Abstract:
Methods and apparatus for ensuring the proper handling of reticles in the manufacturing of microdevices are disclosed. The methods and apparatus employ one or more reticle stop blocks fixed to a reticle handling arm. The one or more reticle stop blocks are designed and arranged to engage an edge of the reticle in order to place the reticle in a desired position on the reticle handling arm should the reticle be improperly arranged in a cassette in which the reticle is stored. By ensuring proper placement of the reticle on the reticle handling arm when the reticle is removed from the cassette, the likelihood of a subsequent fault in handling the reticle is greatly reduced.

Description:
This application is a continuation of U.S. patent application Ser. No. 09/894,482, filed Jun. 28, 2001 now U.S. Pat. No. 6,630,988 which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to photolithography, and in particular to methods and apparatus for ensuring proper handling of reticles in photolithography systems. 
   BACKGROUND OF THE INVENTION 
   The manufacture of certain types of microdevices, such as semiconductor integrated circuits, flat-panel displays, ink-jet heads and the like, involves the process of photolithography and hence the use of photolithography systems, also called “photolithography tools.” Photolithography tools are designed to project an image of a finely patterned mask (“reticle”) onto a photosensitive substrate. The reticle typically includes a pellicle, which is a thin membrane displaced from the patterned side of the reticle by a frame. The pellicle serves to keep dust and other particulates off of the patterned surface that would otherwise be imaged onto the substrate. After the substrate is exposed, it is processed to create a desired structure based on the imaged pattern. 
   The manufacturing process typically involves repeating the photolithography and process steps using different reticles in order to build up the device. Accordingly, photolithography tools typically include (or are operatively coupled with) an automatic reticle handling system to facilitate the rapid loading and unloading of reticles to and from the tool. 
   Reticles are fragile and thus are always contained inside a protective plastic case called a “cassette” until extracted by the reticle handling system. In the reticle handling operation, multiple reticles in their respective cassettes are manually loaded into a reticle library within the photolithography tool. A first reticle handler then inserts a reticle handling arm into a particular cassette to engage the reticle therein. Once engaged, the reticle is then transferred to a second reticle handler, which aligns and delivers the reticle to another location, such as a reticle stage or a pellicle inspection station (e.g., a pellicle particle detector or “PPD”) within the photolithography tool. 
   In many photolithography tools, successful transfer of a reticle from the cassette into its proper position in the tool requires that the reticle be properly positioned on the first reticle handler. Otherwise, the transfer (“handoff”) between the first and second reticle handlers can be faulty. 
     FIG. 1  illustrates a prior art reticle handling system that includes a reticle handling arm  2  that is part of a first reticle handler. The reticle handling arm is in communication with a reticle carrier  4  that is part of a second reticle handler. Reticle carrier  4  includes translatable lifting brackets  6  that are adapted to engage a reticle  8  residing on reticle arm  2  and to lift the reticle from the reticle handling arm. 
   If the reticle is not properly positioned on the reticle handling arm, the lifting brackets can jam against the reticle, as shown, when attempting to engage the reticle. This can damage the reticle and/or the reticle handling arm, and/or can jam the reticle handling system, thereby causing a system failure. 
   The consequences of faulty reticle handling can be financially serious. A jammed reticle stops production, requires expert man-hours to repair, and can damage the reticle handling system and/or the reticle itself. Reticles are relatively expensive, so that having to replace a reticle damaged by faulty handling adds cost to the manufacturing process. Accordingly, it is important in microdevice manufacturing to take appropriate steps to ensure that the likelihood of reticle handling faults is minimized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side view of a prior art reticle handling system having a first reticle handling arm and a reticle carrier with translatable lifting brackets, illustrating how incorrect positioning of the reticle on the reticle handling arm can result in a reticle handling fault, such as a jammed reticle as shown; 
       FIG. 2A  is a schematic block diagram of a photolithography tool in combination with a reticle handling system according to the present invention that includes a reticle library, a first reticle handler, and a second reticle handler; 
       FIG. 2B  is a close-up cut-away side view of the reticle library of  FIG. 2A  showing two of the plurality of cassettes stored in the library, with a reticle in each of the shown cassettes; 
       FIG. 3A  is a plan view of an exemplary two-support-arm reticle handling arm as part of the first reticle handler of  FIG. 2 , showing a reticle supported by the two support arms and a reticle stop block on each support arm, wherein the reticle stop blocks serve to place the reticle at a desired position on the support arms; 
       FIG. 3B  is a cross-sectional view of  FIG. 3A  taken along the line  3 B— 3 B; 
       FIG. 3C  is a plan view similar to that of  FIG. 3A , but showing another example embodiment of the present invention comprising a single reticle stop block attached to the base portion of the reticle handling arm; 
       FIG. 4A  is a plan view of a reticle stop block as shown in  FIG. 3A  illustrating an example embodiment of a reticle stop block that slides over a support arm of the reticle handling arm and that can be fixed to the support arm using a set screw; 
       FIG. 4B  is a cross-sectional view of the reticle stop block of  FIG. 4A ; 
       FIG. 5A  is a side view of the reticle handling arm and the exemplary reticle stop block of  FIGS. 4A and 4B  prior to the reticle being engaged by the translatable lifting brackets of a reticle carrier; and 
       FIG. 5B  is the same side view as  FIG. 5A  subsequent to the reticle being successfully engaged and lifted by the translatable lifting brackets of the reticle carrier, in contrast to the prior art faulty reticle transfer due to reticle misplacement on the reticle handling arm as illustrated in FIG.  1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention relates to photolithography, and in particular to methods and apparatus for ensuring proper handling of reticles in photolithography systems. 
   In the following detailed description of the embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
   With reference now to  FIG. 2A , there is shown a photolithography tool  12  that includes, in order along an axis A, an illumination system  14  and a reticle stage  20  adapted to support a reticle  26  so that it can receive illumination from the illumination system. Reticle  26  includes an upper surface  28 , a lower surface  30  with a pattern  32  formed thereon, and edges  34 . Reticle  26  is, in an example embodiment, made of glass, such as quartz or fused silica. Pattern  32 , in exemplary embodiments, is opaque and made of chrome, a transparent dielectric, or a combination of the two. Reticle  26  typically includes a pellicle  36  arranged adjacent lower surface  30  and covering (but displaced from) pattern  32 . Pellicle  36  is typically formed by stretching an optically neutral polymer over a frame. 
   Further included in photolithography tool  12  along axis A is a projection lens  42 , and a substrate stage  52  that supports a substrate  60  to be processed. Substrate stage  52  supports substrate  60  such that an image of pattern  32  is formed on the substrate during illumination of the reticle. 
   With continuing reference to FIG.  2 A and also to  FIG. 2B , operatively coupled to photolithography tool  12  is a reticle handing system  70  that includes a reticle library  80  that is capable of containing a plurality of cassettes  82  each of which contains a reticle  26 . In an exemplary embodiment of the present invention, reticle library  80  is within photolithography tool  12 . Reticle library  80  includes an open (or openable) side  84  that allows access to cassettes  82  and reticles  26 . 
   Reticle handling system  70  also includes a first reticle handler  86  in operative communication with reticle library  80  to engage and receive reticles stored therein, and a second reticle handler  90  in operative communication with the first reticle handler and reticle stage  20  to engage and receive reticles on the first reticle handler and deliver them to the reticle stage or another location. For example, in addition to reticle handling system  70 , an inspection station  96  may be provided so that reticle  26  can be transferred thereto by second reticle handler  90  and inspected prior to being transferred to photolithography tool  12  and reticle stage  20 . Inspection station  96  may be, for example, a pellicle inspection device such as a pellicle particle detector (“PPD”). Further, second reticle handler  90  may include two or more reticle handling arms (not shown) that are in operate communication with a reticle carrier (described below) to facilitate the transfer of reticle  26  to inspection station  96  or reticle stage  20 . 
   With reference now to  FIGS. 3A and 3B , first reticle handler  86  includes, in an example embodiment, a reticle handling arm  200  having two spaced apart elongate support arms (“arms”)  202  each having an upper surface  206 . Arms  202  extend horizontally outwardly from a base portion  210  and are preferably parallel and spaced apart by a distance sufficient to accommodate pellicle  36  between them when reticle  26  is engaged, received and supported. In an exemplary embodiment, arms  202  and base portion  210  are flat so that reticle handling arm  200  can be easily inserted into cassette  82  in reticle library  80  and other areas of reticle handling system  70 . 
   Base portion  210  is connectable to a motor assembly (not shown) included as part of first reticle handler  86  and that provides the necessary movement of arm  200  for reticle handling. Vacuum lands  220 , connected to respective vacuum lines (not shown), are included on upper surface  206  of each arm  202  and are used to secure reticle  26  to arm  200  by providing a vacuum seal to select areas of reticle lower surface  30  once the reticle is arranged in a desired position on the handling arm. In an exemplary embodiment of the present invention, handling arm  200  is made of aluminum and vacuum lands  220  are made of teflon or conductive plastic. 
   With continuing reference to  FIGS. 3A and 3B , reticle handling arm  200  also includes one or more reticle stop blocks  250  each having a side edge  256 . In an example embodiment, two reticle stop blocks  250  are used, with one stop block fixed to each arm  202  near base portion  210 . Reticle stop block  250  is, in an example embodiment, made of an electrostatic dissipative material such as a polymer, e.g., polypropylene, polystyrene, polysilicon, polytetrafluoroetylene (“TEFLON”), etc. 
   With reference now to  FIG. 3C , in another example embodiment of the present invention, a single reticle stop block  250  may be attached to base portion  210  between arms  202 , with a portion of the block extending outward to a fixed distance in the direction parallel to arms  202 . Reticle stop block  250  in this example embodiment may be formed from a block of material, such as a block of polymer, or machined from stock, such as polymer stock. Reticle stop block  250  is then affixed to base portion  210  by a set screw, adhesive or other known affixing techniques so that side edge  256  engages reticle edge  34  to define a desired position of the reticle on reticle handling arm  200 . 
   With reference now to  FIGS. 4A and 4B , an exemplary reticle stop block  250  of the present invention is shown. A preferred method of forming reticle stop block  250  of  FIGS. 4A and 4B  involves slicing a section (e.g., about 0.5″) of ⅜″ polymer (“poly”) rod stock and forming a threaded bore  260  through the centerline  264 . The method further includes forming a through bore  270  through side edge  256 , the bore being sized to accommodate arm  202  and vacuum lands  220 , if present. A set screw  272  is then used to fix the position of reticle stop block  250  on arm  202  once the block is slid over the arm and positioned in the desired location along the arm. The desired location is that which results in the reticle residing in a desired position on arms  202  after being engaged by reticle handling arm  200 , as discussed further below. 
   It will be apparent to one skilled in the art that any number of techniques, such as the use of adhesives, can be used to fix reticle stop block  250  to arm  200 . Moreover, reticle stop block can be essentially any geometrical shape. In an example embodiment, reticle stop block  250  has a height H that is less than the thickness of reticle  26  so that the reticle stop block does not protrude above upper surface  28  of reticle  26 , to ensure proper clearance when loading and unloading reticles to and from cassette  82  in reticle library  80  (FIG.  2 B). 
   With reference again to  FIGS. 3A and 3B  and also to  FIGS. 2A and 2B , when a particular reticle  26  needs to be loaded onto reticle stage  20  of photolithography tool  12 , reticle handling arm  200  is inserted into open side  84  of library  80  and into cassette  82  to engage and receive the reticle. 
   In the absence of reticle stop block(s)  250 , the x-position of reticle  26  on reticle handling arm  200  may, in some reticle handling systems, be dictated by the position of reticle  26  in cassette  82 . Thus, if a reticle is not fully inserted into cassette  82  or is otherwise not properly arranged therein, the x-position of the reticle on the reticle handling arm will not be correct, i.e., will not be located at the desired position. The desired position, as mentioned above, is one that allows for the successful transfer of the reticle from first reticle handling system  86  to second reticle handling system  90 . Arrangement of the reticle in a position other than the desired position can result in a faulty transfer of the reticle from first reticle handling system  86  to second reticle handling system  90 , with the negative consequences mentioned above and illustrated in  FIG. 1  with respect to the prior art reticle handling system. 
   Accordingly, in the present invention one or more reticle stop blocks  250  are positioned on reticle handling arm  200  such that when the reticle handling arm is inserted into cassette  82  to engage reticle  26 , reticle edge  34  makes contact with side edge  256  of the one or more stop blocks. This moves (e.g., pushes) the reticle to a desired x-position on arms  202 , the desired position being selected to ensure successful transfer of the reticle to second reticle handler  90 , as described below. If reticle  26  is properly positioned in cassette  82 , then reticle edge  34  will not touch side edge  256  of the one or more reticle stop blocks  250  during reticle engagement as the reticle adopts the desired position without the assistance of the one or more reticle stop blocks. 
   With reference now to  FIGS. 5A and 5B , once reticle  26  is properly loaded onto reticle handling arm  200 , the arm transports the reticle to second reticle handler  90 . The latter includes a reticle carrier  400  having a platen  402  that is connectable to a motor assembly (not shown) included as part of second reticle handler  90  and that provides the necessary movement of reticle carrier  400  for reticle transfer. Platen  402  has a lower surface  404  from which extends opposing translatable lifting brackets  408  (also called “fingers”). Lifting brackets  408  are designed to separate (open) to capture reticle  26  and then close to engage the captured reticle so that it can be lifted from reticle handling arm  200 . 
   Again, in the absence of reticle stop blocks  250 , there is a chance that a misalignment of the reticle on reticle handling arm  200  relative to the desired position will cause fingers  408  to forceably contact the reticle, (e.g., jam into upper surface  28 , as shown in  FIG. 1 ) and damage the reticle and/or cause a reticle jam. 
   Once reticle  26  is properly transferred to reticle carrier  400 , the reticle is then carried by the reticle carrier over to a second location. The second location may be, for example, reticle stage  20  in photolithography  12 . Alternatively, the second location may be inspection station  96 , such as a pellicle inspection device (e.g., a PPD), and then moved to reticle stage  20  after inspection. The reticle, once positioned in reticle stage  20 , is then exposed by photolithography tool  12  to pattern substrate  60  in the formation of a microdevice, as described above in connection with FIG.  2 . 
   In an alternative embodiment, reticle handling arm  200  transports reticle  26  to inspection station  96 . This is accomplished by reticle arm  200  delivering reticle  26  to reticle carrier  400 . The vacuum applied via vacuum lands  220  is then released so that reticle  26  is free to move relative to arms  202 . Fingers  408  of reticle carrier  400  are then positioned about reticle  26  and closed. This accurately positions reticle  26  on reticle handling arm  200  prior to the reticle being delivered to the inspection station by the reticle handling arm. Again, if proper initial alignment of reticle  26  on reticle handling arm  200  is not achieved prior to the fine alignment performed by reticle carrier  400 , then there is the aforementioned risk of damage to the reticle when engaged by the reticle carrier. 
   Conclusion 
   The present invention includes apparatus and methods that utilize one or more reticle stop blocks in the automated handling of reticles. The one or more reticle stop blocks are positioned on a reticle handling arm for ensuring the proper positioning of a reticle thereon. Such positioning ensures the successful transfer of the reticle from the reticle handling arm to a reticle carrier so that the reticle can be successfully loaded into a photolithography tool. The use of reticle stop blocks will, for certain reticle handling systems, result in a reduced likelihood of reticle handling faults, which can damage the reticle and/or jam the reticle handling system or phototool, and which can also stop the manufacturing process. The present invention offers a simple and elegant solution to the problem of faulty reticle handling in certain reticle handling systems used in conjunction with photolithography tools. 
   While the present invention has been described in connection with preferred embodiments, it will be understood that it is not so limited. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims.