Abstract:
An immersion lithography tool with a diverter element, positioned between the immersion element and the substrate, for altering the “footprint” or shape of the meniscus of the body of immersion liquid between the last optical element and an immersion element on one side, and the substrate on the other side when the substrate is moved. The apparatus includes a substrate holder to hold the substrate having an imaging surface and a projection optical system having a last optical element. The projection optical system projects an image onto a target imaging area on the substrate through the immersion liquid filled in a gap between the imaging surface of the substrate and the last optical element. An immersion element maintains the immersion fluid in the gap. The diverter element is positioned between the immersion element and the substrate. The diverter element alters the footprint shape of the meniscus of the body of immersion liquid, thereby preventing or reducing the amount of leakage from a space between the substrate and the immersion element.

Description:
RELATED APPLICATIONS 
     This application claims priority on Provisional Application Ser. No. 60/907,178 filed on Mar. 23, 2007, the content of which is incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to immersion lithography tools, and more particularly, to an immersion lithography tool with an element, positioned between an immersion element and an object (e.g., a substrate), to prevent or reduce leakage of immersion fluid when the object is moved. 
     2. Related Art 
     A typical lithography tool includes a radiation source, a projection optical system, and a substrate stage to support and move a substrate to be imaged. A radiation-sensitive material, such as resist, is coated onto the substrate surface prior to placement onto the substrate stage. During operation, radiation energy from the radiation source is used to project an image defined by an imaging element through the projection optical system onto the substrate. The projection optical system typically includes a number of lenses. The lens or optical element closest to the substrate is often referred to as the “last” or “final” optical element. 
     The projection area during an exposure is typically much smaller than the imaging surface of the substrate. The substrate therefore has to be moved relative to the projection optical system to pattern the entire surface. In the semiconductor industry, two types of lithography tools are commonly used. With so-called “step and repeat” tools, the entire image pattern is projected at once in a single exposure onto a target area of the substrate. After the exposure, the wafer is moved or “stepped” in the X and/or Y direction and a new target area is exposed. This step and repeat process is performed over and over until the entire substrate surface is exposed. With scanning type lithography tools, the target area is exposed in a continuous or “scanning” motion. The imaging element is moved in one direction, while the substrate is moved in either the same or the opposite direction during exposure. After each scan, the substrate is then moved in the X and/or Y direction to the next scan target area. This process is repeated until all the desired areas on the substrate have been exposed. 
     It should be noted that lithography tools are typically used to image or pattern semiconductor wafers and flat panel displays. The term “substrate”, as used herein, is intended to generically mean any work piece that can be patterned, including, but not limited to, semiconductor wafers and flat panel displays. 
     Immersion lithography systems use a layer of fluid that fills a gap between the final optical element of the projection optical system and the substrate. The fluid enhances the resolution of the system by enabling exposures with a numerical aperture (NA) greater than one, which is the theoretical limit for conventional “dry” lithography. The fluid in the gap permits the exposure with radiation that would otherwise be completely internally reflected at the optical-air interface. With immersion lithography, numerical apertures as high as the index of refraction of the fluid are possible. Immersion also increases the depth of focus for a given NA, which is the tolerable error in the vertical position of the substrate, compared to a conventional dry lithography system. Immersion lithography therefore has the ability to provide greater resolution than can be performed using conventional dry lithography, as the fluid essentially becomes part of the optical system of the lithography tool. 
     One known way of maintaining the immersion fluid in the gap where exposure of the substrate is to occur is with the use of an air curtain. For more information on air curtain type immersion tools, see for example U.S. Patent publication 2005/0007569 or European Patent Applications EP 1 477 856 A1 and EP 1 420 299 A2, incorporated by reference herein for all purposes. 
     It is also known to maintain the immersion fluid in the gap between the last optical element and the imaging surface of the substrate by submersing both in a container filled with immersion fluid. See for example U.S. Pat. No. 4,509,852, also incorporated by reference herein. 
     Another known way of maintaining the immersion fluid within the gap of a lithography tool is with the use of a confinement member that surrounds the last optical element immediately above the area to be exposed on the substrate. For more information on confinement member type immersion lithography tools, see U.S. application Ser. No. 11/362,833, and PCT Application Serial Numbers. PCT/US2004/22915 and PCT/US2005/14200, all incorporated herein by reference for all purposes, all incorporated herein by reference for all purposes. 
     In yet another approach, which is a variation of the above-described submersion type tool, a large confinement plate is used for submerging the substrate to be imaged in the immersion fluid. For more details on confinement plate type immersion lithography tools, see U.S. patent publication 2007/0279608, incorporated by reference herein. 
     During semiconductor wafer fabrication for example, wafers are typically patterned one after another by the lithography tool. After a wafer has been patterned, it is replaced and the next wafer is exposed. This process is completed over and over, typically as fast as possible, to increase throughput. During a wafer exchange, the just exposed wafer typically has to be moved a relatively long distance from the exposure area to the wafer exchange area. Once the exchange takes place, the new wafer undergoes another relatively long-move to an alignment area. After alignment, the wafer undergoes yet another long-move back to the exposure area for exposure. For the sake of simplicity, all of the above-described moves are hereafter generically referred to as “long-moves”. 
     Long-moves can be problematic with confinement member type immersion tools under certain circumstances. If the speed during a long-move is too fast, there is a tendency for the immersion fluid to leak out from under the confinement member, leaving a trail of water behind on the wafer. This problem can be either mitigated or altogether eliminated by reducing the speed of the long-moves. The drawback of the reduced speed, however, is that throughput is reduced as well. 
     SUMMARY 
     An immersion lithography tool with a diverter element, positioned between the immersion element and the substrate, for altering the “footprint” or shape of the meniscus of the body of immersion liquid between the last optical element and the substrate when the substrate is moved, is disclosed. The apparatus includes a substrate holder to hold a substrate having an imaging surface and a projection optical system having a last optical element. The projection optical system projects an image onto a target imaging area on the substrate through an immersion liquid filled in the gap between the imaging surface of the substrate and the last optical element. The diverter element is positioned between the immersion element and the substrate. The diverter element alters the footprint shape of the meniscus of the body of immersion liquid, thereby preventing or reducing the amount of leakage from a space between the immersion element and the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a diagram of a lithography tool having an immersion element with a diverter element according to the present invention. 
         FIG. 1B  is a diagram of the meniscus footprint of the body of immersion fluid in the immersion tool of the present invention. 
         FIGS. 2A-2B  are top and bottom perspective views of the immersion element with the diverter element according to one embodiment of the present invention. 
         FIG. 3  is a bottom perspective view of another immersion element with a diverter element according to another embodiment of the present invention. 
         FIGS. 4A-4D  are several perspective views of diverter elements according to various embodiments of the present invention. 
         FIGS. 5A-5C  are cross section views of the meniscus of the immersion fluid when the substrate is not being moved, during movement of the substrate but without a diverter element, and during movement of the substrate with the diverter element respectively. 
         FIG. 6  is a footprint view created by the immersion fluid with a diverter element of the present invention during movement of the substrate. 
         FIGS. 7A and 7B  illustrate various embodiments of diverter members of the diverter element of the present invention. 
         FIGS. 8A and 8B  are flow diagrams illustrating the sequence of fabricating semiconductor wafers according to the present invention. 
     
    
    
     Like reference numerals in the figures refer to like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1A , an immersion lithography tool or apparatus is shown. The immersion lithography apparatus  10  includes an imaging element  12  which defines an image, a projection optical system  14  which includes a “last” or “final” optical element  16 , an immersion element  18 , a coarse stage  20 , a fine stage  22 , and a substrate chuck  24  for holding a substrate  26 , and a space  28  under the last optical element  16  and the immersion element  18 . The space  28  includes a gap provided between the top surface of the substrate  26  and the last optical element  16 , when the last optical  16  and the top surface of the substrate  26  are opposite to each other. In one embodiment, the immersion element  18  is a confinement member, by which the gap between the substrate  26  and the last optical element  16  is filled with an immersion fluid  29  (not visible in  FIG. 1A ). Again, for more information on confinement member type immersion lithography tools, see U.S. application Ser. No. 11/362,833, PCT Application Serial Numbers. PCT/US2004/22915 and PCT/US2005/14200, all incorporated herein by reference for all purposes. 
     Referring to  FIG. 1B , a top-down view of the immersion fluid  29  between the immersion element  18  and the last optical element  16  on one side and the substrate  26  on the other side is shown. In one embodiment, the immersion fluid  29  is a liquid, such as water. The perimeter or the meniscus  30  of the immersion fluid  29 , which is defined as the interface where the immersion fluid  29  is in contact with the ambient gas, defines a “footprint” or an outer shape of the body of fluid  29  under the immersion element  18 . When the substrate  26  is moved, during a long-move for example, the meniscus  30  of the body of fluid  29  may be altered in an undesirable way. It should be noted that the diagram of  FIG. 1B  is for illustrative purposes, and is not necessarily drawn to scale. Also a number of elements, such as the remainder of the projection optical system  14  and the substrate chuck  24 , are not shown for the sake of clarity. 
     The present embodiment is directed to a meniscus control element positioned under the immersion element  18 . The meniscus control element may be a diverter element, as described in detail below, which is configured to alter the footprint shape of the body of immersion fluid  29 . In the following explanation, although the substrate  26  is positioned or moved under the immersion element  18  and the optical element  16 , an object other than the substrate  26  can be positioned or moved under the immersion element  18  and the optical element  16 . 
     Referring to  FIGS. 2A-2B , top and bottom perspective views of the immersion element  18  with a meniscus control element  50 , according to one embodiment, is shown. In this embodiment, the meniscus control element  50  is a diverter element. 
       FIG. 2A  shows a top-down perspective view of the immersion element  18 . The immersion element  18  includes a top plate  32 , a bottom plate  44  and a recess  34 . A part of the last optical element  16  is positioned within the recess  34  (for the sake of clarity, the remainder of the projection optical system  14  is not illustrated). The immersion element  18  also includes at least one fluid supply inlet  36  and outlet  38  for supplying and recovering the immersion fluid respectively. Again for the sake of simplicity, only one inlet  36  and outlet  38  is shown. In alternative embodiments, a plurality of inlets  36  and outlets  38  may be used. 
       FIG. 2B  shows a bottom-up perspective view of the immersion element  18 , including a fluid removal element  42  provided on the bottom plate  44 . As illustrated in this view, the fluid removal element  42  is provided between the bottom plate  44  of the immersion element  18  and the diverter element  50 . The immersion element  18  (the bottom plate  44 ) includes an aperture  54 , which is positioned at the center of the concentric diverter elements  52  and under the last optical element  16 , and through which the image is projected onto the top surface of the substrate  26 . The immersion element  18  (the bottom plate  44 ) includes a non-removal area  56  which surrounds the aperture  52 . The non-fluid removal area  56  is substantially flat. The non-fluid removal area  56  and the top surface of the substrate  26  are substantially parallel to one another. The non-fluid removal area  56  is provided for containing the immersion fluid  29 . The fluid removal element  42  is provided further away from the aperture  54  than the non-fluid removal area  56 . In this embodiment, the fluid removal element  42  surrounds the non-fluid removal area  56 . The fluid removal element  42  has a bottom surface that partially faces the diverter element  50 . In this embodiment, the bottom surface of the fluid removal element  42  is substantially co-planar with the surface of the non-fluid removal area  56 . In one embodiment, the bottom surface of the fluid removal element  42  may not be co-planar with the surface of the non-fluid removal area  56 . For example, the bottom surface of the fluid removal element  42  may be provided further away from the top surface of the substrate  26  than the non-fluid removal area  56 . The fluid removal element  42  is configured to contain and remove the immersion fluid  29 . The diverter element  50  is provided under the immersion element  18  (i.e., between the fluid removal element  42  and the substrate  26 ). The diverter element  50  includes a plurality of diverter members  52 . Each of the diverter members  52  is square or rectangular shaped. The diverter members  52  are provided in a concentric arrangement with respect to one another. As illustrated in  FIG. 5C , the diverter members  52  are provided further away from the aperture  54  than the non-fluid removal area  56  in a direction. The diverter members  52  are provided spaced away from one another by a distance in the direction. The diverter members are arranged along the bottom surface of the fluid removal element  42 . As illustrated in  FIG. 5C , the individual diverter members  52  have respective top surfaces which face the bottom surface of the fluid removal element  42  with a gap. The top surfaces of the diverter members  52  are substantially co-planar with one another. In another embodiment, the top surfaces of the diverter members  52  may not be co-planar with one another. As illustrated in  FIG. 5C , the individual diverter members  52  have respective bottom surfaces which face the surface of the substrate  26  with a gap. The bottom surfaces of the diverter members  52  are substantially co-planar with one another. In another embodiment, the bottom surfaces of the diverter members  52  may not be co-planar with one another. 
     During operation, the immersion fluid  29  is introduced into the immersion element  18  through the one or more inlets  36 . The fluid  29  fills at least part of the space  28 , including the gap between the optical element  16  and the substrate  26  and at least part of a gap between the non-fluid removal area  56  and the substrate  26 . The fluid removal element  42  recovers the fluid  29  and passes it through the one or more outlets  38 , where it can be either discarded or reused. In various embodiments, the fluid removal element  42  can be a mesh, a porous material (porous member), or outlets. For more details of these types of fluid recovery elements, see U.S. application Ser. No. 11/362,833, and PCT Application Serial Numbers. PCT/US2004/22915, PCT/US2005/14200, U.S. patent application Ser. No. 11/523,595, U.S. Patent publication 2005/0007569 or European Patent Applications EP 1 477 856 or A1 and EP 1 420 299 A2, again, all of which are incorporated herein by reference. In no way should these embodiments be construed as limiting. Other fluid recovery elements may be used. 
     Referring to  FIG. 3 , a bottom-up perspective view of a diverter element  60  according to another embodiment is shown. In this embodiment, the individual diverter members  62  are “race-track” shaped and arranged in a concentric arrangement. Like the embodiment shown in  FIG. 2B , the diverter members  62  surround the aperture  54  and non-fluid removal area  56 . The embodiment of  FIG. 3  is similar to that illustrated in  FIGS. 2A-2B , except for the shape of the diverter members  62 . Since like elements are given like reference numerals, a detailed explanation of all the elements is not repeated herein. 
     Referring to  FIGS. 4A and 4B , perspective views of the diverter elements  50  and  60  are shown respectively. In each case, a plurality of individual diverter members  52  and  62  are shown in a concentric arrangement. Although the two different diverter elements  50  and  60  are shown, these embodiments should not be construed as limiting the invention. In various embodiments, the diverter members may vary in shape, such but not limited to, round, oval, square, or rectangular for example. 
     Referring to  FIGS. 4C and 4D , the perspective views of the diverter elements  50  and  60  according to two additional embodiments are shown. In these embodiments, the diverter elements  50  and  60  each include only a single diverter member  52  and  62  respectively. Although not illustrated, these diverter elements would be positioned with respect to the immersion element  18  and fluid removal element  42  as illustrated in  FIGS. 2B and 3 . 
     Referring to  FIGS. 5A and 5B , two cross section views of the immersion fluid  29  in the space  28  including the gap between the last optical element  16 , the fluid removal element  42  of the immersion element  18 , and the substrate  26  is shown without the diverter element  50  or  60 . In  FIG. 5A , the substrate  26  is stationary (i.e., is not being moved), whereas in  FIG. 5B , the substrate is being moved, for example during a long-move. In  FIG. 5A , the body of immersion fluid  29 , the shape of which is defined by the meniscus  30 , is substantially uniform in shape. During movements of the substrate  26  on the other hand, the meniscus  30  at both the leading and trailing edges is stretched or pulled toward the direction of the movement, as illustrated in  FIG. 5B . 
     Referring to  FIG. 5C , a cross section view of the immersion fluid  29  with a diverter element  50  or  60 , with the individual diverter members  52 / 62 , positioned within the space  28  is shown. With the movement of the substrate  26  in the direction of the arrow, the meniscus  30  of the fluid  29  tends to be pulled at both the leading and trailing edges in the direction of the movement, similar to that illustrated in  FIG. 5B  for example. With the presence of the diverter members  52 / 62  in the gap between the immersion element  18  and the substrate  26 , however, the meniscus  30  at both the leading and trailing edges is not pulled to such a large degree. Rather the meniscus  30  tends to stay closer to the last optical element  16  in the aperture  54 . The diverter elements  50 / 60  tends to work by restricting the fluid flow under the individual diverter members  52 / 62 , while directing the fluid upward toward the fluid removal element  42  for removal. 
     Referring to  FIG. 6 , a top down view of the footprint  70  of the body of the immersion fluid with either diverter element  50 / 60  during a long-move is shown. As evidenced in the Figure, the individual diverter members  52 / 62  (of either diverter elements  50  or  60 ) divert the immersion fluid, thereby substantially containing the fluid  29  within the confines of the outer most diverter member  52 / 62  of the diverter element  50 / 60 . In other words, the diverter members  52 / 62  cause the fluid  29  to spread out laterally relative to the direction of the movement of the substrate  26 , as designated by the arrows  72 . The members  52 / 62  cause surface tension forces to push or spread in a direction opposite the movement at the leading edge of the meniscus  30 , as designated by arrow  74 . The net effect of these forces is a containment of the immersion fluid within the confines of the outer most diverter element  52 / 62  of the diverter element  50 / 60 . 
     Referring to  FIGS. 7A and 7B , various embodiments of diverter members  52 / 62  of the diverter elements  50 / 60  are illustrated. In  FIG. 7A , the cross section of several diverter elements  52 / 62  are shown. In this embodiment, the top surface  80  of the elements are hydrophilic (liquid-philic), whereas the bottom surface  82  is hydrophobic (liquid-phobic). With this embodiment, the two surfaces  80  and  82  of the individual members  52 / 62  tend to push the immersion fluid upward toward the fluid removal element  42  of the immersion element  18 . In the embodiment of  FIG. 7B , the top surface  84  and the bottom surface  86  are both hydrophobic (liquid-phobic). This embodiment tends to spread the immersion fluid out laterally so as to widen the footprint. 
     It should be noted that the diverter members  52 / 62  as illustrated herein are “plate” like in shape with square or rectangular shaped cross sections (as best illustrated in  FIGS. 7A and 7B . In accordance with various alternative embodiments, the diverter members  52 / 62  may be a variety of shapes, such as for example, round, oval, wedged, etc. The diverter members  52 / 62  also do not necessarily have to be positioned parallel to the substrate or centered in the gap  28  between the substrate  26  and the immersion element  18 . In various embodiments, the diverter members  52 / 62  may be closer to the immersion element  18 , closer to the substrate  26 , or equi-distant between the two. In yet other embodiments, the diverter members  52 / 62  may be angled up, angled down, and/or positioned anywhere in the gap between the substrate  26  and the immersion element  18 . 
     Although the use of the diverter elements  50  and  60  have been described herein with regard to long-moves by the substrate  26 , it should be made clear that the present invention should not be limited to just long-moves. Rather the diverter elements may be used to control the flow of the fluid  29  under the immersion element  18 . In other word, the diverter element may be used to control the footprint of the immersion fluid  29  during movement of the substrate  26 , including during both scanning and step and repeat movements. 
     Although the use of the diverter element has been described, the meniscus control element should not be limited to the diverter element. That is, the meniscus control element may not work as a “diverter”. For example, the one or more plates described in the above embodiments may not work as a “diverter” to prevent or reduce leakage of immersion fluid  29 . 
     Semiconductor devices can be fabricated using the above described systems, by the process shown generally in  FIG. 8A . In step  801  the device&#39;s function and performance characteristics are designed. Next, in step  802 , a mask (reticle) having a pattern is designed according to the previous designing step, and in a parallel step  803  a wafer is made from a silicon material. The mask pattern designed in step  802  is exposed onto the wafer from step  803  in step  804  by a photolithography system described hereinabove in accordance with the present invention. In step  805  the semiconductor device is assembled (including the dicing process, bonding process and packaging process), finally, the device is then inspected in step  806 . 
       FIG. 8B  illustrates a detailed flowchart example of the above-mentioned step  904  in the case of fabricating semiconductor devices. In  FIG. 8B , in step  811  (oxidation step), the wafer surface is oxidized. In step  812  (CVD step), an insulation film is formed on the wafer surface. In step  813  (electrode formation step), electrodes are formed on the wafer by vapor deposition. In step  814  (ion implantation step), ions are implanted in the wafer. The above-mentioned steps  811 - 814  form the preprocessing steps for wafers during wafer processing, and selection is made at each step according to processing requirements. 
     It should be noted that the particular embodiments described herein are merely illustrative and should not be construed as limiting. For example, the substrate described herein does not necessarily have to be a semiconductor wafer. It could also be a flat panel used for making flat panel displays. Rather, the true scope of the invention is determined by the scope of the accompanying claims.