JP2003173975A - Method for baking reaction tube and vapor phase growing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently clarify only the inner wall surface of a reaction tube. <P>SOLUTION: The vapor phase growing apparatus comprises the reaction tube 3 for forming a film by a vapor phase growth, and a gas supply tube 7 for supplying a gas to the tube 3 and having a heating means 12 for baking the tube 3. The method for baking the reaction tube comprises the steps of continuously supplying the gas heated at the upstream side of the tube 3 to the tube 3, and thereby heating the inner wall surface of the tube 3. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reaction tube baking method and a vapor phase growth apparatus.

[0002]

2. Description of the Related Art As a method of growing a crystal of a GaN type compound semiconductor, metal organic chemical vapor deposition (hereinafter referred to as MOCV).
Called D. ) Method and the like are widely known.
The MOCVD method is a method in which an organometallic compound gas is supplied as a reaction gas to a reaction tube provided with a substrate to cause a thermochemical reaction on the substrate held at a predetermined temperature to grow an epitaxial layer of a compound semiconductor crystal.

By the way, in order to prepare a crystal by the MOCVD method, it is necessary to exhaust the inside of the reaction tube to a vacuum state before supplying the reaction gas to the reaction tube. At this time, the inner wall surface of the reaction tube is Impurity gas such as H ₂ O adsorbed on is desorbed in a vacuum and contaminates the inside of the reaction tube, hinders high-quality crystal growth, and lowers the yield. Therefore, it is essential to clean the inner wall surface of the reaction tube before supplying the reaction gas to the reaction tube. As a means to clean the reaction tube,
A so-called baking method is used in which impurities adsorbed on the inner wall surface of the reaction tube are desorbed by heating the reaction tube.

[0004]

However, in the conventional baking, since the heater is wound around the outer peripheral surface of the reaction tube to heat it, when the reaction tube has a complicated shape, the heater is not wound. In some cases, heating becomes non-uniform and sufficient cleaning effect cannot be obtained. Further, since the heating is applied to the entire reaction tube, various inconveniences such as heating even a member having low heat resistance such as an O-ring to damage this member are involved.

Therefore, the present invention has been proposed in view of such conventional circumstances, and a method for baking a reaction tube and a vapor phase growth apparatus capable of efficiently cleaning only the inner wall surface of the reaction tube. The purpose is to provide.

[0006]

In order to achieve the above-mentioned object, the method for baking a reaction tube according to the present invention is characterized in that the gas heated on the upstream side of the reaction tube is continuously supplied to the reaction tube. It is characterized in that the inner wall surface of the reaction tube is heated.

In the reaction tube baking method configured as described above, the gas heated on the upstream side is continuously supplied to the reaction tube to heat the inner wall surface of the reaction tube, so that it does not depend on the shape of the reaction tube. The inner wall surface of the reaction tube is uniformly heated to remove impurities adhering to the inner wall surface. Further, only the inner wall surface of the reaction tube to be baked is surely heated without heating extra members. Furthermore, the time required for baking can be shortened.

Further, the vapor phase growth apparatus according to the present invention comprises a reaction tube for forming a film by vapor phase growth and a gas supply tube for supplying gas to the reaction tube.
A heating means for baking the reaction tube is provided.

The vapor phase growth apparatus configured as described above is
Before performing film formation by vapor phase growth, a heated gas is flowed to efficiently bake only the inner wall surface of the reaction tube.
The gas flowing inside the reaction tube becomes highly pure.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A method for baking a reaction tube and a vapor phase growth apparatus to which the present invention is applied will be described below in detail with reference to the drawings.

FIG. 1 shows a metal organic chemical vapor deposition (hereinafter referred to as MOCVD) apparatus to which the present invention is applied.

The MOCVD apparatus 1 shown in FIG. 1 includes a reaction tube 3 for arranging a substrate 2 therein for crystal growth, and a growth material line 4 for supplying a reaction gas as a group III material to the reaction tube 3. In advance, a reaction gas for forming a vapor phase growth film formed on the vapor phase growth film formed by the reaction gas supplied from the growth raw material line 4 to the reaction tube 3 is prepared in advance. A vent line 5 for supplying the reaction gas, and a group V supply line 6 for supplying a reaction gas serving as a group V raw material to the reaction tube 3.
A heating gas supply line 7 for continuously supplying the heated gas to the reaction tube 3 at the time of baking described later, and a vacuum pump 8 for exhausting the reaction gas in the reaction tube 3 and the reaction gas supplied to the vent line 5. A differential pressure gauge 9 for measuring the differential pressure of the reaction gas flowing through each of the growth raw material line 4 and the vent line 5 is provided.

Nitrogen as a carrier gas is supplied to the growth material line 4 through a mass flow controller (MFC) 10a for adjusting the gas flow rate and a valve 11a. Further, hydrogen serving as a carrier gas is supplied to the growth raw material line 4 via the MFC 10b and the valve 11b.

Further, in the growth raw material line 4, for example, organometallic MO1 is fed as a group III raw material into MF.
Supplied via C10c, 10d and valve 11c,
In addition, MO2 is MFC10e, 10f and valve 11
supplied via d.

Nitrogen as a carrier gas is supplied to the vent line 5 through a valve 11e which is a line different from the line for supplying the carrier gas to the MFC 10a and the growth raw material line 4. In addition, the vent line 5 has an M
Hydrogen serving as a carrier gas is supplied through a valve 11f that is a line different from the line that supplies the carrier gas to the FC 10b and the growth material line 4.

The vent line 5 has an MFC 10
c, 10d and MO1 as a raw material are supplied through a valve 11g which is a line different from a line for supplying the raw material to the growth raw material line 4, and also supplies the raw material to the MFCs 10e, 10f and the growth raw material line 4. MO2 as a raw material is supplied through a valve 11h on a line different from the line.

Further, the vent line 5 is constantly supplied with nitrogen from the most upstream side via 10 g of MFC.

The vent line 5 is evacuated by the vacuum pump 8 which evacuates the reaction gas in the reaction tube 3, and is constantly flowing. As a result, the reaction gas flowing through the vent line 5 is kept at a reduced pressure level comparable to that of the reaction gas flowing through the growth raw material line 4, and film formation is performed by the reaction gas supplied to the growth raw material line 4. Immediately after the above, the valve is switched to move to the growth raw material line 4, and the state of being supplied to the reaction tube 3 is maintained.

The valves 11a and 11e are provided with nitrogen as a carrier gas and a growth raw material line 4 or a vent line 5.
It becomes a nitrogen switching means for supplying to either one of the above.
Further, the valves 11b and 11f serve as hydrogen switching means for supplying hydrogen as the carrier gas to the growth raw material line 4 or the vent line 5 to the side not supplied with hydrogen. These valves 11a, 11b,
11e and 11f are controlled to have two states by opening and closing in conjunction with each other, and selectively supply either nitrogen or hydrogen to the growth material line 4.
The other is supplied to the vent line 5. Specifically, when supplying hydrogen as a carrier gas to the growth raw material line 4, nitrogen is supplied to the vent line 5 so that the valve 11
a is off, valve 11b is on, valve 11e is on,
The valve 11f is turned off. On the contrary, the growth raw material line 4
To supply hydrogen to the vent line 5 when supplying nitrogen as a carrier gas, the valve 11a is turned on, the valve 11b is turned off, the valve 11e is turned off, and the valve 11f is turned on.
Turns on.

In this MOCVD apparatus 1, a differential pressure gauge 9 for detecting a deviation of the differential pressure between the growth raw material line 4 and the vent line 5 from a set value to detect an abnormality in the piping system at an early stage is provided. Valve 11b for supplying hydrogen as a carrier gas to the growth raw material line 4 and a valve 11 for supplying it to the vent line 5.
It is connected between the growth raw material line 4 and the vent line 5 so as to be on the downstream side of f and on the upstream side of the valve for supplying MO1.

The MOCVD apparatus 1 of the present invention has a heating gas supply line 7 for supplying a gas used for baking to be described later to the reaction tube 3, and a heater is provided on the outer peripheral surface of the heating gas supply line 7. 12 are wound. The heating gas supply line 7 is made of, for example, stainless steel having excellent thermal conductivity. In the MOCVD apparatus 1, the heater 12 heats the gas flowing in the heating gas supply line 7 to a predetermined high temperature during baking, and continuously supplies the gas to the reaction tube 3 while maintaining the high temperature. There is.

In the MOCVD apparatus 1 described above, the reaction tube 3 is baked before the film formation by vapor phase growth. When baking the reaction tube 3, first, the inside of the reaction tube 3 is evacuated by the vacuum pump 8 connected to the reaction tube 3 until a predetermined vacuum state is reached.

Next, a valve (not shown) between the reaction tube 3 and the heating gas supply line 7 is opened, and the heater 12 is made highly pure by passing through the purifying device and wound around the heating gas supply line 7. The gas heated to a degree suitable for baking is continuously supplied to the reaction tube 3 without stagnation while maintaining its high temperature. At the same time, the gas supplied to the reaction tube 3 is continuously exhausted by the vacuum pump 8.
In this way, the inner wall surface of the reaction tube 3 is heated by continuously supplying the heated gas, and the impurity gas adsorbed on the inner wall surface of the reaction tube 3 is desorbed. As described above, by continuously supplying the heated gas, the inner wall surface of the reaction tube 3 is sufficiently cleaned, and the baking is completed.

If necessary, an internal heater (not shown) for heating the substrate, which is installed inside the reaction tube 3, is operated to raise the temperature inside the reaction tube 3 so that the inner wall surface of the reaction tube 3 is further increased. It may be cleaned.

In the reaction tube baking method of the present invention, the gas preheated by the heater 12 in the heating gas supply line 7 upstream of the reaction tube 3 is continuously supplied to the reaction tube 3 and the inner wall surface of the reaction tube 3 is supplied. By contacting the gas, the inner wall surface of the reaction tube 3 is heated to remove impurities from the inner wall surface of the reaction tube 3 and the reaction tube 3 can be easily cleaned. Further, unlike the conventional baking method of heating the entire reaction tube, only the inner wall surface of the reaction tube 3 to be baked is reliably heated. Further, it is possible to complete the baking in a shorter time than in the conventional case, and it is possible to obtain an effect that the reaction tube 3 can be easily started up. As described above, according to the baking method of the present invention, the inner wall surface of the reaction tube 3 is efficiently heated / heated.
Purification is achieved, and the gas flowing inside the reaction tube 3 is highly purified.

At this time, it is preferable that the set temperature of the gas is 100 ° C. or higher, which is the boiling point of H ₂ O, so that the gas of H ₂ O adsorbed on the inner wall surface of the reaction tube 3 is easily desorbed. Further, it is more preferable to set the temperature of the gas to 200 ° C. or higher, whereby the gases such as CO, CO ₂ , H ₂ and O ₂ adsorbed on the inner wall surface of the reaction tube 3 are easily desorbed, and the reaction tube 3 Make the cleaning of more reliable.

The gas used here is preferably a high-purity gas in order to make the inside of the reaction tube 3 cleaner. Specifically, it is preferable to use a gas of high purity and an inert gas, such as N ₂ , He, or Ar, which is easily obtained. It is also possible to use H ₂ having a reducing action as a gas. In this case, it is particularly effective for desorbing O ₂ and CO adsorbed on the inner wall surface of the reaction tube 3, and a more excellent baking effect is obtained. be able to. Further, these gases can be mixed and used.

The flow rate of the gas should be appropriately set in consideration of the heating capacity of the heater 12, etc., but in order to ensure the effect of baking, for example, when performing film formation by vapor phase growth. The flow rate of the normal reaction gas supplied to the reaction tube 3 (4 l / min to 10 l / min) is preferably twice or more.

Then, using the MOCVD apparatus 1 after the above-mentioned baking of the reaction tube 3 is completed, a light emitting element is formed by vapor phase growth on a substrate, for example. here,
A GaN-based light emitting diode will be described as an example of the light emitting element.

The light emitting diode 21 shown in FIG.
Of flat GaN on the underlying growth layer 22 made of a base semiconductor layer
The layer 23 is formed. An insulating film (not shown) is present on the underlying growth layer 22, and the GaN layer 23 is formed in the opening of the insulating film by vapor phase growth such as MOCVD which will be described later. The GaN layer 23 is doped with silicon and functions as a clad having a double hetero structure. InGaN layer 2 which is an active layer on GaN layer 23
4 is formed, and a magnesium-doped GaN layer 25 is further formed thereon. The magnesium-doped GaN layer 25 also functions as a clad.

In such a light emitting diode 21, a p electrode 26 and an n electrode 27 are formed. The p-electrode 26 is Ni formed on the magnesium-doped GaN layer 25.
It is formed by depositing a metal material such as / Pt / Au or Ni (Pd) / Pt / Au. The n-electrode 27 is formed by vapor-depositing a metal material such as Ti / Al / Au at the opening of the insulating film (not shown). When the n electrode is taken out from the back surface side of the underlayer growth layer 22, the formation of the n electrode 27 is not necessary on the front surface side of the underlayer growth layer 22.

As a GaN-based light emitting diode, for example, a structure in which an active layer is formed in a band shape, and an inclined S
A hexagonal pyramid structure having a surface or a pyramid structure having a C-plane formed at the upper end may be used. Further, it may be another nitride-based light emitting device or a compound semiconductor device.

In order to manufacture such a light emitting diode 21, first, the substrate 2 for crystal growth is placed inside the reaction tube 3 after completion of baking, and the substrate 2 is heated to about 1000 ° C. by a heater (not shown). To heat. And
NH ₃ whose flow rate is controlled by the MFC from the V group supply line 6
By supplying the reaction gas from the growth raw material line 4 to the reaction tube 3, a thermochemical reaction is caused on the substrate 2 to deposit the raw material elements on the substrate 2, and the GaN layer 23 functioning as a clad layer is formed. Grow. In this case, hydrogen is used as a carrier gas and trimethylgallium (TM) as a group III source material by controlling the opening and closing of the corresponding valves.
Raw material line 4 for growth using a mixed gas with G) as a reaction gas
To the reaction tube 3. At the same time, by controlling opening / closing of the corresponding valve, a reaction gas for forming the InGaN layer 24 after forming the GaN layer 23 is prepared in the vent line 5. During manufacture of the GaN-based light emitting diode, nitrogen is constantly supplied to the vent line 5 via 9 g of MFC.

Next, after the GaN layer 23 is formed, the reaction gas prepared in advance in the vent line 5 is transferred to the growth material line 4 by switching the corresponding valve, and the InGaN layer 24 functioning as an active layer is formed. Start film formation.
And by controlling the opening and closing of the corresponding valve,
A mixed gas of nitrogen as a carrier gas and trimethylindium (TMI) as a Group III source material and TMG is supplied as a reaction gas from the growth source line 4 to the reaction tube 3 to further grow the InGaN layer 24. At the same time, the GaN layer 25 is formed after the InGaN layer 24 is formed.
A reaction gas for film formation is prepared in the vent line 5.

Next, after the formation of the InGaN layer 24 is completed, the corresponding valve is switched to change the vent line 5.
Move the reaction gas prepared in advance to the growth raw material line 4,
The film formation of the GaN layer 25 which functions as a clad layer is started. Then, by controlling the opening / closing of the corresponding valve, nitrogen is used as a carrier gas and T is used as a group III source material.
Raw material line 4 for growth using mixed gas with MG as reaction gas
To the reaction tube 3 to further grow the GaN layer 25.

A metal material thin film is formed and patterned on the laminated film of the light emitting diodes thus laminated to connect the p-electrode 26 and the n-electrode 27, and Ga
The N-type light emitting diode 21 is completed.

As described above, in this MOCVD apparatus 1, prior to the fabrication of the GaN-based light emitting diode 21,
Since the inner wall surface of the reaction tube 3 is efficiently baked by continuously supplying the preheated gas to the reaction tube 3, stable crystal growth can be performed in the high-purity reaction tube 3.
The high-quality GaN-based light emitting diode 21 can be manufactured with high yield.

Here, an experiment in which the reaction tube 3 is baked in the MOCVD apparatus 1 shown in FIG. 1 will be described.

As the baking gas, N ₂ gas having a purity of 99.999999999% by passing through a purifier was used. First, the inside of the reaction tube 3 is evacuated by the vacuum pump 8 connected to the downstream side of the reaction tube 3 to perform a vacuum check, and then the N ₂ gas flowing in the heating gas supply line 7 is heated to 200 ° C. by the heater 12. The inner wall surface of the reaction tube 3 was heated by continuously supplying the high temperature N ₂ gas to the reaction tube 3 for 10 minutes. At this time, there is almost no difference in the temperature of the N ₂ gas between the heated gas supply line 7 and the reaction tube 3,
It was also confirmed that the N ₂ gas was flowing in the reaction tube 3 without stagnation. Then, by continuously supplying the high temperature N ₂ gas for 10 minutes, the reaction tube 3 could be efficiently baked in a short time without heating extra members.

Further, as a gas for baking, was baked in the same manner as the above-mentioned experiments with H ₂ gas and purity 99.9999999% by passing through the purifier, the N ₂ gas as described above It was possible to obtain an excellent cleaning effect for the reaction tube 3 in a shorter time than when used.

It should be noted that the present invention is not limited to the above description, and can be changed as appropriate without departing from the gist of the present invention.

For example, in the above description, the heater 12 wound around the heating gas supply line 7 is taken as an example of the heating means for heating the gas, but the present invention is not limited to this and any kind of heater may be used. May be used.

The material forming the reaction tube 3 can be arbitrarily selected. However, when the vacuum is broken during maintenance or the like, the reaction tube 3 is easily contaminated by CO in the atmosphere, and a heater is provided on the outer peripheral surface. The effect of the present invention can be remarkably obtained especially when quartz is used because it is difficult to attach.

In the present invention, the high temperature gas is used in the reaction tube 3
Since the inner wall surface of the reaction tube 3 is uniformly heated by contacting the inner wall surface of the reactor, even if the reaction tube 3 has a complicated special shape, baking is reliably performed only by a simple operation of continuously supplying gas. it can.

Further, in the MOCVD apparatus 1 shown in FIG.
The heating gas supply line 7 is provided as a pipe for supplying the baking gas to the reaction tube, independently of the growth raw material line 4 and the group V supply line 6 which are group III supply lines. However, the present invention is not limited to this, and the heating raw material line 4 or the group V supply line 6 may be provided with a heating means such as a heater. In this case, prior to the supply of the reaction gas to the reaction tube 3, for example, N ₂ or H _{2 is used} as a carrier gas in the growth raw material line 4 or the group V supply line 6.
While flowing only the gas, the heating means is turned on to heat the carrier gas, and the carrier gas is continuously supplied to the reaction tube 3.
Can be baked.

In the above description, the MOCVD apparatus using the organometallic compound gas as the reaction gas has been described as an example, but the present invention is based on molecular beam epitaxy (MBE).
The present invention can be applied to any vapor phase growth apparatus such as an apparatus and a hydride CVD (HCVD) apparatus.

[0047]

As is clear from the above description, since the gas heated on the upstream side is continuously supplied to the reaction tube to heat the inner wall surface of the reaction tube, the reaction tube does not depend on the shape of the reaction tube. The inner wall surface of is heated uniformly to remove impurities adhering to the inner wall surface. Also, without heating unnecessary members,
Be sure to heat only the inner wall surface of the reaction tube to be baked. Furthermore, the time required for baking can be shortened. Therefore, according to the method for baking a reaction tube of the present invention, the inner wall surface of the reaction tube can be efficiently cleaned and the gas flowing inside the reaction tube can be highly purified.

Further, in the vapor phase growth apparatus according to the present invention, the heated gas is caused to flow to efficiently bake only the inner wall surface of the reaction tube before the film formation by the vapor phase growth. Highly pure gas flowing through. Therefore, according to the present invention, it is possible to provide a vapor phase growth apparatus that realizes the production of high-quality crystal layers with high yield.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the periphery of a reaction tube of a MOCVD apparatus to which the present invention is applied.

FIG. 2 is a cross-sectional view showing an example of a light emitting element.

[Explanation of symbols]

1 MOCVD equipment 2 substrates 3 reaction tubes 4 Raw material line for growth 5 Bent line 6 V group supply line 7 Heating gas supply line 8 vacuum pump 9 Differential pressure gauge 10 MFC 11 valves 12 heater 21 light emitting diode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeshi Biwa             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F-term (reference) 4K030 AA11 AA13 BA08 BA38 DA06                       JA10 KA09 KA25 KA46 LA14                 5F045 AA04 AB14 AC15 AC16 AC17                       EB15 EE14

Claims (15)

[Claims] 1. A method for baking a reaction tube, wherein an inner wall surface of the reaction tube is heated by continuously supplying a gas heated on the upstream side of the reaction tube to the reaction tube. 2. The method for baking a reaction tube according to claim 1, wherein the gas is heated to 100 ° C. or higher. 3. The method for baking a reaction tube according to claim 2, wherein the gas is heated to 200 ° C. or higher. 4. N ₂ , H ₂ , He, Ar as the gas
2. The method for baking a reaction tube according to claim 1, wherein at least one of them is used. 5. The method for baking a reaction tube according to claim 1, wherein the inner wall surface of the reaction tube is made of quartz. 6. The method of baking a reaction tube according to claim 1, wherein the flow rate of the gas is set to be at least twice the flow rate of the reaction gas supplied to the reaction tube during film formation. 7. A reaction tube for forming a film by vapor phase growth, and a gas supply tube for supplying a gas to the reaction tube, wherein the gas supply tube has a heating means for baking the reaction tube. A vapor phase growth apparatus characterized by being provided. 8. The vapor phase growth apparatus according to claim 7, wherein the heating means heats the gas to 100 ° C. or higher. 9. The vapor phase growth apparatus according to claim 8, wherein the heating means heats the gas to 200 ° C. or higher. 10. N ₂ , H ₂ , He, A as the gas
8. The vapor phase growth apparatus according to claim 7, wherein at least one of r is used. 11. The vapor phase growth apparatus according to claim 7, wherein a heater is provided as the heating means around the gas supply pipe. 12. The vapor phase growth apparatus according to claim 7, wherein the reaction tube has a special shape. 13. The vapor phase growth apparatus according to claim 7, wherein the inner wall surface of the reaction tube is made of quartz. 14. The vapor phase growth apparatus according to claim 7, wherein the gas supply pipe is made of stainless steel. 15. The vapor phase growth apparatus according to claim 7, which is a metalorganic chemical vapor deposition apparatus.