode. In particular, the generation efficiency of p-type carriers is essentially low in a GaN-based semiconductor that is a wide gap semiconductor, that is, the carrier concentration of the p-type layer is basically low, so that the carrier concentration is further reduced by being damaged. The increase in contact resistance when this occurs is significant.

The present inventors considered as follows based on this reference experimental example.
(A) In the case where an inorganic sputtered film is formed under the same conditions as in the above reference experimental example using an inorganic material instead of the metal material for the bonding pad, the p-type layer / ITO film interface immediately below the inorganic sputtered film An increased resistance region will be formed. When a bonding pad is separately formed on the ITO film and the LED element is energized, the carrier density injected into the p-type layer immediately below the inorganic sputtered film will decrease.
(A) In the above reference experimental example, when the bonding pad is formed on the ITO film by sputtering, if a metal sputter film is simultaneously formed separately from the bonding pad, when the LED element is energized through the bonding pad, immediately below the bonding pad. In addition to this, the density of carriers injected into the p-type layer will be reduced just below the sputtered metal film.
(C) Below the region where the carrier density injected into the p-type layer has decreased, the current flowing through the active layer also decreases. Therefore, the contact resistance of the p-type layer / TCO film interface immediately below the TCO film is controlled by forming the sputtered film on the TCO film, so that the region where the current flowing through the active layer is reduced below the contact resistance of the sputtered film. It would be possible to form a shape substantially corresponding to the planar shape.
(D) The resistance increasing region once formed at the interface of the p-type layer / TCO film immediately below the sputtered film remains even if the sputtered film is removed later, and it is not preferable to leave the sputtered film on the LED element. This could be removed.

(Embodiment 1)
FIG. 1 shows a schematic cross-sectional view of a GaN-based LED element according to Embodiment 1 of the present invention. In this GaN-based LED element 10, an n-type layer 12, an active layer 13, and a p-type layer 14 each made of a GaN-based semiconductor are sequentially stacked on a substrate 11, and a TCO film 15 and a p-type layer 14 are formed on the surface of the p-type layer 14. A p-electrode composed of the side bonding pad 16 is formed, and an n-side bonding pad 17 is formed on the back surface of the substrate 11. From the viewpoint of the electrode structure, the GaN-based LED element 10 has a vertical electrode type structure. A resistance control film RF is inserted in a part between the TCO film 15 and the p-side bonding pad 16.

  At the interface between the p-type layer 14 and the TCO film 15 immediately below the resistance control film RF, there is a resistance increasing region formed when the resistance control film RF is formed. In this resistance increasing region, the electric resistance in the direction crossing the interface between the p-type layer 14 and the TCO film 15 is higher than that in other regions. Therefore, when a forward voltage is applied to the LED element 10 through the p-side bonding pad 16 and the n-side bonding pad 17, the current flowing across the interface between the p-type layer 14 and the TCO film 15 is reduced in this resistance increasing region. . This means that the current flowing through the active layer 13 decreases below the resistance increasing region. Since such a resistance increasing region exists below the resistance control film RF covered with the p-side bonding pad 16, in the GaN-based LED element 10, light emission of the active layer 13 below the p-side bonding pad 16 is suppressed. ing.

The GaN-based LED element 10 can be manufactured as follows.
First, a GaN-based semiconductor crystal is grown on the substrate 11 using a normal MOVPE method, and an epitaxial wafer in which an n-type layer 12, an active layer 13, and a p-type layer 14 are sequentially stacked is manufactured. In order to obtain a vertical electrode structure, a substrate having conductivity is used as the substrate 11. Examples of the conductive substrate include a single crystal substrate made of silicon carbide, silicon, GaN-based semiconductor, gallium arsenide, gallium phosphide, gallium oxide, zinc oxide, zirconium boride, titanium boride and the like.

Next, a TCO film 15 for forming an ohmic electrode is formed on the p-type layer 14 of the epitaxial wafer formed as described above using a vacuum deposition method. The film thickness of the TCO film 15 can be, for example, 0.01 μm to 0.2 μm, preferably 0.01 μm to 0.15 μm, more preferably 0.01 μm to 0.10 μm, and particularly preferably 0. 0.01 μm to 0.05 μm. As the thickness of the TCO film 15 is reduced, the resistance between the TCO film and the p-type layer 14 is significantly increased in the resistance increasing region formed below the resistance control film RF in a later step. This is because, as the film thickness decreases, the action of the TCO film as a protective material for protecting the p-type layer surface during the formation of the resistance control film becomes smaller.
After the film formation, the TCO film 15 is patterned into a predetermined electrode shape by removing unnecessary portions by wet or dry etching. The wafer may be heat treated before or after patterning.

Next, the resistance control film RF is formed by sputtering in a part of the region on the TCO film 15 where the p-side bonding pad 16 is to be formed in a later step by using a lift-off method.
In this step, the surface of the p-type layer 15 is damaged due to sputtering in a region corresponding to a portion where the resistance control film RF is formed, and a resistance increasing region is formed at the interface between the p-type layer 14 and the TCO film 15. To set the sputtering conditions.

The material of the resistance control film RF may be any metal or inorganic material capable of forming a sputtered film, and can be appropriately selected from those having the strength and durability necessary for the GaN-based LED element. Desirably, a material that absorbs as little light as possible is selected. If it is a metal material, what exhibits silver white is preferable and Ag (silver), Al (aluminum), Rh (rhodium), and Pt (platinum) are illustrated as a particularly preferable thing.
If it is an inorganic material, an insulating inorganic material having a band gap larger than the band gap of the active layer 13 is preferable. In particular, a metal oxide, metal nitride, or metal oxynitride having high chemical stability, specifically, Examples of preferred materials include silicon oxide, silicon oxynitride, silicon nitride, aluminum oxide, aluminum nitride, zirconium oxide, and niobium oxide. Although it is inferior in light absorption in a short wavelength region as compared with an insulating material, various TCOs can also be used.
Among the above examples, an insulating inorganic material is the most preferable material in that light absorption is small.

Next, a p-side bonding pad 16 is formed on the TCO film 15. The p-side bonding pad 16 is formed so as to cover the resistance control film RF. The p-side bonding pad 16 may be composed of only a metal material. However, in a preferred embodiment, a lower layer portion in contact with the TCO film 15 and the resistance control film RF is formed of TCO, and a metal layer is formed thereon as an upper layer portion. A laminated film may be used.
Next, etching is performed from the upper surface side of the epitaxial layer, and an element isolation groove is formed so that at least the light emitting layer 13 of each element on the wafer is independent.

Next, a transparent protective coating (not shown) that covers the entire surface of the wafer on which the epitaxial layer is formed is formed using an electron beam evaporation method. The material of the protective coating is preferably a metal oxide, metal nitride, metal oxynitride or the like. After forming the protective coating, the surface of the p-side bonding pad 16 is exposed by dry etching.
Next, an n-side bonding pad 17 is formed on the back surface of the substrate 11. The n-side bonding pad 17 may not be formed directly on the back surface of the substrate 11 but may be formed through a TCO film having a larger area. The order of formation of the n-side bonding pad 17 is not particularly limited, and may be performed before the formation of the p-electrode, for example.
Finally, the GaN-based LED element 10 is cut out from the wafer by a known method using a dicer, a scriber or the like to obtain a chip.

  The GaN-based LED element 10 manufactured in this way can be used by face-up mounting. Of course, when the substrate 11 is transparent to light generated in the light emitting layer 13, face-down mounting (flip (Also referred to as chip mounting or junction down mounting).

(Embodiment 2)
A GaN-based LED element according to Embodiment 2 of the present invention is schematically shown in FIG. 2A is a plan view of the LED element as viewed from the electrode arrangement surface side, and FIG. 2B is a cross-sectional view taken along the line XX of FIG. 2A.
In this GaN-based LED element 20, an n-type layer 22, an active layer 23, and a p-type layer 24 each made of a GaN-based semiconductor are sequentially stacked on a substrate 21, and a TCO film 25 and a p-type layer 24 are formed on the surface of the p-type layer 24. A p-electrode composed of the side bonding pad 26 is formed, and an n-side bonding pad 27 (also used as an ohmic electrode) is formed on the surface of the n-type layer 22 partially exposed by etching. From the viewpoint of the electrode structure, the GaN-based LED element 20 has a horizontal electrode type structure.
A resistance control film RF is formed on a part of the TCO film 25.

The resistance control film RF in the GaN-based LED element 20 is a region sandwiched between the p-side bonding pad 26 and the n-side bonding pad 27 in the TCO film 25 as shown in FIG. It is formed on the “inter-pad area”. Here, the “inter-pad region” referred to in this specification is a region having a tangent line in contact with two bonding pads when the element is viewed in plan as an outer edge. FIG. 3A is a diagram for explaining this, and two two-dot chain lines in the figure indicate tangent lines that contact two pads, respectively. The inter-pad region is included in a region sandwiched between two two-dot chain lines.
The bonding pad may have an arm portion extending elongated from the main body portion in addition to the main body portion used mainly for connection with a metal wire or solder, but the bonding pad thus has the main body portion and the arm portion. In this case, as shown in FIG. 3 (b), the arm portion is ignored, and only the main body portion is taken into consideration to define a tangent that is the outer edge of the interpad area.

  The inter-pad region of the TCO film is a region where current concentration has occurred in the conventional GaN-based LED element (see, for example, JP-A-10-341038). In the GaN-based LED element 20, since the resistance control film RF is formed on the inter-pad region of the TCO film 25, a resistance increasing region is formed at the interface between the p-type layer 24 and the TCO film 25 below the resistance control film RF. , Current concentration in the inter-pad region of the TCO film 25 is suppressed. By suppressing the current concentration in the specific region of the TCO film, the in-plane distribution of the current flowing through the active layer can be made uniform. Thereby, many portions of the light emitting layer can be effectively used, and thus the light emission efficiency of the LED element is improved. Moreover, the reliability of the LED element is improved by relieving a high load applied to a specific portion of the TCO film or the active layer.

The GaN-based LED element 20 can be manufactured as follows.
First, a GaN-based semiconductor crystal is grown on the substrate 21 using a normal MOVPE method, and an epitaxial wafer in which an n-type layer 22, an active layer 23, and a p-type layer 24 are sequentially stacked is manufactured. The substrate 21 may be any material that is suitable for epitaxial growth of GaN-based semiconductor crystals. Sapphire, spinel, silicon carbide, silicon, GaN-based semiconductors (GaN, AlGaN, etc.), gallium arsenide, gallium phosphide, gallium oxide, zinc oxide Crystal substrates (single crystal substrates, templates) made of materials such as LGO, NGO, LAO, zirconium boride, and titanium boride can be preferably used. The light-transmitting substrate is a material selected from sapphire, spinel, silicon carbide, GaN-based semiconductor, gallium phosphide, gallium oxide, zinc oxide, LGO, NGO, LAO and the like depending on the emission wavelength of the element. A configured substrate can be preferably used.

Next, a TCO film 25 for forming an ohmic electrode is formed on the p-type layer 24 of the epitaxial wafer formed as described above using a vacuum deposition method. The thickness of the TCO film 25 can be, for example, 0.01 μm to 0.2 μm, preferably 0.01 μm to 0.15 μm, more preferably 0.01 μm to 0.10 μm, and particularly preferably 0. 0.01 μm to 0.05 μm. As the thickness of the TCO film 15 is reduced, the resistance between the TCO film and the p-type layer 14 is significantly increased in the resistance increasing region formed below the resistance control film RF in a later step. This is because, as the film thickness decreases, the action of the TCO film as a protective material for protecting the p-type layer surface during the formation of the resistance control film becomes smaller.
After the film formation, the TCO film 25 is patterned into a predetermined electrode shape by removing unnecessary portions by wet or dry etching. The wafer may be heat treated before or after patterning.

  Next, a recess is formed by RIE (reactive ion etching) at a location where the n-side bonding pad 27 of the epitaxial layer is to be formed, and the n-type layer 22 is exposed at the bottom of the recess. At the same time, an element isolation groove having the same depth as the recess is formed to make the light emitting layer 23 of each element on the wafer independent.

  Next, the p-side bonding pad 26 is formed on the TCO film 25 and the n-side bonding pad 27 is formed on the surface of the n-type layer 22 exposed in the above process. Any of these may be formed first, but they are preferably formed simultaneously to reduce the number of steps. Since the n-side bonding pad electrode 27 also serves as an ohmic electrode, at least a portion in contact with the n-type layer 22 is made of a material (Ti, W, TiW, V, Al, TCO, etc.) that is in ohmic contact with the n-type GaN-based semiconductor. Form. Alternatively, the n-side bonding pad 27 may not be directly formed on the surface of the n-type layer 22 but may be formed through a TCO film having a larger area. At least the surface layer portion of each bonding pad is formed of a metal material so that a metal wire, solder, or the like can be satisfactorily bonded.

  Next, a resistance control film RF is formed by sputtering on the inter-pad region of the TCO film 25 using a lift-off method. Sputtering is performed so that the surface of the p-type layer 25 is damaged due to sputtering in a region corresponding to a portion where the resistance control film RF is formed, and a resistance increasing region is formed at the interface between the p-type layer 24 and the TCO film 25. The condition is set in the same manner as in the first embodiment.

The material of the resistance control film RF may be any metal or inorganic material capable of forming a sputtered film, and can be appropriately selected from those having the strength and durability required as a constituent material of the GaN-based LED element. Desirably, a material having low light absorption and no conductivity is selected. When a conductive material is used, the resistance control film RF itself becomes a current diffusion path, and the effect of suppressing current concentration is reduced. Therefore, the most preferable material of the resistance control film RF in the GaN-based LED element 20 is an insulating inorganic material having a band gap larger than the band gap of the active layer 23. Among them, metal oxides, metal nitrides or metal oxynitrides with high chemical stability, specifically silicon oxide, silicon oxynitride, silicon nitride, aluminum oxide, aluminum nitride, zirconium oxide, niobium oxide, etc. Is particularly the same as in the first embodiment.
The order of forming the resistance control film RF, the p-side bonding pad 26, and the n-side bonding pad 27 is not particularly limited. For example, the resistance control film may be formed before the bonding pad is formed.

Next, a transparent protective coating (not shown) that covers the entire surface of the wafer on which the epitaxial layer is formed is formed using an electron beam evaporation method. The material of the protective coating is preferably a metal oxide, metal nitride, metal oxynitride or the like. After forming the protective coating, the surfaces of the p-side bonding pad 26 and the n-side bonding pad 27 are exposed by dry etching.
Finally, the back surface of the substrate is lapped as necessary to reduce the thickness of the wafer, and the GaN-based LED element 20 is cut out from the wafer by a known method using a dicer, a scriber, or the like to obtain a chip.

  The GaN-based LED element 20 manufactured in this way can be used by face-up mounting. Of course, when the substrate 21 is transparent to the light generated in the light emitting layer 23, it is mounted face-down. It can also be used. Alternatively, in the case of face-down mounting, the substrate 21 can be removed after mounting the LED element by using the technique disclosed in JP-T-2007-517404 (WO2005 / 062905).

(Embodiment 3)
FIG. 4 schematically shows a GaN-based LED element according to Embodiment 3 of the present invention. 4A is a plan view of the LED element as viewed from the electrode arrangement surface side, and FIG. 4B is a cross-sectional view taken along the line XX of FIG. 4A.
In this GaN-based LED element 30, an n-type layer 32, an active layer 33 and a p-type layer 34 each made of a GaN-based semiconductor are sequentially stacked on a substrate 31, and a TCO film 35 and a p-type layer 34 are formed on the surface of the p-type layer 34. A p-electrode composed of the side bonding pad 36 is formed, and an n-side bonding pad 37 (also serving as an ohmic electrode) is formed on the surface of the n-type layer 32 partially exposed by etching. Each of the two bonding pads 36 and 37 has a main body portion and arm portions 36a and 37a elongated from the main body portion. The arm portions 36a and 37a are portions provided to assist current diffusion in the surface direction of the element, and are not normally used as joint portions for metal wires. From the viewpoint of the electrode structure, the GaN-based LED element 30 has a horizontal electrode type structure. A resistance control film RF is formed on a part of the TCO film 35. In FIG. 4A, the outline of the resistance control film RF hidden under the bonding pad 36 is indicated by a broken line.

The difference between the GaN-based LED element 30 according to the third embodiment and the GaN-based LED element 20 according to the second embodiment is that the resistance control film RF is the TCO film 25 in the GaN-based LED element 20 according to the second embodiment. In the GaN-based LED element 30, the resistance control film RF is not only covered on the inter-pad area of the TCO film 35, but a part thereof is covered with the p-side bonding pad 36. It is also formed in the region. With this configuration, in the GaN-based LED element 30, light emission of the active layer 33 in the region below the p-side bonding pad 36 is suppressed, and current concentration in the inter-pad region of the TCO film 35 is reduced. It is suppressed.

(Embodiment 4)
FIG. 5 schematically shows a GaN-based LED element according to Embodiment 4 of the present invention. FIG. 5A is a plan view of the LED element as viewed from the electrode arrangement surface side, and FIG. 5B is a cross-sectional view taken along the line XX of FIG.
In the GaN-based LED element 40, an n-type layer 42, an active layer 43, and a p-type layer 44 each made of a GaN-based semiconductor are sequentially stacked on a substrate 41, and a TCO film 45 and a p-type layer 44 are formed on the surface of the p-type layer 44. A p-electrode composed of the side bonding pad 46 is formed, and an n-side bonding pad 47 (also used as an ohmic electrode) is formed on the surface of the n-type layer 42 partially exposed by etching. From the viewpoint of the electrode structure, the GaN-based LED element 40 has a horizontal electrode type structure.
A resistance control film RF is formed on a part of the TCO film 45. Similar to the GaN-based LED element 30 according to the third embodiment described above, in the GaN-based LED element 40, the resistance control film RF is partially inserted between the TCO film 45 and the p-side bonding pad 46. The other part is formed on the inter-pad region of the TCO film 45. In FIG. 5A, a portion hidden under the bonding pad 46 and a portion hidden under the reflective film 49 in the outline of the resistance control film RF are indicated by broken lines.

Unlike the GaN-based LED elements according to the above-described embodiments, the GaN-based LED element 40 further includes a reflective film 49 formed on the TCO film 45 with a part of the resistance control film RF interposed therebetween. . The reflective film 49 is formed of an insulating material at least in contact with the TCO film so as not to substantially affect the current diffusivity of the TCO film. The reflective film 49 may be a dielectric multilayer type reflective film. The reflective film 49 may also have a multilayer structure in which a metal film is laminated on a dielectric film (which may include a multilayer-type reflective film). In this case, preferred metal film materials are Ag (silver), Al (aluminum), Rh (rhodium), and Pt (platinum).
The GaN-based LED element 40 according to the fourth embodiment is preferably used with face-down mounting. After the face-down mounting, the substrate 41 can be removed by using the technique disclosed in Japanese translations of PCT publication No. 2007-517404 (WO2005 / 062905).

  In each of the above embodiments, there are the following two important points to be considered in the process of forming the resistance control film.

  The first point is that, corresponding to the region where the resistance control film is deposited on the surface of the TCO film, a resistance increasing region in which the resistance between the p-type layer and the TCO film is partially increased is formed. It is to set sputtering conditions. This increase in resistance is considered to be caused by the impact of sputtered particles or high-energy particles as described above, and can be promoted, for example, by lowering the sputtering atmosphere. This is because, under a low-pressure atmosphere, the probability that sputtered particles or high-energy particles reach the wafer surface without losing energy due to collision with atmospheric gas molecules increases. In general, high energy particles damage the substrate and the sputtered film. Therefore, it is preferable that the high energy particles are not incident on the substrate as much as possible. In contrast, in forming the resistance increasing region, The action of high energy particles can be preferably used.

  The second point is that in the region covered with the lift-off photoresist film, the sputtering conditions used are set so that the resistance between the p-type layer and the TCO film does not substantially change before and after the formation of the resistance control film. The film thickness of the photoresist film is determined so as to produce a sufficient protective effect according to the above. Photoresists capable of forming a thick film of 10 μm or more, mainly used for the formation of bumps (microelectrodes) by electroplating, are commercially available and can be preferably used.

(Modified Embodiment 1)
In each of the above embodiments, the TCO films 15, 25, 35, and 45 have a single layer structure, but this can be a multilayer structure in which two or more TCO films are stacked. In particular, when the TCO films 15, 25, 35, and 45 have a multilayer structure, it is possible to adopt a structure in which the resistance control film RF is sandwiched between any two layers.
As an example, FIG. 6 shows a cross-sectional view of a GaN-based LED element in which the TCO film 25 has a two-layer structure including a lower layer 25a and an upper layer 25b in the second embodiment. In this LED element, the TCO film 25 and the p-type layer in the resistance increasing region formed below the resistance control film RF are formed by thinly forming the lower layer portion 25a of the TCO film (for example, 0.01 to 0.02 μm). The film thickness of the upper layer portion 25b of the TCO film is secured so that the current diffusion function in the layer direction (direction orthogonal to the thickness direction) to be carried by the TCO film 25 is ensured while sufficiently increasing the resistance between Can be set.

(Modified Embodiment 2)
In each of the above embodiments, in the step of forming the resistance control film, the protective film used for protecting the region where the resistance increasing region is not formed is removed from the LED element structure, but this is not essential. FIG. 7 shows a cross-sectional view of a GaN-based LED element obtained by modifying Embodiment 2 and leaving this protective film in the structure.
The GaN-based LED element shown in FIG. 7 has a protective coating 28 that covers the upper surface of the LED element excluding the surface of the bonding pad. This protective coating has a two-layer structure including a lower coating 28a and an upper coating 28b except for a portion covering the TCO film 25. In the LED element manufacturing process, the lower coating 28a is used as a protective film in the resistance control film forming process. That is, in this step, after forming the lower coating 28a in a pattern having an opening above the region where the resistance increasing region is to be provided at the interface between the p-type layer 24 and the TCO film 25, a sputtering method is applied from above. Is used to form the upper coating 28b. At this time, a portion of the upper coating 28b that is directly deposited on the TCO film 25 through the opening of the lower coating 28a acts as the resistance control film RF, and a resistance increasing region is formed below the portion.

Below, the preferable aspect of each part of the GaN-type LED element which concerns on said each embodiment is demonstrated.
In each of the above-described embodiments, the substrate used for epitaxial growth of the GaN-based semiconductor layer may be one in which a mask layer is formed on the surface, or the surface is processed into an uneven surface. Thereby, ELO (Epitaxial Lateral Overgrowth) and facet growth effective in reducing the dislocation density in the GaN-based semiconductor crystal can be generated.

The formation method of the GaN-based semiconductor layer (n-type layer, active layer, p-type layer) is not limited to the MOVPE method (organic metal compound vapor phase growth method), but the MBE method (molecular beam epitaxy method), the HVPE method. A known method suitable for epitaxial growth of a GaN-based semiconductor crystal, such as (hydride vapor phase growth method), PLD method (pulse laser deposition method), or sputtering method, can be used as appropriate.
When a substrate that does not lattice match with the GaN-based semiconductor crystal is used, it is desirable to interpose a buffer layer between the substrate and the GaN-based semiconductor film. With reference to a known technique, a buffer layer such as a low-temperature buffer layer, a high-temperature buffer layer (single crystal buffer layer), or a superlattice buffer layer made of a GaN-based semiconductor or other materials can be appropriately selected and used. In the case of adopting a vertical electrode type element structure, since the substrate and the n-type layer need to be electrically connected, the buffer layer may be doped to impart conductivity.

  As another method for obtaining a structure in which a GaN-based semiconductor film is laminated on a substrate, a method such as etching, grinding, polishing, laser lift-off, etc. after forming a GaN-based semiconductor film on a growth substrate by an epitaxial growth method It is also possible to use a method in which the growth substrate is removed from the GaN-based semiconductor film using, and a separately prepared substrate is bonded to the removed GaN-based semiconductor film. Alternatively, it is also possible to employ a method in which a metal layer is deposited to a thickness of 50 μm or more by electrolytic plating or electroless plating on the surface of the GaN-based semiconductor film from which the growth substrate has been removed, and the metal layer is used as the substrate.

The n-type layers 12, 22, 32, and 42 can be formed of GaN, AlGaN, InGaN, or AlInGaN to which an n-type impurity such as Si or Ge is added. Preferably, using Al _a Ga _1-a N (0 ≦ a ≦ 0.05) to which Si is added to a concentration of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ , a thickness of 2 μm to 6 μm. To form.

  The active layers 13, 23, 33, and 43 determine the band gap energy so that a double heterostructure is formed. The active layer preferably has a quantum well structure, more preferably a multiple quantum well structure. The well layer in the quantum well structure is preferably formed of a crystal containing In, such as InGaN or AlInGaN.

The p-type layers 14, 24, 34, and 44 can be formed of GaN, AlGaN, InGaN, or AlInGaN to which p-type impurities such as Mg and Zn are added. Preferably, Al _a Ga _1-a N (0 ≦ a ≦ 0.2) to which Mg is added at a concentration of 2 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ is used. It is formed to a thickness of 0.0 μm, more preferably 0.1 μm to 0.5 μm. When the p-type impurity is hydrogen-passivated in the crystal growth process, annealing is performed to dissociate hydrogen and activate the p-type impurity.

Each of the n-type layer and the p-type layer does not need to be uniform in the thickness direction, and the impurity concentration, crystal composition, etc. may change continuously or discontinuously in the thickness direction inside each layer. .
For the inside of the n-type layer or the p-type layer, between the substrate and the n-type layer, between the n-type layer and the active layer, between the active layer and the p-type layer, etc., appropriately take into account known techniques. A layer having various purposes, functions or structures, such as a carrier block layer, a reflection layer, an antireflection layer, a strain relaxation layer, a stress relaxation layer, a dislocation reduction layer, an electrostatic breakdown prevention layer, an impurity diffusion prevention layer, and a superlattice layer. Can be provided.

  As the metal material used for the surface layer portion of the p-side bonding pads 16, 26, 36, 46 and the n-side bonding pad electrodes 17, 27, 37, 47, Ag (silver), Au (gold), Sn (tin), In (Indium), Bi (bismuth), Cu (copper), Zn (zinc) and the like are preferably exemplified. The film thickness of the bonding pad can be, for example, 0.2 μm to 2 μm.

  The TCO films 15, 25, 35, and 45 can be formed using various known TCOs such as indium oxide, zinc oxide, tin oxide, and titanium oxide. Specific examples include ITO (indium tin oxide), IZO (indium zinc oxide), AZO (aluminum zinc oxide), GZO (gallium zinc oxide), and FTO (fluorine-doped tin oxide).

  There is no limitation on the method of forming the TCO film, and an appropriate method may be adopted with reference to known techniques. Specific examples include ion beam assisted deposition, ion plating, laser ablation, CVD, sol-gel, spray, spin coating, dip, and the like in addition to vacuum deposition. The use of the sputtering method is not hindered, and if the high-energy particles are prevented from entering the surface of the p-type layer, for example, by increasing the pressure in the sputtering atmosphere, the resistance to the p-type layer can be maintained even by the sputtering method. A low TCO film can be formed.

  The present invention is not limited to the embodiments explicitly described in the present specification, and various modifications can be made without departing from the spirit of the invention.

10, 20, 30, 40 GaN-based LED elements 11, 21, 31, 41 Substrate 12, 22, 32, 42 n-type layer 13, 23, 33, 43 active layer 14, 24, 34, 44 p-type layer 15, 25, 35, 45 TCO films 16, 26, 36, 46 p-side bonding pads 17, 27, 37, 47 n-side bonding pads 28 Protective coating RF resistance control film 49 Reflective film

Claims (7)

An active layer made of a GaN-based semiconductor and a p-type GaN-based semiconductor layer are sequentially stacked on the n-type GaN-based semiconductor layer,
A p-electrode including a TCO film formed on a main surface opposite to the main surface on the active layer side of the p-type GaN-based semiconductor layer, and a p-side bonding pad connected to the TCO film;
A resistance control film formed on a part of the main surface of the TCO film opposite to the p-type GaN-based semiconductor layer side;
A resistance increasing region formed at an interface between the p-type GaN-based semiconductor layer and the TCO film and reducing a current flowing through the active layer in a region below the resistance control film;
An n-side bonding pad connected to the n-type layer;
A GaN-based LED element having:   The p-side bonding pad is formed on the TCO film, and at least a part of the resistance control film is inserted into a part between the p-side bonding pad and the TCO film. GaN-based LED element.   The n-side bonding pad is provided on a partially exposed surface of the n-type GaN-based semiconductor layer so that a horizontal electrode type device structure is formed, and the TCO film is formed of the p-side bonding pad and the n-side bonding pad. 3. The GaN-based LED element according to claim 1, further comprising an inter-pad region sandwiched between and at least a portion of the resistance control film formed on the inter-pad region.   The GaN-based LED element according to claim 3, wherein the resistance control film is formed only inside the inter-pad region on the TCO film excluding the region covered with the p-side bonding pad.   The GaN-based LED element according to claim 1, wherein the resistance control film is made of an insulating inorganic material. A stacked body in which an n-type GaN-based semiconductor layer, an active layer made of a GaN-based semiconductor, and a p-type GaN-based semiconductor layer are sequentially stacked on a substrate; and a main surface of the p-type GaN-based semiconductor layer on the active layer side Providing a semiconductor wafer having a TCO film formed on the main surface opposite to
Forming a resistance control film on a part of the main surface of the TCO film opposite to the p-type GaN-based semiconductor layer side;
Forming a p-side bonding pad on the TCO film,
In the step of forming the resistance control film, the resistance control film is formed so that the resistance at the interface between the p-type GaN-based semiconductor layer and the TCO film is increased in a region corresponding to a portion where the resistance control film is formed. Forming the resistance control film by a sputtering method in a state where an exposed surface of the TCO film excluding a region to be formed is covered with a protective film;
A method for manufacturing a GaN-based LED element.   A GaN-based LED element formed using the manufacturing method according to claim 6.

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