JP4380666B2 - Epitaxial wafer manufacturing method - Google Patents

Description

  The present invention relates to an epitaxial wafer of a III-V compound semiconductor and a manufacturing method thereof. More specifically, the present invention relates to a method for manufacturing a GaN compound semiconductor.

  FIG. 6 shows a cross-sectional view of GaN blue and green semiconductor light emitting devices (LEDs) using a commercially available sapphire substrate. The LED shown in FIG. 6 is formed on an epitaxial wafer composed of a sapphire substrate 1, a GaN buffer layer 2 formed on the substrate 1, and a hexagonal GaN epitaxial layer 3 formed on the GaN buffer layer 2. The first cladding layer 4, the light emitting layer 5, the second cladding layer 6 and the GaN epitaxial layer 7 are laminated in this order, and ohmic electrodes 8 and 9 are disposed on the GaN epitaxial layers 3 and 7, respectively. In the LED of FIG. 6, the GaN buffer layer 2 is provided to alleviate strain due to the difference in lattice constant between the sapphire substrate 1 and the GaN epitaxial layer 3.

  Since the LED of FIG. 6 uses insulating sapphire for the substrate 1, it is necessary to form two types of electrodes on the same surface side of the substrate when forming an element by forming electrodes. For this reason, patterning by photolithography is required twice or more. In addition, since it is necessary to perform nitride etching by reactive ion etching, the production process becomes complicated. Furthermore, since sapphire has a high hardness, it has a problem that it is difficult to handle at the time of element isolation.

Therefore, an attempt has been made to use conductive GaAs as a substrate instead of sapphire having such defects. For example, in Document 1 below, cubic GaN is grown on the GaAs (100) plane. However, generally, the cubic GaN grown on the GaAs (100) plane has many stacking faults and poor quality as shown in the transmission electron micrograph shown in Reference 1. This is thought to be because cubic GaN is unstable compared to hexagonal GaN.
Journal of Crystal Growth 164 (1996) 149-153 Journal of Electronic Materials vol.24 No.4 (1995) 213-218

  On the other hand, attempts have been made to grow more stable hexagonal GaN on the GaAs (111) plane. For example, the above literature 2 reports the growth of GaN on the GaAs (111) A surface and the GaAs (111) B surface by the MOVPE method. However, the growth of GaN having sufficient characteristics for manufacturing blue LEDs has not been achieved. This is because the epitaxial layer of the semiconductor light emitting device on the sapphire substrate is grown at a growth temperature of 1000 ° C. or higher by the MOVPE method, whereas the growth temperature of the GaN epitaxial layer in Reference 2 is 800 ° C. at the maximum. The reason for this is low. The reason why the growth temperature of the GaN epitaxial layer in Document 2 is low is that when a GaAs substrate is heated, arsenic having a high vapor pressure is released at about 600 ° C.

As described above, when a hexagonal GaN film is epitaxially grown on a conventional GaAs (111) substrate, the substrate temperature can only be raised to about 850 ° C. in order to avoid damage to the GaAs substrate due to heat. As a result, the hexagonal GaN epitaxial film obtained by the conventional organometallic chloride vapor phase epitaxial method has a high carrier concentration of non-doped GaN of 1 × 10 ¹⁹ (cm ⁻³ ), and has sufficient electrical characteristics for the production of blue LEDs. It wasn't.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and provide a GaN epitaxial wafer formed on a GaAs semiconductor substrate and having sufficient electrical characteristics for manufacturing a blue LED, and a method for manufacturing the same. .

  According to the present invention, a cubic semiconductor (111) substrate, a first GaN layer having a thickness of 60 nm or more formed on the substrate, and a thickness of 0.1 μm or more formed on the first GaN layer. There is provided an epitaxial wafer comprising a second GaN layer. In the epitaxial wafer of the present invention, the thickness of the first GaN layer is preferably 200 nm or less, and the thickness of the second GaN layer is preferably 5 μm or less.

  In the epitaxial wafer of the present invention, the cubic semiconductor (111) substrate is preferably a GaAs (111) substrate. When the GaAs (111) substrate is a GaAs (111) A-plane substrate, it is advantageous that arsenic is difficult to escape. When the GaAs (111) substrate is a GaAs (111) B-plane substrate, It is preferable that the surface is easily polished.

  On the other hand, in the present invention, a first raw material gas containing an organic metal containing Ga and HCl and a second raw material gas containing NH3 are supplied into a reaction tube heated from the outside, and a substrate installed in the reaction tube. Vapor phase growth of the buffer layer at a first temperature thereon, increasing the temperature of the substrate on which the buffer layer is formed from the first temperature to improve the crystallinity of the buffer layer, Supplying a second source gas into a reaction tube heated to a second temperature higher than the first temperature, and growing a GaN layer on the buffer layer. A manufacturing method is provided. The first temperature is preferably 400 ° C. or more and 600 ° C. or less, and the second temperature is preferably 850 ° C. or more and 1000 ° C. or less.

In the step of raising the temperature of the substrate on which the buffer layer is formed from the first temperature to improve the crystallinity of the buffer layer, it is also preferable to raise the temperature of the substrate while supplying NH ₃ onto the substrate. On the other hand, the growth rate of the GaN layer is preferably 4 μm / hour or more and 10 μm / hour or less.

  The epitaxial wafer of the present invention comprises a first GaN layer formed on a cubic semiconductor (111) substrate and having a thickness of 60 nm or more. The first GaN layer is an amorphous layer formed at a low temperature of 400 to 600 ° C., and becomes crystalline when the temperature is raised thereafter. Therefore, there are many stacking faults, and the concentration of impurities such as chlorine, hydrogen, and oxygen is high. The primary purpose of the first GaN layer is to protect the semiconductor substrate in the subsequent high-temperature film forming process. Therefore, the semiconductor substrate must be grown at a low temperature of 400 to 600 ° C. which does not damage the substrate, and the thickness needs to be 60 nm or more. On the other hand, since the first GaN layer is grown at a low temperature, the growth rate is slow. Therefore, the formation of a thickness of 200 nm or more is disadvantageous from the viewpoint of manufacturing efficiency, and even if the thickness is formed more than that, the function of protecting the semiconductor substrate is not improved.

  On the other hand, the epitaxial wafer of the present invention comprises a second GaN layer formed on the first GaN layer and having a thickness of 0.1 μm or more. The second GaN layer is a so-called epitaxial layer and preferably has a thickness of 5 μm or less. When the thickness of the second GaN layer exceeds 5 μm, a crack occurs in the GaN film due to stress.

In the method of the present invention, a first source gas containing an organic metal containing Ga and HCl and a second source gas containing NH ₃ are supplied into a reaction tube heated from the outside, and a substrate installed in the reaction tube. A buffer layer is vapor grown at a low first temperature. This buffer layer is formed for protecting the semiconductor substrate as described above, and is formed at a low temperature of 400 to 600 ° C. so as not to damage the semiconductor substrate. The buffer layer is amorphous immediately after the film formation, but becomes crystalline by the subsequent temperature raising step. However, as compared with an epitaxial layer formed later on this buffer layer, the number of stacking faults is so great that it can be distinguished. Therefore, according to the method of the present invention, a GaAs substrate that has been difficult to use can be used. In the step of raising the buffer layer, NH ₃ is preferably supplied onto the substrate. As a result, the GaN buffer layer can be prevented from evaporating and sublimating during the temperature rise.

  On the semiconductor substrate protected by this buffer layer, a GaN layer is formed at a high temperature suitable for epitaxial growth of GaN. This growth temperature is preferably 850 ° C. or higher and 1000 ° C. or lower. The GaN layer is grown to a thickness necessary for the device to be finally produced, but if it is less than 0.1 μm, it is too thin, and if it exceeds 5 μm, there is a risk of cracking.

  The growth rate of the GaN layer is preferably 4 μm / hour or more and 10 μm / hour or less. If the growth rate is less than 4 μm / hour, the substrate may be damaged by heat and the GaN epitaxial film may be peeled off. On the other hand, if the growth rate exceeds 10 μm / hour, the crystallinity of the GaN epitaxial film deteriorates, and it is not possible to obtain GaN having sufficient electrical characteristics for manufacturing a blue LED.

Furthermore, in the present invention, the first source gas containing HCl and the second source gas containing NH ₃ are supplied from the outside into the reaction tube heated and stored in a container disposed inside the reaction tube. Reacting the metal Ga with HCl contained in the first source gas to produce GaCl, and vapor-phase-growing a buffer layer at a first temperature on the substrate installed in the reaction tube; A step of raising the temperature of the substrate on which the layer is formed from the first temperature to improve the crystallinity of the buffer layer; and a second step in which the first and second source gases are higher than the first temperature. And supplying a process tube heated to a temperature to grow a GaN layer on the buffer layer. This method of the present invention is a so-called hydride vapor phase epitaxy (HVPE). In this method of the present invention, it is preferable that the metal Ga is accommodated in, for example, a quartz boat and always kept at 800 ° C. or higher. In addition, it is preferable to generate GaCl by blowing a first source gas containing HCl into a quartz boat containing metal Ga.

Example 1
FIG. 4 is a diagram showing a schematic configuration of a vapor phase growth apparatus that can be used for manufacturing the epitaxial wafer of the present invention by the method of the present invention. 4 includes a quartz reaction chamber 54 having a first gas inlet 51, a second gas inlet 52 and an exhaust 53, and a resistance for heating the entire chamber from the outside of the reaction chamber 54. And a heater 55. Further, a substrate holder 56 is provided in the reaction chamber 54, and a substrate 57 is mounted thereon.

Using the above apparatus, the epitaxial wafer of the present invention was produced by the method of the present invention as follows. First, a GaAs (111) A surface substrate 57 was mounted on the substrate holder 56 in the reaction chamber 54. Next, the inside of the chamber 54 is heated from the outside by the resistance heater 55 and the substrate 57 is held at 450 ° C., and TMG is supplied from the first gas inlet 51 at a partial pressure of 6.4 × 10 ⁻⁴ atm, Hydrogen chloride was introduced at a partial pressure of 6.4 × 10 ⁻⁴ atm, and ammonia gas (NH ₃ ) was introduced from the second gas inlet 52 as a Group V raw material at 0.11 atm. Hydrogen gas was used as the carrier gas. Under such conditions, film formation was performed for 30 minutes to form a GaN buffer layer having a thickness of 100 nm.

Next, the temperature of the substrate 57 on which the GaN buffer layer is formed in this manner is raised to 900 ° C. by the resistance heater 55 in an atmosphere of NH ₃ partial pressure of 0.11 atm, and then TMG, HCl, NH ₃ Film formation was performed for 30 minutes under partial pressure conditions of 2.4 × 10 ⁻³ atm, 2.4 × 10 ⁻³ atm, and 0.11 atm, respectively.

As a result, a mirror-like GaN epitaxial layer having a thickness of 3 μm was formed on the buffer layer. The growth rate was 6 μm / hour. A cross-sectional view of the obtained epitaxial wafer is shown in FIG. The epitaxial wafer shown in FIG. 1 includes a first GaN layer 12 having a high impurity concentration on a GaAs (111) A-plane substrate 11 and a second GaN layer 13 stacked thereon. As a result of X-ray diffraction measurement, a hexagonal GaN peak was observed, and it was confirmed that the second GaN layer 13 was composed of hexagonal GaN. When the electrical characteristics were determined by Hall measurement, the n-type carrier concentration was 1 × 10 ¹⁷ (cm ⁻³ ) and the electron mobility was 500 (cm ² / Vs).

FIG. 2 shows a transmission electron micrograph of a cross section of the obtained epitaxial wafer. A portion where there is a quarter horizontal line from the bottom of FIG. 2 is a buffer layer, and the horizontal line indicates a stacking fault. That is, the portion that was the buffer layer has many stacking faults even after completion of the epitaxial wafer, and can be easily distinguished. Moreover, the result of the secondary ion mass spectrometry (SIMS) of the epitaxial wafer obtained in FIG. 3 is shown. As can be seen from FIG. 3, the portion which was the buffer layer of the epitaxial wafer of the present invention has a high concentration of impurities such as hydrogen, oxygen and chlorine. This is because the buffer layer was grown at a low temperature. The impurity concentration may reach 5 × 10 ²¹ / cm ^{3 for} chlorine, 4 × 10 ¹⁹ / cm ^{3 for} hydrogen, and 1.5 × 10 ¹⁹ / cm ³ for oxygen. In the above embodiment, a GaAs (111) A-plane substrate is used. However, even when an epitaxial wafer is manufactured under the same conditions using a GaAs (111) B-plane substrate, film peeling tends to occur slightly. A GaN layer having almost the same characteristics was obtained.

Example 2
FIG. 5 shows a schematic configuration of a hydride vapor phase epitaxy apparatus that can be used to manufacture the epitaxial wafer of the present invention by the method of the present invention. The apparatus of FIG. 5 includes a quartz reaction chamber 54 having a first gas inlet 51, a second gas inlet 52 and an exhaust 53, and a resistance for heating the entire chamber from the outside of the reaction chamber 54. And a heater 55. In the upper part of the reaction chamber 54, a quartz boat 58 containing a metal Ga 59 is arranged so that the source gas introduced from the first gas introduction port 51 is blown into the quartz boat 58. Further, a substrate holder 56 is provided in the reaction chamber 54, and a substrate 57 is mounted thereon.

In this example, the epitaxial wafer of the present invention was manufactured by the method of the present invention using the above apparatus as follows. First, the metal Ga 59 was accommodated in the quartz boat 58, and the GaAs (111) A surface substrate 57 was mounted on the substrate holder 56 in the reaction chamber 54. Next, the entire inside of the chamber 54 is heated from the outside by the resistance heater 55, and the hydrogen chloride gas (HCl) is supplied from the first gas inlet 51 in a state where the metal Ga59 is held at 800 ° C. or higher and the substrate 57 is held at 500 ° C. ) At a partial pressure of 6.4 × 10 ⁻⁴ atm, and ammonia gas (NH ₃ ) was introduced from the second gas inlet 52 as a Group V raw material at 0.11 atm. Hydrogen gas was used as the carrier gas. The HCl gas was blown into the quartz boat 58 and reacted with the metal Ga59 to produce GaCl, which was carried downstream of the chamber 54. Film formation was performed under such conditions to form a GaN buffer layer. When the GaN buffer layer became 90 nm thick, the supply of HCl gas was stopped to stop the growth of the buffer layer.

Next, the temperature of the substrate 57 on which the GaN buffer layer is formed in this manner is raised to 980 ° C. by the resistance heater 55 while NH ₃ is flowing, and then the supply of HCl gas is started again. A GaN epitaxial layer was grown on the layer. Film formation was performed under conditions of partial pressures of HCl and NH ₃ of 2.4 × 10 ⁻³ atm and 0.11 atm, respectively. Film formation is possible even at a substrate temperature of about 1030 ° C., but the GaAs substrate reacts with NH ₃ gas and is severely damaged.

When the GaN layer grows to about 4 μm, the supply of HCl is stopped and cooling is performed with NH ₃ flowing. Thus, a mirror-like GaN epitaxial layer having a thickness of 4 μm was formed on the buffer layer. According to SIMS analysis, unlike in Example 1, carbon impurities were below the detection limit. When the electrical characteristics were determined by Hall measurement, the n-type carrier concentration was 1 × 10 ¹⁸ (cm ⁻³ ), the electron mobility was 250 (cm ² / Vs), and the X-ray half width was about 5.2 minutes.

Comparative Example 1
In order to compare the difference in the growth of the GaN epitaxial layer due to the difference in the thickness of the buffer layer, a GaN epitaxial layer was formed after forming a 30 nm buffer layer on the GaAs (111) A-plane substrate 1. The growth conditions of the buffer layer and the epitaxial layer other than the thickness of the buffer layer were the same as those in Example 1. As a result, the GaN film on the GaAs substrate was completely peeled off.

Comparative Example 2
In order to compare the difference in GaN epitaxial layer growth due to the difference in growth rate, a GaN epitaxial layer was formed at a growth rate of 3 μm / h. In this comparative example, the partial pressures of the raw materials TMG, HCl, and NH ₃ are 4.8 × 10 ⁻⁴ atm, 4.8 × 10 ⁻⁴ atm, and 0.11 atm, respectively, because the growth rate changes depending on the amount of TMG input. The growth conditions of the buffer layer and the epitaxial layer other than the raw material partial pressure during the epitaxial layer growth were the same as those in Example 1. As a result, the GaN film on the GaAs substrate was completely peeled off.

Comparative Example 3
In order to compare the difference in GaN epitaxial layer growth due to the difference in growth temperature, a GaN epitaxial layer was formed at a growth temperature of 800 ° C. The growth conditions of the buffer layer and the epitaxial layer other than the growth temperature of the epitaxial layer were the same as those in Example 1. As a result, a mirror-like GaN epitaxial layer 13 having a thickness of 3 μm was formed on the buffer layer 12. As a result of X-ray diffraction measurement, a hexagonal GaN peak was observed, confirming that the GaN epitaxial layer 13 was composed of hexagonal GaN. When the electrical characteristics were determined by Hall measurement, the n-type carrier concentration was 1 × 10 ¹⁹ (cm ⁻³ ) and the electron mobility was 100 (cm ² / Vs).

  As described above, according to the present invention, it is possible to manufacture a high-quality GaN epitaxial wafer sufficient for producing a blue LED on a cubic semiconductor (111) substrate. By using a substrate such as GaAs (111), it is possible to obtain a blue LED in which element isolation is easier than before and electrical contacts can be easily formed.

It is sectional drawing which shows the cross-sectional structure of an example of the compound semiconductor epitaxial wafer of this invention. It is an electron micrograph of the section of the compound semiconductor epitaxial wafer of the present invention. It is a graph which shows the secondary ion mass spectrometry result of the compound semiconductor epitaxial wafer of this invention. It is a figure which shows schematic structure of the vapor phase growth apparatus which can be used in order to produce the epitaxial wafer of this invention with the method of this invention. It is a figure which shows schematic structure of the hydride vapor phase epitaxy apparatus which can be used in producing the epitaxial wafer of this invention with the method of this invention. It is sectional drawing which shows the structure of the conventional blue light emitting element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 GaN buffer layer 3 GaN epitaxial layer 4 Clad layer 5 Light emitting layer 6 Clad layer 7 Contact layer 8 Ohmic electrode 9 Ohmic electrode
11 GaAs substrate
12 First GaN layer
13 GaN epitaxial layer
51 First gas inlet
52 Second gas inlet
53 Exhaust vent
54 Reaction chamber
55 Resistance heater
56 Susceptor
57 PCB
58 Quartz boat
59 Metal Ga

Claims (1)

Supplying a first source gas containing an organic metal containing Ga and HCl, and a second source gas containing NH ₃ into a reaction tube heated from the outside;
Alternatively, a first raw material gas containing HCl and a second raw material gas containing NH ₃ are supplied into a reaction tube heated from the outside, and a metal Ga stored in a container disposed inside the reaction tube; React with HCl contained in the first source gas to generate GaCl;
Vapor-phase growth of a buffer layer having a thickness of 60 nm or more on a GaAs (111) A-plane substrate installed in the reaction tube at a temperature of 400 ° C. or higher and 600 ° C. or lower;
Increasing the temperature of the substrate on which the buffer layer is formed while supplying NH ₃ gas to the substrate to improve the crystallinity of the buffer layer;
The first and second source gases are supplied into a reaction tube heated to 850 ° C. or higher and 1030 ° C. or lower, and a GaN layer is formed on the buffer layer at a growth rate of 4 μm / hour or more and 10 μm / hour or less. And a step of growing the epitaxial wafer.

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