1. Field of Invention
The present invention pertains to blending and delivery of fluid mixtures, in particular gaseous or vapor mixtures, during process applications.
2. Related Art
Many processing applications require mixtures of gases containing two or more gas components. The gas mixtures are typically prepared in advance and supplied to the end-user. In particular, a reliable source of gas mixtures is extremely important in semiconductor processing applications. For example, in manufacturing applications involving technologies such as thin film transistor liquid crystal display (TFT-LCD), light emitting diode (LED), and flat panel display (FPD), a mixture of gases such as phosphine and hydrogen is typically provided for various process steps (e.g., ion doping or deposition). Other examples of process gases include hydrides (e.g., silane, germane, phosphine, and arsine), and Group VIA compounds (e.g., hydrogen selenide and hydrogen sulfide).
Many of these process gases are toxic and corrosive, requiring extreme caution and special considerations for storage and delivery of these gases. Typically, these gases are stored under sub-atmospheric conditions (e.g., by use of an adsorbent inside a container or storage vessel that houses such gases) to prevent their inadvertent release to the surrounding environment. While such sub-atmospheric storage prevents catastrophic release, it is limited for use with pure gases and not to mixtures of gases such as those required for semiconductor processing applications.
Some new precursors are emerging which can be in the form of low vapor pressure liquids. Trisilane is an example which is a liquid having a vapor pressure of 95.5 Torr (0.13 bar) at 0° C. Other examples include tetramethylsilane (4 MS), trisilamine (TSA), and octafluorocyclopentene (C5F8). Typically, these products are stored in cylinders normally used for pressurized gases.
A conventional method for mixing one or more gases from a sub-atmospheric gas source is to withdraw the gas under vacuum and to allow mixing with the other gases under vacuum as they transport along delivery lines to the tool. The mixture concentration can be controlled by adjusting the relative flow rates of the different gases. Conceptually, this approach would appear to be relatively safe and reliable so long as the process tool pressure downstream is maintained significantly less than the source pressure.
However, in reality, piping diameters must be sized larger when delivering gases at sub-atmospheric pressure, thus adding to the cost and space requirements that are necessary for delivering the gas mixtures to the process tool. In addition, the purity of gas mixtures becomes more susceptible to surface desorption and dead volume contamination when delivery is under sub-atmospheric conditions. Further, there is a finite time required for constant, stabilized and steady state flow to be established at the sub-atmospheric conditions, and the highly toxic mixture must be vented and abated prior to establishing acceptable process flow conditions. This increases operating costs, process down time, and safety risks to the overall delivery system.
Further still, implementing a sub-atmospheric gas flow process to existing systems that use pressurized gas mixture sources (i.e., gas mixture sources greater than ambient pressures) would be cost prohibitive, since the delivery lines of the systems would need to be significantly modified (e.g., increasing piping diameters, modifying piping line runs, etc.). In addition, while compressor pumps can be used to form gas mixtures and force the gas mixtures to process sites, they can also contaminate the gases (e.g., with particulate material from the compressor equipment that may become entrained with the gas mixture). Thus, the use of compressor pumps is often not acceptable for use in delivering high purity gas mixtures required for semiconductor processes.
A conventional method for making a mixture utilizing a product stored at above atmospheric pressure is to fill a cylinder or vessel with one gas followed by the addition of a second gas. A precise amount of each gas can be obtained by measuring the gas flow rate using flow meters, weighing the gases using balances and/or monitoring the pressures of the gases. The cylinder is then rolled to make the mixture homogenous. However, there are several problems with this approach. One problem is that the rolling step is labor intensive and time consuming. If rolling were not necessary, analysis for certification of the gas mixture prior to use could be conducted upon filling a manifold, thereby expediting the process. In addition, some emerging semiconductor processing applications require large quantities of gas mixtures, which in turn requires an increasing number of rolling cylinders. Preparation and handling of such a large number of rolling cylinders can be cumbersome and economically prohibitive.
It is an object of the present invention to effectively provide gas mixtures in desired amounts and at desired flow rates to a tool or process site.
It is another object of the present invention to provide gas mixtures to a process site while minimizing contamination risks and equipment and operating costs.
It is a further object of the present invention to provide gas mixtures at a variety of different pressures, including sub-atmospheric and/or higher pressures, while minimizing or eliminating the need for mechanical equipment, such as pumps or compressors, to move and mix the gases.
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 gas mixing and delivery system comprises a first gas supply vessel including a first gas stored at a first pressure, a second gas supply vessel including a second gas stored at a second pressure, and a mixing vessel connected to each of the first and second gas supply vessels so as to receive the first and second gases. The system further comprises a buffer tank connected to the mixing vessel to receive a gas mixture including the first and second gases delivered from the mixing vessel. The buffer tank is configured to connect with a process tool. The system is further configured to produce a gas mixture including the first and second gases by facilitating delivery of the first and second gases into the mixing vessel, mixing the first and second gases in the mixing vessel and delivering the gas mixture from the mixing vessel to the buffer tank via a forcing gas that is at a pressure greater than the first pressure.
In another embodiment of the present invention, a method of producing and delivering a gas mixture for an application comprises delivering a first gas stored at a first pressure to a mixing vessel, delivering a second gas stored at a second pressure to the mixing vessel so as to facilitate mixing of the first and second gases within the mixing vessel to form a gas mixture including the first and second gases, and facilitating forced movement of the gas mixture including the first and second gases from the mixing vessel toward the buffer tank utilizing a forcing gas that is at a pressure greater than the first pressure.
The systems and methods of the present invention facilitate the formation of a gas mixture and delivery of the gas mixture to a buffer tank and process tool without the requirement of a pump, compressor or other mechanical compression device. Further, the gas mixture can be continuously or intermittently delivered to the process tool at a high purity level and with precise concentrations of gaseous components as desired for a particular processing application.
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.
In accordance with the present invention, a fluid mixing and supply system is provided that is capable of continuously mixing or blending two or more gases at any selected pressures (e.g., sub-atmospheric or higher pressures) and deliver the gas mixture having selected gas compositions at suitable flow rates and pressures to a process tool or site, while ensuring reliability of delivery of the gas mixture and substantially minimizing or preventing gas contamination or the presence of impurities in the gas mixture. In particular, the system facilitates the mixture of at least one gas that is provided from a gas source at sub-atmospheric or above atmospheric pressure conditions while substantially minimizing or preventing impurity contamination of the gas mixture.
The system facilitates the withdrawal of a first gas into a mixing vessel or chamber, followed by introduction of a second gas into the mixing vessel that is at a higher pressure than the first gas. The gases are mixed within the mixing chamber and then delivered to a second chamber or container that stores the gas mixture prior to delivery to a process tool. Thus, the system of the present invention avoids the use of a compressor or pump and/or other forms of mechanical compression, thus ensuring a high level of reliability of the gas mixture purity upon delivery to the process tool or site.
The system of the present invention is particularly suitable for use in providing gas mixtures at suitable concentrations and acceptable purity levels to semiconductor process tools. Any suitable process tool that provides some form of processing for a semiconductor wafer or chip (e.g., structural formation steps, etching, stripping, cleaning, etc.) can be provided in combination with a gas mixture system of the invention. In addition, any combination of gaseous compounds can be provided to form a gas mixture in accordance with the invention including, without limitation, reactive gases such as hydrogen, hydrides (e.g., silane, germane, phosphine, and arsine), Group VIA compounds (e.g., hydrogen selenide and hydrogen sulfide), and Group VIA compounds (e.g., HCl, HF, HBr), and also non-reactive gases such as carbon dioxide, helium and nitrogen.
In particular, the system could be implemented for use in a manufacturing process for forming a semiconductor device. For example, the system may provide a mixture of germane and hydrogen that is created on site at a semiconductor manufacturing facility. In another example, the system may provide a mixture of phosphine and hydrogen for a TFT-LCD manufacturing application. As noted above, many gases used in semiconductor manufacturing processes, such as thin film formation processes, are toxic and are stored at sub-atmospheric pressure conditions to prevent inadvertent release of such gases from a process system. Such gases can be processed and pressurized safely while preventing contamination with the system of the invention.
An exemplary embodiment of a system that provides a mixture of germane (GeH4) and hydrogen (H2) to a semiconductor process tool is depicted in
A gas mixture storage vessel or buffer tank 20 is disposed downstream from the mixing vessel 6, and an outlet of the mixing vessel is connected to an inlet of the buffer tank via a suitable piping line 14. A valve 15 is disposed along line 14 to control the flow of the gas mixture formed in the mixing vessel to the buffer tank. The buffer tank further includes an outlet connected to a suitable piping line 22 that leads to a semiconductor process tool 26, with a valve 21 disposed along the line 22 to control the flow of the gas mixture from the buffer tank to the process tool. A filter 24 is also disposed along line 22 to filter any particulate material or other impurities that may be present in the gas mixture prior to delivery of the gas mixture to the process tool. The filter can have any suitable mesh or screen size to filter particulate material of selected sizes from the gas mixture.
A vacuum line 16 is also connected to piping line 14 at a location upstream from valve 15, and the vacuum line includes a valve 17 disposed along this line. Vacuum line 16 connects with a negative pressure generator or suction source 30 (e.g., a compressor) to facilitate the generation of a vacuum or pressure differential between mixing vessel 6 and GeH4 storage vessel 2 so as to draw GeH4 gas into the mixing vessel. It is noted that the suction source can also be used to purge buffer tank 20 as desired (i.e., by opening valve 15) and at selected times during system operation.
In operation, valve 9 is opened and a selected amount of hydrogen is delivered into vessel 10 by facilitating the flow of hydrogen until a suitable pressure within this vessel is obtained. The pressure within vessel 10 can be monitored via a pressure and/or temperature sensor connected in any suitable manner with the vessel (or piping line associated with the vessel). Upon achieving a selected pressure within vessel 10, valve 9 is closed. Given the known volume, temperature and pressure of vessel 10, a precise quantity of H2 gas in vessel 10 is also known. Valve 11 remains closed until the hydrogen gas is to be delivered for mixing with GeH4 gas in mixing vessel 6.
Vacuum is established in vessel 6 by opening the valve 17 (while valves 5, 11, 15 remain closed). Once a sufficient vacuum is reached within vessel 6 (e.g., by measuring a pressure at any suitable location within vessel 6), valve 17 is closed. The GeH4 gas is delivered from vessel 2 and into mixing vessel 6 by opening valve 5 (while valves 11 and 15 remain closed). The pressure and/or temperature of the mixing vessel is monitored via one or more suitable sensors connected with the mixing vessel (or any suitable piping line connected with the mixing vessel), such that a precise amount of GeH2 gas is provided within this vessel. Once a selected pressure within the mixing vessel is achieved and is maintained, valves 5 and 17 are closed, and valve 11 is opened to permit flow of H2 gas from vessel 10 into mixing vessel 6. The pressure of H2 in vessel 10 is much greater than the pressure of GeH4 in mixing vessel 6, so the H2 gas flows into the mixing vessel and mixes with the GeH4 gas. Valve 15 is also opened to permit the flow of the gas mixture to buffer tank 20. The pressure within buffer tank 20 is less than the pressure of the gas mixture in mixing tank 6, so as to permit the gas mixture to flow to the buffer tank. Valve 21 is selectively manipulated to open and closed positions to direct the gas mixture through filter 24 and to process tool 26 at any desired flow rate and pressure. Each of the mixing vessel 6, H2 storage vessel 10 and buffer tank 20 can be filled as necessary to form a gas mixture and direct the gas mixture to the buffer tank by repeating the operational steps as described above so as to provide a continuous flow of the gas mixture to the process tool.
The concentrations of GeH4 and H2 in the gas mixture are determined based upon the volumetric sizing of vessels 6 and 10 and the pressures at which each gas is initially provided to each vessel. For example, given a set volume V1 of H2 storage vessel 10 and a set volume V2 of mixing vessel 6 which initially contains GeH4 (i.e., before mixing occurs), the pressure P1 of vessel 10 and the pressure P2 of mixing vessel 6 can be selected so as to obtain the desired concentration of GeH4 in the resultant gas mixture. When the temperature of both vessels is similar or about the same, the molar concentration of GeH4 in the resultant gas mixture that flows to buffer tank 20 is defined as P2V2/(P1V1+P2V2−P1fV1−P2fV2), where P1f and P2f are the final pressures in vessel 10 and vessel 6, respectively, after the gas mixture has been delivered to the buffer tank. For higher pressures where ideal gas laws do not apply, correction factors based on gas compressibility can be used to obtain more accurate results for gas concentrations.
Thus, the system of
Another embodiment of a gas mixing system combined with a process tool is depicted in
A pair of gas supply vessels 112 and 114 are connected via suitable piping lines 111, 113 and 115 to line 104 at a location between valve V5 and mixing vessel 102. In particular, piping line 113 connects with line 104 to a three-way valve V4, and piping line 113 extends from vessel 112 to one end of three-way valve V4. Piping line 115 extends from vessel 114 to another end of three-way valve V4, and a valve V3 is disposed along line 115. A pressure sensor P2 is connected to line 104 at a location proximate mixing vessel 102 and between line 111 and valve V5.
Piping lines 120 and 125 connect a process tool 126 with an outlet of buffer tank 110. Piping line 120 extends from the outlet of buffer tank 120 to one end of a three-way valve V6, and a pressure sensor P3 is disposed along line 120. Piping line 125 extends from another end of three-way valve V6 to process tool 126, and a mass flow controller (MFC) 124 is disposed along line 125. The process tool is preferably a semiconductor processing tool that performs any one or more types of process steps for a semiconductor component (e.g., forming substrate layers, stripping, etching, cleaning, etc.).
A negative pressure generator or suction source 130 is connected to mixing vessel 102 (at longitudinal end A of the vessel) via a suitable piping line 132, and a valve V2 is disposed along the piping line 132. In addition, a pressure sensor P1 is disposed along line 132 between valve V2 and mixing vessel 102. A suitable piping line 134 connects to a portion of line 132 between suction source 130 and valve V2 and further extends to and connects with an end of three-way valve V6 located in line 120 between buffer tank 110 and process tool 126. As described in greater detail below, the suction source 130 is connected within system 100 to generate a negative pressure between the suction source and the mixing vessel 102 and also between the suction source and the buffer tank 110.
Optionally, a suitable piping line 105 is provided to directly connect piping line 104 (at a location upstream from valve V5) to piping line 134. This connection allows system 100 to generate a vacuum within vessel 102, via suction source 130, independent of the buffer tank 110.
A gas supply source 136 (e.g., a storage tank or vessel) houses an inert gas (e.g., nitrogen or helium) that is used to purge gases from the system as well as to force mixing and delivery of the process gases to the buffer tank as described below. The gas supply source 136 is connected to line 132 via a suitable piping line 138 and at a location between valve V2 and pressure sensor P1. A valve V1 is disposed along line 138 to control the flow of the inert gas to the mixing vessel 102.
An interior portion of mixing vessel 102 is shown in
The gas supply vessels 112 and 114 contain the gases that are mixed within vessel 102 and are delivered to the buffer tank and process tool. Any types of gases can be provided in vessels 112 and 114, including pressurized gases as well as gases at sub-atmospheric pressure conditions (e.g., below 1 bar). In a preferred embodiment, vessel 112 includes a gaseous compound A that is stored at pressures ranging from about 0.01 bar to about 100 bar, preferably in the range of about 0.1 bar to about 50 bar. Examples of compounds that can be stored in vessel 112 include hydrates such as germane, silane and phosphine. For example, germane can be stored at a sub-atmospheric pressure of about 0.8 bar or lower, where an adsorbent is provided to maintain sub-atmospheric pressure conditions within the vessel, and phosphine can be stored at pressures of about 0.1 bar to about 40 bar. Other examples of gases that can be stored in vessel 112 and have low vapor pressures and/or are stored at low pressures include, without limitation, boron trichloride, boron trifluoride, halocarbons, hydrogen fluoride, and tungsten fluoride. Other compounds having low vapor pressures and that include liquid precursors can also be stored in vessel 112, such as trimethylsilane and trisilane.
Vessel 114 stores a gaseous compound B that can be an inert gas, such as nitrogen or helium or, alternatively, a reactive gas such as hydrogen. Gaseous compound B is stored in vessel 114 at a pressure that is preferably greater than the pressure at which gaseous compound A is stored. Preferably, gaseous compound B is stored within vessel 114 in the range of about 0.1 bar to about 300 bar, and more preferably in the range of about 1 bar to about 200 bar.
Operation of system 100 is described with reference to
Alternatively, in embodiments in which piping line 105 and valve V7 are provided, valve V7 can be opened while valve V5 remains closed. In this scenario, the suction or vacuum is applied via line 105 (thus bypassing buffer tank 110), and any gases forced out of the mixing vessel flow through line 105 to line 134 and then to the suction source 130.
After a selected time period and/or when a predetermined pressure has been reached (as measured by sensor P1) and the sealing disc has been moved to end B within the mixing vessel (as shown by disc 140 in dashed lines within the mixing vessel), valves V1 and V5 are closed. Valves V2 and V6 are then opened (step 154), where three-way valve V6 is opened to permit fluid communication between lines 120 and 134. Suction source 130 is activated to generate a negative pressure or vacuum within mixing chamber 102 so as to withdraw the inert gas through end A of the mixing chamber and through line 132 to the vacuum source. In addition, the vacuum pulls sealing disc 140 back to end A within the mixing chamber. Any gases within line 104 (between valve V5 and the buffer tank) and buffer tank 110 are also withdrawn through lines 120 and 134 to suction source 130. Once a selected vacuum has been reached within the system (e.g., as determined by pressure sensor P1 and/or pressure sensor P3), valves V2 and V6 are closed, leaving the mixing vessel at sub-ambient pressure conditions (i.e., pressures no greater than about 1 bar) to facilitate the flow of gas from vessel 112 into this vessel without the requirement of any mechanical device. The withdrawn gases delivered to vacuum source 130 can be collected and delivered to a suitable storage or processing location.
Alternatively, it is noted that sealing disc 140 can also be moved back to end A of the mixing vessel by opening three-way valve V4 to permit gas from vessel 114 to flow from line 115 into line 111 and into the mixing vessel at end B. After the disc 140 is moved to end A within vessel 102, suction source 130 can then be activated and valves V5 and V6 opened (where V6 is operated in the manner described above to provide fluid communication between lines 120 and 134) to facilitate the withdrawal of any gases within the system between mixing vessel 102 and buffer tank 110 into piping line 134 and to suction source 130. In this embodiment, the sealing disc is suitably designed and/or the vacuum or negative pressure is selected such that the disc resists and is substantially prevented from moving from its location at end A toward end B within the mixing vessel when a vacuum is established within the mixing vessel by the suction source.
In the next step, three-way valve V4 is opened (step 156) to permit fluid communication between lines 113 and 111, such that gaseous compound A flows from vessel 112 into mixing vessel 102. The pressure within the mixing vessel is monitored via sensor P2. Upon reaching a selected pressure PA within the mixing vessel (e.g., in a range of about 0.01 bar to about 20 bar, preferably about 0.1 bar to about 5 bar), valve V4 is closed. Next, valves V3 and V4 are opened (step 158), where three-way valve V4 is opened such that line 115 is in fluid communication with line 111, to permit gaseous compound B to flow from vessel 114 into mixing vessel 102. The valves remain open until the pressure within the mixing vessel reaches a selected pressure PAB (about 0.5 bar to about 20 bar, preferably about 1 bar to about 5 bar). A suitable device such as a pressure regulator can also be provided at a suitable location along line 115 and/or at an outlet of storage vessel 114 to reduce the pressure of gaseous compound B prior to delivery to the mixing vessel. When the pressure within the mixing vessel reaches a selected value, valves V3 and V4 are closed.
The concentrations of gaseous compounds A and B within the mixing vessel can be precisely controlled by monitoring the pressure within the mixing vessel during the addition of each gas. For example, if it is desired to provide a mixture of these gases with a 10% molar concentration of gaseous compound A, the pressure values can be selected such that PA is 0.1 bar and PAB is 1 bar. It is further noted that any other suitable devices (e.g., flow controllers and/or flow meters) can be provided as an alternative or in combination with one or more pressure sensors to precisely determine and control the concentration of gases provided to the mixing vessel.
Upon achieving the desired concentrations of gases within mixing vessel 102, valves V1 and V5 are opened (step 160), and inert gas is directed from source 136 through lines 138 and 132 into the mixing vessel at end A of the vessel. The pressure of the inert gas flowing into the mixing vessel from source 136 is controlled (e.g., by monitoring pressure sensor P1 and controlling valve V1) so as to force sealing disc 140 toward end B of the mixing vessel, which in turn forces gaseous compounds A and B out of the mixing vessel at end B of the vessel and toward buffer tank 110. The combination of gaseous compounds A and B are directed through mixing unit 106 and filter 108, where they are suitably mixed together and any particulate materials are removed from the gases.
Once sealing disc 140 has reached end B of mixing vessel 102, a transfer of the gas mixture from the mixing vessel to the buffer tank is complete. Valves V1 and V5 are then closed, and valve V2 is opened (step 162) and the suction source activated to generate a vacuum within mixing vessel 102 so as to pull sealing disc 140 back toward end A of the mixing vessel and withdraw the inert gas to the suction source, while creating a vacuum within the mixing vessel to facilitate withdrawal of gas from vessel 112 at sub-ambient pressures (i.e., pressures no greater than about 1 bar) in another successive gas mixing step.
The pressure within buffer tank 110 is continuously monitored by pressure sensor P3. In particular, the pressure of the gas mixture within the buffer tank is preferably maintained within a range of about 0.1 bar to about 20 bar, more preferably within a range of about 1 bar to about 10 bar. The buffer tank delivers the gas mixture to process tool 126 by manipulating valve V6 such that line 120 is in fluid communication with line 125. Mass flow controller 124 controls the flow of the gas mixture to the process tool. When the pressure within the buffer tank falls below a minimum or threshold pressure value Pmin (step 164), the process steps described above (steps 156-164) for generating and providing a mixture of gaseous compounds A and B at precise concentrations to the buffer tank are repeated.
Thus, system 100 is capable of providing a continuous supply of the gas mixture at precise concentrations and at high purity levels to the process tool during system operation. By using a suction source to generate a vacuum in the system and also an inert gas to force the process gas mixture from the mixing vessel to the buffer tank, gases (including one or more gases at sub-atmospheric storage conditions) are delivered without the requirement of mechanical devices (e.g., pumps). This ensures the quality and purity of the gas mixture to be used in the process tool.
In a modification to the previously described system, the inert gas used to push or force the gas mixture from the mixing vessel can be eliminated, and one of the gases that makes up a portion of the gas mixture also forces the gas mixture from the mixing vessel to the buffer tank. Referring to
A negative pressure generator or suction source 230 is connected via a suitable piping line 232 to mixing vessel 202 at the longitudinal end including sub-chamber 202B. A valve V21 is disposed along line 232, and a pressure sensor P21 is also disposed along line 232 at a location between valve V21 and the mixing vessel.
Mixing vessel 202 is further connected, via a suitable piping line 204, to a buffer tank 210. A pressure sensor P22, valve V25, mixing unit 206 and filter 208 are all disposed along line 204. In particular, pressure sensor P22 is disposed between the mixing vessel and valve V25, the valve V25 is disposed between pressure sensor P22 and mixing unit 206, and filter 208 is disposed between mixing unit 206 and buffer tank 210. As in the previous embodiment, the mixing unit can be of any suitable type (e.g., a static mixer disposed within a suitable housing) to facilitate mixing of two or more fluids passing through the unit, and the filter can also be of any suitable type to facilitate separation of particulate materials of any suitable sizes from the gas mixture flowing through the filter.
Piping lines 220 and 225 connect a process tool 226 with an outlet of buffer tank 210. In particular, piping line 220 extends from the outlet of buffer tank 220 to one end of a three-way valve V26, and a pressure sensor P23 is disposed along line 220. Piping line 225 extends from another end of three-way valve V26 to process tool 226, and a mass flow controller (MFC) 224 is disposed along line 225. The process tool is preferably any semiconductor processing tool that performs one or more selected types of conventional or other process steps for a semiconductor component such as those noted above for the previous embodiment.
A suitable piping line 234 connects to a portion of line 232 between suction source 230 and valve V21 and further extends to and connects with an end of three-way valve V26 located in line 220 between buffer tank 210 and process tool 226.
As in the embodiment described above and depicted in
As in the previous embodiment, any types of gases can be provided in vessels 212 and 214, including pressurized gases as well as gases at sub-atmospheric pressure conditions (e.g., below 1 bar) and including, without limitation, any of the exemplary gases that are described above. In a preferred embodiment, vessel 212 includes a gaseous compound A that is stored at pressures ranging from about 0.01 bar to about 100 bar, preferably in the range of about 0.1 bar to about 50 bar, while vessel 214 includes a gaseous compound B that is stored at pressures ranging from about 0.1 bar to about 300 bar, and preferably in the range of about 1 bar to about 200 bar. Most preferably, gaseous compound A is maintained in vessel 212 at a lower pressure than the pressure at which gaseous compound B is maintained in vessel 214.
In operation, all of the valves V21-V26 in system 200 are initially closed, with three-way valve V26 preventing fluid communication of line 220 with each of lines 234 and 225. Valves V21 and V23 are opened and suction source 230 is activated to generate a vacuum within both sub-chambers 202A and 202B of the mixing vessel, such that any gases within the sub-chambers are evacuated and drawn through line 232 to the suction source. Optionally, three-way valve V26 can also be opened to facilitate fluid communication between line 220 and line 234 so as to evacuate any gases that may be present within buffer chamber 210. After a desired vacuum level is achieved within the mixing vessel and/or the buffer chamber (as determined by pressure sensor P21 and/or pressure sensor P23), valves V21, V23 and V26 are closed, such that sub-chambers 202A and 202B are separated from each other via closed valve V23 and the sub-chambers are at selected sub-ambient pressure conditions and, in particular, below the pressure of each of gaseous compounds A and B stored within vessels 212 and 214.
Valve V24 is then opened to permit gaseous compound A to flow from vessel 212) through lines 213 and 204 into sub-chamber 202A (which is at a lower pressure than vessel 212). Once a suitable pressure is obtained within sub-chamber 202A (as measured by pressure sensor P22), a precise amount of gaseous compound A is in the mixing vessel (i.e., the precise amount of gas is determined based upon the measured pressure and the known volume of the sub-chamber). The amount of gaseous compound A that is added to the mixing vessel can also be determined utilizing a suitable flow meter disposed, for example, along line 213. Valve V24 is then closed, and valve V22 is opened to permit gaseous compound B to flow from vessel 214 through lines 215 and 232 into sub-chamber 202B. A precise amount of gaseous compound B is provided to sub-chamber 202B upon reaching a suitable pressure within this sub-chamber (as measured by pressure sensor P21), and valve V22 is then closed. It is further noted that gaseous compounds A and B can be delivered to their respective sub-chambers at about the same time to reduce processing time for achieving a desired gas mixture.
Once the predetermined amounts of gaseous compounds A and B are delivered to sub-chambers 202A and 202B and valves V22 and V24 are closed, valves V23 and V25 are opened (e.g., simultaneously or, alternatively, V23 is opened first followed by V25) to permit mixing of gaseous compounds A and B within mixing vessel 202 and delivery of the gases through line 204, mixing unit 206, and filter 208 and into buffer tank 210. As noted above, gaseous compound B is provided at a greater pressure than gaseous compound A within the mixing vessel. Thus, when valve V23 is opened, gaseous compound B flows from sub-chamber 202B into 202A to mix with gaseous compound A and further force the two gases into line 204 toward the buffer tank. Mixing unit 206 further mixes the two gaseous compounds together, while filter 208 removes particulate material of selected dimensions from the gas mixture prior to entering buffer tank 210.
Prior to opening valve V23, the pressure of gaseous compound B (as measured by pressure sensor P21) is preferably about 1.01 to about 2.5 times the pressure of gaseous compound A (as measured by pressure sensor P22). Alternatively, the pressures of the gases can be selected such that the gas mixture leaving the mixing vessel is within the laminar flow region as determined by the Reynold's Number or NRe, where NRe is defined as:
NRe=D*G/μ
where D is the internal diameter of the vessel/pipe where flow is being characterized, G is the mass velocity of the gas, and μ is the fluid viscosity. In particular, the NRe value of gaseous compound B flowing through valve V23 is preferably less than 10,000, more preferably less than 2,000.
After a predetermined period of time and/or a selected pressure within buffer tank 210 is reached (as measured by pressure sensor P23), the gas mixture including all of gaseous compound A has been delivered to the buffer tank, and valve V25 is closed. The above steps of filling mixing vessel 202 with gaseous compounds A and B and delivering the gases to the buffer tank can be repeated as necessary to achieve and maintain a desired pressure level of the gas mixture within the buffer tank during system operation. Valve V26 is opened to facilitate fluid communication between line 220 and line 225, and the gas mixture from the buffer tank is directed to process tool 226, where the flow rate of the gas mixture to the process tool is controlled by mass flow controller 224. Thus, the system of
All of the previously described systems can also be automatically controlled, via one or more suitable controllers that are in communication with the various pressure sensors, mass flow controllers, valves, etc., so as to selectively and automatically control the generation of a suitable gas mixture at desired flow rates and delivery of gas mixtures at the required capacity for effective operation of one or more process tools. Further, while the systems all describe the formation of a mixture of two gaseous compounds, it is noted that the invention can also effectively provide mixtures of any suitable number of gaseous compounds (e.g., three or more compounds) to any suitably number of process tools (e.g., one, two or more process tools) for any selected number of different applications. Gas mixtures are formed with at least one reactive gas that is provided at a selected pressure (e.g., sub-atmospheric and/or other pressures), and at least one other gas that can be inert or reactive and is preferably at a greater pressure than the reactive gas with which it is to be mixed.
In an example utilizing the system described above and depicted in
The data plotted in
Thus, the systems and corresponding methods of the present invention provide gas mixtures (including gaseous compounds that are stored at sub-atmospheric pressure conditions) without the requirement of a compressor, pump or any other mechanical device to mix and move the gases. The gas mixtures can be provided continuously or intermittently to one or more process tools for a variety of applications, where the gas mixtures are provided in precise amounts, at precise concentrations while preventing or substantially minimizing contamination of the mixtures during mixing and delivery. The buffer tank allows the gas mixtures to be stored for any select time period prior to usage. Further, the systems prevent or substantially minimize the venting of waste gases, which is very beneficial in applications in which expensive and/or toxic gaseous compounds are used.
Having described novel fluid mixing and delivery systems and methods for mixing and delivering fluids, 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.
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/673,183, entitled “Blending and Delivery System For Vapor Mixtures Involving Low-Pressure Source,” and filed Apr. 20, 2005. The disclosure of this provisional patent application is incorporated herein by reference in its entirety.
Number | Date | Country | |
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60673183 | Apr 2005 | US |