Reactive sputtering method

Abstract

The present invention provides a reactive sputtering method capable of forming a high-quality thin film on a main surface of a substrate. This reactive sputtering method is for forming, on a main surface of a substrate, a thin film containing a first element and a second element. The method includes a process of alternately repeating: a step (S11) for forming a first element film on the main surface of the substrate by moving the substrate so the substrate passes through a sputtering space where a target including the first element is provided, and stacking atoms of the first element from the target on the main surface at an average thickness of 3 atoms or less; and a step (S12) which is carried out after step (S11) and in which the first element on the main surface of the substrate is reacted with the second element by moving the substrate through a plasma space in which a reactive gas containing the second element is plasmatized.

Description

Reactive Sputtering Method

[0001] The present disclosure relates to reactive sputtering methods.

[0002] Sputtering apparatuses for forming thin films on the surfaces of substrates have been proposed (e.g., Patent Documents 1 and 2). In Patent Documents 1 and 2, the sputtering apparatuses form a Group III nitride semiconductor film on the surfaces of substrates. The sputtering apparatuses include 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] JP 2009-124100 A JP 2022-83129 A

[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 of the film but has difficulty reacting with the particles deep inside the film. This can result in insufficient nitriding of the film in the thickness direction. In this case, a low-quality film will be formed on the main surface of the substrate.

[0009] Therefore, an object of the present disclosure is to provide a reactive sputtering method that can form a high-quality thin film on a main surface of a substrate.

[0010] A first aspect is a reactive sputtering method for forming a thin film containing a first element and a second element on a main surface of a substrate, the method comprising: a sputtering step of moving the substrate so as to pass through a sputtering space in which a target containing the first element is provided, and depositing atoms of the first element from the target on the main surface of the substrate with an average thickness of 3 atoms or less, thereby forming a first element film on the main surface; and a reaction step, which is performed after the sputtering step, of moving the substrate so as to pass through a plasma space in which a reactive gas containing the 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.

[0011] A second aspect is the reactive sputtering method according to the first aspect, wherein in the sputtering step, the first element film is deposited on the main surface of the substrate with an average film thickness of one atom or less.

[0012] A third aspect is a reactive sputtering method according to the first aspect, wherein in the sputtering step, the first element film is formed on the main surface of the substrate to an average film thickness greater than 1 atom and less than or equal to 2 atoms, and in the reaction step, the reactive gas is turned into plasma with an input power of 3 kW or more.

[0013] According to the first aspect, a first element film is formed on the main surface of the substrate in the sputtering step with an average thickness of 3 atoms or less. This allows the second element to react with the entire first element film in the thickness direction in the subsequent reaction step. This allows a high-quality thin film to be formed on the main surface of the substrate.

[0014] According to the second aspect, the processing time in the reaction step can be shortened.

[0015] According to the third aspect, the second element can be reacted with the entire first element film in the thickness direction in a shorter processing time.

[0016] FIG. 1 is a side view schematically showing an example of the configuration of a sputtering apparatus. FIG. 2 is a plan view schematically showing an example of the configuration of a sputtering apparatus. FIG. 3 is a perspective view schematically showing an example of the configuration of a substrate holding unit and a heater. FIG. 4 is a block diagram schematically showing an example of the configuration of a control unit. FIG. 5 is a flowchart showing an example of the operation of a sputtering apparatus. FIG. 6 is a flowchart showing processes performed on one substrate by the operation of a sputtering apparatus. FIG. 7 is a diagram schematically showing an example of a simulation result. FIG. 8 is a graph showing the relationship between the half width of XRC and the processing time of the reaction step. FIG. 9 is a graph showing the relationship between the half width and the average film thickness of an aluminum film formed in the sputtering step. FIG. 10 is a graph showing the relationship between the half width of XRC and the input power of a second power source.

[0017] 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.

[0018] Furthermore, in the following description, even if ordinal numbers such as "first" or "second" are used, these terms are used for convenience to facilitate understanding of the contents of the embodiments, and are not limited to the order that may result from these ordinal numbers.

[0019] When expressions indicating relative or absolute positional relationships (e.g., "in one direction," "along one direction," "parallel," "orthogonal," "center," "concentric," "coaxial," etc.) are used, unless otherwise specified, the expressions not only strictly represent the positional relationship but also represent a state in which there is a relative displacement in terms of angle or distance within a range in which tolerance or equivalent functionality is obtained. When expressions indicating an equal state (e.g., "identical," "equal," "homogeneous," etc.) are used, the expressions not only represent a state in which there is strict quantitative equality but also represent a state in which there is a difference in which tolerance or equivalent functionality is obtained, unless otherwise specified. When expressions indicating a shape (e.g., "rectangular shape" or "cylindrical shape," etc.) are used, the expressions not only represent a geometrically strict shape but also represent a shape with, for example, irregularities or chamfers within a range in which equivalent effects are obtained. When the expressions "comprise," "include," "have," "includes," "includes," or "have" are used to describe one component, the expressions are not exclusive expressions that exclude the presence of other components. When the phrase "at least one of A, B, and C" is used, the phrase includes A only, B only, C only, any two of A, B, and C, and all of A, B, and C.

[0020] <Sputtering Apparatus> Fig. 1 is a side view that schematically shows an example of the configuration of a sputtering apparatus 100. Fig. 2 is a plan view that schematically shows an example of the configuration of the sputtering apparatus 100. Fig. 1 shows an example of the configuration of the cross section A-A in Fig. 2.

[0021] 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 substrate. The substrate W has, for example, a disk shape. Note that the material and shape of the substrate W are not limited to these and can be changed as appropriate.

[0022] The sputtering apparatus 100 includes a chamber 1 , a sputtering section 2 , a plasma section 3 , a substrate holder 4 , a suction mechanism 5 , and a control section 6 .

[0023] The chamber 1 has a box-like hollow shape. The internal space of the chamber 1 corresponds to a processing space in which a film formation process is performed on a substrate W. The chamber 1 may also be called a vacuum chamber. The chamber 1 is provided with a loading / unloading mechanism (not shown). The loading / unloading mechanism switches between a communicating state in which the internal space of the chamber 1 is connected to the outside space and a sealed state in which the internal space is isolated from the outside space. In the communicating state, a substrate transport unit (not shown) loads an unprocessed substrate W into the chamber 1. Then, 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 loads the substrate W, which has already been processed, out of the chamber 1.

[0024] The suction mechanism 5 has a suction port 5a that 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 may be, for example, a vacuum pump, or more specifically, a turbomolecular pump.

[0025] The processing space within chamber 1 has a sputtering space 1a and a plasma space 1b that are aligned in the circumferential direction about a predetermined revolution axis Q1. The revolution axis Q1 is an axis that runs vertically. Note that a physical structure (e.g., a partition plate) that separates sputtering space 1a and plasma space 1b may or may not be provided within chamber 1.

[0026] As will be described later, a target 21 of the sputtering unit 2 is provided in the sputtering space 1a, and sputtering is performed on the target 21. The target 21 contains a first element (e.g., gallium or aluminum). That is, the material of the target 21 contains the first element. Also, 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).

[0027] The substrate holder 4 is provided in the chamber 1. While holding a substrate W, the substrate holder 4 revolves the substrate W around the revolution axis Q1, alternately moving the substrate W between the sputtering space 1a and the plasma space 1b. FIG. 3 is a perspective view schematically showing an example of the configuration of the substrate holder 4 and a heater 11 (described later). In the example of FIG. 3, the substrate holder 4 holds multiple substrates W arranged in a circumferential direction about the revolution axis Q1. Note that the substrate holder 4 does not necessarily need to hold multiple substrates W; it may hold a single substrate W. The substrate holder 4 holds the substrate W in a horizontal position. Here, the horizontal position means a position in which the thickness direction of the substrate W is aligned vertically. When multiple substrates W are held by the substrate holder 4, the main surface (lower surface in the figure) Wa of each substrate W is exposed in the chamber 1 (see also FIG. 1).

[0028] 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 it alternately passes through the sputtering space 1a and the plasma space 1b. As described below, 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. Then, 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 predetermined thin film is formed on the main surface Wa of the substrate W.

[0029] In the following description, the direction in which the revolution axis Q1 extends will also be referred to as the axial direction, and the circumferential direction and radial direction about the revolution axis Q1 will also be simply referred to as the circumferential direction and radial direction, respectively.

[0030] <Substrate Holding Unit> The substrate holding unit 4 includes a holder 41 and a rotation drive unit 42. The holder 41 holds multiple substrates W arranged in the circumferential direction. While the specific structure of the holder 41 is not particularly limited, for example, the holder 41 has a disk shape centered on the revolution axis Q1. The holder 41 may have multiple through holes 41a formed therein. The multiple through holes 41a are formed, for example, at equal intervals along the circumferential direction and pass through the holder 41 in the axial direction. Each through hole 41a has a stepped shape that narrows vertically downward, and each substrate W is placed in the through hole 41a. The holder 41 supports the periphery of each substrate W at the stepped portion of each through hole 41a.

[0031] The rotation drive unit 42 is controlled by the control unit 6 and rotates the holder 41 around 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 around the revolution axis Q1, thereby rotating the holder 41 around the revolution axis Q1.

[0032] <Heater> The heater 11 is provided in the chamber 1 vertically above the substrate holder 4. The heater 11 is controlled by the controller 6 and 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 the film formation process. 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 may be an optical heater including a light source that irradiates the substrates W with heating light (for example, infrared light).

[0033] <Sputtering Unit> The sputtering unit 2 includes a target 21, a sputtering gas supply unit 23, and a first plasma generation unit 25. In the example of Fig. 2, the sputtering gas supply unit 23 and the first plasma generation unit 25 are not shown in order to avoid complication of the drawing.

[0034] <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 of FIG. 1 , the target 21 is provided vertically below the substrate holding part 4.

[0035] The target 21 has, for example, a plate-like shape, and in the example of FIG. 2 , has a rectangular shape in a plan view. Note that the plan view here 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 is along the vertical direction. 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.

[0036] The target 21 is made of a material containing a 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.

[0037] <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, at least one of argon gas and xenon gas. In the example of FIG. 1 , the sputtering gas supply unit 23 includes an air supply pipe 231, a valve 232, and a flow rate adjuster 233. A sputtering gas supply source 234 is connected to the upstream end of the air supply pipe 231. The sputtering gas supply source 234 supplies sputtering gas to the upstream end of the air supply pipe 231. The air supply pipe 231 has a first air supply port 23a that opens in the sputtering space 1a. The sputtering gas flows through the air supply pipe 231 and flows out from the first air supply port 23a into the sputtering space 1a. A portion of this sputtering gas flows into the space between the movement path R1 of the substrate W and the target 21.

[0038] Valve 232 is provided in air supply pipe 231 and opens and closes air supply pipe 231. Flow rate adjuster 233 is provided in air supply pipe 231 and adjusts the flow rate of the sputtering gas flowing through air supply pipe 231. Flow rate adjuster 233 is, for example, a mass flow controller. Valve 232 and flow rate adjuster 233 are controlled by control unit 6.

[0039] <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.

[0040] In the example of 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 illustrated in FIG. 1 , the chamber 1 may be grounded. Furthermore, the substrate holder 4 may be electrically connected to the chamber 1.

[0041] The first power supply 251 supplies DC power to the target 21, generating an electric field for plasma around the target 21. This electric field acts on the sputtering gas, ionizing the sputtering gas and turning it 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. This causes particles of the first element to fly out of the target 21 and move toward the movement path 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. This forms a film of the first element (hereinafter referred to as the first element film) on the main surface Wa of the substrate W.

[0042] <Chimney> In the example of FIG. 1 , the sputtering unit 2 also includes 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 upper plate portion 271 of the chimney 27 has an opening 27a that faces the target 21 in the axial direction. The opening 27a penetrates the upper plate portion 271 in the axial direction. Particles of the first element 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.

[0043] <Plasma Unit> The plasma unit 3 has a second gas inlet 31a that opens into the plasma space 1b, and 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.

[0044] <Reactive Gas Supply Unit> In the example of FIG. 1 , the reactive gas supply unit 31 includes an air supply pipe 311, a valve 312, and a flow rate adjuster 313. The upstream end of the air supply pipe 311 is connected to a reactive gas supply source 315. The reactive gas supply source 315 supplies a reactive gas to the upstream end of the air supply pipe 311. The air supply pipe 311 has a second air supply port 31a. In the example of FIG. 1 , the opening direction of the second air supply port 31a of the air supply pipe 311 is parallel to the axial direction and toward the substrate holder 4. In the example of FIG. 1 , the air supply pipe 311 branches into two, and the downstream ends of each branch correspond to the second air supply ports 31a. In the example of FIG. 1 , the two second air supply ports 31a are provided at a radial interval.

[0045] 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 applied. The second element is, for example, nitrogen. As a specific example, the reactive gas is nitrogen (N ２ ) gas and ammonia (NH ３ ) gas. For example, when the first element is aluminum and the second element is nitrogen, an aluminum nitride film can be formed on the main surface Wa of the substrate W. The second element may also be oxygen. As a specific example, the reactive gas is oxygen (O ２ For example, when the first element is aluminum and the second element is oxygen, an aluminum oxide film may be formed on the main surface Wa of the substrate W.

[0046] The valve 312 is provided in the air supply pipe 311 and opens and closes the air supply pipe 311. The flow rate adjuster 313 is provided in the air supply pipe 311 and adjusts the flow rate of the reactive gas flowing through the air supply pipe 311. 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.

[0047] 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.

[0048] <Second Plasma Generating Unit> The second plasma generating unit 33 generates plasma from the nitrogen gas supplied from the second gas inlet 31 a into the chamber 1. The highly reactive nitrogen activated species generated by the plasma generation move toward the substrate holder 4 and, when they reach the main surface Wa of the substrate W moving through the plasma space 1 b, nitride the aluminum film on the main surface Wa.

[0049] In the example of FIG. 1 , the second plasma generation unit 33 includes an inductive coupling antenna 331 and a second power supply 332. The inductive coupling antenna 331 is provided in the plasma space 1b vertically below the movement path R1 of the substrate W. The inductive coupling antenna 331 includes a U-shaped conductive member 3311. The conductive member 3311 is provided in the chamber 1 with both ends positioned vertically downward, and more specifically, is attached to the bottom of the chamber 1. In the example of FIG. 2 , the conductive member 3311 is provided with both ends aligned along the circumferential direction. Both ends of the conductive member 3311 penetrate, for example, the bottom of the chamber 1, and are electrically connected to the second power supply 332. The conductive member 3311 functions as an electrode (antenna) for generating plasma.

[0050] 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 of 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 (conductive member 3311) in a plan view.

[0051] The second power supply 332 supplies high-frequency power to the inductively coupled antenna 331. The second power supply 332 includes, 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, and this 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.

[0052] <Controller> The controller 6 controls various components of the sputtering apparatus 100. FIG. 4 is a block diagram showing an example of the configuration of the controller 6. The controller 6 is an electronic circuit device and may include, for example, a data processing device 61 and a storage device 62. The data processing device 61 may be, for example, an arithmetic processing device such as a CPU (Central Processor Unit). The storage device 62 may include a non-transitory storage device (e.g., a ROM (Read Only Memory)) 621 and a temporary storage device (e.g., a RAM (Random Access Memory)) 622. The non-transitory storage device 621 may store, for example, a program that defines the processing to be performed by the controller 6. The data processing device executes this program, allowing the controller 6 to perform the processing defined in the program. Of course, some or all of the processing performed by the controller 6 may be performed by a hardware circuit such as a logic circuit.

[0053] 4, the control unit 6 is electrically connected to a storage unit 63. The storage unit 63 is a non-temporary storage unit such as a memory or a hard disk. For example, the storage unit 63 stores setting data (recipe data) indicating processing conditions to be performed by the sputtering apparatus 100. The control unit 6 can perform a film formation process on the substrate W by controlling the sputtering apparatus 100 based on the setting data.

[0054] <Example of Operation of Sputtering Apparatus> Fig. 5 is a flowchart showing an example of 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. As will be described in detail later, the sputtering apparatus 100 operates in accordance with the flowchart of Fig. 5, whereby step S11 (sputtering step) and step S12 (reaction step) of Fig. 6 are repeatedly performed on each substrate W. This will be described in detail below.

[0055] 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 suctioning gas from the chamber 1 (step S2), and the heater 11 starts heating 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, and the heater 11 adjusts the temperature of the substrates W to within a temperature range suitable for the film formation process.

[0056] Next, the sputtering gas supply unit 23 starts supplying sputtering gas, and the reactive gas supply unit 31 starts supplying reactive gas, while the first plasma generator 25 and the second plasma generator 33 convert the gas into plasma (step S4). Specifically, the control unit 6 opens the valves 232 and 312. This causes the sputtering gas and the reactive gas to be supplied in parallel into the chamber 1. The control unit 6 also starts outputting voltages to the first power supply 251 and the second power supply 332. Furthermore, the rotation drive unit 42 starts rotating the holder 41 around the revolution axis Q1 (step S5). This causes the multiple substrates W to revolve around the revolution axis Q1.

[0057] Here, in the film formation process (step S5), the sputtering gas supply unit 23 constantly supplies sputtering gas, the reactive gas supply unit 31 constantly supplies reactive gas, the first power supply 251 and the second power supply 332 constantly output voltages, and the substrate holder 4 constantly revolves the substrate W.

[0058] 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, step S11 (sputtering step) in which the substrate holder 4 moves the substrate W so that it passes through the sputtering space 1 a and step S12 (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.

[0059] In step S11 (sputtering step), 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.

[0060] In the next step S12 (reaction step), the sputtering apparatus 100 reacts a second element with the first element film formed on the main surface Wa of the substrate W in step S11 (sputtering step). 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.

[0061] Next, the control unit 6 determines whether to end the process (step S13). For example, the control unit 6 may determine whether the number of times that a set of steps S11 and S12 has been performed is less than a predetermined number. If the number of times is less than the predetermined number, the control unit 6 performs step S11 again. That is, the sputtering apparatus 100 continues the film formation process on the substrate W. By repeating the set of steps S11 and S12, aluminum nitride films are 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 thickness of the aluminum nitride film reaches a target value, and may be set to, for example, several tens of times.

[0062] If the number of executions is equal to or greater than the specified number, the control unit 6 terminates the film formation process. For example, the sputtering gas supply unit 23 stops supplying sputtering gas, the reactive gas supply unit 31 stops supplying reactive gas, the first power supply 251 and the second power supply 332 stop output, the substrate holder 4 stops revolving the substrate W, the heater 11 stops heating the substrate W, and the suction mechanism 5 stops suctioning gas (step S6). Next, the substrate transport unit unloads the substrate W that has been subjected to the film formation process from the chamber 1 (step S7).

[0063] As described above, the sputtering apparatus 100 repeatedly performs a set of step S11 (sputtering step) and step S12 (reaction step) on the substrate W. In this way, the sputtering apparatus 100 can form a thin film (e.g., an aluminum nitride film) on the main surface Wa of the substrate W.

[0064] However, the inventors discovered that when the aluminum film formed in step S11 (sputtering process) is thick, it is difficult to nitride the entire thickness of the thick aluminum film in step S12 (reaction process).

[0065] 7 and 8 are diagrams schematically illustrating an example of a simulation result. FIGS. 7 and 8 are schematic diagrams illustrating the results of a simulation based on first-principles calculations, showing the bonding of an aluminum atom A1 and a nitrogen atom A2. FIG. 7 illustrates the simulation results for a case in which an aluminum film is formed to a thickness of two atoms in step S11 (sputtering process) and then nitrided in step S12 (reaction process). That is, FIG. 7 illustrates the simulation results for a case in which a film F1 is formed to a thickness of two atoms using only aluminum atoms A1, and then a simulation is performed to nitride the film F1. FIG. 8 illustrates the simulation results for a case in which an aluminum film is formed to a thickness of one atom in step S11 (sputtering process) and then nitrided in step S12 (reaction process).

[0066] In the following, a layer of the film on the main surface Wa of the substrate W that has a thickness of one atom from the surface will be referred to as the first atomic layer, and a layer that has a thickness of one atom from the Nth (N is a natural number) atomic layer will also be referred to as the (N+1)th atomic layer.

[0067] While Figures 7 and 8 show the results of nitridation at a certain processing time, in actual simulations using first-principles calculations, the positional fluctuations of aluminum atoms A1 and nitrogen atoms A2 are calculated over time. When the inventors confirmed the positional fluctuations over time, they found that nitrogen atoms A2 quickly bonded with aluminum atoms A1 in the first atomic layer. In other words, nitridation of the first atomic layer was completed quickly. Meanwhile, nitrogen atoms A2 had difficulty passing through the first atomic layer, and nitridation of the second atomic layer took time. The inventors confirmed that nitrogen vacancies are likely to occur in the second atomic layer with processing times as short as several picoseconds to several hundred picoseconds. In Figure 7, nitrogen vacancies occur in region DR1 of the second atomic layer, whereas in Figure 8, no nitrogen vacancies occur and nitridation is completed throughout the entire thickness direction (vertical direction of the page).

[0068] Since this simulation based on first-principles calculations can only perform calculations over extremely short processing times, on the order of picoseconds, as mentioned above, experiments were conducted to confirm what thickness of aluminum film can actually be nitrided. Here, the crystalline quality of the aluminum nitride film formed on the main surface Wa of the substrate W is used as an indicator of the degree to which the aluminum film has been nitrided. Here, the half-width of the XRC (X-ray rocking curve) of the (0002) plane of the aluminum nitride film is used as the crystalline quality. The higher the crystalline quality, the smaller the half-width. In other words, the smaller the half-width, the more sufficiently the aluminum film is nitrided in the thickness direction.

[0069] 9 is a graph showing the relationship between the FWHM of the XRC and the processing time of the reaction step. The graph shows experimental results under the following conditions: the temperature of the substrate W is 390° C., the pressure in the chamber 1 is 0.5 Pa, nitrogen gas is used as the reactive gas, the input power of the first power supply 251 is 0.5 kW, the input power of the second power supply 332 is 4.5 kW, and the moving speed of the substrate W is 15 m / min. The moving speed is the moving speed of the substrate W (e.g., the center) as it passes through the sputtering space 1a. Under these processing conditions, in step S11 (sputtering step), an aluminum film is formed on the main surface Wa of the substrate W with an average thickness of 0.75 nm.

[0070] Since the diameter of an aluminum atom is approximately 0.25 nm, under the above-described processing conditions, an aluminum film is formed with an average thickness of three atoms. In other words, when the substrate W passes through the sputtering space 1a, a film of the first element (here, aluminum) with an average thickness of three atoms or less is formed on the main surface Wa of the substrate W (sputtering process). Here, the average thickness refers to the average thickness of the first element film in a target region of the main surface Wa of the substrate W. The target region may be the entire main surface Wa of the substrate W. Such an average thickness is measured, for example, by ellipsometry. Ellipsometry is a device that irradiates light in a spot on the main surface Wa of the substrate W, measures the reflected light, and measures the average film thickness within the spot based on the reflected light. In this case, the spot may correspond to the target region.

[0071] In the experiment, an aluminum nitride film was formed on the main surface Wa of the substrate W by performing a set of step S11 (sputtering step) and step S12 (reaction step) 70 times. The experiment was also conducted multiple times, varying the processing time of step S12 (reaction step). The horizontal axis of FIG. 9 indicates the processing time in the reaction step. In other words, this processing time corresponds to the time during which the main surface Wa of the substrate W is exposed to nitrogen plasma. As can be seen from FIG. 9 , the longer the processing time of step S12 (reaction step), the smaller the half-width. In other words, the longer the processing time, the higher the crystal quality. In other words, the longer the processing time, the more sufficiently the sputtering apparatus 100 can nitride the aluminum film. In FIG. 9 , the half-width is 0.13 deg when the processing time is 120 seconds, achieving sufficient crystal quality. This value can satisfy, for example, the specifications of semiconductor devices requiring high quality.

[0072] According to the relationship shown in Figure 9, when the processing time is less than 20 seconds, the half-width decreases rapidly with increasing processing time, whereas when the processing time is 20 seconds or more, the half-width decreases relatively slowly with increasing processing time. In other words, the rate of decrease in the half-width with respect to processing time changes rapidly around the processing time of 20 seconds. Therefore, the processing time may be set to a value of 20 seconds or more. Furthermore, if a target value of 0.5 deg is applied to the half-width, for example, the processing time may be set to approximately 50 seconds or more.

[0073] Since nitrogen atoms A2 bond with aluminum atoms A1 in order from the surface side of the aluminum film, the processing time of step S12 (reaction step) becomes longer as the number of atomic layers of the aluminum film increases. Specifically, it is considered that the processing time increases logarithmically with the increase in the number of atomic layers. Therefore, when the number of atomic layers becomes four or more, in other words, when the average film thickness becomes equal to or greater than the average film thickness of four atoms, the processing time becomes suddenly longer.

[0074] Therefore, in this embodiment, the sputtering apparatus 100 forms a first element film (e.g., an aluminum film) with an average thickness of three atoms or less in each step S11 (sputtering process). Specifically, the movement speed of the substrate W passing through the sputtering space 1a and the input power of the first power supply 251 are set in advance so that a first element film can be formed with an average thickness of three atoms or less, and the values ​​of these process conditions are stored in the memory unit 63. These process conditions can be set in advance, for example, through experiments or simulations. The control unit 6 reads the movement speed and input power values ​​from the memory unit 63 and controls various components of the sputtering apparatus 100 based on the process conditions. This allows the sputtering apparatus 100 to form a first element film (e.g., an aluminum film) with an average thickness of three atoms or less in each step S11 (sputtering process).

[0075] The sputtering apparatus 100 also performs each step S12 (reaction step) with a processing time and input power of the second power supply 332 that sufficiently reacts the second element with the first element film formed in step S11 (sputtering step) in the thickness direction. That is, the sputtering apparatus 100 performs each step S12 (reaction step) with a processing time and input power that sufficiently reacts the second element with the entire first to third atomic layers. For example, the moving speed of the substrate W through the plasma space 1b, the pressure (total pressure) in the chamber 1, the partial pressure of the nitrogen gas, the input power of the second power supply 332, and the temperature of the substrate W are preset so as to achieve a target value for crystal quality, and the processing conditions are stored in the memory unit 63. These processing conditions can be preset, for example, through experiments or simulations. The control unit 6 reads the values ​​of these processing conditions from the memory unit 63 and controls various components of the sputtering apparatus 100 based on the processing conditions.

[0076] As described above, in this embodiment, the sputtering apparatus 100 forms a first element film (e.g., an aluminum film) with an average thickness of three atoms or less in step S11 (sputtering process). Therefore, the sputtering apparatus 100 can react the entire thickness of the first element film with the second element in step S12 (reaction process). Therefore, the sputtering apparatus 100 can form a high-quality thin film on the main surface Wa of the substrate W.

[0077] <Average Film Thickness of Less Than One Atom> In step S11 (sputtering process), the sputtering apparatus 100 may form a first element film with an average film thickness of less than one atom. For example, the movement speed of the substrate W and the input power of the first power supply 251 for forming a first element film with an average film thickness of less than one atom are set in advance, and these processing conditions are set in the storage unit 63. The control unit 6 reads the values ​​of the processing conditions from the storage unit 63 and controls various components of the sputtering apparatus 100 based on the processing conditions. This allows the sputtering apparatus 100 to form a first element film having substantially only the first atomic layer on the main surface Wa of the substrate W in step S11 (sputtering process).

[0078] Simulations have confirmed that the second element can react more reliably with such a first element film (i.e., first atomic layer). That is, by forming a first element film with an average thickness of one atom or less in step S11 (sputtering process) using the sputtering apparatus 100, the second element can react more reliably with the entire first element film in step S12 (reaction process). This is believed to be due to the following reason: Since the first atomic layer is located on the surface of the first element film, unlike the second atomic layer, the second element does not need to pass through other atomic layers to react with the first atomic layer.

[0079] FIG. 10 is a graph showing the relationship between the average film thickness and the full width at half maximum of the aluminum film formed in the sputtering process. FIG. 10 shows data obtained through experiments. As shown in FIG. 10, the full width at half maximum increases as the average film thickness of the aluminum film formed in step S11 (sputtering process) increases. In other words, FIG. 10 indicates that as the average film thickness of the aluminum film increases, it becomes more difficult to nitride the aluminum film throughout its entire thickness direction. As shown in FIG. 10, when the average film thickness is equal to or less than one atom (0.25 nm in this case), the full width at half maximum is less than 0.5 degrees. In other words, as long as the average film thickness is equal to or less than one atom, the sputtering apparatus 100 can sufficiently nitride the aluminum film. The resulting aluminum nitride film can satisfy, for example, the quality requirements for semiconductor devices. In other words, the sputtering apparatus 100 can form a high-quality thin film on the main surface Wa of the substrate W by forming a first element film with an average film thickness equal to or less than one atom in each sputtering process.

[0080] Furthermore, since the processing time in step S12 (reaction step) increases logarithmically as the thickness of the first element film increases, forming a first element film with an average thickness of one atom or less can significantly reduce the processing time. On the other hand, the thickness of the thin film (here, an aluminum nitride film) that can be formed in a single step of step S11 and step S12 is small, so the number of times each set needs to be performed increases. However, the processing time of step S12 (reaction step) can be significantly reduced logarithmically. For example, compared to forming a first element film with an average thickness of three atoms, the processing time can be reduced to, for example, one-tenth or less. This reduces the overall processing time of the film formation process. In other words, the throughput of the sputtering apparatus 100 can be reduced.

[0081] Furthermore, since the second element easily reacts with the first element film, the processing conditions in step S12 (reaction step) can be set to reduce the input power of the second power source 332. This can suppress deterioration of the second power source 332.

[0082] <Average Film Thickness More Than One Atom and Less Than Two Atoms> In step S11 (sputtering process), the sputtering apparatus 100 may form a first element film with an average film thickness more than one atom and less than two atoms. For example, the movement speed of the substrate W and the input power of the first power supply 251 for forming a first element film with an average film thickness more than one atom and less than two atoms are set in advance, and these process condition values ​​are set in the storage unit 63. The control unit 6 reads the process condition values ​​from the storage unit 63 and controls various components of the sputtering apparatus 100 based on the process conditions. This allows the sputtering apparatus 100 to form a first element film with an average film thickness more than one atom and less than two atoms in step S11 (sputtering process).

[0083] As described above, the reaction of the second element with the second atomic layer of the first element film is less likely to occur than the reaction with the first atomic layer. Therefore, the preferred input power of the second power supply 332 for the reaction of the second atomic layer will be considered.

[0084] 11 is a graph showing the relationship between the FWHM of the XRC and the input power of the second power supply 332. The graph shows experimental results obtained when the temperature of the substrate W was 390° C., the pressure in the chamber 1 was 0.5 Pa, nitrogen gas was used as the reactive gas, and the input power of the first power supply 251 was 0.5 kW. The movement speed of the substrate W was set to a value sufficient to form an aluminum film having an average thickness of 0.29 nm on the main surface Wa of the substrate W. Since the diameter of an aluminum atom is approximately 0.25 nm, the average thickness of 0.29 nm is greater than one atom (0.25 nm) and less than two atoms (0.5 nm).

[0085] 11, when the input power of the second power source 332 is less than 3 kW, the FWHM decreases relatively rapidly as the processing time increases, whereas when the input power of the second power source 332 is 3 kW or more, the FWHM becomes almost zero. In other words, if 3 kW is considered to be a critical value, it can be seen that when the processing time is equal to or greater than this critical value, the crystal quality can be maintained at a significantly high level.

[0086] Therefore, in step S12 (reaction step), the sputtering apparatus 100 causes the second power supply 332 to output an input power of 3 kW or more. For example, a value of 3 kW or more is stored in the memory unit 63 as the input power of the second power supply 332, and the control unit 6 reads out the input power value from the memory unit 63 and controls the second power supply 332 based on this value.

[0087] As a result, in step S12 (reaction step), the sputtering apparatus 100 can react the second element with the first element film formed in step S11 (sputtering step) over the entire thickness direction of the first element film, thereby enabling the sputtering apparatus 100 to form a high-quality thin film on the main surface Wa of the substrate W.

[0088] Furthermore, since the sputtering apparatus 100 forms the first element film with an average thickness greater than one atom in step S11 (sputtering step), it is possible to reduce the moving speed of the substrate W. This makes it possible to suppress deterioration of the rotation drive unit 42.

[0089] As described above, the sputtering apparatus 100 and the reactive sputtering method have been described in detail. However, the above description is merely an example in all respects, and the sputtering apparatus 100 and the sputtering 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.

[0090] For example, in the above example, the substrate W revolves around the revolution axis Q1, thereby passing alternately through the sputtering space 1 a and the plasma space 1 b. However, this is not necessarily limited to this. For example, the substrate W may move back and forth between the sputtering space 1 a and the plasma space 1 b, which are arranged linearly.

[0091] 1a sputtering space 1b plasma space 21 target W substrate Wa main surface

Claims

1. A reactive sputtering method for forming a thin film containing a first element and a second element on a principal surface of a substrate, comprising the steps of alternately repeating a sputtering step in which the substrate is moved so as to pass through a sputtering space in which a target containing the first element is provided, and atoms of the first element from the target are deposited on the principal surface of the substrate with an average thickness of 3 atoms or less, thereby forming a first element film on the principal surface; and a reaction step, which is performed after the sputtering step, in which the substrate is moved so as to pass through a plasma space in which a reactive gas containing the second element is turned into plasma, thereby causing a reaction between the first element film on the principal surface of the substrate and the second element.

2. A reactive sputtering method according to claim 1, wherein in the sputtering step, a film of the first element is laminated on the main surface of the substrate with an average thickness of one atom or less.

3. A reactive sputtering method as claimed in claim 1, wherein in the sputtering step, a film of the first element is formed on the main surface of the substrate with an average film thickness greater than 1 atom and less than 2 atoms, and in the reaction step, the reactive gas is turned into plasma with an input power of 3 kW or more.

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