Abstract:
A method for manufacturing a semiconductor device comprises performing an exposing and developing process using an exposure mask including shading patterns and assistant patterns arranged in parallel to the shading patterns to prevent a scum phenomenon generated when a main pattern is formed in a cell region over a semiconductor substrate, thereby improving characteristics, reliability and yield of the semiconductor device. As a result, the method enables high-integration of the semiconductor device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean patent application No. 10-2008-0130105 filed Dec. 19, 2008, the disclosure of which is hereby incorporated in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to an exposure mask and a method for manufacturing a semiconductor device using the same. More specifically, the present invention relates to an exposure mask that can be used in high integration of semiconductor devices and a method for manufacturing a semiconductor device using the same. 
     Due to development of manufacturing technologies of semiconductor devices, the size of a unit element, e.g., a transistor becomes smaller, and integration of semiconductor devices is increased. In order to develop a highly integrated semiconductor memory device, it is important to reduce the chip size. 
     In the case of Dynamic Random Access Memory (DRAM) devices, various different methods are used to reduce the chip size. For example, the cell structure is changed, and more specifically, the plane arrangement or layout of active regions is changed. 
     The general layout of current active regions is an 8F2 structure. The 8F2 structure includes an active region that has a major axis in a horizontal direction and two word lines arranged in parallel to a minor axis of the active region. In the 8F2 structure, the arrangement of the active regions is changed so that the unit cell size may be reduced although the same minimum critical dimension F is applied. 
     In a DRAM cell that has a folded bit line structure, the 8F2 structure selects one of the two word lines to read data of a cell transistor through one bit line and one sense amplifier (SA). 
     In the 8F2 layout of the DRAM cell, a space between the active regions is 3F, and it is easy to secure a margin. However, this results in the cell area being increased. 
     In order to reduce the cell area to smaller than that of the 8F2 layout, an open bit line cell arrangement structure has been developed. When the DRAM cell structure is changed from the 8F2 structure to a 6F2 structure, the cell size is decreased and the chip size is reduced so as to increase the wafer yield. However, a design rule is gradually reduced so that a space between active regions of a semiconductor device is made smaller. As a result, it becomes more difficult to use a photolithography process using a general exposure mask. In order to avoid such a photolithography issue, an assistant feature is formed in a cell edge of the exposure mask to form a device having a reduced design rule. 
       FIG. 1  is a plane diagram illustrating an edge portion of a conventional exposure mask.  FIG. 2  is a plane diagram illustrating a semiconductor device formed using the exposure mask of  FIG. 1 . 
     Referring to  FIG. 1 , the conventional exposure mask comprises shading patterns and assistant features.  FIG. 1  shows the edge portion of the exposure mask. 
     The exposure mask  100  comprises a first region  100 A including shading patterns  110  and a second region  100 B including assistant features  120 . The shading patterns  110  disposed in the first region  100 A define photoresist patterns (not shown) of a cell region formed over a semiconductor substrate using photolithography. Hereinafter, the first region  100 A of the exposure mask  100  refers to a region where patterns are disposed to define photoresist patterns (not shown) disposed in the cell region of the semiconductor substrate. 
     The assistant features  120  disposed in the second region  100 B are not transferred to the semiconductor substrate after the photolithography. The assistant features  120  are, rather, used to facilitate formation of line patterns of the cell region. It is because the assistant feature  120  reduces optical proximity effect of the light transmitted formed on the cell region. The second region  100 B of the exposure mask  100  refers to a region where the assistant patterns  120  are disposed to facilitate formation of patterns in the cell region of the semiconductor substrate. 
     The shading pattern  110  has an oblique line shape. More specifically, the shading pattern  110  includes a plurality of line-shaped patterns having an X-axis as a major axis arranged obliquely for optical proximity correction (OPC). The assistant feature  120  has line-shaped patterns having a Y-axis as a major axis. The assistant feature  120  has a width (S 1 ) between line-shaped patterns that is larger than a width (L 1 ) of the line-shaped patterns. 
     As shown in  FIG. 2 , a main pattern  210  is transferred onto a semiconductor substrate  200  by using the exposure mask of  FIG. 1  having the shading patterns  110  in a photolithography process. The first region  100 A of  FIG. 1  corresponds to the cell region of the semiconductor substrate. The assistant feature  120  disposed in the second region  100 B of  FIG. 1  is exposed over the region adjacent to the cell region the semiconductor substrate. As a result, only the main pattern  210  is patterned over the semiconductor substrate. Since the assistant feature  120  has a critical dimension less than resolving power, as result, only a main pattern  210  is pattered on the semiconductor substrate. 
     A scum  220  having a band type is formed in the edge of the main pattern  210 . The scum  220  is generated when the assistant feature  120  disposed in the second region  100 B of the exposure mask  100  cannot compensate the optical proximity correction accurately. That is, the assistant feature  120  is not exposed like the shading pattern  110  disposed in the first region  100 A of the exposure mask  100 , so that the scum  220  is generated in the edge of the main pattern  210 . As a result, it is difficult to transfer the shading pattern  110  disposed in the first region  100 A of the exposure mask  100  onto the substrate  200  as the shading pattern  120 . 
     BRIEF SUMMARY OF THE INVENTION 
     Various embodiments of the invention are directed to providing a method for manufacturing a semiconductor device with an exposure mask that comprises shading patterns disposed in parallel to assistant features in which a pitch is regularly formed. 
     According to an embodiment of the present invention, an exposure mask comprises: line-shaped shading patterns; and assistant features (AF) wherein the line-shaped shading patterns and the assistant features have substantially the same slope. 
     Preferably, the line-shaped shading patterns may include a line pattern and a space pattern. 
     Preferably, each of the line-shaped shading patterns may have substantially the same critical dimension. 
     Preferably, the line-shaped shading patterns may be arranged obliquely in a first region corresponding to a cell region of a semiconductor device. 
     Preferably, the assistant features may be arranged in a second region corresponding to the region adjacent of the cell region. 
     Preferably, the second region may have a width (B 1 ) ranging from 0.5 to 50 μm. 
     Preferably, the second region may have a width (B 1 ) ranging from 1 to 10 μm. 
     Preferably, the assistant features may include a line pattern and a space pattern. 
     Preferably, the assistant features may include a line pattern and a space pattern each that have a regular pitch. 
     Preferably, each of the line pattern and the space pattern may have the same critical dimension. 
     Preferably, the line pattern may include a first line pattern, a space pattern and a second line pattern. 
     Preferably, the first line pattern or the second line pattern, or both, has a smaller critical dimension than that of the shading pattern. 
     Preferably, the line-shaped shading pattern is formed to have the same pitch as that of the assistant feature. 
     According to another embodiment of the present invention, an exposure mask comprises: line-shaped oblique shading patterns; and assistant features (AF) wherein the line-shaped oblique shading patterns and the assistant features have substantially the same slope. 
     Preferably, the line-shaped oblique shading pattern and the assistant features may have substantially the same pitch. 
     According to an embodiment of the present invention, the method for manufacturing a semiconductor device comprises: forming a hard mask layer over a semiconductor substrate; and etching the hard mask layer with an exposure mask including line-shaped shading patterns and assistant features wherein the line-shaped shading patterns and the assistant features have substantially the same slope. 
     Preferably, the line-shaped shading patterns and the assistant features are formed to have the substantially same pitch. 
     Preferably, each of the line-shaped shading patterns is formed to have substantially the same critical dimension. 
     Preferably, each of the assistant features is formed to have substantially the same critical dimension. 
     According to another embodiment of the present invention, a method for manufacturing a semiconductor device comprises: forming a hard mask layer over a semiconductor substrate; etching the hard mask layer with an exposure mask including line-shaped shading patterns and assistant features wherein the line-shaped shading patterns and the assistant features have substantially the same slope; etching the hard mask layer with an exposure mask to form a hard mask pattern; etching the semiconductor substrate with the hard mask pattern as a mask to form a trench; and forming a device isolation film by filling the trench. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are diagrams illustrating a conventional exposure mask and a semiconductor device formed by using the same. 
         FIGS. 3 and 4  are diagrams illustrating an exposure mask and a semiconductor device formed by using the same according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIGS. 3 and 4  are diagrams illustrating an exposure mask and a semiconductor device formed by using the same according to an embodiment of the present invention. 
     Referring to  FIG. 3 , an exposure mask  300  of the present invention comprises shading patterns  310  disposed in a first region  300 A and assistant features  320  disposed in a second region  300 B. The first region  300 A is associated with the cell region, and the second region  300 B is associated with the region adjacent to the cell region. The shading patterns  310  of the first region  300 A are arranged as oblique lines that are spaced apart from each other. The oblique lines are substantially parallel to each other (i.e., have substantially the same slope). The assistant features  320  are arranged generally in parallel to the shading patterns  310  in the second region  300 B in the present embodiment. 
     The shading pattern  310  is formed with an oblique line pattern from one end portion to the other end portion. Preferably, the line and space pattern has a regular pitch. The line pattern and the space pattern have substantially the same critical dimension. The same critical dimension of the line pattern and the space pattern is easily to patterning the line pattern. 
     The assistant patterns  320  are formed with line and space patterns in parallel to the shading patterns  310 . The assistant pattern  320  neighboring with the end portion of the shading pattern  310  is separated by a given distance from the shading pattern  310 . The width (B 1 ) of the second region  300 B ranges from 0.5 to 50 μm, preferably from 1 to 10 μm. Preferably, the line and space pattern of the assistant pattern  320  have the same critical dimension. 
     Each assistant feature  302  comprises of at least one line-shaped pattern. In the present embodiment, each assistant feature has two line-shaped patterns that have substantially the same slope. For example, the line pattern of the assistant feature  320  includes a first line pattern  322 , a space pattern  324  and a second line pattern  326 . When the line pattern of the assistant pattern  320  has a critical dimension of 1F, each of the first line pattern  322 , the space pattern  324  and the second line pattern  326  has a critical dimension of 1/3 F. 
     As describe in the foregoing, the assistant feature  320  has the same shape and width as the shading pattern  320 , thereby reducing optical proximity effect of the light transmitted from the cell region and forming the shading pattern  310  without being distorted. 
       FIG. 4  shows a photoresist pattern formed over a semiconductor substrate using the exposure mask of  FIG. 3 . The shading pattern  310  disposed in the first region  300 A of the exposure mask  300  of  FIG. 3  defines a main pattern  410  formed to be oblique over a semiconductor substrate  400 . The assistant feature  320  disposed in the second region  300 B of the exposure mask  300  of  FIG. 3  is not exposed and developed over the semiconductor substrate  400 , but facilitates formation of the main pattern  410 . The assistant feature  320  of the second region  300 B includes the first line pattern  322 , the space pattern  324  and the second line pattern  326 . The assistant feature  320  is arranged in parallel to the shading pattern  310  of the first region  300 A, thereby accurately compensating an optical proximity effect of the shading pattern  310  to prevent generation of scum. 
     In another embodiment of the present invention, a semiconductor substrate is etched with a main pattern defined by an exposure mask of the present invention as an etching mask to form a trench. Then, a device isolation film that fills the trench is formed to define an active region, thereby obtaining a semiconductor device. 
     In still another embodiment of the present invention, a semiconductor device can be applied in an exposure mask of all portions where an island-shaped or line-shaped pattern is formed. An exposure mask for etching may be applied in a method for manufacturing a semiconductor device that comprises an island-shaped or line-shaped pattern formed over a semiconductor substrate. The exposure mask for etching enables patterning of a desired pattern. That is, the exposure mask for etching includes transparent patterns arranged in a region where a pattern is removed, that is, in a region which does not require to be patterned. 
     The above embodiments of the present invention are illustrative and not limitative. Various alternatives and equivalents are possible. The invention is not limited by the type of deposition, etching polishing, and patterning steps describe herein. Nor is the invention limited to any specific type of semiconductor device. For example, the present invention may be implemented in a dynamic random access memory (DRAM) device or non volatile memory device. Other additions, subtractions, or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.