EP1126547A1

EP1126547A1 - Connection structure of electric lead-in terminal

Info

Publication number: EP1126547A1
Application number: EP99951160A
Authority: EP
Inventors: Masanori Applied Materials Japan Inc. ONO
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 1998-10-30
Filing date: 1999-10-29
Publication date: 2001-08-22
Also published as: JP2000133339A; WO2000026995A1; JP3142520B2

Abstract

An electric lead-in terminal connecting structure for connecting an electric lead-in terminal to a conductive element embedded within a ceramic solid. A hole is formed in the ceramic solid so as to traverse the conductive element. The electric lead-in terminal is constituted by a fitting member, made of a high-melting metal having a coefficient of thermal expansion close to that of the ceramic solid, having a form substantially identical to an inner space of the hole, and a chemically durable terminal member connected to the fitting member. The fitting member is fitted into the hole of the ceramic solid, such that the conductive element exposed at an inner wall face of the hole and the fitting member are electrically connected to each other. In this configuration, only the fitting member is in contact with the ceramic solid, whereby the thermal stress between the electric lead-in terminal and the ceramic solid becomes smaller.

Description

Technical Field

The present invention relates to a structure in which a conductive element such as an electrode is embedded in a ceramic solid, such as a heater or electrostatic chuck used in a semiconductor manufacturing apparatus; and, in particular, to a technique for connecting an electric lead-in terminal to a conductive element within the ceramic solid.

Background Art

Currently, ceramic heaters in which an electric heating element (heater) is embedded in a ceramic solid, and electrostatic chucks in which an electrode is embedded in a ceramic solid are used in various fields such as semiconductor manufacturing apparatus.
In general, for introducing electricity to a conductive element such as the electric heating element or electrode, an electric lead-in terminal 1 has conventionally been fitted into a hole 3 formed in a ceramic solid 2, so as to come into contact with a conductive element 4 exposed at the inner wall face of the hole 3 as shown in Fig. 1.
Meanwhile, there are cases where the electrostatic chuck or the like in a semiconductor manufacturing apparatus is exposed to a high-temperature environment of 600°C or higher, for example. In such a high-temperature environment, the difference in thermal expansion between the ceramic solid and electric lead-in terminal becomes problematic.
Therefore, as materials for the electric lead-in terminal, high-meltingmetals having a coefficient of thermal expansion close to that of the ceramic solid, such as tungsten (W), molybdenum (Mo), and tantalum (Ta), for example, have conventionally been used in general.
However, high-melting metals such as W, Mo, and Ta are problematic in that their oxidation resistance is so low that their parts exposed from the ceramic solid are likely to deteriorate when in contact with atmosphere.
Though the above-mentioned problem of low oxidation resistance can be overcome when an electric lead-in terminal constituted by a nickel-iron (Ni-Fe) alloy covered with a nickel (Ni) coat is used, this alloy drastically raises its coefficient of thermal expansion at a temperature of 400°C and above. Consequently, if temperature changes from a lower temperature region to a higher temperature region, a large thermal stress may occur between the ceramic solid and the electric lead-in terminal due to their difference in thermal expansion, thereby losing the reliability in electric connection.
Therefore, it is an object of the present invention to provide means for reducing the thermal stress occurring between the ceramic solid and the electric lead-in terminal.

Disclosure of the Invention

For achieving the above-mentioned object, the present invention provides a connecting structure for an electric lead-in terminal in which the electric lead-in terminal is connected to a conductive element embedded within a ceramic solid; wherein a hole is formed in the ceramic solid so as to traverse the conductive element; wherein the electric lead-in terminal is constituted by a fitting member, made of a high-melting metal having a coefficient of thermal expansion close to that of the ceramic solid, having a form substantially identical to an inner space of the hole, and a chemically durable terminal member connected to the fitting member by way of connecting means; and wherein the fitting member is fitted into the hole of the ceramic solid, such that the conductive element exposed at an inner wall face of the hole and the fitting member are electrically connected to each other.
In this configuration, if the electric lead-in terminal is fitted in the hole of the ceramic solid, then the fitting member fits into the hole, thereby exposing the terminal member alone. Since the difference in thermal expansion between the fitting member and ceramic solid is small, no large stress occurs therebetween. Also, since the exposed terminal member has chemical durability such as oxidation resistance, it is prevented from deteriorating due to contacting gases.
As the high-melting metal constituting the fitting member, W, Mo, Ta, or the like is preferred.
Preferably, the terminal member is made of an Ni-coated Ni-Fe alloy when oxidation resistance is taken into consideration.
The connecting member for connecting the fitting member and the terminal member to each other may comprise a male thread portion disposed at one end of one of the fitting member and terminal member, and a female thread portion disposed at one end of the other of the fitting member and terminal member. Interposing a conductive sealant between the male and female thread portions is effective since it lowers electric resistance.
If a conductive sealant is interposed between the inner wall face (inner peripheral face and bottom face) of the hole and the fitting member, whereas a conductive sealant is disposed at a boundary portion between an outer face of the fitting member and an outer face of the terminal member, and at a boundary portion between the former boundary portion and a surface of the ceramic solid, then the fitting member can be blocked from atmosphere.
The conductive sealant is preferably a conductive solder material such as silver solder or copper solder.
The foregoing and other features and advantages of the present invention will be clear to those skilled in the art upon reading the following detailed explanations with reference to the accompanying drawings.

Brief Description of the Drawings

Fig. 1 is an enlarged sectional view showing a conventional connecting structure between an electric lead-in terminal and an electrode;
Fig. 2 is a schematic view of a semiconductor manufacturing apparatus having an electrostatic chuck to which the present invention is applicable; and
Fig. 3 is an enlarged sectional view showing the connecting structure between an electric lead-in terminal and an electrode in the electrostatic chuck of Fig. 2.

Best Modes for Carrying Out the Invention

In the following, a preferred embodiment of the present invention will be explained in detail with reference to the drawings.
Fig. 2 is a schematic view showing a semiconductor manufacturing apparatus 14, such as a CVD apparatus or PVD apparatus, in which an electrostatic chuck 10 to which the present invention is applicable is disposed within a processing chamber 12. The electrostatic chuck 10 is used for holding and securing a silicon wafer 16. The electrostatic chuck 10 is basically constituted by a ceramic solid 18, which is a dielectric, and an electrode film 20 disposed therewithin in parallel with the upper face of ceramic solid 18; and is based on a principle in which voltage is applied to the electrode film 2.0 so as to induce electric charges with opposite polarities in the silicon wafer 16 and electrode film 20, respectively. Namely, an electrostatic attraction force between the electric charges having polarities opposite to each other pulls the silicon wafer 16 toward the electrostatic chuck 10, thereby securing the silicon wafer 16.
For applying voltage to the electrode film 20, the electrostatic chuck 10 is provided with an electric lead-in terminal 22. Since the electrode film 20 is thin and is disposed at a part very close to the upper face of ceramic solid 18, the electric lead-in terminal 22 is configured so as connect with an electrode 24, electrically connected to the electrode film 20, extending to the lower part of ceramic solid 18.
Fig. 3 is an enlarged sectional view clearly showing the connecting structure between the electrode 24 embedded in the ceramic solid 18 and the electric lead-in terminal 22 in the electrostatic chuck 10 of Fig. 2. As shown in Fig. 3, the ceramic solid 18 is formed with a hole 26 shaped so as to penetrate through the embedded electrode 24, allowing the electric lead-in terminal 22 to fit into this hole 26.
In this embodiment, the electric lead-in terminal 22 is constituted by a fitting member 28, having a form substantially identical to that of the hole 26, adapted to fit into the hole 26; and a terminal member 30, connected to the fitting member 28, enabling connection to a connection terminal of a power circuit (not depicted) and the like. Since the fitting member 28 has a form identical to that of the hole 26, there is no part projecting from the surface (lower face) of the ceramic solid 18. On the other hand, the terminal member 30 as a whole is disposed outside the ceramic solid 18.
The fitting member 28 is made of a high-melting metal, such as W, Mo, or Ta, having a coefficient of thermal expansion close to that of the ceramic solid 18. On the other hand, the terminal member 30 is made of a material excellent in chemical durability. For example, from the viewpoint of oxidation resistance, it is made of an Ni-Fe alloy, preferably Kovar (trademark), more preferably Ni-coated one.
One end of the fitting member 28 is formed with a male thread portion 32, whereas a female thread portion 34 for receiving the male thread portion 32 is formed at one end of the terminal member 30, whereby the fitting member 28 and the terminal member 30 connect with each other. Other members may also be used as the connecting means between the fitting member 28 and terminal member 30, as a matter of course. Here, the thread portion referred to with numeral 36 is used for facilitating connection to a connection terminal of the power circuit (not depicted) and the like.
Preferably, such an electric lead-in terminal 22 is constructed by connecting the terminal member 30 and the fitting member 28 to each other in a state where an appropriate conductive sealant 38, for example, such as silver solder or copper solder, is interposed between the male thread portion 32 and the female thread portion 34. The conductive sealant 38 is interposed between the fitting member 28 and the terminal member 30 in order to increase the contact area between the members 28, 30, so as to make the electric resistance as low as possible.
As mentioned above, the electric lead-in terminal 22 is attached to the ceramic solid 18 as being fitted into the hole 26 formed therein. Only the fitting member 28 of the electric lead-in terminal 22 is positioned within the hole 26, whereby the surface (lower face) of ceramic solid 18 and the end face of fitting member 28 are substantially flush with each other. Further, an appropriate conductive sealant 40, e.g., a conductive solder material such as silver solder or copper solder, is interposed between the fitting member 28 and the inner wall face (inner peripheral face and bottom face) of the hole 28. As a consequence, electric connection is secured between the electrode 24, which is embedded in the ceramic solid 18 and exposed from the inner wall face of the hole 26, and the fitting member 28. It is also effective if a conductive sealant 42 identical to that mentioned above is disposed at a boundary portion between the outer face of fitting member 28 and the outer face of terminal member 30, and at the surface of ceramic solid 18 surrounding the boundary portion. The sealant 42 completely covers the surface of fitting member 28 within the hole 26 and functions as a protective film against oxidation and the like. If the terminal member 30 is Ni-coated, then it exhibits a favorable sealability with respect to solder materials.
In the foregoing configuration, if power is turned on with an unshown connection terminal of the power circuit being connected to the thread portion 36 of terminal member 30, then voltage is applied to the electrode film 20 by way of the electrode 24, whereby the silicon wafer 16 on the electrostatic chuck 10 is electrostatically secured. When a semiconductor manufacturing process is started, temperature may rise within the processing chamber 12. Here, only the fitting member 28 is in contact with the ceramic solid 18, whereas their difference in thermal expansion is small. Consequently, the thermal stress occurring between the ceramic solid 18 and the electric lead-in terminal 22 is quite small, which hardly exerts thermal influence upon these members 18, 22. As a result, the electric connection between the electric lead-in terminal 22 and electrode 24 can be maintained in a highly reliable state. Also, while the degree of thermal expansion begins to drastically increase in the terminal member 30 of electric lead-in terminal 22 at the time when its ambient temperature exceeds 400°C, the terminal member 30 will apply no thermal stress to the ceramic solid 18 since it is located outside the ceramic solid 18. In addition, the terminal member 30 can fully be resistant to oxidation and the like since its material is an Ni-Fe alloy such as Ni-coated Kovar (trademark).
Though a preferred embodiment of the present invention is explained in detail in the foregoing, the present invention is not restricted to the above-mentioned embodiment as a matter of course. For instance, though the above-mentioned embodiment relates to an example in which the present invention is applied to an electrostatic chuck, the present invention is also applicable to cases where an electric lead-in terminal is connected to a conductive element within a ceramic solid, e.g., where an electric lead-in terminal is connected to an electric heating element of a ceramic heater.
Also, the materials used are not limited to those of the above-mentioned embodiment, whereas other materials can also be used as long as they do not deviate from the gist of the present invention.

Industrial Applicability

In a structure in which an electric lead-in terminal is connected to an electrode embedded in a ceramic solid, the present invention makes it possible to lower the thermal stress occurring between the ceramic solid and the electric lead-in terminal, whereby the strength and the reliability of electric connectivity can be improved.
Also, the part of electric lead-in terminal exposed outside can have chemical durability, whereby the durability against gases in its ambient environment can be improved.
Therefore, the present invention is particularly effective when applied to electrostatic chucks and heaters used in an environment, such as a semiconductor manufacturing apparatus, where thermal fluctuations are large.

Claims

A ceramic solid having a conductive element embedded therewithin, and an electric terminal electrically connected to said conductive element;

said ceramic solid being provided with a hole traversing said conductive element;

said electric terminal being constituted by a fitting member, made of a high-melting metal having a coefficient of thermal expansion close to that of said ceramic solid, having a form substantially identical to an inner space of said hole, and a chemically durable terminal member connected to said fitting member by way of connecting means;

said fitting member being fitted into said hole of said ceramic solid, such that said conductive element exposed at an inner wall face of said hole and said fitting member are electrically connected to each other.
A ceramic solid according to claim 1, wherein said high-melting metal is one selected from the group consisting of tungsten, molybdenum, and tantalum.
Aceramic solid according to claim 1 or 2, wherein said terminal member is made of a nickel-iron alloy coated with nickel.
A ceramic solid according to claim 1, wherein said connecting means comprises a male thread portion disposed at one end of one of said fitting member and terminal member, and a female thread portion disposed at one end of the other of said fitting member and terminal member; and wherein a conductive sealant is interposed between said male and female thread portions.
A ceramic solid according to claim 1, wherein a conductive sealant is interposed between an inner wall face of said hole and said fitting member; and wherein a conductive sealant is disposed at a boundary portion between an outer face of said fitting member and an outer face of said terminal member, and at a boundary portion between the former boundary portion and a surface of said ceramic solid.
Aceramic solid according to claim 4 or 5, wherein said conductive sealant is a conductive solder material.
A ceramic solid according to claim 1, wherein said ceramic solid constitutes an electrostatic chuck in a semiconductor manufacturing apparatus.