Abstract:
A valve for redirecting flow in a supercritical fluid or other high pressure processing system is disclosed. In high pressure supercritical carbon dioxide (SCCO2) equipment for semiconductor wafer processing, a major hurtle in providing clean equipment and clean wafers. A clean flow diverting valve is provided having no grease or other contaminants, and having no rubbing seal surfaces, but rather incorporates a magnetically coupled valve actuator to move a ball or other valve seat for diverting flow between a common port and alternative switched ports in a non-rubbing, non-contact manner. The valve is useful in semiconductor wafer high pressure processing tools for redirecting flow from a common inlet to alternative outlets or for admitting flow from alternative inlets to a common outlet.

Description:
This application is related to co-pending U.S. patent application Ser. No. 10/955,326, entitled “Method and System for Controlling a Velocity Field of a Supercritical Fluid in a Processing System”, filed on Sep. 30, 2004. The entire content of this application is herein incorporated by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a method and apparatus for flowing a fluid in a processing system and, more particularly, to the diverting of processing fluid, for example of a supercritical processing fluid, and valve structure useful therefor. 
   DESCRIPTION OF RELATED ART 
   During the fabrication of semiconductor devices for integrated circuits (ICs), a critical processing requirement for processing semiconductor devices is cleanliness. The processing of semiconductor devices includes vacuum processing, such as etch and deposition processes whereby material is removed from or added to a substrate surface, as well as atmospheric processing, such as wet cleaning whereby contaminants or residue accumulated during processing are removed. For example, the removal of residue, such as photoresist (serving as a light-sensitive mask for etching), post-etch residue, and post-ash residue subsequent to the etching of features, such as trenches or vias, can utilize plasma ashing with an oxygen plasma followed by wet cleaning. 
   Other critical processing requirements for the processing of semiconductor devices include substrate throughput and reliability. Production processing of semiconductor devices in a semiconductor fabrication facility requires a large capital outlay for processing equipment. In order to recover these expenses and generate sufficient income from the fabrication facility, the processing equipment requires a specific substrate throughput and a reliable process in order to ensure the achievement of this throughput. 
   Until recently, plasma ashing and wet cleaning were found to be sufficient for removing residue and contaminants accumulated during semiconductor processing. However, recent advancements for ICs include a reduction in the critical dimension for etched features below a feature dimension acceptable for wet cleaning, such as a feature dimension below 45 to 65 nanometers, as well as the introduction of new materials, such as low dielectric constant (low-k) materials, which are susceptible to damage during plasma ashing. 
   Therefore, at present, interest has developed for the replacement of plasma ashing and wet cleaning. One interest includes the development of dry cleaning systems utilizing a supercritical fluid as a carrier for a solvent, or other residue removing composition. Post-etch and post-ash cleaning are examples of such systems. Other interests include other processes and applications that can benefit from the properties of supercritical fluids, particularly of substrates having features with a dimension of 65 nanometers (nm), or 45 nm, or smaller. Such processes and applications may include restoring low dielectric films after etching, sealing porous films, drying of applied films, depositing materials, as well as other processes and applications. 
   Certain challenges occur when attempting to process silicon wafers under high pressure. One such issue is how to switch flow direction or path within the equipment without generating particles. Typically, ball valves have been used for high flow rate applications, but these have many cleanliness issues including rubbing surfaces and trapped internal volumes. Plug valves have similar rubbing issues. Bellows valves, even if rated to high enough pressure, have many convoluted surfaces which can trap and release particles. Diaphragm valves have recently been the valve type of choice, due to their relatively clean construction, but flow rates are typically less than one-tenth that of comparable ball valves. 
   Typical pressures encountered in SCCO2 processing are a minimum of 1,031 psi, but 3,000 psi is not uncommon, and upwards of 10,000 psi has been reported in the literature. Some equipment configurations may require flow diversion, but not total shut-off. Within a high pressure tool, the differences within different sections of the tool may be quite low, maybe 10 to 100 psi. Internal pressure differences can exceed these pressures, but typically inline filters will limit the available pressure gradient possible within the tool. 
   Accordingly, there is a need for improved valving in supercritical fluid processing systems and other high pressure processing systems that will overcome the problems discussed above and more general problems of the prior art. 
   SUMMARY OF THE INVENTION 
   One object of the present invention is to reduce or eliminate any or all of the above-described problems. 
   Another object of the present invention is to provide a valve for switching high pressure fluid, particularly supercritical fluid, and more particularly supercritical carbon dioxide, in a semiconductor wafer processing system while generating fewer particulates than in prior systems. 
   A further object of the present invention is to provide a flow diversion valve having a moveable element and actuating the element without contact therewith. 
   According to one embodiment of the invention, a method and apparatus are provided incorporating magnetic coupling for diverting flow of high pressure processing fluid, particularly supercritical processing fluid, in a non-rubbing, non-contact manner in semiconductor wafer high pressure processing tools. 
   According to one embodiment of the invention, a valve for switching the flow of high pressure processing fluid between a common port and alternative switched ports in a semiconductor processing system is provided in which the valve comprises a valve body having a cavity therein, a common port coupled to the cavity and at least two switched ports coupled to the cavity. The valve element is moveable in the cavity between alternative positions. The alternative positions include a first position and a second position. At the first position, the element blocks flow of the high pressure fluid between the common port and a first one of the switched ports and permits flow of the high pressure fluid between the common port and a second one of the switched ports. At the second position, the element blocks flow of the high pressure fluid between the common port and the second one of the switched ports and permits flow of the high pressure fluid between the common port and the first one of the switched ports. At least two actuators are mounted on said valve body and magnetically coupled to said valve element. When activated in response to a control signal, a first actuator moves the element to the first position. When activated, the second element moves the element to the second position. 
   According to other embodiments of the invention, a high pressure fluid processing system is provided for processing semiconductor wafers. The system comprises a processing chamber, a high pressure fluid flow system coupled to the chamber and operative to flow high pressure processing fluid through the chamber and across a semiconductor wafer supported in the chamber, and a flow diverting valve and a controller. The flow diverting valve has a common port, at least two switched ports and a valve element moveable within the valve between alternative positions, including a first position at which flow of the high pressure fluid is directed between the common port and a first one of the switched ports and a second position at which flow of the high pressure fluid is directed between the common port and a second one of the switched ports. The valve has at least one actuator mounted thereon and magnetically coupled to said valve element. The actuator is operable, when activated in response to a control signal, to move the valve element between the alternative positions. The controller selectively communicates control signals to said actuators to cause the valve to switch. 
   According to another embodiment of the invention, a method of diverting the flow of a high pressure fluid processing fluid is provided in a high pressure fluid system for processing semiconductor wafers. The method comprises magnetically moving a valve element in a valve body to switch flow of the high pressure fluid between a common port and alternative switched ports and alternatively flowing the fluid in the processing system in through the valve in accordance with the position of the valve element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  presents a simplified schematic representation of a high pressure processing system in accordance with one embodiment of the invention; 
       FIG. 1A  is a detailed diagram of one embodiment of the recirculation system portion marked  1 A in  FIG. 1 ; 
       FIG. 2  is an enlarged diagram of a portion of the chamber of the system of  FIG. 1  according to certain embodiments of the invention; 
       FIG. 3  is a perspective view of one embodiment of a diverter valve of the systems of  FIG. 1A  and  FIG. 2 ; 
       FIG. 4  is a cross sectional view of the valve of  FIG. 3 ; 
       FIG. 5  is a disassembled view of a portion of the valve of  FIGS. 3 and 4 ; 
       FIG. 6  is a sectional view of a portion of the valve of  FIGS. 3 and 4 . 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   In the following description, to facilitate a thorough understanding of the invention and for purposes of explanation and not limitation, specific details are set forth, such as a particular geometry of the high pressure processing system and various descriptions of the internal members. However, it should be understood that the invention may be practiced with other embodiments that depart from these specific details. 
   Nonetheless, it should be appreciated that, contained within the description are features which, notwithstanding the inventive nature of the general concepts being explained, are also of an inventive nature. 
   Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 1  illustrates a high pressure processing system  100  according to an embodiment of the invention. In the illustrated embodiment, high pressure processing system  100  comprises processing elements that include a processing chamber  110 , a fluid flow system  120 , a process chemistry supply system  130 , a high pressure fluid supply system  140 , and a controller  150 , all of which are configured to process substrate  105 . The controller  150  can be coupled to the processing chamber  110 , the fluid flow system  120 , the process chemistry supply system  130 , and the high pressure fluid supply system  140 . Alternately, or in addition, controller  150  can be coupled to a one or more additional controllers/computers (not shown), and controller  150  can obtain setup and/or configuration information from an additional controller/computer. 
   In  FIG. 1 , singular processing elements ( 110 ,  120 ,  130 ,  140 , and  150 ) are shown, but this is not required for the invention. The high pressure processing system  100  can comprise any number of processing elements having any number of controllers associated with them in addition to independent processing elements. 
   The controller  150  can be used to configure any number of processing elements ( 110 ,  120 ,  130 , and  140 ), and the controller  150  can collect, provide, process, store, and display data from processing elements. The controller  150  can comprise a number of applications for controlling one or more of the processing elements. For example, controller  150  can include a graphic user interface (GUI) component (not shown), that can provide easy to use interfaces that enable a user to monitor and/or control one or more processing elements. 
   Referring still to  FIG. 1 , the fluid flow system  120  is configured to flow fluid and chemistry from the supplies  130  and  140  through the processing chamber  110  via a flow line  122 . The fluid flow system  120  is illustrated as a recirculation system through which the fluid and chemistry recirculate from and back to the processing chamber  110 . This recirculation is most likely to be the preferred configuration for many applications, but this is not necessary to the invention. Fluids, particularly inexpensive fluids, can be passed through the processing chamber once and then discarded, which might be more efficient than reconditioning them for re-entry into the processing chamber. Accordingly, while the fluid flow system is described as a recirculating system in the exemplary embodiments, a non-recirculating system may, in some cases, be substituted. This fluid flow system or recirculation system  120  can include one or more valves for regulating the flow of a processing solution through the recirculation system  120  and through the processing chamber  110 . The recirculation system  120  can comprise any number of back-flow valves, filters, pumps, and/or heaters for maintaining a specified temperature, pressure or both for the processing solution and flowing the process solution through the recirculation system  120  and through the processing chamber  110 . Furthermore, any one of the many components provided within the fluid flow system  120  may be heated to a temperature consistent with the specified process temperature. 
   Referring still to  FIG. 1 , the processing system  100  can comprise high pressure fluid supply system  140 . The high pressure fluid supply system  140  can be coupled to the recirculation system  120 , but this is not required. In alternate embodiments, high pressure fluid supply system supply system  140  can be configured differently and coupled differently. For example, the fluid supply system  140  can be coupled directly to the processing chamber  110 . The high pressure fluid supply system  140  can include a supercritical fluid supply system. A supercritical fluid as referred to herein is a fluid that is in a supercritical state, which is that state that exists when the fluid is maintained at or above the critical pressure and at or above the critical temperature on its phase diagram. In such a supercritical state, the fluid possesses certain properties, one of which is the substantial absence of surface tension. Accordingly, a supercritical fluid supply system, as referred to herein, is one that delivers to a processing chamber a fluid that assumes a supercritical state at the pressure and temperature at which the processing chamber is being controlled. Furthermore, it is only necessary that at least at or near the critical point the fluid is in substantially a supercritical state at which its properties are sufficient, and exist long enough, to realize their advantages in the process being performed. Carbon dioxide, for example, is a supercritical fluid when maintained at or above a pressure of about 1,070 Psi at a temperature of 31 degrees C. 
   As described above, the fluid supply system  140  can include a supercritical fluid supply system, which can be a carbon dioxide supply system. For example, the fluid supply system  140  can be configured to introduce a high pressure fluid having a pressure substantially near the critical pressure for the fluid. Additionally, the fluid supply system  140  can be configured to introduce a supercritical fluid, such as carbon dioxide in a supercritical state. Additionally, for example, the fluid supply system  140  can be configured to introduce a supercritical fluid, such as supercritical carbon dioxide, at a pressure ranging from approximately the critical pressure of carbon dioxide to 10,000 Psi. Examples of other supercritical fluid species useful in the broad practice of the invention include, but are not limited to, carbon dioxide (as described above), oxygen, argon, krypton, xenon, ammonia, methane, methanol, dimethyl ketone, hydrogen, and sulfur hexafluoride. The fluid supply system can, for example, comprise a carbon dioxide source (not shown) and a plurality of flow control elements (not shown) for generating a supercritical fluid. For example, the carbon dioxide source can include a CO2 feed system, and the flow control elements can include supply lines, valves, filters, pumps, and heaters. The fluid supply system  140  can comprise an inlet valve (not shown) that is configured to open and close to allow or prevent the stream of supercritical carbon dioxide from flowing into the processing chamber  110 . For example, controller  150  can be used to determine fluid parameters such as pressure, temperature, process time, and flow rate. 
   Referring still to  FIG. 1 , the process chemistry supply system  130  is coupled to the recirculation system  120 , but this is not required for the invention. In alternate embodiments, the process chemistry supply system  130  can be configured differently, and can be coupled to different elements in the processing system  100 . The process chemistry is introduced by the process chemistry supply system  130  into the fluid introduced by the fluid supply system  140  at ratios that vary with the substrate properties, the chemistry being used and the process being performed in the processing chamber. Usually the ratio is roughly 1 to 5 percent by volume, which, for a chamber, recirculation system and associated plumbing having a volume of about one liter amounts to about 10 to 50 milliliters of additive in most cases, but the ratio may be higher or lower. 
   The process chemistry supply system  130  can be configured to introduce one or more of the following process compositions, but not limited to: cleaning compositions for removing contaminants, residues, hardened residues, photoresist, hardened photoresist, post-etch residue, post-ash residue, post chemical-mechanical polishing (CMP) residue, post-polishing residue, or post-implant residue, or any combination thereof; cleaning compositions for removing particulate; drying compositions for drying thin films, porous thin films, porous low dielectric constant materials, or air-gap dielectrics, or any combination thereof; film-forming compositions for preparing dielectric thin films, metal thin films, or any combination thereof; healing compositions for restoring the dielectric constant of low dielectric constant (low-k) films; sealing compositions for sealing porous films; or any combination thereof. Additionally, the process chemistry supply system  130  can be configured to introduce solvents, co-solvents, surfactants, film-forming precursors, or reducing agents, or any combination thereof. 
   The process chemistry supply system  130  can be configured to introduce N-Methyl Pyrrolidone (NMP), diglycol amine, hydroxyl amine, di-isopropyl amine, tri-isoprpyl amine, tertiary amines, catechol, ammonium fluoride, ammonium bifluoride, methylacetoacetamide, ozone, propylene glycol monoethyl ether acetate, acetylactone, dibasic esters, ethyl lactate, CHF3, BF3, HF, other fluorine containing chemicals, or any mixture thereof. Other chemicals such as organic solvents may be utilized independently or in conjunction with the above chemicals to remove organic materials. The organic solvents may include, for example, an alcohol, ether, and/or glycol, such as acetone, diacetone alcohol, dimethyl sulfoxide (DMSO), ethylene glycol, methanol, ethanol, propanol, or isopropanol (IPA). For further details, see U.S. Pat. No. 6,306,564B1, filed May 27, 1998, and titled “REMOVAL OF RESIST OR RESIDUE FROM SEMICONDUCTORS USING SUPERCRITICAL CARBON DIOXIDE”, and U.S. Pat. No. 6,509,141B2, filed Sep. 3, 1999, and titled “REMOVAL OF PHOTORESIST AND PHOTORESIST RESIDUE FROM SEMICONDUCTORS USING SUPERCRITICAL CARBON DIOXIDE PROCESS,” both incorporated by reference herein. 
   Additionally, the process chemistry supply system  130  can comprise a cleaning chemistry assembly (not shown) for providing cleaning chemistry for generating supercritical cleaning solutions within the processing chamber. The cleaning chemistry can include peroxides and a fluoride source. For example, the peroxides can include hydrogen peroxide, benzoyl peroxide, or any other suitable peroxide, and the fluoride sources can include fluoride salts (such as ammonium fluoride salts), hydrogen fluoride, fluoride adducts (such as organo-ammonium fluoride adducts), and combinations thereof. Further details of fluoride sources and methods of generating supercritical processing solutions with fluoride sources are described in U.S. patent application Ser. No. 10/442,557, filed May 20, 2003, and titled “TETRA-ORGANIC AMMONIUM FLUORIDE AND HF IN SUPERCRITICAL FLUID FOR PHOTORESIST AND RESIDUE REMOVAL”, and U.S. patent application Ser. No. 10/321,341, filed Dec. 16, 2002, and titled “FLUORIDE IN SUPERCRITICAL FLUID FOR PHOTORESIST POLYMER AND RESIDUE REMOVAL,” both incorporated by reference herein. 
   Furthermore, the process chemistry supply system  130  can be configured to introduce chelating agents, complexing agents and other oxidants, organic and inorganic acids that can be introduced into the supercritical fluid solution with one or more carrier solvents, such as N,N-dimethylacetamide (DMAc), gamma-butyrolactone (BLO), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), N-methylpyrrolidone (NMP), dimethylpiperidone, propylene carbonate, and alcohols (such a methanol, ethanol and 2-propanol). 
   Moreover, the process chemistry supply system  130  can comprise a rinsing chemistry assembly (not shown) for providing rinsing chemistry for generating supercritical rinsing solutions within the processing chamber. The rinsing chemistry can include one or more organic solvents including, but not limited to, alcohols and ketone. In one embodiment, the rinsing chemistry can comprise sulfolane, also known as thiocyclopentane-1,1-dioxide; (Cyclo)tetramethylene sulphone; and 2,3,4,5-tetrahydrothiophene-1,1-dioxide; which can be purchased from a number of venders, such as Degussa Stanlow Limited, Lake Court, Hursley Winchester SO21 2LD UK. 
   Moreover, the process chemistry supply system  130  can be configured to introduce treating chemistry for curing, cleaning, healing, or sealing, or any combination thereof, low dielectric constant films (porous or non-porous). The chemistry can include hexamethyldisilazane (HMDS), chlorotrimethylsilane (TMCS), or trichloromethylsilane (TCMS). For further details, see U.S. patent application Ser. No. 10/682,196, filed Oct. 10, 2003, and titled “METHOD AND SYSTEM FOR TREATING A DIELECTRIC FILM,” and U.S. patent application Ser. No. 10/379,984, filed Mar. 4, 2003, and titled “METHOD OF PASSIVATING LOW DIELECTRIC MATERIALS IN WAFER PROCESSING,” both incorporated by reference herein. 
   The processing chamber  110  can be configured to process substrate  105  by exposing the substrate  105  to high pressure fluid from the high pressure fluid supply system  140 , or process chemistry from the process chemistry supply system  130 , or a combination thereof in a processing space  112  that may be enclosed in an inner wall, lid, or other closure structure  113 . Additionally, processing chamber  110  can include an upper chamber assembly  114 , and a lower chamber assembly  115 . 
   The upper chamber assembly  114  can comprise a heater (not shown) for heating the processing chamber  110 , the substrate  105 , or the processing fluid, or a combination of two or more thereof. Alternately, a heater is not required. Additionally, the upper chamber assembly can include flow components (not shown) for flowing processing fluid through the processing chamber  110 , and particularly through the processing space  112 , which surrounds the substrate  105  and the processing chamber  110 . In one example, a circular flow pattern can be established, and in another example, a substantially linear flow pattern can be established. Alternately, the flow components for flowing the fluid can be configured differently to affect a different flow pattern. 
   The lower chamber assembly  115  can include a platen  116  configured to support substrate  105  and a drive mechanism  118  for translating the platen  116  in order to load and unload substrate  105 , and seal lower chamber assembly  115  with upper chamber assembly  114 . The platen  116  can also be configured to heat or cool the substrate  105  before, during, and/or after processing the substrate  105 . Additionally, the lower assembly  115  can include a lift pin assembly for displacing the substrate  105  from the upper surface of the platen  116  during substrate loading and unloading. 
   A transfer system (not shown) can be used to move a substrate into and out of the processing chamber  110  through a slot (not shown). In one example, the slot can be opened and closed by moving the platen, and in another example, the slot can be controlled using a gate valve. 
   The substrate can include semiconductor material, metallic material, dielectric material, ceramic material, or polymer material, or a combination of two or more thereof. The semiconductor material can include Si, Ge, Si/Ge, or GaAs. The metallic material can include Cu, Al, Ni, Pb, Ti, and Ta. The dielectric material can include silica, silicon dioxide, quartz, aluminum oxide, sapphire, low dielectric constant materials, TEFLON, and polyimide. The ceramic material can include aluminum oxide, silicon carbide, etc. 
   The processing system  100  can also comprise a pressure control system (not shown). The pressure control system can be coupled to the processing chamber  110 , but this is not required. In alternate embodiments, pressure control system can be configured differently and coupled differently. The pressure control system can include one or more pressure valves (not shown) for exhausting the processing chamber  110  and/or for regulating the pressure within the processing chamber  110 . Alternately, the pressure control system can also include one or more pumps (not shown). For example, one pump may be used to increase the pressure within the processing chamber, and another pump may be used to evacuate the processing chamber  110 . In another embodiment, the pressure control system can comprise seals for sealing the processing chamber. In addition, the pressure control system can comprise an elevator for raising and lowering the substrate and/or the platen. 
   There are several places in the systems described above and other systems of these types where flow direction control is useful. Some of these are illustrated in  FIG. 1A . For example, the processing system  100  can comprise an exhaust control system  160 . The exhaust control system  160  can be coupled to the processing chamber  110  via the line  122 , but this is not required. In alternate embodiments, exhaust control system can be configured differently and coupled differently. The exhaust control system  160  can include an exhaust gas collection vessel (not shown) and can be used to remove contaminants from the processing fluid. Alternately, the exhaust control system can be used to recycle the processing fluid. Flow can be diverted from the flow line  122  to the exhaust control system  160  by use of a flow diversion valve  162 . Such a valve may open a line to the exhaust system and totally shut off flow along the line  122 , but total shut off is not necessary in many cases. Similarly, clean processing fluid can be introduced into line  122  from fluid supply system  140  through valve  142 . 
   An example of the use of a flow diversion valve which is not  100 % shut off tight would be for secondary branches which may be used to inject chemistry into the high pressure environment, such as from chemistry supply system  130  through valve  132  in  FIG. 1A , and then recirculate the chemistry-fluid mixture in a local loop  125 . Recirculation can be switched from the chamber  110  through the local loop  125  and back with flow diverter valves, such as valve  126 , which diverts flow from the main line  122  to the local loop  125 , and valve  127 , which combines flow from local loop  125  back to line  122 . Note that pump, filter and heater referred to above may be located between the valves  127  and  126 , but they can be located elsewhere, for example elsewhere in the line  122 . In case of these flow diverter valves, a small amount of leakage into the main line  122  may not be important as mixing will take place after certain amount of mixing has occurred within the secondary branch  125 . Each of the valves  126 ,  127 ,  132 ,  142  and  162  can be controlled by signals from the controller  150 . 
   Another possible use for flow diverter valves is for directing flow to different areas of the wafer  105 . If local high velocity jets are required for cleaning a wafer, it may not be practical to generate very high pressure gradients within the entire area of the tool, for example, because of filtration concerns. Such high velocity jets may be directed to only certain areas of the wafer  105  at a time. In this case, one or more flow diversion valves may be activated to move the high velocity flow to different areas of the wafer for cleaning. Small leakages are insignificant within the valve, as only relatively higher velocity flow is required within the tool to do the processing. Although the leakage will reduce the available flow rate to some degree, this might not outweigh the benefits of a high flow valve solution. An example of the placement of such a valve is the valve  172  illustrated in  FIG. 2 . 
     FIG. 2  is similar to  FIG. 5  described in pending U.S. patent application Ser. No. 09/912,844 (US Patent Application Publication No. 2002/0046707 A1), entitled “High pressure processing chamber for semiconductor substrates”, and filed on Jul. 24, 2001, which is incorporated herein by reference in its entirety. 
   As illustrated in  FIG. 2 , the processing space  112  may be in the form of a wafer cavity enclosed by the lid  113  over the wafer  105  on the platen  116 . Processing fluid may be brought into the cavity  112  through a spacer-injection ring  171  and preferably exhausted through a two port outlet  170 . The two port outlet  170  can include a flow diverter valve  172 , which can be alternated between a first position and a second position to switch flow from the cavity  112  between first and second exhaust ports  176  and  178  to a return port  175 . 
   The valves  126 ,  127 ,  132 ,  142  and  162  in  FIG. 1A  have all been referred to as flow diversion valves. These valves can be structurally similar. Some, namely valves  126  and  162  function to divert flow from a single inlet to one of two alternative outlets by switching an internal valve element. Others of these valves, namely valves  127 ,  132  and  142  operate in reverse, by admitting fluid from one of two alternative inlets to a single outlet by switching a similar valve element. The valve  172  of  FIG. 2  operates in a similar direction to that of valves  127 ,  132  and  142 . 
     FIG. 3  and  FIG. 6  illustrate a non-rubbing, non-contact flow diverting valve  200  according to one embodiment of the invention. The valve  200  can be used in the various locations described above in semiconductor wafer high pressure processing tools, and are particularly useful in SCCO2 processing systems. The valve  200  includes a valve body  202  having two electromagnets  204  and  206  positioned on opposite sides of the valve body  202 . Internally to the valve body  202 , as illustrated in  FIG. 4 , is a cavity  215  in which is mounted a spherical valve element or ball  210 . The ball  210  is edge welded to a thin metal sheet or plate  212 . The metal sheet  212  acts as a spring and a stabilizer for the ball  210 . The valve body  202  has a common port  216  and two switched ports  217  and  218 . The ball  210  as well as the sheet  212  are positioned in the cavity  215  to block flow between the two switched ports  217  and  218 . 
   The ball  210  itself is a composite formulated for use in this valve. Since electromagnets can only operate on magnetic metals, the ball  210  is formed of a magnetic grade steel. Since ferrous metals are generally poor performers with respect to corrosion, stainless steel or some other non-corrosive material is preferably in contact with the working fluid. The ball  210  is, to serve this purpose in this embodiment, composed of a thin shell of austenitic stainless steel welded around a ferrous metal interior ball. Martinsitic stainless steels could also be used. While the corrosion protection and the level of magnetic attraction they provide are usually less good, they could be acceptable in some applications, as can other materials possessing the desired properties. 
   As illustrated in  FIGS. 3 and 4 , the valve body  202  is formed of two blocks,  222  and  224 , into which the cavity  215  is formed. The blocks  222  and  224  are bolted together. Channels  227  and  228  are respectively formed in the blocks  222  and  224  to connect the respective switched ports  217  and  218  to the common port  216 . The ball  210  is positioned in the cavity  215 , and the channels  227  and  228  are shaped, to alternately block flow between one of the switched ports  217 , 218  and the common port  216 , while permitting flow between the other of the switched ports  217 , 218  and the common port  216 . Activation of magnet  204  closes port  217  and opens port  218  to port  216 , while activation of magnet  206  closes port  218  and opens port  217  to port  216 . The two inlet ports  217  and  218  are shown communicating with the channels  227  and  228  the blocks  222  and  224 , respectively, of the body  202  while the one common port  216  is shown communicating with the cavity  215  through the top of an exit plate  226  on the top of the body  202 . Straps hold electromagnets  204  and  206  in place. 
   In  FIG. 5 , the two blocks  222  and  224  that make up the valve body  202  are shown disassembled. The ball  210  and very thin support plate  212  can be seen with the cavity  215  formed in the blocks  222  and  224 . The two blocks or body halves  222 , 224  of the valve  200  have the relief cavity  215  formed therein to accept the ball  210  when it is flexed on the metal support plate  212  by the force of one of the magnets  204 , 206 . Two pin holes  232  are formed in the cavity  215  of one block  224  and two pin holes  233  are formed in the other block  222  to receive two pins  234  that are pressed into the thin spring support plate  212 . A tapered recess  235  at the bottom of the cavity  215  for the spring plate  212  is also shown. The body half or block  222  is similar to the block  224  with one exception being that an o-ring groove (not shown) is added to create a seal between the body halves  222 , 224 . 
   Additional relief for the bottom of the spring support plate  212  is provided in one of the blocks, for example, block  224 . For simplicity of machining, the opposite half does not require this relief, which means the spring plate  212  and ball  210  will be off center by half the thickness of the spring plate  212 , but that is not significant enough to cause any significant difference in performance. Of course, matching reliefs could be present in both blocks  222 , 224  to exactly center the spring plate  212 . 
   The two pins  232  in the spring plate  212  are used for positioning the ball unit and the two body halves  222 , 224 , as well for as stabilizing the spring support plate  212  from moving out of position during use. The channels  227 , 228  are shown with portions that form two flow streams that connect into a single common port. The blocks  222  and  224 , as well as exit block  226 , are conically relieved to expose a tubular stub suitable for the welding thereto of the tube extensions to the ports  216 – 218 . 
   In operation, in a start up mode, the valve  200  is unpowered. When unpowered, the ball  210  assumes will find a natural position in the center of the valve cavity  215  blocking neither port  217  nor  218 . If flow were present in this unpowered condition, the ball  210  could begin to oscillate due to the flow creating unsteady low pressure regions on the side of the ball  210 . The spring stiffness of plate  212  and the flow rate of fluid through the valve  200 , as well as the fluid properties, are factors that determine the rate of vibration under the no-power condition. 
   Once either one of the electromagnets  204 , 206  is switched on, the ball  210  is drawn toward it. The spring plate  212  flexes in an arc, allowing the ball  210  to move toward the actuated electromagnet. Ideally, the stiffness of the plate  212  is sufficient to counterbalance the force from the electromagnet such that the plate never comes into contact with the arc in the body half. Alternatively, the spring flexure of plate  212  can be such that the ball  210  does not come into contact with the body half, so that, instead, the spring plate  212  would rest against the body half at full flexure, producing a gentle contact, that could be beneficial in resulting in fewer particulates being generated. When flow direction needs to be switched, the opposite electromagnet  204 , 206  is turned on and the other electromagnet is switched off. The ball  210  will then be drawn toward the opposite side of the valve cavity  215 , shutting off the previously open flow port  217 , 218  and opening the other. 
   A number of other optional features may be employed. For example, the electromagnets  204 , 206  may be ramped up and ramped down in force for optimum control. Both electromagnets may be actuated at the same time during the transition period, for example with overlapping actuation periods, when switching flow ports to produce smooth control of the ball  210  and spring plate  212 . Voltage and current can also be regulated to the electromagnets  204 , 206  in such a way as to more precisely control the flex of the spring plate  212 . The flow rate and fluid viscosity also play a role in the deflection characteristics of the spring plate  212 , and may vary during operation. 
   As addition optional features, inputs of flow meters and other diagnostics can be input into controller  150  or another controller, which can calculate results in real time and closed loop mode, and output a signal to the electromagnets  204 , 206  to keep the position of the ball  210  in the correct location. A small hole or two can be cross-drilled from the inlet port to the very bottom of the arc  235  on the body half  222 , 224  to allow incoming flow to sweep away the dead flow area that could result at the junction of the body halves  222 , 224  and the spring plate  212 . 
   As further optional features, for example, the ball  210  can contain a high strength permanent magnet instead of an iron based alloy, such that magnetic attraction between the ball  210  and the electromagnets  204 , 206  is enhanced. The ball  210  can contain a high strength permanent magnet, such that magnetic repulsion between the ball and the electromagnets  204 , 206  is utilized rather than magnetic attraction for actuation. Further, sensors can be incorporated to sense the position of the ball to indicate switching. A sensor can be provided to provide electrical feedback from the electromagnet indicating presence within its control field. 
   Although only certain exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.