Method for manufacturing semiconductor device

Abstract

This invention produces a high-quality N-polar gallium nitride layer at a low temperature. Provided is a method for manufacturing a semiconductor device, including a step for forming an N-polar gallium nitride layer. The N-polar gallium nitride layer is formed by a deposition apparatus using plasma generated using an electron cyclotron resonance phenomenon.

Description

Semiconductor device manufacturing method

[0001] The present invention relates to a method for manufacturing a semiconductor device, and relates to a technique that is effective when applied to, for example, a technique for forming a film by utilizing plasma.

[0002] Japanese Patent Application Laid-Open No. 2020-122178 (Patent Document 1) describes a technology in which ions contained in plasma generated using electron cyclotron resonance are collided with a target member, causing target particles ejected from the target member to adhere to the film-forming object, thereby forming a film on the film-forming object.

[0003] Japanese Patent Application Laid-Open No. 2020-122178

[0004] Gallium nitride (GaN) has a Ga-face and an N-face. A gallium nitride layer with a Ga-face on top is called a Ga-polar gallium nitride layer. On the other hand, a gallium nitride layer with an N-face on top is called an N-polar gallium nitride layer.

[0005] In recent years, N-polar gallium nitride layers have been attracting attention in HEMT (High Electron Mobility Transistor) devices with a GaN / AlGaN / GaN structure. Furthermore, N-polar gallium nitride layers have high high-temperature resistance. Furthermore, N-polar gallium nitride layers have a higher indium (In) incorporation efficiency than Ga-polar gallium nitride layers, making it easier to fabricate InGaN devices (semiconductor lasers). Thus, N-polar gallium nitride layers have various advantages.

[0006] The N-polarity gallium nitride layer is manufactured by, for example, MOCVD (Metal Organic Chemical Vapor Deposition). Specifically, an N-polarity gallium nitride layer cannot be obtained unless the surface of the sapphire substrate is nitrided by flowing ammonia gas before GaN formation in a high-temperature process of 800°C or higher. Furthermore, the MOCVD method has a narrow process margin, and may result in a layer in which Ga polarity and N polarity are mixed. Therefore, it is desirable to manufacture a high-quality N-polarity gallium nitride layer at a low temperature.

[0007] In one embodiment, a method for manufacturing a semiconductor device includes forming an N-polarity gallium nitride layer using a deposition apparatus that uses plasma generated by electron cyclotron resonance.

[0008] According to one embodiment, a high-quality N-polar gallium nitride layer can be produced at low temperatures.

[0009] 1 is a schematic diagram showing the external configuration of a cylindrical target used in a film formation apparatus; FIG. 2 is a diagram illustrating the tendency of substrates to be damaged when a disk target is used; FIG. 3 is a diagram illustrating the ability of substrate damage to be reduced when a cylindrical target is used; FIG. 4 is a table showing the advantages and disadvantages of using a cylindrical target and a disk target; FIG. 5 is a diagram illustrating a schematic configuration of a film formation apparatus in an embodied mode; FIG. 6 is a flowchart illustrating the flow of a first operation; FIG. 7 is a flowchart illustrating the flow of a second operation; FIG. 8 is a diagram illustrating a location where SIMS analysis was performed on a substrate on which a film was formed; FIG. 9 is a graph showing the relationship between the thickness of an amorphous silicon film formed on a substrate and the substrate position; FIG. 10 is a graph showing the relationship between silicon concentration and depth; FIG. 11 is a graph showing the relationship between magnesium concentration and depth; and FIG. 12 is a graph showing the relationship between aluminum concentration and depth. (a) is a diagram showing the crystal structure of Ga-polar gallium nitride, and (b) is a diagram showing the crystal structure of N-polar gallium nitride. (a) is a diagram showing a simulated image of Ga-polar gallium nitride, and (b) is a diagram showing a simulated image of N-polar gallium nitride. 1 is a diagram showing a simulated image by time-of-flight atom scattering surface analysis of an N-polar gallium nitride layer formed on an just substrate; 2 is a photograph showing the surface roughness of an N-polar gallium nitride layer formed on an just substrate; 3 is a diagram showing a simulated image by time-of-flight atom scattering surface analysis of an N-polar gallium nitride layer formed on a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction; 4 is a photograph showing the surface roughness of an N-polar gallium nitride layer formed on a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction; 5 (a) is a rocking curve of an N-polar gallium nitride layer formed on a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction, and 6 (b) is a rocking curve of an N-polar gallium nitride layer formed on an just substrate; 7 is a diagram showing the results of pole measurement of GaN(101) based on X-ray reflection;

[0010] In all the drawings for explaining the embodiments, the same components are generally designated by the same reference numerals, and repeated explanations thereof will be omitted. In addition, hatching may be used even in plan views to make the drawings easier to understand.

[0011] <Advantages of Cylindrical Targets> Cylindrical targets are used in film formation devices that implement ECR sputtering technology, while disk targets are used in film formation devices that implement general sputtering technologies such as RF sputtering and magnetron sputtering.

[0012] FIG. 1 is a schematic diagram showing the external configuration of a cylindrical target TA used in a film forming apparatus.

[0013] 1, the cylindrical target TA has a cylindrical shape. Specifically, the cylindrical target TA has a cylindrical backing tube (support member) 100 made of, for example, a copper material, and a cylindrical target member 110 is bonded to the inner wall of the backing tube 100 by a bonding material (adhesive material) not shown.

[0014] The cylindrical target TA configured in this manner can reduce damage to the substrate SUB compared to when a commonly used disk target is used. The advantages of this will be explained below.

[0015] 2 is a diagram illustrating the tendency for damage to occur to the substrate SUB when a disk target is used. In FIG. 2, a disk target TA2 is disposed so as to face the substrate SUB. This disk target TA2 has a support member 120 and a target member 130 disposed on the support member 120. The target member 130 is a member that is bombarded with positive ions, and examples of the positive ions include argon ions, nitrogen ions, krypton ions, and xenon ions.

[0016] 2, for example, positive ions 140 having kinetic energy collide with the target member 130, causing target particles 150 to fly out from the target member 130 and adhere to the surface of the substrate SUB. As a result, a film made up of the target particles 150 is formed on the surface of the substrate SUB.

[0017] However, at this time, the positive ions 140 having high energy that collide with the target member 130 are also recoiled, and when the disk target TA2 is used, the substrate SUB is disposed at a position opposite the disk target TA2, as shown in Fig. 2. Therefore, as shown in Fig. 2, the recoiled positive ions 140 having high energy are also likely to collide with the substrate SUB. In other words, when the disk target TA2 is used to form a film on the surface of the substrate SUB disposed opposite the disk target TA2, not only the target particles 150 that are components of the film but also the recoiled positive ions 140 having high energy are likely to collide with the surface of the substrate SUB.

[0018] For this reason, in a film formation apparatus configured to use a disk target TA2 to form a film on the surface of a substrate SUB arranged opposite the disk target TA2, the probability that high-energy recoiled positive ions 140 will collide with the substrate SUB increases, making it more likely that the substrate SUB will be damaged by the high-energy recoiled positive ions 140.

[0019] In contrast, Fig. 3 is a diagram illustrating that damage to the substrate SUB can be reduced when a cylindrical target TA is used. In Fig. 3, the cylindrical target TA is disposed at a position facing the substrate SUB. In the cylindrical target TA, a cylindrical target member 110 is disposed on the inner wall of a cylindrical backing tube 100. Therefore, in the cylindrical target TA shown in Fig. 3, the target member 110 is not disposed facing the substrate SUB.

[0020] 3, even in the case of the cylindrical target TA, positive ions 140 having kinetic energy collide with the target member 110, causing target particles 150 to fly out from the target member 110 and adhere to the surface of the substrate SUB. As a result, even when the cylindrical target TA is used, a film made of the target particles 150 can be formed on the surface of the substrate SUB.

[0021] On the other hand, in the cylindrical target TA shown in FIG. 3, unlike the disk target TA2 shown in FIG. 2, the target member 110 itself is not disposed opposite the substrate SUB.

[0022] For this reason, as shown in FIG. 3, in the cylindrical target TA, after colliding with the target member 110, the probability that the positive ions 140 having high energy recoil and collide with the substrate SUB is reduced.

[0023] Therefore, in a film forming apparatus configured to form a film on the surface of a substrate SUB using a cylindrical target TA, the probability that recoiled positive ions 140 will collide with the substrate SUB is reduced, thereby reducing damage to the substrate SUB caused by recoiled positive ions 140 with high energy colliding with the substrate SUB.

[0024] From the above, the cylindrical target TA shown in Fig. 3 has the advantage of being able to reduce damage to the substrate SUB compared to using the commonly used disk target TA2 (see Fig. 2). However, after investigations by the inventors, the film formation apparatus using the cylindrical target TA has the following disadvantages.

[0025] <Disadvantages of Cylindrical Targets> Figure 4 is a table showing the advantages and disadvantages of using a cylindrical target and a disk target. As shown in Figure 4, when a cylindrical target is used, damage to the substrate can be reduced compared to when a disk target is used. In other words, the advantage of using a cylindrical target is that damage to the substrate can be reduced.

[0026] On the other hand, as shown in Figure 4, disk targets are superior to cylindrical targets in terms of target price, ease of fabrication, and film deposition rate. In other words, cylindrical targets have the following disadvantages: (1) they are more difficult to fabricate than disk targets, and (2) their film deposition rate is slower than that of disk targets. In response to this, the present inventors have devised an approach that converts the disadvantages of ECR ​​sputtering technology into advantages, and have devised a method to enhance the usefulness of ECR ​​sputtering technology when this approach is adopted. The technical concept behind this devise is explained below.

[0027] <Basic idea (general concept) of the embodiment> The basic idea of ​​the present embodiment is to adopt ECR sputtering technology using a cylindrical target for depositing the first target particles, while adopting sputtering technology using a disk target for depositing the second target particles, assuming that first target particles and second target particles are deposited on a substrate.

[0028] That is, the basic idea is to combine ECR sputtering technology using ECR plasma and a cylindrical target with sputtering technology using plasma with a density different from that of ECR ​​plasma and a disk target.

[0029] In particular, focusing on the film formation rate, this basic concept is effective when a film to be deposited on a substrate is composed of a combination of first target particles and second target particles, and a material that does not require a high film formation rate is used as the first target while a material that does require a high film formation rate is used as the second target. This is because, in this case, by using a material that does not require a high film formation rate as the first target particles, the slow film formation rate, which is one of the disadvantages of ECR ​​sputtering technology using a cylindrical target, is eliminated. In other words, for materials that require a high film formation rate, the film formation rate can be ensured by adopting sputtering technology using a disk target rather than ECR sputtering technology using a cylindrical target. Therefore, according to this basic concept, the slow film formation rate, which is one of the disadvantages of ECR ​​sputtering technology using a cylindrical target, can be made less apparent. Furthermore, if there are advantages to adopting ECR sputtering technology using a cylindrical target as a technology for depositing first target particles on a substrate, an approach can be realized that turns the disadvantages of ECR ​​sputtering technology into advantages, thereby increasing the usefulness of ECR ​​sputtering technology.

[0030] Furthermore, focusing on the ease of target fabrication, this basic concept is also effective when a film to be deposited on a substrate is constructed from a combination of first target particles and second target particles, and the first target is made of a material that is easy to fabricate into a cylindrical target, while the second target is made of a material that is difficult to fabricate into a cylindrical target. This is because, when a material that is difficult to fabricate into a cylindrical target is used as the second target, the ease of target fabrication can be ensured by using a disk target, which is easy to fabricate, rather than constructing the second target from a cylindrical target. In other words, by using a disk target rather than a cylindrical target as the second target, the disadvantage of ECR ​​sputtering technology using a cylindrical target, namely, the difficulty of target fabrication, is eliminated. In other words, for materials that are difficult to fabricate into a cylindrical target, the difficulty of target fabrication can be avoided by using sputtering technology using a disk target rather than ECR sputtering technology using a cylindrical target.

[0031] Therefore, according to the basic concept, it is possible to prevent the difficulty of target fabrication, which is a disadvantage of ECR ​​sputtering technology using a cylindrical target, from becoming apparent. Furthermore, if there is an advantage to adopting ECR sputtering technology using a cylindrical target for the first target, an approach that turns the disadvantages of ECR ​​sputtering technology into advantages can be realized, thereby increasing the usefulness of ECR ​​sputtering technology.

[0032] <Basic idea (intermediate concept) in the embodiment> As described above, when focusing on the film formation rate, this basic idea is effective when a film to be deposited on a substrate is composed of a combination of first target particles and second target particles, and a material that does not require a high film formation rate is used as the first target, while a material that requires a high film formation rate is used as the second target.

[0033] Specifically, for example, a film formed by adding a doping material to a base material may be considered as a film to be deposited on a substrate. In this case, the basic idea is to employ ECR sputtering technology using a cylindrical target for depositing the doping material, while employing sputtering technology using a disk target for depositing the base material.

[0034] Here, the doping material is not the main component of the film deposited on the substrate, but an additive component. Therefore, the doping material does not require a high film formation rate. In other words, the doping material can be said to be a material that does not require a high film formation rate.

[0035] In contrast, since the base material is the main component of the film deposited on the substrate, a high film formation rate is required for the deposition of the base material. In other words, the base material can be said to be a material that requires a high film formation rate. Therefore, when applying the basic concept to deposit a film on a substrate in which a doping material is added to a base material, ECR sputtering technology using a cylindrical target is adopted for depositing the doping material, while sputtering technology using a disk target is adopted for depositing the base material. As a result, by using a doping material that does not require a high film formation rate as the first target particle, the slow film formation rate, which is one of the disadvantages of ECR ​​sputtering technology using a cylindrical target, is no longer a disadvantage.

[0036] In other words, for base materials that require a high film formation rate, the film formation rate can be ensured by adopting sputtering technology using a disk target rather than ECR sputtering technology using a cylindrical target.

[0037] Therefore, by applying this basic concept to the deposition of a film in which a doping material is added to a base material, the slow film formation rate, which is one of the disadvantages of ECR ​​sputtering technology using a cylindrical target, does not become a problem. If there are advantages to adopting ECR sputtering technology using a cylindrical target as a technology for depositing a doping material on a substrate, an approach that turns the disadvantages of ECR ​​sputtering technology into advantages can be realized, thereby increasing the usefulness of ECR ​​sputtering technology.

[0038] Specifically, there are advantages to employing ECR sputtering technology using a cylindrical target as a technology for depositing a doping material on a substrate, as will be explained below.

[0039] For example, sputtering techniques using a disk target are employed for deposition on a base substrate. Specifically, these sputtering techniques use plasma with a density different from that of ECR ​​plasma. Examples include magnetron sputtering and RF sputtering (hereinafter sometimes referred to as general sputtering techniques). In these general sputtering techniques, a large amount of power is supplied to the target from a sputtering power supply. This is because general sputtering techniques generate plasma using the large amount of power supplied to the target from the sputtering power supply. For this reason, when depositing a doping material on a substrate using general sputtering techniques, it is difficult to control the doping concentration to a low level due to the large amount of power applied to the disk target. In other words, because the amount of doping material added is very small, it is difficult to accurately control the doping amount (very small) using the large power supplied from the sputtering power supply.

[0040] In contrast, when ECR sputtering technology using a cylindrical target is adopted as a technology for depositing a doping material on a substrate, ECR sputtering technology utilizes the electron cyclotron resonance phenomenon to generate ECR plasma. Therefore, the power supplied from the sputtering power supply to the cylindrical target can be made smaller than the power supplied from the sputtering power supply to a disk target in general sputtering technology. This is because ECR sputtering technology does not generate ECR plasma using the power supplied from the sputtering power supply to the cylindrical target.

[0041] Therefore, ECR sputtering technology allows for a small power supply to the cylindrical target from the sputtering power supply, thereby reducing the number of target particles (particles constituting the doping material) that fly off the cylindrical target. This means that the small power supplied to the cylindrical target from the sputtering power supply makes it easy to precisely control the doping material concentration. In other words, ECR sputtering technology has the advantage of precisely controlling the amount of doping material added (a small amount) by controlling the small power supplied to the cylindrical target from the sputtering power supply. Thus, according to the basic concept, the disadvantage of ECR ​​sputtering technology, namely its slow film formation rate, is converted into the advantage of precisely controlling the amount of doping material added (a small amount) by adopting ECR sputtering technology using a cylindrical target as a technology for depositing doping material on a substrate. As a result, according to the basic concept, the usefulness of ECR ​​sputtering technology can be enhanced.

[0042] <Basic Concept (Subordinate Concept) of the Embodiments> As described above, when applying the basic concept, for example, a film formed by adding a doping material to a base material can be considered as a film to be deposited on a substrate. More specifically, gallium nitride (GaN) can be used as the base material, and silicon (Si), magnesium (Mg), or aluminum (Al) can be used as the doping material.

[0043] Gallium nitride is a semiconductor material. Adding silicon to gallium nitride produces an n-type semiconductor material, while adding magnesium to gallium nitride produces a p-type semiconductor material. Adding aluminum to gallium nitride produces AlGaN.

[0044] In this way, when gallium nitride is used as the base material and silicon, magnesium, or aluminum is used as the doping material, according to the basic concept, the disadvantage of ECR ​​sputtering technology, that is, the slow film formation speed, is converted into the advantage of being able to precisely control the amount (trace amount) of doping material added by adopting ECR sputtering technology using a cylindrical target as the technology for depositing the doping material (silicon, magnesium, aluminum) on the substrate. As a result, according to the basic concept, the usefulness of ECR ​​sputtering technology can be increased.

[0045] Furthermore, when focusing on the ease of target fabrication, gallium nitride is a material for which it is difficult to fabricate a cylindrical target. Therefore, by applying the basic concept, rather than constructing a target made of gallium nitride from a cylindrical target, it is possible to ensure the ease of target fabrication by adopting a disk target, which has excellent target fabrication ease. In other words, by adopting a disk target rather than a cylindrical target as a target made of gallium nitride, the difficulty of target fabrication, which is a disadvantage of ECR ​​sputtering technology using a cylindrical target, is no longer a disadvantage. In other words, for gallium nitride, for which it is difficult to fabricate a cylindrical target, it is possible to avoid the difficulty of target fabrication by adopting a general sputtering technology using a disk target rather than adopting an ECR sputtering technology using a cylindrical target.

[0046] On the other hand, for the doping materials silicon, magnesium, or aluminum, the cost of producing a cylindrical target is low and they are easy to produce. For this reason, ECR sputtering technology using a cylindrical target is adopted as a technology for depositing silicon, magnesium, or aluminum as a doping material on a substrate. This, according to the basic concept, allows for precise control of the amount of doping material added, thereby increasing the usefulness of ECR ​​sputtering technology.

[0047] <Embodiments> Hereinafter, embodiments that embody the above-described basic concept will be described.

[0048] <<Configuration of Film Forming Apparatus>> FIG. 5 is a diagram showing a schematic configuration of a film forming apparatus 1 in an embodiment.

[0049] 5, the film formation apparatus 1 has a film formation chamber 10. The film formation chamber 10 is provided with a sample stage 11 on which a substrate SUB, which is an object to be film-formed, is placed. The sample stage 11 is equipped with a vertical movement mechanism 12 for moving the sample stage 11 up and down, and a rotation mechanism 13 for rotating the substrate SUB placed on the sample stage 11. The sample stage 11 also has a heating mechanism for heating the substrate SUB. The film formation chamber 10 is provided with a supply port 14a for introducing a process gas, and a vacuum exhaust mechanism 14b for bringing the pressure in the film formation chamber 10 close to a vacuum state.

[0050] Next, the film formation apparatus 1 has an ECR sputtering section 2 connected to the film formation chamber 10. This ECR sputtering section 2 has a microwave oscillator 20 that generates microwaves, a microwave waveguide 21 that serves as a propagation path for the microwaves generated by the microwave oscillator 20, and a microwave introduction window 22 for introducing the microwaves into an ECR plasma chamber 25. The ECR sputtering section 2 has an ECR plasma chamber 25 connected to the microwave introduction window 22, and the microwaves emitted from the microwave introduction window 22 are introduced into the ECR plasma chamber 25.

[0051] 5, microwaves are introduced from the side of an ECR plasma chamber 25. That is, the film forming apparatus 1 is provided with a pair of microwave waveguides 21 branching off from a microwave oscillator 20, and each of the pair of microwave waveguides 21 is provided with a microwave introduction window 22.

[0052] The microwave introduction windows 22 are provided on the opposing side surfaces of the ECR plasma chamber 25, and the film forming apparatus 1 in the embodied embodiment employs a so-called "branch-coupled plasma source."

[0053] Inside the ECR plasma chamber 25, a protection cylinder 26 is provided, while around the periphery of the ECR plasma chamber 25, coils 23 and 24 for generating a magnetic field are arranged.

[0054] A mixed gas of, for example, nitrogen gas and argon gas is introduced into the ECR plasma chamber 25, and ECR plasma is generated from the mixed gas by the magnetic field generated by the coil 24 and microwaves introduced through the microwave introduction window 22. That is, in this embodiment, the microwave oscillator 20, microwave waveguide 21, microwave introduction window 22, coil 23, coil 24, and ECR plasma chamber 25 constitute a plasma generation unit (first plasma generation unit) that generates ECR plasma.

[0055] As described above, the plasma generating section has a microwave oscillator 20 that generates microwaves, a pair of microwave waveguides 21 that are microwave waveguides that propagate the microwaves generated by the microwave oscillator 20 and are arranged to branch off from the microwave oscillator 20, a microwave introduction window 22 provided in each of the pair of microwave waveguides 21, and an ECR plasma chamber 25 into which microwaves are introduced through the microwave introduction window 22, and the microwave introduction window 22 is provided on the side surface of the ECR plasma chamber 25.

[0056] Next, a cylindrical target TA is disposed so as to contact the ECR plasma chamber 25, and this cylindrical target TA is mounted on a cylindrical target mounting part 27. Here, the cylindrical target TA is a component that collides with positive ions (nitrogen ions or argon ions) that constitute the ECR plasma generated in the ECR plasma chamber 25, and is fixed to the cylindrical target mounting part 27. The cylindrical target mounting part 27 is electrically connected to a sputtering power supply 28, and power is supplied from the sputtering power supply 28. As a result, power is supplied to the cylindrical target TA fixed to the cylindrical target mounting part 27. Therefore, the sputtering power supply 28 functions as a power supply part (first power supply part) that can supply power to the cylindrical target TA. This sputtering power supply 28 is composed of, for example, a high-frequency power supply, a direct-current power supply (DC power supply), or a DC pulse power supply.

[0057] Next, the film formation apparatus 1 has a magnetron sputtering unit 3 connected to the film formation chamber 10. This magnetron sputtering unit 3 has a disk target mounting unit 31 on which a disk target TA2 can be mounted, and the disk target mounting unit 31 is provided with a magnetic field generating magnet 32 ​​that functions as a magnetic field generating unit.

[0058] The disk target mounting part 31 is electrically connected to the sputtering power supply 33, and power is supplied from the sputtering power supply 33. As a result, power is supplied to the disk target TA2 mounted on the disk target mounting part 31. Therefore, the sputtering power supply 33 functions as a power supply part (second power supply part) capable of supplying power to the disk target TA2. The sputtering power supply 33 is configured by, for example, a high-frequency power supply, a direct-current power supply (DC power supply), or a DC pulse power supply.

[0059] Here, due to the difference between the mechanism for generating ECR plasma in the ECR sputtering unit 2 and the mechanism for generating plasma (plasma having a different density from ECR plasma) in the magnetron sputtering unit 3, the first power value supplied from the sputtering power supply 28 to the cylindrical target TA is smaller than the second power value supplied from the sputtering power supply 33 to the disk target TA2. In other words, ECR plasma is generated using electron cyclotron resonance rather than the power supplied from the sputtering power supply 28 to the cylindrical target TA, whereas plasma in the magnetron sputtering unit 3 is generated based on the power supplied from the sputtering power supply 33 to the disk target TA2. For this reason, the first power value supplied from the sputtering power supply 28 to the cylindrical target TA is smaller than the second power value supplied from the sputtering power supply 33 to the disk target TA2.

[0060] In this way, in the magnetron sputtering unit 3, plasma having a density different from that of ECR ​​plasma is generated by the power supplied to the disk target TA2 from the sputtering power supply 33. In other words, the magnetron sputtering unit 3 functions as a plasma generating unit (second plasma generating unit) that generates plasma having a density different from that of ECR ​​plasma.

[0061] The disk target TA2 is a component that collides with positive ions (nitrogen ions and argon ions) that constitute the plasma generated in the plasma generating section (second plasma generating section), and is fixed to the disk target mounting section 31 via a magnetic field generating magnet 32.

[0062] The magnetron sputtering unit 3 is an example of a unit that realizes general sputtering technology, and for example, instead of the magnetron sputtering unit 3, a unit that realizes general sputtering technology can be composed of an RF sputtering unit, a DC sputtering unit, a DC pulse sputtering unit, etc.

[0063] In the film forming apparatus 1 configured in this manner, ions (ions that constitute ECR plasma) are collided with the cylindrical target TA mounted on the cylindrical target mounting part 27, causing the ejected target particles (first target particles) to be deposited, and ions (ions that constitute plasma having a density different from that of ECR ​​plasma) are collided with the disk target TA2 mounted on the disk target mounting part 31, causing the ejected target particles (second target particles) to be deposited on the surface of the substrate SUB.

[0064] At this time, in the film forming apparatus 1, a first operation of depositing the first target particles on the substrate SUB and a second operation of depositing the second target particles on the substrate SUB are performed simultaneously, but the first deposition rate of depositing the first target particles on the substrate SUB is slower than the second deposition rate of depositing the second target particles on the substrate SUB.

[0065] The film deposited on the substrate SUB is, for example, a film in which a doping material is added to a base material. In this case, the first target particles constituting the cylindrical target TA are the doping material, and the second target particles constituting the disk target TA2 are the base material. In a specific example, the base material is gallium nitride, while the doping material is any of silicon, magnesium, and aluminum.

[0066] The cylindrical target mounting part 27 is tilted in cross-sectional view so that a first angle θ1 formed between a normal axis VL1 to the surface of the sample stage 11 and a central axis VL2 of the cylindrical target mounting part 27 has a finite value. The disc target mounting part 31 is positioned on the opposite side of the cylindrical target mounting part 27 with respect to the normal axis VL1 in cross-sectional view, and is tilted in cross-sectional view so that a second angle θ2 formed between the normal axis VL1 and a central axis VL3 of the disc target mounting part 31 has a finite value. In this case, for example, the cylindrical target mounting part 27 and the disc target mounting part 31 are each tilted with respect to the normal axis VL1 of the sample stage 11 so that the first angle θ1 and the second angle θ2 are equal.

[0067] The film forming apparatus 1 in the embodied embodiment is configured as described above.

[0068] <<Operation of Film Forming Apparatus>> Next, a film forming operation in the film forming apparatus 1 will be described.

[0069] In the film forming apparatus 1, a first operation based on the ECR sputtering unit 2 and a second operation based on the magnetron sputtering unit 3 are simultaneously performed. As a result, for example, an n-type gallium nitride film, a p-type gallium nitride film, or an AlGaN film can be deposited on the substrate SUB.

[0070] First, a first operation based on the ECR sputtering unit 2 will be described below.

[0071] FIG. 6 is a flowchart illustrating the flow of the first operation.

[0072] First, in FIG. 5 , a mixed gas of, for example, nitrogen gas and argon gas is introduced into an ECR plasma chamber 25 (first plasma generation unit). When a magnetic field is generated by a coil 24 (magnetic field generation unit) disposed around the ECR plasma chamber 25, electrons contained in the mixed gas introduced into the ECR plasma chamber 25 undergo circular motion due to the Lorentz force. At this time, a microwave (electromagnetic wave) having the same period (or frequency) as the period (or frequency) of the circular motion of the electrons is generated by a microwave oscillator 20. This microwave is introduced into the ECR plasma chamber 25 through a microwave introduction window 22 via a microwave waveguide 21. The circularly moving electrons then resonate with the microwave, efficiently supplying the microwave energy to the circularly moving electrons (electron cyclotron resonance phenomenon) (S101 in FIG. 6 ). As a result, the kinetic energy of the electrons contained in the mixed gas increases, causing the mixed gas to separate into positive ions and electrons. This generates an ECR plasma consisting of positive ions and electrons (S102 in FIG. 6 ).

[0073] Next, referring to FIG. 5 , a high-frequency voltage (high-frequency power), for example, is supplied from the sputtering power supply 28 to the cylindrical target TA. In this case, a positive potential and a negative potential are alternately applied to the cylindrical target TA to which the high-frequency voltage is supplied. Among the positive ions and electrons that constitute the ECR plasma, only light-mass electrons can follow the high-frequency voltage applied to the cylindrical target TA, while heavy-mass positive ions cannot. As a result, the positive potential that attracts the following electrons is offset by the negative charge of the electrons, while the negative potential remains, so the average value of the high-frequency power shifts from 0 V to a negative potential. This means that even though a high-frequency voltage is applied to the cylindrical target TA, it can be considered as if a negative potential is applied to the cylindrical target TA. As a result, the positive ions are attracted to the cylindrical target TA, which is considered to have an average negative potential, and collide with the cylindrical target TA (S103 in FIG. 6 ).

[0074] Next, when the positive ions collide with the cylindrical target TA, the first target particles constituting the cylindrical target TA receive part of the kinetic energy of the positive ions and fly out of the cylindrical target TA into the internal space of the film formation chamber 10 (S104 in FIG. 6).

[0075] Thereafter, some of the first target particles that have flown out into the internal space of the film formation chamber 10 adhere to the surface of the substrate SUB placed on the sample stage 11 (S105 in FIG. 6). Then, by repeating this phenomenon, a large number of first target particles adhere to the surface of the substrate SUB, and as a result, the first target particles are deposited on the surface of the substrate SUB (S106 in FIG. 6).

[0076] In this manner, the first operation in the film forming apparatus 1 is realized.

[0077] Next, a second operation based on the magnetron sputtering unit 3 will be described.

[0078] FIG. 7 is a flowchart illustrating the flow of the second operation.

[0079] First, in FIG. 5, a voltage is applied from the sputtering power supply 33 to the disk target mounting part 31. This applies a voltage to the disk target TA2 mounted on the disk target mounting part 31 (S201 in FIG. 7). Meanwhile, the substrate SUB placed on the sample stage 11 in the film formation chamber 10 is set to a predetermined potential (e.g., a floating potential). Therefore, a potential difference occurs between the disk target TA2 and the substrate SUB. As a result, a mixed gas of nitrogen gas and argon gas supplied to the film formation chamber 10 is converted into plasma between the disk target TA2 and the substrate SUB, generating plasma (S202 in FIG. 7).

[0080] 5, the disk target mounting portion 31 is provided with a magnetic field generating magnet 32, which generates a magnetic field on the surface of the disk target TA2. This magnetic field causes the plasma to concentrate near the surface of the disk target TA2. As a result, ions constituting the plasma efficiently collide with the disk target TA2 (S203 in FIG. 7).

[0081] Subsequently, when the ions collide with the disk target TA2, the second target particles constituting the disk target TA2 receive part of the kinetic energy of the ions and fly out of the disk target TA2 into the internal space of the film formation chamber 10 (S204 in FIG. 7).

[0082] Thereafter, some of the second target particles that have flown out into the internal space of the film formation chamber 10 adhere to the surface of the substrate SUB placed on the sample stage 11 (S205 in FIG. 7). Then, by repeating this phenomenon, a large number of second target particles adhere to the surface of the substrate SUB, and as a result, the second target particles are deposited on the surface of the substrate SUB (S206 in FIG. 7).

[0083] In this manner, the second operation in the film forming apparatus 1 is realized.

[0084] The above-described first and second operations are simultaneously performed in the film forming apparatus 1. As a result, both the first target particles and the second target particles are deposited on the surface of the substrate SUB.

[0085] For example, when the first target particles are a doping material and the second target particles are a base material, a film made of the base material to which the doping material has been added is formed on the substrate SUB.

[0086] Further, to give a specific example, when the first target particles are silicon and the second target particles are gallium nitride, an n-type gallium nitride film is formed on the surface of the substrate SUB. On the other hand, when the first target particles are magnesium and the second target particles are gallium nitride, a p-type gallium nitride film is formed on the surface of the substrate SUB. Also, when the first target particles are aluminum and the second target particles are gallium nitride, an AlGaN film is formed on the surface of the substrate SUB.

[0087] By operating the film formation apparatus 1 in the above-described manner, for example, a film formation method having the following steps is realized: that is, this film formation method includes the steps of mounting the cylindrical target TA on the cylindrical target mounting part 27, mounting the disk target TA2 on the disk target mounting part 31, generating ECR plasma, generating plasma having a density different from that of the ECR plasma, and depositing first target particles ejected by colliding the cylindrical target TA mounted on the cylindrical target mounting part 27 with ions constituting the ECR plasma onto the substrate SUB, and depositing second target particles ejected by colliding the disk target TA2 mounted on the disk target mounting part 31 with ions constituting the plasma onto the substrate SUB, thereby forming a film containing the first target particles and the second target particles as components on the substrate SUB.

[0088] <Features of the Realized Aspects> Next, features of the specific aspects will be described.

[0089] A first feature of this specific embodiment is that the film deposition apparatus 1 includes an ECR sputtering unit 2 and a magnetron sputtering unit 3. That is, the first feature is that a film is deposited on a substrate SUB by combining an ECR sputtering technique using a cylindrical target TA and a magnetron sputtering technique using a disk target TA2.

[0090] This first feature is effective when forming a film made of a base material to which a doping material has been added on a substrate SUB. Specifically, when forming a film made of a base material to which a doping material has been added on a substrate SUB, the first feature is applied by forming the cylindrical target TA from the doping material and using ECR sputtering technology to deposit the doping material, and by forming the disk target TA2 from the base material and using magnetron sputtering technology to deposit the base material.

[0091] As a result, the ECR sputtering technique allows a smaller voltage to be applied to the target than the magnetron sputtering technique, which makes it easier to control the amount of first target particles that fly out from the cylindrical target TA, for example. This means that when the cylindrical target TA is made of a doping material, it is easier to control the amount of doping material added (first advantage).

[0092] On the other hand, magnetron sputtering technology has a faster film formation rate than ECR sputtering technology. Therefore, by constructing the disk target TA2 from a base material and using magnetron sputtering technology to deposit the base material, the film formation rate of the base material can be ensured (second advantage). Here, the doping material is a substance added to the base material, and since the deposition amount is smaller than that of the base material, a film formation rate is not required. Therefore, the material that requires a film formation rate is the base material, and the first feature is useful in that it can improve the film formation rate of the base material.

[0093] From the above, according to the first feature, it is possible to obtain both the first and second advantages described above, and therefore the first feature is a technical idea that is particularly effective when applied when forming a film made of a base material to which a doping material has been added on a substrate SUB.

[0094] For example, by using the first feature, it is possible to form an n-type gallium nitride film (dopant: silicon, base material: gallium nitride), a p-type gallium nitride film (dopant: magnesium, base material: gallium nitride), or an AlGaN film (dopant: aluminum, base material: gallium nitride) on the substrate SUB.

[0095] At this time, according to the first feature, a disk target TA2 can be used as the gallium nitride target instead of the cylindrical target TA. In this regard, it is difficult to produce a cylindrical gallium nitride target TA. Therefore, according to the first feature, in which the disk target TA2 is used as the gallium nitride target instead of the cylindrical target TA, the advantage of being able to easily produce a gallium nitride target is obtained.

[0096] As described above, the first feature has great technical significance in that it provides a technical idea that enables a gallium nitride film doped with a doping material to be formed using sputtering technology rather than CVD (Chemical Vapor Deposition).

[0097] Next, a second feature of the embodiment is that, for example, as shown in FIG. 5, the cylindrical target mounting portion 27 is tilted so that a first angle θ1 formed between the normal axis VL1 of the surface of the sample stage 11 and the central axis VL2 of the cylindrical target mounting portion 27 is a finite value.

[0098] As a result, according to the second feature, it is possible to improve the uniformity of deposition of the first target particles (dopant) deposited on the substrate SUB placed on the sample stage 11 compared to when the cylindrical target mounting part 27 and the sample stage 11 are arranged opposite to each other (θ1 = 0). In other words, as a result of extensive research, the inventors have newly discovered that the uniformity of deposition of the first target particles deposited on the substrate SUB can be improved by arranging the cylindrical target mounting part 27 at an angle with respect to the sample stage 11, and the second feature is adopted based on this discovery.

[0099] Similarly, the second feature is that, for example, as shown in FIG. 5, the disk target mounting portion 31 is arranged on the opposite side of the cylindrical target mounting portion 27 with respect to the normal axis VL1, and is arranged at an angle such that the second angle θ2 formed between the normal axis VL1 and the central axis VL3 of the disk target mounting portion 31 is a finite value.

[0100] As a result, according to the second feature, it is possible to improve the uniformity of deposition of the second target particles (base material) deposited on the substrate SUB placed on the sample stage 11 compared to when the disk target mounting part 31 and the sample stage 11 are arranged opposite to each other (θ2 = 0). In other words, as a result of extensive investigation, the inventors have newly discovered that the uniformity of deposition of the second target particles deposited on the substrate SUB can be improved by arranging the disk target mounting part 31 at an angle with respect to the sample stage 11, and the second feature is adopted based on this discovery.

[0101] Here, in the film formation process by the magnetron sputtering unit 3 using the disk target TA2, damage to the substrate SUB is greater than in the film formation process by the ECR sputtering unit 2 using the cylindrical target TA. This is because, as explained in the section "<Advantages of Cylindrical Targets>", when the cylindrical target TA is used, the probability that high-energy recoiled positive ions will collide with the substrate SUB can be reduced compared to when the disk target TA2 is used. In other words, when the disk target TA2 is used, the probability that high-energy recoiled positive ions will collide with the substrate SUB is higher compared to when the cylindrical target TA is used, and therefore damage to the substrate SUB caused by collisions of high-energy recoiled positive ions is greater.

[0102] In this regard, in the second feature, the disk target mounting part 31 is tilted so that the second angle θ2 formed by the normal axis VL1 and the central axis VL3 of the disk target mounting part 31 becomes a finite value. In other words, due to the second feature, the disk target mounting part 31 and the sample stage 11 are not arranged facing each other. Here, the tilted arrangement according to the second feature can reduce the probability that high-energy recoiled positive ions will collide with the substrate SUB compared to the facing arrangement. Therefore, according to the second feature, the effect of reducing damage to the substrate SUB can also be obtained in the film formation process by the magnetron sputtering unit 3 using the disk target TA2.

[0103] 5, a third feature of the specific embodiment is that a microwave introduction window 22 is provided on the side surface of the ECR plasma chamber 25. In other words, the third feature is that a configuration is adopted in which microwaves are introduced into the ECR plasma chamber 25 from the side surface of the ECR plasma chamber 25.

[0104] This third feature provides the advantage of enabling long-term operation of the film forming apparatus 1. For example, a microwave introduction window may be provided in the lower portion (bottom) of the ECR plasma chamber 25. In this configuration, microwaves are introduced into the ECR plasma chamber 25 from the lower portion of the ECR plasma chamber 25.

[0105] Here, positive ions constituting the ECR plasma generated inside the ECR plasma chamber 25 collide with the cylindrical target TA provided at the top (outlet) of the ECR plasma chamber 25, causing first target particles to fly out from the cylindrical target TA. At this time, the first target particles flying out from the cylindrical target TA adhere not only to the substrate SUB but also to the inside of the ECR plasma chamber 25 and the microwave introduction window 22.

[0106] In this regard, in a configuration in which a microwave introduction window is provided at the bottom of the ECR plasma chamber 25, the first target particles flying out from the cylindrical target TA tend to adhere to the microwave introduction window. If an increasing number of first target particles adhere to the microwave introduction window, it becomes difficult to introduce microwaves into the ECR plasma chamber 25 through the microwave introduction window. As a result, in a configuration in which a microwave introduction window is provided at the bottom of the ECR plasma chamber 25, it becomes difficult to operate the film formation apparatus 1 for a long period of time.

[0107] 5, in a configuration in which the microwave introduction window 22 is provided on the side surface of the ECR plasma chamber 25, the amount of first target particles adhering to the microwave introduction window 22 is smaller than in a configuration in which the microwave introduction window is provided in the lower portion of the ECR plasma chamber 25. This is because it is believed that the amount of first target particles adhering is smaller when the microwave introduction window 22 is located on the side surface of the ECR plasma chamber 25 rather than at the lower portion. Also, as shown in FIG. 5, the side surface of the ECR plasma chamber 25 is provided with an adhesion protection tube 26, which is believed to contribute to suppressing adhesion of the first target particles to the microwave introduction window 22 provided on the side surface of the ECR plasma chamber 25.

[0108] In this way, according to the third feature of the embodied aspect, the amount of first target particles adhering to the microwave introduction window 22 can be reduced, which makes it difficult for microwaves to be obstructed from being emitted from the microwave introduction window 22. Therefore, according to the third feature, an advantage is obtained in that the film formation apparatus 1 can be operated for a long period of time.

[0109] <Verification of Effect> Below, we will explain the verification results that, according to the embodiment, when forming a film made of a base material to which a doping material has been added, the amount of doping material added can be controlled by changing the power (voltage) applied to the target.

[0110] Fig. 8 is a diagram showing locations where SIMS analysis was performed on a substrate SUB on which a film was formed. The substrate SUB is formed, for example, from an 8-inch wafer, and Fig. 8 shows the center position (0 mm), a position 20 mm from the center, a position 40 mm from the center, a position 60 mm from the center, and a position 80 mm from the center. For example, in the film forming apparatus 1 shown in Fig. 5, an amorphous silicon film is formed on the substrate SUB using a cylindrical target TA made of silicon while not using a disk target TA2.

[0111] 9 is a graph showing the relationship between the thickness of the amorphous silicon film formed on the substrate SUB and the substrate position. As shown in FIG. 9, the thickness of the amorphous silicon film is approximately 150.0 nm at any position on the substrate, and it can be seen that, according to the embodied embodiment, the amorphous silicon film is uniformly formed. In particular, based on FIG. 9, the thickness uniformity is approximately ±1.7%. As such, it is confirmed that, according to the embodied embodiment, silicon, which is the doping material of the n-type gallium nitride film, can be formed as a highly uniform film on the substrate SUB.

[0112] Next, in the film forming apparatus 1 shown in FIG. 5, a cylindrical target TA made of silicon and a disk target TA2 made of gallium nitride are used to form a silicon-doped gallium nitride film (n-type gallium nitride film) on the substrate SUB.

[0113] Here, during operation of the film forming apparatus 1 (during film formation), the power supplied to the cylindrical target TA is changed in three stages (power P1 > power P2 > power P3).Then, the silicon concentration distribution in the depth direction of the film is measured using the SIMS method at the center position (0 mm), a position 20 mm from the center, a position 40 mm from the center, a position 60 mm from the center, and a position 80 mm from the center.

[0114] FIG. 10 is a graph showing the relationship between silicon concentration and depth.

[0115] 10, it can be seen that the silicon concentration in the film can be controlled depending on the power (electric power) supplied to the cylindrical silicon target TA. For example, it can be seen that the greater the power, the higher the silicon concentration in the film. Furthermore, as shown in FIG. 9, according to the film forming apparatus 1 of the embodied embodiment, an amorphous silicon film with high in-plane uniformity is formed, and as shown in FIG. 10, the silicon concentration distribution in the gallium nitride film is also uniform.

[0116] From the above, it is confirmed that, according to the embodied embodiment, it is possible to form an n-type gallium nitride film with a uniform thickness at any position on the substrate SUB. Furthermore, according to the embodied embodiment, it is also confirmed that the silicon concentration in the n-type gallium nitride film can be controlled by changing the power supplied to the cylindrical target TA. Therefore, it can be said that the film forming apparatus 1 is excellent in that it can form an n-type gallium nitride film having a desired silicon concentration on the substrate SUB with high in-plane uniformity.

[0117] Next, an example will be described in which a magnesium-doped gallium nitride film (p-type gallium nitride film) is formed on a substrate SUB using a cylindrical target TA made of magnesium and a disk target TA2 made of gallium nitride in the film forming apparatus 1 shown in FIG.

[0118] Here, during operation of the film forming apparatus 1 (during film formation), the power supplied to the cylindrical target TA is changed in four stages (power P1 > power P2 > power P3 > power P4).The magnesium concentration distribution in the film depth direction is measured using the SIMS method at the center position (0 mm), a position 20 mm from the center, a position 40 mm from the center, a position 60 mm from the center, and a position 80 mm from the center.

[0119] FIG. 11 is a graph showing the relationship between magnesium concentration and depth.

[0120] 11, it can be seen that the magnesium concentration in the film can be controlled depending on the power (electricity) supplied to the cylindrical target TA made of magnesium. For example, it can be seen that the greater the power, the higher the magnesium concentration in the film can be. Furthermore, the magnesium concentration distribution in the gallium nitride film is also uniform.

[0121] From the above, it is confirmed that, according to the embodied embodiment, it is possible to form a p-type gallium nitride film with a uniform thickness at any position on the substrate SUB. Furthermore, according to the embodied embodiment, it is also confirmed that the magnesium concentration in the p-type gallium nitride film can be controlled by changing the power supplied to the cylindrical target TA. Therefore, it can be said that the film formation apparatus 1 is excellent in that it can form a p-type gallium nitride film having a desired magnesium concentration on the substrate SUB with high in-plane uniformity.

[0122] Next, an example will be described in which a cylindrical target TA made of aluminum and a disk target TA2 made of gallium nitride are used in the film formation apparatus 1 shown in FIG. 5 to form an aluminum-doped gallium nitride film (AlGaN) on a substrate SUB.

[0123] During operation of the film forming apparatus 1 (during film formation), the power supplied to the cylindrical target TA is changed in four stages (power P1 > power P2 > power P3 > power P4).Then, the aluminum concentration distribution in the depth direction of the film is measured using the SIMS method at the center position (0 mm), a position 20 mm from the center, a position 40 mm from the center, a position 60 mm from the center, and a position 80 mm from the center.

[0124] FIG. 12 is a graph showing the relationship between aluminum concentration and depth.

[0125] 12, it can be seen that the aluminum concentration in the film can be controlled depending on the power (electricity) supplied to the cylindrical aluminum target TA. For example, it can be seen that the greater the power, the higher the aluminum concentration in the film. Furthermore, the aluminum concentration distribution in the gallium nitride film is also uniform.

[0126] From the above, it is confirmed that, according to the embodied embodiment, it is possible to form an AlGaN film with a uniform thickness at any position on the substrate SUB. It is also confirmed that, according to the embodied embodiment, it is possible to control the aluminum concentration in the AlGaN film by changing the power supplied to the cylindrical target TA. Therefore, it can be said that the film formation apparatus 1 is excellent in that it can form an AlGaN film having a desired aluminum concentration on the substrate SUB with high in-plane uniformity.

[0127] As described above, according to the embodiment, it has been confirmed by SIMS analysis that the doping distribution can be controlled by power and that the doping distribution is good. In particular, the tilt rotation type film deposition apparatus according to the embodiment is characterized by being able to obtain a highly uniform film thickness distribution, and this characteristic is supported by the results of SIMS analysis shown in Figures 10 to 12.

[0128] In a typical sputtering apparatus, it is difficult to maintain a stable plasma when the power applied to the target is reduced. In contrast, in the film formation apparatus 1 of the embodied embodiment, plasma is generated not at the target but in an ECR plasma source. Therefore, the film formation apparatus 1 of the embodied embodiment is superior in that it enables stable doping of the film even under conditions where the power applied to the target is low.

[0129] <Application Example> In the application example, an example of forming an N-polarity gallium nitride layer using the above-described ECR plasma film forming apparatus will be described.

[0130] Gallium nitride includes Ga-polar gallium nitride, whose upper surface is a Ga face, and N-polar gallium nitride, whose upper surface is an N face. Figure 13(a) is a diagram showing the crystal structure of Ga-polar gallium nitride. On the other hand, Figure 13(b) is a diagram showing the crystal structure of N-polar gallium nitride.

[0131] Next, simulated images of time-of-flight low energy atom scattering spectroscopy (TOFLAS) are shown. Fig. 14(a) shows a simulated image of Ga-polar gallium nitride. On the other hand, Fig. 14(b) shows a simulated image of N-polar gallium nitride.

[0132] A feature of this application example is that an N-polar gallium nitride layer is formed using an ECR plasma deposition apparatus that uses plasma generated by utilizing the electron cyclotron resonance phenomenon. The ECR plasma deposition apparatus generates high-density plasma, which allows the N-polar gallium nitride layer to be formed at temperatures lower than 800°C. For example, the N-polar gallium nitride layer can be formed at a temperature of 350°C. The N-polar gallium nitride layer is formed, for example, on a sapphire substrate (aluminum oxide substrate). However, using an ECR plasma deposition apparatus, the substrate can be nitrided at temperatures as low as 350°C using ECR plasma (high-density plasma). Therefore, an aluminum nitride film (AlN film) is formed on the surface of the sapphire substrate. Here, the gallium nitride layer formed on the aluminum nitride film is an N-polar gallium nitride layer. Therefore, according to this application example, the N-polar gallium nitride layer can be formed at temperatures as low as 350°C by using an ECR plasma deposition apparatus.

[0133] Furthermore, by using the ECR plasma film formation apparatus shown in FIG. 5, it is possible to easily form an n-type, N-polar gallium nitride layer doped with silicon (n-type impurity: donor) and a p-type, N-polar gallium nitride layer doped with magnesium (p-type impurity: acceptor).

[0134] Furthermore, unlike GaN (Ga polarity) / AlGaN structure HEMT devices, GaN (N polarity) / AlGaN / GaN (N polarity) structure HEMT devices have the advantage of being able to achieve high performance without thinning the AlGaN layer. In this regard, the ECR plasma deposition apparatus shown in FIG. 5 can also form an AlGaN layer. Because the ECR plasma deposition apparatus can easily form an N-polarity gallium nitride layer and an AlGaN layer, it is also suitable for manufacturing GaN (N polarity) / AlGaN / GaN (N polarity) structure HEMT devices.

[0135] The N-polarity gallium nitride layer is formed on, for example, a sapphire substrate. Specifically, the N-polarity gallium nitride layer is formed on a sapphire substrate (sometimes called an "off-axis substrate") that does not have an off-axis angle. Fig. 15 shows a simulated image of the N-polarity gallium nitride layer formed on the off-axis substrate, obtained by time-of-flight atom scattering surface analysis.

[0136] In this way, by using an ECR plasma deposition apparatus, an N-polarity gallium nitride layer can be formed on a just-aligned substrate. However, according to the inventor's investigation, it was found that the surface roughness of the N-polarity gallium nitride layer formed on the just-aligned substrate is large. Figure 16 is a photograph showing the surface roughness of the N-polarity gallium nitride layer formed on the just-aligned substrate. For example, the surface roughness of the N-polarity gallium nitride layer formed on the just-aligned substrate is 1.34 nm.

[0137] In this regard, it is desirable that the surface roughness of the N-polar gallium nitride layer be small. For example, when focusing on an N-polar gallium nitride layer used in a HEMT, two-dimensional electron gas is generated at the interface between the AlGaN layer and the N-polar gallium nitride layer. In this case, if the surface roughness of the N-polar gallium nitride layer is large, electron scattering in the two-dimensional electron gas increases. Therefore, in order to suppress electron scattering, it is desirable that the surface roughness of the N-polar gallium nitride layer be small. Therefore, efforts have been made to reduce the surface roughness of the N-polar gallium nitride layer. Specifically, in an application example, the N-polar gallium nitride layer is formed on a sapphire substrate having an off-angle. For example, the N-polar gallium nitride layer is formed on a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction. This reduces the surface roughness of the N-polar gallium nitride layer. The M-axis direction refers to the normal direction to the side surface (M-plane) of the hexagonal prism constituting the hexagonal crystal.

[0138] 17 shows a simulated image by time-of-flight atom scattering surface analysis of an N-polar gallium nitride layer formed on a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction. Also, FIG. 18 is a photograph showing the surface roughness of an N-polar gallium nitride layer formed on a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction. For example, the surface roughness of an N-polar gallium nitride layer formed on a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction is 0.33 nm. Therefore, by forming an N-polar gallium nitride layer on a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction, the surface roughness of the N-polar gallium nitride layer can be made smaller than the surface roughness of an N-polar gallium nitride layer formed on an just substrate.

[0139] In the above example, a sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction is used. However, the present inventors have evaluated gallium nitride layers formed on sapphire substrates having off-angles of 0.2 degrees, 0.5 degrees, 1.0 degrees, 3.0 degrees, 5.0 degrees, 8.0 degrees, or 10.0 degrees in the M-axis direction, in addition to sapphire substrates having off-angles of 0.5 degrees in the M-axis direction. As a result, it was confirmed that all gallium nitride layers formed on sapphire substrates having off-angles of 0.2 degrees, 0.5 degrees, 1.0 degrees, 3.0 degrees, 5.0 degrees, 8.0 degrees, or 10.0 degrees in the M-axis direction using an ECR plasma deposition apparatus were N-polar gallium nitride layers. Furthermore, it was confirmed that the surface roughness of an N-polar gallium nitride layer formed on a sapphire substrate having an off-angle of 0.2 degrees, 0.5 degrees, 1.0 degrees, 3.0 degrees, 5.0 degrees, 8.0 degrees, or 10.0 degrees in the M-axis direction is smaller than the surface roughness of an N-polar gallium nitride layer formed on an just substrate. Therefore, in order to form an N-polar gallium nitride layer with small surface roughness, it is desirable to use an ECR plasma deposition apparatus and a substrate having an off-angle of more than 0 degrees and not more than 10.0 degrees in the M-axis direction.

[0140] Next, Fig. 19 is a graph showing rocking curves of GaN (0002) in X-ray diffraction measurements. In particular, Fig. 19(a) shows the rocking curve of an N-polar gallium nitride layer formed on a sapphire substrate with an off-angle of 0.5 degrees in the M-axis direction. Fig. 19(b) shows the rocking curve of an N-polar gallium nitride layer formed on an just-aligned substrate.

[0141] In Figure 19(a), the full width at half maximum (FWHM) of the rocking curve is 0.06°. On the other hand, in Figure 19(b), the full width at half maximum of the rocking curve is 0.05°. As a result, the crystallinity of the gallium nitride is maintained in both the N-polar gallium nitride layer formed on the sapphire substrate having an off-angle of 0.5 degrees in the M-axis direction and the N-polar gallium nitride layer formed on the just substrate.

[0142] 20A and 20B are diagrams showing the results of pole measurement of GaN (101) based on X-ray reflection peaks. In particular, Fig. 20A shows the results of pole measurement of an N-polarity gallium nitride layer formed on an just substrate. Fig. 20B shows the results of pole measurement of an N-polarity gallium nitride layer formed on a sapphire substrate with an off-angle of 0.5 degrees in the M-axis direction.

[0143] In both FIG. 20(a) and FIG. 20(b), a peak with six-fold symmetry corresponding to GaN with a hexagonal crystal structure is detected, indicating epitaxial growth.

[0144] For these reasons, in the application example, an N-polarity gallium nitride layer is formed using an ECR plasma deposition apparatus that uses plasma generated by utilizing the electron cyclotron resonance phenomenon. In this case, the ECR plasma deposition apparatus generates high-density plasma, and as a result, the N-polarity gallium nitride layer can be formed at a temperature lower than 800°C using this high-density plasma. For example, the N-polarity gallium nitride layer can be formed at a temperature of 350°C.

[0145] As described above, the N-polar gallium nitride layer produced by the ECR plasma deposition apparatus can have a small surface roughness and maintain crystallinity. That is, according to the application example, a high-quality N-polar gallium nitride layer can be produced at a low temperature.

[0146] <<Modifications>> In the application examples, a substrate structure in which an N-polarity gallium nitride layer is formed on a sapphire substrate is described as an example. However, the technical concept of the application examples is not limited to this. For example, the present invention can also be applied to a substrate structure in which an N-polarity gallium nitride layer is formed on a GaN substrate.

[0147] The invention made by the inventor has been specifically described above based on the embodiments thereof, but it goes without saying that the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the invention.

[0148] REFERENCE SIGNS LIST 1 Film formation apparatus 2 ECR sputtering section 3 Magnetron sputtering section 10 Film formation chamber 11 Sample stage 12 Vertical movement mechanism 13 Rotation mechanism 14a Supply port 14b Vacuum exhaust mechanism 20 Microwave oscillator 21 Microwave waveguide 22 Microwave introduction window 23 Coil 24 Coil 25 ECR plasma chamber 26 Protection tube 27 Cylindrical target mounting section 28 Sputtering power supply 31 Disk target mounting section 32 Magnetic field generating magnet 33 Sputtering power supply 100 Backing tube 110 Target member 120 Support member 130 Target member 140 Positive ions 150 Target particles SUB Substrate TA Cylindrical target TA2 Disk target VL1 Normal axis VL2 Central axis VL3 Central axis θ1 First angle θ2 Second angle

Claims

1. A method for manufacturing a semiconductor device, comprising the step of forming an N-polarity gallium nitride layer, wherein the N-polarity gallium nitride layer is formed using a film formation device that uses plasma generated by utilizing the electron cyclotron resonance phenomenon.

2. A method for manufacturing a semiconductor device according to claim 1, wherein the N-polar gallium nitride layer is formed at a temperature lower than 800°C in the step.

3. A method for manufacturing a semiconductor device according to claim 2, wherein the N-polarity gallium nitride layer is formed at a temperature of 350°C in the step.

4. A method for manufacturing a semiconductor device according to claim 1, wherein the N-polar gallium nitride layer is formed on a substrate.

5. A method for manufacturing a semiconductor device according to claim 4, wherein the substrate is a sapphire substrate, and the substrate has an off-angle in the M-axis direction.

6. A method for manufacturing a semiconductor device according to claim 5, wherein the off angle is greater than 0 degrees and equal to or less than 10.0 degrees.

Images