JP2009231591A - Method for manufacturing light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve ESD susceptibility related with a method for manufacturing a light emitting element. <P>SOLUTION: The method for manufacturing a light emitting element has a process to form an MQW active layer 24 including a process to form a well layer 21 composed of a nitride semiconductor layer, a process to form a barrier layer 23 using a carrier gas containing hydrogen of the ratio of 2% or more to nitride and a total flow rate of carrier gas on the well layer 21. Since the barrier layer 23 in the MQW active layer 24 is made to grow using the carrier gas containing hydrogen of the ratio of 2% or more to the nitride and the total flow rate of carrier gas, it is possible to improve the ESD susceptibility. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for manufacturing a light emitting device, and more particularly to a method for manufacturing a light emitting device having a nitride semiconductor layer.

  An LED having a nitride semiconductor layer is used as a light emitting element such as a white LED (Light Emitting Diode). In such an LED, an active layer having an MQW (Multi Quantum Well) structure is used. When forming the MQW active layer, nitrogen is used as a carrier gas as described in Patent Document 1.

Japanese Patent Laid-Open No. 2006-1000047 IEICE technical report Vol.105 No.326 pp.81-84.

  In an LED having a nitride semiconductor layer, there is a problem that an electrostatic discharge (ESD) breakdown voltage is low. When forming the MQW active layer, nitrogen is used as a carrier gas as described in Patent Document 1. Non-Patent Document 1 discloses a method using a carrier gas added with 1% of hydrogen in the growth of a GaN barrier layer in an MQW active layer.

  An object of the present invention is to improve the ESD withstand voltage.

  The present invention provides a step of forming a well layer composed of a nitride semiconductor layer, and a barrier layer using a carrier gas containing nitrogen and hydrogen at a ratio of 2% or more with respect to the total carrier gas flow rate on the well layer. And a step of forming an MQW active layer including the step of forming a light emitting device. According to the present invention, since the barrier layer in the MQW active layer is grown using nitrogen and a carrier gas containing hydrogen at a ratio of 2% or more with respect to the total carrier gas flow rate, the ESD breakdown voltage can be improved. .

  In the above configuration, the carrier gas for forming the well layer is nitrogen, and the step of forming the barrier layer includes the step of forming a first barrier layer using a carrier gas composed of nitrogen, and the first barrier. Forming a second barrier layer on the layer using a carrier gas containing nitrogen and hydrogen at a ratio of 2% or more with respect to the total carrier gas flow rate. According to this configuration, the well layer can be prevented from being scraped by the carrier gas containing hydrogen.

  In the above-described configuration, the step of forming the barrier layer can be performed using a growth gas composed of trimethylgallium and ammonia under conditions of a growth temperature of 820 to 840 ° C. and a growth pressure of 290 to 310 torr. .

  The said structure WHEREIN: The said barrier layer can be set as the structure which consists of either GaN, AlGaN, and InAlGaN. Moreover, the said board | substrate can be set as the structure which is either Si, SiC, GaN, and sapphire. Furthermore, in the above configuration, the MQW active layer can be formed using the MOCVD method.

  According to the present invention, the ESD withstand voltage can be improved.

  As in Patent Document 1, it is conventionally known that nitrogen gas is used as a carrier gas when growing an MQW active layer. The inventor has found that the ESD breakdown voltage is improved by adding a predetermined flow rate of hydrogen to the carrier gas when growing the barrier layer of the MQW active layer. Examples of the present invention will be described below.

  A method for manufacturing a light-emitting element according to Example 1 will be described with reference to FIGS. Referring to FIG. 1, an AlN buffer layer 12, a Si-doped GaN buffer layer 14, and an undoped layer are formed on a sapphire substrate 10 having (0001) as a main surface by using a MOCVD (Metal Organic Chemical Vapor Deposition) method. A GaN buffer layer 16, an n-type GaN intermediate layer 18, an n-type GaN contact layer 20, an n-type GaN layer 22, an MQW active layer 24, and a p-type GaN layer 26 are sequentially grown.

The growth conditions for each layer are as follows.
Growth conditions for AlN buffer layer 12 Film thickness: 580 nm
Dope concentration: undoped Source gas: TMA (trimethylaluminum), NH ₃
Carrier gas: Hydrogen Pressure: 50 Torr
Growth temperature: 1040 ° C. (growth 1), 1140 ° C. (growth 2)
The growth temperature is changed from growth 1 to growth 2 during the growth.

Growth conditions for Si-doped GaN buffer layer 14 Film thickness: 60 nm
Si doping concentration: 1.5 × 10 ¹⁹ cm ⁻³
Source gas: TMG (trimethyl gallium), NH ₃ , SiH ₄
Carrier gas: Hydrogen Pressure: 200 Torr
Growth temperature: 1040 ° C

Growth condition of undoped GaN buffer layer 16 Film thickness: 1330 nm
Dope concentration: undoped Source gas: TMG, NH ₃
Carrier gas: Hydrogen Pressure: 200 Torr
Growth temperature: 1040 ° C

Growth conditions for n-type GaN intermediate layer 18 Film thickness: 1380 nm
Si doping concentration: 1.5 × 10 ¹⁹ cm ⁻³
Source gas: TMG, NH ₃ , SiH ₄
Carrier gas: Hydrogen Pressure: 100 Torr
Growth temperature: 1040 ° C

Growth conditions for n-type InGaNIn contact layer 20 Film thickness: 500 nm
Source gas: TMG, TMI (trimethylindium), NH ₃ , SiH ₄
Si doping concentration: 1.5 × 10 ¹⁹ cm ⁻³
Carrier gas: Hydrogen Pressure: 200 Torr
Growth temperature: 1180 ° C

Growth conditions for n-type GaN layer 22 Film thickness: 170 nm
Si doping concentration: 1.5 × 10 ¹⁹ cm ⁻³
Source gas: TMG, NH ₃ , SiH ₄
Carrier gas: Hydrogen Pressure: 100 Torr
Growth temperature: 1040 ° C

Growth condition of MQW active layer 24 Film thickness: 65 nm
Number of layers: 5 well layers, 7 barrier layers Well layers: In _0.16 Ga _0.84 N
Film thickness: 2.2nm
Dope concentration: undoped Source gas: TEG (triethylgallium), TMI, NH ₃
Carrier gas: Nitrogen Pressure: 300 Torr
Growth temperature: 720 ° C
Barrier layer: GaN
Film thickness: 9.5 nm
Dope concentration: 5 × 10 ¹⁷ cm ⁻³
Source gas: TEG, NH ₃
Carrier gas: Mixed gas of hydrogen 1 SLM and nitrogen 12 SLM: However, in the initial growth of the barrier layer (during the growth of the first barrier layer), the barrier layer is grown only with the nitrogen carrier gas.
Pressure: 300 Torr
Growth temperature: 830 ° C

Growth conditions of p-type GaN layer 26 Film thickness: 200 nm
Mg doping concentration: 4 × 10 ¹⁹ cm ⁻³
Source gas: TMG, NH ₃ , Cp ₂ Mg (biscyclopentadienyl magnesium)
Carrier gas: Hydrogen Pressure: 200 Torr
Growth temperature: 975 ° C

  With reference to FIG. 2, the region where the n-type electrode 30 is to be formed is selectively dry-etched up to the n-type InGaN contact layer 20. A mesa-shaped semiconductor structure remains in the unetched portion, and this portion becomes a light emitting portion. A p-type electrode 28 made of NiAu is formed on a part of the p-type GaN layer 26 using a vapor deposition method so as to be electrically connected to the p-type GaN layer 26. Annealing is performed at 500 ° C. in the atmosphere to form an alloy with the p-type GaN layer 26. An n-type electrode 30 made of Ta / Al / Pt is formed from below on a part of the bottom surface of the groove so as to be electrically connected to the n-type InGaN contact layer 20 by vapor deposition. Annealing is performed at 500 ° C. in the atmosphere to form an alloy with the n-type InGaN contact layer 20. Thus, the structure of FIG. 2 is completed. Thereafter, a protective film (not shown) made of silicon oxide and an electrode pad (not shown) connected to the p-type electrode 28 and the n-type electrode 30 are formed by a known method.

  Using the scribe method, the wafer is divided from the back surface of the substrate 10 and divided into chips of, for example, about 350 μm × 350 μm. After that, it is mounted on the package. Thus, the LED according to Example 1 is completed. The p-type electrode 28 and the n-type electrode 30 may be made of ITO (indium tin oxide) or the like.

  FIG. 3 shows the hydrogen concentration in the carrier gas of the n-type GaN layer 22, the active layer 24, and the p-type GaN layer 26 (the ratio of hydrogen to hydrogen and the total carrier gas flow rate) and the In composition ratio of the growing layer with respect to time. FIG. The number of GaN barrier layers 23 and InGaN well layers 21 in the active layer 24 is not shown. As shown in FIG. 3, when growing the n-type GaN layer 22 and the p-type cladding layer active layer 24, hydrogen is used as a carrier gas. On the other hand, nitrogen is used as a carrier gas when the well layer 21 is grown. This is because, when hydrogen is used as a carrier gas, the InGaN well layer 21 is scraped by hydrogen when the well layer 21 is grown. The GaN barrier layer 23 has a first barrier layer 23a and a second barrier layer 23b.

  The first barrier layer 23 a has a thickness of 1.5 nm, is formed on the well layer 21, and the carrier gas is the same nitrogen as the carrier gas used when forming the well layer 21. The film thickness of the first barrier layer 23a is preferably 1.5 nm or more. This is to suppress the disappearance of the first barrier layer 23a due to the influence of hydrogen attached as a carrier gas during the growth of the second barrier layer 23b. This can prevent the well layer 21 under the first barrier layer 23a from being exposed during the growth of the second barrier layer 23b.

  The second barrier layer 23b has a thickness of 8 nm and is formed on the first barrier layer 23a. The carrier gas contains hydrogen having a hydrogen concentration x in addition to nitrogen. When forming the second barrier layer 23b, the hydrogen flow rate may be gradually increased with respect to nitrogen supplied as a carrier gas. For example, when the ratio of the hydrogen flow rate to the total flow rate of all the carrier gases is finally set to 2%, the hydrogen flow rate ratio is changed in the order of 0.5%, 1.0%, 1.5% and 2.0%. It can be increased step by step.

Table 1 is a table showing the hydrogen concentration x of the carrier gas when forming the second barrier layer 23b of the sample 1 to the sample 3 manufactured as a prototype. Sample 1 is a comparative example, and the carrier gas has a hydrogen concentration of 0% and nitrogen of 100%.

  With respect to the LEDs according to Sample 1 to Sample 3, the ESD withstand voltage in the reverse direction was evaluated. For the ESD application, a human body model to which a resistance of 1.5 kΩ and a capacity of 100 pF were added was used to determine whether or not the LED was destroyed after being applied five times. That is, it is determined whether the LED is broken before and after application of the reverse voltage (implemented five times). If the LED is not broken, the reverse voltage is increased. When the LED was destroyed, the voltage was taken as the ESD withstand voltage. In addition, determination of destruction of LED was performed by the fluctuation | variation of the voltage value at the time of confirmation of light emission of LED, and forward direction electricity supply. Table 1 shows the ESD withstand voltage of each sample.

  FIG. 4 is a diagram showing the ESD withstand voltage with respect to the hydrogen concentration of the carrier gas when the second barrier layer 23b is grown. Here, the hydrogen concentration of 2% indicates that the flow rate of hydrogen is 2% with respect to the total flow rates of nitrogen and all carrier gases.

  From FIG. 4, the hydrogen concentration in the carrier gas is preferably 2% or more, and in that case, the ESD withstand voltage is increased. At this time, a practical level of 2000 V or more can be obtained as the ESD withstand voltage of the LED. This is considered because the crystallinity of the second barrier layer 23b is improved. A more preferable range of the hydrogen concentration is 8% or more. As described above, the growth of the well layer 21 uses a carrier gas not containing hydrogen (for example, a nonvolatile gas such as nitrogen) to suppress the well layer from being scraped. On the other hand, the growth of the barrier layer 23 can improve the ESD withstand voltage by using a carrier gas containing 2% or more of hydrogen.

In the first embodiment, the growth gas for forming the barrier layer 23 is TEG, ammonia (NH ₃ ), the growth temperature is 830 ° C., and the growth pressure is 300 torr. In order to improve the ESD withstand voltage, it is preferable that the growth gas is TEG and NH ₃ , the growth temperature is 820 to 840 ° C., and the growth pressure is 290 to 310 torr.

  The active layer 24 may be a nitride semiconductor layer other than GaN and InGaN as long as it functions as a light emitting layer. In particular, the GaN barrier layer 23 is preferably made of any one of GaN, AlGaN, and InAlGaN.

  The first barrier layer 23a may not be provided, but if the second barrier layer 23b is formed directly on the well layer 21, the well layer 21 may be scraped by hydrogen when the second barrier layer 23b is grown. Therefore, the carrier gas when forming the well layer 21 is nitrogen, and the first barrier layer 23a is formed using the same nitrogen carrier gas as the carrier gas used when forming the well layer 21, and the second barrier layer 23b is preferably formed using a carrier gas having a hydrogen concentration of 2% or more.

  Although the example using the sapphire substrate 10 has been described in the first embodiment, any of a Si substrate, a SiC substrate, and a GaN substrate may be used. The n-type GaN layer 22 and the p-type GaN layer 26 may be nitride semiconductor layers other than GaN as long as the refractive index is higher than that of the active layer 24.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

FIG. 1 is a cross-sectional view illustrating the method for manufacturing the LED according to the first embodiment. FIG. 2 is a cross-sectional view of the LED according to the first embodiment. FIG. 3 is a diagram showing the hydrogen concentration in the carrier gas of Example 1. FIG. 4 is a diagram showing the ESD withstand voltage of each material.

Explanation of symbols

10 substrate 12 AlN buffer layer 14 Si-doped GaN buffer layer 16 undoped GaN buffer layer 18 n-type GaN intermediate layer 20 n-type InGaN contact layer 21 well layer 22 n-type GaN layer 23 barrier layer 23a first barrier layer 23b second barrier layer 24 active layer 26 p-type GaN layer 28 p-type electrode 30 n-type electrode

Claims (6)

  Forming a well layer made of a nitride semiconductor layer; forming a barrier layer on the well layer using nitrogen and a carrier gas containing hydrogen at a ratio of 2% or more with respect to the total carrier gas flow rate; A method for manufacturing a light emitting device, comprising: forming an MQW active layer including:   The carrier gas used to form the well layer is nitrogen, and the step of forming the barrier layer includes the step of forming the first barrier layer using a carrier gas composed of nitrogen, and the first barrier layer. Forming a second barrier layer using a carrier gas containing nitrogen and hydrogen in a proportion of 2% or more with respect to the total carrier gas flow rate. Method.   The step of forming the barrier layer is performed using a growth gas composed of trimethylgallium and ammonia under conditions of a growth temperature of 820 to 840 ° C. and a growth pressure of 290 to 310 torr. The manufacturing method of the light emitting element of description.   The method for manufacturing a light emitting device according to claim 1, wherein the barrier layer is made of any one of GaN, AlGaN, and InAlGaN.   The method for manufacturing a light emitting element according to claim 1, wherein the substrate is one of Si, SiC, GaN, and sapphire. 2. The method of manufacturing a light emitting device according to claim 1, wherein the active layer is formed by MOCVD.

Images