JP4281569B2 - Method for manufacturing epitaxial wafer for semiconductor light emitting device - Google Patents

Description

  The present invention relates to a method for manufacturing an epitaxial wafer for a semiconductor light emitting device, and more particularly, an epitaxial wafer for a semiconductor light emitting device capable of manufacturing a current confinement type light emitting diode (LED) having a current blocking layer with a high manufacturing yield. It relates to the manufacturing method.

  AlGaInP-based semiconductors are direct transition semiconductors having the largest band gap among III-V group compound semiconductors excluding nitride semiconductors, and are extremely bright in the emission band of 560 nm to 660 nm. However, research and development are actively conducted. However, as a recent trend, AlGaInP-based light emitting diodes are in the midst of price reduction competition, and manufacturers of each company are striving to reduce the manufacturing cost of light emitting diodes and improve the throughput.

  Here, the manufacturing cost of manufacturing the AlGaInP-based light emitting diode is mainly the cost of forming the current diffusion layer. One factor for this is that it is necessary to increase the thickness of the current diffusion layer in order to obtain high luminance. In order to solve this problem, it is effective to use a material having a resistivity as low as possible as the material for the current diffusion layer. The materials for the current diffusion layer mainly include GaP and AlGaAs. However, even if these low-resistivity materials are used, in order to improve the current dispersion effect and increase the luminance and the operating voltage of the light emitting diode, the thickness of the current diffusion layer is about 8 μm. It was necessary to do it above. Then, the raw material cost required for the growth of the current spreading layer is increased, and further, the time required for the growth deteriorates the throughput, and the manufacturing cost of the AlGaInP light emitting diode is increased overall.

  As a solution to this problem, ITO, which is a metal oxide transparent conductive film, can be used as a method for obtaining a sufficient current dispersion effect with a very low carrier thickness instead of a semiconductor current diffusion layer. A method using a current diffusion layer made of a film has been developed.

  As a method for achieving sufficient characteristics as an LED, an ITO film can be obtained by using a p-type GaAs contact layer as a semiconductor top layer, that is, a semiconductor layer between a current diffusion layer made of an ITO film and a cladding layer. A technique for reducing the contact resistance with a current diffusion layer made of is developed. With such a technique, the transparent conductive film of the metal oxide can be used for an LED without deteriorating the LED characteristics. For this reason, since the film thickness of the current diffusion layer made of metal oxide can be reduced, it greatly contributed to cost reduction.

Furthermore, as another measure for obtaining high brightness, a current confining type light emitting diode having a current blocking layer has been proposed (see, for example, Patent Document 1). Further, for example, in a light emitting diode disclosed in Japanese Patent Application Laid-Open No. 2001-85742 (see Patent Document 2), a current blocking layer made of AlInP having a conductivity type opposite to that of the upper cladding layer is provided as a current blocking layer.
JP 2002-64219 A JP 2001-85742 A

  As described above, the manufacturing cost for manufacturing the AlGaInP-based light emitting diode is mainly the cost for forming the current diffusion layer. This is because the current diffusion layer has to be grown thick in order to perform current injection into the light emitting portion of the light emitting diode as uniformly as possible. In addition, since it takes a long time to grow thickly, which causes a deterioration in throughput, it occupies most of the manufacturing cost of the light-emitting diode as a result. Therefore, a light emitting diode using an ITO film as a current diffusion layer has been proposed.

  However, in general, when a current diffusion layer made of an ITO film is provided, the surface area of the transparent layer with respect to the emission wavelength is reduced by reducing the thickness of the current diffusion layer as compared with a conventional light emitting diode. That is, the light emitting area is reduced, and as a result, there is a problem that the luminance is slightly lower than that of the conventional light emitting diode.

  In order to solve this problem, in a light emitting diode using an ITO film as a current diffusion layer, it is effective to make the light emitting diode provided with a current blocking layer for the purpose of further improving the luminance. However, the provision of a current blocking layer naturally increases the manufacturing cost as compared with a light emitting diode using a normal ITO film as a current diffusion layer.

  Therefore, the present inventors have not yet publicly known, but in order to reduce the cost for forming the current blocking layer as much as possible, the current confinement type light-emitting diode with an ITO film using a photoresist film as the current blocking layer is first described. Proposed as a wish. Since the photoresist film is an insulator as is well known, it can be applied to a current blocking layer.

  The light emitting diode of Patent Document 2 also includes a current block layer made of AlInP having a conductivity type opposite to that of the upper clad layer in the current block layer, which is effective for increasing the brightness. In this case, the current block layer is formed. Therefore, it is necessary to perform an etching process in addition to patterning with a photoresist. Accordingly, the manufacturing cost is naturally higher than that of the current confinement type light emitting diode using the photoresist as the current blocking layer.

  However, even in the light emitting diode using the above-described photoresist for the current blocking layer, there is a problem that the manufacturing yield is deteriorated. That is, an ITO film peeling phenomenon occurs during a chip forming process of the epitaxial wafer for light emitting diodes, that is, a dicing process and a wire bonding process to the light emitting diode chip. The production yield of the light emitting diode is extremely deteriorated due to the peeling phenomenon of the ITO film, and as a result, it is difficult to reduce the production cost of the current confined light emitting diode with the ITO film.

  Accordingly, an object of the present invention relates to a method of manufacturing a current confinement type light emitting diode which solves the above problems, uses an ITO film as a current diffusion layer, and has a current blocking layer made of a photoresist, and relates to the peeling phenomenon of the ITO film It is an object of the present invention to provide an epitaxial wafer manufacturing method for a semiconductor light emitting device that has a very high manufacturing yield, high brightness, and low cost.

  In order to achieve the above object, the present invention is configured as follows.

The method for manufacturing an epitaxial wafer for a semiconductor light-emitting device according to the invention of claim 1 includes a light-emitting portion having at least an active layer sandwiched between an n-type cladding layer and a p-type cladding layer on a substrate, and a conductivity determining impurity. In the method for manufacturing an epitaxial wafer for a semiconductor light emitting device, in which an ohmic contact layer, a current blocking layer made of a photoresist film, and a transparent conductive film made of an ITO film are sequentially formed, the current block is formed before forming the transparent conductive film. The layer is heat-treated to suppress swelling. Here, the ohmic contact layer containing the conductivity determining impurity means an ohmic contact layer containing 1 × 10 ¹⁹ / cm ³ or more, for example, zinc (Zn) as the conductivity determining impurity.

  According to a second aspect of the present invention, in the method for manufacturing an epitaxial wafer for a semiconductor light emitting device according to the first aspect, the current blocking layer is a positive photoresist film.

According to a third aspect of the present invention, there is provided a method for producing an epitaxial wafer for a semiconductor light emitting device, comprising: a light emitting portion having at least an active layer sandwiched between an n-type cladding layer and a p-type cladding layer; A step of sequentially growing an ohmic contact layer containing a conductivity determining impurity of × 10 ¹⁹ / cm ³ or more, a step of forming a photoresist film having a current blocking effect on the ohmic contact layer, and the photoresist film Forming a current blocking layer by patterning the substrate into a desired shape, forming a transparent conductive film made of an ITO film on the current blocking layer, and forming a surface electrode on the transparent conductive film In the method of manufacturing an epitaxial wafer for a semiconductor light emitting device, comprising: an alloying step of heat-treating the electrode at a desired temperature to form an alloy. Before forming the film, the epitaxial wafer for semiconductor light emitting device is heat-treated in a desired temperature and atmosphere to include a heat treatment step for suppressing swelling of the photoresist film.

  According to a fourth aspect of the present invention, in the method for manufacturing an epitaxial wafer for a semiconductor light emitting device according to the third aspect, the temperature of the heat treatment step (heat treatment temperature) is equal to or equal to the temperature of the alloy step (alloy temperature). It is characterized by the above temperature.

  According to a fifth aspect of the present invention, in the method for producing an epitaxial wafer for a semiconductor light emitting device according to the third or fourth aspect, the atmosphere of the heat treatment step (heat treatment atmosphere) is an inert gas having an oxygen concentration of less than 1%. Or a vacuum.

  According to a sixth aspect of the present invention, in the method for manufacturing an epitaxial wafer for a semiconductor light emitting device according to any one of the third to fifth aspects, the current blocking layer is a positive photoresist film.

  The invention according to claim 7 is the method for manufacturing an epitaxial wafer for a semiconductor light emitting device according to any one of claims 3 to 6, wherein a position corresponding to a central portion of the current blocking layer is directly below a position corresponding to a central portion of the surface electrode. It is formed to come to.

  The invention of claim 8 is the method for producing an epitaxial wafer for a semiconductor light emitting device according to any one of claims 3 to 7, wherein an area on the surface side of the current blocking layer is equal to an area on the surface side of the surface electrode or The area is larger than that.

The invention of claim 9 is the method for producing an epitaxial wafer for a semiconductor light emitting device according to any one of claims 1 to 8, wherein the substrate is gallium arsenide (GaAs), germanium (Ge), silicon (Si), or silicon. (Si) is made of any one of metals having higher thermal conductivity, the light emitting portion is made of any of GaInP, AlInP, and AlGaInP, and the ohmic contact layer is made of Al _X Ga _1-X As (0 ≦ X ≦ 0.3), and the film thickness of the ohmic contact layer is 1 nm or more and 50 nm or less.

  According to a tenth aspect of the present invention, in the method for manufacturing an epitaxial wafer for a semiconductor light emitting device according to any one of the first to ninth aspects, the film thickness of the transparent conductive film is 200 nm or more and 500 nm or less.

  The invention of claim 11 is the method for producing an epitaxial wafer for a semiconductor light emitting device according to any one of claims 3 to 10, wherein the temperature of the alloy process is 300 ° C. or more and 500 ° C. or less.

<Key points of the invention>
As a result of diligent research efforts, the present inventor has swelled at the interface between the ITO film and the current blocking layer due to the generation of organic gas from the photoresist film that is the current blocking layer. Found out that it has occurred. Furthermore, it has also been found that this swelling can be suppressed by heat-treating the current blocking layer under optimum conditions before the ITO film is formed. The present invention has been made based on the knowledge of these inventors, and is an effective manufacturing method for improving the manufacturing yield of light-emitting diodes.

  The epitaxial wafer for a semiconductor light emitting device of the present invention uses an ITO film, which is a transparent conductive film, as a current diffusion layer, and further includes a current blocking layer between the light emitting portion and the ITO film. Since the resist film is used, a high-luminance light-emitting diode that is excellent in productivity and can be manufactured at a low manufacturing cost can be obtained. This is because a conventional method of forming a current blocking layer is a semiconductor layer mainly formed by the MOVPE method, and a current diffusion layer formed on the current blocking layer is again formed by a semiconductor layer by the MOVPE method. Depends on that. In other words, according to the conventional method shown in this specification, after the first epitaxial growth, patterning using a photoresist film on the epitaxial wafer and further an etching process for forming a current blocking layer are required. However, in the present invention, the process is simply completed by patterning with a photoresist.

  Due to the characteristics of the photoresist film used for the current blocking layer, it is preferable to use a positive photoresist film in order not to make a space on the surface of the epitaxial layer and to prevent disconnection.

  The method for producing an epitaxial wafer for a semiconductor light emitting device according to the present invention comprises a light emitting part having at least an active layer sandwiched between an n-type cladding layer and a p-type cladding layer on a substrate, and an ohmic containing a conductivity-determining impurity at a high concentration. When sequentially forming a contact layer, a current blocking layer made of a photoresist film, and a transparent conductive film made of an ITO film, the current blocking layer is heat treated to suppress swelling before forming the transparent conductive film. is there. According to the present invention, by suppressing the swelling of the resist film by heat treatment in advance, the occurrence of swelling at the interface between the ITO film and the current blocking layer is suppressed for the transparent conductive film made of the ITO film formed thereafter, The peeling phenomenon of the transparent conductive film made of the ITO film during the dicing process or the wire bonding process can be prevented.

  That is, by using the method for manufacturing an epitaxial wafer for a semiconductor light emitting device according to the present invention, the manufacturing yield in the wire bonding process when manufacturing a high-intensity light emitting diode using a photoresist film as a current blocking layer is epoch-making. It became possible to improve. It was found that the main cause of the ITO film peeling phenomenon was the occurrence of swelling at the interface between the ITO film and the current blocking layer due to the generation of organic gas from the photoresist that is the current blocking layer. Therefore, this is based on the finding of a method of heat-treating the current blocking layer under the optimum conditions before the ITO film is formed.

  Hereinafter, embodiments of the present invention will be described mainly with reference to examples.

  In the method for manufacturing an epitaxial wafer for a semiconductor light emitting device according to the present invention, a light emitting portion having at least an active layer 5 sandwiched between an n-type cladding layer 4 and a p-type cladding layer 6 on a substrate 1 and a highly conductive type determining impurity. An ohmic contact layer 7 containing, a current blocking layer 11 made of a resist film, and a transparent conductive film 8 made of an ITO film are sequentially formed. Before the ITO film as the transparent conductive film 8 is formed, the resist film of the current blocking layer 11 is heat-treated in a desired temperature and atmosphere to suppress the swelling of the resist film due to the organic gas from the resist film. In addition, the formation method of the ITO film | membrane which is the transparent conductive film 8 is vacuum evaporation, and can reduce manufacturing cost.

<Comparative example: 350 ° C. heat treatment in air>
As a comparative example, a red light emitting diode having an emission wavelength near 630 nm and having the structure shown in FIG. 1 was manufactured. The production process is as follows.

On the n-type GaAs substrate 1, an n-type GaAs buffer layer 2, an n-type Bragg reflection layer 3, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 4, an undoped (Al _0.15 Ga _0.85 ) _0.5 In _{A 0.5} P active layer 5, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 6 and a p-type GaAs contact layer 7 were sequentially grown to produce an epitaxial wafer for a light emitting diode. Incidentally, the n-type Bragg reflective layer has a laminated structure composed of an n-type AlInP layer (about 50 nm) and an n-type GaAs layer (about 40 nm), and the number of pairs is 10 pairs.

  Next, a method for forming the current blocking layer 11 will be described. After the light emitting diode epitaxial wafer was unloaded from the MOVPE apparatus, a positive photoresist was applied to the entire surface of the light emitting diode epitaxial wafer using a spin coater. At this time, the applied positive photoresist was ZWD-6200, and the coating conditions by the spin coater were set at a rotation speed of 7000 rpm and a rotation time of 60 sec.

  After applying the positive photoresist, exposure was performed using a mask aligner so as to form a circular dot with a diameter of 125 μm, and then development was performed, thereby patterning the above shape (circular dot with a diameter of 125 μm).

  After patterning, it was washed with water and dried, and then heat-treated at 350 ° C. for 5 minutes in the air. Further, when the film thickness of the positive photoresist film produced at this time was measured with a step gauge, it was about 0.18 μm. In this way, a current blocking layer 11 made of a positive photoresist film was formed.

After the heat treatment, a transparent conductive film (current diffusion layer) 8 made of an ITO film having a thickness of 300 nm was formed on the patterned positive photoresist film side by a vacuum deposition method. At this time, the glass substrate set in the same batch was taken out, cut into a size capable of Hall measurement, and the electrical properties of the ITO film were evaluated. The carrier concentration was 1.21 × 10 ²¹ / cm ³ , movement The temperature was 21.2 cm ² / Vs, and the resistivity was 2.29 × 10 ⁻⁴ · Ωcm.

  Then, on the upper surface of the epitaxial wafer for light emitting diodes, a circular p-side electrode (surface electrode) 9 having a diameter of 125 μm is deposited in a matrix so as to be positioned almost immediately above the positive photoresist film formed in the previous step. Formed with. For the p-side electrode 9, nickel and gold were deposited in the order of 20 nm and 500 nm, respectively. Further, an n-side electrode (back surface electrode) 10 was formed on the entire bottom surface of the epitaxial wafer. For the n-side electrode 10, gold / germanium alloy, nickel, and gold were vapor-deposited in the order of 60 nm, 10 nm, and 500 nm, respectively, and then an alloying process that was alloying the electrodes was performed at 430 ° C. for 5 minutes in a nitrogen gas atmosphere. .

  Thereafter, the epitaxial wafer for the light emitting diode is processed into a chip shape having a chip size of 300 μm square by dicing or the like, and only 20 of the chips processed into the chip shape are die bonded and wire bonded to form a light emitting diode chip. Produced. However, during this wire bonding process, 10 of the 20 light-emitting diode chips cannot be characterized due to the ITO film peeling phenomenon. In other words, the manufacturing yield is 50%. As a result of evaluating the LED characteristics of only 10 light emitting diode chips produced, the average light emission output was 2.62 mW and the operating voltage was 2.11 V.

<Example 1: Heat treatment at 430 ° C. in nitrogen gas>
As Example 1, a red band light-emitting diode having a structure shown in FIG. The production process is as follows.

On the n-type GaAs substrate 1, an n-type GaAs buffer layer 2, an n-type Bragg reflection layer 3, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 4, an undoped (Al _0.15 Ga _0.85 ) _0.5 In _{A 0.5} P active layer 5, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 6 and a p-type GaAs contact layer 7 were sequentially grown to produce an epitaxial wafer for a light emitting diode. Incidentally, the n-type Bragg reflective layer has a laminated structure composed of an n-type AlInP layer (about 50 nm) and an n-type GaAs layer (about 40 nm), and the number of pairs is 10 pairs.

  Next, a method for forming the current blocking layer 11 will be described. After the light emitting diode epitaxial wafer was unloaded from the MOVPE apparatus, a positive photoresist was applied to the entire surface of the light emitting diode epitaxial wafer using a spin coater. At this time, the applied positive photoresist was ZWD-6200, and the coating conditions by the spin coater were set at a rotation speed of 7000 rpm and a rotation time of 60 sec.

  After applying the positive photoresist, exposure was performed using a mask aligner so that circular dots with a diameter of 125 μm were formed, and then development was performed to pattern the shape.

  After patterning, the substrate was washed with water and dried, and then baked at 430 ° C. for 5 minutes in a nitrogen gas atmosphere. Further, when the film thickness of the positive photoresist film produced at this time was measured with a step gauge, it was about 0.18 μm. In this way, a current blocking layer 11 made of a positive photoresist film was formed.

After the baking, a transparent conductive film 8 made of an ITO film having a thickness of 300 nm was formed on the patterned positive photoresist film side by a vacuum deposition method. At this time, the glass substrate set in the same batch was taken out, cut into a size capable of Hall measurement, and the electrical characteristics of the ITO film were evaluated. The carrier concentration was 1.21 × 10 ²¹ / cm ³ , the mobility was 21. The resistivity was 0 cm ² / Vs, and the resistivity was 2.30 × 10 ⁻⁴ Ω · cm.

  Then, on the upper surface of the epitaxial wafer for light emitting diodes, a circular p-side electrode (surface electrode) 9 having a diameter of 125 μm is deposited in a matrix so as to be positioned almost immediately above the positive photoresist film formed in the previous step. Formed with. For the p-side electrode 9, nickel and gold were deposited in the order of 20 nm and 500 nm, respectively. Further, an n-side electrode (back electrode) 10 was formed on the entire bottom surface of the epitaxial wafer. For the n-side electrode 10, gold / germanium alloy, nickel, and gold were deposited in the order of 60 nm, 10 nm, and 500 nm, respectively, and then alloying of the electrode was performed at 430 ° C. for 5 minutes in a nitrogen gas atmosphere.

  Thereafter, the epitaxial wafer was processed into a chip shape having a chip size of 300 μm square by dicing or the like, and only 20 of the chips processed into the chip shape were subjected to die bonding and wire bonding to manufacture a light emitting diode chip.

  Then, during the wire bonding process, only one of the 20 light-emitting diode chips had an ITO film peeling phenomenon, and the characteristics could not be evaluated. In other words, the manufacturing yield is 95%. As a result of evaluating the LED characteristics of the 19 light-emitting diode chips, the average light-emitting output was 2.63 mW and the operating voltage was 2.10 V.

  As described above, in the heat treatment step after forming the current blocking layer on the light emitting diode epitaxial wafer, the heat treatment temperature is set equal to the alloy temperature, so that the wire bonding step of the light emitting diode chip can be performed. The peeling phenomenon of the generated ITO film can be remarkably suppressed. In other words, the manufacturing yield of a light emitting diode using a photoresist film as a current blocking layer has been improved, and the manufacturing cost can be greatly reduced.

<Example 2: Heat treatment at 430 ° C. in vacuum>
As Example 2, a red band light emitting diode having a structure shown in FIG. The production process is as follows.

On the n-type GaAs substrate 1, an n-type GaAs buffer layer 2, an n-type Bragg reflection layer 3, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 4, an undoped (Al _0.15 Ga _0.85 ) _0.5 In _{A 0.5} P active layer 5, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 6 and a p-type GaAs contact layer 7 were sequentially grown to produce an epitaxial wafer for a light emitting diode. Incidentally, the n-type Bragg reflection layer has a laminated structure composed of an n-type AlInP layer (about 50 nm) and an n-type GaAs layer (about 40 nm), and the number of pairs is 10 pairs.

  Next, a method for forming the current blocking layer 11 will be described. After the light emitting diode epitaxial wafer was unloaded from the MOVPE apparatus, a positive type photoresist film was applied to the entire surface of the light emitting diode epitaxial wafer using a spin coater. At this time, the applied positive photoresist was ZWD-6200, and the coating conditions by the spin coater were set at a rotation speed of 7000 rpm and a rotation time of 60 sec.

  After applying the positive photoresist, exposure was performed using a mask aligner so that circular dots with a diameter of 125 μm were formed, and then development was performed to pattern the shape.

  After patterning, the substrate was washed with water and dried, and baked at 430 ° C. for 5 minutes in a vacuum. Further, when the film thickness of the positive photoresist film produced at this time was measured with a step gauge, it was about 0.18 μm. In this way, a current blocking layer 11 made of a positive photoresist film was formed.

After the baking, a transparent conductive film 8 made of an ITO film having a thickness of 300 nm was formed on the patterned positive photoresist film side by a vacuum deposition method. At this time, the glass substrate set in the same batch was taken out, cut into a size capable of Hall measurement, and the electrical characteristics of the ITO film were evaluated. The carrier concentration was 1.21 × 10 ²¹ / cm ³ , the mobility was 21. The resistivity was 1 cm ² / Vs, and the resistivity was 2.30 × 10 ⁻⁴ Ω · cm.

  A circular p-side electrode 9 having a diameter of 125 μm was formed in a matrix on the upper surface of the light emitting diode epitaxial wafer by vapor deposition so as to be positioned almost immediately above the positive photoresist film formed in the previous step. For the p-side electrode 9, nickel and gold were deposited in the order of 20 nm and 500 nm, respectively. Further, an n-side electrode 10 was formed on the entire bottom surface of the epitaxial wafer. For the n-side electrode 10, gold / germanium alloy, nickel, and gold were deposited in the order of 60 m, 10 m, and 500 m, respectively, and then alloying of the electrode was performed at 430 ° C. for 5 minutes in a nitrogen gas atmosphere.

  Thereafter, the epitaxial wafer was processed into a chip shape having a chip size of 300 μm square by dicing or the like, and only 20 of the chips processed into the chip shape were subjected to die bonding and wire bonding to manufacture a light emitting diode chip.

  Then, during the wire bonding process, the ITO film peeling phenomenon did not occur among the 20 light-emitting diode chips. That is, the manufacturing yield is 100%. As a result of evaluating the LED characteristics of the 20 light-emitting diode chips, the average light-emitting output was 2.61 mW and the operating voltage was 2.11 V.

  As described above, in the heat treatment step after forming the current blocking layer on the light emitting diode epitaxial wafer, the heat treatment temperature is set equal to the alloy temperature, so that the wire bonding step of the light emitting diode chip can be performed. The peeling phenomenon of the generated ITO film can be remarkably suppressed. In other words, the manufacturing yield of a light emitting diode using a photoresist film as a current blocking layer has been improved, and the manufacturing cost can be greatly reduced.

<Reason for optimal conditions>
First, the photoresist film used for the current blocking layer is preferably a positive photoresist film.

  This is because, in general, only the exposed portion of the positive photoresist is dissolved in the developer, and conversely, only the unexposed portion remains on the epitaxial wafer. At that time, the positive photoresist remaining on the epitaxial wafer has a characteristic that the upper side is short and the lower side is tapered. On the other hand, in the negative photoresist, exposed portions remain and unexposed portions dissolve in the developer. The shape of the remaining negative resist is an inversely tapered shape having a long upper side and a short lower side.

  When a current blocking layer is formed with this negative photoresist, gaps are formed between the ITO film formed so as to cover the current blocking layer and the current blocking layer with the negative photoresist. It will be a factor to bring. For example, it may be a film break. In addition, by forming a gap, the component that light emitted upward from the semiconductor is reflected downward in the gap portion is increased, resulting in a decrease in luminance of the light emitting diode.

  For the above reasons, it is desirable to use a positive photoresist for the current blocking layer.

  Second, it is preferable that the size, that is, the diameter of the current blocking layer is substantially equal to or larger than the diameter of the surface electrode, that is, the electrode formed on the ITO film.

  This is because if the diameter of the current blocking layer is smaller than the diameter of the surface electrode, there is a portion where the current flowing directly under the electrode cannot be shielded, and the increase in the light emission output due to the current confinement effect is reduced. Because.

  Further, it is necessary to optimize the diameter of the current blocking layer according to the distance of the semiconductor layer from the current blocking layer to the active layer. For example, in the embodiment of the present invention, the distance from the active layer to the current block layer is about 1 μm, and if this is the case, the current flowing around the current block layer bypasses the semiconductor below the current block layer. There is almost no wrap around between layers, and high brightness can be achieved by the current confinement effect with extremely high efficiency. On the contrary, when the distance of the semiconductor layer from the current block layer to the active layer is as long as about 10 μm, the current flowing around the current block layer flows again to the position immediately below the electrode by the semiconductor layer to the active layer. As a result, light emission directly under the electrode increases, and a significant improvement in luminance cannot be expected. As a countermeasure for such a case, the diameter of the current blocking layer is made larger than the diameter of the electrode.

  Third, it is desirable that the ohmic contact layer in contact with the ITO film is mainly AlGaAs having an Al mixed crystal ratio of 0 to 0.3 to which Zn is added at a high concentration (GaAs when the mixed crystal ratio is 0). .

The ITO film basically belongs to an n-type semiconductor material, and the light emitting diode is generally manufactured by p-side up. For this reason, the light emitting diode with the ITO film attached to the current diffusion layer has an n / p / n junction from the substrate side. For this reason, in the light emitting diode, a large potential barrier is generated at the interface between the ITO film and the p-type semiconductor layer, and the light emitting diode usually has a very high operating voltage. In order to solve this problem, a contact layer having a very high carrier concentration is required for the p-type semiconductor layer. For this purpose, AlGaAs having a low Al mixed crystal ratio is suitable from the above-described GaAs doped with Zn, and specifically, it preferably has a carrier concentration of 1 × 10 ¹⁹ / cm ³ or more.

  Fourth, the contact layer is made of GaAs to AlGaAs having a low Al mixed crystal ratio, and the thickness of the contact layer is preferably in the range of 1 nm to 50 nm.

  This is because all of the contact layers have a band gap that serves as an absorption layer for the light emitted from the active layer, so that the light emission output decreases as the film thickness increases. Therefore, the upper limit of the thickness of the contact layer is set to about 50 nm. However, it is more preferably up to 30 nm. In addition, when the contact layer thickness is less than 1 nm, tunnel junction between the ITO film and the contact layer becomes difficult, which makes it difficult to reduce the operating voltage and stabilize the operating voltage. Become. Therefore, the thickness of the contact layer in contact with the ITO film has an optimum value, which is 1 nm to 50 nm.

  Fifth, the method for forming the ITO film is preferably a vacuum deposition method. The reason will be described below for each manufacturing method.

  First, in the sputtering method, since plasma is generated in an oxygen atmosphere, the same effect as ashing works and the current blocking layer is removed. Further, since the equipment cost of the sputtering apparatus itself is high and the number of charged sheets per batch is small, throughput is also a problem.

  Next, in the spray method using a MOD solution, first, the resistivity of the ITO film cannot be lowered unless the surface temperature of the substrate is heated to 500 ° C. or higher. A large problem is that the surface of the contact layer is oxidized, and a tunnel junction cannot be achieved. Further, since the ITO film is formed at a high temperature, the carrier concentration of the ITO film is lowered, and it is difficult to make a tunnel junction. Furthermore, it is difficult to charge a large number of sheets, that is, to manufacture a manufacturing facility with high throughput, and it is difficult to perform stable mass production.

  Next, in the coating method, it is very difficult to lower the resistivity as compared with the spray method, the sputtering method, and the vacuum deposition method. This makes it very difficult to make a tunnel junction with the contact layer. Furthermore, since it is necessary to repeatedly perform steps such as coating, drying, and baking in order to form the ITO film from about 200 nm to about 500 nm, the throughput is very poor.

  Next, in the coating method, it is very difficult to lower the resistivity as compared with the spray method, the sputtering method, and the vacuum deposition method.

  This makes it very difficult to make a tunnel junction with the contact layer. Furthermore, since it is necessary to repeatedly perform steps such as coating, drying, and baking in order to form the ITO film from about 200 nm to about 500 nm, the throughput is very poor.

  For the above reasons, it is preferable to use the vacuum deposition method as a method with a low manufacturing cost, excellent stability, and high throughput.

  Sixth, the thickness of the ITO film is preferably in the range of 200 nm to 500 nm.

  The reason why the lower limit is 200 nm is that a film thickness of about 200 nm is necessary to obtain a sufficient current dispersion effect. Next, the upper limit is 500 nm. When the film is formed by vacuum deposition, the transparency of the ITO film, that is, the transmittance gradually deteriorates when the film thickness of the ITO film reaches about 500 nm. Because there is. In addition, since a sufficient current dispersion effect can be obtained with an ITO film of about 200 nm to 300 nm, the manufacturing cost is only increased even if it is too thick.

  Accordingly, it can be said that the thickness of the ITO film is preferably in the range of 200 nm to 500 nm, more preferably about 200 nm to 400 m.

  Seventh, the heat treatment step after the formation of the current blocking layer is preferably performed in an inert gas atmosphere having an oxygen concentration of less than 1% or in a vacuum.

  The detailed conditions are described in Example 1 and Example 2 of the present invention. The reason is that an epitaxial wafer for a light-emitting diode was prepared by intentionally selecting a heat treatment in an atmosphere having a low oxygen concentration. This is because the oxidation phenomenon of the contact layer can be prevented beforehand. Since the contact layer is an extremely thin film in the range of about 1 nm to 50 nm, the contact layer may be oxidized when subjected to high-temperature heat treatment in an atmosphere containing oxygen. Then, the tunnel voltage applied between the ITO film and the contact layer is increased, resulting in a light emitting diode with a high operating voltage.

<Modification 1>
In the embodiments of the present invention, the AlGaInP-based light emitting diode has been described in detail. However, other current blocking layers using the photoresist intended by the present invention include, for example, AlGaAs-based light-emitting diodes and InGaAsP-based long-wavelength light-emitting diodes. It is also applicable to.

<Modification 2>
In the embodiment of the present invention, the light emitting part is constituted by the n-type cladding layer 4, the active layer 5, and the p-type cladding layer 6. For example, a semiconductor layer (diffusion suppression layer) for suppressing diffusion of conductivity type determining impurities. Is provided on the upper and lower sides of the active layer, or on the upper side or the lower side, the diffusion suppression layer is undoped or a low-concentration semiconductor layer, and in any case the current confined by the current blocking layer is It is almost impossible to hinder the improvement in light emission luminance caused by the wraparound and current confinement effect.

  In addition, the present invention intends to provide a current blocking layer made of a photoresist film on the surface of the semiconductor layer and further spread the current with an ITO film. Is applicable.

<Modification 3>
In the embodiment of the present invention, a light emitting diode was obtained by forming a light emitting diode structure on a GaAs substrate 1 and sequentially forming a current blocking layer 11 and a transparent conductive film 8 made of an ITO film. When the substrate is Ge, or as in the embodiment, a light emitting diode structure is once formed on a GaAs substrate, and then, using various wafer fusion techniques, the originally formed light emitting diode structure is utilized, Even in a light emitting diode attached to a substrate, the current confinement type light emitting diode composed of a current blocking layer and an ITO film by a photoresist film shown in the present invention can be applied regardless of the material of the substrate. The intended effect of the present invention can be obtained.

<Modification 4>
In the embodiment of the present invention, a simple double hetero structure in which the active layer is sandwiched between the clad layers is used. However, even if the active layer has a quantum well structure, for example, the intended effect of the present invention can be obtained. .

It is sectional drawing of the AlGaInP type red light emitting diode concerning Example 1, Example 2, and a comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 Bragg reflection layer 4 N-type clad layer 5 Active layer 6 P-type clad layer 7 Contact layer 8 Transparent conductive film 9 Front electrode 10 Back electrode 11 Current blocking layer

Claims (11)

On a substrate, at least an active layer sandwiched between an n-type cladding layer and a p-type cladding layer, an ohmic contact layer containing a conductivity determining impurity, a current blocking layer made of a photoresist film, and an ITO film In the method for manufacturing an epitaxial wafer for a semiconductor light emitting device, in which the transparent conductive film is sequentially formed,
A method of manufacturing an epitaxial wafer for a semiconductor light-emitting element, wherein the current blocking layer is heat-treated to suppress swelling before forming the transparent conductive film. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices of Claim 1,
The method of manufacturing an epitaxial wafer for a semiconductor light emitting device, wherein the current blocking layer is a positive photoresist film. A light emitting part having at least an active layer sandwiched between an n-type cladding layer and a p-type cladding layer on a substrate, and an ohmic contact layer containing a conductivity determining impurity of 1 × 10 ¹⁹ / cm ³ or more on the light emitting part Step by step,
Forming a photoresist film having a current blocking effect on the ohmic contact layer;
Patterning the photoresist film into a desired shape to form a current blocking layer;
Forming a transparent conductive film made of an ITO film on the current blocking layer;
Forming a surface electrode on the transparent conductive film;
In the method of manufacturing an epitaxial wafer for a semiconductor light emitting device, including an alloy process in which the electrode is heat-treated at a desired temperature and alloyed,
An epitaxial wafer for a semiconductor light emitting device comprising a heat treatment step for suppressing the swelling of the photoresist film by heat treating the epitaxial wafer for a semiconductor light emitting device in a desired temperature and atmosphere before forming the transparent conductive film. Manufacturing method. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices of Claim 3,
A method of manufacturing an epitaxial wafer for a semiconductor light emitting device, characterized in that a temperature of the heat treatment step is equal to or higher than a temperature of the alloy step. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices of Claim 3 or 4,
The method for producing an epitaxial wafer for a semiconductor light-emitting element, wherein an atmosphere of the heat treatment step is an inert gas having an oxygen concentration of less than 1% or a vacuum. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices in any one of Claims 3 thru | or 5,
The method of manufacturing an epitaxial wafer for a semiconductor light emitting device, wherein the current blocking layer is a positive photoresist film. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices in any one of Claims 3 thru | or 6,
A method of manufacturing an epitaxial wafer for a semiconductor light emitting device, wherein a position corresponding to a central portion of the current blocking layer is formed to be immediately below a position corresponding to a central portion of the surface electrode. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices in any one of Claims 3 thru | or 7,
The method of manufacturing an epitaxial wafer for a semiconductor light emitting element, wherein an area on the surface side of the current blocking layer is equal to or larger than an area on the surface side of the surface electrode. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices in any one of Claims 1 thru | or 8,
The substrate is made of gallium arsenide, germanium, silicon, or any metal having a higher thermal conductivity than silicon,
The light emitting portion is made of any one of GaInP, AlInP, and AlGaInP,
An epitaxial wafer for a semiconductor light-emitting element, wherein the ohmic contact layer is Al _X Ga _1-X As (0 ≦ X ≦ 0.3), and the thickness of the ohmic contact layer is 1 nm or more and 50 nm or less Production method. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices in any one of Claims 1 thru | or 9,
A method for producing an epitaxial wafer for a semiconductor light emitting device, wherein the transparent conductive film has a thickness of 200 nm to 500 nm. In the manufacturing method of the epitaxial wafer for semiconductor light-emitting devices in any one of Claims 3 thru | or 10,
The temperature of the said alloy process is 300 degreeC or more and 500 degrees C or less, The manufacturing method of the epitaxial wafer for semiconductor light-emitting devices characterized by the above-mentioned.

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