Abstract:
A substrate loading system, having a vision system adapted to view a substrate and provide position signals indicative of substrate position. A controller receives the position signals from the vision system, determines the substrate position, and sends transport signals to a robot arm. The robot arm engages the substrate in a beginning location and a beginning position and transports the substrate to a desired location and a desired position, based at least in part on the transport signals received from the controller.

Description:
FIELD 
     This invention relates to the field of integrated circuit fabrication. More particularly, this invention relates to substrate handling during integrated circuit fabrication. 
     BACKGROUND 
     Modern integrated circuits are customarily fabricated on substantially round slices of a semiconductor or other material, commonly called substrates or wafers. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices. 
     In many instances during the fabrication process it is desired to place the substrate within a piece of processing equipment or a piece of inspection equipment (jointly and severally referred to as “tools” herein) in a desired position. As the term is used herein, “position” refers to two components. The first component is offset, or in other words the x,y,z location of the substrate within the plane defined by the substrate. The second component is orientation, or in other words the disposition of the substrate with respect to rotation within the plane, or the pitch and yaw of the plane as determined by a reference. It is understood that the term “position” could also refer to other components of location of an object within a three-dimensional space, but the two components described above are of primary importance in the discussion presented herein. 
     Currently, a variety of methods are used to place a substrate in a desire position. Formerly, the substrate would be placed on a rotating chuck and the edge of the substrate would be rotated against a physical element, such as a pin, that senses a notch or flat in the circumferential edge of the substrate as it rotates past the physical element. The substrate is then placed in a position with respect to the notch. More recently, the substrate is rotated at a relatively high rate of speed with the circumferential edge of the substrate disposed under a linear CCD element that finds the notch. The rotation again a physical element or the high rate of rotation requires that the substrate be retained to the chuck, such as by being gripped at the edge or by a vacuum chuck, but not by gravity alone. 
     Unfortunately, adding such pre-aligner systems to all the tools that might benefit from their use can be quite expensive, in a variety of different ways. Current pre-aligner systems have a relatively high cost of more than about six thousand dollars each, are prone to failure, and take up valuable space. What is needed, therefore, is a system that overcomes problems such as those described above, at least in part. 
     SUMMARY 
     The above and other needs are met by a substrate loading system, having a vision system adapted to view a substrate and provide position signals indicative of substrate position. A controller receives the position signals from the vision system, determines the substrate position, and sends transport signals to a robot arm. The robot arm engages the substrate in a beginning location and a beginning position and transports the substrate to a desired location and a desired position, based at least in part on the transport signals received from the controller. 
     In this manner an expensive pre-alignment system is not required. Instead, a robot arm and a vision system can be used to transport and position the substrate. Many loading mechanisms already have robot arms, and thus only a vision system needs to be added, with appropriate programming and control of the robot arm, to adapt the equipment to this new system. Thus, implementation of the present system can be very cost effective. 
     In various embodiments, the beginning location of the substrate is a cassette and the desired location of the substrate is within a tool. Preferably, the beginning position and the desired position have common pitch and yaw components. In some embodiments, a fiducial is commonly viewed with the substrate by the vision system to provide referenced position signals. The fiducial may be disposed on the robot arm or on an element other than the robot arm and the vision system, which other element is in a known location and position relative to the vision system. The robot arm preferably retains the substrate with gravity alone. Some embodiments use an intermediate stage on which the robot arm places the substrate, releases the substrate, and re-engages the substrate from a different orientation, in order to position the substrate in the desired location in the desire position. In various embodiments, the means that is used to determine the substrate position is at least one of a flat on the substrate, a notch on the substrate, and circuit elements on the substrate. 
     According to another aspect of the invention there is described a method of transporting a substrate from a beginning location and a beginning position to a desired location and a desired position, by: (a) viewing a substrate with a vision system, (b) providing position signals indicative of substrate position, (c) receiving the position signals from the vision system with a controller, (d) determining the substrate position with the controller, (e) sending transport signals to a robot arm from the controller, (f) engaging the substrate with the robot arm in the beginning location and the beginning position, and (g) transporting the substrate with the robot arm to the desired location and the desired position, based at least in part on the transport signals received from the controller. In various embodiments, the steps of the method are performed in the listed order. Alternately, step (f) is performed prior to the other steps as listed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the FIGURE, which is not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements, and which is a top plan view of a system according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments of the invention as described herein take advantage of existing mechanisms in a robot  18 , such as a dual yaw manufactured by Yaskawa Electric Corporation of Kitakyushu, Japan, with the addition of a vision system  28 , such as those manufactured by Cognex Corporation of Natick, Mass. The combined robot  18  and vision system  28  preferably determines the position of the substrate  12  to be aligned, and then places the substrate  12  in a desired location  40 , and in a desired position within that location  40 . 
     This system  10 , especially for tools that do not require orientation and alignment of the substrate  12 , provides a faster means to transfer the substrate  12  from a cassette  14  or other holder, such as in a front opening unified pod, to the stage  30  of the tool. The stage  30  as displayed in the FIGURE is only partially depicted. Although many different beginning  16  and ending points  40  for the substrate  12  are contemplated herein, all such will be exemplified by moving the substrate  12  from a cassette  14  to a stage  30 , where the cassette  14  is the beginning location  16  where the substrate  12  is in a substantially unknown position, and the stage  30  is the ending location  40  where the substrate  12  is in a substantially desired position. 
     In its most basic embodiment, the invention places a substrate  12  in a position by picking up the substrate  12  from a starting location  16  with a robot arm  18 , determining the position of the substrate  12  with the vision system  28 , and transporting the substrate  12  to a desired location  40  and in a desired position with the robot arm  28 . Thus, a vision system  28  is used to determine the position of the substrate  12 , instead of using a mechanical method to determine the position of the substrate  12 . 
     As depicted in the FIGURE, the vision system  28  preferably looks down on the rest of the system  10 , and views it from above, although other references are also contemplated hereunder. Thus, the vision system  28  may have a different field of view than that as depicted in the FIGURE, which is limited to a two dimensional representation of the system  10 . 
     The step of determining the position of the substrate  12  can be accomplished at any point in the process. For example, the vision system  28  could determine the position of the substrate  12  before it is engaged by the robot arm  18 , and the robot arm  18  could then move the substrate  12  to the desired location  40  and position. Alternately, the robot arm  18  could engage the substrate  12  and move it to a given location  20  within the field of view of the vision system  28 , which then determines the position of the substrate  12 , and the robot arm  18  then delivers the substrate  12  to the desired location  40  in the desired position. Further, the robot arm  18  could engage the substrate  12  and move it to the desired location  20 , where the vision system  28  determines the position of the substrate  12 , and the robot arm  18  then moves the substrate  12  into the desired position in that location  20 . Thus, there are many different ways in which the system  10  could be implemented. 
     Typically, some components of the position of the substrate  12  in the starting location  16  will be known. For example, a substrate  12  that is taken from a cassette  14  as a starting location  16  will typically be in a relatively known x,y,z position. Thus, the vision system  28  in such an embodiment would not be required for the robot arm  18  to merely engage the substrate  12 , because only the rotational component of the position of the substrate  12  is not known. However, in other embodiments, fewer components of the starting position of the substrate  12  may be known, and it is conceivable that in some embodiments, none of the components of the starting position of the substrate  12  are known, except that the substrate  12  resides somewhere within a given volume of space. In that embodiment, the vision system  28  would preferably be used to determine the starting location  16  and position of the substrate  12  prior to engagement by the robot arm  18 . 
     The more complex case is when both components of the position of the substrate  12 , offset and orientation, are desired. In this case, the substrate  12  in one embodiment is picked up from the cassette  14  by an end effector  24  and placed in an intermediate location  20 , such as a holding ring  20   a . The substrate  12  is then picked up off of the holding ring  20   a  with a chuck  42  on the robot arm  18 , and is viewed with the vision system  28  to determine the position of the substrate  12  as held by the robot arm  18 , such as by finding the center of the substrate  12  to determine the offset, and the notch  32  of the substrate  12  to determine the orientation. Of course, other elements of the substrate  12  could be used to determine both the offset and the orientation of the substrate  12 . 
     The chuck  42  is preferably attached to the wrist of the robot arm  18 , and may be provided with proper vacuum levels from the robot supply so as to selectively retain the substrate  12 . However, in more preferred embodiments, the substrate  12  is retained on the chuck  42  by gravity alone. The chuck  42  may be fitted with one or more pad or o-ring of rubber or some thermoplastic material, to help with the gravity retention of the substrate  12  as it is rotated. The substrate  12  position with respect to both offset and orientation is now known in relation to the position of the robot arm  18 , and the substrate  12  may be rotated as desired using the robot chuck  42  until the substrate  12  is disposed in a desired orientation with respect to the robot arm  18 . Most preferably, the substrate  12  is rotated at a relatively low rate of speed, so that no mechanical means such as vacuum or edge gripping is required to retain the substrate  12  against the chuck  42  during the rotation. 
     The substrate  12  is placed back onto the holding ring  20   a , with the desired rotational orientation between the substrate  12  and the holding ring  20   a , and with the desired offset between the substrate  12  and the holding ring  20   a , so that the substrate  12  can be picked up directly by the end effector  24  and delivered to the stage  30  of the given tool. 
     In an alternate version, the vision system  28  views the substrate  12  while it is in the initial position  16 , and the controller  38  determines the location of at least one of the notch  32 , the flat  36 , or other elements  34  on the substrate  12 , thus determining the position of the substrate  12 . The robot arm  18  picks up the substrate  12 , and by virtue of the articulation in the arms of the robot arm  18 , is able to place the substrate  12  on the platen  30 , or other ending location  40 , in the correct position. The controller  38  computes how the orientation of the substrate  12  must be changed by the robot arm  18  from where it is picked up in the cassette  14  to where it is set down on the platen  30 . The change in orientation can be effected entirely within the articulation or natural rotation of the robot arm  18 , or by a rotating element  42  on the robot arm  18 , or by setting the substrate down on an intermediate element  20  and then picking it back up with the robot arm  18  from a new direction, so that the articulation of the robot arm  18  is then sufficient to place the substrate  12  in the desired position on the platen  30 . 
     In another version, the holding ring  20   a  can be designed to self center the substrate  12  when it is placed there in its orientated state by the robot arm  18 . In this embodiment, the orientation is provided by the robot arm  18  and vision system  28 , and the offset is provided by the self centering ring, such as by an indentation  22  in the ring  20   a  in which the substrate  12  settles as it is placed thereon. 
     In yet another version, the substrate  12  is picked from the cassette  14  directly by the robot arm  18 , viewed with the viewing system  28  to determine the position of the substrate  12 , and placed directly by the robot arm  18  onto the stage  30  of the tool in the desired offset and orientation, as determined from the viewing system  28 . In this embodiment, no other loading mechanisms or intermediate holding structures are required. 
     In a different embodiment, the substrate  12  orientation and offset are not critical. In this case the vision system  28  determines the position of the substrate  12 , after the substrate  12  is picked up from the cassette  14 . This information is communicated to the controller  38  for correction of the position of the substrate  12  on the stage  30 , as desired. 
     With the embodiments of this invention, the costly pre aligner is eliminated, and with minor changes to the existing robot  18  geometry on the tool and with programming and addition of a vision system  28 , such as a charge couple device array or a camera, the same functions are accomplished. 
     In another embodiment, the substrate  12  is passed under a vision system  28  that has sufficient fields of view to see both a fiducial  26   a  that is mounted to the end-effector  24  or wrist of the robot  28  and elements of the substrate  12  from which at least one of offset and orientation can be determined, such as the notch  32 , flat  36 , or circuit elements  34 . The relative offset and orientation of that element is then determined. The robot  18  then places the substrate  12  on a passive stage  20   b  of the tool, and uses its redundant degree of freedom to pick up the substrate  12  again such that the substrate  12  is delivered to the stage  30  in the desired position. This approach preferably uses a robot  12  with an articulated wrist or additional degree of freedom to correct the orientation. Fortunately, many robots  18  used in dual and triple tool front end module systems already have this extra degree of freedom to eliminate a track. 
     Another embodiment utilizes a vision  28  system with a smaller field of view. In this embodiment, the robot  18  moves the edge of the substrate  12  under the vision system  28 , and continues to move the substrate  12  edge under the vision system  28  until a position-indicating element such as the notch  32  is detected. Position information from the robots positional sensors coupled with position information for the substrate  12  from the vision system  28  is used to determine the substrate  12  offset and orientation in regard to stage  30 . This data is used to place the substrate  30  on the stage  12  in the desired position using the robot  18 . This approach preferably uses a robot  18  with an articulated wrist or additional degree of freedom. 
     Another embodiment uses the system  10  as described above where one of the orientation and offset is adjusted by the stage  30  on which the substrate  12  is finally disposed. The vision system  28  and robot  18  are preferably used to locate and determine at least one of the orientation and offset of the substrate  12  as it is held by the robot  18 . In one embodiment the robot  18  corrects the offset when it places the substrate  12  onto the stage  30 , and the stage  30  then adjusts the orientation based on the data received from the vision system  28 . This embodiment can be implemented by a standard R, Z, Theta robot  18 , and does not require and additional degree of freedom, since the stage  30  is used to adjust the orientation of the substrate  12 . In another embodiment the robot  18  corrects the orientation when it places the substrate  12  onto the stage  30 , and the stage  30  then adjusts the offset, either using the data received from the vision system  28 , or in a simple mechanical method, such as adjusting the location of the substrate  12  with pins or indentations in the stage  30 . 
     In one embodiment, a different type of sensor is used to “view” the substrate  12  instead of the vision system  28  and determine position information, such as an inductive sensor or a capacitive sensor that can detect the notch  32  or flat  36 . However, a vision system  28  can detect other elements besides the notch  32  or the flat  36 , such as the circuit elements  34 , to determine the position of the substrate. 
     In another embodiment, a fiducial  26   b  or  26   c  is fixed in space relative to the vision system  28 . The robot  18 &#39;s position is preferably used in addition to the vision system  28  to determine the offset and orientation of the substrate  12 . Alternately, fixed lights, such as mounted on the tool, could be used to determine the substrate  12  position and orientation. Again, either the robot  18  or the stage  30  could be used to correct the offset and orientation of the substrate  12 . 
     It is generally desired to be able to determine the position of the substrate  12  relative to something known using the vision system  28 , and then deliver the substrate  12  in a desired position to the stage  30 . Thus, two positions are preferably determined, that of the substrate  12 , and that of the “something known.” In the preferred embodiments, the something known is the robot  18 , but it could be something else in other embodiments. 
     The position of the substrate  12  can be determined by finding the notch  32  on the substrate. However, it can also be determined by inspecting for other physical elements, such as a flat  36  on the substrate  12 . Further, the position of the substrate  12  could be determined by looking at the patterns of circuitry  34  on the substrate  12 . Thus, the vision system  28  can be used to inspect the substrate  12  for one or more of a variety of different elements by which the position of the substrate  12  can be determined. 
     The position of the robot arm  18  can likewise be determined according to one or more of a variety of different methods. For example, the robot arm  18  can be calibrated or otherwise “zeroed” to a home position, and then all subsequent movements of the robot arm  18  can be tracked so that the position of the robot  18  at any given time can be determined. This could be referred to as an internal position determination, as the position of the robot  18  is determined by the internal workings of the robot  18  itself. 
     The position of the robot  18  could also be determined by one or more external method. For example, a fiducial  26   a  could be placed on the robot  18 , and the position of the fiducial  26   a  could be determined by the vision system  28 , thus determining the position of the robot  18 . Alternately, a given existing element of the robot  18  could be tracked by the vision system  28 , thereby determining the position of the robot  18 . Either of these external methods could be assisted by the use of a fiducial  26   b  or  26   c  that is mounted on something other than the robot arm  18 , such as a fixed element  20   a , which can be used as a reference to determine the position of the robot arm  18 , such as by using the fiducial  26   a  on the robot arm  18 . It will be appreciated that other fixed elements besides a fiducial  26   b  or  26   c  could also be used as a reference. 
     The position of the robot  18  and the substrate  12  could be determined more or less simultaneously, such as by using a vision system  28  with a relatively broader field of view, or one at a time, such as by using a vision system  28  with a relatively narrower field of view. Once the positions of both the robot  18  and the substrate  12  are determined, the substrate  12  can be placed on the stage  30  in any position desired, relative to the stage  30 , the position of which is known to the system  10 . However, if the vision system  28  has a field of view that includes both the stage  30  and the substrate  12 , then the position of the robot  18  becomes somewhat irrelevant, as the position of the substrate  12  relative to the stage  30  can be directly determined, and the substrate  12  placed on the stage  30  in the desired position. 
     Because many tools already include a robot  18  for loading and unloading the tool, the system  10  as described herein preferably adds only a vision system  28  and a controller  38  to the cost of the tool, while saving the cost of the pre-alignment system, as described above. Most tools also already include processing systems, such as general purpose computers, which can be used for the controller  38  to process the algorithms for position determination as described above. Thus, only the addition of the vision system  28  is needed. Further, even existing robots  18  with more limited capabilities, as described above, can be used to implement the system  10  as described herein, while robots  18  with more advanced capabilities can also be used to the benefit of the present system  10 . 
     The types of robots  18  predominantly contemplated herein are those such as having two, three, or four arm segments that are rotatably connected one to another at distal ends of the arm segments. One end of a first arm segment is mounted, such as to the tool or to some other relatively fixed apparatus at the substrate  12  entrance to the tool. One end of a last arm segment preferably has a chuck  42  or other means  24  for engaging a substrate  12  so that it can be moved using the robot  18 . Most preferably, the chuck  42  is rotatable on the end of the last arm segment. The robot  18  is preferably able to move the substrate  12  up and down in a z direction, to at least a limited extent, which might be as little as a few millimeters. In some cases, the robot  18  may have the ability to adjust the pitch and yaw of the substrate  12 , although such movement is typically not needed. 
     The foregoing description of preferred embodiments for this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.