Joined structures of metal terminals and ceramic members, joined structures of metal members and ceramic members, and adhesive materials

Abstract

The object of the invention is to join a ceramic member and a metal member with a sufficiently high bonding strength and to prevent cracks in a ceramic material constituting the ceramic member. A joined structure of a metal terminal 8 and a ceramic member 1 has a joining layer 12 between the terminal 8 and the ceramic member 1. The joining layer 12 has a metal adhesive layer 6 containing at least metal indium. The invention further provides a joined structure of a metal member 8 and a ceramic member 1. The metal member has a tip face 8a and a side face 8b. A hollow 4 is formed in the ceramic member 1. A joining layer 12 is formed between a bottom surface 4a facing the hollow 4 and the tip face 8a of the member 8, and further formed between a side wall surface 4b facing the hollow 4 and the side face 8b of the member 8. The joining layer 12 has a metal adhesive layer 6 containing at least metal indium.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Title of the Invention

[0002] The invention relates to a joined structure of a metal member, particularly metal terminal, and a ceramic member, and an adhesive material therefor.

[0003] 2. Related Art Statement

[0004] Dense ceramics is noted as a base material of an electrostatic chuck. In a field of a system for producing semiconductors, it has been practically used a susceptor containing an electrode for applying high frequency power to generate plasma. In such device for applying high frequency power, it has been performed to embed the electrode for applying high frequency power in a substrate made of silicon nitride or alumina.

[0005] In such devices, it is necessary to embed a metal electrode in a substrate of a ceramic material such as aluminum nitride, alumina or the like and to electrically connect the metal electrode to an outer connector for supplying electric power. The applicant disclosed a process of producing a ceramic heater, an electrostatic chuck and an electrode system for applying high frequency voltage, used for a system for producing semiconductors (see Japanese patent laid-open “Kokai” number 277, 173A/1996 and 209, 255A/1998). The applicant proposed, in these applications, the following process for producing a joined structure. A hole is formed in a ceramic substrate by machining to expose a part of a metal electrode, embedded in the substrate, to the hole. A metal terminal with a shape of a cylinder is inserted into the hole and its tip face is adhered to the metal electrode by brazing.

SUMMARY OF THE INVENTION

[0006] The inventors have tried the following brazing process of a ceramic member and a metal terminal. In this process, a hollow or a blind hole is formed in a surface region of a ceramic member and the tip face of a metal terminal is inserted into the hollow. A metal foil is interposed between the metal terminal and the inner wall surface of the ceramic member facing the hollow to obtain an assembly, which is then heated to join the terminal and member by brazing. However, in an actual production line, some problems were found in a step of cooling the ceramic member to a room temperature after the brazing (heating) step. That is, cracks may occur in the ceramic member near the inner wall surface, particularly near the corner portions of the hollow, of the member. Such cracks result in off-specification products to reduce the production yield.

[0007] It is an object of the invention to join a ceramic member and a metal member with a sufficiently high bonding strength and to prevent crack formation in a ceramic material constituting the ceramic member.

[0008] The invention provides a joined structure of a metal terminal and a ceramic member. A joining layer is formed between the metal terminal and the ceramic member. The joining layer comprises a metal adhesive layer containing at least indium.

[0009] The invention also provides a joined structure of a metal member and a ceramic member. The metal member has a tip face and a side face. A hollow is formed in the ceramic member, which has a side wall surface and a bottom surface both facing the hollow. A joining layer is formed between the bottom surface facing the hollow and the tip face of the metal member, and formed between the inner wall surface facing the hollow and the side face of the metal member. The joining layer comprises a metal adhesive layer containing at least indium.

[0010] According to the invention, a ceramic member and a metal member may be joined with each other with a sufficiently high bonding strength, with crack formation in the ceramic material constituting the ceramic member prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a cross sectional view showing a joined structure according to one embodiment of the invention;

[0012] FIG. 2(a) is a cross sectional view showing a ceramic substrate 2 with a hollow 11 formed, in which a metal film 5A is formed and a metal adhesive 9 is set;

[0013] FIG. 2(b) is a cross sectional view showing a ceramic substrate 2 with a hollow 11 formed, in which the metal adhesive 9 is melt on the metal film 5A; and

[0014] FIG. 3 is a cross sectional view showing a joined structure according to another embodiment of the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0015] The invention will be further described referring to the attached drawings. FIG. 1 is a cross sectional view schematically showing a joined structure according to one embodiment of the invention. A ceramic member 1 used in this embodiment is an electrostatic chuck also capable of functioning as an electrode for generating high frequency voltage. An electrode 3 for an electrostatic chuck made of an electrical conductor is embedded within a ceramic substrate 2. The electrode may preferably be embedded in a shaped body of ceramic powder and then subjected to a sintering process to produce the substrate 2 including the electrode 3 therein. 2b is an adsorption face and 2a is a back face of the substrate 2. A hollow 4 is formed on the side of the back face 2a. The hollow 4 is defined by a bottom surface 4a and a side wall surface 4b. A part of the electrode 3 is exposed to the bottom surface 4a facing the hollow 4 to form an exposed portion 3a.

[0016] In this embodiment, an intermediate layer 5 is formed so as to cover the bottom surface 4a and side wall surface 4b both facing the hollow 4. A metal terminal 8 has a tip face 8a and a side face 8c. The tip portion of the terminal 8 is inserted into the hollow 4. The tip portion 8b of the side face 8c and tip face 8a of the terminal are covered with a metal film 7. A joining layer 12 is formed between the tip face 8a of the terminal 8 and the bottom surface 4a facing the hollow 4. The joining layer 12 is composed of an intermediate layer 5, a metal adhesive layer 6a and a metal film 7. The joining layer 12 is also formed between the side face 8b of the terminal 8 and the side wall surface 4b facing the hollow 4. The joining layer 12 is composed of an intermediate layer 5, a metal adhesive layer 6b and a metal film 7. The joining layer 12 contacts and joined with the exposed portion 3a of the conductive member 3 exposing the bottom surface 4a of the hollow 4.

[0017] As described above, a joining layer having a metal adhesive layer containing at least metal indium is formed between a metal terminal and a ceramic member, according to the invention. According to the experimental results, it is thereby possible to join the ceramic member and metal terminal with a sufficiently high bonding strength and to prevent the formation of cracks in the ceramic material to improve a production yield. Moreover, when supplying an electric power to the metal terminal, it is also possible to prevent excessive heat generation and to reduce a temperature rise resulting from the heat generation, in the joining portion of the metal terminal and ceramic member.

[0018] The invention may provide a sufficiently high bonding strength between a metal terminal and ceramic member and prevent bonding defects due to crack formation in the ceramic material. The reasons may be speculated as follows. Metal indium has a melting point of about 160° C., and thus needs a relatively low temperature for brazing. Such low temperature for brazing results in a low stress due to the differential thermal expansion (shrinkage) of a metal adhesive and ceramics during a cooling step after the heating step. For example as shown in FIG. 1, the differential thermal expansion between the metal brazing or adhesive and ceramics tends to induce stress concentration near the corner portion 11 of the hollow 4, forming cracks from the corner portion 11 extending inwardly in the substrate 2. A metal brazing material containing indium may be effective for preventing such crack formation by reducing the stress concentration. Moreover, metal indium has a relatively low hardness, and thus tends to induce fracture in the brazing metal containing indium and helps to prevent the stress concentration in the ceramics. Metal indium is thus advantageous for preventing the formation of cracks or fracture in the ceramics. The effects may be synergistic for preventing the formation of cracks or fracture in the ceramic material, or for preventing bonding defects by relaxing a stress in the ceramic material due to a low hardness of metal indium.

[0019] When an electrical resistance is high or contact failure occurs in the interface of a brazing metal and a ceramic substrate, however, excessive and local heat generation might be induced. However, according to experimental results, when supplying high frequency electric power to a metal terminal, heat generation along and near the interface between the metal terminal and ceramic member was relatively small. In such cases, excessive or rapid heat generation, which may adversely affect the stability of indium, has not been observed.

[0020] In another aspect of the invention, a hollow may be formed in a ceramic member. In the aspect, the joining layer of the invention may be interposed between the bottom surface facing the hollow and the tip face of the metal member and between the side wall surface facing the hollow and the side face of the metal member, respectively. According to such structure, the ceramic member and conductive member were joined with a sufficiently high strength and the crack formation was reduced at the same time to successfully improve a production yield. The reasons are not clearly understood, however, it is speculated that the formation of cracks starting from the corner portion 11 or near, frequently observed in prior structures, may be prevented by the invention.

[0021] By the way, it has been proposed to join an electrostatic chuck with a metal cooling plate of a water-cooling type by metal bonding (Japanese Patent laid-open “Kokai” 3249A/1991). According to the technique disclosed in this application, an electrostatic chuck made of alumina and a cooling plate of water-cooling type made of aluminum are joined with metal indium. That is, metal indium is used for bonding the water cooling plate made of a metal. Such cooling plate made of a metal is constantly cooled by flowing water and thus its surface temperature is kept low. Therefore it is technically feasible to bond the metal cooling plate to the back face of the electrostatic chuck using metal indium, even if indium has a low melting point (about 160° C.). It has not been conceivable to apply metal indium, with such a low melting point, to bond a metal terminal, in which heat generation is usually or inevitably induced.

[0022] In a preferred embodiment, when bonding a metal terminal and a ceramic member, a hollow is formed in the ceramic member and a joining layer is interposed between the metal terminal and at least a part of the inner surface facing the hollow. More preferably, the metal terminal has a tip face and a side face, and the joining layer is interposed between the bottom surface facing the hollow and the tip face of the terminal and between the side wall surface facing the hollow and the side face of the terminal. It is thereby possible to effectively prevent the crack formation starting from the corner portion of the hollow extending inwardly in the ceramic member.

[0023] The material of a ceramic member is not particularly limited. In an application where a ceramic member is to be exposed to a corrosive gas containing a halogen element, particularly fluorine element, the material may preferably be a ceramic material containing aluminum element, such as aluminum nitride, alumina or sialon. Alternatively, the material may preferably be a nitride ceramics such as aluminum nitride, silicon nitride or sialon; and a carbide ceramics such as silicon carbide. The material may also be an oxide ceramics such as zirconia, alumina or the like.

[0024] The metal member or metal terminal may be made of a metal not particularly limited. In an application where a ceramic member is to be exposed to a corrosive gas containing a halogen element, particularly fluorine element, the metal may preferably be nickel, molybdenum, tungsten, platinum, rhodium and the alloys of these metals.

[0025] In an embodiment of the invention, electric power may be directly supplied to ceramics constituting a ceramic member through a metal terminal to give current flow. In a preferred embodiment, however, a ceramic member has a conductive member electrically connected with a metal terminal. The conductive member may be mounted and fixed on the ceramic substrate. In a preferred embodiment, however, the conductive member is embedded within a ceramic material constituting a ceramic member.

[0026] The material of the conductive member is not particularly limited. In an application where a ceramic member is exposed to a corrosive gas containing a halogen element, particularly fluorine element, the material may preferably be nickel, molybdenum, tungsten, platinum, rhodium or the alloys of these metals. When the conductive member is embedded within a ceramic member, the material of the conductive member may preferably be molybdenum, tungsten, platinum, rhodium or the alloys of these metals, and more preferably be molybdenum, tungsten or the alloys thereof.

[0027] In a preferred embodiment, a conductive member is exposed to the inner surface facing the hollow of the ceramic member and the exposed portion of the conductive member is contacted with the joining layer. The joining layer may be joined with the ceramic material constituting the ceramic member and further contacted and joined with the conductive member. As a result, the bonding strength of the ceramic member and metal member may be further improved. Even when the wettability of metal indium on the ceramic member is low, the ceramic and metal members may be joined with a feasible bonding strength.

[0028] The metal adhesive layer is composed of metal indium or an alloy containing at least indium. In other words, the adhesive layer is substantially composed of metal indium (pure indium) or composed of an alloy of indium and one or more metal other than indium. The adhesive layer may preferably be substantially made of indium. In this embodiment, however, inevitable impurities derived from raw materials and a small amount, for example not higher than 2 weight percent, of impurities are acceptable.

[0029] In an embodiment where the metal adhesive layer is made of an alloy of indium and another metal, the content of indium in the alloy may preferably be higher for obtaining the effects of the invention. Further, the content of indium in the alloy may preferably be not lower than 80 weight percent and more preferably be not lower than 95 weight percent. The higher limit of the indium content is not particularly limited, and the higher content is better.

[0030] Alternatively, the melting point of the alloy may preferably lower, for example not higher than 300° C. and more preferably be not higher than 200° C. The metal other than indium is not particularly limited and includes nickel, titanium, copper, gold, platinum and palladium.

[0031] In a preferred embodiment, the metal terminal functions as a terminal for applying high frequency voltage on the conductive member. The joined structure according to the invention is advantageous for preventing excessive heat generation when high frequency voltage is supplied through the metal terminal.

[0032] Dc voltage supplied to an electrode of an electrostatic chuck does not induce excessive heat generation. In an electrostatic chuck of a self-bias system generally used in an etcher, however, high frequency current is applied to its electrode to accelerate plasma generated over a wafer so that the accelerated plasma physically attacks the wafer. Alternatively, when an electrostatic chuck adsorbs a wafer by Johnson-Rahbek force, leak current flows through its ceramic substrate, the metal terminal and joining layer. It is thus required that the joining portion of the terminal has a low resistance, because the joining portion or its neighboring portion with a high resistance may result in considerable heat generation. Such possibility of excessive heat generation in the joining portion would have kept those skilled in the art from the conception of joining the metal terminal with a low melting point metal such as indium.

[0033] The conductive member embedded in a ceramic member is not particularly limited. In a preferred embodiment, the conductive member embedded in the ceramic member is a planar and bulky body. The “planar and bulky body” includes a planar and bulky body made of any material such as wires or an elongate planer body. For example, a wire or an elongate planar body may be shaped to produce a planer body, without shaping them in a spiral or zigzag form. The conductive member may be a metal plate, or a wire netting or gauze composed of metal wires knitted along a plane, or a plate with a number of small holes formed therein. Such member may be a punching metal, etching metal, wire mesh, felt or non-woven fabric.

[0034] In a preferred embodiment, the joining layer has an intermediate layer between the metal adhesive layer and ceramic member. The intermediate layer is made of a noble metal, aluminum, nickel, or the alloys thereof. Such layer is effective for improving the wettability of the metal adhesive on the ceramic member. The noble metal may preferably be copper or gold.

[0035] The depth of the hollow is not particularly limited. The depth may preferably be not smaller than 0.5 mm and more preferably be not smaller than 1.0 mm, for preventing the crack formation starting from the corner portion of the hollow. Although the upper limit of the depth of the hollow is not particularly defined, the depth may preferably be not larger than 20 mm for improving production efficiency.

[0036] The surface area of the hollow is not particularly limited. The surface area may preferably be not smaller than 5 mm2 and more preferably be not smaller than 15 mm2, for reducing a temperature rise in the joining portion. When the hollow is circular in a plan view, the diameter of the hollow may preferably be not smaller than 3 mm and more preferably be not smaller than 6 mm.

[0037] One example of producing a joining structure according to the invention will be described below. A metal adhesive material containing at least metal indium is mounted on the surface of a ceramic member. The adhesive material may preferably be set in the hollow formed in the ceramic member. For example as shown in FIG. 2(a), a hollow 4 is formed in a substrate 2 of a ceramic member 1. A part 3a of a conductive member 3 embedded in the substrate 2 is exposed to the hollow 4. An adhesive material 9 is set and fixed in the hollow 4. The adhesive material 9 may be a sheet, powder, or paste made by mixing powder and a binder.

[0038] In this embodiment, a metal film 5A may preferably be formed on a surface to be joined, particularly a bottom surface 4a and a side wall surface 4b facing the hollow 4 of the ceramic member. The metal film usually remains as an intermediate layer 5 after a joining process (see FIG. 1). The metal film may be formed by a gaseous phase process (for example, chemical vapor deposition or sputtering), or a liquid phase process (electrolytic plating, electroless plating or the like). In particular, the surface to be joined of ceramics may be easily covered with electroless plating.

[0039] Alternatively, it is possible to form a metal film on the surface to be joined, by dispersing metal powder into an organic binder to produce paste, applying the paste, and drying the applied paste to remove the organic binder. Further, a metal film may be formed by contacting a metal foil with the surface. The thickness of the metal film 5A may preferably be 0.1 to 20 μm.

[0040] Further, another metal film substantially same as the metal film 5A may be formed on the surface of the metal terminal or metal member.

[0041] At least the metal adhesive 9 is then heated to melt the adhesive as shown in FIG. 2(b). 10 is the melt of the adhesive wetting the surface of the metal film 5A. For heating at least the adhesive, the whole of the ceramic member may be subjected to a heat treatment. Alternatively, only the region of the adhesive 9 may be heated by using a local heating means such as high frequency radiation or laser ray radiation.

[0042] The molten adhesive may then preferably be processed using a supersonic trowel so as to remove an oxide film formed on the surface of metal indium and thus improve the wettability of the molten adhesive to the ceramic member. Alternatively, the molten adhesive may preferably be contacted with the surface of the metal member to wet the surface. The tip portion of the metal member is then inserted into the hollow, and the metal member is fixed so as not to incline using a jig to obtain an assembly. The assembly is then cooled with a load applied on the metal member, preferably in a direction perpendicular to the surface to be joined. The joining process of this example is thus completed.

[0043] FIG. 3 is a cross sectional view showing a joined structure according to another embodiment of the invention. A ceramic member 1A of this example does not have the conductive member as described above and mainly composed of a ceramic substrate 2.

[0044] In this example, the ceramic substrate 2 may have a predetermined conductivity so that high frequency electric power may be supplied to the substrate 2. Alternatively, the substrate 2 may be made of an insulating ceramic material,

EXAMPLES

Experiment “A”

[0045] A ceramic electrostatic chuck was produced and a sample for a tensile test was cut therefrom. That is, aluminum nitride powder was filled in a mold and sealed with a carbon foil. A metal mesh was embedded in the aluminum nitride powder. The mesh is obtained by knitting molybdenum wires a diameter of 0.12 mm at a density of 50 wires per inch. The aluminum nitride powder with the mesh therein was sintered by hot press sintering, at a maximum temperature of 1950° C., a pressure of 200 kg/cm2 and a holding time period of 2 hours at 1950° C., to produce a sintered body. The sintered body had a relative density of not lower than 98.0 percent. The mesh was embedded within the sintered body so that the mesh may function as an electrode for electrostatic chuck. A ceramic member, with a length of 20 mm, a width of 20 mm and a thickness of 2 mm, was cut out from the sintered body. A circular hollow 4 with a diameter of 6 mm and a depth of 1 mm was formed in the central portion of the ceramic member. A part of the embedded electrode (metal mesh) was exposed to the bottom surface facing the hollow 4. The tip face of a molybdenum terminal had a diameter of 5.90 mm.

[0046] The ceramic member and molybdenum terminal were joined as described referring to FIG. 2. That is, a nickel plating layer with a thickness of 5 μm was formed on the bottom surface 4a and side wall surface 4b facing the hollow 4, by electroless plating. A nickel plating layer with a thickness of 2 μm and a gold plating layer with a thickness of 2 μm were formed, in this order, on the tip face and side face of the tip portion of the molybdenum terminal 8. A block of metal indium with a weight of about 0.4 gram was set in the hollow 4. The substrate 2 and terminal 8 were then heated by means of a hot plate to about 200° C. After the block of indium was completely molten, an ultrasonic solder trowel was used to remove an indium oxide film formed on the metal indium to wet the bottom surface 4a and side wall surface 4b facing the hollow 4 with the melt of metal indium. At the same time, an ultrasonic solder trowel was used to wet the tip and side faces of the terminal with the melt of metal indium. The tip portion of the terminal was then inserted into the hollow. The terminal was then fixed by means of a jig so as to prevent the inclination of the terminal. The assembly was then cooled with a load of 500 gram applied on the terminal perpendicularly.

[0047] Four samples were produced as described above. Each sample (joined body) was subjected to visual evaluation for the presence of cracks in the joining layer and ceramic member. As a result, cracks were not observed in each of the samples.

[0048] A tapped hole of M4 with a depth of 2 mm was formed in the central portion of each metal terminal 8 for performing a tensile test of each joined body. Each tapped hole formed in each terminal joined with the substrate 2 was pulled upwardly to measure a breaking load. As a result, the average of the measured breaking load was 20.86 kgf. Each of the joined bodies was broken at a point in metal indium.

Experiment “B”

[0049] The ceramic member and metal terminal same as those used in the experiment “A” were joined with each other to produce four samples. However, the following three conditions were different from those applied in the experiment “A”. That is, an aluminum solder was used, and the solder was heated at 610° C. and under vacuum. Consequently, cracks were confirmed by visual evaluation within AlN in all of the four samples.

Experiment “C”

[0050] The ceramic member and metal terminal same as those used in the experiment “A” were joined with each other to produce four samples. However, the following three conditions were different from those applied in the experiment “A”. That is, a solder of Ag—Cu—Ti system was used, and the solder was heated at 850° C. and under vacuum. Consequently, cracks were confirmed by visual evaluation within AlN in all of the four samples.

Experiment “D”

[0051] An electrostatic chuck was produced. That is, a mesh is used obtained by knitting molybdenum wires with a diameter of 0.12 mm at a density of 50 wires per inch. The mesh was embedded in a primary shaped body of aluminum nitride powder. The primary shaped body was then set in a mold and sealed with a carbon foil. The primary shaped body with the mesh therein was sintered by hot press sintering, at a maximum temperature of 1950° C., a pressure of 200 kg/cm2 and a holding time period of 2 hours at 1950° C., to produce a sintered body. The sintered body had a relative density of not lower than 98.0 percent, a diameter of 200 mm and a thickness of 2 mm. The mesh was embedded within the sintered body so that the mesh may function as an electrode for an electrostatic chuck. The back face of the resulting sintered body was processed using a machining center to form a hollow 4, with a depth of 1 mm and a diameter of 3 mm, 6 mm or 10 mm. A part 3a of the mesh-shaped electrode 3 was exposed to the bottom surface 4a facing the hollow 4. Three kinds of metal terminals with diameters of 2.95 mm, 5.90 mm and 9.80 mm, respectively, were used corresponding to the three kinds of hollows 4 with the different diameters as described above. The electrostatic chuck and molybdenum terminal were joined with each other, according to the substantially same process described in the “experiment “A” section”.

[0052] Joined bodies were produced as described above. Each sample (joined body) was subjected to visual evaluation for the presence of cracks in the joining layer and ceramic member. As a result, cracks were not observed in each of the samples.

[0053] Each tapped hole formed in each terminal joined with the fixed substrate 2 was pulled upwardly to measure a breaking load, as described in the “Experiment “A” section”. The measured breaking load was 10.6 kgf for the hollow of a diameter of 3 mm, 22.5 kgf for the hollow of a diameter of 6 mm, and 30.4 kgf for the hollow of a diameter of 10 mm. Each of the joined bodies was broken at a point in metal indium.

[0054] Further, high frequency current of 40 ampere and a frequency of 13.5 Hz was supplied to each terminal of molybdenum to measure the difference of the temperatures of the terminal 8 and its neighboring portion. As a result, the difference was 10.5° C. for the hollow 4 of a diameter of 3 mm, 2.2° C. for the hollow of a diameter of 6 mm and not larger than 0.5° C. for the hollow of 10 mm.

[0055] As described above, according to the invention, a ceramic member and a metal member may be joined with each other with a sufficiently high bonding strength, with the crack formation in the ceramic material constituting the ceramic member prevented.

Claims

1. A joined structure of a metal terminal and a ceramic member: said structure comprising a joining layer between said metal terminal and said ceramic member, said joining layer comprising a metal adhesive layer containing at least indium.

2. The structure of claim 1, wherein said ceramic member has an inner wall surface facing a hollow formed in said ceramic member and said joining layer is formed between at least a part of said inner wall surface and said metal terminal.

3. The structure of claim 2, wherein said inner wall surface facing said hollow includes a bottom surface and side wall surface, said metal terminal has a tip face and side face, and said joining layer is formed between said bottom surface facing said hollow and said tip face of said terminal and formed between said side wall surface facing said hollow and said side face of said terminal.

4. The structure of claim 1, wherein said ceramic member has a conductive member to be electrically connected with said metal terminal.

5. The structure of claim 4, wherein said conductive member is embedded in said ceramic member, said conductive member comprises an exposed portion exposed to said hollow, and said joining layer is contacted with said exposed portion of said conductive member.

6. The structure of claim 1, wherein said joining layer comprises an intermediate layer, said intermediate layer being formed between said metal adhesive layer and said ceramic member and being made of a metal selected from the group consisting of a noble metal, aluminum, nickel, and the alloys thereof.

7. The structure of claim 4, wherein said metal terminal is a terminal for applying a high frequency voltage on said conductive member.

8. The structure of claim 1, wherein at least 80 weight percent of said metal adhesive layer is composed of indium.

9. The structure of claim 8, wherein said metal adhesive layer is composed of indium.

10. The structure of claim 1, wherein said metal adhesive layer is composed of an alloy containing indium and one or more metal other than indium.

11. The structure of claim 10, wherein said metal constituting said alloy is selected from the group consisting of nickel, titanium, copper, gold, platinum and palladium.

12. The structure of claim 10, wherein said alloy has a melting point of not higher than 300° C.

13. A joined structure of a metal member and a ceramic member, wherein said metal member has a tip face and a side face and said ceramic member has a side wall surface and a bottom surface both facing a hollow formed in said ceramic member, said structure comprising a joining layer, said joining layer being formed between said bottom surface facing said hollow and said tip face of said metal member and being formed between said inner wall surface facing said hollow and said side face of said metal member, and said joining layer comprising a metal adhesive layer containing at least indium.

14. The structure of claim 13, wherein said metal member is a metal terminal.

15. The structure of claim 14, wherein said ceramic member has a conductive member to be electrically connected with said metal terminal.

16. The structure of claim 15, wherein said metal terminal is a terminal for applying a high frequency voltage on said conductive member.

17. The structure of claim 15, wherein said conductive member is embedded in said ceramic member, said conductive member comprises an exposed portion exposed to at least one of said bottom surface and said side wall surface both facing said hollow, and said joining layer is contacted with said exposed portion of said conductive member.

18. The structure of claims 13, wherein said joining layer comprises an intermediate layer, said intermediate layer being formed between said metal adhesive layer and said ceramic member and being made of a metal selected from the group consisting of a noble metal, aluminum, nickel, and the alloys thereof.

19. The structure of claim 13, wherein at least 80 weight percent of said metal adhesive layer is composed of indium.

20. The structure of claim 19, wherein said metal adhesive layer is composed of indium.

21. The structure of claim 13, wherein said metal adhesive layer is composed of an alloy containing indium and one or more metal other than indium.

22. The structure of claim 21, wherein said metal constituting said alloy is selected from the group consisting of nickel, titanium, copper, gold, platinum and palladium.

23. The structure of claim 21, wherein said alloy has a melting point of not higher than 300° C.

24. An adhesive material for joining a metal terminal and a ceramic member, said adhesive is composed of a metal adhesive containing at least indium.

25. The material of claim 24, wherein at least 80 weight percent of said metal adhesive is composed of indium.

26. The material of claim 25, wherein said metal adhesive is composed of indium.

27. The material of claim 24, wherein said metal adhesive is composed of an alloy containing indium and one or more metal other than indium.

28. The material of claim 27, wherein said metal constituting said alloy is selected from the group consisting of nickel, titanium, copper, gold, platinum and palladium.

29. The material of claim 27, wherein said alloy has a melting point of not higher than 300° C.

30. The material of claim 24, wherein said metal terminal is a terminal for applying a high frequency voltage.