Abstract:
A method including placing a wafer active side down in a chamber and reducing the pressure in the chamber. An apparatus or system including a chamber having an interior volume suitable to accommodate a semiconductor wafer and capable of maintaining a vacuum; and a support to maintain a wafer in the volume of the chamber with minimum or no contact with an active side of the wafer, wherein an amount of particles that an active side of a wafer is exposed to during a pressure change in the chamber is minimized when the wafer is loaded in the chamber in an active side down configuration.

Description:
BACKGROUND  
     FIELD  
       [0001]     Semiconductor processing.  
       BACKGROUND  
       [0002]     In the field of semiconductor processing, particularly, at the wafer level, semiconductor substrates (e.g., wafers) are subject to a number of processing operations in one or more processing chambers. One processing environment is a under vacuum condition. To bring a condition to a vacuum, a substrate, such as a wafer, is generally placed in a chamber and the chamber evacuated to bring the pressure to a vacuum. Often times, the vacuum processing is a multi-chamber operation in which a substrate is placed in a first chamber or load lock. The first chamber or load lock is connected to a second chamber (processing chamber) where modifications to the substrate are made. Utilizing a load lock means that a wafer can be loaded into a processing chamber without having to pump-down the processing chamber again. One reason for utilizing the load lock is that a subsequent pumping down to a pressure required in a processing chamber tends to introduce contaminants as particles can get on the substrate during the pump-down. Accordingly, a substrate is loaded in a load lock which is then pumped down to the desired pressure of the processing chamber. After the load lock opens, the substrate is moved into the processing chamber.  
         [0003]     Currently, substrates (e.g., wafers) are predominantly in an active side up orientation while pump-down and purging/venting is done. By active side up orientation is meant that a side of a wafer having either devices formed therein/thereon or intended to have devices formed therein/thereon faces a direction opposite the direction of gravity. In this state, the gravitational forces within the chamber act to pull particles onto an active surface of the substrate particularly during pump down.  
         [0004]     Particle contamination in reduced pressure chambers, such as in a vacuum load lock environment may be a significant source of defects. These particles come from the chamber material itself, from handling operations, from previous operations in the chamber, etc. It is appreciated that contaminating particles have a varied size distribution. The number of small particles (e.g., sub-micron sized particles) far exceeds the number of larger particles. As critical densities increase on wafers, the contribution of smaller particles to particle contamination increases. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     Features, aspects, and advantages of embodiments will become more thoroughly apparent from the following detailed description, appended claims, and accompanying drawings in which:  
         [0006]      FIG. 1  shows a schematic process sequence of loading a wafer into a load lock.  
         [0007]      FIG. 2  shows a wafer in a load lock chamber and illustrates a purge process.  
         [0008]      FIG. 3  shows the load lock of  FIG. 2  during a pump down process.  
         [0009]      FIG. 4  shows the load lock of  FIG. 3  at a process pressure.  
         [0010]      FIG. 5  shows the wafer of  FIG. 4  being loaded from a load lock into a processing chamber at a desired pressure.  
         [0011]      FIG. 6  shows a schematic top view of a wafer supported in an active side down configuration with a support serving also as a particle deflection plate.  
         [0012]      FIG. 7  shows a schematic top view of a wafer supported in an active side down configuration by a support with a particle deflection plate between the support and the wafer.  
         [0013]      FIG. 8  shows a schematic top side view of a wafer supported by an electrostatic charge in an active side down configuration with a particle deflection place beneath the wafer.  
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  schematically illustrates the loading of a substrate (e.g., wafer) into a load lock. Referring to  FIG. 1 , load lock  100  includes chamber  110  that is, for example, a metal (e.g., aluminum) material having a volume  105  that is capable of maintaining a reduced pressure environment, including a vacuum or zero pounds per square inch (psi). Volume  105  is also sized to accommodate at least one wafer (e.g., a 200 millimeters (mm) or 300 mm wafer) therein. Chamber  110  includes exhaust port  120  that may be used to evacuate chamber  110 . Also connected to chamber  110  is pressure sensor  130  such as Baratrome pressure sensor. A pressure indication of pressure sensor  130  may be read by processor  140 . Processor  140 , in one example, includes machine-readable program instructions to record pressure measurements of volume  105 , and to perform a method to evacuate chamber through exhaust port  120  to a predetermined pressure. Chamber  110  also includes gas entry port  155  to introduce a gaseous species into volume  105 . In the embodiment shown in  FIG. 1 , purge gas  150  is connected to entry port  155 . Gas source  150  is, for example, a purge gas, such as nitrogen (N 2 ). Introduction of a gas through gas source  150  is regulated by valve  160 . Valve  160  is controlled, in this example, by processor  140  and machine-readable instructions therein (e.g., instructions to perform a method to purge chamber  110 ).  
         [0015]      FIG. 1  also shows arm  175  such as a robotic arm, holding wafer  170 . In an initial holding phase, wafer  170  includes active side  180  facing, as viewed, upward or against gravity. In one embodiment, arm  175  may be actuated to rotate so that active side  180  of wafer  170  is directed at gravity (e.g., rotated  180  degrees downward as viewed). Arm  175  may maintain wafer  170  in an active side down (with gravity) configuration by, for example, side clamping, electrostatic forces or a vacuum or similar reduced pressure on a back side of wafer  170 . Arm  175  may be advanced to introduce wafer  170  into chamber  110  in an active side down configuration and retracted to be free from the chamber. Machine-readable program instructions in processor  140  or a separate processor may be used to control among other functions the securing of wafer  170  by arm  175 , the rotation of arm  175 , and the placement of wafer  170  into chamber  110 .  
         [0016]     Referring again to the contents of volume  105  of chamber  110 , volume  105  also includes, in one embodiment, particle displacement plate  190 . In one embodiment, particle displacement plate  190  has a diameter that is equal to or slightly less than a diameter of wafer  170 . By slightly less, it is meant, in one embodiment, but not necessarily limited to, one millimeter to three millimeters less in diameter (e.g., 5-7 mm for a 200 mm wafer or 9-11 mm for a 300 mm wafer). In the embodiment shown, particle displacement plate  190  is supported by stage  195  that may be moved up or down (as viewed) within chamber  105  such movement optionally controlled by program instructions in processor  140  or another processor. In one embodiment, particle displacement plate  190  is advanced to a position, in one embodiment, within a few millimeters (e.g., 1-4 mm) from active side  180  of wafer  170 .  
         [0017]      FIGS. 2-4  illustrate a series of processing operations within chamber  110  of load lock  100 . Referring to  FIG. 2 , wafer  170  is placed in chamber  110 , volume  105  of chamber  110  is sealed and purge gas  210  is introduced. In one embodiment, purge gas  210  is a nitrogen gas.  
         [0018]      FIG. 3  shows chamber  110  during a pump-down operation. In one embodiment, volume  105  of chamber  110  is reduced in pressure (pumped down) to a vacuum condition. Referring to  FIG. 1 , pressure sensor  130  may be used to monitor the pressure in chamber  110  and exhaust port  120  may be used to evacuate chamber  110 . With wafer  170  in an active side down (with gravity) position, the pump down process occurs in such a way to allow gravitational force to act against particles moving towards wafer  170 . Particle displacement plate  190  inhibits particles from bouncing towards active side  180  of wafer  170 . As the pressure drops during a pump down process, a Stokes drag experienced by particles  310  decreases significantly. If particles  310  achieve ballistic velocities, the particles can suffer multiple collisions with chamber  110  and other surfaces and ultimately end up on active side  180  of wafer  170 . Particle displacement plate  190  inhibits the possibility of colliding particles ending up on active side  180 .  
         [0019]      FIG. 4  shows chamber  110  following the pump down process. In  FIG. 4 , the pressure in volume  105  of chamber  110  is selected to be, in one embodiment, equivalent to a pressure in a processing chamber where wafer  170  will be transferred. The number of unwanted particles on active side  180  of wafer  170  have been reduced due to the configuration of wafer  170  in chamber  110  and, in this embodiment, the presence of particle displacement plate  190 .  
         [0020]      FIG. 5  shows wafer  170  transferred from chamber  110  to processing chamber  510 . In one embodiment, chamber  110  is connected to processing chamber  510  through entry port  520  that may be sealed while chamber  110  is undergoing a pump down process. In one embodiment, a volume of chamber  510  has been pumped down to a pressure equivalent to the pumped down pressure of volume  105  of chamber  110 . Wafer  170  may be transferred to chamber  510  in an active side up or active side down configuration depending on the desired processing environment. In chamber  510 , one or more semiconductor processing operations may be performed on wafer  170 . Representative processing operations that may be performed under vacuum conditions include implant, etch, extreme ultraviolet lithography, and masked-beam processing. Following processing, wafer  170  may optionally be returned to chamber  110  in an active side down configuration and purging operations may be performed. In this manner, after processing the potential of particle contaminants contacting active side  180  of wafer  170  may be reduced.  
         [0021]      FIGS. 6-8  show various ways to support a wafer within a chamber, such as a load lock, during a pump down process. Each embodiment shows a wafer in an active side down (in a direction with gravity) configuration.  FIG. 6  shows wafer  670  supported by support  690 . In this embodiment, support  690  serves as a support and as a particle displacement plate. Wafer  670  is supported by support  690  in an active edge grip support configuration with vertical supports  695  (e.g., a few millimeters in length) supporting wafer  670  outside an active area (e.g., at several points along an edge of wafer  670 ).  FIG. 7  shows a second embodiment where wafer  770  is supported in an active edge grip configuration by support  775  with vertical supports  795 . Particle displacement plate  790  is placed on support  775  (and supported by vertical supports  777 ) and, in one embodiment, has a diameter smaller than support  775 . In one embodiment, support  775  has a diameter equal to or greater than a diameter of wafer  770 .  
         [0022]      FIG. 8  shows a third embodiment where wafer  870  is chucked by chuck  875 . A passive side of wafer  870  is supported by chuck  875  through, for example, electrostatic forces. In this embodiment, particle displacement plate  890  is not in contact with an active side of wafer  870 .  
         [0023]     In the preceding detailed description, reference is made to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.