JP4593890B2 - Manufacturing method of semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to method for producing a single-crystal sapphire substrate for semiconductor device, especially its semiconductor light emitting element is a blue LED, UV LED, a method for manufacturing a GaN-based semiconductor crystal containing an LED element, such as a white LED.
[0002]
[Prior art]
In an LED, how efficiently the light generated in the light emitting layer can be extracted to the outside (so-called light extraction efficiency) is an important problem. Therefore, conventionally, the upper electrode is a transparent electrode so that the light directed upward from the light emitting layer does not become an obstacle to the outside, or the reflective layer is provided upward for the light directed downward from the light emitting layer. Various measures are taken, such as returning.
[0003]
For light emitted in the vertical direction from the light emitting layer, it is possible to improve the light extraction efficiency to the outside world by providing a transparent electrode or a reflective layer as described above. Of the light generated in the direction, the light that reaches the side wall within the total reflection angle defined by the refractive index difference can be emitted to the outside, but many other lights are repeatedly reflected on the side wall, for example. They are only absorbed and attenuated in the device and disappear. Such lateral light is confined by the upper and lower cladding layers or the substrate (sapphire substrate) and the upper cladding layer, or the substrate and the upper electrode (and coating material outside the device, etc.) and propagates in the lateral direction. It is. The light propagating in the lateral direction occupies most of the total amount of light generated in the light emitting layer, and may reach 60% of the total.
[0004]
As a means for efficiently taking out the light propagating in the lateral direction to the outside, the surface of the first crystal layer for growing the semiconductor layer is processed to have unevenness, and a refractive index different from that of the crystal layer is formed thereon. An element structure in which a second crystal layer made of a semiconductor material having a semiconductor layer including a light-emitting layer is grown on the second crystal layer through the buffer layer or directly, while embedding the unevenness; A semiconductor light emitting device has been proposed (see Patent Document 1 and Non-Patent Document 1).
[0005]
For the same purpose, a semiconductor light emitting device is also proposed in which a light scattering layer that scatters light incident on the substrate from the light emitting region layer is provided to reduce the ratio of total reflection of light incident on the substrate from the light emitting region layer. (See Patent Document 2).
[0006]
In addition, as a method of creating a high-efficiency white LED by effectively utilizing the light that has propagated in the lateral direction by the above method and emitted from the side surface of the light-emitting element, the reflector part is made of a transparent resin by surrounding the semiconductor light-emitting element. And the method of disperse | distributing the fluorescent substance which is excited by the light emission from a semiconductor light-emitting element and light-emits is proposed in the reflector part (refer patent document 3).
[0007]
[Patent Document 1]
JP 2002-280611 A
[0008]
[Patent Document 2]
JP2003-60227
[0009]
[Patent Document 3]
JP2003-142737
[0010]
[Non-Patent Document 1]
Nikkei Electronics March 31, 2003 issue p128-P133
[0011]
[Problems to be solved by the invention]
In the method for forming the unevenness, a photoresist is formed on the main surface of the sapphire substrate, an opening is formed in the photoresist by photolithography, and the underlying sapphire substrate body is selectively etched using the photoresist as a mask. After the formation, the photoresist is removed. This etching is mainly performed by dry etching such as ion beam etching or reactive ion etching.
[0012]
However, ion beam etching or reactive ion etching has a problem that the processing speed is very slow and the number of sheets that can be processed at one time is limited, and is not suitable for mass production. In addition, since dry etching is performed using the mask, the mask itself is also etched during the etching, so that the edge of the mask is irregularly undulated, and the edge of the unevenness formed by dry etching also results in undulation. There was a problem of adversely affecting the epitaxial growth of nitride semiconductors.
[0013]
In order to solve the above problems, an object of the present invention is to provide a sapphire substrate for a semiconductor light-emitting element in which irregularities are efficiently formed on a main surface of a sapphire substrate by a method suitable for mass production, and a method for manufacturing the same.
[0014]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a single crystal sapphire substrate in which a plurality of pyramid-shaped etch pits are formed on at least one main surface, and the etch pits on the one main surface of the single crystal sapphire substrate. A method of manufacturing a semiconductor light-emitting element having a plurality of semiconductor layers including a light-emitting layer, wherein a single crystal is formed using hot phosphoric acid or a mixed acid of hot phosphoric acid and hot sulfuric acid or hot molten potassium hydroxide. Provided is a method for manufacturing a semiconductor light emitting device, comprising the step of wet etching a sapphire substrate to form a plurality of pyramid-shaped etch pits on at least one main surface of the single crystal sapphire substrate.
[0015]
In addition, prior to the wet etching, it is preferable to include a step of applying heat or pressure to the single crystal sapphire substrate to induce crystal defects in the single crystal sapphire substrate.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment using the LED using a GaN-based material (GaN-based LED) will be described as an example.
[0017]
As shown in FIG. 1, a single crystal sapphire substrate 1 used in the manufacturing method of the present invention has a plurality of pyramidal etch pits 1b formed on a main surface 1a. Such a single crystal sapphire substrate 1 is obtained by first pulling up a sapphire material whose plane orientation and axial orientation are determined by the EFG method, and then subjecting this material to appropriate cutting, grinding, polishing, and cleaning, and a nitride semiconductor. When the substrate for forming a film is manufactured and subsequently the substrate is subjected to wet etching treatment in hot phosphoric acid or the like, the etch pit 1b can be formed depending on conditions. Since this etching process can process a large number of sheets at a time by using an appropriate jig, it is very productive and suitable for mass production.
[0018]
In the conventional etching method, since the mask is used for dry etching, not only the productivity is poor, but also the mask itself is etched during the etching, so that the edges of the mask are irregularly waved and formed by dry etching. As a result, the edges of the irregularities also wavy, which adversely affects the subsequent epitaxial growth of the nitride semiconductor. On the other hand, the etch pit 1b used in the manufacturing method of the present invention is a recess formed by the original nature of the crystal by wet etching, and by using this etch pit 1b, the end face as in the case of dry etching is used. There is no problem of waving.
[0019]
The shape of the etch pit 1b formed at this time is characterized by a pyramid shape, and is usually a triangular pyramid although it varies depending on conditions. This pyramid shape is effective for increasing the light extraction efficiency of a light emitting element such as an LED manufactured using the single crystal sapphire substrate 1.
[0020]
It is preferable to adjust the conditions of temperature and time so that the size of the etch pit 1b is 300 μm or less on one side. This is because the size of the LED element is usually about 300 μm × 300 μm, and it is necessary to control the size of the etch pit to be at least smaller than this size in order to efficiently extract the light in the lateral direction. . Here, the preferable range of the depth of the etch pit is preferably 250 μm or less from a geometrical viewpoint, and in the LED manufacturing process, generally the substrate is back-ground before the dicing process to reduce the thickness. Therefore, the depth of the etch pit is preferably 250 μm or less.
[0021]
Similarly, the number of etch pits 1b is preferably 10 ³ / cm ² or more and 10 ¹⁰ / cm ² or less in order to efficiently extract light in the lateral direction. In order to control the number of etch pits, the single crystal sapphire substrate 1 may be subjected to an etching process after intentionally introducing crystal defects by applying heat or pressure. For example, after applying 20 atmospheres at 1200 ° C. to 1400 ° C., a treatment such as further heat treatment may be performed.
[0022]
Further, when the etch pit 1b is viewed from a direction perpendicular to the main surface 1a, at least one side of the bottom is parallel or perpendicular to the A axis of sapphire, or parallel or perpendicular to the M axis, so that the substrate This is effective for reducing defects such as GaN grown on the substrate. This can be achieved by etching the sapphire substrate 1 under appropriate conditions.
[0023]
The number and size of the etch pits 1b are determined depending on the temperature and processing time of hot phosphoric acid or the like. The direction of the etch pit 1b is determined by the crystal orientation and the axial orientation of the single crystal sapphire substrate 1. In order to make the direction and shape of the etch pit 1b constant, the main surface 1a is within C surface ± 2 °, A surface ± 2 °, R surface ± 2 °, M surface ± 2 ° or from the M surface. It is necessary to satisfy any one of 30 ° ± 2 °.
[0024]
In the above description, hot phosphoric acid is used for wet etching, but the etching solution is not limited to this, and a mixed acid of hot phosphoric acid and hot sulfuric acid may be used, and other chemicals such as hot molten potassium hydroxide may be used. May be.
[0025]
The etching rate of sapphire with hot phosphoric acid was as shown in FIG. 3 at each temperature. In the present invention, the use of hot phosphoric acid, a mixed acid of hot phosphoric acid and hot sulfuric acid, or hot molten potassium hydroxide allows the etching rate to be accurately controlled depending on the temperature as shown in FIG. This is because it is most suitable for production.
[0026]
Further, the use of the sapphire substrate 1 produced by the EFG method in the present invention is suitable for the effective use of etch pits because the EFG method can increase the growth speed among the sapphire production methods. This is because it is possible to create conditions.
[0027]
As described above, according to the manufacturing method of the present invention, etch pits are performed in a relatively simple process of performing wet etching with hot phosphoric acid at 200 ° C. to 400 ° C. without forming a special mask on the sapphire substrate. The sapphire substrate 1 having 1b can be mass-produced at a relatively low cost. That is, since a large number of sheets can be processed at a time by using an appropriate jig, the productivity is very high as compared with the conventional reactive ion etching method, which is suitable for mass production.
[0028]
Next, a semiconductor light emitting device manufactured by a manufacturing method using the sapphire substrate 1 provided with the etch pit 1b of the present invention will be described.
[0029]
When a nitride semiconductor is epitaxially grown on the main surface 1a of the sapphire substrate 1, the growth of the nitride semiconductor in the vertical direction and the growth in the horizontal direction are combined to form a nitride semiconductor film having a flat surface. A light emitting element is manufactured using the substrate on which the nitride semiconductor is formed. At this time, the pyramid-shaped etch pit 1b may be completely filled with a nitride semiconductor, or there may be a cavity between the etch pit and the nitride semiconductor, but preferably it is completely filled. Is good.
[0030]
An example of the LED thus manufactured is shown in FIG.
[0031]
An n-type GaN contact layer 3, an n-type AlGaN cladding layer 4, and a GaN-based semiconductor light emitting layer (MQW structure) 5 are formed on the main surface 1 a on which the etch pit 1 b of the single crystal sapphire substrate 1 is formed via an AlGaN low-temperature buffer layer 2. , A p-type AlGaN cladding layer 6 and a p-type GaN contact layer 7 are formed, an upper electrode (usually a p-type electrode) 8 is formed thereon, and a lower electrode (usually an n-type electrode is disposed on the n-type GaN contact layer 3. ) 9 is formed.
[0032]
The main surface 1a having the etch pits 1b forms a light scattering layer, and thus, the light traveling downward from the light emitted from the GaN-based semiconductor light emitting layer 5 is scattered by the light scattering layer on the main surface 1a. Light can be extracted in the lateral direction indicated by the arrow 2. Thereby, the light emitted from the GaN-based semiconductor light emitting layer 5 is not repeatedly attenuated by reflection in the GaN layer, and the light extraction efficiency of the entire LED can be improved.
[0033]
In addition, it is preferable that the AlGaN low-temperature buffer layer 2 or the like as the second crystal layer grows from the main surface 1b of the single crystal sapphire substrate 1 while substantially forming a facet structure.
[0034]
Further, the difference between the refractive index of the single crystal sapphire substrate 1 and the refractive index of the AlGaN low-temperature buffer layer 2 as the second crystal layer in the wavelength of light emitted from the GaN-based semiconductor light emitting layer 5 is 0.05 or more. It is preferable that
[0035]
The buffer layer may be either GaN-based or AlN-based, and the semiconductor crystal layer formed thereon is GaN-based.
[0036]
As still another embodiment, although not shown, the first GaN-based semiconductor crystal is grown on the main surface 1a of the single crystal sapphire substrate 1 so as to cover the etch pit 1b so as to form unevenness. A second GaN-based semiconductor crystal having a refractive index different from that of the first GaN-based semiconductor crystal is grown, covering at least a part of the first GaN-based semiconductor crystal, and further grown until the third GaN-based semiconductor crystal flattens the unevenness. In addition, an element structure in which a semiconductor crystal layer including a light emitting layer is stacked thereon can also be used.
[0037]
Alternatively, on the main surface 1a of the single crystal sapphire substrate 1, the first GaN-based semiconductor crystal grows so as to form irregularities covering the etch pits 1b, and at least the convex portions of the irregularities are covered in a film shape. An element structure in which a GaN-based semiconductor crystal is grown, and a third GaN-based semiconductor crystal is grown until the concavo-convex surface is flattened and a semiconductor crystal layer including a light emitting layer is stacked thereon. The second GaN-based semiconductor crystal may have a multilayer structure.
[0038]
Normally, this semiconductor light emitting element is fabricated on the sapphire substrate 1 having the etch pits 1b, and the semiconductor light emitting element is cut together with the sapphire substrate 1 by cutting such as dicing, and functions as a semiconductor light emitting element. However, in some cases, a method of separating the semiconductor light emitting element portion from the sapphire substrate 1 to obtain a more efficient LED has been proposed. Even in such a case, the sapphire substrate 1 having the etch pit 1b has a structure having a cavity between the etch pit 1b and the nitride semiconductor film, so that the semiconductor light emitting element can be easily peeled from the sapphire substrate. It has the effect of being.
[0039]
Furthermore, the sapphire substrate 1 having the etch pits 1b used in the manufacturing method of the present invention has a low dislocation nitride semiconductor layer on the sapphire substrate 1 having the etch pits 1b for uses other than the manufacture of the semiconductor light emitting device. After the formation of, a low dislocation nitride semiconductor is peeled from the sapphire substrate to produce an independent nitride semiconductor substrate.
[0040]
Furthermore, the sapphire substrate 1 having the etch pit 1b used in the manufacturing method of the present invention can be used not only as a substrate for a semiconductor light emitting element but also as a substrate for an electronic device using a nitride semiconductor.
[0041]
【Example】
Example 1
In this embodiment, a method for manufacturing a sapphire substrate having etch pits for a semiconductor element will be described.
[0042]
First, a sapphire material with a fixed plane orientation and axial orientation was pulled up by the EFG method. In the present embodiment, the main surface 1a of the sapphire substrate 1 is made to be the C-plane, but the surface orientation of the main surface 1a is not limited to the C-plane, but is rotated by 30 degrees from the A-plane, M-plane, R-plane, and M-plane. It can also be applied to surfaces that have been cut.
Further, it may be off-angled within ± 2 ° from these surfaces. Various pulling methods can be used, and a sapphire substrate lifted by the EFG method is particularly suitable for the present invention.
[0043]
Next, this material was appropriately cut, ground, polished, and washed to produce a substrate for forming a nitride semiconductor film. Subsequently, when the substrate was etched in hot phosphoric acid at 300 ° C. for 30 minutes, a large number of etch pits 1b were formed on the main surface 1a of the substrate. At this time, the shape of the etch pit 1b formed on the main surface 1a of the sapphire substrate 1 was a triangular pyramid.
[0044]
At this time, the temperature and time conditions were adjusted so that the size of the etch pits was 300 μm or less on one side. This is because the size of the LED element is usually about 300 μm × 300 μm, and it is necessary to control the size of the etch pit to be at least smaller than this size in order to efficiently extract the light in the lateral direction. . Similarly, the number of etch pits was set to 10 ³ pieces / cm ² or more and 10 ¹⁰ pieces / cm ² or less in order to efficiently extract light in the lateral direction.
[0045]
In order to control the number of etch pits, an etching process may be performed after intentionally introducing crystal defects by applying heat or pressure to the sapphire substrate.
For example, after applying 20 atmospheres at 1200 ° C. to 1400 ° C., a treatment such as further heat treatment may be performed.
[0046]
In addition, it is effective for reducing defects of gallium nitride grown on the substrate that at least one side of the etch pit viewed from a direction perpendicular to the main surface is parallel or perpendicular to the A axis. However, this could be achieved by etching the sapphire substrate under appropriate conditions.
[0047]
In this manufacturing process, it is not necessary to form a special mask on the sapphire substrate, and the substrate with etch pits is relatively inexpensive with a relatively simple process of performing wet etching with hot phosphoric acid at 200 ° C. to 400 ° C. Could be mass-produced. That is, since a large number of sheets can be processed at a time by using an appropriate jig, the productivity is very high as compared with the conventional reactive ion etching method, which is suitable for mass production.
[0048]
Example 2
In this example, as shown in FIG. 2, the etched pits 1b of the sapphire substrate 1 were buried by a facet growth method to form a concavo-convex light scattering surface, and a GaN-based LED was manufactured.
[0049]
First, etch pits were formed on the C-plane sapphire substrate by the process of Example 1. After cleaning the substrate, the substrate was mounted on a MOVPE apparatus, and the temperature was raised to 1100 ° C. in a nitrogen gas main component atmosphere to perform thermal cleaning. The temperature was lowered to 500 ° C., trimethylgallium (hereinafter referred to as TMG) was flown as the Group 3 raw material of the periodic table, and ammonia was flowed as the N raw material to grow the AlGaN low temperature buffer layer 2 having a thickness of 30 nm.
[0050]
Subsequently, the temperature was raised to 1000 ° C., and TMG and ammonia were flown as raw materials and silane was flowed as a dopant to grow an n-type GaN layer (contact layer) 3. The growth of the GaN layer at this time is a growth in which the entire surface is formed without forming a cavity in the concave portion after generating from a top surface of the convex portion and a bottom surface of the concave portion as a ridge-like crystal having a mountain-shaped cross section and including a facet surface. there were.
[0051]
In facet growth, when the C-plane of the GaN crystal is completely extinguished and the top is pointed and convex, the growth conditions are switched to conditions in which lateral growth becomes dominant (e.g., raising the growth temperature), and sapphire A GaN crystal was grown from the upper surface of the substrate to a thickness of 5 μm. In order to obtain a buried layer having a flat upper surface, a thick film growth of 5 μm was necessary.
[0052]
Subsequently, an n-type AlGaN cladding layer 4, an InGaN light-emitting layer (MQW structure) 5, a p-type AlGaN cladding layer 6, and a p-type GaN contact layer 7 are formed in this order to obtain an ultraviolet LED epi-substrate with an emission wavelength of 370 nm, Etching for exposing the n-type contact layer, electrode (8, 9) formation, and element isolation were performed to obtain an LED element.
[0053]
【The invention's effect】
As described above, according to the present invention, irregularities can be produced on the main surface of a sapphire substrate by a method suitable for mass production efficiently. Further, by using etch pits that are formed by wet etching and depending on the nature of the crystal, it is possible to form irregularities that do not have the problem that the end face is wavy. Furthermore, since the LED produced using the sapphire substrate produced by this method can efficiently extract light traveling in the lateral direction, an LED having higher external quantum efficiency than the conventional one can be provided.
[0054]
[Brief description of the drawings]
1A is a perspective view of a single crystal sapphire substrate used in the manufacturing method of the present invention, FIG. 1B is an enlarged view of a portion A in FIG. 1A, and FIG. 1C is a sectional view of the portion A;
FIG. 2 is a cross-sectional view showing a configuration of a semiconductor light emitting device manufactured by the manufacturing method of the present invention.
FIG. 3 is a graph showing the temperature dependence of the etching rate of sapphire.
[Explanation of symbols]
1: Sapphire substrate 1a: Main surface 1b: Etch pit 2: AlGaN low-temperature buffer layer 3: n-type GaN contact layer 4: n-type AlGaN cladding layer 5: GaN-based semiconductor light emitting layer (MQW structure) 6: p-type AlGaN cladding layer 7: p-type GaN contact layer 8: upper electrode 9: lower electrode

Claims (2)

A plurality of semiconductors including a single crystal sapphire substrate in which a plurality of pyramid-shaped etch pits are formed on at least one main surface and a light emitting layer stacked on the etch pits on the one main surface of the single crystal sapphire substrate A method of manufacturing a semiconductor light emitting device having a layer ,
A single crystal sapphire substrate is wet etched using hot phosphoric acid, a mixed acid of hot phosphoric acid and hot sulfuric acid, or hot molten potassium hydroxide, and at least one main surface of the single crystal sapphire substrate has a plurality of pyramid-shaped etch pits. The manufacturing method of the semiconductor light-emitting device characterized by including the process of forming. Prior to the U E Tsu preparative etching, the heat or pressure on the single crystal sapphire substrate addition, a method of manufacturing a semiconductor light emitting device according to claim 1, further comprising a step of inducing crystal defects in the single crystal sapphire substrate .

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