Abstract:
A method for creating a reduced particle environment in a localized area of a mechanically active transport interface is provided. The augmentation of the air flow results in a sweeping air flow to remove particles in and around the desired area. The augmented air, flow will eliminate static or turbulent air flow regions and assist in removing potential particles from the vicinity of the substrate. This will prevent particles from being deposited on substrates thus fostering higher yields and improved quality.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to semiconductor substrate processing equipment, and more particularly to providing a localized ultra-clean mini-environment for substrate processing. 
     2. Description of the Related Art 
     In the manufacture of semiconductor devices, processing equipment is highly automated in order to speed transfer between processing steps. To effect the automation, there exists a large amount of moving mechanical equipment such as robots and automated doors. Any moving mechanical equipment may be a particle generator. The generated particles can be deposited on a substrate in the proximate area of the moving equipment. In addition, the particles may become entrained in air patterns within the processing module, thereby becoming capable of being deposited on any wafers or substrates within the processing module. The generated particles can cause substantial damage to semiconductor circuits formed on the wafer. For example, the particles deposited on the wafer may be entrapped by a thin film deposited on the wafer in the next processing step and render the circuit useless through this latent defect. 
     Semiconductor processing equipment typically employs the use of slot valves for the transport of wafers between modules. The valve covers a slot, port, aperture, etc. that is provided in the wall of the interfaced chambers, thereby isolating the chambers when the door is in a closed position. When a wafer is being transferred between modules the door will open to allow for passage of the wafer. The valves have moving mechanical parts and compressible o-rings capable of generating particles. Additionally, the valves also have an added disadvantage in that they can be located in a static air flow environment of the storage facility or processing module. In such a case, particle density in static slow moving or recirculating air surrounding a particle generation source can quickly rise. Semiconductor devices on wafers exposed to such contamination levels are at risk to damage due to particle deposition. 
     FIG. 1A depicts a typical semiconductor process cluster architecture  100  illustrating the various chambers of the architecture. Vacuum transport module  106  is shown coupled to three processing modules  108   a - 108   c  which may be individually optimized to perform various fabrication processes. By way of example, processing modules  108   a - 108   c  may be implemented to perform transformer coupled plasma (TCP) substrate etching, layer depositions, and/or sputtering. Connected to vacuum transport module  106  is a load lock  104  that may be implemented to introduce substrates into vacuum transport module  106 . The load lock  104  is coupled to an atmospheric transport module (ATM)  103  that interfaces with the clean room  102 . The ATM  103  typically has a region for holding cassettes of wafers and a robot that retrieves the wafers from the cassettes and moves them into and out of the load lock  104 . As is well known, the load lock  104  serves as a pressure-varying interface between vacuum transport module  106  and the ATM  103 . Therefore, vacuum transport module  106  may be kept at a constant pressure (e.g., vacuum), while the ATM  103  and clean room  102  are kept at atmospheric pressure. 
     FIG. 1B illustrates a partial system diagram  110  including an atmospheric transport module (ATM)  111  which includes a filter/blower  112 . The filter/blower  112  is configured to generate an air flow  114  in the ATM  111 . In addition, the ATM  111  is shown connected to the load lock  116 . Although this type of prior art ATM  111  is capable of transferring wafers  124  from the cassette  126  into and out of the load lock  116  quite efficiently, the air flow  114  has been intended to flush particles away from the area in close proximity to the slot valve  118 . However, mechanical or other design constraints may preclude achieving an optimum air flow in certain important regions of ATM  111 . As a result, the air flow pattern is not the downward sweeping action  114 , but rather more of a circular flow  124  or even a substantially static environment. Load lock  116  is isolated from ATM  111  by slot valve  118  making a seal  120 . For example, the seal  120  may be an o-ring type seal. The wafer path  122  proceeds through the area defined by the non-sweeping air flow pattern. 
     During the opening and closing of the slot valve  118  when the door opens and shuts against the seal  120 , particle bursts are generated through the contact of the seal and the door or other mechanically contacting surfaces. It can be appreciated that there is some pressure exerted against the seal by the slot valve in order to isolate the chambers on either side of the closed slot valve. In addition, particles trapped between the seal and the door may be released as the door opens. Therefore, the generated particles become entrained in the air flow patterns in the vicinity of the slot valve and can deposit themselves onto wafers traveling through or near the slot valve opening. 
     Any particles that have been deposited onto the surface of the wafer may remain on the wafer through its processing stage. These particles may cause defects in semiconductor circuits fabricated thereon, resulting in extra costs and lower yields. In some cases, the particles can migrate through an open slot valve door resulting in the potential contamination of both chambers. This problem is not limited to ATM  111  environments, but can also occur at any location where moving parts are in proximity to wafers or wafer transport paths, where off-gassing occurs and where the airflow is non-optimum. It can be appreciated that the processing equipment used in semiconductor manufacturing may include numerous moving mechanical parts capable of generating particle bursts. While the particle bursts may not be completely eliminated, the particles must be removed from the substrate path prior to the substrate moving through the vicinity of the particle burst so that the particles are not deposited on the substrate. 
     In view of the foregoing, what is needed is localized air flow augmentation to sweep any generated particles away from the substrate path and out of the processing module to eliminate particles from being deposited on substrates. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention fills these needs by enhancing an ultra-clean mini-environment with localized air flow augmentation. The mini-environment is preferably configured to generate the air flow in a proximity region around a particle generating device. It should be appreciated that the present invention can be implemented in numerous ways, including as an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below. 
     In one embodiment, a transport passage for transport of a wafer between a first chamber and a second chamber is disclosed. The transport passage includes an air flow supply for directing air flow from a top region towards a bottom region of the first chamber. A moveable door for opening and closing an aperture is also included. The aperture is defined on a wall between the first chamber and second chamber and located between the top region and the bottom region of the first chamber. The aperture further defines a passage between the first chamber and the second chamber. A cowl defining an enclosure in a proximity region of the moveable door is also included. The cowl has a top portion that is more proximate to the top region of the first chamber and a bottom portion that is more proximate to the bottom region of the first chamber. A fan is disposed in proximity to the bottom portion of the cowl so as to augment air flow from around the proximity region at the moveable door and through the enclosure defined by the cowl. 
     In another embodiment, an air flow enhancer for creating a reduced particle mini-environment in a vicinity of a wafer presence is disclosed. The air flow enhancer has an air flow supply for directing air flow from a first region toward a second region. A cowl defining an enclosure in a proximity region of the particle generating device and having a top portion and a bottom portion is included. The cowl being situated so that the top portion is more proximate to the particle generating device. A fan is disposed in proximity to the bottom portion of the cowl so as to augment air flow from around the proximity region and through the enclosure defined by the cowl. 
     In yet another embodiment, a method for creating a reduced particle environment in a vicinity of a mechanically active transport passage interface between a first region and a second region is disclosed. The method includes generating an air flow in the first region, the air flow being directed from a first zone to a second zone of the first region. Then the active transport passage interface is transitioned. Next the air flow in the vicinity of the active transport passage interface is augmented. The augmentation further includes causing a sweeping air flow that is configured to remove particles in and around the vicinity of the active transport interface. 
     In still another embodiment, a method for enhancing an air flow for creating a reduced particle mini-environment in a vicinity of an active particle generating device is disclosed. The method includes generating an air flow directed from a first region towards a second region. Then the air flow in the vicinity of the active particle generating device is augmented. The augmentation further includes creating a sweeping air flow to remove particles in and around the vicinity of the active particle generating device. 
     The advantages of the present invention are numerous. Most notably, the augmented air, flow creates a flushing action which entrains particles in the mini-environment, thereby removing the particles from the proximity region of the transport passage interface or the particle generating device. In addition, the augmented air flow eliminates static air flow regions from which the particles can be deposited on the substrates or wafers. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, in which like reference numerals designate like structural elements. 
     FIG. 1A depicts a typical prior art semiconductor process cluster tool architecture illustrating an atmospheric transport module. 
     FIG. 1B illustrates a partial system diagram including an atmospheric transport module (ATM). 
     FIG. 2 illustrates a diagram of a transport passage with localized air flow augmentation in accordance with one embodiment of the invention. 
     FIG. 3 illustrates another diagram of a transport passage with localized air flow augmentation in accordance with one embodiment of the invention. 
     FIG. 4 illustrates a diagram of a top view of a transport passage with localized air flow augmentation in accordance with one embodiment of the invention. 
     FIG. 5 shows a diagram of a top view of an exemplary transfer module that is connected to a process system, in accordance with one embodiment of the present invention. 
     FIG. 6 illustrates a flowchart defining a method for creating a reduced particle environment in, accordance with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An invention is described for providing a localized ultra-clean mini-environment during wafer processing. As used herein, wafer and substrate are interchangeable. The mini-environment is preferably configured to include a sweeping air flow pattern in proximity to a particle generating device so as to sweep particles away from wafers or the wafer transport path. It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to obscure the present invention. 
     FIG. 2 illustrates in diagram  128  a transport passage with localized air flow augmentation in accordance with one embodiment of the invention. In diagram  128 , chamber wall  130  contains an aperture covered by slot valve  132  shown in the closed position. It can be appreciated that slot valve  132  in the closed position isolates the modules on either side of the wall  130 . In one embodiment of the invention, slot valve  132  may create a seal with the wall  130  through an o-ring type seal. A cowl  134  is attached to wall  130 . The cowl  134  against the wall  130  defines an enclosure which directs an air flow  138 . The air flow  138  is augmented by a fan  136  positioned below the cowl  134 . The fan  136  generates a localized air flow  138  in the vicinity of the slot valve  132 , thereby creating a sweeping action to remove any particles in the proximate region of the slot valve  132 . 
     The cowl  134  as shown in FIG. 2 defines a trapezoidal cross section. It can be appreciated that the cross section can be numerous polygon and non-polygon shapes, such as circular, semi-circular, square, rectangular, etc. It can further be appreciated that the fan  136  may be attached to the cowl  134  or the fan  136  may be a stand-alone unit. In one embodiment of the invention, the fan  136  may have an exhaust line to remove the exhaust out of the wafer processing module through a vent. In another embodiment of the invention, the fan  136  may be positioned above the slot valve  132 . 
     FIG. 3 illustrates in diagram  142 , a transport passage with localized air flow augmentation in accordance with one embodiment of the invention. In diagram  142 , the chamber wall  130  contains an aperture  144  for transport of wafers to a second module located behind the wall  130 . The slot valve  132  is in the open position allowing for the transport of wafers through aperture  144 . O-ring  146  is attached to wall  130  and outlines the aperture  144  so that when the slot valve  132  is in a closed position, as illustrated in FIG. 2, the slot valve  132  will compressibly seal o-ring  146  to isolate the modules on each side of wall  130 . O-ring  146  may be made of any elastomeric material commercially available. It can be appreciated that any suitable gasket material can be used in place of o-ring  146 . It can further be appreciated that the aperture  144  and the o-ring  146  can be any shape to allow, for the passage of a substrate or wafer. A cowl  134  is attached to wall  130 . The cowl  134  against the wall  130  defines an enclosure which directs an air flow  138 . The air flow  138  is generated by a fan  136  positioned below the cowl  134 . The exhaust duct  150  directs the particle laden airflow outside the module. 
     The fan  136  of FIG. 3, generates a localized air flow  138  in the vicinity of the slot valve  132 , thereby creating a sweeping action to remove any particles in the proximate region of the slot valve  132 . In one embodiment of the invention the o-ring seal may be attached to the slot valve  132 . It can further be appreciated that repeated use, i.e. slot valve opening and closing, may wear the o-ring  146  and cause o-ring  146  to shed particles. Accordingly, particles may be introduced into the proximate vicinity of the aperture upon the opening and closing of the slot valve. In one embodiment of the invention, the air flow  138  flushes the particles generated from the opening and closing of the slot valve  132  away from the aperture  144  and through an exhaust duct  150 . It can be appreciated that the exhaust duct  150  can be oriented to exhaust air flow from a side or the bottom of the module. FIG. 3 also includes a cross sectional view of a grid like perforated sheet  148 . 
     FIG. 4 illustrates in diagram  152 , a top view of a transport passage with localized air flow augmentation in accordance with one embodiment of the invention. Module wall  130  contains an aperture (not shown) covered by a slot valve  132  in a closed position. In one embodiment of, the invention, a seal is created by slot valve  132  contacting an o-ring (not shown) attached to wall  130 . Fan  136  is configured to draw air in a sweeping motion past slot valve  132  as directed by the cowl  134 . As mentioned previously, the mechanical activity of slot valve  132  may create particles and may cause the o-ring seal to shed particles through normal wear patterns. It can be appreciated that any particles generated through the mechanical activity for transitioning a wafer through the interface will be entrained in the air flow created by fan  136  and exhausted through exhaust transfer line  150 . In one embodiment of the invention, fan  136  may be located above slot valve  132  to create a sweeping air flow past slot valve  132 . In another embodiment of the invention, the output flow of fan  136  may be filtered. 
     FIG. 5 shows a diagram  198  of a top view of an exemplary transfer module  200  that is connected to a process system, in accordance with one embodiment of the present invention. The architectural geometry of the ATM  200  and the arrangement of the robot with respect to the load locks  240  are described in greater detail a co-pending U.S. Patent Application having application Ser. No. 09/342,669, entitled “Atmospheric Wafer Transfer Module with Nest For Wafer Transport Robot and Method of Implementing Same,” and filed on Jun. 29, 1999 U.S. Pat. No. 6,414,811. This application is hereby incorporated by reference. As shown, the transfer module  200  is designed to communicate with a pair of load locks  240 . The load locks  240  are coupled to a transport chamber  242  by way of gate valves  244 . The transport chamber  242  is then capable of coupling up to processing modules  246 . A robot arm (not shown) is installed in the transport chamber  242  for retrieving wafers from within the load locks  240  and inserting them into selected processing modules  246 , where processing operations are performed. 
     The transfer module  200  of FIG. 5 is shown having an aligner  250  where wafers  214  can be aligned on the arm set  208  before they are inserted into the load locks  240 . The load cell  202  is shown containing cassettes  212  having wafers  214 . In this embodiment, the transfer module  200  is shown having a grid-like perforated sheet  205 . A wall  130  separates the transport module  200  and the load lock  240 . An aperture or passage interface  144  is defined in wall  130 . Slot valve  132  in a closed position, isolates the transport module  200  from the load lock  240 . In one embodiment of the invention, the slot valve compresses against an o-ring (not shown) attached to wall  130  to form a seal. It can be appreciated that the arm  208  can transport a wafer  214  from the cassette  212 , to the aligner  250 , through the aperture  144  and into the load lock  240 . In order to allow for the passage between the interfaced transport module  200  and the load lock  240 , the slot valve  132  will transition to an open position, thus exposing a transport passage through aperture  144 . 
     A cowl  134  of FIG. 5, defines an enclosure in a proximity region of the slot valve  132 . A fan  136  augments the air flow through the enclosure defined by the cowl  134  and the wall  130  so as to create a sweeping air flow in the proximity region of the slot valve  132 . As mentioned above, the mechanically active slot valve  132  repeatedly compressing and uncompressing the o-ring seal is a potential source of particle generation. In one embodiment of the invention, potential particles in the slot valve region will be captured by the air flow augmented by fan  136 , and eventually exhausted out of the bottom or sides of the transport module  200  through a vent. It can further be appreciated that the cross section of the enclosure defined by the cowl  134  and the wall  130  may be numerous polygon and non-polygon shapes. 
     As illustrated in Tables A, B and C below, the air flow augmentation has a significant impact on the particle counts in the proximity region of the slot valve  132 . Table A provides the particle counts without flow augmentation. Table B and C provide results for an air flow speed at the proximity region of the slot valve of 75 feet per minute (fpm) and 350 fpm, respectively. The particle counts were measured by a Lasair model  110  available from Particle Measurement Systems Inc. of Boulder, Colo. Two runs were performed for each of the different air flow speeds represented in Tables A, B and C. The following tables are shown as exemplary test data to prove the effectiveness of the claimed embodiments. The tables are in no way meant to be limiting on the claimed invention. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE A 
               
             
             
               
                   
               
               
                 Without air flow augmentation 
               
             
          
           
               
                 Particle size 
                 Particle counts 
                 Particle counts 
               
               
                 (microns) 
                 Run 1 
                 Run 2 
               
               
                   
               
             
          
           
               
                 0.10 
                 51  
                 65  
               
               
                 0.15 
                 5 
                 3 
               
               
                 0.20 
                 3 
                 0 
               
               
                 0.25 
                 2 
                 0 
               
               
                 0.30 
                 0 
                 0 
               
               
                 0.50 
                 0 
                 0 
               
               
                 0.70 
                 0 
                 0 
               
               
                 1.00 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE B 
               
             
             
               
                   
               
               
                 Air flow augmentation of 75 fpm 
               
             
          
           
               
                 Particle size 
                 Particle counts 
                 Particle counts 
               
               
                 (microns) 
                 Run 1 
                 Run 2 
               
               
                   
               
             
          
           
               
                 0.10 
                 20  
                 11  
               
               
                 0.15 
                 2 
                 1 
               
               
                 0.20 
                 1 
                 0 
               
               
                 0.25 
                 1 
                 0 
               
               
                 0.30 
                 1 
                 0 
               
               
                 0.50 
                 1 
                 0 
               
               
                 0.70 
                 0 
                 0 
               
               
                 1.00 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE C 
               
             
             
               
                   
               
               
                 Air flow augmentation of 350 fpm 
               
             
          
           
               
                 Particle size 
                 Particle counts 
                 Particle counts 
               
               
                 (microns) 
                 Run 1 
                 Run 2 
               
               
                   
               
             
          
           
               
                 0.10 
                 5 
                 1 
               
               
                 0.15 
                 0 
                 0 
               
               
                 0.20 
                 0 
                 0 
               
               
                 0.25 
                 0 
                 0 
               
               
                 0.30 
                 0 
                 0 
               
               
                 0.50 
                 0 
                 0 
               
               
                 0.70 
                 0 
                 0 
               
               
                 1.00 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
     FIG. 6 illustrates a flowchart  252  defining a method for creating a reduced particle environment in accordance with one embodiment of the invention. Flowchart  252  initializes with operation  254  where an air flow is generated. Here, the air flow may be directed to flow in a vertical pattern from a top to a bottom region. In one embodiment of the invention, the air flow may be directed in a horizontal pattern or even an angular pattern from a first zone to a second zone. Next, the method proceeds to operation  256  where an active transport passage interface is transitioned. In one embodiment of the invention, the transport passage interface may be a slot valve opening and closing. In another embodiment of the invention, the active transport passage interface may be an active particle generating device. The particle generating device may contain mechanically active parts which may introduce particles into the vicinity of the device. In yet another embodiment of the invention, the air flow augmentation may be applied to a region where the air flow is static or minimal. For example, the air flow augmentation may be applied to the aligner station  250  of FIG.  5 . 
     From operation  256 , the method terminates with operation  258  where the air flow is augmented. Here, the air flow in the proximity region of the active transport passage interface is locally enhanced. It can be appreciated that the air flow augmentation causes a sweeping flow so as to remove particles in and around the vicinity of the active transport passage interface or the particle generating device. In one embodiment of the invention, a fan is used to augment the air flow and create the sweeping action. In another embodiment of the invention, the air flow is augmented in a proximity region of an active particle generating device. 
     It can be appreciated that the above described method can be applied anywhere localized particles are generated in semiconductor fabrication. For example, operations involving lifter stations, lifter spinners, aligner stations, pick and place by a robot, spin rinse and dry systems, load ports, wafer conditioning stations, etc., all contain active particle generating devices. As used herein a wafer conditioning station may include a wafer cooling station or an off-gassing station. It can further be appreciated that an enhanced localized air flow may be created in a proximity region of the mechanically active device, thereby purging the particles in and around the proximity region through a sweeping air flow. It can further be appreciated that the active particle generating device may produce particles through a mechanical activity, such as moving parts, or non mechanical activity, such as off-gassing. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. For instance, although the cowl has been illustrated to have a particular geometry with regard to the wall the cowl can take on any number of shapes. Of particular significance, however, is the fact that the localized air flow can be applied to any particle generating device in addition to a slot valve. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.