Abstract:
A semiconductor device and a fabrication method thereof are provided. The semiconductor device has a probing pad formed on a chip. The probing pad is connected to an output pad and an internal circuit though a fuse. After an electrical testing of the chip by the probing pad, the fuse is cut by a laser beam. Therefore, the probing pad is disconnected from the output pad and the internal circuit. The output pad is connected to an output lead of a package, which is encapsulating the chip. According to the device and the fabrication methods thereof, performance of the device can be enhanced by a low parasitic capacitance and a low parasitic resistance.

Description:
[0001]    This application relies for priority upon Korean Patent Application No. 2001-15147, filed on Mar. 23, 2001, the contents of which are herein incorporated by reference in their entirety.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to semiconductor devices and fabrication methods thereof and, more particularly, to semiconductor devices having a fuse connected to a pad and fabrication methods thereof.  
         BACKGROUND OF THE INVENTION  
         [0003]    Generally, a semiconductor device consists of a semiconductor chip and a package encapsulating the chip. The semiconductor chip comprises a plurality of conductive pads. The pads are generally located at a peripheral area, i.e., close to the edge of the chip. The pads are used for an electrical testing of the chip during its fabrication process. Generally, a plurality of the chips is fabricated simultaneously on a semiconductor wafer. The electrical testing is performed to sort out defective chips among the plurality of the chips.  
           [0004]    Meanwhile, the pads are also used for a packaging process. The pads are electrically connected to outputs of the semiconductor device during the packaging process. For example, each of the pads is connected to a corresponding one of output leads of the package through conductive wires.  
           [0005]    Generally, each of the pads is used for both the electrical testing and the packaging process. In this case, it is difficult to bond the wires on the pads. This is due to damage on the pad. During the electrical testing, probing tips are physically contacted to the pads. This physical contacting induces the damage on the pads.  
           [0006]    A semiconductor wafer, which is useful for a wafer-level burn-in testing, is disclosed in a document, Japanese laid-open patent No. 2000-124279. FIG. 1 is a plan view of the wafer disclosed in the Japanese document.  
           [0007]    Referring to FIG. 1, a plurality of semiconductor chips  1  is arranged on a wafer. Scribe lanes  3  intervene between each of the plurality of semiconductor chips  1 . A burn-in power line  4  is formed on the scribe lanes  3 . The burn-in power line  4  is connected electrically to a probing pad  2 . The probing pad  2  is connected electrically to internal circuitry (though not shown) of the chip through a bonding pad  7 . A fuse  5  intervenes between the bonding pad  7  and the probing pad  2 .  
           [0008]    The burn-in testing of the wafer of the Japanese documentation is described hereinafter. The wafer is loaded into an oven having a selected temperature and atmosphere. Next, a burn-in voltage is applied to the burn-in power lines  4 . By applying the burn-in voltage, there is electric current flowing into the chips  1 . An electrical current, which is excessively large, flows into a defective chip. The excessive current makes the fuse  5  on the defective chip melt, thereby opening the fuse. That is to say, the defective chip is disconnected from the burn-in power line  4 . If the defective chip were still connected to the burn-in power line  4  with the excessive current, the operating voltage would be decreased. According to the Japanese documentation, there is no decreasing in the burn-in voltage, because the defective chip is disconnected from the burn-in power line  4 . Therefore, the burn-in testing can be performed under a stable condition for the other good chips. After the burn-in testing, the good chips are subject to subsequent manufacturing processes including a packaging process.  
           [0009]    According to the Japanese documentation, the fuse of the defective chip is opened, while the fuse of the good chip remained not opened. The inventor of the present invention found that the probing pad, which is connected to the bonding pad in the good chip through the not-opened fuse, induces increased parasitic capacitance and parasitic resistance. The increased parasitic capacitance and parasitic resistance may induce a speed delay in operation, even though the chip is packaged.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the present invention to provide a semiconductor device, which has an enhanced performance including no delay in device operation.  
           [0011]    Another object of the present invention is to provide a method for forming a semiconductor device, which is free from an affect of a parasitic capacitance and resistance induced by a probing pad.  
           [0012]    According to one aspect of the present invention, a semiconductor device has a chip having an internal circuit. An opened fuse is formed on the chip. The opened fuse has two ends. An output pad is formed on the chip. The output pad has a first exposed portion. The output pad is connected to the one end of the opened fuse. A package has a output lead, which is connected to the output pad. The semiconductor device also has a probing pad. The probing pad has a second exposed portion and is connected to the other end of the opened fuse. Preferably, the opened fuse is located closer to the first exposed portion than the second exposed portion.  
           [0013]    According to another aspect of the invention, a method of forming a semiconductor device comprises providing chips having a plurality of probing pads, a plurality of output pads and a plurality of fuses. Each of the plurality of probing pads is connected to each of the plurality of output pads though each of the plurality of fuses. The chips are electrically tested by a plurality of probing tips to identify a portion of the chips including good chips and repairable chips. All fuses, which are in the good chips and the repairable chips, are cut. A package having a plurality of output leads is provided. Each of the output leads is electrically connected to each of the output pads. The cutting is performed by a laser beam.  
           [0014]    According to another aspect of the invention, a method of forming a semiconductor device comprises providing a wafer. A first layer is formed on the wafer. A second layer is formed on the first layer. The second layer is patterned to expose a portion of the first layer and to form a probing pad and an output pad. The probing pad is electrically connected to the output pad through the exposed portion of the first layer. Electrical testing of the wafer is performed by using the probing pad. A laser beam cuts the exposed portion of the first layer.  
           [0015]    Accordingly, it is possible to significantly reduce the affect of a parasitic capacitance and a parasitic resistance on performance of the device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    Other features of the present invention will be more readily understood from the following detail description of specific embodiment thereof when read in conjunction with the accompanying drawings, in which:  
         [0017]    [0017]FIG. 1 is a plan view illustrating semiconductor devices according to a prior art;  
         [0018]    [0018]FIG. 2 is a plan view illustrating a semiconductor device according to a present invention; and  
         [0019]    FIGS.  3  to  10  are cross sectional views illustrating successive process steps for forming a semiconductor device according to a present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings, even though the scope of the present invention is not limited to the embodiments.  
         [0021]    [0021]FIG. 2 is a schematic plan view illustrating a semiconductor device according to the present invention.  
         [0022]    Referring to FIG. 2, a semiconductor chip  10  of the semiconductor device has a plurality of probing pads  17   p  thereon. The plurality of probing pads  17   p  is formed on a peripheral area, i.e., close to the edge of the chip  10  in order to make it easy to arrange probing tips of a probing card. The probing card is used for subsequent electrical testing of the device.  
         [0023]    The chip  10  has also a plurality of output pads  17 b thereon. The output pads  17   b  are electrically connected to output leads of a package of the device such as balls, though not shown. The output pads  17   b  are formed irregularly on the chip  10 . In detail, the output pads  17   b  are located adjacent to selected internal circuits of the chip  10  like as an input/output circuit, a power source line, a ground line and a control circuit. Preferably, the output pads  17   b  may be located at a central portion of the chip  10  as described in the figure. That is to say, the output pads  17   b  may be formed not at the peripheral area. Such an arrangement of the output pads  17   b  reduces a connection length between the output pads  17   b  and the selected internal circuits, thereby substantially reducing a parasitic capacitance and a parasitic resistance therebetween. Therefore, the performance of the device becomes enhanced.  
         [0024]    The chip  10  has also a plurality of opened fuses  15   f ′. Each of the opened fuses  15   f ′ has one end electrically connected to selected one of the output pads  17   b  and the other end connected to selected one of the probing pads  17   p.  Each of the opened fuse s  15   f ′ electrically disconnects the selected one of the output pads  17   b  from the selected one of the probing pads  17   p.  Preferably, each of the opened fuse  15   f ′ may be located more closely to an exposed portion of the selected one of the output pads  17   b  than to an exposed portion of the selected one of the probing pads  17   p.  Such an arrangement of the opened fuses  15   f ′ reduces a connection length between the output pads  17   b  and the opened fuses  15   f ′, thereby substantially reducing a parasitic capacitance and a parasitic resistance therebetween.  
         [0025]    The semiconductor device also has packaging elements.  
         [0026]    In this embodiment, a flip chip type package is used, though not shown. But, the present invention is not limited to this embodiment. Other kinds of packages may be used in virtue of the present invention. For example, bumps may be replaced by conductive wires. That is to say, a plurality of conductive bumps having a rounded shape each is formed on each of the output pads  17   b . A plurality of under-bump metal patterns may be formed between each of the conductive bumps and each of the output pads  17   b . The under-bump metal patterns act as diffusion barriers, which prevent diffusions of metal atoms from the output pads  17   b  into the conductive bumps or from the conductive bumps into the output pads  17   b . For better understanding and to simplify the drawing, other packaging elements are not described in this embodiment.  
         [0027]    According to the semiconductor device of the present invention, each of the opened fuse  15   f  electrically disconnect the output pads  17   b  from the probing pads  17   p.  And, each of the opened fuse  15   f ′ may locate more closely to the exposed portion of the selected one of the output pads  17   b  than to the exposed portion of the selected one of the probing pads  17   p.  In addition, the output pads  17   b  are preferably located adjacent to the selected internal circuits of the chip  10 . Therefore, it is possible to significantly reduce the effect of a parasitic capacitance and a parasitic resistance on performance of the device.  
         [0028]    FIGS.  3  to  10  are cross sectional views illustrating successive process steps for forming the semiconductor device described above. For better understanding, the drawings show only a portion of a semiconductor wafer. That is to say, the drawings show only one fuse, one probing pad and one output pad. However, a plurality of fuses, a plurality of probing pads and a plurality of output pads may be formed on a chip area of the semiconductor wafer.  
         [0029]    Referring to FIG. 3, an insulating layer  13  is formed on a semiconductor wafer  11 . A metal layer  18  is formed on the insulating layer  13 . The metal layer  18  is formed preferably by sequentially stacking a barrier metal layer  15  and a pad metal layer  17 . The barrier metal layer  15  is a titanium nitride layer. The pad metal layer  17  is an aluminum layer or an aluminum alloy layer. Before the formation of the barrier metal layer  15 , an ohmic metal layer like a titanium layer may be formed on the insulating layer  13 .  
         [0030]    Referring to FIG. 4, the metal layer  18  is patterned to form a metal pattern  18   a  on a selected area of the insulating layer  13  of a chip area. The metal pattern  18   a  comprises a barrier metal pattern  15   a  and a pad metal pattern  17   a , which are continuously stacked on the insulating layer  13 . On a resultant structure having the metal pattern  18   a , a first photoresist pattern  19  is formed to expose a portion of the pad metal pattern  17   a.    
         [0031]    Referring to FIG. 5, the exposed portion of the pad metal pattern  17   a  is selectively etched using the first photoresist pattern  19  as an etching mask to expose a portion of the barrier metal pattern  15   a , thereby forming a probing pad  17 p and an output pad  17   b . The probing pad  17 p and the output pad  17   b  are separated from each other, but electrically connected to each other through the exposed portion of the barrier metal pattern  15   a . The exposed portion of the barrier metal pattern  15   a  is a fuse  15   f.    
         [0032]    The probing pad  17   p  is formed on a peripheral area of the chip area. A probing card has a plurality of probing tips. One of the tips physically and electrically contacts a corresponding probing pad  17   p  during a subsequent electrical testing. Therefore, the arrangement of probing pads  17   p  on the peripheral area is helpful for providing simple arrangement of the tips in the probing card. The output  17   b  is arranged irregularly on the chip area. In detail, the output pad  17   b  is located adjacent to internal circuits like as an input/output circuit, a power source line, a ground line and a control circuit. Preferably, the output  17   b  may be formed at the central portion, not on the peripheral area. This arrangement of the output pad  17   b  reduces parasitic capacitance and parasitic resistance between the output pad  17   b  and the internal circuits, thereby enhancing the performance of the device.  
         [0033]    After formation of the fuse  15   f , the first photoresist pattern  19  is removed. On a resultant structure having the output  17   b  and the probing pad  17   p,  a passivation layer  21  is formed to protect the chip area. The passivation layer  21  comprises a silicon nitride layer.  
         [0034]    Referring to FIG. 6, the passivation layer  21  is patterned to expose a portion of the output pad  17   b  and a portion of the probing pad  17   p.  Preferably, a distance between the fuse  15   f  and the exposed portion of the output pad  17   b  is shorter than a distance between the fuse  15   f  and the exposed portion of the probing pad  17   p.  That is to say, the fuse  15   f  is preferably formed closely to the exposed portion of the output pad  17   b.    
         [0035]    A polyimide layer  23  is formed on the resultant structure. The polyimide layer  23  acts as a buffer layer to protect the chip area from an epoxy-molding compound during a subsequent packaging process. In addition, the polyimide layer  23  substantially prevents alpha particles from penetrating into the chip area. The polyimide layer  23  is patterned to form a probing pad opening  25   p,  a fuse opening  25   f  and an output pad opening  25   b . The probing pad opening  25   p  exposes the exposed portion of the probing pad  17   p.  The fuse opening  25   f  exposes a portion of the passivation layer  21  on the fuse  15   f . The output pad opening  25   b  exposes the exposed portion of the output pad  17   b.    
         [0036]    Referring to FIG. 7, the electrical testing, which is briefly described above, is performed for the resultant structure of FIG. 6. The electrical testing comprises physically and electrically contacting the probing tip  27 , which is briefly described above, onto the exposed portion of the probing pad  17 p. The probing tip  27  is connected to a set of testing equipment. Electrical input signals are applied into the chip from the testing equipment through the probing tip  27 , the fuse  15   f  and output pad  17   b . The testing equipment measures electrical output signals from the chip through the probing tip  27 , the fuse  15   f  and output pad  17   b . With the testing process, it is determined whether the chip is defective or not. If the chip is defective, no subsequent manufacturing process is needed. If the chip is not defective or repairable, subsequent manufacturing process is performed described bellow. If the chip is repairable, the chip may be repaired by a well-known repairing process in a subsequent process step.  
         [0037]    The probing tip  27  induces physical damage  29  on the probing pad  17   p,  because the probing tip  27  physically contacted onto the probing pad  17   p.  If this damage were formed on the output pad  17 , there would be a problem during a subsequent process step. That is to say, there would be week adhesiveness of a wire or a bump during the subsequent packaging process. As a result, reliability of the device would become degraded. However, in the present invention, there is only damage on the probing pad  17   p,  but no damage on the output pad  17   b  on which the wire or the bump is to be connected or formed in a subsequent process step.  
         [0038]    Referring to FIG. 8, the fuse  15   f  is cut by laser beam  31 , thereby forming an opened fuse  15   f ′. That is to say, the probing pad  17   p  and the bump pad  17   p  are electrically disconnected from each other. In case that a plurality of fuses is formed on the chip as described above, all of the fuses  15   f  of the chip are completely cut. Therefore, the device is free from the effect of a parasitic capacitance and a parasitic resistance induces by the probing pads  17   p.  The fuse  15   f  may be cut during the repairing process for the repairable chip.  
         [0039]    Next, the packaging process is performed as described below. In this embodiment, a flip chip type packaging process is used. But, the present invention is not limited to this embodiment. Other kinds of packaging processes may be used in virtue of the present invention. For example, bumps may be replaced by conductive wires.  
         [0040]    Referring to FIG. 9, an under bump metal layer  33  is formed by a well-known method on the resultant structure. The forming of the under bump metal layer  33  is preformed by sequentially stacking a wetting layer and a diffusion barrier layer. On the under bump metal layer  33 , a second photoresist pattern  35  is formed to expose a portion of the under bump layer  33 , which is located on the bump pad  17   b . On the exposed under bump layer  33 , a bump pattern  37  is selectively formed by an electroplating method. The material of the bump pattern  37  is an alloy layer of Pb and Sn.  
         [0041]    Referring to FIG. 10, the second photoresist pattern  35  is removed. A portion of the under bump metal layer  33  is etched using the bump as an etching mask. The portion of the under bump metal layer  33  is etched preferably by wet etching. As a result, an under bump metal pattern  33   a  is formed, intervening between the bump pad  17   b  and the bump pattern  37 . Next, the bump pattern  37  is subject to a reflowing under a selected temperature, thereby forming a bump  37   a  having a rounded shape. During the reflowing step, the under bump metal pattern  33   a  prevents the bump  37   a  and the bump pad  17   b  from react with etch other by inter-diffusions.  
         [0042]    Continuously, subsequent steps of the flip chip type packaging process are completed as well known in the art. And then, a final package testing is performed to check whether the packaging process is properly performed and to classify into a good device or a defective device.  
         [0043]    Though only one chip is formed on the wafer in this embodiment, a plurality of chips may be formed on the wafer with a plurality of scribe lanes between the chips. The plurality of the chips is separated by cutting along with the scribe lanes, after the reflowing step.  
         [0044]    According to the present invention, the probing pad  17   p  is electrically disconnected from the output pad  17   b . And the opened fuse  15   f ′ may be located more closely to the exposed portion of the output pad  17   b  than to the exposed portion of the probing pad  17   p.  In addition, the output pad  17   b  is preferably located adjacent to the selected internal circuits. Therefore, it is possible to significantly reduce the effect of a parasitic capacitance and a parasitic resistance on performance of the device.  
         [0045]    In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purpose of limitation, the scope of the invention being set forth in the following claims: