JP2013123046A - Method of manufacturing semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor light-emitting element that prevents degradation of element characteristics due to the occurrence of cracks and introduction of defects and has high luminous efficiency.SOLUTION: There is provided a method of manufacturing a semiconductor light-emitting element including the steps of: forming a first stress application layer; forming a first-conductivity-type first semiconductor layer; forming a light-emitting layer; and removing a crystal substrate while leaving at least a part of the first stress application layer, after forming a second-conductivity-type second semiconductor layer. Compressive stress from the first stress application layer is applied to the first-conductivity-type first semiconductor layer. The lattice constant of the first-conductivity-type first semiconductor layer is smaller than the equivalent lattice length of the crystal substrate. The average lattice constant of the light-emitting layer is larger than the lattice constant of the first semiconductor layer. The lattice constant of the second-conductivity-type second semiconductor layer is smaller than the equivalent lattice length of the crystal substrate.

Description

  Embodiments described herein relate generally to a method for manufacturing a semiconductor light emitting device.

  Nitride semiconductors are used in semiconductor light emitting devices, and high performance devices are being put into practical use.

  However, when a semiconductor light emitting device is formed by epitaxially growing a nitride semiconductor crystal on a silicon substrate that is cheaper than the sapphire substrate and the manufacturing process is efficient, due to the tensile stress contained in the epitaxial crystal layer, Cracks and defects may occur. In such a case, the device manufacturing process may be hindered or the device characteristics may be deteriorated. It is desired to realize a semiconductor light emitting device with high light emission efficiency by suppressing the deterioration of device characteristics due to the occurrence of cracks in the process due to tensile stress or the introduction of defects.

JP 2006-303154 A

  Embodiments of the present invention provide a method for manufacturing a semiconductor light emitting device with high light emission efficiency by suppressing deterioration of device characteristics due to generation of cracks or introduction of defects.

  According to the embodiment of the present invention, after forming the first stress applying layer, forming the first semiconductor layer of the first conductivity type, forming the light emitting layer, and forming the second semiconductor layer of the second conductivity type. There is provided a method for manufacturing a semiconductor light emitting device, wherein the crystal substrate is removed in a state where at least part of the first stress applying layer is left. The first stress applying layer is formed on a crystal substrate. The first semiconductor layer of the first conductivity type is formed on the first stress applying layer and includes a nitride semiconductor crystal. A compressive stress is applied to the first semiconductor layer of the first conductivity type from the first stress application layer. The lattice constant of the first semiconductor layer of the first conductivity type is smaller than the equivalent lattice length of the crystal substrate. Alternatively, the thermal expansion coefficient of the first conductivity type first semiconductor layer is larger than the thermal expansion coefficient of the crystal substrate. The light emitting layer is formed on the first semiconductor layer and includes a nitride semiconductor crystal. The average lattice constant of the light emitting layer is larger than the lattice constant of the first semiconductor layer. The second conductivity type second semiconductor layer is formed on the light emitting layer and includes a nitride semiconductor crystal. A lattice constant of the second semiconductor layer of the second conductivity type is smaller than an equivalent lattice length of the crystal substrate. Alternatively, the thermal expansion coefficient of the second semiconductor layer of the second conductivity type is larger than the thermal expansion coefficient of the crystal substrate.

1 is a schematic cross-sectional view illustrating the configuration of a semiconductor light emitting element according to an embodiment. FIG. 2A and FIG. 2B are schematic cross-sectional views showing the stress generated in the laminated structure. It is a cross-sectional schematic diagram which shows the example of the crystal laminated structure at the time of producing the semiconductor light-emitting device concerning embodiment. 4A to 4C are schematic cross-sectional views showing a process for manufacturing the semiconductor light-emitting element structure shown in FIG. FIG. 5A to FIG. 5C are schematic cross-sectional views showing a process for manufacturing the semiconductor light emitting device structure shown in FIG. FIG. 6A and FIG. 6B are a schematic cross-sectional view and a photograph showing another example of the semiconductor light emitting device according to the embodiment. It is a cross-sectional schematic diagram which shows the other example of the semiconductor light-emitting device concerning embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.
Note that, in the present specification and each drawing, the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

FIG. 1 is a schematic cross-sectional view illustrating the configuration of a semiconductor light emitting element according to the embodiment.
As illustrated in FIG. 1, the semiconductor light emitting device 110 according to the embodiment includes a first conductive type first semiconductor layer 10, a second conductive type second semiconductor layer 20, a light emitting layer 30, and a first stress. And an application layer 16. The semiconductor light emitting element 110 is, for example, an LED element. The semiconductor light emitting device 110 may be a laser diode. Hereinafter, the case where the semiconductor light emitting element 110 is an LED will be described.

  For example, an n-type semiconductor layer is used for the first semiconductor layer 10. For example, a p-type semiconductor layer is used for the second semiconductor layer 20. However, the first semiconductor layer 10 may be p-type and the second semiconductor layer 20 may be n-type. Hereinafter, the case where the first semiconductor layer 10 is n-type and the second semiconductor layer 20 is on the p side will be described.

  The first semiconductor layer 10 and the second semiconductor layer 20 include a nitride semiconductor crystal. As will be described later, each of the first semiconductor layer 10 and the second semiconductor layer 20 has a tensile stress in the (0001) plane.

  The first semiconductor layer 10 is, for example, an n-type GaN layer. The second semiconductor layer 20 is, for example, a p-type GaN layer. The first semiconductor layer 10 may include, for example, an i-GaN layer (hereinafter also referred to as “non-doped GaN layer”) and an n-type GaN layer. An n-type GaN layer is disposed between the i-GaN layer and the second semiconductor layer 20.

  The light emitting layer 30 is provided between the first semiconductor layer 10 and the second semiconductor layer 20. The light emitting layer 30 includes a nitride semiconductor crystal. The average lattice constant in the light emitting layer 30 is larger than the lattice constant of the first semiconductor layer 10.

  The light emitting layer 30 includes, for example, a plurality of barrier layers 34 and a well layer 32 provided between the barrier layers 34. A plurality of well layers 32 may be provided. For example, the light emitting layer 30 has an MQW (Multiple Quantum Well) structure.

  The average lattice constant in the light emitting layer 30 is a lattice constant obtained by weighting and averaging the lattice constant of the barrier layer 34 and the lattice constant of the well layer 32 by thickness distribution.

  The first stress application layer 16 is bonded to the first semiconductor layer on the surface of the first semiconductor layer 10 opposite to the light emitting layer 30. The first stress application layer 16 applies a compressive stress to the first semiconductor layer 10. The first stress application layer 16 is bonded to, for example, the first semiconductor layer 10. For example, when the first semiconductor layer 10 includes an i-GaN layer and an n-type GaN layer, the first stress application layer 16 may be bonded to the n-type GaN layer via the i-GaN layer. .

  In this example, the semiconductor light emitting device 110 further includes a second stress applying layer 22. The second stress application layer 22 is provided on the opposite side of the second semiconductor layer 20 from the light emitting layer 30. The second stress application layer 22 is bonded to, for example, the second semiconductor layer 20. The second stress application layer 22 applies a compressive stress to the second semiconductor 20 layer. The stress will be described later.

  In this example, the semiconductor light emitting device 110 further includes a first electrode 81, a second electrode 82, and a reflective metal 90. The LED stacked structure including the second semiconductor layer 20, the light emitting layer 30, and the first semiconductor layer 10 includes a Si substrate via a reflective metal 90 containing Ni on the p-type layer side and an electrode film containing AuSn. The support substrate is bonded. The support substrate will be described later.

  As indicated by an arrow 30 </ b> L illustrated in FIG. 1, the light emitted from the light emitting layer 30 is emitted from the main surface (light extraction surface) on the first semiconductor layer 10 side. In other words, the light emitted from the light emitting layer 30 is emitted to the outside of the semiconductor light emitting element 110 through the first semiconductor layer 10 and the first stress applying layer 16. Thus, the main surface on the first semiconductor layer 10 side is a light extraction surface. The light extraction surface is subjected to uneven processing. An LED stacked structure of nitride semiconductor crystals is formed between the second semiconductor layer 20 and the light extraction surface.

  The first semiconductor layer 10 is made of, for example, n-type gallium nitride (GaN) crystal. On the first semiconductor layer 10, a light emitting layer 30 composed of a multilayer film of a well layer 32 and a barrier layer 34 is stacked. For the well layer 32, for example, InGaN is used. For the barrier layer 34, for example, GaN is used. A second semiconductor layer 20 is stacked on the nitride semiconductor quantum well structure to be the light emitting layer 30. The second semiconductor layer 20 is made of, for example, p-type gallium nitride crystal.

  The lattice constant of the InGaN crystal layer (well layer 32) included in the light emitting layer 30 is larger than the lattice constant of gallium nitride (first semiconductor layer 10). The semiconductor light emitting device 110 uses a first nitride semiconductor crystal (for example, a GaN crystal that becomes the first semiconductor layer 10 and the second semiconductor layer 20) as a base material, and is larger than the lattice constant of the first nitride semiconductor crystal. It has a structure in which a second nitride semiconductor crystal having a lattice constant (InGaN layer to be the well layer 32) is included in the base material.

  The a-axis length (lattice length in the a-axis direction) of the lattice of the first semiconductor crystal layer is longer than the a-axis length (lattice constant in the a-axis direction) inherent to the material of the GaN crystal. That is, a tensile stress is applied to the first semiconductor crystal layer (the first semiconductor layer 10 and the second semiconductor layer 20). The average a-axis length of the lattice of the light emitting layer 30 (for example, a stacked body of the InGaN well layer 32 and the GaN barrier layer 34) is longer than the a-axis length of the lattice of the first semiconductor crystal. As described later, the magnitude of the tensile stress applied to the GaN layer can be evaluated by Raman spectroscopy.

FIG. 2A and FIG. 2B are schematic cross-sectional views showing the stress generated in the laminated structure.
FIG. 2A illustrates the stress generated in the semiconductor light emitting device 110LED stacked structure according to the embodiment. FIG. 2B illustrates the stress generated in the LED stack structure of the semiconductor light emitting device of the reference example.

  As shown in FIG. 2B, in the semiconductor light emitting device according to the reference example, a gallium nitride crystal layer having the (0001) plane as the surface is formed on the sapphire substrate having the (0001) plane as the surface. Further, a light emitting layer composed of an InGaN thin film crystal layer is combined. Each semiconductor crystal of the semiconductor light emitting device 119a of the reference example formed on the sapphire substrate having the (0001) plane as a surface is oriented in the c-axis direction.

  Like the semiconductor light emitting device 119a, a light emitting diode having a nitride semiconductor crystal layer stacked on a sapphire substrate has an n-type GaN layer (first semiconductor layer 10) and a quantum well light emitting layer (on a sapphire substrate not shown). The light emitting layer 30) and a p-type GaN layer (second semiconductor layer 20) are stacked. The sapphire substrate is almost transparent to the wavelength band of the blue region of interest. Therefore, for example, a structure (Face-up structure) in which light is extracted from the upper part of the p-type GaN layer on the front surface side after a reflective film is formed on the back surface of the sapphire substrate is employed.

  On the other hand, countermeasures against heat generation are taken under an operating condition that aims at higher light output and increases current injection. For this purpose, for example, an LED structure made of a nitride semiconductor is epitaxially grown on a sapphire substrate, the surface side of the p-type GaN layer is attached to a support substrate having high thermal conductivity, and the sapphire substrate is peeled off (Thin-film). Structure) is adopted.

  In an LED using gallium nitride epitaxially grown on a sapphire substrate, the equivalent lattice length of sapphire serving as a crystal substrate for growing a gallium nitride crystal layer is smaller than the lattice constant of gallium nitride. Further, the thermal expansion coefficient of the gallium nitride crystal is smaller than the thermal expansion coefficient of the sapphire crystal serving as the base. Therefore, a large compressive stress is applied to the gallium nitride crystal layer when the thin film crystal growth at a high temperature is completed and the temperature is lowered to room temperature, as indicated by arrows A1 and A2 shown in FIG. .

  The lattice constant of the InGaN crystal layer that becomes the light emitting layer 30 is larger than the lattice constant of gallium nitride. Therefore, as indicated by arrows A3 and A4 shown in FIG. 2B, stress (tensile stress) is applied in the direction of pulling from the InGaN crystal layer to the gallium nitride crystal layer to which compressive stress from the sapphire crystal is applied. . On the other hand, as indicated by arrows A5 and A6 shown in FIG. 2B, the light emitting layer 30 receives compressive stress from the gallium nitride crystal layer. Such compressive stress and tensile stress are generated in the (0001) plane, in other words, in the a-axis direction, for example.

  As described above, the tensile stress applied from the InGaN crystal layer having a lattice constant larger than that of gallium nitride to the gallium nitride crystal layer is relatively balanced with the compressive stress applied from the sapphire crystal to the gallium nitride crystal layer. For this reason, the occurrence of defects from the end face of the n-type GaN layer or the end face of the p-type GaN layer is relatively small.

According to the knowledge of the present inventor, it is known that the compressive stress and tensile stress applied to the gallium nitride crystal layer remain even in the thin-film structure from which the sapphire substrate is removed. The same applies to a thin-film structure peeled from a silicon substrate described later with reference to FIG. Whether the stress applied to the gallium nitride crystal layer is a compressive stress or a tensile stress can be determined from a Raman spectrum. For example, the peak of the Raman spectrum in a gallium nitride crystal to which no stress is applied is about 568 cm −1, but in the gallium nitride crystal to which a compressive stress is applied, a wave number smaller than 568 cm −1, for example, about 567. In a gallium nitride crystal to which a tensile stress is applied, the value is from 8 to 565.5 cm ^−1, and a value up to about 570 cm ⁻¹ at a wave number larger than 568 cm ⁻¹ .

  As illustrated in FIG. 2A, the semiconductor light emitting device 110 according to the embodiment is formed on a silicon crystal having a (111) plane (not shown) as a surface, and an n-type GaN layer (first semiconductor layer 10) and The LED has a stacked structure in which a quantum well light emitting layer (light emitting layer 30) and a p-type GaN layer (second semiconductor layer 20) are stacked. Each semiconductor crystal of the semiconductor light emitting device 110 formed on the silicon substrate having the (111) plane as a surface is oriented in the c-axis direction.

  In order to use a substrate having a relatively large area that is cheaper than a sapphire substrate and is efficient in the manufacturing process, growth of a gallium nitride crystal on a silicon crystal is attempted. When a semiconductor light emitting device is manufactured using a nitride crystal grown on a silicon substrate as a base material, the silicon substrate is not transparent to the wavelength of light generally handled. For this reason, a thin-film structure is used in which the growth layer is peeled from the silicon substrate.

  The equivalent lattice length of silicon used as a crystal substrate for growing a gallium nitride crystal layer is larger than the lattice constant of gallium nitride. Moreover, the thermal expansion coefficient of the silicon crystal is smaller than that of gallium nitride. Therefore, tensile stress remains in the gallium nitride crystal layer after the completion of crystal growth, as indicated by arrows A11 and A12 shown in FIG. Further, the nitride semiconductor crystal system formed on the silicon crystal is subjected to further tensile stress from the InGaN light emitting layer 30 as indicated by arrows A13 and A14 shown in FIG. On the other hand, as indicated by arrows A15 and A16 shown in FIG. 2A, the light emitting layer 30 receives compressive stress from the gallium nitride crystal layer. Such compressive stress and tensile stress are generated in the (0001) plane, in other words, in the a-axis direction, for example.

  Thus, in the semiconductor light emitting device 110 according to the embodiment, the tensile stress applied from the InGaN crystal layer having a lattice constant larger than that of gallium nitride to the gallium nitride crystal layer is changed from the silicon crystal to the gallium nitride crystal layer. Synergistic with the applied tensile stress. For this reason, when a nitride semiconductor crystal is epitaxially grown on a silicon substrate to form a semiconductor light emitting device, cracks, defects, and the like are likely to occur due to the tensile stress contained in the epitaxial crystal layer. In such a case, the device manufacturing process may be hindered or the device characteristics may be deteriorated.

  Further, when the In composition of the light emitting layer 30 is high and the average lattice constant of the light emitting layer 30 is large, the tensile stress applied from the InGaN crystal layer to the gallium nitride crystal layer is large, and the obstacles that occur in the device manufacturing process are remarkable. is there. Even when the thickness of the InGaN crystal layer is large, obstacles occurring in the element manufacturing process are significant.

  On the other hand, in the semiconductor light emitting device 110 according to the embodiment, as illustrated in FIG. 1, the first stress application layer 16 provided at the end of the first semiconductor layer 10 and the second semiconductor layer 20 are provided. And a second stress applying layer 22 provided at the end. Thereby, the first stress application layer 16 and the second stress application layer 22 apply a compressive stress to the first semiconductor layer 10 and the second semiconductor layer 20, that is, the first semiconductor crystal layer as the base material layer.

The first stress application layer 16 includes, for example, an AlN layer. The first stress applying layer 16 is not limited to including a single layer of AlN, and may include a plurality of AlN layers. The first stress application layer 16 may include an AlGaN layer.
The second stress application layer 22 includes an AlGaN layer. Further, the second stress application layer 22 may include an AlN layer.

  According to the semiconductor light emitting device 110 according to the embodiment, the first stress application layer 16 and the second stress application layer 22 are provided in the first stress application layer 16 and the second stress application layer 22 even under a condition in which a tensile stress is applied to the first semiconductor crystal as a base material. A compressive stress can be applied to one semiconductor crystal layer. Therefore, the generation of cracks or the introduction of defects can be suppressed, and a semiconductor light emitting element with high luminous efficiency can be provided.

  For example, as described above with reference to FIG. 2A, in the element structure in which the light emitting layer 30 that further applies the tensile stress is included in the thin film crystal (first semiconductor crystal) including the tensile stress, the first semiconductor crystal layer The first stress application layer 16 and the second stress application layer 22 that apply compressive stress are disposed on both end faces of the first and second stress layers. For this reason, it is possible to suppress degradation of device characteristics due to generation of cracks or introduction of defects during the process due to tensile stress.

  In the thin-film structure peeled from the silicon substrate, the main surface (light extraction surface) of the first semiconductor layer 10 is an open end (open surface). Therefore, when the first stress application layer 16 and the second stress application layer 22 are not provided, no stress is applied to the main surface (light extraction surface) of the first semiconductor layer 10 that is an open surface. In such an open surface, a failure due to tensile stress included in the epitaxial crystal layer is likely to occur. On the other hand, in the semiconductor light emitting device 110 according to the embodiment, since the first stress application layer 16 and the second stress application layer 22 are provided, the main surface (light extraction surface) of the first semiconductor layer 10 is open. Even at the edge, compressive stress is applied to the first semiconductor crystal layer.

FIG. 3 is a schematic cross-sectional view illustrating an example of a crystal stacked structure when manufacturing the semiconductor light emitting device according to the embodiment.
As shown in FIG. 3, in the semiconductor light emitting device 120 according to this embodiment, the buffer layer 12 having an AlN layer and an AlGaN layer is disposed on the silicon substrate 50. On the buffer layer 12, a non-doped barrier layer 14 having a thickness of 300 nanometers (nm) is sandwiched, and an AlN layer 16 (first stress applying layer) 16 having a thickness of 15 nm is repeatedly provided three times. A first semiconductor layer 10 is stacked on the AlN layer 16. On the first semiconductor layer 10, an n-type GaN layer 18 having a thickness of 2 micrometers (μm) and a non-doped GaN layer 17 having a thickness of 1 μm are stacked.

  On the n-type GaN layer 18, an SLS (Super lattice structure) having a structure in which a GaN layer made of GaN having a thickness of 3 nm and an InGaN layer having an In composition of 7% and a thickness of 1 nm are repeatedly formed 30 times. A (superlattice structure) layer 60 is disposed. On the SLS layer 60, the MQW light emitting layer 30 is laminated. The MQW light emitting layer 30 has a structure in which a 5 nm thick barrier layer 34 made of GaN and a well layer 32 made of an InGaN layer having an In composition of 15% and a thickness of 3 nm are repeated eight times. In the semiconductor light emitting device 120 of the embodiment, the In composition ratio in the well layer 32 is, for example, not less than 0.12 and not more than 0.20.

  On the light emitting layer 30, a p-type AlGaN layer (second stress applying layer 22) having an Al composition of 20% is disposed. A p-type GaN layer (second semiconductor layer 20) is disposed on the p-type AlGaN layer (second stress applying layer 22). A reflective metal 90 is disposed on the p-type GaN layer (second semiconductor layer 20).

Next, an example of a manufacturing process of the semiconductor light emitting element 120 will be described.
FIGS. 4A to 5C are schematic cross-sectional views showing a process for manufacturing the semiconductor light emitting device structure shown in FIG.

  First, a silicon substrate 50 having a (111) plane as a surface is prepared as a substrate for crystal growth of a thin film nitride semiconductor. The thickness of the crystal of the silicon substrate 50 is about 525 μm, for example. However, the crystal thickness of the silicon substrate 50 is not limited to this, and may be, for example, about 250 μm to 800 μm.

  Generally, the surface of the Si substrate 50 placed in the atmosphere is covered with a natural oxide film. Therefore, in order to remove the natural oxide film and perform a hydrogen termination treatment on the substrate surface, an acid treatment cleaning is performed. Thereafter, the thin film growth substrate is treated with a diluted hydrofluoric acid solution having a concentration of about 1% for about 1 minute. By this treatment, the surface of the Si layer becomes a surface structure terminated with hydrogen and becomes a water-repellent surface.

  Subsequently, the Si substrate 50 whose surface is hydrogen-terminated is introduced into a film forming apparatus (MOCVD apparatus) using organic metal and ammonia gas as raw materials, and an AlN layer having a thickness of 100 nm is stacked at a film forming temperature of 1200 ° C. . Although an example in which the MOCVD apparatus is used for forming the AlN layer has been described here, the selection of the film forming method is arbitrary. For example, an ECR plasma sputtering apparatus or an MBE apparatus may be used as the AlN layer deposition apparatus.

When the AlN layer is formed on the Si substrate 50 by a device other than the MOCVD apparatus, the substrate is introduced into the MOCVD apparatus after the AlN layer is formed, and the following film forming process is continued.
After laminating a 100 nm AlN layer on the Si substrate 50, the substrate temperature is set to 1100 ° C. and an AlGaN layer having an Al composition of 25% and a thickness of 250 nm is laminated.
The AlN layer and the AlGaN layer thus formed correspond to the buffer layer 12 shown in FIG.

Thereafter, a 0.3 μm gallium nitride layer 14 is formed using TMG (trimethylgallium) and NH ₃ (ammonia) as raw materials. After laminating the 0.3 μm gallium nitride layer 14, the film forming temperature is lowered to 700 ° C. to grow an AlN layer 16 (first stress applying layer) having a thickness of 15 nm. Further, the barrier layer 14 having a thickness of 300 nm is grown again at a film forming temperature of 1100 ° C. In this way, the low-temperature grown AlN layer 16 is inserted three times with the 300 nm barrier layer 14 interposed therebetween.

Subsequently, an n-type GaN (first semiconductor layer) 10 is stacked. At this time, Si is added to the n-type GaN 10 as an impurity at a concentration of 1 × 10 ¹⁹ cm ⁻² . Here, as shown in FIG. 3, the n-type GaN 10 is not directly formed on the AlN layer 16, but a barrier layer 17 containing no impurities (non-doped barrier layer) 17 having a thickness of about 1 to 3 μm. After the growth, the n-type GaN layer 18 may be stacked. That is, the first semiconductor layer 10 may have a structure in which the non-doped GaN layer 17 and the n-type GaN layer 18 are stacked.

  After the growth of the n-type GaN 10, an SLS layer 60 and a light emitting layer (MQW light emitting layer) 30 made of a multilayer film of InGaN and GaN are stacked on the n-type gallium nitride crystal layer 10. Further, in order to inject current for making the light emitting layer 30 shine, p-type (Mg) doping is performed on the upper side of the crystal structure. At this time, an AlGaN layer 22 (second stress applying layer) having an Al composition of 20% and a p-type GaN (first semiconductor layer) 20 containing no Al are formed on the light emitting layer 30.

  Here, a vapor phase growth method (MOCVD method) using an organic metal is mentioned as a method for growing a thin film crystal of the n-type GaN crystal layer 10, the light emitting layer 30, and the p-type GaN 20, but it is not limited to this. is not. As a method of growing a thin film crystal of the n-type GaN crystal layer 10, the light emitting layer 30, and the p-type GaN 20, a molecular beam epitaxy method (MBE: Molecular Beam) which is a thin film crystal growth method generally used for growing a nitride semiconductor crystal. Any method such as Epitaxy) or HVPE method (Hydride Vapor Phase Epitaxy) may be used.

  In this way, as shown in FIG. 4A, the thin film crystal layer (crystal growth layer) 70 having the LED structure can be epitaxially grown. Thereafter, as shown in FIG. 4B, a metal film (reflection metal 90) containing Ag as a reflection film and contact layer, for example, a silver nickel layer, is laminated on the surface of the second semiconductor layer 20, and then bonded metal. (For example, a gold-tin alloy) is sandwiched and bonded to a conductive support substrate 40 such as silicon or copper.

Next, as shown in FIG. 4C, the Si substrate 50 which is a thin film crystal growth substrate is removed. After the support substrate 40 is attached to the second semiconductor layer 20 side, the growth Si substrate 50 can be removed by grinding the growth substrate. At this time, after the Si substrate 50 is removed by grinding, the remaining Si is finally removed by dry etching using SF ₆ gas as an etchant, whereby an AlN layer (first formed on the Si substrate 50 ( The buffer layer 12) can be exposed.

  Here, the AlN layer has a property of increasing the resistance component. Therefore, for example, in the semiconductor light emitting device having the stacked structure described above with reference to FIG. 3, the AlN buffer layer (for example, the buffer layer 12 including the AlN layer) and the AlN stress applying layer (for example, the first stress applying layer including the AlN layer). There is an example in which an unevenness processing (see FIG. 1) is performed after removing 16) and exposing the n-type GaN layer 18.

Specifically, the AlN buffer layer or the AlN stress application layer has a high contact resistance when electrode formation is considered. In addition, the series resistance component increases. Therefore, in a general process, the AlN buffer layer and the AlN stress application layer are removed to expose the n-type GaN layer 18, and then the concavo-convex process is performed. In this case, compressive stress cannot be applied to the first semiconductor crystal layer, and a failure due to tensile stress is likely to occur. In an experiment conducted by the present inventor, after removing the silicon substrate 50 (epitaxial growth substrate), an AlN buffer layer (for example, a buffer layer 12 including an AlN layer) and an AlN stress applying layer (for example, an AlN layer) are removed. When the n-type GaN layer 18 is exposed by removing the first stress applying layer 16), the density is increased at intervals of 5 to 0.5 millimeters (mm) due to the tensile stress applied to the n-type GaN layer 18. It is known that a new crack of about 2 to 20 cm ⁻¹ occurs. Further, since the element temperature rises when the LED is actually operated, in the structure in which the first stress application layer 16 is not provided, new cracks and defects are generated even during the operation of the element. May cause deterioration.

  On the other hand, in the semiconductor light emitting device of the embodiment, the AlN-based stress application layer remains without being removed (see, for example, “first stress application layer 16” illustrated in FIG. 1). Therefore, a compressive stress can be applied to the first semiconductor crystal layer, and the occurrence of failures due to the tensile stress can be suppressed.

Thereafter, as shown in FIG. 5A, the crystal growth layer 70 is divided into nitride semiconductor crystal layer portions 70a in the element size. At this time, the substrate side below the p-type electrode (second electrode 82) metal is held without being divided. Subsequently, as illustrated in FIG. 5B, the portion where the n-side electrode (first electrode 81) is formed is protected with a mask 89, and then the surface of the nitride semiconductor (first semiconductor layer 10) with a KOH solution. An uneven surface with a depth of about 500 nm is formed on the side. At this time, the AlN and AlGaN layers (buffer layer 12) exposed on the surface are removed by etching. Further, for example, for the three AlN layers 16 included in the crystal growth layer 70 (nitride semiconductor crystal layer portion 70a), the uppermost layer (layer on the nitride semiconductor surface side) is formed by uneven processing on the nitride semiconductor surface. ) Are divided, and the two AlN layers 16 below the uppermost layer are left as continuous films below the recesses. This will be described in detail later.
Finally, as shown in FIG. 5C, the mask 89 protecting the n-type electrode generation portion is removed, and the n-type GaN is exposed by etching to form an n-type electrode.

Next, another example of the semiconductor light emitting device according to the embodiment will be described with reference to the drawings.
FIG. 6A and FIG. 6B are a schematic cross-sectional view and a photograph showing another example of the semiconductor light emitting device according to the embodiment.
FIG. 7 is a schematic cross-sectional view showing still another example of the semiconductor light emitting element according to the embodiment.
FIG. 6B is an enlarged photograph of the range B1 shown in FIG.

  Similar to the semiconductor light emitting device 110 described above with reference to FIG. 1, the semiconductor light emitting device 130 illustrated in FIG. 6A includes the second semiconductor layer 20, the MQW light emitting layer 30, the first semiconductor layer 10, and the first stress. The application layer 16, the second stress application layer 22, the first electrode 81, and the second electrode 82 are provided. The first semiconductor layer 10 has a structure in which a non-doped GaN layer 17 and an n-type GaN layer 18 are stacked. These are as described above with reference to FIGS.

  Note that an SLS layer 60 made of a multilayer film of InGaN and GaN may be disposed on the MQW light emitting layer 30 as in the semiconductor light emitting device 140 shown in FIG. The second stress application layer may include an SLS layer 24 made of an AlN-based multilayer film.

As shown in FIG. 6B, the light extraction layer is provided on the opposite side of the first stress application layer 16 from the first semiconductor layer 10. The surface of the light extraction layer opposite to the first stress application layer 16 (light extraction surface) is provided with unevenness. A protective film 15 containing SiO ₂ is formed on the surface of the concavo-convex process applied to the light extraction surface. Further, in the semiconductor light emitting device 130 shown in FIG. 6A, of the three AlN layers 16 included in the crystal growth layer 70 (see FIG. 4A, etc.) due to the uneven processing of the semiconductor surface. The uppermost layer (the layer on the light extraction surface side) and the first AlN layer 16 below the uppermost layer are divided. On the other hand, the second AlN layer 16 below the uppermost layer is left as a continuous film below the recess.

The form of the AlN layer (first stress application layer) 16 left as a continuous film is not limited to this. For example, as shown in FIG. 1, the unevenness of the light extraction surface with respect to the position of the uppermost AlN layer 16 may be shallow, and all the AlN layers 16 may be left as a continuous film.
Thus, any one of the plurality of AlN layers 16 is left as a continuous film, so that the AlN layer 16 can apply compressive stress to the first semiconductor crystal layer. . As a result, it is possible to provide a semiconductor light emitting device with high light emission efficiency by suppressing deterioration of device characteristics due to generation of cracks or introduction of defects.

That is, the thickness of AlN required as the first stress application layer 16 is 15 nm or more when the AlN layer is a single layer. The AlN layer may be a plurality of layers. When multiple layers of AlN are adjacent to each other, the total thickness may be 15 nm or more.
Further, in the semiconductor light emitting device 130 illustrated in FIG. 6A, the first semiconductor layer 10 includes a non-doped GaN layer 17 having a thickness of 1 μm and an n-type GaN layer 18 having a thickness of 2 μm. Although it has a thickness of 3 μm, the thickness of AlN required as the first stress application layer 16 depends on the thickness of the first semiconductor layer 10. That is, when the first semiconductor layer 10 is thin, the first stress applying layer 16 may be thin. More specifically, when the first semiconductor layer 10 is composed of an n-type GaN layer having a thickness of 2 μm, the thickness of AlN of the first stress application layer 16 may be 10 nm or more.

  The first stress application layer 16 may be composed of an AlGaN layer. In the case where the first stress application layer 16 is made of AlGaN, the relationship between the Al composition and the thickness should be equivalent to the thickness of the equivalent AlN layer. That is, when the thickness of the first semiconductor layer 10 is 3 μm, in order to use the AlGaN layer having an Al composition of 50% as the first stress applying layer 16, the thickness of the AlGaN may be 30 nm or more. Further, the first stress applying layer 16 may be composed of a composite layer of AlN and AlGaN or a plurality of AlGaN having different compositions. Even in that case, the required thickness can be estimated by the equivalent AlN thickness.

  The first stress application layer 16 is provided on the light extraction surface side which is an open surface, while the second stress application layer 22 is a second semiconductor layer disposed on the side in contact with the reflective metal 90 and the bonding metal. 20 is formed in contact with. That is, since the second semiconductor layer 20 is fixed by the reflective metal 90 film, cracks and defects are less likely to occur in the second semiconductor layer 20 than in the first semiconductor layer 10. Therefore, the equivalent thickness of the AlN layer required for the second stress application layer 22 is thinner than the equivalent thickness of the AlN layer required for the first stress application layer 16. As the second stress applying layer 22 of the semiconductor light emitting device 130 shown in FIG. 6A, an AlGaN layer having a thickness of 5 nm and an Al composition of 20% is used. Further, as the second stress applying layer of the semiconductor light emitting device 140 shown in FIG. 7, an SLS layer (3 periods) 24 in which an AlGaN layer having a thickness of 3 nm and an Al composition of 15% is sandwiched between GaN layers having a thickness of 3 nm is used. ing. The second stress applying layer may be an AlGaN layer having an Al composition of 10% and a thickness of 5 nm. Further, the second stress application layer 22 can be omitted.

  When compressive stress cannot be applied to the first semiconductor layer 10 by the first stress application layer 16, cracks are generated due to the influence of tensile stress or element characteristics are deteriorated due to the introduction of defects. Further, these obstacles due to the influence of tensile stress become prominent when the average In composition of the MQW light emitting layer 30 is high and the average lattice constant of the MQW light emitting layer 30 is large. Further, the obstacle due to the influence of the tensile stress becomes significant even when the MQW light emitting layer 30 is thick.

  Specifically, in the MQW light emitting layer 30, when the In composition of the well layer 32 made of the InGaN layer is 16% and the thickness of the well layer 32 is thicker than 3.5 nm, the barrier made of the GaN layer When the thickness of the layer 34 is less than 10.5 nm, the obstacle due to the influence of tensile stress becomes significant. Under the conditions described above, the average In composition is 4.0%. Here, in the present specification, “average In composition” means that the thickness of the well layer 32 is t1, the In composition in the well layer 32 is x1, the thickness of the barrier layer 34 is t2, and the barrier layer 34 When the In composition in x is x2, the ratio represented by (t1 × x1 + t2 × x2) / (t1 + t2) is used. Moreover, when the number of well layers 32 is larger than 4 pairs under the above-described conditions, the failure due to the influence of tensile stress becomes significant. This corresponds to a thickness of 56 nm or more in the case of the MQW light emitting layer 30 described above.

  Further, in the MQW light emitting layer 30, when the In composition of the well layer 32 made of the InGaN layer is 12% and the thickness of the well layer 32 is thicker than 3 nm, the thickness of the barrier layer 34 made of the GaN layer When the thickness is smaller than 5 nm, the obstacle due to the influence of the tensile stress becomes more remarkable. Under the conditions described above, the average In composition is 4.5%. Under the above-described conditions, when the number of well layers 32 is larger than 6 pairs, the failure due to the influence of tensile stress becomes significant. This corresponds to a thickness of 48 nm or more in the case of the MQW light emitting layer 30 described above.

  Further, even when InGaN containing In is used for the barrier layer 34 of the MQW light emitting layer 30, the failure due to the tensile stress applied to the GaN layer becomes more prominent. Also in this case, the risk of occurrence of a failure such as the occurrence of a crack or the introduction of a defect can be evaluated with an equivalent average In composition size.

  The first electrode 81 penetrates the first stress application layer 16 and is electrically connected to the first semiconductor layer 10. In the second electrode 82, an unillustrated lead portion is formed in a direction perpendicular to the cross section shown in FIG.

In this specification, “nitride semiconductor” means B _x In _y Al _z Ga _1-xyz N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z ≦ 1) Semiconductors having all compositions in which the composition ratios x, y, and z are changed within the respective ranges are included. Furthermore, in the above chemical formula, those further containing a group V element other than N (nitrogen), those further containing various elements added for controlling various physical properties such as conductivity type, and unintentionally Those further including various elements included are also included in the “nitride semiconductor”.

The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, regarding the specific configuration of each element such as a light emitting layer and a semiconductor layer included in the semiconductor light emitting device, those skilled in the art can implement the present invention in a similar manner by appropriately selecting from a known range, and obtain the same effects. As long as it is possible, it is within the scope of the present invention.
Moreover, what combined any two or more elements of each specific example in the technically possible range is also included in the scope of the present invention as long as the gist of the present invention is included.

  In addition, all semiconductor light-emitting elements that can be implemented by those skilled in the art based on the semiconductor light-emitting elements described above as embodiments of the present invention are included in the scope of the present invention as long as they include the gist of the present invention. Belonging to.

  In addition, in the category of the idea of the present invention, those skilled in the art can conceive of various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention. .

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  10 first semiconductor layer, 12 buffer layer, 14 gallium nitride layer, 15 protective film, 16 first stress applying layer, 17 gallium nitride layer (GaN layer), 18 n-type GaN layer, 20 second semiconductor layer, 22 second Stress application layer, 24 SLS layer, 30 light emitting layer, 32 well layer, 34 barrier layer, 40 support substrate, 50 silicon substrate, 60 SLS layer, 70 crystal growth layer, 70a nitride semiconductor crystal layer portion, 81 first electrode, 82 Second electrode, 89 Mask, 90 Reflective metal, 110, 120, 130, 140 Semiconductor light emitting device

FIG. 1 is a schematic cross-sectional view illustrating the configuration of a semiconductor light emitting element according to the embodiment.
As illustrated in FIG. 1, the semiconductor light emitting device 110 according to the embodiment includes a first semiconductor layer 10 having a first conductivity type, a second semiconductor layer 20 having a second conductivity type, a light emitting layer 30, and a first stress. And an application layer 16. The semiconductor light emitting element 110 is, for example, an LED element. The semiconductor light emitting device 110 may be a laser diode. Hereinafter, the case where the semiconductor light emitting element 110 is an LED will be described.

  The light emitting layer 30 includes, for example, a plurality of barrier layers 34 and a well layer 32 provided between the barrier layers 34. A plurality of well layers 32 may be provided. For example, the light emitting layer 30 has an MQW (Multiple Quantum Well) structure.

FIG. 2A and FIG. 2B are schematic cross-sectional views showing the stress generated in the laminated structure.
FIG. 2A illustrates the stress generated in the LED stacked structure of the semiconductor light emitting device 110 according to the embodiment. FIG. 2B illustrates the stress generated in the LED stack structure of the semiconductor light emitting device of the reference example.

  The lattice constant of the InGaN crystal layer that becomes the light emitting layer 30 is larger than the lattice constant of gallium nitride. Therefore, as indicated by arrows A3 and A4 shown in FIG. 2B, stress (tensile stress) is applied in the direction of pulling from the InGaN crystal layer to the gallium nitride crystal layer to which compressive stress from the sapphire crystal is applied. . On the other hand, as indicated by arrows A5 and A6 shown in FIG. 2B, the light emitting layer 30 receives compressive stress from the gallium nitride crystal layer. Such compressive stress and tensile stress are generated in the (0001) plane, in other words, in the a-axis direction, for example.

According to the knowledge of the present inventor, it is known that the compressive stress and tensile stress applied to the gallium nitride crystal layer remain even in the thin-film structure from which the sapphire substrate is removed. The same applies to a thin-film structure peeled from a silicon substrate described later with reference to FIG. Whether the stress applied to the gallium nitride crystal layer is a compressive stress or a tensile stress can be determined from a Raman spectrum. For example, the peak of the Raman spectrum in a gallium nitride crystal to which no stress is applied is about 568 cm ⁻¹ , but in the gallium nitride crystal to which a compressive stress is applied, a wave number smaller than 568 cm ⁻¹ , for example, about 567. a 8～565.5Cm ^-1, in the gallium nitride crystal stress is applied tensile, with larger wave numbers than 568cm ^-1, a value of up to about 570 cm ^-1.

  The equivalent lattice length of silicon used as a crystal substrate for growing a gallium nitride crystal layer is larger than the lattice constant of gallium nitride. Moreover, the thermal expansion coefficient of the silicon crystal is smaller than that of gallium nitride. Therefore, tensile stress remains in the gallium nitride crystal layer after the completion of crystal growth, as indicated by arrows A11 and A12 shown in FIG. Further, the nitride semiconductor crystal system formed on the silicon crystal is subjected to further tensile stress from the InGaN light emitting layer 30 as indicated by arrows A13 and A14 shown in FIG. On the other hand, as indicated by arrows A15 and A16 shown in FIG. 2A, the light emitting layer 30 receives compressive stress from the gallium nitride crystal layer. Such compressive stress and tensile stress are generated in the (0001) plane, in other words, in the a-axis direction, for example.

Next, an example of a manufacturing process of the semiconductor light emitting element 120 will be described.
FIGS. 4A to 5C are schematic cross-sectional views showing a process for manufacturing the semiconductor light emitting device structure shown in FIG.

Claims (9)

Forming a first stress applying layer on the crystal substrate;
A first semiconductor layer of a first conductivity type including a nitride semiconductor crystal and applied with compressive stress from the first stress application layer on the first stress application layer, and having a lattice constant equivalent to that of the crystal substrate Forming a first semiconductor layer of a first conductivity type smaller than a general lattice length or a first semiconductor layer of a first conductivity type having a thermal expansion coefficient larger than that of the crystal substrate;
On the first semiconductor layer, a light emitting layer including a nitride semiconductor crystal and having an average lattice constant larger than that of the first semiconductor layer is formed.
A second semiconductor layer of a second conductivity type including a nitride semiconductor crystal on the light emitting layer and having a lattice constant smaller than an equivalent lattice length of the crystal substrate, or a thermal expansion coefficient is greater than a thermal expansion coefficient of the crystal substrate. After forming a second semiconductor layer having a larger second conductivity type,
A method of manufacturing a semiconductor light emitting device, wherein the crystal substrate is removed while leaving at least a part of the first stress application layer. 2. The method of manufacturing a semiconductor light emitting element according to claim 1, wherein the first stress application layer includes Al _x1 Ga _1-x1 N (0 <x1 ≦ 1). Forming a plurality of first stress applying layers;
3. The method for manufacturing a semiconductor light emitting element according to claim 1, wherein the step of removing the crystal substrate includes a step of removing the crystal substrate while leaving at least one of the plurality of first stress applying layers.   4. The method for manufacturing a semiconductor light emitting element according to claim 1, further comprising forming a second stress applying layer for applying a compressive stress to the second semiconductor layer on the second semiconductor layer. 5. 5. The method of manufacturing a semiconductor light emitting element according to claim 4, wherein the second stress application layer contains Al _x2 Ga _1-x2 N (0 <x2 <1).   The conductive support substrate that supports the first stress application layer, the first semiconductor layer, the light emitting layer, and the second semiconductor layer is further formed on the second stress application layer. The manufacturing method of the semiconductor light-emitting device of description.   The method for manufacturing a semiconductor light emitting element according to claim 1, further comprising forming irregularities on the opposite side of the first stress applying layer from the first semiconductor layer after removing the crystal substrate. Forming three first stress applying layers;
Of the three first stress applying layers, the uneven side layer is divided by the uneven surface processing,
8. The method of manufacturing a semiconductor light emitting element according to claim 7, wherein two other layers different from the layer on the concave and convex side of the three first stress applying layers are left as continuous films below the concave and convex portions of the concave and convex.   The method for manufacturing a semiconductor light emitting element according to claim 1, further comprising forming a first electrode that penetrates the first stress application layer and is electrically connected to the first semiconductor layer.