Patent Publication Number: US-2006000711-A1

Title: In-situ corrosion controlling system for chemical vessels or tanks

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This is a continuation application of U.S. patent application Ser. No. 10/710,271 filed Jun. 30, 2004 by Lin et al. 
    
    
     BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The present invention relates to a monitoring and controlling system for chemical vessels or tanks. More particularly, the present invention relates to an in-situ and real-time semiconductor process controlling system capable of effectively monitoring the integrity of an interior lining of chemical vessels and controlling the wet processing unit, thereby promoting quality and yield of the semiconductor process.  
      2. Description of the Prior Art  
      Chemical supply system is essential to the semiconductor manufacturing. Typically, various processing chemicals are shipped from a dock or a chemical provider to a utility zone of a semiconductor factory by means of tank truck carriers. The tank truck carrier then discharges the liquidized processing chemicals to respective storage tanks or vessels via suitable piping systems. To maintain production yield of the semiconductor manufacturing, it is always required to provide processing chemicals of the highest industry standards.  
      As known in the art, semiconductor processing and manufacturing generally requires numerous manufacturing steps to produce a desired integrated circuit chip. The numerous steps may include etching, photoresist stripping, prediffusion cleaning and so on. Corrosive chemicals such as oxidants, strong acids or alkaline liquids may be frequently used in different stages in the semiconductor manufacturing and any changes in the chemicals could significantly affect product outcomes. The corrosive chemicals are ordinarily stored in the specifically designed tanks lined with special materials. Though these tanks are theoretically corrosion-proof containers, periodic manual sampling and off-line analysis are still put on routine lists to make sure the quality of the stored chemicals. However, it has been found that in some cases undesired trace metal contamination happens due to rouging or pitting of the interior lining of the storage tanks.  
      Unfortunately, the conventional periodic sampling and off-line analysis procedures seem does not help much to reduce damages caused by the contaminated processing chemicals. The above-described manual sampling and off-line analysis method is ineffective and costly. Further, since the chemicals used in the manufacturing steps are often quite toxic to humans, care must be taken to minimize the risk of exposure to the plant personnel working in the manufacturing facility.  
      Hitherto, there is still no effective monitoring system capable of in-situ and real-time monitoring the integrity of the lined tanks, thereby providing the facility operators or QA/QC managers with newest quality status of the processing chemicals in a timely manner. Clearly, a need exists for such an in-situ monitoring system.  
     SUMMARY OF INVENTION  
      It is therefore the primary object of the present invention to provide an inexpensive, in-situ, continuous, real-time corrosion monitoring system for various chemical vessels such as stationary storage tanks in the factories or those vessels for transportation purposes such as tank truck carriers.  
      It is another object of the present invention to provide an effective, in-situ and real-time semiconductor process monitoring and controlling system capable of monitoring the integrity of the interior lining of a chemical vessel and controlling the semiconductor processing unit, thereby promoting quality and yield of the semiconductor process.  
      To achieve the above objects, in accordance with the claimed invention, an in-situ corrosion monitoring system is provided. The in-situ corrosion monitoring system includes a chemical vessel for containing chemical liquid. The chemical vessel comprises a conductive shell body and an insulating interior lining coated therein. The interior lining has potential of being attacked by the chemical liquid. A robust detection electrode is immersed in the chemical liquid. A measurement means such as an ohmmeter is electrically connected to the detection electrode. The measurement means is also electrically connected to the conductive shell body. When the interior lining is damaged or pitted due to chemical attack by the chemical liquid and the chemical liquid thus contacts the conductive shell body, the measurement means receives a corresponding signal.  
      From one aspect of this invention, an in-situ and real-time semiconductor process monitoring and controlling system is provided. The semiconductor process monitoring and controlling system includes a processing vessel for accommodating at least a semiconductor wafer to be wet-treated; a wafer transferring means for loading or un-loading the semiconductor wafer into or out of the processing vessel; and a chemical vessel for containing chemical liquid and supplying the chemical liquid to the processing vessel through a piping system. The chemical vessel comprises a conductive shell body and an insulating interior lining coated therein. The interior lining has potential of being attacked by the chemical liquid. A robust detection electrode is immersed in the chemical liquid. A measurement means is electrically connected to the detection electrode. The measurement means is further electrically connected to the conductive shell body. When the interior lining is damaged or pitted due to chemical attack by the chemical liquid and the chemical liquid thus contacts the conductive shell body, the measurement means promptly receives a corresponding signal. The semiconductor process monitoring and controlling system further includes a controller unit connected to the measurement means. Once the measurement means receives the corresponding signal, the controller unit sends a first control signal to the wafer transferring means.  
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:  
       FIG. 1  is a schematic diagram illustrating a corrosion monitoring system for chemical vessels containing corrosive chemicals in accordance with one preferred embodiment of the present invention;  
       FIG. 2  is a schematic diagram showing the monitoring data and real-time curve plot continuously measured by the measurement means of the corrosion monitoring system according to the preferred embodiment of this invention;  
       FIG. 3  is a schematic diagram showing an in-situ and real-time semiconductor process monitor and control system capable of continuously monitoring the quality of chemical liquids used in a semiconductor wet processing unit in accordance with a second preferred embodiment of this invention; and  
       FIG. 4  illustrates a third preferred embodiment according to the present invention. 
    
    
     DETAILED DESCRIPTION  
      Please refer to  FIG. 1 .  FIG. 1  is a schematic diagram illustrating a corrosion monitoring system  10  for chemical vessels or chemical tanks in accordance with one preferred embodiment of the present invention. Hereinafter, the term: “vessel” or “chemical vessel” refers to those containers including “tank”, “drum”, “tube”, “cylinder”, “reactor” or whatever employed to contain corrosive liquid chemicals either for storage/transportation purposes or for processing purposes. As shown in  FIG. 1 , the corrosion monitoring system  10  comprises a chemical vessel  12  comprising a conductive shell body  14  coated with an insulating interior lining  16 . The chemical vessel  12  contains corrosive chemical liquid  18  in contact with the interior lining  16 . The shell body  14  may be made of metal materials such as stainless steel, carbon steel, coated steel, aluminum or alloys.  
      It is to be understood that various types of piping or piping elements such as valves, gauges, or analytical instruments for different purposes may be installed on the shell body  14 , which are not germane to this invention and are therefore not explicitly shown in the figures. In general, the shell body  14  is typically, but not necessarily, installed with a drain  22 , a vent pipe  24 , an inlet pipeline  26 , and an outlet pipeline  28 , but not limited thereto. It is to be understood that the sizes and number of these pipelines connected to the shell body  14  as well as the shell body  14  depend upon the practical requirements on site.  
      The interior lining  16  of the chemical vessel  12  is made of corrosion-proof insulating materials such as fluoropolymer resins. Preferably, the interior lining  16  is made of poly-tetra-fluoroethylene (PTFE) and/or per-fluoroalkoxy (PFA). However, other Teflon materials such as ethylene tetra-fluoroethylene (ETFE) or fluorinated ethylene propylene (FEP) may be used.  
      The corrosive chemical liquid  18 , by way of example, may be industry-grade (or higher grade) sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, hydrogen peroxide, ferric chloride, halogenated organics or other corrosive chemicals, but not limited thereto.  
      The present invention corrosion monitoring system  10  features a robust detection electrode  32  installed inside the chemical vessel  12 . The robust detection electrode  32  is immersed in the corrosive chemical liquid  18  contained by the chemical vessel  12 . Preferably, the detection electrode  32  is made of corrosion-resistant materials such as platinum (Pt) or the like. As shown in  FIG. 1 , the detection electrode  32  is electrically connected to a measurement means  36  installed outside the chemical vessel  12  via a conductive wiring  34 . According to the preferred embodiment of this invention, the measurement means  36  is an ohmmeter. The ohmmeter has a measurement range of about 1 M Ohm to 40 G Ohm, and an output voltage of about 50 volts to 200 volts, but not limited thereto. The measurement means  36  is electrically connected to the conductive shell body  14  via a conductive wiring  38 . A computer unit  42  equipped with a monitor  44  may be provided to process and store data transmitted from the measurement means  36 . The computer unit  42  may be further connected with an alarm device  52 .  
      Please refer to  FIG. 2 .  FIG. 2  is a schematic diagram showing the monitoring data and real-time curve plot continuously measured by the measurement means  36 , which are demonstrated on the monitor  44  of the corrosion monitoring system  10  according to the preferred embodiment of this invention. Since the interior lining  16  of the chemical vessel  12  is made of insulating resins such as PTFE, a high-level resistance R 1  is continuously detected by the measurement means  36  (an ohmmeter in this case) in a normal status. When the interior lining  16  is damaged or pitted due to the chemical attack by the chemical liquid and the chemical liquid contacts the conductive shell body  14 , the measurement means  36  promptly receives a corresponding signal: a relatively low-level resistance R 2 . Once the measurement means  36  receives the low-level signal R 2 , the computer unit  42  transmits a signal to the alarm device  52  and triggers the alarm system to warn the operators. In  FIG. 2 , a reference alert line is also illustrated. The low-level signal R 2  may be set a percentage lower than the reference alert line.  
      Please refer to  FIG. 3 .  FIG. 3  is a schematic diagram showing an in-situ and real-time semiconductor process monitor and control system  100  capable of continuously monitoring the quality of chemical liquids used in a semiconductor wet processing unit in accordance with a second preferred embodiment of this invention, wherein like numerals designate similar or the same parts, elements or devices. The monitor and control system  100  comprises a stationary processing vessel  60  that is used to contain aqueous chemical solution  68  or agents with specific recipes and is adapted to accommodate wafers  70  to be wet-treated. The wet process may be a wafer cleaning process or a wet etching process, but not limited thereto. The processing vessel  60  may be single-wafer type or multi-wafer type. Besides, the processing vessel  60  may be hermetic or open to air.  
      According to the second preferred embodiment, the monitor and control system  100  further comprises a wafer transferring means  80  such as a robotic arm or a mechanical lifting device that is used to load or un-load the wafers  70 . For a batch type wet process, conventionally, the wafers are arranged in a wafer lot, and the mechanical lifting device lifts the wafer lot that have been dipped in the aqueous chemical solution  68  for a prescribed time period. The chemical liquid  18  is transferred from the chemical vessel  12  to the processing vessel  60  through a piping system  90 .  
      According to the second preferred embodiment, the monitor and control system  100  comprises the corrosion monitor system  10  including the storage chemical vessel  12  that is used to store various corrosive chemical liquids  18 . Likewise, the storage chemical vessel  12  comprises a conductive shell body  14  and an insulating lining  16  therein. Depending on practical needs, various types of piping or piping elements such as valves, gauges, nozzles or analytical instruments for different purposes may be installed on the shell body  14 . Generally, the shell body  14  is installed with a drain  22 , a vent pipe  24 , an inlet pipeline  26 , and an outlet or exhaust pipeline  28 , but limited thereto. The aforesaid piping system  90  is connected to the outlet pipeline  28 .  
      The shell body  14  may be made of metal materials such as stainless steel, carbon steel, coated steel, aluminum or alloys. The interior lining  16  of the chemical vessel  12  is made of corrosion-proof insulating materials such as fluoropolymer resins. Preferably, the interior lining  16  is made of poly-tetra-fluoroethylene (PTFE) and/or per-fluoroalkoxy (PFA). However, ethylene tetra-fluoroethylene (ETFE) or fluorinated ethylene propylene (FEP) may be used.  
      A robust detection electrode  32  is installed inside the storage chemical vessel  12 . The robust detection electrode  32  is immersed in the corrosive chemical liquid  18  contained by the storage chemical vessel  12 . The corrosive chemical liquid  18 , by way of example, may be industry-grade (or higher grade) sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, hydrogen peroxide, ferric chloride, halogenated organics or other corrosive chemicals. The detection electrode  32  is made of corrosion-resistant materials such as platinum (Pt) or the like. The detection electrode  32  is electrically connected to a measurement means  36  installed outside the chemical vessel  12  via a conductive wiring  34 . According to the second preferred embodiment of this invention, the measurement means  36  is an ohmmeter. The ohmmeter has a measurement range of about 1 M Ohm to 40 G Ohm, and an output voltage of about 50 volts to 200 volts, but not limited thereto. The measurement means  36  is electrically connected to the conductive shell body  14  via a conductive wiring  38 . A computer controller unit  42  equipped with a monitor  44  may be provided to process and store data transmitted from the measurement means  36 . The computer controller unit  42  may be further connected with an alarm device  52 .  
      According to the second preferred embodiment of this invention, the computer controller unit  42  of the semiconductor process monitor and control system  100  is further connected to an automatic on/off valve  92  that is installed in the piping system  90  and connected to the wafer transferring means  80 . When the interior lining  16  of the storage chemical vessel  12  is pitted due to the chemical attack by the chemical liquid and the chemical liquid  18  contacts the conductive shell body  14 , the measurement means  36  promptly receives a corresponding signal such as a low-level resistance signal. Once the measurement means  36  receives the low-level signal, the computer controller unit  42  transmits a signal to the alarm device  52  and triggers the alarm system to warn the operators. Simultaneously, the computer controller unit  42  sends a control signal to the wafer transferring means  80  to stop loading the wafers  70  into the processing vessel  60 , thereby minimizing the damage. Besides, the computer controller unit  42  sends a control signal to the automatic on/off valve  92  to cut off the supply path between the storage chemical vessel  12  and the processing vessel  60  so as to prevent contaminated chemical liquids from flowing into the wet processing unit.  
      Please refer to  FIG. 4 .  FIG. 4  illustrates a third preferred embodiment according to the present invention. The present invention can be applied to chemical vessels for transportation purposes such as tank truck carriers or the like. As shown in  FIG. 4 , the monitor system  200  includes a vehicle chemical vessel  112  lined with insulating materials such as PTFE and/or PFA. The vehicle chemical vessel  112  is fixed on a truck. The vehicle chemical vessel  112  is used to contain and transport corrosive chemical liquids, for example, sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, hydrogen peroxide, ferric chloride, halogenated organics or other corrosive chemicals.  
      Likewise, a robust detection electrode  32  is installed inside the vehicle chemical vessel  12 . The robust detection electrode  32  is immersed in the corrosive chemical liquid  18  contained by the vehicle chemical vessel  12 . The detection electrode  32  is electrically connected to a measurement means  36  installed outside the vehicle chemical vessel  112  via a conductive wiring  34 . According to this invention, the measurement means  36  is an ohmmeter. The ohmmeter may have a measurement range of about 1 M Ohm to 40 G Ohm, and an output voltage of about 50 volts to 200 volts, but not limited thereto. The measurement means  36  is electrically connected to the conductive outer shell of the vehicle chemical vessel  112  via a conductive wiring  38 . A vehicle computer unit equipped with an LCD monitor may be provided to process, store and display data transmitted from the measurement means  36 .  
      Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.