Abstract:
A method and apparatus for cleaning, rinsing and drying a reticle used in semiconductor device manufacturing, tilts the reticle during the drying process to prevent water from the rinsing process from collecting and remaining on the reticle. The rectangularly shaped reticle is held in a carrier and the top and bottom edges of the reticle may form an angle of at least about 8° with the horizontal to maximize drying efficiency, when the carrier is placed on a horizontal surface or suspended from above.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a method and apparatus for cleaning and drying a reticle used in the production of semiconductor integrated circuits.  
       BACKGROUND  
       [0002]     Reticles are used in the semiconductor device manufacturing process and are typically formed of a quartz substrate with an opaque pattern formed on one of the surfaces of the quartz substrate. The opaque pattern is generally formed of chrome. The reticle is generally thin, flat and rectangular in shape. Reticles are used to produce patterns of very small dimensions on semiconductor substrates. The patterns may include device features with dimensions in the nanometer range. It is therefore important to keep the reticle very clean because any foreign contamination on the reticle can produce an irregular or distorted pattern. Several reticles are required to produce a single semiconductor device which includes multiple device levels. Since a pattern irregularity due to a dirty reticle at any level of device processing can cause device failure, it is even more critical to maintain each of the several reticles in clean condition to maximize device yield.  
         [0003]     Many techniques are used for cleaning reticles and most of these techniques include disposing the reticle in a cleaning solution then rinsing the cleaning solution from the reticle. After the reticle is rinsed, a drying operation takes place. A shortcoming of the present technology is that the rectangular reticles are transported from station to station and then allowed to dry in carriers that orient the reticle with its opposed upper and lower edges essentially in a horizontal position. In conventional reticle carriers, this is true when the carrier is placed on a flat horizontal surface and also if the carrier is suspended from above. When the reticle dries in such a horizontal configuration, the rinsing liquid, typically deionized water, will remain on the top edge of the reticle as well as along the bottom edge of the reticle. When allowed to dry in the ambient air of a semiconductor device fabrication facility, the deionized water remains on the top edge and bottom edge of the horizontally positioned reticle, even after 30 minutes of drying. This residual deionized water is undesirable because it can potentially move to the surface of the reticle, distorting the pattern, when the reticle is eventually maneuvered. If a turbulent airflow is used to remove the residual water, the turbulent airflow itself and/or the disbursing deionized water can result in particles or water droplets on the reticle surface and these particles or water droplets can cause pattern defects and device failure.  
         [0004]     It would therefore be desirable to provide a reticle cleaning and drying method and apparatus that cleans and dries the reticle without leaving contaminating particles or residual water.  
       SUMMARY OF THE INVENTION  
       [0005]     To address these and other objects and in view of its purposes, the invention provides a method for wet processing and drying a reticle. The method includes providing a substantially flat and rectangular reticle that is wet and drying the reticle by orienting a bottom edge of the reticle at an angle of at least about 8° with the horizontal.  
         [0006]     In another aspect, the invention provides a reticle drying apparatus comprising a carrier that holds a rectangular and flat reticle such that a bottom edge of the reticle forms an angle of at least 8° with the horizontal when the carrier is suspended from a carrier handle.  
         [0007]     In a further aspect, the invention provides a reticle drying apparatus with at least a first bath that contains a cleaning liquid, a second bath with a rinsing liquid, and means for mechanically transporting a reticle out of the second bath in a carrier that positions a bottom edge of the reticle at an angle of at least about 8° with the horizontal when the carrier is suspended from a handle. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]     The invention is best understood from the following detailed description when read in conjunction with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not necessarily to scale. On the contrary, the dimensions of the various features are arbitrarily or expanded or reduced for clarity. Like numerals denote like features throughout the specification and drawing. Included in the drawing are the following figures.  
         [0009]      FIG. 1  is a side and perspective view showing a carrier holding a reticle according to an embodiment of the invention;  
         [0010]      FIG. 2  is a side and perspective view of another embodiment of a carrier holding a reticle according to the invention;  
         [0011]      FIG. 3  is a side and perspective view showing a reticle, held by an exemplary carrier, being processed in a bath, according to the invention; and  
         [0012]      FIG. 4  is a side view showing a tilted reticle drying. 
     
    
     DETAILED DESCRIPTION  
       [0013]     The invention provides a carrier that holds a reticle such that the bottom edge of the rectangularly shaped reticle forms an angle of about at least 8 to 10° with the horizontal. The carrier may be used for transporting the reticle between wet cleaning and rinsing operations, it may be used to hold the wafer during the wet cleaning or rinsing operations and it is advantageously used for subsequent drying processes.  
         [0014]      FIG. 1  shows an exemplary reticle  2  held within carrier  10 . Reticle  2  is flat and rectangular in shape and includes opposed top edge  4  and bottom edge  6  as well as opposed side edges  8 . Conventional reticles used in the semiconductor manufacturing industry may include an opaque pattern formed on a substrate. The substrate is typically formed of quartz but other transparent materials such as soda lime, borosilicate glass, or fused silica may be used as the substrate. The opaque pattern is typically formed of chrome but other suitable materials may also be used. Carrier  10  may be formed of PFA, polyfluoro alcohol, which is resistant to attack in the acidic and basic cleaning solutions used to clean reticles in various embodiments. In other exemplary embodiments, carrier  10  may be formed of other suitable plastics, PVC, polyvinyl chloride, or other materials chosen in conjunction with the materials that will contact the carrier. Although only one reticle  2  is illustrated as being received within carrier  10  in the side view illustration of  FIG. 1 , carrier  10  may hold a plurality of reticles  2  in the same orientation and they may be aligned behind the illustrated reticle  2 .  
         [0015]     When received within exemplary carrier  10 , reticle  2  rests on a mechanical support or mechanical supports that position bottom edge  6  and top edge  4  at angle  16  with respect to the horizontal indicated by the dashed lines. In one exemplary embodiment, angle  16  is 10° and in other exemplary embodiments angle  16  may range from about 5° to 45°. In one particular exemplary embodiment, angle  16  may be at least about 8°. In another exemplary embodiment angle  16  may be at least about 10° and in yet another embodiment, angle  16  may range from 10° to 15°. In the illustrated embodiment, the mechanical supports are bar  12  and recession  14  that the opposed corners of bottom edge  6  rest upon, but in other exemplary embodiments, other mechanical supports such as a continuous groove may be used to maintain reticle  2  positioned at angle  16  with respect to the horizontal.  
         [0016]     In one embodiment, reticle  2  is maintained at above-described angle  16  with respect to the horizontal when carrier  10 , in particular bottom plane  20  of carrier  10 , is placed on substantially horizontal surface  22 . Bottom plane  20  may consist of a number of discrete support members arranged in a plane or a continuous flat surface. As such, when reticle  2  is held by exemplary carrier  10 , bottom edge  6  is disposed at angle  16  with respect to bottom plane  20 . Carrier  10  also maintains reticle  2  at angle  16  with respect to the horizontal when carrier  2  is suspended from above. For example, when exemplary carrier  10  is suspended in air by means of carrier handle  24  and arm  26 , reticle  2  is maintained at angle  16  with respect to the horizontal. The illustrated exemplary embodiment shows carrier handle  24  aligned in an essentially vertical position and arm  26  generally in a horizontal position. Carrier handle  24  may grasp carrier  10  using various conventional mechanical means. In one exemplary embodiment such as illustrated in  FIG. 1 , carrier  10  may include receptacles  22  that receive a corresponding protuberance from carrier handle  24 .  
         [0017]     Arm  26  may be a robotic arm coupled to movement means  28  which moves robotic arm  26  and therefore carrier handle  24 , carrier  10  and reticle  2 . Movement means  28  may include a motor, software, various mechanical couplings, and a control panel to automatically or manually move carrier  10 . For example, in a wet bench used to clean and rinse reticle  2 , arm  26 , in conjunction with movement means  28 , may move reticle  2  into and out of numerous cleaning baths, rinsing stations, and to a drying position.  
         [0018]      FIG. 2  shows another exemplary arrangement of carrier  50  and carrier handle  54  in which reticle  2  is disposed at angle  16  with respect with to the horizontal (i.e. the dashed line), when carrier  50  is grasped by and suspended from carrier handle  54 . In this exemplary embodiment, bottom plane  52  of carrier  50  is substantially parallel to bottom edge  6  of reticle  2  when reticle  2  is received within carrier  50 . In the illustrated arrangement, carrier handle  54  grasps carrier  50  such that bottom edge  6  and bottom plane  52  are tilted at angle  16  with respect to the horizontal. In the illustrated embodiment, protuberances  56  of carrier handle  54  are received within corresponding recesses  58  of carrier  50  to position reticle  2  at angle  16 . In other exemplary embodiments, other mechanical features may be used so that bottom edge  6  of reticle  2  is disposed at angle  16  with respect to the horizontal when carrier  50  is coupled to carrier handle  54  and suspended. In other exemplary embodiments, angle  16  may be achieved by various combinations of tilting the carrier with respect to the horizontal and tilting reticle  2  with respect to the carrier.  
         [0019]      FIG. 3  shows exemplary carrier  10  and reticle  2  positioned in exemplary bath  34  and also in liquid  36 . In another exemplary embodiment, the exemplary arrangement shown in  FIG. 2 , including carrier  50  and carrier handle  54 , may be used. Bath  34  and liquid  36  may represent any of various cleaning or rinsing operations. In one aspect of the invention, the reticle wet cleaning process may include a two step chemical cleaning process. The first chemical bath may be an H 2 SO 4 /H 2 O 2  bath maintained at 80-90° C. with the sulfuric acid constituting a large majority of the solution. The second chemical bath may include NH 4 OH at about 1% concentration and H 2 O also at about 1% concentration, in DI H 2 O, deionized water, at about 40° C. Other temperatures, other cleaning solutions and other sequences may be used in other exemplary embodiments. Reticle  2  is held by carrier  10  during the cleaning operation or operations and is transported in and out of the cleaning solutions using movement means  28 , arm  26  and carrier handle  24 . The various cleaning solutions such as may be represented by liquid  36 , may be stagnant solutions or they may be dynamic solutions. While in a chemical bath such as exemplary bath  34 , reticle  2  may be maintained at an angle such as angle  16  with respect to horizontal or it may be maintained in various other orientations such as with top edge  4  and bottom edge  6  being essentially horizontal.  
         [0020]     After the chemical cleaning solutions, movement means  28  and arm  26  move carrier  10  and reticle  2  into a rinsing bath. Exemplary bath  34  may alternatively be a rinsing bath. Deionized water is preferred as the rinsing medium, but other rinsing agents may be used. Various rinsing baths may be used. For example, the rinsing bath may include a stagnant solution, or it may be a dump-rinser or cascade rinser. Other methods may be used to create laminar or turbulent flow of the rinsing solution with respect to reticle  2 . Spray nozzles and water jets may be used.  
         [0021]     After a sufficient rinsing time, reticle  2  and carrier  10  are removed from the rinsing bath and reticle  2  is then dried. Carrier  10  holds reticle  2  during the drying process. In one exemplary embodiment, the drying may take place in air with carrier  10  suspended from above such as from arm  26  and in another exemplary embodiment, carrier  10  may be placed on a horizontal surface to dry. In yet another exemplary embodiment, the carrier  50 /holder  54  arrangement shown in  FIG. 2  may be used and the drying takes place with carrier  50  suspended from above such as by arm  26  and carrier handle  54 . The drying may take place in the ambient environment and at the ambient temperature of the production facility or an elevated temperature may be used. In one exemplary embodiment, drying takes place in the unheated calm air of the production facility.  
         [0022]     Reticle  2  is tilted at angle  16  during the drying process. The tilted orientation of reticle  2  during the drying process prevents water from being retained on top edge  4  or bottom edge  6  of reticle  2 .  FIG. 4  shows that any water present on edges  4 ,  6  or  8  of reticle  2  will preferably drip off of reticle  2  at tip  40  and produce a dry reticle free of water droplets and particles. In one embodiment in which DI water was the rinsing agent, applicants have found that the reticle was substantially free of DI water after only 6 minutes of ambient drying.  
         [0023]     The preceding merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principals of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes and to aid the reader in understanding the principals of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principals, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.  
         [0024]     This description of the exemplary embodiments is intended to be read in connection with the figures of the accompanying drawing, which are to be considered part of the entire written description. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.  
         [0025]     Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.