Method for manufacturing a group III nitride semiconductor

Abstract

To provide a technique capable of manufacturing a group III nitride semiconductor with a small carbon content and good surface morphology.SOLUTION: A method for manufacturing a group III nitride semiconductor includes carrying-in step S1, decompression step S2, heating step S3, first deposition step S5, and second deposition step S6. The carrying-in step S1 carries a substrate into a chamber. The decompression step S2 decreases a pressure in the chamber. The heating step S3 heats the substrate. The first deposition step S5 supplies an organic metal gas containing a group III element into the substrate in the chamber, plasma-excites a first gas containing a hydrogen gas and a nitrogen gas, and supplies the first gas to the substrate in the chamber. The second deposition step S6 supplies the organic metal gas containing the group III element into the substrate in the chamber, plasma-excites a second gas not containing hydrogen but containing a nitrogen gas, and supplies the second gas to the substrate in the chamber.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present application relates to a method for producing a Group III nitride semiconductor. [Background technology]

[0002] Metalorganic chemical vapor deposition methods using plasma have been proposed in the past (for example, Patent Document 1). In the manufacturing apparatus described in Patent Document 1, a mixed gas of nitrogen (N2) gas and hydrogen (H2) gas is converted into plasma in a chamber while a metalorganic gas of a group III element is supplied into the chamber. This allows a group III nitride semiconductor film to be formed on a substrate at a relatively low temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6516482 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 allows for the formation of a Group III nitride semiconductor film at low temperatures, but has the problem that a large amount of carbon is incorporated into the semiconductor film at lower temperatures. If the carbon content in the semiconductor film increases, the bulk mobility of the semiconductor film decreases, resulting in a deterioration in film quality.

[0005] In addition to bulk mobility, the properties for evaluating a Group III nitride semiconductor film include surface morphology, and good surface morphology is desirable.

[0006] Therefore, an object of the present invention is to provide a technique capable of producing a group III nitride semiconductor having a low carbon content and good surface morphology. [Means for solving the problem]

[0007] a first gas supply unit supplying an organometallic gas containing a Group III element to the substrate in the chamber, a second gas supply unit supplying a first gas containing hydrogen gas and nitrogen gas to a plasma generation unit, the plasma generation unit plasma-exciting the first gas and supplying it to the substrate in the chamber; and a second film formation unit supplying the organometallic gas containing a Group III element to the substrate in the chamber, the second gas supply unit supplying a second gas containing nitrogen gas but not hydrogen to the plasma generation unit, the plasma generation unit plasma-exciting the second gas and supplying it to the substrate in the chamber.

[0008] A second aspect of the method for producing a Group III nitride semiconductor is the method for producing a Group III nitride semiconductor according to the first aspect, further comprising a hydrogen gas removal step of exhausting the hydrogen gas from the chamber between the first film formation step and the second film formation step.

[0009] A third aspect of the method for producing a Group III nitride semiconductor is the method for producing a Group III nitride semiconductor according to the second aspect, wherein the hydrogen gas removal step is performed by adjusting the partial pressure of the hydrogen gas in the chamber to 1×10 -8 This is continued until the pressure drops below Pa.

[0010] A fourth aspect of the method for producing a Group III nitride semiconductor is the method for producing a Group III nitride semiconductor according to the first aspect, wherein the second film forming step is carried out successively to the first film forming step.

[0011] A fifth 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 fourth aspects, wherein, in the second film formation step, after a predetermined time has elapsed since a valve of the first gas supply unit for switching on and off the supply of the organometallic gas is closed, the supply of the second gas by the second gas supply unit and the operation of the plasma generation unit are stopped, thereby terminating the second film formation step.

[0012] A sixth aspect of the method for producing a Group III nitride semiconductor is the method for producing a Group III nitride semiconductor according to any one of the first to fifth aspects, wherein the substrate is heated to a temperature of 600°C or more and 1000°C or less in the heating step.

[0013] A seventh aspect of the method for producing a Group III nitride semiconductor is the method for producing a Group III nitride semiconductor according to any one of the first to sixth aspects, wherein the organometallic gas contains trimethylgallium, triethylgallium, or trisdimethylamidogallium. [Effects of the Invention]

[0014] According to the first to seventh aspects of the method for manufacturing a Group III nitride semiconductor, in the first film-forming step, the first gas to be turned into plasma contains hydrogen gas, which allows the Group III nitride semiconductor to be grown on a substrate made of a different material with high film thickness uniformity.

[0015] On the other hand, in the second film formation step, the second gas to be turned into plasma does not contain hydrogen, which allows a Group III nitride semiconductor with a low carbon content to be formed in the second film formation step.

[0016] Furthermore, in the second film formation step, a Group III nitride semiconductor of the same type is crystal-grown on the flat Group III nitride semiconductor formed in the first film formation step, so that a flat Group III nitride semiconductor can also be formed in the second film formation step.

[0017] As described above, a group III nitride semiconductor having a low carbon content and good surface morphology can be formed.

[0018] According to the second and third aspects of the method for manufacturing a Group III nitride semiconductor, the second film-forming step can be performed with a small amount of hydrogen gas in the chamber, thereby further reducing the carbon content in the Group III nitride semiconductor film formed in the second film-forming step.

[0019] According to the fourth aspect of the method for producing a Group III nitride semiconductor, a Group III nitride semiconductor can be formed with high throughput.

[0020] According to a fifth aspect of the method for producing a Group III nitride semiconductor, the pressure in the chamber is low, so that the metal-organic gas is supplied into the chamber even after the valve is closed. According to the fifth aspect, the plasma generating unit generates nitrogen radicals until the predetermined time has elapsed, so that the metal-organic gas reacts with the nitrogen radicals. Therefore, crystal growth of the Group III nitride semiconductor continues even during the predetermined time.

[0021] For comparison, we will explain the case where the operation of the plasma generating unit stops simultaneously with the closing of the valve. In this case, the organometallic gas reacts with the Group III nitride semiconductor without reacting with nitrogen. This may lead to deterioration of the surface condition of the Group III nitride semiconductor.

[0022] In contrast to this, in the fifth aspect, the metal-organic gas reacts with nitrogen radicals even for a predetermined period of time, so that deterioration of the surface state can be suppressed or avoided. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a manufacturing apparatus for a group III nitride semiconductor. [Figure 2] FIG. 2 is a block diagram showing an example of the internal configuration of a control unit. [Figure 3]2 is a flowchart showing an example of a method for manufacturing a Group III nitride semiconductor according to the first embodiment. [Figure 4] 4 is a graph showing an example of the distribution of carbon concentration in a semiconductor film according to the first embodiment. [Figure 5] FIG. 2 is a diagram showing an image of the surface of a group III nitride semiconductor film obtained by a scanning electron microscope. [Figure 6] FIG. 1 is a diagram showing an image of the surface of a group III nitride semiconductor film according to a comparative example, obtained by a scanning electron microscope. [Figure 7] 10 is a flowchart showing an example of a method for manufacturing a Group III nitride semiconductor according to a second embodiment. [Figure 8] 1 is a graph showing an example of a change in partial pressure of hydrogen gas over time. [Figure 9] 10 is a graph showing an example of the distribution of carbon concentration in a semiconductor film according to the second embodiment. [Figure 10] 10 is a flowchart showing an example of a method for manufacturing a Group III nitride semiconductor according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments will be described with reference to the accompanying drawings. Note that the components described in the embodiments are merely examples and are not intended to limit the scope of the present disclosure. In the drawings, the dimensions or number of each part may be exaggerated or simplified as necessary for ease of understanding.

[0025] Unless otherwise specified, expressions indicating relative or absolute positional relationships (e.g., "in one direction," "along one direction," "parallel," "orthogonal," "center," "concentric," "coaxial," etc.) not only indicate that positional relationship exactly, but also indicate a state where there is a relative displacement in terms of angle or distance within a range where tolerance or equivalent functionality is obtained. Expressions indicating an equal state (e.g., "identical," "equal," "homogeneous," etc.) not only indicate a state where there is strict quantitative equality, but also indicate a state where there is a difference where tolerance or equivalent functionality is obtained, unless otherwise specified. Expressions indicating shape (e.g., "square shape" or "cylindrical shape") not only indicate a strict geometric shape, but also indicate a shape with, for example, concaves and convexes or chamfers, within a range where equivalent effects are obtained. The expressions "comprise," "include," "have," "includes," "includes," or "have" of one component are not exclusive expressions that exclude the presence of other components. The expression "at least one of A, B, and C" includes A only, B only, C only, any two of A, B, and C, and all of A, B, and C.

[0026] First Embodiment <Outline of manufacturing equipment> 1 is a diagram schematically illustrating an example of the configuration of a group III nitride semiconductor manufacturing apparatus 100. This manufacturing apparatus 100 is a film formation apparatus that forms a group III nitride semiconductor film on a main surface of a substrate W by a metal-organic chemical vapor deposition method using plasma. This group III nitride semiconductor is used in, for example, a lateral transistor.

[0027] The substrate W is, for example, a substrate made of sapphire, silicon carbide, silicon, or the like. The substrate W has, for example, a disk shape. Because a group III nitride semiconductor film is crystal-grown on the main surface of the substrate W, the substrate W may also be called a growth substrate. Note that the material and shape of the substrate W are not limited to these and may be changed as appropriate.

[0028] The manufacturing apparatus 100 includes a chamber 1, a substrate holder 2, a first gas supply unit 3, a plasma generator 4, a second gas supply unit 5, a suction unit 6, a heater 7, and a controller 9. Below, each component will be outlined, and then a specific example will be described in detail.

[0029] The chamber 1 has a hollow box shape. The internal space of the chamber 1 corresponds to a processing space where a film formation process is performed on a substrate W. The chamber 1 may also be called a vacuum chamber.

[0030] The substrate holder 2 is provided in the chamber 1. The substrate holder 2 holds the substrate W in a horizontal position. Here, the horizontal position means that the thickness direction of the substrate W is aligned with the vertical direction.

[0031] The suction unit 6 sucks gas from the chamber 1 to reduce the pressure inside the chamber 1. The suction unit 6 adjusts the pressure inside the chamber 1 to within a predetermined reduced pressure range suitable for the film formation process.

[0032] 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 formation process.

[0033] The first gas supply unit 3 supplies a metal-organic gas containing a group III element to the substrate W in the chamber 1. The group III element is also called a group 13 element, and is, for example, gallium. In this case, the metal-organic gas may be TMGa (trimethylgallium), TEGa (triethylgallium), or TDMAGa (trisdimethylamidogallium).

[0034] The second gas supply unit 5 supplies a gas containing a group V element to the plasma generation unit 4. The group V element is also called a group 15 element, and in this case, it is nitrogen. The second gas supply unit 5 supplies a first gas containing nitrogen gas and hydrogen gas to the plasma generation unit 4, or supplies a second gas containing nitrogen gas but not hydrogen to the plasma generation unit 4. In other words, the second gas supply unit 5 selectively supplies hydrogen gas to the plasma generation unit 4. This gas switching will be described in detail later. Hereinafter, the gas supplied to the plasma generation unit 4 by the second gas supply unit 5 will also be referred to as a group V gas.

[0035] The plasma generating unit 4 excites the Group V gas into plasma. In other words, the plasma generating unit 4 converts the Group V gas into plasma. This generates active species such as highly reactive ions or neutral radicals. When the Group V gas contains hydrogen gas and nitrogen gas, hydrogen radicals and nitrogen radicals are generated as active species. When the Group V gas does not contain hydrogen but nitrogen gas, nitrogen radicals are generated without generating hydrogen radicals. In the example of FIG. 1, the plasma generating unit 4 has a plasma chamber 4a, in which the Group V gas is converted into plasma, generating the above-mentioned active species according to the type of Group V gas. The active species flow out of the plasma chamber 4a and flow through the chamber 1 toward the substrate W. As a result, the active species are supplied to the substrate W in the chamber 1.

[0036] The control unit 9 comprehensively controls the entire manufacturing apparatus 100. For example, the control unit 9 controls the substrate holder 2, the first gas supply unit 3, the plasma generator 4, the second gas supply unit 5, the suction unit 6, and the heater 7.

[0037] Next, a specific example of each configuration will be described in detail.

[0038] <Substrate holding part> The substrate holder 2 holds the substrate W in a horizontal position. In the example of FIG. 1, the substrate holder 2 includes a susceptor 21 and a susceptor holder 22. The susceptor 21 is a table on which the substrate W is placed, and has, for example, a flat plate shape. The susceptor 21 is provided in a horizontal position, 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 inside the chamber 1.

[0039] The susceptor holder 22 is provided in the chamber 1 and holds the susceptor 21. In the example of FIG. 1, the susceptor holder 22 includes a holder pedestal 221 and a holding protrusion 222. The holder pedestal 221 is provided vertically below the susceptor 21 and faces the susceptor 21 with a gap therebetween in the vertical direction. The holder pedestal 221 has, for example, a horizontal upper surface on which a holding protrusion 222 is provided upright. For example, a plurality of holding protrusions 222 are provided, and are arranged side by side along the periphery of the lower surface of the susceptor 21. The tips of the holding protrusions 222 abut against the susceptor 21 to support or hold the susceptor 21.

[0040] In the example of FIG. 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 in the vertical direction. The rotation mechanism 23 includes, for example, a shaft and a motor. The upper end of the shaft is coupled to the underside of the holder 221. The shaft extends along the rotation axis Q1 and is journaled in the chamber 1 so as to be rotatable about the rotation axis Q1. The motor rotates the shaft around the rotation axis Q1. This causes the susceptor holder 22, the susceptor 21, and the substrate W to rotate together around the rotation axis Q1.

[0041] <Heater> The heater 7 heats the substrate W held by the substrate holder 2 in the chamber 1. In the example of Fig. 1, the heater 7 is provided vertically below the susceptor 21 and faces the susceptor 21 in the vertical direction. In the example of Fig. 1, the heater 7 is provided between the susceptor 21 and the holder 221 and radially inward of the holding protrusion 222. The heater 7 may be, for example, an electric resistance heater including an electric heating wire, or an optical heater including a light source that irradiates light for heating.

[0042] Here, the heater 7 is provided 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 rotation mechanism 23 is a hollow shaft, and the heater 7 is fixed to the chamber 1 via a fixing member 71 that passes through the hollow portion.

[0043] <Suction part> The suction unit 6 suctions gas within the chamber 1. In the example of FIG. 1, the suction unit 6 includes a suction pipe 61 and a suction mechanism 62. The upstream end of the suction pipe 61 is connected to an exhaust port 1a of the chamber 1. In the example of FIG. 1, the exhaust port 1a is formed vertically below the substrate W held by the substrate holder 2, and is formed, for example, in 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 pipe 61. The suction mechanism 62 is controlled by the control unit 9, and suctions gas within the chamber 1 through the suction pipe 61.

[0044] <Second gas supply unit> The second gas supply unit 5 supplies a group V gas to the plasma generation unit 4 (more specifically, the plasma chamber 4a). As shown in FIG. 1, the second gas supply unit 5 includes a nitrogen gas supply unit 51 and a hydrogen gas supply unit 52. The nitrogen gas supply unit 51 supplies nitrogen gas to the plasma generation unit 4, and the hydrogen gas supply unit 52 supplies hydrogen gas to the plasma generation unit 4.

[0045] 1, nitrogen gas supply unit 51 includes a supply pipe 511, a valve 512, and a flow rate adjuster 513. In the example of FIG. 1, the downstream end of supply pipe 511 is connected to the upstream end of common pipe 50, and the upstream end of supply pipe 511 is connected to a nitrogen gas supply source 514. Nitrogen gas supply source 514 supplies nitrogen gas to the upstream end of supply pipe 511. The downstream end of common pipe 50 is connected to plasma generation unit 4.

[0046] Valve 512 is provided in supply pipe 511. Valve 512 is controlled by control unit 9, and when valve 512 is opened, nitrogen gas is supplied from nitrogen gas supply source 514 through supply pipe 511 and common pipe 50 to plasma generation unit 4. When valve 512 is closed, the supply of nitrogen gas is stopped.

[0047] Flow rate adjusting unit 513 is installed in supply pipe 511. Flow rate adjusting unit 513 is controlled by control unit 9, and adjusts the flow rate of nitrogen gas flowing through supply pipe 511. Flow rate adjusting unit 513 is, for example, a mass flow controller.

[0048] 1, hydrogen gas supply unit 52 includes a supply pipe 521, a valve 522, and a flow rate adjuster 523. In the example of Fig. 1, the downstream end of supply pipe 521 is connected to the upstream end of common pipe 50, and the upstream end of supply pipe 521 is connected to a hydrogen gas supply source 524. Hydrogen gas supply source 524 supplies hydrogen gas to the upstream end of supply pipe 521.

[0049] Valve 522 is interposed in supply pipe 521. Valve 522 is controlled by control unit 9, and when valve 522 is opened, hydrogen gas is supplied from hydrogen gas supply source 524 through supply pipe 521 and common pipe 50 to plasma generation unit 4. When valve 522 is closed, the supply of hydrogen gas stops.

[0050] Flow rate adjusting unit 523 is installed in supply pipe 521. Flow rate adjusting unit 523 is controlled by control unit 9, and adjusts the flow rate of hydrogen gas flowing through supply pipe 521. Flow rate adjusting unit 523 is, for example, a mass flow controller.

[0051] By opening valve 512 and valve 522, the second gas supply unit 5 can supply a first gas containing nitrogen gas and hydrogen gas as a Group V gas to the plasma generation unit 4. By opening valve 512 and closing valve 522, the second gas supply unit 5 can supply a second gas containing nitrogen gas but not hydrogen as a Group V gas to the plasma generation unit 4. In this way, the second gas supply unit 5 can switch between the first gas and the second gas as a Group V gas.

[0052] <Plasma generating unit> The plasma generating unit 4 generates plasma from the Group V gas supplied from the second gas supply unit 5. In the example of FIG. 1, the plasma generating unit 4 is provided on the ceiling of the chamber 1. The plasma generating unit 4 includes a conductive member 41 and a plasma power supply 43. The conductive member 41 is provided, for example, in 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, and applies a voltage for plasma (for example, a high-frequency voltage) to the conductive member 41. As a result, an electric field (or a magnetic field) for generating plasma is formed around the conductive member 41.

[0053] In the example of Fig. 1, electrodes 411 and 412 are shown as the conductive member 41. The electrodes 411 and 412 are arranged facing each other with a gap in the horizontal direction. The plasma power supply 43 is electrically connected to the electrodes 411 and 412, and applies a voltage for plasma between the electrodes 411 and 412. The plasma power supply 43 outputs, for example, a high-frequency voltage between the electrodes 411 and 412. As a result, an electric field for plasma is generated in the space between the electrodes 411 and 412.

[0054] 1, the downstream end of the common pipe 50 of the second gas supply unit 5 is connected to the upper part of the plasma chamber 4a. The group V gas supplied from the common pipe 50 flows vertically downward between the electrodes 411 and 412 in the plasma chamber 4a, and an electric field for plasma generation is applied to the group V gas between the electrodes 411 and 412. As a result, at least a portion of the group V gas is converted into plasma, and activated species are generated. The excited gas containing these activated species flows vertically downward through the plasma chamber 4a and flows toward the substrate W.

[0055] In the example of FIG. 1, the plasma generating unit 4 generates plasma by a so-called capacitive coupling method, but plasma may also be generated by an inductive coupling method.

[0056] <First gas supply unit> The first gas supply unit 3 supplies the metal-organic gas into the chamber 1. In the example of FIG. 1, the first gas supply unit 3 includes a discharge nozzle 31, a supply pipe 32, a valve 33, and a flow rate adjuster 34. The discharge nozzle 31 is provided in the chamber 1. In the example of FIG. 1, the discharge nozzle 31 is provided vertically above the substrate holding unit 2 and discharges the metal-organic gas toward the substrate W held by the substrate holding unit 2. In the example of FIG. 1, the discharge nozzle 31 has an elongated shape extending horizontally and faces the substrate holding unit 2 in the vertical direction. In a plan view, the discharge nozzle 31 extends, for example, along the radial direction of the substrate W. In other words, the longitudinal direction of the discharge nozzle 31 is aligned with the radial direction of the substrate W. In the example of FIG. 1, the discharge nozzle 31 is provided so that the tip of the discharge nozzle 31 faces the center of the substrate W in the vertical direction.

[0057] 1, the discharge nozzle 31 has a discharge port 31a formed therein. In the example of Fig. 1, the discharge ports 31a are arranged at intervals along the longitudinal direction of the discharge nozzle 31. The discharge ports 31a are provided at positions facing the substrate W in the vertical direction, and the metal-organic gas is discharged from each discharge port 31a toward the upper surface of the substrate W.

[0058] Since the metal-organic gas flows toward the substrate holder 2 on the opposite side from the plasma generator 4, the electric field (or magnetic field) of the plasma generator 4 is hardly applied to the metal-organic gas. In other words, the discharge nozzle 31 is provided at a distance from the plasma generator 4 such that the electric field (or magnetic field) of the plasma generator 4 is not substantially applied to the metal-organic gas. Therefore, the metal-organic gas is not substantially converted into plasma.

[0059] Discharge nozzle 31 is connected to metal-organic gas supply source 35 via supply pipe 32. That is, the downstream end of supply pipe 32 is connected to the upstream end of discharge nozzle 31, and the upstream end of supply pipe 32 is connected to metal-organic gas supply source 35. Metal-organic gas supply source 35 supplies metal-organic gas to the upstream end of supply pipe 32.

[0060] Valve 33 is provided in supply pipe 32 and is controlled by control unit 9. When valve 33 is opened, metal-organic gas is supplied from metal-organic gas supply source 35 through supply pipe 32 and discharge nozzle 31 into chamber 1. When valve 33 is closed, the supply of metal-organic gas is stopped.

[0061] Flow rate adjusting unit 34 is installed in supply pipe 32. Flow rate adjusting unit 34 is controlled by control unit 9, and adjusts the flow rate of the metal-organic gas flowing through supply pipe 32. Flow rate adjusting unit 34 is, for example, a mass flow controller.

[0062] <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)). The non-temporary storage medium 921 may store, for example, a program that defines the processing executed by the control unit 9. By the data processing device 91 executing this program, the control unit 9 can execute the processing defined in the program. Of course, part or all of the processing executed by the control unit 9 may be executed by a hardware circuit such as a logic circuit.

[0063] <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. That is, FIG. 3 is a flowchart showing an example of the method for manufacturing a group III nitride semiconductor.

[0064] First, the substrate W is transported into the chamber 1 by a transport device (not shown) (step S1: loading step).

[0065] Next, the suction unit 6 sucks the gas in the chamber 1 to reduce the pressure in the chamber 1 (step S2: decompression step). Specifically, the control unit 9 causes the suction mechanism 62 to perform a suction operation. As a result, the gas in the chamber 1 is sucked into the suction mechanism 62 through the suction pipe 61, and the pressure in the chamber 1 decreases. The suction unit 6 adjusts the pressure so that the pressure in the chamber 1 becomes a predetermined process pressure suitable for the film formation process. The predetermined process pressure is, for example, 100 Pa or more and 500 Pa or less. The suction unit 6 adjusts the pressure in the chamber 1 until the film formation process ends.

[0066] Next, the heater 7 heats the substrate W (step S3: heating step). Specifically, the control unit 9 controls the heater 7 to perform a heating operation. The heater 7 adjusts the temperature of the substrate W to a predetermined temperature suitable for the film formation process. The predetermined temperature is, for example, 600°C or higher and 1000°C or lower. The heater 7 adjusts the temperature of the substrate W until the film formation process is completed.

[0067] Next, the substrate holding unit 2 rotates the substrate W around the rotation axis Q1 (step S4: rotation step). Specifically, the control unit 9 controls the rotation mechanism 23 to rotate the susceptor holding unit 22. As a result, the susceptor holding unit 22, the susceptor 21, and the substrate W rotate together around the rotation axis Q1. The substrate holding unit 2 continues to rotate the substrate W until the film formation process is completed.

[0068] Next, the first gas supply unit 3 supplies an organometallic gas to the substrate W, the second gas supply unit 5 supplies a first gas containing nitrogen gas and hydrogen gas to the plasma generation unit 4, and the plasma generation unit 4 excites the first gas into plasma (step S5: first film formation step). An example of a more specific operation will be described below.

[0069] First, the control unit 9 opens the valves 512 and 522 of the second gas supply unit 5. As a result, the first gas containing nitrogen gas and hydrogen gas is supplied to the plasma generation unit 4 through the common pipe 50, passes through the plasma generation unit 4, and flows inside the chamber 1 toward the substrate W.

[0070] Then, the control unit 9 controls the plasma power supply 43 to output a high-frequency voltage. This generates an electric field for plasma between the electrode 411 and the electrode 412. As the first gas passes through this electric field, at least a portion of the first gas is converted into plasma. This conversion of the first gas into plasma generates nitrogen radicals and hydrogen radicals, and an excited gas containing these active species flows out of the plasma chamber 4a and flows within the chamber 1 toward the upper surface of the substrate W.

[0071] Next, control unit 9 opens valve 33 of first gas supply unit 3. For example, after plasma power supply 43 outputs voltage, when the plasma generated by plasma generation unit 4 stabilizes, control unit 9 opens valve 33. As a result, metal-organic gas is supplied from metal-organic gas supply source 35 through supply pipe 32 and discharge nozzle 31 into chamber 1 and flows toward the upper surface of substrate W. Here, the metal-organic gas is TMGa, TEGa, or TDMAGa.

[0072] The metal-organic gas is thermally decomposed on the upper surface of the substrate W, and the group III element (here, gallium) produced by the thermal decomposition reacts with nitrogen radicals to form a group III nitride semiconductor film (here, gallium nitride film) on the substrate W. In other words, crystal growth of the group III nitride semiconductor occurs.

[0073] In this first film formation step, a mixed gas of a group V gas and hydrogen gas is used, which allows the group III nitride semiconductor to be grown with high film thickness uniformity on the top surface of the substrate W made of a different material (i.e., the top surface of the base film), as will be described below.

[0074] That is, in the early stage of the first film-forming step, highly reducing hydrogen radicals react with the upper surface of the substrate W to form dangling bonds. More specifically, the highly reducing hydrogen radicals react with impurities such as carbon and oxygen on the upper surface of the substrate W and remove the impurities from the substrate W, thereby forming dangling bonds on the upper surface of the substrate W. Nitrogen radicals then bond with these dangling bonds, resulting in nitrogen atoms being uniformly arranged on the upper surface of the substrate W and reacting with the Group III elements produced by thermal decomposition, thereby causing crystal growth of a Group III nitride semiconductor on the upper surface of the substrate W. This allows crystal growth of a Group III nitride semiconductor with high film thickness uniformity on the upper surface of the substrate W. In other words, in the first film-forming step, a Group III nitride semiconductor film having a flat upper surface can be formed.

[0075] On the other hand, hydrogen radicals also react with organometallic gases to generate methane-based compounds, which are easily incorporated into Group III nitride semiconductors, increasing the carbon content in the semiconductor film.

[0076] That is, in the first film formation step, a Group III nitride semiconductor film with a high carbon content can be formed with a uniform film thickness.

[0077] In the first film formation step, when a Group III nitride semiconductor film is formed to a predetermined first thickness, the second gas supply unit 5 supplies a second gas containing nitrogen gas but not hydrogen to the plasma generation unit 4 (step S6: second film formation step). Specifically, the control unit 9 closes the valve 522 of the hydrogen gas supply unit 52. This causes the second gas supply unit 5 to stop supplying hydrogen gas. Since the plasma generation unit 4 plasma-excites the second gas containing nitrogen gas but not hydrogen, hydrogen radicals are not substantially generated, but nitrogen radicals are generated. These nitrogen radicals are supplied to the substrate W.

[0078] In the second film formation process, the first gas supply unit 3 also supplies the same organometallic gas containing a Group III element (here, gallium) as in the first film formation process. This organometallic gas is thermally decomposed on the upper surface of the substrate W, and the Group III element produced by the thermal decomposition reacts with the nitrogen radicals. This results in crystal growth of a Group III nitride semiconductor of the same type as the Group III nitride semiconductor in the first film formation process.

[0079] In the second film formation step, the amount of methane-based gases generated is reduced because no hydrogen gas is supplied to the plasma generating unit 4. Therefore, in the second film formation step, a Group III nitride semiconductor film with a lower carbon content is formed.

[0080] Furthermore, in the second film formation step, a Group III nitride semiconductor of the same type is crystal-grown on the flat Group III nitride semiconductor film formed in the first film formation step, so that the Group III nitride semiconductor film can be formed in the second film formation step with a more uniform thickness.

[0081] In the second film formation step, when a Group III nitride semiconductor film is formed to a predetermined second thickness, the control unit 9 terminates the second film formation step. Specifically, the control unit 9 closes the valve 33 of the first gas supply unit 3 and the valve 512 of the nitrogen gas supply unit 51, and stops the voltage output from the plasma power supply 43. The control unit 9 also stops the operations of the rotation mechanism 23, the heater 7, and the suction unit 6.

[0082] Next, the transfer device unloads the substrate W from the chamber 1 (step S7: unloading step). Specifically, the transfer device unloads the substrate W placed on the susceptor 21 from the chamber 1.

[0083] As described above, in the first film-forming step, the manufacturing apparatus 100 uses hydrogen gas and nitrogen gas as the group V gas to be turned into plasma. Therefore, as described above, a group III nitride semiconductor film can be formed with a flatter surface even on the top surface (top surface of the base film) of the substrate W made of a different material. However, the group III nitride semiconductor film formed in the first film-forming step has a higher carbon content.

[0084] On the other hand, in the second film formation process, the Group V gas to be converted into plasma does not contain hydrogen but nitrogen gas. Therefore, in the second film formation process, the amount of methane-based gases produced can be reduced. In other words, the amount of methane-based gases that are easily incorporated into the semiconductor film can be reduced, making it possible to form a Group III nitride semiconductor film with a low carbon content.

[0085] FIG. 4 is a graph showing an example of experimental results, illustrating the carbon concentration distribution 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 carbon concentration in the group III nitride semiconductor film. The experiment was conducted under the following processing conditions: In the first film formation process, the pressure in chamber 1 was 400 Pa, the flow rates of hydrogen gas and nitrogen gas were 100 sccm and 1900 sccm, respectively, the output power of plasma power supply 43 was 1000 W, and the flow rate of metalorganic gas was 6 μmol / min. In the second film formation process, the pressure in chamber 1 was 400 Pa, the flow rate of nitrogen gas was 2000 sccm, the output power of plasma power supply 43 was 1000 W, and the flow rate of metalorganic gas was 6 μmol / min.

[0086] As can be seen from Figure 4, the carbon content in the semiconductor film formed in the second film formation process is one order of magnitude smaller than the carbon content in the semiconductor film formed in the first film formation process. This shows that the second film formation process can form a Group III nitride semiconductor film with high bulk mobility. In this way, the carbon content can be reduced, thereby increasing bulk mobility and improving film quality.

[0087] Furthermore, in the second film formation process, a Group III nitride semiconductor film of the same type is formed on the flat Group III nitride semiconductor film formed in the first film formation process. Therefore, a Group III nitride semiconductor film having a flat upper surface can be formed in the second film formation process as well. In other words, the surface morphology can be improved.

[0088] FIG. 5 is a graph showing an example of experimental results, and shows an image of the surface (upper surface) of a group III nitride semiconductor film obtained by a scanning electron microscope. FIG. 6 shows an image of the surface of a group III nitride semiconductor film according to a comparative example. In the comparative example, a group III nitride semiconductor film was formed on the upper surface of the substrate W by the second film formation step without performing the first film formation step. That is, as the group V gas, a second gas containing nitrogen gas without hydrogen was employed. From the comparison between FIGS. 5 and 6, it can be seen that the surface morphology can be improved by performing the first film formation step.

[0089] As described above, according to the manufacturing apparatus 100 according to the first embodiment, a group III nitride semiconductor film having a low carbon content and a good surface morphology can be formed.

[0090] Also, in the above-described specific example, the second film formation step (step S6) is performed continuously with the first film formation step (step S5). That is, the manufacturing process can be shifted from the first film formation step to the second film formation step simply by stopping the supply of hydrogen gas. According to this, a group III nitride semiconductor film can be formed on the substrate W with high throughput.

[0091] <Flow rate of group V gas> In the second film formation step, the second gas supply unit 5 may supply the group V gas to the plasma generation unit 4 at the same flow rate as the flow rate of the group V gas in the first film formation step. In other words, the flow rate of nitrogen gas in the second film formation step may be set equal to the sum of the flow rates of hydrogen gas and nitrogen gas in the first film formation step.

[0092] For comparison, a case will be described in which the flow rate of nitrogen gas is set to the same in the first and second film formation processes. In this case, when transitioning from the first film formation process to the second film formation process, the flow rate of the Group V gas decreases by the amount of the flow rate of the hydrogen gas. Although the suction unit 6 adjusts the exhaust flow rate to absorb this decrease and adjusts the pressure in the chamber 1, the pressure in the chamber 1 may fluctuate transiently. In contrast, if the flow rate of the Group V gas is the same in the first and second film formation processes, pressure fluctuations in the chamber 1 can be suppressed.

[0093] Furthermore, when the suction mechanism 62 is connected to other equipment, fluctuations in the exhaust flow rate of gas from the chamber 1 may cause pressure fluctuations in the other equipment, but such pressure fluctuations can also be suppressed.

[0094] <Board temperature> The heater 7 may adjust the temperature of the substrate W to the same value in the first film formation process and the second film formation process. In other words, the heater 7 may control the temperature of the substrate W to be constant in the first film formation process and the second film formation process. Note that a constant temperature includes a case where the temperature fluctuates by a few degrees or less.

[0095] For comparison, consider the case where the heater 7 sets different temperatures for the first and second film formation processes. Because the temperature changes with low responsiveness, it takes a relatively long time for the temperature of the substrate W to change. In particular, if the heater 7 is separated from the susceptor 21 and heats the susceptor 21 and the substrate W by thermal radiation, a longer time is required. Therefore, changing the temperature of the substrate W during processing by the heater 7 results in a decrease in throughput.

[0096] In contrast, if the heater 7 adjusts the temperature of the substrate W to be constant in the first film formation step and the second film formation step, the aforementioned decrease in throughput can be avoided.

[0097] <Second embodiment> The second embodiment aims to further reduce the carbon content in the group III nitride semiconductor film formed in the second film formation step.

[0098] The manufacturing apparatus 100 according to the second embodiment has the same configuration as the manufacturing apparatus 100 according to the first embodiment. However, the operation of the manufacturing apparatus 100 according to the second embodiment is different from that of the first embodiment.

[0099] 7 is a flowchart showing an example of the operation of the manufacturing apparatus 100 according to the second embodiment. Steps S11 to S15 are similar to steps S1 to S5, respectively.

[0100] In the second embodiment, after step S15, the hydrogen gas in chamber 1 is evacuated (step S16: hydrogen gas removal process). Specifically, first gas supply unit 3 stops the supply of metal-organic gas, second gas supply unit 5 stops the supply of hydrogen gas, and plasma generation unit 4 stops operating. That is, control unit 9 closes valve 33 of first gas supply unit 3 and valve 522 of hydrogen gas supply unit 52, and causes plasma power supply 43 to stop outputting voltage. As a result, the hydrogen gas in chamber 1 is pushed out by the nitrogen gas supplied from second gas supply unit 5, and is discharged from chamber 1 by suction unit 6.

[0101] This hydrogen gas removal process reduces the amount of hydrogen gas in the chamber 1 over time. When the hydrogen gas in the chamber 1 has been sufficiently discharged, the control unit 9 terminates the hydrogen gas removal process. This hydrogen gas removal process is carried out, for example, when the partial pressure of hydrogen gas in the chamber 1 reaches 1×10 -8 As a more specific example, the control unit 9 may perform the hydrogen gas removal process from the start of the hydrogen gas removal process until the partial pressure of the hydrogen gas reaches 1×10 Pa or less. -8 When a predetermined exhaust time (for example, 5 minutes) has elapsed that is sufficient to make the pressure drop to 0 Pa or less, the hydrogen gas removal step is terminated.

[0102] Next, the control unit 9 starts the second film formation step (step S17). Specifically, the control unit 9 controls the plasma power supply 43 to output a voltage. Then, when the plasma generated by the plasma generation unit 4 becomes stable, the control unit 9 opens the valve 33 of the first gas supply unit 3. This essentially starts the second film formation step. In this second film formation step, a flat Group III nitride semiconductor film having a low carbon content can be formed, similar to the first embodiment.

[0103] In the second film formation step, when a group III nitride semiconductor film is formed to a predetermined second thickness, the control unit 9 ends the second film formation step. Next, the substrate W is unloaded from the chamber 1 (step S18).

[0104] As described above, in the second embodiment, the hydrogen gas removal step (step S16) is performed between the first film formation step (step S15) and the second film formation step (step S17). Therefore, the second film formation step can be started with the hydrogen gas in the chamber 1 sufficiently exhausted.

[0105] FIG. 8 is a graph showing an example of the change over time in the partial pressure of hydrogen gas in chamber 1. As shown in FIG. 8, the partial pressure of hydrogen gas is relatively high in the first film formation process, but decreases over time in the hydrogen gas removal process, and is very low in the second film formation process. In the example of FIG. 8, the partial pressure of hydrogen gas in the second film formation process is 1×10 -8 Pa, and is about two orders of magnitude lower than the partial pressure of hydrogen gas in the first film formation step.

[0106] In the second film formation step, the amount of hydrogen gas in chamber 1 is very small, so the reaction between the metalorganic gas and hydrogen does not occur much. That is, according to the second embodiment, the amount of methane-based compounds produced in the second film formation step can be further reduced. Therefore, the carbon content in the Group III nitride semiconductor film formed in the second film formation step can be further reduced.

[0107] FIG. 9 shows the carbon content distribution in the group-III nitride semiconductor film formed by the manufacturing apparatus 100 according to the second embodiment. As can be understood from the comparison between FIGS. 4 and 9, the carbon content in the semiconductor film formed in the second film formation step can be reduced more than in the first embodiment. That is, the bulk mobility and the film quality can be further improved.

[0108] <Flow rate of group-V gas> The flow rate of the group-V gas in the hydrogen gas removal step may be set the same as the flow rate of the group-V gas in the first film formation step. That is, the second gas supply unit 5 may supply nitrogen gas at the same flow rate as the flow rate of the group-V gas in the first film formation step in the hydrogen gas removal step. According to this, fluctuations in the pressure and the exhaust flow rate in the chamber 1 when shifting from the first film formation step to the hydrogen gas removal step can be suppressed.

[0109] Also, the flow rate of the group-V gas in the second film formation step may be set the same as the flow rate of the group-V gas in the hydrogen gas removal step. According to this, fluctuations in the pressure and the exhaust flow rate in the chamber 1 when shifting from the hydrogen gas removal step to the second film formation step can be suppressed.

[0110] <Third Embodiment> In the third embodiment, an example of the operation when the second film formation step is completed will be described. The manufacturing apparatus 100 according to the third embodiment has the same configuration as the manufacturing apparatus 100 according to the first and second embodiments.

[0111] FIG. 10 is a flowchart showing an example of the operation of the manufacturing apparatus 100 at the end of the second film formation step. The control unit 9 determines whether or not the end condition of the second film formation step is satisfied (step S21). For example, when a predetermined processing time has elapsed since the start of the second film formation step, the control unit 9 determines that the end condition is satisfied. When the end condition is not satisfied, the control unit 9 executes step S21 again.

[0112] ​When the termination condition is met, control unit 9 closes valve 33 of first gas supply unit 3. However, even when valve 33 is closed, the discharge of the metal-organic gas does not immediately stop, and the metal-organic gas continues to be discharged from outlet 31a of discharge nozzle 31. This is because the pressure inside chamber 1 is low. In other words, due to the pressure difference between the pressure inside discharge nozzle 31 and the pressure inside chamber 1, the metal-organic gas remaining in discharge nozzle 31 continues to be discharged from outlet 31a into chamber 1. Eventually, the discharge of the metal-organic gas will stop.

[0113] In the third embodiment, for a predetermined time after the closure of valve 33, the supply of nitrogen gas by second gas supply unit 5 and the operation of plasma generation unit 4 are continued. That is, control unit 9 keeps valve 512 of nitrogen gas supply unit 51 open and causes plasma power supply 43 to continue outputting voltage. The predetermined time here is, for example, a sufficient time required from the time valve 33 is closed until the discharge of metal-organic gas stops. Even during this predetermined time, the metal-organic gas discharged from discharge nozzle 31 is thermally decomposed on substrate W, and the Group III elements produced by the thermal decomposition react with nitrogen radicals, resulting in crystal growth of a Group III nitride semiconductor.

[0114] The control unit 9 determines whether a predetermined time has elapsed since the valve 33 was closed (step S23). If the predetermined time has not elapsed, the control unit 9 executes step S23 again. If the predetermined time has elapsed, the control unit 9 stops the voltage output from the plasma power supply 43 and closes the valve 512 of the nitrogen gas supply unit 51 (step S24). This stops the operation of the plasma generation unit 4 and the supply of nitrogen gas from the second gas supply unit 5, and the second film formation process is essentially completed.

[0115] As described above, in the third embodiment, the control unit 9 stops the supply of nitrogen gas and the operation of the plasma generation unit 4 after a predetermined time has elapsed since the valve 33 of the first gas supply unit 3 was closed, thereby terminating the second film formation step. Therefore, crystal growth of the group III nitride semiconductor film continues even during the predetermined time.

[0116] For comparison, a case will be described in which valves 33 and 512 are closed and the operation of plasma generation unit 4 is stopped simultaneously. While the metal-organic gas continues to be discharged from discharge nozzle 31 even after valve 33 is closed, the nitrogen radicals in chamber 1 quickly disappear when the operation of plasma generation unit 4 is stopped. Therefore, the metal-organic gas thermally decomposes on substrate W and reacts with substrate W without reacting with nitrogen radicals. In other words, the group III element can react with the group III nitride semiconductor film without reacting with nitrogen radicals. This may deteriorate the surface condition of the group III nitride semiconductor film.

[0117] In contrast, in the third embodiment, nitrogen radicals are supplied to the substrate W for a predetermined time after the valve 33 is closed. Therefore, even during this predetermined time, the metal-organic gas reacts with the nitrogen radicals to form a group III nitride semiconductor on the substrate W. Therefore, deterioration of the surface condition of the semiconductor film can be suppressed or avoided.

[0118] Although the third embodiment has described the termination operation of the second film formation step, this termination operation may also be applied to the first film formation step in the second embodiment. Specifically, the plasma generating unit 4 may stop operating after a predetermined time has elapsed since the valve 33 of the first gas supply unit 3 was closed. This makes it possible to suppress or avoid deterioration of the surface condition of the Group III nitride semiconductor film formed in the first film formation step.

[0119] As described above, the Group III nitride semiconductor manufacturing apparatus 100 and the manufacturing method thereof have been described in detail. However, the above description is merely an example 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 departing from the scope of this disclosure. The configurations described in the above embodiments and variations can be combined or omitted as appropriate, as long as they are not mutually inconsistent. [Explanation of symbols]

[0120] 1 chamber 3. First gas supply section 33 Valve 4. Plasma generating unit 5 Second gas supply section 6 Suction part 7 Heater S1, S11 Carry-in process (step) S2, S12 Decompression process (step) S3, S13 Heating process (step) S5, S15 First film formation process (step) S6, S17 Second film formation process (step) S16 Hydrogen gas removal process (step) W substrate

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; a first film formation step in which a first gas supply unit supplies an organometallic gas containing a Group III element to the substrate in the chamber, a second gas supply unit supplies a first gas containing hydrogen gas and nitrogen gas to a plasma generation unit, the plasma generation unit plasma-excites the first gas and supplies it to the substrate in the chamber, and a first layer made of a Group III nitride semiconductor is formed; a second film formation step in which the first gas supply unit supplies an organometallic gas containing the Group III element to the substrate in the chamber, the second gas supply unit supplies a second gas containing nitrogen gas but not containing hydrogen to the plasma generation unit, the plasma generation unit plasma-excites the second gas and supplies it to the substrate in the chamber, and a second layer made of a Group III nitride semiconductor having the same composition as the first layer is formed on the first layer; a hydrogen gas removal step of exhausting the hydrogen gas from the chamber between the first film formation step and the second film formation step; 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, In the hydrogen gas removal step, the partial pressure of the hydrogen gas in the chamber is 1×10 －８ The method for producing a Group III nitride semiconductor is carried out until the pressure drops to 0 Pa or less.

3. 3. A method for producing a Group III nitride semiconductor according to claim 1 or 2, comprising: and a valve of the first gas supply unit for switching on and off the supply of the metal-organic gas is closed, and then, after a predetermined time has elapsed since the valve of the first gas supply unit was closed, the supply of the second gas by the second gas supply unit and the operation of the plasma generation unit are stopped, thereby terminating the second film formation step.

4. A method for producing a Group III nitride semiconductor according to any one of claims 1 to 3, comprising: In the heating step, the substrate is heated to a temperature of 600° C. or higher and 1000° C. or lower.

5. 5. A method for producing a Group III nitride semiconductor according to claim 1, comprising: The method for producing a Group III nitride semiconductor, wherein the organometallic gas contains trimethylgallium, triethylgallium, or trisdimethylamidogallium.

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