Low vapor pressure high purity gas delivery system

Abstract

Systems, apparatuses and methods for vapor phase fluid delivery to a desired end use are provided, wherein the conditions of the system are monitored to determine when the water concentration or supply vessel surface temperature exceeds a specified value or when the low vapor pressure fluid pressure falls below a specified value for the purpose of removing a first supply vessel from service by discontinuing vapor flow from the first supply vessel and initiating vapor flow from a second supply vessel.

Description

DETAILED DESCRIPTION OF THE DRAWINGS

Other objects, features, embodiments and advantages will occur to those skilled in the art from the following description of preferred embodiments and the accompanying drawings, in which:

FIGS. 1 a and 1b are cross-sectional diagrams of conventional supply vessel systems with heating features positioned adjacent to the outer vessel wall.

FIG. 2 is a graph charting vapor pressure as a function of liquid level in the vessel relative to heating units.

FIG. 3 is a graph charting vessel wall temperature as a function of liquid level relative to heating units.

FIG. 4 is a graph charting vapor phase water concentration as a function of liquid level relative to heaters.

FIG. 5 is a schematic diagram of a conventional low vapor pressure fluid supply system.

FIGS. 6-8 are schematic diagrams of preferred embodiments of the low vapor pressure fluid supply systems of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Known techniques in the field of low vapor pressure high purity gas delivery systems fail to recognize that the key liquid level will vary depending on whether pressure degradation, vessel wall temperature increase or water level increase is most important. In the example cited in U.S. Pat. No. 6,025,576, allowing the liquid level to fall below the heater would cause the pressure to degrade and the water level to increase before the vessel is removed from service. The '576 patent also fails to recognize that the key liquid level will vary depending on equipment and operational parameters, such as heater configuration and vapor draw rate.

Co-pending and commonly assigned U.S. patent application Ser. No. 11/476,042, filed Jun. 28, 2006 describes, according to certain embodiments, a means for attaching heaters to the lower portion of a supply vessel containing low vapor pressure gas. This application states that known low vapor pressure gas supply systems can produce “hot spots” and vigorous low vapor pressure gas boiling, which can result in the delivery of contaminants to the customer. This application further describes the accumulation of moisture due to simple vapor/liquid equilibrium, and that, because of this equilibrium based moisture accumulation, a percentage of the low vapor pressure gas must be discarded (typically 10%-20%). The contents of this co-pending and commonly-assigned U.S. patent application are incorporated by reference in its entirety herein, as if made a part of the present application.

As a result, in known systems, the supply vessel is likely to be removed from service too early (i.e. prior to the on set of the challenges listed above) or too late (after the supply vessel wall temperature, water level or have exceeded acceptable limits). If the supply vessel is removed from service too early, some of the low vapor pressure gas that could be utilized will be wasted. If the supply vessel is removed from service too late, one of the key parameters could exceed acceptable limits. For example, the water level could become too high, which would have an adverse effect on the semiconductor, LED, LCD or solar cell manufacturer process, resulting in poor product quality or product loss. Allowing the water level to exceed acceptable limits could also increase the cost of ammonia purification downstream of the supply vessel at those sites where ammonia purification systems are utilized.

According to one embodiment of the present invention, the systems and apparatuses of the present invention recognize and use these variations to maximize low vapor pressure product utilization without negatively impacting the semiconductor, LCD, LED or solar cell manufacturing process.

It is difficult for conventional low vapor pressure gas supply systems to consistently meet semiconductor, LED, LCD and solar cell manufacturer requirements. For example, heat transfer becomes ineffective when a significant portion of the heat is applied to that portion of the supply vessel wall that is not in contact with liquid phase low vapor pressure gas. Experiments were conducted to determine the ability to transfer heat to liquid phase ammonia as the liquid level falls, causing the portion of the supply vessel wall that is in contact with liquid phase ammonia to decrease. While ammonia was selected for illustrative purposes, the methods and apparatuses of the present invention also lend significant advantage to the processing of gases including, but not limited to boron trichloride, carbon dioxide, chlorine, dichlorosilane, halocarbons, hydrogen bromide, hydrogen chloride, hydrogen fluoride, methylsilane, nitrous oxide, nitrogen trifluoride, trichlorosilane, and mixtures thereof. As depicted in FIG. 1, vapor phase ammonia was withdrawn from a supply vessel at a constant rate via conduits 4 and 13. To replenish the withdrawn vapor and maintain supply vessel pressure, heat was applied to the outside, bottom surface of the supply vessel using surface mounted heaters 3 and 12. The ability to transfer heat to the liquid phase ammonia was determined by monitoring the vessel pressure using pressure measuring devices 6 and 15. If heat transfer is ineffective, the supply vessel pressure will fall.

FIG. 2 shows the pressure measured as a function of liquid level (x-axis positive values indicate that the liquid level is above the heater and vice versa). Note that when the liquid level is above the heater, the supply vessel pressure is generally sustained (heat transfer is effective). When the liquid level approaches the heater, the supply vessel pressure is not sustained (heat transfer is ineffective). Therefore, at some liquid level referred to as “key pressure liquid level”, the supply vessel pressure will no longer be sustainable. This key pressure liquid level will vary from system to system and will depend on a number of variables, such as vapor draw rate, heater configuration, heater temperature and contact intimacy between the heater and supply vessel wall. The key pressure liquid level is likely to be lower than the point at which the liquid level is equal to the heater level, although as shown in FIG. 2, it may also be located above the heater level.

The key liquid level will also vary from system to system based on, for example, vapor draw rate, heater configuration, heater temperature and contact intimacy between the heater and supply vessel wall. For example, at low vapor draw rates, the key pressure liquid level will be lower than at high vapor draw rates, since the heater area required to maintain supply vessel pressure is lower at low vapor draw rates.

The supply vessel wall temperature may increase beyond design limits locally when a significant portion of the heat is applied to that portion of the supply vessel wall that is not in contact with liquid phase low vapor pressure gas. Experiments were conducted to determine the effect of liquid level on supply vessel wall temperature. The results are shown in FIG. 3 (x-axis positive values indicate that the liquid level is above heater and vice versa). It was determined that when the liquid level drops below the key temperature liquid level, the supply vessel wall temperature begins to increase in that portion of the supply vessel wall that is not in contact with liquid phase low vapor pressure gas. Supply vessels are designed to operate near ambient temperature and typically have a very low maximum acceptable operating temperature. A typical maximum acceptable operating temperature is about 125° F. Operating at temperatures in excess of the maximum acceptable operating temperature is a safety issue and could result in vessel failure. As shown in FIG. 3, this temperature limitation is approached as the liquid level falls below the key temperature liquid level. The key temperature liquid level (−0.7 inches, liquid level below the heater) is different than the key pressure liquid level (0.35 inches, liquid level above the heater).

The low-volatility contaminant level in the vapor phase substantially exceeds equilibrium levels when a significant portion of the heat is applied to that portion of the supply vessel wall that is not in contact with liquid phase low vapor pressure gas. Because they do not evaporate readily, low-volatility contaminants preferentially remain in the liquid phase as vapor phase low vapor pressure gas is withdrawn from the supply vessel. As a result, as explained above, the low-volatility contaminant concentration in both the vapor and liquid phases increases with time.

The low-volatility contaminant level resulting from this phenomenon is referred to as the equilibrium contaminant level. Experiments were conducted to determine the low-volatility contaminant level observed in vapor ammonia drawn from the supply vessel as liquid level falls, causing the portion of the supply vessel that is in contact with liquid phase ammonia to decrease. In these experiments, the low-volatility contaminant was water. The results are shown in FIG. 4. Note that the water concentration observed as the liquid level decreases reflects the projected equilibrium concentration until the key water liquid level is reached. At that key water liquid level, the water concentration substantially exceeds predicted equilibrium values. For these experiments, the key water liquid level occurs when the liquid level falls about to a level substantially equivalent to the heater level.

As stated above, previously known systems fail to recognize that the key liquid level will vary depending on whether pressure degradation, vessel wall temperature increase or water level increase is most important. Allowing the liquid level to fall below the heater would cause the pressure to degrade and the water level to increase before the vessel is removed from service. Previous systems also fail to recognize that the key liquid level will vary depending on equipment and operational parameters, such as heater configuration and vapor draw rate. According to one preferred embodiment, the present invention recognizes and uses these variations to maximize low vapor pressure product utilization without negatively impacting the semiconductor, LCD, LED or solar cell manufacturing process.

Further, presently known methods and systems do not describe a means to maximize low vapor pressure gas utilization by maintaining a supply vessel in service until the moisture level, wall temperature or pressure exceed some value, and further fail to provide a means to identify the appropriate time to remove a supply vessel from service.

When the water concentration or supply vessel surface temperature exceeds a specified value or when the low vapor pressure fluid pressure falls below a specified value, the supply vessel is removed from service by discontinuing vapor flow from the first supply vessel and initiating vapor flow from a second supply vessel. The liquid level at which this occurs is located near the plane determined by the upper edges of the heaters.

According to one embodiment, the present invention provides a means to maximize low vapor pressure gas utilization without supply vessel pressure degradation, supply vessel overheating or high water level product delivery to the semiconductor, LCD, LED or solar cell manufacturer. Supply vessel overheating is an issue with respect to safe operation. Pressure degradation and high moisture level are an issue with respect to semiconductor, LCD, LED or solar cell yield.

FIG. 5 depicts a conventional low vapor pressure fluid supply configuration. In general, the system intent is to deliver liquid or two-phase low vapor pressure fluid contained in a supply vessel to a semiconductor, LED, LCD or solar cell manufacturing facility and to convert it into vapor phase low vapor pressure fluid. Supply vessels 20 and 30 containing, for example, vapor and liquid phase ammonia are installed in parallel so that as one vessel is consumed, the other can be brought into service without disrupting supply to the semiconductor, LED, LCD or solar cell manufacturer. Vapor phase ammonia is withdrawn from whichever vessel is in service via conduit 21 or 31. It is then transferred to a gas panel 40, which regulates the ammonia pressure and temperature prior to delivery to a semiconductor, LED, LCD or solar cell manufacturing facility via conduit 41.

As vapor phase ammonia is withdrawn from supply vessel 20 or 30, the supply vessel pressure is maintained using one or more heater systems 22 and 32 and a closed loop heater control means. Typically, a pressure transducer 23 or 33 monitors the supply vessel pressure and sends a signal to a programmable logic controller 24 or 34, where the signal is compared to a set point value. Based on the difference between these values, the energy delivered to supply vessel 20 or 30 from heater system 22 or 32 is adjusted. This facilitates vaporization of ammonia to sustain the required supply vessel pressure.

Although a number of heater types may be employed, a common heater type is a silicone rubber blanket heater. This silicone rubber blanket heater may be affixed to the vessel in a variety of ways. A typical silicon rubber heater is that available from Watlow Electric Manufacturing Company (St. Louis, Mo.). The heater preferably is installed so that its heat is evenly distributed to the bottom of the vessel and such that it does not rise to too high a level on the vessel. According to one embodiment of the present invention, a method for discontinuing flow from the vessel is used. If the heater rises to too high a level on the vessel, a significant portion of the ammonia will be wasted. The heater typically covers from about 5% to about 50% of the vessel circumference, preferably from about 10% to about 40% of the vessel circumference and most preferably from about 20% to about 35% of the vessel circumference. The silicone rubber heater typically operates at a temperature ranging from about 100 to about 500° F., preferably from about 120 to about 300° F. and most preferably from about 130 to about 200° F. Such a heating configuration is preferably used with a number of supply vessel types. For example, a horizontally mounted Y-cylinder, which initially contains approximately 500 lbs of ammonia, could be used.

Ammonia is withdrawn from supply vessel 20 or 30 until the mass remaining drops to from about 10% to about 30% of the original level. When this level is reached, the supply vessel is removed from service and the remaining liquid, which is referred to as the heel, is discarded. The heel is enriched in contaminants that have a lower vapor pressure than ammonia, such as water.

Preferred embodiments of the present invention are depicted in FIGS. 6, 7 and 8. As described previously, according to embodiments of the present invention, the present systems and apparatuses determine the point at which a supply vessel 20 or 30 should be removed from service. More specifically, FIG. 6 depicts a means for determining the point at which the supply vessel 20 or 30 should be removed from service based on pressure. The pressure at the outlet of each supply vessel 20 and 30 is monitored using pressure transducer 23 and 33, respectively. This pressure is maintained, typically within the range of from about 50 to about 250 psig, preferably within the range of from about 100 to about 200 psig and most preferably in the range of from about 120 to about 180 psig. When the liquid content of supply vessel 20 or 30 drops to a level at which the desired pressure cannot be sustained and falls below some predetermined value, a controller 64 will cause vapor flow from the supply vessel that is in use to cease by closing either valve 25 or valve 35, depending on which supply vessel is in service. The switch-over pressure typically occurs when the pressure decreases by an amount of from about 1 to about 100 psi, preferably when the pressure decreases by an amount of from about 5 to about 50 psi and more preferably when the pressure decreases by an amount of from about 5 to about 20 psi. Flow is then initiated from the supply vessel that was not in service by opening valve 25 or 35.

FIG. 7 depicts a further embodiment of the present invention whereby a means for determining the point at which the supply vessel 20 or 30 should be removed from service based on supply vessel wall temperature. The vessel wall temperature is monitored using temperature elements 74, 76 respectively. This temperature is typically within the range of from about 0° to about 125° F., preferably within the range of from about 30° to about 125° F. and most preferably within the range of from about 60° to about 125° F. When the liquid contents of the supply vessel drop to a level at which the surface temperature approaches the set point range, typically from about 70° to about 125° F., preferably within the range of from about 100° to about 125° F. and most preferably within the range of from about 115° to about 125° F., a controller 78 will cause vapor flow from the supply vessel that is in use to cease by closing either valve 25 or valve 35, depending on which supply vessel is in service. Flow is then initiated from the supply vessel that was not in service, by opening valve 25 or 35.

FIG. 8 depicts a means for determining the point at which the supply vessel 20 or 30 should be removed from service based on water concentration. The water concentration at the outlet of each supply vessel 20 and 30 is monitored using moisture analyzer 80. The water concentration is typically within the range of from about 0.001 to about 10 ppm, preferably within the range of from about 0.01 to about 5 ppm and most preferably within the range of from about 0.1 to about 2 ppm. When the liquid contents of the supply vessel 20 or 30 drops to a level at which the water concentration increases beyond the level predicted by vapor/liquid equilibrium, a controller 90 will cause vapor flow from the supply vessel that is in use to cease by closing either valve 25 or valve 35, depending on which supply vessel is in service. Flow is then initiated from the supply vessel that was not in service by opening valve 25 or 35.

The proposed control mechanisms can be applied to any size vessel, such as a T-cylinder, a Y-cylinder (ton container) or an ISO container, tube trailer or tanker that contains any desired liquid or two phase low vapor pressure gas, such as, for example, ammonia, thereby producing a vapor phase low vapor pressure gas stream. For example, ton containers are typically horizontally oriented and made from 4130X alloy steel and can contain, for example, 510 pounds of ammonia when filled to capacity. The vessels may be pre-filled and self-contained, or may be fillable from a source as would be readily understood by one skilled in the field of gas delivery systems.

A number of heater types may be used for delivering heat to the larger vessel. The most common are electrical resistance heaters, including blanket heaters, heating bars, cables and coils, band heaters, and heating wires. Heaters are preferably installed at the lower portion of the vessel and a heater controller preferably regulates the amount of heat delivered to the low vapor pressure gas maintaining the vapor output. Other potentially useful heater types include, for example, bath heaters, inductive heaters, heat exchangers that contain a heat transfer medium (such as, for example, silicone oil), etc.

Vapor low vapor pressure non-air gas leaving the second vessel may be further purified by, for example, adsorption, filtration or distillation means to further improve purity. It is further contemplated that the gas stream could be sent to a mist eliminator to remove any liquid phase low vapor pressure gas droplets that carry over from the supply vessel due to vigorous boiling. These droplets would be collected by a mist eliminator, and could be returned to the supply vessel by suitable delivery means, such as, for example, by gravity.

While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one skilled in the field that various changes, modifications and substitutions can be made, and equivalents employed without departing from, and are intended to be included within, the scope of the claims.

Claims

1. A method for delivering vapor phase fluid under pressure from a vessel comprising the steps of providing at least a first and second vessel having a fluid therein, each vessel having a vessel wall;providing a heater in communication with each of the first and second vessel;beating the vessel to achieve a predetermined pressure within the first and second vessel;providing a controller in communication with the heater;withdrawing an amount of vapor phase fluid from the first or second vessel;providing a sensor to monitor at least one condition in the first and second vessels, said condition selected from the group consisting of: vapor phase fluid pressure; vessel wall temperature, vapor phase fluid low vapor pressure contaminant concentration, and combinations thereof, to determine the key fluid level in the first and second vessels;monitoring the condition in the first and second vessels to determine the key fluid level in the first and second vessels;providing a controller in communication with the sensor and a valve having an on/off position, said valve directing flow from the first or second vessel to an end use, said sensor optionally activating the valve on/off position.

2. The method of claim 1, further comprising the step of: activating a first valve in communication with the first vessel to the off position, said valve diminishing the flow of vapor phase fluid from the first vessel to an end use when the condition reaches a predetermined level; andactivating a second valve in communication with the second vessel to the on position, said valve increasing the flow of vapor phase fluid from the second vessel to an end use when the condition reaches a predetermined level.

3. The method of claim 1, wherein the vapor phase fluid is a non-air based gas selected from the group consisting of: ammonia, boron trichloride, carbon dioxide, chlorine, dichlorosilane, halocarbons, hydrogen bromide, hydrogen chloride, hydrogen fluoride, methylsilane, nitrous oxide, nitrogen trifluoride, trichlorosilane and mixtures thereof.

4. The method of claim 1, wherein the low vapor pressure contaminant is water.

5. The method of claim 1, wherein the first and second vessels are made from a material selected from the group consisting of: 304 stainless steel, 316 stainless steel, Hasteloy, carbon steel and mixtures thereof.

6. The method of claim 1, wherein the first and second vessels are selected from the group consisting of: ISO container vessels, ton container vessels and drum container vessels.

7. The method of claim 1, wherein the heater is an electrical resistance heater selected from the group consisting of: silicon blanket heaters, band heaters, heating bars, heating tape and combinations thereof.

8. The method of claim 1, wherein the vapor phase fluid is selected from the group consisting of: high purity vapor phase fluid, ultra-high purity vapor phase fluid, and combinations thereof.

9. The method of claim 1, further comprising the steps of: substantially controlling the amount of heat delivered to the first or second vessel; andmaintaining a substantially constant pressure within the first or second vessel.

10. The method of claim 2, wherein the end use is the manufacture of a device, said device selected from the group consisting of: a semiconductor, a liquid crystal display, a light emitting diode and a solar cell.

11. A system for delivering vapor phase fluid comprising: at least a first and second vessel, each vessel having a vessel wall, each vessel containing an amount of liquid phase fluid;a heater in communication with each of the first and second vessel;a controller in communication with the heater, said controller controlling an amount of heat delivered to the first and second vessels and an amount of heat delivered to the liquid phase fluid contained within the first and second vessels;a sensor to monitor at least one condition, said condition selected from the group consisting of: vapor phase fluid pressure vessel wall temperature, vapor phase fluid low vapor pressure contaminant concentration, and combinations thereof, in the first and second vessels; anda controller in communication with the sensor, and at least one valve having an on/off position, said valve directing flow from the first or second vessel to an end use, said sensor activating the valve on/off position to an off position when the condition reaches a predetermined level.

12. The system of claim 11, further comprising: a vapor phase fluid delivery control loop in communication with the first and second vessels and an end use, such that, as flow from a first vessel is diminished, flow from a second level is increased.

13. The system of claim 11, wherein the vapor phase fluid is a non-air based gas selected from the group consisting of: ammonia, boron trichloride, carbon dioxide, chlorine, dichlorosilane, halocarbons, hydrogen bromide, hydrogen chloride, hydrogen fluoride, methylsilane, nitrous oxide, nitrogen trifluoride, trichlorosilane, and mixtures thereof.

14. The system of claim 11, wherein the low vapor pressure contaminant is water.

15. The system of claim 11, wherein the first and second vessel are made from a material selected from the group consisting of: 304 stainless steel, 316 stainless steel, Hasteloy, carbon steel and mixtures thereof.

16. The system of claim 11, wherein the first and second vessels are selected from the group consisting of: ISO container vessels, ton container vessels and drum container vessels.

17. The system of claim 11, wherein the heater is an electrical heater selected from the group consisting of: silicon blanket heaters, band heaters, heating bars, heating tape and combinations thereof.

18. The system of claim 11, wherein the end use is the manufacture of a device, said device selected from the group consisting of: a semiconductor, a liquid crystal display and a light emitting diode.

19. The system of claim 11, wherein the vapor phase fluid is selected from the group consisting of: high purity vapor phase fluid, ultra-high purity vapor phase fluid, and combinations thereof.

20. A device made according to the method of claim 2, selected from the group consisting of: a semiconductor, a liquid crystal display and a light emitting diode.

21. The system of claim 11, wherein the vessel wall temperature set point range is from about 0° to about 125° F.

22. The system of claim 11, wherein the vessel wall temperature set point range is from about 30° to about 125° F.

23. The system of claim 11, wherein the vessel wall temperature set point range is from about 60° to about 125° F.

24. The system of claim 11, wherein the heater covers from about 5% to about 50% of the first and second vessel's circumference, respectively.

25. The system of claim 26, The system of claim 11, wherein the heater covers from about 10% to about 40% of the fist and second vessel's circumference, respectively.

26. The system of claim 27, The system of claim 11, wherein the heater covers from about 20% to about 35% of the first and second vessel's circumference, respectively.