Patent Application
20060196541
The present invention relates to an apparatus and method for controlling the fluid conditions of a fluid in a fluid distribution system. More particularly, the present invention provides improved apparatus and methods for controlling the pressure of ultra-high purity or slurry fluids in a bulk fluid distribution loop that supplies process fluid to points of use in a semiconductor manufacturing process or other related applications.
The manufacture of semiconductor devices is a complex process that often requires over 200 process steps. Each step requires an optimal set of conditions to produce a high yield of semiconductor devices. Many of these process steps require the use of fluids to inter alia etch, expose, coat, and polish the surfaces of the devices during manufacturing. In high purity fluid applications, the fluids must be substantially free of particulate and metal contaminants in order to prevent defects in the finished devices. In chemical-mechanical polishing slurry applications, the slurries must be free from large particles capable of scratching the surfaces of the devices. Moreover, during manufacturing there must be a stable and sufficient supply of the fluids to the process tools carrying out the various steps in order to avoid process fluctuations and manufacturing downtime.
Since their introduction to the semiconductor market in the 1990s, bulk fluid distribution systems have played an important role in semiconductor manufacturing processes. Because these systems are substantially constructed of inert wetted materials, such as perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polyvinylchloride (PVC), polyvinylidine difluoride (PVDF) or polyethylene (PE), and because they use either an inert pressurized gas or pump having inert wetted materials as the motive force for supplying the fluids, they do not substantially contribute to particulate and metal contamination of the process fluids. In addition, a single bulk fluid distribution system can provide a continuous supply of process fluid at a sufficient pressure to multiple points of use. Thus, the advent of fluid distribution systems has served an important need in semiconductor manufacturing processes.
For many reasons, bulk fluid distribution systems (e.g. o-ring failures, valve failures, or contaminated incoming fluid) include filters in the fluid supply line. However, an abrupt change in the flow rate of the fluid through the filters causes hydraulic shock to the filters which results in a release of previously filtered particles into the fluid thereby causing a spike in the particle concentration. Although maintaining a minimum flow rate of the fluid through the filters helps reduce particulate release, the problem is not eliminated. Accordingly, pressure and flow fluctuations of the fluid can result in fluctuations of the particle concentration in the fluid, which may lead to defects in the semiconductor wafers.
Moreover, as discussed above, fluid distribution systems often supply many tools. When a tool demands process fluid it begins pumping the fluid from the supply line which causes the pressure of the fluid in the supply line to drop by about 5 to about 25 psi. Typical fluid distribution systems having pump-pressure vessel engines or pump-pulse-dampener engines do not adequately maintain a constant or sufficient pressure in the process fluid supply line. Accordingly, there is a need for a fluid distribution system that provides a constant pressure and flow rate and eliminates pressure and flow fluctuations of the fluid in the supply line.
A known fluid distribution system having a pump-pressure vessel engine is shown in
System 100 further includes a pressure vessel 111 constructed of an inert wetted material such as perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polyvinylchloride (PVC), polyvinylidine difluoride (PVDF) or polyethylene (PE). An inert gas source 113 supplies an inert gas, such as nitrogen, to vessel 111 to act as a motive force for driving fluid from the vessel 111 through the filters (not shown) and to the fluid supply line 115. The pressure of the inert gas supplied to vessel 111 is regulated to a constant pressure by mechanical regulator 117. As mentioned above, the fluid supply line 115 often supplies fluid to several points of use (e.g. semiconductor process tools) (not shown).
The pump 101 receives fluid from a fluid source 119 and dispense the fluid into the top of the vessel 111. A vent (not shown) in the vessel 111 permits any gas to escape while fluid is being added to the vessel 111. Two level sensors 121 and 123 (i.e. capacitive sensors) are used to monitor the fluid level at a high position (indicated by sensor 121) and a mid-point position (indicated by sensor 123) in the vessel 111. The vessel 111 contains an internal pipe (not shown) that extends from the fluid inlet to a point just below the mid-point sensor 123 in order to prevent splashing when the fluid enters the vessel.
During operation, when the fluid level in the vessel 111 reaches mid-point sensor 123, the pump 101 activates to refill the vessel 111 up to high sensor 121. The stroke rate and gas pressure applied to the pump are the same every time the pump is activated. Similarly, regulator 117 maintains a constant inert gas pressure to vessel 111.
In a pump-pressure vessel fluid distribution system, there are several factors that may contribute to a loss in fluid pressure including: 1) pressure loss across the filters; 2) frictional losses from piping, valves and other such components; 3) changes in the head pressure of the fluid between the high and mid-point sensors 121 and 123; and 4) demands for fluid from the points of use. The first two factors typically create a constant loss of pressure in the fluid, although in some applications, the pressure loss across the filters will increase over time as more particles are captured. In contrast, the third and fourth factors cause the pressure to fluctuate depending upon the level of the fluid in the vessel 101 or whether or not there is a demand for fluid from a point of use. Thus, the pressure of the fluid in the supply line 115 of system 100 continuously fluctuates during operation which, as discussed above, may cause hydraulic shock to the filters and unpredictable fluid conditions at the points of use.
Accordingly, there is a need for an improved pump-pressure vessel fluid distribution system that substantially reduces or eliminates pressure fluctuations of the fluid in the supply line and assures uniform fluid conditions at the points of use.
Another type of fluid distribution system utilizes a pump-pulse-dampener engine. A common pump-pulse-dampener fluid distribution system is shown in
During operation, the pump 201 withdraws fluid from a fluid source 219 and distributes the fluid to the fluid supply line 215. Filters (not shown) are typically located downstream from the pulse-dampener 211.
In a pump-pulse-dampener fluid distribution system, there are several factors that may contribute to a loss in fluid pressure including: 1) pressure loss across the filters; 2) frictional losses from piping, valves and other such components; 3) pulsations resulting from operation of the positive displacement pump; and 4) demands for fluid from the points of use. As with the pump-pressure vessel system, the first two factors create a constant pressure loss in the fluid, although in some applications, the pressure loss across the filters will increase over time as more particles are captured. In contrast, the third factor causes a decrease in the fluid pressure by about 5 psi to about 25 psi resulting from the demand of one or more points of use (e.g. a process tool). Thus, the pressure of the fluid in the supply line 215 continuously fluctuates during operation.
Accordingly, there is a need for an improved pump-pulse-dampener fluid distribution system that substantially reduces or eliminates pressure fluctuations of the fluid in the supply line and assures uniform fluid conditions at the points of use.
It should be noted that systems 100 and 200 are operated in one of two configuration: 1) with fab-wide recirculation; and 2) with internal recirculation. When a system is configured to operate with fab-wide recirculation, the fluid continuously flows from the outlet of the system, through the supply line 115 or 215 and back to the fluid source 119 or 219 (typically a daytank or drum). However, such a system requires a significant amount of facilities, such as gas and energy, to operate, so it is often preferred to operate in an internal recirculation mode. When a system is configured to operate with internal recirculation, a slipstream is installed to recirculate the fluid from a point just downstream from the filters in the supply line 115 or 215 to the fluid source 119 or 219. When there is no demand for fluid from a point of use, the fab-wide recirculation is stopped (usually by closing a valve positioned in the supply line downstream from the slipstream). The internal recirculation line maintains a constant flow rate through the filters and reduces the amount of facilities required to operate the system.
An apparatus for controlling the pressure of a fluid in a supply line of a fluid distribution system comprising a pump adapted to receive the fluid from a fluid source; a vessel comprising a level sensor for measuring a level of the fluid in the vessel wherein the vessel is adapted to receive the fluid from the pump and dispense the fluid to the supply line; a source of inert gas for supplying an inert gas to the vessel wherein a regulator is adapted to regulate the pressure of the inert gas; a fluid sensor positioned in the supply line; and a controller adapted to receive a control signal from the fluid sensor and to send a dispense signal to the regulator to adjust the pressure of the inert gas to maintain a predetermined pressure of the fluid in the supply line.
A method for controlling the pressure of a fluid in a bulk fluid distribution system comprising a pump, a vessel having a level sensor and adapted to receive an inert gas for pressurizing the vessel and dispense the fluid to a supply line, an inert gas regulator for regulating the pressure of the inert gas, a fluid sensor, and a controller adapted to receive a control signal from the fluid sensor and send a signal to the inert gas regulator comprising the steps of maintaining a first level of the fluid in the vessel by adjusting the flow rate of the pump based upon a signal from the level sensor; pressurizing the vessel to dispense the fluid to the supply line; and adjusting the inert gas pressure supplied to the vessel to maintain the pressure of the fluid in the supply line at a user defined setpoint.
Embodiments of the present invention are shown in
Where an external shuttle valve is employed, the controller 309 controls the cycle rate of the solenoid valves 303a and 303b by alternately sending electric signals (not shown in
System 300 further includes a pressure vessel 311 constructed of an inert wetted material such as perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polyvinylchloride (PVC), polyvinylidine difluoride (PVDF) or polyethylene (PE). A source of inert gas 313 (e.g. nitrogen) supplies inert gas to vessel 311 to provide a driving force for the fluid through a filter (not shown) and fluid supply line 315. Master regulator 318 (e.g. an electro-pneumatic regulator) and slave regulator 317 (e.g. a dome-loaded pressure regulator) control and regulate the pressure of the inert gas supplied to vessel 311. While it is preferable to use a master and slave regulator configuration, a single regulator (e.g. an electro-pneumatic regulator) may be used to provide active control of the inert gas pressure based upon signals from the controller 309. The fluid supply line 315 supplies fluid to several points of use (e.g. semiconductor process tools) (not shown).
A source of process fluid 319 is connected to the inlet side of pump 301 which dispenses the fluid into the top of the vessel 311 as shown in
During operation, the controller 309 receives a signal from the load cell 321 and determines if the weight of the vessel 311, or the fluid in the vessel, is between a high or low setpoint which are preferably user configurable. When the controller 309 determines that the weight is at the low setpoint, it sends a signal to master regulator 308 and solenoid valve 303 and activates the pump 301. In contrast, when the controller 309 determines that the weight is at the high setpoint, it deactivates the pump 301. Load cells, as compared to capacitive, optical and digital sensors, are very sensitive to changes in the fluid level in the vessel, so the setpoints can be configured to control the weight within a narrow tolerance, which would minimize fluctuations of fluid pressure in the supply line 315 resulting from changes in fluid head pressure in the vessel 311. Likewise, the setpoints could be configured to maintain the same weight, which would eliminate any pressure fluctuations resulting from changes in head pressure; however, in this configuration, the pump 301 would operate continuously.
While system 300 has been described as having load cells, in a less preferred embodiment, capacitive, optical or digital sensors can also be used instead of load cells. In this configuration, one sensor would be positioned at a high level of the vessel 311 and another sensor would be positioned at a midpoint level of the vessel 311. When the fluid level reaches the midpoint sensor, the controller 309 would activate the pump 301 to fill the vessel up to the high level sensor. Thus, in this configuration, the fluid in the vessel 311 would alternate between a high and a midpoint level thereby causing the head pressure to fluctuate in the vessel 311 and pressure fluctuations in the supply line 315.
System 300 further includes a sensor 325 positioned preferably at a midpoint in the supply line 315 near the feed lines to the points of use (not shown). The sensor continuously or periodically monitors the pressure of the fluid in the supply line 315 and sends a corresponding signal to the controller 309. Thereafter, the controller 309 sends an electric signal to master regulator 318 to adjust the inert gas dispense pressure (regulated by slave regulator 317) to the vessel 311 in order to maintain the fluid pressure in the supply line 315 at a user configurable setpoint. Thus, the system 300 is configured to provide stable control of the pressure and fluid conditions of the fluid in the supply line 315.
The pump-pressure vessel system 300 of the present invention substantially reduces or eliminates pressure fluctuations in the fluid in the supply line 315 resulting from the following factors: 1) pressure loss across the filters; 2) frictional losses from piping, valves and other such components; 3) changes in the head pressure of the fluid between the high and low setpoints; and 4) demands for fluid from the points of use. Because the pressure is controlled at the position of the sensor 325 in the supply line 315, the controller 309 will automatically adjust the inert gas dispense pressure to the vessel 311 to overcome the nearly constant pressure losses from the filters and other system components. In addition, as discussed above, the head pressure losses can be substantially reduced or eliminated by maintaining the fluid level within a narrow band or at the same level. However, because demands for fluid from points of use are sudden and unpredictable it is difficult to eliminate any fluctuations resulting from such sudden pressure losses. Moreover, points of use may demand fluid simultaneously thereby compounding the pressure losses. Regardless, the sensor 325 will detect any changes in fluid pressure in the supply line 315 and the controller 309 will adjust the inert gas dispense pressure to the vessel 311 accordingly. Thus, the system 300 of the present invention substantially improves the fluid conditions in the supply line 315 as compared to the prior art system 100 shown in
System 300 may also be configured to receive a signal from each point of use every time it demands fluid. This signal would be used by the controller 309 to predict the appropriate signal to send to the master regulator 318 in order to achieve the necessary inert gas dispense pressure to the vessel 311. The reaction time of the controller 309 to dynamic changes in the supply line 315 may be faster in this configuration than in system 300 without transmission of a demand signals to the controller 309.
As shown in
Similarly, in the system 300 shown in
Another embodiment of the present invention is shown in
The system 400 also includes a pulse-dampener 411 to minimize pressure fluctuations in the fluid resulting from operation of the pump 401. Reciprocating pumps, in particular, cause pressure fluctuations in the fluid being pumped due to the mechanical oscillations of the pump and turbulence that is created in the fluid. The pulse-dampener 411 includes an internal diaphragm or a bellows (not shown). High pressure gas 405 is supplied to the top of the diaphragm and is regulated by mechanical regulator 417 (e.g. a dome-loaded pressure regulator). As the pressure of the fluid in the supply line 415 fluctuates, the upward force against the bottom of the diaphragm fluctuates and the diaphragm mechanically adjusts to dampen any pressure oscillations in the fluid. The mechanical regulator 417 could be replaced with an electro-pneumatic regulator (not shown) that would enable the controller 409 to actively adjust the pressure of the gas 405 supplied to the pulse-dampener in order to improve its performance in reducing pressure pulsations of the fluid in the supply line 415. In addition, the pressure of the high pressure gas supplied to the pulse-dampener could be regulated based upon a demand signal from the point of use or the sensor 425 positioned in the supply line.
Like system 300, there are several factors that may lead to fluid pressure fluctuations in the supply line 415 including: 1) pressure loss across the filters; 2) frictional losses from piping, valves and other such components; 3) pressure pulsations from the pump; and 4) demands for fluid from the points of use. To compensate for such pressure fluctuations, system 400 monitors the pressure in the supply line 415 and adjusts the pump pressure and/or stroke rate to compensate for any changes.
During operation, the controller 409 either continuously or periodically receives a signal from sensor 425 corresponding to the pressure of the fluid in the supply line 415. The controller 409 attempts to maintain the pressure of the fluid in the supply line 415 at a user configurable setpoint by adjusting the speed of the pump 401. The controller 409 can accomplish this by adjusting the pressure of the gas 405 supplied to the shuttle valve 403 or adjusting the cycle rate of the solenoid valves 403a and 403b, or by doing both.
When the controller 409 adjusts the pressure of the gas supplied to the pump 401, it sends a signal to master regulator 408 to adjust the gas pressure supplied to the solenoid valves 403a and 403b. If the pressure is higher, a greater force of pressure will be applied to the diaphragms of the pump thereby causing them to move more quickly. This results in a higher flow rate and a higher pressure of the fluid in the supply line. If a lower pressure is supplied to the solenoid valves 403a and 403b, then the diaphragms move more slowly and with less force, thus reducing the fluid pressure in the supply line 415.
When the controller 409 adjusts the cycle rate of the solenoid valves 403a and 403b, it simply changes the rate at which it triggers and fires the valves. To increase the pressure, the controller 409 cycles the valves at a faster rate whereas to reduce the pressure, the controller cycles the solenoid valves 403a and 403b at a slower rate.
The controller 409 may also adjust both the pressure of the gas supplied to the pump 401 and the cycle rate of the solenoid valves 403a and 403b to achieve optimum performance. For example, when the pressure in the supply line 415 drops, increasing the pressure to the solenoid valves 403a and 403b may quickly cause the pressure of the fluid in the supply line to increase, but the pressure pulsations resulting from operation of the pump 401 could be larger. Thus, it may be beneficial to increase the pressure to the solenoid valves 403a and 403b by a percentage of the required pressure and to make up the additional pressure by increasing the cycle rate of the solenoid valves 403a and 403b.
The present invention as shown in
It is anticipated that other embodiments and variations of the present invention will become readily apparent to the skilled artisan in light of the foregoing description and examples, and it is intended that such embodiments and variations likewise be included within the scope of the invention as set forth in the following claims.
| Number | Date | Country | |
|---|---|---|---|
| 60659047 | Mar 2005 | US |
