JP2003342716A - METHOD FOR GROWING GaN CRYSTAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a method for growing a GaN crystal so as to continuously maintain the crystal growth in the method for growing the GaN crystal using metal Ga vapor and a nitrogen plasma. <P>SOLUTION: In the method for growing the GaN crystal, comprising providing a reaction tube 1 into which the nitrogen plasma is introduced from an upper part, providing a crucible 2 for evaporating metal Ga 12 at the bottom part of the reaction tube, arranging a substrate holding base 3 for holding a substrate at the upper part of the crucible 2, mounting the substrate for growing the GaN crystal on the substrate holding base, and reacting the vapor of the metal Ga evaporated from the crucible with the nitrogen plasma 13a introduced from the upper part of the reaction tube on the substrate, when a GaN film is formed on the surface of a melt of the metal Ga in the crucible, or the melt of the metal Ga is consumed completely, the melt 14d of Ga is additionally supplied into the crucible from the outside of the reaction tube. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor phase growth method for GaN crystals, and more particularly to an improvement of the GaN crystal growth method using metallic Ga vapor and nitrogen plasma.

[0002]

2. Description of the Related Art As is well known in recent years, there is an increasing demand for GaN semiconductor crystals that can be used for semiconductor light emitting diodes, semiconductor lasers, etc. for emitting blue light and ultraviolet light.
Therefore, it is desired to manufacture a GaN crystal simply and quickly at low cost.

As a method for growing a GaN crystal, for example, a hydride vapor phase epitaxy method, a metal organic vapor phase epitaxy method, a chemical vapor transport method or the like can be used.

Here, in the hydride vapor phase epitaxy method and the metalorganic vapor phase epitaxy method, HCl, NH ₃ , H ₂ etc. which are not incorporated as constituent components in the GaN crystal in the reaction of the raw material gas introduced into the reaction chamber. Remain in the reaction chamber, it is necessary to discharge these gases from the reaction chamber to the outside. That is, in the hydride vapor phase epitaxy method and the metal organic vapor phase epitaxy method, most of the raw material gas is discarded without contributing to the GaN crystal growth, and there is a problem that the raw material yield is poor. In addition, a large-scale detoxification equipment is required to discard a large amount of HCl, NH ₃ , H _2, etc., resulting in high process cost.

On the other hand, according to the chemical vapor transport method in which the raw material gas vaporized in the high temperature portion in the closed tube is transported to the low temperature portion and the crystal is grown in the low temperature portion, the gas is not discharged to the outside of the reaction tube. The yield is good. However, the chemical vapor transport method, in which the source gas is not supplied from the outside, cannot increase the transport rate of the source gas, and therefore cannot increase the growth rate of the GaN crystal.

In view of the problems involved in each of the above-described hydride vapor phase epitaxy method, metalorganic vapor phase epitaxy method, chemical vapor transport method, etc., Japanese Patent Laid-Open No. 2001-77038 discloses that vapor of metal Ga and nitrogen are contained in a reaction tube. Disclosed is a vapor phase growth method of reacting plasma to grow a GaN crystal on a substrate.

FIG. 2 is a schematic sectional view illustrating an example of a prior art in which metallic Ga vapor and nitrogen plasma are reacted in a reaction tube to grow a GaN crystal. In each drawing of the present application, dimensional relationships such as length and height are appropriately changed for simplification and clarification of the drawings, and do not represent actual dimensional relationships.

In FIG. 2, for example, the inner diameter is 23 to 26.
A nitrogen gas introduction pipe 1a is provided above the reaction pipe 1 having a height of about 600 mm and a diameter of mm. The bottom of the reaction tube 1 has an outer diameter of, for example, 17
A crucible 2 having a height of 21 mm and a height of about 30 mm is provided, and a substrate holding table 3 for holding a substrate 11 is arranged above the crucible 2. This substrate holder 3
Has an outer diameter of 18.5 to 22 mm and a height of about 40, for example.
It includes a cylindrical portion 3a of mm and a mesh plate 3b having a diameter of 19 to 25 mm and a thickness of 1.2 mm, for example. The mesh plate 3b serving as a substrate holding surface includes, for example, 21 openings 3c having a diameter of 2 mm. These reaction tube 1, crucible 2,
The substrate holder 3 can be preferably made of quartz. Further, the nitrogen gas introducing pipe 1a can be formed of, for example, stainless steel together with the flange portions thereof,
It can be connected to the reaction tube 1.

The inside of the reaction tube 1 is once evacuated to a high vacuum degree by a vacuum pump (not shown). Nitrogen gas 13 is introduced into the reaction tube 1 depressurized to a high degree of vacuum up to a predetermined pressure from a nitrogen gas introduction tube 1a provided in the upper part of the reaction tube 1. At that time, the microwave 4a is applied to the nitrogen gas 13 through the microwave introduction tube 4 provided at the upper part of the reaction tube 1, and the nitrogen plasma 13a is generated.

The metal Ga 12 placed in the crucible 2 is heated and melted by a heating device (not shown) provided outside the reaction tube 1. Ga from the Ga melt
The vapor passes through the opening 3c of the substrate holding surface 3b and reaches the upper surface of the heated substrate 11. Then, the Ga vapor reacts with the nitrogen plasma, and a GaN crystal can grow on the upper surface of the substrate 11.

Ga vapor reacts with nitrogen plasma to cause Ga
As the growth of the N crystal progresses, the nitrogen gas in the reaction tube 1 is consumed and the pressure in the reaction tube 1 drops from a predetermined pressure.
The nitrogen gas 13 is additionally introduced through the nitrogen gas introduction pipe 1a. That is, the pressure inside the reaction tube 1 is monitored by a vacuum gauge (not shown), and the nitrogen gas 13 is replenished so as to be maintained at a predetermined pressure.

That is, in the GaN crystal growth method illustrated in FIG. 2, nitrogen gas is introduced into the reaction tube 1 from the outside, but Ga vapor and nitrogen gas need to be substantially discharged to the outside of the reaction tube 1. (However, it goes without saying that a small amount of Ga vapor or nitrogen gas may be discharged out of the reaction tube in order to maintain a preferable reaction gas pressure). Therefore,
The vapor phase epitaxy method as shown in FIG. 2 does not require a large-scale exhaust gas treatment equipment unlike the hydride vapor phase epitaxy method and the metalorganic vapor phase epitaxy method, and is a raw material for GaN crystal growth. The yield is also good. Further, in the vapor phase growth method as shown in FIG. 2, a large amount of Ga vapor can be generated from the Ga melt, and the consumed nitrogen gas can be introduced from the outside, so that chemical vapor transport is possible. G compared to the law
The growth rate of the aN crystal can be increased.

[0013]

As described above, in the vapor phase growth method as shown in FIG. 2, the large-scale exhaust gas as in the case of the hydride vapor phase growth method or the metalorganic vapor phase growth method is used. The processing equipment is not required, the raw material yield in GaN crystal growth is good, and the GaN crystal growth rate can be increased as compared with the chemical vapor transport method.

However, when the vapor phase growth method as shown in FIG. 2 is carried out, a good growth rate is obtained at the initial stage of GaN crystal growth, but after a growth time of about 1 to 2 hours. Growth rate is about 1/3 to 1 compared to the initial growth
The present inventor has found that the value is reduced to / 5.

Therefore, an object of the present invention is to improve the GaN crystal growth method so that the GaN crystal growth can be continuously maintained in the vapor phase growth method utilizing metallic Ga vapor and nitrogen plasma.

[0016]

According to the present invention, a reaction tube into which nitrogen plasma is introduced from the top is prepared, a crucible for evaporating metal Ga is provided at the bottom of the reaction tube, and a crucible is provided above the crucible. , A substrate holder for holding the substrate is placed, a substrate for growing a GaN crystal is placed on the substrate holder, and the metal G evaporated from the crucible is placed.
In the method of growing a GaN crystal by reacting the vapor of a and the nitrogen plasma introduced from the upper part of the reaction tube on the substrate, Ga is formed on the melt surface of the metal Ga in the crucible.
When the N film is formed or when the Ga melt is depleted, the Ga melt is additionally supplied from the outside of the reaction tube into the crucible.

The additionally supplied Ga melt can be supplied by pushing out the Ga melt held in the cylinder connected to the conduit introduced into the reaction tube with a piston. Further, it is preferable that the nitrogen plasma is generated by excitation with microwaves. Further, as the material of the substrate for growing the Ga crystal, sapphire,
It can be appropriately selected from GaN, AlN, SiC, GaAs, Si and the like.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION First, as shown in FIG. 2, the present inventor uses GaN that utilizes Ga vapor and nitrogen plasma.
When the crystal growth method is performed, Ga for about 1 to 2 hours
The growth rate after N crystal growth is about 1 compared to the initial growth.
The cause of the decrease to about ⅓ to ⅕ was investigated. As a result, the present inventor found the following causes.

That is, in the GaN crystal growth method according to the prior art as illustrated in FIG.
3a can reach the surface of the metal Ga melt 12 through the opening 3c of the substrate holding surface 3b. Then, the nitrogen plasma 13a directly reacts with the surface of the metal Ga melt 12 to form a GaN film on the surface of the melt. Ga like this
The N coating hinders evaporation of the metallic Ga melt 12, reduces Ga vapor reaching the substrate 11, and finally stops GaN crystal growth.

Therefore, the inventor of the present invention has found that the metal Ga in the crucible 2 is
Consideration was made to enable generation of Ga vapor in the reaction tube 1 even after the GaN film is formed on the surface of the melt 12 or after the metal Ga melt 12 is consumed and exhausted.

FIG. 1 is a schematic sectional view illustrating an example of a method for growing a GaN crystal by utilizing Ga vapor and nitrogen plasma according to the present invention. Also in the crystal growth method of FIG. 1, as in the case of FIG. 2, a nitrogen gas introduction tube 1a is provided above the reaction tube 1 having an inner diameter of 23 to 26 mm and a height of about 600 mm, for example. In order to evaporate the metal Ga12, a crucible 2 having an outer diameter of 17 to 21 mm and a height of about 30 mm is provided at the bottom of the reaction tube 1, and a crucible 2 for holding the substrate 11 above the crucible 2 is provided. A substrate holder 3 is arranged. The substrate holder 3 has, for example, a cylindrical portion 3a having an outer diameter of 18.5 to 22 mm and a height of about 40 mm, and a diameter of, for example, 19 to 25.
The mesh plate 3b has a thickness of 1.2 mm and a thickness of 1.2 mm. This mesh plate 3b, which serves as a substrate holding surface, has a diameter of 2 mm, for example.
21 openings 3c are included. The reaction tube 1, the crucible 2 and the substrate holder 3 can be preferably made of quartz. Further, the nitrogen gas introducing pipe 1a can be formed of, for example, stainless steel together with the flange portions thereof, and can be connected to the reaction pipe 1.

The inside of the reaction tube 1 is temporarily evacuated to a high vacuum degree of, for example, 10 ^-5 Pa by a vacuum pump (not shown). Then, from the nitrogen gas introduction pipe 1a provided on the upper portion of the reaction pipe 1, for example, 10 Pa to 1000 P
The nitrogen gas 13 having a predetermined pressure set within the range of a is introduced into the reaction tube 1. At this time, the microwave 4a having a frequency of 2.45 GHz and an output of 250 W is applied to the nitrogen gas 13 through the microwave introduction tube 4 provided at the upper part of the reaction tube 1 to generate the nitrogen plasma 13a.

The metal Ga 12 placed in the crucible 2 is heated to, for example, 1100 ° C. and melted by a heating device (not shown) provided outside the reaction tube 1. The Ga vapor from the Ga melt is the opening 3c of the substrate holding surface 3b.
To reach the upper surface of the heated substrate 11. Then, the Ga vapor reacts with the nitrogen plasma, and the substrate 11
GaN crystals may grow on the upper surface of the. As the substrate 11, for example, a 5 mm square sapphire substrate or a GaN seed crystal substrate having a crystallographic (0001) plane as a main surface can be preferably used. However, the substrate 11 is not limited to these, and a substrate made of AlN, SiC, GaAs, Si or the like can be appropriately selected.

Ga vapor reacts with nitrogen plasma to cause Ga
As the growth of the N crystal progresses, the nitrogen gas in the reaction tube 1 is consumed and the pressure in the reaction tube 1 drops from a predetermined pressure.
The nitrogen gas 13 is additionally introduced through the nitrogen gas introduction pipe 1a. That is, the pressure inside the reaction tube 1 is monitored by a vacuum gauge (not shown), and the nitrogen gas 13 is replenished so as to be maintained at a predetermined pressure. At this time, the pressure is controlled by PID (Proportional Integral Derivative) control in the nitrogen gas flow rate controller.

That is, in the GaN crystal growth method illustrated in FIG. 1, nitrogen gas is introduced into the reaction tube 1 from the outside, but Ga vapor and nitrogen gas must be substantially discharged to the outside of the reaction tube 1. (However, it goes without saying that a small amount of Ga vapor or nitrogen gas may be discharged out of the reaction tube in order to maintain a preferable reaction gas pressure). Therefore,
As in the case of FIG. 2, the GaN crystal growth method using Ga vapor and nitrogen plasma as shown in FIG. 1 has a large scale like the case of the hydride vapor phase epitaxy method and the metal organic vapor phase epitaxy method. It is possible to improve the raw material yield during GaN crystal growth without requiring any exhaust gas treatment equipment, and to increase the GaN crystal growth rate as compared with the chemical vapor transport method.

Further, in the GaN crystal growth method shown in FIG. 1, means 14 for supplying an additional Ga melt into the reaction tube 1 from the outside of the reaction tube 1 is provided.
That is, the Ga melt transport pipe 14a is inserted in the reaction pipe 1. The Ga melt transport pipe 14a is a cylinder 14
connected to b. The cylinder 14b is heated by a heater (not shown) and holds the Ga melt. Then, by pressing the Ga melt in the cylinder 14b with the piston 14c, the Ga melt transport pipe 1
Additional Ga melt droplets 14d can be injected into the reaction tube 1 via 4a. The additional Ga melt droplets 14d injected into the reaction tube 1 are the openings 3d provided in the mesh plate 3b.
Through which it is dripped into the crucible 2. Of course, the means 14 for supplying the additional Ga melt shown in FIG. 1 is an example, and the additional Ga melt is supplied into the crucible 2 while maintaining the airtightness of the reaction tube 1. Any means may be used as long as it can be obtained.

The additional Ga melt supply means 14 as illustrated in FIG. 1 can be made of, for example, preferably stainless steel. The metal Ga is about 29.
Since it has a low melting point of 8 ° C., it is easy to obtain a Ga melt and also easy to transport it.

FIG. 1 with additional Ga melt supply means 14.
In the above crystal growth method, even if a GaN film is formed on the surface of the Ga melt 12 in the crucible 1 and the evaporation from the Ga melt is hindered, the Ga melt transport pipe 14a causes the Ga melt droplets 14d to be removed. By dropping into the crucible 2, GaN
The film is broken to expose the Ga melt surface, or the Ga melt surface is exposed.
Ga molten droplets can spread on the N film to generate new Ga vapor. Even if the Ga melt in the crucible 2 is completely evaporated and consumed, by supplying new Ga melt from the Ga melt supply means 14 into the crucible 2,
The growth of the aN crystal can be continued.

That is, in the case of the crystal growth method of FIG. 2, the GaN crystal growth rate remarkably decreased in about 1 to 2 hours and finally the growth stopped, whereas in the crystal growth method of FIG. In this case, the GaN crystal growth can be maintained and continued as long as the supply of the additional Ga melt from the Ga melt supply means 14 can be continued.

[0030]

As described above, according to the present invention, GaN vapor and nitrogen plasma which can have superior advantages over the hydride vapor phase epitaxy method, the metal organic vapor phase epitaxy method, the chemical vapor transport method and the like. In GaN crystal growth using and,
The growth method of the GaN crystal can be improved so that its growth can be continuously maintained.

[Brief description of drawings]

FIG. 1 is a sectional view schematically illustrating a GaN crystal growth method according to the present invention.

FIG. 2 is a sectional view schematically illustrating a GaN crystal growth method according to the prior art.

[Explanation of symbols]

1 Reaction Tube, 1a Nitrogen Gas Introducing Tube, 2 Crucible for Evaporating Metal Ga, 3 Substrate Holding Table, 3a Cylindrical Section of Substrate Holding Table, 3b Net Plate of Substrate Holding Table, 3c, 3d Included in Net Plate 3b Opening, 4 microwave introduction tube, 4a microwave, 11 substrate for growing GaN crystal, 1
2 metal Ga, 13 nitrogen gas, 13a nitrogen plasma, 14 additional Ga melt supply means, 14a Ga melt transport pipe, 14b cylinder, 14c piston, 14d
Additional Ga melt droplets.

Claims (4)

[Claims] 1. A reaction tube into which nitrogen plasma is introduced from above is prepared, a crucible for evaporating metal Ga is provided at the bottom of the reaction tube, and a substrate holder for holding a substrate above the crucible. And placing the substrate for growing a GaN crystal on the substrate holder, and vapor of the metal Ga evaporated from the crucible and the nitrogen plasma introduced from the upper part of the reaction tube. In the method of growing a GaN crystal by reacting with the substrate, the GaN film is formed on the melt surface of the metal Ga in the crucible, or when the Ga melt is consumed and exhausted, A method for growing a GaN crystal, characterized in that a Ga melt is additionally supplied into the crucible from the outside of the reaction tube. 2. The additionally supplied Ga melt is supplied by pushing out a Ga melt held in a cylinder connected to a conduit introduced into the reaction tube with a piston. The method for growing a GaN crystal according to claim 1. 3. The method for growing a GaN crystal according to claim 1, wherein the nitrogen plasma is generated by excitation with microwaves. 4. The material of the substrate is sapphire or Ga
The method for growing a GaN crystal according to any one of claims 1 to 3, wherein the method is selected from N, AlN, SiC, GaAs, and Si.