Holding device

Abstract

To provide a holding device including a plate-shaped member whose main component is high-purity ceramics and a holding substrate that has excellent adhesion to an electrode layer disposed inside the plate-shaped member.SOLUTION: A holding device 100 according to the present invention includes a holding substrate 10 having a plate-shaped member 11 including a first surface S1 for holding an object W and a second surface S2 disposed on the opposite side of the first surface, and containing ceramics as a main component, and an electrode layer 12 disposed inside the plate-shaped member 11 and containing a conductive material 40 as a main component and ceramics 50 as a subcomponent. The plate-shaped member 11 includes a first dielectric layer 111 disposed on the first surface S1 side of the electrode layer 12 and having a main component content of 99 mass% or more, and a second dielectric layer 112 disposed on the second surface S2 side of the electrode layer 12 and having a main component content of 99 mass% or more. The fractal dimension D of a surface 12a on the first surface S1 side of the electrode layer 12 is 1.18 or more.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a retaining device. [Background technology]

[0002] Electrostatic chucks are used as holding devices to hold wafers (semiconductor wafers) when manufacturing semiconductors. Electrostatic chucks are equipped with a holding substrate (ceramic substrate) mainly made of alumina, an insulating ceramic, and the wafer is held on the surface of the holding substrate by electrostatic attraction. The electrostatic attraction is generated by applying a voltage to an electrode layer (chuck electrode) provided inside the holding substrate.

[0003] In recent years, this type of electrostatic chuck is required to apply high-power radio frequency power in plasma processing such as plasma etching. Therefore, high-purity alumina (99.99% purity) having excellent plasma resistance is used as a material for forming the base material (plate-shaped member) of the holding substrate (see, for example, Patent Document 1). If the base material of the holding substrate is made of high-purity alumina, there is a risk that the adhesion between the base material and the electrode layer formed therein may decrease. Therefore, in the case of a holding substrate whose base material is made of high-purity alumina, a metallization paste containing alumina powder added thereto for the purpose of improving the adhesion with the base material is used in addition to conductive powder (Pd powder) and binder when forming the electrode layer. In the electrode layer made of such a metallization paste, a three-dimensional network of alumina is formed connecting one surface side and the other surface side in the thickness direction, so that the adhesion between the electrode layer and the base material is ensured. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5441020 Summary of the Invention [Problem to be solved by the invention]

[0005] It is necessary to ensure adhesion between the base material (plate-shaped member) and the electrode layer.

[0006] Furthermore, if a large amount of alumina powder is used when forming the electrode layer, the adhesion between the electrode layer and the base material of the holding substrate is improved, but there is a problem that the thermal conductivity of the holding substrate (especially in the vicinity of the electrode layer) is reduced.

[0007] When one surface (upper surface) of the holding substrate is heated during plasma processing, heat moves inside the holding substrate from one surface to the other surface (lower surface). A base member is disposed on the other surface, and when the base member is heated, the base member is cooled by a cooling mechanism (coolant flow path, etc.) provided inside. However, as described above, if a large amount of alumina powder is used when forming the electrode layer, a portion of the alumina powder with low thermal conductivity is formed inside the electrode layer, and this portion impedes the transfer of heat in the holding substrate, causing a decrease in the heat dissipation ability of the holding substrate.

[0008] An object of the present invention is to provide a holding device including a plate-shaped member whose main component is high-purity ceramics and a holding substrate that has excellent adhesion to an electrode layer disposed inside the plate-shaped member.

[0009] Furthermore, a further object of the present invention is to provide a holding device comprising a plate-shaped member whose main component is high-purity ceramics and a holding substrate which has excellent adhesion to an electrode layer placed therein and also has excellent heat dissipation properties (thermal conductivity). [Means for solving the problem]

[0010] The means for solving the above problems are as follows. <1> A holding device comprising a holding substrate having a plate-shaped member including a first surface for holding an object and a second surface disposed opposite the first surface and containing ceramics as a main component, and an electrode layer disposed inside the plate-shaped member and containing a conductive material as a main component and the ceramics as a secondary component, wherein the plate-shaped member includes a first dielectric layer disposed on the first surface side of the electrode layer and having a content of the main component of 99% by mass or more, and a second dielectric layer disposed on the second surface side of the electrode layer and having a content of the main component of 99% by mass or more, and the fractal dimension D of the surface of the electrode layer on the first surface side is 1.18 or more.

[0011] <2> The area ratio of the ceramic to an observation range set on the center side of the electrode layer in a cut surface of the electrode layer along the thickness direction is 30% or less. <1> A holding device as described in

[0012] <3> The ceramic is not present in the cut surface of the electrode layer in a form that connects the first dielectric layer and the second dielectric layer. <1> or <2> A holding device as described in

[0013] <4> In a plan view of the plate-like member, the area ratio of the electrode layer to the first surface is 80% or more. <1> from <3> 13. A holding device according to any one of the preceding claims. Effect of the Invention

[0014] According to the present invention, it is possible to provide a holding device including a plate-shaped member whose main component is a high-purity ceramic and a holding substrate that has excellent adhesion to an electrode layer disposed inside the plate-shaped member.

[0015] Furthermore, according to the present invention, a holding device can be provided that includes a plate-shaped member whose main component is high-purity ceramics and a holding substrate that has excellent adhesion to an electrode layer placed therein and also has excellent heat dissipation properties (thermal conductivity). [Brief description of the drawings]

[0016]

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Figure 12

[0017] <Embodiment 1> A holding device 100 according to a first embodiment will be described below with reference to Figs. 1 to 5. The holding device 100 is an electrostatic chuck that attracts and holds an object (wafer W) by electrostatic attraction. The electrostatic chuck is used as a table on which the wafer W is placed, for example, in a process of performing etching using plasma in a reduced pressure chamber.

[0018] 1 is an explanatory diagram showing a schematic cross-sectional configuration of a holding device 100 according to embodiment 1. The holding device 100 includes a disk-shaped holding substrate (ceramic substrate) 10 and a disk-shaped base member 20 that is larger than the holding substrate 10. For example, when the holding substrate 10 is disk-shaped with a diameter of 300 mm and a thickness of 3 mm, the base member 20 is set to be disk-shaped with a diameter of 340 mm and a thickness of 20 mm.

[0019] The holding substrate 10 and the base member 20 are stacked on top of each other in the vertical direction, with the holding substrate 10 disposed on the upper side and the base member 20 disposed on the lower side. The holding substrate 10 and the base member 20 are bonded to each other by a bonding material 30 interposed therebetween.

[0020] The holding substrate 10 has a first surface S1 of a substantially circular shape disposed on the upper side, and a second surface S2 of a substantially circular shape disposed on the opposite side (i.e., the lower side) of the first surface S2 and facing the base member 20. The base member 20 has a third surface S3 of a substantially circular shape disposed on the upper side and facing the holding substrate S2, and a fourth surface S4 of a substantially circular shape disposed on the opposite side (i.e., the lower side) of the third surface S3. The above-mentioned bonding material 30 is sandwiched between the second surface S2 of the holding substrate 10 and the third surface S3 of the base member 20 and spreads out in a layer.

[0021] The holding substrate 10 has a disk-shaped plate-shaped member (base material) 11 and an electrode layer 12 disposed inside the plate-shaped member 11. The upper surface of the plate-shaped member 11 becomes a first surface S1 of the holding substrate 10, and the lower surface (rear surface) of the plate-shaped member 11 becomes a second surface S2 of the holding substrate 10.

[0022] The plate-shaped member 11 is a plate-shaped (disk-shaped) insulating member containing ceramics as a main component. In this specification, the term "main component" means the component with the highest content. In this embodiment, the content of the main component in the plate-shaped member 11 is 99 mass % or more (preferably 99.5 mass % or more). In this embodiment, the main component of the plate-shaped member 11 is alumina (Al 2 O 3 ). In other words, the plate-shaped member 11 of this embodiment contains high-purity alumina as a main component. In other embodiments, the main component of the plate-shaped member may be other ceramics such as aluminum nitride (AlN) as long as the object of the present invention is not impaired.

[0023] As shown in FIG. 1, the plate-like member 11 includes a first dielectric layer 111 arranged on the first surface S1 side of the electrode layer 12 and having a main component (alumina) content of 99 mass% or more (preferably 99.5 mass% or more), and a second dielectric layer 112 arranged on the second surface S2 side of the electrode layer 12 and having a main component (alumina) content of 99 mass% or more (preferably 99.5 mass% or more).

[0024] The electrode layer 12 is disposed inside the plate-like member 11 and contains a conductive material as a main component and ceramics as a secondary component.

[0025] The electrode layer 12 is generally planar (layered) and substantially parallel to the first surface S1. As shown in FIG. 1, the electrode layer 12 is disposed on the first surface S1 side inside the holding substrate 10 (plate-shaped member 11).

[0026] The electrode layer 12 contains a conductive material such as tungsten (W), molybdenum (Mo), platinum (Pt), or palladium (Pd) as a main component. The electrode layer 12 also contains the ceramics used as the main component of the plate-like member 11 as a secondary component. In this embodiment, the electrode layer 12 contains alumina (Al 2 O 3 ) is contained.

[0027] The electrode layer 12 in this embodiment is a chuck electrode, and is connected to an external power source via a terminal (not shown) etc. When power is supplied to the electrode layer 12, an electrostatic force is generated, and the wafer W is attracted and held on the first surface S1 of the holding substrate 10 by this electrostatic force.

[0028] Fig. 2 is an explanatory diagram that shows a schematic plan view of the holding substrate 10 (plate-shaped member 11) of the holding device 100 according to the embodiment 1. As shown in Fig. 2, in the plan view of the plate-shaped member 11, the area ratio of the electrode layer 12 to the first surface S1 is 80% or more. As shown in Fig. 2, the electrode layer 12 has a substantially circular shape in plan view, and is disposed inside the plate-shaped member 11 so as to overlap most of the first surface S1.

[0029] Fig. 3 is a diagram showing an SEM image of a cross section of the electrode layer 12 in the plate-like member 11 cut along the thickness direction. As shown in Fig. 3, in this embodiment, the surface 12a on the first surface S1 side (upper side) of the electrode layer 12 is roughened. In other words, the surface 12a of the electrode layer 12 is an uneven surface including many protrusions and many recesses.

[0030] The fractal dimension D of surface 12a on the first surface S1 side of electrode layer 12 is 1.18 or more. The fractal dimension of surface 12a of electrode layer 12 is determined by a box counting method.

[0031] A fractal dimension D of 1.18 or more means that the shape of the surface 12a of the electrode layer 12 is complex. The fractal dimension is an index of geometric complexity, and in this embodiment, the fractal dimension when the electrode layer 12 is viewed in a cut surface (i.e., a two-dimensional fractal dimension) is defined. It is generally known that in a two-dimensional fractal dimension, for example, when the contour shape is a simple shape such as a perfect circle, a square, or a rectangle, the fractal dimension is about 1, and the more complex the shape is, such as a shape with many projections and recesses, the larger the fractal dimension becomes, approaching 2.

[0032] Here, we will briefly explain the method (principle) of analyzing fractal dimension by the box counting method. For example, when a figure existing in a plane is divided into squares with a side length of d, if the figure is covered with N(d) squares, then between N(d) and d, N(d)=ad -D (a is a positive integer) (I) When the above relationship holds, D is defined as the fractal dimension of the figure. Furthermore, taking the logarithm of both sides of the above formula (I) gives: log 10 N(d) = -D log 10 d+log 10 a (a is a positive integer) (II) If we plot a log-logarithmic plot of d versus N(d), we can find the fractal dimension D from the slope of the line.

[0033] 4 is a graph showing a common logarithm plot of box pixel size (d) versus number of boxes (N(d)) based on the contour line of surface 12a extracted from the cut surface of electrode layer 12. Details of how to obtain the fractal dimension using the box counting method will be described later.

[0034] In this embodiment, surface 12b on the second surface S2 side (lower side) of electrode layer 12 is not roughened and has smaller irregularities and is flatter than surface 12a. That is, in the electrode layer 12 of this embodiment, at least surface 12a on the first surface S1 side on which the wafer W is placed is roughened to have an irregular surface represented by a desired fractal dimension D.

[0035] In the present embodiment, the area ratio of the ceramic to the observation range set on the center side of the electrode layer 12 in the cut surface of the electrode layer 12 along the thickness direction is 30% or less.

[0036] As shown in the SEM image of FIG. 3, the conductive material 40, which is the main component of the electrode layer 12, exists in a layered form. A plurality of ceramic (alumina) 50 chunks exist inside the layered conductive material 40. However, in the case of this embodiment, the ceramic 50 does not exist in a form that connects the first dielectric layer 111 and the second dielectric layer 112 on the cut surface of the electrode layer 12. That is, in the case of this embodiment, the ceramic 50 does not exist in a form that penetrates the electrode layer 12 (conductive material) in the thickness direction. The upper surface of the layered conductive material 40 becomes the surface 12a of the electrode layer 12, and the lower surface of the conductive material 40 becomes the surface 12b of the electrode layer 12.

[0037] When the area ratio of the ceramic is 30% or less (preferably 25% or less), the electrode layer 12 has excellent thermal conductivity. A method for calculating the area ratio of the ceramic in a cut surface of the electrode layer 12 along the thickness direction will be described later. From the viewpoint of ensuring adhesion between the electrode layer 12 and the plate-like member 11, the lower limit of the area ratio is preferably 3% or more, and more preferably 5% or more.

[0038] The holding substrate 10 may have other configurations, such as a gas flow path for supplying an inert gas (for example, helium gas, which is a thermally conductive gas) to the first surface S1 side.

[0039] The base member 20 is mainly composed of, for example, a metal (aluminum, aluminum alloy, etc.), a composite of metal and ceramics (Al-SiC), or ceramics (SiC).

[0040] A coolant flow path 21, which is a cooling mechanism, is provided inside the base member 20. A coolant (e.g., a fluorine-based inert liquid, water, etc.) is caused to flow through the coolant flow path 21 to cool the plasma heat. When the coolant flows through the coolant flow path 21, the base member 20 is cooled, and the holding substrate 10 is cooled by heat transfer (heat withdrawal) between the base member 20 and the holding substrate 10 via the bonding material 30. As a result, the wafer W held on the first surface S1 of the holding substrate 10 is cooled. The temperature of the wafer W held on the first surface S1 can be controlled by appropriately adjusting the coolant flow rate through the coolant flow path 21.

[0041] The base member 20 may have other configurations, such as a gas flow passage for supplying an inert gas.

[0042] The bonding material 30 is composed of, for example, a bonding sheet containing a silicone-based organic bonding agent, an inorganic bonding agent, or an Al-based metal adhesive. The bonding material is preferably one that has high adhesive strength to both the holding substrate 10 and the base member 20, as well as high pressure resistance and thermal conductivity. The bonding material 30 may also be formed with a gas flow path for supplying an inert gas, if necessary.

[0043] Next, an example of a manufacturing method for the holding device 100 of this embodiment will be described. First, a manufacturing method for the holding substrate 10 provided in the holding device 100 will be described with reference to Fig. 5. Fig. 5 is an explanatory diagram that shows a schematic representation of the manufacturing method for the holding substrate 10. This manufacturing method for the holding substrate 10 is an application of a sheet lamination method that uses green sheets (ceramic green sheets).

[0044] First, as shown in Fig. 5(A), in order to form the first dielectric layer 111 of the plate-like member 11, a plurality of green sheets are laminated to prepare a first laminate 111X. The slurry for the green sheets is obtained by, for example, mixing a mixture containing alumina powder, an acrylic binder, a dispersant, a plasticizer, a sintering aid (for example, glass, rare earth oxide), etc., to which an organic solvent is further added, using a ball mill. This slurry is formed into a sheet shape using a casting device, and then the obtained molded product is dried to obtain a plurality of green sheets.

[0045] Next, as shown in Fig. 5(B), a surface roughening treatment is performed on the surface 111Xa of the first laminate 111X. The surface roughening treatment is performed for the purpose of roughening the surface 12a of the electrode layer 12 to be finally obtained so that it becomes an uneven surface represented by a desired fractal dimension D. The surface roughening treatment may be performed directly on the surface of the metallization paste 12X for forming the electrode layer 12, or may be performed on the surface 111Xa of the counterpart (first laminate 111X) that comes into contact with the surface. Here, the case where the surface roughening treatment is performed on the surface 111Xa of the counterpart first laminate 111X is illustrated as an example.

[0046] The surface roughening treatment is not particularly limited as long as it can obtain the desired fractal dimension D (1.18 or more). For example, sandblasting, sputtering, corona (discharge) treatment, flame treatment, ultraviolet irradiation treatment, electron beam irradiation treatment, etc. may be performed.

[0047] Thereafter, as shown in FIG. 5(C), a metallization paste 12X for forming an electrode layer 12 is laminated on the surface 111Xa of the first laminate 111X after the surface roughening treatment. The metallization paste 12X is obtained by adding conductive powder (main component) such as tungsten or molybdenum to a mixture of alumina powder (secondary component), acrylic binder, and organic solvent, and kneading the mixture. This metallization paste 12X is formed in a layer on the surface 111Xa of the first laminate 111X, for example, using a screen printing device. When the metallization paste 12X is formed in a layer in this way, the surface in contact with the surface 111Xa of the first laminate 111X finally becomes an uneven surface represented by a desired fractal dimension D (1.18 or more).

[0048] When the metallized paste 12X on the first laminate 111X is viewed from above, a frame-shaped green sheet (not shown) is disposed around the metallized paste 12X. This frame-shaped green sheet is disposed in a portion of the surface 111Xa of the first laminate 111X where the metallized paste 12X is not formed.

[0049] Next, as shown in FIG. 5(D), a second laminate 112X for forming the second dielectric layer 112 of the plate-like member 11 is prepared, and the second laminate 112X is laminated on the metallization paste 12X on the first laminate 111X.

[0050] The second laminate 112X is formed by stacking a plurality of green sheets, similar to the above-mentioned first laminate 111X. The second laminate 112X thus formed is stacked on the metallization paste 12X on the first laminate 111X so as to sandwich the metallization paste 12X between the first laminate 111X and the second laminate 112X. These laminates are thermally pressed together.

[0051] The outer periphery of the laminate consisting of the first laminate 111X, the metallizing paste 12X, and the second laminate 112X may be cut as appropriate. The laminate is then cut by machining to obtain a disk-shaped molded body. The obtained molded body is then degreased and fired, and the molded body after degreasing and firing is further fired (main firing) to obtain a sintered body. Thereafter, the surface of the sintered body is appropriately processed, polished, or the like to obtain a holding substrate 10 having a plate-shaped member 11 as shown in FIG. 5(E).

[0052] The method of manufacturing the base member 20 is basically the same as that of the conventional product, and therefore a detailed description thereof will be omitted.

[0053] After the holding substrate 10 and the base member 20 are produced, they are bonded together using a bonding material 30. The bonding of the holding substrate 10 and the base member 20 with the bonding material 30 is basically the same as that in conventional products. Therefore, a detailed description will be omitted. In this manner, the holding device 100 is manufactured.

[0054] As described above, the holding device 100 of this embodiment includes a plate-shaped member 11 whose main component is high-purity alumina (an example of a ceramic), and a holding substrate 11 that has excellent adhesion to the electrode layer 12 placed therein and also has excellent heat dissipation properties (thermal conductivity).

[0055] Since the electrode layer 12 contains a predetermined amount of alumina as a secondary component in addition to the conductive material 40 which is the main component, the surface 12a of the electrode layer 12 can be made to be an uneven surface with a fractal dimension D of 1.18 or more. The surface 12a of such an electrode layer 12 has excellent adhesion to the surface of the adjacent first dielectric layer 111, so that the formation of a gap (space) between them which would hinder the transfer of heat is suppressed.

[0056] Since the amount of alumina in the electrode layer 12 is relatively small, the electrode layer 12 does not include ceramics (alumina) 50 that has poor thermal conductivity and connects the first dielectric layer 111 and the second dielectric layer 112, but is mainly composed of the conductive material 40 that has excellent thermal conductivity. Therefore, the electrode layer 12 of this embodiment has excellent thermal conductivity itself. Even if the first dielectric layer 111 side laminated on the surface 12a side of such an electrode layer 12 is heated during plasma processing, the heat can be transferred quickly from the first dielectric layer 111 to the electrode layer 12. The heat transferred to the electrode layer 12 moves to the second dielectric layer 112 and further moves to the base member 20 side. The holding device 100 including such a holding substrate 10 has excellent heat dissipation (thermal conductivity).

[0057] Furthermore, in the case of this embodiment, when the plate-shaped member 11 is viewed in a planar manner from the front side (first surface S1 side), the area ratio of the surface 12a of the electrode layer 12 to the first surface S1 is 80% or more, so it can be said that the electrode layer 12 has a large effect on the heat dissipation properties (thermal conductivity) of the holding substrate 10 (holding device 100).

[0058] <Embodiment 2> Next, the holding substrate 10A included in the holding device according to the second embodiment will be described with reference to FIG. 6. FIG. 6 is a diagram showing an SEM image of a cut surface along the thickness direction of the plate-like member 11 included in the holding substrate 10A of the second embodiment. In the case of this embodiment, both surfaces of the electrode layer 12A formed in the plate-like member 11 are roughened. A surface 12Aa on the first surface side (upper side) of the electrode layer 12A and a surface 12Ab on the second surface side (lower side) are uneven surfaces including a large number of convex portions and a large number of concave portions. The holding device (holding substrate 10A) of this embodiment basically has the same configuration as that of the first embodiment, except that both surfaces of the electrode layer 12A are roughened.

[0059] The fractal dimension D of the surface 12Aa of the electrode layer 12A and the fractal dimension D of the surface 12Ab of the electrode layer 12A are both 1.18 or more.

[0060] Also in this embodiment, similarly to the first embodiment, in a cut surface of the electrode layer 12A along the thickness direction, the ceramic area ratio to the observation range set on the center side of the electrode layer 12A is 30% or less.

[0061] A method for roughening the upper surface 12Aa of the electrode layer 12A may include, for example, performing the above-mentioned surface roughening treatment on the surface of a first laminate of green sheets for forming the first dielectric layer 111 during the manufacture of the holding substrate 10A, and laminating a metallization paste for forming the electrode layer 12A on the surface of the first laminate.

[0062] In addition, a method of roughening the lower surface 12Ab of the electrode layer 12A can be, for example, a method in which, during the manufacture of the holding substrate 10A, the surface of a second laminate of green sheets for forming the second dielectric layer 112 is subjected to the above-mentioned surface roughening treatment, and the second laminate is laminated on the metallization paste so as to press the surface of the second laminate against the metallization paste on the first laminate.

[0063] As in this embodiment, not only the upper surface 12Aa of the electrode layer 12A but also the lower surface 12Ab may be roughened to have an uneven surface expressed by a desired fractal dimension D (1.18 or more). By roughening both surfaces of the electrode layer 12A in this manner, the heat extraction property (thermal conductivity) of the holding substrate 10A (holding device) of this embodiment is further improved. EXAMPLES

[0064] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples in any way.

[0065] Example 1 (Preparation of metallizing paste) A metallization paste was prepared by adding conductive powder to a mixture of alumina powder, acrylic binder, and organic solvent, and kneading the mixture. The amount of alumina powder in the metallization paste was adjusted to 20% by volume, relative to the total volume of the alumina powder and conductive powder (100%).

[0066] (Preparation of green sheets) A mixture containing alumina powder, acrylic binder, dispersant, plasticizer, sintering aid, etc. was mixed with an organic solvent using a ball mill to produce a slurry for green sheets to form high-purity plate-shaped components (alumina content: 99.5% by mass or more).

[0067] (Preparation of holding substrate) Except for using the obtained metallization paste and the slurry for the green sheet, a sample of Example 1 simulating a holding substrate was produced by the same method as the manufacturing method of the holding substrate explained in the embodiment 1. In Example 1, only the upper surface of the layered metallization paste for forming the electrode layer was roughened by the surface roughening treatment.

[0068] [Examples 2 to 4] Each sample of Examples 2 to 4 was produced in the same manner as Example 1, except that the amount of alumina powder in the metallizing paste was changed to the value (volume %) shown in Table 1. In Examples 2 to 4, slurries were produced for forming high-purity plate-shaped members with an alumina content of 99.5 mass % or more.

[0069] [Comparative Examples 1 to 3] Each sample of Comparative Examples 1 to 3 was produced in the same manner as Comparative Example 1, except that the amount of alumina powder in the metallizing paste was changed to the value (volume %) shown in Table 1. In Comparative Examples 1 to 3, slurries were produced for forming high-purity plate-shaped members with an alumina content of 99.5 mass % or more.

[0070] 〔evaluation〕 For each sample relating to each example and each comparative example, the "area ratio of ceramics in the cut surface of the electrode layer," "fractal dimension D of the surface of the electrode layer," "adhesion strength," "thermal conductivity," etc. were evaluated using the methods described below.

[0071] (Area ratio of ceramics on the cut surface of the electrode layer) A sample simulating a holding substrate was cut in the thickness direction, and the cut surface was polished. The cut surface was then photographed using a scanning electron microscope (SEM) to obtain an SEM image (magnification: 3000 times) of the cut surface. FIG. 7 is an explanatory diagram showing an observation range R set on the center side of the electrode layer 12 in the SEM image of the cut surface. As shown in FIG. 7, the observation range R is set between a linear upper reference line L1 set to pass through the uppermost part (top) of the electrode layer 12 and a linear lower reference line L2 set to pass through the lowermost part (bottom). The upper reference line L1 and the lower reference line L2 are arranged parallel to each other, and when the range between such upper reference line L1 and lower reference line L2 is 100%, the observation region R is the area excluding 30% of the area below the upper reference line L1 and 30% of the area above the lower reference line L2. In other words, the observation region R consists of the central 40% of the range (100%) between the upper reference line L1 and the lower reference line L2.

[0072] The SEM image is then binarized, and the conductive material 40 constituting the electrode layer 12 and the ceramic portion 50 present inside the conductive material 40 are distinguished from the obtained binarized image using image processing software. The area ratio of the ceramic to the observation area R (100%) is then calculated using image processing software. Three observation areas R were set for each sample, and the area ratio was calculated as the average value of these three areas. The results are shown in Table 1.

[0073] (Fractal Dimension D) The fractal dimension D of the surface of the electrode layer in each sample was obtained by the box counting method shown below. FIG. 8 is an explanatory diagram showing the image processing performed when obtaining the fractal dimension D. First, the SEM image (magnification: 3000 times) of the cut surface of the electrode layer taken during the evaluation of the above-mentioned area ratio was binarized using image processing software (ImageJ created by Wayne Rasband, National Institutes of Health, USA), and further, the contour of the electrode layer 12 (conductive material 40) was extracted from the obtained binarized image. FIG. 8(A) shows an example of an image from which the contour is extracted. Note that the contour of the electrode layer 12 shown at the bottom of FIG. 8(A) corresponds to the roughened surface. Thereafter, as shown in FIG. 8(B), the inside of the contour was filled in using the image processing software, and the contour portion corresponding to the roughened surface was extracted from the obtained filled-in image as shown in FIG. 8(C). Note that, as shown in FIG. 8(C), coordinates were set for the extracted contour portion.

[0074] Then, for the extracted contour portion, the square box side length d was changed stepwise from 2 to 64 pixels (2, 3, 4, 6, 8, 12, 16, 32, 64) using the box counting tool of the image processing software, and the covering number N(d) for each d was measured. The obtained square box side length d and the corresponding covering number N(d) were plotted in common logarithm according to the above formula (II), and the fractal dimension was calculated from the slope of the straight line. The results are shown in Table 1.

[0075] (Surface roughness Ra) For reference, the surface roughness (arithmetic mean roughness) Ra of the electrode layer in each sample was determined based on the contour portion (roughness curve) shown in FIG. 8(C) in accordance with JIS B0601-2001. The results are shown in Table 1.

[0076] The surface roughness Ra is the value, expressed in micrometers (μm), calculated by the following formula (1) when a reference length L is extracted from the contour portion (roughness curve) in the direction of the average line, the X axis is set in the direction of the average line of the extracted portion, and the Y axis is set in the direction of the longitudinal magnification, and the roughness curve is expressed as y=f(X).

[0077]

number

[0078] (Adhesion strength) A specimen TP shown in FIG. 9 was prepared using the metallizing paste for the electrode layer prepared in each Example. FIG. 9 is an explanatory diagram that shows a schematic representation of the specimen TP used for measuring adhesion strength. The specimen TP shown in FIG. 9 is a laminate in which a test electrode layer 12T and a conductive electrode layer (electrode layer for plating adhesion) 13T are formed on a surface 11Ta of a test plate-shaped member 11T including a recess. A rod-shaped Kovar terminal 80T is fixed to the conductive electrode layer 13T of this laminate via a nickel plating layer 60T and a brazing material (Ag-Cu). For convenience of explanation, the surface side of the electrode layer 12T with a roughened surface is indicated by the symbol 12Ta in FIG. 9.

[0079] The test plate-like member 11T was produced using the slurry for the green sheet prepared in Example 1 and the like.

[0080] For the specimens TP of Examples 1 to 4, an electrode layer 12T was formed on a surface 11Ta of a plate-like member 11T roughened by a surface roughening treatment, in the same manner as in the production of the samples simulating the holding substrates described above.

[0081] For the test piece TP produced as described above, the adhesion strength of the electrode layer 12T was measured using an autograph (precision universal testing machine) manufactured by Shimadzu Corporation in the following manner. Specifically, with the laminate side of the test piece TP fixed so that the bar-shaped Kovar terminal 80T was arranged horizontally, a force was applied using the autograph to push down on the Kovar terminal 80T at a point 15 mm away from the root side at a rate of 5 mm / min. Then, the strength (N) at the moment when the test piece TP was destroyed by applying such a force was measured. In each example and each comparative example, the strength (N) was measured five times each. The results are shown in FIG. 10. FIG. 10 is a diagram showing a graph summarizing the results of measuring the adhesion strength (N) of the electrode layers of each example and each comparative example. Note that the average value of the five measurement results was taken as the adhesion strength (N) of each example, etc. And when the adhesion strength (N) was 80 N or more, it was regarded as "having adhesion", and when the adhesion strength (N) was less than 80 N, it was regarded as "having no adhesion". In Table 1, "having adhesion" was represented by the symbol "○", and "having no adhesion" was represented by the symbol "×".

[0082] (Thermal conductivity) Using the metallizing paste for the electrode layer prepared in each example, etc., a test electrode layer was prepared. Then, using the obtained test electrode layer, the thermal conductivity was measured in the following manner. The results are shown in Table 1.

[0083] The metallizing paste for the electrode layer was shaped into a predetermined shape after degreasing, and the obtained shaped body was fired to obtain a fired body. Then, after appropriately performing cutting and grinding on the fired body, for the fired body, the thermal diffusivity and specific heat were measured based on the laser flash method in accordance with JIS R1611. Also, for the fired body, the bulk density was measured in accordance with JIS R1634. The product of the thermal diffusivity, specific heat, and bulk density thus obtained was taken as the thermal conductivity.

[0084]

Table 1

[0085] (About adhesion) As a result of the above-mentioned adhesion strength test, it was confirmed that the electrode layers of Examples 1 to 4 have excellent adhesion to the plate-shaped member (high-purity alumina). In the cases of Examples 1 to 3, the alumina content (5 to 20 vol%) in the electrode layer is relatively low, but the surface of the electrode layer is roughened so as to have a desired fractal dimension D (1.18 or more). In the case of Example 4, the surface of the electrode layer is roughened so as to have a desired fractal dimension D (1.18 or more). In the cases of Examples 1 to 4, during the adhesion strength test using an autograph, no destruction occurred at the interface between the electrode layer of the specimen TP and the plate-shaped member, but destruction occurred inside the electrode layer.

[0086] In contrast, it was confirmed that the electrode layers of Comparative Examples 1 to 3 did not have sufficient adhesion to the plate-shaped member (high-purity alumina). In the cases of Comparative Examples 1 to 3, the alumina content (5 to 20 vol%) in the electrode layer was relatively low, so it can be said that the electrode layer would not be able to exhibit sufficient adhesion to the plate-shaped member unless the surface of the electrode layer was roughened to have the desired fractal dimension D. In the cases of Comparative Examples 1 to 3, destruction occurred at the interface between the electrode layer of the specimen TP and the plate-shaped member during an adhesion strength test using an autograph.

[0087] (Thermal conductivity) As shown in Table 1, it was confirmed that the thermal conductivity of the electrode layer decreases as the alumina content in the electrode layer increases. In particular, among Examples 1 to 4, the electrode layers of Examples 1 to 3 have a thermal conductivity of 60 W / mK or more, and are excellent in thermal conductivity. As for the electrode layers of Comparative Examples 1 to 3, as described above, they have excellent thermal conductivity even though they do not have sufficient adhesion to the plate-like member.

[0088] (Relationship between fractal dimension D and adhesion) Here, FIG. 11 shows a graph of the relationship between the fractal dimension D of the electrode layer in each example and each comparative example and the adhesion of the electrode layer. The vertical axis of the graph in FIG. 11 represents the fractal dimension D, and the horizontal axis represents the content (vol%) of alumina contained in the electrode layer. In the graph in FIG. 11, if each example and each comparative example are classified into a case where the adhesion strength of the electrode layer is 80N or more (with adhesion) and a case where the adhesion strength of the electrode layer is less than 80N (without adhesion) based on the fractal dimension D, it is possible to set a range Z1 (with adhesion) and a range Z2 (without adhesion) as shown in FIG. 11. These ranges Z1 and Z2 can be classified in the vicinity of the fractal dimension D of 1.18. From the graph in FIG. 11, it can be said that the adhesion strength of the electrode layer is ensured when the fractal dimension D of the surface of the electrode layer is 1.18 or more.

[0089] As shown in the graph of Fig. 11, the fractal dimension D of the surface of the electrode layer tends to increase as the alumina content (vol%) in the electrode layer increases. Also, as shown in the graph of Fig. 11, the fractal dimension D is larger when the surface of the electrode layer is roughened than when it is not roughened.

[0090] (Relationship between surface roughness Ra and adhesion) For reference, FIG. 12 shows a graph of the relationship between the surface roughness Ra of the electrode layer and the adhesion of the electrode layer in each example and each comparative example. The vertical axis of the graph in FIG. 12 represents the surface roughness Ra, and the horizontal axis represents the content (vol%) of alumina contained in the electrode layer. In such a graph, even if one tries to distinguish between the examples and comparative examples based on the surface roughness Ra, when the adhesion strength of the electrode layer is 80 N or more (with adhesion) and when the adhesion strength of the electrode layer is less than 80 N (without adhesion), it is not possible to distinguish between them. In other words, the adhesion of the electrode layer needs to be represented by the fractal dimension D, not by the surface roughness Ra. [Explanation of symbols]

[0091] Reference Signs List 10...holding substrate, 11...plate-shaped member, 12...electrode layer, 20...base member, 21...coolant flow path, 30...bonding material, 40...conductive material, 50...ceramics, 100...holding device, 111...first dielectric layer, 112...second dielectric layer, R...observation area, S1...first surface, S2...second surface, S3...third surface, S4...fourth surface

Claims

1. A holding device comprising a holding substrate having a plate-shaped member including a first surface for holding an object and a second surface disposed on the opposite side of the first surface, the plate-shaped member containing ceramics as a main component, and an electrode layer disposed inside the plate-shaped member, the electrode layer containing a conductive material as a main component and the ceramics as a sub-component, the plate-like member includes a first dielectric layer disposed on the first surface side of the electrode layer, the first dielectric layer having a content of the main component of 99% by mass or more, and a second dielectric layer disposed on the second surface side of the electrode layer, the second dielectric layer having a content of the main component of 99% by mass or more, A holding device, wherein the fractal dimension D of the surface on the first surface side of the electrode layer is 1.18 or more.

2. 2. The holding device according to claim 1, wherein an area ratio of the ceramic to an observation range set on a center side of the electrode layer in a cut surface of the electrode layer along a thickness direction is 30% or less.

3. A holding device as described in claim 1 or claim 2, wherein, in the cut surface of the electrode layer along the thickness direction, the ceramics are not present in a form that connects the first dielectric layer and the second dielectric layer.

4. 3. The holding device according to claim 1, wherein an area ratio of the electrode layer to the first surface is 80% or more in a state in which the plate-like member is viewed from above.

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