Abstract:
A robotic semiconductor handling system includes two robot arms for transferring substrates between processing, cooling, and storage stations. The first robot arm has a paddle-type end effector adapted such that it can support one substrate at a primary location as well as a second substrate at a secondary staging location. The second robot arm is a Bernoulli-style wand that transfers a substrate from the primary location to the secondary one, and transfers substrates from either location to the process chamber. The use of the dual-location paddle allows for a significant reduction in cycle-time over a single paddle location and a Bernoulli wand system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a system and method of substrate handling in semiconductor processing, and specifically to a robot arm with primary and secondary substrate locations on a paddle-type end effector. 
     2. Description of the Related Art 
     In the processing of semiconductor devices, such as transistors, diodes, and integrated circuits, a plurality of such devices are fabricated simultaneously on a thin slice of semiconductor material, termed a substrate or wafer. Such wafers are extremely brittle, and easily contaminated. During manufacturing of semiconductor integrated circuits, therefore, care must be taken to avoid physical damage and particulate contamination to the wafers. 
     Various systems are known for handling wafers within semiconductor processing systems. The particular application or environment from which the wafer is lifted often determines the type of pickup device. One class of pickup devices, known as Bernoulli wands are typically used for high temperature applications. Bernoulli wands utilize jets of gas downward from the wand toward the wafer to create a region of low pressure above the wafer, therefore lifting it. The advantage being that the hot wafer need not contact the pickup wand, except perhaps at one or more small locators depending from the wand. Such a Bernoulli wand is shown in U.S. Pat. No. 5,080,549 to Goodwin, et al. 
     Another type of wafer pickup device is a simple paddle which relies on friction due to gravity between wafer support surfaces and the back of the wafer. In a variation of that, the paddle is augmented with a vacuum to hold the wafers on the paddles. 
     U.S. Pat. No. 5,135,349 to Lorenz, et al., discloses a robotic handling system utilizing two paddle style pickups mounted on a common rotating base. Both pickups are adapted to extend linearly away from one another to speed up handling of wafers within the processing system. Again, the paddles are augmented with a vacuum generated through a plurality of holes in an end effector portion of each paddle. 
     In a more recent method of wafer handling, a dual-arm transfer assembly is provided with one arm having a spatula-type end effector, and the other a Bernoulli wand end effector. This method uses the spatula to retrieve or deposit a wafer from or to a cassette. Prior to insertion into the process chamber for deposition, the wafer is “handed off” to the Bernoulli wand, which then places the wafer into the process chamber. Following processing, the Bernoulli wand retrieves the wafer from the process chamber and retracts it into the wafer handling chamber, where the wafer is deposited in a cooling station. When sufficiently cool, the spatula is used to return the wafer to the cassette in the load lock. This sequence of placing/retrieving a wafer from the cool station and returning it to it&#39;s cassette, fetching the next wafer and returning to the Bernoulli hand-off position is relatively short, but yet reducing the time is desirable. These robotic motions are typically conducted during the etch cycle where the process chamber is not available to process wafers. As improvements are made in process technology, the etch cycle may be significantly shortened or eliminated. Hence, there is a need for a system that reduces wafer handling time. 
     SUMMARY OF THE INVENTION 
     It is therefore one object of the present invention to provide a first robot arm with a paddle-type end effector capable of holding two substrates at primary and secondary locations. This arm is preferably to be used in conjunction with a second robot arm having a Bernoulli wand end effector, both of which are actors in a pivoting linear robot. The secondary location is effectively a staging area for a wafer prior to its being processed. By using the Bernoulli wand to retrieve a hot, processed wafer, placing that wafer on the cooling station, and having another wafer staged on the secondary location on the paddle, the loading time of the next wafer into the process chamber may be significantly reduced. This effectively results in a significant improvement in throughput for the overall wafer processing system. 
     The two robot arms are mounted such that they can translate linearly within a wafer handler of the semiconductor processing system. A wafer can be moved in and out of a cassette of many wafers staged in a load lock chamber. The cassette or the paddle may be independently vertically movable such that the paddle can be positioned underneath a wafer and lift it from the cassette. 
     In order to transfer a wafer from the primary location to the secondary location, the first robot arm returns to its “home” position which places the wafer on the primary location directly below the Bernoulli wand. The Bernoulli wand then lifts the wafer from the paddle by initiating the flow of gas through the Bernoulli wand, creating a low pressure region above the wafer, and thus lifting it. Once the wafer has been lifted by the Bernoulli wand, the first robot arm translates forward to a position such that the secondary wafer location is directly below the wafer being held by the Bernoulli wand. The wafer is then deposited onto the paddle at the secondary position by stopping the flow of gas through the Bernoulli wand. The paddle is then retracted to the “home” position. Note that this is done while a wafer, previously deposited in the process chamber, is processing so as not add to the overall cycle time. 
     The Bernoulli wand then translates forward and into the process chamber in order to retrieve a “hot” processed wafer. The “hot” wafer is lifted by the Bernoulli wand as described above, and the wand is then retracted to its “home” position. Assuming the paddle is made of material which can handle the heat, such as quartz, the hot wafer is dropped on the paddle at the primary position. Next, the paddle extends toward the process chamber to the point which the “cold” wafer in position two is under the wand. Then the wand lifts the “cold” wafer and the paddle retracts to its home position. The wand then places the “cold” wafer in the reactor and retracts to its “home” position. 
     The wafer handler then rotates to face the cooling station where the “hot wafer is deposited for cooling. The handler can then be rotated to retrieve another “cold” wafer from the load lock for transfer to the second position on the paddle. The first robot arm can be used to transfer cooled wafers to the load lock while waiting for a wafer to be processed. 
     In an alternate sequence, a “hot” wafer can be deposited directly in a cooling station, and then an unprocessed wafer transferred to the reactor. That leaves the reactor empty longer than in the first described systems, but the paddle is not subjected to the hot wafer. Wafers can be transferred from a cooling station to the load lock while a wafer is in the reactor. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is an isometric view of the wafer handling system. 
     FIG. 2 is a top view of the dual-location robot arm of the present invention. 
     FIG. 3 is a side view of the dual-location robot arm of the present invention. 
     FIG. 4 is a top view of the dual-arm substrate transfer assembly of the present invention. 
     FIG. 5 is a side view of the dual-arm substrate transfer assembly of the present invention. 
     FIGS. 6A-6H are sequential drawings of a cycle of transferring substrates between the various stations. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 provides an isometric view of the wafer processing system in which the present invention operates. As will be described in greater detail below, a wafer handler  50  positioned in a handling chamber  51  preferably operates between two load lock  120 , cooling stations  110 , and a processing chamber  122 . The handler is preferably rotatably mounted on an axis  55  such that it can be rotated to “face” the load lock chamber  120 , processing chamber  122 , or either one of the two cooling stations  110 . The term “face” and its various forms are used herein to describe the orientation of the handler  50  in terms of the position of the port  42  relative to the load lock chamber  120 , process chamber  122 , and cooling stations  110 . Referring now to FIGS. 1,  4 , and  5 , a dual-arm wafer transfer robot assembly  25  is mounted within the handler  50 , and interacts with the process chamber  122 , load lock chamber  120 , and cooling stations  110  through a port  42  in the handler  50 . The dual-arm wafer transfer robot  25  comprises first and second robot arms  20  and  30  respectively, as described below. 
     Shown in FIGS. 2 and 3, the first robot arm  20  preferably comprises a dual-location paddle-type end effector, a proximal arm portion  24 , and a support paddle  26  having a distal free end  39  which extends substantially forward from said arm portion  24 . Additionally, the first robot arm  20  preferably comprises support pins  14  for supporting a wafer in a primary position identified by a wafer  10 , and support pins  16  for supporting a wafer in a secondary position indicated by a phantom line circle  12 . The proximal end of the arm portion  24  is preferably fastened within a manifold bracket  40  which is in turn, mounted to a linearly movable carriage  28  adapted to move along a linear pathway (not shown in FIGS. 2 and 3) generally centrally located in a longitudinal direction within the handler  50 . The movement of the first robot arm  20  in relation to the other elements of the system will be described below in more detail with respect to FIGS. 6A-6H. 
     The first arm  20  is fabricated from materials able to withstand the temperatures typically experienced. 
     FIGS. 2,  3 ,  4  and  5  illustrate the dual-location robot arm  20  of the present invention in relation to the second robot arm  30  which is preferably a Bernoulli-type wand which lifts the wafer by using jets of substantially non-reactive gas directed downward toward the upper surface of the wafer to create a reduced pressure region above the wafer. The Bernoulli wand is preferably fabricated from quartz or other material suitable for use in high temperature environments such as the process chamber  122 , FIG.  1 . The details of the operation and fabrication of the Bernoulli wand  30  are schematically shown and described herein, and reference can also be made to U.S. Pat. No. 5,080,549 which is incorporated herein by reference. 
     The dual-location paddle  20  and the Bernoulli wand  30  are preferably mounted within the handler  50  such that they translate along intersecting paths. The term ‘intersecting paths’ is used herein to describe paths of motion which bring the two robot arms  20  and  30  into relative positions allowing for wafers to be transferred, or “handed off,” therebetween. In the present embodiment, upper and lower robot arms  30  and  20 , respectively, translate along parallel and vertically spaced linear axes to allow for robot arm overlap. Note from FIG. 5 that with the wafer  10  positioned on the free end  39  of the paddle  26  there is a slight gap between the wafer and the Bernoulli wand  30 . 
     The function of the carriages  28  and  34  is described schematically herein, and in greater detail in application Ser. No. 08/784,711 which is incorporated herein by reference. Also, the details regarding the rotational and linear motion systems, are available from Cybeq Systems Inc. of Menlo Park, Calif. Other suitable drive arrangements are apparent to those with skill in this particular art and are described in the above-mentioned patents. 
     Referring to FIG. 1, the cooling stations  110  preferably comprise a plurality of supports  102  on which a wafer or other substrate can be placed, a lower shower head assembly  104 , and an upper shower head assembly (not shown) through which cooling gasses may flow. The gas flowing through the outlet  104  and over the wafer cools the wafer to a temperature at which it can be handled by the paddle  26  and the cassette in the load lock chamber  120 . The details and operation of the cooling station are schematically shown and described herein, and reference can also be made to the pending application No. 60/052263 which is incorporated herein by reference. 
     FIGS. 6A-6H schematically illustrate a preferred sequence of movement of the robot arms  20  and  30  of the wafer transfer system. As mentioned above, the handler  50  is preferably rotatably mounted on an axis  55  such that it can be rotated to face a load lock chamber  120 , a processing chamber  122 , or either one of two cooling stations  110 . The port  42  of the handling chamber  50  is preferably aligned with similarly sized ports in the load locks and processing chambers  120  and  122 , respectively, when the handler  50  is rotated to face that position. A cassette  124  of multiple wafers is positioned within the load lock chamber  120 , and may be adjustable in a vertical direction to align a particular wafer with the port  42 . A controlling computer (not shown) provides instructions to the motors driving the carriages  34  and  28  to cause arms  20  and  30  to translate along a guideway schematically indicated at  36  in FIG.  6 A. 
     In a first position, as shown in FIG. 6A, the first robot arm  20  translates toward the load lock chamber  120 . The free end  39  of the dual-location paddle end effector  26  of the first arm  20  extends through the port  42  and underneath a wafer in the cassette  124  to lift the wafer from the cassette. 
     In FIG. 6B, the first robot arm  20  returns to its “home” position which places the wafer  68  directly underneath the Bernoulli wand  30 . The wafer can then be transferred to the wand  30 , but it is preferable that the handler be rotated to be aligned with the cooling station  110 . This avoids the need to insert the paddle partially into the load lock again. Gas flow to the Bernoulli wand is then initiated through the extension hose  72  to enable transfer of the wafer  68  from the paddle  20  to the Bernoulli wand  30  as described above. 
     As indicated in FIG. 6C, after the wafer  68  has been lifted by the Bernoulli wand  30 , the first robot arm  20  translates partially into the cooling station  120  to a point where the secondary wafer location  12  (FIG. 2) is directly below the wafer  68  being held by the Bernoulli wand  30 . The wafer  68  is then deposited onto the paddle  26  at the secondary position  12  by stopping the flow of gas through the Bernoulli wand  30 . The paddle is then retracted. 
     The handler  50  then rotates to a position such that it faces the process chamber  122 , as illustrated in FIG.  6 D. While facing the process chamber  122 , the Bernoulli wand  30  translates forward through the port  42  and into the process chamber  122  to retrieve a “hot” wafer  67  from the support  123  in process chamber  122 . The Bernoulli wand  30  then lifts the “hot” wafer  67 , translates back to its home position as in FIG. 6E, and deposits the hot wafer onto the paddle primary position  10 . 
     FIG. 6F shows the first robot arm  20  still carrying the hot wafer at position  10  translated toward the process chamber  122  to a position such that the Bernoulli wand  30  is directly above the secondary wafer location  12 , FIG.  4 . The Bernoulli wand  30  then lifts the wafer  68  from the secondary position  12  and the paddle retracts to the “home” position. 
     As shown in FIG. 6G, the Bernoulli wand  30  translates toward the process chamber  122  wherein it places the unprocessed wafer  68  on the support  123  for processing. 
     Finally, as illustrated in FIG. 6H, the handler  50  rotates to face the cooling station  110  where the first robot arm  20  translates into the station and deposits the processed wafer  67 . The first robot arm  20  then retracts to its home position in preparation to return the cooled wafer  67  to the load lock  120 . The transfer to the load lock is just prior to getting a fresh wafer in primary position  10  on the paddle at the start of the next cycle. This activity of course is occurring while a wafer is being processed, thereby maximizing wafer throughput. As mentioned above, being able to transfer a hot wafer directly from the Bernoulli wand to a paddle requires that the paddle be made of quartz or other material able to withstand the hot wafer. 
     As an alternate procedure, the hot wafer can be transferred directly to the cooling station by the Bernoulli wand rather than being first transferred to the paddle. The wafer handler then has to be rotated to be aligned with the process chamber before the unprocessed wafer on the paddle can be transferred to the wand for insertion into the process chamber. Thus, while this approach permits the use of a paddle not made of high heat tolerant material, the cycle time is increased. 
     Although the present invention is particularly suited for transferring wafers to and from the load lock chamber  120 , processing chamber  122 , and cooling stations  110 , it may be positioned in other locations within a deposition processing system where the advantageous attributes disclosed herein would be useful. 
     Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments or sequences to other alternative embodiments and other sequences or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.