Abstract:
A method for forming vias in a substrate, including the following steps: (a) providing a substrate having a first surface and a second surface; (b) forming a groove on the substrate; (c) filling the groove with a conductive metal; (d) removing part of the substrate which surrounds the conductive metal, wherein the conductive metal is maintained so as to form an accommodating space between the conductive metal and the substrate; (e) forming an insulating material in the accommodating space; and (f) removing part of the second surface of the substrate to expose the conductive metal and the insulating material. In this way, thicker insulating material can be formed in the accommodating space, and the thickness of the insulating material in the accommodating space is even.

Description:
This application claims priority to Taiwan application 096128415 filed on Aug. 2, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for forming vias in a substrate, and more particularly to a method for forming an insulating layer on the side wall of vias in a substrate by using polymer. 
     2. Description of the Related Art 
       FIGS. 1 to 3  show schematic views of a conventional method for forming vias in a substrate. First, referring to  FIG. 1 , a substrate  1  is provided. The substrate  1  has a first surface  11  and a second surface  12 . Afterward, a plurality of grooves  13  is formed on the first surface  11  of the substrate  1 . An insulating layer  14  is then formed on the side wall of the grooves  13  by chemical vapor deposition, and a plurality of accommodating spaces  15  is formed. The material of the insulating layer  14  is usually silicon dioxide. 
     Afterward, referring to  FIG. 2 , the accommodating spaces  15  are filled with a conductive metal  16 . The material of the conductive metal  16  is usually copper. Finally, the first surface  11  and the second surface  12  of the substrate  1  are ground or etched so as to expose the conductive metal  16 , as shown in  FIG. 3 . 
     In the conventional method, the insulating layer  14  is formed by chemical vapor deposition, so that the thickness of the insulating layer  14  on the side wall of the grooves  13  is limited, and is usually under 0.5 μm. Moreover, the thickness of the insulating layer  14  on the side wall of the grooves  13  is not even, that is, the thickness of the insulating layer  14  on the upper side wall of the grooves  13  is not exactly equal to that on the lower side wall of the grooves  13 . Thus, the electrical capacity is not uniform. 
     Therefore, it is necessary to provide a method for forming vias in a substrate to solve the above problems. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method for forming vias in a substrate, which comprises the following steps: (a) providing a substrate having a first surface and a second surface; (b) forming a groove on the substrate; (c) filling the groove with a conductive metal; (d) removing part of the substrate which surrounds the conductive metal, wherein the conductive metal is maintained so as to form an accommodating space between the conductive metal and the substrate; (e) forming an insulating material in the accommodating space; and (f) removing part of the second surface of the substrate to expose the conductive metal and the insulating material. 
     In the present invention, thicker polymer can be formed in the accommodating space. Also, the thickness of the insulating material in the accommodating space is even. Moreover, the polymer is used as an insulating material in the present invention, so that the polymers with different materials can be chosen for specific processes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 to 3  are schematic views of a conventional method for forming vias in a substrate; 
         FIGS. 4 to 19  are schematic views of a method for forming vias in a substrate according to a first embodiment of the present invention; and 
         FIGS. 20 to 27  are schematic views of a method for forming vias in a substrate according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 4 to 19  show the schematic views of the method for forming vias in a substrate according to the first embodiment of the present invention. Referring to  FIG. 4 , a top view of the substrate  2 , and  FIG. 5 , a cross-sectional view of the substrate  2  along line  5 - 5  in  FIG. 4 , first, a substrate  2  is provided. The substrate  2  has a first surface  21  and a second surface  22 . The substrate  2  is, for example, a wafer or made from silicon. Afterward, a first photo resist layer  23  is formed on the first surface  21  of the substrate  2 , and a first opening  231  is formed on the first photo resist layer  23 . In the embodiment, the first opening  231  is circular from the top view. It is understood that the first opening  231  may be square from the top view. 
     Referring to  FIG. 6 , a groove  24  is formed on the substrate  2  according to the first opening  231  by etching or other methods, and the groove  24  does not penetrate the substrate  2 . Afterward, the first photo resist layer  23  is removed. Then, referring to  FIG. 7 , the groove  24  is filled with a conductive metal  25 . In the embodiment, the material of the conductive metal  25  is copper, and the conductive metal  25  fills up the groove  24  by electroplating. It is understood that the conductive metal  25  may not fill up the groove  24 , and forms a central groove  26 , that is, the conductive metal  25  is formed on the side wall of the groove  24  only, as shown in  FIG. 8 . 
     Referring to  FIG. 9 , the conductive metal  25  which is outside the groove  24  is removed by etching or grinding so as to expose the first surface  21  of the substrate  2 . Then, referring to  FIGS. 10 to 12 , part of the substrate  2  which surrounds the conductive metal  25  is removed, and the conductive metal  25  is maintained so as to form an accommodating space  28  between the conductive metal  25  and the substrate  2 . In the embodiment, the accommodating space  28  is formed by the following methods. Referring to  FIG. 10 , a top view of the substrate  2 , and  FIG. 11 , a cross-sectional view of the substrate  2  along line  11 - 11  in  FIG. 10 , first, a second photo resist layer  27  is formed on the first surface  21  of the substrate  2 . A second opening  271  is then formed on the second photo resist layer  27 , and is at a position corresponding to the groove  24 . The second opening  271  is larger than the first opening  231  ( FIGS. 4 and 5 ) so as to expose the conductive metal  25 . In the embodiment, the second opening  271  is circular and has a central axis, the groove  24  is circular and has a central axis, and the central axes of the second opening  271  and the groove  24  are the same, that is, the central axis of the second opening  271  is the central axis of the groove  24 . It is understood that the central axes of the second opening  271  and the groove  24  may not be the same, but the conductive metal  25  must be exposed. Then, referring to  FIG. 12 , part of the substrate  2  which surrounds the conductive metal  25  is removed by etching or other methods, and the conductive metal  25  is maintained so as to form an accommodating space  28  between the conductive metal  25  and the substrate  2 . The accommodating space  28  surrounds the conductive metal  25 . The second photo resist layer  27  is then removed. 
     Referring to  FIGS. 13 to 18 , an insulating material is formed in the accommodating space  28 . In the embodiment, the insulating material is polymer  29 . However, the insulating material may be silicon dioxide or other material with a property of insulation. In the present invention, the method for forming the polymer  29  in the accommodating space  28  includes but is not limited to the following three methods. 
     The first method is that the polymer  29  is dispersed on the first surface  21  of the substrate  2 , and the position of the polymer  29  corresponds to the accommodating space  28 , as shown in  FIG. 13 . Afterward, the polymer  29  is sucked into the accommodating space  28  by vacuuming, as shown in  FIG. 14 . Finally, part of the polymer  29  which is outside the accommodating space  28  is removed, as shown in  FIG. 18 . 
     The second method is that a plurality of vents  30  is formed to connect the accommodating space  28  to the second surface  22  of the substrate  2 , as shown in the top view of  FIG. 15 . Afterward, the polymer  29  is dispersed on the first surface  21  of the substrate  2 , and the position of the polymer  29  corresponds to the accommodating space  28 . The accommodating space  28  and the vents  30  are then filled with the polymer  29 , as shown in  FIG. 16 . Finally, part of the polymer  29  which is outside the accommodating space  28  and the vents  30  is removed. 
     The third method is that the polymer  29  is atomized and deposited in the accommodating space  28  by spray coating, as shown in  FIG. 17 . Finally, part of the polymer  29  which is outside the accommodating space  28  is removed, as shown in  FIG. 18 . 
     It should be noted that in the previous steps, if the conductive metal  25  does not fill up the groove  24 , it forms a central groove  26  instead, as shown in  FIG. 8 . In the above-mentioned three methods, the polymer  29  fills up both the accommodating space  28  and the central groove  26 . 
     Finally, referring to  FIG. 19 , part of the second surface  22  of the substrate  2  is removed by etching or grinding so as to expose the conductive metal  25  and the insulating material (the polymer  29 ). Part of the first surface  21  of the substrate  2  may preferably be removed by etching or grinding at the same time. 
       FIGS. 20 to 27  show the schematic views of the method for forming vias in a substrate according to the second embodiment of the present invention. Referring to  FIG. 20 , a top view of the substrate  4 , and  FIG. 21 , a cross-sectional view of the substrate  4  along line  21 - 21  in  FIG. 20 , first, a substrate  4  is provided. The substrate  4  has a first surface  41  and a second surface  42 . The substrate  4  is, for example, a wafer or made from silicon. Afterward, a first photo resist layer  43  is formed on the first surface  41  of the substrate  4 , and a first opening  431  is formed on the first photo resist layer  43 . 
     Referring to  FIG. 22 , a groove  44  is formed on the substrate  4  according to the first opening  431  by etching or other methods, and the groove  44  does not penetrate the substrate  4 . Afterward, the first photo resist layer  43  is removed. Then, referring to  FIG. 23 , the groove  44  is filled with a conductive metal  45 . In the embodiment, the material of the conductive metal  45  is copper, and the conductive metal  45  fills up the groove  44  by electroplating. It is understood that the conductive metal  45  may not fill up the groove  44 . 
     Referring to  FIGS. 24 to 25 , part of the substrate  4  which surrounds the conductive metal  45  is removed, and the conductive metal  45  is maintained to form an accommodating space  48  between the conductive metal  45  and the substrate  4 . In the embodiment, the accommodating space  48  is formed by the following methods. First, referring to  FIG. 24 , a second photo resist layer  47  is formed on the second surface  42  of the substrate  4 . A second opening  471  is then formed on the second photo resist layer  47 , and is at a position corresponding to the groove  44 . The second opening  471  is larger than the first opening  431  ( FIG. 21 ). In the embodiment, the second opening  471  is circular and has a central axis, the groove  44  is circular and has a central axis, and the central axes of the second opening  471  and the groove  44  are the same, that is, the central axis of the second opening  471  is the central axis of the groove  44 . It is understood that the central axes of the second opening  471  and the groove  44  may not be the same. Then, referring to  FIG. 25 , part of the substrate  4  which surrounds the conductive metal  45  is removed by etching or other methods, and the conductive metal  45  is maintained so as to form an accommodating space  48  between the conductive metal  45  and the substrate  4 . The accommodating space  48  surrounds the conductive metal  45 . The second photo resist layer  47  is then removed. 
     Referring to  FIG. 26 , an insulating material is formed in the accommodating space  48 . In the embodiment, the material of the insulating material is polymer  49 . However, the material of the insulating material may be silicon dioxide or other material with a property of insulation. In the present invention, the method for forming the polymer  49  in the accommodating space  48  includes but is not limited to the three methods described above in the first embodiment. 
     Finally, referring to  FIG. 27 , part of the second surface  42  of the substrate  4  is removed by etching or grinding to expose the conductive metal  45  and the insulating material (the polymer  49 ). Part of the first surface  41  of the substrate  4  may preferably be removed by etching or grinding at the same time. 
     In the present invention, thicker insulating material (polymer  29 ,  49  for example) can be formed in the accommodating space  28 ,  48 . Also, the thickness of the insulating material (polymer  29 ,  49  for example) in the accommodating space  28 ,  48  is even. Moreover, the polymer  29 ,  49  is used as an insulating material in the present invention, so that the polymers with different materials can be chosen for specific processes. 
     While several embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention should not be limited to the particular forms as illustrated, and that all modifications which maintain the spirit and scope of the present invention are within the scope defined in the appended claims.