Boron carbide coating film

Abstract

To coat a boron carbide that causes such the problem that it is difficult to be processed in the form of a sintered compact and a vacancy occurs when being subjected to thermal spraying, to various substrates as a close coating film.SOLUTION: A boron carbide coating film comprising 55-85 mol% boron and the balance carbon is deposited on a substrate. The substrate is a silicon wafer for a member for manufacturing semiconductor, quartz, aluminum, a stainless steel, or a PEEK material (plastic), for example. A PVD method may be adapted as a method for depositing a film. The film has an amorphous structure. Whereby a film having excellent homogeneity and isotropic property is formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to coatings comprising boron carbide. [Background technology]

[0002] Boron carbide is a superhard material that has been known since the 19th century and has excellent properties such as low density, high melting point, wear resistance, chemical stability, and high neutron absorption. However, boron carbide products have often been molded by processing sintered materials, but the material tends to be prone to cracking during processing, the processing labor is expensive, and the processing precision tends to be low.

[0003] Therefore, Patent Document 1 discloses a technique of using a sintering aid to improve the workability of boron carbide sintered bodies, which are difficult to process, but this means that it is difficult to obtain the processing precision of boron carbide substrates.

[0004] Patent Document 2 discloses a thermal spray feed material containing boron carbide and a method for thermally spraying the material onto a substrate to form a coating corresponding to the substrate surface, but the coating material contains aggregates of metal-coated particles or metal alloy-coated particles, and the metal-coated particles are composed of an inner core and an outer layer, with the inner core containing not only boron carbide but also silicon carbide and silicon nitride. This means that boron carbide alone cannot form a good coating, i.e., a dense coating.

[0005] Furthermore, the thermal spraying and sintering processes described in Patent Documents 1 and 2 involve high-temperature treatments and pose the risk of generating toxic gases, so that sufficient consideration must be given to their impact on the environment and the human body. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent application 2012-96970 [Patent Document 2] Patent application 2019-508869 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above-mentioned problems, and aims to form a smooth and dense hard boron carbide coating on a wide variety of substrates by, for example, a PVD method using low-temperature processing, which makes it possible to significantly alleviate the problems on the coating side and the substrate side that are problems in Patent Documents 1 and 2.

[0008] The process according to the present invention makes it possible to provide products with hard boron carbide coatings without generating toxic gases and with minimal impact on the environment and human body. Furthermore, it is possible to form high-purity hard boron carbide coatings without using sintering aids. [Means for solving the problem]

[0009] To achieve the above object, the boron carbide coating of claim 1 is formed by depositing a film-forming raw material containing 55 to 85 mol% boron and the remainder carbon on a substrate, thereby enabling the formation of a boron carbide coating that conforms to the shape and surface configuration of the substrate.

[0010] The boron carbide coating of claim 2 exhibits conductivity with a surface resistance of 10 kΩ or less, and can prevent electrostatic discharge.

[0011] The boron carbide coating of claim 3 has an amorphous structure and has excellent homogeneous and isotropic properties.

[0012] The boron carbide coating of claim 4 is characterized in that it is coated on the surface of a substrate to a thickness in the range of 0.5 to 10 μm.

[0013] In claim 5, a metal coating is formed on the surface of the substrate as an undercoat, and a boron carbide coating is formed on the undercoat, thereby achieving an excellent coating effect through the cooperation of the composite coating.

[0014] In claim 6, a metal carbonitride coating is formed on the surface of the substrate as an undercoat, and a boron carbide coating is formed on this undercoat, thereby achieving an excellent coating effect through the cooperation of the composite coatings.

[0015] In claim 7, the boron carbide coating is formed by the PVD method, which allows for the formation of smooth and dense coatings on a wide variety of substrates through low-temperature processing, without generating toxic gases.

[0016] In claim 8, the PVD method is an ion-assisted deposition method (IAD method).

[0017] In claim 9, the PVD method is a sputtering method. [Effects of the Invention]

[0018] According to the present invention, boron carbide, which is difficult to process as a sintered body and has problems such as the generation of voids when sprayed, can be formed into a dense coating on a variety of substrates. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a photograph recording an image of a cross section of the boron carbide coating of Example 1 observed with a scanning electron microscope. [Figure 2] 1 is a photograph showing a cross section of the coating of Comparative Example 6 observed with a scanning electron microscope. [Figure 3] 1 is a table showing the composition elements of boron and carbon in the boron carbide coating of Example 1. [Figure 4] 10 is a table showing the composition elements of boron and carbon in the boron carbide coating of Comparative Example 5. [Figure 5] 1 is a table showing the physical properties of the coatings of Example 1 and Comparative Examples 4 to 6. [Figure 6] 1 is a graph showing the crystal structure of the coating of Example 1. [Figure 7] 1 is a table showing film formation conditions for Examples 1 to 6 and Comparative Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0020] Next, preferred embodiments of the present invention will be described with reference to the drawings.

[0021] Figure 1 is a photograph of a cross section observed with a scanning electron microscope of a boron carbide coating M formed by ion-assisted deposition (IAD) of the PVD method on a substrate B, a silicon wafer substrate used in semiconductor manufacturing. As is clear from Figure 1, the coating M is dense and has a smooth surface.

[0022] The film-forming raw material used in Example 1 was 55 to 85 mol% boron, with the remainder being carbon. The film-forming conditions were a pressure of 5 × 10 ―3 ~5×10 ―1 [Pa] and temperatures of 250-350°C, and good results were obtained. The deposition temperature was below the heat resistance temperature of the substrate, and deposition was performed intermittently at appropriate time intervals, resulting in a lower temperature than with the conventional PDV method. The film thickness (measured by step height) was 1.3-1.5 μm. A solid molded target was used as the deposition material, but powder or crushed material can also be used. Quartz, aluminum, stainless steel, and PEEK (plastic) can also be used as the substrate.

[0023] Figure 3 shows the results of detecting the composition at three locations on boron carbide coating M. At location P1, carbon was 24.2 mol% and boron was 75.8 mol%; at location P2, carbon was 23.6 mol% and boron was 76.4 mol%; and at location P3, carbon was 24.8 mol% and boron was 75.2 mol%.

[0024] On the other hand, Comparative Example 5 shows the results of varying the element ratio of the film-forming raw material under the same film-forming conditions as Example 1. It was found that when the boron content was 29.8 [mol%], 28.6 [mol%], and 29.4 [mol%], or less than 55 [mol%], it was not possible to form boron carbide. Furthermore, when the boron content exceeded 85 [mol%], boron carbide did not form, and an unreacted boron film was formed. For these reasons, the element ratio of the film-forming raw material was set as in Example 1.

[0025] 5 compares the surface resistance of the boron carbide coating M in Example 1 and Comparative Examples 4 to 6, with Example 1 having a resistance of 100 Ω and Comparative Examples 4 to 6 having a resistance of 10 Ω. For example, in a semiconductor device manufacturing process, electrostatic discharge may occur if the resistance of an equipment component is higher than 10 KΩ, but Example 1 has a sufficiently low surface resistance of 100 Ω, so there is no risk of electrostatic discharge.

[0026] Figure 6 is a graph showing the X-ray diffraction pattern of Coating M formed to a thickness of 1.3 μm on silicon wafer substrate B. The portion marked "halo due to amorphous components" indicates that amorphous coating portions were detected. In other words, the crystalline structure of the boron carbide coating is amorphous, and it has excellent homogeneous and isotropic properties.

[0027] In Example 1, the thickness of the boron carbide coating M was 1.3 to 1.5 μm, but it is known that a hard coating does not function at 0.5 μm, and that a coating thickness of 10 μm or more is prone to peeling due to the influence of residual stress.

[0028] As shown in Figure 7, when a plastic PEEK substrate was used as the base material B, the film formation temperature was set to 100 to 200°C based on its heat resistance temperature, and good results were obtained. The film thickness (measured by step height) was 1.5 to 3.0 μm. [Example 3]

[0029] 7, the output of the evaporation source in Example 1 is 0.35 A, but in Example 3, this is reduced to 0.25 A, and further, an aluminum undercoat is formed on a silicon wafer substrate B, and a boron carbide coating M is formed as the outermost layer. Even under such low evaporation source output film formation conditions, a good boron carbide coating M was obtained.

[0030] On the other hand, in Comparative Example 1, in which an aluminum undercoat was not formed under the film-forming conditions of Example 3, cracks occurred in the coating, demonstrating the improvement in adhesion due to the aluminum undercoat. [Example 4]

[0031] In Example 4, a pressure of 5 × 10 was applied by the PVD method of the sputtering method. ―1 ~5×10 ―0 A boron carbide film M was formed on a silicon wafer. As a result, a good film with a thickness of 0.5 to 1.5 μm was obtained. [Example 5]

[0032] In Example 5, a nitride CrN undercoat was used instead of the aluminum undercoat used in Example 3, and a low evaporation source power was used, as in Example 3, and a good coating was obtained. This shows that, like Example 3, a superior coating was achieved compared to Comparative Example 1, which did not have a undercoat. [Example 6]

[0033] In Example 6, a carbonitride CrCN undercoat was used instead of the aluminum undercoat of Example 3, and a low evaporation source power was used, as in Example 3, and a good coating was obtained. This shows that, as in Example 3, a superior coating was achieved compared to Comparative Example 1, which did not have a undercoat.

[0034] FIG. 2 shows Comparative Example 6, which is a coating formed by conventional thermal spraying. Although high hardness was obtained, the surface condition was rough and the quality of the coating was insufficient.

[0035] [Comparative Examples 2 and 3] In Examples 1 to 3, 5, and 6 using the IAD method, films were formed in a plasma environment with an output of 480 W, and in Example 4 using the sputtering method, films were formed in a plasma environment with an output of 200 W. However, in Comparative Examples 2 and 3, the plasma output was changed. In Comparative Example 2, films were formed in an environment without plasma, and in Comparative Example 3, the plasma output was increased to 640 W. As a result, in Comparative Example 2, the adhesion of the boron carbide coating to the substrate was reduced, making film formation impossible. Furthermore, in Comparative Example 3, the boron carbide coating cracked on the substrate surface, preventing normal film formation. In other words, to achieve normal film formation, it is essential to optimize the plasma output as in Examples 1 to 6, as shown in FIG. 7. [Industrial Applicability]

[0036] Boron carbide is used in semiconductor device manufacturing processes due to its hardness and electrical conductivity despite not containing heavy metal elements. The coating of the present invention can be formed on a wide variety of substrates that are easy to process, whereas substrates that require fine processing and high processing accuracy, which are difficult to process with boron carbide sintered bodies, by using the PVD method, making it possible to utilize the properties of boron carbide in a variety of situations that were previously not possible.

[0037] The coating of the present invention can be formed not only as a single layer of hard boron carbide coating, but also as a layered coating in combination with a metal layer, nitride, carbonitride, etc., and can impart the properties of boron carbide to the surfaces of a wide variety of substrates, such as ceramics, ferrous metals, non-ferrous metals, and plastics, which are used as components of equipment used in semiconductor device manufacturing processes. [Explanation of symbols]

[0038] B Base material M Coating

Claims

1. A boron carbide coating formed using a film-forming raw material containing 55 to 85 mol % boron, with the remainder being carbon.

2. 2. The boron carbide coating according to claim 1, wherein the surface resistivity is 10 kΩ or less.

3. 3. The boron carbide coating according to claim 1, which has an amorphous structure.

4. The boron carbide coating according to any one of claims 1 to 3, which is formed to a thickness in the range of 0.5 to 10 µm.

5. The boron carbide coating according to any one of claims 1 to 4, which is formed as an outermost layer on a substrate having a primer coating formed thereon.

6. 6. The boron carbide coating of claim 5, wherein the undercoat is a metallic coating.

7. 6. The boron carbide coating of claim 5, wherein the undercoat is a metal nitride coating.

8. The boron carbide coating according to any one of claims 1 to 7, which is formed by a PVD method.

9. 9. The boron carbide coating according to claim 8, wherein the PVD method is an ion-assisted deposition method (IAD method).

10. 9. The boron carbide coating according to claim 8, wherein the PVD method is a sputtering method.

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