Patent Publication Number: US-7898070-B2

Title: Image sensor package and fabrication method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of application Ser. No. 11/822,011, filed on Jun. 29, 2007, now U.S. Pat. No. 7,595,220 and for which priority is claimed under 35 U.S.C. §120; the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to image sensor packages, and more particularly to an image sensor package with reduced dimensions and a method for fabricating the same. 
     2. Description of the Related Art 
     An essential step in the manufacturing of all integrated circuit devices is known as packaging. Integrated circuit devices are widely used in digital applications subsequent to packaging. For example, digital cameras, digital video recorders, mobile phones, and computers. 
       FIG. 1  is a cross section of a conventional image sensor package. A chip  2  is provided with a sensor device  4  formed thereon. A bonding pad  6  is formed on the chip  2  and electrically connects to the sensor device  4 . In  FIG. 1 , a covering plate  8  is bonded to the chip  2  followed by attaching to a carrying substrate  10 . A conductive layer  12  is formed on a backside and extends to a sidewall of the carrying substrate  10  to electrically connect to the bonding pad  6 . A solder ball  14  is formed on the conductive layer  12  and electrically connects to the bonding pad  6 . In the conventional image sensor package, a chip, a covering plate, and a carrying substrate are all required. Thus, the dimensions of a conventional image sensor package are large. Because the conductive layer is formed on the exterior disposition of the image sensor package, the conductive layer is easily damaged during fabrication. 
     Thus, an image sensor package and fabrication method thereof improving upon the described problems is needed. 
     BRIEF SUMMARY OF INVENTION 
     Accordingly, the invention provides an image sensor package. An exemplary embodiment of the image sensor package comprises a first substrate comprising a sensor device thereon and a hole therein; a bonding pad comprising a first opening formed on an upper surface of the first substrate; a second substrate disposed on the first substrate; a spacer element comprising a second opening formed on the second substrate; a conductive plug formed in the hole and through the first and second openings to the second substrate to electrically contact with the bonding pad; a conductive layer formed on a lower surface of the first substrate and electrically connected to the conductive plug; and a solder ball formed on the conductive layer and electrically connected to the bonding pad. The image sensor package further comprises a second substrate bonded to the first substrate. The thickness of the image sensor package is reduced because a chip substrate, on which the sensor device is formed, is ground and another substrate serving as carrying plate is not necessary. Thus, the dimensions of the image sensor package are reduced. Moreover, the conductive layer is formed on the lower surface of the first substrate and electrically connects to the bonding pad by the conductive plug rather than extending on the exterior sidewall of the first substrate to the bonding pad. Thus, damage of the conductive layer during fabrication is avoided to increase fabrication yield. 
     The invention also provides a method for fabricating an image sensor package. The method comprises providing a first substrate comprising a sensor device thereon and a hole therein; forming a bonding pad comprising a first opening on an upper surface of the first substrate; disposing a second substrate on the first substrate; forming a spacer element comprising a second opening on the second substrate; forming a conductive plug in the hole and through the first and second openings to second substrate to electrically contact with the bonding pad; forming a conductive layer on a lower surface of the first substrate and electrically connected to the conductive plug; and forming a solder ball on the conductive layer and electrically connected to the bonding pad. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is cross section of a conventional image sensor package; 
         FIGS. 2-8  are cross sections of a method for fabricating an image sensor package according to an embodiment of the invention; and 
         FIG. 9  is a flowchart of a method for fabricating an image sensor package according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIGS. 2-8  are cross sections of a method for fabricating an image sensor package according to an embodiment of the invention. Although the invention will be described with respect to preferred embodiments of a method for fabricating an image sensor package. The invention may also be applied to fabricating package for others semiconductor devices. 
     In  FIG. 2 , a first substrate  102  having an upper surface  1021  and a lower surface  1022  is provided. Preferably, the first substrate  102  is made of bulk silicon, silicon on insulator, or other suitable semiconductor material. The upper surface  1021  may be referred to as a foreside, and the lower surface  1022  may also be referred to as a backside. A sensor device  104  such as complementary metal oxide semiconductor (CMOS) or charge coupled device (CCD) is formed on the upper surface  1021  of the first substrate  102 . In one embodiment, the sensor device  104  may be formed by CMOS processes. Moreover, the first substrate  102  may also be referred to as an image sensor chip substrate. 
     As shown in  FIG. 2 , a bonding pad  106  comprising an opening  108  is subsequently formed on the upper surface  1021  of the first substrate  102  and electrically connects to the sensor device  104 . In one embodiment, a conductive material layer such as copper is formed on the upper surface  1021  of the first substrate  102  by, for example, sputtering, evaporating, or plasma enhanced chemical vapor deposition (PEVCD). The conductive material layer is then patterned by photolithography and etching to form the bonding pad  106  and the opening  108  therein. The opening  108  may be a circular shape and surround and expose a portion of the upper surface  1021  of the first substrate  102 . 
     In  FIG. 3 , a cavity  110  is formed in the first substrate  102  by dry-etching. In some embodiments, the portion of upper surface  1021  of the first substrate  102  exposed by the opening  108  is removed by dry-etching such as plasma etching. An insulating layer  112  is subsequently formed in the cavity  110 . In one embodiment, the insulating material layer such as silicon oxide, silicon nitride or other suitable insulating material is conformingly deposited on the upper surface  1021  of the first substrate  102  and disposed on the sidewalls and the bottom of the cavity  110  by chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD), or plasma enhanced chemical vapor deposition (PECVD). Then, a patterned photoresist layer (not shown) is formed in the cavity  110 , which servers as a masking layer, followed by removal of a portion of the insulating material layer to form the insulating layer  112 , as shown in  FIG. 3 . 
     In  FIG. 4 , a second substrate  114 , also referred to as a covering plate, is provided with a spacer element  116  comprising an opening  118  formed thereon. Preferably, the second substrate  114  may be a transparent material such as glass, quartz, opal, or plastic. In one embodiment, a protecting layer (not shown) is optionally formed on a surface of the second substrate  114  opposite the spacer element  116  to prevent from abrasion. 
     In one embodiment, a layer such as polyimide, photoresist material or epoxy is conformingly formed on the second substrate  114 . The layer is subsequently patterned by photolithography and etching to form the spacer element  116  having the opening  118  therein, as shown in  FIG. 4 . 
     In  FIG. 5 , the second substrate  114  is then disposed on the first substrate  102  to form a distance therebetween. In one embodiment, an adhesive layer  120  is coated on the spacer element  116  followed by bonding the second substrate  114  to the first substrate  102 . Note that the cavity  110  (shown in  FIG. 3 ) is sealed by bonding to form an airtight space (not shown) between the first and second substrates  102  and  114 . Moreover, the opening  118  is correspondingly disposed on the opening  108  and a distance between sidewalls of the opening  118  is more than that of the opening  108 . That is, the opening  118  is larger than the opening  108 . Thus, a potion of an upper surface of the bonding pad  106  is exposed to contact a conductive plug subsequently formed. 
       FIG. 6  is a plan view of an image sensor package shown in  FIG. 5 , in which the plan view is illustrated in a local view to describe an embodiment of the invention. In  FIG. 6 , a portion of the second substrate  114  is outlined by dotted and non-doted lines, and a sensor device region  126  depicts an area where the sensor device  104  (not labeled) is formed. The bonding pad  106  extends to the sensor device region  126  and electrically connects to the sensor device  104 . The spacer element  116  is formed outside the sensor device region  126  and covers a portion of the bonding pad  106 . Note that because the opening  118  is larger than the opening  108 , a portion of the bonding pad  106  is thus exposed so that the overlapping openings  118  and  108  become concentric circles, which likes that of a donut, as shown in  FIG. 6 . 
     It&#39;s appreciated that the shape of the overlapping openings  118  and  108  may be any shape such as triangle or polygon. In  FIG. 6 , although one overlapping opening  118  and  108  is shown, the overlapping opening may be numerous and surround the sensor device region  126 . 
     As shown in  FIG. 5 , the first substrate  102  is thinned to form a hole  124 . In one embodiment, a portion of the first substrate  102  from the lower surface  1021  to the airtight space and further to the insulating layer  112  on the bottom of the cavity  110  (not labeled) is removed to form the hole  124  by grinding or polishing. The grinding or polishing may be performed by chemical mechanical polishing (CMP) process. 
     In  FIG. 7 , a conductive plug  128  is subsequently formed in the hole  124 , passes through the bonding pad  106  and spacer element  116  and electrically contacts with the bonding pad  106 . In one embodiment, a conductive material such as copper, gold, aluminum, tungsten or alloy thereof is formed in the hole  124  and passes through the opening  108  formed in the bonding pad  106  and the opening  118  formed in the spacer element  116  and further extends to the second substrate  114  by electroplating, or electroless-plating. 
     Note that the spacer element  116  and bonding pad  106  may surround the conductive plug  128  due to the openings  108  and  118 , respectively. Moreover, since the opening  118  is larger than the opening  108  the conductive plug  128  has a top surface larger than its bottom surface. Because the conductive plug  128  contacts the upper surface and sidewall of the bonding pad  106 , the conductive area of the subsequently formed image sensor package is increased. 
     As shown in  FIG. 7 , a trench  130  is formed in the first substrate  102  followed by depositing of an insulating layer  132  on the lower surface  1022  of the first substrate  102 . In some embodiments, a portion of the first substrate  102  is dry-etched along a predetermined dicing line to form the trench  130 . Then, the insulating layer  132  such as silicon oxide, silicon nitride, silicon oxynitride is conformingly formed on the lower surface  1022  of the first substrate  102  and the trench  130 . A portion of the insulating layer  132  is subsequently removed to expose the conductive plug  128 . In  FIG. 7 , a cushioning layer  134  such as polyimide (PI), or photoresist material is formed on the insulating layer  132 . The cushioning layer  134  is formed at the location where a solder ball is to be subsequently formed. 
     In  FIG. 8 , a conductive layer  136 , also referred to as re-distribution layer, is subsequently formed on the cushioning layer  134  and electrically connects to the conductive plug  128 . In one embodiment, a conductive material layer such as aluminum, copper, nickel, or any suitable conductive material is formed on the lower surface  1022  of the first substrate  102  by sputtering, evaporating, electroplating or PECVD. Then, the conductive material layer is patterned by photolithographic and etching to form the conductive layer  136 . Because the conductive material layer is patterned, the signal path from the sensor device  104  may be re-layout. 
     A solder mask  138  is coated on the conductive layer  136  and exposes a portion of the conductive layer  136  to define the location where the solder ball is formed. Then, the solder ball  140  is formed on the conductive layer  136  to electrically connect thereto. In one embodiment, a solder material is formed on the exposed conductive layer  136  followed by a reflow step to form the solder ball  140 . After described steps, an individual die is cut along a predetermined cutting line thereof. Thus, fabrication of an image sensor package  150  according to an embodiment of the invention, as shown in  FIG. 8 , is complete. 
     Note that because the first substrate, on which the sensor device is formed, is further thinned. Thus, the image sensor package according to an embodiment of the invention has an overall thickness thinner than that of a conventional image sensor package using three substrates including an image sensor chip substrate, covering plate and carrying substrate. Moreover, since the conductive layer is formed on the lower surface of the first substrate and electrically connects the bonding pad by the conductive plug formed inside the hole of the first substrate, the conductive layer is not formed on a sidewall of the first substrate. Thus, damage to the conductive layer during fabrication, for example cutting, is eliminated and fabrication yield is further improved. 
     Furthermore, the conductive plug of the image sensor package according to an embodiment of the invention has a top surface larger than a bottom surface thereof. Thus, the mechanical strength of the image sensor package is enhanced and the firmness is further improved. 
       FIG. 9  is a flowchart of a method for fabricating an image sensor package according to an embodiment of the invention. In  FIG. 9 , the method comprises: providing a first substrate having a sensor device, as shown in S 5 ; forming a bonding pad having an opening on the first substrate, as shown in S 10 ; removing a portion of the first substrate to form a cavity, as shown in S 15 ; bonding a second substrate to the first substrate to form a distance therebetween, as shown in S 20 ; thinning the first substrate to form a hole therein, as shown in S 25 ; filling a conductive material in the hole to form a conductive plug passing through the opening of the bonding pad, as shown in S 30 ; forming a trench in the first substrate, as shown in S 35 ; forming an insulating layer on a lower surface of the first substrate, as shown in S 40 ; forming a conductive layer on the lower surface of the first substrate and electrically connected to the conductive plug, as shown in S 45 ; forming a solder ball on the conductive layer, as shown in S 50 ; and complete an image sensor package by dicing, as shown in S 55 . 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.