Patent Application
20120031562
The present invention relates to an inductively coupled plasma processing device that can be used for the surface processing of a base body or for other purposes.
Inductively coupled plasma processing devices are widely used for the thin-film formation on or the etching process of the surface of a base body. In inductively coupled plasma processing devices, a plasma production gas, such as hydrogen gas, is introduced into a vacuum container, after which a radio-frequency electric field is induced to decompose the plasma production gas and thereby produce plasma. Subsequently, another kind of gas, which serves as a film-forming material gas or an etching gas, is introduced into the vacuum container. In the former case, the molecules of the film-forming material gas are decomposed by the plasma and deposited on a base body. In the latter case, the molecules of the etching gas are decomposed into ions or radicals for the etching process.
Patent Document 1 discloses a plasma processing device using an external antenna, in which a radio-frequency antenna for inducing a radio-frequency electric field is disposed above the ceiling of the vacuum container and the portion of the ceiling located directly below the radio-frequency antenna is made of a dielectric material serving as a window for allowing the passage of the induced radio-frequency electric field. In this external antenna type plasma processing device, when the device size is increased to deal with the recent increase in the size of the base body to be processed, it is necessary to increase the thickness of the dielectric window in order to maintain its mechanical strength, which results in a decrease in the strength of the radio-frequency electric field introduced into the vacuum container. Given this problem, an internal antenna type plasma processing device, in which the radio-frequency antenna is provided inside the vacuum container, has also been conventionally used (see Patent Documents 2 and 3).
The invention described in Patent Document 3 uses a radio-frequency antenna consisting of a one-dimensional conductor that is terminated without completing one turn (which corresponds to an inductively coupled antenna with the number of turns less than one), such as a U-shaped or semicircular antenna. Such a radio-frequency antenna has an inductance lower than that of an inductively coupled antenna whose number of turns is equal to or greater than one. The lower inductance reduces the radio-frequency voltage occurring at both ends of the radio-frequency antenna and thereby suppresses radio-frequency fluctuation of the plasma potential due to electrostatic coupling to the generated plasma. As a result, an excessive loss of electrons to the ground potential due to the fluctuation of the plasma potential is decreased, whereby the plasma potential is decreased. Therefore, a film formation process with a low level of ion damage to the base body can be performed.
In the internal antenna type plasma processing device, the ions in the plasma are accelerated toward the radio-frequency antenna by a self-bias DC voltage which occurs between the conductor of the radio-frequency antenna and the plasma. Therefore, the conductor of the radio-frequency antenna itself undergoes sputtering, which shortens the life of the conductor. Furthermore, the atoms or ions sputtered from the conductor are mixed in the plasma and adhere to the surface of the base body being processed or the inner wall of the vacuum container, causing impurities to be mixed in the thin film being formed or the base body being etched. Another problem of the internal antenna type is that the temperature of the radio-frequency antenna conductor increases since the radio-frequency antenna conductor is located within the plasma. A change in the temperature of the radio-frequency antenna changes the impedance of the radio-frequency antenna, which prevents stable supply of power to the plasma. To address these problems, in the invention described in Patent Document 2, the radio-frequency antenna is sheathed in a pipe made of a dielectric (insulating) material, such as ceramic or quartz, which is less likely to be sputtered than the material of the radio-frequency antenna conductor, such as copper or aluminum, and cooling water is passed through this dielectric pipe. However, this configuration requires both an electrical connector for inputting a radio-frequency power and a connector for supplying or discharging the cooling water to be provided at the ends of the antenna conductor and the dielectric pipe. Such a structure will be complex, making it difficult to attach or detach the antenna or perform maintenance and inspection thereof.
In the internal antenna type, since the radio-frequency antenna protrudes into the internal space of the vacuum container, the plasma is produced in the vicinity of the radio-frequency antenna. Therefore, the plasma density particularly increases in the vicinity of the radio-frequency antenna and the density distribution becomes less uniform. Furthermore, since the radio-frequency antenna is located within the vacuum container, the material of the thin film used in the film formation process or a by-product resulting from the etching process may possibly adhere to the surface of the radio-frequency antenna (or a dielectric pipe around this antenna). Such a material or by-product may fall onto the surface of the base body and form so-called particles.
Furthermore, as compared to the external antenna type, the internal antenna type needs a vacuum container having a larger capacity in order to ensure a space for the radio-frequency antenna within the vacuum container. Therefore, the gas or plasma easily diffuses, which decreases the amount of ions or radicals reaching the base body and lowers the film-formation rate or etching rate.
The problem to be solved by the present invention is to provide a plasma processing device capable of inducing a strong radio-frequency electric field within a vacuum container while preventing sputtering of the antenna conductor, an increase in the temperature of the antenna conductor and the formation of particles.
A plasma processing device according to the present invention aimed at solving the aforementioned problem includes:
a) a vacuum container;
b) an antenna-placing section provided between an inner surface and an outer surface of a wall of the vacuum container;
c) a radio-frequency antenna placed in the antenna-placing section; and
d) a dielectric separating member for separating the antenna-placing section from an internal space of the vacuum container.
In the plasma processing device according to the present invention, the radio-frequency antenna is placed in the antenna-placing section provided between the inner and outer surfaces of a wall of the vacuum container. Therefore, a stronger radio-frequency electric field can be induced within the vacuum container as compared to the external antenna type.
Since the radio-frequency antenna is separated from the internal space of the vacuum container by a dielectric separating member, the formation of particles and the sputtering of the radio-frequency antenna are prevented. Simultaneously, an increase in the temperature of the radio-frequency antenna is suppressed.
Since it is unnecessary to provide a space for placing the radio-frequency antenna within the vacuum container, the capacity of the vacuum container can be smaller than in the case of the internal antenna type. Therefore, the diffusion of the gas or plasma is suppressed, which increases the amount of ions or radicals reaching the base body and improves the film-formation rate or the etching rate.
The separating member may be a dielectric member provided apart from the wall of the vacuum container. Alternatively, if the wall of the vacuum container is made of a dielectric material, a portion of the wall may be used as the separating member.
Although the radio-frequency antenna may be embedded in the wall, it is easier to place it in a hollow space formed between the aforementioned inner and outer surfaces. In the former case, the portion of the wall of the vacuum container in which the radio-frequency antenna is embedded corresponds to the antenna-placing section. In the latter case, the hollow space corresponds to the antenna-placing section.
The hollow space may be a hermetically closed space. This design prevents foreign matters from entering the hollow space. When this hollow space is in the vacuum state or filled with an inert gas, no unnecessary electric discharge occurs in the hollow space.
The hollow space may be filled with a solid dielectric material. This also prevents the occurrence of unnecessary electric discharge in the hollow space. In this case, it is unnecessary to hermetically close the hollow space. Instead of using the hollow space, it is possible to adopt the structure in which at least a portion of the wall is made of a solid dielectric and the radio-frequency antenna is embedded in the solid dielectric.
A cover may be provided on the outer-surface side of the hollow space. The use of such a cover facilitates maintenance, inspection or similar tasks; when the cover is opened, the radio-frequency antenna can be easily removed from the hollow space through the wall of the vacuum container to the outside and then set to the original position. Furthermore, the radio-frequency antenna may be fixed to the cover. In this case, users can more easily remove or set the radio-frequency antenna by merely detaching or attaching the cover.
The plasma processing device according to the present invention may be provided with a plurality of antenna-placing sections. This design further improves the uniformity in the density of the plasma created within the vacuum container.
The plasma processing device according to the present invention is capable of inducing a strong radio-frequency electric field within a vacuum container while preventing sputtering of the antenna conductor, an increase in the temperature of the antenna conductor and the formation of particles.
Embodiments of the plasma processing device according to the present invention are hereinafter described by means of
The separating member 16 is made of a dielectric material. Examples of the available materials include oxides, nitrides, carbides and fluorides. Among these materials, quartz, alumina, zirconia, yttria, silicon nitride or silicon carbide can be suitably used.
A step 111C protruding inwards is formed at the lower end of the inner circumferential surface of the hollow space 113. The separating plate 16 is fixed to this step 111C in such a manner that its outer circumferential edge is mounted on the step 111C. The cover 23 has a projecting portion on its lower surface so that it can fit in the hollow space 113 from the outside of the vacuum container 11.
The gas discharge port 13 is connected to a vacuum pump. By this vacuum pump, the air, steam and other contents in the internal space 112 of the vacuum container are discharged through the gas discharge port 13 to create a high vacuum state. The gas introduction port 14 is used for introducing a plasma production gas (e.g. hydrogen gas) and a film-forming material gas into the internal space 112 of the vacuum container. The base body S to be held on the base-body holder 12 is loaded into the internal space 112 of the vacuum container or unloaded from the same space through a base-body transfer opening 15 formed in the side wall of the vacuum container 11. The base-body transfer opening 15 is hermetically closed except when the base body is loaded into or unloaded from the vacuum container.
The radio-frequency antenna unit 20 is hereinafter described.
The radio-frequency antenna 21 is placed within the hollow space 113, with both ends fixed to the cover 23 via feedthroughs 24. Since the radio-frequency antenna 21 is fixed to the cover 23 in this manner, the radio-frequency antenna 21 can be easily detached from or attached to the plasma processing device by detaching or attaching the cover 23. The radio-frequency antenna 21 consists of an electrically conductive pipe, through which a cooling water or similar coolant can be passed. One end of the radio-frequency antenna 21 is connected to the radio-frequency power source, while the other end is connected to a ground.
The shape of the radio-frequency antenna 21 is hereinafter described. As shown in
The cover 23 is provided with a hollow-space exhaust port 25 for evacuating the hollow space 113. The gaps between the radio-frequency antenna 21 and the feedthrough 24, between the feedthrough 24 and the cover 23, between the cover and the top wall 111, and between the separating member 16 and the top wall 111 are hermetically sealed by vacuum seals. The hollow space 113 is maintained in a high vacuum state by the hollow-space exhaust port 25 and the vacuum seals.
One example of the connection between the radio-frequency antennae 13 and radio-frequency power sources is hereinafter described by means of
As one example of the operation of the plasma processing device 10 of the present embodiment, the process of depositing a film-forming material on the base body S is hereinafter described. Initially, a base body S is loaded through the base-body transfer opening 15 into the internal space 112 of the vacuum container and placed onto the base-body holder 12. After the base-body transfer opening 15 is closed, the vacuum pump is energized, whereby the air, steam and other contents in the internal space 112 of the vacuum container are discharged through the gas discharge port 13, and the air, steam and other contents in the hollow space 113 are also discharged through the hollow-space exhaust port 25. Thus, the internal space 112 of the vacuum container and the hollow space 113 are evacuated. Subsequently, a plasma production gas and a film-forming material gas are introduced from the gas introduction port 14. A radio-frequency power is supplied to each radio-frequency antenna 21, while a coolant is passed through the pipe of the radio-frequency antenna 21. By this radio-frequency power supply, a radio-frequency electric field is induced around the radio-frequency antenna 21. This radio-frequency electric field is introduced through the dielectric separating member 16 into the internal space 112 of the vacuum container and ionizes the plasma production gas, whereby plasma is produced. The film-forming material gas, which has been introduced into the internal space 112 of the vacuum container together with the plasma production gas, is decomposed by the resultant plasma, to be deposited on the base body S.
As compared to the external antenna type, the plasma processing device 10 of the present embodiment can create a stronger radio-frequency electric field within the internal space 112 of the vacuum container 11 since the radio-frequency antenna 21 is located in the hollow space 113 provided between the outer surface 111A and the inner surface 111B of the top wall 111 of the vacuum container. The separation of the hollow space 113 including the radio-frequency antenna 21 from the internal space 112 of the vacuum container by the separating member 16 has the effects of: preventing plasma produced in the aforementioned space from etching the radio-frequency antenna 21 and shortening its life; preventing the material of the radio-frequency antenna 21 from becoming an impurity to be mixed in the film being formed or the base body being processed; and preventing the formation of particles. Furthermore, since the hollow space 113 in which the radio-frequency antenna 21 is placed is maintained in a high vacuum state, no unnecessary electric discharge occurs in the hollow space 113.
In the present embodiment, a magnetic field created in the first U-shape part 212A of the radio-frequency antenna 21 by an electric current flowing from one end 212A1 to the bottom part of the U-shaped body, and a magnetic field created by an electric current flowing from the bottom part of the U-shaped body to the other end 212A2, have vertical components oscillating in the same phase. Magnetic fields having such vertical components are similarly created in the second U-shape part 212B. As a result, the magnitude of the vertical component of the magnetic field below the antenna will be greater than in the case of using a single straight radio-frequency antenna. Therefore, as compared to the case of using a single straight radio-frequency antenna, a higher plasma density can be achieved under the same strength of the radio-frequency power and/or the same pressure of the plasma production gas, or the same plasma density can be achieved under a lower strength of the radio-frequency power and/or a lower pressure of the plasma production gas.
A first variation of the first embodiment is hereinafter described by means of
A second variation of the first embodiment is hereinafter described by means of
A plasma processing device of the second embodiment is hereinafter described by means of
A plasma processing device of the third embodiment is hereinafter described by means of
In the third embodiment, since the hollow space 113 is filled with the dielectric member 27, no unnecessary electric discharge occurs in the vicinity of the radio-frequency antenna 21.
In place of the dielectric member 27, a dielectric powder may be filled into the hollow space 113. In this case, the hollow space 113 should be hermetically closed so that the powder will not leak from the hollow space 113.
In any of the previous examples, the radio-frequency antenna 21 was provided within the hollow space 113. However, it is possible to embed the radio-frequency antenna 21 between the outer surface 111A and the inner surface 111B without using any hollow space, as shown in
One example using a radio-frequency antenna having a shape different from any of the previous embodiments is described by means of
In any of the previous embodiments, there was only one radio-frequency antenna placed in each antenna-placing section (hollow space). However, it is possible to provide two or more radio-frequency antennae in one antenna-placing section. In the example shown by the top view in
A seventh embodiment of the plasma processing device according to the present invention is described by means of
In the Faraday shield 51, an almost entire portion of the lower surface is thermally in contact with the separating member 16, with both ends thermally connected to the top wall 111. Therefore, the heat from the separating member 16, which receives energy from the plasma and becomes hotter, is released through the Faraday shield 51 to the top wall 111. In this manner, an increase in the temperature of the separating member 16 is suppressed and the degradation of the separating member 16 due to the heat is prevented. To further improve this effect, the Faraday shield 51 may be cooled by a coolant, or a means for suppressing the temperature increase, such as a cooling pipe, may be additionally provided apart from the Faraday shield 51.
The number of radio-frequency antennae 21, which was eight in the previous embodiments, can be appropriately determined according to the capacity of the vacuum container or other factors. Using only one radio-frequency antenna 21 may be sufficient for a vacuum container having a rather small capacity. Unlike the previous embodiments, in which the radio-frequency antenna unit 20 was provided in the top wall of the vacuum container, the radio-frequency antenna unit may be provided in a different wall, such as the side wall.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-057328 | Mar 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/054019 | 3/10/2010 | WO | 00 | 10/20/2011 |
