Method for manufacturing III-nitride semiconductor

Abstract

To provide a technique capable of producing a group III nitride semiconductor with low carbon content.SOLUTION: A method for producing a group III nitride semiconductor includes a delivery step S1, a pressure reduction step S2, a heating step S3, an excited gas supply step S5, and an organic metal gas supply step S6. In the delivery step S1, a substrate is delivered into a chamber. In the pressure reduction step S2, a suction unit lowers the pressure within the chamber. In the heating step S3, a heater provided within the chamber heats the substrate. In the excited gas supply step S5, a hydrogen-free, nitrogen-containing first gas is supplied to a plasma generating unit, and the plasma generating unit supplies an excited gas obtained by converting the first gas into plasma to the substrate within the chamber. In the organic metal gas supply step S6, a second gas, which is an organic metal gas including a group III element, is supplied to the substrate within the chamber.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This application relates to a method and an apparatus for manufacturing a group III nitride semiconductor.

Background Art

[0002] Conventionally, a technique for forming a gallium nitride (GaN) film on a substrate by metalorganic chemical vapor deposition has been proposed. In the metalorganic chemical vapor deposition method, generally, a substrate is heated near atmospheric pressure, and an organometallic gas (e.g., trimethylgallium) as a gallium source and ammonia (NH3) gas as a nitrogen source are supplied to the substrate, and a gallium nitride film is grown on the substrate from gallium and nitrogen generated by thermal decomposition.

[0003] In such a manufacturing method, it is necessary to thermally decompose ammonia gas, and for this thermal decomposition, a high temperature of 1100 °C or higher is required. When the temperature becomes high, stress is applied to the substrate by heat, and the film is likely to crack. Therefore, the yield of the device decreases.

[0004] Therefore, a metalorganic chemical vapor deposition method using plasma has been proposed (for example, Patent Document 1). In the manufacturing apparatus described in this Patent Document 1, in a chamber, while a mixed gas of nitrogen (N2) gas and hydrogen (H2) gas is being converted into plasma, an organometallic gas of a group III element is supplied into the chamber. According to this, since there is no need to thermally decompose ammonia gas as a nitrogen source, a group III nitride semiconductor film can be formed on a substrate at a relatively low temperature.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technology described in Patent Document 1 allows for the formation of a group III nitride semiconductor film at low temperatures, but it has the problem that lower temperatures lead to the incorporation of more carbon into the semiconductor film. When the carbon content in the semiconductor film increases, the bulk mobility of the semiconductor film decreases, resulting in a decrease in film quality.

[0007] Therefore, the present invention aims to provide a technology that can manufacture group III nitride semiconductors with a low carbon content. [Means for solving the problem]

[0008] A first embodiment of a method for manufacturing a group III nitride semiconductor is a method for manufacturing a group III nitride semiconductor, comprising: a loading step of loading a substrate into a chamber; a depressurization step of reducing the pressure inside the chamber using a suction unit; a heating step of heating the substrate with a heater provided inside the chamber; an excitation gas supply step of supplying a first gas containing nitrogen gas but not hydrogen to a plasma generation unit, and supplying an excited gas, which is the plasma generated by the plasma generation unit turning the first gas into plasma, to the substrate inside the chamber; and an organometallic gas supply step of supplying a second gas, which is an organometallic gas containing a group III element, to the substrate inside the chamber.

[0009] A second embodiment of the method for producing a group III nitride semiconductor is the method for producing a group III nitride semiconductor according to the first embodiment, wherein the ratio of the density of nitrogen radicals to the flow rate of the second gas is 1 or more and 10 or less.

[0010] A third aspect of the method for manufacturing a group III nitride semiconductor is a method for manufacturing a group III nitride semiconductor according to the first or second aspect, wherein in the heating step, the temperature of the substrate is heated to 800°C or higher and 1000°C or lower.

[0011] A fourth aspect of the method for producing a group III nitride semiconductor is a method for producing a group III nitride semiconductor according to any one of the first to third aspects, wherein the second gas includes trimethylgallium, triethylgallium, or trisdimethylamidogallium.

[0012] A fifth aspect of the method for manufacturing a group III nitride semiconductor is a method for manufacturing a group III nitride semiconductor according to any one of the first to fourth aspects, wherein in the depressurization step, the pressure in the chamber is reduced to 100 Pa or more and 500 Pa or less.

[0013] A first embodiment of a group III nitride semiconductor manufacturing apparatus is a group III nitride semiconductor manufacturing apparatus comprising: a chamber; a substrate holding section provided in the chamber for holding a substrate; a suction section for reducing the pressure inside the chamber; a heater provided in the chamber for heating the substrate; a first gas supply section for supplying a first gas containing nitrogen gas but not hydrogen; a plasma generation section for supplying an excited gas generated by plasma-generating the first gas supplied from the first gas supply section to the substrate inside the chamber; and a second gas supply section for supplying a second gas, which is an organometallic gas containing a group III element, to the substrate inside the chamber. [Effects of the Invention]

[0014] According to the method and apparatus for manufacturing a group III nitride semiconductor, since hydrogen does not become plasma, the reaction between the second gas and hydrogen can be suppressed, and the formation of methane-based compounds can be suppressed. Methane-based compounds are easily incorporated into group III nitride semiconductors, increasing the carbon content in the semiconductor, whereas the formation of methane-based compounds can be suppressed, thus reducing the carbon content in the semiconductor. In other words, a group III nitride semiconductor with a low carbon content can be formed on a substrate. [Brief explanation of the drawing]

[0015] [Figure 1] This diagram schematically shows an example of the configuration of a manufacturing apparatus for group III nitride semiconductors. [Figure 2] This is a block diagram showing an example of the internal configuration of the control unit. [Figure 3] A flowchart shows an example of a method for manufacturing a group III nitride semiconductor. [Figure 4]It is a graph showing an example of the concentration distribution of carbon in a semiconductor film. [Figure 5] It is a graph showing an example of the concentration distribution of carbon in a semiconductor film according to a comparative example. [Figure 6] It is a graph showing an example of the relationship between the flow rate of the second gas and the concentration of carbon in a semiconductor film. [Figure 7] It is a graph showing an example of the relationship between the ratio of the density of nitrogen radicals to the flow rate of the second gas and the concentration of carbon in a semiconductor film. [[ID=*12]]

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments will be described with reference to the accompanying drawings. Note that the components described in this embodiment are merely examples, and are not intended to limit the scope of the present disclosure only to them. In the drawings, for ease of understanding, the dimensions or numbers of each part may be exaggerated or simplified as necessary.

[0017] Expressions indicating relative or absolute positional relationships (for example, "in one direction", "along one direction", "parallel", "orthogonal", "center", "concentric", "coaxial", etc.) are not only to strictly represent the positional relationship, but also to represent a state in which the angle or distance is displaced within a range where the same degree of function can be obtained, unless otherwise specified. Expressions indicating an equal state (for example, "identical", "equal", "homogeneous", etc.) are not only to strictly represent a quantitatively equal state, but also to represent a state in which there is a difference within a range where the same degree of function can be obtained, unless otherwise specified. Expressions indicating a shape (for example, "quadrilateral shape" or "cylindrical shape", etc.) are not only to geometrically strictly represent the shape, but also to represent a shape having, for example, unevenness or chamfering within a range where the same degree of effect can be obtained, unless otherwise specified. The expression "comprising", "having", "including", or "possessing" one component is not an exclusive expression excluding the existence of other components. The expression "at least any one of A, B, and C" includes only A, only B, only C, any two of A, B, and C, and all of A, B, and C.

[0018] <Overview of the manufacturing apparatus> FIG. 1 is a diagram schematically showing an example of the configuration of a manufacturing apparatus 100 for a group III nitride semiconductor. This manufacturing apparatus 100 is a film forming apparatus that forms a group III nitride semiconductor film on the main surface of a substrate W by metalorganic chemical vapor deposition using plasma.

[0019] The substrate W is, for example, a substrate such as sapphire. The substrate W has, for example, a disc shape. Since a group III nitride semiconductor film grows on the main surface of this substrate W, the substrate W is also called a growth substrate. Note that the material and shape of the substrate W are not limited to these and can be appropriately changed.

[0020] The manufacturing apparatus 100 includes a chamber 1, a substrate holding unit 2, a first gas supply unit 3, a plasma generation unit 4, a second gas supply unit 5, a suction unit 6, a heater 7, and a control unit 9. Hereinafter, after outlining each component, a specific example thereof will be described in detail.

[0021] The chamber 1 has a box-shaped hollow shape. The internal space of the chamber 1 corresponds to a processing space for performing a film forming process on the substrate W. The chamber 1 may also be called a vacuum chamber.

[0022] The substrate holding unit 2 is provided in the chamber 1. The substrate holding unit 2 holds the substrate W in a horizontal posture. The horizontal posture referred to here is a posture in which the thickness direction of the substrate W is along the vertical direction.

[0023] The suction unit 6 sucks the gas in the chamber 1 to reduce the pressure in the chamber 1. The suction unit 6 adjusts the pressure in the chamber 1 within a predetermined decompression range suitable for the film forming process.

[0024] The heater 7 is provided in the chamber 1 and heats the substrate W. Specifically, the heater 7 heats the substrate W so that the temperature of the substrate W falls within a temperature range suitable for the film forming process.

[0025] The first gas supply unit 3 supplies the first gas to the plasma generation unit 4. The first gas is a gas that does not contain hydrogen but contains nitrogen. The first gas may contain only nitrogen gas.

[0026] The plasma generation unit 4 converts at least a portion of the first gas into plasma. This generates highly reactive species such as nitrogen ions or neutral radicals. Hereafter, the gas and plasma obtained by converting the first gas into plasma will be collectively referred to as the excited gas. The excited gas includes nitrogen reactive species and nitrogen gas. In the example in Figure 1, the plasma generation unit 4 has a plasma chamber 4a, and the first gas is converted into plasma in the plasma chamber 4a. The excited gas flows out of the plasma chamber 4a and flows through the chamber 1 towards the substrate W. In this way, the excited gas is supplied to the substrate W in the chamber 1.

[0027] The second gas supply unit 5 supplies the second gas to the substrate W in the chamber 1. The second gas is an organometallic gas containing a group III element. Group III elements are also called group 13 elements. For example, a group III element is gallium, and in this case, TMG (trimethylgallium), TEG (triethylgallium), or TDMAG (trisdimethylamidogallium) can be used as the second gas.

[0028] The control unit 9 provides overall control of the manufacturing apparatus 100. For example, the control unit 9 controls the substrate holding unit 2, the first gas supply unit 3, the plasma generation unit 4, the second gas supply unit 5, the suction unit 6, and the heater 7.

[0029] According to this manufacturing apparatus 100, the plasma generation unit 4 converts the first gas into plasma, generating highly reactive nitrogen active species. These highly reactive nitrogen active species react with the group III element thermally decomposed from the second gas on the heated upper surface of the substrate W, forming a group III nitride semiconductor film on the upper surface of the substrate W. When the group III element is gallium, a gallium nitride (GaN) film is formed as the group III nitride semiconductor film.

[0030] As described above, the manufacturing apparatus 100 forms a group III nitride semiconductor film not only through thermal chemical reactions but also by utilizing highly reactive species produced by plasma generation. Therefore, even at low temperatures, a group III nitride semiconductor film can be formed on the upper surface of the substrate W. Consequently, cracks in the substrate can be suppressed and the yield can be improved.

[0031] Furthermore, according to the manufacturing apparatus 100, the gas to be plasma-generated (first gas) does not contain hydrogen. As a result, as will be detailed later, the carbon content in the group III nitride semiconductor film can be reduced. Therefore, the bulk mobility of the group III nitride semiconductor film can be improved, and its film quality can be improved.

[0032] The following sections will detail specific examples of each configuration and specific examples of the operation of the manufacturing apparatus 100.

[0033] <Substrate holding part> The substrate holder 2 holds the substrate W in a horizontal position. In the example shown in Figure 1, the substrate holder 2 includes a susceptor 21 and a susceptor holder 22. The susceptor 21 is a platform for placing the substrate W and has, for example, a flat plate shape. The susceptor 21 is positioned horizontally, and the substrate W is placed on the upper surface of the susceptor 21 in a horizontal position. The upper surface of the substrate W placed on the susceptor 21 is exposed within the chamber 1.

[0034] The susceptor holding section 22 is provided within the chamber 1 and holds the susceptor 21. In the example shown in Figure 1, the susceptor holding section 22 includes a holding base 221 and holding projections 222. The holding base 221 is provided vertically below the susceptor 21 and faces the susceptor 21 with a vertical gap between them. The holding base 221 has, for example, a horizontal upper surface, on which the holding projections 222 are erected. For example, there are multiple holding projections 222, arranged along the periphery of the lower surface of the susceptor 21. The tips of the holding projections 222 abut against the susceptor 21 and support or hold the susceptor 21.

[0035] In the example shown in Figure 1, the substrate holder 2 further includes a rotation mechanism 23. The rotation mechanism 23 rotates the susceptor holder 22 around a rotation axis Q1. The rotation axis Q1 is an axis that passes through the center of the substrate W and is aligned vertically. The rotation mechanism 23 includes, for example, a shaft and a motor. The upper end of the shaft is connected to the lower surface of the holder base 221. The shaft extends along the rotation axis Q1 and is pivotally supported in the chamber 1 so as to be rotatable around the rotation axis Q1. The motor rotates the shaft around the rotation axis Q1. As a result, the susceptor holder 22, the susceptor 21, and the substrate W rotate together around the rotation axis Q1.

[0036] <Heater> The heater 7 heats the substrate W held by the substrate holding part 2 within the chamber 1. In the example in Figure 1, the heater 7 is positioned vertically below the susceptor 21 and faces the susceptor 21 in the vertical direction. In the example in Figure 1, the heater 7 is located between the susceptor 21 and the holding base 221, and is positioned radially inward from the holding projection 222. The heater 7 may be, for example, an electrically resistive heater including a heating wire, or an optical heater including a light source that emits heating light.

[0037] Here, the heater 7 is positioned so as not to rotate around the rotation axis Q1. In other words, the heater 7 is non-rotating. For example, the shaft of the rotating mechanism 23 is a hollow shaft, and the heater 7 is fixed to the chamber 1 via a fixing member 71 that penetrates the hollow portion.

[0038] <Suction part> The suction unit 6 draws gas from inside the chamber 1. In the example shown in Figure 1, the suction unit 6 includes a suction tube 61 and a suction mechanism 62. The upstream end of the suction tube 61 is connected to the exhaust port 1a of the chamber 1. In the example shown in Figure 1, the exhaust port 1a is formed vertically below the substrate W held by the substrate holding unit 2, and is formed, for example, on the side wall of the chamber 1. The suction mechanism 62 is, for example, a pump (more specifically, a vacuum pump) and is connected to the suction tube 61. The suction mechanism 62 is controlled by the control unit 9 and draws gas from inside the chamber 1 through the suction tube 61.

[0039] <First Gas Supply Department> The first gas supply unit 3 supplies the first gas to the plasma generation unit 4 (more specifically, the plasma chamber 4a). In the example shown in Figure 1, the first gas supply unit 3 includes a supply pipe 31, a valve 32, and a flow rate adjustment unit 33. The downstream end of the supply pipe 31 is connected to the plasma generation unit 4, and its upstream end is connected to the first gas supply source 34. The first gas supply source 34 supplies the first gas to the upstream end of the supply pipe 31.

[0040] Valve 32 is interposed in the supply pipe 31. Valve 32 is controlled by the control unit 9, and when valve 32 opens, the first gas is supplied from the first gas supply source 34 to the plasma generation unit 4 through the supply pipe 31. When valve 32 closes, the supply of the first gas stops.

[0041] The flow rate adjustment unit 33 is interposed in the supply pipe 31. The flow rate adjustment unit 33 is controlled by the control unit 9 and adjusts the flow rate of the first gas flowing through the supply pipe 31. The flow rate adjustment unit 33 is, for example, a mass flow controller.

[0042] <Plasma generation unit> The plasma generation unit 4 converts the first gas supplied from the first gas supply unit 3 into plasma. In the example shown in Figure 1, the plasma generation unit 4 is located on the ceiling of the chamber 1. The plasma generation unit 4 includes a conductive member 41 and a plasma power supply 43. The conductive member 41 is located inside the plasma chamber 4a, and the plasma power supply 43 is electrically connected to the conductive member 41. The plasma power supply 43 is controlled by the control unit 9, which applies a plasma voltage (e.g., a high-frequency voltage) to the conductive member 41. This creates an electric field (or magnetic field) around the conductive member 41 for generating plasma.

[0043] In the example shown in Figure 1, electrodes 411 and 412 are shown as conductive members 41. Electrodes 411 and 412 are positioned opposite each other with a gap between them in the horizontal direction. A plasma power supply 43 is electrically connected to electrodes 411 and 412 and applies a plasma generation voltage between electrodes 411 and 412. The plasma power supply 43 outputs, for example, a high-frequency voltage between electrodes 411 and 412. This creates a plasma generation electric field in the space between electrodes 411 and 412.

[0044] In the example shown in Figure 1, the downstream end of the supply pipe 31 of the first gas supply unit 3 is connected to the upper part of the plasma chamber 4a. The first gas supplied from the supply pipe 31 flows vertically downward between electrodes 411 and 412 within the plasma chamber 4a, so that a plasma field is applied to the first gas between electrodes 411 and 412. As a result, at least a portion of the first gas is converted into plasma, and active nitrogen species are generated. This excited gas containing the active nitrogen species flows out vertically downward from the plasma chamber 4a and flows toward the substrate W.

[0045] In the example shown in Figure 1, the plasma generation unit 4 generates plasma using a so-called capacitive coupling method, but it may also generate plasma using an inductive coupling method.

[0046] <Second Gas Supply Department> The second gas supply unit 5 supplies the second gas into the chamber 1. In the example shown in Figure 1, the second gas supply unit 5 includes a discharge nozzle 51, a supply pipe 52, a valve 53, and a flow rate adjustment unit 54. The discharge nozzle 51 is located inside the chamber 1. In the example shown in Figure 1, the discharge nozzle 51 is located vertically below the plasma generation unit 4 and vertically above the substrate holding unit 2, and discharges the second gas toward the substrate W held by the substrate holding unit 2. In the example shown in Figure 1, the discharge nozzle 51 has a long, horizontally extending shape and faces the substrate holding unit 2 in the vertical direction. In a plan view, the discharge nozzle 51 extends, for example, along the radial direction of the substrate W. In other words, the longitudinal direction of the discharge nozzle 51 is along the radial direction of the substrate W. In the example shown in Figure 1, the discharge nozzle 51 is positioned such that its tip faces the center of the substrate W in the vertical direction.

[0047] The discharge nozzle 51 has discharge ports 51a formed therein. In the example shown in Figure 1, multiple discharge ports 51a are arranged at intervals along the longitudinal direction of the discharge nozzle 51. The multiple discharge ports 51a are positioned facing the substrate W in the vertical direction, and the second gas is discharged from each discharge port 51a toward the upper surface of the substrate W.

[0048] Since the second gas flows toward the substrate holding section 2 on the opposite side of the plasma generation section 4, the electric field (or magnetic field) of the plasma generation section 4 is hardly applied to the second gas. In other words, the discharge nozzle 51 is positioned at a distance from the plasma generation section 4 such that the electric field (or magnetic field) of the plasma generation section 4 is substantially not applied to it. Therefore, the second gas is not substantially converted into plasma.

[0049] The discharge nozzle 51 is connected to the second gas supply source 55 via the supply pipe 52. In other words, the downstream end of the supply pipe 52 is connected to the upstream end of the discharge nozzle 51, and the upstream end of the supply pipe 52 is connected to the second gas supply source 55. The second gas supply source 55 supplies the second gas to the upstream end of the supply pipe 52.

[0050] The valve 53 is installed in the supply pipe 52 and is controlled by the control unit 9. When the valve 53 opens, the second gas is supplied from the second gas supply source 55 into the chamber 1 through the supply pipe 52 and the discharge nozzle 51. When the valve 53 closes, the supply of the second gas stops.

[0051] The flow rate adjustment unit 54 is installed in the supply pipe 52. The flow rate adjustment unit 54 is controlled by the control unit 9 and adjusts the flow rate of the second gas flowing through the supply pipe 52. The flow rate adjustment unit 54 is, for example, a mass flow controller.

[0052] <Control Unit> FIG. 2 is a block diagram schematically showing an example of the configuration of the control unit 9. The control unit 9 is an electronic circuit device and may have, for example, a data processing device 91 and a storage medium 92. The data processing device 91 may be an arithmetic processing device such as a CPU (Central Processor Unit). The storage medium 92 may have a non-temporary storage medium 921 (e.g., ROM (Read Only Memory) or hard disk) and a temporary storage medium 922 (e.g., RAM (Random Access Memory)). A program that defines the processes executed by the control unit 9 may be stored in the non-temporary storage medium 921. By the data processing device 91 executing this program, the control unit 9 can execute the processes defined in the program. Of course, some or all of the processes executed by the control unit 9 may be executed by a hardware circuit such as a logic circuit.

[0053] <Operation of the Group III Nitride Semiconductor Manufacturing Apparatus> Next, an example of the operation of the group III nitride semiconductor manufacturing apparatus 100 will be described. FIG. 3 is a flowchart showing an example of the operation of the group III nitride semiconductor manufacturing apparatus 100. In other words, FIG. 3 is a flowchart showing an example of the method for manufacturing a group III nitride semiconductor.

[0054] First, the substrate W is transported into the chamber 1 by a transport device (not shown) (step S1: loading process).

[0055] Next, the suction unit 6 sucks the gas from inside the chamber 1, reducing the pressure inside the chamber 1 (Step S2: Pressure reduction step). Specifically, the control unit 9 causes the suction mechanism 62 to perform a suction operation. As a result, the gas inside the chamber 1 is sucked into the suction mechanism 62 through the suction tube 61, and the pressure inside the chamber 1 decreases. The suction unit 6 adjusts the pressure inside the chamber 1 so that it becomes a predetermined process pressure suitable for the film deposition process. The predetermined process pressure is, for example, 100 Pa or more and 500 Pa or less. The suction unit 6 adjusts the pressure inside the chamber 1 until the film deposition process is completed.

[0056] Next, the heater 7 heats the substrate W (step S3: heating process). Specifically, the control unit 9 causes the heater 7 to perform the heating operation. The heater 7 adjusts the temperature of the substrate W so that it reaches a predetermined temperature suitable for the film deposition process. The predetermined temperature is, for example, 800°C or higher and 1000°C or lower. The heater 7 adjusts the temperature of the substrate W until the film deposition process is completed.

[0057] Next, the substrate holder 2 rotates the substrate W around the rotation axis Q1 (Step S4: Rotation process). Specifically, the control unit 9 rotates the susceptor holder 22 using the rotation mechanism 23. As a result, the susceptor holder 22, the susceptor 21, and the substrate W rotate together around the rotation axis Q1. The substrate holder 2 continues to rotate the substrate W until the film deposition process is completed.

[0058] Next, the first gas supply unit 3 supplies the first gas to the plasma generation unit 4, and the plasma generation unit 4 converts the first gas into plasma and supplies the generated excitation gas to the substrate W in the chamber 1 (Step S5: Excitation gas supply process). Specifically, first, the control unit 9 opens the valve 32. As a result, the first gas is supplied from the first gas supply source 34 to the plasma generation unit 4 through the supply pipe 31, passes through the plasma generation unit 4, and flows through the chamber 1 toward the substrate W. Here, the first gas is nitrogen gas. The first gas supply unit 3 supplies nitrogen gas until the film deposition process is completed.

[0059] The control unit 9 then causes the plasma power supply 43 to output a high-frequency voltage. This generates a plasma field between electrodes 411 and 412. As nitrogen gas passes through this field, at least a portion of it becomes plasma. This plasma formation of nitrogen gas generates active nitrogen species, and the excited gas containing these active species flows out of the plasma chamber 4a and flows through the chamber 1 towards the upper surface of the substrate W. The plasma generation unit 4 continues to plasmaize the nitrogen gas until the film deposition process is completed.

[0060] Next, the second gas supply unit 5 supplies the second gas into the chamber 1 (step S6: organometallic gas supply process). For example, when the plasma generated by the plasma generation unit 4 is stable, the second gas supply unit 5 starts supplying the second gas. Specifically, the control unit 9 opens the valve 53. As a result, the second gas is supplied from the second gas supply source 55 into the chamber 1 through the supply pipe 52 and discharge nozzle 51 and flows toward the upper surface of the substrate W. Here, the second gas is TMG, TEG, or TDMAG.

[0061] The second gas undergoes thermal decomposition on the upper surface of the substrate W, and the group III elements produced by this decomposition react with the active species of nitrogen, causing a group III nitride semiconductor film to crystallize on the upper surface of the substrate W. Any gas supplied to the upper surface of the substrate W that does not contribute to the formation of the group III nitride semiconductor film is discharged to the outside through the exhaust port 1a.

[0062] In this configuration, the substrate holder 2 rotates the substrate W around the rotation axis Q1, allowing for a more uniform formation of a group III nitride semiconductor film on the upper surface of the substrate W.

[0063] Once a group III nitride semiconductor film is formed on the upper surface of the substrate W with a predetermined thickness, the supply of the first and second gases, the output of a high-frequency voltage (i.e., plasma generation), the rotation of the substrate W, the heating of the substrate W, and the depressurization of the chamber 1 are terminated in order to substantially complete the film deposition process (step S7).

[0064] Next, the transport device removes the substrate W from the chamber 1 (Step S8: Removal Process). For example, the transport device removes the substrate W placed on the susceptor 21 from the chamber 1.

[0065] As described above, according to the manufacturing apparatus 100, the active species of nitrogen and the organometallic gas (second gas) containing a group III element react with each other on the upper surface of the substrate W to form a group III nitride semiconductor film on the upper surface of the substrate W. In other words, because energy other than heat (plasma) is utilized in the film formation process, a group III nitride semiconductor film can be formed on the upper surface of the substrate W even at a relatively low temperature of 1000°C or less.

[0066] Furthermore, in the manufacturing apparatus 100, the first gas targeted for plasma generation does not contain hydrogen. Therefore, the generation of methane-based compounds through the reaction between hydrogen and the second gas (organometallic gas) can be suppressed. Since methane is readily incorporated into group III nitride semiconductors, suppressing the generation of methane can suppress the incorporation of carbon into the group III nitride semiconductor film. In other words, a group III nitride semiconductor film with a low carbon content can be formed on the substrate W. Consequently, a group III nitride semiconductor film with high bulk mobility and excellent film quality can be formed on the substrate W.

[0067] Figures 4 and 5 are graphs showing an example of experimental results, illustrating the concentration distribution of carbon in a group III nitride semiconductor film obtained by secondary ion mass spectrometry. The horizontal axis represents the depth from the surface of the group III nitride semiconductor film, with zero representing the surface of the semiconductor film. The vertical axis represents the concentration of carbon in the group III nitride semiconductor film. Figure 4 shows the experimental results when only nitrogen gas is used as the first gas, which does not contain hydrogen, while Figure 5 shows the experimental results when a mixed gas of nitrogen gas and hydrogen gas is used instead of the first gas, as a comparative example. Specifically, Figure 5 shows the experimental results when a mixed gas of nitrogen gas and hydrogen gas is supplied to the plasma generation unit 4, and the plasma generation unit 4 generates plasma from the mixed gas. In Figure 4, the flow rate of nitrogen gas was 2000 sccm, while in Figure 5, the flow rates of nitrogen gas and hydrogen gas were 1900 sccm and 100 sccm, respectively.

[0068] As can be seen from the comparison of Figures 4 and 5, when a hydrogen-free first gas is supplied, the carbon concentration can be reduced by more than an order of magnitude compared to when a mixture of hydrogen and nitrogen gases is supplied. This significantly improves the bulk mobility of the group III nitride semiconductor film, and thus significantly improves the film quality.

[0069] <Supply amount of active nitrogen species and secondary gas (organometallic gas)> Next, we will consider the relationship between the flow rate of the second gas and the carbon concentration in the group III nitride semiconductor film. Figure 6 is a graph showing the relationship between the flow rate of the second gas and the carbon concentration. Here, the experimental results when only nitrogen gas is supplied as the first gas at a flow rate of 2000 sccm are shown as black circles. As a comparative example, the experimental results when nitrogen gas and hydrogen gas are supplied at flow rates of 1900 sccm and 100 sccm, respectively, are shown as black triangles, and the experimental results when nitrogen gas and hydrogen gas are supplied at flow rates of 1950 sccm and 50 sccm, respectively, are shown as black squares.

[0070] As can be seen from Figure 6, when a mixture of nitrogen and hydrogen gases is supplied instead of the first gas, the carbon concentration increases as the flow rate of the second gas (organometallic gas) increases. In contrast, when nitrogen gas without hydrogen is plasma-generated, the carbon concentration initially decreases as the flow rate of the second gas (organometallic gas) increases, and then increases again as the flow rate of the second gas increases further. In other words, the carbon concentration has a downward-convex waveform with respect to the flow rate of the second gas.

[0071] Such findings are disclosed for the first time in this application. According to these findings, when the first gas to be plasma-generated does not contain hydrogen, unlike when the gas to be plasma-generated contains hydrogen gas, there is a preferred range for the flow rate of the second gas. In other words, there is a more preferred flow rate range for the second gas that reduces the carbon content in the group III nitride semiconductor film.

[0072] By the way, since Group III nitride semiconductor films are formed by the reaction of nitrogen active species (radicals) with a second gas, it is necessary to consider not only the flow rate of the second gas but also the nitrogen radicals. Therefore, the density of nitrogen radicals (number of radicals / cm³) relative to the flow rate of the second gas (μmol / min) is calculated. 3 The ratio of ) is introduced. It is believed that there is a preferred range within this ratio for reducing the carbon content.

[0073] Figure 7 is a graph showing the relationship between the ratio of nitrogen radical density to the flow rate of the second gas and the carbon concentration in the group III nitride semiconductor film. The nitrogen radical density was measured at a position 1 cm above the top surface of the substrate W.

[0074] As shown in Figure 7, as the ratio increases, the carbon concentration initially decreases, and then increases again as the ratio increases further. In other words, the carbon concentration exhibits a downward-convex waveform with respect to this ratio. The reason why the carbon concentration shifts from decreasing to increasing is considered to be as follows: When the density of nitrogen radicals exceeds a certain critical value (approximately 4) relative to the flow rate of the second gas, crystal growth occurs partially in the three-dimensional direction on the upper surface of the substrate W, forming irregularities on the upper surface of the substrate W. This increases the surface area of ​​the semiconductor film, and the number of carbon adsorption sites on the surface increases. Therefore, it is considered that more carbon is adsorbed at the adsorption sites, and as a result, the carbon concentration in the semiconductor film increases.

[0075] As shown in Figure 7, the carbon concentration exhibits a downward-convex waveform with respect to this ratio, indicating that there is a preferred ratio range for reducing the carbon concentration. Here, the carbon concentration when a mixture of hydrogen and nitrogen gases is supplied is used as an indicator of the carbon concentration for determining the preferred ratio range. As can be seen from Figure 6, when a mixture of hydrogen and nitrogen gases is supplied, the carbon concentration in the group III nitride semiconductor film is 10 20 It will be greater than 10. 20 It is possible to adopt this.

[0076] Refer to Figure 7, and set the carbon concentration to 10 20 To achieve the following, it is desirable that the above ratio be 1 or more and 10 or less. In other words, it is desirable that the control unit 9 controls the flow rate of the first gas by the flow rate adjustment unit 33, the flow rate of the second gas by the flow rate adjustment unit 54, and the output voltage of the plasma power supply 43 so that the ratio is 1 or more and 10 or less.

[0077] Furthermore, in the plotted point cloud of Figure 7, the minimum and maximum values ​​of the ratio are approximately 2 and 6, respectively. Therefore, the control unit 9 should, more preferably, control the flow rate of the first gas by the flow rate adjustment unit 33, the flow rate of the second gas by the flow rate adjustment unit 54, and the output voltage of the plasma power supply 43 so that the ratio is 2 or greater and 6 or less.

[0078] <Temperature of the substrate> In the example described above, the heater 7 heats the substrate W so that its temperature is between 800°C and 1000°C. Within this temperature range, the amount of methane-based compounds readily incorporated into the group III nitride semiconductor is small, and the carbon content of the group III nitride semiconductor can be effectively reduced.

[0079] As described above, the manufacturing apparatus 100 and the manufacturing method for this group III nitride semiconductor have been described in detail. However, the above description is illustrative in all respects, and the manufacturing apparatus 100 and the manufacturing method are not limited thereto. It is understood that countless variations not illustrated can be envisioned without falling outside the scope of this disclosure. The components described in each of the above embodiments and variations can be combined or omitted as appropriate, as long as they do not contradict each other. [Explanation of Symbols]

[0080] 1 Chamber 2 Board holding part 3. First Gas Supply Department 4. Plasma generation unit 5. Second Gas Supply Department 6 Suction part 7 Heater S1 Loading process S2 Depressurization process (step) S3 Heating process (step) S5 First gas supply process (step) S6 Plasma process (step) S7 Second gas supply process (step) W board

Claims

1. A method for producing a Group III nitride semiconductor, comprising the steps of: a loading step of loading a substrate into a chamber; a depressurization step in which a suction unit reduces the pressure in the chamber; a heating step in which a heater provided in the chamber heats the substrate; an excitation gas supply step of supplying a first gas containing no hydrogen but containing nitrogen gas to a plasma generating unit, and supplying the excitation gas obtained by converting the first gas into plasma by the plasma generating unit to the substrate in the chamber; a metal-organic gas supply step of supplying a second gas, which is a metal-organic gas containing a group III element, to the substrate in the chamber; A method for manufacturing a Group III nitride semiconductor, comprising:

2. 2. The method for producing a Group III nitride semiconductor according to claim 1, a ratio of the density of nitrogen radicals to the flow rate of the second gas is 1 or more and 10 or less.

3. 3. A method for producing a Group III nitride semiconductor according to claim 1 or 2, comprising: In the heating step, the substrate is heated to a temperature of 800° C. or higher and 1000° C. or lower.

4. A method for producing a Group III nitride semiconductor according to any one of claims 1 to 3, comprising: The method for producing a Group III nitride semiconductor, wherein the second gas contains trimethylgallium, triethylgallium, or trisdimethylamidogallium.

5. 5. A method for producing a Group III nitride semiconductor according to claim 1, comprising: In the depressurization step, the pressure in the chamber is reduced to 100 Pa or more and 500 Pa or less.

6. An apparatus for manufacturing a Group III nitride semiconductor, comprising: a chamber; a substrate holder provided in the chamber and configured to hold a substrate; a suction portion that reduces the pressure in the chamber; a heater provided in the chamber for heating the substrate; a first gas supply unit that supplies a first gas that does not contain hydrogen but contains nitrogen gas; a plasma generating unit that generates an excited gas by plasmatizing the first gas supplied from the first gas supply unit and supplies the excited gas to the substrate in the chamber; a second gas supply unit that supplies a second gas, which is an organometallic gas containing a group III element, to the substrate in the chamber; A manufacturing apparatus for a Group III nitride semiconductor, comprising:

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