Abstract:
A solar cell and manufacturing method of back electrodes thereof are disclosed. The method includes a step of implementing a screen printing process to a semiconductor substrate. The method also includes a step of measuring a deviation which exists between laser ablation recesses and back electrodes in the screen printing process. The method further includes a step of adjusting the distance between the laser ablation recess and the back electrode according to the deviation. After adjusting, a deviation between laser ablation recesses and back electrodes will be controlled to a narrower range when the screen printing process is implemented to another semiconductor substrate. Thus, the defect is caused by the back electrodes incompletely covering the laser ablation recesses can be improved significantly.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 104111042 filed in Taiwan, R.O.C. on 2015/04/02, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The instant disclosure relates to a solar cell and a manufacturing method of back electrodes thereof. 
         [0004]    2. Related Art 
         [0005]    Solar cells currently are the most widely used and developed green energy. To enhance electricity generation efficiency and reduce its generating cost, various types of solar cell have been developed. Solar cells roughly can be divided into three types: silicon solar cells; compound semiconductor solar cells; and organic solar cells. In particular, silicon solar cells are the most developed and widely used type, with the single crystal silicon solar cells having highest conversion efficiency among all of the solar cells. 
         [0006]    Currently ten plus types of silicon solar cells with high conversion efficiency have already been known. Among those for mass commercial production roughly includes the hetero-junction with intrinsic thin layer (HIT) solar cells, interdigitated back contact (IBC) solar cells, bifacial solar cells, and passivated emitter rear locally diffused cell (PERL). 
         [0007]    When fabricating bifacial or PERC solar cells, laser ablation technique is used for etching the antireflection layer and passivation layer on the backside of the cells. Thus, the semiconductor layer underneath the passivation layer can be exposed, with the resulting openings typically of elongated shape and spaced apart from one another. Next, based on the screen-printing technique, the pre-formulated aluminum paste is scraped into the openings obtained by laser ablation. Then, the aluminum paste undergoes a firing process to form multiple fence-shaped back electrodes at the back side of the solar cells. 
         [0008]    Before printing the aluminum paste, the screen pattern has to align with the pattern defined by the openings, which are formed by laser ablation. Without considering the tolerances of the screen printing machine itself, material fatigue tends to occur after the screen has been used for a prolonged period or after repeated use. Consequently, misalignment between the back electrodes and the etched holes (by laser ablation) may happen. Please refer to  FIG. 1 , which is a first schematic view showing the misalignment condition. As shown, the back electrodes  91  are adversely misalignment from the laser ablated holes  92 , yet the back electrodes  91  are still able to completely cover the laser ablated holes  92 . If the misalignment is minor, that is to say the back electrodes  91  are still able to completely cover the laser ablated holes  92 , such issue does not significantly affect the conversion efficiency of the solar cells. Next, please refer to  FIG. 2 , which is a second schematic view showing another misalignment condition. When the misalignment error is to the point where the back electrodes  91  do not completely cover the laser ablated holes  92 , even if only a few laser ablated holes  92  aren&#39;t completely covered by the back electrodes  91 , the conversion efficiency of the solar cells drops dramatically. In the field of solar cells, since the power generated by solar cell plants is in the range of millions of watts, even a slight dip of 0.1% in conversion efficiency means the total electric power in watts will take a significant drop, which translates to higher cost per watt. 
         [0009]    Based on the actual screen-printing practice, the abovementioned misalignment often appears for back electrodes situated on the side regions of the solar cells. The further away the central region is, the more likely the misalignment will occur, and the extent of misalignment is more severe. 
       SUMMARY 
       [0010]    The instant disclosure provides a manufacturing method of back electrodes of a solar cell, which comprises the steps of: (a) providing a semiconductor substrate doped with a first type dopant, where the semiconductor substrate has a first surface and a second surface opposite thereto, and the first surface defines at least m number of first openings and m being an integer greater than 1, with the first openings arranged alternately along an X axis direction, and the centers between adjacent first openings are separated by a first distance a; (b) providing a screen, which defines at least m number of screen holes alternately arranged along the X axis direction, with the centers of adjacent screen holes being substantially separated by the first distance a, and the m number of screen holes corresponding to respective first openings; (c) forming at least m number of back electrodes on the first surface via the screen; (d) measuring a largest distance s defined along the X axis direction between the centers of the back electrodes and the centers of the first openings underneath; and (e) adjusting a distance between the centers of adjacent first openings of another semiconductor substrate to be a second distance b according to the largest distance s, with the second distance b being greater than the first distance a. 
         [0011]    In one embodiment, the second distance b satisfies 
         [0000]    
       
         
           
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             = 
             
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         [0012]    In one embodiment, the first surface of the other semiconductor substrate defines a central region and at least two side regions, with the two side regions arranged on opposite sides of the central region, where in step (e) the distance between the centers of adjacent first openings of the two side regions is adjusted to the second distance b. 
         [0013]    In one embodiment, the central region extends along a Y axis direction to an edge of the other semiconductor substrate, with the two side regions arranged along the X axis direction on opposite sides of the central region, wherein the surface area of the central region occupies one tenth to one third of the surface area of the first surface. 
         [0014]    In one embodiment, the first surface defines a center line parallel to the Y axis direction, and the second distance b increases further away from the center line. 
         [0015]    In one embodiment, the first surface defines a center line parallel to the Y axis direction, with the second distance b ranging from 500 to 2500 μm. 
         [0016]    The instant disclosure also provides a solar cell, which comprises: a semiconductor substrate doped with a first type dopant, where the substrate has a first surface and a second surface opposite thereto; a first passivation layer disposed on the first surface, where the first passivation layer defines m number of first openings, with m being an integer greater than 1, and the first openings are alternately arranged along an X axis direction; a first anti-reflection layer disposed on the first passivation layer, the first anti-reflection layer defines m number of second openings corresponding to respective m number of first openings; a plurality of back surface field regions at the first surface and corresponding to respective m number of first openings, where the concentration of the first type dopant of the back surface field regions being greater than that of the first type dopant of the semiconductor substrate; a plurality of back electrodes alternately arranged along the X axis direction, with the back electrodes making electrical contact with respective back surface field regions via m number of second openings and m number of first openings, where any of the back electrodes defines a first center line along a Y axis direction, with the first openings corresponding to the back electrodes each defining a second center line along the Y axis direction, and the first center line and the second center line are separated by a distance less than 250 μm; a second doping layer disposed on the second surface, where the second doping layer is doped with a second type dopant; a second passivation layer disposed on the second doping layer and defines a plurality of third openings; a second anti-reflection layer disposed on the second passivation layer, with the second anti-reflection layer defining a plurality of fourth openings corresponding to the third openings; and a plurality of front electrodes making electrical contact with the second doping layer via respective third and fourth openings. 
         [0017]    In one embodiment, the first surface of the semiconductor substrate of the solar cell defines a third center line parallel to the Y axis direction, with the second center lines of adjacent first openings being separated by a second distance b, and the second distance b ranges from 500 to 2500 μm. 
         [0018]    In one embodiment, the first surface of the semiconductor substrate of the solar cell defines a third center line parallel to the Y axis direction, with the second center lines of adjacent first openings being separated by a second distance b, and the second distance b increases further away from the third center line. 
         [0019]    In one embodiment, the first surface of the semiconductor substrate of the solar cell defines a third center line parallel to the Y axis direction and a central region and at least two side regions. The central region extends along the Y axis direction to the edge of the semiconductor substrate, where the two side regions are arranged along the X axis direction on opposite sides of the central region, and where the surface area of the central region occupies one tenth to one third of the surface area of the first surface, with the second center lines of adjacent first openings of the two side regions being separated by a second distance b. 
         [0020]    In one embodiment, the second distance b ranges from 500 to 2500 μm. 
         [0021]    In one embodiment, the second distance b increases further away from the third center line. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a first schematic view showing the misalignment in the prior art. 
           [0023]      FIG. 2  is a second schematic view showing the misalignment in the prior art. 
           [0024]      FIG. 3  is a flowchart illustrating the manufacturing method of back electrodes of a solar cell of the instant disclosure. 
           [0025]      FIG. 4  is a first schematic view illustrating the manufacturing process with a screen of the instant disclosure. 
           [0026]      FIG. 5  is a first top view illustrating the back electrodes of the solar cell of the instant disclosure. 
           [0027]      FIG. 6  is a second schematic view illustrating the manufacturing process with the screen of the instant disclosure. 
           [0028]      FIG. 7  is a second top view illustrating the back electrodes of the solar cell of the instant disclosure. 
           [0029]      FIG. 8  is a first sectional view of the solar cell of the instant disclosure. 
           [0030]      FIG. 9  is a third top view illustrating the back electrodes of the solar cell of the instant disclosure. 
           [0031]      FIG. 10  is a second sectional view of the solar cell of the instant disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    The manufacturing method of back electrodes of a solar cell of the instant embodiment is explained hereinbelow. It should be noted that the steps described in sequence below are not used to restrict the implementation sequence of the instant embodiment. 
         [0033]    Please refer to  FIGS. 3 to 5 , which are the flow chart of the manufacturing method of back electrodes of a solar cell of the instant disclosure, a first schematic view of the manufacturing process with a screen, and a first top view of back electrodes of the solar cell, respectively. A semiconductor substrate  101  is provided in step S 01 . The semiconductor substrate  101  is doped with a first type dopant (e.g., p-type dopant). The semiconductor substrate  101  has a first surface  1011  and a second surface  1012  opposite thereof. As a final product after processing, for the solar cells, the second surface  1012  is utilized as a light-receiving surface, while the first surface  1011  is a light-receiving or non-light-receiving surface. As shown in  FIG. 3 , a first passivation layer  103  is formed on the first surface  1011 , and a first anti-reflection layer  104  is formed on the first passivation layer  103 . By laser ablation, at least m number of first openings  103   a  can be formed on the first passivation layer  103 , which on the first surface  1011 . In practice, the first openings  103  may be solid-line openings, dashed-line openings, dotted openings, or any combination thereof (e.g., dash dotted openings). Meanwhile, the first anti-reflection layer  104  defines at least m number of second openings  104   a , where m is an integer greater than one. The opening size of each first opening  103   a  and second opening  104   a  is the same, and all of the holes are alternately arranged along an X axis direction, where the centers of adjacent first openings  103   a  are separated by a first distance a. The X axis direction is different from the extended directions of first openings  103   a  and second openings  104   a.    
         [0034]    For step S 02 , a screen  99  for screen-printing is provided. The screen  99  is defined with at least m number of screen holes  99   a  corresponding to respective first openings  103   a . The screen holes  99   a  are alternately arranged along the X axis direction. 
         [0035]    Step S 03  is to scrape the aluminum paste into the first and second openings  103   a  and  104   a  via the screen  99  during screen-printing process. Then, an aluminum paste firing process is performed to form at least m number of back electrodes  106  on the first surface  1011 , as shown in  FIGS. 4 and 5 . 
         [0036]    Step S 04  is to measure the largest distance between the center C 3  of the back electrode  106  and the center C 2  of the first opening  103   a , which is arranged along the X axis direction and under the back electrode  106 . Under normal circumstances, the distance between any two adjacent screen holes  99   a  of the screen  99  substantially equal to the first distance a between the centers of two adjacent first openings  103   a . Via screen-printing, although the distance between two adjacent back electrodes  106  does not directly equal to the first distance a, but usually each back electrode  106  is sufficient to cover the corresponding first opening  103   a  underneath, as shown in  FIG. 1 . However, when material fatigue occurs due to extended use of the screen  99 , the distance between two adjacent screen holes  99   a  of the screen  99  changes, which leads to misalignment. As illustrated in  FIG. 4 , the center C 1  of the screen hole  99   a  and the center C 2  of the first opening  103   a  are misalignment from each other. Hence, via screen-printing, the center C 3  of the back electrode  106  and the center C 2  of the first opening  103   a  underneath are also misalignment from each other, as shown in  FIG. 5 . As a result, some of the back electrodes  106  do not completely cover the corresponding laser ablated holes  92  underneath (i.e., the first and second openings  103   a  and  104   a  in  FIG. 4 ). The further away the center of the first surface  1011  is, the more severe the level of misalignment. In other words, the extent of misalignment is relatively less for a central region  1011   a  of the first surface  1011  of a solar cell  1 , while the misalignment is more severe for two side regions  1011   b  on opposite sides of the central region  1011   a . As shown in  FIG. 5 , the largest distance S between the center C 3  of the back electrode  106  and the center C 2  of the underlying first opening  103 , which are arranged along the X axis direction, occurs at the outer edge portion of the semiconductor substrate  101 . 
         [0037]    The above described steps are mainly for evaluating the largest misalignment distance between the back electrodes  106  of the semiconductor substrate  101  and the laser ablated first openings  103   a , during the formation of the back electrodes  106  on the first surface  1011  of the semiconductor substrate  101  via the screen  99 . That is to say the largest distance s between the center C 3  of the back electrodes  106  and the center C 2  of the first opening  103   a  along the X axis direction. Next, in step  505 , the distance between adjacent etched holes during the laser ablation process is adjusted according to the largest distance s. In other words, the original first distance a between adjacent first openings  103   a  is adjusted to a second distance b, where b&gt;a. In addition, as shown in  FIG. 4 , the manufacturing method of back electrodes of the solar cell  1  for the instant embodiment, a second passivation layer  108  and a second anti-reflection layer  109  can further be formed over the second surface  1012 . 
         [0038]    Please refer to  FIGS. 6 and 7 , which are a second schematic view of the screen manufacturing process and a second top view of back electrodes of solar cell of the instant disclosure, respectively. After the largest misalignment has been confirmed by using the screen  99  to perform screen-printing, that is to measure the largest distance s between the center C 3  of the back electrode  106  and the center C 2  of the underlying first opening  103   a  along the X axis direction, the distance between each laser scribing during the laser ablation process can be adjusted according to the largest distance s. Now, another semiconductor substrate, which is labeled as  201  and will be processed to form the actual solar cell product, is utilized. This element is structurally the same as the semiconductor substrate  101  in general. Using laser ablation, a plurality of first openings  203   a  and second openings  204   a  are formed on a first passivation layer  203  and a first anti-reflection layer  204 , respectively, with the first passivation layer  203  and first anti-reflection layer  204  disposed over a first surface  2011  of the semiconductor substrate  201 . However, the distance between the centers C 3  of adjacent first openings  203   a  is no longer the original first distance a but is the second distance b instead, with b&gt;a. Thus, the centers of the first openings  203   a  are more aligned with the centers of the screen holes  99   a . Consequently, when forming the back electrodes  206 , the back electrodes  206  more easily cover the first and second openings  203   a  and  204   a , such that the probability of improper manufacturing with the back electrodes  206  not completely covering the first and second openings  203   a  and  204   a  is reduced. As illustrated in  FIG. 7 , the back electrodes  206  of an adjusted solar cell  2  fully cover the laser ablated holes  92  underneath (i.e., the first and second openings  203   a  and  204   a ). It should be noted that the back electrodes  206  of a solar cell  2  has a unique characteristic that the distances between the centers C 3  of the back electrodes  206  of a central region  2011   a  and respective centers C 2  of the underlying first and second openings  203   a  and  204   a  are slightly increased than before. In other words, without the adjustment, the centers C 3  of the back electrodes  206  of the central region  2011   a  may overlap or are very close to overlap respective laser ablated holes  92  underneath. However, after the adjustment is made, the centers C 3  of the back electrodes  206  of the central region  2011   a  are further misalignment from respective centers C 2  of the underlying first and second openings  203   a  and  204   a . The reason being originally, significant misalignment between the centers C 3  of the back electrodes  206  of the central region  2011   a  and respective centers C 2  of the first and second openings  203   a  and  204   a  underneath are less likely to occur. Hence, misalignment condition gets slightly worse after the adjustment is made. Nevertheless, as previously mentioned, as long as the back electrodes  206  completely cover the laser ablated holes  92 , the presence of misalignment does not inflict significant adverse effect with regard to conversion efficiency of the solar cell. The abovementioned central region  2011   a  also extends along a Y axis direction to an edge  201   e  of the semiconductor substrate  201 . Meanwhile, in the X axis direction, at least two side regions  2011   b  are defined along opposite sides of the central region  2011   a . Therefore, the X axis direction is different from the Y axis direction, and the X axis direction crosses the Y direction at any angle. In addition, as shown in  FIG. 6 , for the manufacturing method of back electrodes of the solar cell  2  for the instant embodiment, a second passivation layer  208  and a second anti-reflection layer  209  can further be formed over a second surface  2012 . 
         [0039]    The abovementioned technique of adjusting the second distance b depends on the nature of the misalignment, where one type of adjustment technique utilizes the following equation: 
         [0000]    
       
         
           
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         [0040]    The above equation calls for multiplying the largest misalignment, which is the largest distance s, by 2. The product is then divided by the number of spaces (m−1) between the first openings  203   a  on the first surface  2011 . The reason for multiplying by 2 is due to the fact that misalignment usually gets worse toward opposite sides of the central region of the first surface  2011 . Practically speaking, the largest distance s gradually increases from the center of the first surface  2011  toward the edges thereof. Thus, the largest distance s is defined cumulatively by the (m−1)/2 number of spaces from the center of the first surface  2011  to the outer sides thereof. In other words, the above equation directly divides the largest distance s by (m−1)/2 number of spaces in getting a correction value. Comparing to the first distance a, the corrected second distance b is increased by an amount of 
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         [0000]    Based on the above described adjustment, the probability of improper manufacturing of the back electrodes  206  not completely covering the first and second openings  203   a  and  204   a  is reduced from greater than 10% to less than 3%. 
         [0041]    Another adjustment technique is based on the fact that most misalignments occur at the side regions  2011   b  of the first surface  2011 . Therefore, only the second distance b between adjacent first openings  203   a  defined in the side region of the first surface  2011  needs to be adjusted. Meanwhile, the distance between the centers of adjacent first openings  203   a  in the central region  2011   a  of the first surface  2011  remains as the first distance a. The surface area of abovementioned central region  2011   a  ranges from one tenth to one third of the surface area of the first surface  2011 . Based on such adjustment, the probability of improper manufacturing of the back electrodes  206  not completely covering the first and second openings  203   a  and  204   a  is reduced from greater than 10% to less than 3%. 
         [0042]    Yet further still another adjustment technique relates to the misalignment condition that gradually worsens from the center of the first surface  2011  to the edges thereof. Hence, after the adjustment, the second distance b for the distance between the centers of adjacent first openings  203   a  is not a fixed value, instead increases gradually from the center of the first surface  2011  toward the sides thereof. 
         [0043]    The abovementioned gradual increase may be characterized linearly. For instance, assuming the first surface  2011  defines a center line CL. Next, the first opening  203   a  closest to the center line CL of the first surface  2011  is labeled as numeral  1 , with the rest first openings  203   a  labeled sequentially as numerals  2 ,  3  . . . n−1, and n in the X axis direction toward the outer edges of the semiconductor substrate  201 . Thus, for the distance between the first openings  203   a  that are labeled  2  and  3  and the distance between the first openings  203   a  that are labeled  1  and  2 , the difference between the two distances are Δs; for the distance between the first openings  203  a that are labeled  3  and  4  and the distance between the first openings  203   a  that are labeled  2  and  3 , the difference between the two distances are Δ2s ; for the distance between the first openings  203   a  that are labeled  4  and  5  and the distance between the first openings  203   a  that are labeled  3  and  4 , the difference between the two distances are Δ3s; . . . . Based on such approach, for the distance between the outer most first openings  203   a  that are labeled n−1 and n and the distance between the first openings  203   a  that are labeled n−2 and n−1, the difference between the two distances are (n−2)Δs. In turn, Δs+2Δs+3Δs+ . . . +(n−2)Δs=largest distance s. In other words, the largest distance s satisfies the following equation: 
         [0000]    
       
         
           
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         [0000]    Based on such adjustment, the probability of improper manufacturing of the back electrodes  206  not completely covering the first and second openings  203   a  and  204   a  is reduced from greater than 10% to less than 1%. 
         [0044]    Please refer to  FIGS. 8 and 9 , which illustrate a first sectional view of the solar cell and a third top view of back electrodes of the solar cell of an embodiment of the instant disclosure, respectively. The figures disclosed a solar cell  3 , which comprises a semiconductor substrate  301 , a first passivation layer  303 , a first anti-reflection layer  304 , a plurality of back surface field regions  305 , a plurality of back electrodes  306 , a second doping layer  307 , a second passivation layer  308 , a second anti-reflection layer  309 , and a plurality of front electrodes  310 . 
         [0045]    The semiconductor substrate  301  is doped with a first type dopant. For the instant embodiment, the first type dopant is a p-type dopant (e.g., boron of Group IIIA). The semiconductor substrate  301  has a first surface  3011  and a second surface  3012  opposite thereto. 
         [0046]    The first passivation layer  303  is disposed on the first surface  3011  and defines m number of first openings  303   a , where m is an integer greater than 1. Each of the first openings  303   a  is alternately arranged along the X axis direction. 
         [0047]    The first anti-reflection layer  304  is disposed on the first passivation layer  303  and defines m number of second openings  304   a , which correspond to m number of first openings  303   a . The abovementioned first and second openings  303   a  and  304   a  are formed by the same laser scribe. 
         [0048]    The back surface field regions  305  are defined at the first surface  3011 , each of which corresponds to one of the m number of first openings  303   a . The p-type dopant concentration of the back surface field regions  305  is greater than that of the p-type dopant for the semiconductor substrate  301 . The formation of the back surface field regions  305  of the first surface  3011  relates to the fact that after aluminum paste had filled the first and second openings  303   a  and  304   a , a firing process is utilized to form the back electrodes  306 . During the firing process, aluminum atoms disperse into the first surface  3011  of the semiconductor substrate  301 . Since aluminum and boron both belong to Group IIIA elements, local back surface field regions having higher concentration of p-type dopant are formed at contacting areas between the first surface  3011  and the back electrodes  306 . These local fields are the back surface field regions  305  of the instant embodiment. The formation of the back surface field regions  305  of instant embodiment are reducing warping and fragmentations phenomenon after the firing process is over. 
         [0049]    The back electrodes  306  are alternately arranged with one another, while making electrical contacts with the back surface field regions  305  via the first and second openings  303   a  and  304   a . Any of the back electrodes  306  defines a center line C 3  along the Y axis direction. Meanwhile, for the first openings  303   a  that correspond to the back electrodes  306 , each of which defines a center line C 2  along the Y axis direction. The distance between the centerlines C 2  and C 3  along the X axis direction does not go beyond 250 μm, while preferably not greater than 20 μm. Yet, the distance b between adjacent first openings  303   a  is a fixed value. 
         [0050]    The second doping layer  307  is disposed on the second surface  3012 , where the second doping layer  307  is doped with a second type dopant. For the instant embodiment, the second type dopant is an n-type dopant (e.g., phosphorus of Group VA elements). The second passivation layer  308  is disposed on the second doping layer  307  and defines a plurality of third openings  308   a . The second anti-reflection layer  309  is disposed on the second passivation layer  308 , where the second anti-reflection layer  309  defines a plurality of fourth openings  309   a  corresponding to the third openings  308   a . The front electrodes  310  make electrical contact with the second doping layer  307  via the third and fourth openings  308   a  and  309   a.    
         [0051]    The first surface  3011  of the semiconductor substrate  301  for the solar cell  3  of the instant embodiment defines a center line CL parallel to the Y axis direction. The center lines C 2  of adjacent first openings  303   a  are separated by a distance b, with b increases further away from the center line CL of the first surface  3011 . 
         [0052]    Please refer to  FIG. 10 , which shows a second sectional view of the solar cell of the instant disclosure. This figure depicts another configuration of the embodiment above. For the configuration illustrated by  FIG. 10 , the distance b between the center lines C 2  of adjacent first openings  303   a  is not a fixed value, but rather increases linearly further away from the center line CL of the first surface  3011 . For example, the first opening  303   a  closest to the center line CL of the first surface  3011  is labeled as numeral  1 , and other first openings  303   a  toward the outer edges of the semiconductor substrate  301  along the X axis direction are labeled as numerals  2  ,  3  . . . n−1, and n. Further, the distance between the first openings  303   a  labeled as numerals  1  and  2  is defined as b 1 , the distance between the first openings  303   a  labeled as numerals  2  and  3  is defined as b 2 , and so forth. The distance between the first openings  303   a  labeled as n−1 and n is defined as b n−1 . Specifically, b 2 −b 1  is equivalent to the unit distance Δs, b 3 −b 1  is equivalent to the unit distance 2Δs, b 4 −b 1  is equivalent to the unit distance 3Δs, and so forth. Further, starting with the first opening  303   a  off one side of the center line CL, the sum of the distance differences Δs between adjacent first openings  303   a  is equivalent to the largest distance s, that is to say Δs+2Δs+3Δs+ . . . +(n−2)Δs=largest distance s. 
         [0053]    For another configuration, the first surface  3011  of the semiconductor substrate  301  defines a central region  3011   a  and two side regions  3011   b . The two side regions  3011   b  are arranged on opposite sides of the central region  3011   a  along the X axis direction. Meanwhile, the central region  3011   a  extends along the Y axis direction to the edges  301   e  of the semiconductor substrate  301 , where the surface area of the central region  3011   a  occupies one tenth to one third of the surface area of the first area  3011 . Yet, the distance between the center lines C 2  of adjacent first openings  303   a  on the side regions  3011   b  increases further away from the center line CL of the first surface  3011 . However, the distance between the center lines C 2  of adjacent first openings  303   a  of the central region  3011   a  remains substantially unchanged. 
         [0054]    While the instant disclosure has been described by way of example and in terms of the preferred embodiments, it is to be understood that the instant disclosure needs not be limited to the disclosed embodiments. For anyone skilled in the art, various modifications and improvements within the spirit of the instant disclosure are covered under the scope of the instant disclosure. The covered scope of the instant disclosure is based on the appended claims.