JP5317898B2 - Method for manufacturing light-emitting diode element - Google Patents

Description

  The present invention relates to a light emitting diode element and a method for manufacturing the light emitting diode element.

Reference numeral 110 in FIG. 3 shows an example of a conventional light emitting diode element.
The light emitting diode element 110 includes a light emitting layer 119, a transparent electrode film 116, and a reflective electrode film 117. The light emitting layer 119 includes an n-type cladding layer 113, an active layer 114, and a p-type cladding layer 115.
The buffer layer 112 and the n-type cladding layer 113 are arranged in this order on the transparent substrate 111, and the active layer 114 and the p-type are formed on the n-type cladding layer 113 so that the n-type cladding layer 113 is partially exposed. The clad layer 115, the transparent electrode film 116, and the reflective electrode film 117 are arranged in this order.

On the partially exposed surface of the n-type cladding layer 113, a negative terminal 122 is disposed apart from the active layer 114, and a positive terminal 121 is disposed on the reflective electrode film 117.
When a positive electrode of a DC power source (not shown) is electrically connected to the positive terminal 121 and a negative electrode is electrically connected to the negative terminal 122, a DC voltage is applied between the positive terminal 121 and the negative terminal 122, and a DC current flows. The active layer 114 emits light.

The light emitted from the active layer 114 to the p-type cladding layer 115 side is transmitted through the transparent electrode film 116 and reflected by the reflective electrode film 117, and the transparent electrode film 116, the light emitting layer 119, the buffer layer 112, the transparent substrate 111, and the like. In order and released to the outside.
An ITO film is preferably used as the transparent electrode film 116, and as a method for forming the transparent electrode film 116 on the light emitting layer 119, a vacuum deposition method is preferably employed in order to reduce damage to the light emitting layer 119. ing.

Conventionally, in the vacuum evaporation of an ITO film used for a light emitting diode element, the substrate is heated to a temperature of 250 ° C. or higher and is formed at a film formation rate of about 0.2 nm / s.
The arithmetic average roughness of the ITO film surface formed under such conditions is about 20 nm or more, and the light emitted from the light emitting layer is scattered and absorbed at the interface between the ITO film surface and the reflective electrode film. There is a problem that the luminance of the light emitting diode element is lowered.
In order to solve this problem, Patent Document 1 discloses a method of forming an alternating electromagnetic field and ionizing the vapor of the ITO material. However, a vacuum deposition apparatus having an alternating electromagnetic field forming means is newly prepared. It was necessary and was not preferable in terms of cost.

JP 2008-182138 A

  The present invention was created to solve the above-mentioned disadvantages of the prior art, and an object of the present invention is to provide a light-emitting diode element having a high light extraction efficiency using a conventional vacuum evaporation apparatus and a method for manufacturing the same. It is.

When the present inventors investigated the relationship between the arithmetic average roughness of the ITO film surface and the reflectance, it was found that the smaller the arithmetic average roughness, the higher the reflectance.
The wavelength of light emitted from the light emitting diode element is, for example, 460 nm for a short wavelength (blue system), and the graph of FIG. 4 shows the relationship between the reflectance of light at that wavelength and the arithmetic average roughness of the ITO film surface. Is shown.
It can be seen from the graph of FIG. 4 that the reflectance necessary for practical use as a light-emitting diode element is 80% or more, and the arithmetic average roughness necessary for obtaining the reflectance of 80% or more is 2.7 nm or less.

The present invention made on the basis of this finding has a light emission layer, and the ITO film disposed on the light emitting layer, and a reflective electrode film disposed on the ITO film, emitted from the light emitting layer The light transmitted through the ITO film is reflected by the reflective electrode film, passes through the ITO film and the light emitting layer, and is emitted to the outside. A substrate exposed on the surface and the ITO material are disposed in a vacuum chamber, and the ITO material is heated and melted while evacuating the vacuum chamber to generate vapor, and the vapor is deposited on the light emitting layer of the substrate. An evaporation process for forming the ITO film on the light emitting layer at a film formation rate of 0.26 nm / s or less while cooling the substrate to a temperature of 100 ° C. or lower; and oxygen gas is applied to the substrate. 400 ° C or higher while in contact with the contained gas And annealing steps of the high-speed high-temperature annealing at 850 ° C. below the annealing temperature, a method of manufacturing a light emitting diode element having a.

The arithmetic average roughness (Ra) is defined in JIS B0601: 2001.
The present invention is configured as described above. When the arithmetic average roughness of the transparent electrode film surface is small, the surface of the reflective electrode film that is in close contact with the transparent electrode film is smooth when the reflective electrode film is formed on the surface. Therefore, light is not scattered or absorbed by the reflective electrode film, and the reflectance is increased.

Since an ITO film having a small arithmetic average roughness on the surface can be produced, a light-emitting diode element with high light extraction efficiency can be produced.
Since a conventional vacuum deposition apparatus can be used, there is no cost for newly preparing a special vacuum deposition apparatus.
Since the light emitting layer is less damaged during the formation of the transparent electrode film than the sputtering method, the light emission amount does not decrease.

(A)-(e): The figure for demonstrating the manufacturing method of the light emitting diode element of this invention. The figure for explaining the structure of the vacuum evaporation system of the transparent electrode film The figure for demonstrating the structure of the conventional light emitting diode element Graph showing the relationship between the arithmetic mean roughness of the ITO film surface and the reflectance Graph showing the relationship between the substrate heating temperature and the arithmetic average roughness of the ITO film surface Graph showing the relationship between the deposition rate of the ITO film and the arithmetic average roughness of the surface

The structure of the light-emitting diode element according to the present invention will be described.
Reference numeral 10e in FIG. 1 (e) denotes a light emitting diode element according to the present invention.
The light emitting diode element 10 e includes a light emitting layer 19, a transparent electrode film 16, and a reflective electrode film 17. The light emitting layer 19 includes an n-type cladding layer 13, an active layer 14, and a p-type cladding layer 15.

A buffer layer 12 is disposed on a transparent transparent substrate 11, and an n-type cladding layer 13 is disposed on the buffer layer 12.
On the n-type cladding layer 13, the active layer 14, the p-type cladding layer 15, the transparent electrode film 16, and the reflective electrode film 17 are arranged in this order so that the n-type cladding layer 13 is partially exposed. Has been.
The transparent electrode film 16 is made of a transparent conductive material, and an ITO film is used here. Here, an Ag film is used as the reflective electrode film 17.
A positive terminal 21 is disposed on the reflective electrode film 17, and a negative terminal 22 is disposed on the exposed surface of the n-type cladding layer 13 so as to be separated from the active layer 14.

When a positive electrode of a DC power source (not shown) is electrically connected to the positive terminal 21 and a negative electrode is connected to the negative terminal 22, respectively, and a DC voltage is applied between the positive terminal 21 and the negative terminal 22, The active layer 14 emits light.
The light emitted from the active layer 14 to the p-type cladding layer 15 side is transmitted through the transparent electrode film 16 and reflected by the reflective electrode film 17, and the transparent electrode film 16, the light emitting layer 19, the buffer layer 12, the transparent substrate 11, and the like. In order and released to the outside.
By the manufacturing method described later, the arithmetic average roughness of the surface of the transparent electrode film 16 that is in close contact with the reflective electrode film 17 is set to 2.7 nm or less, and the resistivity of the transparent electrode film 16 is 1.0 × 10 ⁻³ Ω · cm. It is below.

Since the arithmetic average roughness of the surface of the transparent electrode film 16 that is in close contact with the reflective electrode film 17 is 2.7 nm or less, when the wavelength of light emitted from the active layer 14 is 460 nm, the light enters the reflective electrode film 17. More than 80% of the light is reflected without being scattered or absorbed.
Moreover, since the resistivity of the transparent electrode film 16 is 1.0 × 10 ⁻³ Ω · cm or less, the light-emitting diode element 10 e can be preferably used for use as a light-emitting diode.

Next, an apparatus for manufacturing the light emitting diode element 10e will be described.
Reference numeral 30 in FIG. 2 indicates a vacuum deposition apparatus for the transparent electrode film 16.
The vacuum evaporation apparatus 30 includes a vacuum chamber 39, a stage 32, and a crucible 31.
The vacuum chamber 39 is provided with a vacuum exhaust device 41, and the inside of the vacuum chamber 39 can be evacuated.

The stage 32 and the crucible 31 are arranged in a vacuum chamber 39.
A substrate holding surface 36 is provided on the surface of the stage 32 facing the crucible 31. The substrate holding surface 36 is configured to be able to hold the substrate by electrostatic adsorption or the like.
The stage 32 is provided with a cooling pipe (not shown), and the substrate on the substrate holding surface 36 can be cooled to a predetermined temperature by flowing a cooling medium whose temperature is controlled from the control device 45 to the cooling pipe. .

A concave portion 34 having a concave shape is provided on the surface of the crucible 31 facing the stage 32.
On the opposite side of the crucible 31 from the recess 34, an electron beam generator 35 is disposed here as a heating device. A power supply device 42 disposed outside the vacuum chamber 39 is electrically connected to the electron beam generator 35. A control device 45 is connected to the power supply device 42.

When electric power is supplied from the power supply device 42 to the electron beam generator 35 while evacuating the vacuum chamber 39, the electron beam generator 35 emits electrons into the vacuum chamber 39. The emitted electrons pass through a magnetic field by a coil (not shown), are bent, and enter the vapor deposition material in the recess 34 so that the vapor deposition material can be heated.
A shutter 33 is disposed between the crucible 31 and the stage 32. A control device 45 is connected to the shutter 33 and can be opened and closed at a predetermined timing.

Next, a method for manufacturing the light emitting diode element 10e will be described. The code | symbol 10a-10d of Fig.1 (a)-(d) has shown the process target object in each manufacturing process.
First, as shown in FIG. 1A, a buffer layer 12, an n-type cladding layer 13, an active layer 14, and a p-type cladding layer 15 are arranged on a transparent substrate 11. Reference numeral 10a indicates the object to be processed.
Next, as a vapor deposition step, the object to be processed 10a is carried into the vacuum chamber 39 of the vacuum vapor deposition apparatus 30, and the transparent substrate 11 is opposed to the substrate holding surface 36 on the substrate holding surface 36 of the stage 32, and the p-type cladding layer. Hold so that 15 is exposed facing the crucible 31 side.
A transparent electrode material such as ITO material is disposed in the recess 34 of the crucible 31.

The vacuum exhaust device 41 is activated to evacuate the vacuum chamber 39. Thereafter, evacuation in the vacuum chamber 39 is continued until the vapor deposition process is completed.
A cooling medium is passed through a cooling pipe provided on the stage 32 to cool the processing target 10a to a predetermined temperature. When an ITO material is used as the transparent electrode material, a temperature of 100 ° C. or lower is preferable. Thereafter, the cooling of the processing object 10a is continued until the vapor deposition processing is completed.

While the shutter 33 is closed, the vacuum chamber 39 is evacuated and a predetermined power is supplied from the power supply device 42 to the electron beam generator 35 to emit the electron beam into the vacuum chamber 39. The transparent electrode material is irradiated, and the transparent electrode material is heated and melted to generate vapor.
The method for heating and melting the transparent electrode material in the present invention is not limited to the electron beam irradiation method, and vapor may be generated by heating and melting the transparent electrode material by a heating method such as a resistance heating method.

The shutter 33 is opened so that the vapor of the transparent electrode material reaches the p-type cladding layer 15 of the object to be processed 10a, and the transparent electrode film 16 is formed on the p-type cladding layer 15 as shown in FIG. Film.
During the formation of the transparent electrode film 16, the electron beam is set to a predetermined output value and is formed at a predetermined film formation rate. When an ITO film is formed as the transparent electrode film 16, a film formation rate of 0.26 nm / s or less is preferable.

After forming the transparent electrode film 16 with a predetermined film thickness, the shutter 33 is closed, the power supply to the electron beam generator 35 is stopped, and the vapor deposition process is completed. The code | symbol 10b of FIG.1 (b) has shown the process target object after a vapor deposition process.
As shown in the examples described later, when an ITO film is formed as the transparent electrode film 16, the processing object 10a is cooled to a temperature of 100 ° C. or lower and a film forming rate of 0.26 nm / s or lower. By vapor deposition, the arithmetic average roughness of the ITO film surface can be reduced to 2.7 nm or less.
Further, the transparent electrode film 16 can be formed without damaging the light emitting layer 19 by forming the transparent electrode film 16 by a vacuum deposition method.

Next, as the annealing step, the processing target 10b after the vapor deposition is carried out of the vacuum chamber 39 and placed in a gas atmosphere containing oxygen gas.
While the object to be treated 10b is in contact with a gas containing oxygen gas, the transparent electrode film 16 is subjected to high-temperature and high-temperature annealing (RTA) by a heating method such as irradiation with heating light from a halogen lamp or the like. When the transparent electrode film 16 is an ITO film, an annealing temperature of 400 ° C. or higher and 850 ° C. or lower is preferable.

As shown in the examples described later, when the transparent electrode film 16 is an ITO film by high-speed high-temperature annealing at an annealing temperature of 400 ° C. or higher and 850 ° C. or lower, the arithmetic average roughness of the ITO film surface is annealed. As before, the resistivity of the ITO film can be reduced to 1.0 × 10 ⁻³ Ω · cm or less.

  Next, the object to be processed 10b after the annealing treatment is carried into a film forming apparatus (not shown), and a reflective electrode film is formed on the transparent electrode film 16 by a vacuum vapor deposition method, a sputtering method or the like as shown in FIG. 17 is formed. Reference numeral 10 c in FIG. 1C indicates a processing target after the reflective electrode film 17 is formed.

  Next, the processing object 10c after forming the reflective electrode film 17 is carried into an etching apparatus (not shown), and the reflective electrode film 17, the transparent electrode film 16, the p-type cladding layer 15, and the active layer 14 are partially formed. The n-type cladding layer 13 is partially exposed by etching. Reference numeral 10d in FIG. 1D indicates a processing object after the etching process.

Next, the processed object 10d after the etching process is carried into a film forming apparatus (not shown), and the positive terminal 21 is formed on the reflective electrode film 17 as shown in FIG. A negative terminal 22 is formed on the exposed surface of the n-type cladding layer 13, spaced from the active layer 14.
The light emitting diode element 10e is manufactured by the above-described process.

  In the above manufacturing method, after the reflective electrode film 17 is formed, the transparent electrode film 16, the p-type cladding layer 15 and the active layer 14 are partially removed together with the reflective electrode film 17 by etching. The reflective electrode film 17 may be formed after the transparent electrode film 16, the p-type cladding layer 15 and the active layer 14 are partially removed by etching.

<Example 1>
In the vapor deposition step, the object to be treated and the ITO material were carried into the vacuum chamber 39, and then the vacuum chamber 39 was evacuated to a pressure of 1 × 10 ⁻⁴ Pa. Next, while evacuating the inside of the vacuum chamber 39, an electron beam is generated with an output of 360 W from the electron beam generator 35, irradiated to the ITO material in the recess 34, and the ITO material is heated and melted to generate vapor. It was.

While adjusting the pressure so that the inside of the vacuum chamber 39 during film formation becomes a pressure of 3.0 × 10 ⁻² Pa, the shutter 33 is opened, the vapor of the ITO material reaches the object to be processed, and the ITO film is formed. Started.
During film formation, the film formation rate was set to 0.05 nm / s, and the object to be processed was cooled to a temperature of 24 ° C.
After the ITO film was formed to a thickness of 40 nm, the shutter 33 was closed, the electron beam generator 35 was stopped, and the vapor deposition process was completed.
Next, the object to be treated was taken out of the vacuum chamber 39, and the arithmetic average roughness of the ITO film surface was measured using an AFM (atomic force microscope).

The above measurement was repeated by changing the object to be processed during film formation to a predetermined temperature of 24 ° C. or higher and 150 ° C. or lower.
The graph of FIG. 5 shows the relationship between the temperature of the processing object during film formation and the arithmetic average roughness of the ITO film surface after film formation.
From the graph of FIG. 5, it can be seen that in order to reduce the arithmetic average roughness to 2.7 nm or less, it is necessary to cool the object to be processed to a temperature of 100 ° C. or less during film formation.

<Example 2>
In the same measurement as in Example 1, the film formation rate was set to 0.05 nm / s or more by cooling the processing target during film formation to a temperature of 24 ° C. and changing the electron beam to an output of 360 W or more and 460 W or less. It changed and changed to the predetermined | prescribed rate of 0.4 nm / s or less, and repeated.
The graph of FIG. 6 shows the relationship between the deposition rate during the deposition of the ITO film and the arithmetic average roughness of the surface.
From the graph of FIG. 6, it can be seen that in order to make the arithmetic average roughness 2.7 nm or less, the film formation rate must be 0.26 nm / s or less during the ITO film formation.

<Example 3>
In the annealing step, the object to be treated after the ITO film deposition was placed in a gas atmosphere of 80% nitrogen and 20% oxygen. At this time, the pressure in the annealing apparatus was adjusted to atmospheric pressure.
High-speed high-temperature annealing (RTA) was performed for 1 minute at an annealing temperature of 350 ° C. using a halogen lamp.
Next, the object to be treated was taken out of the annealing apparatus, and the resistivity and arithmetic average roughness of the ITO film were measured.

The above measurement was repeated by changing the annealing temperature to a predetermined temperature of 350 ° C. or higher and 850 ° C. or lower.
Table 1 shows the relationship between the annealing temperature, the resistivity of the ITO film, and the arithmetic average roughness.

From Table 1, even if the annealing temperature is changed, the arithmetic average roughness does not change, and in order to make the resistivity 1.0 × 10 ⁻³ Ω · cm or less, the annealing temperature needs to be 400 ° C. or higher. I know that there is.

10e: Light emitting diode element 16: Transparent electrode film 17: Reflective electrode film 19: Light emitting layer

Claims (1)

A light emitting layer, an ITO film disposed on the light emitting layer, and a reflective electrode film disposed on the ITO film;
The light emitted from the light emitting layer and transmitted through the ITO film is reflected by the reflective electrode film, passes through the ITO film and the light emitting layer, and is emitted to the outside. ,
The substrate having the light emitting layer exposed on the surface and the ITO material are disposed in a vacuum chamber, and the ITO material is heated and melted while the vacuum chamber is evacuated to generate vapor, and the vapor is generated on the substrate. A vapor deposition step of depositing the ITO film on the light emitting layer at a film forming rate of 0.26 nm / s or less while reaching the light emitting layer and cooling the substrate to a temperature of 100 ° C. or less;
An annealing step of performing high-speed high-temperature annealing at an annealing temperature of 400 ° C. or higher and 850 ° C. or lower while contacting the substrate with a gas containing oxygen gas;
The manufacturing method of the light emitting diode element which has this.

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