JP2006196543A - Nitride semiconductor light emitting element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the structure of a GaN series light emitting element which can improve a light extraction efficiency and, further, can improve a heat dissipation, and to provide its manufacturing method. <P>SOLUTION: Surface roughening is given to the principal surface Ax of a basic substrate A to provide, a recess and protrusion surface having a recess bottom surface A1 and a protrusion top surface A2 partitioned with a level difference, and unit crystals 1a and 1b are separately grown up from the above recess bottom surface A1 and the protrusion top surface A2. They are made to unite mutually and it is made as a GaN series crystal layer 1. Furthermore on it, a laminate S including a light emitting layer 2 is formed, the basic substrate is partially removed from a rear surface side, and only the protrusion of the basic substrate or the protrusion and a part with a λ/4 thickness or thinner from the bottom of the recess are left into the light emitting element. The λ is the wavelength of this light at the time of light emitted from the light emitting layer passing basic substrate. Consequently, the residual part is utilized for light scattering. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a nitride semiconductor light emitting device and a method for manufacturing the same.

The nitride semiconductor light-emitting device uses a nitride semiconductor at least in the light-emitting layer, and can emit light in a short wavelength region from blue to ultraviolet by selecting the composition.
The nitride semiconductor is a compound semiconductor represented by a general formula In _x Al _y Ga _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). By selecting the composition ratios x, y, and z in the above formula, a mixed crystal having an arbitrary composition such as GaN, InGaN, AlGaN, AlInGaN, AlN, or InN can be obtained. Here, a part of the group 3 element is substituted with B (boron), Tl (thallium) or the like, or a part of N (nitrogen) is P (phosphorus), As (arsenic), Sb (antimony), Those substituted with Bi (bismuth) or the like are also included in the nitride semiconductor.
Hereinafter, the nitride semiconductor is also abbreviated as “GaN-based”, and the conventional technology and the present invention will be described using GaN-based crystals, GaN-based light emitting devices, GaN-based LEDs, and the like as necessary.

GaN-based light emitting devices (particularly GaN-based LEDs) have a problem of low light extraction efficiency. The light extraction efficiency is a ratio indicating how much light is extracted out of the element out of the total amount of light generated in the light emitting layer. The reason why the light extraction efficiency of the GaN-based LED is low is the high refractive index of the GaN-based crystal as described below.
First, the element structure of a GaN-based light-emitting element is obtained by growing a GaN-based crystal layer on a substrate, but sapphire, which is widely used as the most preferable substrate material, has a lower refractive index than a GaN-based crystal. On the other hand, on the upper side of the element (the side far from the substrate), the material and medium surrounding the element (for example, passivation film (silicon dioxide, etc.), sealing resin (epoxy resin, etc.), air (when not sealed with resin), etc.) Although the GaN-based crystal layer is in contact with each other, these materials and media almost always have a lower refractive index than that of the GaN-based crystal. When an electrode made of a transparent conductive film material such as indium tin oxide (ITO) or zinc oxide (ZnO) is used as the p-side electrode, the refractive index of the electrode is lower than that of the GaN-based crystal.

In this way, since the GaN-based crystal layer, which is the main part of the light-emitting structure, is sandwiched from above and below by a material having a lower refractive index, a part of the light emitted from the light-emitting layer can The light is totally reflected at the interfaces on both sides (for example, [interface between the substrate and the GaN-based crystal layer] and [interface between the GaN-based crystal layer and air]) and confined inside the device by multiple reflection. This light is attenuated by internal absorption while propagating inside the device.
In a GaN-based LED mounted by flip-chip bonding, the p-side electrode is entirely formed on one surface of the GaN-based crystal layer (in some cases, it is formed via a transparent conductive film such as ITO). ) Since this electrode is made light reflective, a problem of multiple reflection occurs.

As a method for solving the problem of multiple reflection and improving the light extraction efficiency of the LED, a method of scattering light from the light emitting layer by providing an uneven structure on the substrate surface is disclosed (for example, Patent Document 1). .
As another method, a method of increasing the light extraction efficiency by scattering the light from the light emitting layer by performing uneven processing on the light extraction surface of the LED is disclosed (Patent Document 2). Furthermore, even when the back surface of the substrate is the surface opposite to the light extraction surface, a method is known in which light from the light-emitting layer is scattered and reflected by performing uneven processing on the back surface of the substrate to increase the light extraction efficiency. It has been.

However, the present inventors do not totally reflect a certain amount of light when light passes through the concavo-convex surface from the GaN-based crystal side even if the element surface and the growth surface of the substrate are uneven. Focusing on the fact that it could not be taken out of the device, this was the first problem to be solved.
JP 2004-193619 A JP 2003-218394 A JP 2000-106455 A JP 2000-331947 A Japanese Patent Laid-Open No. 2001-210598 JP 2002-164296 A

  An object of the present invention is to provide a structure of a GaN-based light-emitting element capable of improving light extraction efficiency and further improving heat dissipation, and a method for manufacturing the same.

The present invention has the following features.
(1) One main surface of the base substrate on which the nitride semiconductor crystal can grow is made an uneven surface by uneven processing, the uneven surface has a concave bottom surface and a convex upper surface partitioned by a stepped portion,
On the concavo-convex surface, a nitride semiconductor crystal layer in which unit crystals grown from the concave bottom surface and the convex top surface are combined to embed the concavo-convex surface, and another nitride semiconductor crystal layer grown thereon And a laminate including an n-type layer, a light-emitting layer, and a p-type layer as a light-emitting element structure.
The base substrate is partially removed from the back side, which is the other main surface,
(A) Only the convex part of the basic substrate, or
(Ii) where the light emitted from the light emitting layer passes through the base substrate, the wavelength of the light is λ, and the portion composed of the convex portion and the portion having a thickness of λ / 4 or less from the bottom surface of the concave portion,
A nitride semiconductor light-emitting device, which is left in the device.
(2) The nitride semiconductor light emitting device according to (1) above, wherein the refractive index of the basic substrate is smaller than the refractive index of the nitride semiconductor crystal layer in which the uneven surface is embedded.
(3) The nitride semiconductor light emitting device according to (1) or (2), wherein the basic substrate is a sapphire substrate.
(4) The nitride semiconductor light-emitting element according to any one of (1) to (3), further including a support substrate bonded onto the stacked body.
(5) A method for manufacturing a nitride semiconductor light emitting device,
(I) Concavity and convexity processing is performed on one main surface of a base substrate on which a nitride semiconductor crystal can grow, and the main surface is an uneven surface having a concave bottom surface and a convex top surface partitioned by stepped portions. Process,
(Ii) A nitride semiconductor unit crystal is separately grown from the concave bottom surface and the convex top surface of the concave and convex surfaces, and united with each other to form a nitride semiconductor crystal layer that embeds the concave and convex surfaces. A crystal growth step of growing a nitride semiconductor crystal layer and forming a stacked body including an n-type layer, a light-emitting layer, and a p-type layer as a light-emitting element structure;
(Iii) From the back side that is the other main surface of the base substrate, a process for partially removing the base substrate is performed,
(A) Only the convex part of the basic substrate, or
(Ii) The wavelength of the light emitted from the light emitting layer when passing through the base substrate is λ, and a portion composed of a convex portion and a portion having a thickness of λ / 4 or less from the bottom surface of the concave portion,
The basic substrate removal process left in the element,
A method for manufacturing a nitride semiconductor light emitting device, comprising:
(6) The manufacturing method according to (5), further including a step of bonding a support substrate on the laminate before the basic substrate removing step.
(7) In the above (5), the partial removal method of the basic substrate in the basic substrate removal step is chemical lift, mechanical polishing, or laser lift-off by laser irradiation from the back side of the basic substrate to the concavo-convex surface. Or the manufacturing method of (6) description.

In the present invention, first, one main surface (hereinafter referred to as the upper surface) of the base substrate is made an uneven surface, and a facet LEPS method described later is applied as a crystal growth method, whereby light emission comprising a high-quality crystal layer on the base substrate. An element structure is formed. From the viewpoint of device handling and mechanical strength, it is preferable that a support substrate is further laminated on the uppermost surface of the device.
Next, the base substrate is removed by a specific thickness from the back surface side, which is the other main surface of the base substrate, and as shown in FIG. It is used as a light extraction surface or a light reflection surface.
By setting it as such a manufacturing procedure and element structure, the uneven | corrugated | grooved part of the basic substrate left in the element works as a light-scattering layer. This light scattering layer is a surface from which more light can be extracted while scattering the light when extracting light from the original base substrate side. Thus, the light extraction efficiency can be improved without forming new irregularities for light scattering in each case.
Further, when the base substrate is a sapphire substrate, the sapphire substrate has a problem that heat conductivity is poor and heat tends to be trapped in the light emitting element. However, in the present invention, since the substrate is made thin and only the uneven portion is left, it is possible to improve the “heat dissipation” while improving the “light extraction efficiency”.

  In the present invention, words suggesting the vertical direction such as “bottom surface of concave portion”, “upper surface of convex portion”, “on the concave and convex surface”, etc. are used. It is defined by positioning, and is intended to clearly explain the positional relationship between the substrate and each layer in the element structure. That is, in the present invention, it is indispensable to remove most of the basic substrate. When the base substrate removal surface is a new element upper surface with the support substrate provided on the uppermost layer facing down, Flip chip mounting is sometimes performed with the provided support substrate as it is, and the vertical direction of the element is difficult to understand. Therefore, the basic substrate used at the beginning of the manufacturing process is positioned as the lowest layer, and it is defined that [GaN-based crystal layer is stacked on top of it], and the explanation is clearly given by giving the vertical direction to the stacked structure of the element. did. This vertical direction has nothing to do with the vertical image received from the shape of the final product or the mounting orientation.

In the following, while explaining the manufacturing method according to the present invention, the structure of the GaN-based light emitting device according to the present invention will also be described along with it.
FIG. 1 is a schematic diagram showing a processing state in each step of the manufacturing method according to the present invention.
The manufacturing method according to the present invention has at least the unevenness processing step (i), the crystal growth step (ii), and the basic substrate removal step (iii).

In the concavo-convex processing step (i), as shown in FIG. 1A, the concavo-convex surface is formed on the upper surface Ax of the base substrate on which the nitride semiconductor crystal is grown.
The concavo-convex surface has a concave bottom surface A1 and a convex top surface A2 partitioned by a stepped portion, and a facet LEPS method (a known method for vapor-phase growth of a GaN-based crystal layer on the concavo-convex surface) described later. As long as the irregularities are applicable. The shape and dimensional specifications of the unevenness will also be described later.

The base substrate may be any substrate as long as a GaN-based crystal can be epitaxially grown. For example, sapphire (C plane, A plane, R plane), SiC (6H, 4H, 3C), Si, spinel, ZnO, GaAs, NGO, LGO etc. are mentioned. Moreover, the board | substrate which has a crystal layer which consists of these materials as a surface layer may be sufficient.
From the viewpoint of carrying out the preferred facet LEPS method, a substrate on which the GaN-based crystal to be grown can grow with c-axis orientation perpendicular to the main surface of the base substrate is preferable.
A sapphire substrate is the most versatile and preferable as a basic substrate for growing a GaN-based crystal. However, as described in the background art, a sapphire substrate confines light because it has a lower refractive index than a GaN-based crystal. It has a problem of low heat dissipation. Therefore, when a sapphire substrate is used as the basic substrate, the effects of the present invention [improvement of light extraction efficiency, improvement of heat dissipation] are most prominent.

A method for processing unevenness on the upper surface of the base substrate and specifications of the unevenness will be described.
The pattern drawn by the unevenness when the uneven surface is viewed from above may be any pattern that can be subjected to the facet LEPS method described below, and a conventionally known uneven substrate pattern may be referred to. As a preferred embodiment, a polygonal convex portion (or concave portion) in which all of the constituent sides are oriented in an equivalent direction in relation to the crystal orientation of the substrate is a regularly arranged pattern, linear or curved concave portion. Examples include a stripe pattern in which grooves (or convex ridges) are arranged at regular intervals.
Among these patterns, a stripe pattern in which linear grooves (or convex ridges) are arranged at regular intervals is preferable because it is easy to process.

  The longitudinal direction of the stripe when the uneven pattern is formed into a stripe shape, and the direction of the constituent side of the polygon when the convex portion or the concave portion is formed into a polygonal shape are <11− for the GaN-based crystal grown thereon. 20> direction, <1-100> direction, and the like are preferable. These directions may be appropriately combined with the growth conditions (growth atmosphere, growth temperature, atmospheric pressure, etc.) in which a crystal growth mode peculiar to the facet LEPS method is likely to occur with reference to a known facet LEPS method.

When the irregularities are formed in a stripe pattern, the band width (concave groove width) W1 of the bottom surface of the recess and the band width (convex ridge width) W2 of the top surface of the projection shown in FIG. 3A are both 1 μm to 10 μm, particularly 2 μm to 6 μm is preferable. When the band width is 1 μm or more, the resist mask can be exposed with an inexpensive contact exposure apparatus when patterning the etching mask. When using an exposure apparatus such as a stepper capable of higher-accuracy exposure, a narrower band width may be used. When the band width exceeds 10 μm, the density of the unevenness on the substrate is reduced, and the effect of the facet LEPS method using the unevenness is reduced.
W1: W2 is preferably 2: 3 to 3: 2, particularly 1: 1.
These values may be applied as the height of the polygon or the interval between the constituent sides of the adjacent polygon when the irregularities are polygonal.

  The unevenness step h is such that the crystal unit can grow from the bottom surface of the concave portion and can merge with the crystal unit grown from the top surface of the convex portion. As shown, it is preferably 0.1 μm to 5 μm, particularly 0.5 μm to 2 μm. As a result, it becomes easy to grow the concavo-convex shape with high accuracy, and the light scattering effect can be obtained most efficiently.

As a method of processing the unevenness on the main surface of the substrate, there is a method of forming a recess by dry etching using a photoresist film as an etching mask. Photolithographic techniques may be used to form an opening pattern in the photoresist film in accordance with the target concave shape.
An etching mask used in dry etching is not limited to a photoresist, and a mask made of an inorganic material or a metal material can also be used. A resin-made photoresist film is the most preferable mask because it can be easily subjected to film forming, patterning, and removal operations and can be removed without particularly damaging the substrate surface. However, since it is made of a resin material, if the processing time by dry etching is excessively long, the surface of the substrate is seized, which hinders the growth of good GaN-based crystals.

  Dry etching includes plasma etching and reactive ion etching (RIE), and any of them can be preferably used. The etching gas used for these dry etchings can be selected from conventionally known gases according to the material of the substrate to be used.

As shown in FIGS. 1 (a) and 3 (a), the concave-convex cross-sectional shape is basically preferably rectangular (including trapezoidal) wavy from the viewpoint of securing the concave bottom surface A1 and the convex top surface A2.
As shown in FIG. 3A, the angle θ formed between the main surface Ax and the step surface A3 is preferably 10 ° ≦ θ ≦ 90 °, and particularly preferably 45 ° ≦ θ ≦ 90 °.

In the crystal growth step (ii), first, as shown in FIG. 1B, the facet LEPS method is applied to the uneven surface of the base substrate A, and separately from the concave bottom surface A1 and the convex top surface A2. Nitride semiconductor unit crystals 1a and 1b are vapor-phase grown, and united with each other to flatten the upper surface, thereby forming a GaN-based crystal layer (hereinafter referred to as a buried layer) 1 that fills the uneven surface.
Further, as shown in FIG. 1C, another GaN-based crystal layer is grown on the buried layer, and includes a n-type layer, a light-emitting layer, and a p-type layer as a light-emitting element structure. A laminate S made of is formed.

The vertical relationship of the conductivity type of each layer of the stacked body S is not limited as to which of the n-type layer and the p-type layer is on the lower side, but the buried layer 1 always becomes a current path in the final element structure. The conductivity type of the lower layer of the laminate should be the same.
In the example of FIG. 1, the buried layer 1 and the clad layer 2 are separate layers having different carrier concentrations and crystal compositions, but may be combined into one layer.

A preferable GaN-based material for the buried layer is GaN, which is the same material as the facet-formed material, and the carrier concentration is preferably in the range of 1 × 10 ¹⁷ to 1 × 10 ²¹ cm ⁻³ .

The LEPS method (Lateral Epitaxy on a Patterned Substrate), which is the basic technology of the facet LEPS method, is a method in which a main surface of a substrate is subjected to uneven processing and a GaN crystal is grown on the uneven surface. LEPS method, and finishes the processing into the main surface of the substrate, a method to grow a GaN group crystal including substrate surface treatment described above (formation of a buffer layer, nitriding treatment, etc.), also, SiO ₂ A selective growth mask made up of or the like is not used. From these points, the LEPS method is the method that can most simplify the manufacturing process and minimize the contamination and alteration of the GaN-based crystal among the methods that intentionally generate the lateral growth of the crystal. .

  Among the LEPS methods, the facet LEPS method is an excellent crystal growth method in which the dislocation density (density of threading transition) on the crystal layer surface after planarization is uniformly reduced (for example, Patent Documents 3 to 6). By growing a high-quality crystal layer by the facet LEPS method, the light emitting efficiency in the active layer is improved, the withstand voltage characteristic of the pn junction is improved, and the contact layer is improved in electrical conductivity, which is related to the reduction of the operating voltage of the device, Desirable effects such as reduction in contact resistance between the layer and the electrode can be expected.

In the facet LEPS method, a combination of unevenness specifications and growth conditions is important. As shown in FIG. 1A, the concavo-convex surface is a main surface on which the GaN-based crystal can be c-axis oriented (when the GaN-based crystal is grown on the main surface, the c-axis of the crystal is the main surface. A plate surface that is perpendicular to the surface Ax) is formed by subjecting it to irregularities.
On this main surface, using growth conditions (relatively low temperature, relatively high hydrogen gas concentration, relatively high pressure) in which the growth rate in the c-axis direction is high and the growth rate in the direction perpendicular to the c-axis is low. GaN-based crystals are grown. As a result, facets oriented obliquely with respect to the main surface (hereinafter referred to as {1-101} facets and {11-22} facets) are respectively formed on the concave bottom surface A1 and the convex top surface A2 during crystal growth. Independent crystal units with 1f as side walls are generated (called "oblique facets"). This is facet growth.

As described above, in facet growth, a large number of fine crystals having oblique facets as side wall surfaces are formed in the initial stage of the growth. In the process in which the small crystals are repeatedly united and become larger, the propagation direction of the dislocations is bent, and the dislocations in the opposite direction form loops and disappear, thereby reducing the dislocation density.
Also, when shifting from facet growth to flattening, lateral growth occurs from the side wall surface of the crystal generated on the bottom surface of the concave portion and the top surface of the convex portion, and the propagation direction of the dislocation is bent. Density is reduced.
In order to maximize the latter effect, it is preferable that the crystal generated in the facet growth process has a shape that maximizes the area of the oblique facet that becomes the side wall surface. In the case of a crystal growing from a polygonal concave or convex portion, the shape is a pyramid with the polygon as the bottom, and in the case of a crystal growing from a striped concave or convex portion, It is a roof shape with a triangular cross section extending in the longitudinal direction of the stripe.

  If the growth continues even after the independent crystal units are generated on the concave bottom surface and the convex top surface by the facet growth, each crystal unit gradually expands in the lateral direction. Eventually, when adjacent crystal units come into contact with each other, faster lateral growth occurs, and the space between the side wall surfaces (diagonal facets) of the adjacent crystal units gradually fills, flattening the surface.

  In order to start the flattening process quickly, when independent crystal units are formed on the bottom surfaces of the respective recesses and the top surfaces of the projections, the growth conditions are changed so that two-dimensional growth becomes dominant (higher temperature, Switch to lower atmospheric hydrogen gas concentration, lower pressure). When such growth conditions are switched, the substrate surface is completely covered with the GaN-based crystal in a short time, and the subsequent filling between the side wall surfaces of adjacent crystal units also proceeds in a short time, thereby flattening the surface. Is achieved faster.

The method for growing the GaN-based crystal on the concavo-convex substrate is not particularly limited. In addition to the MOVPE method, a conventionally known method such as a hydride vapor phase epitaxy (HVPE) method or a molecular beam deposition (MBE) method is appropriately used. can do.
From the viewpoint of manufacturing efficiency, it is preferable that the growth of the GaN-based semiconductor layer stacked on the base substrate is performed consistently in one growth furnace by the MOVPE method.

The GaN-based crystal layer that is sequentially grown on the buried layer may be appropriately designed according to the light emitting element structure. In the example of FIG. 1C, the buried layer 1 is an n-type contact layer that also serves as an n-type cladding layer, and includes a GaN-based light emitting layer 2, a p-type AlGaN cladding layer 3, and a p-type GaN contact layer 4. It has an element structure. The light emitting layer may be further subdivided into multiple layers such as a multiple quantum well structure.
Moreover, you may provide required functional layers, such as a Bragg reflective layer, as needed.
The p-type layer, which is the uppermost layer, does not necessarily have to have a flat top surface. By applying a surfactant treatment such as tetraethylsilane, silane, disilane, biscyclopentadienylmagnesium, or Si, the underlying GaN-based layer It may be a three-dimensional crystal grown in the form of dots on the upper surface of the crystal layer.

Since most of the basic substrate is removed in the present invention, in order to handle the element as a product, it is preferable to provide a support substrate on the uppermost layer of the laminate S as shown in FIG. By providing the support substrate, even if most of the base substrate is removed, sufficient mechanical strength is ensured in the final product, and the handleability of the element is improved.
Although the thickness of a support substrate is not limited, 90 micrometers-1000 micrometers, especially 100 micrometers-500 micrometers are a preferable dimension from the point which prevents the curvature of a light emitting element.

The material of the support substrate is not limited, but preferred examples include GaAs, SiC, CuW, GaP, InP, ZnO, and ZnSe.
The method of bonding the support substrate to the uppermost layer of the laminate varies depending on the material of the support substrate, but adhesion via a conductive material is preferable. Examples of the conductive material that can be interposed in the bonding include Au, Al, In, solder, and Ag paste.
When a conductive material such as n-type GaAs or p-type GaAs is used as the material for the support substrate, an electrode can be formed on the support substrate as shown in FIG. 2B, and the n-electrode E2 and the p-electrode E1. Can be arranged so as to face each other in a parallel plate shape, and the element structure portion is sandwiched from above and below by these electrodes.

In the basic substrate removing step (iii), the basic substrate A is partially removed from the back surface side as shown in FIG. The part to be left in the element is the part shown in (a) or (ii) below.
(A) As shown in FIG. 3B, only the convex portion A10 of the irregularities.
(Ii) As shown in FIG. 3 (c), a portion comprising a convex portion A10 and a portion A11 from the concave bottom surface A1 to the thickness t. However, t is 0 <t ≦ λ / 4, where λ is the wavelength of the light emitted from the light emitting layer through the base substrate.
By leaving the part (a) or (ii) in the element, the unevenness used in the facet LEPS method is used for light scattering.

From the point of improving the light extraction efficiency by light scattering, the part to be left in the element should be only the convex part A10 or as close as possible to the convex part A10 as shown in (a) above. preferable.
If 0 <t ≦ λ / 4, even if the refractive indexes of the base substrate and the GaN-based crystal of the buried layer are different from each other, it becomes a transparent region with respect to the light from the light emitting layer. Therefore, the basic substrate may be left in the element as the above-mentioned (ii).
However, even if the crystal is grown theoretically at 1 / 4λ or less, there is a possibility that a substrate of 1 / 4λ or more may remain depending on the location. Therefore, when 1 / 4λ or more remains, in order to prevent the light extraction efficiency from being lowered due to reflection at the interface, a form in which only the convex portion A10 or less remains is preferable.

The substrate removal method in the substrate removal process includes chemical etching (for example, wet etching, dry etching (acidic, alkaline solution, etc.)), mechanical polishing, and laser lift-off by irradiating the uneven surface with laser from the lower surface side. Etc.
Among these basic substrate removal methods, mechanical polishing is a preferred removal method in that the total thickness (h or h + t) of the remaining portion can be controlled with favorable accuracy.

FIG. 2 is a cross-sectional view schematically showing the device structure of a GaN-based light emitting device (GaN-based LED) obtained by the manufacturing method according to the present invention. In the figure, for easy comparison with the structure of a conventionally known light-emitting element, the stacking direction is reversed upside down with respect to the example of FIG. 1, and the newly added support substrate B is drawn on the lower side of the figure. Yes.
In the light emitting device of FIG. 2A, as described in the description of the manufacturing method, a buried layer (n-type contact / cladding layer) is formed on the uneven substrate (removed and only the remaining portion A10 remains). 1 is formed, and a light emitting layer 2, a p-type cladding layer 3, a p-type contact layer 4, and a support substrate B are formed in order downward. As for the remaining portion A10, a portion from the convex portion upper surface A2 of the basic substrate to a thickness of 0.1 μm to 5 μm is left in the element.
An n-type side electrode E1 is formed on the base substrate removal surface.

In the light emitting device of FIG. 2A, an insulating support substrate is used, and a p-type electrode cannot be formed on the support substrate. Therefore, like the GaN-based LED using the conventional sapphire substrate, a part of the stacked body S is removed by the dry etching method from the base substrate removal surface to the depth at which the p-type GaN contact layer 4 is exposed, and thus exposed. A p-type side electrode E2 is formed on the p-type GaN contact layer 4.
On the other hand, in the light emitting element of FIG. 2B, a conductive support substrate is used, and a p-type side electrode E2 is formed on the support substrate, and is opposed to the n-type side electrode E1 in a parallel plate shape. The light emitting layer 2 is sandwiched between them.

A conventional method may be used for forming the electrode, but at least the n-type GaN layer needs to be in contact with the electrode in order to ensure conduction. Specifically, aluminum alone is deposited on the surface of a GaN-based crystal layer grown by doping with an n-type dopant such as Si, Ge, Se, S, or the surface of a non-doped GaN-based crystal layer by a technique such as vapor deposition or sputtering. Alternatively, an alloy film made of titanium and aluminum is formed.
If a non-conductive sapphire substrate remains on the surface on which the electrode is to be formed, that is, if the sapphire substrate remains ¼λ, at least the electrode forming portion is etched after the substrate removal step. Processing is performed to expose the GaN-based crystal layer and form an electrode.
Further, when the GaN-based crystal layer on the substrate is non-doped, the GaN-based crystal layer is removed to expose a GaN-based crystal layer having a carrier concentration higher than a certain level that can be a contact layer, and an electrode is formed on the layer. The formation is preferable in that the energized state is improved.
Examples of the electrode include an aperture electrode, a comb electrode, and a transparent electrode. For example, when a transparent electrode (for example, ITO) is used, ITO may be formed on the entire surface of the n layer, or a current diffuser may be selectively provided on the remaining sapphire and an ITO film may be formed on the entire surface. good.

  The present invention is useful as a method for manufacturing not only LEDs but also all GaN-based semiconductor light-emitting elements (light-emitting elements other than LEDs), light-receiving elements, and electronic devices. Known techniques may be referred to for the structure of the element and the techniques required for its manufacture (eg, a GaN-based semiconductor multilayer structure formation technique, patterning technique, electrode material technique, element isolation technique, etc.).

Example 1
In this example, a GaN-based LED having a structure shown in FIG. 2A (that is, a mode in which an insulating support substrate is bonded and only a convex portion of the basic substrate is left) was manufactured, and performance was evaluated.
[Roughing process]
First, a c-plane sapphire substrate (disk-shaped wafer) having a diameter of 2 inches was used as a basic substrate.
Using a photolithography method, strip-shaped etching masks having a width of 3 μm were arranged in parallel stripes on the main surface of the base substrate with an interval of 3 μm. The longitudinal direction of the stripe was parallel to the <1-100> direction of sapphire.
Next, dry etching was performed on a portion of the main surface of the base substrate that is not covered with the etching mask (a portion where the main surface is exposed) to form a groove having a substantially rectangular wave shape with a depth of 1 μm. Thereafter, the etching mask was removed, and organic cleaning and acid cleaning were performed to obtain an uneven surface.
In FIG. 3A, the size of each part of the concave and convex surface is the width W1 of the bottom surface of the concave portion = the width W2 of the top surface of the convex portion = 3 μm and the step height h of the concave and convex portions = 1 μm.

[Thermal cleaning and low temperature buffer layer formation]
An uneven sapphire substrate is placed in a MOVPE device (on a susceptor heated by a heater), and the substrate temperature is increased to 1100 ° C in an atmosphere where hydrogen gas is introduced at a flow rate of 25 L / min. And vapor phase etching (thermal cleaning) for about 10 minutes was performed. As a result, the natural oxide film on the surface of the sapphire substrate was removed.
Thereafter, the substrate temperature was lowered to 400 ° C., trimethylgallium (TMG) and ammonia were introduced, and a low-temperature buffer layer made of GaN was formed on the bottom surface of the recess and the top surface of the projection.

[Formation of buried layer by facet LEPS method]
Subsequently, the supply of TMG and TMA was stopped, and the substrate temperature was raised to 1000 ° C. with only ammonia flowing. Thereafter, hydrogen gas and nitrogen gas were supplied as carrier gases, ammonia and TMG were supplied as raw materials, and facet growth was performed by performing facet LEPS method to grow an undoped GaN buried layer. The thickness of the undoped GaN buried layer was about 2 μm from the upper surface of the convex portion on the surface of the sapphire substrate.
In the initial stage of growth of the undoped GaN buried layer, first, a three-dimensional GaN crystal having a facet surface inclined with respect to the substrate surface is separately grown on each of the convex and concave portions of the concave and convex portions of the substrate surface. did. When the undoped GaN buried layer is grown through such a process, the concave and convex recesses on the substrate surface are buried by the undoped GaN buried layer almost without leaving a cavity.
After the growth of the undoped GaN buried layer, silane was introduced into the growth tank, thereby forming an n-type GaN contact layer having a thickness of about 4 μm.

[Formation of multiple quantum well structure as light emitting layer]
After the growth of the buried layer, supply of TMG and silane is stopped, the substrate temperature is lowered to 700 ° C., the carrier gas is switched to only nitrogen gas, ammonia and TMG are introduced, and a barrier layer made of GaN (barrier layer) Grew.
Next, trimethylindium (TMI) was introduced to grow a well layer made of InGaN. The supply amounts of TMG and TMI are adjusted so that the InN mixed crystal ratio of InGaN becomes an appropriate value according to the design emission wavelength of the LED. In this example, the mixed crystal ratio was set so that the center emission wavelength was 405 nm.
Barrier layers and well layers were alternately grown a predetermined number of times to obtain a multiple quantum well structure.

[Formation of p-type cladding layer and p-type contact layer]
The temperature in the tank is raised to 1000 ° C., the carrier gas is switched between hydrogen gas and nitrogen gas, TMG, trimethylaluminum (TMA), biscyclopentadienylmagnesium (Cp ₂ Mg) is introduced, and a p-type with a thickness of 50 nm An AlGaN cladding layer 15 was grown.
Subsequently, the supply of TMA was stopped and the flow rate of Cp ₂ Mg was increased to grow a p-type GaN contact layer (high carrier concentration layer) having a thickness of 100 nm.

[Joining of support substrate]
The wafer having the laminated body was taken out of the MOVPE apparatus, and a support substrate made of GaAs having a thickness of 100 μm was bonded onto the uppermost p-type GaN contact layer using a conductive material as an adhesive.

[Basic substrate removal process]
The base substrate was removed from the back surface side by mechanical polishing so as to reduce the thickness, and only the 1 μm portion remained on the back surface side with respect to the upper surface of the convex portion of the base substrate.
On the removal surface, stripes of a band-like region made of sapphire and a band-like region made of n-type GaN in the buried layer appeared.

[Electrode formation and chip formation]
This wafer is further dry-etched from the base substrate removal surface side to a depth at which the p-type GaN contact layer is exposed partially (so that the region where the p-type electrode of each element is to be formed is exposed after division). Then, on the exposed p-type GaN contact layer, a p-type side electrode made of Ni (the side in ohmic contact with the crystal) / Au (the coated side) was formed.
An n-type side electrode made of Al was formed on the base substrate removal surface that was not subjected to dry etching.
The wafer obtained as described above was divided into a square bare chip having a side of 0.35 mm by using a scribe braking method.

[Evaluation]
When the obtained chip was mounted on a To can and made to emit light at 20 mA drive, the output was 15 mW, and the light emitted from the light emitting layer was scattered by the remaining part, and the light extraction efficiency was improved. all right.
It was also found that the removal of the substrate as well as the output improved the heat dissipation, the influence of heat due to current injection could be avoided, and the LED element life increased.

Example 2
In this example, a GaN-based LED having the structure shown in FIG. 2B was manufactured and performance was evaluated.
A GaN-based LED is used in the same element structure and formation process as in Example 1 except that a conductive support substrate made of p-type GaAs is used and thereby a p-type side electrode is formed on the support substrate. Was made.
When the obtained chip was evaluated in the same manner as in Example 1, the output was 18 mW, and as in Example 1, the light emitted from the light emitting layer was scattered by the remaining part, and the light extraction efficiency was improved. In addition, it was also found that the heat dissipation is improved, the influence of heat due to current injection can be avoided, and the element life of the LED is increased.

  According to the present invention, the light extraction efficiency of a GaN-based light emitting device (particularly a GaN-based LED) has been improved. Further, when a sapphire substrate is used as the base substrate, most of the sapphire substrate is removed, so that heat dissipation is improved.

It is the schematic diagram which showed the processing state in each process of the manufacturing method by this invention. In FIGS. 4A and 4B, the uneven portion is shown enlarged. It is sectional drawing which showed typically the element structure of the GaN-type light emitting element (GaN-type LED) obtained by the manufacturing method by this invention. It is a figure which expands and shows the unevenness processed into the main surface, and the remaining part after a base substrate removal.

Explanation of symbols

A Basic substrate A1 Concave bottom A2 Convex top A3 Stepped surface A10 Remaining part 1 Buried layer 2-4 GaN-based crystal layer S Laminated body made of GaN-based crystal B Support substrate

Claims (7)

One main surface of the base substrate on which the nitride semiconductor crystal can grow is formed into a concavo-convex surface by concavo-convex processing, and the concavo-convex surface has a concave bottom surface and a convex top surface partitioned by a stepped portion,
On the concavo-convex surface, a nitride semiconductor crystal layer in which unit crystals grown from the concave bottom surface and the convex top surface are combined to embed the concavo-convex surface, and another nitride semiconductor crystal layer grown thereon And a laminate including an n-type layer, a light-emitting layer, and a p-type layer as a light-emitting element structure.
The base substrate is partially removed from the back side, which is the other main surface,
(A) Only the convex part of the basic substrate, or
(Ii) where the light emitted from the light emitting layer passes through the base substrate, the wavelength of the light is λ, and the portion composed of the convex portion and the portion having a thickness of λ / 4 or less from the bottom surface of the concave portion,
A nitride semiconductor light-emitting device, which is left in the device.   The nitride semiconductor light-emitting element according to claim 1, wherein the refractive index of the base substrate is smaller than the refractive index of the nitride semiconductor crystal layer in which the uneven surface is embedded.   The nitride semiconductor light-emitting device according to claim 1, wherein the base substrate is a sapphire substrate.   Furthermore, the nitride semiconductor light emitting element in any one of Claims 1-3 which has a support substrate joined on the said laminated body. A method for manufacturing a nitride semiconductor light emitting device, comprising:
(I) Concavity and convexity processing is performed on one main surface of a base substrate on which a nitride semiconductor crystal can grow, and the main surface is an uneven surface having a concave bottom surface and a convex top surface partitioned by stepped portions. Process,
(Ii) A nitride semiconductor unit crystal is separately grown from the concave bottom surface and the convex top surface of the concave and convex surfaces, and united with each other to form a nitride semiconductor crystal layer that embeds the concave and convex surfaces. A crystal growth step of growing a nitride semiconductor crystal layer and forming a stacked body including an n-type layer, a light-emitting layer, and a p-type layer as a light-emitting element structure;
(Iii) From the back side that is the other main surface of the base substrate, a process for partially removing the base substrate is performed,
(A) Only the convex part of the basic substrate, or
(Ii) The wavelength of the light emitted from the light emitting layer when passing through the base substrate is λ, and a portion composed of a convex portion and a portion having a thickness of λ / 4 or less from the bottom surface of the concave portion,
The basic substrate removal process left in the element,
A method for manufacturing a nitride semiconductor light emitting device, comprising:   The manufacturing method of Claim 5 which has the process of joining a support substrate on the said laminated body further before the said base substrate removal process.   The partial removal method of the basic substrate in the basic substrate removal step is chemical lift, mechanical polishing, or laser lift-off by laser irradiation from the back surface side of the basic substrate to the concavo-convex surface. Production method.

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