Reactive sputtering method

Abstract

Provided is a technology with which it is possible to form a high-quality film on a main surface of a substrate without significantly reducing the productivity. In this reactive sputtering method, a thin film that contains a first element and a second element is formed on a main surface of a substrate by alternately repeating a sputtering step for forming a first element film on the main surface and a reaction step for reacting the first element film and the second element after the sputtering step. The reactive sputtering method includes: (a) a first reactive sputtering step (S11) that includes a first sputtering step (S21) and a first reaction step (S22); and (b) a second reactive sputtering step (S12) that is executed after the first reactive sputtering step (S11) and includes a second sputtering step (S23) and a second reaction step (S24). The reaction time for reacting the first element film with the second element is longer in the first reaction step (S22) than in the second reaction step (S24).

Description

Reactive Sputtering Method

[0001] The subject matter disclosed herein relates to reactive sputtering methods.

[0002] Sputtering apparatuses for forming thin films on the surfaces of substrates have been proposed (for example, see Patent Document 1). In Patent Document 1, the sputtering apparatus forms a Group III nitride semiconductor film on the surfaces of the substrates. The sputtering apparatus includes a chamber, a rotating jig, a target, a first plasma generating means, and a second plasma generating means.

[0003] A target chamber and a nitrogen chamber are provided within the chamber. The target chambers and the nitrogen chambers are provided alternately around a predetermined revolution axis. The rotating jig revolves the substrate W within the chamber around the predetermined revolution axis. This moves the substrate W from the target chamber to the nitrogen chamber and vice versa.

[0004] The target is provided in the target chamber. The first plasma generating means generates a first plasma of argon in the target chamber. The argon ions collide with the target, and the collisions cause raw material particles (e.g., atoms) to be ejected from the target. The raw material particles are supplied to the substrate and deposited on the substrate.

[0005] The second plasma generating means is provided in the nitrogen chamber and generates a second plasma of nitrogen in the nitrogen chamber, whereby the highly reactive nitrogen reacts with the raw material particles of the substrate.

[0006] The target chamber and the nitrogen chamber are connected in the circumferential direction, and the substrate passes through the target chamber and the nitrogen chamber as the substrate revolves around the rotating jig. As the substrate passes through the target chamber, raw material particles of a Group III element are deposited on the substrate, and as the substrate passes through the nitrogen chamber, nitrogen reacts with the raw material particles on the substrate. This allows a Group III nitride semiconductor to be formed on the substrate.

[0007] Japanese Patent Application Laid-Open No. 2022-083129

[0008] However, if the thickness of the raw material particles deposited on the main surface of the substrate in the target chamber is too large, nitrogen can react with the raw material particles located on the surface side of the film but has difficulty reacting with the particles deeper in the film. This can result in insufficient nitriding of the film in the thickness direction. In this case, a low-quality nitride film with poor crystallinity is formed on the main surface of the substrate.

[0009] One possible solution is to make the film sufficiently nitrided by making the film thickness of the raw material particles formed in the target chamber sufficiently small, but this method takes time to form a high-quality nitride film with good crystallinity, which significantly reduces productivity.

[0010] An object of the present invention is to provide a technique that can form a high-quality film on the main surface of a substrate without significantly reducing productivity.

[0011] In order to solve the above problem, a first aspect is a reactive sputtering method for forming a thin film containing the first element and the second element on a main surface of the substrate by alternately repeating a sputtering step of moving a substrate so as to pass through a sputtering space in which a target containing a first element is provided, and depositing atoms of the first element from the target on the main surface of the substrate to form a first element film on the main surface of the substrate, and a reaction step of moving the substrate after the sputtering step so as to pass through a plasma space in which a reactive gas containing a second element is plasmatized, and causing the first element film on the main surface of the substrate to react with the second element, the method comprising: a) a first reactive sputtering step including a first sputtering step and a first reaction step; and b) a second reactive sputtering step that is performed after the first reactive sputtering step and includes a second sputtering step and a second reaction step, and the reaction time for reacting the first element film with the second element is longer in the first reaction step than in the second reaction step.

[0012] A second aspect is the reactive sputtering method of the first aspect, wherein the deposition rate of the first element is lower in the first sputtering step than in the second sputtering step.

[0013] A third aspect is the reactive sputtering method of the first or second aspect, wherein the moving speed of the substrate moving through the plasma space is slower in the first reaction step than in the second reaction step.

[0014] A fourth aspect is a reactive sputtering method according to any one of the first to third aspects, wherein when the thickness of the first element film formed on the substrate in the first sputtering step is defined as a first thickness, the reaction time in the first reaction step is defined as a first reaction time, the thickness of the first element film formed on the substrate in the second sputtering step is defined as a second thickness, and the reaction time in the second reaction step is defined as a second reaction time, the ratio of the first reaction time to the first film thickness is greater than the ratio of the second reaction time to the second film thickness.

[0015] A fifth aspect is a reactive sputtering method according to any one of the first to fourth aspects, wherein the control conditions for controlling the plasma density of the second element in the plasma space are the same in the first reaction step and the second reaction step.

[0016] A sixth aspect is a reactive sputtering method according to any one of the first to fifth aspects, wherein the first reactive sputtering step is a step of depositing one or more molecules of a compound of the first element and the second element in a direction perpendicular to the main surface of the substrate.

[0017] A seventh aspect is the reactive sputtering method of the sixth aspect, wherein the first reactive sputtering step is a step of depositing four or more molecules of a compound of the first element and the second element in a direction perpendicular to the main surface of the substrate.

[0018] An eighth aspect is a reactive sputtering method for forming a thin film containing the first element and the second element on a main surface of the substrate by alternately repeating a sputtering step of moving the substrate so as to pass through a sputtering space in which a target containing a first element is provided, and depositing atoms of the first element from the target on the main surface of the substrate to form a first element film on the main surface of the substrate, and a reaction step of moving the substrate after the sputtering step so as to pass through a plasma space in which a reactive gas containing a second element is plasmatized, and reacting the first element film on the main surface of the substrate with the second element, the method comprising: a) a first reactive sputtering step including a first sputtering step and a first reaction step; and b) a second reactive sputtering step that is performed after the first reactive sputtering step and includes a second sputtering step and a second reaction step, wherein the deposition rate of the first element is lower in the first sputtering step than in the second sputtering step.

[0019] A ninth aspect is a reactive sputtering method for forming a thin film containing the first element and the second element on a main surface of the substrate by alternately repeating a sputtering step of moving the substrate so as to pass through a sputtering space in which a target containing a first element is provided, and depositing atoms of the first element from the target on the main surface of the substrate to form a first element film on the main surface of the substrate, and a reaction step of moving the substrate after the sputtering step so as to pass through a plasma space in which a reactive gas containing a second element is plasmatized, and causing the first element film on the main surface of the substrate to react with the second element, the method comprising: a) a first reactive sputtering step including a first sputtering step and a first reaction step; and b) a second reactive sputtering step that is performed after the first reactive sputtering step and includes a second sputtering step and a second reaction step, wherein the plasma density of the reactive gas in the plasma space is higher in the first reaction step than in the second reaction step.

[0020] According to the reactive sputtering methods of the first to seventh aspects, by making the reaction time of the first reaction step longer than the reaction time of the second reaction step, a high-quality film with good crystallinity can be formed in the first reactive sputtering step. Furthermore, by forming a high-quality film in the first reactive sputtering step, even if the reaction time of the second reaction step is shortened, the film can be formed while maintaining high quality. Therefore, a high-quality film can be formed on the main surface of the substrate without significantly reducing production efficiency.

[0021] According to the reactive sputtering method of the second aspect, the deposition rate of the first element is lower in the first sputtering step than in the second sputtering step, so that the thickness of the first element film formed by the first sputtering step can be reduced. In the first reactive sputtering step, the second element can be sufficiently reacted with the first element film, so that a high-quality film can be formed in the first reactive sputtering step.

[0022] According to the reactive sputtering method of the third aspect, the reaction time can be extended by slowing down the moving speed of the plasma space.

[0023] According to the reactive sputtering method of the fourth aspect, a high-quality film can be formed on the main surface of the substrate in the first reactive sputtering step.

[0024] According to the reactive sputtering method of the fifth aspect, the control conditions for the plasma density in the first reactive sputtering step and the second reactive sputtering step are kept constant, thereby making it possible to improve the reproducibility of the process.

[0025] According to the reactive sputtering method of the eighth aspect, the deposition rate of the first element is lower in the first sputtering step than in the second sputtering step, so the thickness of the first element film formed in the first sputtering step can be reduced. In the first reaction step, the second element can be sufficiently reacted with the first element film, so a high-quality film can be formed in the first reactive sputtering step. Furthermore, by forming a high-quality film in the first reactive sputtering step, a film can be formed while maintaining high quality even if the reaction time in the second reaction step is shortened. Therefore, a high-quality film can be formed on the main surface of the substrate without significantly reducing production efficiency.

[0026] According to the reactive sputtering method of the ninth aspect, the plasma density of the reactive gas is higher in the first reaction step than in the second reaction step, so that the reaction rate between the first element film and the second element can be increased in the first reaction step. This allows a high-quality film to be formed in the first reactive sputtering step. This allows a high-quality film to be formed on the main surface of the substrate without significantly reducing production efficiency.

[0027] FIG. 1 is a side view schematically showing an example of the configuration of a sputtering apparatus according to an embodiment. FIG. 2 is a plan view schematically showing an example of the configuration of the sputtering apparatus shown in FIG. 1. FIG. 3 is a perspective view schematically showing an example of the configuration of a substrate holding unit and a heater shown in FIG. 1. FIG. 4 is a block diagram showing the hardware configuration of a control unit shown in FIG. 1. FIG. 5 is a flowchart showing an example of the operation of the sputtering apparatus. FIG. 6 is a flowchart showing processes performed on one substrate W by the operation of the sputtering apparatus. FIG. 7 is a diagram showing the relationship between the film thickness (horizontal axis) of an aluminum nitride film (AlN film) formed under first film formation conditions with a long reaction time and the full width at half maximum FWHM (vertical axis) of the X-ray rocking curve (XRC) measured for the finally obtained AlN film.

[0028] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the components described in the embodiment are merely examples and are not intended to limit the scope of the present invention. In the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary to facilitate understanding.

[0029] 1. Embodiment Fig. 1 is a side view schematically showing an example of the configuration of a sputtering apparatus 100 according to an embodiment. Fig. 2 is a plan view schematically showing an example of the configuration of the sputtering apparatus 100 shown in Fig. 1. Fig. 1 is a view schematically showing a cross section of the sputtering apparatus 100 taken along a plane along the bent line A-A shown in Fig. 2.

[0030] The sputtering apparatus 100 is a film formation apparatus that performs a film formation process on a substrate W by reactive sputtering. Specifically, the sputtering apparatus 100 forms a thin film containing a first element and a second element on the main surface Wa of the substrate W. The first element is, for example, a metal element, more specifically, gallium (Ga) or aluminum (Al). The second element is, for example, oxygen (O) or nitrogen (N). When the first element is aluminum and the second element is nitrogen, the sputtering apparatus 100 forms an aluminum nitride film on the main surface Wa of the substrate W. The substrate W is, for example, a sapphire, silicon (Si), or silicon carbide (SiC) substrate. The substrate W has, for example, a circular disk shape. Note that the material and shape of the substrate W are not limited to these and can be changed as appropriate.

[0031] The sputtering apparatus 100 includes a chamber 1, a sputtering unit 2, a plasma unit 3, a substrate holder 4, a suction mechanism 5, and a control unit 6. 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 is a vacuum chamber, and is a container that can be sealed so that a vacuum state can be maintained. The chamber 1 is provided with a loading / unloading mechanism (not shown). The loading / unloading mechanism can switch the internal state of the chamber 1 between a communicating state connected to the outside space and a sealed state isolated from the outside space. In the communicating state, a substrate transport unit (not shown) loads an unprocessed substrate W into the chamber 1. In the sealed state, the sputtering apparatus 100 performs a film formation process on the substrate W. Next, the loading / unloading mechanism connects the chamber 1 to the outside, and in this communicating state, the substrate transport unit unloads the processed substrate W from the chamber 1.

[0032] The suction mechanism 5 has a suction port 5a. The suction port 5a opens into the processing space. The suction mechanism 5 is controlled by a control unit 6. The suction mechanism 5 reduces the pressure inside the chamber 1 by sucking gas through the suction port 5a, and adjusts the pressure to within a predetermined reduced pressure range. The suction mechanism 5 is, for example, a vacuum pump, and a more specific example is a turbomolecular pump.

[0033] The processing space within the chamber 1 includes a sputtering space 1a and a plasma space 1b. The sputtering space 1a and the plasma space 1b are aligned along the circumferential direction about a predetermined revolution axis Q1. The revolution axis Q1 is an axis extending along the vertical direction. A physical structure (e.g., a partition plate) may be provided within the chamber 1 to separate the sputtering space 1a and the plasma space 1b.

[0034] A target 21 of the sputtering unit 2 is placed in the sputtering space 1a. In the sputtering space 1a, sputtering is performed on the target 21. The target 21 contains a first element (e.g., gallium or aluminum). In other words, the material of the target 21 contains the first element. As will be described later, a reactive gas is supplied to the plasma space 1b by the plasma unit 3, and the reactive gas is converted into plasma by the plasma unit 3. The reactive gas contains a second element (e.g., nitrogen).

[0035] The substrate holder 4 is disposed in the chamber 1. The substrate holder 4 holds the substrate W and revolves the substrate W around the revolution axis Q1, thereby moving the substrate W alternately between the sputtering space 1 a and the plasma space 1 b.

[0036] 3 is a perspective view schematically illustrating an exemplary configuration of the substrate holder 4 and heater 11 shown in FIG. 1. In the example shown in FIG. 3, the substrate holder 4 holds multiple (six in this example) substrates W arranged in a circumferential direction about the revolution axis Q1. Note that the substrate holder 4 does not necessarily have to hold multiple substrates W. The substrate holder 4 may be configured to hold only a single substrate W. The substrate holder 4 holds the substrate W in a horizontal position. Here, the horizontal position refers to a position in which the thickness direction of the substrate W (the normal direction to the main surface Wa) is aligned vertically. When multiple substrates W are held by the substrate holder 4, the main surface Wa (the lower surface in FIG. 3) of each substrate W is exposed within the chamber 1 (see FIG. 1).

[0037] The substrate holder 4 revolves the substrate W around the revolution axis Q1, causing each substrate W to alternately pass through the sputtering space 1a and the plasma space 1b. In other words, the substrate holder 4 moves the substrate W so that the substrate W alternately passes through the sputtering space 1a and the plasma space 1b. When the substrate W passes through the sputtering space 1a, particles of the first element from the target 21 are deposited on the main surface Wa of the substrate W. When the substrate W passes through the plasma space 1b, activated species (including at least one of ions and radicals) of the second element generated by the plasma generation of the reactive gas react with atoms of the first element on the main surface Wa of the substrate W. As a result, a thin film containing a compound of the first and second elements is formed on the main surface Wa of the substrate W.

[0038] Hereinafter, the direction in which the revolution axis Q1 extends may be referred to as the "axial direction," the direction of rotation around the revolution axis Q1 may be referred to as the "circumferential direction," and the direction in which a straight line perpendicular to the axial direction extends may be referred to as the "radial direction."

[0039] <Substrate Holding Unit> The substrate holding unit 4 has a holder 41 and a rotation drive unit 42. The holder 41 holds multiple substrates W lined up in the circumferential direction. The holder 41 has, for example, a circular disk shape centered on the revolution axis Q1. Multiple through holes 41a may be formed in the holder 41. The multiple through holes 41a are formed, for example, at equal intervals along the circumferential direction and penetrate the holder 41 in the axial direction. Each through hole 41a has a stepped shape that narrows vertically downward. One substrate W is placed in each through hole 41a. The holder 41 supports the periphery of each substrate W at the stepped portion of each through hole 41a.

[0040] The rotation drive unit 42 is controlled by the control unit 6. The rotation drive unit 42 rotates the holder 41 about the revolution axis Q1. As a result, the multiple substrates W held by the holder 41 revolve around the revolution axis Q1. The rotation drive unit 42 includes, for example, a motor and a shaft. The motor is connected to the holder 41 via the shaft. The upper end of the shaft is connected to the underside of the holder 41 and extends along the revolution axis Q1. The motor rotates the shaft about the revolution axis Q1, thereby rotating the holder 41 about the revolution axis Q1.

[0041] The heater 11 heats the plurality of substrates W held by the substrate holder 4. The heater 11 adjusts the temperature of the substrates W to within a temperature range suitable for film formation processing. The heater 11 is controlled by the controller 6. The heater 11 is located vertically above and spaced apart from the substrate holder 4 within the chamber 1. The heater 11 has, for example, a circular ring shape centered on the revolution axis Q1. The heater 11 may be, for example, an electric resistance heater including an electric heating wire, or an optical heater including a light source that irradiates the substrates W with heating light (e.g., infrared light).

[0042] The sputtering unit 2 includes a target 21, a sputtering gas supply unit 23, and a first plasma generation unit 25. Note that the sputtering gas supply unit 23 and the first plasma generation unit 25 are not shown in FIG.

[0043] <Target> The target 21 is provided in the sputtering space 1a and faces the substrate holding part 4 in the axial direction. More specifically, the target 21 is provided at a position facing a part of the circumferential direction of the movement path R1 of the substrate W in the axial direction. In the example shown in Fig. 1, the target 21 is located vertically below the substrate holding part 4.

[0044] The target 21 is formed, for example, in a plate shape. In the example shown in FIG. 2 , the target 21 has a rectangular shape in a plan view. Plan view refers to viewing with the line of sight along the axial direction. The target 21 has a first main surface 21 a and a second main surface 21 b. The second main surface 21 b is the surface opposite to the first main surface 21 a. The target 21 is held by a target holder 22. The target holder 22 holds the target 21 in a horizontal position with the first main surface 21 a of the target 21 facing the substrate holder 4. The horizontal position here refers to a position in which the thickness direction of the target 21 (the normal direction to the first main surface 21 a) is aligned vertically. When the target 21 is held by the target holder 22, the first main surface 21 a of the target 21 is exposed within the chamber 1.

[0045] The target 21 is made of a material containing the first element in the thin film to be formed on the main surface Wa of the substrate W. The first element is, for example, gallium or aluminum. As a more specific example, the target 21 is a metal target made of aluminum.

[0046] <Sputtering Gas Supply Unit> The sputtering gas supply unit 23 supplies sputtering gas to the sputtering space 1a. The sputtering gas is an inert gas, such as a rare gas. The rare gas may be, for example, argon gas or xenon gas. In the example shown in FIG. 1 , the sputtering gas supply unit 23 includes multiple (two in this example) gas supply pipes 231, a valve 232, a flow rate adjuster 233, and a common pipe 234. The upstream end of each gas supply pipe 231 is connected to the downstream end of a single common pipe 234. The upstream end of the common pipe 234 is connected to a sputtering gas supply source 235. The sputtering gas supply source 235 supplies sputtering gas to the upstream end of the gas supply pipe 234. The gas supply pipe 231 includes a first gas supply port 23a that opens into the sputtering space 1a. The sputtering gas flows through the common pipe 234 and each gas supply pipe 231 and flows out from the first gas supply port 23a into the sputtering space 1a. A part of this sputtering gas flows into the space between the movement path R1 of the substrate W and the target 21.

[0047] The valve 232 is provided in the common pipe 234 and opens and closes the common pipe 234. The flow rate adjustment unit 233 is provided in the common pipe 234 and adjusts the flow rate of the sputtering gas flowing through the common pipe 234. The flow rate adjustment unit 233 is, for example, a mass flow controller. The valve 232 and the flow rate adjustment unit 233 are controlled by the control unit 6.

[0048] <First Plasma Generating Unit> The first plasma generating unit 25 generates plasma from the sputtering gas in the sputtering space 1a, and causes ions (e.g., argon ions) in the plasma to collide with the first main surface 21a of the target 21. This collision causes sputtered particles (e.g., aluminum particles) to fly out from the first main surface 21a of the target 21. The sputtered particles move vertically upward toward the substrate holding unit 4.

[0049] In the example shown in FIG. 1 , the first plasma generation unit 25 includes a first power supply 251. The first power supply 251 is controlled by the control unit 6 and supplies DC or AC (high-frequency) power for sputtering to the target 21. Here, since the target 21 is a conductive metal target, a DC power supply can be used as the first power supply 251. The first power supply 251 outputs a DC voltage between the target 21 and the chamber 1, for example. More specifically, the first power supply 251 includes, for example, a switching power supply circuit (not shown) and outputs a DC voltage so that a negative potential is applied to the target 21. As shown in FIG. 1 , the chamber 1 may be grounded. Furthermore, the substrate holder 4 may be electrically connected to the chamber 1.

[0050] When the first power supply 251 supplies DC power to the target 21, an electric field for plasma is generated around the target 21. When this electric field acts on the sputtering gas, the sputtering gas is ionized and converted into plasma. Ions in the plasma (e.g., argon ions) collide with the first main surface 21a of the target 21, causing sputtering of the target 21. That is, particles of the first element fly out from the target 21 and move toward the movement path R1 of the substrate W. When the particles of the first element reach the main surface Wa of the substrate W passing through the sputtering space 1a, they are deposited on the main surface Wa. As a result, a film of the first element (hereinafter referred to as a "first element film") is formed on the main surface Wa of the substrate W.

[0051] 1, the sputtering unit 2 has a chimney 27. The chimney 27 is provided in the sputtering space 1a. The chimney 27 has a hollow box shape and surrounds the periphery of the target 21. An opening 27a is formed in an upper plate portion 271 of the chimney 27, facing the target 21 in the axial direction. The opening 27a penetrates the upper plate portion 271 in the axial direction. Gallium particles that fly out from the first main surface 21a of the target 21 pass through the opening 27a and move toward the substrate holding unit 4.

[0052] <Plasma Unit> The plasma unit 3 has a second gas inlet 31a that opens into the plasma space 1b. The plasma unit 3 supplies a reactive gas from the second gas inlet 31a to the plasma space 1b. The plasma unit 3 also converts the reactive gas in the plasma space 1b into plasma. Specifically, the plasma unit 3 includes a reactive gas supply unit 31 and a second plasma generation unit 33.

[0053] <Reactive Gas Supply Unit> In the example shown in FIG. 1 , the reactive gas supply unit 31 includes a plurality of (two in this example) gas supply pipes 311, valves 312, flow rate adjusters 313, and a common pipe 314. The upstream end of each gas supply pipe 311 is connected to the downstream end of one common pipe 314. The upstream end of the common pipe 314 is connected to a reactive gas supply source 315. The reactive gas supply source 315 supplies reactive gas to the upstream end of the common pipe 314. Each gas supply pipe 311 includes a second gas supply port 31a. In the example shown in FIG. 1 , the opening direction of the second gas supply port 31a in the gas supply pipe 311 is parallel to the axial direction and toward the substrate holder 4. In the example shown in FIG. 1 , the downstream end of each gas supply pipe 311 corresponds to the second gas supply port 31a. In the example shown in FIG. 1 , the two second gas supply ports 31a are provided at a radial interval.

[0054] As the reactive gas, a gas containing a second element in the thin film to be formed on the main surface Wa of the substrate W can be used. The second element is, for example, nitrogen. As a specific example, the reactive gas is nitrogen (N ２ ) gas and ammonia (NH ３ For example, when the first element is aluminum and the second element is nitrogen, an aluminum nitride film is formed on the main surface Wa of the substrate W. The second element includes at least one of oxygen (O ２ For example, when the first element is aluminum and the second element is oxygen, an aluminum oxide film is formed on the main surface Wa of the substrate W.

[0055] The valve 312 is provided in the common pipe 314 and opens and closes the gas supply pipe 311. The flow rate adjuster 313 is provided in the common pipe 314 and adjusts the flow rate of the reactive gas flowing through the common pipe 314. The flow rate adjuster 313 is, for example, a mass flow controller. The valve 312 and the flow rate adjuster 313 are controlled by the control unit 6.

[0056] The following description will be focused on the case where aluminum is used as the first element and nitrogen is used as the second element, in which an aluminum target is used as the target 21 and nitrogen gas is used as the reactive gas.

[0057] The second plasma generator 33 generates plasma from the nitrogen gas supplied into the chamber 1 through the second gas inlet 31 a. Highly reactive nitrogen active species generated by the plasma generation move toward the substrate holder 4. When the nitrogen active species reach the main surface Wa of the substrate W moving through the plasma space 1 b, they nitride the aluminum film on the main surface Wa.

[0058] 1, the second plasma generation unit 33 has an inductive coupling antenna 331 and a second power supply 332. The inductive coupling antenna 331 is located in the plasma space 1b vertically below the movement path R1 of the substrate W. The inductive coupling antenna 331 has a substantially U-shaped conductive member 3311 that is convex vertically upward.

[0059] The conductive member 3311 is provided in the chamber 1 with both ends positioned vertically downward. The conductive member 3311 is attached to the bottom of the chamber 1. In the example shown in Fig. 2, the conductive member 3311 is provided with both ends aligned in the circumferential direction. Both ends of the conductive member 3311, for example, penetrate the bottom of the chamber 1, and the both ends are electrically connected to the second power source 332. The conductive member 3311 functions as an electrode (antenna) for generating plasma.

[0060] 1 and 2, multiple (two in this example) inductive coupling antennas 331 are provided, and each inductive coupling antenna 331 is provided near a corresponding second air supply port 31a. In the example shown in Fig. 1 and 2, the inductive coupling antenna 331 is provided so as to face the second air supply port 31a of the air supply pipe 311 in the axial direction. In other words, the second air supply port 31a is located between both ends of the inductive coupling antenna 331 (the conductive member 3311) in a plan view.

[0061] The second power supply 332 supplies high-frequency power to the inductively coupled antenna 331. The second power supply 332 has, for example, an inverter circuit and a matching circuit, and is controlled by the control unit 6. When the second power supply 332 applies a high-frequency voltage to both ends of the inductively coupled antenna 331, a high-frequency induction magnetic field for generating plasma is generated around the inductively coupled antenna 331. This high-frequency induction magnetic field acts on the reactive gas, ionizing the reactive gas and turning it into plasma. Such inductively coupled plasma has a spatial electron density of 3×10 １０ pieces / cm ３ This is a high density plasma.

[0062] <Controller> Fig. 4 is a block diagram showing the hardware configuration of the controller 6 shown in Fig. 1. The controller 6 is an electronic circuit device that controls the operation of each part in the sputtering apparatus 100. The controller 6 includes a processor 61 and a memory 62. The memory 62 is electrically connected to the processor 61 via a bus wiring (not shown).

[0063] The processor 61 includes, for example, a CPU (Central Processor Unit). The memory 62 includes a ROM (Read Only Memory), which is a read-only memory that stores a basic program, and a RAM (Random Access Memory), which is a readable and writable memory that stores various information. The memory 62 may also include storage such as a hard disk drive (HDD) or a solid-state drive (SSD).

[0064] The memory 62 stores a computer program P and setting data. The computer program P is provided to the control unit 6 via a recording medium or a network line such as the Internet. The setting data is recipe data that indicates processing conditions to be performed by the sputtering apparatus 100. The processor 61 executes processing in accordance with the computer program P and setting data, and the control unit 6 controls the sputtering apparatus 100. This allows the film formation process on the substrate W to proceed.

[0065] The control unit 6 is electrically connected to a display 661 and an input device 662. The display 661 is a device that displays various information, such as a liquid crystal display device. The input device 662 is a device that allows a user to input commands to the control unit 6, such as a mouse and keyboard. Note that the display 661 may function as the input device 662 by providing a touch panel on the display 661.

[0066] The control unit 6 is electrically connected to the heater 11, the valve 232, the flow rate adjustment unit 233, the first power source 251, the valve 312, the flow rate adjustment unit 313, the second power source 332, the rotation drive unit 42, and the suction mechanism 5, and controls the operation of these components.

[0067] <Example of Operation of Sputtering Apparatus> Fig. 5 is a flowchart showing an example of the operation of the sputtering apparatus 100. Fig. 6 is a flowchart showing the steps performed on one substrate W by the operation of the sputtering apparatus 100. By operating the sputtering apparatus 100 according to the flowchart of Fig. 5, a sputtering step and a reaction step are alternately performed on each substrate W, as shown in Fig. 6.

[0068] First, a substrate transport unit (not shown) transports a plurality of unprocessed substrates W into the chamber 1 (step S1). As a result, the substrate holder 4 holds the plurality of substrates W. Next, the suction mechanism 5 starts to suction gas from the chamber 1 (step S2), and the heater 11 starts to heat the substrates W (step S3). The suction mechanism 5 adjusts the pressure in the chamber 1 to within a reduced pressure range suitable for the film formation process. The heater 11 also adjusts the temperature of the substrates W to within a temperature range suitable for the film formation process.

[0069] Next, the sputtering gas supply unit 23 supplies sputtering gas, and the reactive gas supply unit 31 begins supplying reactive gas. The first plasma generator 25 and the second plasma generator 33 then convert the gas into plasma (step S4). Specifically, the control unit 6 opens the valves 232 and 312. This causes the sputtering gas and reactive gas to be supplied in parallel into the chamber 1. The control unit 6 also controls the first power supply 251 and the second power supply 332 to output voltages. Furthermore, the rotation drive unit 42 rotates the holder 41 around the revolution axis Q1 (step S5). This causes the multiple substrates W to revolve around the revolution axis Q1.

[0070] In the film formation process (step S5), the sputtering gas supply unit 23 constantly supplies a sputtering gas, the reactive gas supply unit 31 constantly supplies a reactive gas, the first power supply 251 and the second power supply 332 constantly output a voltage, and the substrate holder 4 constantly revolves the substrate W.

[0071] As the substrate W revolves around the revolution axis Q1, the substrate W passes alternately through the sputtering space 1 a and the plasma space 1 b. That is, a sputtering step in which the substrate holder 4 moves the substrate W so that it passes through the sputtering space 1 a and a reaction step in which the substrate holder 4 moves the substrate W so that it passes through the plasma space 1 b are performed alternately.

[0072] In the sputtering process, the sputtering apparatus 100 deposits particles of a first element (e.g., aluminum) from the target 21 on the main surface Wa of the substrate W. Specifically, by sputtering the target 21, particles of the first element ejected from the target 21 move toward the substrate W, and adhere to the main surface Wa of the substrate W while the particles of the first element are moving. As a result, a first element film is formed on the main surface Wa of the substrate W.

[0073] In the reaction step, the sputtering apparatus 100 reacts the second element with the first element film formed by the sputtering step on the main surface Wa of the substrate W. Specifically, activated species of the second element in the plasma in the plasma space 1b react with the first element film on the main surface Wa of the substrate W, causing the second element to penetrate into the first element film. Here, since the first element is aluminum and the second element is nitrogen, the aluminum film on the main surface Wa of the substrate W is nitrided.

[0074] In this embodiment, while step S5 is being performed, the processes shown in Fig. 6 are performed on the substrate W. Specifically, a first reactive sputtering process S11 and a second reactive sputtering process S12 are performed. The second reactive sputtering process S12 is a process performed after the first reactive sputtering process S11. The first reactive sputtering process S11 includes a first sputtering process S21 and a first reaction process S22 performed after the first sputtering process S21. The second reactive sputtering process S12 includes a second sputtering process S23 and a second reaction process S24 performed after the second sputtering process S23.

[0075] After the second reactive sputtering step S12, the control unit 6 determines whether to terminate the process (determination step S13). For example, the control unit 6 determines whether the number of times the second reactive sputtering step S12 has been performed is less than a predetermined number of times. If the number of times is less than the predetermined number of times, the control unit 6 performs the second reactive sputtering step S12 again. That is, the sputtering apparatus 100 continues the film formation process on the substrate W. In this way, by repeating the second reactive sputtering step S12 after the first reactive sputtering step S11, a first element film containing the second element is sequentially stacked on the main surface Wa of the substrate W, and the film thickness increases. The predetermined number of times is set to a value such that the film thickness reaches a target value, and can be set to, for example, several tens of times.

[0076] In this embodiment, the film formation conditions are changed between the first reactive sputtering step S11 and the second reactive sputtering step S12. Examples of the film formation conditions include the rotation speed of the substrate W by the rotation drive unit 42 (hereinafter simply referred to as the "rotation speed"), the power input to the target 21 by the first power supply 251 of the first plasma generation unit 25 (hereinafter referred to as the "target input power"), and the power input to the inductively coupled antenna 331 by the second power supply 332 of the second plasma generation unit 33 (hereinafter referred to as the "plasma-generation input power").

[0077] Table 1 shows an example of the film formation conditions in the first reactive sputtering step S11 and the second reactive sputtering step S12. Table 1 shows the film formation conditions when the target 21 is an aluminum target and the reactive gas is nitrogen gas.

[0078]

[0079] The first film formation conditions shown in Table 1 are an example of conditions employed in the first reactive sputtering step S11. The second film formation conditions shown in Table 1 are an example of conditions employed in the second reactive sputtering step S12.

[0080] The slower the rotation speed, the slower the moving speed of the substrate W passing through the sputtering space 1 a and the plasma space 1 b. The slower the moving speed of the substrate W, the longer the time the substrate W passes through the sputtering space 1 a and the plasma space 1 b. In particular, the longer the time passing through the plasma space 1 b, the longer the reaction time (hereinafter simply referred to as "reaction time") during which the first element film reacts with the second element becomes.

[0081] In this embodiment, as shown in Table 1, the rotation speed is set to a low speed (20 rpm) in the first reactive sputtering step S11 and a high speed (60 rpm) in the second reactive sputtering step S12. In other words, the rotation speed of the substrate W is lower in the first reactive sputtering step S11 than in the second reactive sputtering step S12. Therefore, the movement speed of the substrate W passing through the plasma space 1b is lower in the first reaction step S22 than in the second reaction step S24, and the reaction time is therefore longer.

[0082] Furthermore, the smaller the target input power, the smaller the sputtering amount of the target 21 in the sputtering process, and as a result, the lower the deposition rate (film formation rate) of the first element on the substrate W. In this embodiment, as shown in Table 1, the target input power is set to low power (1 kW) in the first reactive sputtering process S11 and high power (3 kW) in the second reactive sputtering process S12. In other words, the target input power is lower in the first reactive sputtering process S11 than in the second reactive sputtering process S12. Therefore, the deposition rate is lower in the first sputtering process S21 than in the second sputtering process S23. Specifically, under the conditions shown in Table 1, the deposition rate in the first reactive sputtering process S21 is 5 nm / min (= 0.25 nm × 20 rpm), and the deposition rate in the second sputtering process S23 is 15 nm / min (= 0.25 nm × 60 rpm).

[0083] Furthermore, the higher the plasma generation input power, the higher the plasma density of the second element in the plasma space 1b, and therefore the higher the reaction rate (hereinafter simply referred to as "reaction rate") between the first element film and the second element in the reaction step. In this embodiment, as shown in Table 1, the plasma generation input power is the same in the first reactive sputtering step S11 and the second reactive sputtering step S12. Therefore, the plasma density in the plasma space 1b in the first reaction step S22 and the second reaction step S24 is approximately the same. Therefore, the reaction rate in the first reaction step S22 and the reaction rate in the second reaction step S24 are approximately the same.

[0084] Under the film formation conditions shown in Table 1, the target input power in the first sputtering step S21 is 1 / 3 of the target input power in the first reaction step S22, resulting in a deposition rate (film formation rate) that is 1 / 3 times higher. However, the rotation speed in the first sputtering step S21 is 1 / 3 of the rotation speed in the second sputtering step S23. Therefore, the film thickness of the first element film (aluminum film) formed in the first sputtering step S21 is approximately equal to the film thickness of the first element film formed in the second sputtering step S23. Meanwhile, the rotation speed in the first reaction step S22 is 1 / 3 of the rotation speed in the second reaction step S24. Therefore, the reaction time in the first reaction step S22 is three times the reaction time in the second reaction step S24.

[0085] In this way, by extending the reaction time in the first reaction step S22, the incorporation of the second element into the first element film can be increased, and a high-quality film with high crystallinity can be formed on the main surface Wa of the substrate W. In particular, in heteroepitaxial growth, which forms a film on a heterogeneous substrate, extending the reaction time allows the compound of the first element and the second element to reach its most stable structure. Therefore, a high-quality film with high crystallinity can be formed.

[0086] Furthermore, since the second reactive sputtering step S12 forms a film of the same type on the film formed in the first reactive sputtering step S11, the crystals are likely to reach the most stable structure in the second reactive sputtering step S12. Therefore, even if the reaction time in the second reaction step S24 is shortened, a high-quality film can be formed. Therefore, by shortening the reaction time in the repeatedly performed second reaction step S24, the processing time can be shortened. This allows a high-quality film to be formed without significantly reducing production efficiency.

[0087] Furthermore, if the thickness of the first element film formed in the first sputtering step S21 is too large, it becomes difficult to sufficiently react the first element film with the second element in the thickness direction, even if the reaction time in the first reaction step S22 is extended. Therefore, it is desirable for the film thickness to be small enough to allow the reaction to proceed sufficiently. In this embodiment, the deposition rate in the first sputtering step S21 is reduced by reducing the target input power. This allows the film thickness of the first element film to be reduced, thereby allowing the first element film to sufficiently react with the second element in the thickness direction in the first reaction step S22. Therefore, a high-quality film with high crystallinity can be formed on the main surface Wa of the substrate W. Furthermore, by increasing the deposition rate in the second sputtering step S23, a high-quality film can be formed without significantly reducing production efficiency.

[0088] The first reactive sputtering step S11 is a step of depositing preferably one or more molecules, more preferably four or more molecules, of a compound of a first element and a second element in a direction perpendicular to the main surface Wa of the substrate W. For example, in the case of an aluminum nitride film, if one molecule of aluminum nitride is 0.25 nm, it is preferable to form a compound film of 0.25 nm or more, more preferably 1 nm or more, in the first reactive sputtering step S11.

[0089] The thickness of the first element film formed on the main surface Wa of the substrate W in the first sputtering step S21 is defined as the first film thickness, the reaction time in the first reaction step S22 is defined as the first reaction time, the thickness of the first element film formed on the main surface Wa of the substrate W in the second sputtering step S23 is defined as the second film thickness, and the reaction time in the second reaction step is defined as the second reaction time. In this case, it is desirable to set the film formation conditions so that the ratio of the first reaction time to the first film thickness is greater than the ratio of the second reaction time to the second film thickness.

[0090] For example, under the film formation conditions shown in Table 1, as described above, the first film thickness of the first element film formed in the first sputtering step S21 is approximately equal to the second film thickness of the first element film formed in the second sputtering step S23. The first reaction time in the first reaction step S22 is three times the second reaction time in the second reaction step S24. Therefore, the ratio of the first reaction time to the first film thickness is three times the ratio of the second reaction time to the second film thickness. By making the ratio of the first reaction time to the first film thickness greater than the ratio of the second reaction time to the second film thickness, a high-quality film can be formed while avoiding a significant decrease in productivity.

[0091] In addition, under the film formation conditions shown in Table 1, the plasma generation input power is the same in the first reactive sputtering step S11 and the second reactive sputtering step S12. In other words, the control conditions for controlling the plasma density of the second element in the plasma space 1b are the same in the first reaction step S22 and the second reaction step S24. By using the same control conditions in this way, the reproducibility of the process can be improved.

[0092] It is not necessary to use the same plasma generation input power between the first reactive sputtering process S11 and the second reactive sputtering process S12. For example, the plasma generation input power may be higher in the first reactive sputtering process S11 than in the second reactive sputtering process S12. In this case, the reaction rate in the first reactive sputtering process S11 is higher than that in the second reactive sputtering process S12. In this way, by increasing the reaction rate in the first reactive sputtering process S11, it becomes easier to incorporate the second element into the first element film, and a high-quality film with good crystallinity can be formed in a short time. This allows a high-quality film to be formed without reducing productivity. Furthermore, by reducing the plasma generation input power in the second reactive sputtering process S12, power consumption can be reduced.

[0093] FIG. 7 shows the relationship between the film thickness (horizontal axis) of an aluminum nitride film (AlN film) formed under the first film-forming conditions with a long reaction time and the full width at half maximum (FWHM) (vertical axis) of the X-ray rocking curve (XRC) measured for the finally obtained AlN film. The full width at half maximum (FWHM) of the XRC is an index of the crystallinity of the film, with a smaller full width at half maximum indicating better crystallinity. The full width at half maximum (FWHM) shown in FIG. 7 represents the measurement results when an AlN film was formed on a sapphire substrate. More specifically, an initial AlN film 91 with a predetermined thickness (0 nm to 30 nm) was formed under the first film-forming conditions shown in Table 1, and then an AlN film 92 was formed under the second film-forming conditions shown in Table 2 so that the final film thickness would be 30 nm.

[0094] As shown in FIG. 7 , when the initial AlN film 91 had a thickness of 0 nm (i.e., when only the 30-nm AlN film 92 was used), the half-width was 0.82°, resulting in poor crystallinity. This is thought to be due to insufficient plasma nitridation in the initial stage caused by film formation under only the second film formation conditions with a short reaction time, resulting in poor film quality at the substrate interface and, consequently, poor overall film quality. On the other hand, when the initial AlN film 91 had a thickness of 30 nm (i.e., when the AlN film 92 was not used), the half-width was 0.13°, resulting in good crystallinity. This indicates that film quality can be improved by forming the AlN film 91 under the first film formation conditions with a long reaction time. Furthermore, as shown in FIG. 7 , by forming the initial AlN film 91 with a thickness of 0.25 nm or more, more preferably 1 nm or more, a high-quality AlN film with good crystallinity could be formed. 0.25 nm corresponds to the length of one molecule of an AlN compound, and 1 nm corresponds to the length of four molecules of an AlN compound.

[0095] 2. Modifications Although the embodiments have been described above, the present invention is not limited to the above and various modifications are possible.

[0096] 7, the first reactive sputtering step S11 is performed only once, but the first reactive sputtering step S11 may be repeated two or more times. In this case, a step in which the control unit 6 determines whether or not to terminate the first reactive sputtering step S11 may be provided between the first reactive sputtering step S11 and the second reactive sputtering step S12.

[0097] In the sputtering apparatus 100, the sputtering spaces 1a and the plasma spaces 1b are alternately arranged around the revolution axis Q1. The substrate W is caused to revolve about the revolution axis Q1, thereby passing alternately through the sputtering spaces 1a and the plasma spaces 1b. However, the configuration of the sputtering apparatus 100 is not limited to this. For example, the sputtering spaces 1a and the plasma spaces 1b may be arranged in a straight line. In this case, the substrate W may be moved back and forth between the sputtering spaces 1a and the plasma spaces 1b.

[0098] Although the present invention has been described in detail, the above description is merely illustrative in all respects and does not limit the present invention. It is understood that countless variations not illustrated can be envisioned without departing from the scope of the present invention. The configurations described in the above embodiments and variations can be combined or omitted as appropriate as long as they are not mutually inconsistent.

[0099] 1a: Sputtering space 1b: Plasma space 3: Plasma section 6: Control section 21: Target S11: First reactive sputtering step S12: Second reactive sputtering step S21: First sputtering step S22: First reaction step S23: Second sputtering step S24: Second reaction step W: Substrate Wa: Main surface

Claims

1. A reactive sputtering method for forming a thin film containing the first element and the second element on a main surface of the substrate by alternately repeating a sputtering step of moving a substrate through a sputtering space in which a target containing a first element is provided, and depositing atoms of the first element from the target on the main surface of the substrate to form a first element film on the main surface of the substrate, and a reaction step of moving the substrate after the sputtering step so as to pass through a plasma space in which a reactive gas containing a second element is turned into plasma, and causing the first element film on the main surface of the substrate to react with the second element, the reactive sputtering method comprising: a) a first reactive sputtering step including a first sputtering step and a first reaction step; and b) a second reactive sputtering step that is performed after the first reactive sputtering step and includes a second sputtering step and a second reaction step, wherein the reaction time for reacting the first element film with the second element is longer in the first reaction step than in the second reaction step.

2. A reactive sputtering method according to claim 1, wherein the deposition rate of the first element is lower in the first sputtering step than in the second sputtering step.

3. A reactive sputtering method according to claim 1 or 2, wherein the substrate moves through the plasma space at a slower speed in the first reaction step than in the second reaction step.

4. A reactive sputtering method according to any one of claims 1 to 3, wherein, when the thickness of the first element film formed on the substrate in the first sputtering step is defined as a first film thickness, the reaction time in the first reaction step is defined as a first reaction time, the thickness of the first element film formed on the substrate in the second sputtering step is defined as a second film thickness, and the reaction time in the second reaction step is defined as a second reaction time, the ratio of the first reaction time to the first film thickness is greater than the ratio of the second reaction time to the second film thickness.

5. A reactive sputtering method according to any one of claims 1 to 4, wherein the control conditions for controlling the plasma density of the second element in the plasma space are the same in the first reaction step and the second reaction step.

6. A reactive sputtering method according to any one of claims 1 to 5, wherein the first reactive sputtering step is a step of depositing one or more molecules of a compound of the first element and the second element in a direction perpendicular to the main surface of the substrate.

7. A reactive sputtering method according to claim 6, wherein the first reactive sputtering step is a step of depositing four or more molecules of a compound of the first element and the second element in a direction perpendicular to the main surface of the substrate.

8. A reactive sputtering method for forming a thin film containing the first element and the second element on a main surface of the substrate by alternately repeating a sputtering step of moving the substrate so as to pass through a sputtering space in which a target containing a first element is provided, and depositing atoms of the first element from the target on the main surface of the substrate to form a first element film on the main surface of the substrate, and a reaction step of moving the substrate after the sputtering step so as to pass through a plasma space in which a reactive gas containing a second element is converted into plasma, and causing the first element film on the main surface of the substrate to react with the second element, the reactive sputtering method comprising: a) a first reactive sputtering step including a first sputtering step and a first reaction step; and b) a second reactive sputtering step that is performed after the first reactive sputtering step and includes a second sputtering step and a second reaction step, wherein the deposition rate of the first element is lower in the first sputtering step than in the second sputtering step.

9. A reactive sputtering method for forming a thin film containing the first element and the second element on a main surface of the substrate by alternately repeating a sputtering step of moving a substrate through a sputtering space in which a target containing a first element is provided, and depositing atoms of the first element from the target on the main surface of the substrate to form a first element film on the main surface of the substrate, and a reaction step of moving the substrate after the sputtering step so as to pass through a plasma space in which a reactive gas containing a second element is plasmatized, and causing the first element film on the main surface of the substrate to react with the second element, the reactive sputtering method comprising: a) a first reactive sputtering step including a first sputtering step and a first reaction step; and b) a second reactive sputtering step that is performed after the first reactive sputtering step and includes a second sputtering step and a second reaction step, wherein the plasma density of the reactive gas in the plasma space is higher in the first reaction step than in the second reaction step.

Images