Abstract:
In a semiconductor device including a plurality of chip areas arranged in a matrix and a grid-like scribe areas a plurality of L-shaped alignment segments and a plurality of pairs of I-shaped alignment segments are provided within the scribe area. Each of the L-shaped alignment segments is located within a first quadrant defined by an X direction center line and a Y direction center line of the scirbe area, and each pair of the I-shaped alignment segments is located within a second quadrant defined by the X direction center line and the Y direction center line adjacent to the first quadrant.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device, and more particularly, to an improvement of alignment marks of a semiconductor device (or wafer). 
     2. Description of the Related Art 
     Generally, the same chip pattern is repetitively formed by an electron beam exposure apparatus on a wafer. In the formation of chip patterns, alignment marks are required. There are two kinds of alignment methods, i.e., a wafer alignment method and a chip alignment method. 
     In the wafer alignment method, several alignment marks, for example, five alignment marks on an upper-right portion, an upper-left portion, a lower-right portion, a lower-left portion, and a center portion of a wafer with respect to an orientation flat (so-called &#34;orifla&#34;) are detected to statistically correct the location of all chips of the wafer. According to this wafer alignment method, since the number of alignment measurements is small, the alignment speed is high; however, a high precision of position control of a stage such as a smaller minimum resolution, a high repetition accuracy and a high precision of step feed are required. 
     In the chip alignment method, alignment marks of all the chips are detected to correct, the location of each chip in accordance with the detection of its corresponding alignment marks. Thus, a high precision of position control of a stage can be obtained; however, since the number of aligment measurements is large, the alignment speed is low. 
     The present invention is particularly related to a chip alignment method. 
     Also, there are three kinds of methods for detecting alignment marks. 
     In a first alignment detecting mentod, an alignment mark is scanned with light such as a laser beam, and reflected light is detected to calculate a center of the alignment mark. 
     In a second alignment detecting method, a plurality of alignment marks are irradiated with light, and an intensity of diffracted light from the alignment marks is detected to calculate a center of the alignment marks. 
     In a third alignment detecting method, an image of an alignment mark is compared with a stored image, to calculate a difference therebetween. 
     The present invention is particularly related to the first alignment detecting method. 
     Also, alignment marks may be provided within chip areas and within a scribe area partitioning the chip areas. If the alignment marks are provided within the chip areas, the integration is decreased. Contrary to this, if the alignment marks are provided within the scribe area, the integration is increased. Therefore, it is preferable to provide the alignment marks within the scribe area. 
     A first prior art semiconductor device (wafer) includes a plurality of chip areas arranged in rows and columns, a scribe area partitioning the chip areas, and a plurality of cross-type alignment marks arranged at intersections between center lines of the scribe area along an X direction and center lines of the scribe area along a Y direction. This will be explained later in detail. 
     In the first prior art semiconductor device, however, since the cross-type alignment marks of an outermost chip are lacking, chip alignment of the outermost chip has to be carried out by using cross-type alignment marks other than the lacking alignment mark, thus increasing the alignment time. Also, the accuracy of alignment for the outermost chip may be deteriorated. 
     A second prior art semiconductor device (wafer) includes a plurality of chip areas arranged in rows and colunms, a scribe area partitioning the chip areas, and a plurality of rectangular-strip-shaped alignment marks arranged at intersections between center lines of the scribe area along the X direction and center lines of the scribe area along the Y direction. This will be explained later in detail. 
     In the second prior art semiconductor devices however, since parts of the alignment marks remain after dicing of the scribe area, a short-circuit may occur between the remaining parts of the alignment marks and bonding wires. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a semiconductor device (wafer) capable of effectively performing an alignment method for outermost chips and avoiding a short-circuit between alignment marks and bonding wires. 
     According to the present invention, in a semiconductor device including a plurality of chip areas arranged in a matrix and a grid-like scribe area, a plurality of L-shaped alignment segments and a plurality of pairs of I-shaped alignment segments are provided within a dicing area within the scribe area. Each of the L-shaped alignment segments is located within a first quadrant defined by an X direction center line and a Y direction center line of the scribe area, and each pair of the I-shaped alignment segments are located within a second quadrant defined by the X direction center line and the Y direction center line adjacent to the first quadrant. 
     Also, if diffraction grating alignment segments are present in the proximity of intersections between the X direction center line and the Y direction center line, other pairs of I-shaped alignment segments are provided instead of the L-shaped alignment segments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the description as set forth below, as compared with the prior art, with reference to the accompanying drawings, wherein: 
     FIG. 1 is a layout diagram illustrating a first prior art semiconductor device; 
     FIG. 2 is a layout diagram of one exposure unit of the device-of FIG. 1; 
     FIG. 3 is a partly-enlarged layout diagram of the alignment mark and its neighborhood of FIG. 1; 
     FIGS. 4A and 4B are diagrams for explaining the segments of the alignment of FIG. 3; 
     FIG. 5 is a layout diagram of the alignment mark and its neighborhood of FIG. 3 after a dicing operation is carried out; 
     FIG. 6 is a layout diagram illustrating a second prior art semiconductor device, 
     FIG. 7 is a layout diagram of one exposure unit of the device of FIG. 6; 
     FIG. 8 is a partly-enlarged layout diagram of the alignment mark and its neighborhood of FIG. 6; 
     FIGS. 9A and 9B are diagrams for explaining the segments of the alignment of FIG. 8; 
     FIG. 10 is a layout diagram of the alignment mark and its neighborhood of FIG. 8 after a dicing operation is carried out; 
     FIG. 11 is a layout diagram illustrating a first embodiment of the semiconductor device according to the present invention; 
     FIG. 12 is a layout diagram of one exposure unit of the device of FIG. 11; 
     FIG. 13A is a partly-enlarged layout diagram of the alignment mark and its neighborhood of FIG. 11; 
     FIG. 13B is a cross-sectional view taken along the line X III--X III of FIG. 13A; 
     FIGS. 14A and 14B are diagrams for explaining the segments of the alignment of FIG. 13; 
     FIG. 15 is a layout diagram of the alignment mark and its neighborhood of FIG. 13 after a dicing operation is carried out; 
     FIG. 16 is a diagram for explaining a size of a rectangular alignment segment; 
     FIGS. 17A, 17B and 17C are graphs showing light reflectance characteristics of the rectangular alignment segment of FIG. 16; 
     FIG. 18A is a diagram for explaining the size of the L-shaped alignment segment of FIG. 11; 
     FIG. 18B is a diagram for explaining the size of the I-shaped alignment segment of FIG. 11; 
     FIG. 19 is a diagram for explaining calculation of an X direction deviation, a Y direction deviation and a gradient deviation of a chip; 
     FIG. 20 is a layout diagram illustrating a second embodiment of the semiconductor device according to the present invention; 
     FIG. 21 is a layout diagram of one exposure unit of the device of FIG. 20; 
     FIG. 22 is a partly-enlarged layout diagram of the alignment mark and its neighborhood of FIG. 20; 
     FIGS. 23A and 23B are diagrams for explaining the segments of the alignment of FIG. 22; and 
     FIG. 24 is a layout diagram of the aligment mark and its neighborhood of FIG. 22 after a dicing operation is carried out. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the description of the preferred embodiments, prior art semiconductor devices will be explained with reference to FIGS. 1, 2, 3, 4A and 4B, 5, 6, 7, 8, 9A and 9B, and 10. 
     In FIG. 1, which illustrates a first prior art semiconductor device (wafer), chip areas 1a, 1b, . . . , 1h are arranged in a matrix along an X direction and along a Y direction. Also, a grid-shape scribe area 2 is formed to partition the chip areas 1a, 1b, . . . , 1h. Further, cross-type alignment marks 3a, 3b, . . . , 3f are provided at intersections between center lines L X1 , L X2 , . . . of the scribe area 2 along the X direction and center lines L Y1 , L Y2 , . . . of the scribe area 2 along the Y direction. 
     A chip alignment for each chip is carried out by scanning two alignment marks with a laser beam. For example, a chip alignment for the chip are 1e is carried out as follows. First, the alignment mark 3d is scanned with the laser beam as indicated by an arrow along the X direction and as indicated by an arrow along the Y direction to obtain a location A of the alignment mark 3d. Next, the alignment mark 3e is scanned with the laser beam as indicated by an arrow along the X direction and as indicated by an arrow along the Y direction to obtain a location B of the alignment mark 3d. From comparison of the locations A and B with reference locations, an X direction deviation, a Y direction deviation and a gradient deviation of the chip area 1e can be obtained, and as a result, correction of deflection of an electron beam or the like can be carried out in accordance with the X direction deviation, the Y direction deviation and the gradient deviation. 
     In FIG. 2, which illustrates one exposure unit of the device of FIG. 1, the exposure unit is comprised of one chip area such as 1e and four quadrantal segments of alignment marks such as a quadrantal segment 3a-1 of the alignment mark 3a, a quadrantal segment 3b-1 of the alignment mark 3b, a quadrantal segment 3d-1 of the alignment mark 3d, and a quadrantal segment 3e-1 of the alignment mark 3e. 
     In FIG. 3, which is an enlarged diagram of one alignment mark such as 3d of FIG. 1, the alignment mark 3d is located at art intersection between the center line L X2  and the center line L Y1 . The alignment mark 1d is formed by assembling four quadrantal segments as illustrated in FIG. 4A into one cross-type mark-as illustrated in FIG. 4B. 
     In FIG. 5, which illustrates the device of FIG. 3 after a dicing operation is carried out, a dicing area 4 is removed, and accordingly, the alignment mark such as 3d of FIG. 3 is completely removed. Therefore, there is no anxiety about a short-circuit between the remaining parts of the alignment marks and bonding wires. 
     In the above-described prior art semiconductor device, however, in the outermost chip area such as 1f of FIG. 1, segments of the alignment mark 3f are lacking, so that it is impossible to calculate an accurate location of the alignment mark 3f. Therefore, chip alignment of the outermost chip area such as if has to be carried out by using another alignment mark such as 3b instead of the lacking alignment mark 3f. This increases the alignment time, and also, the accuracy of alignment for the outermost chip areas may be deteriorated. 
     In FIG. 6, which illustrates a second prior art semiconductor device (wafer), a plurality of rectangular strip-shaped alignment marks 3a&#39;, 3b&#39;, . . . , 3f&#39; are provided instead of the cross-type alignment marks 3a, 3b, . . . , 3f of FIG. 1. 
     A chip alignment for each chip is carried out by scanning a laser beam on two alignment marks, particularly, two quadrantal segments. For example, a chip alignment for the chip area 1e is carried out as follows. First, the lower-right side quadrantal segment of the alignment mark 3d&#39; is scanned with a laser beam as indicated by an arrow along the X direction and as indicated by an arrow along the Y direction to obtain a location A&#39; of the lower-right side quadrantal segment of the alignment mark 3d&#39;. Next, the lower-left side quadrantal segment of the alignment mark 3e&#39; is scanned with a laser beam as indicated by an arrow along the X direction and as indicated by an arrow along the Y direction to obtain a location B&#39; of the lower-left side quadrantal segment of the alignment mark 3e&#39;. From comparison of the locations A&#39; and B&#39; with reference locations, an X direction deviation, a Y direction deviation and a gradient deviation of the chip area 1e can be obtained, and as a result, correction of deflection of an electron beam or the like can be carried out in accordance with the X direction deviation, the Y direction deviation and the gradient deviation. 
     In the outermost chip area such as 1f of FIG. 6, even if some segments of the alignment mark 3f&#39; are lacking, it is possible to calculate an accurate location of the alignment mark 3f&#39;. 
     In FIG. 7, which illustrates one exposure unit of the device of FIG. 6, the exposure unit is comprised of one chip area such as 1e and four quadrantal segments of alignment marks such as a quadrantal segment 3a&#39;-1 of the alignment mark 3a&#39;, a quadrantal segment 3b&#39;-1 of the alignment mark 3b&#39;, a quadrantal segment 3d&#39;-1 of the alignment mark 3d&#39;, and a quadrantal segment 3e&#39;-1 of the alignment mark 3e&#39;. 
     In FIG. 8, which is an enlarged diagram of one alignment mark such as 3d&#39; of FIG. 6, the alignment mark 3d&#39; is located at an intersection between the center line L X2  and the center line L Y1 . The alignment mark 1d&#39; is formed by assembling four quadrantal segments as illustrated in FIG. 9A into one rectangular strip-shaped mark as illustrated in FIG. 9B. 
     In FIG. 10, which illustrates the device of FIG. 8 after a dicing operation is carried out, a dicing area 4 is removed; however, in this case, the alignment mark such as 3d&#39; of FIG. 8 is not completely removed. Therefore, there is anxiety about a short-circuit between the remaining parts of the alignment marks and bonding wires. 
     In FIG. 11, which illustrates a first embodiment of the present invention, L-I type alignment marks 3a&#34;, 3b&#34;, . . . , 3f&#34; are provided at intersections between center lines L X1 , L X2 , . . . of the scribe area 2 along the X direction and center lines L Y1 , L Y2 , . . . of the scribe area 2 along the Y direction. 
     In FIG. 12, which illustrates one exposure unit of the device of FIG. 11, the exposure unit is comprised of one chip area such as 1e and four quadrantal segments of alignment marks. For example, the alignment mark 3a&#34; has an L-shaped alignment segment 3a&#34;-1, the alignment mark 3b&#34; has two I-shaped alignment segments 3b&#34;-2 and 3b&#34;-3, the alignment mark 3d&#34; has two I-shaped alignment segments 3d&#34;-2 and 3d&#34;-3, and the alignment mark 3e&#34; has an L-shaped alignment segment 3e&#34;-I. 
     A chip alignment for each chip is carried out by scanning a laser beam on two alignment marks, particularly, two quadrantal segments. For example, a chip alignment for the chip area 1e is carried out as follows. First, the I-shaped alignment segments 3d&#34;-2 and 3d&#34;-3 of the alignment mark 3d&#34; are scanned with a laser beam as indicated by an arrow along the X direction and as indicated by an arrow along the Y direction to obtain a location A&#34; of the lower-right side quadrantal segment of the alignment mark 3d&#34;. Next, the L-shaped alignment segment 3e&#34;-1 of the alignment mark 3e&#34; is scanned with a laser beam as indicated by an arrow along the X direction and as indicated by an arrow along the Y direction to obtain a location B&#34; of the lower-left side quadrantal segment of the alignment mark 3e&#34;. From comparison of the locations A&#34; and B&#34; with reference locations, an X direction deviation, a Y direction deviation and a gradient deviation of the chip area 1e&#34; can be obtained. As a result, correction of deflection of an electron beam, correction of the location of probes in a wafer testing step, correction of the location of a laser beam in a laser trimming step, and correction of alignment of cutting blades in a dicing step can be carried out in accordance with the X direction deviation, the Y direction deviation and the gradient deviation. 
     In FIG. 13A, which is an enlarged diagram of one alignment mark such as 3d of FIG. 11, the alignment mark 3d&#34; is located at an intersection between the center line L X2  and the center line L Y1 . The alignment mark 1d&#34; is formed by assembling four quadrantal segments as illustrated in FIG. 14A into one alignment mark as illustrated in FIG. 14B. 
     As illustrated in FIG. 13B, which is a cross-sectional view taken along the line X III--X III of FIG. 13A, the alignment marks are made of the same metal as a metal connection layer. 
     Also, as illustrated in FIG. 13A, dead spaces are required both sides of each of the L-shaped alignment segments 3d&#34;-1 and 3d&#34;-4 and the I-shaped alignment segments 3d&#34;-2, 3d&#34;-3, 3d&#34;-5 and 3d&#34;-6, thus surely enabling scanning of the alignment segments with a laser beam. In other words, none of the I-shaped alignment segments ever face the L-shaped alignment segments. For example, the I-shaped alignment segment 3d&#34;-2 is shifted down along the Y direction with respect to the L-shaped alignment segment 3d&#34;-1. 
     In FIG. 15, which illustrates the device of FIG. 13 after a dicing operation is carried out, a dicing area 4 is removed, and accordingly, the alignment mark such as 3d&#34; of FIG. 13 is completely removed. In this case, note that the scribe area 2 is about 100 μm wide and the dicing area 4 is about 80 μm wide. Therefore, there is no anxiety about a short-circuit between the remaining parts of the alignment marks and bonding wires. 
     In the outermost chip area such as 1f of FIG. 11, even if some segments of the alignment mark 3f&#34; are lacking, it is possible to calculate an accurate location of the alignment mark 3f&#34;. 
     Next, the sizes of the L-shaped alignment segments and the I-shaped alignment segments will be discussed with reference to FIGS. 16, 17A, 17B, 17C, 18A and 18B. 
     In FIG. 16, assume that a rectangular alignment segment having a size of L 1  ×L 2  is scanned with a laser beam having a radius D such as 3 μm. In this case, in order to obtain an optimum light reflectance from the alignment segment, the length L 2  has to satisfy the following: ##EQU1## 
     For example, if L 1  =10 μm, light reflectance from the alignment mark as shown in FIG. 17A by a laser beam scanning operation is obtained, and accordingly, it is easy to calculate a center location C of the alignment segment. Also, if L 1  =4 μm, light reflectance from the alignment mark as shown in FIG. 17B by a laser beam scanning operation is obtained, and accordingly, it is difficult to calculate a center location C of the alignment segment. Further, if L 2  =2 μm, light reflectance from the alignment mark as shown in FIG. 17C by a laser beam scanning operation is obtained, and accordingly, it is impossible to calculate a center location C of the alignment segment. 
     From the formula (1) and (2), if L 1  =10 μm and L 2  =35 μm, each of the L-shaped alignment segments is shown as in FIG. 18A, and each of the I-shaped alignments is shown in FIG. 18B. In FIGS. 18A and 18B, note that shaded portions on the sides of the alignment segments indicate dead spaces in which light reflectance is almost zero, thus easily carrying out a laser beam scanning operation. 
     In FIG. 19, which is a diagram for explaining calculation of an X direction deviation, a Y direction deviation and a gradient deviation of a chip, assume that reference locations A R  &#39;(X 1R , Y 1R ) and B R  (X 2R , Y 2R ) are as follows: 
     
         (X.sub.1R, Y.sub.1R)=(0, 6) 
    
     
         (X.sub.2R, Y.sub.2R)=(4, 6) 
    
     Also, assume that locations A(X 1 , Y 1 ) and B(X 2 , Y 2 ) are obtained as follows: 
     
         (X.sub.1, Y.sub.1)=(-3, 5.196) 
    
     
         (X.sub.2, Y.sub.2)=(0.464, 7.196) 
    
     In this case, an X direction deviation ΔX a  and a Y direction deviation ΔY a  of the location A are ##EQU2## Also, an X direction deviation ΔX b  and a Y direction deviation ΔY b  of the location B are ##EQU3## 
     Therefore, an X direction deviation of the center O the chip with respect to a reference center O R  is ##EQU4## 
     Also, a Y direction deviation of the center O the chip with respect to the reference center O R  is ##EQU5## 
     Further, a gradient deviation θ of the chip is ##EQU6## 
     In FIG. 20, which illustrates a second embodiment of the present invention, dicing alignment marks, i.e., diffraction gratings 5 are provided at intersections between center lines L X1 , L X2 , . . . of the scribe area 2 along the X direction and center lines L Y1 , L Y2 , . . . of the scribe area 2 along the Y direction. As a result, I--I type alignment marks 3a&#34;&#39;, 3b&#34;&#39;, . . . 3f&#34;&#39; are provided instead of the L-type alignment marks 3a&#34;, 3b&#34;, . . . , 3f&#34; of FIG. 11. 
     In FIG. 21, which illustrates one exposure unit of the device of FIG. 20, the exposure unit is comprised of one chip area such as 1e and four quadrantal segments of alignment marks. For example, the alignment mark 3a&#34;&#39; has two I-shaped alignment segments 3a&#34;&#39;-0 and 3a&#34;&#39;-1, the alignment mark 3b&#34;&#39; has two I-shaped alignment segments 3b&#34;&#39;-2 and 3b&#34;&#39;-3, the alignment mark 3d&#34; has two I-shaped alignment segments 3d&#34;&#39;-2 and 3d&#34;&#39;-3, and the alignment mark 3e&#34;&#39; has two I-shaped alignment segments 3e&#34;&#39; -0 and 3e&#34;&#39;-1. 
     A chip alignment for each chip is carried out by scanning a laser beam on two alignment marks, particularly, two quadrantal segments. For example, a chip alignment for the chip area 1e is carried out as follows. First, the I-shaped alignment segments 3d&#34;&#39;-2 and 3d&#34;&#39;-3 of the alignment mark 3d&#39;&#34; are scanned with a laser beam as indicated by an arrow along the X direction and as indicated by an arrow along the Y direction to obtain a location A&#34;&#39; of the lower-right side quadrantal segment of the alignment mark 3d&#34;&#39;. Next, the I-shaped alignment segments 3e&#34;&#39;-0 and 3e&#34;&#39;-1 of the alignment mark 3e&#34;&#39; are scanned with a laser beam as indicated by an arrow along the X direction and as indicated by an arrow along the Y direction to obtain a location B&#34;&#39; of the lower-left side quadrantal segment of the alignment mark 3e&#34;&#39;. From comparison of the locations A&#34;&#39; and B&#34;&#39; with reference locations, an X direction deviation, a Y direction deviation and a gradient deviation of the chip area 1e&#34;&#39; can be obtained. As a result, correction of deflection of an electron beam, correction of the location of probes in a wafer testing step, correction of the location of an laser beam in a laser trimming step, and correction of alignment of cutting blades in a dicing step can be carried out in accordance with the X direction deviation, the Y direction deviation and the gradient deviation. 
     In FIG. 22, which in an enlarged diagram of one alignment mark such as 3d&#34;&#39; of FIG. 20, the alignment mark 3d&#34;&#39; is located at an intersection between the center line L X2  and the center line L Y1 . The alignment mark 1d&#34;&#39; is formed by assembling four quadrantal segments as illustrated in FIG. 23A into one alignment mark as illustrated in FIG. 23B. 
     Also, as illustrated in FIG. 23A, dead spaces are required on both sides of each of the I-shaped alignment segments 3d&#34;&#39;-0, 3d&#34;&#39;-1, 3d&#34;&#39;-3, 3d&#34;&#39;-4, 3d&#34;&#39;-5, 3d&#34;&#39;-6 and 3d&#34;&#39;-7, thus surely enabling scanning the alignment segments with a laser beam. In other together words, none of the I-shaped alignment segments ever face the I-shaped alignment segments. For example, the I-shaped alignment segment 3d&#34;&#39;-0 is shifted down along the Y direction with respect to the L-shaped alignment segment 3d&#34;&#39;-2. 
     In FIG. 24, which illustrates the device of FIG. 22 after a dicing operation is carried out, a dicing area 4 is removed, and accordingly,-the alignment mark such as 3d&#34;&#39; of FIG. 22 is completely removed. Therefore, there is no anxiety about a short-circuit between the remaining parts of the alignment marks and bonding wires. 
     In the outermost chip area such as if of FIG. 20, even if some segments of the alignment mark 3f&#34;&#39; are lacking, it is possible to calculate an accurate location of the alignment mark 3f&#34;&#39;. 
     As explained hereinbefore, according to the present invention, chip alignment can he effectively carried out for outermost chips, and also a short circuit between alignment marks and bonding wire can be avoided.