Abstract:
Introduction of substrates into vacuum environment is accomplish by gradually reducing the number of substrates being transferred simultaneously as the clean and evacuated environment is progressed. Cassettes are maintained in clean atmospheric environment and do not enter the vacuum environment. Several vacuum locks are linearly staggered so as to introduce progressively higher level of vacuum environment. The number of substrates transported through this arrangement is a portion of the number of substrates present in each cassette. The staggered vacuum locks lead to a series of processing chambers, wherein a yet smaller number of substrates, e.g., one or two, are transported.

Description:
RELATED APPLICATIONS 
     This application claims priority benefit from U.S. provisional application Ser. Nos. 61/077,067 and 61/084,600, filed on Jun. 30, 2008 and Jul. 29, 2008, respectively, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     The subject invention relates to transporting of substrates for processing in a vacuum processing environment. 
     2. Related Art 
     Vacuum processing systems are used to fabricate hard-drive disks, semiconductor computer chips, solar panels, and the like, from substrates made of materials such as semiconductor wafers, glass, stainless steel, etc. Typically, the vacuum processing systems include several substrate chambers that perform various processes that modify the substrate by performing deposition, cleaning, etching, heating/cooling, etc., on the substrate The substrates are generally transported to the processing systems in cassettes holding several substrates in a clean atmospheric environment, and then the substrates are transported from the cassette, one by one, through a loadlock into the vacuum environment of the system. 
       FIG. 1  illustrates a prior art system that includes tracks  164  for transporting cassettes  162  containing a given number of substrates  166 . The tracks  164  are maintained in a clean atmospheric environment, and leads to loading chamber  170 , which is maintain in vacuum. Once cassette  162  enters the vacuum environment of loading chamber  170 , a knife blade  168  removes substrates  166 , one by one, from the cassette  162  and transfers them into a loading module, which loads each substrate  166  onto a single substrate carrier  156 . In an alternative embodiment the carriers are double substrate carriers, in which case the loading module loads two substrates at a time. Thereafter the carrier  156  and substrate  166  are moved into elevator  160  and raised to the second level to begin traversing the plurality of processing chambers  140 , each of which operating in vacuum environment and is isolated from other processing chambers during processing. The motion of the carrier  156  is shown by the arrows. Once processing is completed, the substrate  166  is removed from the carrier  156  and is placed in the cassette  162  by knife blade  168 . The cassette then exists from the other side of loading chamber  170  on a second set of tracks. An example of such a system is disclosed in U.S. Pat. No. 6,919,001, which is commercially available under the trademark 200 Lean® for fabrication of, e.g., hard disk used in hard disk drives. 
     Another system for disk fabrication brings the cassettes into a vacuum environment. In such system, a front end module is maintained in vacuum, and a loadlock permits transporting a cassette carrying, e.g., 25 substrates into the vacuum environment. A secondary vacuum chamber may be provided, wherein a buffer station supporting the 25 substrates is stationed between two robots. The first robot transfer the 25 substrates from the cassette to the buffer station, and a second robot transfers the substrates onto carriers. The carriers may be single or double substrate carriers. As can be understood, having the cassettes travel into a vacuum environment necessitates a rather large gate valve and either a large pump or long pumping period, which slows the system. Also, since the cassette travels over tracks, particles may be generated, which may be brought into the vacuum environment when the cassette travels into the vacuum chamber. Such particles can introduce unwanted defects. Also, since the cassettes travel in atmospheric environment, the cassettes and substrates tend to absorb a lot of water vapor, which then is brought into the vacuum environment and needs to be pumped out. This is especially true for cassettes made of plastic material. Moreover, the secondary chamber housing the two robots and the buffer station must be constructed to be rather large, which requires long pumping time to maintain vacuum environment. An example of such a system is illustrated in U.S. Pat. No. 6,319,373. 
       FIG. 2  illustrates a prior art system wherein a front end system  260  includes provisions for supporting cassette  262  containing a plurality of substrates  266 . The front end  260  maintains therein a clean atmospheric environment. A robotic arm  268  removes substrates  266 , one by one, from the cassette  262  and transfers them into a loadlock  270 . Mainframe system  272  maintains therein a vacuum environment and includes therein a transfer robot arm  274 , operating in the vacuum environment. The robot arm  274  removes substrates  266 , one by one, from loadlock  270  and transfer each substrate  266  to one of processing chambers  276   a - 276   e . Notably, substrates  266  cannot be transferred from one of processing chambers  276  to another one, without first going through main frame  272 , which drastically slows processing throughput in such architecture. Once processing is completed, the substrate  166  is removed from the processing chamber by the arm  274  and is placed in the loadlock  270 , to be removed by robot arm  268  and placed in the cassette  262 . Several examples of such an architecture are disclosed in U.S. Pat. No. 5,844,195, which also discloses systems transporting two wafers in tandem. 
     The prior art systems suffer from the problem of synchronizing transport time, vacuum pumping time, and process time. That is, when a substrate is moved from atmospheric condition into vacuum condition, a loadlock or transfer chamber is used together with a vacuum pump to evacuate the air entering the chamber during the transfer of the substrate. However, transporting the substrate and pumping the chamber into a vacuum environment may take considerable time, such that it slows the throughput of the entire system. 
     SUMMARY 
     The following summary of the invention is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
     The subject invention aims to solve the problems present in the prior art. According to aspects of the invention, introduction of substrates into vacuum environment is accomplish by gradually reducing the number of substrates being transferred simultaneously as the clean and evacuated environment is progressed. In embodiments of the invention the cassettes are maintained in clean atmospheric environment and do not enter the vacuum environment. Several vacuum locks are linearly staggered so as to introduce progressively higher level of vacuum environment. The number of substrates transported through this arrangement is a fraction or a portion of the number of substrates present in each cassette. The staggered vacuum locks lead to a series of processing chambers, wherein a yet smaller number of substrates, e.g., one or two, are transported. 
     According to one aspect of the invention, conventional cassettes are used to transfer plurality of substrates in an atmospheric environment. Multiple-substrate carriers are used to each move a fraction or a subset of the substrates, e.g., five or six substrates, from the cassettes in an atmospheric environment into vacuum environment. Then, single or dual-substrate carriers are used to each transfer one or two substrates among the processing chambers. Once processing is completed, the reverse process takes place, i.e., multiple-substrate carriers are used to move fraction/subsets of substrates from vacuum to atmospheric environment, and then several subsets are placed together into one cassette. The use of multiple-substrate carriers to transfer a reduced number of substrates at once from atmospheric to vacuum environment allows for constructing a relatively small vacuum lock chambers, which allows for relatively slow vent and pump of the vacuum locks since the space needed to be evacuated is rather small. Additionally, it allows for the use of relatively slow actuating load lock valves, which reduces particles and increases meantime between failures and meantime between services. Moreover, since the multi-substrate carriers spend a relatively short time in atmospheric environment, they have little time to absorb water vapor, so that the amount of vapor entering the loadlock system in each cycle is very small and can be easily pumped out. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
         FIG. 1  illustrates a system according to the prior art; 
         FIG. 2  illustrates another system according to the prior art; 
         FIG. 3  is a simplified schematic illustrating a processing system in accordance with an embodiment of the invention; 
         FIG. 4  is a top view of the front end module and the buffer module according to an embodiment of the invention. 
         FIG. 5  illustrates an embodiment of a loading station. 
         FIG. 6  illustrates another embodiment of a loading station. 
         FIG. 7  illustrates a multi-substrate carrier according to an embodiment of the invention. 
         FIG. 8  is a flow chart of a loading process according to an embodiment of the invention. 
         FIG. 9  illustrates a process carrier that can be used in the system of  FIG. 3  for simultaneously processing two substrates. 
         FIG. 10  illustrates another embodiment of a system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description will now be given of embodiments of the invention for introducing substrates into vacuum environment of a substrate processing system.  FIG. 3  is a simplified schematic illustrating a processing system in accordance with an embodiment of the invention. The system of  FIG. 3  includes a plurality of processing chambers  340  arranged linearly and stacked one row above the other. A carrier elevator  380  is provided at the end of the stacked processing chambers. At the front of the stacked chambers are front end module  360  and substrate loading module  370 . Front end module  360  has tracks  364  upon which cassettes  362  are transported in atmospheric environment, so as to deliver substrates  366  to the system. However, unlike the prior art system of  FIG. 1 , this embodiment further includes buffer module  390 . Buffer module  390  includes a series of vacuum locks—here only two are shown, i.e.,  392  and  394 , but the number of vacuum locks can be changes as necessary. Multi-substrate carriers  396  transport substrates within the vacuum locks and between the vacuum locks and the atmospheric environment of front end unit  360 . 
     In operation, each of cassettes  362  transports a plurality of substrates  366 , e.g., 25 substrates per cassette, to and from the front end unit  360 . At each cycle, robot arm  368  transfers a subset of the substrates  366  from the cassette  362  onto one of the multi-substrate carriers  396 . For example, each of the multi-substrate carriers may carry only four, five or six substrates. The multi-substrate carrier  396  then transports the subset of substrates through the vacuum locks,  392 ,  394 , so as to introduce the substrates into a vacuum environment. In this embodiment, each successive vacuum lock  392 ,  394 , introduces a higher vacuum environment, so that the substrates go from atmospheric environment to high vacuum environment in gradual steps. Vacuum locks  392 ,  394 , may include vapor removal system, such as Meissner trap, etc. 
     The carrier then moves into the substrate loading station  370 , where each substrate is loaded individually onto a single-substrate carrier. Thence, the carrier transports the substrate for processing in the top row of processing chambers  340 , moves to the lower row via elevator  380 , and then traverses the lower row of processing stations  340 . The carrier then moves back into the loading station  370 , wherein the substrate is removed from the carrier and is placed, together with several other substrates in a multi-substrate carrier  396 . The multi-substrate carrier  396  is then moved through another series of vacuum locks so as to remove the substrates from vacuum environment and into an atmospheric environment of the front end unit  360 . At the front end the robot arm  368  unloads the substrates from the multiple-substrate carrier and into the cassette. 
       FIG. 4  is a top view of the front end module and the buffer module according to an embodiment of the invention. Cassettes  462 A-C travel on conveyor  464  in a clean atmospheric environment. Loading arm  468 A removes a subset of the substrates that are in approaching cassette  462 A. For example, approaching cassette  462 A may hold 25 substrates, while loading arm  468 A may remove a subset of the 25 substrates, e.g., only 3, 4, 5, etc. An empty multi-substrate transport carrier  496 A, stationed on turn table  498 , accepts the subset of substrates from loading arm  468 A. Then the now loaded multi-substrates transport carrier  496 A enters the first of vacuum locks  492 A, passing gate  452 A. In this embodiment, three loading vacuum locks,  492 A-C, are utilized, so as to form a graduated vacuum lock system. Each or any of vacuum locks  492 A-C may include vapor removal system, such as Meissner trap, etc. Also, in this embodiment each of the vacuum locks  492 A-C includes a linear motor therein, so as to transport the multi-substrate carrier  496 . Also, gate valves  452 A-D are provided to isolate the vacuum lock from the environment and from each other. 
     Once the carrier exits vacuum lock  492 C, it enters loading station  470 . In load station  470  the substrates are removed from the multi-substrates carrier  496 A and loaded onto a waiting station  472 , which has the same capacity as multi-substrates carrier  496 A. Carrier  496 A is then moved to unload station  471 , in which processed substrates have been placed onto a waiting station  473 . The processed substrates from waiting station  473  are then loaded onto the empty carrier  496 A, upon which the carrier starts traversing the unloading vacuum locks  494 C-A, so as to gradually in a step-wise fashion introduce the processed substrates into an atmospheric environment. The carrier then exits the vacuum lock  494 A onto the turntable  498 , which is designated as carrier  496 B in  FIG. 4 . An unloading arm  468 B then transfers the group of wafers, all at once, onto the cassette  462 C. The turn table  498  then rotates so as to place the now empty carrier  496 B in the loading position ( 496 A) to receive fresh substrates from the cassette  462 A. Also, gate valves  454 A-D are provided to isolate the vacuum lock from the environment and from each other. 
     Meanwhile, the substrates from the waiting station  472  are loaded, one by one, onto single-substrate process carriers at loading station  470 . It should be noted that while a single-substrate process carrier is shown in  FIG. 4 , a dual-substrate carrier may also be used. However, the number of substrates that can be loaded onto the process carrier is less that that which can be loaded onto the transport carrier. Each process carrier transports its substrate through all of the processing stations and then exits into unload station  471 , wherein the substrate is unloaded from the process carrier and placed onto the multiple-substrate waiting station  473 . 
       FIG. 5  illustrates an embodiment of a loading station, such as the loading station  470  of  FIG. 4 . Multi-substrate transport carrier  552  is shown positioned on turn table  599  and holding four substrates  566 . An elevator  502  travels down for removing the substrates  566  from the carrier  552 , and then moves up to deliver these substrates to preload mechanism  512  (here shown holding three substrates for illustration purposes, but in operation when the elevator  502  delivers substrates to the preload  512 , the preload  512  is empty). Preload mechanism  512  transfers substrates, one by one, onto single-substrate process carrier  596 , positioned in loading chamber  522 . It should be appreciated that the processing system may include a mirror unloading station that is constructed and operates the same as loading station shown in  FIG. 5 , except that the preload mechanism  512  removes processed substrates from single-substrate process carrier  596 . When preload mechanism  512  collected sufficient number of substrates, the elevator  502  removes these substrates and load them onto a multiple-substrate transport carrier  552 . 
       FIG. 6  illustrates another embodiment of the loading station. This embodiment is similar to that of  FIG. 5 , except that elevator  602  does not remove substrates from carrier  652  (shown positioned on turn table  699  and holding four substrates  666 ). Instead, carrier  652  is made of two parts: a base having the wheels and motive elements, and a removable part which supports the substrates. The elevator  602  includes a fork mechanism  604  structured to engage and remove the removable part of carrier  652  and carry it up to the preload mechanism, wherein the substrates are transferred to the preload mechanism; after which the elevator lowers the removable part back to its seat on the base. Preload mechanism  612  transfers substrates  666 , one by one, onto single-substrate process carrier  696 , positioned in loading chamber  622 . 
       FIG. 7  illustrates a multi-substrate transport carrier according to an embodiment of the invention. This embodiment can be beneficially utilized in the loading station of either  FIGS. 5 and 6 , but is most suitable for the embodiment of  FIG. 6 . The multi-substrate transport carrier  752  is composed of a base  710  and a removable substrate support part  720 . The substrate support part  720  can be attached to the transport part  710  using mechanical means, e.g., clips, or by magnets. Alignment pins (obscured in  FIG. 7 ) can be used to ensure consistent alignment of the substrate support part  720  on base  710 . Base  710  has wheels  730  which ride on tracks positioned in the various chambers and turntables. To avoid slippage the wheels may be magnetized. Base  710  also includes motive means. In this embodiment, the motive means is a linear motor, for which magnets  750  are placed on the base  710 , while the remaining parts of the linear motor are placed in the various chambers and turn tables, together with the tracks. The substrate support part  720  includes support arms  740  having support cylinders  742  attached at the end thereof. The support cylinders  742  may be formed by making grooves in cylinders made of DuPont® Vespel® to avoid particles contamination. A third support cylinder can be positioned at the bottom of the support part  720 . The support part  720  may also include holes  760  for engaging the lift fork  604 . Further, for stability, magnetic forces can be used to hold the detachable substrate support part  720  on the lift fork  604 . That is, the magnets used to stabilize the support part  720  over the base  710  may also be used to stabilize the support part  720  on the lift fork  604 . Alternatively, magnets can be included on the lift fork  604 , in which case ferromagnetic material should be included on the support part  720 . 
       FIG. 8  is a flow chart of a loading process according to an embodiment of the invention. At step  800  a loading arm removes several substrates from a load cassette. For example, load cassette may have 25 fresh substrates and load arm may remove five of them. The unload arm removes the substrates from a multi-substrate carrier having processed substrates thereon. At step  810  load arm rotates and places its substrates in the empty load carrier. The unload arm rotates and places the processed substrates in the unload cassette. At step  820  the loaded carrier moves through the first shutter and into the first rough vacuum chamber. From here, independently of the process of this flow chart, the carrier will progress through the series of vacuum locks until it reaches the turn table on the other side of the system and its wafers will be unloaded, upon which it will traverse the vacuum chambers in the other direction to return as an empty carrier. Meanwhile, at step  830  the turn table rotates so as to place the now empty carrier in a loading position. The process then repeats itself. 
     In the system of  FIG. 3  the process carrier is illustrated as carrying a single substrate which may be processed on both sides. For example, when the system is used for fabricating disks for hard disk drives, processing is performed on both sides of the disk, since both faces of the disk are used for data storage. On the other hand, the system may be used for processing other substrates, e.g., solar cells. In such a case, the substrate needs to be processed only on one side thereof.  FIG. 9  illustrates a process carrier that can be used in the system of  FIG. 3  for simultaneously processing two substrates, each on one side thereof, such that the throughput of the system can be doubled. 
       FIG. 9  illustrates a process carrier, which may be similar to that shown in  FIG. 4A  of the above-noted U.S. Pat. No. 6,919,001. The carrier  952  has a base  910  having wheels  930  and magnets  950 . The substrates are supported by arc  940 , which has clips  942  to hold the substrates at the periphery only. In this manner, the entire surface of the substrate is exposed for processing. As illustrated in  FIG. 9 , two substrates,  966 A and  966 B are held by clips  942 , facing back to back. In this manner, when the carrier enters a processing chamber, the front surfaces of both substrate are processed simultaneously. 
       FIG. 10  illustrates another embodiment of a system according to an embodiment of the invention, which enables simultaneous processing of two substrates, each on both surfaces. Alternatively, it can be used to process fours substrates simultaneously, each on one surface only, by supporting the substrates back to back, as in the embodiment of  FIG. 9 . In  FIG. 10  the processing system itself is only suggested by phantom lines, as it is identical to that disclosed in the above noted U.S. Pat. No. 6,319,373. On the other hand, the front loading part is implemented according to an embodiment of the invention, wherein the number of substrates being transported is reduced, as the level of vacuum is increased. 
     As illustrated in  FIG. 10 , a conveyor  1064  is used to transport cassettes in a clean atmospheric environment. The system has loading module  1005  and unloading module  1010 , which are similar, but which operate in opposite direction to each other. The loading module  1005  has a three stage staggered vacuum lock, having three vacuum chambers  1092 A-C and corresponding gates  1052 A-D. Tracks and linear motors  1020  are provided in each vacuum chamber so as to enable transport of carriers  1096 A-D. Carriers to be loaded, i.e.,  1096 A and  1096 B are positioned on loading station  1098 A, which may or may not include a turn table (shown in broken line), while carriers to be unloaded are positioned on unloading station  1098 B, which also may or may not include a turn table. 
     Fresh substrates arriving on cassettes  1062 A and  1062 C are loaded onto transport carriers  1098 A and  1098 B by arms  1068 A and  1068 B. The number of substrates loaded is smaller than the total number of substrates held in each cassette. For example, each cassette may holds 25 substrates, and each transport carrier may hold five substrates. Once the transport carriers  1098 A and  1098 B are loaded, they are transported on the tracks  1020  so as to successively progress through the staggered vacuum locks until they reach loading turntables  1030 . At turntable  1030  a robot arm  1040  removes one substrate from each transport carrier  1096 A and  1096 B and loads the two substrates onto a processing carrier  1050  in tandem, one behind the other. This loading of processing carriers is repeated until all of the substrates have been removed from the transport carriers  1096 A and  1096 B. 
     Once all of the substrates have been removed from transport carriers  1096 A and  1096 B, the carriers  1096 A and  1096 B are moved to unload turntables  1035 . There, robot arm  1045  removes substrates from tandem-substrate carriers  1055 , and places the substrates onto transport carriers  1096 A and  1096 B. Once transport carriers  1096 A and  1096 B are fully loaded, turntables  1035  rotate to align with the tracks  1020 , so that carriers  1096 A and  1096 B be transported in successively reduced vacuum conditions in vacuum chambers  1094 C-A until they emerge onto unloading station  1098 B. At unload station  1098 B arms  1068 C and  1068 D remove the substrates from the carriers  1096 A and  1096 B and place the substrates onto cassettes. Once the substrates have been removed from transport carriers  1096 A and  1096 B, the carriers can be removed from the system for cleaning or be transported to load station  1098 A. To transfer the carrier from unload station  1098 B to load station  1098 A, the station may include a turntable and tracks with linear motors may be provided between the two stations, as shown in broken lines. 
     It should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations will be suitable for practicing the present invention. 
     The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of will be suitable for practicing the present invention. Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.