Abstract:
A photomask with photoresist test patterns and pattern inspection method using four test patterns on the photomask to perform the exposure on the first photoresist layer in order to adjust the photomask. The present invention prevents misalignment of the first photomask. The information associated with the misalignment is provided to the process engineer based on the location of the test patterns.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photomask, and more particularly, to a photomask with photoresist test patterns and a pattern inspection method. 
     2. Description of the Prior Art 
     In the current lithography process, a stepper is used to perform photomask pattern transfer in order to obtain an image with high resolution and better particle tolerance. However, the main problem of this method is that a wafer needs to be exposed separately in order to complete the fabrication of a single patterned layer. Exposure needs to be performed several times in order to finish one single patterned layer. In order to ensure that the patterns between the layers are stacked accurately, layers of photoresist material can be inspected following development (after-develop-inspection or “ADI”) to ensure that the pattern transfer process has been performed correctly and/or that the pattern is within specified tolerances. From such inspection, mistakes or unacceptable process variations associated with the layer of photoresist material can be identified and corrected. However, from this inspection, the patterned exposure status of the first layer can not be monitored, thereby resulting in mistakes associated with the patterned exposure of the first layer being undefectable. Further, it wastes processing time and increases cost. 
     In the view of this, the present invention provides a photomask with photoresist test patterns and a pattern inspection method, which eliminates misalignment errors of the first layer of photomask in step exposure to effectively overcome the problems that exist in the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a photomask with photoresist test patterns and a pattern inspection method for monitoring the patterned exposure status of the first layer. 
     The present invention also provides information associated with which the step causes misalignment for the process engineer. 
     Additionally, the present invention reduces the expense in processing due to mistakes in the first layer of patterned exposure. 
     To achieve the aforementioned objects, a preferred embodiment of the present invention provides a photomask with photoresist test pattern, comprising a layout pattern area and an external pattern area located surrounding the layout pattern area. The external pattern area comprises first/second/third/fourth alignment areas formed thereon. The arrangement of the test pattern uses the center of the first alignment pattern area as a coordinate axis (0,0) center. The points of the test pattern of the first alignment area are picked based on the coordinates (1+4a, 0), (−1−4b, 0), (0, 1+4c), (0, −1−4d), (1+4e, 1+4e), (−1−4f, −1−4f), (1+4g, −1−4g), and (−1−4h, 1+4h), wherein a, b, c, d, e, f, g, and h are natural numbers. The arrangement of the second test pattern uses the center of the second alignment pattern area as a coordinate axis (0,0) center. The points of the test pattern of the second alignment area are picked based on the coordinates (2+4i,0), (−2−4j,0), (0,2+4k), (0,−2−4l), (2+4m,2+4m), (−2−4n,−2−4n), (2+4p,−2−4p), and (−2−4q,2+4q), wherein i, j, k, l, m, n, p, and q are natural numbers. The arrangement of the third test pattern uses the center of the third alignment pattern area as a coordinate axis (0,0) center. The points of the test pattern of the third alignment area are picked based on the coordinates (3+4r,0), (−3−4s,0), (0,3+4t), (0,−3−4u), (3+4v,3+4v), (−3−4w,−3−4w), (3+4z,−3−4z), and (−3−4A,3+4A), wherein r, s, t, u, v, w, z, and A are natural numbers. The arrangement of the fourth test pattern uses the center of the fourth alignment pattern area as a coordinate axis (0,0) center. The points of the test pattern of the fourth alignment pattern area are picked based on the coordinates (4+4B,0), (−4−4C,0), (0,4+4D), (0,−4−4E), (4+4F,4+4F), (−4−4G,−4−4G), (4+4H,−4−4H), and (−4−4I, 4+4I), wherein B, C, D, E, F, G, H, and I are natural numbers. 
     Another embodiment of the present invention provides an inspection method of the photoresist test patterns, comprising the steps of: providing a silicon substrate having a photoresist layer formed thereon; performing a step exposure on the photoresist layer by using a photomask with a layout pattern area and an external pattern area, wherein the external pattern area is located surrounding the layout pattern area, and wherein the external pattern area comprises first/second/third/fourth alignment pattern areas; the test patterns of the first alignment pattern area are arranged by using a center of the first alignment pattern area as a coordinate axis (0,0), and the points of the test patterns of the first alignment area are picked based on the coordinates (1+4a, 0), (−1−4b, 0), (0, 1+4c), (0, −1−4d), (1+4e, 1+4e), (−1−4f, −1−4f), (1+4g, −1−4g), and (−1−4h, 1+4h), and wherein a, b, c, d, e, f, g, and h are natural numbers; the test patterns of the second alignment pattern area are arranged by using a center of the second alignment pattern area as a coordinate axis (0,0), and the points of the test patterns of the second alignment pattern area are picked based on the coordinates (2+4i,0), (−2−4j, 0), (0, 2+4k), (0,−2−4l), (2+4m, 2+4m), (−2−4n,−2−4n), (2+4p,−2−4p), and (−2−4q, 2+4q), and wherein i, j, k, l, m, n, p, and q are natural numbers; the test patterns of the third alignment pattern area are arranged by using a center of the third alignment pattern area as a coordinate axis (0,0), and the points of the test patterns of the third alignment pattern area are picked based on the coordinates (3+4r,0), (−3−4s,0), (0,3+4t), (0,−3−4u), (3+4v,3+4v), (−3−4w,−3−4w), (3+4z, −3−4z), and (−3−4A,3+4A), and wherein r, s, t, u, v, w, z and A are natural numbers; the test patterns of the fourth alignment pattern area are arranged by using a center of the fourth alignment pattern area as a coordinate axis (0,0), and the points of the test patterns of the fourth alignment pattern area are picked based on the coordinates (4+4B,0), (−4−4C,0), (0,4+4D), (0,−4−4E), (4+4F,1+4F), (−4−4G,−4−4G), (4+4H,−4−4H), and (−4−4I,4+4I), and wherein B, C, D, E, F, G, H and I are Natural numbers; and developing the photoresist layer to form a layout pattern and a photoresist test pattern in order to form the test patterns for monitoring the patterned exposure status of the first layer in completing step exposure. 
     These and other objectives of the present invention will become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
         FIG. 1  is a photomask profile diagram in accordance with an embodiment of the present invention, showing the relative location of the layout pattern areas, the external pattern areas, and the first/second/third/fourth alignment pattern areas; 
         FIGS. 2   a  to  2   d  illustrate the first/second/third/fourth alignment patterns in accordance with an embodiment of the present invention; 
         FIGS. 3   a  and  3   b  illustrate that the first/second/third/fourth alignment pattern areas of the photomask are stacked to present the optimum alignment patterns of the first/second/third/fourth test patterns in accordance with an embodiment of the present invention under the optimum exposure status; and 
         FIGS. 4   a  and  4   b  illustrate that the test patterns are presented in accordance with an embodiment of the present invention as applied under the photomask on the upper right area having stacking exposure status. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention uses different test patterns having four alignment pattern areas on the external pattern area of the photoresist to detect stacking faults in the exposure process. 
     The present invention relates to a photomask  10  with photoresist test patterns, as shown in  FIG. 1 . The photomask  10  mainly comprises the layout pattern area  12  located in the center of the photomask  10 , and external pattern areas  14  located surrounding the layout pattern area  12 . The external pattern areas  14  comprise a first alignment pattern area  16 , a second alignment pattern area  18 , a third alignment pattern  20 , and a fourth alignment pattern area  22 . The first alignment pattern area  16  is represented by the dotted area in  FIG. 1 . The test pattern of the first alignment pattern area  16  forms a first test pattern  24  as shown in  FIG. 2   a . In order for easy recognition, the first test pattern  24  and first alignment pattern area  16  are represented by the same dots, and other test patterns and alignment pattern areas are represented in a similar way. The arrangement of the first test pattern  24  uses the first alignment pattern area  16  as a coordinate axis (0,0) center. The point of the test pattern is picked based on the coordinates (1+4a, 0), (−1−4b, 0), (0, 1+4c), (0, −1−4d), (1+4e, 1+4e), (−1−4f, −1−4f), (1+4g, −1−4g), and (−1−4h, 1+4h), wherein a, b, c, d, e, f, g, and h are natural numbers. If a=b=c=d=e=f=g=h=0, the points of the test patterns are (0,0), (1,0), (−1,0), (0, 1), (0, −1), (1, 1), (−1, −1), (1, −1), and (−1, 1). 
     The second alignment pattern area  18  forms a second test pattern  26  as shown in  FIG. 2   b.  The arrangement of the second test pattern  26  uses the second alignment pattern area  18  as a coordinate axis (0,0) center. The point of the test pattern is picked based on the coordinates (2+4i,0), (−2−4j,0), (0,2+4k), (0,−2−4l), (2+4m,2+4m), (−2−4n,−2−4n), (2+4p,−2−4p), and (−2−4q,2+4q), wherein i, j, k, l, m, n, p, and q are natural numbers. If i=j=k=l=m=n=p=q=0, the points of test patterns are (2,0), (−2,0), (0,2), (0,−2), (2,2), (−2,−2), (2,−2), and (−2, 2). 
     The third alignment pattern area  20  forms a third test pattern  28  as shown in  FIG. 2   c . The arrangement of the third test pattern  28  uses the third alignment pattern area  20  as a coordinate axis (0,0) center. The point of the test pattern is picked based on the coordinates (3+4r,0), (−3−4s,0), (0,3+4t), (0,−3−4u), (3+4v,3+4v), (−3−4w,−3−4w), (3+4z,−3−4z), and (−3−4A,3+4A), wherein r, s, t, u, v, w, z, and A are natural numbers. If r=s=t=u=v=w=z=A=0, the points of the test patterns are (3,0), (−3,0), (0, 3), (0, −3), (3, 3), (−3,−3), (3,−3), and (−3,3). 
     The fourth alignment pattern area  22  forms a fourth test pattern  30  as shown in  FIG. 2   d . The arrangement of the fourth test pattern  30  uses the fourth alignment pattern area  22  as a coordinate axis (0,0) center. The point of the test pattern is picked based on the coordinates (4+4B,0), (−4−4C,0), (0, 4+4D), (0,−4−4E), (4+4F,4+4F), (−4−4G,−4−4G), (4+4H,−4−4H), and (−4−4I, 4+4I), wherein B, C, D, E, F, G, H, and I are natural numbers. If B=C=D=E=F=G=H=I=0, the points of test patterns are (4,0), (−4,0), (0, 4), (0,−4), (4,4), (−4,−4), (4,−4), and (−4, 4). 
     Refer to  FIG. 3   a  and  FIG. 3   b , which is an illustration of a preferred embodiment of the present invention showing the photoresist test patterns, comprising the following steps: 
     First, a silicon substrate, having a photoresist layer coated on the surface of the silicon substrate, is provided. Then, step exposure is performed by using the photomask. In step exposure, the test pattern for performing the exposure is formed in the scribe line. The optimum exposure result is shown as  FIG. 3   a , wherein the external pattern areas  14  are stacked in the write line. The pattern coordinates of the first alignment pattern area  16 , second alignment pattern area  18 , third alignment pattern area  20 , and fourth alignment pattern area  22  are overlapped to form the patterns based on the coordinates (0,0), (1,0), (−1,0),(0, 1), (0, −1), (1, 1), (−1, −1), (1, −1), (−1, 1), (2,0), (−2,0), (0, 2), (0, −2), (2, 2), (−2, −2), (2, 2), (−2, 2), (3,0), (−3,0), (0, 3), (0, −3), (3, 3), (−3,−3), (3,−3), (−3,3), (4,0), (−4,0), (0, 4), (0,−4), (4,4), (−4,−4), (4,−4), and (−4, 4), shown as the star-shaped alignment test pattern in  FIG. 3   b.    
     When the star-shaped alignment test pattern is formed as shown with test points (3,0), (−3,0), (0, 3), (0, −3), (3, 3), (−3,−3), (3,−3), and (−3,3) in  FIG. 4   a  due to the stacking faults of the photomask. The third alignment pattern area provides the test points by inducing the coordinates of the test points. The stacking faults of the photomask on the upper right area are detected as shown in  FIG. 4   b.    
     In order to illustrate easily, the stacking portions of the alignment pattern areas are shown by the meshed patterns in  FIG. 3   a  and  FIG. 3   b.    
     According to the present invention, a photomask with photoresist test patterns and pattern inspection method are provided. The test patterns are formed on the external pattern area of the photomask. After performing step exposure, the test patterns can be inspected using ADI to obtain the stacking faults of the photomask in the first photoresist layer, thereby preventing wasted expense. The stacking portions of the test patterns are detected, thereby identifying which step caused the misalignment. 
     The embodiment above is only intended to illustrate the present invention; it does not, however, to limit the present invention to the specific embodiment. Accordingly, various modifications and changes may be made without departing from the spirit and scope of the present invention as described in the following claims.