Abstract:
There are provided a semiconductor package comprising: a semiconductor substrate including an integrated circuit unit, and a crack-propagation preventing unit at least partially formed around a peripheral of the integrated circuit unit of the semiconductor substrate and filled with a heterogeneous material different from a material of the semiconductor substrate, and a method of fabricating the semiconductor package, comprising: at least partially forming a trench around the peripheral of the integrated circuit unit of the semiconductor substrate, and filling the trench with a heterogeneous material different from that of the semiconductor substrate. In accordance with the present invention, the structural and mechanical strength and durability of the semiconductor package, specifically, the wafer level semiconductor package, are improved and the reliability of the product is significantly improved. Furthermore, a fail rate including crack/chipping during a subsequent mounting process lowers, to improve the yield and reduce the whole manufacturing cost.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 2007-101343, filed Oct. 9, 2007, the contents of which are incorporated herein by reference in their entirety. 
     FIELD OF TIE INVENTION 
     The present invention relates to a semiconductor package and a method of fabricating the same, and more particularly, to a new semiconductor package which fundamentally prevents a physical defect such as a crack or partial chipping from propagating within the package. 
     BACKGROUND OF THE INVENTION 
     A semiconductor device is capable of performing diverse operations with a number of electric devices integrated in a single substrate. For this purpose, various high-technical fabrication methods have been used, and each device in the semiconductor device being fabricated has been developed to be miniaturized as a component in smaller dimensions. 
     SUMMARY 
     Semiconductor systems of high-integration and high-capacity have been proposed by developing packaging technology of semiconductor devices. The semiconductor packaging technology has been changed from a wire bonding to a flip-chip bumping capable of realizing a chip scale, to meet the market requirements. 
     Further, there has been proposed a method of completing a semiconductor package at wafer level, to reduce the size of each electronic applicable device by reducing a package area.  FIG. 1  illustrates a semiconductor package  100  which is individually separated after a packaging process is performed on a plurality of semiconductor chips at wafer level. An integrated circuit unit  120  is formed in a semiconductor substrate  110 . An electrode terminal  125  of the integrated circuit unit  120  is electrically connected to one end of a redistribution conductive layer  140 . The redistribution conductive layer  140  having one end which is partially exposed by a plurality of dielectric layers  130  and  132  is electrically connected to a lower metal layer  150  and a solder bump  160  as electrode terminals for external connection. 
     When a semiconductor chip or a semiconductor package is formed in a very small size and to a very thin thickness as a semiconductor device has been developed to be light, thin, short and small, it becomes brittle by a mechanical impact. 
     Specifically, when a semiconductor package is fabricated at wafer level and is sawed to be separated in individual packages as illustrated in  FIG. 1 , the mechanical defect or fail, such as a fine crack  170  or a partial chipping  172 , may occur around a sawing line X. 
     This defect is likely to propagate in the semiconductor chip in a subsequent process, to considerably decrease the structural stability of the semiconductor chip or semiconductor package. Moreover, there is a serious problem in that the propagation of the structural defect results in the operational incapability of the semiconductor device. 
     Specifically, in a wafer level semiconductor package, when a semiconductor chip is mounted on an external substrate such as a printed circuit board (PCB), the back of the semiconductor chip may be exposed. Then, when a drop test or a physical impact test of applying a mechanical impact is performed, the possibility of the crack or partial chipping becomes high because the edge part of the semiconductor chip is brittle. 
     The mechanical or structural defect of the semiconductor chip or semiconductor package drops the reliability of the wafer level package process and becomes an obstacle in providing a light, thin, short and small semiconductor device. 
     Therefore, the present invention is directed to provide to a new semiconductor package which has high structural stability against an internal mechanical defect or an external impact. 
     Another object of the present invention is to provide a method of fabricating a wafer level semiconductor package which prevents a defect such as a crack from propagating and secures impact-resistance. 
     The other objects and characteristics of the present invention will be presented in more detail below. 
     In accordance with an aspect of the present invention, the present invention provides a semiconductor package which has crack-resistance, comprising: a semiconductor substrate including an integrated circuit unit, and a crack-propagation preventing unit at least partially formed around the integrated circuit unit of the semiconductor substrate and filled with a heterogeneous material different from a material of the semiconductor substrate. 
     The crack-propagation preventing unit may be formed by filling a trench vertically perforating through the semiconductor substrate with a heterogeneous material different from the material of the semiconductor substrate. Further, the trench may be integrally formed in a closed curve or closed polygonal shape, along the peripheral of the integrated circuit unit of the semiconductor substrate, it may be formed in a regular section structure, or it may be formed to have different width in a vertical section. Further, the crack-propagation preventing unit may be formed to partially cover an edge part of the integrated circuit unit, to partially protect the integrated circuit unit. 
     In accordance with another aspect of the present invention, the present invention provides a method of fabricating a semiconductor package, comprising steps of: at least partially forming a trench around an integrated circuit unit of a semiconductor substrate, and filling the trench with a heterogeneous material different from a material of the semiconductor substrate. 
     The trench may be formed by performing dry etching or wet etching on the semiconductor substrate or by partially sawing the semiconductor substrate. Preferably, the heterogeneous material to be filled inside the trench may be a material different from the material of the semiconductor substrate in the physical or mechanical properties such as elastic coefficient strength and viscosity, for example, epoxy resin. 
     After the inside of the trench is filled, a bottom surface of the semiconductor substrate may be thinned to expose a crack-propagation preventing unit and to reduce a thickness of the whole package. 
     In accordance with another aspect of the present invention, the present invention provides a semiconductor package comprising: a semiconductor substrate including an integrated circuit unit, and a crack-propagation preventing unit formed to expose the integrated circuit unit of the semiconductor substrate and to cover side and bottom surfaces of the semiconductor substrate and filled with a heterogeneous material different from a material of the semiconductor substrate. 
     In accordance with another aspect of the present invention, the present invention provides a method of fabricating a semiconductor package, comprising steps of: forming a trench around a sawing line of each unit device on the semiconductor substrate including a plurality of integrated circuit units, thinning the bottom surface of the semiconductor substrate to expose the trench, applying a heterogeneous material different from the material of the semiconductor substrate to the bottom surface of the semiconductor substrate and the trench, and sawing the semiconductor substrate into each integrated circuit unit. 
     Preferably, the thinning of the semiconductor substrate may be performed by polishing the other surface of the semiconductor substrate after attaching a supporting member to the surface of the semiconductor substrate on which the integrated circuits are formed. The method may further comprise a step of removing the material formed on the bottom surface of the semiconductor substrate by thinning the bottom surface of the semiconductor substrate, prior to the sawing of the semiconductor substrate. 
     In accordance with the present invention, the structural and mechanical intensity and durability of the semiconductor package, specifically, the wafer level semiconductor package, are improved, and the reliability of the product is greatly improved. Furthermore, the thin semiconductor package is prevented from warping, so that the package is easily handled during a subsequent process, such as package mounting, to increase the yield and generally reduce the manufacturing cost. Furthermore, the impact-resistance of brittle materials is improved so that various materials can be used in the packaging process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a sectional view of an example of a wafer level semiconductor package; 
         FIG. 2  is a sectional view of a semiconductor package according to an embodiment of the present invention; 
         FIG. 3  is a plan view of the semiconductor package according to an embodiment of the present invention; 
         FIGS. 4 through 9  illustrate an example of a method of fabricating a semiconductor package according to the present invention; 
         FIGS. 10 through 13  are sectional views of various examples of the semiconductor package according to the present invention; 
         FIGS. 14 and 15  are sectional views of a semiconductor package according another embodiment of the present invention; and 
         FIGS. 16 through 22  are fabrication flows of an example of a method of fabricating the semiconductor package of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. 
     In a semiconductor package, specifically, a wafer level semiconductor package, according to the present invention, a crack-propagation preventing unit for preventing a physical defect, such as a crack, from propagating toward the inside of a semiconductor chip is provided by forming a trench or moat to surround an outer edge of a semiconductor chip nearby a scribe lane as a sawing part to saw an individual semiconductor chip unit and by filling the inside of the trench or moat with resin, such as epoxy mold, so that the impact-resistance of the semiconductor package is improved. 
     Accordingly, when a sawing or dicing process is performed to separate an individual semiconductor chip during a wafer level semiconductor packaging process, although a fine crack or partial chipping occurs, this defect is fundamentally prevented from propagating in a subsequent process. Further, since a crack or partial chipping path is prevented, the semiconductor chip or semiconductor package is prevented from being damaged while a process is performed, a mechanical impact test is performed or it is used by a user. Further, since the durability of a semiconductor device against a mechanical impact is improved, the reliability of the product is significantly improved. 
       FIG. 2  is a sectional view of a semiconductor package  200  according to an embodiment of the present invention. 
     A semiconductor substrate  210 , in which an integrated circuit unit  220  including various circuit elements, such as a transistor or an electrode interconnection, is formed through a pre-process of fabricating a semiconductor, is electrically connected to an electrode terminal  225  of the integrated circuit unit  220  and a solder bump  260  for connection to an external circuit through a post process thereof. 
     The solder bump  260  is formed at a position different from that of the electrode terminal  225  through a redistribution conductive layer  240 . The redistribution conductive layer  240  is covered by a plurality of dielectric layers  230  and  232 , to be disconnected to the outside. A lower metal layer  250  is formed between the solder bump  260  and the redistribution conductive layer  240 , to improve the adhesiveness of the solder bump  260 . 
     After the redistribution conductive layer and the solder bump for each semiconductor chip are simultaneously formed at wafer level, the semiconductor package may be divided into individual semiconductor chip units. To prevent the propagation of a defect such as a crack, which may occur during a separating process into the semiconductor chip unit, a filling unit, that is, a crack-propagation preventing unit  270 , which at least partially perforates through the semiconductor substrate  210 , is formed outside the integrated circuit unit  220  of the semiconductor package. 
     The crack-propagation preventing unit  270  may be completed by forming a trench partially or entirely perforating through the semiconductor substrate  210  and by filling the trench with a heterogeneous material different from a material of the semiconductor substrate  210 . The crack-propagation preventing unit  270  may be formed partially around a peripheral of the integrated circuit unit  220  or it may be formed in a closed figure, along an edge of the semiconductor chip around the peripheral of the integrated circuit unit  220  as illustrated in  FIG. 3 . The crack-propagation preventing unit  270  in the closed figure has a similar shape to a moat formed along an edge of the semiconductor substrate  210 . 
     Preferably, the crack-propagation preventing unit  270  may be filled with a heterogeneous material different from the material of the semiconductor substrate  210 . Specifically, the material having physical and mechanical properties different from those of the semiconductor substrate  210  may be used, and the material is excellent in elasticity, viscosity and fragility compared to that of the semiconductor substrate  210 , to have high resistance to an external impact and high durability to a defect such as a crack. For this purpose, a high molecular substance, such as resin, may be filled in the trench structure formed on the semiconductor substrate  210 . The present invention does not limit the material for filling the inside of the trench as the crack-propagation preventing unit  270  but it would be favorable to fill the trench with a substance using a mold material in light of the characteristic of a semiconductor packaging process. 
     Further, the material used for the crack-propagation preventing unit  270  preferably uses a material being little different from that of the semiconductor substrate  210  in the coefficient of thermal expansion in order to achieve purposes of preventing distortion by thermal stress in relation to the substrate as well as functioning as a buffer against a mechanical impact. For this purpose, the material used for the crack-propagation preventing unit  270  may be a first substance having the physical property to absorb the mechanical impact and a second substance having the coefficient of thermal expansion being same as or similar to that of the material of the semiconductor substrate  210 . In addition, the inside of the trench of the crack-propagation preventing unit  270  may be filled with a mixture of various substances having different physical properties or a compound thereof. 
     The crack-propagation preventing unit  270  vertically perforates through the semiconductor substrate  210 , partially expands on the top surface of the semiconductor substrate  210 , and functions as a protective layer  272  to cover a side of a thin-film layer including the redistribution conductive layer  240  and the dielectric layers  230  and  232  as an upper region of the edge part of the integrated circuit unit  220 . The shape of the crack-propagation preventing unit  270  may vary as illustrated later. 
     In  FIG. 2 , the crack-propagation preventing unit  270  is exposed at a back surface of the semiconductor substrate  210 . Even though the trench is formed not to completely perforate through the semiconductor substrate  210 , the trench structure may be formed to be exposed outward by partially forming the trench in a direction of the thickness of the semiconductor substrate  210  and then, by polishing one side of the semiconductor substrate  210 . 
     The crack-propagation preventing unit  270  formed nearby an outer edge of the semiconductor chip functions as a dam for preventing the defect such as a crack or partial chipping, which may occur around the edge part of the semiconductor chip in the wafer level semiconductor package, from propagating toward a peripheral. 
     Accordingly, the stability of the semiconductor package is secured during a process of sawing the wafer level package by an individual package unit or during a process of mounting an individual semiconductor package, or during other mechanical impact tests. 
     Further, a semiconductor chip or wafer level semiconductor package is prevented from warping which occurs when the semiconductor chip is made to be thinner in order to fabricate semiconductor chips being lighter, thinner, shorter and smaller. Therefore, it is very easy to handle the semiconductor chip or semiconductor package during a process of mounting it onto an external circuit board, or during the other subsequent processes. 
     As the integration density and the operation speed of a semiconductor device have increased, an electrical connection structure for a terminal for external connection (for example, solder) of a semiconductor device has been replaced with a Cu/low-k dielectric substance lamination structure. In this case, upon the packaging process, partial chipping or crack, or delamination may occur in an electrical connection unit due to the fragility of the low-k dielectric substance. However, the aforementioned problems can be solved or fundamentally prevented by the crack-propagation preventing structure of the semiconductor package according to the present invention as above. 
     In the semiconductor package according to the present invention, the crack-propagation preventing unit  270  may be formed during the wafer level packaging process. As an example, a method of fabricating the semiconductor package will be described with reference to  FIGS. 4 through 9 . 
       FIG. 4  illustrates a semiconductor substrate  210  in which an integrated circuit unit is formed through pre-processes of fabricating a semiconductor. In this embodiment two semiconductor chips will be described for clarification but it will be understood by those skilled in the art that a plurality of semiconductor chips on a wafer will be able to be processed. By the wafer level packaging process, each redistribution conductive layer  240  is formed on the integrated circuit unit of the semiconductor substrate  210  and it is partially exposed by a dielectric layer. A sawing part X, which will be used for individually separating chips during a subsequent process, is disposed between unit semiconductor chips. 
     A trench or moat is formed nearby an edge of the integrated circuit unit of each semiconductor chip, adjacent to the sawing part X as illustrated in  FIG. 5 . The trench or moat may be formed by, for example, dry etching or wet etching. Alternatively, the trench or moat may be formed through partial-sawing by mechanical methods. 
     The trench or moat may be formed in a linear shape having the vertically same width but it may be formed in a vertically non-linear shape as illustrated in  FIG. 5 . For example, after a linear trench  270   a  is formed by performing anisotropic dry etching from the top surface of the semiconductor substrate  210 , a non-linear trench  270   b  may be subsequently formed by performing isotropic wet etching. Alternatively, the sectional shape of the trench or moat may be variously changed by changing the sequence of the wet etching and the dry etching or by performing the combination thereof. 
     As described above, the shape of the trench or moat is variously changed to effectively improve the durability against the physical or mechanical defect occurring in the semiconductor chip or semiconductor package. 
     After the trench or moat is formed in the semiconductor substrate  210 , the inside of the trench or moat is filled by a heterogeneous material different from a material of the semiconductor substrate  210 , to complete a crack-propagation preventing unit  270  as illustrated in  FIG. 6 . 
     Subsequently, a back surface of the semiconductor substrate  210  is polished to be thin under the necessity as illustrated in  FIG. 7 . The polished back surface  210 ′ of the semiconductor substrate is capable of securing the durability against an external impact or an internal defect because a part of the crack-propagation preventing unit  270  is exposed. 
     Subsequently, a solder bump  260  is formed on the integrated circuit unit, to be electrically connected to a part of the redistribution conductive layer  240  as illustrated in  FIG. 8 . Before the solder bump  260  is formed, preferably, a lower metal layer may be further formed to improve the adhesiveness between the redistribution conductive layer  240  and the solder bump  260 . 
     Finally, a plurality of semiconductor packages fabricated at wafer level are sawed to be separated to individual packages  200   a  and  200   b  as illustrated in  FIG. 9 . 
     In this embodiment, the crack-propagation preventing unit  270  is formed after forming the redistribution conductive layer  240  and before forming the solder bump  260 . However, the order of forming the crack-propagation preventing unit  270  may be changed under the necessity. Further, the semiconductor package according to the present invention may be effectively applied to not only the wafer level package but also an individual semiconductor package or a laminated semiconductor package. 
       FIGS. 10 through 13  illustrate various shapes of a crack-propagation preventing unit  270  in the semiconductor package according to the present invention. The crack-propagation preventing unit  270  may be formed in an hourglass shape, in which the width at each end of both ends of the crack-propagation preventing unit  270  is widen in view of a vertical section thereof as illustrated in  FIG. 10 , or in a funnel shape, in which the width at only one end thereof is widen. Or, the crack-propagation preventing unit  270  may be formed so as to differentiate the width at each of both ends, so that a stair shape is internally formed as illustrated in  FIG. 12 . As described above, the semiconductor package has the advantage in that the physical defect which may occur on the top surface or bottom surface of the semiconductor package is prevented from propagating inside, by varying the shape of the top end or bottom end of the crack-propagation preventing unit  270 . 
     Further, the top part of the crack-propagation preventing unit  270  may be further expanded to partially cover a neighboring integrated circuit unit as illustrated in  FIG. 13 . Through this structure, the propagation of the mechanical chipping or crack which may be applied to the integrated circuit unit is effectively prevented. As the case may be, a molding part formed on the top surface of the semiconductor package may be replaced with the crack-propagation preventing unit  270 . 
       FIG. 14  illustrates a semiconductor package according to another embodiment of the present invention. The semiconductor package comprises: a semiconductor substrate  210  including an integrated circuit unit  220 , and a crack-propagation preventing unit  400  exposing the integrated circuit unit of the semiconductor substrate  210  and covering sides and bottom surface of the semiconductor substrate  210  and formed of a heterogeneous material different from a material of the semiconductor substrate  210 . 
     A plurality of dielectric layers and a redistribution conductive layer  240  are formed on the integrated circuit unit  220 . A solder bump  260  for external connection is formed at one end of the redistribution conductive layer  240 . 
     As a surface layer corresponding to a kind of an external molding unit, the crack-propagation preventing unit  400  protects the semiconductor substrate  210  and simultaneously prevents a crack from occurring or propagating by an external physical impact applied to the semiconductor substrate  210 . 
     Since the crack-propagation preventing unit  400  makes it easy to form a trench and to fill the trench with a heterogeneous material from the material of the semiconductor substrate  210  in the wafer level semiconductor packaging process, which will be described later, it is very effective in realizing the semiconductor package having crack-resistance. 
     As illustrated in  FIG. 15 , the crack-propagation preventing unit  400  may be formed to be present only at the side of the semiconductor substrate  210 , so that it is not formed at the surface on which the integrated circuit unit  220  of the semiconductor substrate  210  is not formed. 
     An example of a method of fabricating a semiconductor package according to the embodiment of  FIG. 14  will be described with reference to  FIGS. 16 through 22 . 
     As illustrated in  FIG. 16 , a plurality of integrated circuit units are formed in a semiconductor substrate  210  at wafer level, and subsequently, a redistribution conductive layer  240  is further formed under the necessity. 
     A trench Y is formed nearby a region (X-region) for sawing the semiconductor substrate  210  in which a redistribution conductive layer  240  is formed at wafer level by device units (by integrated circuit units) as illustrated in  FIG. 17 . Then, since the trench Y does not need to be formed in a small scale like the trench of the aforementioned embodiment (for example,  270  in  FIG. 2 ), it may be favorable in view of a process margin. 
     The trench Y may be formed to perforate through the semiconductor substrate  210 , along the peripheral of the integrated circuit unit, but it may be formed to a predetermined depth inside the semiconductor substrate  210 . 
     While a supporting member  300  is attached to a top surface of the semiconductor substrate  210  in which the trench is formed, and the surface on which the integrated circuit unit is formed, a bottom surface  210 ′ of the semiconductor substrate is thinned to expose the trench to the outside as illustrated in  FIG. 18 . In this process, since the thickness of the semiconductor substrate  210  becomes thin, it is favorable to slim the semiconductor package. 
     Subsequently, a crack-propagation preventing unit  400  is formed in the bottom surface  210 ′ of the semiconductor substrate and the trench as illustrated in  FIG. 19 . In the aforementioned embodiment, the crack propagation preventing unit is formed by filling the trench only. However, in this embodiment, the crack-propagation preventing unit  400  is formed by filling the bottom surface  210 ′ of the semiconductor substrate and the trench simultaneously, unlike the aforementioned embodiment. Accordingly, the fabrication process is easy, a material formed on the bottom surface  210 ′ of the semiconductor substrate protects the semiconductor substrate, and a crack is effectively prevented from propagating upon the sawing process of the semiconductor substrate  210 . 
     Preferably, the material forming the crack-propagation preventing unit  400  may be a material different from that of the semiconductor substrate  210 , that is, a resin material, for example, epoxy and so on. The resin material may be formed at the bottom surface  210 ′ of the semiconductor substrate and inside the trench by, for example, dispensing, coating or printing. 
     After the crack-propagation preventing unit  400  is formed, the supporting member is removed as illustrated in  FIG. 20 , and a lower metal layer  250  and a solder bump  260  are formed at a part of the redistribution conductive layer  240  as illustrated in FIR  21 . 
     Finally, the trench Y region in which the crack-propagation preventing unit  400  is formed is sawed by each integrated circuit unit, to separate the semiconductor substrate  210  as illustrated in  FIG. 22 . As the case may be, the method of fabricating the semiconductor package may further include a step of removing the crack-propagation preventing unit  400  formed on the bottom surface  210 ′ of the semiconductor substrate or polishing the bottom surface  210 ′ of the semiconductor substrate before the semiconductor substrate  210  is sawed. 
     The invention has been described using preferred exemplary embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, the scope of the invention is intended to include various modifications and alternative arrangements within the capabilities of persons skilled in the art using presently known or future technologies and equivalents. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.