Cleaning apparatus

The problem to be addressed by the present invention is to provide a cleaning apparatus capable of obtaining a cleaning liquid having a high degree of cleanliness. A cleaning apparatus 10 includes a dissolution tank 20 for dissolving a gas in a liquid, a transfer pump 30 for sending the liquid together with the gas into the dissolution tank 20, and a feed nozzle 40 for feeding the liquid stored in the dissolution tank 20 to a workpiece W. The transfer pump 30 is a positive displacement pump. Portions of the dissolution tank 20, the transfer pump 30, and the feed nozzle 40 that come into contact with the liquid are made of a fluororesin.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2015/071519, filed Jul. 29, 2015, claiming priority based on Japanese Patent Application No. 2014-155963, filed Jul. 31, 2014, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a cleaning apparatus to be used, for example, in a cleaning process of a semiconductor.

BACKGROUND ART

In a semiconductor manufacturing process, cleaning for removing particles, organic substances or the like adhered to a silicon wafer or a thin film is performed.

Typical examples of the semiconductor cleaning technique is RCA cleaning method. The RCA cleaning method is a wet cleaning method for Si substrates that are based on cleaning with ammonium and hydrogen peroxide solution (SC1), and cleaning with hydrochloric acid and hydrogen peroxide solution (SC2).

A semiconductor cleaning method is also known which utilizes the decomposition ability of OH radicals contained in ozone water to decompose an organic substance. For example, Patent Document 1 discloses a semiconductor wafer cleaning system including a cleaning apparatus for cleaning a semiconductor wafer with ozone water, and an ozone water producing apparatus for supplying ozone water into the cleaning apparatus.

PRIOR ART LITERATURE

Patent Literature

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

It is said to be difficult to maintain the concentration of ozone dissolved in water at a high level over a long period of time. This is because the ozone dissolved in water quickly decomposed to be oxygen. Another reason is that ozone dissolved in water is immediately released into the atmosphere.

The present inventors have discovered that generation of microbubbles in water containing dissolved ozone can make it possible to maintain the concentration of ozone in ozone water at a high level over a long period of time, and have filed applications for inventions relating to apparatuses for producing ozone water (see, for example, JP 2012-101222A).

The present inventors have confirmed that a very excellent cleaning effect is obtained when water in which ozone is dissolved and microbubbles are generated (hereinafter, such water may be referred to as “microbubbles ozone water”) is used for cleaning semiconductors.

However, application of the conventional ozone water production apparatus to a semiconductor cleaning step raises the following problems.

The conventional ozone water production apparatus uses metals for those portions of a pipe, a tank, a valve and a pump or the like which come into contact with a liquid, and sometimes metal ions are eluted into water. In addition, metal debris generated at a sliding portion, or a foreign matter or the like produced by corrosion of a metal is sometimes mixed into water. Therefore, it is difficult to apply ozone water produced using the conventional ozone water production apparatus to the semiconductor cleaning step that requires an extremely high cleanliness.

Further, the conventional ozone water production apparatus sucks ozone together with water by means of a centrifugal pump (e.g., volute pump), and mixes the water with the ozone by the agitation force of an impeller. However, the use of a metal material for the shaft portion of the impeller of the centrifugal pump makes it difficult to avoid the problem of contaminating cleaning water with the elution of metal ions and the mixing of a foreign matter or the like.

The present invention has been made in view of the above problems, and an object of the invention is to provide a cleaning apparatus capable of obtaining a cleaning liquid having a high degree of cleanliness.

Means for Solving the Problems

The problems are solved by the following invention.

A cleaning apparatus including:

a dissolution tank for dissolving a gas in a liquid;

a transfer pump for sending the liquid together with the gas into the dissolution tank; and

a feed nozzle for feeding the liquid stored in the dissolution tank to a workpiece,

wherein

the transfer pump is a positive displacement pump, and

portions of the dissolution tank, the transfer pump, and the feed nozzle that come into contact with the liquid are made of a fluororesin.

The feed nozzle is preferably a microbubble generating nozzle.

The gas is preferably ozone.

The liquid is preferably water.

It is preferable that the transfer pump is a diaphragm pump, and

a diaphragm of the diaphragm pump is made of a fluororesin.

It is preferable that an injection pipe is provided inside the dissolution tank, and

an injection hole for injecting the liquid sent by the positive displacement pump toward an inner wall of the dissolution tank is provided in an outer periphery of the injection pipe.

It is preferable that two injection holes are provided in the outer periphery of the injection pipe, and

the two injection holes are provided in positions separated by approximately 90 degrees from each other in the outer periphery of the injection pipe.

It is preferable that a gas release valve for releasing the gas accumulated inside the dissolution tank to outside is provided at an upper portion of the dissolution tank.

It is preferable that the cleaning apparatus includes:

a level gauge for measuring a height of a level of the liquid stored in the dissolution tank; and

control means for controlling the gas release valve so that the height of the liquid level measured by the level gauge becomes constant.

It is preferable that the control means controls the gas release valve so that the height of the liquid level measured by the level gauge becomes 1 mm or more and 20 mm or less from an upper base of the dissolution tank.

It is preferable that the workpiece is s a semiconductor wafer, a liquid crystal substrate, or a solar cell substrate.

Effect of the Invention

The present invention can provide a cleaning apparatus capable of obtaining a cleaning liquid having a high degree of cleanliness.

MODE FOR CARRYING OUT THE INVENTION

FIG. 1is a flow diagram of a cleaning apparatus according to a first embodiment.FIG. 2is a plan view of the cleaning apparatus.FIG. 3is a front view of the cleaning apparatus.FIG. 4is a side view of the cleaning apparatus.

As shown inFIGS. 1 to 4, the cleaning apparatus10includes a dissolution tank20for dissolving ozone (O3) in water, a transfer pump30for sending ozone (O3) together with water to the dissolution tank20, and a feed nozzle40for supplying the water stored in the dissolution tank20to a workpiece W. Those portions of the dissolution tank20, the transfer pump30and the feed nozzle40which come in contact with water are made of a fluororesin.

The dissolution tank20is a cylindrical sealed tank which is formed of a steel material such as stainless steel, and is configured to be capable of holding a high pressure therein. All portions of the dissolution tank20which come in contact with water are made of a fluororesin. Specifically, the entire inner surface of the dissolution tank20is formed of a fluororesin, or is lined with a fluororesin. Polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy fluorocarbon resin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE) and the like are available as the fluororesin. Among them, polytetrafluoroethylene (PTFE) is preferred.

The transfer pump30is a positive displacement pump, not a non-positive displacement pump such as a centrifugal pump. The positive displacement pump increases the pressure of a liquid in its space by changing the volume of the space. There are a reciprocating positive displacement pump and a rotating positive displacement pump, for example, a diaphragm pump, a gear pump, a piston pump, and a plunger pump. Although either type of positive displacement pump may be used as the transfer pump30in the present invention, it is preferable to use the diaphragm pump.

Portion of the transfer pump30which comes in contact with water is formed of a fluororesin. Specifically, at least an inner surface of a casing of the transfer pump30is lined with a fluororesin. Alternatively, the casing itself is formed of a fluororesin. An actuating member disposed inside the casing is also made of a fluororesin. When the transfer pump30is the diaphragm pump, for example, the diaphragm is formed of a fluororesin. When the transfer pump30is the gear pump, the gear is formed of a fluororesin. When the transfer pump30is the piston pump, the piston is formed of a fluororesin. When the transfer pump30is the plunger pump, the plunger is formed of a fluororesin. Although any one of the aforementioned fluororesins can be used as the fluororesin, it is preferable to use polytetrafluoroethylene (PTFE).

The feeding nozzle40serves to supply the workpiece W with cleaning water stored in the dissolution tank20. In this embodiment, a microbubble generating nozzle is used as the feed nozzle40. The use of the microbubble generating nozzle can cause bubbles with a particle size of, for example, 1 to 50 μm (microbubbles) to be generated in the cleaning water in which ozone is dissolved. The feed nozzle40may be, for example, an injection nozzle capable of injecting water stored in the dissolution tank20to a workpiece W. The details of the feed nozzle40will be given later.

Using the feed nozzle40makes it possible to generate microbubbles in the cleaning water in which ozone is dissolved. In this specification, microbubbles refer to, for example, bubbles with a particle size of 1 μm or larger and 50 μm or smaller. The number of microbubbles in the water may be measured by, for example, the liquid particle counter “LiQuilaz-E20” manufactured by Particle Measuring Systems Co. It is preferable to use a liquid particle counter of a light-shielding type in measuring the number of microbubbles in a liquid.

All bubbles generated by the feed nozzle40need not be microbubbles. Microbubbles may be, preferably, 30% or more of bubbles generated by the feed nozzle40, more preferably, 50% or more of the bubbles, more preferably, 70% or more of the bubbles, and most preferably, 90% or more of the bubbles.

Next, the overall configuration of the cleaning apparatus10is described in detail.

As shown inFIGS. 1 to 4, the suction port of the transfer pump30is coupled via a pipe14to a pure water tank12. The transfer pump30is capable of sucking pure water stored in the pure water tank12, and feeding the pure water to the dissolution tank20.

The suction port of the transfer pump30is also coupled to an ozone generator (not shown) via a pipe15branched from the pipe14. The transfer pump30can suck the ozone generated by the ozone generator via the pipe15. That is, the transfer pump30can suck the ozone together with pure water via the pipe14and the pipe15. The sucked pure water and ozone are mixed inside the transfer pump30, and then fed to the dissolution tank20.

An end of the pipe14which is located on opposite to the other end connected to the transfer pump30is inserted into the pure water in the pure water tank12. This end of the pipe14that is inserted into the pure water is attached with a cup16that is largely opened, on one side, in a trumpet shape. The ozone gas blown into the pure water can be collected by this cup16. That is, the transfer pump30can not only suck the ozone gas through the pipe15, but also suck the ozone gas blown into the pure water tank12through the pipe17. The cup16is preferably formed of a fluororesin.

An injection pipe21for injecting the water fed by the transfer pump30toward the inner wall of the dissolution tank20is provided inside the dissolution tank20. The injection pipe21is disposed almost vertically, and extends substantially over the entire area from the lower base of the dissolution tank20to the upper base thereof. The upper end of the injection pipe21is closed. Two injection holes22a,22bare provided at a portion which is slightly lower than the upper end of the injection pipe21. The two injection holes22a,22bwill be described later in detail. The injection pipe21is preferably formed of a fluororesin.

A discharge port of the transfer pump30is coupled to the lower end of the injection pipe21via a pipe18. The pure water and ozone gas that are pressurized by the transfer pump30are supplied to the lower end of the pipe21, and then injected toward the inner wall of the dissolution tank20through the two injection holes22a,22bformed in the upper portion of the injection pipe21. Note that, in normal operation of the cleaning apparatus10, the two injection holes22a,22bare positioned below a liquid level20aof the dissolution tank20.

A level gauge23capable of measuring the height of the liquid level20aof the water stored in the dissolution tank is provided inside the dissolution tank20. Although any type of level gauge may be used as the level gauge23, a pulse guide type liquid level gauge is used in this embodiment. Preferably, that portion of the level gauge23which come in contact with water is either formed of a fluororesin, or lined with a fluororesin. Specifically, a contact (probe) of the level gauge23which comes in contact with water is preferably covered with a fluororesin.

As shown inFIG. 5, the level gauge23is provided at a center portion of the dissolution tank20, and the injection pipe21is disposed at a position near the wall surface of the dissolution tank20. The two injection holes22a,22bare provided in the outer periphery of the injection pipe21having substantially a circular cross section at positions separated by approximately 90 degrees in the circumferential direction. That is, the size of the central angle obtained by connecting the center of the injection pipe21to the two injection holes22a,22bis substantially 90 degrees. For example, the two injection holes22a,22bare provided at positions separated by 70 degrees to 110 degrees in the circumferential direction, preferably, 80 degrees to 100 degrees, and more preferably, 85 degrees to 95 degrees. The water and ozone gas are injected from the two injection holes22a,22b, in directions different from each other by about 90 degrees. The injection of the water and ozone gas in directions different from each other by about 90 degrees in this way produces, inside the dissolution tank20, at least two swirling flows rotating in the reverse directions. This promotes the contact and stirring of the water and the ozone gas, so that more ozone gas can be dissolved in water. Although an example where the two injection holes22a,22bare provided in the injection pipe21is illustrated inFIG. 5, one injection hole or three or more injection holes may be provided in the injection pipe21.

In addition, the water and ozone gas are injected from the injection pipe21in the direction opposite to the liquid level gauge23. That is, inFIG. 5, the injection pipe21is separated into two areas by a line that is perpendicular to a line connecting the center point of the level gauge23to the center point of the injection pipe21, and passes through the center point of the injection pipe21. An injection hole is not provided in that one of the two regions which is closer to the level gauge23, thereby preventing the water and ozone gas from hitting the level gauge23which otherwise may influence the measurements of the level gauge23.

A gas release valve24for releasing the ozone gas accumulated above the liquid level20ain the dissolution tank20to the outside is provided at the upper portion of the dissolution tank20. It is preferable to use an air actuated valve as the gas release valve24. When a solenoid valve is used, the metal portion of the solenoid valve may be corroded, so that a foreign matter may be mixed in the cleaning water in the dissolution tank20. Pipes14,15,17,18,25for connecting a plurality of devices included in the cleaning apparatus10are not provided with valves. This is because, in light of the configuration of the cleaning apparatus10, the use of air actuated valves in those pipes does not have a good technical significance, or the use of an electromagnetic valve may face the aforementioned probable mixture of a foreign matter.

As the gas release valve24, a regulating valve capable of regulating the flow rate of the gas may be used, or an on-off valve that can change over the degree of opening only between 100% and 0% may be used.

As the gas release valve24, for example, a ball valve, globe valve, a diaphragm valve or the like may be used; it is preferable to use the diaphragm valve among those valves. Further, as the gas release valve24, it is preferable to use a valve whose pipe part is formed of a fluororesin.

As shown inFIG. 1, the cleaning apparatus10includes a control means60. The control means60is electrically coupled to the gas release valve24and the liquid level gauge23. The control means60can control the gas release valve24so that the height of the liquid level20awhich is measured by the level gauge23becomes constant. Specifically, the control unit60compares the height of the liquid level20ameasured by the level gauge23with a preset target value, and controls the gas release valve24on the basis of the comparison result. A known control device capable of controlling an actuator, such as a valve, may be used as the control unit60; for example, a sequencer may be used.

For example, when the height of the liquid level20ameasured by the level gauge23is much higher than the target value (HH), the gas release valve24is fully closed (the degree of opening being 0%). When the liquid level20ameasured by the level gauge23is higher than the target value (H), the gas release valve24is closed to some extent (the degree of opening being 30%). When the height of the liquid level20ameasured by the level gauge23is lower than the target value (L), the gas release valve24is opened to some extent (the degree of opening being 70%). When the height of the liquid level20ameasured by the level gauge23is significantly lower than the target value (LL), the gas release valve24is fully opened (the degree of opening being 100%).

Although an example of a method of controlling the gas release valve24has been illustrated, the gas release valve24may be controlled by other methods.

As shown inFIG. 1, the dissolution tank20is coupled to the feed nozzle40via the pipe25. Since the pressure inside the dissolution tank20is set high (for example, 0.4 MPa) by the transfer pump30, the cleaning water is swiftly discharged from the feed nozzle40. The pressure inside the dissolution tank20may be adjusted by the discharge pressure of the transfer pump30. Alternatively, the pressure inside the dissolution tank20may also be adjusted by opening or closing the gas release valve24.

The pipes14,15,17,18,25for connecting a plurality of devices included in the cleaning apparatus10are formed of a fluororesin. Although any one of the aforementioned fluororesins can be used as the fluororesin, it is preferable to use polytetrafluoroethylene (PTFE).

FIG. 6is a cross-sectional view of the feed nozzle40.

As shown inFIG. 6, the feed nozzle40includes a cylindrical outer member42having one end closed by a wall portion42aand an other end open, and a cylindrical inner member44having one end closed by a wall portion44aand an other end open. The inner diameter of the outer member42is larger than the outer diameter of the inner member44. The inner member44is disposed inside the outer member42in such a way that their axial centers are aligned with each other.

The feed nozzle40includes a connector46formed in substantially a cylindrical shape. One end46aof the connector46is connected to the pipe25having one end connected to the dissolution tank20. A cylindrical recess46cis formed at an other end46bof the connector46. That end of the inner member44which is open is fitted in this recess46c. That end of the outer member42which is open is fitted in the outer periphery of the end46bof the connector46. The outer member42, the inner member44and the connector46are assembled integrally with one another by screw-in or the like.

An orifice48, three perforated plates50ato50c, and seven spacers52ato52gare disposed inside the inner member44. These members are disposed in the order of the orifice48, the spacer52a, the spacer52b, the spacer52c, the spacer52d, the perforated plate50a, the spacer52e, the perforated plate50b, the spacer52f, the perforated plates50c, and the spacer52gfrom the upstream side.

Although an example where three perforated plates50ato50care disposed is illustrated, the number of perforated plates is not limited to three. For example, the number of perforated plates may be adjusted within the range of one to six in accordance with the water quality. Bubbles suitable for an intended work may be generated by adjusting the number of perforated plates.

The orifice48is a circular plate having a predetermined thickness, holes are provided in the center.

The spacer52a,52e,52fis a circular plate having a predetermined thickness (e.g. 2.0 mm).

The spacer52b,52c,52d,52gis a circular plate having a predetermined thickness (e.g. 1.0 mm).

The perforated plate50a,50cis a circular plate having a plurality of small holes (for example, 1.0 mmϕ) formed therein.

The perforated plate50bis a circular plate having a plurality of small holes (for example, 0.5 mmϕ) formed therein.

The spacer is preferably placed between the perforated plates. It is preferable to provide a space of at least 0.5 mm between the perforated plates. A space of 3 mm to 5 mm may be provided between the perforated plate plates. The provision of a space between the perforated plates makes it possible to generate bubbles efficiently.

Those parts constituting the feed nozzle40are preferably formed of a fluororesin. That is, the outer member42, the inner member44, the connector46, the three perforated plates50ato50c, and the seven spacers52ato52gare preferably formed of a fluororesin. Although any one of the aforementioned fluororesins can be used as the fluororesin, it is preferable to use polytetrafluoroethylene (PTFE).

A first pressure relief chamber54is formed between the spacer52gand the wall portion44aof the inner member44, and a plurality of through holes56are formed in the peripheral wall of the first pressure relief chamber54. A second pressure relief chamber57is formed between the inner wall surface of the outer member42and the outer wall surface of the inner member44. A substantially circular nozzle hole58for supplying water containing microbubbles is opened in the wall portion42aof the outer member42.

The following describes the mechanism of generating microbubbles by means of the feed nozzle40.

The water that is supplied from the dissolution tank20via the pipe25passes through the interior of the connector46, and then passes through the orifice48. Part of the ozone dissolved in the water becomes air bubbles due to the differential pressure between the upstream and downstream of the orifice48, thereby generating the bubbles.

The water passes through the orifice48, and then passes through the perforated plate50a, perforated plate50b, and a perforated plate50c. A plurality of small holes are opened in these perforated plates. The sizes of the small holes are 1.0 mmϕ, 0.5 mmϕ, and 1.0 mmϕ, respectively, from the upstream side. That is, the sizes of the small holes of the adjacent perforated plates are different from each other.

As water passes through the three perforated plate50ato50c, an extremely complex turbulent flow is generated in the water. Because this turbulence shears the bubbles finely, the particle size of the bubbles is reduced.

After passing through the three perforated plates50ato50c, the water then flows into the first pressure relief chamber54. The water that has flowed into the first pressure relief chamber54then passes through the through hole56formed in a side wall of the first pressure relief chamber54. At this time, the traveling direction of the water changes 90 degrees, so that the bubbles are further sheared by the turbulence.

The water passes through the through hole56, and hits the inner wall surface of the outer member42. As the water hits the inner wall surface of the outer member42, the particle size of the bubbles becomes smaller.

After hitting the inner wall surface of the outer member42, the water flows into the second pressure relief chamber57. At this time, the traveling direction of the water changes 90 degrees, the bubbles are further sheared by the turbulence.

The water that has flowed into the second pressure relief chamber57is supplied from the nozzle hole58toward a workpiece W. The water supplied from the nozzle hole58includes bubbles (microbubble) whose particle size is reduced to 1 to 50 μm by the mechanism described above.

The action and effects of the cleaning apparatus10are described next.

The conventional ozone water production apparatus uses metals for those portions of a tank, a pipe, a valve and a pump or the like which come into contact with a liquid. Accordingly, sometimes metal ions are eluted into pure water, or a foreign matter produced by corrosion of the metals is mixed into wash water.

According to the cleaning apparatus10of the present embodiment, those portions of the dissolution tank20, the transfer pump30, and the feed nozzle40which come in contact with water are formed of a fluororesin. This prevents the elution of metal ions and mixing of a foreign matter, thus ensuring that cleaning water with a higher degree of cleanliness can be obtained.

In addition, those portions of the pipes14,15,17,18, and25, the cup16, the injection pipe21, and the level gauge23which come in contact with water are also formed of a fluororesin. This prevents the contamination of cleaning water with a metal more effectively.

Further, when the transfer pump30is a diaphragm pump, the diaphragm is formed of a fluororesin. This further prevents the contamination of cleaning water with a metal effectively.

The transfer pump30feeds the pure water pumped up from the pure water tank12to the dissolution tank20. The internal pressure of the dissolution tank20is kept high. Specifically, the pressure in the space20babove the liquid level20aof the dissolution tank20is kept at 0.2 to 0.6 MPa, preferably, at 0.3 to 0.5 MPa, and, more preferably, at 0.4 MPa. Accordingly, a larger amount of ozone gas may be dissolved in water in the dissolution tank20. Further, a larger amount of microbubbles may be generated by the feed nozzle40.

In order to increase the concentration of ozone in the cleaning water, an excess amount of ozone gas needs to be fed into the dissolution tank20by the transfer pump30. Therefore, the ozone gas released from the water is accumulated in the space20babove the liquid level20aof the dissolution tank20.

When transfer pump30is a diaphragm pump, for example, the pressure of the water that is transported by the diaphragm pump fluctuates (pulsates). In this case, the amount of the cleaning water supplied from the feed nozzle40is not constant, uneven cleaning undesirably occurs when the cleaning water is used to clean semiconductor wafers or the like. Therefore, it has not been thought possible to use a positive displacement pump (diaphragm pump) as a pump in the conventional ozone water production apparatus for feeding water and ozone into the tank.

The cleaning apparatus10according to the present embodiment secures the space20babove the liquid level20aof the dissolution tank20, so that the space20bcan absorb the pressure fluctuation caused by the transfer pump30. Therefore, even in the case of using a positive displacement pump as a pump for feeding water and ozone, the amount of cleaning water supplied from the feed nozzle40is kept constant.

The height of the liquid level20aof the dissolution tank20is kept at 1 mm or more and 100 mm or less, preferably, at 1 mm or more and 70 mm or less, more preferably, at 1 mm or more and 50 mm or less, more preferably, at 1 mm or more and 30 mm or less, and, most preferably, at 1 mm or more and 20 mm or less, from the upper base20cof the dissolution tank20. When the height of the liquid level20ais above the position which is 1 mm from the upper base20c, the volume of the space20bis too small to sufficiently absorb the pressure fluctuation caused by the transfer pump30. When the height of the liquid level20ais below the position which is 100 mm from the upper base20c, the volume of the space20bis too large so that it is difficult to control the flow rate of the cleaning water supplied from the feed nozzle40at a constant rate.

Accordingly, it is preferable that the control means60should control the gas release valve24in such a way that the height of the liquid level20awhich is measured by the level gauge23becomes 1 mm or more and 100 mm or less, preferably, 1 mm or more and 70 mm or less, more preferably, 1 mm or more and 50 mm or less, more preferably, 1 mm or more and 30 mm or less, and, most preferably, 1 mm or more and 20 mm or less, from the upper base20cof the dissolution tank20. How to control the gas release valve24to make the height of the liquid level20aconstant is as described above.

The cleaning apparatus10according to the present embodiment can supply cleaning water with an extremely high degree of cleanliness to a workpiece W. Microbubbles which are included in the cleaning water will remain for a long period of time in the cleaning water. The cleaning effect of ozone and microbubbles is enormous to enable an extremely high degree of cleaning of the workpiece W.

FIG. 7is a flow diagram of a cleaning apparatus according to a second embodiment of the present invention. InFIG. 7, the same reference numerals are given to the same elements as those of the first embodiment.

The cleaning apparatus11illustrated inFIG. 7includes a return pipe26for returning cleaning water stored in the dissolution tank20to the pure water tank12. An end of the return pipe26is inserted into the pure water stored in the pure water tank12. A feed nozzle41for generating the microbubbles is attached to that end of the return pipe26which is inserted into the pure water. The return pipe26and the feed nozzle41are formed of a fluororesin.

According to the cleaning apparatus11illustrated inFIG. 7, the cleaning water stored in the dissolution tank20can be returned to the pure water tank12via the return pipe26. This makes it possible to circulate the cleaning water between the dissolution tank20and the pure water tank12until the concentration of a gas in the cleaning water or the density of the microbubbles in the cleaning water reaches a predetermined value.

As illustrated inFIG. 7, a temperature control device27for controlling the temperature of the cleaning water may be provided in a midway of the pipe25. The temperature control device27can control the temperature of the cleaning water that is fed to the feed nozzle40at a given temperature. For example, it is possible to heat (or cool) the cleaning water which is fed to the feed nozzle40to a temperature effective to clean the workpiece W.

The cleaning apparatus10cleans a workpiece W with microbubbles ozone water. Examples of the workpiece W include a semiconductor wafer, a liquid crystal substrate, a solar cell substrate, a glass substrate, and a mask blank, which require a high degree of cleanliness, but are not limited thereto.

The cleaning apparatus10according to the present invention may be applied to, for example, a medical field (visceral washing or the like) in addition to cleaning of semiconductor wafers.

Although the gas to be dissolved in water is illustrated to be ozone in the above example, the present invention may also be applied when other gases are dissolved in water. For example, the present invention may also be applied when the gas to be dissolved in water is oxygen (O2), hydrogen peroxide (H2O2), nitrogen (N2), hydrogen (H2) or the like. Further, the present invention may also be applied when a plurality of types of gases are dissolved in water. For example, the present invention may also be applied when carbon dioxide and ozone even are dissolved in water. When carbon dioxide and ozone are dissolved in water, the time of dissolution of ozone in ozone water can be extended.

Although the liquid in which a gas is dissolved is illustrated to be water in the above example, the present invention may also be applied to other liquids. For example, the present invention may also be applied in case of liquids such as an organic solvent, aqueous sulfuric acid, aqueous ammonia, and a slurry.

Although a single feed nozzle40is provided in the cleaning apparatus10in the above example, two or more feed nozzles40may be provided.

Although a single cleaning apparatus10alone is provided in the above example, a plurality of cleaning apparatuses10may be provided in parallel.

FIG. 8is a flow diagram of a cleaning apparatus according to a third embodiment of the present invention. InFIG. 8, the same reference numerals are given to the same elements as those of the first embodiment or the second embodiment.

The cleaning apparatus100illustrated inFIG. 8includes a return pipe104for returning ozone water (cleaning water) stored in the dissolution tank20to a circulation tank102. The ozone water stored in the dissolution tank20can be circulated between the dissolution tank20and the circulation tank102through the return pipe104. The circulation of the ozone water between the dissolution tank20and the circulation tank102can increase the concentration of the ozone water in the dissolution tank20. Note that a pure-water supply pipe106for supplying pure water into the circulation tank102is connected to the circulation tank102.

The cleaning apparatus100illustrated inFIG. 8includes an ozone producing apparatus105. The ozone water stored in the circulation tank102is fed into a lower portion of the dissolution tank20by the transfer pump30. The ozone (O3) that is produced by the ozone producing apparatus105is fed together with the ozone water stored in the circulation tank102to the lower portion of the dissolution tank20by the transfer pump30. Accordingly, the concentration of the ozone water in the dissolution tank20can be increased further.

The cleaning apparatus100illustrated inFIG. 8includes a heater108for heating the ozone water. The heater108is provided at a position immediately before the feed nozzle40. That is, the heater108can heat the ozone water produced in the dissolution tank20just before the ozone water is supplied to the workpiece W. This makes it possible to suppress a reduction in the concentration of ozone water produced in dissolution tank20, which otherwise is caused by heating by the heater108, before the ozone water is supplied to the workpiece W.

Heating the ozone water with the heater108can further enhance the cleaning effect of the ozone water. The temperature of heating the ozone water with the heater108is, for example, 30° C. or higher and 80° C. or lower, preferably, 40° C. or higher and 70° C. or lower, and, more preferably, 50° C. or higher and 60° C. or lower. Any type of heater may be used as the heater108for heating ozone water. For example, the “Super Clean Heater” manufactured by Techno Vision Ltd. may be used as the heater108for heating ozone water.

The cleaning apparatus100illustrated inFIG. 8includes the feed nozzle40for supplying cleaning water (ozone water) to a workpiece W. In the third embodiment, the feed nozzle40is disposed in such a way that the direction of ejection of the ozone water is a transverse direction (horizontal direction). The transverse arrangement of the feed nozzle40can prevent the ozone water remaining in the feed nozzle40from falling over the workpiece W when the supply of the ozone water is stopped. This makes it possible to precisely control the duration of supplying the ozone water to the workpiece W. From the viewpoint of preventing the ozone water remaining in the feed nozzle40from falling over the workpiece W, the direction of the ozone water ejected from the feed nozzle40may be upward (vertical direction), or at an any angle between the transverse direction (horizontal direction) and the upward direction (vertical direction). This may be achieved by aligning the orientation of the feed nozzle40with the direction of ejection of the ozone water. A pipe for vacuum suction of the ozone water remaining inside the feed nozzle40may be provided on a side of the feed nozzle40. The suction of the ozone water remaining inside the feed nozzle40makes it possible to control the duration of supplying the ozone water to the workpiece W more precisely.

The cleaning apparatus according to the present invention may be used to clean semiconductor substrates. For example, the cleaning apparatus according to the present invention may be applied to a single wafer cleaning apparatus for cleaning semiconductor substrates one by one. As illustrated inFIG. 9, the cleaning apparatus according to the present invention may also be applied to a cleaning apparatus of a type which immerses a plurality of semiconductor substrates into the cleaning tank110at once (dipping type cleaning apparatus).

DESCRIPTION OF REFERENCE NUMERALS