Patent Application
20060104878
1. Field of the Invention
The present invention relates to a thermal reactor apparatus used to treat industrial effluent fluids, for example effluent gases produced in semiconductor and liquid crystal display manufacturing processes. Specifically, the present invention relates to improved safety, reliability, monitoring and control features and components for said thermal reactor apparatus.
2. Description of the Related Art
The gaseous effluents from the manufacturing of semiconductor materials, devices, products and memory articles involve a wide variety of chemical compounds used and produced in the process facility. These compounds include inorganic and organic compounds, oxidizers, breakdown products of photo-resist and other reagents, and a wide variety of other gases and suspended particulates that must be removed from the effluent streams before being vented from the process facility into the atmosphere.
Semiconductor manufacturing processes utilize a variety of chemicals, many of which have extremely low human tolerance levels. Such materials include, but are not limited to: gaseous hydrides of antimony, arsenic, boron, germanium, nitrogen, phosphorous, silicon, and selenium; silane; silane mixtures; hydrogen; organosilanes; halosilanes; halogens; acid gases; organometallics; oxidizers such as O3, NF3 and ClF3; and other organic compounds such as alcohols.
A significant problem of the semiconductor industry has been the consistent and effective removal of these materials from the effluent streams. While virtually all U.S. semiconductor manufacturing facilities utilize scrubbers or similar means for treatment of their effluent streams, the technology employed in these facilities is subject to failure and inefficiencies and as such, not all toxic or otherwise unacceptable impurities are removed.
Point-of-use abatement systems add a level of redundancy, reliability, and capability by removing pollutants from an effluent stream before the effluent is diluted in a house scrubber system. Combining and diluting effluent streams in the house system is disadvantageous for several reasons including, but not limited to, decreasing abatement efficiency due to the large, diluted volumes that must be treated, and increasing risk of unwanted side reactions, particle formation, and corrosion in a house scrubber duct system. Further, failures of the house scrubbing technology present substantial safety hazards to the personnel, facility, and the environment. The, point-of-use abatement systems combined with the house scrubbing system adds a level of redundancy and reliability consistent with critical safety standards practices of the semiconductor manufacturing industry.
Thermal reactors are increasingly being used to process effluent waste streams to decompose the toxic materials, converting them to less toxic forms. For example, the improved thermal reaction unit disclosed in co-pending U.S. Patent Application Ser. No. ______, filed Nov. 12, 2004 in the name of Ho-Man Rodney Chiu et al., and entitled “Reactor Design to Reduce Particle Deposition During Process Abatement,” abates at least 95%, preferably at least 99%, of waste effluent components including, but not limited to, CF4, C2F6, SF6, C3F8, C4F8, C4F8O, SiF4, BF3, BH3, B2H6, B5H9, NH3, PH3, SiH4, SeH2, F2, Cl2, HCl, HF, HBr, WF6, H2, Al(CH3)3, alcohols, oxidizers such as O3, NF3 and ClF3, primary and secondary amines, acid gases, organosilanes, organometallics, and halosilanes. Importantly, the decomposition removal efficiency (DRE) of the improved thermal reaction unit is greater than 99% and it is designed to reduce the deposition of unwanted reaction products, such as silicon oxides, within the thermal reaction unit.
As the art of thermal abatement develops, so has the necessity for developing safety, reliability, monitoring and control features for said thermal reactors. Safety features are especially important because the abatement of effluent waste streams in thermal reactors is facilitated by the introduction of fuels, e.g., methane, natural gas and/or hydrogen, to the thermal reactors for combustion and oxidation therein. The high temperature generated by the combustion of said fuels assists in decomposing the toxic materials of the effluent stream therein. Clearly, monitoring and control components are necessary to minimize the risk of ignition and deflagration within the reactor or reactor housing due to fuel leaks, as well as making sure the reactor efficiently abates the effluent waste stream.
Accordingly, it would be advantageous to provide improved safety, monitoring and control features for thermal reactors to ensure personnel safety and improve the efficiency of the abatement process.
The present invention relates to improved safety, monitoring and control features for thermal reactors and other abatement processes.
In one aspect, the present invention relates to an apparatus for removing pollutant from waste effluent, said apparatus comprising:
In yet another aspect, the present invention relates to method for sequentially operating the start-up of a thermal reactor having a thermal reaction chamber, said method comprising:
Other aspects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims
The present invention relates generally to a thermal reactor apparatus used to efficiently and controllably decompose pollutants contained in effluent streams. More specifically, the present invention relates to improved safety, monitoring and control features for said thermal reactor apparatus to ensure personnel safety and improve the efficiency of abatement processes.
U.S. patent application Ser. No. ______, filed Nov. 12, 2004 in the names of Ho-Man Rodney Chiu, Daniel O. Clark, Shaun W. Crawford, Jay J. Jung, Leonard B. Todd and Robbert Vermeulen, entitled “Reactor Design to Reduce Particle Deposition During Process Abatement,” is hereby incorporated by reference herein in its entirety.
Effluent streams to be abated may include species generated by a semiconductor process and/or species that were delivered to and egressed from the semiconductor process without chemical alteration. As used herein, the term “semiconductor process” is intended to be broadly construed to include any and all processing and unit operations in the manufacture of semiconductor products and/or LCD products, as well as all operations involving treatment or processing of materials used in or produced by a semiconductor and/or LCD manufacturing facility, as well as all operations carried out in connection with the semiconductor and/or LCD manufacturing facility not involving active manufacturing (examples include conditioning of process equipment, purging of chemical delivery lines in preparation of operation, etch cleaning of process tool chambers, abatement of toxic or hazardous gases from effluents produced by the semiconductor and/or LCD manufacturing facility, etc.). As used herein, “effluent streams” and “waste streams” are intended to be synonymous terms.
A generalized thermal reactor having a thermal reaction unit 30 and a lower quenching chamber 100 is shown in
In practice, waste streams enter the thermal reaction chamber 32 from at least one waste stream inlet provided in the inlet adaptor 10, and the fuel/oxidant mixture enters the thermal reaction chamber 32 from at least one burner jet 22. The pilot 16 includes a pilot flame which is used to ignite the burner jets 22 of the inlet adaptor, creating thermal reaction unit temperatures in a range from about 500° C. to about 2000° C. The high temperatures facilitate decomposition of the pollutants contained in the waste streams that enter the thermal reaction chamber 32.
Following decomposition/combustion, the effluent gases pass to the lower chamber 100 wherein a water curtain 104 may be used to cool the walls of the lower chamber and inhibit deposition of particulate matter thereon. Further downstream of the water curtain, a water spraying means 102 may be positioned within the lower chamber 100 to cool the gas stream and remove the particulate matter and water soluble or reactive gases. Gases passing through the lower chamber may be released to the atmosphere or alternatively may be directed to additional treatment units including, but not limited to, liquid/liquid scrubbing, physical and/or chemical adsorption, coal traps, electrostatic precipitators, and cyclones.
During combustion start-up, a low flow of fuel, e.g., flowing at a rate of 5-8 slm, is ignited at the pilot 16. Following successful ignition of the pilot, the fuel flow is opened to the burner jets 22 at a flow of about 30-90 slm to generate the high temperatures necessary to decompose species such as CF4. Unfortunately, if the pilot does not ignite during start-up and this failure goes unnoticed, the increase in fuel flow to the burner jets concomitantly increases the risk of deflagration in the thermal reactor.
In one embodiment of the present invention, the ignition and combustion processes are monitored using a flame sensor, which may be incorporated into the inlet adaptor. Referring to
A radiation sensor 56 is positioned to radiatively communicate with the thermal reaction chamber via the radiation conduit 50. As defined herein, “radiative communication” means that radiation from the thermal reaction chamber is able to be detected by the radiation sensor. The radiation sensor is hermetically sealed and mechanically resilient and includes a radiation cell with a quartz or sapphire lens, a lamp with lamp power supply and a detector assembly. The lens isolates the detector from the hot reactor atmosphere. The spectral range for the radiation sensor preferably corresponds to the ultraviolet range and may be in a range from about 10 nm to about 400 nm, preferably in a range from about 190 nm to about 320 nm. It is understood by one skilled in the art that the radiation sensor may employ a different spectral range depending on the fuel used in the thermal reactor. For example, when the fuel is natural gas, the emission of interest is the OH* emission, corresponding to λ=309 nm (see, Timmerman, B. H., Bryanston-Cross, P. J., Dunkley, P., The 16th Symposium on Measuring Techniques in Transonic and Supersonic Flow in Cascades and Turbomachines, Cambridge, UK, September 2002, pp. 1-7). An example of a suitable radiation sensor is the UVS 6, manufactured by Kromschroder, Inc. (Hudson, Ohio).
The radiation sensor may be communicatively connected with a controller, which monitors the input from the radiation sensor and in response, generates outputs to the various components (to be discussed in more detail hereinafter).
To ensure that the radiation sensor 56 does not detect false readings, an actuator 54 may be incorporated into the flame sensor apparatus. The actuator provides a self-check to determine if the radiation sensor 56 is operating correctly. In operation, when the actuator 54 is closed (see
During start-up, the flame sensor is on-line to sense the presence of a radiation-producing flame within the thermal reaction chamber, said flame verifying that the pilot has been successfully ignited. If the flame is detected, the fuel-flow to the burner jets may be started. If no radiation-producing flame is detected during start-up, the controller should activate an alarm and halt fuel flow to minimize the risk of deflagration within the reactor.
In addition to the importance of sensing the flame at start-up, the flame sensor should be operated throughout the abatement process to ensure the flame has not been inadvertently extinguished. Similar to start-up, if the flame sensor detects that the flame has been lost (at some time other than during the actuated self-check), the controller should activate the alarm and halt fuel flow to minimize the risk of deflagration within the reactor.
In another embodiment of the present invention, an intrinsically safe flammable gas sensor may be operated exteriorly and proximately to the thermal reactor and in close proximity to the main enclosure vent. Referring to
In general, a main enclosure 120 includes an electrical enclosure 125 and a exhausted enclosure 122. The electrical enclosure is isolated from the exhausted enclosure and is continuously purged with N2, making it substantially impervious to flammable gases. In contrast, the exhausted enclosure, which is where the thermal reactor, the fuel panel and other devices are installed, corresponds to the location within the main enclosure where flammable gases would be readily detected and reactable in the event of a fuel leak. “Substantially impervious,” as defined herein means that less than 0.1%, preferably less than 0.05%, of available flammable gas molecules are detectable in the specified region.
Within the exhausted enclosure 122 are numerous components which use electrical energy for operation, the energy of said components exceeding the minimum amount of energy needed to ignite gaseous constituents that may be present. As such, it is imperative that a flammable gas sensor be positioned within the exhausted enclosure to detect fuel leaks and remove all possible sources of ignition (electrical energy) when a leak is detected.
Unfortunately, flammable gas sensors of the prior art use substantial quantities of electrical energy, i.e., they may be the source of ignition if a gas leak occurs. Additionally, presently marketed sensors designed for use in hazardous environments are bulky and expensive. Therefore, it would be a significant advance in the art to provide an improved flammable gas sensor that has a small footprint, is affordable and is a low energy, intrinsically safe sensor.
As defined herein, “low energy sensor” relates to sensing devices that utilize an energy input which can be provided by an intrinsically safe barrier, and can be maintained below the ignition energy of the fuel used. As defined herein, “intrinsically safe” relates to a power limit rating for electronics used in an explosive or flammable environment. An “intrinsically safe method” means that the energy available in the exhausted enclosure, or equivalent thereof, is below that necessary to ignite the fuel therein.
The flammable gas sensor of the present invention has two elements positioned in the exhausted enclosure 122: a heating element and a sensing element. The heating element is used to maintain the sensing element at a temperature optimal for sensing. The sensing element is highly sensitive to the flammable gas to be sensed. Two intrinsically safe barriers, which are preferably located in the electrical enclosure 125 (see, e.g.,
An embodiment of the electronic schematic of the flammable gas sensor of the present invention is illustrated in
If the concentration of flammable gas detected is determined to be too high, the emergency machine off (EMO) is activated. Emergency machine off (EMO) is a modality wherein all of the electrical components located inside the exhausted enclosure are shut-down immediately, including ignition sources, fuel flows, oxidizer flows, waste effluent flows, and water flows. Importantly, the threshold for EMO activation may correspond to the concentration necessary to ignite the fuel gas, however, preferably the threshold is less than one-quarter, preferably less than one-twentieth of said ignition concentration. For example, the threshold for methane gas detection and alarm may be set at 1000 ppm, which corresponds to a concentration 1/50th of the concentration at which methane is readily ignited in air. Importantly, the chosen threshold should simultaneously be substantial enough to minimize background effects.
Similar to the flame sensor, the second output (fault condition) of the flammable gas sensor may be communicatively connected to the controller, and if a fault, e.g., a cable disconnection, is sensed, an alarm may sound, the fuel flow may be halted and a delayed shutdown is initiated. The flammable gas sensor is preferably on-line continuously.
The novel flammable gas sensor including at least two intrinsically safe barriers provides an affordable and compact improvement over fuel sensing devices of the prior art. Once installed, the exhausted enclosure may be safely monitored for fuel leaks because the flammable gas sensor, and its associated components, cannot be a source of ignition. It is to be appreciated by one skilled in the art that the intrinsically safe flammable gas sensor of the present invention having two intrinsically safe barriers may be utilized with any apparatus or method where the concentration of flammable fuels must be safely monitored.
In yet another embodiment of the present invention, the stability of the fuel flame is controlled to maintain stable combustion within the thermal reactor. In practice, fuel enters the thermal reaction chamber at burner jets 22 (see, e.g.,
Towards that end, an embodiment of a preferred fuel circuit 200 includes a fuel booster pump 202 positioned within the fuel circuit between the fuel source and the inlet adaptor 10 of the thermal reactor, wherein the fuel booster pump 202 boosts the pressure of the fuel (see,
Typically, without a booster pump, the fuel is introduced to the burner jets at less than 1 psi and may continuously fluctuate. When the fuel booster pump is incorporated into the fuel circuit, the fuel pressure is boosted in a range of from about 1 psi to about 3 psi and then stepped down at the regulator to less than 1 psi prior to passage through the burner jets. Importantly, in the latter embodiment, a stable and consistent fuel pressure flows from the burner jets and changes in exhaust draw and/or static pressure within the thermal reaction chamber do not readily affect the stability of the flame.
In addition to maintaining the flame stability in real time, the fuel booster pump, MFM and regulator may be communicatively connected to the controller whereby the pressure, and hence flow, of the fuel may be controlled to maintain a constant flow of fuel to the burner jets. For example, if the fuel line pressure upstream of the fuel booster pump is low, the rpm of the pump may be increased to draw in fuel from the fuel line. Analogously, if the fuel line pressure upstream of the fuel booster pump is high, the rpm of the pump may be decreased to drive fuel downstream. Importantly, the rpm of the booster pump should be controlled so that the pressure upstream of the regulator is always greater than the pressure downstream of the regulator.
In the alternative, when the pressure in the fuel line is high, e.g., greater than 15 psi, a mass flow controller (MFC) or needle valve may be substituted for the booster pump 202, and the MFM 206.
It is noted that a series of valves and other controllers may be situated between the fuel source and the burner jets, for example, pressure regulating valves, check valves, shut-off valves, isolation valves, over-pressure relief valves, mass-flow control valves, flashback arrestors, etc., as readily determined by one skilled in the art.
In a further embodiment of the present invention, a sequential mode of operation using at least two controllers for safety redundancy is disclosed for a thermal abatement reactor apparatus. It should be appreciated by one skilled in the art that the improved sequential mode of operation is not limited to thermal abatement reactors, but may be appropriately altered for use with other abatement tools.
Prior art thermal reactor controllers relied on hardware, e.g., relay boards, etc., for all safety interlocks. However, hardware interlocks require complicated electrical wiring and cannot be easily modified or applied to any other application.
The present invention overcomes the deficiencies of the prior art hardware interlocks by utilizing a control platform which includes at least two controllers to monitor and control all critical operations and processes of the components in the thermal reactor apparatus. The controllers are programmed to systematically follow a sequence of operations to verify that each particular component is working properly before proceeding to the next step of the sequence. The control platform sequentially monitors start-up of the thermal reactor and continues to monitor the reactor during abatement to ensure that a negative condition has not occurred.
If it is determined that a component is not operating properly during start-up, alarms and warnings will be enabled and start-up will be halted until the negative condition is cleared. If the control platform determines that a component is not operating properly during abatement, alarms and warnings will be enabled and the thermal reactor will be brought to a safe state, e.g., shut-off of fuel-flow, ignition sources, waste effluent, etc.
Surprisingly, the control platform disclosed herein enables an immediate hot shut-down of the thermal reactor without residual heat flux causing damage to the reactor apparatus downstream. In other words, immediately following a hot shut down, and rectification of the problem that triggered shut down of the apparatus, the thermal reactor may be restarted immediately. This design is a substantial improvement over previous generations of thermal abatement reactors, which frequently became unsafe or unusable for future operations following a hot shut down (e.g., due to an unplanned power outage or an emergency power off) because of thermal induced damage to downstream equipment. An immediate restart of the thermal reactor described herein is possible in part because the thermal reactor includes reticulated ceramic walls 34, which have a low thermal mass and may be continuously cooled during abatement by passing fluid, e.g., CDA, through the pores of the walls. Further, this improved thermal reactor design reduces preventive maintenance time (and costs) because the cool-down period is minimal.
As introduced in a foregoing paragraph, the control platform includes at least two controllers, preferably programmable controllers, to monitor and control all critical operations and processes of the components in the thermal reactor apparatus. As defined herein, “controllers” control at least one automated system and/or process. Proprietary software programs may be used to interface the controller to the automated system and/or process using transistors, switches, relays and other circuitry. Controller channel specifications include a total number of inputs and outputs. Contemplated inputs for a controller include, but are not limited to, DC, AC, analog, thermocouple, resistant thermal device (RTD), frequency or pulse, transistor and interrupts. Contemplated outputs for a controller include, but are not limited to, DC, AC, relay, analog, frequency or pulse, transistor and triac. Software programming languages commonly employed include, but are not limited to, IEC 61131-3, sequential function chart (SFC), function block diagram (FBD), ladder diagram (LD), structured text (ST), instruction list (IL), relay ladder logic (RLL), Flow Chart, C and BASIC.
The two controllers are preferably arranged to operate independently of one another to ensure proper operation of the thermal reactor apparatus. Controller 1 (hereinafter “CTRL1”) is intended to monitor and control the start-up and operation of the apparatus and the Controller 2 (hereinafter “CTRL2”) is designed to enable the critical items, including water flow, pilot flame operation, fuel flow and the circulation pump, during start-up and operation of the apparatus. If CTRL1 registers a component or operational failure, the control platform is directed through a specific holding pattern or full shut down depending on the component and stage of operation. If CTRL2 registers a component or operational failure, the control platform will not enable the operation of the component and the control platform will exit to critical alarms with a delayed shutdown. It should be appreciated that for the critical items, CTRL1 should identify that the component is non-operational. However, if CTRL1 fails to identify such non-operation, CTRL2 will provide the back-up check to halt start-up or continued operation.
Referring to
Referring to
Once the level of water in the circulation tank is appropriate, water circulation is activated and water flow switches checked. The temperature of the headspace 145 in the circulation tank (see, e.g.,
Referring to
Referring to
Referring to
Referring to
It is noted that many other checks/verifications may be incorporated into the process control sequence including, but not limited to, logic to maintain the water level in the circulation tank between a pre-determined maximum and minimum level, logic to monitor the operability of the flame sensor and logic to monitor the usage of all components of the thermal reactor to signal when preventive maintenance of a particular component is necessary.
The sequence of steps enumerated in
In still another embodiment, the thermal abatement reactor is modified for smart abatement. Generally speaking, the embodiment quantifies the volume of waste effluent that will enter the thermal reactor over a given period of time. Prior to this invention, it was not possible to determine, in real-time, how much waste effluent was to be treated by the thermal reactor. Real-time information such as this would be highly advantageous because the critical items of the thermal reactor may be responsively adjusted to optimize abatement performance as well as lower operating costs.
An essential component of the smart abatement embodiment includes a detector system, for example the infrared thermopile (TPIR) detector disclosed in U.S. Pat. No. 6,617,175 issued Sep. 9, 2003 in the name of Jose Arno, which is incorporated by reference herein in its entirety. It is to be appreciated by one skilled in the art that the detector system is not limited to the TPIR, but may be any type of electromagnetic radiation detector available for the analysis required.
The TPIR output includes a square wave change (see, e.g.,
The detector system may be communicatively connected to a controller. In practice, the analytical signal generated by the TPIR or other analytical device is captured by the controller, which adjusts the operation of the thermal reactor accordingly. For example, the fuel flow and/or oxidant flow may be altered depending on the volume of waste effluent generated and preventative maintenance cycles may be scheduled based on number of wafers processed.
Specifically, the controller may be programmed to “count” wafers using appropriate logic that “counts” square waves. For example, the controller may be programmed to increment its “count” variable by 1 when the TPIR voltage output exceeds a certain value, e.g., about 0.25 V, for a specific period of time, e.g., 1 minute, and then drops to a specified baseline value.
Thus, the communication of the TPIR, or equivalent thereof, with a controller permits smart abatement whereby the thermal reactor may be adjusted in real-time to efficiently and safely abate waste effluent.
Although the invention has been variously described herein with reference to illustrative embodiments and features, it will be appreciated that the embodiments and features described hereinabove are not intended to limit the invention, and that other variations, modifications and other embodiments will readily suggest themselves to those of ordinary skill in the art, based on the disclosure herein. The invention therefore is to be broadly construed, consistent with the claims hereafter set forth.
