Abstract:
An article holder has sensors that detect whether an article held in the holder is a workpiece or a piece of packaging material. Examples are end effectors suitable for picking up semiconductor wafers and packaging material from a pod or some other carrier.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to article handling, and more particularly to article holders that handle semiconductor wafers and other articles.  
           [0002]    During fabrication of integrated circuits from semiconductor wafers, the wafers are stored and transported in cassettes. FIG. 1 illustrates a cassette  110  holding a number of wafers  120 . Each wafer rests on shoulders  130 A,  130 B formed on cylindrical cassette walls  140 A,  140 B. A robot (not shown) transports the wafers between the cassette and wafer processing equipment. An article holder (“end effector”) mounted on a robot arm holds the wafers by vacuum or electrostatic forces, or using a gas vortex, or by other means.  
           [0003]    When a wafer is thin (below 100 μm), the wafer is difficult to store in a cassette. The wafer sags under its own weight, and can fall off the cassette shoulders  130 A,  130 B. A thin wafer can also be warped due to the internal stresses caused by the presence of different materials (semiconductor materials, metals, dielectrics) which constitute the wafer circuitry. Therefore, thin wafers have been stored in horizontal wafer shipment containers (“pods”), such as pod  210  in FIG. 2. Wafers  120  are stacked in the pod on top of each other, with paper or plastic inserts  220  separating the wafers. Foam  230  is provided at the top and bottom of the stack (the top piece of foam is not shown). The foam and the paper or plastic inserts have roughly the same shape as the wafers, and most or all of the bottom surface of each wafer is in physical contact with the paper inserts above and below the wafer. The wafer circuitry is protected however. A typical fabrication process starts with fairly thick wafers (e.g. 600 to 800 μm for silicon wafers) which are stored in a cassette. When the wafer circuitry has been fabricated and a protective passivation layer has been formed on the circuitry side of the wafer, the wafer is thinned down from the other side to a final thickness (which may be 100 μm or less), and is stored in a pod. At this stage, the wafer circuitry is protected by the passivation layer, so the physical contact between the wafer  120  and the paper or plastic  220  is acceptable.  
           [0004]    It is desirable to provide wafer handling techniques suitable for storage of wafers in pods.  
         SUMMARY  
         [0005]    The present invention provides end effectors suitable for handling of wafers stored in pods such as pod  210  of FIG. 2. The end effectors have sensors that allow automatic detection of whether an article held by the end effector is a wafer or a piece of packaging material, e.g. paper or plastic, or foam. Some embodiments can handle wafers stored in pods as well as wafers stored in cassettes.  
           [0006]    The invention is not limited to thin wafers, and is applicable to thick wafers stored in pods or cassettes. The invention is also applicable to containers other than pods and cassettes.  
           [0007]    The invention is not limited to semiconductor wafers. Some embodiments include article holders that handle glass or polymer wafers, or wafers made from other materials. In some embodiments, the articles handled by the end effector are multiple wafers bonded together. Such articles can be formed in the process of manufacture of vertically integrated circuits. See U.S. Pat. No. 6,184,060 issued Feb. 6, 2001 to O. Siniaguine and incorporated herein by reference. An article may include a combination of semiconductor and non-semiconductor wafers. See U.S. patent application Ser. No. 09/791,977 filed on Feb. 22, 2001 by O. Siniaguine and incorporated herein by reference. In other embodiments, the articles are flat-panel displays or other types of articles extending generally along a plane. Packaging materials other than paper or foam can be used.  
           [0008]    The invention is not limited to article holders that are part of a robot. Some embodiments include hand-held article holders, or article holders mounted on non-electronically-controlled machinery. The invention is defined by the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view of a conventional wafer storage cassette.  
         [0010]    [0010]FIG. 2 is a perspective view of a conventional pod for storing semiconductor wafers.  
         [0011]    [0011]FIGS. 3, 4 are perspective views showing an end effector according to one embodiment of the present invention.  
         [0012]    [0012]FIG. 5 is a bottom view showing the end effector of FIGS. 3, 4.  
         [0013]    [0013]FIG. 6- 8  are side views showing the end effector of FIGS.  3 - 5 . 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]    [0014]FIG. 3 is a perspective view showing the top and a side of an end effector  310  according to one embodiment of the present invention. FIG. 4 is a perspective view showing the same side and the bottom of the end effector. FIG. 5 is a plan bottom view. The end effector is suitable for picking up wafers  120 , paper  220  and foam  230  from pod  210 , and for placing wafers, paper and foam in the pod. The end effector can also place wafers in, and pick up wafers from, a cassette  110  (FIG. 1). The end effector has a color sensor  320 , a capacitance sensor  330 , a top of stack sensor  340  (shown as an emitter/receiver pair  340 E,  340 R), a sensor  350  (shown as an emitter/receiver pair  350 E,  350 R), and a sensor  360  (shown as emitter  360 E, receiver  360 R). These sensors are used to detect whether the end effector is holding a wafer, a paper insert, or foam. These sensors are also used to detect the presence of a wafer in a cassette and whether or not the wafer is cross slotted.  
         [0015]    The end effector is mounted on an adaptor  370  attached to a robot arm  380  (FIG. 3). The robot can be a conventional robot, for example, model GBY7S available from Genmark Automation of Sunnyvale, Calif. The robot may be controlled by its computer  384  which receives commands from a programmable logic controller (PLC)  390 . The robot receives signals from the sensors, sends them to the PLC, and performs actions as directed by its computer  384  and the PLC. The invention is not limited to robots, PLCs, adaptors, or any particular end effector control techniques. FIGS.  3 - 5  also show mounting holes (such as  394 ) and screws that hold the structure together. Such mounting means are not limiting.  
         [0016]    The end effector of FIGS.  3 - 5  is a non-contact type. It holds articles with gas vortices emitted from openings  410  (FIGS. 4, 5) in its bottom surface. Only a few of the openings are labeled in the drawings. Gas vortex end effectors are described in U.S. Pat. No. 6,095,582 issued Aug. 1, 2000 to Siniaguine et al. and incorporated herein by reference. See also U.S. patent application Ser. No. 09/632,236 filed Aug. 4, 2000 by S. Casarotti et al.; U.S. patent application Ser. No. 09/633,086 filed Aug. 4, 2000 by S. Kao; U.S. patent application Ser. No. 09/877,366 entitled “Article Holders That Use Gas Vortices To Hold An Article In A Desired Position”, filed Jun. 8, 2001 by S. Kao. In an exemplary embodiment, the end effector has a body  310 B made of a top plate and a bottom plate. A number of vortex chucks are positioned in a hollow region (not shown) between the two plates. Gas is supplied under pressure into the hollow region. The gas enters the vortex chucks, and exits in vortices through openings  410  in the bottom plate. The gas vortices create an attraction force that holds the wafer, paper, or foam article near the body of the end effector. The gas also creates a cushion that prevents the article from touching the bottom surface of the end effector except at break pads  420 . Break pads  420  protrude from the bottom surface of the end effector to prevent the article from sliding laterally. The article is pressed against the break pads by the attraction force of the gas vortices. FIG. 5 shows at  120  a contour of a wafer held in the end effector. The paper and foam occupy a similar position. The invention is not limited to gas vortex end effectors, break pads, or end effectors made of two plates.  
         [0017]    Color sensor  320  allows the end effector to distinguish between a wafer  120  and a paper or plastic insert  220 . Color sensor  320  includes an emitter and a receiver, and generates a binary signal indicating whether or not the color of the article held by the end effector is the color of paper  220 . In some embodiments, the inserts are black, the wafers are gray, and the color sensor generates a signal indicating the presence of the black color. In other embodiments, the sensor  320  generates a signal indicating the presence of the gray color. In some embodiments, the sensor is programmable to indicate the presence of a color programmed into the sensor. Such color sensors are known. One example is model CZ-K1 available from Keyence Corporation of Woodcliff Lake, N.J. Other embodiment use sensors that generate a non-binary signal whose value indicates which of a set of colors the sensor has detected.  
         [0018]    In FIGS.  3 - 5 , the color sensor  320  is mounted in a hole passing through the body of the end effector. Sensor  320  is connected to the robot by means of a fiber optic conduit  440  (FIG. 3) that houses two fiber optic cables, one cable for the emitter of the sensor and the other cable for the receiver. Fiber optic conduit  440  is positioned in a groove in the top surface of the end effector body  310 B. The invention is not limited to such conduits, or a particular position of the conduits, or any other construction. For example, conduit  440  can be positioned between the top and bottom plates of the end effector, or under the bottom plate, and can be a non-fiber-optic wire.  
         [0019]    Capacitance sensor  330  (FIGS. 4, 5) is a redundant sensor provided, like the color sensor, to distinguish between a wafer  120  and a paper or plastic insert  220 . Capacitance sensor  330  is positioned on the bottom surface of the end effector, and is connected to the robot by means of a cable  450 . Such sensors are known, and one example is model SK-25-10/25-b available from SIE Sensors of Toledo, Ohio. The control logic (e.g. computer robot  384  and/or PLC  390 ) can be programmed to recognize a wafer when both of the sensors  320 ,  330  indicate a wafer, or at least one of the two sensors indicates a wafer, or when one specific sensor (e.g. the color sensor) indicates a wafer. Similarly, the control logic can be programmed to recognize a paper or plastic insert or foam when at least one of the two sensors, or a specific one of the two sensors, or both, indicate a paper insert or foam. (In some embodiments, the foam is detected by sensor  340  as described below, and the sensors  320 ,  330  are not used for foam detection.) The control logic can be programmed to generate an alarm signal when the sensor data are inconsistent, e.g. one of the sensors  320 ,  330  indicates a wafer and the other one of the sensors  320 ,  330  indicates paper or plastic.  
         [0020]    Additional redundant sensors can be provided, which recognize articles based on physical properties other than color or capacitance. For example, magnetic properties can be exploited. Other embodiments do not have redundant sensors, for example, only a capacitance sensor or only a color sensor is provided. Multiple sensors of the same type, e.g., multiple color sensors, can be provided. Their signals can be averaged.  
         [0021]    In some embodiments, the sensors  320 ,  330  are flush with the bottom surface of the end effector body  310 B to provide a smooth surface which is easy to clean and which does not accumulate particles.  
         [0022]    Top of stack sensor  340  (shown as an emitter/receiver pair  340 E,  340 R) detects the top article in pod  210  and/or cassette  110  when the end effector is not holding any article and is moving down searching for the top article to pick up. When the end effector has picked up the article, sensor  340  is used to determine whether or not the article is foam  230 . Sensor  340  is also used when the end effector is placing a wafer  120  or an insert  220  into a pod or a cassette. As explained below, the wafers and the inserts do not block the sensor  340 , so the sensor can detect the top of stack in the pod with a wafer or insert in the end effector. When the top of stack is detected, the end effector can place the wafer article or the insert article on the stack and release the article.  
         [0023]    Sensor  340  is a thru-beam sensor. Emitter  340 E is mounted on the “nose” of the end effector (the nose is the part away from the robot). Receiver  340 R is mounted on the “tail” of the end effector (close to the robot). When the end effector picks up an article (wafer, paper or foam), the article is between emitter  340 E and receiver  340 R. See FIG. 5 showing the contour of wafer  120 . See also FIG. 6 showing schematically a side view of the end effector holding a wafer  120 . A wafer  120  or a paper or plastic insert  220  are closer to the end effector body  310 B than the light apertures  340 A of emitter  340 E and receiver  340 R. (The term “light aperture” is used herein for the light emitting area of the emitter and the light detecting area of the receiver respectively.) Therefore, a wafer or a paper or plastic insert will not break a beam of light  460  from emitter  340 E to receiver  340 R. Foam  230  is thicker and will break the beam, as shown in FIG. 7. In some embodiments, wafers  120  and inserts  220  are at most 0.6 mm thick. The “flying gap” (the distance between the wafer or insert article and the end effector body  310 B) is at most 0.5 mm. Foam pieces  230  are about 3 mm to 26 mm thick. Emitter  340 E protrudes down less than receiver  340 R in order to make the end effector thinner at the nose. The thinner nose makes it easier for the end effector to enter cassette  110 . In some embodiments, sensor  340  is model FU-16 available from Keyence Corporation. The aperture  340 A is at the center of emitter  340 E, and is 1.27 mm below the end effector body  310 B. Aperture  340 A of receiver  340 R is at the center of the receiver, and is 7.62 mm below the body  310 B. These dimensions are not limiting. In some embodiments, the emitter and receiver apertures  340 A are equidistant from body  310 B, so beam  460  is horizontal. Therefore, when the end effector is looking for the top of stack, and the beam is broken, the distance between the article breaking the beam and the body  310 B is precisely determined by the robot.  
         [0024]    In some embodiments, the receiver protrudes down less or by the same amount as the emitter. In some embodiments, the emitter is positioned at the tail of the end effector, and the receiver is at the nose, and the receiver may or may not protrude down less than the emitter. The emitter and receiver position can be chosen as needed for a particular application. For example, if the end effector is used with plasma processing equipment, it may be desirable to position the receiver so as to minimize disturbance of the sensor by the light emitted by the plasma.  
         [0025]    [0025]FIG. 3 shows a fiber optic cable  470  used to connect the transmitter  340 E to the robot. Cable  470  is positioned in a groove in the top surface of the end effector body. This construction is not limiting.  
         [0026]    The invention is not limited to thru-beam sensors or to particular positioning of the sensor elements. For example, a retroreflective sensor can be used.  
         [0027]    Sensor  350  (shown as an emitter/receiver pair  350 E,  350 R) helps detect the presence of an article in the end effector. Emitter  350 E is positioned on a side of the end effector body  310 B. When the end effector is holding an article, light aperture  350 A of emitter  350 E is above the article. See FIG. 8. Receiver  350 R is positioned on the tail portion of the end effector, laterally to the side of the article. Light aperture  350 A of receiver  350 R is below the top surface of the article. Any article held by the end effector, including a wafer, a paper insert, or foam, will break the beam  480  from the emitter to the receiver. FIG. 8 schematically illustrates this for a wafer  120 .  
         [0028]    The position of emitter  350 E and receiver  350 R can be interchanged.  
         [0029]    Fiber optic cable  490  (FIG. 3) is used to connect the emitter  350 E to the robot. Cable  490  is positioned in a groove in the top surface of the end effector body. This construction is not limiting.  
         [0030]    Sensor  360 , shown in FIGS. 4, 5 as an emitter/receiver pair  360 E,  360 R, is similar. It detects the article on the other side of the end effector. When the end effector is holding an article, the light aperture of emitter  360 E is above the article. Receiver  360 R is positioned on the tail portion of the end effector, away from the position of the article. The receiver&#39;s light aperture is below the top surface of the article. Any article held by the end effector, including a wafer, a paper insert, or foam, will break the beam from the emitter to the receiver.  
         [0031]    The position of emitter  360 E and receiver  360 R can be interchanged.  
         [0032]    Fiber optic cable  494  (FIG. 3) is used to connect the emitter  360 E to the robot. Cable  494  is positioned in a groove in the top surface of the end effector body. This construction is not limiting.  
         [0033]    In some embodiments, sensors  350 ,  360  are positioned to detect some types of articles (e.g. foam) but not other types.  
         [0034]    In some embodiments, sensors  350 ,  360  are used to detect a wafer in cassette  110 . When one of these sensors detects a wafer and the other one of these sensors does not, the wafer may be broken or cross-slotted. See the aforementioned U.S. patent application Ser. No. 09/632,236.  
         [0035]    Sensors  350 ,  360  can be conventional devices, such as model FX-7 available from SUNX Ltd. of West Des Moines, Iowa. They can also be retroreflective or other types of sensors. The invention is not limited to the positioning of these sensors on the end effector.  
         [0036]    Sensor  340  can be used with sensors  350 ,  360  to detect the presence of an article lying in a cassette or a pod before the article is picked up by the end effector. Sensor  340  can also be used to detect an article after the article is picked up. Sensor  340  can detect the middle of the article, and each of sensors  350 ,  360  can detect one side of the article. If the sensors&#39; signals are inconsistent, i.e., only one or two of the three sensors detect an article, the article may be broken.  
         [0037]    How the sensors are used depends on the programming of robot computer  384  and PLC  390 . For the purpose of illustration and not to limit the invention, Table 1 below shows one possible use of the sensors. In the embodiment of Table 1, color sensor  320 , capacitance sensor  330 , and top of stack sensor  340  are ignored when a wafer is picked up or placed in a cassette. Each sensor provides a binary detection signal, i.e. detect or no detect. Color sensor  320  detects the color of inserts  220 . Capacitance sensor  330  detects the wafer capacitance. In Table 1, “D” means detection, “ND” means no detection, “X” means “don&#39;t care”.  
                                   TABLE 1                           Sensor   Sensor   Top of   Color           Condition   350   360   Stack 340   320   Cap. 330                   End Effector   ND   ND   ND   ND   ND       Clear       Wafer Present   D   D   ND   ND   D       Paper or Plastic   D   D   ND   D   ND       Present       Foam Present   X   X   D   X   X       Top of Stack   X   X   D   X   X       Found       Wafer cross   D   ND   X   X   X       slotted (if being       taken from a       cassette) or       broken (if picked       up and held in the       end effector)       Wafer cross   ND   D   X   X   X       slotted (if being       taken from a       cassette) or       broken (if picked       up and held in the       end effector)                  
 
         [0038]    In some embodiments, inconsistent signals are taken as indications of a broken wafer. For example, a piece of a wafer may block both of the sensors  350 ,  360 , thus indicating a good wafer, but color sensor  320  or capacitance sensor  330  may indicate no wafer, thus signaling a broken wafer. Pieces of a broken wafer may move one over another in the end effector, blocking the top of stack sensor  340 . When different color sensors and/or different capacitance sensors are present, inconsistent signals from such sensors may also indicate a broken wafer. The robot can be programmed to put broken wafers into a specially designated area.  
         [0039]    The invention is not limited to the embodiments described above. Other types of sensors, for example, CCD cameras, can be used. The invention is applicable to article holders that hold an article from below or at some angle. Other embodiments and variations are within the scope of the invention, as defined by the appended claims.