JP2013128150A - Method of manufacturing group-iii nitride semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a group-III nitride semiconductor light-emitting element using a GaN substrate serving as a growth substrate, in which the GaN substrate is processed to have membrane-like structure with high reproducibility.SOLUTION: A stopper layer 11 consist of AlGaN having an Al compositional proportion of 20% is formed on a top surface of a GaN substrate 10. An n-type layer 12, an active layer 13, a p-type layer 14 and a p-electrode 15 are formed on the stopper layer 11, and the p-electrode 15 is joined to a support substrate 16. Subsequently, a mask 20 having a center-opening shape is formed, and a rear face of the GaN substrate 10 is subjected to PEC etching. Light to be irradiated has wavelength of energy higher than a band gap of GaN, but lower than a band gap of the AlGaN having the Al composition proportion of 20%. Since etching stops when it proceeds to a depth reaching the stopper layer 11, membrane structure can be formed with high reproducibility.

Description

  The present invention relates to a method for producing light emission made of a group III nitride semiconductor using GaN as a growth substrate.

  Conventionally, in order to improve the crystallinity of a semiconductor layer, a group III nitride semiconductor light emitting device using a GaN substrate as a growth substrate is known. In such a light emitting device, it is desirable to process the back surface of the GaN substrate. This is because the light extraction efficiency can be improved and the light distribution can be improved.

  On the other hand, photoelectrochemical (PEC) etching is known as a wet etching method for GaN. This is an etching method in which the etching rate is increased by irradiating GaN with light having a wavelength of energy larger than the band gap of GaN while GaN is immersed in an etching solution.

  Patent Document 1 discloses a group III nitride semiconductor laser having a membrane structure by forming a recess in the substrate. However, the method for forming the recess in the substrate is specifically shown. It has not been. The membrane structure is a structure in which a frustum-like or columnar recess is formed in the center of the substrate and the end of the substrate is left, the bottom of the recess is a plane parallel to the substrate surface, and the side surface of the recess is It is a tapered surface inclined with respect to the substrate surface or a surface perpendicular to the substrate surface.

JP 2004-55854 A

  Although processing by mechanical polishing or dry etching can be considered for processing the back surface of the GaN substrate, these methods have a problem in mass productivity. Therefore, it is conceivable to use wet etching for processing the back surface of the GaN substrate.

  However, in the processing of a GaN substrate by wet etching, it is difficult to control the etching depth, and the reproducibility of the processed shape is poor.

  Accordingly, an object of the present invention is a light emitting device in which a GaN substrate is etched to an appropriate depth, and a method for manufacturing the same.

  According to a first aspect of the present invention, there is provided a method for manufacturing a light emitting device in which a semiconductor layer made of a group III nitride semiconductor is laminated on a surface side of a growth substrate, the growth substrate is made of GaN, and a wet etching solution is formed on the growth substrate. A stopper layer forming step of forming a stopper layer made of a material having a resistance to the growth and having a larger band gap than the growth substrate, and a semiconductor layer made of a group III nitride semiconductor is laminated on the stopper layer, An element layer forming step of forming an element layer having the uppermost layer as a p-type contact layer, a substrate bonding step of bonding the p-type contact layer to a support substrate, and the entire growth substrate from the back side of the growth substrate The stopper is removed by wet etching with PEC using light whose wavelength is larger than the band gap and smaller than the band gap of the stopper layer. An exposure step of exposing the entire surface, on the exposed surface of the stopper layer, a light emitting device manufacturing method characterized by having the n-electrode forming step of forming an n electrode.

The group III nitride semiconductor is represented by a general formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) such as GaN, AlGaN, InGaN, and AlGaInN. Is. Si or the like is used as the n-type impurity, and Mg or the like is used as the p-type impurity.

  As the growth substrate, those having various plane orientations such as c-plane, m-plane, a-plane and r-plane can be used. When a c-plane substrate is used, it is desirable that the side on which the stopper layer is formed (growth substrate surface side, semiconductor layer growth surface side) be a Ga polar surface. That is, it is desirable that the surface to be etched be an N-polar surface. This is because the Ga polar face is less likely to be etched than the N polar face.

  The stopper layer may be any material that is larger than the band gap of the growth substrate. When the material of the stopper layer is a group III nitride semiconductor, the band gap can be adjusted by the composition ratio of the group III element. The stopper layer is preferably a material having a lattice constant close to that of the growth substrate. This is because the crystallinity of the semiconductor layer formed on the stopper layer is improved.

  AlGaN can be used for the stopper layer. In the case of AlGaN, the Al composition ratio is preferably 5 to 40%.

  If the Al composition ratio is lower than 5%, it is difficult to selectively etch only the growth substrate, which is not desirable. On the other hand, when the Al composition ratio is larger than 40%, the crystallinity is deteriorated, and the quality of the semiconductor layer formed on the stopper layer is problematic. A more desirable Al composition ratio is 20 to 30%.

  The growth substrate is a c-plane substrate, and the front surface side is preferably a Ga polar surface and the back surface side is preferably an N polar surface.

  The etching solution used in the wet etching is, for example, an aqueous solution such as potassium hydroxide or sodium hydroxide, phosphoric acid or the like.

In addition, the present invention describes the following inventions as product inventions.
In a light emitting device in which a semiconductor layer made of a group III nitride semiconductor is laminated on the surface side of a growth substrate made of a group III nitride semiconductor, the light emitting device has a support substrate bonded on the side opposite to the growth substrate side of the semiconductor layer. A stopper layer made of a material having a larger band gap than the growth substrate is formed between the growth substrate and the semiconductor layer, and a frustum-like or columnar recess is formed at the center of the back surface of the growth substrate. The light-emitting element is characterized in that a stopper layer or a semiconductor layer is exposed on the bottom surface.

The group III nitride semiconductor is represented by a general formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) such as GaN, AlGaN, InGaN, and AlGaInN. Is. Si or the like is used as the n-type impurity, and Mg or the like is used as the p-type impurity.

  As the growth substrate, those having various plane orientations such as c-plane, m-plane, a-plane and r-plane can be used. When a c-plane substrate is used, it is desirable that the side on which the stopper layer is formed (growth substrate surface side, semiconductor layer growth surface side) be a Ga polar surface. That is, it is desirable that the surface to be etched be an N-polar surface. This is because the Ga polar face is less likely to be etched than the N polar face.

  The stopper layer may be any material that is larger than the band gap of the growth substrate. When the material of the stopper layer is a group III nitride semiconductor, the band gap can be adjusted by the composition ratio of the group III element. The stopper layer is preferably a material having a lattice constant close to that of the growth substrate. This is because the crystallinity of the semiconductor layer formed on the stopper layer is improved.

  A light-emitting element is described in which a stopper layer is exposed at the bottom of the recess.

  A light-emitting element is described in which the stopper layer is a group III nitride semiconductor.

  A light-emitting element is described in which the stopper layer is AlGaN.

  A light-emitting element is described in which the composition ratio of Al in the stopper layer is 5 to 40%.

  If the Al composition ratio is lower than 5%, it is difficult to selectively etch only the growth substrate, which is not desirable. On the other hand, when the Al composition ratio is larger than 40%, the crystallinity is deteriorated, and the quality of the semiconductor layer formed on the stopper layer is problematic. A more desirable Al composition ratio is 20 to 30%.

  A light-emitting element is described in which the growth substrate is a GaN substrate.

  The light-emitting element is described in which the growth substrate is a c-plane substrate, the front surface side is a Ga polar surface, and the back surface side is an N polar surface.

  According to the present invention, by forming a stopper layer between the growth substrate and the semiconductor layer, the back surface of the growth substrate can be processed with high precision. In particular, since PEC etching is used, processing with higher precision is possible. The reproducibility of the processed shape is also high.

  As a product invention, it has a structure (membrane structure) with a frustum-like or columnar recess formed in the center of the back of the growth substrate, so it has a higher mechanical strength than when all of the growth substrate is removed It has become. In addition, since a stopper layer made of a material having a larger band gap than the growth substrate is formed on the growth substrate surface, it can be processed into a membrane structure with high accuracy by PEC etching, and the reproducibility of the processing shape of the growth substrate is excellent. It is a light emitting element.

FIG. 6 shows a structure of a light-emitting element 1. FIG. 6 shows a manufacturing process of the light-emitting element 1. FIG. 6 shows a structure of a light-emitting element 2.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating the structure of the light-emitting element 1 of Example 1. In the light emitting element 1, a stopper layer 11 is formed on the surface of the GaN substrate 10, an n-type layer 12, an active layer 13, and a p-type layer 14 are sequentially stacked on the stopper layer 11, and a p-type layer 14 is formed on the p-type layer 14. The electrode 15 is formed, the p-electrode 15 and the support substrate 16 are bonded via the solder layer 17, and the n-electrode 18 is formed on the back surface of the GaN substrate 10. The GaN substrate 10 corresponds to the growth substrate of the present invention, and the n-type layer 12, the active layer 13, and the p-type layer 14 correspond to the semiconductor layer of the present invention.

The GaN substrate 10 is a c-plane substrate having a dislocation density of 1 × 10 ⁷ / cm ² or less, the surface on which the stopper layer 11 is formed is a Ga polar surface, and the surface on which the N electrode 18 is formed. Is an N-polar plane. The GaN substrate 10 has a membrane structure having a recess 19 having a depth from the back surface of the GaN substrate 10 to the stopper layer 11. Here, the membrane structure is a structure in which a frustum-like or columnar recess 19 is provided in the center of the back surface of the GaN substrate 10 and the end portion of the back surface of the GaN substrate 10 is left. The side surface 19 a of the recess 19 has an inclination of about 60 degrees with respect to the back surface of the GaN substrate 10. Due to this membrane structure, mechanical strength against twisting and bending is higher than that of the light emitting element in which the GaN substrate 10 is completely removed to form a thin structure.

  The stopper layer 11 is an n-type AlGaN doped with Si with an Al composition ratio of 20%. The stopper layer 11 is formed to keep the etching depth constant when the GaN substrate 10 is processed into a membrane structure by PEC etching. Note that Si may not be doped.

  The composition ratio of Al is not necessarily 20%, but is preferably 5 to 40%. If the Al composition ratio is less than 5%, the difference in the band gap from GaN is too small, so that it becomes difficult to selectively etch only the GaN substrate 10 by PEC etching, and the etching depth cannot be made constant. . Further, if the Al composition ratio is larger than 40%, the crystallinity of the stopper layer 11 is deteriorated, and there is a problem with the crystallinity of the n-type layer 12, the active layer 13, and the p-type layer 14 formed on the stopper layer 11. This is undesirable because it occurs.

  The thickness of the stopper layer 11 can be made as thin as possible as long as the etching resistance of the stopper layer 11 is sufficiently satisfied, but is desirably 200 to 500 nm. This is because if the thickness is less than 200 nm, the stopper layer 11 may be entirely etched by PEC etching. On the other hand, if it is thicker than 500 nm, the n-type layer 12, the active layer 13, and the p-type layer 14 are adversely affected.

  As the structures of the n-type layer 12, the active layer 13, and the p-type layer 14, various known structures can be used. The n-type layer 12 and the p-type layer 15 may be a single layer, a multilayer, or a superlattice layer. For example, the n-type layer 12 includes an n-type contact layer and an n-type cladding layer, and the p-type layer 14 includes a p-type cladding layer and a p-type contact layer. The active layer 13 can use a structure such as MQW or SQW.

For the p-electrode 15, a metal having high light reflectivity and low contact resistance, such as Ag, Rh, Pt, Ru, Al, or an alloy containing these metals as a main component, Ni, Ni alloy, Au alloy, or the like may be used. it can. Moreover, the composite layer which consists of transparent electrode films, such as ITO, and a highly reflective metal film may be sufficient. Further, a DBR (distributed Bragg reflector) structure may be formed between the p-type layer 14 and the p-electrode 15 with ITO, TiO ₂ or the like to increase the reflectance.

  As the support substrate 16, a conductive substrate made of Si, GaAs, Cu, Cu—W, or the like can be used. Moreover, what formed the electrode pattern etc. on the surface of the insulating board | substrate may be used.

  For the solder layer 17, a metal eutectic such as Au—Sn, Au—Si, Ag—Sn—Cu, Sn—Bi can be used. Moreover, you may join with the support substrate 16 by a gold bump. Alternatively, a method may be used in which a thick Au layer of 10 μm or more is formed by Au plating or Au paste instead of the solder layer 17 and the Au layer and the support substrate 16 are joined.

  Next, a method for manufacturing the light-emitting element 1 of Example 1 will be described with reference to FIG.

First, the stopper layer 11 is formed on the surface of the GaN substrate 10 which is a Ga polar surface, and the n-type layer 12, the active layer 13, and the p-type layer 14 are formed on the stopper layer 11 in this order (FIG. 2A). These are all formed by the MOCVD method, TMG (trimethylgallium) as the Ga source, TMA (trimethylaluminum) as the Al source, (trimethylindium) as the In source, ammonia as the N source, and silane as the Si source as the n-type dopant. Cp ₂ Mg (biscyclopentadienylmagnesium) is used as the Mg source which is a p-type dopant.

  Next, after forming a p-electrode 15 on the p-type layer 14 by vapor deposition, it is joined to the support substrate 16 via the solder layer 17 (FIG. 2B).

Next, the back surface of the GaN substrate 10 is polished by mechanical polishing and CMP (chemical mechanical polishing) to form a mask 20 made of SiO ₂ and patterned into a shape having an open central portion (FIG. 2C). In polishing the back surface of the GaN substrate 10, dry etching may be used in combination. For the mask 20, a material having wet etching resistance other than SiO ₂ may be used, and for example, resist, TiN, Pt, Ir, or the like can be used.

  Next, the back surface of the GaN substrate 10 is etched by PEC etching. The wavelength of the irradiated light is larger than the band gap of GaN and smaller than the band gap of AlGaN with an Al composition ratio of 20%. The etching solution contains KOH (potassium hydroxide) and NaOH (hydroxide). Sodium) and phosphoric acid. When a material that does not have resistance to the etching solution is used for the support substrate 16, a protective film such as a resist is formed on the support substrate 16. Irradiation with light of such a wavelength increases the etching rate of GaN because the light energy is larger than the band gap of GaN, but the etching rate of AlGaN is smaller than the band gap of AlGaN with an Al composition ratio of 20%. Very slow. Therefore, of GaN and AlGaN having an Al composition ratio of 20%, only GaN is selectively etched.

  Therefore, the back surface of the GaN substrate 10 that is not covered by the mask 20 is etched and gradually etched deeper toward the front surface side of the GaN substrate 10, but when the etching proceeds to a depth that reaches the stopper layer 11, the etching is performed there. Almost stops. As a result, a concave portion 19 having a depth from the back surface of the GaN substrate 10 to the stopper layer 11 is formed, resulting in a membrane shape (FIG. 2D). Here, since the wet etching with respect to GaN has anisotropy, the concave portion 19 has a tapered shape in which the side surface 19 a has an inclination of about 60 degrees with respect to the back surface of the GaN substrate 10.

  Alternatively, normal wet etching may be performed first with hot phosphoric acid, and then finishing may be performed by PEC etching. Moreover, you may etch on the conditions that a fine unevenness | corrugation is formed in an etching surface (the bottom face and side surface of a recessed part). The light extraction efficiency can be improved by providing the unevenness. Further, the n-type layer 13 may be exposed by further progressing etching.

  Thereafter, the mask 20 is removed, and the n-electrode 18 is formed on the back surface of the GaN substrate 10, whereby the light emitting device 1 shown in FIG. 1 is manufactured.

  Note that the mask 20 may be formed of a metal having resistance to the etching solution and having a low contact resistance with respect to GaN, and may be used as an electrode as it is without being removed after the PEC etching process.

  As described above, by forming the stopper layer 11 made of AlGaN, which is a material having a larger band gap than GaN, on the surface of the GaN substrate 10, the PEC etching on the back surface of the GaN substrate 10 has a depth that reaches the stopper layer 11. Since it stops, it can be processed into a membrane structure with good reproducibility.

  FIG. 3 is a diagram illustrating the structure of the light-emitting element 2 of Example 2. The light emitting element 2 has a structure in which the GaN substrate 10 is completely removed from the light emitting element 1 and an n electrode 28 is formed on the back surface of the stopper layer 11. That is, in the light emitting element 2, the n-type layer 12, the active layer 13, and the p-type layer 14 are sequentially formed on the surface of the stopper layer 11, the p-electrode 15 is formed on the p-type layer 14, and the p-electrode 15 and the support substrate 16 is joined via a solder layer 17 and an n-electrode 28 is formed on the back surface of the stopper layer 11. In addition, the same code | symbol is attached | subjected to the component same as the light emitting element 1 of Example 1. FIG.

  Next, a method for manufacturing the light emitting element 2 will be described. The manufacturing process of the light emitting element 2 is the same as the manufacturing process of the light emitting element 1 up to FIG. After the step shown in FIG. 2B, the entire back surface of the GaN substrate 10 is PEC etched without forming the mask 20. As described in the first embodiment, this etching stops when the etching proceeds to a depth that reaches the stopper layer 11. As a result, the GaN substrate 10 is completely removed. Then, the light emitting element 2 is manufactured by forming the n electrode 28 on the back surface of the stopper layer 11 exposed by etching.

  Thus, since the stopper layer 11 is formed, a structure in which only the GaN substrate 10 is removed with high accuracy by PEC etching can be accurately reproduced.

  In addition, since the light emitting element 2 has a structure in which the GaN substrate 10 as a growth substrate is completely removed, the mechanical strength is lower than that of the light emitting element 1, but fine uneven processing is performed on the surface exposed by the removal of the GaN substrate 10. Is advantageous over the light emitting element 1 in terms of light extraction efficiency and light distribution.

  A structure similar to that of the light-emitting element 2 can also be realized by forming a semiconductor layer on a sapphire substrate and using a laser lift-off (LLO) method in which the sapphire substrate is peeled and removed by laser irradiation. The light emitting element 2 is advantageous in the following points as compared with the case of using LLO. First, when the sapphire substrate is removed by LLO, there is damage due to laser or physical impact, but since the GaN substrate is removed by wet etching, the light emitting element 2 is less damaged, compared to LLO. This is advantageous in that the leakage current is small and the reliability is high. Second, since the semiconductor layer is epitaxially grown on the GaN substrate, the light-emitting element 2 is advantageous in that the number of dislocations is smaller and the internal quantum efficiency is higher than when the semiconductor layer is epitaxially grown on the sapphire substrate.

  In any of the embodiments, a c-plane GaN substrate is used as a growth substrate. However, the present invention is not limited to this, and any substrate made of a group III nitride semiconductor may be used. Group III nitride semiconductor substrates having various plane orientations such as m-plane, a-plane, and r-plane can be used. However, when a c-plane substrate is used, it is desirable that the surface on the PEC etching side be an N-polar surface. This is because etching is easier than the Ga polar face.

  In each embodiment, AlGaN is used as the material for the stopper layer, but the present invention may be any material that has a larger band gap than the growth substrate. The stopper layer may be doped with impurities, and the etching rate can be controlled by the type and amount of impurities.

  In any of the embodiments, the light emitting element has a structure in which electrodes are provided on the upper and lower sides. However, the present invention is not limited to such a structure. For example, the present invention can also be applied to a flip-chip type light emitting element in which an n electrode is formed on the same side as a p electrode.

  In Example 1, the growth substrate is processed into a membrane shape, but the present invention can be applied to processing into other shapes.

  Moreover, although all are joined with the support substrate in the Example, it is not necessary to use a support substrate.

  The present invention can be applied to a display device, a lighting device, and the like.

10: GaN substrate 11: Stopper layer 12: n-type layer 13: active layer 14: p-type layer 15: p-electrode 16: support substrate 18, 28: n-electrode

Claims (5)

In a method for manufacturing a light emitting device in which a semiconductor layer made of a group III nitride semiconductor is laminated on the surface side of a growth substrate,
The growth substrate is made of GaN;
A stopper layer forming step for forming a stopper layer made of a material having resistance to a wet etching solution and having a larger band gap than the growth substrate on the growth substrate;
An element layer forming step of forming an element layer having a p-type contact layer as a top layer by laminating a semiconductor layer made of a group III nitride semiconductor on the stopper layer;
A substrate bonding step of bonding the p-type contact layer to a support substrate;
The entire growth substrate is removed from the back side of the growth substrate by wet etching with PEC using light having a wavelength of energy larger than the band gap of the growth substrate and smaller than the band gap of the stopper layer, An exposure process that exposes the entire surface of the layer;
An n-electrode forming step of forming an n-electrode on the exposed surface of the stopper layer;
A method for manufacturing a light-emitting element, comprising:   The method for manufacturing a light emitting device according to claim 1, wherein the stopper layer is a group III nitride semiconductor.   The method for manufacturing a light emitting device according to claim 2, wherein the stopper layer is made of AlGaN.   The method for manufacturing a light emitting device according to claim 3, wherein the composition ratio of Al in the stopper layer is 5 to 40%.   5. The method for manufacturing a light-emitting element according to claim 1, wherein the growth substrate is a c-plane substrate, the front surface side is a Ga polar surface, and the back surface side is an N polar surface.

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