Abstract:
A semiconductor device has a first semiconductor die having at least one metal pillar formed along an inner perimeter and at least one bond pad formed along an outer perimeter. A second semiconductor die has at least one metal pillar. A conductive bump connects the at least one metal pillar of the first semiconductor die to the at least one metal pillar of the second semiconductor die. At least one metal dam is formed on the first semiconductor die between the at least one metal pillar of the first semiconductor die and the at least one bond pad.

Description:
FIELD OF THE INVENTION 
     This invention relates to a semiconductor device and, more specifically, to a semiconductor device with metal dam and a fabricating method thereof. 
     BACKGROUND OF THE INVENTION 
     Multiple semiconductor dies may be mounted in a single package in one of two ways. Firstly, two or more semiconductor dies may be arranged next to one another in a horizontal direction along a substrate. Secondly, multiple semiconductor dies may be mounted on top of one another in a vertical direction, i.e. packaging the semiconductor dies into a chip-on-chip (COC) structure (‘COC packaging method’). 
     The COC packaging method includes preparing a bottom semiconductor die having a plurality of bond pads and a top semiconductor die having a plurality of bond pads. The bond pads of the bottom semiconductor die are interconnected to the bond pads of the top semiconductor die using conductive bumps. An underfill is injected into a gap between the bottom semiconductor die and the top semiconductor die. Bond pads formed around the circumference of the bottom semiconductor die are connected to a circuit board through conductive wires. 
     In the COC packaging method, a problem may occur in that an excessive flow of the underfill in the circumferential direction of the bottom semiconductor die may occur during injection. The underfill may cover the bond pads formed around the circumference of the bottom semiconductor die thus making it impossible for the wires to be bonded to the bond pads. 
     Therefore, a need existed to provide a system and method to overcome the above problem. 
     SUMMARY OF THE INVENTION 
     A semiconductor device has a first semiconductor die having at least one metal pillar formed along an inner perimeter and at least one bond pad formed along an outer perimeter. A second semiconductor die has at least one metal pillar. A conductive bump connects the at least one metal pillar of the first semiconductor die to the at least one metal pillar of the second semiconductor die. At least one metal dam is formed on the first semiconductor die between the at least one metal pillar of the first semiconductor die and the at least one bond pad. 
     The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view illustrating a semiconductor device having a metal dam according to an embodiment of the present invention; 
         FIG. 2  is a partial cross-sectional view illustrating a semiconductor device having a metal dam according to a further embodiment of the present invention; 
         FIG. 3  is a partial cross-sectional view illustrating a semiconductor device having metal dams according to another embodiment of the present invention; 
         FIG. 4  is a partial cross-sectional view illustrating a semiconductor device having metal dams according to another embodiment of the present invention; 
         FIG. 5  is a flow chart illustrating a method for fabricating a semiconductor device having a metal dam according to an embodiment of the present invention; and 
         FIGS. 6A through 6E  are cross-sectional views sequentially illustrating the method of  FIG. 5 . 
     
    
    
     Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a partial cross-sectional view of a semiconductor device  100  having a metal dam according to one embodiment of the present invention is illustrated. The semiconductor device  100  may include a first semiconductor die  110 , a second semiconductor die  120 , conductive bumps  130 , an underfill  140 , substrate  150  and a conductive wire  160 . 
     There is no restriction on the type of die for the first semiconductor die  110 . For example, the first semiconductor die  110  may be selected from silicon semiconductors, GaAs semiconductors and equivalents thereof that are commonly known in the art. The first semiconductor die  110  may include at least one bond pad  111  formed substantially along a circumference thereof. Further, the first semiconductor die  110  may include first metal pillars  112  disposed substantially at a central area thereof. 
     The first semiconductor die  110  may include at least one metal dam  113  formed between the bond pad  111  and the first metal pillars  112 . The metal dam  113  may be used to prevent an underfill  140  from bleeding out. 
     The first metal pillars  112  may be made of a material selected from gold (Au), nickel (Ni), copper (Cu), eutectic solders, lead-free solders, nickel-gold (Ni—Au) alloys, copper-nickel (Cu—Ni) alloys, copper (Cu) lead-free solders, and equivalents thereof. However, there is no restriction on the material of the first metal pillars  112 . Bond pads or redistribution layers (RDLs)  115  may be positioned under the first metal pillars  112 . The metal dam  113  may be made of a material selected from gold, nickel, copper, eutectic solders, lead-free solders, nickel-gold alloys, copper-nickel alloys, copper lead-free solders, and equivalents thereof. However, there is no restriction on the material of the metal dam  113 . 
     A seed metal layer  114  may be formed under the metal dam  113 . The seed metal layer  114  may be formed of a material selected from titanium (Ti), titanium tungsten (TiW) and equivalents thereof. However, there is no restriction on the material of the seed metal layer  114 . The metal dam  113  may be greater in thickness than the first metal pillars  112 . With these dimensions, the metal dam  113  can efficiently prevent the underfill  140  from bleeding out. The metal dam  113  may have a width of 1 to 100 μm, at which the form factor of the semiconductor device  100  can be improved. 
     There is no restriction on the kind of the second semiconductor die  120 . For example, the second semiconductor die  120  may be selected from silicon semiconductors, GaAs semiconductors and equivalents thereof that are commonly known in the art. The second semiconductor die  120  includes a plurality of second metal pillars  122  disposed substantially at a central area center thereof. The second metal pillars  122  may be made of a material selected from gold (Au), nickel (Ni), copper (Cu), eutectic solders, lead-free solders, nickel-gold (Ni—Au) alloys, copper-nickel (Cu—Ni) alloys, copper (Cu) lead-free solders, and equivalents thereof. However, there is no restriction on the material of the second metal pillars. Bond pads or redistribution layers (RDLs)  125  may be positioned under the second metal pillars  122 . The second semiconductor die  120  may have a width smaller than that of the first semiconductor die  110 . Accordingly, the bond pad  111  of the first semiconductor die  110  is positioned outside the second semiconductor die  120 . This configuration allows wire bonding of the bond pad  111 . 
     The conductive bumps  130  may be used to electrically connect the first metal pillars  112  of the first semiconductor die  110  to the second metal pillars  122  of the second semiconductor die  120 . The conductive bumps  130  may be made of a material selected form eutectic solders, lead-free solders, and equivalents thereof. However, there is no restriction on the material of the conductive bumps  130 . The conductive bumps  130  may have a melting point lower than the melting points of the first metal pillars  112 , the metal dam  113  and the second metal pillars  122 . Accordingly, when the conductive bumps  130  are melted, the first metal pillars  112 , the metal dam  113  and the second metal pillars  122  maintain their fine pitches without collapsing. 
     In accordance with one embodiment, the thicknesses of the first metal pillars  112 , the metal dam  113  and the second metal pillars  122  may be in the range of approximately 5 to 50 μm. However, the thicknesses of the aforementioned are not limited to this range. The thickness of the conductive bumps  130  may be in the range of approximately 1 to 20 μm. However, the conductive bumps  130  are not limited to this range. The first metal pillars  112  and the second metal pillars  122  may be designed to be greater in thickness than the conductive bumps  130 , so that stress can be sufficiently absorbed. Of course, the metal dam  113  may be designed to be greater in thickness than the conductive bumps  130 , so that the underfill  140  can be sufficiently prevented from bleeding out. 
     The underfill  140  is filled between the first semiconductor die  110  and the second semiconductor die  120  to substantially surround the first metal pillars  112 , the second metal pillars  122  and the conductive bumps  130 . The underfill  140  serves to remove stress resulting from the difference in coefficient of thermal expansion between the first semiconductor die  110  and the second semiconductor die  120 . The underfill  140  in a liquid state flows outwardly (‘bleeding out’) from the second semiconductor die  120  during injection. If bleeding out of the underfill  140  is excessive, the bond pad  111  of the first semiconductor die  110  is covered with the underfill  140 , making it impossible for the wire to bonded thereto. In this embodiment, the metal dam  113  formed between the bond pad  111  and the first metal pillars  112  of the first semiconductor die  110  prevents excessive bleed-out of the underfill  140  to protect the bond pad  111  of the first semiconductor die  110  from being contaminated by the underfill  140 . 
     The substrate  150  may be adhered to the semiconductor die  110  by means of an adhesive  151 . The adhesive  151  may be an adhesive tape, a liquid adhesive, or the like. The listing of the above adhesive types should not be seen as to limit the scope of the present invention. The substrate  150  may be selected from laminated substrates, printed circuit boards, lead frames and equivalents thereof that are commonly known in the art, but is not limited thereto. 
     The conductive wire  160  serves to electrically interconnect the bond pad  111  of the first semiconductor die  110  to the circuit board  150 . 
     In the semiconductor device  100 , the metal dam  113  can be formed simultaneously with the first metal pillars  112 , thereby eliminating the need for additional epoxy dam writing. This contributes to an improvement in the form factor of the semiconductor device  100  and enables the fabrication of the semiconductor device  100  in a stable manner. Further, since the metal dam  113  is made of a metal, not a solder, it is not melted during subsequent high-temperature processing. Accordingly, no short-circuiting occurs between the metal dam  113  and the bond pad  111 . 
     Referring to  FIG. 2 , a partial cross-sectional view of a semiconductor device  200  having a metal dam according to a further embodiment of the present invention is illustrated. The structure of the semiconductor device  200  is similar to that of the semiconductor device  100  illustrated in  FIG. 1 , and the structural differences between the semiconductor devices  100  and  200  will be explained below. 
     As illustrated in  FIG. 2 , the semiconductor device  200  may include a metal dam  213  and a conductive bump  230  formed on the metal dam  213 . The conductive bump  230  may be made of a material selected form eutectic solders, lead-free solders, and equivalents thereof. However, there is no restriction on the material of the conductive bump  230 . 
     The formation of the metal dam  213  and the conductive bump  230  leads to an increase in the thickness of the dam to more effectively prevent the underfill  140  from bleeding out. In addition, the need for an additional process is substantially eliminated due to the formation of the conductive bump  230 . Metal plating is carried out on both the first metal pillars  112  and the metal dam  213  to simultaneously form the conductive bumps  130  and the conductive bump  230  thereon. That is, as a result of the metal plating, the conductive bump  230  is essentially formed on the metal dam  213 . An additional process for removing the conductive bump  230  from the metal dam  213  is required in the fabrication of the semiconductor device  100 , whereas the need for the removal of the conductive bump  230  is eliminated in the fabrication of the semiconductor device  200 . 
     Referring to  FIG. 3 , a partial cross-sectional view of a semiconductor device  300  having metal dams according to another embodiment of the present invention is illustrated. The structure of the semiconductor device  300  is similar to that of the semiconductor device  100  illustrated in  FIG. 1 , and the structural differences between the semiconductor devices  100  and  300  will be explained below. 
     As illustrated in  FIG. 3 , two metal dams  313   a  and  313   b  may be spaced apart from each other in the horizontal direction. The two metal dams  313   a  and  313   b  may be made of a material selected from gold, nickel, copper, eutectic solders, lead-free solders, nickel-gold alloys, copper-nickel alloys, copper lead-free solders, and equivalents thereof. However, there is no restriction on the material of the metal dams  313   a  and  313   b . Seed metal layers  314   a  and  314   b  may be formed under the metal dams  313   a  and  313   b , respectively. The seed metal layers  314   a  and  314   b  may be formed of a material selected from titanium, titanium tungsten and equivalents thereof. However, there is no restriction on the material of the seed metal layers  314   a  and  314   b.    
     In the semiconductor device  300 , the two successive metal dams  313   a  and  313   b  more effectively prevent the underfill  140  from bleeding out to reduce the possibility that the underfill  140  overflowing the first metal dam  313   a  will overflow the second metal dam  313   b.    
     Referring to  FIG. 4 , a partial cross-sectional view of a semiconductor device  400  having metal dams according to another embodiment of the present invention is illustrated. The structure of the semiconductor device  400  is almost the same as that of the semiconductor device  300  illustrated in  FIG. 3 , and the structural differences between the semiconductor devices  300  and  400  will be explained below. 
     As illustrated in  FIG. 4 , the semiconductor device  400  may include two metal dams  413   a  and  413   b  and conductive bumps  430   a  and  430   b  formed on the metal dams  413   a  and  413   b , respectively. The conductive bumps  430   a  and  430   b  may be made of a material selected form eutectic solders, lead-free solders, and equivalents thereof. However, there is no restriction on the material of the conductive bumps  430   a  and  430   b.    
     The formation of the metal dams  413   a  and  413   b  and the conductive bumps  430   a  and  430   b  may lead to an increase in the thickness of the dam to more effectively prevent the underfill  140  from bleeding out. In addition, the need for an additional process is substantially eliminated due to the formation of the conductive bumps  430   a  and  430   b . Metal plating is carried out on both the first metal pillars  112  and the two metal dams  413   a  and  413   b  to simultaneously form the conductive bumps  130  and the conductive bumps  430   a  and  430   b  thereon. That is, as a result of the metal plating, the conductive bumps  430   a  and  430   b  are essentially formed on the metal dams  413   a  and  413   b , respectively. An additional process for removing the conductive bumps  430   a  and  430   b  from the metal dams  413   a  and  413   b , respectively, is required in the fabrication of the semiconductor device  300 , whereas the need for the removal of the conductive bumps  430   a  and  430   b  is eliminated in the fabrication of the semiconductor device  400 . 
     Referring to  FIG. 5 , a flow chart of a method for fabricating a semiconductor device having a metal dam according to an embodiment of the present invention is illustrated. As illustrated in  FIG. 5 , the method includes the following steps: preparation of a first semiconductor die (S 1 ), preparation of a second semiconductor die (S 2 ), die attach (S 3 ), interconnection (S 4 ), underfill injection (S 5 ), and wire bonding (S 6 ). 
     Referring to  FIGS. 6A through 6E , cross-sectional views sequentially illustrating the method of  FIG. 5  are illustrated. As illustrated in  FIG. 6A , a first semiconductor die  110  may have a plurality of first metal pillars  112  and at least one metal dam  213  may be prepared in step S 1 , and a second semiconductor die  120  having a plurality of second metal pillars  122  may be prepared in step S 2 . 
     Specifically, the first metal pillars  112  of the first semiconductor die  110  may be formed by metal plating, and the metal dam  213  may be formed between the bond pad  111  and the first metal pillars  112  by metal plating. The first metal pillars  112  may be simultaneously formed with the metal dam  213 . 
     The first metal pillars  112  may be formed on bond pads and redistribution layers  115 . The metal dam  213  may be formed on a seed metal layer  114 . Conductive bumps  130  and a conductive bump  230  may be formed on the first metal pillars  112  and the metal dam  213 , respectively. The conductive bumps  130  and  230  are formed at the same time. 
     The second metal pillars  122  of the second semiconductor die  120  may be formed by metal plating. The second metal pillars  122  may be formed on bond pads or redistribution layers  125 . The first metal pillars  112  and the second metal pillars  122  may have the same pitches. The conductive bumps  130  may also be formed on the second metal pillars  122 . That is, the conductive bumps  130  may be formed on the first metal pillars  112  and/or the second metal pillars  122 . 
     Although steps S 1  and S 2  are sequentially illustrated in  FIGS. 6A and 6B , respectively, the present invention is not limited to this sequence. That is, the first semiconductor die  110  and the second semiconductor die  120  may be prepared simultaneously or in the reverse order. 
     As illustrated in  FIG. 6B , in step S 3 , the first semiconductor die  110  may be adhered to a substrate  150  using an adhesive  151 . The adhesive  151  may be an adhesive tape, a liquid adhesive, or the like. The substrate  150  may be selected from laminated substrates, printed circuit boards, lead frames and equivalents thereof. 
     As illustrated in  FIG. 6C , in step S 4 , the first semiconductor die  110  and the second semiconductor die  120  may be electrically interconnected to each other. First, the second metal pillars  122  of the second semiconductor die  120  are positioned on the first metal pillars  112  of the first semiconductor die  110 . The first metal pillars  112  and or the second metal pillars  122  are formed with the conductive bumps  130  thereon. Subsequently, the conductive bumps  130  may be melted by increasing the temperature to approximately 150 to 250° C. Then, the temperature may be reduced to cool the conductive bumps  130  down to room temperature. This cooling allows the first metal pillars  112  to be electrically connected to the second metal pillars  122 . 
     As illustrated in  FIG. 6D , in step S 5 , an underfill  140  is filled in a gap between the first semiconductor die  110  and the second semiconductor die  120 . The underfill  140  flows into the gap between the first semiconductor die  110  and the second semiconductor die  120  and surrounds the first metal pillars  112 , the second metal pillars  122  and the conductive bumps  130 . 
     The underfill  140  flowing in the circumferential direction of the first semiconductor die  110  is stopped by the metal dam  213  of the first semiconductor die  110 . That is, excessive bleed-out of the underfill  140  is prevented by the metal dam  213 , and therefore, the bond pad  111  of the first semiconductor die  110  is protected from contamination by the underfill  140 . 
     As illustrated in  FIG. 6E , in step S 6 , the bond pad  111  of the first semiconductor die  110  and the substrate  150  may be bonded to each other through a conductive wire  160 . The method may further include encapsulating the first semiconductor die  110 , the second semiconductor die  120  and the conductive wire  160  by an encapsulant after step S 6 . Marking, sawing and solder ball attachment steps may be further carried out after the encapsulation. 
     In the fabrication of the semiconductor device  200 , a metal dam  210  may be further formed between the bond pad  111  and the first metal pillars  112  in step S 1 . In step S 5 , bleeding-out of the underfill  140  is efficiently prevented by the metal dam  213 . The metal dam  213  and the first metal pillars  112  may be formed at the same time, which eliminates the need for an additional process for forming a dam in subsequent processing steps. The metal dam  213  may be formed with a width and a thickness similar to those of the first metal pillars  112 . These dimensions may improve the form factor of the semiconductor device  200 . 
     In step S 1 , an electrode for metal plating is connected to sequentially form the outermost first semiconductor die  110  and the first metal pillars  112 , which makes the metal dam  213  relatively thicker than the first metal pillars  112 . As a result of the metal plating, the thicknesses of the first metal pillars  112  become relatively uniform. 
     The method may further include removing the conductive bump  230  formed on the metal dam  213  after step S 4 . The removal of the conductive bump  230  completes the fabrication of the semiconductor device  100  illustrated in  FIG. 1 . That is, the semiconductor device  100  has the same structure as the semiconductor device  200  of  FIG. 2 , except that the conductive bump  230  is removed. 
     This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.