Abstract:
The present invention provides a system and method for calibrating pressure sensors associated with chambers in a processing facility. The system calibrates the pressure sensors while the chamber are open to each other, such as through an open slit valve or vacuum sealed door. Maintaining the pressure in the chambers relative to each other prevents a rush of gases, condensate or other foreign materials into an adjacent chamber that may occur when the pressure between the chambers is not equalized. This prevents contamination of the materials being processed, and eliminates the need for system shutdown to calibrate sensors. Also, since calibration occurs every time the slit valve is open, the calibration is real-time and does not allow the pressure differential between the chambers to become too great.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation in part of patent application Ser. No. 09/137,354, filed Aug. 20, 1998 which claims priority from U.S.  
         [0002]    Provisional Patent Application Ser. No. 60/056,821, filed Aug. 22, 1997. 
     
    
     
       TECHNICAL FIELD  
         [0003]    This invention relates generally to semiconductor processing and, more particularly, to a system and method for calibrating gas or liquid pressure during wafer processing.  
         BACKGROUND  
         [0004]    Contamination of materials is a factor in many manufacturing processes, and is of particular concern in the fabrication of integrated circuits.  
           [0005]    In general, integrated circuit technology is based on the ability to form numerous transistor structures on a single semiconductor substrate. Typically, multiple integrated circuits will be formed on a single silicon wafer, the wafer providing the semiconductor substrate for the circuits. The intricacy of the circuits and the large number of steps involved in the fabrication make it essential that each of the process steps be tightly controlled and meet very stringent specifications to prevent any type of contamination. To increase the purity and hence the quality and reliability of manufacturing processes, most are done in sealed rooms or chambers, where the environment, including temperature, pressure and purity of liquids or gases introduced can be controlled. One of the biggest sources of contamination occurs when the product being manufactured is transferred from one area of the manufacturing process to the next, which necessitates opening a door or valve to introduce the material into the next chamber or room. When the door or valve is open, if there is a pressure differential between the chambers, the potential for contamination is increased. Processing fluid and/or gas will rush from the chamber with the higher pressure to the chamber with the lower pressure to equalize the pressure, bringing solids and liquids along with the gas, which may cause such problems as condensation and particulate contamination on the material being manufactured.  
           [0006]    The solutions used to mitigate the above-identified problem have included: reducing the amount of time that the door or valve is opened to reduce the amount of contaminants that enter the chamber; making the transfer in two stages; utilizing an intermediate or transfer chamber into which only one of the other chambers is opened at a given time; placing calibrated pressure sensors in each chamber; and tying the pressure sensors into the valve-opening mechanisms in both chambers to obtain a desired, consistent pressure balance before the valve between the chambers is opened. However, these solutions, separately or in combination, do not always adequately resolve the aforementioned problems.  
           [0007]    Even minimizing the time the door or valve is open will result in some contamination, especially if the pressure is not equalized between the two chambers before opening the door or valve. One of the biggest problems in equalizing the pressure is keeping the pressure sensors calibrated, as sensors tend to drift in calibration over time. If the pressure sensor in either chamber is out of calibration, the pressure between the two chambers will not actually be equal, and when the door or valve is open, the gas will rush from the higher to lower pressure chamber to equalize the pressure. The effective drift of the pressure sensors is actually doubled if the two sensors drift calibration in opposite directions. If a sensor has drifted, process overseers are generally unaware of the problem until a rush of gas between the chambers has occurred, resulting in contamination of a manufactured product. In order to re-calibrate sensors that have drifted, the manufacturing process generally has to be shut down, and the sensor taken off-line to be calibrated, resulting in production down-time.  
           [0008]    U.S. Pat. No. 5,808,175 issued Sep. 15, 1998 to Shen-Yan Chang discloses a method of temporarily, manually mounting a second, in-line calibrated sensor to the same chamber for the purpose of monitoring or correcting the first sensor. However, Chang only utilizes the second sensor for comparison to the readings obtained from the first sensor for the same chamber, to determine if it needs replacing. If there is drift in the sensors used to read the pressure in different chambers, a situation may still occur wherein the pressure differential between two chambers is such that a rush of gas and contaminants occurs when the door or valve between the two chambers is opened.  
           [0009]    It would, therefore, be desirable to be able to provide a method and apparatus wherein the pressure in the two chambers between which materials are being transferred can be kept equal so that there will not be a rush of gas between the two chambers when the door or valve is opened.  
         SUMMARY  
         [0010]    The present invention overcomes the above outlined problems and a technical advance is achieved by a system and method that equalizes and calibrates the pressure of two or more chambers on either side of a valve (door) during operation. In one embodiment, the method is performed each time the valve is opened. When the valve is opened, the pressure in the chambers will equalize. After the pressure in the chambers has equalized, pressure readings from sensors mounted in each chamber are calibrated relative to each other.  
           [0011]    In some embodiments, the pressure readings are sent to a control module. The control module evaluates the readings taken from the sensors and adjusts them to match each other.  
           [0012]    In some embodiments, there may be an intermediate, or transfer chamber between a process chamber and a loading chamber. The sensor readings from the process and loading chambers are adjusted to match the sensor readings of the transfer chamber. As a result, all the chambers will be calibrated with the transfer chamber, and therefore with each other.  
           [0013]    Since calibration occurs every time the valve is open, the pressure differential between the chambers never becomes too great. As a result, there is little if any fluid flow (e.g., a flow processing gases and/or contaminants) between the chambers and a very clean chamber environment is maintained.  
           [0014]    Also, because the relative calibration is done during actual use, the system does not have to be shut down to perform calibration routines. This, of course, results in increased productivity and cycle time. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a diagram of an exemplary processing facility that utilizes a transfer chamber between operational chambers.  
         [0016]    [0016]FIG. 2 is a diagram of an exemplary processing facility that does not utilize a transfer chamber between operational chambers.  
         [0017]    [0017]FIG. 3 is a method flow diagram showing the steps taken in calibrating the pressure sensors.  
         [0018]    [0018]FIG. 4 is a diagram of two chambers of FIG. 1, separated by a valve.  
         [0019]    [0019]FIG. 5 is a diagram of the two chambers of FIG. 4 showing the pressure in each chamber being calibrated relative to the other chamber while the valve is open. 
     
    
     DETAILED DESCRIPTION  
       [0020]    Referring to FIG. 1, reference numeral  10  designates a portion of an integrated circuit processing facility including two loading chambers  12 ,  14 , a transfer chamber  16 , and two process chambers  18 ,  20 . Loading chambers are typically used for loading and unloading one or more materials for processing. Processing chambers are typically used for performing processing operations, and may include additional components for varying the temperature of the chamber or for adding processing fluids and/or constituents into the chamber. Transfer chambers are often used as an intermediate chamber between loading chambers and processing chambers, and may include a robot arm or some equivalent device for moving materials between the different chambers. To facilitate processing and maintain a clean environment, the different chambers must be hermetically sealed from each other at particular times.  
         [0021]    The loading chambers  12 ,  14  are connected to the transfer chamber  16  through slit valves  22 ,  24 , respectively. Likewise, the process chambers  18 ,  20  are connected to the transfer chamber  16  through slit valves  26 ,  28 , respectively. Connected to the transfer chamber  16  is an exhaust line  40  with a variable restriction control valve  42  used for controlling the pressure in the chamber. Likewise, connected to the loading and process chambers  12 ,  14 ,  18 ,  20  are exhaust lines  44 ,  46 ,  48 ,  50  with variable restriction control valves  52 ,  54 ,  56 ,  58 , respectively. Each of the variable restriction control valves  42 ,  52 ,  54 ,  56 ,  58  is controlled by a control module  60 .  
         [0022]    The control module  60  receives pressure readings from pressure sensors (e.g. transducers)  62 ,  64 ,  66 ,  68 ,  70  connected to loading chambers  12  and  14 , transfer chamber  16 , and process chambers  18 ,  20 , respectively. Furthermore, the control module  60  is informed of the status (open or closed) of slit valves  22 ,  24 ,  26 , and  28  through monitor lines  72 ,  74 ,  76 ,  78  respectively.  
         [0023]    In operation, the control module  60  reads the pressure of the loading chamber  12  through the pressure sensor  64  and the transfer chamber  16  through the pressure sensor  62 . The control module  60  then equalizes the pressure in the two chambers  16  and  12  by adjusting the variable restriction control valves  42  and  52  accordingly. As a result, the pressure in the loading chamber  12  matches that of the transfer chamber  16 . Every time that the slit valve  22  is open between the chambers, the control module  60  calibrates the pressure sensors  62  and  64  relative to each other. The same process is performed every time the slit valve  24 ,  26 , or  28  is open between the transfer chamber  16  and the loading or process chamber  14 ,  18 , or  20 , respectively. In a configuration of the system that utilizes a transfer chamber  16 , such as that shown in FIG. 1, the pressure sensors for the chambers on either side of the transfer chamber are calibrated in reference to the pressure sensor for the transfer chamber so that it will be accurate regardless of which chamber connecting into it is opened at any one time.  
         [0024]    Referring now to FIG. 2, the reference numeral  80  designates a portion of an integrated circuit processing facility with a direct chamber-to-chamber connection, including a loading chamber  12 , and a process chamber  18 . In this embodiment, the loading chamber  12  and the process chamber  18  are similar to those described in FIG. 1, except that no intermediate transfer chamber exists there between. The loading chamber  12  is connected to the process chamber  18  through the valve  22 . Connected to the loading chamber  12  is an exhaust line  44  with a variable restriction control valve  52 , used for controlling the pressure in the chamber. Likewise, connected to the process chamber  18  is exhaust line  48  with variable restriction control valve  56 . Each of the variable restriction control valves  52 ,  56  is controlled by a control module  60 .  
         [0025]    The control module  60  receives pressure readings from pressure sensors (e.g. transducers)  64 ,  68  connected to the loading chamber  12  and the process chamber  18 , respectively. Furthermore, the control module  60  is informed of the status (e.g. open or closed) of the slit valve  22  through the monitor line  72 .  
         [0026]    In operation, the control module  60  reads the pressure of the loading chamber  12  through the pressure sensor  64  and the process chamber  18  through the pressure sensor  68 . The control module  60  then equalizes the pressure in the two chambers  12  and  18  by adjusting the variable restriction control valves  52  and  56  accordingly so the pressure in the loading chamber  12   10  matches that of the process chamber  18 . Every time that the slit valve  22  is open between the chambers, and after the pressure of the two chamber has equalized, the control module  60  calibrates the pressure sensors  64  and  68  relative to each other.  
         [0027]    Referring to FIG. 3, a calibration method  100  may be performed on a sensor inside the system  10  (FIG. 1). For the sake of example, the calibration method  100  is used after a wafer  82  is placed in the loading chamber  12  and is ready to be transferred to the transfer chamber  16 . FIG. 4 shows a magnified portion of the system  10  for discussion with the present example.  
         [0028]    Referring also to FIG. 4, a wafer  82  is in the loading chamber  12 , ready for transfer to the next chamber  16  through the slit valve  22 . At step  102 , it is determined if the wafer  82  is ready for transfer to the next chamber. Since in the present example, the wafer is in the loading chamber  12 , step  102  determines that the chamber has been properly closed and sealed. At step  104 , the control module  60  equalizes the pressure between the loading chamber  12  and the next chamber (the transfer chamber, in the present example)  16 . The control module  60  will not open the slit valve  22  until the pressure between loading chamber  12  and transfer chamber  16  is equalized. Specifically, the control module  60 , using readings obtained from pressure sensors  62  and  64 , will equalize the pressure in the transfer chamber  16  and loading chamber  12  by adjusting the variable restriction control valves  42  and  52 , connected to the exhaust lines  40  and  44  respectively.  
         [0029]    Referring now to FIGS. 3 and 5, at step  106 , when the control module  60  receives readings from the pressure sensors  62  and  64  that indicate the pressures in the loading chamber  12  and transfer chamber  16  are equal, execution proceeds to step  108 . The control module  60  sends a signal to the slit valve  22  to open, as shown in FIG. 5. The wafer  82  will then be shifted to the transfer chamber  16  through the slit valve  22 .  
         [0030]    While the slit valve  22  is open for the transfer of material, if there is any difference in the actual pressure between the loading chamber  12  and transfer chamber  16 , it will be equalized automatically. At step  110 , the control module  60  will then check the readings on the pressure sensors  62  and  64 . At step  112 , a determination is made as to whether the pressure sensors  62 ,  64  are calibrated relative to each other. If so, then execution proceeds to step  114  where the slit valve  22  is closed and processing continues on in a normal progression.  
         [0031]    If at step  112  the pressure sensors  62 ,  64  read differently, execution proceeds to step  116  where the sensors are calibrated relative to each other. In one embodiment, the pressure sensor  64  is calibrated to the pressure sensor  62 . By so doing, all of the pressure sensors  64 ,  66 ,  68 ,  70  (FIG. 1) will eventually be calibrated relative to pressure sensor  62  and thus to each other. It may be desirable, on a periodic basis, to calibrate pressure sensor  62  to a reference measurement. However, even this calibration has been simplified because only one sensor needs to be calibrated. Execution then returns to step  110 . It is understood, however, that the control module  60  may have certain error modules so that the method will not continually loop to step  110  if the pressure sensors cannot be properly calibrated.  
         [0032]    Because the pressure in the two chambers is known to be equal while the slit valve  22  is open, calibrating the sensors  62  and  64  relative to each other eliminates the potential for a rush of processing fluid and constituents between the chambers the next time the valve is open. Also, because the process of relative calibration is performed every time the slit valve  22  is opened, a variation of no more than 0.01-0.02 Torr should occur between any two calibrations. This is an improvement over the prior art, where variations of 5 Torr or greater between chambers would be common because of the infrequency of calibration.  
         [0033]    Furthermore, because the relative calibration is done during actual use, the system does not have to be shut down to perform calibration routines quite as often as conventional systems. This, of course, results in increased productivity and cycle time.  
         [0034]    Further still, the control module  60  can maintain a history of calibrations to determine if any of the pressure sensors must be repeatedly calibrated. This may indicate that the particular pressure sensor or corresponding chamber is faulty. Likewise, if a majority of the pressure sensors must be repeatedly calibrated, this may indicate that the pressure sensor for the transfer chamber  16 , or corresponding chamber, is faulty.  
         [0035]    Although the invention has been described with reference to specific embodiments, such as the manufacture of integrated circuit semiconductors, this description is not meant to be construed in a limited sense. The invention can be used in a variety of processes. Also, different types of valves and chamber may equally benefit from the present invention. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.