Sputtering target for depositing gallium nitride film

Abstract

To provide a sputtering target for depositing a gallium nitride film that can deposit a gallium nitride film that is suppressed in contamination of oxygen.SOLUTION: A sputtering target for depositing a gallium nitride film includes a body part comprising a single crystal gallium nitride. The body part may have a thickness of 2 mm or less. The sputtering target for depositing a gallium nitride film may further include a backing plate and a joining material for joining the body part to the backing plate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a sputtering target for forming a gallium nitride film. [Background technology]

[0002] Conventionally, known sputtering targets for forming gallium nitride films can be manufactured at relatively low cost and can be made large, and therefore include gallium nitride sintered bodies, i.e., polycrystalline bodies of gallium nitride (see Patent Document 1), and composite targets having a plurality of gallium nitride single crystal bodies and a metallic indium filling material that fills the gaps between the plurality of gallium nitride single crystal bodies (see Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-172437 A [Patent Document 2] Patent Publication No. 2021-181595 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the gallium nitride sintered body described in the above Patent Document 1, i.e., a polycrystalline body of gallium nitride, is used as a sputtering target, oxygen is likely to be mixed into the resulting gallium nitride film. Also, when the composite target described in the above Patent Document 2 is used, the filling material such as metallic indium is likely to be mixed into the resulting gallium nitride film. Moreover, oxygen is likely to be mixed into the resulting gallium nitride film.

[0005] The inventors of the present disclosure considered that when the gallium nitride sintered body described in the above Patent Document 1, i.e., a polycrystalline body of gallium nitride, is used as a sputtering target, oxygen and moisture attached to the grain boundaries between multiple gallium nitride crystals will tend to mix into the formed gallium nitride film. Also, when the composite target described in the above Patent Document 2 is used, oxygen and moisture attached between multiple gallium nitride single crystals contained in the composite target will tend to mix into the formed gallium nitride film.

[0006] An object of the present disclosure is to provide a sputtering target for forming a gallium nitride film that enables the formation of a gallium nitride film with reduced oxygen contamination. [Means for solving the problem]

[0007] The contents of the present invention are as described in the claims, and the gist of the present disclosure is as follows. (1) A sputtering target for forming a gallium nitride film, comprising a main body made of single crystal gallium nitride. (2) The oxygen content in the main body is 5×10 18 atoms / cm 3 A sputtering target for forming a gallium nitride film according to (1), which is as follows: (3) The sputtering target for forming a gallium nitride film according to (1) or (2), wherein the thickness of the main body is 2 mm or less. (4) The sputtering target for forming a gallium nitride film according to (1) or (2), further comprising a backing plate and a bonding material for bonding the main body and the backing plate, the bonding material containing indium. Effect of the Invention

[0008] According to the present disclosure, there is provided a sputtering target for forming a gallium nitride film, which is capable of forming a gallium nitride film with reduced oxygen contamination. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing one embodiment of a sputtering target for forming a gallium nitride film according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of the present disclosure will be described in detail below by way of an example, however, the present disclosure is not limited to the following embodiment.

[0011] <Sputtering target for gallium nitride film deposition> First, one embodiment of a sputtering target for forming a gallium nitride film according to the present disclosure will be described with reference to FIG.

[0012] As shown in FIG. 1, a sputtering target for forming a gallium nitride film (hereinafter also simply referred to as a "target") 100 includes a main body 10 made of single crystal gallium nitride. The target 100 may further include a backing plate 20 and a bonding material 30 that bonds the main body 10 and the backing plate 20 together.

[0013] According to target 100, main body 10 is made of single crystal gallium nitride, and adhesion of oxygen, moisture, etc. to the grain boundaries between crystals is suppressed. Therefore, when a gallium nitride film is formed using target 100, a gallium nitride film in which the inclusion of oxygen is suppressed can be formed. Furthermore, since main body 10 is made of single crystal gallium nitride, it is believed that when main body 10 is sputtered, the gallium nitride particles ejected from main body 10 are more likely to be aligned in the same direction, thereby improving the film formation speed. In addition, since the main body 10 is made of single crystal gallium nitride, the surface of the main body 10 is less likely to have irregularities, which is thought to prevent an excessive electric field from being applied locally to the surface of the main body 10 during film formation, making it less likely that parts of the main body 10 will be detached as coarse particles. In this case, sputtering prevents coarse particles of gallium nitride from adhering to the surface of the gallium nitride film. This makes it possible to prevent the performance of the device from being reduced when a device is fabricated by stacking multiple other layers on the gallium nitride film.

[0014] The main body 10, the backing plate 20 and the bonding material 30 will be described in detail below.

[0015] (Main body) The main body 10 is made of single crystal gallium nitride. More preferably, the crystal structure of the single crystal gallium nitride is a hexagonal structure. When the crystal structure of the single crystal gallium nitride is a hexagonal structure, the direction of the c-axis is preferably perpendicular to the surface of the main body 10. The direction of the c-axis may be parallel to the surface of the main body 10.

[0016] The oxygen content in the main body 10 is sufficiently small because the main body 10 is made of single crystal gallium nitride, but is preferably 5×10 18 atoms / cm 3 More preferably, it is 1×10 18 atoms / cm 3 or less, and particularly preferably 5×10 17 atoms / cm 3 The oxygen content in the main body 10 is 5×10 18 atoms / cm 3 By satisfying the above condition, when a gallium nitride film is formed using the target 100, it is possible to form a gallium nitride film in which inclusion of oxygen is particularly sufficiently suppressed. The oxygen content in the main body 10 is 0 atoms / cm 3 It may be more than 1×10 15 atoms / cm 3 That's it, 5 x 1015 atoms / cm 3 or more or 1×10 16 atoms / cm 3 It may be more than that. The upper and lower limits of the oxygen content may be any combination of the above. The oxygen content in the main body 10 refers to the oxygen content at a depth of 50 nm from the surface of the main body 10, measured along the depth direction from the surface of the main body 10 using secondary ion mass spectrometry (SIMS). The unit of oxygen content is "atoms / cm 3 " is 1 cm 3 is the number of atoms per unit mass.

[0017] The relative density of the main body 10 is not particularly limited, but is preferably 80% or more, more preferably 90% or more, and particularly preferably 95% or more. The relative density of the main body 10 may be 100% or less, 99% or less, or 98% or less. The upper and lower limits of the relative density may be any combination of the above. The relative density can be calculated as a percentage of the density of the main body 10 relative to the true density of single crystal gallium nitride.

[0018] The thickness of the main body 10 is not particularly limited, but is preferably 2 mm or less, more preferably 1.5 mm or less, and particularly preferably 1.0 mm or less. Furthermore, the thickness of the main body 10 may be 0.1 mm or more, 0.2 mm or more, or 0.3 mm or more. The upper and lower thickness limits may be any combination of the above.

[0019] (Backing plate) The backing plate 20 is a metal member for cooling the main body 10 during sputtering of the main body 10, and examples of the metal member include copper, titanium, and stainless steel.

[0020] (bonding material) The bonding material 30 is not particularly limited as long as it is made of a material capable of bonding the main body 10 and the backing plate 20, but in terms of suppressing thermal diffusion and thermal expansion during sputtering, at least one of indium and tin (indium, tin, or an alloy of indium and tin) is preferably used. Among these, indium is particularly preferably used.

[0021] <Method of manufacturing sputtering target for forming gallium nitride film> The method for manufacturing a sputtering target for forming a gallium nitride film according to the present disclosure includes a first step of preparing a main body 10 made of single crystal gallium nitride. The method for manufacturing a sputtering target for forming a gallium nitride film according to the present disclosure may further include a second step of bonding a backing plate 20 to the main body 10 via a bonding material 30 to obtain a sputtering target for forming a gallium nitride film 100 after the first step.

[0022] According to the above-described method for producing a sputtering target for forming a gallium nitride film, it is possible to produce the sputtering target for forming a gallium nitride film 100 capable of forming a gallium nitride film in which inclusion of oxygen is suppressed.

[0023] In the first step, the main body 10 is obtained by processing a single crystal of gallium nitride into a plate shape, for example, by grinding or cutting. Specific processing means include machining machines such as a surface grinder, a cylindrical grinder, a lathe, a cutting machine, or a machining center.

[0024] <Gallium nitride film formation method> A gallium nitride film can be formed on a film-forming substrate by sputtering the above-mentioned sputtering target for forming a gallium nitride film.

[0025] (Substrate for film formation) The film-formation substrate is not particularly limited, and examples of the film-formation substrate include a sapphire substrate and a silicon substrate. The surface roughness Ra of the film-formation substrate is not particularly limited, but is preferably 1 nm or less, and more preferably 0.5 nm or less. The surface roughness Ra of the film-formation substrate may be preferably 0 nm or more, or 0.01 nm or more. The surface roughness Ra represents a calculated average roughness.

[0026] (Pre-treatment for film formation) The ultimate vacuum level in the deposition apparatus before deposition is not particularly limited, but is preferably 3×10 -5 Pa or less, and 1×10 -5 It is more preferable to set the vacuum level to 3×10 Pa or less. -5 By setting the pressure at or below Pa, residual gas is less likely to be mixed in as an impurity during film formation, improving the crystallinity of the gallium nitride film. In the film formation apparatus, it is preferable to perform a baking process on the film formation apparatus before evacuating the apparatus in order to remove residual gas.

[0027] It is preferable to hold the film-forming substrate at the film-forming temperature for a certain period of time before starting the formation of the gallium nitride film. This makes the temperature of the film-forming substrate before film formation uniform, improving the crystallinity of the formed gallium nitride film. For example, the holding time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. On the other hand, from the viewpoint of improving productivity, the holding time is preferably 1 hour or less, and more preferably 30 minutes or less.

[0028] (Sputtering) The sputtering method may be one or more selected from the group consisting of DC sputtering, RF sputtering, AC sputtering, DC magnetron sputtering, RF magnetron sputtering, ECR sputtering, pulsed laser deposition deposition and ion beam sputtering. Among these, at least one of DC magnetron sputtering and RF magnetron sputtering is preferred because it allows for uniform and high-speed film formation over a large area.

[0029] The gas pressure during sputtering (film formation pressure) is not particularly limited, but may be, for example, 5 Pa or less, preferably 3 Pa or less, more preferably 2 Pa or less, and particularly preferably 1 Pa or less. The gas pressure during sputtering may be, for example, 0 Pa or more, or 0.1 Pa or more. The lower the gas pressure during sputtering, the more easily particles (sputtered particles) emitted from the target reach the film formation substrate while still retaining their high energy, and the more easily the film formation substrate is epitaxially rearranged.

[0030] (film formation) It is preferable to form the gallium nitride film while the film-forming substrate is heated. This promotes migration of particles deposited on the film-forming substrate, and allows the deposition film to be formed in a stable crystalline state. The heating temperature (film-forming temperature) of the film-forming substrate is preferably 100°C or higher and 1000°C or lower, and more preferably 200°C or higher and 800°C or lower.

[0031] The gas used for film formation preferably contains, for example, nitrogen as a main component. The gas used for film formation preferably further contains argon, which is commonly used. In this case, the partial pressure ratio (flow rate ratio) of nitrogen / (nitrogen + argon) is preferably 0.7 or more.

[0032] The power density during discharge (discharge density) is 1W / cm 2 More than 20W / cm 2 It is preferable that the power consumption is less than 1.5 W / cm 2 More than 10W / cm 2More preferably, it is 2.5 W / cm or less. 2 More than 5W / cm 2 It is more preferable that the power density is 20 W / cm or less. The power density is calculated by dividing the power applied during discharge by the area of ​​the target surface of the sputtering target. 2 If the power density is less than 1 W / cm, the power applied to the target makes it difficult for coarse single crystal particles to peel off from the sputtering target. 2 At the above level, the plasma is stable, which facilitates discharge, and the film formation speed is increased, improving film productivity. Furthermore, the energy during sputtering is high, improving the adhesion during film formation.

[0033] The deposition time may be adjusted appropriately depending on the thickness of the gallium nitride film. The longer the deposition time, the thicker the gallium nitride film can be. EXAMPLES

[0034] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0035] Example 1 A main body was prepared, made of single crystal gallium nitride (manufactured by Shinyosha Co., Ltd.) having the target characteristics shown in Table 1. At this time, the c-axis of the single crystal gallium nitride was set to be perpendicular to the surface of the main body. The body was then bonded to a copper backing plate using an indium-based solder material. In this manner, a sputtering target for forming a gallium nitride film was produced.

[0036] Comparative Example 1 A sputtering target for forming a gallium nitride film was produced in the same manner as in Example 1, except that the main body was made of polycrystalline gallium nitride having the target characteristics shown in Table 1 instead of single crystal gallium nitride.

[0037] <Characteristics of sputtering targets for gallium nitride film deposition> The oxygen content, thickness and relative density of the target (main body) properties shown in Table 1 were measured or calculated as follows.

[0038] (oxygen content) The oxygen content was measured continuously from the surface of the main body in the depth direction using SIMS. The oxygen content at a depth of 50 nm from the surface of the main body was determined as the oxygen content of the main body.

[0039] (Main body thickness) The thickness of the main body was measured with a vernier caliper.

[0040] (Relative Density) The density of the target was measured according to JIS R 1601 and the true density of gallium nitride was 6.08 g / cm 3 The relative density (%) was then calculated.

[0041] <Gallium nitride film formation> As a film-forming substrate, a sapphire substrate (off-angle: none, surface roughness Ra: 0.09 nm, diameter: 50.8 mm (2 inches)) manufactured by Shinkosha Co., Ltd. was prepared. At this time, the surface of the sapphire substrate was set to be the (0001) plane. Next, sputtering was performed using the sputtering target for forming a gallium nitride film of Example 1 or Comparative Example 1 and the above-mentioned film-forming substrate under the film-forming conditions shown in Table 1 to form a gallium nitride film on the surface of the film-forming substrate.

[0042] <Evaluation of Gallium Nitride Films> (Film thickness) The measurement was performed by measuring the step between the substrate surface and the thin film (gallium nitride film) formed on it using a stylus profiling system (DekTak XT-S, manufactured by Bruker). The results are shown in Table 1.

[0043] (oxygen content) The oxygen content of the obtained gallium nitride film was measured from the surface of the gallium nitride film along the depth direction using secondary ion mass spectrometry. The oxygen content at a depth of 50 nm from the surface of the gallium nitride film was taken as the oxygen content of the gallium nitride film. The results are shown in Table 1.

[0044] [Table 1]

[0045] From the results shown in Table 1, in the sputtering target for forming a gallium nitride film of Example 1, the oxygen content in the gallium nitride film was 5.00 × 10 19 atoms / cm 3 In contrast, in the sputtering target for forming a gallium nitride film of Comparative Example 1, the oxygen content in the gallium nitride film was 3.00 × 10 20 atoms / cm 3 It was. From the above, it was confirmed that the sputtering target for forming a gallium nitride film according to the present disclosure makes it possible to form a gallium nitride film with reduced oxygen contamination. [Explanation of symbols]

[0046] 10...main body, 20...backing plate, 30...bonding material, 100...sputtering target for forming gallium nitride film.

Claims

1. A sputtering target for forming a gallium nitride film, comprising a main body made of single crystal gallium nitride.

2. The oxygen content in the main body is 5×10 １８ atoms / cm 3 2. The sputtering target for forming a gallium nitride film according to claim 1, wherein:

3. 3. The sputtering target for forming a gallium nitride film according to claim 1, wherein the main body has a thickness of 2 mm or less.

4. 3. The sputtering target for forming a gallium nitride film according to claim 1, further comprising: a backing plate; and a bonding material that bonds the main body and the backing plate, the bonding material containing indium.

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