Vapor phase growth apparatus and vapor phase growth method

Abstract

To provide a vapor phase growth device and a vapor phase growth method capable of stably supplying a proper amount of organic metal raw material onto a substrate.SOLUTION: A cold-wall type vapor phase growth apparatus 10 for forming a compound semiconductor thin film on a substrate 14 includes a reactor 11 having a reaction tube 12 for supplying an organometallic raw material to a substrate 14 in a state where vapor of the organometallic raw material supplied from a vessel filled with the organometallic raw material is accompanied by carrier gas, and a heater 16 capable of heating an upstream part 11a of the reactor 11 to which the vapor of the organometallic raw material is supplied from the outside of the reaction tube 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vapor phase growth apparatus and a vapor phase growth method. [Background technology]

[0002] In a vapor phase growth apparatus for forming a compound semiconductor thin film on a substrate, a method of supplying a raw material containing a metal element to a substrate by supplying the raw material to a reactor in a state where the raw material is accompanied by a carrier gas is generally used (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-150497 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, metalorganic sources such as trimethylgallium (TMG), trimethylaluminum (TMA), and trimethylindium (TMI) have been investigated as sources containing metal elements. In this case, a carrier gas such as nitrogen or hydrogen gas is supplied to a container filled with the metalorganic source in liquid form, and the vapor of the metalorganic source is supplied to the reactor together with the carrier gas. Because the vapor pressure of the metalorganic source depends on its temperature, in order to supply the metalorganic source at a constant temperature, the container filled with the source must be placed in a thermostatic chamber or similar and kept at a predetermined temperature. In addition, the temperature of not only the source container filled with the metalorganic source but also the supply path from the source container to the reactor must be kept constant.

[0005] However, when the vapor pressure of the metalorganic precursor is low or when a large amount of the precursor needs to be supplied, it is necessary to maintain the temperature of the metalorganic precursor at a relatively high level to ensure the supply rate of the metalorganic precursor. In this case, unless the temperature of the supply path from the source container to the reactor is also maintained at a high temperature corresponding to the temperature of the source container, the temperature in the supply path piping may drop, causing the metalorganic precursor to condense and reducing the supply rate that reaches the substrate. Furthermore, the metalorganic precursor that has condensed in the piping may be released during the next film formation, increasing the supply rate due to impurity levels, resulting in a so-called memory effect. Condensation of the metalorganic precursor in the supply path piping thus presents a problem: it is not possible to supply the appropriate amount of the metalorganic precursor to the substrate.

[0006] The present invention has been proposed in view of the above-described conventional circumstances, and aims to provide a vapor phase growth apparatus and a vapor phase growth method that are capable of stably supplying an appropriate amount of organic metal precursor onto a substrate. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides the following means. [1] A cold-wall type vapor phase growth apparatus for forming a compound semiconductor thin film on a substrate, comprising: a reactor having a reaction tube that supplies vapor of an organic metal precursor, which is supplied from a container filled with the organic metal precursor, to a substrate in a state where the vapor of the organic metal precursor is entrained in a carrier gas; and a heater that can heat the upstream part of the reactor, to which the vapor of the organic metal precursor is supplied, from the outside of the reaction tube. [2] The vapor phase growth apparatus according to [1], wherein the heater is detachable from the reactor. [3] A cold-wall vapor phase growth method for forming a compound semiconductor thin film on a substrate, comprising: a raw material supply step of supplying an organic metal precursor to the substrate through a reaction tube in a state where the organic metal precursor vapor is supplied from a container filled with the organic metal precursor and is accompanied by a carrier gas; and a heating step of heating an upstream portion of a reactor equipped with the reaction tube with a heater from outside the reaction tube, wherein the heating step is performed at least during the raw material supply step. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a vapor phase growth apparatus and a vapor phase growth method that are capable of stably supplying an appropriate amount of metalorganic material onto a substrate. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a vapor phase growth apparatus equipped with a heater. [Figure 2] FIG. 1 is a cross-sectional view showing an example of a vapor phase growth apparatus with a heater removed. [Figure 3] FIG. 1 is a configuration diagram showing an example of a vapor phase growth apparatus including a supply device for metal organic raw materials. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings used in the following description, characteristic parts may be shown schematically for the sake of convenience in order to make the features easier to understand. The number of components and dimensional ratios may not necessarily be the same as in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited to them. Appropriate changes may be made within the scope of the present invention.

[0011] 1 and 2 are cross-sectional views showing an example of a vapor phase growth apparatus according to this embodiment, with Fig. 1 showing a state in which a heater is attached and Fig. 2 showing a state in which the heater is removed. Fig. 3 is a structural diagram showing an example of a vapor phase growth apparatus including a supply device for metalorganic raw materials.

[0012] 1, the vapor phase growth apparatus 10 of this embodiment is a cold-wall type vapor phase growth apparatus for forming a compound semiconductor thin film on a substrate. The vapor phase growth apparatus 10 includes a reactor 11 having a reaction tube 12 that supplies an organic metal source to a substrate 14, and a heater 16 that can heat an upstream portion 11a of the reactor 11 from outside the reaction tube 12.

[0013] The vapor phase growth apparatus 10 of this embodiment can be used to form a compound semiconductor thin film using an organic metal as a raw material. As a film formation method, for example, metal organic chemical vapor deposition (MOCVD) can be used.

[0014] The reaction tube 12 supplies the metal-organic raw material vapor entrained in a carrier gas to the substrate 14. The metal-organic raw material vapor is supplied from a container filled with the metal-organic raw material (see source container 23 in FIG. 3). The material of the reaction tube 12 is not particularly limited, but examples include ceramics, glass, metal, etc., and specific examples include quartz (SiO2), stainless steel (SUS), etc.

[0015] The reactor 11 has, along the flow direction, an upstream section 11a on the gas inlet section 13 side, a midstream section 11b where the substrate 14 is placed, and a downstream section 11c on the gas exhaust section 15 side. Here, the flow direction is the direction in which the gas flows from the gas inlet section 13 side to the gas exhaust section 15 side. In the illustrated example, the flow direction of the reactor 11 is horizontal, but the flow direction may be set in another direction.

[0016] The reaction tube 12 constitutes a flow channel in the reaction furnace 11. Although not particularly shown, the reaction furnace 11 may be equipped with an exhaust mechanism or the like for reducing the pressure inside the reaction tube 12 to a predetermined level. In a cold-wall type reaction furnace 11, a cooling mechanism for the reaction tube 12 using water cooling or the like may be provided, or the cooling mechanism may be omitted at least in the location where the heater 16 is used.

[0017] The carrier gas is a gas used to transport raw material gases, reactive gases, doping gases, etc., which are components of compound semiconductors. There are no particular limitations on the carrier gas as long as it does not react with the raw material gases, etc. Examples of the carrier gas include hydrogen (H), nitrogen (N), argon (Ar), and helium (He).

[0018] In the illustrated example, in the upstream section 11a of the reactor 11, the interior of the reaction tube 12 is partitioned into multiple channels 13a and 13b via a partition 13c. More specifically, the interior of the reaction tube 12 is partitioned into three layers of channels 13a and 13b by two partitions 13c, constituting a top channel, a middle channel, and a bottom channel from top to bottom. The number of layers partitioned into the multiple channels 13a and 13b is not limited to three, and may be more than three. In the illustrated example, the partition 13c is disposed only at a position away from the substrate 14, but the range of partitioning the channels 13a and 13b can be set appropriately. For example, although not specifically illustrated, the partition 13c may be disposed near or immediately before the substrate 14.

[0019] At the end of the range partitioned by the partition 13c, the gases supplied from the channels 13a and 13b can be mixed with each other. The channel used to supply the metalorganic precursor is not particularly limited, and for example, the metalorganic precursor may be supplied from a channel sandwiched between other channels, such as a middle channel. The metalorganic precursor and the reactive gas may be supplied from different channels. If a doping gas is required, it may be supplied in a state mixed with either the metalorganic precursor or the reactive gas.

[0020] The substrate 14 is held so that the substrate surface 14a is exposed inside the reaction tube 12. The vapor phase growth apparatus 10 may be equipped with a substrate holding mechanism such as a susceptor (not shown) for holding the substrate 14. In the illustrated example, the substrate 14 is held so that the substrate surface 14a faces upward. Although not specifically shown, the substrate 14 can also be held so that the substrate surface 14a faces downward. A compound semiconductor thin film is formed on the substrate surface 14a.

[0021] The substrate 14 may be any of various substrates such as a semiconductor substrate or an insulator substrate. The material of the substrate 14 is not particularly limited, but may be a silicon substrate, a silicon carbide (SiC) substrate, a sapphire substrate, a gallium arsenide substrate, a gallium nitride substrate, a gallium oxide substrate, etc. A compound semiconductor thin film may be epitaxially grown on the substrate 14.

[0022] The substrate may be thinly sliced ​​like a wafer. The planar shape of the substrate 14 when viewed from a direction perpendicular to the substrate surface 14a is generally circular, but may be other shapes. The substrate 14 may have a cutout portion such as an orientation flat or a notch at one or more locations on the circumference.

[0023] During the formation of the compound semiconductor thin film, the substrate 14 may be rotated about a rotation axis perpendicular to the substrate surface 14a. The method for rotating the substrate 14 is not particularly limited, but for example, the substrate 14 held by the susceptor may be rotated by rotating the susceptor. The rotation direction of the substrate 14 is preferably about a central axis that is a perpendicular line passing through or near the center of the substrate surface 14a, and may be clockwise or counterclockwise.

[0024] In the cold-wall type reactor 11, a substrate heating device (not shown) such as a heater is used to heat the substrate 14. The substrate heating device heats the substrate 14 to a temperature equal to or higher than the thermal decomposition temperature of the raw material. However, in the cold-wall type reactor 11, the heating direction may be controlled or the upstream part 11a of the reactor 11 may be shielded from heat by the substrate heating device so that the heat from the substrate heating device is not transmitted to the reaction tube 12 in the upstream part 11a.

[0025] In other words, in the conventional cold-wall type reactor 11, there is no heating mechanism in the region from the gas inlet 13 of the reactor 11 to the upstream end of the substrate 14 (i.e., the upstream portion 11a), which poses a problem that the metal-organic raw material is likely to aggregate before it reaches the substrate 14.

[0026] Therefore, when reactor 11 is not heated by heater 16, upstream section 11a of reactor 11 is not heated from the outside, and the temperature of upstream section 11a becomes lower. If the metal-organic raw material aggregates before reaching substrate 14, the metal-organic raw material cannot be stably supplied to substrate 14.

[0027] In the upstream section 11a of the reactor 11, a heater 16 is provided outside the reaction tube 12, thereby allowing the upstream section 11a to be heated to a predetermined temperature. The type of heater 16 is not particularly limited, but an electric heater is preferred, and examples include resistance heating, infrared radiation, and electromagnetic induction. When the vapor deposition apparatus 10 is in use (when performing the vapor deposition method), the heater 16 heats the upstream section 11a (heating step) at least when the vapor of the metalorganic precursor is supplied (source supply step). The heating step may be performed only during the source supply step, or may be started before the source supply step begins, or may be ended after the source supply step ends. The heater 16 may constantly heat the upstream section 11a, with some periods during which the source is supplied and others during which the source is not supplied.

[0028] The heater 16 can be divided into an upper portion 16a and a lower portion 16b to fit the shape of the existing reactor 11 and installed so as to sandwich the reactor 11. This allows the heater 16 to be attached to and detached from the reactor 11 as needed.

[0029] 2 is a vapor phase growth apparatus 20 that does not include a heater 16, and is also a vapor phase growth apparatus 20 in a state where the detachable heater 16 has been removed from the reactor 11. The shape of the heater 16 can be designed appropriately to match the shape of the upstream section 11a of the reactor 11.

[0030] Since the heater 16 is detachable from the reactor 11, it is possible to add a heater 16 to an existing reactor 11. This makes it easy to repurpose existing facilities for new material production applications. In addition, the heater 16 may be attached or detached depending on the film formation conditions, such as the type of organometallic raw material.

[0031] The detachable heater 16 is not limited to the structure divided into two parts, upper and lower, as shown in the figure, but may be divided into two parts in other appropriate directions, or into three or more parts. Also, the heater 16 may be configured to be deformable, for example, by winding the heater 16 spirally around the outer periphery of the reaction tube 12.

[0032] It is preferable that the heater 16 can be attached and detached without moving it in the gas flow direction in the reactor 11. This makes it possible to attach and detach the heater 16 without affecting the connections of the piping, even when piping, etc. is connected to the upstream side of the gas inlet 13 and the downstream side of the gas exhaust 15 of the reactor 11.

[0033] When the reactor 11 is heated by the heater 16, the temperature of the reactor 11 heated by the heater 16 can be set appropriately depending on the situation, such as when the vapor pressure of the metalorganic raw material is low or when a large amount of metalorganic raw material needs to be supplied. By installing a thermocouple or the like near the heater 16, it is also possible to monitor the temperature of the heater 16 while the metalorganic raw material is being supplied. Using such a temperature monitoring function makes it easy to set the heating temperature appropriately.

[0034] In reactor 11, the metal-organic raw material vapor is supplied to substrate 14, and upstream section 11a of reactor 11 is heated by heater 16, thereby enabling a stable supply of the metal-organic raw material. By maintaining the metal-organic raw material in a vapor state in upstream section 11a of reactor 11, condensation of the metal-organic raw material in upstream section 11a can be suppressed. Because the metal-organic raw material is stably supplied to substrate 14, productivity of compound semiconductor thin films can be improved.

[0035] The lower limit of the temperature of the reactor 11 heated by the heater 16 is preferably set to at least the temperature of the metalorganic source section at which sufficient vapor pressure can be ensured even for metalorganic sources with low vapor pressure. For example, when tris(cyclopentadienyl)scandium (CpSc), which is currently being used as a source of scandium (Sc), is used as the metalorganic source, the lower limit of the temperature is preferably 130°C or higher.

[0036] The upper limit of the temperature of the reactor 11 heated by the heater 16 can be set appropriately depending on the thermal decomposition temperature of the metalorganic raw material, and is preferably lower than the thermal decomposition temperature, for example. Since the thermal decomposition temperatures of metalorganic raw materials such as TMG, TMA, and TMI, which are generally used in the MOCVD growth of nitride semiconductors, are approximately 400°C to 450°C, the upper limit of the temperature is preferably 400°C or lower. If the metalorganic raw material has a different thermal decomposition temperature, the upper limit of the temperature can also be changed to match the thermal decomposition temperature, and the upper limit of the temperature may be set in a range higher than the example given above.

[0037] Ammonia (NH3), the nitrogen source for nitride semiconductors, does not thermally decompose above the thermal decomposition temperature of the organometallic precursor, so there is no need to consider the upper limit temperature. However, if there is a possibility that the thermal decomposition temperature may change due to the addition of other components mixed with the organometallic precursor, the upper limit temperature can be set lower as necessary.

[0038] The method for supplying the metal-organic precursor to the substrate in a state in which the vapor of the metal-organic precursor is supplied from a container filled with the metal-organic precursor and is accompanied by a carrier gas is not particularly limited, but may be a method in which a carrier gas is supplied to a container of the metal-organic precursor.

[0039] 3, a carrier gas may be supplied from a carrier gas container 21 to a source container 23 via a carrier gas supply line 22. The vapor of the metal-organic source is supplied to the reactor 11 via a source supply line 24, entrained in the carrier gas. The carrier gas may be bubbled through the metal-organic source filled in the source container 23.

[0040] Furthermore, the reaction gas is supplied to the reaction furnace 11 from a reaction gas container 25 via a reaction gas supply line 26, separate from the raw material supply line 24. Although not shown, a path may be provided through which the carrier gas is supplied to the raw material supply line 24 or the reaction gas supply line 26 without passing through the raw material container 23. The carrier gas supply line 22, the raw material supply line 24, and the reaction gas supply line 26 may be provided with control devices such as valves and mass flow controllers.

[0041] The source container 23 filled with the metal-organic source may be equipped with a heating mechanism to promote vaporization of the metal-organic source. It is also possible to employ a method in which the metal-organic source in the source container 23 is vaporized by direct heating, and then the vapor of the metal-organic source is mixed with a carrier gas.

[0042] The metal element contained in the organometallic raw material is not particularly limited, but examples thereof include Group 2 elements such as magnesium (Mg); Group 13 elements such as aluminum (Al), gallium (Ga), and indium (In); Group 14 elements such as silicon (Si) and germanium (Ge); transition metal elements such as scandium (Sc), titanium (Ti), manganese (Mn), iron (Fe), nickel (Ni), yttrium (Y), niobium (Nb), molybdenum (Mo), hafnium (Hf), and tungsten (W); and rare earth elements such as lanthanum (La), europium (Eu), and gadolinium (Gd).

[0043] The organometallic raw materials are not particularly limited, but include TMG, TMA, TMI, etc. for Group 13 elements, organosilanes, organosilazanes, etc. for Group 14 elements, and (MCp)3Sc, Cp3Sc, Cp3Y, EuCppm2, etc. for rare earth elements, where MCp represents a methylcyclopentadienyl group, Cp represents a cyclopentadienyl group, and Cppm represents a normal propyl tetramethylcyclopentadienyl group.

[0044] The organic group contained in the organometallic raw material is not particularly limited, but examples thereof include alkyl groups such as methyl, ethyl, and propyl groups, and cyclopentadienyl groups which may have substituents such as Cp, MCp, and Cppm. The substituent contained in the organic group is not particularly limited, but examples thereof include alkyl groups such as methyl, ethyl, and propyl groups.

[0045] The organometallic raw material may have a hydrogen atom, a halogen atom, an amino group, an imino group, or the like as a substituent or ligand other than the organic group. The organic group may be a hydrocarbon group consisting only of carbon (C) and hydrogen (H), and may contain elements other than C and H. Examples of elements other than C and H include oxygen (O), nitrogen (N), and halogens.

[0046] An example of an organometallic material with a relatively low vapor pressure is (MCp)3Sc, which has a vapor pressure of 10 mTorr at 100°C. Cp3Sc and Cp3Y have a vapor pressure of 6.5 mTorr at 100°C and 65 mTorr at 130°C. EuCppm2 has a vapor pressure of 0.27 mTorr at 100°C and 0.0062 Torr at 130°C. An example of an organometallic material with a relatively high vapor pressure is TMA, which has a vapor pressure of approximately 12 Torr at 20°C. Here, 1 Torr = (101325 / 760) Pa ≒ 133.32 Pa.

[0047] The compound semiconductor thin film formed by the vapor phase growth apparatus 10 of this embodiment may be a thin film made of one type of compound semiconductor, or may be a thin film made of two or more types of compound semiconductors. Furthermore, the thin film may be a thin film made of a mixture of two or more types of compound semiconductors, or may be a stacked film of two or more types of compound semiconductor thin films.

[0048] The compound semiconductor constituting the compound semiconductor thin film is not particularly limited, but examples thereof include nitrides, oxides, oxynitrides, phosphides, and arsenides of the metal elements. The compound semiconductor may be doped to be P-type or N-type. Examples of reactive gases that react with the metal elements include NH3, O2, PH3, and AsH3.

[0049] When forming a compound semiconductor thin film using the vapor phase growth apparatus 10 of this embodiment, only an organic metal source may be used as the metal element source. Metal element sources other than the organic metal source may also be used in combination as doping gases, etc., and specific examples include inorganic silanes such as monosilane and disilane. [Explanation of symbols]

[0050] 10, 20... vapor phase growth apparatus, 11... reactor, 11a... upstream section, 11b... midstream section, 11c... downstream section, 12... reaction tube, 13... gas inlet section, 13a, 13b... channel, 13c... partition, 14... substrate, 14a... substrate surface, 15... gas exhaust section, 16... heater, 16a... upper section, 16b... lower section, 21... carrier gas container, 22... carrier gas supply line, 23... raw material container, 24... raw material supply line, 25... reaction gas container, 26... reaction gas supply line.

Claims

1. In a cold-wall vapor phase growth apparatus for forming a compound semiconductor thin film on a substrate, a reaction furnace including a reaction tube for supplying a metal-organic precursor to a substrate in a state in which the metal-organic precursor vapor is carried by a carrier gas, the reaction furnace being provided with a vessel filled with the metal-organic precursor; a heater capable of heating, from the outside of the reaction tube, an upstream portion of the reaction furnace to which the vapor of the metal-organic raw material is supplied; A vapor phase growth apparatus comprising:

2. 2. The vapor phase growth apparatus according to claim 1, wherein the heater is detachable from the reactor.

3. A cold-wall vapor phase growth method for forming a compound semiconductor thin film on a substrate, comprising: a source supply step of supplying the metalorganic source, which is supplied from a container filled with the metalorganic source, to the substrate through a reaction tube in a state where the metalorganic source vapor is carried by a carrier gas; a heating step of heating an upstream portion of a reactor including the reaction tube from outside the reaction tube with a heater; and performing the heating step at least in the source supply step.

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