KR20070027689A - Method and system for supplying carbon dioxide - Google Patents

Abstract

Provided is a novel method and system for supplying high-pressure carbon dioxide to an application having a variable carbon dioxide flow requirement. The method includes providing a high-pressure carbon dioxide feed stream to a buffer volume (80) and determining the amount of carbon dioxide to be delivered to the application tool (100). The pressure in the buffer volume (80) is maintained at a pressure that exceeds the pressure required by the application tool (100). The temperature in the buffer volume (80) is further adjusted to modify the density of the carbon dioxide and based thereon the size of the buffer volume (80). Thereafter, the carbon dioxide from the buffer volume (80) is delivered at a variable flow rate as required by the application tool (100). ® KIPO & WIPO 2007

Description

METHOD AND SYSTEM FOR SUPPLYING CARBON DIOXIDE}

The present invention relates to a method for supplying high pressure carbon dioxide to an application that requires a variable carbon dioxide flow. Specifically, the present invention relates to the supply of carbon dioxide to semiconductor application tools with instantaneous demands, which are significantly higher than the average demand.

There has long been a need for instantaneous fluid delivery. In related applications, high pressure gas sources have been used where momentary demands on the fluid are required. For example, US Pat. No. 4,977,921 to Knight et al. Uses a modified tube trailer that stores high pressure air or nitrogen to provide a high degree of instantaneous gas flow for cleaning large lines. This is discussed. United States Patent No. 5,417,615 to Beard et al. Relates to the use of a pressurized gas source to store high pressure air used to accelerate a ride in an amusement park.

Bishop's US Pat. No. 6,725,671 B2 discloses the effect of temperature and pressure on the capacity of a natural gas storage system. The temperature and pressure and the thickness of the storage vessel wall are selected to minimize the storage cost of natural gas.

There was a need in the semiconductor industry to supply large amounts of fluid to applications such as cleaning tools. In this regard, US Pat. No. 6,085,762 to Baton and US Pat. No. 6,403,544 B1 to Davenhall et al. Disclose the use of buffer volumes or ballast tanks in the supply of supercritical fluids to semiconductor wafer processing applications. . The processing includes sending pressure pulses of supercritical fluid to the application.

US Pat. No. 6,612,317 B2 to Costantini et al. Describes the use of buffer volumes or ballast tanks to supply supercritical fluids for semiconductor wafer processing applications. Changing the pressure of the fluid in the buffer volume is disclosed as a means of controlling the fluid delivered to the application tool, which results in a rapid discharge of the fluid in the buffer volume into the wafer processing chamber. As used herein and in the claims, the term "buffer volume" is understood to mean a pressure vessel, such as a ballast tank, used to deliver fluid to semiconductor applications.

One disadvantage of the systems of the related art is that the temperature selection in the buffer volume has not been recognized as an important factor in controlling the amount of carbon dioxide available for delivery to semiconductor application tools. Another disadvantage is that the related art does not provide a means for controlling the release of pressure in the buffer vessel.

In order to alleviate these shortcomings, it is an object of the present invention to provide a means for controlling the amount of carbon dioxide available for delivery to the application tool during a high degree of instantaneous demand period.

It is another object of the present invention to adjust the buffer volume capacity without changing the physical size of the buffer volume.

In addition, once the maximum amount of carbon dioxide to be delivered to the semiconductor application tool is identified, it is a further object to size the buffer volume by manipulating the temperature of the carbon dioxide.

It is another object of the present invention to replace expensive large pumps needed for delivery to semiconductor cleaning tools at high flow rates.

It is also a further object to eliminate the time delay that may be required when using a pump to instantaneously deliver the required carbon dioxide flow rate and thus provide the required flow rate.

Other objects and advantages of the invention will be apparent to those skilled in the art upon review of the specification, drawings and appended claims.

Summary of the Invention

The above objects are met by the process of the present invention.

According to one aspect of the present invention, a method is provided for supplying high pressure carbon dioxide to an application tool having varying carbon dioxide flow requirements. The method comprises providing a high pressure carbon dioxide feed stream to a buffer volume; The average density of carbon dioxide contained in the buffer volume at the minimum pressure is maintained by maintaining the pressure in the buffer volume between the minimum pressure and the maximum pressure exceeding the pressure required by the application tool, so that the average of carbon dioxide contained in the buffer volume at the maximum pressure. This includes varying the density.

The average temperature in the buffer volume is adjusted to vary the difference between the average density of carbon dioxide contained in the buffer volume at minimum pressure and the average density of carbon dioxide contained in the buffer volume at maximum pressure so that the flow requirements associated with the application tool are met. . The high pressure carbon dioxide feed stream is delivered from the buffer volume at varying flow rates required by the application tool.

According to another aspect of the present invention, a system is provided for supplying high pressure carbon dioxide to an application that has variable carbon dioxide flow requirements. The system includes a buffer volume that receives a high pressure carbon dioxide feed stream, wherein the pressure in the buffer volume is maintained between a minimum pressure and a maximum pressure in excess of the pressure required by the application tool, such that the density of carbon dioxide at the minimum pressure is reduced. Different from the density of carbon dioxide at maximum pressure and allow the temperature in the buffer volume to be controlled.

The carbon dioxide purification unit is disposed upstream of the buffer volume to deliver the high pressure carbon dioxide feed stream, and the application tool is located downstream of the buffer volume to receive carbon dioxide from the buffer volume at the variable flow rate required by the application tool.

<Brief Description of Drawings>

The invention will be better understood with reference to the drawings, wherein like numerals refer to like features.

1 shows a schematic diagram of an overall system for delivering carbon dioxide to a semiconductor application tool with variable flow requirements.

2 depicts a five minute cycle of exemplary manipulations for delivery of carbon dioxide, in accordance with the present invention.

3 shows a schematic of an entire system with a single core heat exchanger.

4 shows a schematic view of the entire system according to another embodiment in which the device upstream of the pressurization means is changed.

5 shows a schematic diagram of an entire system according to another embodiment with a single core heat exchanger disposed upstream of the pressurizing means.

6 shows a schematic diagram of an entire system, according to another embodiment where recirculation is redesigned.

<Detailed Description of the Invention>

Fabrication of integrated circuit devices requires a number of complex steps required to form various shapes on a wafer substrate. Some steps include cleaning the substrate with high pressure carbon dioxide. As used herein, the term “high pressure carbon dioxide” refers to carbon dioxide at a pressure above a critical pressure of 1060 psig. It will be appreciated that when the temperature with respect to carbon dioxide is below its critical temperature of 88 ° F. and at high pressure, the fluid is liquid. On the other hand, if the temperature with respect to carbon dioxide exceeds 88 ° F., the fluid will be supercritical. Thus, if greater than 1060 psig, carbon dioxide, whether liquid or supercritical, has only one phase (ie, no discontinuous phase transition).

The semiconductor cleaning process of the present invention provides an effective means of supplying high pressure carbon dioxide to semiconductor cleaning applications where there is a very high instantaneous need for high pressure carbon dioxide but a much lower average demand for high pressure carbon dioxide during a given operating cycle. Typically, a wafer cleaning application processes one wafer per cycle, and the carbon dioxide demand during that cycle varies from very high speed to substantially zero.

As shown in FIG. 1, the supply system includes a carbon dioxide bulk tank 10 for holding carbon dioxide delivered to the semiconductor application tool 100. As described below with specific embodiments below, carbon dioxide removed from the bulk tank 10 is delivered through heat exchangers 29 and 30 and carbon dioxide purification unit 40. A high pressure carbon dioxide stream 75 is generated and delivered to a buffer volume tank / vessel 80 that is used to meet the instantaneous needs of the application for high pressure carbon dioxide.

To illustrate, the application tool 100 requires a maximum instantaneous flow rate S _max of carbon dioxide at a certain pressure level setting P. The pressure P _bv at the buffer volume 80 must always be at least equal to the set pressure (ie P _bv = or> P). However, in order to compensate for some pressure drop in the line from the buffer volume 80 to the application tool 100, the pressure P _{bv in the} buffer volume is equal to the minimum required pressure (higher than the pressure required by the application tool). P _min ) cannot be lowered (ie, P _bv = or> P _min = or> P).

The average flow rate F _avg (F _i ) of the high pressure carbon dioxide feed stream 75 delivered to the buffer volume 80 is the average of the high pressure carbon dioxide feed stream 85 delivered to the application tool 100. It must be equal to or greater than the flow rate (S _avg ) (S _i ). Thus, when F _i is greater than S _i , the pressure in the buffer volume 80 increases. Conversely, if S _i is greater than F _i , the pressure in the buffer volume 80 will decrease. Thus, over the course of the processing cycle, if the flow rate to the application tool 100 is greater than the flow rate of the high pressure carbon dioxide feed stream 75, the additional carbon dioxide required by the application tool 100 is stored in the buffer volume 80. It must be delivered from carbon dioxide.

Applicants have found that, according to the present invention, a suitably sized buffer volume 80 allows the required amount of carbon dioxide to be delivered to the application tool during an operation cycle without replacing it or changing its physical properties. In order to appropriately size the buffer volume 80, the flow rate of carbon dioxide into the buffer volume and the application tool 100 can be integrated over time to determine the exact amount of change of carbon dioxide in the buffer volume. The buffer volume provides accurate changes in carbon dioxide by changing the pressure from maximum pressure to minimum pressure when carbon dioxide is required by the application. The temperature in the buffer volume at the maximum and minimum pressure will determine the density of carbon dioxide in the buffer volume. Thus, the size of the buffer volume necessary for the accurate supply of the change amount of carbon dioxide can be determined. Once the buffer volume is controlled, the amount of carbon dioxide supplied from the buffer volume to the application tool can be changed without changing the physical properties by changing the volume temperature.

Referring to FIG. 2, the application tool 100 is shown to have a five minute cycle. The tool requires 14 lbs / min of high pressure carbon dioxide for the first minute of the cycle, 11 lbs / min for the third minute of the cycle, and no carbon dioxide for any other time of the 5 minute cycle. . The average carbon dioxide demand S _avg of the application tool 100 is 5 lbs / min. The flow rate F _i of the high pressure carbon dioxide feed stream 75 remains constant at 5 lb / min over the cycle. The largest carbon dioxide deficiency that the buffer volume 80 must replenish is at the end of the third minute of the cycle. The deficiency can be calculated by integrating the difference between F _i and S _i over the entire cycle, or by checking the visual representation on the graph.

As shown in FIG. 2, in the third minute, an additional 10 lbs of carbon dioxide was sent to the application from the high pressure carbon dioxide feed stream 85 than entered the buffer volume through the high pressure carbon dioxide feed stream 75. Thus, the buffer volume 80 should have a carbon dioxide buffer capacity of 10 lbs.

The buffer capacity required by any application tool 100 can be calculated in a manner similar to that shown in FIG. Once the required buffer capacity for the buffer volume 80 is known, the buffer volume 80 can be sized. In addition to the required buffer capacity, the density of carbon dioxide should be known at the maximum and minimum pressure loading of the buffer volume 80. Returning to the cycle depicted in FIG. 2, the maximum pressure loading of the buffer volume 80 occurs at 0 and 300 seconds. The minimum pressure loading of the buffer volume 80 occurs at 180 seconds. At minimum loading the pressure in the buffer volume 80 is P _min . Once the temperature in the buffer volume 80 is known, the carbon dioxide density can be determined.

Preferably, the buffer volume is maintained at isothermal for the specific operating cycle. Thus, the buffer volume temperature at the maximum and minimum loading pressures is approximately the same. As mentioned above, the minimum pressure loading P _min must be greater than the pressure P in the line required by the application tool 100. In a preferred embodiment the maximum loading pressure is selected to be less than or equal to 90% of the maximum allowable operating pressure of the buffer volume 80. Manipulation of the buffer volume under these conditions considers safety so that the safety devices installed in the system do not need to operate and an unexpected emergency does not occur.

By selecting the maximum loading pressure, it is possible to determine the carbon dioxide density at this particular maximum loading pressure as well as at the minimum loading pressure. This allows calculation of the buffer volume by dividing the buffer volume capacity by the density difference at the maximum and minimum loading pressures. Once the buffer volume is configured, the amount of carbon dioxide that can be delivered instantaneously can be adjusted by changing the buffer volume temperature.

For example, the operator of the system indicates that a 5 minute machining cycle would be desirable for the application tool 100 to require an instant 1.35 lbs at a pressure of 2850 psig. Since the carbon dioxide demand of 1.35 lbs is instantaneous, the high pressure carbon dioxide stream 75 is continuously delivered to the buffer volume 80 during discharge. However, the amount delivered is insignificant compared to the amount emitted by the application tool. Similar analysis as discussed and shown in FIG. 2 was performed at different temperature points. Assuming a 50 psi pressure drop in the line from the buffer volume to the application tool, the minimum loading pressure is 2900 psig. The maximum loading pressure for the buffer volume is chosen to be 3100 psig at a temperature of 110 ° F. At 3100 psig and 110 ° F, the density of carbon dioxide is 52.238 lb / ft ³ . At 2900 psig and 110 ° F, the density of carbon dioxide is 51.418 lb / ft ³ . Thus, dividing the required buffer volume capacity of 1.35 lbs by the difference in density (ie, 52.238-51.418 lb / ft ³ ) represents the buffer volume of 1.65 ft ³ . Changing this temperature changes the amount of carbon dioxide delivered to the application tool.

As illustrated in the table below, the temperature associated with the buffer volume 80 was changed to a temperature other than 110 ° F. and the calculations were performed in the manner described above.

Max loading pressure (psig) Temperature at Buffer Volume 80 (℉) Carbon dioxide density at maximum loading (lbs / ft ³ ) Carbon dioxide density at 2900 psig (lbs / ft ³ ) Required size of buffer volume (90) (ft ³ ) 3100 50 61.654 61.264 3.46 3100 70 58.767 58.277 2.76 3100 85 56.445 55.855 2.29 3100 100 53.973 53.256 1.88 3100 110 52.238 51.418 1.65 3100 120 50.433 49.492 1.43 3100 150 44.611 43.192 0.95 3100 200 34.502 32.377 0.64

As shown in the table above, the density of carbon dioxide decreases as the buffer volume temperature increases, and less total carbon dioxide is contained in the buffer volume 80. The density difference between the pressure maximum and minimum loading increases with the buffer volume temperature. The required size of the buffer volume 80 decreases as the buffer volume temperature increases. Similarly, even if less carbon dioxide is contained in the buffer volume at maximum pressure, the amount of carbon dioxide available for delivery to the application tool increases for a given buffer volume as the temperature increases. This finding is exceptional because it is common practice to reduce the buffer volume temperature at a given temperature to increase the amount of carbon dioxide contained in the buffer volume. Increasing the volume of carbon dioxide that can be stored or delivered to the application tool 100 is useful in the present invention.

Increasing the buffer volume temperature increases the ability of the buffer volume to instantaneously deliver large volumes of carbon dioxide. Therefore, the buffer volume temperature should be chosen as case by case and balanced against other factors that suggest lower temperatures. These factors include: (a) thicker walls are required for the buffer volume / container because the strength of the wall material decreases as the buffer volume temperature increases; (b) additional heat will be lost to the environment and the cost of maintaining the buffer volume temperature will increase with temperature; (c) More energy will be needed to raise the temperature of the carbon dioxide in the buffer volume 80 to the desired temperature.

In addition, the desired carbon dioxide temperature for the application 100 should be taken into account in selecting the buffer volume temperature. In a preferred embodiment, the buffer volume temperature should be kept slightly above ambient temperature at approximately 110-120 ° F.

Returning to FIG. 1, the entire carbon dioxide supply system according to one embodiment is described in detail. The carbon dioxide (C0 ₂ ) source for the system is a CO ₂ bulk tank 10. The tank may range in size from 200 liters Dewar to a tank holding 300 tons of CO ₂ . Typically, the bulk tank has a capacity in the range of 6 to 100 tons. For example, the CO ₂ bulk tank 10 can be refilled from a CO ₂ delivery trailer without interrupting operation of the CO ₂ supply system.

The CO ₂ bulk tank 10 usually maintains liquid CO ₂ with a vapor headspace that maintains a pressure of 250 to 350 psig and a temperature of −9 ° F. to 10 ° F. Saturated liquid carbon dioxide is drawn from the bottom of the bulk tank 10 and proceeds to a CO ₂ booster pump 15. The pump raises the pressure of CO ₂ to approximately 50 to 120 psi and the temperature increases only incrementally. Subcooled liquid CO ₂ presence booster pump 15 is partially conveyed to pressurizing means 20. The pressurizing means can be a pump selected from a diaphragm pump, a metal diaphragm pump, a piston pump or other pumping means.

That the C0 ₂ CO ₂ the pressure means 20 from the plus line pressure drop between the pressure at the maximum load of the buffer volume (80) CO ₂ pressure means 20 and the buffer volume 80 is pressurized to a pressure of as much as . CO ₂ is usually increased at temperatures up to approximately 20 ° F. via CO ₂ pressurization means 20 and released at temperatures in the range of about 10-30 ° F.

A portion of the subcooled CO ₂ liquid discharge booster pump 15 beyond the maximum capacity of the CO ₂ pressurizing means 20 is circulated through the backpressure regulator 16 and recovered to the CO ₂ bulk tank 10. A small portion of the subcooled liquid C0 ₂ is flashed with steam as it passes through the back pressure regulator 16. Over time, this steam will increase the pressure in the CO ₂ bulk tank 10. To prevent this phenomenon, the cooling system 12 draws coolant through the cooling coil 11 in the CO ₂ bulk tank 10 to recondensate the CO ₂ vapors that form from the plate via the back pressure regulator 16. To carry. This cooling also recondenses the CO ₂ vapors formed due to heat leakage from the environment into the CO ₂ bulk tank 10.

Pressurized CO ₂ release pressurizing means 20 carries through heat exchangers 29 and 30 which indirectly exchanges heat with some or all of the CO ₂ recovered from the CO ₂ purification unit 40. The heat exchangers 29 and 30 enable heat recovery from the CO ₂ purification unit 40 which takes place at a temperature higher than the temperature of the CO ₂ release CO ₂ pressurizing means 20. CO ₂ is the temperature of the flow, wherein the CO ₂ through the heater unit 35 is raised to the temperature required for the CO ₂ purification unit 40. The heater 35 is necessary because heat recovery in the heat exchangers 29 and 30 is not as efficient as a whole.

The CO ₂ purification unit 40 may be selected from any purification apparatus capable of operating at a temperature higher than the temperature of the CO ₂ release pressurizing means 20. Preferably, the unit is operated at a temperature of 100 ° F to 1000 ° F, most preferably at a temperature of 200 ° F to 700 ° F. Exemplary purification units include adsorption, absorption, chemical reactions, catalytic oxidation, and filtration.

Filtration at elevated temperature may be part of the function of the CO ₂ purification unit. Filters, such as sintered metal filters commonly used in electronic commerce, are known to perform better in the vapor phase than in liquid phase applications. This is mainly due to the increased dispersibility of particles in the vapor phase and Brownian motion. The behavior of the filter in supercritical service (ie, pressures above 1060 psig and temperatures above 88 ° F.) has not been well studied, but the temperature of the supercritical fluid increases its behavior, including its dispersibility, and is similar to that of gas. It is known to become.

When the CO ₂ purification unit 40 operates at a temperature higher than the buffer volume 80 temperature, the CO ₂ is further gasified. Therefore, filtration is more effective. If a filter is included as part of the CO ₂ purification unit 40, it must be located downstream of the purification means to produce particles such as adsorption and catalytic oxidation.

CO ₂ proceeds again through a purification unit 40 the CO ₂ is the heat exchanger 30 is removed from, where it exchanges heat with the CO ₂ from the CO ₂ there indirect towards the pressing means (20). The CO ₂ required in the buffer volume 80 flows to the high pressure carbon dioxide feed stream heating or cooling means 74. Based on the pressure sensed in the buffer volume 80 at the valve 60, more than a predetermined level of CO ₂ is recycled to the bulk tank 10. CO _{2, which} is not necessary for the buffer volume 80, proceeds through the heat exchanger 29 where additional heat is regenerated. The CO ₂ discharge heat exchanger 29 flows to the recycle stream 59 through a valve 60 that releases pressure close to the pressure of the CO ₂ bulk tank 10. Some of the CO ₂ is flashed as steam through the steam through valve 60, but this steam is recondensed to the cooling coil 11 in the CO ₂ bulk tank 10 by the coolant supplied by the cooling system 12. do.

The CO ₂ is recycled to the bulk tank 10 because there are several times when it is desirable to have an average demand of the application 100, an average flow beam through the CO ₂ pressurizing means 20 and a CO ₂ purification 40 greater than Savg. To do is arbitrary. For example, the application 100 is because it requires the holding case to stop pulling the carbon dioxide, maintaining the removed energy / heat from the CO ₂ pressure means 20, and continue the operation of the carbon dioxide supply system to CO ₂ It is desirable to provide energy / heat to the purification unit 40.

In one embodiment, heat regeneration from the CO ₂ purification 40 is performed using two heat exchangers 29 and 30 rather than one heat exchanger. Alternatively, all CO ₂ from the purification unit 40 will be cooled to a temperature below the desired temperature in the buffer volume 80 when exchanging energy / heat with CO ₂ from the pressurizing means 20. Two heat exchangers 29 and 30 may be used to direct CO ₂ to the high pressure carbon dioxide feed stream heating or cooling means 74 at a temperature close to the desired temperature in the buffer volume 80 on the discharge heat exchanger 30. . Thus, recycle stream 59 is further cooled in heat exchanger 29 before restoring flow to bulk tank 10.

The temperature of the CO ₂ which proceeds through the high pressure carbon dioxide feed stream heating or cooling means 74 is adjusted to the desired temperature in the inlet CO ₂ temperature or the buffer volume 80. Exemplary apparatus that can be used as heating or cooling means 74 include air-cooling coils, water-cooling or coolant-cooling heat exchangers, and heaters. The high pressure carbon dioxide feed stream 75 discharges the high pressure carbon dioxide feed stream heating or cooling means 74 and proceeds to the buffer volume 80.

The CO ₂ in the buffer volume 80 may be heated or cooled by the buffer volume temperature control means 81. Since the high pressure carbon dioxide feed stream heating or cooling means 74 adjusts the temperature of the high pressure carbon dioxide feed stream 75 to the desired temperature in the buffer volume 80, the required efficiency of the buffer volume temperature adjusting means 81 is maintained. ) Is the minimum. Typically designed to compensate for heat loss or increase between buffer volume 80 and ambient temperature. Apparatus that can be used in the buffer volume temperature control means 81 includes a heat trace, an inner peter, an outer band or cable heater, an outer cooling coil and an inner cooling coil. The buffer volume 80 is usually insulated to reduce the amount of heat exchange with the surrounding environment. Alternatively, it may be beneficial to adjust the buffer volume such that the temperature in the buffer volume / tank is lower at the bottom than at the top. The temperature of the fluid contained at the top of the buffer volume can be adjusted by drawing the fluid from the bottom of the buffer volume (not shown), heating the fluid utilization temperature control means, and recovering this flow to the top of the buffer volume 80. have.

If the application tool 100 requires CO ₂ , the fluid releases a buffer volume 80 in the high pressure carbon dioxide feed stream 85. The high pressure carbon dioxide feed stream 85 is then heated or cooled using heating or cooling means 86 to produce the temperature required for the application tool 100. This proceeds across the valve 90, through the filter 88. Filter 88 is used to facilitate the supply of particle-free CO ₂ even when buffer volume 80 does not have an electropolished inner surface. The valve 90 regulates the flow of the high pressure carbon dioxide feed stream 85 and ensures that the pressure downstream of the valve 90 is the pressure required for the application tool 100. CO ₂ then proceeds through the filter 92 on the path to the application tool 100, where it is used for semiconductor wafer processing.

Returning to the embodiment shown in FIG. 3, the heat exchanger may be combined with the heat exchanger core 31. This arrangement reduces the space required for the CO ₂ supply system and can reduce costs compared to having two heat exchangers. One type of heat exchanger that would be suitable for this efficiency is a micro like a Printed Circuit heat exchanger (PCHE) supplied by the Heattric division of Meggitt (UK) Ltd. It will be a channel heat exchanger.

4 shows another embodiment of a supply system. The CO ₂ booster pump 15 and back pressure regulator 16 shown in FIG. 1 are replaced with a cooling system 13 and a subcooler heat exchanger 14. The modified system provides an alternative supply of subcooled liquid to the CO ₂ pressurizing means 20. CO ₂ from the CO ₂ advanced bulk tank 10 is above the super-cooling the super-cooling exchanger 20 ℉ from heat exchanger 14 prior to the CO ₂ pressure means (20).

The cooling system 13 is used to provide coolant to the condenser heat exchanger 65. Instead of using the cooling coil 11 to recondense the steam introduced into the bulk tank 10, the condenser before returning the CO ₂ vapor formed from the pressure drop through the valve 60 to the CO ₂ bulk tank 10. Recondensation in the heat exchanger (65).

Alternatively, although not shown, the supply system may be arranged to include a CO ₂ booster pump 15, a back pressure regulator 16 connected with the condenser heat exchanger 65, and a cooling system 13. The system may also contain a cooling system 12 and a cooling coil 11 together with the cooling system 13 and the subcooling heat exchanger 14 and / or the condenser heat exchanger 65.

Returning to FIG. 5, one embodiment where another heat exchanger configuration system is used is shown. The heat exchangers 29 and 30, the subcooled heat exchanger 14 and the condenser heat exchanger 65 shown in FIG. 4 may be replaced with a heat exchanger core such as the heat exchanger 21. The heat exchanger 21 will include high and low pressure sides. An advantage associated with the embodiment of the heat exchanger 21 is that the space will be reduced and the cost for the system will potentially be reduced. One type of heat exchanger that would be suitable for this efficiency would be a microchannel heat exchanger, such as a printed circuit heat exchanger (PCHE), supplied from the tactile portion of the MEGITT (UK) LTI.

6 illustrates another embodiment where the recycle stream 59 is behind the high pressure carbon dioxide feed stream heating or cooling means 86 and the filter 88. Those skilled in the art will appreciate that recycle stream 59 may be at another point in the system. The other position is downstream of the valve 90, but upstream of the high pressure carbon dioxide feed stream heating or cooling means 86, between the high pressure carbon dioxide feed stream heating or cooling means 74 and the buffer volume 80, with the CO ₂ pressurizing means; It includes between the heat exchanger (33).

In addition to using a pump such as CO ₂ pressurization means 20, a compressor may be used. In the case where a compressor is used as the CO ₂ pressurizing means 20, the CO ₂ from the bulk tank 10 is required to be transported through a vaporizer before proceeding to the CO ₂ pressurizing means 20. Therefore, the CO ₂ booster pump 15 and back pressure regulator 16 will not be used in such an arrangement.

High pressure carbon dioxide feed stream heating or cooling means 74 and high pressure carbon dioxide feed stream heating or cooling means 86 are optional, such as filters 88, 89 and 92.

The purification section of the supply system is also optional. In some cases, CO ₂ CO ₂ from bulk tank 10 is sufficiently pure for use in the application tool 100. If this is the case, the heat exchangers 29 and 30, heater 35 and CO ₂ purification 40 are removed. CO ₂ proceeds directly from the CO ₂ pressurization means 20 to the high pressure carbon dioxide feed stream heating or cooling means 74.

While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made and equivalents may be used without departing from the scope of the appended claims.

Claims (10)

Providing a high pressure carbon dioxide feed stream to the buffer volume; The pressure of the buffer volume is maintained between the minimum and maximum pressures exceeding the pressure required by the application tool, such that the average density of carbon dioxide contained in the buffer volume at the minimum pressure is the buffer volume at the maximum pressure. Varying the average density of carbon dioxide contained therein; Varying the difference between the average density of carbon dioxide contained in the buffer volume at the minimum pressure and the average density of carbon dioxide contained in the buffer volume at the maximum pressure so that the flow volume associated with the application tool is met. Adjusting the average temperature in the water; And Delivering a high pressure carbon dioxide feed stream from the buffer volume at a variable flow rate required by an application tool Method for supplying high pressure carbon dioxide to the application tool having a variable carbon dioxide flow request comprising a. The method of claim 1, further comprising reducing the buffer volume requirement to deliver a predetermined amount of carbon dioxide to an application tool based on temperature control to the buffer volume. The method of claim 1, wherein the flow request to the application tool is discontinuous. The method of claim 1 wherein the application tool is a semiconductor application tool. The method of claim 1 wherein the carbon dioxide requirements for delivery to the application tool are predefined. The method of claim 1 wherein the buffer volume is one or more pressure vessels. The method of claim 1, further comprising heating or cooling the carbon dioxide contained in the buffer volume via a heating or cooling device. The pressure in the buffer volume is maintained between the minimum and maximum pressures exceeding the pressure required by the application tool such that the density of the carbon dioxide at the minimum pressure is different from the density of the carbon dioxide at the maximum pressure, A buffer volume receiving a high pressure carbon dioxide feed stream for controlling the temperature in the buffer volume; A carbon dioxide purification unit disposed upstream of the buffer volume for delivering a high pressure carbon dioxide feed stream; And An application tool disposed downstream of the buffer volume receiving carbon dioxide from the buffer volume at a variable flow rate required by the application tool A system for supplying high pressure carbon dioxide to an application having a variable carbon dioxide flow request, including. The system of claim 8 further comprising a high pressure carbon dioxide feed stream heating or cooling device disposed downstream of said carbon dioxide purification unit. The system of claim 8, further comprising a carbon dioxide pressurization device disposed upstream of the purification unit for providing carbon dioxide supplied from the bulk storage tank.

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