JP7825397B2 - Film forming apparatus and film forming method - Google Patents

Description

The present invention relates to a film formation apparatus and a film formation method.

GaN (gallium nitride) is attracting attention as a next-generation device material. Examples of devices that use GaN include light-emitting devices, power devices, and high-frequency communication devices. These GaN devices are manufactured by forming GaN films on silicon (Si) wafers, silicon carbide (SiC) wafers, sapphire substrates, and glass substrates. GaN films have traditionally been formed using the metal organic chemical vapor deposition (MO-CVD) method. MO-CVD is a deposition method in which a material gas containing organic metals is transported by a carrier gas onto a heated substrate, and the material is decomposed and chemically reacted at high temperatures to deposit a film through chemical vapor deposition.

JP 2015-103652 A

However, the deposition of GaN films using the MO-CVD method has the following productivity problems. First, gallium (Ga) is liquid at room temperature and pressure, but a large amount of _NH3 gas is required for the process to suppress Ga evaporation and to react Ga with nitrogen (N). This results in poor material utilization efficiency. Furthermore, handling the material gas is difficult, and maintaining a stable state of the equipment is difficult, resulting in poor yield. The MO-CVD method requires high-temperature processing at the 1000°C level to completely decompose _NH3 gas, which requires a high-power heating device and increases costs. Furthermore, hydrogen (H) contained in the processing gas during processing is incorporated into the deposited GaN film, necessitating an extra step called dehydrogenation.

The present invention has been proposed to solve the above-mentioned problems, and aims to provide a film formation apparatus and film formation method that can form GaN films with high productivity.

In order to achieve the above object, the film formation apparatus of this embodiment includes a chamber capable of evacuating the interior thereof, a rotary table provided within the chamber for holding a workpiece and circulating and transporting the workpiece along a circular trajectory, a target made of a film formation material containing GaN, and a plasma generator for generating plasma from a sputtering gas introduced between the target and the rotary table, the apparatus comprising: a GaN film formation processing section for depositing particles of the film formation material containing GaN by sputtering on the workpiece circulated and transported by the rotary table; and a nitriding processing section for nitriding the particles of the film formation material deposited in the GaN film formation processing section on the workpiece circulated and transported by the rotary table. The apparatus comprises: a target made of a film formation material containing p-type impurities or n-type impurities; a plasma generator that converts a sputtering gas introduced between the target made of the film formation material containing the p-type impurities or n-type impurities and the rotary table into plasma; and an impurity addition processing section that adds n-type impurities or p-type impurities by sputtering to particles of the film formation material containing GaN deposited on the workpiece in the GaN film formation processing section, wherein the GaN film formation processing section, the nitriding processing section, and the impurity addition processing section are arranged on the circulation transport path, and the rotary table transports the workpiece by repeatedly passing it through the GaN film formation processing section, the nitriding processing section, and the impurity addition processing section in that order, thereby repeatedly forming a GaN film containing the n-type impurities or the p-type impurities on the workpiece .

The film formation method of this embodiment is a film formation method in which a workpiece is held by a rotary table and circulated and transported along a circular path in a chamber capable of being evacuated, while a film is formed on the workpiece, the inside of which can be evacuated. The method includes a GaN film formation processing unit having a target made of a film formation material containing GaN and a plasma generator that converts a sputtering gas introduced between the target and the rotary table into plasma, which deposits particles of the film formation material containing GaN by sputtering on the workpiece that is circulated and transported by the rotary table, and a nitriding processing unit having a GaN film formation processing unit that deposits particles of the film formation material containing GaN by sputtering on the workpiece that is circulated and transported by the rotary table. and an impurity addition process in which n-type impurities or p-type impurities are added by sputtering to the particles of the film formation material containing GaN deposited on the workpiece in the GaN film formation processing section by circulating and transporting the workpiece. The process is characterized in that the GaN film formation process, the nitriding process, and the impurity addition process are repeated in this order by circulating and transporting the workpiece, thereby forming a GaN film containing the n-type impurity or the p-type impurity in a predetermined number of layers on the workpiece .

Embodiments of the present invention provide a film formation apparatus and film formation method that can form GaN films with high productivity.

1 is a perspective plan view schematically illustrating a configuration of a film forming apparatus according to an embodiment. 2 is a cross-sectional view taken along the line AA in FIG. 1, showing in detail the internal configuration of the film forming apparatus according to the embodiment of FIG. 1 as viewed from the side. 3 is a flowchart of a process performed by the film forming apparatus according to the embodiment. FIG. 10 is a perspective plan view schematically showing a modified example of the embodiment. FIG. 10 is a perspective plan view schematically showing a modified example of the embodiment. 1A is a cross-sectional view showing an example of a layer structure of an LED, and FIG. 1B is an enlarged cross-sectional view of a buffer layer.

An embodiment of a film forming apparatus will be described in detail with reference to the drawings.
[overview]
1 is an apparatus for forming a GaN (gallium nitride) film or an AlN (aluminum nitride) film by sputtering on a workpiece 10, which is a film formation target. The workpiece 10 is, for example, a silicon (Si) wafer, a silicon carbide (SiC) wafer, a sapphire substrate, or a glass substrate.

The film formation apparatus 1 has a chamber 20, a transport unit 30, a film formation processing unit 40, a nitriding processing unit 50, a heating unit 60, a transfer chamber 70, a preheating chamber 80, a cooling chamber 90, and a control device 100. The chamber 20 is a container that can be evacuated. The chamber 20 is cylindrical, and its interior is divided into multiple compartments. The film formation processing unit 40 is separated by a partition 22 and is arranged in two fan-shaped compartments. The nitriding processing unit 50 and the heating unit 60 are arranged in the compartments other than the compartment where the film formation processing unit 40 is located.

The film formation processing section 40 has one section as a GaN film formation processing section 40A, which uses a material containing GaN as the target 42 to form a GaN film, and the other section as an Al film formation processing section 40B, which uses a material containing Al as the target 42 to form an Al film. The workpiece 10 rotates around the circumferential direction within the chamber 20 multiple times, passing alternately through the GaN film formation processing section 40A and the nitriding processing section 50. GaN film formation and Ga nitriding are alternately repeated on the workpiece 10, growing a GaN film of the desired thickness.

In addition, as the workpiece 10 rotates around the chamber 20 multiple times in the circumferential direction, it passes alternately through the Al film formation processing unit 40B and the nitriding processing unit 50, and the formation of an Al film and the nitriding of Al are repeated alternately on the workpiece 10, growing an AlN film of the desired thickness. In this way, the formation of GaN films and the formation of AlN films are repeated, and GaN films and AlN films are stacked alternately.

The reason why a nitriding treatment section 50 is provided in addition to using a material containing GaN as the target 42 is as follows. Ga has a low melting point and is in a liquid state at room temperature and pressure, so in order to make the target 42 solid, it must contain nitrogen (N). For this reason, it is also possible to simply increase the nitrogen content of the target 42 and form a film by sputtering the target 42 alone.

Here, to improve the film formation rate, DC discharge sputtering is preferable to RF discharge. However, if the target 42 contains a large amount of nitrogen, the surface becomes an insulator. With a target 42 whose surface has become an insulator in this way, DC discharge may not occur.

In other words, there is a limit to the amount of nitrogen that can be contained in the GaN target 42, and the nitridation of Ga in the target 42 remains insufficient. In other words, the GaN-containing target 42 contains Ga atoms that are missing bonds with N (nitrogen) atoms.

Furthermore, if nitrogen gas is added to the sputtering gas introduced into the film formation processing unit 40 during sputtering, the surface of the target 42 is nitrided, turning the surface into an insulator. Therefore, to compensate for the lack of nitrogen, the GaN film formation processing unit 40A cannot add nitrogen gas to the sputtering gas. On the other hand, if the nitrogen content in the formed GaN film is low and there are nitrogen defects, the film's crystallinity will deteriorate and its flatness will be impaired. Therefore, to compensate for the lack of nitrogen in the GaN film formed by the GaN film formation processing unit 40A, nitridation is further performed in the nitriding processing unit 50 after film formation by the GaN film formation processing unit 40A.

[Chamber]
2, the chamber 20 is surrounded by a disk-shaped ceiling 20a, a disk-shaped inner bottom surface 20b, and an annular inner peripheral surface 20c. The partitions 22 are rectangular wall plates arranged radially from the center of the cylindrical shape, and extend from the ceiling 20a toward the inner bottom surface 20b, but do not reach the inner bottom surface 20b. In other words, a cylindrical space is secured on the inner bottom surface 20b side.

A rotary table 31 that transports the workpiece 10 is placed in this cylindrical space. The lower end of the partition 22 faces the surface of the rotary table 31 on which the workpiece 10 is placed, with a gap allowing the workpiece 10 placed on the rotary table 31 to pass through. The partition 22 separates the processing space 41 in which the workpiece 10 is processed by the film-forming processing unit 40. Furthermore, the processing space 59 is separated by a cylindrical body 51 (described below) of the nitriding processing unit 50. In other words, the film-forming processing unit 40 and the nitriding processing unit 50 each have processing spaces 41, 59 that are smaller than the chamber 20 and are separated from each other. The partition 22 prevents the sputtering gas G1 from the film-forming processing unit 40 from diffusing into the chamber 20. Furthermore, the cylindrical body 51 of the nitriding processing unit 50 prevents the process gas G2 from diffusing into the chamber 20.

Furthermore, as will be described later, plasma is generated in the processing spaces 41 and 59 in the film formation processing unit 40 and the nitriding processing unit 50. However, since it is only necessary to adjust the pressure in the processing spaces 41 and 59, which are partitioned into spaces smaller than the chamber 20, pressure adjustment can be easily performed and plasma discharge can be stabilized. Therefore, to achieve the aforementioned effect, it is sufficient to have at least two partitions 22 sandwiching the film formation processing unit 40 in a plan view.

The chamber 20 is provided with an exhaust port 21. An exhaust unit 23 is connected to the exhaust port 21. The exhaust unit 23 has piping and a pump, a valve, etc. (not shown). By exhausting air by the exhaust unit 23 through the exhaust port 21, the inside of the chamber 20 can be depressurized and a vacuum can be created. The exhaust unit 23 exhausts air until the degree of vacuum reaches, for example, 10 ⁻⁴ Pa in order to keep the oxygen concentration low.

[Transport unit]
The transport unit 30 has a rotary table 31, a motor 32, and a holding unit 33, and circulates and transports the workpiece 10 along a transport path L, which is a circular trajectory. The rotary table 31 has a disk shape and is wide enough not to come into contact with the inner peripheral surface 20c. The motor 32 continuously rotates the rotary table 31 at a predetermined rotational speed around the center of the circle as the rotation axis. The rotary table 31 rotates at a speed of, for example, 1 to 150 rpm.

The holding units 33 are grooves, holes, protrusions, jigs, holders, etc., arranged at evenly spaced positions on the upper surface of the turntable 31, and hold the tray 34 on which the workpieces 10 are placed using a mechanical chuck or adhesive chuck. The workpieces 10 are arranged, for example, in a matrix on the tray 34, and six holding units 33 are arranged on the turntable 31 at 60° intervals. In other words, the film deposition apparatus 1 can simultaneously deposit films on multiple workpieces 10 held by multiple holding units 33, resulting in extremely high productivity. It is also possible to omit the tray 34 and place the workpieces 10 directly on the upper surface of the turntable 31.

[Film forming processing section]
The film forming processing unit 40 generates plasma and exposes a target 42 made of a film forming material to the plasma. As a result, particles of the film forming material (hereinafter referred to as sputter particles) are knocked out by ions contained in the plasma colliding with the target 42, and the particles are deposited on the workpiece 10 to form a film. As shown in Fig. 2, the film forming processing unit 40 includes a sputtering source made up of the target 42, a backing plate 43, and an electrode 44, and a plasma generator made up of a power supply unit 46 and a sputtering gas inlet unit 49.

The target 42 is a plate-shaped member made of a film-forming material that will be deposited on the workpiece 10 to form a film. The film-forming material that makes up the target 42 in the GaN film-forming processing unit 40A of this embodiment is a material containing Ga and GaN, and the target 42 serves as a supply source of sputtered particles containing Ga atoms that are deposited on the workpiece 10. Because the nitrogen content is limited as described above, the target 42 contains GaN and incomplete GaN that is deficient in nitrogen, i.e., Ga atoms that are missing bonds with N (nitrogen).

The film-forming material constituting the target 42 in the Al film-forming processing unit 40B is a material containing Al, and the target 42 serves as a supply source of sputtering particles containing Al atoms to be deposited on the workpiece 10. Note that the sputtering target 42 can contain elements other than Ga, Al, and N (nitrogen), as long as it is capable of supplying sputtering particles containing Ga atoms and sputtering particles containing Al atoms.

The targets 42 are provided at a distance on the transport path L of the workpiece 10 placed on the rotary table 31. The surface of the target 42 is supported on the ceiling 20a of the chamber 20 so as to face the workpiece 10 placed on the rotary table 31. For example, three targets 42 are installed. The three targets 42 are positioned so that they line up on the vertices of a triangle in a plan view.

The backing plate 43 is a support member that holds the targets 42. This backing plate 43 holds each target 42 individually. The electrode 44 is a conductive member that applies power to each target 42 individually from outside the chamber 20 and is electrically connected to the targets 42. The power applied to each target 42 can be changed individually. In addition, the sputtering source may be appropriately equipped with magnets, cooling mechanisms, etc. as needed.

The power supply unit 46 is, for example, a DC power supply that applies high voltage and is electrically connected to the electrode 44. The power supply unit 46 applies power to the target 42 through the electrode 44. The rotary table 31 is at the same potential as the grounded chamber 20, and applying a high voltage to the target 42 generates a potential difference.

As shown in FIG. 2, the sputtering gas introduction unit 49 introduces sputtering gas G1 into the chamber 20. The sputtering gas introduction unit 49 has a sputtering gas G1 supply source such as a cylinder (not shown), piping 48, and a gas introduction port 47. The piping 48 is connected to the sputtering gas G1 supply source, airtightly penetrates the chamber 20, and extends into the chamber 20, with its end opening as the gas introduction port 47. In this embodiment, the sputtering gas introduction unit 49 introduces the sputtering gas G1 into the processing space 41 so that the pressure in the processing space 41 is 0.3 Pa or less and 0.1 Pa or more.

The gas inlet 47 opens between the turntable 31 and the target 42 and introduces the sputtering gas G1 for film formation into the processing space 41 formed between the turntable 31 and the target 42. A rare gas can be used as the sputtering gas G1, and argon (Ar) gas is preferable. The sputtering gas G1 does not contain nitrogen (N), and can be argon (Ar) gas alone.

In this type of film formation processing unit 40, sputtering gas G1 is introduced through the sputtering gas inlet 49, and when the power supply 46 applies a high voltage to the target 42 via the electrode 44, the sputtering gas G1 introduced into the processing space 41 formed between the rotary table 31 and the target 42 is converted into plasma, generating active species such as ions. The ions in the plasma collide with the target 42, ejecting sputtered particles. In the GaN film formation processing unit 40A, sputtering particles containing Ga atoms collide with the target 42 made of a material containing Ga and GaN. In the Al film formation processing unit 40B, sputtering particles containing Al atoms collide with the target 42 made of a material containing Al, ejecting sputtered particles.

The workpiece 10, which is circulated and transported by the rotary table 31, passes through this processing space 41. The ejected sputtered particles are deposited on the workpiece 10 as it passes through the processing space 41, and a film containing Ga atoms and a film containing Al atoms are formed on the workpiece 10. The workpiece 10 is circulated and transported by the rotary table 31, and the film formation process is carried out by repeatedly passing through this processing space 41. Note that the formation of the GaN film containing Ga and the AlN film containing Al is not carried out in parallel, but rather by forming one film first and then the other.

[Nitriding treatment section]
The nitriding unit 50 generates an inductively coupled plasma in a processing space 59 into which a process gas G2 containing nitrogen gas has been introduced. That is, the nitriding unit 50 converts nitrogen gas into plasma to generate chemical species. The nitrogen atoms contained in the generated chemical species collide with the film containing Ga atoms and the film containing Al atoms formed on the workpiece 10 by the film forming unit 40, and bond with Ga atoms that are deficient in bonding with nitrogen in the film containing Ga atoms and Al atoms in the film containing Al atoms. This allows for the production of GaN films and AlN films that are free of nitrogen defects.

As shown in Figure 2, the nitriding treatment unit 50 has a plasma generator composed of a cylindrical body 51, a window member 52, an antenna 53, an RF power supply 54, a matching box 55, and a process gas inlet 58.

The cylindrical body 51 is a member that covers the periphery of the processing space 59. As shown in Figures 1 and 2, the cylindrical body 51 is a tube with a rounded rectangular cross section and has an opening. The cylindrical body 51 is fitted into the ceiling 20a of the chamber 20 so that its opening faces away from the turntable 31 and protrudes into the internal space of the chamber 20. The cylindrical body 51 is made of the same material as the turntable 31.

The window member 52 is a flat plate made of a dielectric material such as quartz and having a shape similar to the horizontal cross section of the cylindrical body 51. The window member 52 is disposed to close the opening of the cylindrical body 51 and separates the interior of the cylindrical body 51 from a processing space 59 into which a process gas G2 containing nitrogen gas is introduced in the chamber 20. The window member 52 must suppress oxidation caused by oxygen flowing into the processing space 59. For example, the required oxygen concentration is very low, 10 ¹⁹ (atoms/cm ³ ) or less. To address this, a protective coating is applied to the surface of the window member 52. For example, coating the surface of the window member 52 with Y ₂ O ₃ (yttrium oxide) can suppress wear of the window member 52 by plasma while suppressing oxygen release from the surface of the window member 52, thereby maintaining a low oxygen concentration.

In the nitriding treatment unit 50, a treatment space 59 is formed between the turntable 31 and the interior of the cylindrical body 51. The workpieces 10, which are circulated and transported by the turntable 31, pass through this treatment space 59 repeatedly, thereby performing the nitriding treatment. The window member 52 may be a dielectric material such as alumina, or a semiconductor material such as silicon.

The antenna 53 is a coiled conductor located in the internal space of the cylindrical body 51, which is isolated from the processing space 59 in the chamber 20 by the window member 52. An electric field is generated when an alternating current is passed through it. It is desirable to position the antenna 53 near the window member 52 so that the electric field generated by the antenna 53 is efficiently introduced into the processing space 59 via the window member 52. An RF power supply 54, which applies a high-frequency voltage, is connected to the antenna 53. A matching box 55, which is a matching circuit, is connected in series to the output side of the RF power supply 54. The matching box 55 stabilizes the plasma discharge by matching the impedances on the input and output sides.

As shown in FIG. 2, the process gas inlet 58 introduces a process gas G2 containing nitrogen gas into the processing space 59. The process gas inlet 58 has a process gas G2 supply source such as a cylinder (not shown), a pipe 57, and a gas inlet 56. The pipe 57 is connected to the process gas G2 supply source, penetrates the chamber 20 while hermetically sealing it, and extends into the interior of the chamber 20, with its end opening as the gas inlet 56.

The gas inlet 56 opens into the processing space 59 between the window member 52 and the rotary table 31 and introduces the process gas G2. A rare gas can be used as the process gas G2, and argon gas is preferred.

In this nitriding treatment unit 50, a high-frequency voltage is applied to the antenna 53 from the RF power supply 54. This causes a high-frequency current to flow through the antenna 53, generating an electric field due to electromagnetic induction. The electric field is generated in the treatment space 59 via the window member 52, generating an inductively coupled plasma in the process gas G2. At this time, nitrogen chemical species containing nitrogen atoms are generated, which collide with the film containing Ga atoms and the film containing Al atoms on the workpiece 10, bonding with the Ga atoms and Al atoms. As a result, the nitrogen content of the film on the workpiece 10 can be increased, allowing the formation of GaN and AlN films free of nitrogen defects.

[Heating section]
The heating unit 60 heats the workpiece 10 that is circulated and transported by the turntable 31 within the chamber 20. The heating unit 60 has a heat source provided at a position facing the transport path L of the workpiece 10 on the turntable 31. The heat source is, for example, a halogen lamp. The heating temperature is preferably set to a temperature that heats the workpiece 10 to, for example, about 500°C.

[Transfer room]
The transfer chamber 70 is a container for loading and unloading the workpieces 10 into and from the chamber 20 via a gate valve. As shown in FIG. 1 , the transfer chamber 70 has an internal space in which the workpieces 10 are accommodated before being loaded into the chamber 20. The transfer chamber 70 is connected to the chamber 20 via a gate valve GV1. Although not shown, a transport means is provided in the internal space of the transfer chamber 70 for loading and unloading trays 34 carrying the workpieces 10 between the chamber 20 and the transfer chamber 70. The transfer chamber 70 is depressurized by an exhaust means such as a vacuum pump (not shown). With the vacuum of the chamber 20 maintained by the transport means, the trays 34 carrying unprocessed workpieces 10 are loaded into the chamber 20, and the trays 34 carrying processed workpieces 10 are unloaded from the chamber 20.

The load lock unit 71 is connected to the transfer chamber 70 via gate valve GV2. The load lock unit 71 is a device that uses a transport means (not shown) to transport trays 34 carrying unprocessed workpieces 10 from the outside into the transfer chamber 70 and transports trays 34 carrying processed workpieces 10 out of the transfer chamber 70 while maintaining the vacuum in the transfer chamber 70. The load lock unit 71 switches between a vacuum state in which the pressure is reduced by an exhaust means such as a vacuum pump (not shown), and an open-to-air state in which the vacuum is broken.

[Preheating chamber]
The preheating chamber 80 heats the workpiece 10 before it is carried into the chamber 20. The preheating chamber 80 is equipped with a container connected to the transfer chamber 70 and has a heat source that heats the workpiece 10 before it is carried into the transfer chamber 70. The heat source may be, for example, a heater or a heat lamp. The preheating temperature is preferably a temperature at which the workpiece 10 is heated to about 300°C. The tray 34 is transported between the preheating chamber 80 and the transfer chamber 70 by a transport means (not shown).

[Cooling room]
The cooling chamber 90 cools the workpieces 10 carried out from the chamber 20. The cooling chamber 90 is equipped with a container connected to the transfer chamber 70 and has a cooling means for cooling the workpieces 10 carried on the trays 34 carried out from the transfer chamber 70. For example, a spraying unit for spraying cooling gas can be used as the cooling gas. For example, Ar gas from the supply source of the sputtering gas G1 can be used as the cooling gas. The cooling temperature is preferably a temperature at which the workpieces can be transported in the atmosphere, for example, 30°C. The trays 34 carrying the processed workpieces 10 from the transfer chamber 70 are carried into the cooling chamber 90 by a transport means (not shown).

[Control device]
The control device 100 controls various elements constituting the film forming apparatus 1, such as the exhaust unit 23, the sputtering gas introduction unit 49, the process gas introduction unit 58, the power supply unit 46, the RF power supply 54, the transport unit 30, the heating unit 60, the transfer chamber 70, the load lock unit 71, the preheating chamber 80, and the cooling chamber 90. The control device 100 is a processing device including a PLC (Programmable Logic Controller) and a CPU (Central Processing Unit), and stores a program describing the control contents.

Specific controlled items include the initial exhaust pressure of the film formation apparatus 1, the power applied to the target 42 and antenna 53, the flow rates of the sputtering gas G1 and process gas G2, the introduction and exhaust times, the film formation time, and the rotation speed of the motor 32. This allows the control device 100 to accommodate a wide variety of film formation specifications. The control device 100 also controls the heating temperature and heating time of the heating unit 60, the heating temperature and heating time of the preheating chamber 80, and the cooling temperature and cooling temperature of the cooling chamber 90.

[Operation]
Next, the operation of the film formation apparatus 1 controlled by the control device 100 will be described. Note that a film formation method using the film formation apparatus 1, as described below, is also an aspect of the present invention. FIG. 3 is a flowchart of a film formation process using the film formation apparatus 1 of this embodiment. This film formation process involves alternately stacking AlN and GaN films on a workpiece 10, followed by forming a GaN layer. Because silicon wafers and sapphire substrates have different crystal lattices from GaN, directly forming a GaN film on them can result in a problem of reduced GaN crystallinity. To resolve this crystal lattice mismatch, a buffer layer is formed by alternately stacking AlN and GaN films, and then a GaN layer is formed on this buffer layer. This method can be used, for example, to form a GaN layer on a silicon wafer via a buffer layer in the manufacture of lateral MOSFETs and LEDs.

First, the chamber 20 is evacuated through the exhaust port 21 by the exhaust unit 23, constantly reducing the pressure to a predetermined level. In addition, as the exhaust proceeds, the heating unit 60 begins heating, and the turntable 31 begins rotating, heating the turntable 31 as it passes through the heating unit 60. Radiation from the heated turntable 31 heats the chamber 20. Heating along with the exhaust promotes the desorption of residual gases, such as water molecules and oxygen molecules, within the chamber 20. This reduces the likelihood of residual gases being mixed in as impurities during film formation, improving the crystallinity of the film. After a gas analyzer such as a Q-Mass detects that the oxygen concentration within the chamber 20 has fallen below a predetermined value, the heating unit 60 stops heating and the turntable 31 stops rotating. In the preheating chamber 80, the workpieces 10 placed on the tray 34 are preheated to approximately 300°C (step S01).

Trays 34 carrying preheated workpieces 10 are loaded into the transfer chamber 70 by the transport means, and then sequentially loaded into the chamber 20 via the gate valve GV1 (step S02). In step S02, the rotary table 31 sequentially moves the empty holders 33 from the transfer chamber 70 to the loading location. The holders 33 individually hold each tray 34 loaded by the transport means. In this way, all trays 34 carrying workpieces 10 are placed on the rotary table 31.

The heating unit 60 starts heating again, and the turntable 31 carrying the workpiece 10 starts rotating, heating the workpiece 10 (step S03). After a predetermined time determined in advance through simulation, experiment, etc., has elapsed, the workpiece 10 is heated to approximately 500°C. During heating, the turntable 31 is rotated at a relatively high speed of approximately 100 rpm to ensure more uniform heating.

Then, a buffer layer is formed by alternately repeating the deposition of an AlN film by the Al deposition unit 40B and the nitriding unit 50 and the deposition of a GaN film by the GaN deposition unit 40A and the nitriding unit 50. First, an AlN film is deposited on the workpiece 10 by the Al deposition unit 40B and the nitriding unit 50 (step S04). Specifically, the sputtering gas inlet 49 supplies sputtering gas G1 through the gas inlet 47. The sputtering gas G1 is supplied around the target 42, which is made of Al. The power supply 46 applies a voltage to the target 42, thereby converting the sputtering gas G1 into plasma. Ions generated by the plasma collide with the target 42 and eject sputter particles containing Al atoms.

When the unprocessed workpiece 10 passes through the Al film-forming unit 40B, a thin film is formed on the surface, with sputtered particles containing Al atoms deposited on it. In this embodiment, each time the workpiece passes through the Al film-forming unit 40B, a film is deposited to a thickness that can contain one to two Al atoms in the thickness direction.

In this way, the workpiece 10 passes through the Al film forming treatment section 40B due to the rotation of the turntable 31, and then passes through the nitriding treatment section 50, during which the Al atoms in the thin film are nitrided. That is, the process gas inlet 58 supplies process gas G2 containing nitrogen gas through the gas inlet 56. The process gas G2 containing nitrogen gas is supplied to a treatment space 59 sandwiched between the window member 52 and the turntable 31. The RF power supply 54 applies a high-frequency voltage to the antenna 53.

When a high-frequency voltage is applied, a high-frequency current flows through the antenna 53, generating an electric field in the processing space 59 via the window member 52. This electric field then excites the process gas G2, which contains nitrogen gas, supplied to this space, generating plasma. The nitrogen species generated by the plasma collide with the thin film on the workpiece 10, bonding with Al atoms and forming a fully nitrided AlN film.

The rotary table 31 continues to rotate until an AlN film of the specified thickness is formed on the workpiece 10, that is, until a specified time determined in advance through simulation, experiment, etc. has elapsed. In other words, the workpiece 10 continues to circulate between the film formation processing unit 40 and the nitriding processing unit 50 until an AlN film of the specified thickness is formed. Since nitriding is preferably performed each time Al is deposited to an atomic-level film thickness, the rotation speed of the rotary table 31 is set to a relatively slow speed of 50 to 60 rpm in order to balance film formation and nitriding.

After a predetermined time has elapsed, the operation of the Al film forming unit 40B is stopped. Specifically, the application of voltage to the target 42 by the power supply unit 46 is stopped.

Next, a GaN film is formed on the workpiece 10 in the GaN film forming unit 40A and the nitriding unit 50 (step S05). That is, the sputtering gas G1 is supplied to the periphery of the target 42 by the sputtering gas inlet 49, and a voltage is applied to the target 42 by the power supply 46, thereby converting the sputtering gas G1 into plasma. Ions generated by the plasma collide with the target 42, knocking out sputtered particles containing Ga atoms.

This results in the formation of a thin film on the surface of the AlN film, in which sputtered particles containing Ga atoms are deposited. In this embodiment, each time the AlN film passes through the film-forming processing unit 40, it is possible to deposit a film with a thickness that can contain one to two Ga atoms.

In this way, the workpiece 10 passes through the GaN film forming processing unit 40A due to the rotation of the turntable 31, and then passes through the nitriding processing unit 50, during which the Ga atoms in the thin film are nitrided. In other words, as described above, nitrogen chemical species generated by the plasma collide with the thin film on the workpiece 10, bonding with Ga atoms that are missing bonds with nitrogen, resulting in the formation of a GaN film without nitrogen defects.

The turntable 31 first stops operation of the film formation processing unit 40 after the time required for a GaN film of a predetermined thickness to be formed on the workpiece 10, determined by simulation or experiment. That is, after the predetermined time has elapsed, operation of the GaN film formation processing unit 40A is stopped. Specifically, the application of voltage to the target 42 by the power supply unit 46 is stopped. The formation of the AlN film and GaN film as described above is repeated until the predetermined number of layers is reached (Step S06 No). When the predetermined number of layers is reached (Step S06 Yes), the formation of the buffer layer is terminated.

Furthermore, a GaN layer is formed on the buffer layer (step S07). This GaN layer is formed in the same manner as the GaN film in the buffer layer described above. However, the film is formed for a time that will allow the GaN layer to reach the specified thickness.

After the buffer layer and GaN layer are formed as described above, the operation of the GaN film forming unit 40A is stopped as described above, and then the operation of the nitriding unit 50 is stopped (step S09). Specifically, the supply of high-frequency power to the antenna 53 by the RF power supply 54 is stopped. Then, rotation of the turntable 31 is stopped, and the tray 34 on which the film-formed workpiece 10 is placed is transported by the transport means through the transfer chamber 70 into the cooling chamber 90. After the workpiece 10 is cooled to a predetermined temperature, it is removed from the load lock unit 71 (step S09).

In the above description, the nitriding unit 50 is operated continuously during the formation of the buffer layer (steps S04 to S06). However, the operation of the nitriding unit 50 may be stopped after each step S04 to S06 is completed. In this case, the operation of the nitriding unit 50 is stopped after the operation of the Al film forming unit 40B and the GaN film forming unit 40A has been stopped. This allows the surface of the film formed on the workpiece 10 to be sufficiently nitrided, resulting in AlN and GaN films without nitrogen defects.

[effect]
(1) The film forming apparatus 1 according to this embodiment includes a chamber 20 capable of evacuating the interior thereof, a rotary table 31 provided within the chamber 20, which holds the workpiece 10 and circulates the workpiece 10 along a circular trajectory, a target 42 made of a film forming material containing GaN, and a plasma generator which converts a sputtering gas G1 introduced between the target 42 and the rotary table 31 into plasma. The film forming apparatus 1 also includes a GaN film forming processing unit 40A which deposits particles of the film forming material containing GaN by sputtering onto the workpiece 10 which is circulated and transported by the rotary table 31, and a nitriding processing unit 50 which nitrides the particles of the film forming material deposited in the GaN film forming processing unit 40A onto the workpiece 10 which is circulated and transported by the rotary table 31.

The film formation method of this embodiment is a film formation method in which a film is formed on a workpiece 10 while the workpiece 10 is held by a rotary table 31 and circulated and transported along a circular trajectory in a chamber 20 capable of being evacuated. The method includes a GaN film formation process in which a GaN film formation processing unit 40A having a target 42 made of a film formation material containing GaN and a plasma generator that converts sputtering gas G1 introduced between the target 42 and the rotary table 31 into plasma deposits particles of the film formation material containing GaN on the workpiece 10 circulated and transported by the rotary table 31, and a nitriding process in which a nitriding processing unit 50 nitrides the particles of the film formation material deposited in the GaN film formation processing unit 40A on the workpiece 10 circulated and transported by the rotary table 31.

In this embodiment, GaN films can be formed with high productivity by sputtering the workpiece 10 circulated and transported by the rotary table 31 in the chamber 20. Unlike the MOCVD method, there is no need to use large amounts of _NH3 gas. Instead, sputtering gas G1 and process gas G2 are flowed into a limited area within the vacuum chamber 20, depositing and nitriding the target 42 material to an atomic-level thickness, resulting in high material utilization efficiency. Furthermore, because no reactive gas containing hydrogen (H) is used, extra processes such as dehydrogenation are unnecessary. Furthermore, since only an easily handled rare gas can be introduced into the chamber 20, the device condition can be easily maintained stably, resulting in high yields. The heating temperature is relatively low, at approximately 500°C, and the output required for the heating device is low. Because the entire process of forming the buffer layer and GaN layer is completed within the chamber 20, film formation can be performed in the same low-oxygen environment without the need to transfer between chambers to form other layers in different chambers during the process.

In addition, because the process involves repeatedly stacking and nitriding film-forming materials to atomic-level thicknesses, it is possible to form films with high crystallinity and minimal surface irregularities despite the shorter film-forming time compared to MO-CVD methods.

Here, the results of evaluation of films formed under the following film forming conditions are shown.
Workpiece: Si (111) substrate Rotational speed of the rotating table: 60 rpm
High frequency power applied to antenna (nitriding treatment part): 4000 W
DC power applied to sputtering source: GaN film forming section 800 to 1500 W, Al film forming section 2000 to 3500 W (for a film forming section equipped with two sputtering sources, the value of the power applied to each sputtering source)
Film formation rate: GaN layer 0.28 nm/sec, AlN layer 0.43 nm/sec
Ar gas flow rate in the film forming section: GaN film forming section: 80 sccm, Al film forming section: 45 sccm
N2 gas flow rate in nitriding treatment section: 30 sccm
In the above embodiment, heating is not performed during film formation.

X-ray diffraction analysis was performed on the following films deposited on the workpieces: a 3 μm AlN film (No. 1), a 3 μm GaN film (No. 2), a 30-layer stack of 5 nm AlN/5 nm GaN (No. 3), and a 30-layer stack of 5 nm AlN/5 nm GaN with a 3 μm GaN film stacked on top (No. 4). The rocking curves obtained by 2θ/ω scanning of the (002) plane on the film surface were found to have half-widths (°) of 0.246 for No. 1, 0.182 for No. 2, 0.178 for No. 3, and 0.197 for No. 4.

Generally, the smaller the half-width, the less variation there is in the crystal orientation, and the higher the crystallinity. In this embodiment, it is possible to deposit a highly crystalline film with a half-width (2θ/ω) of 0.2° or less. Furthermore, the thickness of the GaN buffer layer used in GaN-based devices is generally considered to be 3 to 10 μm, but the film deposition rate using the MO-CVD method is said to be several μm/h. In this embodiment, the film deposition rate is similar, but the hydrogen desorption step can be omitted, thereby shortening the film deposition time compared to the MO-CVD method. Furthermore, it is possible to obtain a highly crystalline film even at a lower temperature than the MO-CVD method.

Furthermore, if the solid target 42 contains a large amount of nitrogen, the surface becomes an insulator. Therefore, the target 42 cannot contain a large amount of nitrogen, and contains Ga atoms with nitrogen-bonding defects. Sputtering using such a target 42 results in the deposition of a GaN film with nitrogen defects. However, in this embodiment, by providing a nitriding unit 50 separate from the GaN deposition unit 40A, even if the target 42 contains Ga atoms with nitrogen-bonding defects, the nitriding unit 50 can ultimately increase the nitrogen content and produce a GaN film without nitrogen defects. Furthermore, the GaN deposition unit 40A does not use nitrogen gas, but instead uses argon as the sputtering gas G1. This allows the particles of the deposition material deposited on the workpiece W to be nitrided in the nitriding unit 50, which is separate from the GaN deposition unit 40A. Therefore, the surface of the target 42 does not become an insulator, and the deposition rate can be improved using DC discharge.

(2) The film forming apparatus 1 has a target 42 made of a film forming material containing Al, and an Al film forming processing unit 40B that deposits particles of the film forming material containing Al by sputtering on the workpiece 10 that is circulated and transported by the rotary table 31, and the nitriding processing unit 50 nitrides the particles of the film forming material deposited in the Al film forming processing unit 40B on the workpiece 10 that is circulated and transported by the rotary table 31.

For this reason, when using a workpiece 10 such as silicon, which has a different crystal lattice from GaN, the GaN film forming unit 40A, Al film forming unit 40B, and nitriding unit 50 can be used to form a buffer layer, which is a film made by alternately stacking GaN films and AlN films, thereby preventing a decrease in the crystallinity of the GaN.

Furthermore, since the GaN layer can be formed without exposing the buffer layer to the atmosphere after it has been formed, alteration of the outermost surface of the buffer layer is suppressed, and alteration of the GaN layer that is further formed on top of the buffer layer can be prevented. Furthermore, there is no need to move the buffer layer to an environment separate from the buffer layer formation environment to form the GaN layer, reducing transport time and eliminating the need to provide a separate space with adjusted oxygen concentration, etc.

Furthermore, in the Al film forming processing unit 40B, the sputtering gas G1 is argon gas alone, without using nitrogen gas, and the particles of film forming material deposited on the workpiece W can be nitrided in the nitriding processing unit 50, which is separate from the Al film forming processing unit 40B. As a result, the surface of the target 42 does not become an insulator, and the film forming rate can be improved using DC discharge.

(3) The film forming apparatus 1 has a heating unit 60 that heats the workpiece 10 that is circulated and transported by the rotary table 31. This allows for the formation of a film with even better crystallinity.

(4) The film forming apparatus 1 further includes a preheating chamber 80 that heats the workpiece 10 before it is loaded into the chamber 20. By preheating the workpiece 10 in the preheating chamber 80, the heating time by the heating unit 60 can be shortened, thereby increasing productivity.

[Modification]
(1) In the above embodiment, as shown in FIG. 4 , an impurity addition unit may be provided to add n-type or p-type impurities (dopants) to the deposited GaN film. In this case, the GaN film formation unit, nitriding unit, and impurity addition unit are arranged in this order on the circulation transport path. The impurity addition unit has a configuration similar to that of the film formation units 40A and 40B. More specifically, the impurity addition unit has a target made of a film formation material containing n-type or p-type impurities and a plasma generator, and can sputter the target to add particles (sputtered particles) of the film formation material containing impurity ions to the film deposited on the workpiece 10. For example, the impurity addition unit may be a Mg film formation unit 40C having a target 42 made of a film formation material containing Mg, or a Si film formation unit 40D having a target 42 made of a film formation material containing Si. The Mg film formation unit 40C and the Si film formation unit 40D have a configuration similar to that of the GaN film formation unit 40A, except for the material of the target 42. That is, the Mg film forming unit 40C and the Si film forming unit 40D are provided with a sputtering source consisting of a target 42, a backing plate 43 and an electrode 44, and a plasma generator consisting of a power supply unit 46 and a sputtering gas inlet unit 49.

In this embodiment, by operating the Mg film formation unit 40C together with the GaN film formation unit 40A and the nitriding unit 50 during GaN film formation, a layer containing a p-channel (p-type semiconductor) in which Mg ions have been added to the GaN layer can be formed. Furthermore, by operating the Si film formation unit 40D together with the GaN film formation unit 40A and the nitriding unit 50 during GaN film formation, a layer containing an n-channel (n-type semiconductor) in which Si ions have been added to the GaN layer can be formed.

Conventionally, to form n-channel and p-channel ions, after the GaN film is formed, Mg or Si ions are implanted using an ion implanter such as an ion beam, followed by heat treatment. However, with this method, ions are implanted into a film that has already reached a predetermined thickness, so the implantation depth and implantation amount (dose) may differ from the designed values, making control difficult. According to this embodiment, GaN film deposition and the addition of Si ions or Mg ions are alternately repeated until the GaN film reaches the predetermined thickness. This makes it easy to control the implantation depth and implantation amount of Mg ions and Si ions according to the thickness of the GaN layer formed per rotation by changing the power applied to the target 42 and the rotation speed of the turntable 31.

In addition, a series of depositions of the buffer layer, GaN layer, layer containing an n-channel, and layer containing a p-channel can be performed within a single chamber 20. This eliminates the need to move the layers to an environment separate from the GaN layer deposition environment to form the n-channel and p-channel, reducing transport time and eliminating the need to provide a separate space with an adjusted oxygen concentration.

(2) In addition to the above embodiment, as shown in FIG. 5, the film formation processing unit 40 may include an InN film formation processing unit 40E having a target 42 made of a film formation material containing InN. Since indium (In) has a low melting point, an InN target is actually made by adding nitrogen (N) to make a solid target 42. As described above, the InN target contains In atoms that are insufficiently bonded to nitrogen.

In this configuration, an InGaN film can be formed by operating the InN film formation unit 40E together with the GaN film formation unit 40A and nitriding unit 50 during GaN film formation. This InGaN film functions as the light-emitting layer 14 of the LED, as shown in FIG. 6(A). FIG. 6(A) shows the LED's layered structure, in which a buffer layer 11, a GaN layer 12 containing an n-channel, the buffer layer 11, a GaN layer 13 containing a p-channel, a light-emitting layer 14, and a transparent conductive film 15 are stacked on a silicon workpiece 10. The transparent conductive film 15 is an ITO (indium tin oxide) film. Note that electrodes are not shown. FIG. 6(B) also shows the buffer layer 11.

In this embodiment, the LED's buffer layer 11, GaN layer 12 containing an n-channel, buffer layer 11, GaN layer 13 containing a p-channel, and light-emitting layer 14 can be formed in a single chamber 20. This eliminates the need to move the LED to an environment separate from the GaN layer formation environment to form the light-emitting layer 14, reducing transport time. It also eliminates the need to provide a separate space with an adjusted oxygen concentration, etc. Furthermore, the color can be changed by changing the thickness of the light-emitting layer 14, and in this embodiment, the thickness can be easily controlled, making it easier to create light-emitting layers 14 of different colors.

(3) Different types of power supplies may be used in the film formation units forming films of different materials. For example, one film formation unit may be a DC power supply, and the other film formation unit may be a pulsed power supply equipped with a pulse switch. In this case, when adding Mg ions as described above, the GaN film formation unit 40A may be a DC power supply, and the Mg film formation unit 40C may be a pulsed power supply. Alternatively, when adding Si ions, the GaN film formation unit 40A may be a DC power supply, and the Si film formation unit 40D may be a pulsed power supply. In particular, by setting the pulse width and power so that a large amount of pulsed power is applied in a short period of time to perform HiPIMS (High Power Impulse Magnetron Sputtering), a high-density plasma can be generated, dramatically increasing the ionization rate of sputtered particles and enabling more efficient ion implantation.

Alternatively, the power supplies used in the film deposition processing units depositing films of the same type of material may be a combination of different types of power supplies, which may be switched at a predetermined timing. For example, a DC power supply and a pulsed power supply equipped with a pulse switch may be combined and switched at a predetermined timing. In this case, when depositing a GaN film, the pulsed power supply may be used only for the initial layer that comes into contact with the substrate or other types of film, and after the film has been deposited to a predetermined thickness, the film may be deposited using the DC power supply.

Other Embodiments
Although the embodiments and modifications of each part of the present invention have been described, these embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments described above can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and modifications are included within the scope and spirit of the invention, and are also included in the invention described in the claims.

The type and number of film formation units 40 and the number of nitriding units 50 provided within the chamber 20 are not limited to the above. The film formation apparatus 1 may be configured with only the GaN film formation unit 40A as the film formation unit 40 for forming a GaN film. Furthermore, in addition to the above-described film formation unit 40, a film formation unit 40 using a different target material, a film formation unit using the same target material, or a nitriding unit 50 may be added. For example, a film formation unit 40 having a target 42 containing indium oxide and tin oxide, which are ITO film formation materials, may be added to form an ITO film within the chamber 20. In this case, oxygen gas may be introduced into the nitriding unit 50 instead of nitrogen gas to compensate for oxidation of the ITO film. For example, the GaN film formation unit 40A, the Al film formation unit 40B, and the nitriding unit 50 may be operated simultaneously to form an AlGaN (aluminum gallium nitride) film containing Ga, Al, and N.

Furthermore, the n-type impurities or p-type impurities added in the impurity addition processing unit are not limited to those in the above-described embodiment. For example, n-type impurities can also be Ge or Sn. In this case, the film formation material that constitutes the target provided in the impurity addition processing unit can be a film formation material containing Ge or Sn instead of Si.

1 Film forming apparatus 10 Work 11 Buffer layer 12 GaN layer 13 GaN layer 14 Light emitting layer 15 Transparent conductive film 20 Chamber 20a Ceiling 20b Inner bottom surface 20c Inner peripheral surface 21 Exhaust port 22 Partition section 23 Exhaust section 30 Transport section 31 Rotary table 32 Motor 33 Holding section 34 Tray 40 Film forming processing section 40A GaN film forming processing section 40B Al film forming processing section 40C Mg film forming processing section 40D Si film forming processing section 40E InN film forming processing section 41 Processing space 42 Target 43 Backing plate 44 Electrode 46 Power supply section 47 Gas inlet 48 Piping 49 Sputtering gas inlet 50 Nitriding processing section 51 Cylindrical body 52 Window member 53 Antenna 54 RF power supply 55 Matching box 56 Gas inlet 57 Piping 58 Process gas inlet 59 Processing space 60 Heating section 70, Transfer chamber 71, Load lock section 80, Preheating chamber 90, Cooling chamber 100, Control device

Claims (11)

a chamber capable of creating a vacuum inside;
a rotary table provided in the chamber, which holds a workpiece and circulates the workpiece along a circular path;
a GaN film formation processing section including a target made of a film formation material containing GaN and a plasma generator for generating plasma from a sputtering gas introduced between the target and the rotary table, and for depositing particles of the film formation material containing GaN by sputtering on the workpiece circulated and transported by the rotary table;
a nitriding unit that nitrides particles of the film-forming material deposited in the GaN film-forming unit on the workpiece circulated and transported by the rotary table;
an impurity addition processing unit including a target made of a film formation material containing p-type impurities or n-type impurities, and a plasma generator for generating plasma from a sputtering gas introduced between the target made of the film formation material containing p-type impurities or n-type impurities and the rotary table, and for adding n-type impurities or p-type impurities by sputtering to particles of the film formation material containing GaN deposited on the workpiece in the GaN film formation processing unit;
and
The GaN film forming unit, the nitriding unit, and the impurity addition unit are arranged on the circulating transport path, and the turntable transports the workpiece so that GaN film formation, nitriding, and impurity addition are repeated by repeatedly passing the workpiece through the GaN film forming unit, the nitriding unit, and the impurity addition unit in that order, thereby forming a GaN film containing the n-type impurity or the p-type impurity on the workpiece with a predetermined number of layers . The film formation apparatus according to claim 1, characterized in that the sputtering gas is argon gas alone. an Al film forming processing unit that has a target made of a film forming material containing Al, and deposits particles of the film forming material containing Al by sputtering on the workpiece that is circulated and transported by the rotary table;
3. The film forming apparatus according to claim 1, wherein the nitriding unit nitrides particles of the film forming material deposited in the Al film forming unit onto the workpiece circulated and transported by the rotary table. The film formation apparatus of claim 3, characterized in that the GaN film formation processing unit, the Al film formation processing unit, and the nitriding processing unit form a film in which GaN films and AlN films are alternately stacked. the impurity addition processing unit has a target made of a film formation material containing Mg, and is an Mg film formation processing unit that deposits particles of the film formation material containing Mg by sputtering on the workpiece that is circulated and transported by the rotary table,
2. The film forming apparatus according to claim 1 , wherein the GaN film forming section, the nitriding section, and the Mg film forming section form a film of GaN doped with Mg. The impurity addition processing unit has a target made of a film formation material containing Si, and is a Si film formation processing unit that deposits particles of the film formation material containing Si by sputtering on the workpiece that is circulated and transported by the rotary table,
2. The film forming apparatus according to claim 1 , wherein the GaN film forming section, the nitriding section, and the Si film forming section form a film of GaN doped with Si. an InN film formation processing unit that has a target made of a film formation material containing InN and deposits particles of the film formation material containing InN by sputtering on the workpiece that is circulated and transported by the rotary table;
7. The film forming apparatus according to claim 1 , wherein the GaN film forming section, the nitriding section, and the InN film forming section form an InGaN film. 8. The film forming apparatus according to claim 1, further comprising a heating section for heating the workpieces circulated and transported by the rotary table. 9. The film forming apparatus according to claim 8 , further comprising a preheating chamber for heating the workpiece before it is carried into the chamber. 10. The film forming apparatus according to claim 1, wherein the power applied to the impurity doping processing section is applied by a pulse power supply. A film forming method in which a workpiece is held by a rotary table and circulated and transported along a circumferential path in a chamber capable of being evacuated, and a film is formed on the workpiece,
a GaN film formation process in which a GaN film formation processing unit having a target made of a film formation material containing GaN and a plasma generator that converts a sputtering gas introduced between the target and the rotary table into plasma deposits particles of the film formation material containing GaN by sputtering on the workpiece that is circulated and transported by the rotary table;
a nitriding process in which particles of the film-forming material deposited in the GaN film-forming process unit are nitrided on the workpiece circulated and transported by the rotary table by a nitriding process unit;
an impurity addition process of adding n-type impurities or p-type impurities by sputtering to particles of the GaN-containing film formation material deposited on the workpiece in the GaN film formation processing unit,
A film formation method characterized by forming a GaN film containing the n-type impurity or the p-type impurity on the workpiece with a predetermined number of layers by repeatedly performing the GaN film formation process, the nitriding process, and the impurity addition process in this order by circulating and transporting the workpiece.