Abstract:
Provided are an aperture unit, an exposure system including the aperture unit, and a method for replacing an aperture of the aperture unit. The aperture unit rotates a revolver on which a plurality of apertures is installed, in order to selectively dispose an aperture in an optical path and convert light emitted onto a reticle into various shapes. The apertures installed on the revolver are removed by a conveying unit and loaded onto a cassette. Other apertures loaded on the cassette are installed on the revolver by means of the conveying unit. A housing is provided in the optical path to enclose the aperture unit, revolver, conveying unit, and cassette. The housing isolates a path of movement for the aperture conveyed between the revolver and the cassette from the outside.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 of Korean Patent Application No. 10-2006-89332, filed on Sep. 14, 2006, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention disclosed herein relates to an aperture unit capable of changing the form of incident light in a variety of ways, and more particularly, to an aperture unit capable of easily replacing apertures. 
         [0003]    A photolithography process is performed to form a photoresist pattern on a layer. The layer is formed on a semiconductor substrate through a deposition process in order to make the layer into a pattern having specific electrical characteristics. The photoresist pattern is used as a mask in an etching process for forming the pattern. 
         [0004]    Such a photolithography process includes an exposing process. In the latter, a reticle is used to form a photoresist pattern from a photoresist layer on a semiconductor substrate. 
         [0005]    Recently, as the integration of semiconductor devices increases, the size of patterns formed on semiconductor substrates gradually decreases, so that the resolution and Depth of Focus (DOF) in a photolithography process become more crucial. The resolution and DOF vary depending on the wavelength of light and the Numerical Aperture (NA) of a projection lens used in the exposing process. 
         [0006]    One drawback is that when the NA of a projection lens is increased in order to increase resolution, the DOF decreases. Off-axis illumination is used to avert the above limitation, and is a method of increasing the DOF by emitting 0 th  and a 1 st  light beam from a light beam diffracted by the retical. 
         [0007]    Off-axis illumination includes annular illumination, dipole illumination, and quadrupole illumination. As an example of off-axis illumination, a projection lithography system that provides a quadrupole illumination pattern is disclosed in U.S. Pat. No. 6,388,736, which is hereby incorporated by reference. 
         [0008]    In order to obtain the best resolution and optimum DOF using off-axis illumination, an aperture is provided that has a shape suitable for the pattern laid out on the reticle. That is, a desired pattern on a wafer is formed and a high resolution and optimum DOF are achieved when light of a suitable direction and energy is incident according to the size, shape, gaps, etc. of the pattern laid out on the reticle. 
         [0009]    In modern integrated circuit fabrication processes, between 20 and 30 sheets of reticles with different pattern shapes are required to fabricate one device. Unfortunately, every time a new reticle is needed for the next step in the process, it is likely that the equipment must be stopped to replace the aperture plate associated with the reticle. This downtime severely lengthens the manufacturing time. 
         [0010]    Accordingly, the efficient replacement and presentation of the next aperture plate in the process is highly desired. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides an aperture unit and an aperture replacing method capable of facilitating the replacing of an aperture in an optical path to one of a desired shape or pattern. 
         [0012]    The present invention also provides an aperture unit and an aperture replacing method capable of shortening the time it takes to replace an aperture. 
         [0013]    The present invention further provides an aperture unit and an aperture replacing method capable of providing an aperture with a suitable shape according to a pattern laid out on a reticle, in order to achieve a high resolution and an optimum depth of focus. 
         [0014]    Embodiments of the present invention provide aperture units including: a cassette on which apertures are loaded, the apertures disposed in an optical path to convert a form of incident light in various ways; a revolver including a plurality of slots formed about a rotating axis of the revolver for installing the apertures respectively in, the revolver for rotating and selectively positioning the apertures in the optical path; and a conveying unit for conveying the apertures from the cassette and installing the apertures in the slots. 
         [0015]    In some embodiments, the slots may be recessed from an outer perimeter of the revolver toward a center of the revolver, and the apertures may be inserted into the slots. 
         [0016]    In other embodiments, guide rails may be formed on side surfaces of the slots, guide slots into which the guide rails are inserted may be formed in side surfaces of the apertures, and the apertures may be installed in predetermined positions along the guide rails. 
         [0017]    In still other embodiments, the side surfaces of the slots may have guide slots formed therein, guide rails that insert in the guide slots may be formed in side surfaces of the apertures, and the apertures may be installed along the guide rails to a predetermined position. 
         [0018]    In even other embodiments, the aperture unit may further include a housing for isolating a moving path of the aperture from the cassette to the revolver from an outside, wherein the cassette, the revolver, and the return unit may be provided within the housing. 
         [0019]    In other embodiments of the present invention, exposure systems including: a light source for emitting light; an illumination part for transmitting the light emitted from the light source toward a reticle; and a projection part for radiating light transmitted through the reticle onto a substrate loaded on a substrate stage; wherein the illumination part includes an aperture unit provided in an optical path, the aperture unit for adjusting a coherence factor (σ) of incident light, the aperture unit having: a cassette on which apertures are loaded, the apertures disposed in an optical path to convert a form of incident light in various ways, a revolver including a plurality of slots formed about a rotating axis of the revolver for installing the apertures respectively in, the revolver for rotating and selectively positioning the apertures in the optical path, and a conveying unit for conveying the apertures from the cassette and installing the apertures in the slots. 
         [0020]    In yet other embodiments, the slots may be recessed from an outer perimeter of the revolver toward a center of the revolver, and the apertures may be inserted into the slots. 
         [0021]    In further embodiments, guide rails are formed on side surfaces of the slots, guide slots into which the guide rails are inserted are formed in side surfaces of the apertures, and the apertures are installed in predetermined positions along the guide rails. 
         [0022]    In still further embodiments, the side surfaces of the slots may have guide slots formed therein, guide rails that insert in the guide slots may be formed in side surfaces of the apertures, and the apertures may be installed along the guide rails to a predetermined position. 
         [0023]    In even further embodiments, the exposure system may further include a housing for isolating a moving path of the aperture from the cassette to the revolver from an outside, wherein the cassette, the revolver, and the return unit may be provided within the housing. 
         [0024]    In still other embodiments of the present invention, methods for replacing apertures installed on a rotatable revolver, the apertures disposed in an optical path, for converting incident light into various shapes according to a rotation of the revolver, the methods including: separating the apertures on the revolver using a conveying unit, and loading the separated apertures on a cassette; and installing another aperture loaded on the cassette onto the revolver, using the conveying unit. 
         [0025]    In even other embodiments of the present invention, the cassette, the revolver, and the conveying unit may be provided within a housing disposed in the optical path, and the housing may isolate a moving path of the aperture. 
         [0026]    In yet other embodiments of the present invention, the aperture may be inserted into a slot recessed from an outer circumference of the revolver toward a center of the revolver. 
         [0027]    In further embodiments of the present invention, the slot may include a guide rail formed on a side surface thereof, and the aperture may include a guide slot formed in a side surface thereof for inserting the guide rail, the guide slot for sliding along the guide rail to install the aperture into the slot. 
         [0028]    In still further embodiments of the present invention, the slot may include a guide slot formed in a side surface thereof, the aperture may include a guide rail formed on a side surface thereof, the guide rail for inserting into the guide slot, and the guide rail may slide along the guide slot to install the aperture into the slot. 
     
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0029]    The accompanying figures are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the figures: 
           [0030]      FIG. 1  is a schematic diagram of an exposure system according to the present invention; 
           [0031]      FIG. 2  is a schematic diagram of an aperture unit according to the present invention; 
           [0032]      FIG. 3  is a perspective view of a revolver according to the first embodiment of the present invention; 
           [0033]      FIG. 4  is a perspective view of an aperture according to the first embodiment of the present invention; 
           [0034]      FIGS. 5   a  and  5   b  are a plan view and a side view showing the assembly of the revolver in  FIG. 3  and the aperture in  FIG. 4 ; 
           [0035]      FIG. 6  is a perspective view of a revolver according to the second embodiment of the present invention; 
           [0036]      FIG. 7  is a perspective view of an aperture according to the second embodiment of the present invention; and 
           [0037]      FIGS. 8   a  and  8   b  are a plan view and a side view showing the assembly of the revolver in  FIG. 6  and the aperture in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]    Preferred embodiments of the present invention will be described below in more detail with reference to  FIGS. 1 through 8   b . The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the figures, the dimensions of the respective elements shown in the drawings may be exaggerated for clarity of illustration. 
         [0039]    Hereinafter, an exemplary embodiment of the present invention in conjunction with the accompanying drawings will be described. 
         [0040]    While the functions of respective elements of an exposure system  1  made by different manufacturers may generally be the same, the arrangement or order of elements disposed according to an optical path and the respective operating principles of each element may differ slightly. Therefore, in the description of an exposure system  1  below, the functions of the elements will be stressed, while the arrangement of the elements may be varied. 
         [0041]    The exposure system  1  described below is disclosed in detail by Nikon Corp. in U.S. Pat. No. 6,331,885 (issued to Nishi) and in U.S. Pat. No. 6,538,719 (issued to Takahashi, et al.), and in Korean Patent Registration No. 10-0571371 disclosed by ASML, which are all hereby incorporated by reference. Since the functions of the components of the exposure system  1  are already well known to those skilled in the art, detailed descriptions of the components will not be given. 
         [0042]    Also, while the substrate in the below description is exemplified by a wafer W, the present invention is not limited thereto. 
         [0043]      FIG. 1  is a schematic diagram of an exposure system  1  according to the present invention. 
         [0044]    A wafer W is mounted on a wafer stage  800 . A photoresist layer (not shown) is formed on the wafer W, and a photoresist pattern is formed through performing an exposing process and a developing process using the photoresist layer. The photoresist layer is formed on the wafer W through a photoresist coating process and a soft bake process, and the photoresist pattern formed using these processes may be used as a mask for etching layers therebelow or as a mask for use in an ion implantation process. 
         [0045]    A plurality of shot regions are installed on the wafer W, where each shot region includes at least one die region. The size of a die region may vary depending on the type of semiconductor device required, and the sizes of each shot region and the number of shot regions may be determined according to the size of the die regions. 
         [0046]    An exposure system  1  includes a light source  100 , an illumination part (I), a mask stage  600 , a projection part  700 , and a wafer stage  800 . 
         [0047]    The light source  100  generates light for exposure. The light source  100  may include a mercury lamp, an ArF laser generator, a KrF laser generator, and an extreme ultraviolet or electron beam generator. The light source  100  is connected to the illumination part (I). 
         [0048]    The illumination part (I) transmits light generated by the light source  100  onto a reticle R. Here, the light generated in the form of point light by the illumination part (I) is converted to surface light and transmitted to the reticle R at a certain-sized contact region thereon. 
         [0049]    The illumination part (I) includes a light distribution control unit  200 , an aperture unit  300 , a blind unit  400 , and a condenser lens  500 . 
         [0050]    The light distribution control unit  200  increases the uniformity of light generated by the light source  100 . The aperture unit  300  adjusts the coherence factor (σ) of light. The blind unit  400  blocks a portion of light and regulates the illuminated region of the reticle R. Thus, during exposure, the blind unit  400  is used to limit the illuminated region, preventing exposure of other regions not requiring exposure. The condenser lens  500  provides a uniform intensity distribution of incident light, and light that passes through the condenser lens  500  is transmitted onto a preset illumination region of the reticle R. 
         [0051]    The light generated by the light source  100  passes through the illumination part (I) so that it is in a state suitable for forming a photoresist pattern on a wafer W. Here, what is meant by ‘suitable’ is light that is of a certain quantity, intensity, density, etc. that corresponds to the characteristics of the photoresist pattern. Those skilled in the art will be able to easily select conditions suitable for the aspect ratio, etching selection ratio, etc. of fine structures to be formed on a wafer W. 
         [0052]    Light that passes through the illumination part (I) is illuminated on the reticle R disposed on the reticle stage  600 . A plurality of circuit patterns for projecting onto the shot regions of the wafer W are formed on the reticle R. The light transmitted to the reticle R passes through the reticle R and reflects the image data of the circuit patterns. Here, the reticle R may be moved in a predetermined direction by the reticle stage  600 . 
         [0053]    The light that passes through the reticle R is transmitted to the projection part  700 . The projection part  700  transmits the light reflecting the image data of the circuit patterns onto the wafer W at multiple focal points, and performs a focus latitude extended exposure (FLEX) process. FLEX is a technology in which a circuit pattern image of a reticle R is transmitted onto a wafer at various superposed focal points, so that not only can the margin for image formation be increased, but the depth of focus (DOF) can also be increased. The projection part  700  has an overall cylindrical shape, of which the upper end is directed toward the reticle R and the lower end is directed toward the wafer W. 
         [0054]      FIG. 2  is a schematic diagram of an aperture unit  300  according to the present invention. 
         [0055]    As described above, the form of light incident on the aperture unit  300  is converted to adjust the coherence factor (σ) of the light. The aperture unit  300  converts the form of light into an annular or quadruple form. 
         [0056]    The aperture unit  300  includes a first and second revolver  320  and  340  and a cassette  380 , and a conveying unit  360  disposed between the first and second revolvers  320  and  340  and the cassette  380 . 
         [0057]    The first revolver  320  and the second revolver  340  are superimposed with a predetermined gap therebetween. The first revolver  320  is connected at its upper surface to a first rotating shaft  322 , and the first revolver  320  is rotated by the first rotating shaft  322 . Likewise, the second revolver  340  is connected at its upper surface to a second rotating shaft  342 , and the second revolver  340  is rotated by the second rotating shaft  342 . The second rotating shaft  342  is a hollow shaft, and the first rotating shaft  322  is installed within the second rotating shaft  342 . The first rotating shaft  322  passes through the inside of the second rotating shaft  342  and a through hole  341  formed in the center of the second revolver  340 , and is connected to the upper surface of the first revolver  320 . 
         [0058]    A plurality of first slots  324 , on which an aperture  10  (to be described below) is installed, is formed around the perimeter of the first revolver  320 , and a plurality of second slots  344 , on which the aperture  10  is installed, is formed around the perimeter of the second revolver  344 . 
         [0059]    The cassette  380  is provided to a side of the first and second revolvers  320  and  340 . A plurality of apertures  10  for the above-described off-axis illumination is loaded in various ways on the cassette  380 , and the form of light is converted to an annular, dipole, or quadrupole type form according to the type of aperture  10 . A plurality of slots  382  is provided on the cassette for loading the apertures  10 . 
         [0060]    The conveying unit  360  is installed between the first and second revolvers  320  and  340  and the cassette  380 . The conveying unit  360  either removes apertures  10  installed in the first and second slots  324  and  344  to load them on the cassette  380 , or installs apertures  10  loaded on the cassette  380  in the first or second slots  324  and  344 . 
         [0061]    The conveying unit  360  includes a driver  362  generating driving force, a drive shaft  364  connected perpendicularly to the lower end of the driver  362 , a first arm  366  connected to the upper end of the drive shaft  364 , a second arm  368  connected to the upper end of the first arm  366 , and a hand  369  connected to the second arm  368 . 
         [0062]    The hand  369  holds the apertures  10 . The apertures  10  held by the hand  369  are moved to desired positions by the first and second arms  366  and  368 . The first and second arms  366  and  368  are a type of linking device, and are capable of rotating relative to each other. The second arm  368  is capable of rotating with respect to the drive shaft  364 , and the apertures  10  may be moved freely by the first and second arms  368  within the same plane. The height of the head  369  may be controlled by elevating the drive shaft  364 . 
         [0063]    The aperture unit  300  further includes a housing  390 . The housing  390  is provided in the optical path, encloses the first and second revolvers  320  and  340  and the cassette  380 , and also functions to isolate a path of movement for a returned aperture  10  between the first and second revolvers  320  and  340  and the cassette  380 . The housing  390  is provided together with a separate housing that encloses the light distribution control unit  200  or the blind unit  400 , and separately seals the moving path of the aperture  10  in order to prevent contamination of the aperture  10 . 
         [0064]      FIG. 3  is a perspective view of a revolver according to the first embodiment of the present invention. 
         [0065]    The first revolver  320  has four first slots  324  that include one normal slot  324   a  and three installing slots  324   b . The normal slot  324   a  does not have an aperture  10  installed therein, and the installing slots  324   b  are slots in which apertures  10  are installed. Also, the second revolver  340  has four second slots  344  that include one normal slot  344   a  and three installing slots  344   b . Similarly, the normal slot  344   a  does not have an aperture  10  installed therein, while the installing slots  344   b  have apertures installed therein. 
         [0066]    The first and second revolvers  320  and  340  are used in collaboration. For example, when an aperture  10  is to be used while installed in an installing slot  324   b  of the first revolver  320 , the installing slot  324   b  in which the aperture  10  is installed and the normal slot  344   a  of the second revolver  340  are aligned in the optical path, so that the incident light passes through the aperture  10  and the normal slot  344   a  aligned in the optical path, whereby the light is converted only by the aperture  10 . When an aperture  10  installed in an installing slot  344   b  of the second revolver  340  is to be used, the installing slot  344   b  with the aperture installed therein and the normal slot  324   a  of the first revolver  320  are aligned in the optical path, so that the incident light passes through the aperture  10  and the normal slot  324   a  in the optical path, such that the light is only converted by the aperture  10 . While in the description of the present embodiment, the number of slots formed in the revolver is four, it is not limited thereto. 
         [0067]    The first revolver  320  and the second revolver  340  have the same structure and function. Accordingly, by providing a detailed description on the structure of the second revolver  340  below, a description on the structure of the first revolver  320  is also included in the provided description of the second revolver  340 . 
         [0068]    Because an aperture  10  is not installed in the normal slot  344   a , there are no restrictions to the shape and size of the normal slot  344   a . Preferably, however, the normal slot  344   a  may be of a shape and size that will not affect the optical passage. 
         [0069]    Apertures  10  are installed in the installing slots  344   b . Therefore, a structure capable of securing the aperture  10  must be provided. Referring to  FIG. 3 , an installing slot  344   b  is recessed from the outer perimeter of the second revolver  340  toward the center of the second revolver  340 , such that the installing slot  344   b  is formed in a wedge shape corresponding to the aperture  10  (to be described below). That is, the sectional area of the installing slot  344   b  gradually narrows toward the center of the second revolver  340 . Alternately, as described below, the shapes of the aperture  10  and the installing slot  344   b  may be rectangular. These shapes do not affect the present invention overall. 
         [0070]    A guide rail  345   b  is provided on the side walls of the installing slot  344   b . The guide rail  345   b  guides the direction of movement of an aperture  10  that inserts into the installing slot  344   b , and at the same time, prevents the aperture  10  inserted into the installing slot  344   b  from moving vertically. 
         [0071]      FIG. 4  is a perspective view of an aperture  10  according to the first embodiment of the present invention. 
         [0072]    As described above, an aperture  10  performs the function of converting the shape of incident light to adjust the coherence factor. Light that passes through the aperture  10  is converted to annular, dipole, or quadrupole type light. 
         [0073]    The aperture  10  is shaped as a wedge, and includes a front wall  12  that is disposed at the front when inserted into the installing slots  324   b  or  344   b , a rear wall  14  parallel to the front wall  12 , and two side walls  16  connecting the front wall  12  and the rear wall  14 . An opening  18  is formed and enclosed by the front wall  12  and rear wall  14 , and the two side walls  16 . Various filters may be provided in the opening  18  to convert the shape of light. A guide slot  16   a , into which the above-described guide rail  345   b  is inserted, is formed on the side walls  16 . Alternately, the shape of the aperture  10  according to other embodiments of the present invention may be rectangular, without affecting the present invention overall. 
         [0074]      FIGS. 5   a  and  5   b  are a plan view and a side view showing the assembly of the revolver  340  in  FIG. 3  and the aperture  10  in  FIG. 4 . Below, the process of installing an aperture  10  loaded on a cassette  380  to an installing slot  344   b  will be described. 
         [0075]    An aperture  10  loaded on a cassette  380  is held by a hand  369 , and is moved by first and second arms  366  and  368  to the installing slot  344   b . Here, by elevating the drive shaft  364 , the hand  369  may be moved to the height at which a desired aperture  10  is installed in a slot  382  ( FIG. 2 ), so that the first and second arms  366  and  368  can pull the aperture  10  out from the slot  382 . 
         [0076]    The hand  369  holding the aperture  10  moves to the height of an installing slot  344   b . Particularly, the hand  369  is moved to a height at which the guide rail  345   b  formed on the side wall of the slot  344   b  corresponds to a guide slot  16   a  of the aperture  10 . 
         [0077]    Next, as shown in  FIG. 5   a , the hand  369  is moved toward the center of the second revolver  340 , and the aperture  10  is inserted into the installing slot  344   b  by sliding the guide slot  16   a  along the guide rail  345   b . When the insertion is completed, the aperture  10  is installed in the installing slot  344   b , as shown in  FIG. 5   b.    
         [0078]    To remove the aperture  10  installed in the installing slot  344   b , the reverse process (of which a detailed description will not be provided) of the installing process may be performed. 
         [0079]      FIG. 6  is a perspective view of a revolver according to the second embodiment of the present invention,  FIG. 7  is a perspective view of an aperture  10  according to the second embodiment of the present invention, and  FIGS. 8   a  and  8   b  are a plan view and a side view showing the assembly of the revolver in  FIG. 6  and the aperture  10  in  FIG. 7 . 
         [0080]    Unlike in the above description, a guide slot  345   b  is provided on the side wall of the installing slot  344   b , and a guide rail  16   a  is provided on the side wall  16  of the aperture  10 . Here, the installing process of the aperture  10  in the installing slot  344   b  may be the same as the process described above, or different in that the aperture  10  is inserted onto the installing slot  344   b  by sliding the guide rail  16   a  provided on the aperture  10  along the guide slot  345   b . When the insertion is complete, the aperture  10  is installed in the installing slot  344   b , as shown in the diagrams. 
         [0081]    As described above, by replacing apertures in installing slots, the process of replacing the first or second revolvers  320  or  340  does not have to be performed. Also, in order to replace an aperture  10 , the aperture unit  300  does not have to be disassembled, and the conveying unit  360  may be used to replace an aperture  10  installed on a revolver with a new aperture  10  loaded on a cassette  380  within the housing  390 . 
         [0082]    The present invention allows an aperture in an optical path to be easily replaced with an aperture of a desired shape, so that the time required to replace apertures can be reduced. 
         [0083]    The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.