Abstract:
A liquid immersion scanning exposure system utilizes an immersion liquid confined within a watertight lens hood having a base portion formed from a solid optical element. During operation, a bottom portion of a lens assembly is disposed within the immersion liquid and the solid optical element is placed upon a photoresist material or layer (to be patterned). The lens assembly moves laterally through the immersion liquid parallel to the photoresist material. Because the solid optical element separates the immersion liquid from the photoresist material and does not move relative to the photoresist material, the photoresist material does not contact with the immersion liquid and the solid optical element and is not susceptible to damage or scratching by the solid optical element.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to the manufacture of semiconductor devices, and more particularly, to the manufacture of integrated circuits using immersion lithography. 
       BACKGROUND 
       [0002]    As the size of integrated circuit line widths continue shrinking to as low as forty five nanometers (45 nm), utilization of immersion lithography is becoming more and more common. To provide a better understanding of the principles of immersion lithography, a prior art dry optics lithography system will first be described. 
         [0003]      FIG. 1  illustrates an exemplary arrangement of a prior art dry optics lithography system  100  for performing a lithography process on a photoresist material  110 . As shown in  FIG. 1 , dry optics lithography system  100  includes a first lens  120 , a second lens  130 , and a third lens  140 . The three lenses  120 ,  130 , and  140  are aligned along a vertical optical axis  150  perpendicular to a top surface of the photoresist material  110 . An air gap  160  is disposed between the top surface of the photoresist material  110  and the bottom surface of the first lens  120 . 
         [0004]    In an dry optics lithography system of the type illustrated in  FIG. 1 , the numerical aperture (NA) is given by the expression NA=sin θ, where θ is the angle between the vertical optical axis  150  and the outermost optical ray  170  that passes through the dry optics system  100 . The numerical aperture (NA) is a dimensionless number that characterizes the range of angles over which an optical system can accept or emit light. 
         [0005]      FIG. 2  illustrates an exemplary arrangement of a prior art immersion lithography optics system  200  for performing a lithography process on a photoresist material  210 . As shown in  FIG. 2 , the immersion lithography optics system  200  includes a first lens  220 , a second lens  230 , and a third lens  240 . The three lenses  220 ,  230 , and  240  are aligned along a vertical optical axis  250  perpendicular to a top surface of the photoresist material  210 . A gap  260  disposed between the top surface of the photoresist material  210  and the bottom surface of the first lens  220  is filled with an immersion material  270 . The immersion material may be either a liquid or a solid. 
         [0006]    According to the theory of immersion lithography, the immersion material  270  filling the gap  260  between the first lens  220  and the photoresist material  210  reduces phase error of the incident ray and helps increase depth of focus (DOF) and resolution of the optical system. 
         [0007]    In an immersion optics system of the type illustrated in  FIG. 2 , The numerical aperture (NA) is given by the expression NA=n sin θ, where θ is the angle between the vertical optical axis  250  and the outermost optical ray  280  that passes through the immersion lithography optical system  200  and where the letter “n” designates the value of the index of refraction of the immersion material  270 . 
         [0008]    When the immersion material  270  is a liquid, several practical production problems may occur. These problems include a leaching effect, a liquid evaporation cooling effect, an immersion defect, and so on. For at least some of these reasons, a solid is sometimes utilized for the immersion material  270  and the process is referred to as solid immersion lithography. 
         [0009]    In solid immersion lithography, the solid immersion material  270  is in direct contact (or in close proximity to) the photoresist material  210 . This makes it difficult to have relative motion between the lens assembly and the photoresist material  210  without scratching the surface of the photoresist material  210  which makes it virtually impossible to engage in high speed scanning. This also limits the throughput of the process. 
         [0010]    Accordingly, there is a need in the art for an improved immersion lithography apparatus and method that remedies the above described deficiencies of the prior art. 
       SUMMARY 
       [0011]    In accordance with one embodiment, there is provided a liquid immersion scanning system including a watertight lens hood having a bottom portion and a plurality of wall portions defining an interior volume. 
         [0012]    In accordance with another advantageous embodiment, a liquid immersion scanning exposure system is provided that uses an immersion liquid confined within a watertight lens hood. A bottom portion of a lens assembly is disposed within the immersion liquid within the watertight lens hood. The watertight lens hood includes a base portion formed from a solid optical element. The solid optical element is placed upon a photoresist layer and the lens assembly is moved laterally through the immersion liquid parallel to the photoresist layer. 
         [0013]    In accordance with yet another embodiment, there is provided a method for operating a liquid immersion scanning system. The method includes providing a watertight lens hood, placing a lens assembly within the watertight lens hood, and operating the lens assembly within the watertight lens hood. 
         [0014]    In another embodiment, there is provided another method for operating a liquid immersion scanning system. the method includes providing a watertight lens hood having a bottom portion and a plurality of wall portions defining an interior volume, the bottom portion including a solid optical element; placing an immersion liquid within the watertight lens hood; placing a lens assembly within the immersion liquid within the watertight lens hood; and operating the liquid immersion scanning system by moving the lens assembly laterally within the immersion liquid within the watertight lens hood. 
         [0015]    A major advantage of this system and method is that the immersion liquid does not come into contact with the photoresist material layer because the liquid remains contained within the watertight lens hood. As a result, the photoresist layer remains dry at all times. This overcomes the shortcomings of the conventional liquid immersion process. 
         [0016]    Another major advantage of this system and method is that the solid optical element is in direct contact with the top surface of the photoresist layer. Therefore, no focus or leveling metrology is needed and focus variation can be minimized. 
         [0017]    The foregoing has outlined rather broadly the features and technical advantages of the present disclosure so that those skilled in the art may better understand the detailed description that follows. Additional features and advantages will be described hereinafter that form the subject of the claims. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes as the present disclosure. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope in its broadest form. 
         [0018]    Before undertaking the Detailed Description below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent&#39;document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior uses, as well as future uses, of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which: 
           [0020]      FIG. 1  is a diagram illustrating an exemplary arrangement of a prior art dry optics lithography system utilized to perform a lithography process on a photoresist material; 
           [0021]      FIG. 2  illustrates an exemplary arrangement of a prior art immersion lithography optics system utilized to perform a lithography process on a photoresist material; 
           [0022]      FIG. 3  illustrates an exemplary arrangement of a prior art liquid immersion optics system in which a lens assembly is moved (or scanned) within an immersion liquid located over an underlying photoresist material; 
           [0023]      FIG. 4  illustrates an exemplary arrangement of a liquid immersion optics system in accordance with the present disclosure in which a lens assembly is moved (or scanned) within an immersion liquid confined within a lens hood and a solid material is disposed over an underlying photoresist material; and 
           [0024]      FIG. 5  is a diagram illustrating a flowchart of an advantageous embodiment of a method of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIGS. 3 through 5  and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit its scope. Those skilled in the art will understand that these principles may be implemented in any type of suitably arranged immersion lithography apparatus. 
         [0026]    To simplify the drawings the reference numerals from previous drawings will sometimes not be repeated for structures that have already been identified. 
         [0027]    To better provide a thorough explanation of the technical advantages, a description of a prior art liquid immersion optics system will first be given. 
         [0028]      FIG. 3  illustrates an exemplary arrangement of a prior art liquid immersion optics system  300 . In the exemplary arrangement shown in  FIG. 3 , a layer of photoresist material  310  is covered with a top coating  320 . A lens assembly  330  (designated with the word “Lens” in  FIG. 3 ) is positioned over the top surface of the top coating  320  in such a manner that a gap is formed between the bottom surface of the lens assembly  330  and the top surface of the top coating  320 . 
         [0029]    An immersion liquid  340  (e.g., water  340 ) is placed over the top coating  320  and fills the gap between the bottom surface of the lens assembly  330  and the top surface of the top coating  320 . The lens assembly  330  is capable of and operable for being moved (or scanned) laterally with respect to the top surface of the top coating  320  to achieve a whole field exposure. 
         [0030]    The immersion liquid  340  directly contacts the bottom surface of the lens assembly  330  and the top surface of the top coating  320 . This causes a number of physical and chemical reactions to occur during exposure to the immersion liquid  340 . These physical and chemical reactions will sometimes negatively impact the process performance in terms of focus, overlay, defects, etc. As will be seen, these problems may be avoided by using the apparatus and method of the present disclosure described below. 
         [0031]      FIG. 4  illustrates an exemplary arrangement of a liquid immersion optics system  400  in accordance with the present disclosure. As shown in  FIG. 4 , an underlying layer of photoresist material  410  is provided (the photoresist material is utilized for masking purposes during an integrated circuit manufacturing process). The system  400  includes a lens hood  440  and a lens assembly  460 . The lens hood  440  includes a solid optical element  420  forming a base portion and a plurality of walls  430  attached or coupled to outer edges of the solid optical element  420 . When assembled, these components form a watertight (or liquid impervious) container (i.e., the lens hood  440 ). The solid optical element  420  forms the base of the lens hood  440  and the junctures between the walls  430  of the lens hood  440  and the solid optical element  420  are watertight (or liquid impervious) so that the lens hood  440  structured and operable to contain an immersion liquid  450  within the lens hood  440  without leakage. Thus, the base and walls are structured to define an interior volume which holds or contains the immersion liquid  450  (and at least a portion of the lens assembly  460 ). 
         [0032]    The lens assembly  460  (designated with the word “Lens” in  FIG. 4 ) is positioned above the top surface of the solid optical element  420  of the lens hood  440 , and in such a manner so as to form a gap between the bottom surface of the lens assembly  460  and the top surface of the solid optical element  420 . 
         [0033]    The immersion liquid  450  is disposed (or contained or confined) within the lens hood  440  to fill the gap between the bottom surface of the lens assembly  460  and the top surface of the solid optical element  420 . The lens assembly  460  is capable of being moved (or scanned) laterally with respect to the top surface of the solid optical element  420  to achieve a whole field exposure while the bottom portion of the lens assembly  460  is immersed in the immersion liquid  450  and moves within the lens hood  460 . The solid optical element  420  (and lens hood  440 ) is stationary (does not move) during the scan exposure of the lens assembly  460 . 
         [0034]    As will be appreciated, the type or composition of the immersion liquid  450  may be any type or composition suitable for the process utilized. For example, and without limitation, the immersion liquid  450  may be water, argon fluoride, or a combination thereof. 
         [0035]    In one embodiment, the solid optical element  420  is selected to have an index of refraction that equals (or substantially equals) the index of refraction of the photoresist material  410  and/or that equals (or substantially equals) the index of refraction of the immersion liquid  450 . In other embodiments, each index of refraction for the optical element  420 , photoresist material  410  and the immersion liquid  450  may be different. For example, the optical element  420  may be CaF (calcium fluoride), or LuAG (lutetium aluminum garnet) for high index immersion lithography. 
         [0036]    In one embodiment, the solid optical element  420  directly contacts the top surface of the photoresist material  410 . In another embodiment, the solid optical element contacts a buffer layer (not shown) formed on top of the photoresist material  410 . The buffer layer, for example, may be an organic material that blocks components leaching from the photoresist that may contaminate the lens hood. In one embodiment, the buffer layer may have a thickness in the range of between about 200 to about 300 nm. 
         [0037]    One major advantage of the system  400  is that the immersion liquid  450  does not come into contact with the photoresist material  410  and remains dry. The immersion liquid  450  remains contained or confined within the lens hood  440 . This overcomes the shortcomings of the conventional liquid immersion process. 
         [0038]    Another major advantage of the system  400  is that the solid optical element  420  directly contacts the top surface of the photoresist material  410 . Therefore, no focus or leveling metrology is needed, and focus variation can be minimized. 
         [0039]    Another major advantage of the present invention is that because the immersion liquid  470  does not come into contact with the photoresist material  410 , no top coating (such as top coating  320  in  FIG. 3 ) is needed to protect the photoresist material  410  from leaching. This means that the cost of providing a top coating may be eliminated in the immersion process of the present invention. 
         [0040]    Surface contamination may occur due to the contact between the solid optical element  420  and the underlying photoresist material  410 . This problem may be overcome by applying a thin layer of an anti-adhesion film (e.g., buffer layer) on the top surface of the photoresist material  410  or the bottom surface of the solid optical element  420 . The presence of a thin layer of an anti-adhesion film minimizes the surface contamination. The thin layer of the anti-adhesion film is not shown in  FIG. 4  due to the scale of the drawing. In one example, the anti-adhesion film may be Teflon or Teflon-like material. 
         [0041]      FIG. 5  is a diagram illustrating a flowchart  500  of an advantageous embodiment of a method in which the system  400  may be utilized for liquid immersion scanning using an immersion liquid confined within a lens hood. 
         [0042]    The solid optical element  420  is provided as a base for the lens hood  440  (step  510 ). Walls  430  are attached to the solid optical element  420  to form a watertight (or liquid impervious) lens hood  440  (step  520 ). The solid optical element  420  of the lens hood  440  is placed on the surface of a photoresist material (step  530 ). 
         [0043]    The immersion liquid  450  is disposed or placed in the bottom of the watertight lens hood  440  (step  540 ) to a level at which a bottom portion of the lens assembly  460  is or will be immersed. The lens assembly  460  is placed within the lens hood  440  and the bottom of the lens assembly  460  is immersed within the immersion liquid  450  (step  550 ). Conventional operation of the lens assembly  460  is performed, such as scanning laterally within the immersion liquid  450  contained within the lens hood  440  (step  560 ). 
         [0044]    It will be understood that well known processes have not been described in detail and have been omitted for brevity. Although specific steps (and not necessarily occurring in the order described), structures and materials may have been described, the present disclosure may not limited to these specifics, and others may be substituted as is well understood by those skilled in the art. 
         [0045]    While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.