Patent Application
20060127245
This invention relates to a pump and, in particular, relates to a vacuum pump for use in a vacuum processing system and a manufacturing method thereof.
Generally, vacuum processing systems for use in manufacturing semiconductor devices or the like include a cluster type system and an in-line type system and these systems each comprise a plurality of chambers and a transfer mechanism for transferring processing members (wafers, glass substrates). In these vacuum processing systems, various treatments such as various film formation and etching are applied to a processing member in each chamber in a state lower than the atmospheric pressure (i.e. vacuum state). In this connection, each chamber constituting the vacuum processing system is provided with a plurality of vacuum pumps for evacuating the chamber. Further, it is a recent trend that members or objects to be processed, such as wafers and glass substrates, become large in size and the vacuum processing systems are also increased in size with an increase of the objects to be processed. As a result, the vacuum processing systems tend to have a heavy weight such that they are too heavy to be transported by normal transportation means.
Recently, a plasma processing system has been proposed that performs plasma oxidation or oxygen radical oxidation in a particular chamber. This plasma processing system is implemented by a cluster type vacuum processing system. In such a plasma processing system, since a gas or the like that is a medium to be exhausted is highly reactive, a vacuum pump itself should be formed by a material that is strong against corrosion due to the reactive medium.
The processing system of this type uses, as evacuation vacuum pumps, a wide variety of pumps such as a turbomolecular pumps, cryopumps, booster pumps, dry pumps, and scroll pumps. These vacuum pumps each include vacuum pump members, such as rotors, blades, shafts, and gears which are accommodated in a casing provided with an inlet port and a discharge port.
Normally, the vacuum pump members or articles constituting the vacuum pump are each made of an aluminum alloy such as duralumin, a stainless steel, or the like. In view of lightening the vacuum pump in weight, the aluminum alloy is preferable.
However, even if the aluminum alloy would be used in a vacuum pump in the plasma processing system, the inner walls of the vacuum pump is corroded by media such as ions and other active species generated upon dissociation of various gases due to a plasma and corrosive gases. Therefore, the aluminum alloy cannot be used in the plasma processing system.
On the other hand, if the stainless steel would be also used in the vacuum pump made, it is not possible to obtain sufficient corrosion resistance against the media such as the active species. These problems are not limited to the vacuum pumps in the plasma processing system but shall apply to the whole range of pumps that discharge corrosive media.
There has been a proposal for applying an anodic oxidation treatment shown in Japanese Unexamined Patent Application Publication (JP-A) No. H7-216589 (patent document 1) to a vacuum pump to thereby form a corrosion resistant alumina film (Al2O3) on the surface of a member made of aluminum or an aluminum alloy.
Actually, Japanese Unexamined Patent Application Publication (JP-A) No. 2003-21062 (patent document 2) describes a cryopump having an anodically oxidized cryopanel.
However, an Al2O3 coating film formed by anodic oxidation is basically a porous film and the surface thereof is also rough. Therefore, the anodically oxidized Al2O3 coating film is very low in corrosion resistance against a reactive gas or chemical liquid such as, for example, a Cl-based gas, a F-based gas, HCl, H2SO4, or HF.
Further, a post treatment of the the anodically oxidized Al2O3 coating film is also performed by applying a high-temperature steam to the coating film and by thereby sucking up molecules into the coating film to expand it. As a result, voids are filled with the above-mentioned method.
Herein, it is assumed that the anodically oxidized aluminum alloy subjected to the foregoing post treatment is used for gas exhaust vacuum pump members for the plasma system. In this event, it is to be noted that processing in such a plasma system is generally carried out at a high degree of pressure-reduction. Under the circumstances, it takes much time to reach a predetermined degree of pressure-reduction when the above-mentioned anodically oxidized aluminum alloy is used in the plasma system.
This is because, since the oxide coating film at the surface of the anodically oxidized aluminum alloy is primarily porous, it takes an unnecessarily long time to evacuate to the predetermined degree of the pressure-reduction due to a problem of outgassing and the presence of the voids formed and remaining in the film.
Further, when electroless nickel plating is applied to an aluminum alloy, nickel serves as a catalyst to decompose, for example, a SiH4, B2H8, PH3, AsH3, or ClF3 gas and, as a result, accelerates generation of corrosive gas and product.
It is therefore an object of this invention to provide a vacuum pump that is usable against a corrosive gas in a vacuum processing system.
It is another object of this invention to provide a vacuum pump that is small in size and light in weight.
It is still another object of this invention to provide a pump having high corrosion resistance against a reactive gas or chemical liquid.
A pump of this invention is characterized in that a portion exposed to an exhausted medium is made of aluminum or an aluminum alloy and, further, has an oxide coating film oxidized by a plasma treatment.
As the oxide coating film oxidized by the plasma treatment, it is possible to cite, for example, an oxide coating film oxidized by oxygen radicals produced by plasma.
According to researches by the present inventors, it has been confirmed that an oxide coating film formed on the surface of aluminum or an aluminum alloy by a plasma treatment, for example, by oxygen radicals produced by a plasma, is extremely dense with the surface thereof being flat and, further, has almost no voids existing in the film. Further, it has been found that such an oxide coating film is strong and has an improved corrosion resistance.
Therefore, it has been found that, by using a member having such a coating film as a pump member, particularly a pump member that contacts a reactive medium, a time required for evacuation to a predetermined degree of pressure-reduction can be shortened than conventional and the corrosion resistance is also improved. The oxidation by oxygen radicals is implemented by transforming an oxygen-containing gas into plasma to thereby apply a plasma treatment to the aluminum or aluminum alloy surface in a manner to be described later.
A pump member of this invention may be made of aluminum or an aluminum alloy and the surface of the vacuum pump member has a coating film of an oxide of aluminum or an aluminum alloy containing a very small amount of a noble gas component.
By the addition of the noble gas, the film stress is suppressed to improve adhesion and reliability. As the noble gas, a krypton (Kr) gas or a xenon (Xe) gas is particularly preferable.
Further, it may be configured such that a pump member of this invention is made of an aluminum alloy containing at least one of magnesium, strontium, and barium in aluminum, the surface of the vacuum pump member has an oxide coating film, and the oxide coating film contains an oxide of aluminum and at least one oxide among respective oxides of magnesium, strontium, and barium. Such a member for a plasma processing system has a further improved corrosion resistance.
The aluminum alloy may contain at least zirconium or at least hafnium. When it is contained, the mechanical strength is improved.
Further, the content of each of Fe, Mn, Cr, and Zn in the aluminum alloy is preferably 0.01 wt % or less. This is because the corrosion resistance is degraded when the above-mentioned metals are contained.
In the foregoing, the description has been made about the case where the aluminum or aluminum alloy is used as a base material of the vacuum pump member. However, this invention is not limited thereto at all. The surface of a base material formed by iron containing aluminum may be processed by a plasma oxidation treatment or an oxygen radical oxidation treatment to form an aluminum oxide coating film on the surface of the base material. In this case, use may be made of a technique that selectively oxidizes aluminum contained in the base material by the plasma treatment to thereby form an aluminum oxide film on the surface. As such a base material containing aluminum, there is a stainless steel or the like.
As a method of forming an aluminum oxide coating film on the surface of a necessary portion of a pump member by a plasma treatment or the like, it is possible to apply a plasma processing method described in Patent Application No. 2003-028476 Specification.
According to this invention, as compared with the conventional anodic oxidation treatment, there is formed a coating film that is dense and has a flat surface and further the corrosion resistance is improved.
Hereinbelow, an embodiment of this invention will be described. Referring to
Further, in order to bring the inside of each of the reaction chambers (vacuum containers) 10, 11, and 12 into a pressure-reduced or vacuum state, the reaction chambers (vacuum containers) 10, 11, and 12 are coupled with high vacuum pumps 1, 2, and 3, one or more pumps per chamber. Booster pumps 4a, 5a, and 6a and back pumps (dry pumps) 4b, 5b, and 6b are arranged at subsequent stages of the high vacuum pumps, respectively, In the illustrated example, booster pumps 7a, 8a, and 9a and back pumps 7b, 8b, and 9b are connected to the load lock chambers 13 and 14 and the transfer chamber 15, respectively. Further, valves 22, 23, and 24 are provided between the high vacuum pumps 1, 2, and 3 and the booster pumps 4a, 5a, and 6a, respectively.
This invention may be applicable to various pumps that may be, for example, a turbomolecular pump (thread groove pump), a cryopump, a mechanical booster pump, a dry pump (back pump), and a scroll pump. Hereinbelow, the back pump (
Herein, at first, description will be made about operation of the vacuum processing system shown in
Further, although not illustrated, the reaction chambers (vacuum containers) 10, 11, and 12 are each provided with a gas inlet and heating means such as a heater to thereby carry out predetermined processing, such as film formation, while a predetermined gas is being introduced for heating. A plasma oxidation treatment or an oxidation treatment using oxygen radicals is executed in at least one of the reaction chambers 10, 11, and 12. When such an oxidation treatment is carried out, the gas is decomposed into a corrosive gas in the reaction chamber and this corrosive gas is successively exhausted by the illustrated vacuum pumps of the plurality of the stages.
In
The illustrated vacuum processing system is first put on a standby state. In this standby state, the transfer chamber 15 and the reaction chambers (vacuum containers) 10, 11, and 12 are each held in a pressure-reduced or vacuum state.
In this state, a cassette with a plurality of processing objects such as wafers placed therein is brought into the load lock chamber 13 from the outside of the vacuum processing system kept in an atmosphere and the load lock chamber 13 is evacuated.
Subsequently, a gate valve (not illustrated) between the load lock 1S chamber 13 and the transfer chamber 15 is opened and the processing object transfer robot extends its transfer arm to pick up one of the processing objects from the cassette and moves it into the transfer chamber 15.
Thereafter, a gate between the reaction chamber (vacuum container) 10 and the transfer chamber 15 is opened and the processing object is placed on a stage in the reaction chamber (vacuum container) 10 by the use of the transfer arm. After the predetermined processing such as film formation, the processed object is transferred into the other reaction chamber 11 or 12 or the load lock chamber 14 by the use of the transfer arm. After the processing, the processed object is finally transferred to the exterior from the load lock chamber 14.
Among the foregoing reaction chambers 10, 11, and 12, at least one chamber is used to form an oxide layer on the processing object by plasma oxidation or oxygen radicals and to discharge the reactive gas to the back pump through the high vacuum pump and the booster pump. Although this invention may be applied only to the vacuum pumps that exhaust the reactive gas, description will be made on the assumption that this invention is applied to all of the pumps, such as the high vacuum pumps 1, 2, and 3 provided for all the reaction chambers 1, 2, and 3, the booster pumps 4a to 9a, and the back pumps (dry pumps) 4b to 9b.
Referring to
The screw rotors 25 and 26 are housed in a casing 27 and rotatably supported by bearings 35 at one-side ends of shafts 28 supporting the screw rotors 25 and 26. Timing gears 30 are attached to the shafts 28 at one-end portions thereof while a motor (not illustrated) is coupled to the other end of the shaft 28. When the shaft 28 is rotated by the motor, the pair of screw rotors 25 and 26 are synchronously rotated through the timing gears 30.
An inlet port 31 is formed on a one-end side of the casing 27 housing therein both screw rotors 25 and 26 while a discharge or an outlet port 32 (
On the discharge port 32 side of the illustrated casing 27, a jacket 33 is formed which has a cavity portion and which can circulate cooling water through the cavity portion. This structure makes it possible on the discharge port 32 side to particularly cool heat generation caused by compression operation of a gas.
At the other-end portion of the casing 27 having both screw rotors 25 and 26 housed therein, a cover 34 is attached and the shaft 28 supporting the screw rotor 26 projects from the cover 34 so as to be directly coupled to a rotation shaft of the later-described motor. Further, seal members 29 are provided between the bearings 35 and the screw rotors 25 and 26, respectively.
Let all the members of the back pump (dry pump) shown in
By applying the treatment according to this invention to all the members constituting the back pump, the whole back pumps can have corrosion resistance. However, plasma oxidation or oxygen radical oxidation according to this invention may be executed only at least those surfaces of the members to be exposed to the corrosive gas, i.e. the rotors 25 and 26, the casing 27, the seal members 29, the inlet port 31, and the discharge port 32. As shown by thick lines in
Referring to
An evacuation device 41, such as a turbomolecular pump, Is connected to bottom portions of the process container 2 through exhaust pipes 42 so that the inside of the process container 2 is evacuated by the evacuation device 41. Further, a supply pipe 44 is extended through an inner wall of the process container 2 so as to supply a process gas from a process gas supply source 43. In this embodiment, the process gas supply source 43 is connected to supply sources 45 and 46 of an oxygen gas (O2) and an argon (Ar) gas being an inert gas.
At the upper opening of the process container 2, a dielectric window 22 made of, for example, a quartz glass is mounted on a seal member 21, such as an O-ring for ensuring airtightness. By this dielectric window 22, a process space S is formed in the process container 2.
An antenna member 51 is provided above the dielectric window 22. In this example, the antenna member 51 comprises, for example, a radial slot antenna 52 located on the bottommost position, a wave-shortening plate or a wave retardation plate 53 located at an upper portion thereof, and an antenna cover 54 covering the wave-shortening plate 53 to protect and cool it.
The radial slot antenna 52 is in the form of a thin disk made of a conductive material such as copper and the disk is formed with pairs of slits concentrically arranged wherein each pair of slits form an acute angle approximate to a right angle.
At the center of the wave-shortening plate 53 is disposed a bump 55 which is made of a conductive material such as a metal and which forms a part of a conical shape. This bump 55 is electrically connected to an inner conductor 56a of a coaxial waveguide 56 composed of the inner conductor 56a and an outer pipe 56b. The coaxial waveguide 56 is configured so that a microwave of, for example, 2.45 GHz produced by a microwave supply device 57 is propagated to the antenna member 51 through a load matching device 58 and the coaxial waveguide 56.
Next, description will be made about a plasma processing method implemented in the illustrated vacuum processing system 1. At first, the vacuum pump member 40 formed by aluminum or an aluminum alloy is placed on the susceptor 3. In this state, the oxygen gas containing krypton is supplied from the supply source 45 and plasma is produced in the process container 2. In this case, the vacuum pump member 40 is maintained at a temperature of 450° C. or less (preferably 150° C. to 250° C.). It is to be noted that even in the state where the vacuum pump member 40 was maintained at a room temperature (e.g. 23° C.), it was possible to generate plasma in the process container 2.
When the plasma was generated, oxygen radicals were produced in the process container 2 and thus the surface of the vacuum pump member 40 was oxidized by the oxygen radicals so that an oxide coating film was formed.
It was confirmed that the oxide coating film produced by the oxidation treatment using the oxygen radicals was an Al2O3 coating film that had no voids and was extremely dense and flat on its surface. This is because the aluminum or aluminum alloy surface was reformed or modified in properties due to the oxygen radicals.
A reaction formula in this case is as follows.
2Al+3O*→Al2O3
Further, when the vacuum pump member 40 was formed by an aluminum alloy containing magnesium (Mg), an oxide coating film (Al2O3) containing much MgO was able to be formed on the aluminum alloy surface due to oxygen radicals. The oxide coating film containing MgO in this manner can improve the strength. In this case, the content of magnesium is preferably 0.5 wt % to a solid-solution maximum amount (about 6.0 wt %). When an oxygen gas containing krypton was transformed into a plasma to produce oxygen radicals, an oxide coating film containing MgO was able to be obtained even with an extremely small content of magnesium like 0.5 wt % to 1.0 wt %.
As the aluminum alloy, use can be made of an aluminum alloy containing, other than magnesium as described above, strontium, barium, zirconium, or hafnium. By forming an oxide coating film containing much SrO or BaO on the aluminum alloy surface, it was possible to improve the corrosion resistance and strength of the vacuum pump member 40.
Further, when use was made of an aluminum alloy containing about 0.1 to 0.15 wt % zirconium, it was possible to provide the vacuum pump member 40 with high corrosion resistance and mechanical strength by suppressing the growth of alloy particles. Further, also when use was made of an aluminum alloy containing 0.1 to 0.15 wt % hafnium, it was confirmed that the vacuum pump member with high corrosion resistance and mechanical strength was obtained by suppressing the grain growth of the aluminum alloy.
On the other hand, the aluminum alloy often contains Fe, Mn, Cr, and Zn but, since they reduce the corrosion resistance of the aluminum alloy, the content of each of them is preferably 0.01 wt % or less. Fe, Mn, Cr, and Zn in the aluminum alloy can be removed by hydrogen reduction of the vacuum pump member 40 at a temperature of 450° C. or less prior to the oxidation treatment.
The description has been made about the case where krypton (Kr) was added to the oxygen-containing gas to produce the plasma so as to generate oxygen radicals by the plasma. This is because, by the addition of the krypton gas, krypton excited to a high energy state collides with an oxygen molecule so that two oxygen radicals can be easily generated.
Further, when producing oxygen radicals, oxygen plasma may be generated by the use of a gas obtained by adding an argon (Ar) gas to an oxygen-containing gas. When the argon gas is used, since the argon gas is easy to handle and is inexpensive, the vacuum pump member 40 can be easily and inexpensively processed actually.
As described above, when the plasma oxidation treatment such as the oxidation treatment using oxygen radicals is performed by generating the plasma by the use of the noble gas, such as krypton or argon, the produced oxide coating film contains a very small amount of the noble gas component, This noble gas component serves to suppress a film stress of the oxide coating film to improve adhesion and reliability thereof.
As the plasma source for generating the oxygen plasma, use was made of the 2.45 GHz frequency microwave plasma in the foregoing plasma processing system 1. Since the microwave plasma is highly dense and is not so strong with a relatively low Vdc, the oxide coating film can be formed by the radical oxidation of the surface of the vacuum pump member 40 without giving damage to the aluminum or aluminum alloy surface.
Further, in the foregoing examples, the description has been made only about the case where the vacuum pump member 40 is made of aluminum or the aluminum alloy. However, this invention is not limited thereto at all. A similar effect was obtained in the case of forming an aluminum oxide coating film on the surface of a vacuum pump member formed by a stainless steel containing aluminum.
Further, the pump to which this invention is applicable is not limited to that shown in
A pump according to this Invention can be used as a vacuum pump for evacuating the inside of a chamber in a vacuum processing system for use In manufacturing semiconductor devices or the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-66689 | Mar 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/02858 | 3/5/2004 | WO | 9/9/2005 |
