JP5706696B2 - Light emitting device manufacturing method and light emitting device - Google Patents

Description

The present invention relates to a light-emitting element made of a semiconductor material and a method for manufacturing the same, and more particularly to a light-emitting element in which a nitride semiconductor layer is formed on a Ga ₂ O ₃ (gallium oxide) substrate via a buffer layer and a method for manufacturing the same.

  Conventionally, light emitting elements of blue and short wavelength regions using GaN-based semiconductors are known. For example, a sapphire substrate or a SiC substrate has been used as a base substrate for such a light-emitting element, but the sapphire substrate does not have conductivity, and thus has a structural restriction that the electrode structure of the light-emitting element is a horizontal type. In addition, since the SiC substrate has poor crystallinity of the single crystal wafer and there are so-called micropipe defects penetrating in the vertical direction of the single crystal, the n-type layer and the p-type layer are formed by avoiding the micropipe defects. There is a problem that it must be cut out.

Therefore, from the characteristics that III-V group compound semiconductor has light transmittance in the entire wavelength range of the light emitting region, particularly in the ultraviolet region, has relatively small lattice mismatch with GaN, and can obtain a good quality bulk single crystal. In addition, it has been proposed to use a Ga ₂ O ₃ substrate as a light emitting element material in a blue or short wavelength region (see, for example, Patent Document 1).

JP 2006-310765 A

In the method for manufacturing a light emitting element described in Patent Document 1, a buffer layer made of AlN is formed on a Ga ₂ O ₃ substrate, and a GaN layer is formed on the buffer layer. When forming the GaN layer, N ₂ is supplied into the MOCVD apparatus and the temperature is raised to 1050 ° C. to form an n ⁺ -GaN layer having a thickness of 1 μm, and then H ₂ is supplied into the MOCVD apparatus. Then, an n ⁺ -GaN layer having a thickness of 2 μm is further formed.

However, it has been confirmed by the present inventors that when a light emitting element is manufactured by this manufacturing method, peeling (peeling) may occur between the Ga ₂ O ₃ substrate and the buffer layer during the manufacturing. .

  Accordingly, an object of the present invention is to provide a method for manufacturing a light emitting element and a light emitting element that can suppress the occurrence of peeling of a buffer layer during the manufacture of the light emitting element.

Therefore, the present inventors diligently studied the cause and countermeasures of this peeling, and as a result of various investigations on the relationship between the composition of each layer of the light emitting element, the supplied raw material gas, the growth temperature, and the occurrence rate of peeling, The inventors have found a condition that can suppress the occurrence and have made the present invention. That is, this invention provides the manufacturing method of the light emitting element of the following [1]-[ 7 ], and a light emitting element.

[1] was subjected to a nitriding treatment to _Ga 2 _{O 3} surface of the substrate in the MOCVD apparatus, a first step of forming a buffer layer on a surface of the _Ga 2 _{O 3} substrate, a nitrogen atmosphere in the MOCVD apparatus A second step of forming a first nitride semiconductor layer on the buffer layer at a growth temperature of 700 ° C. to 1035 ° C., a hydrogen atmosphere in the MOCVD apparatus, and a first step in the second step. And a third step of forming a second nitride semiconductor layer on the first nitride semiconductor layer at a growth temperature higher than the growth temperature of the nitride semiconductor layer .

[2] The light-emitting element according to [1], wherein the buffer layer is an Al _x Ga _y In _z N (x + y + z ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) layer. Manufacturing method.

[3] The method for manufacturing a light-emitting element according to [1] or [2] , wherein the third step includes setting the growth temperature of the second nitride semiconductor layer to 1025 ° C. or higher.

[4] The method for manufacturing a light-emitting element according to [1] or [2] , wherein the third step includes setting the growth temperature of the second nitride semiconductor layer to 1050 ° C. or higher.

[5] The method for manufacturing a light-emitting element according to any one of [1] to [4] , wherein the nitride semiconductor layer is a GaN semiconductor layer.

[6] A first step of forming a buffer layer on the surface of the Ga ₂ O ₃ substrate after nitriding the surface of the Ga ₂ O ₃ substrate in an MOCVD apparatus, and growth at 700 ° C. to 1035 ° C. At a temperature, a source gas is supplied into the MOCVD apparatus using nitrogen as a carrier gas, a second step of forming a first nitride semiconductor layer on the buffer layer, and a growth temperature of 1050 ° C. or more, And a third step of forming a second nitride semiconductor layer on the first nitride semiconductor layer by supplying a source gas into the MOCVD apparatus using hydrogen as a carrier gas.

[7] A buffer layer formed on the Ga ₂ O ₃ substrate in the MOCVD apparatus, and a first atmosphere formed on the buffer layer at a growth temperature of 700 ° C. to 1035 ° C. in the MOCVD apparatus with a nitrogen atmosphere . The nitride semiconductor layer and the MOCVD apparatus are formed in a hydrogen atmosphere on the first nitride semiconductor layer at a growth temperature higher than the growth temperature of the first nitride semiconductor layer in the second step. And a second nitride semiconductor layer formed .

  According to the present invention, it is possible to suppress the occurrence of peeling of the buffer layer during manufacturing of the light emitting element.

FIG. 1 is a cross-sectional view showing a schematic configuration example of an MOCVD apparatus according to an embodiment of the present invention. FIG. 2 is a schematic process diagram schematically showing a manufacturing process of the LED element according to the embodiment of the present invention. FIG. 3 is a schematic process diagram schematically showing an example of the manufacturing process of the LED element. FIG. 4 is a graph showing the relationship between the growth temperature of the first GaN layer and the yield rate. FIGS. 5A to 5C are micrographs and contour diagrams of the surface of the LED element. FIGS. 6A to 6D are micrographs of the surface of the second GaN layer.

(Configuration of MOCVD equipment)
FIG. 1 is a schematic cross-sectional view illustrating the configuration of an MOCVD (Metal Organic Chemical Vapor Deposition) apparatus according to an embodiment.

  The MOCVD apparatus 2 is an apparatus for epitaxially growing a plurality of layers on a substrate by MOCVD. The MOCVD method is a method in which a raw material gas generated by heating an organic metal material is supplied to a reaction chamber, and thermal decomposition and chemical reaction are performed on a substrate crystal to perform epitaxial growth of a thin film crystal.

The MOCVD apparatus 2 includes an airtight reaction vessel 21 that forms a reaction chamber 20 inside and a substrate stand (susceptor) that holds a substrate made of β-Ga ₂ O ₃ (hereinafter referred to as “Ga ₂ O ₃ substrate”) 10. 22, a shaft 23 that supports the substrate table 22, a heater 24 that heats the substrate table 22, a reaction tube 25 that guides the source gas supplied from the gas supply source 3 to the Ga ₂ O ₃ substrate 10, and the substrate table 22 And a cooling pipe 26 arranged opposite to the vacuum pump 26 and a vacuum pump 27 for forcibly exhausting the gas in the reaction chamber 20.

The substrate table 22 can be rotated by a driving force of a motor (not shown) connected to the shaft 23. The temperature of the substrate table 22 can be controlled by a heater 24. The Ga ₂ O ₃ substrate 10 held on the substrate table 22 is heated by heat conduction from the substrate table 22.

  The cooling pipe 26 is a pipe that circulates the cooling water cooled by the cooling water supply source 261, and cools the opposing portion of the substrate base 22 in the reaction chamber 20 whose temperature rises as the substrate base 22 is heated by the heater 24. To do.

  The reaction tube 25 includes a first reaction tube 25a and a second reaction tube 25b. A first piping system 31 for circulating ammonia gas, nitrogen gas, and hydrogen gas from the gas supply source 3 is connected to the first reaction tube 25a outside the reaction vessel 21. Further, a second piping system 32 for circulating various source gases from the gas supply source 3 is connected to the second reaction tube 25b outside the reaction vessel 21.

An ammonia (NH ₃ ) gas supply source 311, a nitrogen (N ₂ ) gas supply source 312, and a hydrogen (H ₂ ) gas supply source 313 are connected to the first piping system 31.

In addition to the nitrogen gas supply source 312 and the hydrogen gas supply source 313, the second piping system 32 includes a TMA (trimethylaluminum; Al (CH ₃ ) ₃ ) gas generator 321, TMG (trimethylgallium; Ga (CH ₃ )). ₃ ) A gas generator 322, a TMI (trimethylindium; In (CH ₃ ) ₃ ) gas generator 323, a Cp ₂ Mg (cyclopentadienylmagnesium) gas generator 324, and a silane (SiH ₄ ) gas supply source 325 It is connected.

A nitrogen gas supply source 312 and a hydrogen gas supply source 313 are respectively connected to the TMA gas generator 321, the TMG gas generator 322, the TMI gas generator 323, and the CP ₂ Mg gas generator 324 for bubbling. ing.

(Configuration of LED element)
FIG. 2 is a cross-sectional view showing a configuration example of an LED (Light Emitting Diode) element according to the embodiment of the present invention.

This LED element 1 has a Ga ₂ O ₃ substrate 10, a buffer layer 11 formed on the Ga ₂ O ₃ substrate 10, a Si-doped n ⁺ -GaN layer 12 which is a nitride semiconductor layer, and a Si-doped N-AlGaN layer 13, MQW (Multiple-Quantum Well) 14 having an InGaN / GaN multiple quantum well structure, Mg-doped p-AlGaN layer 15, Mg-doped p ⁺ -GaN layer 16, ITO The current diffusion layer 17 made of (Indium Tin Oxide) is sequentially laminated using the MOCVD apparatus 2.

The LED element 1 further includes a p-side electrode 18 provided on the upper surface of the current diffusion layer 17 and an n-side electrode 19 provided on the n ⁺ -GaN layer 12 exposed by etching from the current diffusion layer 17. Have.

The buffer layer 11 is a nitride represented by Al _x Ga _y In _z N (x + y + z ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). For example, AlN, GaN, AlGaN , InGaN, AlGaInN, or AlInN. When the buffer layer 11 is made of, for example, AlN, the buffer layer 11 can be formed by using hydrogen as a carrier gas and supplying TMA and ammonia into the reaction chamber 20. The buffer layer 11 buffers a lattice constant difference between the Ga ₂ O ₃ substrate 10 and the n ⁺ -GaN layer 12.

The n ⁺ -GaN layer 12 includes a first GaN layer 12a as a first nitride semiconductor layer formed on the buffer layer 11 side and a second nitride semiconductor layer formed on the n-AlGaN layer 13 side. As a second GaN layer 12b.

  The first GaN layer 12a is epitaxially grown on the buffer layer 11 by using nitrogen as a carrier gas and supplying TMG and ammonia into the reaction chamber 20 at a growth temperature of 700 ° C. to 1035 ° C. in a nitrogen atmosphere. Is formed. A temperature lower than 700 ° C. is not desirable because electric resistance increases. Preferably, the growth temperature of the first GaN layer 12a is 900 ° C. or higher in order to reduce the electrical resistance. Further, when the growth temperature is higher than 1035 ° C., the buffer layer 11 is easily peeled off as described later.

  The second GaN layer 12b is epitaxially grown on the first GaN layer 12a by using hydrogen as a carrier gas and supplying TMG and ammonia to the reaction chamber 20 at a growth temperature of 1025 ° C. or higher in a hydrogen atmosphere. Is formed. When the growth temperature is lower than 1025 ° C., the generation of pits (holes) on the layer surface increases, which is not preferable. The growth temperature of the second GaN layer 12b is preferably 1050 ° C. or higher.

The n ⁺ -GaN layer 12 (the first GaN layer 12a and the second GaN layer 12b) uses silane (SiH ₄ ) as a Si raw material as a dopant for imparting n-type conductivity.

  The n-AlGaN layer 13 is formed by supplying TMA, TMG, and ammonia to the reaction chamber 20.

  The MQW 14 is formed by using hydrogen as a carrier gas and supplying TMI and TMG in the reaction chamber 20 in addition to ammonia. TMI and TMG are supplied when InGaN is formed, and TMG is supplied when GaN is formed.

  The p-AlGaN layer 15 is formed by supplying TMA, TMG, and ammonia to the reaction chamber 20.

The p ⁺ -GaN layer 16 is formed by using nitrogen as a carrier gas and supplying TMG and ammonia into the reaction chamber 20. Then, the Cp 2 _Mg used as the Mg raw material as a dopant for imparting p-type conductivity.

(Manufacturing process of LED element 1)
FIG. 3 is a schematic process diagram schematically showing an example of the manufacturing process of the LED element 1. In FIG. 3, the horizontal axis represents time and the vertical axis represents the temperature (° C.) of the Ga ₂ O ₃ substrate 10, along with the film formed in each time zone and the atmosphere in the reaction chamber 20. Hereinafter, each step will be described.

(Substrate cleaning process)
First, the Ga ₂ O ₃ substrate 10 used in the present manufacturing process is subjected to organic cleaning with acetone and methanol, respectively, then acid cleaning with nitric acid (HNO ₃ ), and then ultrasonic waves for 5 minutes in pure water. Substrate cleaning is performed by cleaning. Then, the cleaned Ga ₂ O ₃ substrate 10 is mounted on the substrate table 22 in the reaction chamber 20.

(Nitriding treatment of substrate surface)
Next, the inside of the reaction chamber 20 is made an ammonia atmosphere diluted with nitrogen, and the temperature of the Ga ₂ O ₃ substrate 10 is raised by the heater 24. At time t _{1 when} the temperature of the Ga ₂ O ₃ substrate 10 reaches 550 ° C., the temperature rise is stopped, and the temperature is maintained to nitride the surface of the Ga ₂ O ₃ substrate 10. The temperature of the Ga ₂ O ₃ substrate 10 (hereinafter referred to as “substrate temperature”) can be measured by a radiation thermometer (not shown).

(Buffer layer 11 formation process)
Then, to start the supply of hydrogen at the time t _2, the the reaction chamber 20 and a hydrogen atmosphere. Then, TMA and ammonia are supplied into the reaction chamber 20 at time t _{3 when} the temperature of the Ga ₂ O ₃ substrate 10 reaches 450 ° C. by stopping heating by the heater 24, and Ga is maintained while maintaining the substrate temperature of 450 ° C. _A buffer layer 11 is grown to 50 nm on the surface of the ₂ O ₃ substrate 10 subjected to the nitrogenation treatment.

(Step of forming n ⁺ -GaN layer 12)
Next, by stopping the supply of hydrogen to the reaction chamber 20 at time t ₄ to start supplying nitrogen to the reaction chamber 20 and a nitrogen atmosphere. Following the heating of Ga ₂ O ₃ substrate 10 starts from time t _5, the Atsushi Nobori was stopped at time t ₆ became 900 ° C., and nitrogen as a carrier gas into the reaction chamber 20 while maintaining the temperature By supplying TMG and ammonia, a first GaN layer 12a having a thickness of 1 μm is formed on the buffer layer 11 in a nitrogen atmosphere.

Next, by stopping the supply of nitrogen to the reaction chamber 20 to start the supply of hydrogen at the time t _7, the reaction chamber 20 and a hydrogen atmosphere. Following the heating of _Ga 2 _{O 3} substrate 10 starts from time _{t 8,} the Atsushi Nobori was stopped at the time _{t 9} became 1050 ° C., hydrogen TMG and ammonia into the reaction chamber 20 while maintaining the temperature As a carrier gas, the second GaN layer 12b is formed on the first GaN layer 12a in a hydrogen atmosphere. The film thickness of the second GaN layer 12b is larger than the film thickness of the first GaN layer 12a, for example, 2 μm.

Thereafter, the n-AlGaN layer 13, the MQW 14, the p-AlGaN layer 15, the p ⁺ -GaN layer 16, the current diffusion layer 17, the p-side electrode 18, and the n-side electrode 19 are sequentially formed. Will not be described.

(Relationship between separation of buffer layer 11 and growth temperature of first GaN layer 12a)
FIG. 4 is a graph showing the relationship between the growth temperature of the first GaN layer 12a (substrate temperature when the first GaN layer 12a is formed) and the yield rate of the LED elements 1.

When the LED element 1 was manufactured by the above manufacturing method and temperature conditions, the yield rate of the LED element 1 was almost 100%, but when the growth temperature of the first GaN layer 12a was set higher than 1035 ° C. It was confirmed that the buffer layer 11 was peeled from the Ga ₂ O ₃ substrate 10 with more than half of the LED elements 1. The cause of this peeling is considered to be related to the stress caused by heat at the time of forming the first GaN layer 12a.

  As shown in FIG. 4, when the growth temperature of the first GaN layer 12a was set to 850 ° C., 975 ° C., 1000 ° C., 1010 ° C., and 1025 ° C., peeling of the buffer layer 11 was not confirmed. When the growth temperature was higher than 1025 ° C., peeling of the buffer layer 11 was confirmed. The yield rate was suppressed to 60% at 1035 ° C, but 20% at 1040 ° C, 10% at 1050 ° C, and 0% at 1075 ° C and 1100 ° C.

  FIGS. 5A and 5B are micrographs of the surface of the LED element 1, FIG. 5A is a photograph of the surface when no peeling of the buffer layer 11 occurs, and FIG. 5B is the surface of the buffer layer 11. It is a photograph of the surface when peeling occurs. FIG. 5C is a diagram depicting the outline of the region where the separation occurred in FIG.

  When the growth temperature of the first GaN layer 12a is set to 1025 ° C. or lower, the LED element 1 having a flat surface is obtained as shown in FIG. 5A, whereas the first GaN layer 12a is obtained. In the case where the LED element 1 was manufactured at a growth temperature higher than 1035 ° C., the buffer layer 11 was peeled off in the peeling generation region 1a shown in FIG. 5C, as shown in FIG. 5B. Each layer from the buffer layer 11 to the current diffusion layer 17 in the peeling occurrence region 1a has disappeared.

(Relationship between growth temperature and pit of second GaN layer 12b)
FIG. 6 is a micrograph (500 times) of the surface of the second GaN layer 12b when the growth temperature of the second GaN layer 12b is changed, and (a) shows the growth temperature of the second GaN layer 12b. When the temperature is 1000 ° C., (b) is the same growth temperature is 1025 ° C., (c) is the same growth temperature is 1040 ° C., (d) is the photomicrograph when the same growth temperature is 1050 ° C. It is.

  As shown in FIG. 6A, when the growth temperature of the second GaN layer 12b is 1000 ° C., countless pits are generated on the surface of the second GaN layer 12b, and the appearance is cloudy. It becomes.

  As shown in FIG. 6B, when the growth temperature of the second GaN layer 12b is 1025 ° C., the density of pits is lower than when the growth temperature is 1000 ° C., which is practically used. It is the level to get. However, a large number of pits 1b are still observed.

  As shown in FIG. 6C, when the growth temperature of the second GaN layer 12b is set to 1040 ° C., the density of the pits 1b is further lowered than when the growth temperature is set to 1025 ° C. However, the occurrence of pits 1b is observed in some places.

  As shown in FIG. 6D, when the growth temperature of the second GaN layer 12b is set to 1050 ° C., it can be seen that almost no pits are generated and a high-quality crystal is obtained. Even when the growth temperature of the second GaN layer 12b was 1075 ° C. or higher, almost no pits were observed.

(Effect of embodiment)
According to the present embodiment, the occurrence of peeling of the buffer layer 11 can be suppressed. Moreover, generation | occurrence | production of a pit can be reduced and the deterioration of the transmittance | permeability of the light emitted by MQW14 by white turbidity can be suppressed.

(Other embodiments)
As mentioned above, although the manufacturing method of the light emitting element of this invention and the light emitting element were demonstrated based on said embodiment, this invention is not limited to said embodiment, In the range which does not deviate from the summary. It can be implemented in various ways. For example, the nitride semiconductor layer is not limited to GaN but may be AlGaN. The structure of the LED element is not limited to the horizontal type, and may be a vertical type structure having electrodes on the surface of the Ga ₂ O ₃ substrate opposite to the buffer layer.

1 ... LED element, 1a ... delamination region, 1b ... Pit, 2 ... MOCVD apparatus, 3 ... gas supply source, 10 ... _Ga 2 _{O 3} substrate, 11 ... buffer layer, 12 ^... n + -GaN layer, 12a ... first 1 GaN layer, 12 b ... second GaN layer, 13 ... n-AlGaN layer, 14 ... MQW, 15 ... p-AlGaN layer, 16 ... p ⁺ -GaN layer, 17 ... current diffusion layer, 18 ... p-side electrode 19 ... n-side electrode, 20 ... reaction chamber, 21 ... reaction vessel, 22 ... substrate base, 23 ... shaft, 24 ... heater, 25 ... reaction tube, 25a ... first reaction tube, 25b ... second reaction tube , 26 ... cooling piping, 27 ... vacuum pump, 31 ... first piping system, 32 ... second piping system, 261 ... cooling water supply source, 311 ... ammonia gas supply source, 312 ... nitrogen gas supply source, 313 ... Hydrogen gas supply source, 321 ... TMA gas generator 322 ... TMG gas generator, 323 ... TMI gas generator, 324 ... Cp ₂ Mg gas generator, 325 ... Silane gas supply source

Claims (7)

A first step of forming a buffer layer on the surface of the Ga ₂ O ₃ substrate after nitriding the surface of the Ga ₂ O ₃ substrate in an MOCVD apparatus;
A second step of forming a first nitride semiconductor layer on the buffer layer at a growth temperature of 700 ° C. to 1035 ° C. under a nitrogen atmosphere in the MOCVD apparatus ;
The MOCVD apparatus has a hydrogen atmosphere, and a second nitride semiconductor layer is formed on the first nitride semiconductor layer at a growth temperature higher than the growth temperature of the first nitride semiconductor layer in the second step. And a third step of forming the light-emitting element. 2. The method of manufacturing a light-emitting element according to claim 1, wherein the buffer layer is an Al _x Ga _y In _z N (x + y + z ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) layer. Wherein the third step is a manufacturing method of a light emitting device according to claim 1 or 2, wherein the second nitride growth temperature of the semiconductor layer 1025 ° C. or higher. Wherein the third step is a manufacturing method of a light emitting device according to claim 1 or 2, the growth temperature of the second nitride semiconductor layer 1050 ° C. or higher. The nitride semiconductor layer manufacturing method of a light-emitting element according to any one of claims 1 to 4, which is a GaN semiconductor layer. A first step of forming a buffer layer on the surface of the Ga ₂ O ₃ substrate after nitriding the surface of the Ga ₂ O ₃ substrate in an MOCVD apparatus;
A second step of forming a first nitride semiconductor layer on the buffer layer by supplying a source gas into the MOCVD apparatus using nitrogen as a carrier gas at a growth temperature of 700 ° C. to 1035 ° C .;
A third step of forming a second nitride semiconductor layer on the first nitride semiconductor layer by supplying a source gas into the MOCVD apparatus using hydrogen as a carrier gas at a growth temperature of 1050 ° C. or higher; A method for manufacturing a light emitting device having A buffer layer formed on a Ga ₂ O ₃ substrate in an MOCVD apparatus;
A first nitride semiconductor layer formed on the buffer layer at a growth temperature of 700 ° C. to 1035 ° C. in the MOCVD apparatus ;
A second nitride formed on the first nitride semiconductor layer at a growth temperature higher than the growth temperature of the first nitride semiconductor layer in the second step, wherein the MOCVD apparatus has a hydrogen atmosphere. A light-emitting element having a semiconductor layer .