DC sputtering device

Abstract

Provided is technology capable of performing DC sputtering using a gallium target while reducing metal contamination. This DC sputtering device comprises: a substrate holding part that holds a substrate; a target container that holds a gallium target including gallium so as to face a main surface of the substrate in a first direction; a DC power supply that applies DC power to the gallium target; and a conductor that has one end connected to a negative electrode side of the DC power supply and the other end in contact with the gallium target in the target container, the conductor being formed of a gallium corrosion resistant metal. In addition, the DC sputtering device includes: a sputtering gas supply unit having a gas supply port for supplying a sputtering gas between the target container and the substrate holding part; and a magnet unit which is positioned on the opposite side of the target container from the substrate holding part, and forms, on the surface of the gallium target on one side in the first direction, an annular high-density plasma region in which the density of the plasma-converted sputtering gas is higher than the periphery.

Description

DC sputtering equipment

[0001] The subject matter disclosed herein relates to a DC sputtering apparatus.

[0002] Gallium nitride (GaN) used in power devices or LEDs is sometimes deposited by vacuum deposition, typically MOCVD. GaN deposition by MOCVD uses triethylgallium (TEG), ammonia (NH ３ ), which has a large environmental impact. In addition, more than 90% of these gases may be exhausted, resulting in low gas usage efficiency. In contrast, sputtering, which is one of the vacuum film deposition methods, is a technology in which positive ions are implanted into a solid sputtering target and a film is formed using the sputtered particles. Sputtering is usually performed using argon (Ar) and nitrogen (N ２ ) and uses metal or solid compounds as targets, so film formation costs and environmental impact are low.

[0003] As the sputtering target, a gallium nitride (GaN) sintered target or metallic gallium can be used. Because GaN sintered targets are insulating, they require sputtering using a high-frequency RF power source, resulting in a low film formation rate and low productivity. On the other hand, when metallic gallium is used as the sputtering target, its conductivity allows direct current (DC) sputtering, improving productivity. Therefore, from the viewpoint of productivity, a gallium target is more preferable as a sputtering target than a GaN sintered target.

[0004] Gallium has a melting point of 29.76°C, so it melts due to the heat during sputtering. Therefore, a target container capable of storing liquid gallium is required. Patent Document 1 discloses the use of a conductive container made of copper (Cu) or the like. Since a conductive container is used, when electricity is applied to the target container, electricity is also applied to the metallic gallium, making it possible to perform sputtering.

[0005] JP 2015-229782 A

[0006] However, because liquid metallic gallium is highly corrosive to other metals, when a metal container is used as in Patent Document 1, the container itself may become embrittled or the container material may dissolve into the gallium. If other metals dissolve into the gallium target, the other metals may be incorporated into the gallium film as impurities, which may cause deterioration of the film quality and ultimately deterioration of the device performance.

[0007] An object of the present invention is to provide a technique that enables DC sputtering using a gallium target while reducing metal contamination.

[0008] In order to solve the above problem, a first aspect is a DC sputtering apparatus comprising: a substrate holding unit that holds a substrate; a target vessel that holds a gallium target so as to face a main surface of the substrate in a first direction; a DC power supply that applies DC power to the gallium target; a conductor that has one end connected to the negative electrode of the DC power supply and the other end in contact with the gallium target in the target vessel, the conductor being formed of a gallium corrosion-resistant metal; a sputtering gas supply unit that has an inlet for supplying sputtering gas between the target vessel and the substrate holding unit; and a magnet unit that is located on the opposite side of the substrate holding unit with respect to the target vessel and forms an annular high-density plasma region on one side of the gallium target in the first direction, in which the density of the plasmatized sputtering gas is higher than that of the surrounding area.

[0009] A second aspect is the DC sputtering apparatus of the first aspect, wherein the conductor contains molybdenum, copper, or stainless steel as a main component.

[0010] A third aspect is the DC sputtering apparatus of the first or second aspect, wherein the target vessel is made of a ceramic material.

[0011] A fourth aspect is the DC sputtering apparatus of the third aspect, wherein the target vessel is formed from a ceramic material containing gallium nitride, aluminum nitride, or boron nitride as a main component.

[0012] A fifth aspect is the DC sputtering apparatus of any one of the first to fourth aspects, wherein the conductor is disposed away from the high-density plasma region in a second direction intersecting the first direction.

[0013] A sixth aspect is a DC sputtering apparatus according to any one of the first to fifth aspects, wherein the magnet portion includes a ring-shaped first permanent magnet, and the conductor is positioned away from the first permanent magnet in a second direction that intersects the first direction.

[0014] A seventh aspect is a DC sputtering apparatus according to any one of the first to sixth aspects, wherein the target container comprises a container body in which the gallium target is accommodated, and a concave passage portion that communicates with the inside of the container body and extends in a second direction that intersects the first direction, and the other end of the conductor is arranged within the passage portion.

[0015] An eighth aspect is a DC sputtering apparatus according to the seventh aspect, wherein the target vessel further comprises a cover portion covering an opening on one side of the passage portion in the first direction, and the other end of the conductor is positioned in the portion of the passage portion covered by the cover portion.

[0016] A ninth aspect is the DC sputtering apparatus according to any one of the first to eighth aspects, wherein the sputtering gas contains argon.

[0017] A tenth aspect is a DC sputtering apparatus according to any one of the first to ninth aspects, further comprising a reactive gas supply unit that supplies a reactive gas, wherein the reactive gas supply unit supplies the reactive gas so that the gallium deposited on the main surface of the substrate reacts with the reactive gas plasma.

[0018] An eleventh aspect is the DC sputtering apparatus of the tenth aspect, wherein the reactive gas contains nitrogen.

[0019] A twelfth aspect is a DC sputtering apparatus according to any one of the first to eleventh aspects, wherein the target vessel has a bottom surface and a side surface that hold the gallium target inside, and the conductor penetrates the target vessel at the bottom surface or the side surface.

[0020] According to the DC sputtering apparatus of the first to twelfth aspects, DC power can be applied directly to the gallium target via a conductor made of a gallium corrosion-resistant metal, without using a target vessel, thereby enabling DC sputtering using the gallium target while reducing metal contamination.

[0021] According to the DC sputtering apparatus of the third aspect, the target vessel is made of a ceramic material, so that metal contamination due to the target vessel can be reduced.

[0022] According to the DC sputtering apparatus of the fifth aspect, sputtering of the conductor can be reduced, and therefore metal contamination due to the conductor can be reduced.

[0023] According to the DC sputtering apparatus of the sixth aspect, sputtering of the conductor can be reduced, and therefore metal contamination due to the conductor can be reduced.

[0024] According to the DC sputtering apparatus of the seventh aspect, the conductor can be separated from the high density plasma region, thereby reducing sputtering of the conductor.

[0025] According to the DC sputtering apparatus of the eighth aspect, the conductor can be prevented from being exposed to high density plasma, thereby reducing sputtering of the conductor.

[0026] FIG. 1 is a side view schematically showing an example of the configuration of a DC sputtering apparatus according to a first embodiment. FIG. 2 is a plan view schematically showing an example of the configuration of the DC sputtering apparatus shown in FIG. 1. FIG. 3 is a perspective view schematically showing an example of the configuration of a substrate holding unit and a heater shown in FIG. 1. FIG. 4 is a schematic cross-sectional view showing a target container of the sputtering unit shown in FIG. 1. FIG. 5 is a plan view of the target container of the sputtering unit shown in FIG. 1, viewed from vertically above. FIG. 6 is a block diagram showing the hardware configuration of a control unit shown in FIG. 1. FIG. 7 is a flowchart showing an example of the operation of a DC sputtering apparatus. FIG. 8 is a flowchart showing processes performed on one substrate by the operation of a DC sputtering apparatus. FIG. 9 is a schematic cross-sectional view of a target container according to a second embodiment. FIG. 10 is a plan view of the target container according to the second embodiment, viewed from vertically above. FIG. 11 is a diagram showing a target container according to a third embodiment.

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the components described in the embodiment are merely examples and are not intended to limit the scope of the present invention. In the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary to facilitate understanding.

[0028] 1. First Embodiment Fig. 1 is a side view schematically showing an example of the configuration of a DC sputtering apparatus 100 according to a first embodiment. Fig. 2 is a plan view schematically showing an example of the configuration of the DC sputtering apparatus 100 shown in Fig. 1. Fig. 1 is a view schematically showing a cross section of the DC sputtering apparatus 100 taken along a plane along the bent line A-A shown in Fig. 2.

[0029] The DC sputtering apparatus 100 is a film formation apparatus that performs a film formation process on a substrate W by reactive sputtering. Specifically, the DC sputtering apparatus 100 forms a thin film containing a first element and a second element on the main surface Wa of the substrate W. Specifically, the first element is gallium (Ga). The second element is, for example, oxygen (O) or nitrogen (N). When the first element is gallium and the second element is nitrogen, the DC sputtering apparatus 100 forms a gallium nitride film on the main surface Wa of the substrate W. The substrate W is, for example, a substrate made of sapphire, silicon (Si), silicon carbide (SiC), or the like. 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.

[0030] The DC sputtering apparatus 100 includes a chamber 1, a sputtering unit 2, a plasma unit 3, a substrate holder 4, a suction mechanism 5, and a control unit 6. The chamber 1 has a hollow box shape. The internal space of the chamber 1 corresponds to a processing space where a film formation process is performed on a substrate W. The chamber 1 is a vacuum chamber, and is a container that can be sealed so that a vacuum state can be maintained. The chamber 1 is provided with a loading / unloading mechanism (not shown). The loading / unloading mechanism can switch the internal state of the chamber 1 between a communicating state connected to the outside space and a sealed state isolated from the outside space. In the communicating state, a substrate transport unit (not shown) loads an unprocessed substrate W into the chamber 1. In the sealed state, the DC sputtering apparatus 100 performs a film formation process on the substrate W. Next, the loading / unloading mechanism connects the chamber 1 to the outside, and in this communicating state, the substrate transport unit unloads the processed substrate W from the chamber 1.

[0031] The suction mechanism 5 has a suction port 5a. The suction port 5a opens into the processing space. The suction mechanism 5 is controlled by a control unit 6. The suction mechanism 5 reduces the pressure inside the chamber 1 by sucking gas through the suction port 5a, and adjusts the pressure to within a predetermined reduced pressure range. The suction mechanism 5 is, for example, a vacuum pump, and a more specific example is a turbomolecular pump.

[0032] The processing space within the chamber 1 includes a sputtering space 1a and a plasma space 1b. The sputtering space 1a and the plasma space 1b are aligned along the circumferential direction about a predetermined revolution axis Q1. The revolution axis Q1 is an axis extending along the vertical direction. A physical structure (e.g., a partition plate) may be provided within the chamber 1 to separate the sputtering space 1a and the plasma space 1b.

[0033] A gallium target 21 is disposed in the sputtering space 1a. In the sputtering space 1a, sputtering is performed on the gallium target 21. The gallium target 21 contains gallium as a first element. A reactive gas is supplied to the plasma space 1b by the plasma unit 3. The reactive gas contains a second element (e.g., nitrogen). The plasma unit 3 converts the reactive gas into plasma.

[0034] The substrate holder 4 is disposed in the chamber 1. The substrate holder 4 holds the substrate W and revolves the substrate W around the revolution axis Q1, thereby moving the substrate W alternately between the sputtering space 1 a and the plasma space 1 b.

[0035] 3 is a perspective view schematically illustrating an exemplary configuration of the substrate holder 4 and heater 11 shown in FIG. 1. In the example of FIG. 3, the substrate holder 4 holds multiple (six in this example) substrates W arranged in a circumferential direction about the revolution axis Q1. Note that it is not essential that the substrate holder 4 be able to hold multiple substrates W simultaneously. The substrate holder 4 may be configured to hold only a single substrate W. The substrate holder 4 holds the substrates W in a horizontal position. A horizontal position refers to a position in which the thickness direction of the substrate W (the normal direction to the main surface Wa) is aligned vertically. When multiple substrates W are held by the substrate holder 4, the main surface Wa (the lower surface in FIG. 3) of each substrate W is exposed within the chamber 1 (see FIG. 1).

[0036] The substrate holder 4 revolves the substrate W around the revolution axis Q1, causing each substrate W to alternately pass through the sputtering space 1a and the plasma space 1b. In other words, the substrate holder 4 moves the substrate W so that the substrate W alternately passes through the sputtering space 1a and the plasma space 1b. When the substrate W passes through the sputtering space 1a, gallium particles from the gallium target 21 are deposited on the main surface Wa of the substrate W. 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 the plasma generation of the reactive gas react with gallium atoms on the main surface Wa of the substrate W. As a result, a predetermined thin film containing gallium and the second element is formed on the main surface Wa of the substrate W.

[0037] Hereinafter, the direction in which the revolution axis Q1 extends may be referred to as the "axial direction," the direction of rotation about the revolution axis Q1 may be referred to as the "circumferential direction," and the direction in which a straight line perpendicular to the axial direction extends may be referred to as the "radial direction." The axial direction is an example of the "first direction." The radial direction is an example of the "second direction."

[0038] <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 at intervals in the circumferential direction. The holder 41 has, for example, a disk shape centered on the revolution axis Q1. Multiple through holes 41a may be formed in the holder 41. The multiple through holes 41a are formed, for example, at equal intervals along the circumferential direction and penetrate the holder 41 in the axial direction. Each through hole 41a has a stepped shape that narrows vertically downward. One substrate W is placed in each through hole 41a. The holder 41 supports the periphery of each substrate W at the stepped portion of each through hole 41a.

[0039] The rotation drive unit 42 is controlled by the control unit 6. The rotation drive unit 42 rotates the holder 41 about the revolution axis Q1. As a result, the multiple substrates W held by the holder 41 revolve around the revolution axis Q1. The rotation drive unit 42 has, for example, a motor and a shaft. The motor is connected to the holder 41 via the shaft. The upper end of the shaft is connected to the underside of the holder 41 and extends along the revolution axis Q1. The motor rotates the shaft about the revolution axis Q1, thereby rotating the holder 41 about the revolution axis Q1.

[0040] The heater 11 heats the plurality of substrates W held by the substrate holder 4. The heater 11 adjusts the temperature of the substrates W to within a temperature range suitable for film formation processing. The heater 11 is controlled by the controller 6. The heater 11 is located vertically above and spaced apart from the substrate holder 4 within the chamber 1. The heater 11 has, for example, a circular ring shape centered on the revolution axis Q1. The heater 11 may be, for example, an electric resistance heater including an electric heating wire, or an optical heater including a light source that irradiates the substrates W with heating light (e.g., infrared light).

[0041] The sputtering unit 2 has a gallium target 21, a sputtering gas supply unit 23, and a first plasma generation unit 25. Note that the sputtering gas supply unit 23 and the first plasma generation unit 25 are not shown in FIG.

[0042] The gallium target 21 is disposed in the sputtering space 1a and faces the substrate holding unit 4 in the axial direction (first direction). More specifically, the gallium 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 shown in FIG. 1 , the gallium target 21 is positioned vertically below the substrate holding unit 4.

[0043] The gallium target 21 has, for example, a plate-like shape, and in the example shown in FIG. 2 , has a circular 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 gallium target 21 has a main surface 21a facing vertically upward. The gallium target 21 is held by a target vessel 22. The target vessel 22 holds the gallium target 21 in an orientation in which the main surface 21a of the gallium target 21 faces the substrate holder 4. The main surface 21a of the target 21 is a surface of the target 21 on one side in the axial direction (first direction). With the gallium target 21 held by the target vessel 22, the main surface 21a of the gallium target 21 is exposed within the chamber 1.

[0044] <Sputtering Gas Supply Unit> The sputtering gas supply unit 23 supplies sputtering gas to the sputtering space 1a. The sputtering gas is an inert gas, such as a rare gas. The rare gas may be, for example, argon gas or xenon gas. In the example shown in FIG. 1 , the sputtering gas supply unit 23 includes multiple (two in this example) gas supply pipes 231, a valve 232, a flow rate adjuster 233, and a common pipe 234. The upstream end of each gas supply pipe 231 is connected to the downstream end of one common pipe 234. The upstream end of the pipe 234 is connected to a sputtering gas supply source 235. The sputtering gas supply source 235 supplies sputtering gas to the upstream end of the common pipe 234. The gas supply pipe 231 includes a first gas supply port 23a that opens into the sputtering space 1a. The sputtering gas flows through the common pipe 234 and each gas supply pipe 231, and flows out from the first gas supply port 23a into the sputtering space 1a. A part of this sputtering gas flows into the space between the movement path R1 of the substrate W and the gallium target 21.

[0045] The valve 232 is provided in the common pipe 234 and opens and closes the common pipe 234. The flow rate adjustment unit 233 is provided in the common pipe 234 and adjusts the flow rate of the sputtering gas flowing through the common pipe 234. The flow rate adjustment unit 233 is, for example, a mass flow controller. The valve 232 and the flow rate adjustment unit 233 are controlled by the control unit 6.

[0046] <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 main surface 21a of the gallium target 21. This collision causes sputtered particles (here, gallium particles) to fly out from the main surface 21a of the gallium target 21. The sputtered particles move vertically upward toward the substrate holding unit 4.

[0047] In the example shown in FIG. 1 , the first plasma generation unit 25 has a first power supply 251, which is a DC power supply. The first power supply 251 is controlled by the control unit 6. The first power supply 251 supplies DC power for sputtering to the gallium target 21. The first power supply 251 outputs a DC voltage, for example, between the gallium target 21 and the chamber 1. More specifically, the first power supply 251 has, for example, a switching power supply circuit (not shown), and applies DC power so that a negative potential is applied to the gallium target 21. As shown in FIG. 1 , the chamber 1 may be grounded. Furthermore, the substrate holder 4 may be electrically connected to the chamber 1.

[0048] When the first power supply 251 supplies DC power to the gallium target 21, an electric field for plasma is generated around the gallium 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 main surface 21a of the gallium target 21, causing sputtering of the gallium target 21. That is, gallium particles fly out from the gallium target 21 and move toward the movement path R1 of the substrate W. When the gallium particles 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 gallium film (hereinafter referred to as a "gallium film") is formed on the main surface Wa of the substrate W.

[0049] 1, the sputtering unit 2 has a chimney 27. The chimney 27 is provided in the sputtering space 1a. The chimney 27 has a hollow box shape and surrounds the periphery of the gallium target 21. An upper plate portion 271 of the chimney 27 has an opening 27a that faces the gallium target 21 in the axial direction. The opening 27a penetrates the upper plate portion 271 in the axial direction. Gallium particles that fly out from the main surface 21a of the gallium target 21 pass through the opening 27a and move toward the substrate holding unit 4.

[0050] FIG. 4 is a schematic cross-sectional view showing the target vessel 22 of the sputtering unit 2 shown in FIG. 1. FIG. 5 is a plan view of the target vessel 22 of the sputtering unit 2 shown in FIG. 1, viewed vertically from above. As shown in FIG. 4, the target vessel 22 has a shallow, bottomed cylindrical shape. In other words, the target vessel 22 has a bottom surface for holding the gallium target 21 and an annular side surface rising vertically upward from the periphery of the bottom surface. Since the melting point of gallium is 29.76°C, the gallium target 21 may melt due to heat during sputtering, or may be partially liquefied even at room temperature. For this reason, the target vessel 22 has a shape that allows the liquid gallium target 21 to be stored inside.

[0051] The target vessel 22 is preferably made of a ceramic material. Specifically, the target vessel 22 may be made of a ceramic material containing gallium nitride, aluminum nitride, or boron nitride as its main component. If the target vessel 22 is made of aluminum or boron nitride, which are both III-V group III-V nitrides of gallium, the effect on the gallium nitride film device can be reduced compared to when other metal nitrides are used.

[0052] If a conductive container is used as the target container 22, gallium in a liquid state is highly corrosive to other metals, causing embrittlement of the container itself and elution of the container material into the gallium target 21. If other metals elute into the gallium target 21, they may be incorporated as impurities into the gallium film, causing deterioration of film quality and device performance. The possibility of elution can be reduced by using, for example, molybdenum as a metal that is resistant to gallium corrosion, but it is a rare metal that is expensive and has high hardness, making it difficult to process.

[0053] If the target vessel 22 is made of molybdenum, when the gallium target 21 in the vessel decreases due to continuous film formation, the liquid gallium will sway, exposing the vessel bottom, and the molybdenum in the vessel material may be sputtered and contaminate the gallium film. In addition, because the same potential as the gallium target 21 is applied to the molybdenum, there is a possibility that the molybdenum will be incorporated into the gallium film by sputtering with argon ions.

[0054] The sputtering unit 2 includes a magnet unit 28. The magnet unit 28 is located on the opposite side of the target vessel 22 from the substrate holder 4. The magnet unit 28 includes a ring-shaped (circular ring) first permanent magnet 281 and a second permanent magnet 282 positioned radially inside the first permanent magnet 281. The positive pole of the first permanent magnet 281 faces vertically upward, and the positive pole of the second permanent magnet 282 faces vertically downward. The magnet unit 28 forms magnetic field lines on the main surface 21a of the gallium target 21, directing from the first permanent magnet 281 to the second permanent magnet 282. Electrons in the plasma generated by the first plasma generation unit 25 are held near the main surface 21a of the gallium target 21 by the magnetic field lines and accelerated (EB drift). The electrons, having gained high energy due to the drift, collide with argon gas, the sputtering gas, generating electrons and argon ions. As a result, a circular high-density plasma region PA1 is formed on the main surface 21a of the gallium target 21, where argon gas plasma exists at a high concentration.

[0055] The first permanent magnet 281 does not necessarily have to be formed in a circular ring shape, and may be formed in a ring shape other than a circular ring. That is, the first permanent magnet 281 may have any shape as long as it can form a closed loop-shaped high-density plasma region. For example, the first permanent magnet 281 may be formed in a racetrack shape (an oval shape, or a rounded rectangular shape consisting of two parallel lines (straight portions) of equal length and two semicircles (corner portions)).

[0056] A cooling vessel 29 is disposed vertically below the target vessel 22. The cooling vessel 29 cools the target vessel 22, thereby cooling the gallium target 21. Cooling water 291 is stored in the cooling vessel 29. The first permanent magnet 281 and the second permanent magnet 282 are disposed in the cooling vessel 29. The cooling water 291 in the cooling vessel 29 can be replaced by a pump (not shown).

[0057] 4, the first plasma generation unit 25 has a conductor 253. The conductor 253 has a metal conductor. One end of the conductor 253 is connected to the negative electrode side of a first power source 251, which is a DC power source, and the other end of the conductor 253 is connected to the gallium target 21. That is, the other end of the conductor 253 is immersed in liquid gallium obtained by liquefying the gallium target 21.

[0058] The metal lead wire of the conductor 253 is formed of a gallium corrosion-resistant metal. The gallium corrosion-resistant metal may be molybdenum, copper, or stainless steel. Titanium or a nickel alloy may also be used as the gallium corrosion-resistant metal. By using a gallium corrosion-resistant metal, corrosion of the conductor 253 by the gallium target 21 can be prevented. Furthermore, the conductor 253 is preferably coated with an insulating material such as resin. This reduces sputtering of the conductor 253.

[0059] As shown in FIG. 4 , the other end of the conductor 253 is disposed radially outside the annular high-density plasma region PA1. The high-density plasma region PA1 is a region where positive ions of the sputtering gas (argon) are present at a high density. Therefore, by disposing the conductor 253 outside the high-density plasma region PA1, sputtering of the conductor 253 can be reduced. This reduces metal contamination of the gallium film by the conductor 253.

[0060] 5, the other end of the conductor 253 is disposed radially outward from the outer peripheral end of the annular first permanent magnet 281. Magnetic field lines are generated from the first permanent magnet 281 toward the inner second permanent magnet 282. Therefore, by disposing the conductor 253 outside the first permanent magnet 281, sputtering of the conductor 253 can be further reduced.

[0061] <Plasma Unit> Returning to Figure 1, the plasma unit 3 has a second gas inlet 31a that opens into the plasma space 1b. The plasma unit 3 supplies a reactive gas from the second gas inlet 31a to the plasma space 1b. The plasma unit 3 also converts the reactive gas in the plasma space 1b into plasma. Specifically, the plasma unit 3 has a reactive gas supply unit 31 and a second plasma generation unit 33.

[0062] <Reactive Gas Supply Unit> In the example shown in FIG. 1 , the reactive gas supply unit 31 includes a plurality of (two in this example) gas supply pipes 311, valves 312, flow rate adjusters 313, and a common pipe 314. The upstream end of each gas supply pipe 311 is connected to the downstream end of one common pipe 314. The upstream end of the common pipe 314 is connected to a reactive gas supply source 315. The reactive gas supply source 315 supplies reactive gas to the upstream end of the common pipe 314. Each gas supply pipe 311 includes a second gas supply port 31a. In the example shown in FIG. 1 , the opening direction of the second gas supply port 31a in the gas supply pipe 311 is parallel to the axial direction and toward the substrate holder 4. In the example shown in FIG. 1 , the downstream end of each gas supply pipe 311 corresponds to the second gas supply port 31a. In the example shown in FIG. 1 , the two second gas supply ports 31a are provided at a radial interval.

[0063] As the reactive gas, a gas containing a second element in the thin film to be formed on the main surface Wa of the substrate W can be used. The second element is, for example, nitrogen. As a specific example, the reactive gas is nitrogen (N ２ ) gas and ammonia (NH ３ For example, when the reactive gas is nitrogen, a gallium nitride film is formed on the main surface Wa of the substrate W. The reactive gas may also include at least one of oxygen (O ２When the reactive gas is oxygen, a gallium oxide film can be formed on the main surface Wa of the substrate W. Note that the following description will mainly focus on the case where nitrogen gas is used as the reactive gas.

[0064] The valve 312 is provided in the common pipe 314 and opens and closes the common pipe 314. The flow rate adjustment unit 313 is provided in the common pipe 314 and adjusts the flow rate of the reactive gas flowing through the common pipe 314. The flow rate adjustment unit 313 is, for example, a mass flow controller. The valve 312 and the flow rate adjustment unit 313 are controlled by the control unit 6.

[0065] <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 gallium film on the main surface Wa.

[0066] 1, the second plasma generation unit 33 has an inductive coupling antenna 331 and a second power supply 332. The inductive coupling antenna 331 is located in the plasma space 1b vertically below the movement path R1 of the substrate W. The inductive coupling antenna 331 has a substantially U-shaped conductive member 3311 that is convex vertically upward.

[0067] The conductive member 3311 is provided in the chamber 1 with both ends positioned vertically downward. The conductive member 3311 is attached to the bottom of the chamber 1. In the example shown in Fig. 2, the conductive member 3311 is provided with both ends aligned in the circumferential direction. Both ends of the conductive member 3311, for example, penetrate the bottom of the chamber 1, and the both ends are electrically connected to the second power source 332. The conductive member 3311 functions as an electrode (antenna) for generating plasma.

[0068] 1 and 2, multiple (two in this example) inductive coupling antennas 331 are provided, and each inductive coupling antenna 331 is provided near a corresponding second air supply port 31a. In the example shown in Figures 1 and 2, the inductive coupling antenna 331 is provided so as to face the second air supply port 31a of the air supply pipe 311 in the axial direction. In other words, the second air supply port 31a is located between both ends of the inductive coupling antenna 331 (the conductive member 3311) in the radial direction.

[0069] The second power supply 332 supplies high-frequency power to the inductively coupled antenna 331. The second power supply 332 has, for example, an inverter circuit and a matching circuit, and is controlled by the control unit 6. When the second power supply 332 applies a high-frequency voltage to both ends of the inductively coupled antenna 331, a high-frequency induction magnetic field for generating plasma is generated around the inductively coupled antenna 331, 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.

[0070] <Controller> Fig. 6 is a block diagram showing the hardware configuration of the controller 6 shown in Fig. 1. The controller 6 is an electronic circuit device that controls the operation of each component in the DC sputtering apparatus 100. The controller 6 includes a processor 61 and a memory 62. The memory 62 is electrically connected to the processor 61 via a bus line (not shown).

[0071] The processor 61 includes, for example, a CPU (Central Processor Unit). The memory 62 includes a ROM (Read Only Memory), which is a read-only memory that stores a basic program, and a RAM (Random Access Memory), which is a readable and writable memory that stores various information. The memory 62 may also include storage such as a hard disk drive (HDD) or a solid-state drive (SSD).

[0072] The memory 62 stores a computer program P and setting data. The computer program P is provided to the control unit 6 via a recording medium or a network line such as the Internet. The setting data is recipe data that indicates the processing conditions to be performed by the DC sputtering apparatus 100. The processor 61 executes processing in accordance with the computer program P and setting data, and the control unit 6 controls the DC sputtering apparatus 100. This allows the film formation process on the substrate W to proceed.

[0073] The control unit 6 is electrically connected to a display 661 and an input device 662. The display 661 is a device that displays various information, such as a liquid crystal display device. The input device 662 is a device that allows a user to input commands to the control unit 6, such as a mouse and keyboard. Note that the display 661 may function as the input device 662 by providing a touch panel on the display 661.

[0074] The control unit 6 is electrically connected to the heater 11, the valve 232, the flow rate adjustment unit 233, the first power source 251, the valve 312, the flow rate adjustment unit 313, the second power source 332, the rotation drive unit 42, and the suction mechanism 5, and controls the operation of these components.

[0075] <Example of Operation of Sputtering Apparatus> Fig. 7 is a flowchart showing an example of the operation of the DC sputtering apparatus 100. Fig. 8 is a flowchart showing the steps performed on one substrate W by the operation of the DC sputtering apparatus 100. By operating the DC sputtering apparatus 100 according to the flowchart of Fig. 7, step S11 (sputtering step) and step S12 (reaction step) of Fig. 8 are repeatedly performed on each substrate W.

[0076] First, a substrate transport unit (not shown) transports a plurality of unprocessed substrates W into the chamber 1 (step S1). As a result, the substrate holder 4 holds the plurality of substrates W. Next, the suction mechanism 5 starts to suction gas from the chamber 1 (step S2), and the heater 11 starts to heat the substrates W (step S3). The suction mechanism 5 adjusts the pressure in the chamber 1 to within a reduced pressure range suitable for the film formation process. The heater 11 adjusts the temperature of the substrates W to within a temperature range suitable for the film formation process.

[0077] Next, the sputtering gas supply unit 23 supplies sputtering gas, and the reactive gas supply unit 31 begins supplying reactive gas. The first plasma generator 25 and the second plasma generator 33 then convert the gas into plasma (step S4). Specifically, the control unit 6 opens the valves 232 and 312. This causes the sputtering gas and reactive gas to be supplied in parallel into the chamber 1. The control unit 6 also controls the first power supply 251 and the second power supply 332 to output voltages. Furthermore, the rotation drive unit 42 rotates the holder 41 around the revolution axis Q1 (step S5). This causes the multiple substrates W to revolve around the revolution axis Q1.

[0078] 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.

[0079] 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.

[0080] In step S11 (sputtering step), the DC sputtering apparatus 100 deposits gallium particles from the gallium target 21 on the main surface Wa of the substrate W. Specifically, by sputtering the gallium target 21, gallium particles flying out from the gallium target 21 move toward the substrate W, and adhere to the main surface Wa of the substrate W while the gallium particles are moving. As a result, a gallium film is formed on the main surface Wa of the substrate W.

[0081] In the next step S12 (reaction step), the DC sputtering apparatus 100 reacts the second element with the gallium 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 gallium film on the main surface Wa of the substrate W, and the second element penetrates into the gallium film. Here, since the reactive gas is nitrogen, the gallium film on the main surface Wa of the substrate W is nitrided.

[0082] Next, the control unit 6 determines whether to terminate 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 executed is less than a predetermined number. If the number of times is less than the predetermined number, the control unit 6 executes step S11 again. This causes the DC sputtering apparatus 100 to continue the film formation process on the substrate W. By repeating the set of steps S11 and S12, gallium 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 gallium nitride film reaches a target value, and may be set to, for example, several tens of times.

[0083] If the number of executions is equal to or greater than the specified number, the control unit 6 terminates the film formation process. Specifically, the supply of sputtering gas by the sputtering gas supply unit 23, the supply of reactive gas by the reactive gas supply unit 31, the output of power by the first power supply 251 and the second power supply 332, the revolution of the substrate W by the substrate holder 4, the heating of the substrate W by the heater 11, and the suction of gas by the suction mechanism 5 are all stopped (step S6). Then, the substrate transport unit unloads the substrate W that has been subjected to the film formation process from the chamber 1 (step S7).

[0084] As described above, the DC 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 DC sputtering apparatus 100 can form a thin gallium nitride film on the main surface Wa of the substrate W.

[0085] As described above, the DC sputtering apparatus 100 includes the substrate holding unit 4 that holds the substrate W, the target vessel 22 that holds the gallium target 21 so as to face the main surface Wa of the substrate W in the first direction (axial direction), a DC power supply (first power supply 251) that applies DC power to the gallium target 21, a conductor 253 that has one end connected to the negative pole of the DC power supply and the other end in contact with the gallium target 21 in the target vessel 22, and is made of a corrosion-resistant gallium metal, a sputtering gas supply unit 23 that has an inlet (first inlet 23 a) that supplies sputtering gas between the target vessel 22 and the substrate holding unit 4, and a magnet unit 28 that is located on the opposite side of the substrate holding unit 4 with respect to the target vessel 22 and forms an annular high-density plasma region PA1 on one surface (main surface 21 a) of the gallium target 21 in the first direction, in which the density of the plasmatized sputtering gas is higher than that of the surrounding area.

[0086] According to this configuration, DC power can be applied directly to the gallium target 21 via the conductor 253 made of a gallium corrosion-resistant metal, without going through the target vessel 22. Therefore, DC sputtering using a gallium target can be performed while reducing metal contamination.

[0087] 2. Second Embodiment Next, a second embodiment will be described. In the following description, elements having the same functions as elements already described will be given the same reference numerals or reference numerals with an additional alphabetical character, and detailed description thereof may be omitted.

[0088] Fig. 9 is a schematic cross-sectional view showing a target container 22a according to the second embodiment. Fig. 10 is a plan view of the target container 22a according to the second embodiment, as seen from vertically above. The target container 22a has a container body 221, a passage 223, and a cover 225. The container body 221 is a portion in which the gallium target 21 is accommodated. The container body 221 has a shallow, bottomed cylindrical shape except for the portion connected to the passage 223. The passage 223 is connected to the inside of the container body 221 and is formed in a concave shape extending radially from the container body 221.

[0089] The cover portion 225 is disposed above the passage portion 223 and covers the opening on the vertically upper side (one side in the first direction) of the passage portion 223. The container body portion 221 and the passage portion 223 are integrally formed, but may be separate bodies. The container body portion 221, the passage portion 223, and the cover portion 225 are preferably formed of a ceramic material, and more preferably formed of a ceramic material containing gallium nitride, aluminum nitride, or boron nitride as a main component.

[0090] The other end of conductor 253 is disposed within passage portion 223, which is covered with cover portion 225. That is, conductor 253 is inserted into passage portion 223 from an upper opening of passage portion 223 that is not covered by cover portion 225. Then, the end of conductor 253 is disposed directly below cover portion 225 within passage portion 223.

[0091] The height (axial position) of the bottom surface of the passage portion 223 is the same as the height of the bottom surface of the container body portion 221, and the connecting portion between the bottom surface of the passage portion 223 and the bottom surface of the container body portion 221 is formed flush. When the gallium target 21 is placed in the container body portion 221, the liquid gallium moves to the passage portion 223. As a result, the end of the conductor 253 placed in the passage portion 223 comes into contact with the liquid gallium. Therefore, a DC voltage can be applied to the gallium target 21 placed in the container body portion 221.

[0092] In this way, by arranging the end of the conductor 253 in the passage portion 223, the other end of the conductor 253 can be separated from the high-density plasma region PA1. This makes it possible to reduce sputtering of the conductor 253. Furthermore, the other end of the conductor 253 is arranged in a portion of the passage portion 223 whose vertically upper side is covered by the cover portion 225. This makes it possible to avoid exposure of the conductor 253 to the high-density plasma. This makes it possible to further reduce sputtering of the conductor 253.

[0093] 3. Third Embodiment FIG. 11 illustrates a target vessel 22b according to a third embodiment. The target vessel 22b is formed in a shallow, bottomed cylindrical shape, with a through-hole 227 formed in a sidewall extending vertically upward from the bottom. A conductive bolt 255, which is part of a conductor 253a, is inserted into the through-hole 227. In other words, the conductive bolt 255 penetrates the target vessel 22b at the side surface of the target vessel 22b. The conductive bolt 255 corresponds to the other end of the conductor 253a and is made of a gallium-corrosion-resistant metal such as molybdenum, copper, or stainless steel. The conductive bolt 255 is connected to the first power supply 251 via the metal conductor of the conductor 253a. The metal conductor of the conductor 253a does not contact the gallium target 21, and therefore may be made of a metal other than a gallium-corrosion-resistant metal. Note that the metal conductor of the conductor 253a is preferably coated with an insulating material such as resin.

[0094] When the gallium target 21 is placed in the target container 22, the conductive bolt 255 of the conductor 253a comes into contact with the gallium target 21. This electrically connects the first power supply 251 to the gallium target 21, making it possible to apply a DC voltage to the gallium target 21.

[0095] Since the conductive bolt 255 is provided on the side wall of the target vessel 22, it is possible to prevent the conductive bolt 255 from being exposed to the high-density plasma of argon gas formed above the gallium target 21. This reduces sputtering of the conductor 253a, thereby reducing metal contamination of the gallium film.

[0096] Since the conductive bolts 255 are provided on the sidewall of the target vessel 22, the metal conductor wire of the conductor 253a can be connected to the conductive bolts 255 exposed radially outward from the target vessel 22. This prevents the metal conductor wire of the conductor 253a from interfering with the cooling vessel 29 and the like disposed below the target vessel 22.

[0097] The through-hole 227 of the target vessel 22 may be provided in the bottom of the target vessel 22, and the conductive bolt 255 may be disposed in the bottom of the target vessel 22. In other words, the conductive bolt 255 may be disposed on the bottom surface of the target vessel 22 so as to penetrate the target vessel 22. In this case, even if the gallium target 21 is reduced as sputtering progresses, exposure of the conductive bolt 255 can be reduced.

[0098] 4. Modifications Although the embodiments of the DC sputtering apparatus have been described above, the present invention is not limited to the above and various modifications are possible.

[0099] For example, in the above embodiment, the target vessel 22 is formed to have a uniform depth, but this is not essential. For example, the target vessel 22 may have a shape that becomes deeper toward the center of the target vessel 22. Furthermore, the target vessel 22 does not necessarily have to have a circular shape in a plan view. For example, the target vessel 22 may have a rectangular shape in a plan view.

[0100] In the DC sputtering apparatus 100, the sputtering spaces 1a and the plasma spaces 1b are alternately arranged around the revolution axis Q1. The substrate W is caused to revolve about the revolution axis Q1, thereby passing alternately through the sputtering spaces 1a and the plasma spaces 1b. However, the configuration of the DC sputtering apparatus 100 is not limited to this configuration. For example, the sputtering spaces 1a and the plasma spaces 1b may be aligned in a straight line. In this case, the substrate W may be moved back and forth between the sputtering spaces 1a and the plasma spaces 1b.

[0101] Although the present invention has been described in detail, the above description is merely illustrative in all respects and does not limit the present invention. It is understood that countless variations not illustrated can be envisioned without departing from the scope of the present invention. The configurations described in the above embodiments and variations can be combined or omitted as appropriate as long as they are not mutually inconsistent.

[0102] 4: Substrate holder 21: Gallium target 22, 22a, 22b: Target vessel 23: Sputtering gas supply section 23a: First gas inlet 28: Magnet section 31: Reactive gas supply section 100: DC sputtering device 221: Vessel body 223: Passage section 225: Cover section 227: Through hole 251: First power supply 253, 253a: Conductor 255: Conductive bolt (conductor) 291: Cooling water PA1: High-density plasma region W: Substrate

Claims

1. A DC sputtering apparatus comprising: a substrate holding unit that holds a substrate; a target vessel that holds a gallium target so as to face a main surface of the substrate in a first direction; a DC power supply that applies DC power to the gallium target; a conductor that has one end connected to the negative electrode of the DC power supply and the other end in contact with the gallium target in the target vessel, the conductor being made of a gallium corrosion-resistant metal; a sputtering gas supply unit that has an inlet for supplying sputtering gas between the target vessel and the substrate holding unit; and a magnet unit that is located on the opposite side of the substrate holding unit with respect to the target vessel and forms an annular high-density plasma region on one side of the gallium target in the first direction, in which the density of the plasmatized sputtering gas is higher than that of the surrounding area.

2. A DC sputtering apparatus according to claim 1, wherein the gallium corrosion-resistant metal comprises molybdenum, copper, or stainless steel.

3. A DC sputtering apparatus according to claim 1 or 2, wherein the target vessel is made of a ceramic material.

4. A DC sputtering apparatus according to claim 3, wherein the target vessel is formed from a ceramic material containing gallium nitride, aluminum nitride, or boron nitride as its main component.

5. A DC sputtering apparatus according to any one of claims 1 to 4, wherein the conductor is arranged away from the high-density plasma region in a second direction intersecting the first direction.

6. A DC sputtering apparatus according to any one of claims 1 to 5, wherein the magnet section includes a first annular permanent magnet, and the conductor is positioned away from the first permanent magnet in a second direction intersecting the first direction.

7. A DC sputtering apparatus according to any one of claims 1 to 6, wherein the target vessel comprises: a vessel body in which the gallium target is accommodated; and a concave passageway communicating with the vessel body and extending in a second direction intersecting the first direction; and the other end of the conductor is disposed within the passageway.

8. A DC sputtering apparatus as set forth in claim 7, wherein the target vessel further comprises a cover portion covering an opening on one side of the passage portion in the first direction, and the other end of the conductor is positioned in the portion of the passage portion covered by the cover portion.

9. A DC sputtering apparatus according to any one of claims 1 to 8, wherein the sputtering gas contains argon.

10. A DC sputtering apparatus according to any one of claims 1 to 9, further comprising a reactive gas supply unit that supplies a reactive gas, wherein the reactive gas supply unit supplies the reactive gas so that the gallium deposited on the main surface of the substrate reacts with the reactive gas in plasma form.

11. A DC sputtering apparatus as defined in claim 10, wherein said reactive gas comprises nitrogen.

12. A DC sputtering apparatus according to any one of claims 1 to 11, wherein the target vessel has a bottom surface and side surfaces for holding the gallium target therein, and the conductor penetrates the target vessel at the bottom surface or the side surface.

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