Patent Publication Number: US-2006000358-A1

Title: Purification and delivery of high-pressure fluids in processing applications

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority from U.S. Provisional Patent Application Ser. No. 60/583,714, entitled “High-Pressure Delivery System”, and filed Jun. 29, 2004. The disclosure of this provisional patent application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF INVENTION  
      1. Field of Invention  
      The present invention pertains to pressurizing and delivering fluids, in particular carbon dioxide, to processing systems at sufficiently high pressures and purity levels.  
      2. Related Art  
      Many applications are emerging in electronics, pharmaceutical and food areas which require high-pressure carbon dioxide. For example, in the electronics industry, high-pressure carbon dioxide (e.g., at pressures of 3000 psig or 207 bar or higher) can be used in wafer processing techniques such as stripping of photoresist, formation of micro and nano-particles or structures and layer depositions. In the pharmaceutical industry, researchers are investigating the use of supercritical carbon dioxide to formulate nano-drug particles. In food applications, carbon dioxide is used, for example, in beverage carbonation.  
      These applications require a continuous supply of large quantities of substantially pure, high-pressure carbon dioxide fluid flows that can be delivered to a process area or end-point in a safe and cost-effective manner. Since carbon dioxide is typically not consumed in many of these processes, it is also desirable to recycle the used carbon dioxide for economic as well as environmental reasons.  
      In pressurized carbon dioxide delivery systems, liquid carbon dioxide is typically pressurized within or proximate the storage vessel, and the high pressure carbon dioxide is then delivered to the point of use via piping which can withstand high pressures. For example, liquid carbon dioxide is typically stored at low pressures (e.g., about 300 psig (about 20.7 bar) or less) in one or more storage tanks or vessels. The storage vessels can be physically located at large distances (e.g., 50 meters or more) from the process area or usage point, such that a low pressure pump is often necessary to transport the carbon dioxide from the storage vessels to the process area via suitable piping.  
      Many emerging applications in the semiconductor industry require high-purity, high-pressure carbon dioxide (CO 2 ) at the point-of-use (e.g., in a process tool) that is substantially free of impurities. For electronics applications, the process area must be very clean and is typically provided in a fabrication or processing room. For example, a process tool to remove photoresist from a wafer surface using high-pressure CO 2  typically is situated in a clean room to prevent exposure to impurities or contaminants of the process tool and wafers processed by the tool. A “class 100” clean room is an exemplary room for processing a semiconductor wafer in which photoresist is removed from the wafer. Such a clean room is designed to maintain less than one hundred particles at sizes larger than 0.5 micron per cubic foot of air space. Equipment associated with high-pressure carbon dioxide delivery systems, such as CO 2  storage tanks, pressurization pumps, heat exchangers, etc. must be kept outside the clean room so as minimize the dimensional requirements of the clean room and to facilitate ease of service of the delivery system components.  
      In many cases, the distance between the CO 2  storage tank and the process tool can be very large (e.g., on the order of one hundred meters or more). There are several challenges in transporting high-pressure CO 2  over large distances. For example, to maintain high purity levels of the carbon dioxide, special electropolished stainless steel piping is used to transport CO 2  streams, and this piping can be very expensive, particularly when designed to withstand the high-pressures required for the CO 2  streams. In addition, when high-pressure CO 2  streams are transported over large distances, there can be substantial pressure drops in the piping lines. Another important consideration is the safety risk associated with transferring high-pressure carbon dioxide over large distances, where any leak or rupture in the lines can result in the release of large quantities of carbon dioxide to the surrounding environment.  
      A further problem associated with transporting high-pressure carbon dioxide over large distances is maintaining the temperature and pressure of the CO 2  stream within desired ranges. For example, in processing systems where CO 2  is used sporadically (i.e., not continuously), the CO 2  may become stagnant in the piping lines (e.g., during a period of non-use of a process tool). This in turn may lead to an increase in temperature of the CO 2  (due to the higher ambient temperatures surrounding the piping lines), which in turn may lead to increased pressures of CO 2  in the piping supply lines. Depending upon the increase in temperature, carbon dioxide vaporization may occur, leading to subsequent problems such as the inability of carbon dioxide pumps to pressurize the vapor-liquid mixture because of cavitation in the pump.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to supply fluids, such as CO 2 , to a process site requiring use of the fluids at high pressures, where the fluids are delivered from a supply source over long distances (e.g., 50 meters or more) while maintaining desired temperature and pressure conditions of the fluids during delivery and at the process site.  
      It is another object of the present invention to supply such fluids to the process site at desired temperature and pressure conditions while maintaining a sufficient purity level of the fluids.  
      It is a further object to recover at least a portion of the fluids from the process site after use of the fluids in a processing application.  
      The aforesaid objects are achieved individually and/or in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto.  
      In accordance with the present invention, a purification and delivery system that delivers a high-pressure fluid to a process area comprises a fluid supply tank with a fluid in a liquid state, a purification section including at least one purification unit to remove at least one component from the fluid, and a high-pressure pump disposed downstream from the fluid supply tank and proximate the process area. The high-pressure pump pressurizes the fluid to a process pressure that is greater than the pressure of the fluid within the fluid supply tank.  
      In another embodiment of the present invention, a method of purifying and delivering a high-pressure fluid to a process area comprises providing fluid in a liquid state from a fluid supply tank for delivery to the process area, removing at least one component from the fluid via at least one purification unit of the purification section, and pressurizing fluid flowing from the fluid supply tank to a process pressure, via a high-pressure pump disposed at a location proximate the process area. The process pressure is greater than the pressure of fluid within the fluid supply tank. The method further comprises delivering the fluid at the process pressure to the process area.  
      By providing the high-pressure pump proximate the process area in accordance with the invention, the distance at which high-pressure fluid must be transported while maintaining required operating temperatures and pressures is minimized.  
      The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, particularly when taken in conjunction with the accompanying drawings wherein like reference numerals in the figures are utilized to designate like components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram of an exemplary embodiment of a high-pressure fluid supply, purification and recovery system in accordance with the present invention.  
       FIG. 2  is a diagram of a portion of a modified embodiment of the system of  FIG. 1  employing multiple process chambers within the system, with all of the process chambers receiving fluid from a single high-pressure pump and purification section in accordance with the present invention.  
       FIG. 3  is a diagram of a portion of another modified embodiment of the system of  FIG. 1 , in which multiple process chambers are employed, each with its own respective high-pressure pump and purification section in accordance with the present invention.  
       FIG. 4  is a diagram of a portion of a further modified embodiment of the system of  FIG. 1 , including a pump installed between the secondary tanks and the primary tank in accordance with the present invention.  
       FIG. 5  is a diagram of a portion of still another modified embodiment of the system of  FIG. 1 , in which one of the secondary tanks includes a purification section with controlled feedback in accordance with the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
      In accordance with the present invention, purification and delivery of high-pressure fluids is achieved by providing the fluids from a supply source located at a site remote from a processing site, selectively purifying the fluids during transport, and pressurizing the fluids proximate the processing site prior to delivery to the process site.  
      Preferably, a two-stage pressurization of the fluid is provided, where the fluid is stored at the remote supply source, purified and transported at least a portion of the distance to the supply site at one or more pressures that are below the required processing pressure for the fluid. The fluid is pressurized to the desired high-pressure immediately upstream from the process site.  
      Other features of the invention include recycling of the fluids after use at the process site, and by-pass features as described below that maintain the temperature and pressure conditions of the fluids within desired ranges during periods in which the fluids are not being delivered to the process site. Fluids can be delivered in accordance with the invention at the desired temperature and high-pressure ranges for both batch and continuous processes.  
      In the embodiments described below, carbon dioxide (CO 2 ) is purified and pressurized to a selected high-pressure prior to delivery to a process site. However, the invention is not limited to processing carbon dioxide, and can include any one or combination of fluids for processing including, without limitation, oxygen, carbon dioxide, nitrogen, water, ammonia, and selected alkyls. The levels to which the fluids are to be pressurized can vary depending upon a particular application. When utilizing CO 2  for semiconductor processing applications, for example, the CO 2  fluids can be pressurized to high pressures in the range of about 3000 psig (about 207 bar) to about 8000 psig (about 552 bar).  
      In systems where carbon dioxide is to be delivered to a process site or area, the process area could be, for example, a tool utilized in an integrated circuit manufacturing step in the semiconductor industry. The integrated manufacturing step may include, for example, wafer cleaning, where photoresist or residue is stripped or removed from a silicon wafer using high-pressure carbon dioxide. Another example in which high-pressure carbon dioxide is used is in healthcare or pharmaceutical industries, where high-pressure carbon dioxide can be used to make certain compounds or for sterilization purposes. Still another example in which high-pressure carbon dioxide is used is in the food preparation industry (e.g., for carbonation of beverages). The systems and methods of the invention, as described below, can be utilized to deliver purified, high-pressure carbon dioxide to any selected process area.  
      As noted above, the invention preferably employs a two-stage pressurization for the carbon dioxide, where carbon dioxide is first pressurized remotely to a low pressure at or proximate the CO 2  supply source (e.g., a storage tank or vessel). Exemplary low pressures are in to the range of about 300 psig (about 21 bar) to about 1800 psig (about 124 bar). The low-pressure carbon dioxide is then sent to the process site or area where it is then pressurized further using a secondary or high-pressure pump. Preferably, the secondary pump is situated proximate or immediately upstream in relation to the process area or tool. In semiconductor applications, in which the process area is a clean room as described above, the secondary pump can be situated just outside of the clean room (e.g., in a sub-fab area as described below).  
      Alternatively, in certain embodiments of the invention, a two-stage pressurization may not be required. In these embodiments, the CO 2  tank is at a sufficient pressure to deliver CO 2  streams to the high-pressure pump for pressurization to the desired pressures prior to being sent to the process site.  
      A recirculation loop can be provided between the CO 2  supply source and the process site to maintain the temperature and pressure conditions of the CO 2  stream within desired ranges in the event ambient conditions around the transport lines fluctuate and/or the process area is not operational. For example, the recirculation loop prevents the CO 2  stream from becoming stagnant in the transport piping lines during periods in which the process site is shut down or brought off-line.  
      In other embodiments of the invention, multiple storage tanks can be provided to facilitate an uninterrupted supply of CO 2  (e.g., switching between storage tanks when one tank becomes depleted). For example, a system may include a main tank to supply CO 2  to the process site, and one or more secondary tanks to store CO 2  that has been processed and recycled from the process site, where the secondary tanks optionally purify and feed the CO 2  to the main tank for reuse at the process site.  
      An exemplary embodiment of a two-stage pressurization system for supplying purified and high-pressure CO 2  to a semiconductor process chamber in accordance with the invention is depicted in  FIG. 1 . System  1  includes a primary storage tank  10  that supplies CO 2  for the system. The primary storage tank stores liquid CO 2  at suitable conditions, for example, at a temperature of about −5° F. (about −20° C.) and a pressure ranging from about 300 psig (about 21 bar) to about 350 psig (about 24 bar). Primary storage tank  10  is connected to a first pump  2  via a supply line  20  to facilitate delivery of liquid CO 2  to the pump. Primary storage tank  10  and pump  2  are located remotely from a process area  7  but are preferably in close proximity with each other. For example, the primary storage tank can be situated at distances from about 50 meters to about 1 kilometer or more from the process area. Preferably, the primary storage tank is situated at least about 100 meters from the process area.  
      Pump  2  pressurizes the liquid CO 2  and then delivers the pressurized CO 2  to a purification section  35  via a supply line  30 . Preferably, pump  2  pressurizes the CO 2  to a pressure in the range of about 300 psig (about 21 bar) to about 1800 psig (124 bar), preferably in the range of about 300 psig (about 21 bar) to about 1200 psig (about 83 bar), prior to delivery to the purification section. The temperature conditions of the CO 2  stream are also maintained in the supply lines and corresponding equipment (e.g., via suitable insulating materials), such that the carbon dioxide is maintained below its critical temperature and above its vapor pressure at the process temperatures, thus ensuring the CO 2  stream remains in a liquid state during transport to the process area. In system designs where the storage tank is relatively close to the process area (e.g., within about 100 meters of the process area), and depending upon the CO 2  pressure within the primary tank, the fluid pressure within the tank may be sufficient to deliver the CO 2  stream to the process area so as to eliminate the need for pump  2 .  
      A purification section is optionally provided within system  1  to remove impurities within the CO 2  stream prior to delivery to the process area. The number and types of different purification units that are provided in purification section  35  will depend upon the amount and/or types of impurities that may be present in the CO 2  stream being delivered from tank  10 . In particular, the purification section may include any suitable number and types of purification units to remove any number of different types of impurities that may exist in the CO 2  stream. Exemplary purification units that may be provided in the purification section include, without limitation, adsorption units (e.g., pressure swing adsorption units, vacuum swing adsorption units, thermal swing adsorption units, etc.), absorber units, distillation units, filtration units (e.g., one or more filters with selected mesh sizes), catalytic oxidation units, coalescer units and mechanical separators (e.g., cyclonic separators).  
      Further, two or more purification sections may be provided in the system between the storage tank and the process area, and any suitable configuration of purification sections and purification units may be employed. Exemplary purification section configurations that may be provided in the system of the present invention include, without limitation, purification sections as described in U.S. patent application Ser. No. 10/860,599, the disclosure of which is incorporated herein by reference in its entirety. The CO 2  stream can be purified so as to be substantially free of impurities (e.g., containing at least about 99.99% by volume of CO 2 ). Further, it is noted that the purification can consist of a filtration unit (e.g., a single filter) for filtering particulate materials of selected sizes from the CO 2  stream.  
      The purification section or sections may be disposed proximate the primary tank and/or proximate the process area. In certain applications, a simple filtration system may be sufficient to obtain a CO 2  stream at the desired purity level. In such applications, the filtration system is preferably situated proximate the process area.  
      Purification section  35  is connected with process area  7  via a supply line  36 . A valve  38  is disposed along supply line  36  and is selectively adjustable to control the flow of the CO 2  stream to the process area. A recirculation line  40  is connected between supply line  36  (at a location upstream from valve  38 ) and primary storage tank  10  to facilitate selective recirculation of the CO 2  stream back to the primary storage tank. A valve  39  is disposed along recirculation line  40  so as to facilitate selective control of the amount of CO 2  fluid recirculating to the storage tank during system operation. Valves  38  and  39  can be controlled manually or automatically (via a suitable controller) based upon the temperature and pressure conditions of the CO 2  stream within supply line  36 . In addition, suitable temperature and/or pressure sensors can be provided at one or more suitable locations to measure the conditions of the CO 2  stream within supply line  36  and/or at other locations in system  1  so as to provide feedback control for selective adjustment of valves  38  and  39  during system operation.  
      The recirculation loop maintains the temperature and pressure conditions of the CO 2  stream by selectively diverting some or all of the carbon dioxide back to tank  10  when processing within process area  7  is shut down and/or due to temperature fluctuations of the ambient surroundings. For example, in situations where there is no carbon dioxide flow to the process area for several hours, the carbon dioxide in the supply lines can become stagnant if there is no recirculation loop, which can in turn result in an increase in temperature if the ambient temperature is higher than the liquid CO 2  temperature. Even in systems where the supply lines are insulated, there can be some temperature increase and formation of vapor-liquid phase mixtures. The increase in temperature can result in substantial increases in line pressures due to vaporization of the CO 2  stream. The recirculation loop provided in system  1  ensures that the CO 2  stream remains in the liquid state and at desired temperature and pressure conditions.  
      Process area  7  includes a process tool  6  disposed in a clean room  100 . The process tool can be, e.g., a tool that utilizes supercritical carbon dioxide to remove photoresist from and/or process a semiconductor wafer in any other suitable manner. The CO 2  processing pressure in the tool can be in the range of about 3000 psig (about 207 bar) to about 8000 psig (about 552 bar). A high-pressure pump  4  is situated in close proximity to process tool  6  and increases the pressure of the liquid CO 2  stream to the required processing pressure for the tool (e.g., to the previously noted pressures). The high-pressure pump is preferably situated as close to the process tool as possible while preferably being outside of the clean room (e.g., within about 50 meters of the process tool). As noted above, the process tool for semiconductor processes often must be kept in a substantially clean environment that is separated from other process equipment. Preferably, high-pressure pump  4  is provided in an enclosed space  102  partitioned from and disposed beneath the clean room, typically referred to as the sub-fab area. When disposed within the sub-fab area, it is possible to provide the high-pressure pump at a very close distance from the process tool while keeping the pump outside of the clean room. For example, in the configuration as set forth in  FIG. 1 , the pump can be located within about 10 meters of the process tool, preferably within about 5 meters of the process tool.  
      The high-pressure pump is of a suitable type to minimize any addition of impurities in the CO 2  stream. For example, the high-pressure pump is preferably a diaphragm pump or any other pump of similar design that minimizes direct contact between the CO 2  fluid and any moving parts in the pump. Optionally, in applications where it is desirable to further purify the CO 2  stream after pressurization, a second purification section  45  is also provided in sub-fab area  102  directly downstream from high-pressure pump  4 . For example, the second purification section can include a filter to remove particulate material that may have been introduced into the pressurized CO 2  stream from pump  4 . Alternatively, any number of purification units as described above can be provided in the second purification section.  
      A conditioning module  5  is provided sub-fab area  102  at a location downstream from second purification section  45 . The conditioning module can be any suitable device (e.g., heat exchanger or other heating and/or cooling unit) that adjusts the temperature of the high-pressure CO 2  stream, while preferably maintaining the CO 2  stream in liquid state, prior to delivery to process tool  6  in clean room  100 . Preferably, the conditioning module thermally treats the CO 2  stream such that the stream is within a temperature range of about 15° C. to about 200° C., more preferably in the range of about 35° C. to about 100° C., prior to delivery to the process tool.  
      Optionally, any suitable additives (e.g., co-solvents and/or surfactants) can be added in the high-pressure CO 2  stream at any suitable location along the supply line and preferably within the sub-fab area (e.g., upstream or downstream from the conditioning module). For example, additives such as alcohols, halogenated hydrocarbons, saturated hydrocarbons, unsaturated hydrocarbons, aromatic hydrocarbons, amines, aldehydes, anhydrides, organic acids, inorganic acids, ketones, esters, glycols, fluoride containing materials and combinations thereof, can be added in the high-pressure CO 2  stream in the sub-fab area.  
      A third purification section  8  is provided downstream from process area  7  and is connected with process tool  6 , via a supply line  50 , to receive the CO 2  stream emerging from the process tool. Optionally, the pressure of the CO 2  stream is reduced to a selected pressure range (e.g., upon emerging from the process tool and/or at any other suitable area within the process area) prior to delivery to the third purification section. The third purification section can include any suitable combination of purification units as described above for the first and second purification units so as to remove impurities and additives from the CO 2  stream prior to recycling for reuse by the process tool. In an exemplary embodiment, the third purification section includes only a filter for filtering particulate materials of selected sizes from the CO 2  stream prior to delivery of the stream to the process tool.  
      The third purification section can deliver the purified CO 2  stream directly to primary storage tank  10  or, alternatively, to one or more secondary storage tanks that serve as back-up tanks for the primary storage tank. Referring to  FIG. 1 , system  1  includes secondary storage tanks  9  and  11  that are connected in parallel between third purification section  8  and primary storage tank  10 . In particular, secondary storage tank  9  is connected to purification unit  8  via a supply line  60 , with a valve  61  being disposed along line  60  to selectively control the flow of CO 2  fluid to tank  9 . A supply line  62  branches from supply line  60  at a location upstream from valve  61  and connects with another secondary storage tank  11 . A valve  63  is disposed along line  62  to selectively control the flow of CO 2  fluid to tank  11 .  
      Each of secondary storage tanks  9  and  11  connect with primary storage tank  10  via a supply line  70 , where each tank  9 ,  11  includes a respective valve  71 ,  72  at its outlet end to selectively control the flow of CO 2  fluid from the tanks to the primary storage tank. Carbon dioxide within tanks  9  and  11  is preferably maintained at temperature and pressure conditions that are similar to the conditions in the primary storage tank. Further, valves  61 ,  63 ,  71  and  72  can be manually or automatically controlled (e.g., via a suitable controller), with appropriate fluid level sensors and/or temperature and pressure sensors being provided in the primary and secondary tanks, to facilitate supply of CO 2  from either or both secondary tanks as necessary to the primary storage tank.  
      Each of secondary tanks  9  and  11  is further connected via supply lines  64  and  66  to an external liquid CO 2  stream supply source  12  (e.g., a tanker as depicted in  FIG. 1  or, alternatively, an on-site CO 2  generation plant). The external CO 2  supply source provides make-up CO 2  to the secondary storage tanks to account for processing losses and thus ensure an adequate supply of liquid CO 2  is available at all times during system operation. An internal pressurizing device (e.g., pressure-building coils) can be provided in any or all of tanks  9 ,  10  and  11  to selectively increase and maintain the pressure of CO 2  fluid within the tanks as well as transfer of CO 2  fluid at selective flow rates between the tanks.  
      In operation, liquid CO 2  is stored in primary storage tank  10  at selected temperature and pressure conditions (e.g., a temperature of about −5° F. (about −20° C.) and a pressure ranging from about 300 psig (about 21 bar) to about 350 psig (about 24 bar)). The liquid CO 2  is delivered from tank  10  to pump  2 , where the liquid CO 2  stream is first pressurized to a suitable pressure (e.g., in the range of about 300 psig (about 21 bar) to about 1800 psig (124 bar), preferably in the range of about 300 psig (about 21 bar) to about 1200 psig (about 83 bar)), prior to delivery to purification section  35 . The liquid CO 2  stream is purified within purification section  35  and then delivered to process area  7  at the selected purity level. Depending upon the temperature and pressure conditions of the CO 2  stream within supply line  36  and whether process tool  6  is in operation or shut down, a portion (e.g., some or all) of the CO 2  stream is selectively diverted back to tank  10 , via recirculation line  40  and selective manipulation of valves  38  and  39 , to ensure the CO 2  stream is maintained as a liquid and at the desired temperature and pressure conditions.  
      The CO 2  stream emerging from purification section  35  is then directed into sub-fab area  102 , where the C 02  is further pressurized by high-pressure pump  4  to the required processing pressure (e.g., in the range of about 3000 psig (about 207 bar) to about 8000 psig (about 552 bar)), optionally purified in second purification section  45 , and adjusted to the required temperature conditions within conditioner  5 . The CO 2  stream is then directed into process tool  6  in clean room  100 , where it is utilized to process a semiconductor wafer. After a processing operation is complete, the CO 2  stream emerges from the process tool and is recycled, via line  50 , to third purification unit  8  for removal of impurities and/or additives from the CO 2  stream. The CO 2  stream is then directed to one or both of secondary storage tanks  9  and  11 , where the CO 2  is stored at suitable temperature and pressure conditions (e.g., conditions similar to those described above for tank  10 ) prior to delivery back to primary storage tank  10 . Liquid carbon dioxide is replenished as necessary to tanks  9  and  11  via the external CO 2  supply source  12  so as to maintain an adequate supply of CO 2  through operation of the process tool.  
      Thus, system  1  facilitates a continuous supply of high-pressure CO 2  to the process area at the desired purity levels while ensuring the CO 2  stream is maintained in a liquid state and at the desired temperature and pressure conditions throughout all areas of the system. The CO 2  storage tanks can be situated remotely (e.g., 50 meters or more, preferably 100 meters or more, and more preferably 1 kilometer or more) from the process area, and the CO 2  stream can be maintained in liquid state and at the desired temperatures and pressures despite ambient temperature fluctuations and/or halting of CO 2  supply to the process tool. Further, the transport of high-pressure CO 2  (e.g., at pressures in the range of about 3000 psig (about 207 bar) to about 8000 psig (about 552 bar)) is minimized or substantially reduced to the relatively short distance between the high-pressure pump and the process tool.  
      While the system described above and depicted in  FIG. 1  shows a number of purification sections disposed at different locations within the system, the system is in no way limited to this configuration and can be modified to include a single purification section disposed between the high-pressure pump and the process tool (i.e., as indicated by purification section  45  in  FIG. 1 ). The purification section can be as simple as a filtration unit (e.g., a single filter) to remove particulate material from the CO 2  stream prior to delivery of the stream to the process tool.  
      In another modification to the embodiment of  FIG. 1 , system  1  can be designed to provide CO 2  at the required pressure and temperature conditions to any selected number of process tools  6 . For example, in the embodiment of  FIG. 2 , process area  7  is modified to include a series of process tools  6   a  to  6   n  that are each connected at their inlets via a suitable manifold piping system  104  to the main CO 2  supply from conditioner  5 . The manifold piping system  104  can include a series of valves (not shown) along the branch lines to the inlets of the process tools  6  so as to selectively control the flow of CO 2  to each process tool. The process tools are further connected at their outlets via a suitable manifold piping system  105  to supply line  50  (which delivers the CO 2  to third purification unit  8 ). In this embodiment, the process area includes each process tool, and a single high-pressure pump is utilized to provide the CO 2  to multiple process tools.  
      Alternatively, the system of  FIG. 1  can be modified to include a selected number of process areas, where each process tool is connected with a separate high-pressure pump. Referring to  FIG. 3 , system  1  is modified to include a selected number of process areas  7   a  through  7   n,  where each process area  7  is substantially similar in configuration as the process area described above and depicted in  FIG. 1 . In particular, each process area  7   a,  . . . 7   n  includes a process tool  6   a,  . . .  6   n  disposed in a clean room  100   a,  . . .  100   n,  and a sub-fab area  102   a,  . . .  102   n  that includes a high-pressure pump  4   a,  . . .  4   n,  purification section  45   a,  . . .  45   n  and conditioner  5   a,  . . .  5   n.  The process areas are connected in parallel at their inlet sections to supply line  36  via a manifold configuration, and are further connected at their outlet sections to supply line  50  via a manifold connection, such that the CO 2  streams emerging from the process tools are combined for recycling in line  50 . The branch lines in each manifold section can include valves (not shown) to selectively control the flow of CO 2  fluid to each supply area.  
      Thus, the process area design of  FIG. 3  enables each process tool to have its own dedicated pressurization, purification, and conditioning of CO 2  fluid. This design is particularly useful in applications in which two or more process tools are remote in distance from each other and therefore avoids the transport of high-pressure CO 2  over large distances (i.e., since the high-pressurization occurs individually proximate each process tool). This design is also useful in applications where two or more process tools are operating under different processing conditions at the same time. For example, one process tool may be in a loading stage (i.e., where a wafer is being loaded into the chamber) while another process tool is processing a wafer with high-pressure CO 2 , and further still while another process tool is in a depressurization or reducing pressure stage (e.g., immediately following wafer processing).  
      Still another modification to the system of  FIG. 1  is depicted in  FIG. 4 . In this embodiment, the primary storage tank is maintained at a higher pressure than in the previous embodiments, such that liquid carbon dioxide can be directly transported to purification section  35  without the use of a pump. In particular, primary storage tank  10   a  is a high-pressure storage tank that is initially filled with liquid CO 2  at cryogenic conditions. The temperature of the CO 2  can be allowed to increase within the primary storage tank to facilitate an increase in pressure within the tank. For example, the temperature of CO 2  may be allowed to increase to ambient temperature (e.g., about 68° F. or about 20° C.), resulting in a corresponding increase in pressure (e.g., about 840 psig or about 58 bar, which is the vapor pressure of CO 2  at the ambient temperature described above). The advantage of this embodiment is that the CO 2  in the primary storage tank is pressurized without the requirement of additional and externally applied mechanical or thermal energies. Thus, the CO 2  stream from tank  10   a  can be transported via supply line  20  directly to purification unit  35 .  
      A pump  2  is optionally provided along supply line  70  between secondary storage tanks  9  and  11  and primary storage tank  10   a  to facilitate transfer of CO 2  fluids from the secondary tanks to the primary tank. In addition, pump  2  can be used to increase the pressure in tank  10   a  above the vapor pressure for CO 2  at the ambient temperature. Alternatively, as noted above, the secondary storage tanks can include internal heating coils to heat and pressurize the CO 2  fluid as necessary to facilitate flow of CO 2  from the secondary storage tanks to the primary storage tank. The pressure in the primary storage tank can be adjusted depending upon the distance between tank  10   a  and process area  7  (e.g., larger distances and/or increased flow rates of the CO 2  stream may require an increased pressure within tank  10   a ). Exemplary pressures of CO 2  within tank  10   a  are the range of about 300 psig (about 21 bar) to about 1500 psig (about 103 bar), and preferably in the range of about 700 psig (about 48 bar) to about 1200 psig (about 83 bar).  
      In yet another modification of the system described above, one or more of the secondary storage tanks can be directly connected with purification sections to facilitate additional purification of CO 2  within the storage tanks prior to delivery to the primary storage tank. Referring to  FIG. 5 , secondary storage tank  9  is further connected to a purification section  18  via a supply line  80 , where a valve  81  is disposed along line  80 . The purification section can include any one or more of the previously described purification units to facilitate removal of impurities from the CO 2  being stored in tank  9 .  
      A recycle line  90  extends between purification section  18  and tank  9 , with a valve  91  disposed along line  90 , to facilitate recirculation of CO 2  fluids between the tank and the purification unit(s). In addition, an analyzer module  28  is provided in-line along recycle line  90 . The analyzer module includes any suitable number and types of analyzers to continuously measure the concentrations of impurities in the CO 2  stream passing through line  90 . The valves  81  and  91  may be manually or automatically controlled (e.g., via a suitable controller) to facilitate flow of CO 2  to the purification section based upon feedback information provided by the analyzer module regarding impurity concentrations in the CO 2  stream. Thus, the closed loop recirculation and purification design of  FIG. 5  facilitates the purification of the CO 2  stream until a selected purity level is reached. Upon achieving the desired purity level, the CO 2  can be delivered to the primary storage tank and/or any other secondary storage tanks of the system.  
      The system of  FIG. 5  allows the impurity levels of the stored liquid carbon dioxide to be reduced to extremely low levels, preferably on the order of less than 1 part per million (ppm), more preferably in the range of parts per billion (ppb), and most preferably in the range of parts per trillion (ppt). Such purity levels are required for certain processing applications.  
      In an exemplary embodiment of the system of  FIG. 5 , the purification section  8  includes a catalytic oxidation unit that removes hydrocarbon based impurities, where hydrocarbon impurities are oxidized to simpler molecules (e.g., H 2 O and CO 2 ) in presence of an oxidant (e.g., O 2 ) and a catalyst. The in-line analyzer module  28  includes hydrocarbon and oxygen analyzers. The hydrocarbon analyzer measures the concentrations of selected hydrocarbons in the CO 2  stream emerging from purification section  18 . If the hydrocarbon concentration is determined to be above an acceptable level, oxygen is injected into the catalytic oxidation unit via an injection line (not shown). The CO 2  stream emerging from the oxidation unit is also analyzed for oxygen concentration. If the O 2  concentration exceeds a threshold level, the amount of oxygen injected into the oxidation unit is decreased. The recirculation of the CO 2  stream via line  90  is carried out until the measured hydrocarbon concentration levels within the CO 2  is within acceptable levels. Purification section  18  can include additional purification units, such as an adsorption unit to remove reaction byproducts like water to acceptable levels.  
      The secondary tank configuration of  FIG. 5  can also be provided proximate the process area to purify and recycle the CO 2  stream emerging from the process tool. In particular, a secondary storage tank  9 , as depicted in  FIG. 5 , can be situated proximate (e.g., within about 100 meters) of the process area to receive a selected portion (e.g., about 80% by volume) of the CO 2  stream emerging from the process tool, where the CO 2  stream is purified via purification section  18  to a selected purity level prior to delivery to the high-pressure pump for re-use by the process tool. The remainder (e.g., about 20%) of the CO 2  stream emerging from the process tool is directed to the primary storage tank in the manner described above and depicted in  FIG. 1 .  
      As noted above, the systems described above are not limited to use with semiconductor process chambers. Rather, the systems can be implemented for use with any number of different process stations in which carbon dioxide or other fluids are utilized for cleaning or any other process, where the fluids are preferably maintained in liquid state prior to being pressurized by the high-pressure pump disposed proximate the process area.  
      Having described novel systems and method for purification and delivery of high-pressure fluids in processing applications, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention as defined by the appended claims.