JPH0547666A - Vapor growth apparatus - Google Patents

Abstract

PURPOSE:To alternately perform an ALE and a VPE without exposing a substrate with the atmosphere and without cooling it to the ambient temperature by narrowing between an inner wall of a reaction tube and the substrate on an ALP executing region, extending it on a VPE executing region, and optimizing material gas flowing speeds on the regions. CONSTITUTION:One reaction tube 1 is defined on an ALF optimized region and a VPE optimized region, a substrate 8 is moved to the regions by a susceptor 7, and a compound semiconductor layer of a molecular layer and an atomic layer by a crystalline growth of VPE and an ALF is formed. In this case, the flowing speed of the material gas in the tube 1 is set to a limit value or more for exhibiting a self-limiting effect on the ALE optimized region and to a limit value or less on the VPE optimized region. Thus, a sectional area of the tube 1 is reduced on the ALE optimized region and increased on the VPE optimized region. In this manner, the ALE and the VPE are alternately executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for epitaxially growing a semiconductor layer on a substrate by using a source gas made of an organic metal.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices, a vapor phase in which a desired semiconductor layer is grown on a substrate by thermal decomposition of a raw material gas containing a component of silicon or a compound semiconductor or reaction between a plurality of raw material gases. Growth method (CVD: chemica
l vapor deposition or VPE: vapor phase epitaxi) is in practical use. In addition, compound semiconductor layers are grown one by one using the surface reaction of the substrate and the organometallic gas.
So-called atomic layer epi-tax (ALE)
i) is being put into practical use. According to this method, it is possible to form a pn junction or a heterojunction composed of a semiconductor layer in the atomic layer order with good controllability, and to use a heterobipolar transistor.
It is possible to control the doping of ultra-high-concentration impurities of about 1 × 10 ²⁰ / cm ³ like the base layer in (HBT) with good controllability.

[0003]

[Problems to be Solved by the Invention] However, ALE
Is usually required to alternately introduce an organometallic gas containing a cation component and a source gas containing an anion component into the reaction tube. Therefore, the growth rate of the semiconductor layer is higher than that of VPE. Low. Therefore, it is economically advantageous to apply VPE to form a semiconductor layer having a relatively large thickness in one semiconductor device, but at present,
Vapor deposition equipment that can perform both ALE and VPE has not been put to practical use. For this reason, it was necessary to transfer the substrate from, for example, a vapor phase growth apparatus dedicated to ALE to another vapor phase growth apparatus dedicated to VPE. As a result, there is a problem that the grown semiconductor layer is exposed to the atmosphere and is contaminated. Further, since it is necessary to cool the substrate temperature to room temperature once when the vapor phase growth apparatus is transferred, it is unavoidable that the already grown semiconductor layer undergoes a relatively large thermal cycle, and further growth is performed on the semiconductor layer. There is a problem that the crystallinity at the interface with the semiconductor layer deteriorates. The basic problem cannot be solved even by connecting the above-mentioned two kinds of vapor phase growth devices by a load lock device capable of vacuum evacuation.

It is an object of the present invention to provide a vapor phase growth apparatus capable of alternately performing ALE and VPE without having to take out the substrate into the atmosphere and without needing to cool it to room temperature. .. As this VPE, MOVPE (metal or metal or
ganic VPE) is applied.

[0005]

The above object is to introduce a raw material gas containing at least a cation component from an organometal and a raw material gas containing an anion component into the reaction tube. A vapor phase growth apparatus for growing a single crystal layer of a compound composed of a cation component and an anion component on a substrate installed in the reaction tube, wherein an inner wall of the vapor phase growth device and the substrate are narrowed. Having a first region and a second region between the inner wall of the substrate and the substrate, and the substrate inside the reaction tube, the first region and the second region. And a means for heating the substrate to a predetermined temperature in each of the first and second regions, which is achieved by the vapor phase growth apparatus according to the present invention. To be done.

[0006]

[Function] In ALE, a compound semiconductor crystal of a monolayer grows every time a source gas containing an organic metal containing a cation component and a source gas containing an anion component are alternately introduced into the reaction tube. , The so-called self-limiting effect is used.

In order for the above self-limiting effect to appear, it is necessary to blow the source gas onto the substrate at a high speed. It is considered that this is because the raw material gas introduced into the reaction tube needs to be adsorbed to the substrate before thermal decomposition in the gas phase. That is, a boundary layer having a low flow velocity is formed near the surface of the substrate that comes into contact with the raw material gas flowing at high speed. Therefore, the supply of the source gas to the substrate is limited by the diffusion in the boundary layer. Since the thickness of this boundary layer is inversely proportional to the flow velocity, by increasing the flow velocity to thin the boundary layer, the source gas can quickly diffuse in the boundary layer.

Taking an example of growing gallium arsenide (GaAs) by ALE using an organometallic compound such as trimethylgallium (TMG) as a source gas for gallium, the substrate is not thermally decomposed as described above. The TMG molecules that reach the surface are adsorbed on the substrate surface to form a surface layer. TMG is less likely to be adsorbed on this surface layer and thermal decomposition is less likely to occur, which is the cause of the self-limiting effect.

When the above-mentioned surface layer, for example, arsine (AsH ₃ ) which is a raw material gas of an anion component is introduced, it reacts with this gas to form a monolayer of GaAs. Excess AsH ₃ is discharged. By repeating this process, a GaAs crystal with a desired layer thickness grows.

As described above, the thickness of the boundary layer that enables ALE is determined by the thermal decomposition time of the raw material gas (the induction period from the heating to a predetermined temperature until the start of thermal decomposition) and the diffusion rate. There is an upper limit. To realize a boundary layer of this thickness, the flow velocity is increased.

On the other hand, MOVPE mainly utilizes a process in which a thermal decomposition product of a source gas in a gas phase is diffused and deposited on a substrate. Therefore, the flow velocity in MOVPE must be lower than the flow velocity required in ALE, that is, the flow velocity that causes the boundary layer of the thickness where the self-limiting effect appears.

In the present invention, as described above, the space between the inner wall of the reaction tube and the substrate is narrowed in the area where ALE is carried out, while expanded in the area where MOVPE is carried out. Optimize the flow rate. The narrowing and expansion described above is realized by changing the cross-sectional area of the reaction tube in each of the regions.

[0013]

1 is a schematic cross-sectional view showing the structure of a horizontal vapor phase growth apparatus to which the present invention is applied. For example, a reaction tube 1 having a rectangular cross section made of transparent quartz has a tube axis substantially It is installed horizontally. The reaction tube 1 is provided with a first area (ALE optimization area) having a small cross-sectional area perpendicular to the tube axis and a second area (MOVPE optimization area) having a large cross-sectional area. There is. One end 5 of the reaction tube 1
For example, as a source gas source composed of an organometallic compound for supplying a cation component, a bubbler 2 of TMG and a bubbler 4 of trimethylaluminum (TMA) 4, and as a source gas source for supplying an anion component. Each of the AsH ₃ cylinders 3 is connected via a mass flow controller 6. The reaction tube 1 can be evacuated by an exhaust device (not shown) connected to the other end.

A susceptor 7 made of, for example, a graphite is installed inside the reaction tube 1, and a substrate 8 made of, for example, a GaAs crystal is placed on the susceptor 7. The susceptor 7 is connected to, for example, a rod-shaped moving mechanism 9 extending in the axial direction of the reaction tube 1.
Moved to E and MOVPE optimized regions. The cross-sectional area of the reaction tube 1 and the distance between the upper inner wall surface of the reaction tube 1 and the substrate 8 are as follows, for example.

ALE Optimization Area MOVPE Optimization Area Cross-sectional Area (cm ² ) 5.0 50 Distance (cm) 0.5 5.0 First, the substrate 8 is moved to the MOVPE optimization area. After the inside of the reaction tube 1 was evacuated, while introducing AsH ₃ from the cylinder 3, the induction heating coil and susceptor 7 was installed, for example, outside of the built-in resistance heating type heater or the reaction tube 1 to The substrate 8 is heated to 700 ° C. Needless to say, when the induction heating coil is used, the induction heating coil may be moved together with the movement of the susceptor 7.

While continuing the introduction of AsH ₃ , TMG is introduced from the bubbler 2 into the reaction tube 1. At this time, TMG and AsH ₃
Are set to 10 SCCM and 500 SCCM, respectively, and the exhaust speed is adjusted so that the total pressure in the reaction tube 1 becomes 20 Torr. In this state, the flow rate of TMG in the MOVPE optimized region does not reach the self-limiting effect, and these source gases are thermally decomposed in the gas phase and diffused to the surface of the substrate 8. That is, crystal growth by MOVEP is performed. In this way, a GaAs crystal having a thickness of about 1 μm is grown on the substrate 8.

Then, the introduction of TMG from the bubbler 2 is stopped, the introduction of AsH ₃ from the cylinder 3 is continued for a while, and the substrate 8 is moved to the ALE optimization region while the substrate 8 is kept at 500 times.
After adjusting the temperature of the susceptor 7 so that it becomes ℃,
Stop the introduction of H ₃ .

Next, TMA is introduced into the reaction tube 1 from the bubbler 4. At this time, the flow rate of TMA is set to 20 SCCM, and the exhaust speed is adjusted so that the pressure in the reaction tube 1 becomes 20 Torr. In this state, the flow rate of TMA in the ALE optimization region becomes a value that produces the self-limiting effect, and the substrate 8
A diatomic layer of Al grows on the surface.

Then, the introduction of TMA from the bubbler 4 is stopped, and AsH ₃ from the cylinder 3 is introduced into the reaction tube 1.
To introduce. As a result, a bilayer of AlAs grows on the surface of the substrate 8.

Next, the introduction of TMA from the bubbler 4 is stopped and the TMG is introduced from the bubbler 2. The flow rate of TMG at this time is set to 20 SCCM, and the pressure in the reaction tube 1 is 20 T
Adjust the pumping speed to be orr. In this state, A
The flow rate of TMG in the LE optimization region is a value that produces the self-limiting effect, and the surface of the substrate 8 has a thickness of one atomic layer.
Ga grows.

Then, the introduction of TMG from the bubbler 2 is stopped, and AsH ₃ is introduced from the cylinder 3 into the reaction tube 1. As a result, a GaAs monomolecular layer grows on the surface of the substrate 8.

Growth of AlAs and GaAs by the above ALE is repeated to form a strained superlattice layer having a desired thickness. While continuing the introduction of AsH ₃ from the cylinder 3 at the end of this process,
The substrate 8 is moved to the MOVPE optimization area again, and 700
The temperature of the septa 7 is adjusted so as to be maintained at 0 ° C. After that, TMG is introduced from the bubbler 2 into the reaction tube 1. As a result, a 100 nm thick G layer is formed on the substrate 8 as a cap layer.
Grow an aAs crystal.

FIG. 2 is a schematic sectional view showing an example in which the present invention is applied to a so-called chimney type vapor phase growth apparatus, particularly a vapor phase growth apparatus capable of carrying out the pulse jet method. For example, the cylindrical reaction tube 11 made of transparent quartz is installed so that its central axis is oriented in the vertical direction. Reaction tube
Reference numeral 11 is provided with a first region (ALE optimization region) having a small cross section perpendicular to the central axis and a second region (MOVPE optimization region) having a large cross section. Similar to the above-mentioned embodiment, one end 12 of the reaction tube 11 is provided with a source gas source of an organometallic compound for supplying a cation component and an AL.
Other source gas sources used in E are connected. The inside of the reaction tube 11 can be evacuated by an exhaust device (not shown) connected to the other end. A source gas introduction pipe 13 is provided penetrating the reaction pipe 11 near the boundary between the ALE optimization region and the MOVPE optimization region.

Inside the reaction tube 11, a columnar susceptor 14 made of, for example, graphite is held by a rod-shaped moving mechanism 15. A substrate 17 made of, for example, GaAs crystal is fixed to the susceptor 14 so as to face the end portion 12. The susceptor 14 drives the moving mechanism 15 manually or by a motor in the directions of arrows A ₁ and A ₂ ,
They are moved to the ALE optimization area and the MOVPE optimization area, respectively. The cross-sectional area of the reaction tube 11 and the distance between the inner wall surface of the reaction tube 11 and the substrate 17 are as follows, for example.

ALE optimization area MOVPE optimization area Cross-sectional area (cm ² ) 50 530 Distance (cm) 1 10 First, as shown in FIG. 2B, the substrate 17 is moved to the MOVPE optimization area. After evacuating the inside of the reaction tube 11,
While introducing AsH ₃ into the reaction tube 11 through one of the raw material gas introduction tubes 13, a susceptor 14 is installed, for example, a resistance heating type heater built in the susceptor 14 or an induction heating coil installed outside the reaction tube 11. The substrate 17 is maintained at 700 ° C. by heating. Needless to say, when the induction heating coil is used, the induction heating coil may be moved together with the movement of the susceptor 14.

While continuing to introduce AsH ₃ , TMG is introduced into the reaction tube 11 through another source gas introduction tube 13. At this time, the flow rates of TMG and AsH ₃ are 20 SCCM and 500 SC, respectively.
Set to CM and adjust the exhaust speed so that the total pressure in the reaction tube 11 is 10 Torr. In this state, the flow rate of TMG in the MOVPE optimized region does not reach the self-limiting effect, and these source gases are thermally decomposed in the gas phase and diffused to the surface of the substrate 17. That is, crystal growth by MOVEP is performed. In this way, the thickness of 500n on the substrate 17
Grow a m GaAs crystal.

Then, the introduction of TMG from the raw material gas introduction pipe 13 is stopped, and the introduction of AsH ₃ is continued for a while.
As shown in (a), the substrate 17 is moved to the ALE optimization region, and the temperature of the susceptor 14 is adjusted so that the substrate 17 reaches 500 ° C., and then AsH ₃ is introduced from the source gas introduction pipe 13. Stop.

Next, TMA is introduced into the reaction tube 1 from the end 12. At this time, the flow rate of TMA is set to 20 SCCM, and the exhaust speed is adjusted so that the pressure in the reaction tube 11 becomes 10 Torr. In this state, TMA molecules collide with the surface of the substrate 17 in an undecomposed state. That is, the flow velocity of TMA at this time has a value that produces the self-limiting effect, and diatomic layer Al grows on the surface of the substrate 17.

Then, the introduction of TMA from the end 12 is stopped and AsH ₃ is introduced into the reaction tube 11 through the end 12. As a result, bilayer AlAs grows on the surface of the substrate 17.

Then, the introduction of AsH ₃ is stopped and TMG is introduced from the end 12. The flow rate of TMG at this time
Set it to 20 SCCM and adjust the pumping speed so that the pressure in the reaction tube 1 becomes 10 Torr. In this state, the flow rate of TMA in the ALE optimization region has a value that produces the self-limiting effect, and Ga of a monoatomic layer grows on the surface of the substrate 8.

Then, the introduction of TMG is stopped, and AsH ₃ is introduced into the reaction tube 1 from the end 12. As a result, a monomolecular layer of GaAs grows on the surface of the substrate 17. AlAs by ALE above
And GaAs are repeatedly grown to form a strained superlattice layer having a desired thickness. After that, as shown in FIG. 2 (b), the substrate 17 is moved to the MOVPE optimization region again, and at 700 ° C.
The temperature of the septa 14 is adjusted so that it is held at. Then, the introduction of AsH ₃ from the end 12 is stopped, and TMG and AsH ₃ are introduced from the source gas introduction pipe 13 into the reaction pipe 11. As a result, the thickness of the cap layer is formed on the substrate 17.
Grow a 100 nm GaAs crystal.

In the above embodiment, the case where a GaAs crystal and a strained superlattice composed of GaAs and AlAs are formed on a substrate made of GaAs has been described. However, when a compound semiconductor other than the above is grown on another substrate. Needless to say, the present invention can be applied to the case where a source gas containing an impurity element for imparting a predetermined conductivity type is introduced into them. Further, at present, VPE used in combination with ALE is advantageous in MOVPE using a raw material gas composed of an organometallic compound, because a common raw material gas can be used.
From the principle of the present invention, it is clear that the vapor phase growth method (VPE or CVD) using a source gas other than the organometallic compound may be used in combination with ALE.

[0033]

According to the present invention, the ALE and VPE are not required to be taken out of the substrate into the atmosphere or cooled to room temperature.
Can be alternately carried out, and there is an effect that it contributes to improvement in performance and reliability of an electronic device using a compound semiconductor crystal having a thickness that requires control of atomic layer order, and improvement in manufacturing yield.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a second embodiment of the present invention.

[Explanation of symbols]

 1, 11 Reaction tube 2, 4 Bubbler 3 Cylinder 5, 12 End 6 Mass flow controller 7, 14 Susceptor 8, 17 Substrate 9, 15 Transfer mechanism 13 Raw material gas introduction pipe

Claims (3)

[Claims] 1. A raw material gas containing at least a cation component is made of an organic metal, and a raw material gas containing an anionic component and the organometallic raw material gas are introduced into a reaction tube and installed in the reaction tube. A vapor phase growth apparatus for growing a single crystal layer of a compound comprising a cation component and an anion component on a substrate, the first region having a narrow space between the inner wall and the substrate and the inner wall A reaction tube having a second region extending between the substrate and the substrate, and means for moving the substrate between the first region and the second region inside the reaction tube. , A means for heating the substrate to a predetermined temperature in each of the first and second regions. 2. The flow velocity of the organometallic gas in the first region is such that a boundary layer having a thickness that allows passage of the organometallic gas molecules by diffusion within the time required for its decomposition is generated near the substrate surface. And the flow velocity of the organic metal gas in the second region is equal to or less than the flow velocity. 3. The vapor phase growth apparatus according to claim 1, wherein the means for heating the substrate is a heater movable in parallel with the movement of the substrate.