Patent Application
20100229794
The present invention relates to a vapor phase epitaxy apparatus (MOCVD apparatus) for a III nitride semiconductor, and more specifically, to a vapor phase epitaxy apparatus for a III nitride semiconductor including a susceptor for holding a substrate, a heater for heating the substrate, a raw material gas-introducing portion, a reactor, and a reacted gas-discharging portion.
A vapor phase epitaxy method (MOCVD method) has been employed for the crystal growth of a nitride semiconductor as frequently as a molecular beam epitaxial method (MBE method). In particular, the MOCVD method has been widely employed in apparatuses for the mass production of compound semiconductors in the industrial community because the method provides a higher crystal growth rate than the MBE method does and obviates the need for a high-vacuum apparatus or the like unlike the MBE method. In association with recent widespread use of blue or ultraviolet LEDs and of blue or ultraviolet laser diodes, numerous researches have been conducted on increases in apertures and number of substrates each serving as an object of the MOCVD method in order that the mass productivity of gallium nitride, gallium indium nitride, and gallium aluminum nitride may be improved.
Such vapor phase epitaxy apparatuses are, for example, vapor phase epitaxy apparatuses each having a susceptor for holding a substrate, a heater for heating the substrate, a raw material gas-introducing portion provided at the central portion of the susceptor, a reactor formed of a gap between the susceptor and the opposite face of the susceptor, and a reacted gas-discharging portion provided on an outer peripheral side relative to the susceptor as described in Patent Documents 1 to 3. Each of those vapor phase epitaxy apparatuses is of such a constitution that multiple substrate holders are provided for the susceptor and the substrate holders each rotate and revolve in association with the rotation of the susceptor by driving means.
However, any such vapor phase epitaxy apparatus involves a large number of problems that still remain unsolved. In the reactor of the vapor phase epitaxy apparatus, various raw material gases decompose on the surface of the substrate heated to a high temperature, and then crystallize on the surface of the substrate. However, in association with increases in apertures and number of substrates, the following problem arises. That is, a raw material gas channel in the reactor lengthens to preclude efficient distribution of the raw material gases toward a downstream side, and hence a crystal growth rate on the surface of a substrate on the downstream side reduces. In addition, an opposite face installed on the opposite side of a substrate serving as an object of metal organic chemical vapor deposition is heated by the heater, and hence the raw material gases each undergo a reaction on the surface of the opposite face to crystallize. As the growth is repeated for a certain number of times, a crystal is gradually deposited. As a result, the efficiency with which the raw material gases each react on the substrate reduces, and hence economical efficiency reduces. Moreover, it becomes difficult to obtain high-quality crystalline films with good reproducibility.
It should be noted that Patent Document 4 exemplifies an MOCVD apparatus for a III nitride semiconductor characterized in that the opposite face of the susceptor of an MOCVD reactor is cooled, and any other portion of a reaction tube is formed of quartz. In the invention, the following fact is described. That is, an AlN film formation rate on sapphire reached a value 2.4 times as high as a conventional film formation rate with no water-cooling as a result of the water-cooling of the opposite face. However, the AlN film formation rate obtained in the invention is still as low as 1.2 μm/h, and hence the invention is insufficient in terms of efficient utilization of raw material gases. When aluminum nitride (AlN) or gallium nitride (GaN) is grown on an industrial scale, a growth rate of 2.5 μm/h is not economically viable, and a growth rate of 4.0 μm/h or more is requested. In actuality, GaN films currently produced on an industrial scale are grown at growth rates of about 4.0 μm/h each. In addition, stainless steel and quartz are used as materials of which the reactor is constituted in the invention. However, it is well known that stainless steel deteriorates at a temperature of 700° C. or higher, and quartz has such a small thermal conductivity that it is difficult to keep the temperature of the reactor uniform.
Therefore, a problem to be solved by the invention is to provide such a vapor phase epitaxy apparatus for a III nitride semiconductor as described above, the vapor phase epitaxy apparatus being capable of high-quality crystal growth at a growth rate of 4.0 μm/h or more even when a crystal is grown on the surface of each of many large-aperture substrates held by a susceptor having a large diameter or even when a substrate is heated at a temperature of 1000° C. or higher.
The inventors of the present invention have made extensive studies with a view to solving the problem. As a result, the inventors have found that, with such a constitution that a gap between a susceptor and the opposite face of the susceptor is narrowed and the temperature of the opposite face is controlled to a low level in order that a situation where raw material gases each undergo a reaction on the surface of the opposite face to crystallize may be suppressed, the efficiency with which the raw material gases each react on a substrate is improved and high-quality crystalline films can be obtained with good reproducibility. Thus, the inventors have reached a vapor phase epitaxy apparatus of the present invention.
That is, the present invention provides a vapor phase epitaxy apparatus for a III nitride semiconductor including a susceptor for holding a substrate, an opposite face of the susceptor, a heater for heating the substrate, a raw material gas-introducing portion provided at a central portion of the susceptor, a reactor formed of a gap between the susceptor and the opposite face of the susceptor, and a reacted gas-discharging portion provided on an outer peripheral side relative to the susceptor. The vapor phase epitaxy apparatus for a III nitride semiconductor is characterized in that a gap between the substrate and the opposite face of the susceptor is 8 mm or less at a position on an upstream side of the substrate and is 5 mm or less at a position on a downstream side of the substrate, a constitution through which a coolant is flown is provided for the opposite face of the susceptor, and materials for portions, with which raw material gases are brought into contact in the reactor, are each formed of a carbon-based material, a nitride-based material, a carbide-based material, molybdenum, copper, alumina, or a composite material of these materials.
The vapor phase epitaxy apparatus of the present invention can alleviate or solve, by narrowing the gap between the susceptor and the opposite face of the susceptor and flowing a coolant through the opposite face of the susceptor to cool the surface of the opposite face, such a problem that a crystal growth rate on the surface of a substrate on a downstream side reduces even when a crystal is grown on the surface of each of many large-aperture substrates or even when a substrate is heated at a temperature of 1000° C. or higher. As a result, the efficiency with which the raw material gases each react on the substrate is improved and high-quality crystalline films can be obtained with good reproducibility.
The present invention is applied to a vapor phase epitaxy apparatus for a III nitride semiconductor having a susceptor for holding a substrate, an opposite face of the susceptor, a heater for heating the substrate, a raw material gas-introducing portion provided at the central portion of the susceptor, a reactor formed of a gap between the susceptor and the opposite face of the susceptor, and a reacted gas-discharging portion provided on an outer peripheral side relative to the susceptor. The vapor phase epitaxy apparatus of the present invention is a vapor phase epitaxy apparatus for performing the crystal growth of a nitride semiconductor mainly formed of a compound of one or two or more kinds of metals selected from gallium, indium, and aluminum, and nitrogen. In the present invention, an effect can be sufficiently exerted particularly in the case of such vapor phase epitaxy that multiple substrates of such sizes as to have diameters of 3 inches or more are held.
Hereinafter, the vapor phase epitaxy apparatus of the present invention is described in detail with reference to
It should be noted that
As illustrated in
Alternatively, as illustrated in
In the present invention, both of the vapor phase epitaxy apparatuses are such apparatuses in which a gap between the substrate and the opposite face of the susceptor is 8 mm or less at a position on an upstream side of the substrate and is 5 mm or less at a position on a downstream side of the substrate, and materials for portions, with which raw material gases are brought into contact in the reactor, are each formed of a carbon-based material, a nitride-based material, a carbide-based material, molybdenum, copper, alumina, or a composite material of these materials. The materials for the portions, with which the raw material gases are brought into contact, are each particularly preferably the carbon-based material or a material whose surface is coated with the carbon-based material because thermal conduction is good and the raw material gases can be heated to a uniform temperature.
It should be noted that the form of the susceptor in the present invention is, for example, a disk shape having spaces for holding multiple substrates in its peripheral portion as illustrated in
In the vapor phase epitaxy apparatus of the present invention, an organometallic compound (such as trimethyl gallium, triethyl gallium, trimethyl indium, triethyl indium, trimethyl aluminum, or triethyl aluminum) and ammonia serving as the raw material gases, a carrier gas (an inert gas such as hydrogen or nitrogen, or a mixed gas of them), and the like are supplied from an external tube 11 to the raw material gas-introducing portion 5 and then introduced from the raw material gas-introducing portion 5 to the reactor 6, and the gases after the reaction are discharged from the discharging portion 7 to the outside as illustrated in each of
As illustrated in each of
The phenomenon leads to such a problem that high-quality crystalline films cannot be obtained with good reproducibility with regard to the growth of the nitride semiconductor. In addition, when the surface of the opposite face 3 is installed at a position distant from the substrate by 10 mm or more, the raw material gases cannot sufficiently approach the surface of the substrate. As a result, the growth rate of the nitride semiconductor reduces. The reduction of the growth rate is particularly remarkable on the downstream side of the substrate. For example, when the size of the substrate is 3 inches or more, on the surface of the substrate on the downstream side, nearly none of the raw material gases may reach the surface of the substrate. As a result, the possibility that the growth of the nitride semiconductor is completely prevented on the surface on the downstream side of the substrate increases.
In the vapor phase epitaxy apparatus of the present invention, the opposite face was brought close to the substrate, and furthermore the temperature of (a constituent of) the opposite face was controlled to a low level by flowing a coolant through the constitution 8 through which the coolant was flown installed on (the constituent of) the opposite face in order that the crystallization of the nitride semiconductor on the surface of the opposite face might be suppressed. To be specific, when the distance was 8 mm or less, or preferably 2 to 8 mm at a position 16 (
It should be noted that, with regard to the gap between the susceptor (substrate) and the opposite face of the susceptor, for example, when the gap between the substrate and the opposite face is 8 mm and the substrate is heated to 1050° C., the surface temperature of the opposite face can be reduced to typically about 400° C., or about 200° C. depending on a condition under which the coolant (water) is flown, in the case where the coolant is flown in contrast to the fact that the surface temperature of the opposite face reaches around 800° C. in the case where the coolant (water) is not flown. When the surface temperature of the opposite face reaches around 800° C., a crystal growth reaction occurs on the surface of the opposite face, and hence the crystal of the nitride semiconductor is deposited. In contrast, when the surface temperature of the opposite face is 400° C. or lower, the crystal growth reaction is extremely slow, and hence the amount in which the crystal of the nitride semiconductor is deposited can be made extremely small.
The following materials are used for the portions, with which the raw material gases are brought into contact in the reactor of the vapor phase epitaxy apparatus of the present invention (referring to, for example, the susceptor 2, the opposite face 3 of the susceptor, and the susceptor-rotating shaft 12 in
A tube is typically installed as the constitution 8 through which a coolant is flown in (the constituent of) the opposite face. The number of tubes may be one or two or more. In addition, the constitution of the tube is not particularly limited, and examples of the constitution include such a constitution that multiple tubes are installed radially from the central portion of (the constituent of) the opposite face and such a constitution that a tube is installed in an eddy fashion from the central portion. The direction in which the coolant flows is not particularly limited. An arbitrary high-boiling solvent is used as the coolant flown through the tube 8, and a solvent having a boiling point of 90° C. or higher is particularly preferable. Examples of such coolant include water, an organic solvent, and oil.
In addition, as illustrated in each of
In the present invention, the ejection of the inert gas from the fine porous portion toward the inside of the reactor can effectively prevent the crystallization of the nitride semiconductor on the surface of the opposite face. Even in the vapor phase epitaxy apparatus of such structure as illustrated in each of
Next, the present invention is described specifically by way of examples. However, the present invention is not limited by these examples.
Such a vapor phase epitaxy apparatus as illustrated in
(Chemical Vapor Deposition Experiment)
Gallium nitride (GaN) was grown on the surfaces of the five sapphire substrates with such vapor phase epitaxy apparatus by causing the susceptor to hold the substrates so that a gap at a position on the upstream side of each substrate (reference numeral 16 in
After the growth of the buffer layer, the supply of only TMG was stopped, and then the temperature was increased to 1050° C. After that, undoped GaN was grown for 1 hour by using TMG (flow rate: 120 cc/min) and ammonia (flow rate: 50 L/min) as raw material gases, and hydrogen (flow rate: 80 L/min) and nitrogen (flow rate: 95 L/min) as carrier gases. It should be noted that all growth including that of the buffer layer was performed while each substrate was caused to rotate at a rate of 10 rpm. The surface temperature of the opposite face of the susceptor in this case was 410° C.
After the nitride semiconductor had been grown as described above, the temperature was decreased, and then the substrates were taken out of the reaction vessel. After that, GaN thicknesses were measured. As a result, the average of the GaN thicknesses was 4.23 μm. The foregoing shows that a GaN average growth rate was 4.23 μm/h. In addition, nearly no crystal was observed on the surface of the opposite face of the susceptor.
Vapor phase epitaxy apparatuses were each produced in the same manner as in Example 1 except that the material for the opposite face of the susceptor was changed to a nitride-based material (Example 2), a carbide-based material (Example 3), molybdenum (Example 4), copper (Example 5), or alumina (Example 6) in the production of the vapor phase epitaxy apparatus of Example 1.
Gallium nitride (GaN) was grown on the surfaces of substrates in the same manner as in the chemical vapor deposition experiment of Example 1. As a result, the averages of the GaN thicknesses each fell within the range of 4.1 to 4.3 μm.
A chemical vapor deposition experiment was performed in the same manner as in Example 1 except that no substrates were caused to rotate during chemical vapor deposition in the chemical vapor deposition experiment of Example 1 (the vapor phase epitaxy apparatus, and conditions such as the flow rates of gases and the temperature are exactly the same).
A vapor phase epitaxy apparatus was produced in the same manner as in Example 1 except that the tilt of the opposite face of the susceptor was changed in the production of the vapor phase epitaxy apparatus of Example 1. As a result, when the susceptor was caused to hold the five sapphire substrates, a gap at a position on the upstream side of each substrate (reference numeral 16 in
Gallium nitride (GaN) was grown on the surfaces of the substrates in the same manner as in the chemical vapor deposition experiment of Example 1. As a result, the average of the GaN thicknesses was 1.70 μm. The foregoing shows that a GaN average growth rate was 1.70 μm/h. The result shows that an efficient growth rate cannot be obtained merely by cooling the opposite face. The thickness distribution of a GaN film in the surface of a 3-inch substrate in Comparative Example 1 is as illustrated in
A vapor phase epitaxy apparatus was produced in the same manner as in Example 7 except that the tilt of the opposite face of the susceptor was changed in the production of the vapor phase epitaxy apparatus of Example 7. As a result, when the susceptor was caused to hold the five sapphire substrates, a gap at a position on the upstream side of each substrate (reference numeral 16 in
Gallium nitride (GaN) was grown on the surfaces of the substrates in the same manner as in the chemical vapor deposition experiment of Example 7 (no substrates were caused to rotate during chemical vapor deposition).
A vapor phase epitaxy apparatus was produced in the same manner as in Example 7 except that the tilt of the opposite face of the susceptor was changed in the production of the vapor phase epitaxy apparatus of Example 7. As a result, when the susceptor was caused to hold the five sapphire substrates, a gap at a position on the upstream side of each substrate (reference numeral 16 in
Gallium nitride (GaN) was grown on the surfaces of the substrates in the same manner as in the chemical vapor deposition experiment of Example 7 (no substrates were caused to rotate during chemical vapor deposition).
As described above, it was found that the vapor phase epitaxy apparatus of the present invention was able to significantly suppress crystallization on the surface of the opposite face of the susceptor upon chemical vapor deposition onto the surfaces of substrates and to provide high-quality crystalline films efficiently.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-043947 | Feb 2009 | JP | national |
| 2009-052247 | Mar 2009 | JP | national |
| 2009-134165 | Jun 2009 | JP | national |
