Reactive sputtering method

Abstract

To provide a reactive sputtering method capable of forming a high quality thin film on a principal surface of a substrate.SOLUTION: A reactive sputtering method for forming a thin film containing first and second elements on a principal surface of a substrate includes a step for alternately repeating a step 11 for moving the substrate through a sputter space, in which a target containing the first element is provided, laminating atoms of the first element from the target on the principal surface of the substrate with average film thickness of 3 atoms or less, and forming a first element film on the principal surface, and a step S12 performed after the step S11, for moving the substrate through a plasma space, in which reactive gas containing the second element is made into plasma, and reacting the first element film on the principal surface of the substrate with the second element.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] Conventionally, sputtering apparatuses for forming a thin film on a surface of a substrate have been proposed (e.g., Patent Documents 1 and 2). In Patent Documents 1 and 2, the sputtering apparatus forms a Group III nitride semiconductor film on the surface of a substrate. 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 in the chamber. The target chambers and the nitrogen chambers are provided alternately around a predetermined revolution axis. The rotating jig revolves the substrate W around the predetermined revolution axis in the chamber. This moves the substrate W from the target chamber to the nitrogen chamber and also moves from the nitrogen chamber to the target chamber.

[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 collision causes 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. The second plasma generating means generates a second plasma of nitrogen in the nitrogen chamber. This causes the highly reactive nitrogen to react with the raw material particles of the substrate.

[0006] The target chamber and the nitrogen chamber are in communication with each other in the circumferential direction, and the substrate passes through the target chamber and the nitrogen chamber as the substrate revolves around the rotating jig. When the substrate passes through the target chamber, raw material particles of a group III element are deposited on the substrate, and when 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. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-124100 A [Patent Document 2] Patent Publication No. 2022-83129 Summary of the Invention [Problem to be solved by the invention]

[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 deeper parts of the film. As a result, the film may not be sufficiently nitrided in the thickness direction. In this case, a low-quality film is formed on the main surface of the substrate.

[0009] Therefore, an object of the present disclosure is to provide a reactive sputtering method capable of forming a high-quality thin film on a main surface of a substrate. [Means for solving the problem]

[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 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 to form a first element film on the main surface; and a reaction step, which is performed after the sputtering step, of moving the substrate through a plasma space in which a reactive gas containing the second element is turned into plasma, and reacting the first element film on the main surface of the substrate with the second element. The reaction step is repeated alternately.

[0011] A second aspect is the reactive sputtering method according to the first aspect, wherein in the sputtering step, the first element film is laminated 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 with an average film thickness greater than 1 atom and less than 2 atoms, and in the reaction step, the reactive gas is converted into plasma with an input power of 3 kW or more. Effect of the Invention

[0013] According to the first aspect, a first element film is formed on the main surface of the substrate in an average thickness of 3 atoms or less in the sputtering step. Therefore, in the subsequent reaction step, the second element can react with the entire first element film in the thickness direction. Therefore, a high-quality thin film can 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, it is possible to cause the second element to react with the entire first element film in the thickness direction in a shorter treatment time. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a side view illustrating an example of a configuration of a sputtering apparatus. [Diagram 2] FIG. 1 is a plan view illustrating an example of a configuration of a sputtering apparatus. [Diagram 3] FIG. 2 is a perspective view illustrating an example of a configuration of a substrate holding part and a heater. [Figure 4] FIG. 2 is a block diagram illustrating an example of the configuration of a control unit. [Diagram 5] 4 is a flowchart showing an example of the operation of the sputtering apparatus. [Figure 6] 4 is a flow chart showing steps performed on one substrate by the operation of a sputtering apparatus. [Figure 7] FIG. 13 is a diagram illustrating an example of a simulation result. [Figure 8] FIG. 13 is a diagram illustrating an example of a simulation result. [Figure 9] 1 is a graph showing the relationship between the half-width of XRC and the processing time of the reaction step. [Figure 10] 1 is a graph showing the relationship between the average film thickness and the half width of an aluminum film formed in a sputtering process. [Figure 11] 13 is a graph showing the relationship between the half-width of XRC and the input power of the second power source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment 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 disclosure. In the drawings, the dimensions or numbers of each part may be exaggerated or simplified as necessary for ease of understanding.

[0018] In addition, in the description below, 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 ordering that may result from these ordinal numbers.

[0019] When an expression indicating a relative or absolute positional relationship (e.g., "in one direction," "along one direction," "parallel," "orthogonal," "center," "concentric," "coaxial," etc.) is used, the expression not only strictly indicates the positional relationship, but also indicates a state in which the relative positional relationship is displaced with respect to angle or distance within a range in which a tolerance or similar function is obtained, unless otherwise specified. When an expression indicating an equal state (e.g., "same," "equal," "homogeneous," etc.) is used, the expression not only strictly indicates a quantitatively equal state, but also indicates a state in which a difference exists within a range in which a tolerance or similar function is obtained, unless otherwise specified. When an expression indicating a shape (e.g., "square shape" or "cylindrical shape," etc.) is used, the expression not only strictly indicates the shape geometrically, but also indicates a shape having, for example, unevenness or chamfering within a range in which a similar effect is obtained, unless otherwise specified. When an expression "comprises," "has," "includes," "includes," or "has" a component is used, the expression is not an exclusive expression that excludes 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 equipment> Fig. 1 is a side view that shows a schematic example of the configuration of a sputtering apparatus 100. Fig. 2 is a plan view that shows a schematic example of the configuration of a sputtering apparatus 100. Fig. 1 shows an example of the configuration of a cross section taken along the line AA of Fig. 2.

[0021] The sputtering apparatus 100 is a film forming apparatus that performs a film forming process on a substrate W by reactive sputtering. Specifically, the sputtering apparatus 100 forms a thin film including a first element and a second element on a main surface Wa of the substrate W. The first element is, for example, a metal element, and 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 substrate such as sapphire. The substrate W has, for example, a disk shape. 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 holding section 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 the 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 external space and a sealed state in which the internal space is blocked from the external 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 that has been subjected to the film formation process out of the chamber 1.

[0024] The suction mechanism 5 has a suction port 5a, which 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 from the suction port 5a, and adjusts the pressure to within a predetermined reduced pressure range. As the suction mechanism 5, for example, a vacuum pump, or more specifically, a turbomolecular pump, can be used.

[0025] The processing space in the chamber 1 has a sputtering space 1a and a plasma space 1b arranged in the circumferential direction about a predetermined revolution axis Q1. The revolution axis Q1 is an axis along the vertical direction. A physical structure (e.g., a partition plate) for dividing the sputtering space 1a and the plasma space 1b may or may not be provided in the chamber 1.

[0026] As described below, 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. As described below, a reactive gas is supplied to the plasma space 1b by the plasma unit 3, and the reactive gas is turned 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 the substrate W, the substrate holder 4 revolves the substrate W around the revolution axis Q1, and alternately moves the substrate W to the sputtering space 1a and the plasma space 1b. FIG. 3 is a perspective view that shows 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 a plurality of substrates W in a state in which they are arranged along the circumferential direction about the revolution axis Q1. Note that the substrate holder 4 does not necessarily need to hold a plurality of substrates W, and may hold a single substrate W. The substrate holder 4 holds the substrate W in a horizontal position. The horizontal position here means a position in which the thickness direction of the substrate W is aligned along the vertical direction. With a plurality of substrates W 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, so that each substrate W passes alternately through the sputtering space 1a and the plasma space 1b. In other words, the substrate holder 4 moves the substrate W so that it passes alternately 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, active species (including at least one of ions and radicals) of the second element generated by turning the reactive gas into plasma 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, 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 part> The substrate holder 4 includes a holder 41 and a rotation drive unit 42. The holder 41 holds a plurality of substrates W arranged in a circumferential direction. Although 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 a plurality of through holes 41a. The plurality of 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 toward the vertically downward side, and each substrate W is disposed 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 disposed vertically above the substrate holder 4 within the chamber 1. The heater 11 is controlled by the controller 6 and heats the multiple 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 a 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 section> 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 omitted 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, in the axial direction, a part of the circumferential direction of the movement path R1 of the substrate W. 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 a view in which the line of sight is along the axial direction. The target 21 has a first main surface 21a and a second main surface 21b. The second main surface 21b is the surface opposite to the first main surface 21a. 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 21a 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 21a of the target 21 is exposed to the inside of the chamber 1.

[0036] The material of the target 21 is 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 a sputtering gas to the sputtering space 1a. The sputtering gas is an inert gas, for example, a rare gas. For example, at least one of argon gas and xenon gas can be used as the rare 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 adjustment unit 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 a 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 part of this sputtering gas flows into the space between the moving 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 adjustment unit 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 adjustment unit 233 is, for example, a mass flow controller. Valve 232 and flow rate adjustment unit 233 are controlled by control unit 6.

[0039] <First plasma generating section> 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. Due to the collision, sputtered particles (e.g., aluminum particles) 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 generating unit 25 includes a first power supply 251. The first power supply 251 is controlled by the control unit 6 and supplies direct current or alternating current (high frequency) power for sputtering to the target 21. Here, since the target 21 is a conductive metal target, a direct current power supply can be applied as the first power supply 251. The first power supply 251 outputs a direct current 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 direct current voltage so that a negative potential is applied to the target 21. As exemplified in FIG. 1, the chamber 1 may be grounded. In addition, 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. The electric field acts on the sputtering gas, ionizing the sputtering gas into plasma. Ions in the plasma (e.g., argon ions) collide with the first main surface 21a of the target 21, and sputtering of the target 21 is performed. As a result, particles of the first element 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. 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.

[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 section> 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 adjustment unit 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 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 end of each of the two branches corresponds to the second air supply port 31a. In the example of FIG. 1, the two second air supply ports 31a are provided with a gap in the radial direction.

[0045] As the reactive gas, a gas containing a second element in the thin film 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 ) 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 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 can be formed on the main surface Wa of the substrate W.

[0046] Valve 312 is provided in air supply pipe 311 and opens and closes air supply pipe 311. Flow rate adjustment unit 313 is provided in air supply pipe 311 and adjusts the flow rate of the reactive gas flowing through air supply pipe 311. Flow rate adjustment unit 313 is, for example, a mass flow controller. Valve 312 and flow rate adjustment unit 313 are controlled by control unit 6.

[0047] In the following, a case where aluminum is used as the first element and nitrogen is used as the second element will be mainly described. Here, an aluminum target is used as the target 21, and nitrogen gas is used as the reactive gas.

[0048] <Second plasma generating section> The second plasma generating unit 33 turns the nitrogen gas supplied from the second gas supply port 31a into the chamber 1 into plasma. Highly reactive nitrogen active species generated by the plasma movement toward the substrate holding unit 4, and when they reach the main surface Wa of the substrate W moving in the plasma space 1b, they nitride the aluminum film on the main surface Wa.

[0049] In the example of FIG. 1, the second plasma generating unit 33 includes an inductive coupling antenna 331 and a second power source 332. The inductive coupling antenna 331 is provided vertically below the moving path R1 of the substrate W in the plasma space 1b. 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 below, 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 the both ends are electrically connected to the second power source 332. The conductive member 3311 functions as an electrode (antenna) for generating plasma.

[0050] 1 and 2, a plurality of (here, two) inductive coupling antennas 331 are provided, and each inductive coupling antenna 331 is provided near each 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 density of electrons of 3×1010 pieces / cm 3 This is a high density plasma.

[0052] <Control Unit> The control unit 6 controls various components of the sputtering apparatus 100. FIG. 4 is a block diagram showing an example of the configuration of the control unit 6. The control unit 6 is an electronic circuit device, and may have, for example, a data processing device 61 and a storage unit 62. The data processing device 61 may be an arithmetic processing device such as a CPU (Central Processor Unit). The storage unit 62 may have a non-transient storage unit (for example, a ROM (Read Only Memory)) 621 and a temporary storage unit (for example, a RAM (Random Access Memory)) 622. The non-transient storage unit 621 may store, for example, a program that specifies the processing to be executed by the control unit 6. The data processing device executes this program, so that the control unit 6 can execute the processing specified in the program. Of course, a part or all of the processing executed by the control unit 6 may be executed by a hardware circuit such as a logic circuit.

[0053] 4, the control unit 6 is electrically connected to the 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 for 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 sputtering equipment operation> 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. As will be described in detail later, the sputtering apparatus 100 operates according to 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. A specific description will be given below.

[0055] First, a substrate transport unit (not shown) transports a plurality of unprocessed substrates W into the chamber 1 (step S1). This causes the substrate holding unit 4 to hold the plurality of substrates W. Next, the suction mechanism 5 starts to suck gas from within the chamber 1 (step S2), and the heater 11 starts to heat the substrates W (step S3). The suction mechanism 5 adjusts the pressure within 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 the sputtering gas, and the reactive gas supply unit 31 starts supplying the reactive gas, while the first plasma generation unit 25 and the second plasma generation unit 33 convert the gas into plasma (step S4). Specifically, the control unit 6 opens the valves 232 and 312. As a result, the sputtering gas and the reactive gas are supplied in parallel into the chamber 1. The control unit 6 also starts outputting voltages to the first power source 251 and the second power source 332. Furthermore, the rotation drive unit 42 starts rotating the holder 41 around the revolution axis Q1 (step S5). As a result, the multiple substrates W revolve around the revolution axis Q1.

[0057] Here, 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, and the first power supply 251 and the second power supply 332 constantly output a voltage. Also, 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 1a and the plasma space 1b. That is, step S11 (sputtering step) in which the substrate holder 4 moves the substrate W so as to pass through the sputtering space 1a and step S12 (reaction step) in which the substrate holder 4 moves the substrate W so as to pass through the plasma space 1b 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 flying out 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 causes a second element to react with the first element film on the main surface Wa of the substrate W formed in step S11 (sputtering step). Specifically, active 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, and the second element penetrates 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 or not to end the process (step S13). For example, the control unit 6 may determine whether or not the number of times that a set of steps S11 and S12 have been performed is less than a preset specified number of times. If the number of times is less than the specified number of times, the control unit 6 executes 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 specified number of times is set to a value such that the film thickness of the aluminum nitride film reaches a target value, and may be set to, for example, several tens of times.

[0062] When the number of executions is equal to or greater than the specified number, the control unit 6 ends the film formation process. For example, the sputtering gas supply unit 23 stops supplying the sputtering gas, the reactive gas supply unit 31 stops supplying the reactive gas, the first power supply 251 and the second power supply 332 stop outputting, the substrate holder 4 stops revolving the substrate W, the heater 11 stops heating the substrate W, and the suction mechanism 5 stops suctioning the gas (step S6). Next, the substrate transport unit carries the substrate W that has been subjected to the film formation process out of 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 have 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 that show an example of a simulation result. FIG. 7 and FIG. 8 show a schematic diagram of a simulation result based on a first-principles calculation, showing a bond between an aluminum atom A1 and a nitrogen atom A2. FIG. 7 shows a simulation result in the case where an aluminum film is formed to a thickness of two atoms in step S11 (sputtering process) and the aluminum film is nitrided in step S12 (reaction process). That is, FIG. 7 shows a simulation result in the case where a film F1 is formed to a thickness of two atoms using only aluminum atoms A1, and a simulation is performed to nitride the film F1. FIG. 8 shows a simulation result in the case where an aluminum film is formed to a thickness of one atom in step S11 (sputtering process) and the aluminum film is 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 is 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 is also referred to as the (N+1)th atomic layer.

[0067] In FIG. 7 and FIG. 8, the result of the nitriding process at a certain processing time is shown, but in the actual simulation by the first principle calculation, the positional fluctuation of the aluminum atom A1 and the nitrogen atom A2 is calculated with the passage of time. When the inventor confirmed the positional fluctuation with the passage of time, the nitrogen atom A2 quickly bonded with the aluminum atom A1 in the first atomic layer. In other words, the nitriding of the first atomic layer was quickly completed. On the other hand, the nitrogen atom A2 had difficulty passing through the first atomic layer, and it took time to nitriding the second atomic layer. The inventor confirmed that nitrogen vacancies are likely to occur in the second atomic layer at least in a short processing time of about several picoseconds to several hundred picoseconds. In FIG. 7, nitrogen vacancies occur in the region DR1 of the second atomic layer, whereas in FIG. 8, no nitrogen vacancies occur and nitriding is completed in the entire thickness direction (vertical direction of the paper).

[0068] Since this simulation based on first-principles calculations can only perform calculations over a very short processing time, on the order of picoseconds as mentioned above, an experiment was conducted to confirm what thickness of aluminum film can actually be nitrided sufficiently. Here, the crystal quality of the aluminum nitride film formed on the main surface Wa of the substrate W is used as an index 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 crystal quality. The higher the crystal 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 half-width of the XRC and the processing time of the reaction process. Here, the experimental results are shown in a state where the temperature of the substrate W is 390 degrees Celsius, 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 source 251 is 0.5 kW, the input power of the second power source 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) when passing through the sputtering space 1a. Under these processing conditions, in step S11 (sputtering process), an aluminum film is formed on the main surface Wa of the substrate W with an average film thickness of 0.75 nm.

[0070] Since the diameter of an aluminum atom is about 0.25 nm, under the above-mentioned processing conditions, an aluminum film is formed with an average thickness of three atoms. That is, when the substrate W finishes passing through the sputtering space 1a, a film of the first element (here, aluminum) having 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 means the average thickness of the first element film in the target area of ​​the main surface Wa of the substrate W. The target area 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 shape on the main surface Wa of the substrate W, measures the reflected light, and measures the average thickness of the film in the spot based on the reflected light. In this case, the spot may correspond to the target area.

[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. In addition, the experiment was performed multiple times by changing the processing time of step S12 (reaction step). The processing time on the horizontal axis of FIG. 9 indicates the processing time in the reaction step. In other words, the 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, and sufficient crystal quality can be achieved. This value can satisfy, for example, the specifications of semiconductor devices that require high quality.

[0072] According to the relationship in Fig. 9, when the processing time is less than 20 seconds, the half-width decreases rapidly with increasing processing time, and 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 the 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. Also, if 0.5 deg is applied as the target value of the half-width, for example, the processing time may be set to about 50 seconds or more.

[0073] Incidentally, since the nitrogen atoms A2 are bonded to the aluminum atoms A1 in sequence from the surface side of the aluminum film, the processing time of step S12 (reaction process) 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 (for example, an aluminum film) with an average thickness of three atoms or less in each step S11 (sputtering process). Specifically, the moving 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 the first element film can be formed with an average thickness of three atoms or less, and the values ​​of the processing conditions are stored in the storage unit 63. These processing conditions can be set in advance, for example, by experiment or simulation. The control unit 6 reads out the values ​​of the moving speed and the input power from the storage unit 63, and controls various components of the sputtering apparatus 100 based on the processing conditions. As a result, the sputtering apparatus 100 can form a first element film (for example, an aluminum film) with an average thickness of three atoms or less in each step S11 (sputtering process).

[0075] Moreover, the sputtering apparatus 100 performs each step S12 (reaction step) with a processing time and input power of the second power source 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 allows the second element to react with the entire first atomic layer to the third atomic layer. For example, the moving speed of the substrate W passing 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 source 332, and the temperature of the substrate W are set in advance so as to achieve a target value of the crystal quality, and the processing conditions are stored in the storage unit 63. These processing conditions can be set in advance, for example, by experiments or simulations. The control unit 6 reads out the values ​​of these processing conditions from the storage 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 3 atoms or less in step S11 (sputtering process). Therefore, the sputtering apparatus 100 can react the entire first element film in the thickness direction 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 thickness of one atom or less. For example, the moving speed of the substrate W and the input power of the first power source 251 for forming a first element film with an average thickness of one atom or less are set in advance, and these processing conditions are set in the storage unit 63. The control unit 6 reads out 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 a first atomic layer on the main surface Wa of the substrate W in step S11 (sputtering process).

[0078] It has been confirmed by simulation that the second element can react more reliably with such a first element film (i.e., first atomic layer). That is, by the sputtering apparatus 100 forming the first element film with an average thickness of one atom or less in step S11 (sputtering process), the second element can react more reliably with the entire first element film in step S12 (reaction process). This is considered to be due to the following reason. That is, since the first atomic layer is located on the surface of the first element film, unlike the second atomic layer, it is not necessary for the second element to pass through other atomic layers in order to react with the second element and the first atomic layer.

[0079] FIG. 10 is a graph showing the relationship between the average film thickness and the half-width of the aluminum film formed in the sputtering process. FIG. 10 shows data obtained by an experiment. As shown in FIG. 10, as the average film thickness of the aluminum film formed in step S11 (sputtering process) increases, the half-width increases. In other words, FIG. 10 shows that as the average film thickness of the aluminum film increases, it becomes more difficult to nitride the aluminum film in the entire thickness direction. As shown in FIG. 10, when the average film thickness is one atom or less (0.25 nm in this case) the half-width is below 0.5 deg. In other words, if the average film thickness is one atom or less, the sputtering device 100 can sufficiently nitride the aluminum film. The aluminum nitride film at this time can satisfy, for example, the required quality for a semiconductor device. In other words, the sputtering device 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 of one atom or less in each sputtering process.

[0080] In addition, the processing time in step S12 (reaction process) increases logarithmically as the thickness of the first element film increases, so if the first element film is formed with an average thickness of one atom or less, the processing time can be significantly shortened. On the other hand, the thickness of the thin film (here, aluminum nitride film) that can be formed in one step S11 and step S12 is small, so the number of times that the set needs to be performed increases. However, the processing time in step S12 (reaction process) can be significantly shortened logarithmically. For example, compared to the case where the first element film is formed with an average thickness of three atoms, the processing time can be reduced to, for example, one tenth or less. Therefore, the processing time of the overall film formation process can be shortened. In other words, the throughput of the sputtering device 100 can be shortened.

[0081] In addition, since the second element easily reacts with the first element film, the processing condition in step S12 (reaction process) can be such that the input power of the second power source 332 can be reduced. This can suppress deterioration of the second power source 332.

[0082] <Average film thickness greater than 1 atom and less than 2 atoms> In step S11 (sputtering process), the sputtering apparatus 100 may form a first element film with an average thickness greater than one atom and equal to or less than two atoms. For example, the moving speed of the substrate W and the input power of the first power source 251 for forming a first element film with an average thickness greater than one atom and equal to or less than two atoms are set in advance, and the values ​​of these processing conditions are set in the storage unit 63. The control unit 6 reads out 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 with an average thickness greater than one atom and equal to or 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 source 332 for the reaction of the second atomic layer will be considered.

[0084] 11 is a graph showing the relationship between the half-width of the XRC and the input power of the second power supply 332. Here, experimental results are shown in a state where the temperature of the substrate W is 390 degrees Celsius, the pressure in the chamber 1 is 0.5 Pa, nitrogen gas is used as the reactive gas, and the input power of the first power supply 251 is 0.5 kW. The movement speed of the substrate W is set to a value that allows an aluminum film having an average thickness of 0.29 nm to be formed 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 half-width decreases relatively rapidly with an increase in the treatment time, and when the input power of the second power source 332 is 3 kW or more, the half-width becomes almost zero. In other words, if 3 kW is considered to be a critical value, it can be seen that when the treatment time is equal to or more than the critical value, the crystal quality can be maintained significantly high.

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

[0087] As a result, the sputtering apparatus 100 can react the first element film formed in step S11 (sputtering step) with the second element over the entire thickness direction of the first element film in step S12 (reaction step). Therefore, the sputtering apparatus 100 can 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 larger 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 driving unit .

[0089] As described above, the sputtering apparatus 100 and the reactive sputtering method have been described in detail, but 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 appropriately combined or omitted as long as they are not mutually contradictory.

[0090] For example, in the above example, the substrate W revolves around the revolution axis Q1, and passes through the sputtering space 1a and the plasma space 1b alternately. However, this is not necessarily limited to this. For example, the substrate W may move back and forth between the sputtering space 1a and the plasma space 1b that are aligned in a straight line. [Explanation of symbols]

[0091] 1a Sputtering space 1b Plasma space 21 Target W substrate Wa Main surface

Claims

1. 1. A reactive sputtering method for forming a thin film including a first element and a second element on a main surface of a substrate, comprising: a sputtering step of moving the substrate 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 film thickness of 3 atoms or less to form a first element film on the main surface; a reaction step, which is performed after the sputtering step, of moving the substrate through a plasma space in which a reactive gas containing the second element is plasmatized, thereby causing the first element film on the main surface of the substrate to react with the second element; and repeating the steps of:

2. 2. The reactive sputtering method of claim 1, a sputtering step of depositing a film of the first element on the main surface of the substrate to an average thickness of one atom or less.

3. 2. The reactive sputtering method of claim 1, In the sputtering step, the first element film is formed on the main surface of the substrate to an average thickness greater than one atom and less than or equal to two atoms; In the reaction step, A reactive sputtering method, comprising converting the reactive gas into plasma with an input power of 3 kW or more.

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