Mechanical seal

A mechanical non-contact gas seal including a rotary scaling ring and a stationary sealing ring that is engaged and held in an inner periphery of a seal case by means of O-rings so as to move in an axial direction thereof. The O-rings engage with the outer periphery of the stationary sealing ring and come in press contact with the inner periphery of the seal case to seal a gap between the stationary sealing ring and the seal case while allowing the stationary sealing ring to move in an axial direction. A resin coating of a thickness in the range of 5 to 100 μm is formed on the inner periphery of the seal case at least within a range in which the O-rings relatively move with the movement of the stationary sealing ring.

TECHNICAL FIELD

The present invention relates to a mechanical seal including a rotary sealing ring that is fixed to a rotating shaft, and a stationary sealing ring that is held by means of O-rings in a seal case through which the rotating shaft passes, so as to move in an axial direction thereof, the seal case being made of a metal, wherein the O-rings are held engaging with the periphery of the stationary sealing ring and come in press contact with the periphery of the seal case so as to give a secondary seal to a gap between the stationary sealing ring and the seal case, while allowing the stationary sealing ring to move in the axial direction thereof.

BACKGROUND ART

A static pressure type non-contact gas seal has been known as a conventional mechanical seal, including a rotary sealing ring that is fixed to a rotating shaft; a stationary sealing ring that is held by means of a pair of O-rings in a seal case through which the rotating shaft passes, so as to move in an axial direction thereof; and a spring that is interposed between the stationary sealing ring and the seal case so as to push the stationary sealing ring against the rotary sealing ring, wherein a communicating space sealed by the pair of O-rings is formed between the seal case and the stationary sealing ring, and a seal gas ejecting passage is formed as a series of passages that communicate with each other through the communicating space in the seal case and the stationary sealing ring, and is open between the sealing end faces serving as the opposite end faces of the both sealing rings, thereby so as to maintain the sealing end faces in proper non-contact state by introducing the seal gas under a predetermined pressure between the sealing end faces through the seal gas ejecting passage (for example, see Patent Document 1).

Meantime, when the seal conditions or the structural conditions taken into account in the above-mentioned static pressure type non-contact gas seal, it may be preferable or may be inevitable to hold the O-rings engaging with the periphery of the stationary sealing ring, as the case may be.

However, the O-rings, being held engaging with the stationary sealing ring, slide in press contact with the periphery of the seal case in accordance with the movement of the stationary sealing ring in the axial direction thereof, and consequently cause the following problems.

That is, since the seal case is made of a metal having an excellent strength in view of the function, the O-rings do not slide smoothly following the movement of the stationary sealing ring owing to the high contact resistance between the O-rings and the seal case. As a result, the stationary sealing ring, which does not move smoothly in the axial direction thereof, deteriorates its own following ness so as to result in failure of an effective sealing function by the mechanical seal. Particularly, when the supply of the seal gas stops in the above-mentioned static pressure type non-contact gas seal, it is concerned that the stationary sealing ring, which does not smoothly move toward the rotary sealing ring, may intensively collide against the rotary sealing ring, so that the sealing end faces may be damaged by some possibility. To the contrary, when the supply of the seal gas stops, the stationary sealing ring does not move, but may form a gap between the sealing end faces. In this case, it is concerned that the resumed supply of the seal gas does not generate a proper static pressure between the sealing end faces but leads to the lost sealing function.

There occurs, similarly, such a problem in an end face contact type mechanical seal, in which the both sealing rings are slidably rotated relative to each other to obtain a sealing function, and also in a dynamic pressure type non-contact type mechanical seal which is configured to maintain the sealing end faces in non-contact state by dynamic pressure generated therebetween.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a mechanical seal that has an excellent following ness of a stationary sealing ring and performs a good sealing function without the above-mentioned problem.

According to an aspect of the present invention, a mechanical seal includes a rotary sealing ring that is fixed to a rotating shaft; and a stationary sealing ring that is held by means of O-rings in a seal case through which the rotating shaft passes, so as to move in an axial direction thereof, the seal case being made of a metal, wherein the O-rings are held engaging with the periphery of the stationary sealing ring, and come in press contact with the periphery of the seal case so as to give a secondary seal to a gap between the stationary sealing ring and the seal case, while allowing the stationary sealing ring to move in an axial direction thereof. It is particularly proposed to achieve the afore-mentioned object that a resin coating film is formed on the periphery of the seal case, and at least within a range in which the O-rings relatively move in accordance with the movement of the stationary sealing ring in the axial direction.

As a preferred embodiment of the mechanical seal according to the present invention, the mechanical seal is the static pressure type non-contact gas seal which includes a communicating space sealed by a pair of O-rings between the seal case and the stationary sealing ring, the pair of O-rings being provided away from each other at a predetermined interval, and a seal gas ejecting passage formed as a series of passages that communicate with each other through the communicating space in the seal case and the stationary sealing ring, with being open between the sealing end faces serving as the opposite end faces of the both sealing rings, thereby so as to maintain the sealing end faces in proper non-contact state by introducing the seal gas under a predetermined pressure into the space between the sealing end faces through the seal gas ejecting passage.

The above-mentioned static pressure type non-contact gas seal is also adopted as an effective seal device for the treatment device that performs a cleaning treatment on substrates (for example, a semiconductor wafer, a substrate of an electronic device, a liquid crystal substrate, a photomask, a glass substrate, and the like) by using a rotary table and the like, wherein advanced preventive measures against contamination are required in a treatment area in which the rotary table is disposed. For example, the above-mentioned static pressure type non-contact gas seal is used as the seal device for a treatment device, in which a driving unit of a rotary table is covered with a cylindrical plastic cover, so as to shield a space between a treatment area where the rotary table is disposed and an area inside the plastic cover. In this embodiment, the rotary sealing ring is fixed to the rotary table concentrically with the rotary axis thereof, the seal case is a cylindrical case which is disposed in the plastic cover and mounted on a supporting case of the driving unit, and the stationary sealing ring is held on an inner periphery of the seal case so as to move in an axial direction thereof, with being concentric with the rotary sealing ring and directly facing the rotary sealing ring. In this case, it is preferred that an annular cover shoulder contacting with an end of the seal case is formed on the inner periphery of the plastic cover, and that a seal gas supply passage is formed in the plastic cover for supplying the seal gas to the seal gas ejecting passage, and also that the seal gas supply passage and the seal gas ejecting passage formed in the seal case are connected so as to communicate with each other at a portion where the cover shoulder and the seal case end come in contact.

Furthermore, the afore-mentioned static pressure type non-contact gas seal is provided with a dynamic pressure generating channel formed on the sealing end face of one sealing ring so as to maintain the sealing end faces in non-contact state by generating a dynamic pressure in the space between the sealing end faces by means of the dynamic pressure generating channel, in addition to a static pressure by means of the seal gas.

In addition, when it is necessary for the sealed fluid to evade mixture of metal ingredients (metal ions or the like) or when the sealed fluid has a concerned possibility of metal corrosion, it is preferred to form the resin coating film on a portion with which the sealed fluid comes in contact, of the periphery of the seal case, inclusive of a portion on which the O-rings relatively move, in order to prevent the sealed fluid from coming in direct contact with the seal case made of a metal. Specifically, in the afore-mentioned static pressure type non-contact gas seal, it is preferred that the resin coating film be formed on the surface of the seal case and, if required, on portions with which the sealed fluid and/or the seal gas come in contact (inclusive of portions with which it or they may possibly come in contact), including a portion on which the O-rings slide, in order to prevent metal ingredients from generating because of the seal gas coming in contact with the seal case as well as the sealed fluid.

A low-friction plastic, which has a low contact resistance between the O-rings and the resin coating film, may be preferably used as a material of the resin coating film. Further, it may be preferred that a material having high corrosion resistance or chemical resistance is used as a material of the resin coating film depending on the property of the sealed fluid or sealing conditions. In general, a fluorocarbon polymer such as polytetrafluoroethylene (PTFE), which has a low friction and high corrosion resistance, is preferably used as a material of the resin coating film. In addition, the resin coating film preferably has a thickness in the range of 5 to 100 μm, and optimally 20 to 40 μm. The surface of the resin coating film (at least a portion on which the O-rings slide) is preferably machined to be a smooth surface.

According to the present invention, it is possible to provide a mechanical seal in which the O-rings smoothly slide on the seal case in accordance with the movement of a stationary sealing ring and has an excellent following ness of the stationary sealing ring. Accordingly, in a mechanical seal such as a static pressure type non-contact gas seal or the like, it is always possible to obtain excellent sealing function without the deterioration of the sealing function. A resin coating film covers a portion, with which the sealed fluid comes in contact (plus a portion with which the seal gas comes in contact in case of the static pressure type non-contact gas seal) of the seal case, as well as a portion, with which the O-rings come in contact, of the seal case. Accordingly, it is possible to prevent metal ions, which are generated by contacting the sealed fluid and/or seal gas with the seal case made of a metal, from being generated. In addition, even when it is necessary to prevent metal ions from being generated, it is possible to obtain an excellent sealing function. Moreover, a portion, with which the seal fluid comes in contact, of the case is covered with the resin coating film having high corrosion resistant or chemical resistant. Therefore, even when the sealed fluid has corrosiveness, the mechanical seal can obtain an effective sealing function without corrosion of the seal case made of a metal.

Meanwhile, when a substrate such as a semiconductor wafer is cleaned by means of the rotary table, it is necessary to maintain a treatment area, at which a rotary table is disposed, clean. In addition, it is necessary to reliably prevent particles from entering the treatment area from the driving unit of the rotary table. The conventional treatment device requiring such an advanced contamination-prevention measures has been proposed. That is, the conventional treatment device is provided with a seal between the rotary table and the plastic cover covering the driving unit thereof, in order to shield the treatment area, at which the rotary table is disposed, from the inside area of the cover. In general, a labyrinth seal or magnetic fluid seal is adopted as the above-mentioned seal (for example, see JP-A-11-265868). Since the conventional treatment device is provided with the seal, it is possible to prevent the particles from entering the treatment area from the inside area of the cover, whereby the substrate or the like is not contaminated. Furthermore, there is no problem that treatment remainders (cleaning solution, harmful matters or the like) generated at the treatment area enter the inside area of the cover to generate troubles in the driving system of the rotating shaft. However, the seal such as the labyrinth seal or the like provided in the conventional treatment device cannot sufficiently shield the treatment area from the inside area of the cover, and cannot provide complete contamination-prevention measures to the treatment device such as a substrate cleaning device. That is, in the labyrinth seal, an annular gap forming a labyrinth easily becomes unbalanced depending on accuracy of the rotation or device, and respiration caused by the unbalance of the labyrinth gap is generated. Therefore the both areas are not sufficiently shielded from each other. Further, even in the magnetic fluid seal, the quality is unstable. Therefore, the both areas are not sufficiently shielded from each other, like the labyrinth seal.

However, when the treatment device, in which the driving unit of the rotary table is covered with the cylindrical plastic cover, uses the mechanical seal of the invention as the seal for isolating the treatment area, at which the rotary table is disposed, from the are inside cover, it is possible to reliably shield the treatment area, at which the rotary table is disposed, from the inside area of the cover, at which the driving unit of the rotating shaft is disposed, compared to when the above-mentioned labyrinth seal is used as the seal. The mechanical seal according to the aspect of the invention is composed of a static pressure type non-contact gas seal in which the seal gas is ejected to the treatment area and the inside area of the cover through a gap between the rotary sealing ring of the rotary table and the stationary sealing ring of the plastic cover. Accordingly, when the mechanical seal (static pressure type non-contact gas seal) of the invention is used, it is possible to maintain the treatment at the treatment area in the clean atmosphere in which the particle is prevented from entering the treatment area from the inside area of the cover. Therefore, it is possible to satisfactorily perform the treatment such as a treatment of cleaning the substrate, and to provide the advanced contamination-prevention measures. Furthermore, it is possible to remove the problem that remainders of cleaning solution or harmful matters, which are generated at the treatment area, enter the inside area of the cover to generate troubles in the driving system of the rotating shaft. In addition, when a seal gas supply passage, which is used to supply seal gas to the seal gas ejecting passage, is formed in the plastic cover, if the seal gas supply passage is configured so that the gas flows from the seal gas supply passage to the seal gas ejecting passage (seal gas ejecting passage formed in the seal case) in the radial direction of the plastic cover, the plastic cover is deformed in the radial direction due to the gas pressure applied to the connection portion between the seal gas supply passage and the seal gas ejecting passage. Therefore, there has been a possibility that the seal gas is not satisfactorily supplied to the seal gas ejecting passage. However, in the mechanical seal (static pressure type non-contact gas seal) of the invention, since the seal gas supply passage is configured so that the gas flows from the seal gas supply passage to the seal gas ejecting passage (seal gas ejecting passage formed in the seal case) in the axial direction of the plastic cover, the plastic cover is not deformed regardless of a material and thickness (thickness in the radial direction) of the plastic cover, whereby the above-mentioned problem does not occur. Accordingly, it is possible to freely set a material and shape (thickness) of the plastic cover in accordance with working conditions of the treatment device, regardless of strength of the plastic cover against the gas pressure.

In addition, the mechanical gas seal according to the aspect of the invention, which is composed of the static pressure type non-contact gas seal, can maintain the sealing end faces in the non-contact state by dynamic pressure generated by the dynamic pressure generating channel as well as static pressure caused by the seal gas. A seal function and contamination-prevention function can be obtained by the mechanical gas seal of the invention, under the condition that a seal function is not satisfactorily obtained by the conventional static pressure type non-contact gas seal (static pressure type non-contact gas seal for maintaining the sealing end faces in the non-contact state only by static pressure).

REFERENCE NUMERALS

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1is a front cross-sectional view showing an embodiment of a treatment device having a mechanical seal4according to the invention, andFIG. 2is an enlarged view showing the main parts thereof. In the treatment device, a driving unit2of a rotary table1is covered with the cylindrical plastic cover3. When appropriate treatments (cleaning treatment, chemical treatment, and the like) are performed on substrates (which are objects to be treated, such as a semiconductor wafer, a substrate of an electronic device, a liquid crystal substrate, a photomask, a glass substrate, and the like) by using the rotary table1, a treatment area A (a fluid sealed area) and an inside area B (which is an atmosphere area, and hereinafter referred to as a ‘inside area of cover’) of a plastic cover3(a fluid non-sealed area) in which the rotary table1is disposed are screened from each other by the mechanical seal4so that the treatment area A is kept clean.

In addition, the driving unit2includes a rotating shaft2athat is connected to the rotary table1and extends in a vertical direction, bearings by which the rotating shaft2ais rotatably supported, and a supporting case2bthat supports the bearings, the rotating shaft, and a driving means of the rotating shaft2ain the inside area of the cover. The driving unit is configured so as to rotate the rotary table1. The rotary table1is made of silicon carbide, is horizontally disposed in the treatment area, and is formed in the shape of a rotator such as a disc. In addition, as shown inFIG. 1, the plastic cover3is made of chemical resistant plastic (for example, PTFE), is integrally formed in the shape of a cylinder with an open upper end, and covers the driving unit2disposed on the lower side of the rotary table1. If necessary, as shown inFIG. 1, a labyrinth seal1acan be provided between the rotary table1and the plastic cover3. If the labyrinth seal1ais provided, it is possible to effectively prevent seal gas10to be described below from being ejected from the labyrinth seal1ato the treatment area A, and thus to effectively prevent chemicals from entering from the treatment area A to the inside area B of the cover.

As shown inFIGS. 1 and 2, the mechanical seal4is a static pressure type non-contact mechanical seal. The mechanical seal includes a rotary sealing ring5fixed to the rotary table1to be coaxial with the rotary axis of the table; a cylindrical seal case6which is provided in the plastic cover3so as to be mounted on the supporting case2b; a stationary sealing ring7, which is held by means of a pair of O-rings12on an inner periphery of the seal case6(inner periphery of a sealing ring holder61to be described below) so as to move in an axial direction thereof in a state in which the stationary sealing ring directly faces the rotary sealing ring5so as to be concentric with the rotary sealing ring; a spring member8, which is provided between the seal case6and the stationary sealing ring7, and presses the stationary sealing ring7on the rotary sealing ring5; an annular cover shoulder3a,which is formed on the inner periphery of the plastic cover3and comes in contact with the end face6bof the seal case6(lower end face of a sealing ring holder61to be described below); a successive seal gas passage9, which passes through the plastic cover3, the seal case6, and the stationary sealing ring7and is open at a gap between the sealing end faces5aand7a.In this case, while keeping the sealing end faces5aand7anot to come in contact with each other by ejecting the seal gas10through the seal gas passage9to a gap between the sealing end faces5aand7a,the mechanical seal shields both of the areas A and B from each other.

As shown inFIGS. 1 and 2, the seal case6includes a cylindrical sealing ring holder61and an annular spring holder62extending inward from the lower side of the sealing ring holder, and is made of a metal (for example, a stainless steel such as an SUS316). The seal case6is mounted on the supporting case2bwith the spring holder62interposed between the seal case and the supporting case so that the lower end face6bof the seal case6(lower end face of the sealing ring holder61) comes in contact with the cover shoulder3a,and so that the outer periphery thereof (outer periphery of the sealing ring holder61) comes in close contact with the upper inner periphery of the plastic cover3(inner periphery above the cover shoulder3a) with an O-ring11(which is made of fluorocarbon rubber) interposed therebetween.

The rotary sealing ring5is a ring-shaped body made of a harder material (for example, silicon carbide) than the material (for example, carbon) of the stationary sealing ring7, and is fixed to the lower side of the rotary table1as shown inFIG. 1. The rotary sealing ring5has a flat and annular sealing end face (hereinafter, referred to as a ‘rotary sealing end face’)5aon the lower surface thereof.

As shown inFIG. 1, the stationary sealing ring7is a ring-shaped body, which has a flat and annular sealing end face (hereinafter, referred to as a ‘stationary sealing end face’)7aon the upper surface thereof. The stationary sealing ring is fitted and held on the inner periphery6aof the sealing ring holder61of the seal case6with the pair of O-rings12and12(which is made of fluorocarbon rubber, and is arranged in the vertical direction) interposed therebetween so as to move in the axial direction thereof. An outer diameter of the stationary sealing end face7ais set slightly smaller than that of the rotary sealing end face5a,and an inner diameter of the stationary sealing end face7ais set slightly larger than that of the rotary sealing end face5a.The O-rings12are is fitted and held in annular O-ring grooves7b,respectively, which are formed on the outer periphery of the stationary sealing ring7, in a state in which the O-rings comes in press contact with the inner periphery of the seal case6. Accordingly, while allowing the stationary sealing ring7to move in the axial direction of the stationary sealing ring7, the O-rings secondarily seals a gap between the stationary sealing ring7and the seal case6. In addition, a circular hole7cextending in the axial direction is formed on the lower surface of the stationary sealing ring7. When a drive pin13, which is fixed to the spring holder62of the seal case6and made of a metal (for example, a stainless steel such as an SUS316), is inserted into the circular hole7c,the stationary sealing ring7cannot be rotated relative to the seal case6while the stationary sealing ring7moves in the axial direction thereof. Furthermore, the numbers of the circular hole7cand the drive pin13inserted thereinto are not limited, and a plurality of holes and drive pins may be provided if necessary.

As shown inFIG. 1, the spring member8is composed of a plurality of coil springs (only one spring is shown), which are provided between the stationary sealing ring7and the spring holder62disposed below the stationary sealing ring, and presses the stationary sealing ring7on the rotary sealing ring5. Furthermore, the spring member generates a closing force that acts in a direction of closing the gap between the sealing end faces5aand7a.

As shown inFIGS. 1 and 2, the seal gas passage includes a seal gas supply passage90formed in the plastic cover3, and a successive seal gas ejecting passage91formed in the seal case6and the stationary sealing ring7. The seal gas ejecting passage91includes a case-side passage92formed in the seal case6; a static pressure generating channel93formed on the stationary sealing end face7a; an annular communicating space94, which is formed between the opposite peripheries of the stationary sealing ring7and the seal case6and is sealed by the O-rings12and12; and a sealing ring-side passage95penetrating the stationary sealing ring7to reach the static pressure generating channel93from the communicating space94.

As shown inFIG. 1, the seal gas supply passage90penetrates the plastic cover3in the vertical direction (in the axial direction of the plastic cover3) so that the upper end (downstream end) of the seal gas supply passage is open at the cover shoulder3aand the lower end (upstream end) of the seal gas supply passage is connected to the proper seal gas supply line (not shown).

As shown inFIG. 1, the case-side passage92penetrates the sealing ring holder61from the lower side sealing ring holder to the inner periphery6aso as to be connected to the seal gas supply passage90and the communicating space94. The upstream end of the case-side passage92and the downstream end of the seal gas supply passage90are connected to each other so that a gap therebetween is sealed by an O-ring16. The O-ring16is made of fluorocarbon rubber and provided between the cover shoulder3aand the seal case end face6b.

The static pressure generating channel93is a shallow channel, which has an annular and continuous or intermittent shape so as to be concentric with the stationary sealing end face7a.The following channel (intermittent channel) is adopted as an example of the static pressure generating channel. That is, as shown inFIG. 3, the static pressure generating channel93includes a plurality of arc channels93a,which stands in line so as to be concentric with the stationary sealing end face7a.The vertical width (a distance between the O-rings12and12) of the communicating space94is set depending on a displacement in the axial direction (vertical direction), which is required to secure the following ness of the stationary sealing ring7. Even though the stationary sealing ring7moves, the case-side passage92and the communicating space94are not disconnected from each other. In addition, one end (upstream end) of the sealing ring-side passage95is open at the outer periphery of the stationary sealing ring7between the O-rings7aand7b(is open at the communicating space94). Furthermore, the other end (downstream end) thereof branches off at a plurality of branches95aso that each of the branches95ais open at the arc channels93aconstituting the static pressure generating channel93as shown inFIG. 3. In addition, a proper throttling unit96(having a throttling function of an orifice, a capillary tube, a porous member, or the like) is provided at a proper position (for example, an upstream position of the branches95a,which are properly provided on the sealing ring-side passage95) on the seal gas passage9. Accordingly, even though the distance between the sealing end faces5aand7ais varied, the distance therebetween is automatically adjusted and properly held. That is, when the distance between the sealing end faces5aand7aincreases due to the vibration of the rotary device (rotary table1), the amount of seal gas ejected from the static pressure generating channel93through the gap between the sealing end faces5aand7abecomes unbalanced with that of seal gas supplied to the static pressure generating channel93through the throttling unit96. As a result, the pressure in the static pressure generating channel93decreases, and an opening force caused by the seal gas10becomes smaller than a closing force caused by the spring member8. Accordingly, the distance between the sealing end faces5aand7adecreases so that the gap therebetween is properly adjusted. In contrast, when the distance between the sealing end faces5aand7adecreases, the pressure in the static pressure generating channel93increases due to the above-mentioned throttling function of the throttling unit96, and the opening force becomes larger than the closing force. Accordingly, the distance between the sealing end faces5aand7aincreases so that the gap therebetween is properly adjusted.

Clean seal gas10, which has higher pressure and less particles than those of both areas A and B, is supplied to the static pressure generating channel93through the seal gas passage9(the seal gas supply passage90, the case-side passage92, the communicating space94, and sealing ring-side passage95). Gas, which has no bad effect even when being flown out to each area A and B, is properly selected as the seal gas10depending on sealing conditions. In the embodiment, clean nitrogen, which has inert effect on various materials and is harmless to humans, is used as the seal gas. Furthermore, the seal gas10is generally supplied during the operation of the rotary table1(driving of the rotating shaft2a), and the supply of the seal gas stops after stop of the operation. After the seal gas10begins to be supplied and the distance between the sealing end faces5aand7ais held in a proper non-contact state, the rotary table1begins to be operated. Furthermore, after the rotary table1is stopped and the rotating shaft2ais completely stopped, the supply of the seal gas10stops. Moreover, if necessary, the seal gas10can be always or intermittently supplied regardless of whether the rotary table1is operated.

When the seal gas10is supplied to the static pressure generating channel93, the opening force, which acts in a direction of opening the gap between the sealing end faces5aand7a,is generated between the sealing end faces5aand7a.The opening force is caused by a static pressure, which is generated by the seal gas10supplied to the gap between the sealing end faces5aand7a.Accordingly, the sealing end faces5aand7aare held in a non-state state in which the opening force and the closing force (spring load) are balanced against each other. The closing force is generated by the spring member8, and acts in the direction of closing the gap between the sealing end faces5aand7a.That is, the seal gas10supplied to the static pressure generating channel93forms a fluid film having static pressure between the sealing end faces5aand7a,and the fluid film shields the outer peripheral area (treatment area) A of the sealing end faces5aand7afrom the inner peripheral area (inside area of cover) B thereof. The pressure of the seal gas10and the spring force (spring load) of the spring member8are properly set depending on the sealing conditions so that the distance between the sealing end faces5aand7ais proper (in general, 5 to 15 μm).

However, the stationary sealing ring7moves in the axial direction due to the supply of the seal gas10, stop thereof, or the adjustment of the gap by the throttling unit96. Then, when the stationary sealing ring moves satisfactorily and smoothly, a proper sealing function can be obtained by the mechanical seal. As a result, when the O-rings12and12, which are fitted and held on stationary sealing ring7, smoothly and relatively move (slide) on the inner periphery6aof the seal case6, the following ness of the stationary sealing ring7is secured. However, the seal case6is made of a metal, a friction coefficient between the inner periphery6aof the seal case and the O-rings12and12made of fluorocarbon rubber is large, and the O-rings12and12are compressed between the seal case6and the stationary sealing ring7on which the secondary sealing function of the O-rings acts. As a result, the O-rings12and12are comes in press contact with the inner periphery6aof the seal case6. Accordingly, the O-rings12and12are difficult to move in accordance with the movement of the stationary sealing ring7, whereby there has been a possibility that the following ness of the stationary sealing ring7deteriorate.

As shown inFIG. 2, in the mechanical seal4of the invention, a low-friction resin coating film63is formed on the inner periphery of the sealing ring holder61, on which the O-rings12and12slide, so that the O-rings12and12can smoothly slide and the following ness of the stationary sealing ring7is improved.

In addition, in the embodiment, the resin coating film63is formed on a portion of the seal case, with which the sealed fluid comes in contact (or may come in contact), as well as on the portion6aof the seal case, on which the O-rings12and12come in contact with and slide. That is, as shown inFIG. 2, the successive resin coating film63is formed on the surface of the sealing ring holder61of the seal case6so that the sealed fluid does not directly comes in contact with the metal portion of the seal case6. In this way, it is possible to prevent metal ions, which are generated by contacting the sealed fluid with the seal case6made of a metal, from being generated. Therefore, it is possible to prevent the treatment at the treatment area A from being poor due to the metal ions. In addition, among components of the treatment device and the mechanical seal4provided to the treatment device, a member coming contact with the sealed fluid is made of a non-metal material, which does not completely generate metal ions, by removing the seal case6therefrom, or is coated with a non-metal material. That is, the rotary sealing ring5is made of silicon carbide, the stationary sealing ring7is made of carbon, and each of O-rings11,12, and16is made of fluorocarbon rubber. Furthermore, the rotary table1and the cover3are also made of a non-metal material such as PTFE or the like, or portions coming contact with portions thereof, faces the treatment area A, are coated with a resin such as PTFE or the like. Meanwhile, all of the spring members8made of a metal and the drive pin13, which are made of a metal, are disposed in the inside area B of the cover. Accordingly, even when an object to be treated is a material, which should be protected from metal ions, such as a semiconductor wafer, it is possible to satisfactorily treat the object.

Meanwhile, a low-friction plastic such as fluorocarbon polymer, which has a low friction coefficient between the O-rings12and the resin coating film, is preferably used as a material of the resin coating film63, and for example, PTFE is used as a material of the resin coating film.

In addition, the resin coating film63preferably has a thickness in the range of 5 to 100 μm, and optimally has a thickness in the range of 20 to 40 μm. If the resin coating film has the above-mentioned thickness, it is possible to obtain a constant thickness of the resin coating film without thickness deviation thereof. As a result, since the deviation of the contact resistance between the O-rings12and the resin coating film decreases, it is possible to considerably improve the following ness of the stationary sealing ring7. Furthermore, the surface of the resin coating film63, particularly the surface of a portion63awith which the O-rings12and12come in contact, is preferably machined to be a smooth surface with high accuracy.

Meanwhile, for example, as shown by a two-dot chain line inFIG. 1, in the seal gas passage9, the downstream end90aof the seal gas supply passage90is open at the inner periphery of the plastic cover3, and the upstream end91aof the seal gas ejecting passage91is open at the outer periphery of the seal case6so that both of the open ends90aand91aare connected to each other. However, since the pressure caused by the high-pressure seal gas10is applied to the communicating portion between the open ends90aand91a,the plastic cover3is deformed in the radial direction. As a result, since the sealing function deteriorates or is lost at the communicating portion between the open ends90aand91a,there has a possibility that the seal gas is not smoothly supplied.

However, in the mechanical seal4, the seal gas supply passage90formed in the plastic cover3and the seal gas ejecting passage (case-side passage92) formed in the seal case6are connected to each other at the portion at which the cover shoulder3aand the seal case end face6bcomes in contact with each other so that the gas flows from the seal gas supply passage90to the seal gas ejecting passage91in the axial direction of the plastic cover3. As a result, the plastic cover3is not deformed in the radial direction due to the pressure of the seal gas10, regardless of a material and thickness (thickness in the radial direction) of the plastic cover3. Therefore, it is possible to freely set a material and shape (thickness) of the plastic cover3in accordance with working conditions of the treatment device, regardless of strength of the plastic cover against the pressure of the seal gas10. In addition, when the above-mentioned labyrinth seal1ais provided between the cover3and the rotary table1, the plastic cover3is not deformed. Accordingly, the function of the labyrinth seal1adoes not deteriorate.

Furthermore, the structure of the invention is not limited the above-mentioned embodiment, and the invention can have proper modifications and variations without departing from the scope of the invention.

For example, in the mechanical seal4show inFIGS. 1 and 2, the resin coating film63is formed on the portion6aof the seal case, with which the sealed fluid comes in contact (or may come in contact), as well as on the portion of the seal case, on which the O-rings12and12come in contact with and slide. However, in addition to the portions of the seal case, the resin coating film may be also formed on the portion of the seal case, with which the seal gas10comes in contact (or may come in contact). That is, as shown inFIG. 4, the successive resin coating film63is formed on the surface of the sealing ring holder61of the seal case6and the inner surface of the sealing ring-side passage95so that the sealed fluid and seal gas10does not directly come in contact with the metal portion of the seal case6. In this way, it is possible to prevent metal ions, which are generated by contacting the sealed fluid and seal gas10with the seal case6made of a metal, from being generated. Therefore, it is possible to prevent the treatment at the treatment area A from being poor due to the metal ions.

Moreover, although the seal case6is formed as one component in the mechanical seal4shown inFIG. 1or4, the seal case6can be composed of a plurality of components made of metal. For example, as shown inFIGS. 5 and 6, the seal case6can be composed of a cylindrical upper body64, and lower bodies65and66. The lower bodies includes a cylindrical sealing ring holder65and an annular spring holder66extending inward from the lower side of the sealing ring holder. The upper body64and the lower bodies65and66are connected to one another by proper connectors. The seal case6is mounted on the supporting case2bwith the spring holder62interposed between the seal case and the supporting so that the lower end face6aof the seal case6(lower end face of the sealing ring holder65) comes in contact with the cover shoulder3a,and so that the outer periphery thereof (outer periphery of the upper body64) comes in close contact with the upper inner periphery of the plastic cover3(inner periphery above the cover shoulder3a) by means of an O-ring11(which is made of fluorocarbon rubber). The O-rings12and12are provided in annular spaces. The annular spaces are formed between an annular protrusion7dthat is formed on the outer periphery of the stationary sealing ring7, and annular protrusions64aand65athat are formed on the upper body64and the sealing ring holder65, respectively, so as to face each other on the upper and lower sides of the annular protrusion7d.In addition, a circular hole7cextending in the axial direction is formed on the lower surface of the stationary sealing ring7. When a drive pin13, which is fixed to the spring holder66of the seal case6and made of a metal (for example, a stainless steel such as an SUS316), is inserted into the circular hole7c,the stationary sealing ring7cannot be rotated relative to the seal case6while the stationary sealing ring7moves in the axial direction thereof. The case-side passage92includes a first gas passage92a,which penetrates the sealing ring holder65in the axial direction thereof, and a second gas passage92b,which penetrates the upper body64from the lower end thereof to the inner periphery thereof. The upper end of the first gas passage92aand the lower end of the second gas passage92bare connected to each other so that a gap therebetween is sealed by an O-ring15. The O-ring15is made of fluorocarbon rubber and provided at the contact portion between the upper body64and the sealing ring holder65. The upper end (downstream end) of the second gas passage92bis connected to the communicating space94. The lower end (upstream end) of the first gas passage92adirectly faces the upper opening (downstream opening) of the seal gas supply passage90, and is open at the seal case end face6a.Furthermore, the seal gas supply passage90and the first gas passage92aare connected to each other so that a gap therebetween is sealed by an O-ring16. The O-ring16is made of fluorocarbon rubber and provided between the cover shoulder3aand the seal case end face6a.

Even though the seal case6is formed as several divided components, the resin coating film63is formed on the portion of the seal case, on which the O-rings12and12come in contact with and slide, and on the portion of the seal case, with which the sealed fluid comes in contact, that is, on the surface of the upper body64, as shown inFIGS. 5 and 6. If necessary, as shown inFIG. 7, the resin coating film63can be formed on the portion of the seal case, with which the seal gas10comes in contact, that is, on the inner periphery of the case-side passage92and the surface of the sealing ring holder65.

The invention can be also applied to an end face contact type mechanical seal, in which both sealing rings are rotated and slide relative to each other. However, the invention can be more preferably applied to a non-contact mechanical gas seal (the above-mentioned static pressure type non-contact gas seal or a dynamic pressure type non-contact mechanical seal in which a dynamic pressure generating channel is formed on one sealing end face to generate dynamic pressure and sealing end faces are maintained in a non-contact state by dynamic pressure generated in the channels) of which following ness is emphasized.

Furthermore, the mechanical seal shown inFIGS. 1,4,5, or7is composed of a static pressure type non-contact gas seal4in which the sealing end faces5aand7aare maintained in the non-contact state only by the static pressure caused by the seal gas10. However, as shown inFIGS. 8 and 9, the mechanical seal of the invention can be composed of a complex non-contact gas seal104in which the sealing end faces5aand7aare maintained in the non-contact state by generating dynamic pressure as well as static pressure. Whether the following ness of the stationary sealing ring7is satisfactory is considered as an important factor in the function of the complex non-contact gas seal104.

That is, in the complex non-contact gas seal104shown inFIG. 8or9, a dynamic pressure generating channel is formed on the sealing end face5a(rotary sealing end face, that is, one sealing end face) of the rotary sealing ring5to generate dynamic pressure between the sealing end faces5aand7a.It is possible to properly set the shape of the dynamic pressure generating channel19in accordance with sealing conditions. However, the dynamic pressure generating channel19of this embodiment includes a plurality of grooves20, which stands in line in the circumferential direction of the sealing end face5a,as shown inFIG. 11or12. Each of the grooves20has a first groove part20aand a second groove part20b.The first groove part20ais inclined and extends outward in the radial direction and the reverse direction of the rotation direction (direction indicated by an arrow) of the rotary sealing ring5from the portion facing the static pressure generating channel93on the rotary sealing end face5a.The second groove part20bis inclined and extends inward in the radial direction and the reverse direction of the rotation direction (direction indicated by an arrow) of the rotary sealing ring5from the portion. Each of the grooves20is a groove that has a constant and shallow depth in the range of 1 to 10 μm. The outermost end (outer end of the first groove part20a) and the inmost end (inner end of the second groove part20b) are positioned in the overlapped area in which the sealing end faces5aand7aare overlapped each other. That is, as shown inFIG. 10, the inner and outer diameters E and F of the dynamic pressure generating channel19are properly set in the range, which satisfies relations of B<F<A and D<E<C, with respect to the outer diameter (≦the outer diameter of the rotary sealing end face5a) A of the sealing end face (stationary sealing end face)7aof the stationary sealing ring7, the inner diameter thereof (≧the inner diameter of the rotary sealing end face5a) D, and the outer and inner diameters B and C of the static pressure generating channel93(arc channels93a). In this embodiment, the inner and outer diameters E and F are set so as to satisfy a relation of 0.5≦(F−B)/(A−B)≦0.9 or 0.5≦(C−E)/(C−BD)≦0.9. As shown inFIG. 11, each of the grooves20is formed in a substantial V shape in which the first groove part20aand the second groove part20bare connected to each other at a base part, or as shown inFIG. 12, each of the grooves is formed in a zigzag shape in which the base parts of the first groove part20aand the second groove part20balternate each other in the circumferential direction of the rotary sealing ring. Furthermore, other configurations of the complex non-contact gas seal104except for the above-mentioned configuration are the same as those of the static pressure type non-contact gas seal4shown inFIGS. 1,4,5, or7.

According to the complex non-contact gas seal104, dynamic pressure is generated by the dynamic pressure generating channel19as well as static pressure is generated by the seal gas10between the sealing end faces5aand7a,and the sealing end faces5aand7aare maintained in the non-contact state by the static pressure and dynamic pressure. Accordingly, even when the sealing end faces5aand7acannot be maintained in the proper non-contact state by the static pressure and dynamic pressure, the sealing end faces can be maintained in the proper non-contact state by the dynamic pressure. In addition, when the mechanical seal of the invention is compared to the static pressure type non-contact gas seal for maintaining the non-contact state only by the static pressure, the mechanical seal of the invention can reduce required amount of the seal gas10to be supplied by means of the static pressure caused by the seal gas10. Furthermore, the dynamic pressure generating channel19is not open on the outside of the overlapped area. Accordingly, the outermost end and the inmost end of each groove20serve as weirs for the seal gas10, which is supplied to the gap between the sealing end faces5aand7a,and function to narrow a leak gap between the sealing end faces5aand7a.As a result, since the leakage of the seal gas10, which is supplied to the gap between the sealing end faces5aand7a,to be leaked to the treatment area (a fluid sealed area) A is suppressed, the dynamic pressure generating channel19can very satisfactorily collect the seal gas10. Therefore, it is possible to reduce consumption of the seal gas10. Even if there are particles accompanied with the seal gas10, it is possible to suppress the infiltration of the particles as much as possible. Furthermore, the rotary table1or rotating shaft2aare may be rotated not in one direction but in the normal and reverse directions, depending on the configuration and working conditions of the treatment device that includes the complex non-contact gas seal104. However, in this case, the dynamic pressure generating channel19may be configured so that the dynamic pressure is generated even though the rotary sealing ring5is rotated in one direction of the normal and reverse directions. The dynamic pressure generating channel19can be set to have any shape in accordance with sealing conditions or the like, and various shapes have been proposed for the dynamic pressure generating channel in the related art. For example, a plurality of pairs of dynamic pressure generating channel units is formed on the rotary sealing end face5aso as to stand in line in the circumferential direction of the rotary sealing end face at a predetermined interval. Each of the dynamic pressure generating channel units includes a first dynamic pressure generating channel and a second dynamic pressure generating channel, which are arrayed in the radial direction and symmetric with respect to the diameter line. When the rotary sealing ring5is rotated in the normal direction, the first dynamic pressure generating channel generates dynamic pressure. When the rotary sealing ring5is rotated in the reverse direction, the second dynamic pressure generating channel generates dynamic pressure. For example, an L-shaped channel having a constant depth and width can be used as each of the first and second dynamic pressure generating channels.

In addition, under the condition in which the generation of metal ions does not need to be suppressed, the resin coating film63may be formed only on the portion6aof the seal case6, on which the O-rings12relatively move (slide) in accordance with the movement of the stationary sealing ring7, of the portion of the seal case, with which the O-rings12come in contact. Furthermore, under the condition in which the contact resistance between the O-rings12and the resin coating film decreases, the material of the resin coating film63is properly selected depending on the property or sealing conditions of the sealed fluid. For example, when the sealed fluid has a possibility to erode the seal case6, a resin coating film63made of corrosion resistant or chemical resistant material is formed on the portion of the seal case6, with which the sealed fluid comes in contact. In this case, components of the mechanical seal4, or components or portion of the seal case6, with which the sealed fluid comes in contact, other than the seal case6are made of or coated with corrosion resistant or chemical resistant material. Accordingly, even when the sealed fluid has corrosiveness, an effective sealing function can be obtained by the mechanical seal.

Moreover, the rotary sealing ring5may be fixed to the other rotating shaft, which is fixed to the rotary member (for example, rotary table1) other than the rotating shaft2a,or a sleeve thereof. Furthermore, depending on the sealing conditions, the stationary sealing ring7can be fixed to the seal case6, and the rotary sealing ring5can be held on the rotary member so as to move in the axial direction and so as not to be rotated relative to the rotary member.