JP7708684B2 - Metallic materials and plasma generating equipment - Google Patents

Description

The present invention relates to a metal material having a porous oxide film on its surface and a plasma generating device using the same.

Surface treatment equipment for surface treatment of semiconductor wafers may plasma treat the inner surface of the treatment chamber by spraying or irradiating plasma generated by an external plasma generator, for example, to clean and remove deposits (contaminants) that have accumulated on the inner surface of the treatment chamber after surface treatment of the semiconductor wafer. Known plasma generators used for such purposes include a chamber having a reaction chamber into which a reactive gas is introduced, an electrode that supplies high-frequency power into the reaction chamber, and an outlet that releases the plasma generated in the reaction chamber.

The chamber used in such a plasma generating device is generally made of a metal material such as an alloy containing aluminum, magnesium, or the like as a main element. It is known that the inner surface of the reaction chamber of this chamber is corroded by etching as plasma is generated within the reaction chamber. In order to protect the inner surface of the reaction chamber from etching by plasma, an insulating layer such as an oxide film formed by anodizing (anodic oxidation) or the like is provided on the metal material constituting the chamber, particularly on the inner surface of the reaction chamber.

As such, as a technology for forming a film (insulating layer) having corrosion resistance and wear resistance on the surface of a metal material made of an aluminum alloy or magnesium alloy, for example, Patent Document 1 discloses a method for forming an oxide film having an amorphous dense barrier layer and a porous layer composed of multiple hollow columnar cells by performing plasma electrolytic oxidation (PEO) on the surface of an aluminum base material. Although such an oxide film is said to provide sufficient corrosion resistance, the thickness of the barrier layer is extremely thin, at around several hundred nm, and it cannot be said that it is sufficient to be applied to the chamber of the above-mentioned plasma generation device to obtain sufficient effects.

In response to this, Patent Document 2 discloses a plasma electrolytic oxidation coating having a dense layer containing pores with a pore size of 0.01 to 1 μm formed on the surface of a magnesium or magnesium alloy component. Patent Document 2 also describes the problem that conventional plasma electrolytic oxidation coatings have poor corrosion resistance due to the presence of coarse pores with a pore size of about 1 to 30 μm.

Meanwhile, Patent Document 3 discloses a composite coating having a porous oxide-ceramic matrix coating formed by plasma electrolytic oxidation on the surface of an alloy such as Al, Mg, or Ti, and a structure in which a functional compound is inserted into the pores of the porous oxide-ceramic matrix coating. A composite coating with such a structure is said to exhibit good wear resistance and a low coefficient of friction, and to have the ability to withstand dynamic contact loads and vibrations.

JP 2010-215945 A JP 2007-308757 A JP 2008-144281 A

Oxide films formed by plasma electrolytic oxidation have a higher hardness than oxide films formed by anodizing, and because they contain a porous layer, they have the property of absorbing internal stress at high temperatures due to the difference in thermal expansion coefficient with the base material. On the other hand, oxide films formed by plasma electrolytic oxidation have the problem that the pores formed inside are connected to the fine pores, forming cavities from the oxide film surface to the base material surface, reducing the insulation of the base material.

Regarding this point, Patent Document 2 discloses a method for adjusting the pore size to 0.01 to 1 μm, but making the pore size smaller results in a slower film formation speed, which poses a problem in terms of productivity (production costs). Furthermore, making the pores smaller sacrifices the ability to absorb internal stress, which is one of the characteristics of the oxide film formed by the above-mentioned plasma electrolytic oxidation treatment.

On the other hand, Patent Document 3 discloses a method of forming an oxide film by plasma electrolytic oxidation treatment and then filling the pores in the oxide film with functional compounds. However, because the pores for absorbing stress are filled with functional compounds that have anti-wear, anti-corrosion, etc., this sacrifices the ability to absorb internal stress, which is one of the characteristics of the oxide film formed by the above-mentioned plasma electrolytic oxidation treatment, just as in Patent Document 2.

The present invention was made based on these circumstances, and aims to provide a metal material with an insulating oxide film that has sufficient corrosion resistance against plasma generation and can fully absorb the internal stress that occurs at high temperatures, and a plasma generating device using the same.

In order to solve the above problems, one of the representative aspects of the present invention is a metal material having a porous oxide film on its surface, characterized in that a protective film made of an insulating material having plasma resistance is formed on the inner surface of a plurality of pores contained in the porous oxide film.

Another aspect of the present invention is a plasma generating device that applies high-frequency power to a reactive gas to generate plasma, comprising a chamber having a reaction chamber into which the reactive gas is introduced, an electrode that supplies high-frequency power into the reaction chamber, and an outlet that releases plasma from the reaction chamber, the chamber being made of a metal material having a porous oxide film on the surface layer on the reaction chamber side, and a protective film made of an insulating material having plasma resistance being formed on the inner surface of a plurality of pores contained in the porous oxide film.

According to the present invention having such a configuration, a protective film made of a plasma-resistant insulator is formed on the inner surface of a plurality of pores contained in a porous oxide film formed on the surface layer of a metal material, so that the metal material has sufficient corrosion resistance, particularly against plasma generation, and can fully absorb internal stresses that occur at high temperatures.

1A and 1B are a side view and a cross-sectional view showing an outline of a metal material according to Example 1, which is a representative example of the present invention. FIG. 2 is an enlarged cross-sectional view showing a schematic view of a portion indicated by an area A3 in FIG. 1 is a flowchart showing steps of a method for manufacturing a metal material according to Example 1. FIG. 4 is a partial cross-sectional view showing an outline of the process of step S2 shown in FIG. 3. FIG. 4 is a partial cross-sectional view showing an outline of the process of step S3 shown in FIG. 3. FIG. 4 is a partial cross-sectional view showing an outline of the process of step S4 shown in FIG. 3. 1 is a graph showing an outline of the results of a plasma exposure test performed on the metal material according to Example 1. FIG. 6 is a schematic diagram showing a configuration example of a plasma generation device according to a second embodiment of the present invention.

Below, typical examples of the metal material according to the present invention and the plasma generating device using the same will be described with reference to Figures 1 to 8.

Example 1
Fig. 1 is a side view and a cross-sectional view showing an outline of a metal material according to Example 1, which is a representative example of the present invention. Fig. 2 is an enlarged cross-sectional view showing a schematic view of a portion shown in region A3 in Fig. 1(b). The metal material according to Example 1 can be used as a metal material constituting a chamber of a plasma generating device according to Example 2, which will be described later.

As shown in FIG. 1(a), the metal material 10 according to the first embodiment includes, as an example, a metal substrate 20 and an oxide film 30 formed on at least one surface of the metal substrate 20. Here, FIG. 1(a) illustrates a case in which the oxide film 30 is formed only on the top surface of the metal substrate 20, but the oxide film 30 may be formed on the entire surface of the metal substrate 20, including the side and bottom surfaces.

The metal substrate 20 is made of a metal that can form a dense coating by oxidizing the surface and can be used as a structural component for various structures. Examples of such metal substrates 20 include so-called light metals such as aluminum, titanium, and magnesium, and alloys of these. In this Example 1, a case will be described in which a 5000 series (Al-Mg series) or 6000 series (Al-Mg-Si series) aluminum alloy is used as the metal substrate 20.

As shown in FIG. 1(b), which is an enlarged view of region A1 in FIG. 1(a), the oxide film 30 is configured as a two-layer oxide structure consisting of a porous layer 32 located on the metal substrate 20 side and a dense layer 34 exposed on the surface side. An example of a method for forming such an oxide film 30 is plasma electrolytic oxidation, which forms an oxide film by plasma electrolysis in an electrolyte such as an aqueous potassium hydroxide (KOH) solution.

As shown in Fig. 1(c), which is an enlarged view of region A2 in Fig. 1(b), the porous layer 32 is composed of a base 32a made of an oxide such as aluminum oxide ( _Al2O3 ), and pores 32b dispersed within the base 32a. The oxide constituting the base 32a _can be selected arbitrarily depending on the type of the metal base 20. The porous layer 32 allows the pores 32b to absorb stress caused by the difference in thermal expansion coefficient between the metal base 20 and the oxide coating 30, thereby preventing cracks from occurring in the oxide coating 30.

2, the dense layer 34 is formed as a hard portion 34a made of an oxide such as Al ₂ O ₃ by adjusting the conditions of plasma electrolysis in the plasma electrolytic oxidation treatment. The oxide constituting the hard portion 34a can also be arbitrarily selected depending on the type of the metal substrate 20 described above.

In addition, the dense layer 34 has elongated through-holes 34b that penetrate the hard portion 34a and reach the exposed surface 34c. These through-holes 34b communicate with the pores 32b of the porous layer 32. As a result, if left as is, the surface 20a of the metal substrate 20 will be partially exposed to the external atmosphere (particularly plasma).

Therefore, in the metal material 10 according to Example 1, as shown in FIG. 2, a protective film 36 made of an insulating material having plasma resistance is formed on the inner surfaces of the voids 32b of the porous layer 32 and the through holes 34b of the dense layer 34. As a result, for example, when the metal material 10 according to Example 1 is used as the metal material constituting the chamber (see reference numeral 110 in FIG. 7) of the plasma generating device (see reference numeral 100 in FIG. 7) according to Example 2 described below, etching of the inner surface of the chamber 110 by the generated plasma is suppressed.

The insulating material constituting the protective film 36 is a material that is resistant to etching by plasma, and is formed from ceramics such as oxides, nitrides, fluorides, and carbides. Among these, ceramics that mainly contain elements of Groups 2, 3, 4, 13, or 14 of the periodic table are preferable. These ceramics can be selected by adjusting the atmosphere when forming the protective film 36.

Next, an overview of the method for manufacturing a metal material according to Example 1, which is a representative example of the present invention, will be described with reference to Figures 3 to 6.

Figure 3 is a flow chart showing the steps of the method for manufacturing a metal material according to Example 1. Figure 4 is a partial cross-sectional view showing an overview of the step S2 shown in Figure 3. Figure 5 is a partial cross-sectional view showing an overview of the step S3 shown in Figure 3. Figure 6 is a partial cross-sectional view showing an overview of the step S4 shown in Figure 3.

As shown in FIG. 3, the metal material 10 according to the first embodiment of the present invention includes, as an example, a step of preparing a metal substrate 20 as a base material (step S1), a step of performing an oxidation treatment by plasma electrolysis on the surface of the prepared metal substrate 20 (step S2), a step of applying a slurry, which is a precursor of a protective film 36, to the formed oxide film 30 (step S3), and a step of baking the metal material 10 to which the slurry has been applied (step S4).

In the process of preparing the metal substrate 20 (step S1), the above-mentioned 5000 series or 6000 series aluminum alloy is prepared with a predetermined surface property and shape. At this time, a process of removing the oxide film that has already been formed, or at least a process of adjusting the surface roughness of the surface on which the oxide film 30 is to be formed may be added.

In the process of performing plasma electrolysis (step S2), an oxide film 30 is formed on the surface of the metal substrate 20 by a known plasma electrolytic oxidation process. Specifically, as one example, the metal substrate 20 is immersed in a weakly alkaline electrolyte aqueous solution (potassium hydroxide KOH), and in this state, an AC pulse current of predetermined conditions is passed through the electrolyte aqueous solution, whereby an oxide film 30 is formed on the surface 20a of the metal substrate 20, as shown in FIG. 4.

In the step of applying the slurry (step S3), a slurry of a material that will eventually become a precursor for forming the protective film 36 is applied to the exposed surface 34c of the oxide film 30. At this time, since a plurality of through holes 34b are formed in the dense layer 34 of the oxide film 30 as described above, the applied precursor slurry fills the through holes 34b as well as the pores 32b of the porous layer 32 as shown in FIG. 5. Note that, as an example, the precursor slurry for the protective film 36 is configured as a basic aqueous solution containing a salt of an element of the above-mentioned Groups 2, 3, 4, or 14.

In the baking process (step S4), the metal material 10 coated with the slurry in step S3 is baked in a furnace with a predetermined gas atmosphere. At this time, the basic components are volatilized together with the moisture contained in the slurry by heating during the baking process, and as shown in FIG. 6, the volume of the slurry is greatly reduced and the slurry contracts in the direction of arrow B in the figure. Then, the gas in the furnace combines with the above-mentioned elements of Groups 2, 3, 4, 13, or 14 to form a protective film 36 containing ceramics such as oxides and nitrides of these elements.

As described above, by appropriately selecting the atmosphere (reactive gas sealed in the heating furnace) in the heating furnace when the baking step (step S4) is performed, it is possible to adjust the ceramic material forming the protective film 36. For example, by baking the metal material 10 coated with a slurry containing titanium (Ti), which is a group 4 element, in an atmosphere of nitrogen gas _N2 , the protective film 36 containing titanium nitride (TiN) is formed on the inner surface of the pores 32b in the porous layer 32 of the oxide film 30.

An example of a specific embodiment of a metal material manufactured by the method for manufacturing a metal material according to Example 1 described above will be described below with reference to FIG. 7. FIG. 7 is a graph showing an outline of the results of a plasma exposure test performed on a metal material according to the conventional technology and a metal material according to Example 1.

In conducting the plasma exposure test, a 6000 series aluminum alloy was used as the metal substrate, and various film formation treatments were performed on the surface of the metal substrate, and a test was performed in which the metal substrate was exposed to a plasma generation environment. In order to compare the present application with the prior art, an "anodized material" in which only an anodized treatment was performed on the surface of the metal substrate, a "PEO-treated material" in which only a PEO treatment was performed on the surface, and the "material of the present invention" in which a protective film formation treatment was performed in addition to the PEO treatment on the surface were prepared.

As shown in Figure 7, the amount of film (thickness) etched by plasma tended to decrease in the order of "anodized material," "PEO-treated material," and "material of the present invention." In particular, as one example, the amount of etching for the "material of the present invention" was approximately 40% less than the amount of etching for the "PEO-treated material."

By being provided with the above-mentioned configuration, the metal material 10 according to Example 1 has a protective film 36 made of a plasma-resistant insulator formed on the inner surface of the multiple voids 32b contained in the porous oxide film 30 formed on its surface, and therefore has sufficient corrosion resistance, particularly against plasma generation, and can fully absorb internal stresses that occur at high temperatures.

Example 2
In the technical field of manufacturing equipment for semiconductor products applied to semiconductor devices, solar panels, flat panel displays, etc., a plasma cleaning process is sometimes performed in which plasma is sprayed into a processing chamber to clean the wall surface in order to remove contaminants and the like generated in various processing steps for semiconductor substrates from the processing chamber. A remote plasma generator (RPS) that supplies plasma from outside the processing chamber is known as an apparatus for generating such plasma.

Figure 8 is a schematic diagram showing an example of the configuration of a plasma generating device according to Example 2 of the present invention. In describing the plasma generating device 100 according to Example 2, components having the same or similar configuration as in Example 1 are given the same reference numerals as in Example 1 and will not be described again.

As shown in FIG. 8, the plasma generating device 100 according to the second embodiment includes, as an example, a chamber 110 having a reaction chamber R into which a reactive gas is introduced, an electrode 120 for supplying high-frequency power into the reaction chamber R, and an outlet 130 for discharging the plasma generated in the reaction chamber R. The plasma generating device 100 generates plasma by applying high-frequency power to the introduced reactive gas, and discharges the plasma from the outlet 130 into a processing chamber of a manufacturing device that manufactures semiconductor devices and is connected downstream.

The chamber 110 is connected to an inlet pipe 112 for introducing reactive gas into the chamber 110 at a position opposite the outlet 130. The generation of plasma increases the internal pressure inside the reaction chamber R (the reactive gas expands due to the plasma reaction), and the plasma generated from the reactive gas introduced at a predetermined pressure is released downstream of the chamber 110.

The chamber 110 is, for example, made of an aluminum alloy or a magnesium alloy, and is preferably configured as a hollow columnar member having a circular or regular polygonal cross section. An oxide film 30 including a porous layer 32 as described for the metal material 10 of Example 1 is formed on at least the inner surface of the chamber 110 facing the reaction chamber R.

As an example, the electrode 120 is made of a metal wound into a coil shape. As shown in FIG. 8, both ends of the electrode 120 are connected to a high-frequency AC power source 122 via a pair of terminals 120a, 120b. By using an electrode 120 with this shape, the center of the winding of the electrode 120 can be positioned in the center of the reaction chamber R of the chamber 110, which prevents deviation in distance and stabilizes the generation of plasma.

In the plasma generating device 100 shown in FIG. 8, a reactive gas is supplied into the reaction chamber R of the chamber 110 at a predetermined pressure or flow rate from a gas supply source (not shown) connected to the inlet pipe 112. In this state, when a high-frequency alternating current is applied to the electrode 120 from the high-frequency AC power supply 122, plasma is generated inside the reaction chamber R of the chamber 110 due to the magnetic field caused by the current flowing through the electrode 120, and the generated plasma is discharged from the outlet 130.

At this time, the inner surface of the reaction chamber R is etched by the generated plasma. In contrast, in the plasma generating device 100 according to Example 2, an oxide film 30 similar to that shown in Example 1 is formed on the inner surface of the chamber 110 on the reaction chamber R side, and a protective film 36 made of an insulating material having plasma resistance is present in the pores 32b of the porous layer 32, so that it is possible to prevent the oxide film 30 from being etched even if it is exposed to plasma.

Since the electrode 120 is also etched by the plasma generated between the electrode 120 and the chamber 110, it may be made of an aluminum alloy or magnesium alloy, like the chamber 110, with an oxide film 30 formed on its surface. Also, the electrode 120 may be made as a hollow tube made of an aluminum alloy or magnesium alloy to cool the heat generated when electricity is applied.

By being provided with the above-mentioned configuration, the plasma generating device 100 according to the second embodiment, like the first embodiment, has a protective film 36 made of a plasma-resistant insulator formed on the surface of the multiple holes 32b contained in the porous oxide film 30 formed on the inner surface on the reaction chamber R side of the metal material constituting the chamber 110, and therefore has sufficient corrosion resistance, particularly against plasma generation, and can sufficiently absorb internal stresses that occur at high temperatures.

The above description of the embodiment is merely an example of the metal material or plasma generating device according to the present invention, and the present invention is not limited to each embodiment. Furthermore, a person skilled in the art can make various modifications without departing from the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

Reference Signs List 10 Metal material 20 Metal substrate 30 Oxide film 32 Porous layer 32a Base 32b Hole portion 34 Dense layer 34a Hard portion 34b Through hole 34c Exposed surface 36 Protective film 100 Plasma generator 110 Chamber 112 Inlet tube 120 Electrodes 120a, 120b Terminal 122 High frequency AC power source 130 Discharge port R Reaction chamber

Claims (6)

A metal material having a porous oxide film on a surface layer,
the porous oxide coating has a two-layer structure including a porous layer formed on the metal substrate side and a dense layer laminated on the porous layer,
A metal material characterized in that a protective film made of an insulator having plasma resistance is formed on the inner surface of a plurality of pores contained in the porous layer while maintaining the internal space of the pores. The metal material according to claim 1, characterized in that the protective film is made of ceramics. The metallic material according to claim 2, characterized in that the ceramic contains an oxide mainly consisting of an element of Group 2, Group 3, Group 4, Group 13 or Group 14 of the periodic table. A plasma generating device that applies high frequency power to a reactive gas to generate plasma,
a chamber having a reaction chamber into which the reactive gas is introduced, an electrode for supplying the high frequency power into the reaction chamber, and an outlet for emitting the plasma from the reaction chamber;
the chamber is made of a metal material having a porous oxide film on a surface layer on the reaction chamber side,
the porous oxide coating has a two-layer structure including a porous layer formed on the metal substrate side and a dense layer laminated on the porous layer,
A plasma generating device, characterized in that a protective film made of an insulating material having plasma resistance is formed on the inner surface of a plurality of pores contained in the porous layer while maintaining the internal space of the pores. The plasma generating device according to claim 4, characterized in that the protective film is made of ceramics. The plasma generating device according to claim 5, characterized in that the ceramic contains an oxide mainly consisting of Group 2 elements, Group 3 elements, Group 4 elements, Group 13 elements, or Group 14 elements of the periodic table.