Thermal-sprayed film forming method

Abstract

A thermal-sprayed film forming method according to one example of the present invention involves supplying two powders A, B having different average particle diameters D50 from first and second ports 73, 74 to a plasma flame PF which is emitted from a nozzle 70a of a thermal spray gun 70, thereby forming an insulating thermal-sprayed film on the surface of a conductive member. When the average particle diameter D50 of the smaller powder A among the at least two powders is a μm and the average particle diameter D50 of the larger powder B is b μm, the expression 1.5 ≤ b / a ≤ 2.5 is satisfied.

Description

Thermal spray coating method

[0001] The present invention relates to a method for forming a thermal sprayed film.

[0002] Conventionally, composite parts have been known in which an insulating sprayed film is formed on the surface of a conductive member. For example, a composite part described in Patent Document 1 includes a metal support plate as the conductive member, which has a circular first surface, a second surface that is an outer peripheral surface adjacent to the first surface, and an outer curved surface that is the boundary between the first and second surfaces. The insulating sprayed film also includes an insulating film that covers the first surface, the second surface, and the outer curved surface. Patent Document 1 describes a process in which an insulator is sprayed from a direction perpendicular to the first surface while moving parallel to the first surface, an insulator is sprayed from a direction perpendicular to the outer curved surface while moving parallel to the outer curved surface, and an insulator is sprayed from a direction perpendicular to the second surface while moving parallel to the second surface. Patent Document 1 explains that the breakdown voltage (withstand voltage) of the insulating film obtained in this manner is higher than conventional methods.

[0003] Patent No. 7422130

[0004] However, although Patent Document 1 explains that the insulating film formed by thermal spraying on the outer curved surface has a high withstand voltage, it does not mention the insulating film formed by thermal spraying on the inner curved surface. When the inventor measured the withstand voltage of the insulating film formed by thermal spraying on the inner curved surface, it was found that a sufficient withstand voltage could not be obtained. Note that the outer corner refers to a mountain fold corner, and the inner corner refers to a valley fold corner.

[0005] The present invention has been made to solve such problems, and its main object is to form an insulating sprayed film with high withstand voltage on the surface of a conductive member.

[0006] [1] The method for forming a thermal sprayed film of the present invention is a method for forming an insulating thermal sprayed film on the surface of a conductive member by supplying at least two powders having different average particle sizes D50 from two or more ports to a plasma flame emitted from the nozzle of a thermal spray gun, wherein, when the average particle size D50 of powder A, the smallest of the at least two powders, is a [μm] and the average particle size D50 of powder B, the largest, is b [μm], the relationship 1.5≦b / a≦2.5 is satisfied.

[0007] This thermal spray coating method allows for the formation of an insulating spray coating with high withstand voltage on the surface of a conductive member, particularly when the conductive member has an interior curved surface, allowing for the formation of an insulating spray coating with high withstand voltage on the interior curved surface.

[0008] [2] In the thermal spray coating forming method of the present invention (the thermal spray coating forming method described in [1] above), it is preferable that the two or more ports are provided around the nozzle at intervals of 30° or more and 150° or less.

[0009] [3] In the method for forming a thermal sprayed film of the present invention (the method for forming a thermal sprayed film described in [1] or [2] above), it is preferable that a=1 to 40 and b=10 to 80.

[0010] [4] In the method for forming a thermal sprayed film of the present invention (the method for forming a thermal sprayed film according to any one of [1] to [3] above), among the properties of the thermal sprayed film, the porosity may be 8.0% or less, and the average distance between nearest pores having a pore diameter of 5.0 μm or more may be 4.0 μm or more. In this way, the withstand voltage of the formed thermal sprayed film becomes high regardless of location.

[0011] [5] In the method for forming a thermal sprayed film of the present invention (the method for forming a thermal sprayed film described in any one of [1] to [4] above), the conductive member may have a first plane, a second plane that is angled with respect to the first plane, and an interior curved surface that is a boundary surface between the first plane and the second plane, and the thermal sprayed film may be formed on the first plane, the interior curved surface, and the second plane. Generally, a thermal sprayed film formed on an interior curved surface tends to have a lower withstand voltage than a thermal sprayed film formed on the first or second plane, but according to the method for forming a thermal sprayed film of the present invention, the thermal sprayed film formed on the interior curved surface also has a high withstand voltage.

[0012] 1. A perspective view of the wafer mounting table 10. A cross-sectional view taken along line A-A in FIG. 1. A partially enlarged cross-sectional view of the periphery of the interior angle curved surface covering portion 56. A perspective view of the cooling plate 30. A cross-sectional view of a thermal spray gun 70. A front view of the thermal spray gun 70. An explanatory diagram showing how an insulating sprayed film 50 is formed by the thermal spray gun 70.

[0013] Next, preferred embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view of the wafer mounting table 10, Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1 (with a partially enlarged view), Fig. 3 is a partially enlarged cross-sectional view of the periphery of the interior curved surface covering portion 56, and Fig. 4 is a perspective view of the cooling plate 30. The shaded areas in Figs. 1 and 4 indicate the insulating sprayed film 50.

[0014] In this specification, "upper" and "lower" do not represent absolute positional relationships, but rather relative positional relationships. Therefore, depending on the orientation of the wafer mounting table 10, "upper" and "lower" may become "lower" and "upper," "left" and "right," or "front" and "rear."

[0015] As shown in FIG. 2, the wafer mounting table 10 includes a ceramic plate 20, a cooling plate 30, and a bonding layer 60.

[0016] The ceramic plate 20 is a circular plate (e.g., 300 mm in diameter and 5 mm in thickness) made of ceramic such as sintered alumina or sintered aluminum nitride. The upper surface of the ceramic plate 20 serves as a wafer mounting surface 21 on which a wafer W is placed. The ceramic plate 20 incorporates an electrode 22. The electrode 22 is a planar mesh electrode used as an electrostatic electrode and is connected to an external DC power supply via a power supply member (not shown). When a DC voltage is applied to the electrode 22, the wafer W is attracted and fixed to the wafer mounting surface 21 by electrostatic attraction, and when the application of the DC voltage is stopped, the wafer W is released from the attraction and fixation to the wafer mounting surface 21.

[0017] The cooling plate 30 is formed by providing an insulating sprayed film 50 on a substantially disc-shaped conductive plate 40 (an example of a conductive member).

[0018] The conductive plate 40 is a stepped circular plate (a circular plate with the same diameter as or larger than the ceramic plate 20) with good thermal conductivity. A refrigerant flow path 32 through which a refrigerant circulates is formed within the conductive plate 40. In a plan view, the refrigerant flow path 32 is formed in a single stroke across the entire conductive plate 40 from one end (inlet) to the other end (outlet). One end and the other end of the refrigerant flow path 32 are connected to a supply port and a recovery port, respectively, of an external refrigerant device (not shown). The refrigerant supplied from the supply port of the external refrigerant device to one end of the refrigerant flow path 32 passes through the refrigerant flow path 32, returns from the other end of the refrigerant flow path 32 to the recovery port of the external refrigerant device, and is temperature-adjusted before being supplied again from the supply port to one end of the refrigerant flow path 32. The conductive plate 40 is connected to a radio frequency (RF) power source and also serves as an RF electrode.

[0019] Examples of materials for the conductive plate 40 include metal materials and composite materials of metal and ceramic. Metal materials include Al, Ti, Mo, and alloys thereof. Metal-ceramic composite materials include metal matrix composites (MMCs) and ceramic matrix composites (CMCs). Specific examples of such composite materials include materials containing Si, SiC, and Ti (also known as SiSiCTi), porous SiC impregnated with Al and / or Si, and composite materials of Al2O3 and TiC. It is preferable to select a material for the conductive plate 40 that has a thermal expansion coefficient similar to that of the material for the ceramic plate 20.

[0020] The conductive plate 40 has a circular upper surface 41 joined to the underside of the ceramic plate 20, an upper peripheral wall surface 42 (an example of a first plane) extending downward from the periphery of the circular upper surface 41, an annular surface 43 (an example of a second plane) extending radially outward from the lower end of the upper peripheral wall surface 42, and a lower peripheral wall surface 44 extending downward from the periphery of the annular surface 43. The circular upper surface 41, the upper peripheral wall surface 42, the annular surface 43, and the lower peripheral wall surface 44 are flat. An R-shaped (rounded) upper outer curved surface 45 is provided at the boundary between the circular upper surface 41 and the upper peripheral wall surface 42, an R-shaped inner curved surface 46 is provided at the boundary between the upper peripheral wall surface 42 and the annular surface 43, and an R-shaped lower outer curved surface 47 is provided at the boundary between the annular surface 43 and the lower peripheral wall surface 44. The angle between the annular surface 43 and the upper peripheral wall surface 42 is 90°. However, this angle is not limited to 90°, and may be, for example, 100° or 120°. The R-shape is a rounded shape, for example, a curved surface having a predetermined radius of curvature. The predetermined radius of curvature is, for example, 0.3 to 5 mm.

[0021] The insulating sprayed film 50 covers the outer periphery 41a of the circular upper surface 41, the upper outer curved surface 45, the upper peripheral wall surface 42, the inner curved surface 46, the annular surface 43, the lower outer curved surface 47, and the lower peripheral wall surface 44. Of the insulating sprayed film 50, the portion covering the outer periphery 41a of the circular upper surface 41 is referred to as the circular upper surface covering portion 51a, the portion covering the upper outer curved surface 45 is referred to as the upper outer curved surface covering portion 55, the portion covering the upper peripheral wall surface 42 is referred to as the upper peripheral wall surface covering portion 52, the portion covering the inner curved surface 46 is referred to as the inner curved surface covering portion 56, the portion covering the annular surface 43 is referred to as the annular surface covering portion 53, the portion covering the lower outer curved surface 47 is referred to as the lower outer curved surface covering portion 57, and the portion covering the lower peripheral wall surface 44 is referred to as the lower peripheral wall surface covering portion 54. The circular upper surface covering portion 51a, the upper peripheral wall surface covering portion 52, the annular surface covering portion 53, and the lower peripheral wall surface covering portion 54 are flat covering portions. Therefore, these may be collectively referred to as flat covering portions 51a, 52, 53, and 54. The upper outer corner curved surface covering portion 55 and the lower outer corner curved surface covering portion 57 ... Examples of materials for the insulating sprayed film 50 include metal oxides such as alumina and yttria.

[0022] In this embodiment, the porosity of the flat coating portions 51a, 52, 53, 54, the outer curved surface coating portions 55, 57, and the inner curved surface coating portion 56 is 8.0% or less, and the average distance between nearest pores with a pore diameter of 5.0 μm or more is 4.0 μm or more. This ensures that the withstand voltage of the thermal sprayed insulating film 50 is high (e.g., 5.0 kV or more) regardless of location. It is more preferable that the porosity of each of these portions is 4.0% or less, and the average distance between nearest pores with a pore diameter of 5.0 μm or more is 5.8 μm or more. This ensures that the withstand voltage of the thermal sprayed insulating film 50 is higher.

[0023] The porosity of the flat covering portions 51 a, 52, 53, and 54 and the porosity of the outer curved surface covering portions 55 and 57 may be smaller than the porosity of the inner curved surface covering portion 56. The average distance between nearest pores with a pore diameter of 5.0 μm or more in the flat covering portions 51 a, 52, 53, and 54 and the average distance between nearest pores with a pore diameter of 5.0 μm or more in the outer curved surface covering portions 55 and 57 may be larger than the average distance between nearest pores with a pore diameter of 5.0 μm or more in the inner curved surface covering portion 56.

[0024] The average pore diameter of the flat coating portions 51a, 52, 53, 54, the outer curved surface coating portions 55, 57, and the inner curved surface coating portion 56 is preferably 5.0 μm or less. The inner curved surface coating portion 56 preferably has pores containing spherical splashes. During thermal spraying, the powder of the spray material collides with the surface of the conductive plate 40, flattens, and scatters around. The scattered material is called splashes, and the remaining material is called splats. The particle diameter of the spherical splashes is preferably 3.0 μm or less.

[0025] The bonding layer 60 bonds the lower surface of the ceramic plate 20 to the upper surface of the cooling plate 30 (the circular upper surface 41 of the conductive plate 40). The bonding layer 60 may be a resin layer or a metal layer. The resin layer may be formed, for example, of a silicone resin adhesive, an acrylic resin adhesive, or a bonding sheet. Examples of bonding sheets include a sheet having an acrylic resin layer on both sides of a polypropylene core material, a sheet having a silicone resin layer on both sides of a polyimide core material, and a sheet made of epoxy resin alone. The metal layer may be formed, for example, of TCB (thermal compression bonding), or may be a layer formed of solder or metal brazing material.

[0026] Next, an example of how the wafer mounting table 10 configured as described above is described. First, the wafer mounting table 10 is installed in a chamber (not shown), and a wafer W is placed on the wafer mounting surface 21. The chamber is then depressurized using a vacuum pump to a predetermined vacuum level, and a DC voltage is applied to the electrode 22 of the ceramic plate 20 to generate an electrostatic attraction force, thereby attracting and fixing the wafer W to the wafer mounting surface 21. Next, the chamber is filled with a reactive gas atmosphere at a predetermined pressure (e.g., several tens to several hundreds of Pa). In this state, a high-frequency voltage is applied between an upper electrode (not shown) installed on the ceiling of the chamber and the conductive plate 40 to generate plasma. The surface of the wafer W is then processed by the generated plasma. A coolant is circulated through the coolant flow paths 32 of the cooling plate 30.

[0027] Next, a manufacturing example of the wafer mounting table 10 will be described. Since the ceramic plate 20 and the conductive plate 40 can be manufactured by known methods, a method for forming the insulating sprayed film 50 on the conductive plate 40 (sprayed film forming method) will be described here. Fig. 5 is a cross-sectional view of the spray gun 70, Fig. 6 is a front view of the spray gun 70, and Fig. 7 is an explanatory diagram showing the process of forming the insulating sprayed film 50. The front of the spray gun 70 is the surface where the nozzle 70a opens.

[0028] The insulating sprayed film 50 is formed on the surface of the conductive plate 40 (the outer peripheral portion 41a of the circular upper surface 41, the upper outer curved surface 45, the upper peripheral wall surface 42, the inner curved surface 46, the annular surface 43, the lower outer curved surface 47, and the lower peripheral wall surface 44) by atmospheric plasma spraying using a spray gun 70.

[0029] In atmospheric plasma spraying, a DC voltage is first applied between the anode 71 and the opposing cathode 72 that make up the nozzle 70a of the spray gun 70, generating an arc between the two electrodes. Simultaneously, plasma gas (e.g., Ar gas) is supplied to the nozzle 70a. This causes a plasma flame PF to be emitted from the nozzle 70a. Next, powder A is supplied through a first port 73, and powder B is supplied through a second port 74 into the plasma flame PF. Letting a [μm] be the average particle size D50 of powder A and b [μm] be the average particle size D50 of powder B, a is smaller than b. a and b preferably satisfy the relationship 1.5≦b / a≦2.5, and more preferably 1.8≦b / a≦2.2. a is preferably 5 to 40, and b is preferably 10 to 80. a is more preferably 5 to 30, and b is more preferably 10 to 60. Examples of materials for powders A and B include metal oxides such as alumina and yttria. Powders A and B supplied to the plasma flame PF are accelerated at a high temperature, becoming molten or in a nearly molten state, and are deposited on the surface of the conductive plate 40. This forms an insulating sprayed film 50 on the surface of the conductive plate 40. This method of atmospheric plasma spraying, in which powder A with a small particle size is supplied from one port (first port 73) and powder B with a large particle size is supplied from another port (second port 74), is called a two-port spraying method.

[0030] 6, the first port 73 and the second port 74 are arranged so that the angle θ formed between the axis of the first port 73 and the axis of the second port 74 with the nozzle 70a at the center is a predetermined angle. The angle θ is set in the range of 0 to 180°, and is preferably set in the range of 30 to 150°.

[0031] 7, while the conductive plate 40 is rotated about its axis, the thermal spray gun 70 is moved along the thick arrow (radial direction). At this time, the attitude of the thermal spray gun 70 is controlled while the thermal spray gun 70 is moved so that the axis of the nozzle 70a of the thermal spray gun 70 (plasma flame PF) is angled rather than perpendicular to the surface of the conductive plate 40 (the outer periphery 41a of the circular upper surface 41, the upper outer curved surface 45, the upper peripheral wall surface 42, the inner curved surface 46, the annular surface 43, the lower outer curved surface 47, and the lower peripheral wall surface 44). For example, the angle of the axis of the nozzle 70a with respect to the normal to the surface of the conductive plate 40 may be set in the range of 1 to 50 degrees.

[0032] The formed insulating sprayed film 50 has flat coating portions, namely, a circular upper surface coating portion 51a, an upper peripheral wall surface coating portion 52, an annular surface coating portion 53, and a lower peripheral wall surface coating portion 54, and outer curved surface coating portions, namely, an upper outer curved surface coating portion 55 and a lower outer curved surface coating portion 57, and an inner curved surface coating portion 56. The flat coating portions 51a, 52, 53, 54, the outer curved surface coating portions 55, 57, and the inner curved surface coating portion 56 all satisfy the above-mentioned characteristics (such as porosity and the average distance between nearest pores having a pore diameter of 5.0 μm or more).

[0033] According to the method for forming a thermal sprayed film of this embodiment described above in detail, where a denotes the average particle size D50 of powder A supplied from first port 73 and b denotes the average particle size D50 of powder B supplied from second port 74, the relationship 1.5≦b / a≦2.5 is satisfied, and therefore an insulating sprayed film 50 with a high withstand voltage can be formed on the surface of conductive plate 40. In particular, conductive plate 40 has an interior curved surface 46, and an insulating sprayed film with a high withstand voltage (interior curved surface covering portion 56) can be formed on this interior curved surface 46.

[0034] The first port 73 and the second port 74 are preferably provided around the nozzle 70a at intervals of 30° to 150°. It is also preferable that a=1 to 40 and b=10 to 80.

[0035] Furthermore, among the properties of the thermal sprayed insulating film 50, the porosity is preferably 8.0% or less, and the average distance between nearest pores having a pore diameter of 5.0 μm or more is preferably 4.0 μm or more. In this way, the withstand voltage of the formed thermal sprayed insulating film 50 becomes high regardless of location.

[0036] Furthermore, the insulating sprayed film 50 is formed on the upper peripheral wall surface 42 (an example of a first plane), the interior curved surface 46, and the annular surface 43 (an example of a second plane) of the conductive plate 40. Generally, the sprayed film formed on the interior curved surface 46 tends to have a lower withstand voltage than the sprayed film formed on the upper peripheral wall surface 42 or the annular surface 43, but according to the sprayed film formation method of this embodiment, the sprayed film formed on the interior curved surface 46 also has a higher withstand voltage.

[0037] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms as long as they fall within the technical scope of the present invention.

[0038] In the above-described embodiment, an example was shown in which the two-port thermal spraying method was performed using a thermal spray gun 70 with two ports, but this is not particularly limited. For example, a thermal spray gun with three or more ports may be used. When using a thermal spray gun with three or more ports, all of the ports may be used, or two or more of the ports may be used instead of all of them. In any case, the two-port thermal spraying method can be performed by supplying two types of powder with different average particle sizes to the plasma flame from at least two ports.

[0039] Although the above-described embodiment illustrates a two-port thermal spraying method, the thermal spray coating formation method of the present invention is not limited to the two-port thermal spraying method. For example, a thermal spray gun with three or more ports may be used, and at least three types of powders with different average particle sizes may be supplied from three or more of the ports to form the insulating thermal spray coating 50 on the surface of the conductive plate 40. In this case, when the average particle size D50 of the smallest powder among the at least three types of powders with different average particle sizes is a [μm] and the average particle size D50 of the largest powder is b [μm], the relationship 1.5≦b / a≦2.5 is satisfied.

[0040] In the above-described embodiment, an example of manufacturing a cooling plate 30 by forming an insulating sprayed film 50 on a conductive plate 40 is shown, but the sprayed film forming method of the present invention is not limited to being used specifically for manufacturing a cooling plate 30.

[0041] In the above-described embodiment, the ceramic plate 20 has an electrostatic electrode built in as the electrode 22, but the ceramic plate 20 may have a heater electrode (resistive heating element) or an RF electrode (plasma generating electrode) built in as the electrode 22 instead of or in addition to the electrostatic electrode.

[0042] In the above-described embodiment, the insulating sprayed film 50 is provided on a portion (outer periphery 41 a ) of the circular upper surface 41 of the conductive plate 40 , but the insulating sprayed film 50 may be provided on the entire circular upper surface 41 .

[0043] [Experimental Examples 1 to 9] In Experimental Examples 1 to 6, the cooling plate 30 was manufactured by forming an insulating sprayed film 50 on an aluminum conductive plate 40 using the two-port spraying method described in the above embodiment. The powder used was alumina powder. Specific conditions for the two-port spraying method in Experimental Examples 1 to 6 are shown in Table 1.

[0044] In Experimental Examples 7 to 9, cooling plates were manufactured by forming an insulating sprayed film on the conductive plate 40 using a one-port spraying method (a method in which powder of a predetermined average particle size is supplied only from the first port 73 of the spray gun 70 to perform atmospheric plasma spraying) rather than a two-port spraying method. Specific conditions for the one-port spraying method in Experimental Examples 7 to 9 are shown in Table 1.

[0045] In Table 1, "two ports (120° apart)" indicates that the angle θ (see FIG. 6) between the axis of the first port 73 and the axis of the second port 74 is 120°. "Current" refers to the current that flows between the poles 71 and 72 of the thermal spray gun 70 when an arc is generated. "Spraying distance" refers to the distance from the tip of the nozzle 70a of the thermal spray gun 70 to the surface of the conductive plate 40.

[0046]

[0047] [Characteristics] Test Pieces Test pieces were cut from the cooling plates 30 of Experimental Examples 1 to 6, and various characteristics (average distance between nearest pores with a pore diameter of 5.0 μm or more, porosity, average pore diameter, presence or absence of splash, and withstand voltage) were measured. The test pieces were cut from the cooling plates 30 so that they formed a sector shape with a central angle of approximately 30° when viewed from above (see the dotted line in Figure 4). The polished surface for the evaluation test was a mirror-finished cut surface of the test piece by polishing. Polishing was performed using 3 μm diamond abrasive grains and 0.5 μm diamond abrasive grains, with final finishing performed by lapping using diamond abrasive grains of 0.1 μm or less. Test pieces were also cut from Experimental Examples 7 to 9 in the same manner as Experimental Examples 1 to 6, and various characteristics were measured. The measurement methods for various characteristics are described below. The measurement results are shown in Table 2. Note that the "inner corner portion" refers to the inner corner curved surface covering portion 56, and the "flat portion" refers to the annular surface covering portion 53.

[0048] - Average distance between nearest pores with a pore diameter of 5.0 μm or more For the inner corner portion, the polished surface for evaluation test was observed under SEM at a magnification of 100x, and for each pore with a circumscribed circle diameter of 5.0 μm or more present per 450 μm x 450 μm, the distance to other pores with a circumscribed circle diameter of 5.0 μm or more was measured. The smallest distance among these was taken as the distance between nearest pores with a pore diameter of 5.0 μm or more, and the average value of all the distances between nearest pores with a pore diameter of 5.0 μm or more was calculated, which was taken as the average distance between nearest pores with a pore diameter of 5.0 μm or more. For the flat surface portion, the average distance between nearest pores with a pore diameter of 5.0 μm or more was determined in the same manner as for the inner corner portion, except that the area in the SEM observation was set to 1200 μm x 400 μm. However, as a prerequisite for image processing, in order to suppress noise, pores that were too small (with an area of ​​2.5 μm or more) were excluded. 2 This also applies to the porosity and average pore diameter described below.

[0049] Porosity The porosity of the inner corners was calculated based on the area ratio of the total pores present per 450 μm × 450 μm measured in the SEM observation described above. The porosity of the flat surface was calculated based on the area ratio of the total pores present per 1200 μm × 400 μm measured in the SEM observation described above.

[0050] Average pore diameter The average pore diameter of the inner corners was determined by measuring the number of pores present per 450 μm × 450 μm and the maximum length of the pores in the above-mentioned SEM observation, and the average value of the maximum pore lengths was used. The average pore diameter of the flat surface was determined by measuring the number of pores present per 1200 μm × 400 μm and the maximum length of the pores in the above-mentioned SEM observation, and the average value of the maximum pore lengths was used.

[0051] Presence or absence of splashes: For the inner corners, the SEM observation described above was used to check whether splashes (spheres with a diameter of 3.0 μm or more) existed in pores present per 450 μm × 450 μm. For the flat surface, the SEM observation described above was used to check whether splashes (spheres with a diameter of 3.0 μm or more) existed in pores present per 1200 μm × 400 μm.

[0052] - Dielectric strength The test piece was placed on an aluminum electrode plate, and the measurement point of the test piece was pressed from above with a jig equipped with a weight (550 g). A DC voltage was applied between the electrode plate and the jig to measure the breakdown voltage (dielectric strength). The measurement points were three points on the left, center, and right of the inner corners, and three points on the left, center, and right of the flat surface. The dielectric strength was the average value of the three measured points. Test pieces with a dielectric strength of 5.0 kV or more were judged to be good products.

[0053]

[0054] [Evaluation] The test pieces of Experimental Examples 1 to 6 had a withstand voltage of 5.0 kV or more at both the inner corners and flat surfaces, and were considered to be good products. In Experimental Examples 1 to 6, the average distance between nearest pores with a pore diameter of 5.0 μm or more was 4.0 μm or more at both the inner corners and flat surfaces, and the porosity was 8.0% or less. Therefore, it was found that if these conditions are met, the withstand voltage will be high. In addition, the characteristics of the outer corners (outer corner curved surface covering portions 55, 57) were equivalent to the characteristics of the flat surfaces.

[0055] Furthermore, the test pieces of Experimental Examples 1 to 4 had a significantly higher withstand voltage of 6.0 kV or more in both the inner corners and flat surfaces. In Experimental Examples 1 to 4, the average distance between nearest pores with a pore diameter of 5.0 μm or more was 5.8 μm or more, and the porosity was 4.0% or less in both the inner corners and flat surfaces. In Experimental Examples 1 to 4, the average pore diameter was 5.0 μm or less.

[0056] In contrast, the test pieces of Experimental Examples 7 to 9 had a withstand voltage of 5.0 kV or more at the flat portions, but had a withstand voltage of less than 5.0 kV at the inner corners. In Experimental Examples 7 to 9, the withstand voltage was low because the average distance between nearest pores with a pore diameter of 5.0 μm or more at the inner corners was less than 4.0 μm and the porosity was 8.0% or more.

[0057] It should be noted that Experimental Examples 1 to 6 correspond to working examples of the thermal spray coating formation method of the present invention, and Experimental Examples 7 to 9 correspond to comparative examples. However, the Examples are merely preferred examples of the present invention, and therefore the present invention is not limited in any way by the Examples.

[0058] This application claims priority from Japanese Patent Application No. 2024-114830, filed on July 18, 2024, the entire contents of which are incorporated herein by reference.

[0059] The present invention can be used to form a thermal sprayed film.

[0060] 10 wafer mounting table, 20 ceramic plate, 21 wafer mounting surface, 22 electrode, 30 cooling plate, 32 coolant flow path, 40 conductive plate, 41 circular upper surface, 41a outer periphery, 42 upper peripheral wall surface, 43 annular surface, 44 lower peripheral wall surface, 45 upper outer curved surface, 46 inner curved surface, 47 lower outer curved surface, 50 insulating sprayed film, 51a circular upper surface coating portion, 52 upper peripheral wall surface coating portion, 53 annular surface coating portion, 54 lower peripheral wall surface coating portion, 55 upper outer curved surface coating portion, 56 inner curved surface coating portion, 57 lower outer curved surface coating portion, 60 bonding layer, 70 spray gun, 70a nozzle, 71 anode, 72 cathode, 73 first port, 74 second port, PF plasma flame, W wafer.

Claims

1. A method for forming an insulating thermal spray coating on the surface of a conductive material by supplying at least two powders with different average particle sizes D50 from two or more ports to a plasma flame emitted from the nozzle of a thermal spray gun, wherein the average particle size D50 of powder A, the smallest of the at least two powders, is a [μm], and the average particle size D50 of powder B, the largest, is b [μm], and the thermal spray coating formation method satisfies 1.5≦b / a≦2.

5.

2. The method for forming a thermal sprayed film according to claim 1, wherein the two or more ports are provided around the nozzle at intervals of 30° to 150°.

3. The method for forming a thermal sprayed film according to claim 1 or 2, wherein a=1 to 40, and b=10 to 80.

4. A method for forming a thermal sprayed film according to claim 1 or 2, wherein the properties of the thermal sprayed film are a porosity of 8.0% or less, and an average distance between nearest pores having a pore diameter of 5.0 μm or more of 4.0 μm or more.

5. A method for forming a thermal sprayed film according to claim 1 or 2, wherein the conductive member has a first plane, a second plane that is angled relative to the first plane, and an interior curved surface that is the boundary surface between the first plane and the second plane, and the thermal sprayed film is formed on the first plane, the interior curved surface, and the second plane.

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