Abstract:
There is provided a method of fabricating a lithography mask, the method including: forming a transparent polymer layer on a surface of a first substrate where a convex-concave pattern is formed; separating the transparent polymer layer from the first substrate, the transparent polymer layer having a convex-concave surface formed by the convex-concave pattern of the first substrate transferred thereonto; depositing a metal thin film on the convex-concave surface; forming a viscous film on a second substrate; disposing the transparent polymer layer on the second substrate such that the viscous film and metal thin film are partially bonded together; and separating the transparent polymer layer from the second substrate such that a portion of the metal thin film bonded to the viscous film is removed, wherein a metal thin film pattern having the portion of the metal thin film removed therefrom is formed on the convex-concave surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 2008-69184 filed on Jul. 16, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to photo lithography, and more particularly, to a lithography mask and a method of forming a fine pattern using the same. 
         [0004]    2. Description of the Related Art 
         [0005]    Photo lithography is a process for forming a fine pattern in a semiconductor device and the like, and widely used in the semiconductor industry, electronic parts and electronic devices. Recently, a smaller size and more integration of a semiconductor device requires a finer pattern. Even a fine pattern of a submicron scale such as several nanometers is needed. 
         [0006]    However, in a conventional lithography process, even in case of using an ultraviolet ray lamp providing a short wavelength light as a light source, a fine pattern of one micron or less can be hardly realized due to limitation caused by diffraction. For now, formation of the fine pattern of a submicron scale essentially necessitates holography or E-beam lithography using an expensive laser interferometer. 
         [0007]    However, this equipment is very costly, and also entails delays in forming the pattern. Moreover, the equipment is not appropriate for forming the pattern in a large area and thus has considerable limitations in actual applications in the industrial field. 
         [0008]    Furthermore, in the case of a conventional transmissive photomask, a metal pattern may be formed on a hard transparent substrate such as quartz and glass by various patterning techniques to selectively block transmission of light. This process, however, requires superior contact between the photomask and a photoresist layer to attain higher resolution than in the photo lithography process. 
         [0009]    Therefore, a predetermined pressure is applied to ensure contact between the photomask and the photoresist. This process, when repeated, may contaminate the photomask and impair a deposited metal pattern, thereby requiring regular cleaning, maintenance and repair. Notably, the conventional photomask disadvantageously renders it impossible to perform a precise photo lithography process on a non-planar object such as a curved surface. 
       SUMMARY OF THE INVENTION 
       [0010]    An aspect of the present invention provides a novel method of fabricating a lithography mask which ensures high resolution required for forming a fine pattern and allows for superior contact between a photomask and a pattern forming surface. 
         [0011]    An aspect of the present invention also provides a lithography mask of a novel structure which ensures high resolution required for forming a fine pattern and allows for superior contact between a photomask and a pattern forming surface. 
         [0012]    An aspect of the present invention also provides a method of forming a fine pattern using the lithography mask. 
         [0013]    According to an aspect of the present invention, there is provided a method of fabricating a lithography mask, the method including: forming a transparent polymer layer on a surface of a first substrate where a convex-concave pattern is formed; separating the transparent polymer layer from the first substrate, the transparent polymer layer having a convex-concave surface formed by the convex-concave pattern of the first substrate transferred thereonto; depositing a metal thin film on the convex-concave surface of the transparent polymer layer; forming a viscous film on a second substrate; disposing the transparent polymer layer on the second substrate such that the viscous film and the metal thin film are partially bonded together; and separating the transparent polymer layer from the second substrate such that a portion of the metal thin film bonded to the viscous film is removed, wherein a metal thin film pattern having the portion of the metal thin film removed therefrom is formed on the convex-concave surface of the transparent polymer layer. 
         [0014]    The transparent polymer layer may be formed of a transparent silicon resin-based elastomer. The second substrate may be a glass substrate, and the method further includes plasma-treating a top surface of the second substrate, before the forming a viscous film on a second substrate. 
         [0015]    The viscous film may be a self-assembled monolayer. The self-assembled monolayer may be a thiol-based monolayer. 
         [0016]    The metal thin film may be formed of one of Ag and Cu. The metal thin film may have a thickness of 20 to 100 nm. 
         [0017]    According to another aspect of the present invention, there is provided a lithography mask including: a transparent polymer layer including a first main surface formed of a convex-concave surface and a second surface opposing the first surface; and a metal thin film pattern formed on the first main surface such that the transparent polymer layer is exposed at convexes of the convex-concave surface. 
         [0018]    The transparent polymer layer may be a transparent resin-based elastomer. The metal thin film may be formed of one of Ag and Cu. The metal thin film may have a thickness of 20 to 100 nm. 
         [0019]    According to still another aspect of the present invention, there is provided a method of forming a fine pattern, the method including: providing a lithography mask including a transparent polymer layer including a first main surface formed of a convex-concave surface and a second surface opposing the first surface; and a metal thin film pattern formed on the first main surface such that the transparent polymer layer is exposed at convexes of the convex-concave surface; forming a photoresist layer on a surface of an object where a fine pattern is to be formed; disposing the lithography mask on the object such that the first main surface of the lithography mask is in contact with the photoresist; selectively photo-etching the photoresist using the lithography mask to form a photoresist pattern; and forming a desired fine pattern on the object using the photoresist pattern. 
         [0020]    The method for forming the fine pattern may be very beneficially employed as a process for forming a nano pattern of a submicron for a quantum crystal structure of a semiconductor light emitting diode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0022]      FIGS. 1A to 1E  are procedural cross-sectional views illustrating a method of fabricating a lithography mask according to an exemplary embodiment of the invention; 
           [0023]      FIG. 2  is a cross-sectional view illustrating a lithography mask fabricated according to an exemplary embodiment of the invention shown in  FIGS. 1A to 1E ; and 
           [0024]      FIGS. 3A to 3D  are procedural cross-sectional views illustrating a method of forming a fine pattern using the lithography mask shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0026]      FIGS. 1A to 1E  are procedural cross-sectional views illustrating a method of fabricating a lithography mask according to an exemplary embodiment of the invention. 
         [0027]    As shown in  FIG. 1A , in order to fabricate the lithography mask, first, a transparent polymer layer  14  is formed on a surface of a first substrate  11  where a convex-concave pattern  12  is formed. 
         [0028]    In the present embodiment, the convex-concave pattern  12  is formed on an additional layer formed on a top of the first substrate  11 . Alternatively, the convex-concave pattern  12  may be directly formed on the first substrate  12 . 
         [0029]    The convex-concave pattern  12  provided on the first substrate  11  may be formed by a known semiconductor process. In forming the convex-concave pattern, to fabricate fine convexes and concaves, equipment such as E-beam lithography equipment may be employed. The first substrate  11  having the convex-concave pattern  12  formed thereon may serve as a kind of master to fabricate a mask which is to be obtained in a later process. A material for the first substrate  11  is not limited, but may adopt a material capable of being separated smoothly from the transparent polymer layer  14  which is to be formed on a surface of the first substrate  11  where the convex-concave pattern is formed. 
         [0030]    The polymer layer  14  formed on the convex-concave pattern surface of the first substrate  11  is made of a transparent material. The transparent polymer layer  14  can be formed by applying a liquid polymer material on the convex-concave pattern surface, spin-coating and curing the polymer material. 
         [0031]    The transparent polymer layer  14  of the present embodiment may adopt a transparent silicon resin-based elastomer such as polydimethylsiloxane (PDMS). Here, the transparent polymer layer may have appropriate elasticity and thus can be solidly bonded to the photoresist in a later lithography process to enhance resolution. 
         [0032]    Thereafter, as shown in  FIG. 1B , the cured transparent polymer layer  14  is separated from the first substrate. The cured transparent polymer layer has a convex-concave surface. The convex-concave surface of the transparent polymer layer  14  is a surface onto which the convex-concave pattern  12  of the first substrate  11  is transferred. Accordingly, the convex-concave surface includes convexes  14   a  and concaves  14   b  corresponding to the convex-concave pattern of the first surface. 
         [0033]    As shown in  FIG. 1C , a metal thin film  15  is deposited on the convex-concave surface of the transparent polymer layer  14 . The metal thin film may be formed of Ag or Cu. The metal thin film may have a thickness of 20 to 100 nm. 
         [0034]    As shown in  FIG. 1D , a viscous film  26  is formed on a second substrate  21 . Then, the transparent polymer layer  14  is disposed on the second substrate  21  such that the viscous film  26  and the metal thin film  15  are partially bonded together. 
         [0035]    The second substrate  21  may be a glass substrate. Before the forming of the viscous film  26  on the second substrate  21 , a top surface of the second substrate  21  may be plasma-treated for some hours. 
         [0036]    The viscous film  26  may be a self-assembled monolayer (SAM). In specific examples, the self-assembled monolayer may employ a thiol material such as 3-MPTMS, which is mercaptopropyltrimethoxy-silane. An MPTMS vapor is exposed on the plasma-treated glass substrate, and a condensation reaction between hydroxyl (—OH) group and silane group of the MPTMS is induced on a substrate to form a desired self-assembled monolayer. 
         [0037]    As shown in  FIG. 1E , the transparent polymer layer  14  is separated from the second substrate  21  such that portions  15   a  of the metal thin film  15   a  bonded to the viscous film  26  are removed. This could be understood as a similar process to a nanotransfer printing method. 
         [0038]    More specifically, the convex-concave surface having the metal thin film  15  formed thereon is adhered to the viscous film  26  and then the transparent polymer layer  14  is carefully released. Accordingly, portions of the metal thin film  15   a  located on the convexes are transferred onto the second substrate  21  having the viscous film  26  in contact therewith due to strong adhesion with a thiol-based (—SH) SAM. 
         [0039]    With these processes, a metal thin film pattern M where the metal thin film  15   a  located at the convexes is partially removed is formed on the transparent polymer layer  14 . 
         [0040]      FIG. 2  is a cross-sectional view illustrating a lithography mask fabricated according to an exemplary embodiment of the invention shown in  FIGS. 1A to 1E . 
         [0041]    The lithography mask shown in  FIG. 2  includes a transparent polymer layer  14  having a first main surface formed of a convex-concave surface and a second main surface opposing the first main surface, and a metal thin film pattern  15   b  (M) formed on the convex-concave surface. The metal thin film pattern M has exposed portions of the transparent polymer layer  14  at convexes  14   a  on the convex-concave surface of the transparent polymer layer  14 . In a process shown in  FIG. 1D , portions of the metal thin film bonded to the viscous film, i.e., portions located below a reference plane R are removed. 
         [0042]    The first main surface of the transparent polymer layer  14  is a contact surface with a photoresist layer and the second main surface is a surface where light such as ultraviolet rays is irradiated. As indicated with an arrow, through the exposed portions of the transparent polymer layer  14 , a portion of the photoresist layer adjacent to an open area of the transparent polymer layer is exposed and the other portion is blocked. 
         [0043]    The convexes and concaves may be shaped such that portions between convexes and concaves each have an inclined surface toward the second main surface to prevent a decline in resolution resulting from scattering of light. That is, the convexes and concaves are configured to have inclined surfaces toward the second main surface. This prevents ultraviolet rays propagating toward the metal thin film pattern (M) from being scattered and exposed around the open area but allows the ultraviolet rays to be guided into the second main surface. 
         [0044]    The transparent polymer layer  14  constituting the lithography mask may be a transparent silicon resin-based elastomer. The metal thin film may employ Ag or Cu. The metal thin film may have a thickness of 20 to 10 mm. 
         [0045]    The lithography mask of the present embodiment has a body defined by the transparent polymer layer  14  and a metal thin film pattern formed on a convex-concave surface of the transparent polymer layer  14  to effectively prevent a decline in resolution resulting from diffraction-induced interference. That is, when light enters the transparent polymer layer which is formed of a transparent material, the transparent polymer layer  14  may serve as a light source and be solidly bonded to a photoresist layer so as to be exposed through the open area of the convexes. This prevents a decrease in resolution due to diffraction and ensures high resolution in an exposure process using a general ultraviolet lamp. 
         [0046]    Moreover, the transparent polymer layer  14  has predetermined elasticity. Thus, despite any unevenness on a surface of the photoresist layer, the mask can be adequately bonded along the surface without external pressure and can be prevented from being contaminated due to the external pressure. 
         [0047]      FIGS. 3A to 3D  are procedural cross-sectional view illustrating a method of forming a fine pattern using a lithography mask shown in  FIG. 2 . 
         [0048]    In order to form the fine pattern according to the present embodiment, first, a lithography mask shown in  FIG. 2  is provided. 
         [0049]    Then, as shown in  FIG. 3A , a photoresist layer  32  is formed on a surface of an object  31  where the fine pattern is to be formed. 
         [0050]    This object  31  may be a semiconductor device manufactured in various shapes or a wafer for manufacturing the semiconductor device. The object may be a wafer for a semiconductor light emitting device requiring a photon crystal structure. The photon crystal structure of the semiconductor light emitting device needs to have a fine pattern of a submicron scale periodically formed and thus can be obtained effectively by a method of the present embodiment. 
         [0051]    Afterwards, as shown in  FIG. 3C , the lithography mask  10  is disposed on the object such that the first main surface of the lithography mask is in contact with the photoresist  32 . Subsequently, an exposure process is performed to employ a photoetching process. 
         [0052]    In the present embodiment, portions of the pattern where the metal thin film M is removed are in contact with the photoresist layer  32  but an ultraviolet ray is selectively irradiated onto only the contact portions  32 ″. Accordingly, the transparent polymer layer  14  formed of, for example, a silicon elastomer can be closely bonded to the photoresist layer  32 , thereby allowing an ultraviolet ray to be irradiated more precisely. 
         [0053]    Furthermore, the mask  10  of the present embodiment has the transparent polymer layer  14  as a body and thus can be superbly in contact with a large-scale substrate or a non-planar curved substrate. Thus, an additional pressure does not need to be applied to achieve superior contact. Also, the open area  14   a  located on the convexes is in contact with the photoresist layer  3 . This prevents the pattern from being damaged due to repetitive use and the resolution from being degraded. 
         [0054]    As shown in  FIG. 3C , portions of the photoresist layer where light is irradiated using the lithography mask  10  is developed and removed to form a desired photoresist pattern  32 ′. Thereafter, as shown in  FIG. 3D , a fine pattern P is formed on the object  31  using the photoresist pattern  32 ′. 
         [0055]    As set forth above, according to exemplary embodiments of the invention, a lithography mask is employed to ensure a fine pattern is easily formed. A micro pattern of a submicron scale can be easily fabricated without utilizing expensive equipment such as E-beam lithography or laser holography. Also, this easily produces the fine pattern of a submicron scale which cannot be obtained by a conventional mask, for example, a chrome coating mask due to diffraction limitation even when identical light source, i.e., an ultraviolet lamp is employed 
         [0056]    Moreover, a process of fabricating a mask is very simple, and not different or limited compared with conventional photo lithography. Therefore, the fabrication process has little barrier to application of the conventional semiconductor process. Furthermore, a material and structure of the lithography mask of the present embodiment can be applied to a large scale substrate and a curved substrate due to excellent contact with a photoresist layer where a pattern is to be formed. 
         [0057]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.