Patent Application
20070181703
This invention relates generally to vapor delivery systems. More particularly, embodiments of the present invention relate to efficient vapor delivery systems. Even more particularly, embodiments of the present invention relate to stable, high-flow rate vapor delivery systems operating at sub-atmospheric conditions.
There are many applications for which delivery of vapor of different types of liquids is desired. In semiconductor processing, for example, it may be desired to deliver photochemicals, such as photoresist chemicals, in vapor form to a process chamber to control the amount and rate at which these photochemicals are applied to a semiconductor wafer. Moreover, the use of many of these photochemicals may result in the production of less than desirable byproducts. To deal with these harmful byproducts and clean a process chamber of these byproducts or other chemicals before another processing stage, water vapor may be delivered to the process chamber. The water vapor may be used to convert these byproducts to less reactive compounds which are more easily disposed of through a chemical reaction.
Both delivering chemicals to a process chamber and the delivery of water vapor to a process chamber in order to react with process byproduct require precise delivery of vapor of different types. To that end, many types of systems have been designed and utilized to deliver vapor at precisely controlled flow rates and pressures for use in a variety of applications.
A typical vapor delivery system, such as one that may be used for delivery of water vapor to a process chamber, employs a vaporizer chamber. At least some portions of this vaporizer chamber are kept at a temperature high enough to vaporize liquid water substantially instantaneously when the liquid water contacts these portions (e.g. 125° C.). The delivery of the vapor formed through this instantaneous vaporization is then controlled with one or more flow controllers.
This type of system has many drawbacks, however. First and foremost, because the vaporization chamber of these types of systems must be maintained at a relatively high temperature these types of systems are relatively inefficient. Part and parcel with this problem, is the problem of condensation. As the water vapor is usually at a relatively high temperature, systems of the type described usually require that components in the flow path of the vapor be maintained at a higher temperature (e.g. 140° C.) than the vapor itself so condensation does not form in the flow path. Not only does this requirement entail higher energy consumption for such systems, but additionally, these higher temperatures may affect the reliability and stability of system components while making the use of such systems hazardous to technicians or other operators.
The use of these high temperatures has other adverse effects as well. By vaporizing the liquid at a higher temperature contaminants within the liquid are more likely to be vaporized, resulting in potential corrosion along the flow path of the vapor, or contamination of the process itself. Additionally, as the flow controllers used to regulate the delivery of vapor may be pressure based mass flow controllers (MFC), the high temperature used in these systems may cause these pressure based MFCs to drift, affecting the precession with which these systems can regulate the flow of vapor. This drift may be especially prevalent with MFCs that utilize capacitance-based pressure sensors, as in most cases the signal-conditioning electronics are typically positioned very close to the sensors in these types of MFCs.
Other lower temperature systems for delivery vapor have also been tried. These systems suffer from a number of failings as well. The majority of these shortcomings pertain to the inability of these systems to deliver either a high flow rate of vapor or to deliver vapor over long periods of time. In the main, these shortcomings are the result of the conditions required by the majority of these systems to produce vapor, such as that many of these systems may maintain precise equilibrium conditions or that relatively low pressure may need to be applied to create a significant flow of vapor. As a consequence, many of these systems may produce a lower head pressure of vapor, and commensurately be constrained as to the flow rates which they can achieve.
Still other types of systems for the production of water vapor have also been utilized, where the production of water vapor is accomplished by reacting hydrogen and oxygen in the presence of a catalyst. As the reaction utilized to produce vapor in these systems is severely exothermic air-cooling is usually required, making these systems prohibitively expensive for most uses. Additionally, these systems suffer from some of the same problems discussed above. Namely, variation in the reaction used to create water vapor may result in variable flow rates while a single ongoing reaction may not produce the desired flow rate of water vapor.
Thus, as can be seen, systems and methods for the production and delivery of vapor which can maintain consistent, stable and accurate vapor delivery, and which may also operate at sub-atmospheric conditions, are desired.
Systems and methods for producing and delivering vapor are disclosed. A vaporizer tank containing a liquid may be heated such that liquid within the tank is heated and vapor generated. The flow of this vapor to a destination may then be regulated. Embodiments of the present invention may control the temperature of this liquid such that a saturated vapor condition is substantially maintained in the vaporizer tank. The vaporizer tank is coupled to a mass flow controller which regulates the delivery of the vapor to downstream components. By substantially maintaining the saturated vapor condition within the vaporizer tank the pressure of vapor at the mass flow controller can be substantially maintained and a stable and consistent flow rate of vapor achieved.
In one embodiment, a vaporizer tank may be heated to a first temperature to produce a saturated vapor condition in the vaporizer tank. Vapor can then be flowed from the vaporizer tank while maintaining the temperature of the vaporizer tank.
In another embodiment, a system may comprise a vaporizer tank, heaters for heating the vaporizer tank, a mass flow controller mounted to, or near, the vaporizer tank, heaters for heating the mass flow controller, and a control system operable to control the heaters and the mass flow controller.
In still another embodiment, the vaporizer tank is refilled when the liquid in the tank falls below an operating level. The refill may be accomplished by gating, or controlling the duty cycle of, a fill valve such that the fill valve is substantially opened and closed to minimize the disturbance to the conditions in the vaporizer tank when admitting liquid to the vaporizer tank.
Various and sundry technical advantages may be provided by embodiments of the present invention. For example, certain embodiments of the present invention provide an advantage by allowing an accuracy which is within one percent of reading to be achieved.
Another advantage provided by embodiments of the present invention is a broad range of vapor flow rates. In particular, embodiments of the present invention may provide full scale ranges of 6SLM or higher.
Embodiments of the present invention may also provide the advantage of reduced calibration and setup times coupled with a longer mean time between failures. Calibration for embodiments of the present invention may occur less than once every 6 months, while mean time between failures may exceed 24 months.
The present invention may also have the advantage of reducing contamination in the vapor produced for all metals to less that 1 part per billion (ppb), for Calcium to less than 2ppb, and for Boron to less than 5ppb. Thus, the systems and methods of the present invention, in addition to downstream components, may be less affected by contamination.
Reduced size may be another advantage of the present invention. Embodiments of the present invention may provide vapor delivery systems which are 11.25 inches×5.5 inches×8.5 inches, 10 inches×5 inches×9 inches, or smaller.
Embodiments of the present invention may provide an advantage of allowing portions of the vapor delivery system to achieve a set of conditions both more quickly and more efficiently and may allow a finer granularity of control over these operating conditions. For example, heaters may be controlled to within +/−2° C. of a setpoint.
Other embodiments of the present invention provide the technical advantage of a consistent vapor saturation and vapor delivery while operating at sub-atmospheric conditions for better safety. In some embodiments, these advantages may, in part, be achieved by utilizing components that are less affected by the operating conditions of the system, for example a thermal based mass flow controller.
Embodiments of the present invention may also be able to continue delivery of vapor in the event of a temporary interruption to a liquid source by utilizing the liquid remaining in a vaporizer tank.
Additionally, embodiments of the present invention may provide the advantage that pressure within the vapor tank does not have to be lowered for vapor production or delivery to occur.
Certain embodiments of the invention may further have the ability to communicate with external devices and provide valuable data which can be recorded and analyzed. This data may include, but is not limited to, flow, temperature, valve status, etc.
These, and other, aspects of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. The following description, while indicating various embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many substitutions, modifications, additions or rearrangements may be made within the scope of the invention, and the invention includes all such substitutions, modifications, additions or rearrangements.
The drawings accompanying and forming part of this specification are included to depict certain aspects of the invention. A clearer impression of the invention, and of the components and operation of systems provided with the invention, will become more readily apparent by referring to the exemplary, and therefore nonlimiting, embodiments illustrated in the drawings, wherein identical reference numerals designate the same components. Note that the features illustrated in the drawings are not necessarily drawn to scale.
The invention and the various features and advantageous details thereof are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well known starting materials, processing techniques, components and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure.
Before explaining embodiments of the present invention it should be noted that though the specific embodiments of the present invention described herein have been depicted with reference to their use for production and delivery of water vapor embodiments of the present invention may be utilized to produce and deliver vapor from other liquids. Those of ordinary skill in the art will have a conception of how the present invention may utilized in conjunction with these other fluids after reviewing the following disclosure.
Attention is now directed to systems and methods for producing and delivering vapor. A vaporizer tank containing a liquid may be heated such that liquid within the tank is heated and vapor generated from the liquid. The flow of this vapor to a destination may then be regulated. Embodiments of the present invention may control the temperature of this liquid such that a saturated vapor condition is substantially maintained in the vaporizer tank. The vaporizer tank is coupled to a mass flow controller which regulates the delivery of the vapor to downstream components. By substantially maintaining the saturated vapor condition within the vaporizer tank the pressure of vapor at the mass flow controller can be substantially maintained and a stable and consistent flow rate of vapor achieved. These systems and methods may be especially useful for semiconductor fabrication applications such as post etch polymer removal, dry strip processes and delivery of low vapor pressure materials.
Turning to
Vaporizer tank 170, mass flow controller 180, and printed circuit board (PCB) 190 comprising digital electronics (which may included embedded control system(s)), reside inside case 110. Vaporizer tank 170 may be coupled to one or more heaters 172. Vapor delivery system may also comprise level sensor 176 which, in one embodiment may comprise PCB 174 having sensors operable in combination with a float (not shown) to sense the level of liquid within vaporizer tank 170.
Vapor delivery system 100 may be coupled to a source of water (usually de-ionized) through system inlet 120, which is in turn coupled to inlet filter 122, dosing valve 124 and eventually to tank inlet 126 of vaporizer tank 170. Drain connection 136 of vaporizer tank 170 is similarly coupled to drainage port 130 via drain valve 134 and drain filter 132. These components may be coupled using platinum or stainless steel tubing, however, plastic tubing may, in some cases, be used to couple drain connection 136 to drainage port 130. Vapor delivery system 100 may also be coupled to a power source through power outlet 140 and may communicate with an external device (e.g. a control system from which it may receive a setpoint) through I/O port 150. Notice that some of the electronics of vapor delivery system 100 may be separated from the liquid flow path by a splash guard 192 which serves to protect these electronics from possible leaks.
Moving on to
Tank inlet 126 and drain port 136 may be located at the bottom of vaporizer tank 170 (relative to the orientation with which vaporizer tank 170 may be utilized in operation) to reduce temperature fluctuations caused to liquid in vaporizer tank 170 during the addition or drainage of liquid to or from vaporizer tank 170. Similarly, to reduce variations in the fill rate, which may be caused by inlet pressure variation, a flow restrictor may be used in conjunction with tank inlet 126. In some embodiments, this flow restrictor may a 0.023 inch thick stainless VCR gasket on tank inlet 126 where the gasket has a 0.01 inch diameter hole.
To sense the level of the liquid in vapor tank 170, vapor delivery system 100 may utilize level sensor 176 comprising PCB 174 having one or more reed sensors and float 220 comprising a magnet, as will be detailed below. Before elaborating on specific embodiments of various components of vapor delivery system 100, however, it may be helpful to present a block diagram of an embodiment of vapor delivery system 100 to aid the reader in a greater understanding of such a system.
In one embodiment, level sensor 176 comprises float 220 having a magnet which, when used in conjunction with PCB 174 having one or more reed sensors, is operable to sense the level of a liquid in vaporizer tank 170. The liquid in vaporizer tank 170 may be heated indirectly through one or more tank heaters 172 which are coupled to vaporizer tank 170. When liquid within vaporizer tank 170 is heated vapor may be produced. The flow of this vapor out of vapor outlet 160 may be controlled through the use of a mass flow controller 180, for example a temperature based mass flow controller such as a Tylan thermal-based VC4900 series mass flow controller.
To ensure that condensation does not form from vapor flowing from vaporizer tank 170 and through vapor outlet 160, mass flow controller 180, outlet plumbing coupling vaporizer tank 170 to mass flow controller 180, and outlet plumbing coupling mass flow controller 180 to vapor outlet 160, may be kept at a temperature slightly higher than the temperature of vaporizer tank 170 (e.g. between 5° and 15° C. hotter than vaporizer tank 170). The heating of mass flow controller 180 and the associated output plumbing may be accomplished through the use of one or more mass flow controller heaters 182 coupled to the mass flow controller 180.
Over time metallic ions which leach into the water and other contaminants may accumulate such that the vapor being delivered by the system is unacceptably contaminated. In this case it may be desirable to drain vaporizer tank 170 in order that contaminated water may be removed. To this end, vaporizer tank 170 is coupled to drain outlet 130. Liquid may flow from vaporizer tank 170 through filter 132 (which may be similar to the filters discussed above with respect to filter 122) and drain valve 134 which is operable to control the flow of water from vaporizer tank 170. In one embodiment, drain valve 134 may be. a Bio-chem Valve Inc., 075T series having a CV of 0.0305 (e.g. Bio-chem MFG P/N 075T2-S126x).
Now that a general overview of vapor delivery system 100 has been given, it may be useful to describe in more detail embodiments of various components which may be utilized in conjunction with embodiments of vapor delivery system 100.
In one embodiment, heaters 172, 182 may comprise a dual-zone heating system. Heaters 182 on mass flow controller 182 may utilize direct current (DC) power and comprise one heating zone while heaters 172 on vaporizer tank 170 may utilize alternating current (AC) power and form another heating zone. By utilizing dual AC heaters 172 on vaporizer tank 170, vapor delivery system 100 may operate using, for example, either 110 VAC or 220 VAC by configuring heaters 172 in series or in parallel appropriately based on the voltage utilized, so that the overall heat output of heaters 172 is substantially identical no matter the voltage. In some cases heaters 172 may be configured in parallel or series using jumpers or a fuse assembly residing on power supply circuitry on PCB 190.
In operation, each set of heaters 172, 182 may be controlled by a Proportional Integral Derivative (PID) controller loop, such that heaters 172 comprising one heating zone are controlled by one PID control loop and heaters 182 comprising the other heating zone controlled by another PID control loop. Each of these control loops may receive a setpoint and control its respective heaters 172, 182 based on a sensed temperature associated with the vaporizer tank 170 or mass flow controller 180, respectively. The temperatures associated with vaporizer tank 170 and mass flow controller 180 may be sensed by a temperature sensor (e.g. a resistive thermal device (RTD)). For example, the temperature sensor for the heating zone comprising heaters 182 may be located near, or between, tank inlet 126 and drain outlet 136, while the temperature sensor for the heating zone comprising heaters 172 may be located at or near a thermal sensor of a thermal based mass flow controller comprised by mass flow controller 180.
As mass flow controller 180 may be mounted on, in close proximity, or physically coupled to, vaporizer tank 170, the heaters 182 on vapor controller 180 may receive a “boost⇄ from heaters 172 on vaporizer tank 182 (e.g. heaters 172 may also provide some heat to mass flow controller 180). Consequently, heaters 182 may have to consume less energy to reach a setpoint or to maintain a setpoint, thus increasing the efficiency of vapor delivery system 100. Additionally, this “boost” may allow heaters 182 to reach a setpoint more quickly. The presence of an integrator in the control loops utilized with both of the heating zones, coupled with what may be the inherently slow nature of the system with which heaters 172 and 182 are being utilized, substantially alleviates crosstalk issues between each of the two heating zones.
We now turn to embodiments of liquid level sensor 176 for use with embodiments of vapor delivery system 100.
A more detailed view of an example of a float device for use with an embodiment of a level sensor is depicted in
Float 220, and hence magnet 620, rises and falls with the level of liquid in vaporizer tank 180. This movement may be detected by reed switches on PCB 174 of level sensor 176.
While embodiments of the present invention may use a set of reed switches 710 along with magnetic float 220 to sense the level of liquid in vaporizer tank 170, other methods of level sensing may also be utilized, where these methods may be point of use or continuous. For example, ultrasonic sensors may be utilized to monitor a liquid level by determining the time it takes an ultrasonic pulse to travel a certain distance. Additionally, one or more optical switches such as those of the Honeywell LLE series may be utilized.
It may occur to the reader that during the vaporization process occurring in vaporization tank 170 the liquid may be at or near boiling and the surface level of the liquid may be variable. Thus, it may be desirable to employ one or more techniques to stabilize the signal output of whatever type of level sensor is utilized with a particular embodiment of vapor delivery system 100. These techniques may include physical means. For example, the float utilized with reed switches may be coupled to two shafts and be heavy relative to the liquid with which it is being utilized which may somewhat temper the effects of varying liquid levels. Alternatively, the float for a reed switch may contained in a vertically oriented tube with holes near the bottom so liquid may enter the tube, where the tube serves as a barrier against the movement of the liquid.
Furthermore, if an optical level sensor is utilized baffles may be attached to an optical sensors sensing area to attenuate the effects of the varying liquid level, as depicted in
During operation of vapor delivery system 100, liquid in vaporizer tank 170 is heated to a substantially stable temperature using heaters 172. This temperature may be between 70° C. and 150° C. in general, between about 90° C. and 100° C. for water, and may be around 93° C. for water in many cases. When vaporizer tank 170 has reached this stable temperature (and thus, indirectly, liquid within vaporizer tank 170 has reached a substantially stable temperature) vapor within vaporizer tank 170 may be in a substantially saturated condition.
This temperature may then be substantially maintained using heaters 172 such that the saturated vapor conditions inside vaporizer tank 170 persists, resulting in a substantially fixed relationship of pressure and temperature inside vaporizer tank and providing substantially steady vapor pressure at mass flow controller 180 which, in turn, may regulate the flow of vapor from vaporizer tank 170 to downstream components.
Additionally, during operation of vapor delivery system 100, mass flow controller 180 may be maintained at a higher temperature than the desired stable temperature of vaporizer tank 170 to prevent re-condensation of vapor flowing through mass flow controller 180. Usually this temperature is 5° C. to 15° C. higher than the stable temperature of vaporizer tank 170. For example, when the vapor tank is to be maintained at around 93° C., heaters 182 may be set to maintain mass flow controller 180 at around 105° C.
More detailed embodiments of the operation of embodiments of a vapor delivery system may be explained better with reference to
DSP controller 1010 may comprise a processor, associated memory operable, and a set of executable instructions operable to control vapor delivery system or components of vapor delivery system 100 (e.g. Xicor Serial EEPROM P/N X5163S8-2.7A, Texas Instruments DSP Controller TMS320LF2407APGEA).
Instructions executed by DSP controller may comprise firmware operable for operating vapor delivery system 100, where this firmware may, in embodiments, be conceptually divided into three modules, a module for monitoring and maintaining a liquid level in vaporizer tank 170, a module for heating, including heating of vaporizer tank 170 to a setpoint to generate vapor and the heating of mass flow controller 180, and a module for the delivery of vapor at a setpoint. Firmware executing in conjunction with DSP controller 1010 may also record errors that occur during operation in the associated memory, such as an EEPROM or another data saving device within vapor delivery system 100. Each error detected by the firmware may have an error code. This error code may be stored in a circular buffer in an EEPROM along with a time stamp, such that locations in the buffer may be overwritten if a certain number of errors occur. In one embodiment, DSP controller 1010 may reside on PCB 190 along with associated electronic components for operating or controlling vapor delivery system.
Initially, during operation of vapor delivery system 100 in one embodiment, DSP controller 1010 may send a signal to close fill valve 124 and drain valve 134, after which vaporizer tank 170 may be pumped down by drawing a vacuum through at vapor outlet 160. This reduces the pressure in vaporizer tank 170 such that if vaporizer tank 170 is subsequently filled with liquid, such as de-ionized water, pressure in vaporizer tank 170 will not increase substantially as the vaporizer tank 170 is filled. Additionally, DSP controller 1010 may turn on heaters 182 to heat mass flow controller 182 to an operating temperature which may be around 5° C. to 15° C. higher than the operating temperature to be utilized in conjunction with vaporizer tank 170. In some embodiments, control of heaters 182 may be accomplished utilizing a PID control loop in the firmware operating on DSP controller and operable to control heaters 182, as detailed above.
After the initial pumpdown of vaporizer tank 170, DSP controller 1010 may send a signal to open fill valve 124 such that liquid is allowed to flow, and is admitted to, vaporizer tank 170. DSP controller 1010 may receive a signal from level sensor 176 indicating when the liquid in vaporizer tank 170 has reached an operating level and may then close fill valve 124. In some embodiments this operating or working level may be around 300 ml.
Alternatively, after it is determined that the liquid in vaporizer tank 170 has reached the working level, vaporizer tank 170 may continue to be filled for a certain amount of time. This time period may be predetermined or operator set, and may depend on the vapor flow rate desired, type of liquid etc. In some embodiments this time period may be around two minutes. During this time period fill valve 124 may be held open or fill valve may be “strobed” by DSP controller 1010 such that fill valve 124 is opened and closed at intervals, as will be described later. After this time period DSP controller 1010 may send a signal operable to close fill valve 124. Additionally, DSP controller 1010 may turn on heaters 172 to heat vaporizer tank 172 to an operating temperature, which, in the case of de-ionized water, may be around 93° C. The control of heaters 172 may be accomplished using a PID control loop operating in the firmware of DSP controller 1010, as elaborated on above.
Once the temperature of vapor tank 170 has stabilized (e.g. within +/−2° C. of an operating temperature for a certain amount of time), which may be determined using a signal from a temperature sensor associated with vaporizer tank 170, vapor delivery system 100 may be in a ready state for commencing vapor flow. In one embodiment, before a ready state for vapor delivery system 100 is reached it may also be determined if the operating temperature for mass flow controller 180 has been reached and is stable utilizing temperature sensor associated with mass flow controller 180.
Subsequent to vapor delivery system 100 reaching a ready state vapor may be flowed to components downstream of mass flow controller 180. DSP controller 1010 may receive a vapor flow setpoint (which may have been received at a prior point) and operate mass flow controller 180 such that a flow rate of vapor corresponding to the vapor flow setpoint is substantially achieved, or alternatively, may provide the flow rate setpoint to mass flow controller 180 such that mass flow controller 180 regulates vapor flow from vaporizer tank 170 to substantially achieve the desired vapor flow setpoint. Vapor delivery system 100, may, in some embodiments, be operable to deliver vapor at flow rates up to 6 SLM.
While vapor delivery system 100 is flowing vapor from vapor outlet 160, DSP controller 1010 may substantially maintain the operating temperatures of vaporizer tank 170 and mass flow controller 180. These operating temperatures may be maintained by controlling heaters 172 and 182 using their respective PID control loops, as discussed above. By substantially maintaining the temperature of vaporizer tank 170 (and thus the liquid in vaporizer tank 170) the saturated vapor condition in vaporizer tank 170 may be substantially maintained and the upstream pressure of vapor at mass flow controller 180 may be substantially steady, allowing vapor delivery system to deliver a substantially steady and consistent flow rate of vapor.
Briefly, one embodiment of a set of possible operating conditions for vapor delivery system 100 is depicted with respect to a pressure versus temperature curve in
Returning to
However, if DSP controller 1010 receives a signal from level sensor 174 that water has fallen below the operating level DSP controller 1010 may operate fill valve 124 to introduce liquid into vaporizer tank 170. In one embodiment, after receiving a signal from level sensor DSP controller 1010 may wait 5 to 10 seconds and verify that the signal from level sensor 176 still indicates that the liquid level in vaporizer tank 170 is below the operating level. After verifying that the signal from level sensor 176 indicates that the liquid level is below the operating level, DSP controller 1010 may operate fill valve 124 to achieve a certain fill rate during a refill period. This fill rate may be determined by several variables such as liquid source pressure, pressure drop from fittings and filters, the type and operation of fill valve 124, etc. In one embodiment, this fill rate may be twice the liquid consumption rate of vapor delivery system 100 utilized to produce vapor flow at full scale. For example, if approximately 2.5 ml per minute is flowing from vapor control system 100 the fill rate may be approximately 5 ml per minute.
This addition of liquid to vaporizer tank 170 may cause temperature and pressure fluctuations in the liquid in vaporizer tank 170. While the liquid present in vaporizer tank 170 may serve to dampen these temperature and pressure fluctuations somewhat, in order to further minimize these temperature fluctuations and pressure fluctuations, which may be exacerbated by differences in liquid source pressure, fill valve 124 may be gated, or the duty cycle of the fill valve controlled, to open and close the fill valve during the refill period to achieve a desired fill rate during the refill period. By minimizing disturbance to the state of vaporizer tank 170 while adding liquid to vaporizer tank 170 a substantially steady flow rate of vapor may be maintained while the addition of liquid is occurring.
This advantage may be better illustrated with reference to
At time 1302, notice that the line 1310 indicates that the vapor flow rate is approximately 90% of FS. At time 1304, then, signal 1320 goes low, indicating that the level of liquid in vaporizer tank 170 has dropped below the operating level. After a pause of approximately 30 seconds, at time 1306 signal 1330 oscillates indicating that fill valve 124 is being opened and closed to achieve the desired fill rate, until at time 1308 signal 1320 goes high, indicating that the liquid in vaporizer tank 170 has again reached the operating level. Signal 1330 indicates, however, that fill valve continues to be cycled for an amount of time after signal 1320 indicates that the operating level has been reached. In the embodiment depicted, fill valve 124 may be cycled for approximately 30 seconds before, as indicated by signal 1320, it is closed around time 1312. In other embodiments, the refill period may continue for approximately 2-5 minutes after level sensor 176 signals that the liquid in vaporizer tank 170 has reached the operating level.
Notice that during the time between time periods 1302 and 1312 when liquid is being added to vapor tank 170 the flow of vapor from vapor delivery system 100 (indicated by signal 1310) remains substantially steady. Notice, as well, that between time periods 1302 and 1312 (and during the other points of operation depicted in
In addition to oscillating fill valve 124 to refill vaporizer tank 170, in one embodiment, to combat the effect of the addition of liquid to vaporizer tank 170, DSP controller 1010 may signal heaters 172 to provide a heater kick for a certain time period during the refill process. For example, temperature of vaporizer tank 170 may be elevated to a predetermined temperature, to add more heat to substantially maintain a vapor saturation in the vaporizer tank 170 in order that the temperature of vaporizer tank may substantially return to the first setpoint once fill valve 124 has stopped pulsing opened and closed.
Returning to
Even if the flow from a liquid source is cutoff or otherwise impaired, however, vapor flow system 100 may still continue delivering vapor at a set flow rate after the liquid level in vaporizer tank 170 falls below the operating level. For example, if vaporizer tank 170 is 2.5 inches×3.5 inches×4.0 inches after the liquid level drops below an operating level of about 330 ml vapor delivery system may continue to deliver vapor at about a 3SLM flow rate for approximately two hours.
Occasionally, it may be desired to purge vaporizer tank 170 of water to eliminate built up contaminants, or for a wide variety of other reasons. This purge cycle may be initiated from a signal provided to DSP controller 1010 by an external controller, or by DSP controller 1010 after a certain number of uses of vapor delivery system 100, etc. DSP controller 1010 may operate heaters 182 of mass flow controller device 180 according to a setpoint and substantially close mass flow controller 180. DSP controller 1010 may signal both fill valve 124 and drain valve 134 to open and nitrogen gas may then be flowed in through fill valve 124 and utilized to purge vaporizer tank 170 by forcing contents of vaporizer tank 170 through drain valve 134. Nitrogen may be flowed for a predetermined amount of time to ensure that vaporizer tank 170 is properly purged.
While various advantages of the operation of embodiments of the present invention have been described, it may be helpful to depict the conditions during operation of embodiments of the present invention graphically so that advantages accruing to various embodiments of the present invention may be better appreciated. To this end FIGS. 14—depict various graphs of conditions occurring during operation of embodiments of the present invention.
More particularly,
Area 1430 of
Finally,
Although the present invention has been described in detail herein with reference to the illustrative embodiments, it should be understood that the description is by way of example only and is not to be construed in a limiting sense. It is to be further understood, therefore, that numerous changes in the details of the embodiments of this invention and additional embodiments of this invention will be apparent to, and may be made by, persons of ordinary skill in the art having reference to this description. It is contemplated that all such changes and additional embodiments are within the scope of this invention as claimed below.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.
