Abstract:
A load lock is provided for a semiconductor substrate processing system having a transport robot mounted therein. The load lock transport supplies substrates directly to a processing chamber without the need for a central transport robot. The load lock transport is a dual element robot designed for minimum clearance and space and operates within a matching load lock chamber of minimum volume.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the transport of substrates through a load lock which forms part of a semiconductor processing system. The load lock services an individual process chamber. 
       BACKGROUND OF THE INVENTION 
       [0002]    The processing of semiconductors often involves multiple process steps such as the deposit of a film on a substrate or substrate by chemical vapor deposition (CVD), the photo etching of the film, as well as heating, cooling and cleaning. 
         [0003]    Each of the process operations is generally performed under vacuum in a specialized process chamber. Because of the need for extreme cleanliness and the delicate nature of each process, batch processing of semiconductor substrates has generally been replaced by individual substrate processing. This allows more control of the processing of each substrate, but limits the overall throughput of the system, because, for each process step, the process chamber must be vented, the substrate loaded, the chamber sealed and pumped to vacuum. After processing, the steps are reversed. 
         [0004]    To improve the process volume, a cluster of processing chambers are arranged around a substrate transport chamber which is constructed to be kept under vacuum. One or more load lock chambers are connected through slit valves to the transport chamber. 
         [0005]    The load locks accommodate cassettes of substrates to be processed. The cassettes are delivered to the load lock by the front end delivery transport of the system. A load lock constructed to accommodate such cassettes is shown in U.S. Pat. No. 5,664,925 owned in common with the subject application. The disclosure of the &#39;925 patent is incorporated herein by reference, in its entirety. 
         [0006]    In this manner cycling times are reduced, while significantly increasing system throughput. The process and transport chambers are maintained continuously under vacuum, while only the load lock is cycled. The load lock receives the substrates to be processed after being sealed from the transport chamber and vented to atmosphere. The front end port is than sealed and the load lock is pumped to a vacuum consistent with the transport and processing chambers. 
         [0007]    A robotic transfer mechanism is mounted within the transport chamber and operates to remove substrates from the load lock and deliver them to the selected process chambers. After processing, the substrates are picked up by the robot and transported to the next process chamber or to a load lock for removal from the transport chamber. In some instances, for timing purposes, these systems may employ buffer stations which are adapted to store substrates either before loading or at other times during the transport of the substrate through the system. 
         [0008]    A system of this type is described, in U.S. Pat. No. 5,882,413 and an example of a robotic transfer mechanism is shown in U.S. Pat. No. 5,647,724, each of which is assigned to a owner common to this application. The disclosures of these patents are incorporated herein by reference in their entirety. 
         [0009]    It has been found that substrates up to 200 mm in diameter can be effectively processed with the cluster type systems. However, there is a trend towards increasing diameters and the cluster systems become unduly large when processing substrates of 300 mm or more in diameter. There is a need to provide a more compact process handling module, which is capable of being installed in a side by side relation within a small envelope of space. In addition there is a need for system modules which are more adaptable to the wide variety of process chambers and front end delivery transports. 
         [0010]    It is a purpose of this invention to provide a load lock chamber which is constructed to service an individual process chamber directly, without a transport chamber and a transport robot. It is a second purpose of this invention to construct a load lock having its own transfer mechanism. It is another purpose of this invention to provide a transport which will accommodate at least two substrates and allow unloading and loading to and from the front end transport during the process cycle. 
       SUMMARY OF THE INVENTION 
       [0011]    The load lock chamber of a semiconductor processing system is provided with an active transport mechanism for extracting substrates from a buffer station or other delivery means provided by the front end of a system. The load lock transport mechanism has the additional capability of delivering the substrates directly to a processing chamber of the system. The load lock chamber therefore becomes the active transfer robot for the system, as opposed to the more passive transfer passage of prior systems. This allows the use of the load locks of this invention in a wide variety of applications and system configurations. The active transport mechanism provides at least one end effector for picking up and holding substrates for transport. A first buffer shelf may be provided within the load lock to store processed substrates for pickup by the unload mechanism and a second buffer shelf may be provided receive and store unprocessed substrates. 
         [0012]    Sealable ports are provided at the processing side and the front end delivery side of the load lock for sequential operation as needed in the process cycle. A front end delivery module locks into the delivery port and delivers a substrate for processing. This is accomplished while the processing port is closed and the load lock is vented to atmosphere. 
         [0013]    A substrate is deposited on one of the buffer shelves within the load lock by the front end transfer mechanism or is picked up by the load lock transport from the delivery module and moved into the load lock. After closing and sealing the delivery port, the load lock is pumped to the processing chamber operating vacuum. The processing port is then opened and the substrate is transported to the operating chamber. 
         [0014]    During the processing cycle of a substrate, the load lock processing port is closed and the load lock is vented to atmosphere. The delivery port is opened and another substrate is inserted on one of the load lock buffer shelves for processing. The pipe line, namely the load lock, of the system is now filled and the load lock is cycled to vacuum. As soon as the processing cycle is completed, the processed substrate is removed from the processing chamber, moved into the load lock and stored on an empty buffer shelf. An unprocessed substrate is transported into the processing chamber and the effector withdrawn. The processed substrate is stored in the load lock while it is vented and then transferred to the front end transport. A new substrate is loaded into the load lock chamber for processing. To maximize efficiency the cycling of the load lock, including, venting, unloading, loading, sealing, and pumping back to vacuum, occurs while a substrate is being processed. One of the factors which limits the reduction of cycle time is the pumping to vacuum. Since the pumping process is dependent on the volume of the load lock, the interior space of the load lock of this invention is minimized. The interior shape of the load lock chamber is designed according to the motion of the transport to minimize the containment to extension ratio of the load lack system. 
         [0015]    Systems and designs of the prior art emphasized elaborate mechanisms in a separate transport chamber and at the front end for loading and unloading the substrates. The load lock merely held a cassette or was constructed with buffer shelves on which the substrates can be loaded and unloaded. The load lock of the prior art performed the function of a conduit to get the substrates to vacuum. In the load lock of this invention, an active robotic transfer mechanism is provided within the load lock to accomplish the needed functions of delivering and picking up the substrates to and from the process chamber. 
         [0016]    The front end delivery system is provided with a front end transport capable of delivering the substrates to the load lock. In this instance a substrate shelf within the load lock provides a temporary buffer to receive the substrates from the front end transport. The end effector, therefore, need not extend out of the delivery port, but will load and unload substrates from the buffer shelves. 
         [0017]    The transport mechanism is constructed as a modified scara arm consisting of a lower arm and an extended end effector. One end of the lower arm is connected to a drive for rotation about a primary axis. The end effector is pivotally mounted on the free end of the lower arm. The lower arm is driven directly by a first motor of a coaxial drive. The end effector is driven by a second motor of the coaxial drive through a belt and pulley contained within the envelope of the lower arm. 
         [0018]    A control algorithm for the drive motors provides a pickup motion in which the end effector is moved to the buffer shelf to acquire a substrate for processing and a drop off motion in which the end effector is moved to extend outward from the processing port to deliver the substrate to the processing chamber. During the pickup motion, the drive motors are controlled to rotate such that the ratio of the angular motion of the second motor to the first drive motor is 2:1. This moves the substrate platform of the end effector in a straight line radially through the primary axis. During the drop off motion, the algorithm directs the controller to rotate the lower arm to allow the end effector to clear the interior walls of the load lock and enter the processing port. To extend the effector into the processing chamber, the drive motors are controlled to move the substrate platform in a straight line through the distal axis of the lower arm. To extract the processed substrate the reverse sequence of motions would be performed. 
         [0019]    A Z axis movement, i.e. up and down, may be provided by the transport mechanism within the load lock to provide the required pickup and dropoff motion at the buffer shelves or the processing shelf. 
         [0020]    As the end effector pivots over the lower arm, the lower arm is rotated to allow the end effector to clear the processing side wall of the load lock. The end effector continues to pivot until the substrate is aligned with the delivery port of the load lock. A forward motion of the lower arm at this time, extends the end effector through the processing port to deposit a substrate at the process chamber shelf. In this manner the straight line path of the substrate platform in the pick up mode is displaced from the straight line path of the substrate platform in drop off mode. The trajectory of the substrate is adjusted midstream by the drive control algorithm to adjust the position of the lower arm, as indicated above, to provide the displacement. 
         [0021]    In an alternate embodiment a second another extended end effector is mounted on the lower arm described above. The second end effector is driven by third drive motor of a triaxial drive system and is controlled for alternating use with first end effector. The second end effector is driven through similar trajectories. When one end effector is in use the other is withdrawn to the back of the load lock chamber. With the use of dual arms, buffer shelves are no longer necessary. 
         [0022]    The load lock of this mechanism, in association with its particular transport mechanism, allows the use of a processing port that is offset from the delivery port. This is particular useful when the processing stations are set up in a line, as there are minimum dimensions for separation of the processing stations. When existing front ends are used within the allowed envelope, the ports may not be aligned. The transport mechanism can accommodate the offset relationship minimizing retrofit design considerations. 
     
    
     
       DESCRIPTION OF THE DRAWING 
         [0023]    The invention is described in more detail below with reference to the attached drawing in which: 
           [0024]      FIG. 1  is a top view of a semiconductor processing system of the prior art; 
           [0025]      FIG. 2  is a perspective view of the semiconductor processing system of the subject invention; 
           [0026]      FIG. 3  is a top view of a dual module processing system using the load lock system of this invention; 
           [0027]      FIG. 4  is a flow chart of the process of this invention; 
           [0028]      FIG. 5  is an open view of the interior of the load lock of this invention; 
           [0029]      FIGS. 6   a - 6   d  are top views of the load lock of this invention showing the movement of the transport mechanism; 
           [0030]      FIG. 7  is a block diagram of the control system, for this invention; and 
           [0031]      FIG. 8  is an open view of the load lock of this invention showing an alternate embodiment of the transport mechanism. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    Throughout this application the term substrate will be used to refer to planar substrates such as silicon substrates and flat glass panels. This term is meant in its broadest sense. 
         [0033]    A semiconductor processing system  21  is shown in  FIG. 1  and is generally representative of the state of the art. The system consists of a cluster of processing chambers  24  arranged in a group in communication with a closed transport chamber  26 . A transport robot  28  is contained in the transport chamber in operative range of each of the processing chambers  24 . The processing chambers  24  and transport chamber  26  form a sealed enclosure which can be pumped down to the required processing vacuum and maintained under vacuum. A front end delivery transport  29  provides cassettes  27  of stacked substrates for processing. A door opening mechanism  25  provides access to load lock  22  through a delivery port. The cassette of substrates is loaded in the load lock at ambient conditions. The load lock  22  is closed at the delivery port by operation of valve  23  so that it can be pumped down to the operating vacuum of the system. The valve  30  is then opened to enable the robot  28  to extract the substrates in sequence for processing. Processing systems of this type have proven very useful and capable of processing large numbers of substrates in a reliable manner. As the size of the substrates has increased in diameter, systems, such as processing system  21 , have necessarily become larger to the extent that they have outgrown the space that can be allotted in the production line for these systems. 
         [0034]    The processing module  1  of this invention is shown in simple form in  FIG. 2  and is constructed of a load lock  2  which serves a single processing chamber  4 . The load lock chamber has a processing port  6  and a delivery port  7  to enable the loading of substrates to be processed and the unloading of processed substrates. Ports  6  and  7  are controlled by valves  9  and  10  respectively. A front end delivery system engages valve  10  through an exit port  8 . The process chamber is connected to valve  9  through entrance port  5 . Substrates are transported by a robot  30 , as shown in  FIGS. 6   a - d,  into the load lock  2  by the front end transport  3  under ambient conditions. The load lock is closed, pumped to vacuum and opened to processing chamber  4  through operation of slit valve  9 . In this manner the substrates are supplied to the processing chamber using a much more compact system. 
         [0035]    As shown in  FIG. 3 , multiple processing modules can be aligned sequentially. According to industry standards the processing chambers  4  must be spaced with a minimum clearance resulting in a separation of the operational paths  13  of the adjacent processing chambers of 750 mm. Existing front end delivery systems which can accommodate the dual processing chambers have operational paths  14  that are 505 mm. apart. The load lock  2  of this invention is designed to accommodate an offset of the operational paths. 
         [0036]    The front end delivery system  3  is equipped with door openers  15  and  16  which allow the docking of substrate cassettes  17  and  18 . Delivery system  3  includes a robot  19  which may be fixed or mounted on a track  20  depending on the number of docking ports that it serves. A transport of this type is described in commonly owned, U.S. Pat. No. 6,002,840, the disclosure of which is included in this application in its entirety. 
         [0037]    The load lock two of this invention is best shown in  FIG. 5 . Transport  30  is mounted within the cavity  31  of the load lock  2  and consists of a lower arm  32  mounted on an appropriate drive (not shown) for rotation about primary axis  33 . An effector  34  is formed as an extended arm and is pivotally attached to the distal end of lower arm  32  for rotation about distal axis  35 . The free end of effector  34  is constructed with an appropriate platform  36  designed to receive and support substrates  37 . 
         [0038]    The operative cavity  31  of load lock  2  is designed to allow only enough space to permit the free operation of the transport  30 . By raising the floor  38  to provide only sufficient operating clearance and shaping the interior walls  39  for the same purpose, the volume of the load lock is minimized. This enables the cycling time to vacuum to be reduced in order to provide a cycle time consistent with the processing cycle time. 
         [0039]    Load lock  2  is equipped with a processing port  6  and a delivery port  7  which are controlled respectively by slit valves  9  and  10 . The valves are operated by a process control system  42 , as shown in  FIG. 7 . Port  7  allows access to the chamber  31  for front end delivery module  3 . Front end delivery module  3  employs a robot  19  to load substrates for processing on buffer shelf  40 . End effector  34  is moved by control system  42  into alignment with shelf  40  to pickup substrates such as indicated by reference numeral  37 . A second buffer shelf  41  is provided to accommodate processed substrates until they can be removed by front end module  3 . 
         [0040]    Process control system  42  is shown in  FIG. 7  and illustrates a typical system which can be used to accomplish the various functions required in the load lock based substrate processing system of this invention. Each of the process modules will be provided with appropriate sensing elements to feedback information to the control processor to monitor the progress of the process and time the sequence of operational steps. 
         [0041]    The principal cycling event is the operation of the vacuum pump  44  to pump the load lock  2  to vacuum. Pump  44  also operates to maintain a vacuum in the operating chamber  4 . A pressure monitor senses the pressure in the load lock chamber  31  and provides the system control processor  45  with an indication of load lock pressure. Control processor  45  is controlled by an algorithm for the overall process. As previously indicated, the time needed to pump the load lock to vacuum is dependent on the volume of chamber  31 . To minimize the volume of the load lock chamber, all space within the chamber, that is not needed for buffer shelves  40  and  41  and the movement of the transport, is filled by shaping the contour of the top, bottom, and side walls that define the extent of chamber  31 . This minimizes the containment to extension ration of the load lock. 
         [0042]    The motion of the transport  30  within the load lock  2  is illustrated in  FIGS. 6   a - 6   d.  The overall trajectory of the substrate holder  36  is shown by sequence arrow  43 . It should be noted that arrow  43  indicates the process loading direction and assumes that substrate  37  is already stored on shelf  40  for processing. The position of the transport in  FIG. 6   a  will be referred to as the start position for convenience. In this position effector  34  is aligned over lower arm  32 . In order to move the holder  36  to the pickup position at shelf  40 , lower arm  32  is moved through an angle θ while effector  34  is moved through an angle φ, as shown in  FIG. 6   b . The transport drive  46  moves the arms as directed by the control algorithm. The relative motion of effector  34  to lower arm  32  is maintained at a two to one ratio during this motion, thereby generating the straight line trajectory shown by arrow  43   a . After pickup the transport returns to the start position. Effector arm  34  is then moved into alignment with the process port  6  to allow the extension of the transport into the process chamber  4 . This motion is accomplished by rotating lower arm  32  through an angle θ b  and by moving effector  34  through angle φ b . The control algorithm adjusts the relative motion of lower arm  32  and effector  34  to provide the clearing motion along trajectory portion  43   b . The transport elements are extended by a two one relative motion to achieve the straight line extension trajectory  43   c . 
         [0043]    Initially load lock  2  is vented and delivery port  7  is open. Front end transport  19  is actuated to deliver a substrate  37  to shelf  40  for processing. Delivery port valve  10  is sealed and load lock chamber  31  is pumped to vacuum. When the process operational vacuum is obtained, the process port  6  is opened through slit valve  9 . At this point process chamber  4  is empty and transport  30  is at its so called start position. Transport  30  acquires substrate  37  from buffer shelf  40  and translates through its delivery trajectory  43  to full extension where it will drop off substrate  37  for processing. Transport  30  retracts to its start position and the process valve  9  is closed and sealed. Whereupon substrate  37  is subjected to the process cycle in chamber  4 . Simultaneously load lock  2  is vented, opened and receives a new substrate from delivery robot  19 . When the new substrate is loaded, delivery valve  10  is closed and the load lock is cycled to vacuum. When the delivery port is opened transport  30  extends, picks up processed substrate  37  and loads it in buffer shelf  41 . The system at this point has completed a cycle and a new cycle is initiated to process the new substrate. 
         [0044]    In the alternate embodiment shown in  FIG. 8 , a second extended end effector  50  is shown mounted over end effector  34 . End effector  50  has a yolk or similar tip at its outer end to receive substrates for transport. Each of the end effectors is driven for alternating use to pickup or drop off substrates as they are processed. The drive mechanism of this requires a triaxial drive to enable each arm to be separately controlled in coordination with the lower arm  32 . The second end effector  50  will be moved through a similar trajectory  43  as indicated in  FIG. 6   a . The additional end effector allows a substrate to be stored without the need for buffer shelves. 
         [0045]    In operation, each of the end effectors will initially hold a substrate for processing. After the load lock is pumped to vacuum and with one end effector disengaged in a storage position, a substrate is loaded for processing. After the processing cycle is completed, the processed substrate is picked up by the empty end effector and retracted from the processing chamber. The end effector holding the processed substrate is moved into the storage position while the end effector holding the unprocessed substrate is moved forward. With the processed substrate effector disengaged the lower arm  32  loads the unprocessed substrate for processing. During processing, as before, the load lock is vented and opened to allow a new substrate to be loaded by front end  3 . With the second end effector, it would be possible to extend an effector arm out of the load lock to pick up a substrate from a more passive front end system. 
         [0046]    In this manner a simplified, highly flexible load lock is constructed to service an individual process chamber. The integral transport mechanism provides a mechanism to deliver substrates to the process chamber and to recycle for the next process cycle during the period of processing. This provides the ability to mount complete process modules to existing front end systems to allow the side by side arrangement of the process modules, thereby avoiding the cumbersome systems which have emerged due to the increase in substrate diameter.