Abstract:
A packaged semiconductor device (a wafer-level chip scale package) containing no UBM between a chip pad and an RDL pattern is described. As well, the device contains only a single non-polymeric insulation layer between the RDL pattern and the solder bump. The single non-polymeric insulation layer does not need high temperature curing processes and so does not induce thermal stresses into the device. As well, manufacturing costs are diminished by eliminating the UBM between the chip pad and the RDL pattern.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 10/295,281, the entire disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention generally relates to methods for fabricating integrated circuits (ICs) and semiconductor devices and the resulting structures. Specifically, the invention relates to a semiconductor package and a method for fabricating and using the same. More particularly, the invention relates to a wafer level chip scale package and a method for fabricating and using the same.  
       BACKGROUND OF THE INVENTION  
       [0003]     Recent advancements in the electronics industry, especially with personal computers (PC), mobile phones, and personal data assistants (PDA), have triggered a need for light, compact, and multi-functional power systems that can process large amounts of data quickly. These advancements have also triggered a reduction in the size of semiconductor chips and the packaging used for these chips. One type of packaging that has recently been used is wafer-level chip size packaging (WLCSP). See, for example, U.S. Pat. Nos. 6,187,615 and 6,287,893, the disclosures of which are incorporated herein by reference.  
         [0004]     In general, to fabricate WLCSP, a wafer is processed and then packaged by a photolithography process and a sputtering process. This method is easier than general packaging processes that use die bonding, wire bonding, and molding. Processes for WLCSP also have other advantages when compared to general packaging processes. First, it is possible to make solder bumps for all chips formed on a wafer at a time. Second, a wafer-level test on the operation of each semiconductor chip is possible during WLSCP processes. For these—and other reasons—WLCSP can be fabricated at a lower cost than general packaging.  
         [0005]      FIGS. 1-3  illustrate several known wafer-level chip scale packages. As shown in  FIG. 1 , chip pads  40  are formed of a metal such as aluminum on a silicon substrate  5 . A passivation layer  10  is formed to expose a portion of each of the chip pads  40  on the silicon substrate  5  while protecting the remainder of the silicon substrate  5 . A first insulating layer  15  is formed over the passivation layer  10  and then a re-distribution line (RDL) pattern  20  (which re-distributes electrical signals from the bond pad  40  to solder bump  35 ) is formed over portions of the first insulating layer  15  and the exposed chip pads  40 . A second insulating layer  25  is formed on portions of the RDL pattern  20  while leaving portions of the RDL pattern  20  exposed. Under bump metals (UBM)  30  are formed between solder bumps  35  and the exposed portions of the RDL pattern  20 . The RDL pattern  20  contains inclined portions on the first insulating layer  15  near the chip pads  40 . In these areas, short circuits can occur and the pattern  20  can crack and deform in these areas due to stresses.  
         [0006]     As depicted in  FIG. 2 , package  50  contains an RDL pattern  54  that adheres to a solder connection  52  in a cylindrical band. Such a configuration has several disadvantages. First, the contact area between the RDL pattern  54  and the solder connection  52  is minimal, thereby deteriorating the electrical characteristics between them. Second, short circuits may occur due to the stresses in the contact surface between the RDL pattern  54  and the solder connection  52 . Third, the solder connection  52 —which is connected with a solder bump  58  formed on a chip pad  56 —is exposed to the outside of the package  50 , i.e., to air. Thus, there is a higher possibility that moisture penetrates into the solder connection  52  and decreases the reliability of the solder connection  52 . Fourth, the package  50  is completed only by carrying out many processing steps and, therefore, manufacturing costs are high.  
         [0007]     As shown in  FIG. 3 , package  60  contains a RDL pattern  76  that is electrically connected with a chip pad  72  via a connection bump  74 . The RDL pattern  76  is, however, inclined on the connection bump  74 , causing cracks therein due to stresses as described above. As well, the connection bump  74  is made by a plating process and is formed of aluminum, copper, silver, or an alloy thereof. Accordingly, the package  60  is not easy to manufacture.  
         [0008]     Other problems exist with conventional WLSCP. Often, such packaging uses UMB (i.e., layer  30  in  FIG. 1 ) and two insulating layers (i.e., layers  15  and  25  in  FIG. 1 ) that are made of polymeric materials such as polyimide and benzocyclobutene (BSB).  
         [0009]     Such structures are complicated to manufacture. As well, the coefficient of thermal expansion (CTE) between the various layers can induce thermal stresses into the ICs and damage the ICs during high temperature curing of these polymeric materials.  
       SUMMARY OF THE INVENTION  
       [0010]     The invention provides a packaged semiconductor device (a wafer-level chip scale package) containing no UBM between a chip pad and an RDL pattern. As well, the device contains only a single non-polymeric insulation layer between the RDL pattern and the solder bump. The single non-polymeric insulation layer does not need high temperature curing processes and so does not induce thermal stresses into the device. As well, manufacturing costs are diminished by eliminating the UBM between the chip pad and the RDL pattern. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIGS. 1-17  are views of one aspect of the devices and methods of making the devices according to the invention, in which:  
         [0012]      FIG. 1  is a cross-sectional view of a conventional wafer-level chip scale page;  
         [0013]      FIG. 2  is a cross-sectional view of another conventional wafer-level chip scale package;  
         [0014]      FIG. 3  is a cross-sectional view of another conventional wafer-level chip scale package;  
         [0015]      FIG. 4  is a cross-sectional view showing a stage in a method of fabricating a wafer-level chip scale package according to an aspect of the invention;  
         [0016]      FIG. 5  is a cross-sectional view showing a stage in a method of fabricating a wafer-level chip scale package according to an aspect of the invention;  
         [0017]      FIG. 6  is a cross-sectional view showing a stage in a method of fabricating a wafer-level chip scale package according to an aspect of the invention;  
         [0018]      FIG. 7  is a cross-sectional view showing a stage in a method of fabricating a wafer-level chip scale package according to an aspect of the invention;  
         [0019]      FIG. 8  is a cross-sectional view showing a stage in a method of fabricating a wafer-level chip scale package according to an aspect of the invention;  
         [0020]      FIG. 9  is a cross-sectional view showing a stage in a method of fabricating a wafer-level chip scale package according to an aspect of the invention;  
         [0021]      FIG. 10  is a cross-sectional view showing a stage in a method of fabricating a wafer-level chip scale package according to an aspect of the invention;  
         [0022]      FIG. 11  is a cross-sectional view of a wafer-level chip scale package according to another aspect of the invention;  
         [0023]      FIGS. 12-15  illustrate stages in a method of fabricating a wafer-level chip scale package in one aspect of the invention;  
         [0024]      FIG. 16  depicts another stage in a method of fabricating a wafer-level chip scale package in one aspect of the invention; and  
         [0025]      FIG. 17  depicts a process for making a wafer-level chip scale package in another aspect of the invention. 
     
    
       [0026]      FIGS. 1-17  presented in conjunction with this description are views of only particular—rather than complete—portions of the devices and methods of making the devices according to the invention. Together with the following description, the Figures demonstrate and explain the principles of the invention. In the Figures, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. The same reference numerals in different drawings represent the same element, and thus their descriptions will be omitted.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     The invention will now be described more fully with reference to the accompanying drawings, in which one aspect of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the aspects set forth herein. Rather, these aspects are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art. Although the invention is described with respect to IC chips, the invention could be used for other devices where packaging is needed, i.e., silicon MEMS devices.  
         [0028]      FIGS. 4 through 10  illustrate one aspect of the invention for fabricating a wafer-level chip scale package containing a re-distributed line (RDL) pattern that is not inclined between the bottom of a solder bump and the top surface of a chip pad. Referring to  FIG. 4 , a substrate  100  is prepared on which a passivation layer  110  and a chip pad  115  are formed. The substrate  100  can be any known semiconductor substrate known in the art, including “compound” semiconductors and single crystal silicon. The passivation layer  110  can be made of any dielectric material known in the art, such as silicon nitride, silicon oxide, or SOG.  
         [0029]     Then, the chip pad  115  is formed on the upper surface of substrate  100 . First, a portion of passivation layer in this area is removed by a conventional masking and etching process. Then, the metal for the chip pad  115  is blanket deposited and the portions of the metal layer not needed for the bond pad are removed by etching or planarization. The chip pad  115  can be made of conductive material, such as metals and metal alloys. In one aspect of the invention, the chip pad comprises aluminum.  
         [0030]     A wire  120  is next attached to the chip pad  115  using a capillary  130 . As shown in  FIG. 5 , the bottom of the wire  120  is bonded to the chip pad  115 . Then a coining process is performed to press the wire  120  under a predetermined pressure, thereby forming a coined stud bump  125 . By using the capillary  130 , the coined stud bump  125  can be formed with a simple structure and with a simple manufacturing process.  
         [0031]     As depicted in  FIG. 6 , a first insulating layer  135  is then deposited to cover the coined stud bump  125  and passivation layer  110 . In this aspect of the invention, the first insulating layer  135  is formed of a dielectric polymer material such as BCB, polyimide (PI), and EMC. As illustrated in  FIG. 7 , the first insulating layer  135  and the coined stud bump  125  are planarized using conventional processing. In the planarization process, a stud bump  125 ′ and a first insulating layer  135 ′ are formed. In one aspect of the invention, a chemical mechanical polishing (CMP) process is used to planarize the first insulating layer  135  and the stud bump  125 .  
         [0032]     As shown in  FIG. 8 , a re-distributed line (RDL) pattern  140  is formed on the stud bump  125 ′ and the first insulating layer  135 ′. The RDL pattern  140  electrically connects the stud bump  125 ′ and the solder bump that is formed during subsequent processing (as described below). The RDL pattern is formed by blanket depositing a metal layer and then removing—typically by masking and etching—the portions of the metal layer not needed for the DRL pattern  140 . The RDL pattern  140  can contain any electrically conductive material, such as metals and metal alloys. Examples of such metal and metal alloys include Cu, Al, Cr, NiV, and Ti. In one aspect of the invention, the RDL comprises a composite layer of Cu, Al, Cr, and Cu, or a material selected from NiV and Ti. In conventional wafer-level chip scale package as shown in  FIG. 1 , the RDL pattern  20  was formed of Al, NiV, Cu, NiV, and Cu that are sequentially deposited on the chip pad  40 . Such a configuration has poor adhesive characteristics and reliability, is not easy to fabricate, and has high manufacturing costs.  
         [0033]     As depicted in  FIG. 9 , a second insulating layer  150  is then formed to cover the RDL pattern  140  and the first insulating layer  135 ′. A portion of the second insulating layer  150  is removed—typically by masking and etching—to expose a portion of the RDL pattern  140  to which a solder bump is later attached. As shown in  FIG. 10 , a solder bump  160  is then attached to the exposed portion of the RDL pattern  140  as known in the art. The stud bump comprises any conductive material such as metal and metal alloys. In one aspect of the invention, the stud bump comprises gold (Au) or copper (Cu).  
         [0034]     The wafer-level chip scale package  1000  is illustrated in  FIG. 10 . The silicon substrate  100  contains an IC (not shown) and chip pad  115  which extends into the passivation layer  110  and is encircled by the passivation layer  110 . Electrical signals from the IC contained in substrate  100  are transmitted through chip pad  115 , through RDL pattern  140 , to solder bump  160 , and then to the outside of the packaged semiconductor device (i.e., to a circuit board).  
         [0035]     In the device of  FIG. 10 , the first insulating layer  135 ′ encircles and covers the stud bump  125 ′. Since the top surface of the first insulating layer  135 ′ and stud bump  125 ′ are coplanar in this aspect of the invention, the RDL pattern  140  may be formed as a substantially planar layer without an inclined portion. Therefore, cracks in the RDL pattern  140  due to stresses are prevented.  
         [0036]     The RDL pattern  140  shown in  FIG. 10  is illustrated as on only a portion of the upper surface of the stud bump  125 ′. In another aspect of the invention, the RDL pattern can be formed to cover the entire stud bump  125 ′, thus enhancing the electrical characteristics and reliability of the wafer-level chip scale package  1000 .  
         [0037]     The RDL pattern  20  of  FIG. 1  contains an inclined portion in the conventional wafer-level chip scale package. Accordingly, it is extremely difficult to form a thick first insulating layer  15  in  FIG. 1 . In this aspect of the invention, however, the first insulating layer  135 ′ in  FIG. 10  is formed as a thick layer.  
         [0038]      FIG. 11  illustrates another aspect of the invention where a wafer-level chip scale package has a two-layer RDL pattern. A wafer-level chip scale package  2000  contains: a substrate  100 ; a passivation layer  110 ; chip pads  115 ; stud bumps  125 ′ that are formed on chip pads  115  and are encircled by a first insulating layer  135 ′; intermediate RDL pattern  210  that connects the stud bumps  125 ′ and intermediate stud bumps  220 ; an intermediate insulating layer  230  that insulates the intermediate RDL pattern  210 ; RDL pattern  140  that connects the intermediate stud bumps  220  and solder bumps  160 ; a second insulating layer  150  that insulates the RDL patterns  140 ; and solder bumps  160  that are attached to a portion of each of the RDL pattern  140 .  
         [0039]     Components not described in  FIG. 11  are the same as those components explained with reference to  FIG. 10 . The same reference numerals in  FIGS. 10 and 11  denote the same elements that have substantially the same functions and are formed of the same materials and in substantially the same manner. The structure, functions, materials, and effects of the intermediate stud bumps  220 , the intermediate RDL pattern  210  and the intermediate insulating layer  230  are substantially the same as those of the stud bump  125 , the RDL pattern  140 , and the second insulating layer  150 , respectively. The intermediate stud bumps  220  connect the intermediate RDL pattern  210  and the RDL pattern  140 . Each intermediate RDL pattern  210  is formed at the bottom of each intermediate stud bump  220 . The intermediate insulating layer  230  exposes a portion of the intermediate RDL pattern  210  so it can be connected with the intermediate stud bumps  220 .  
         [0040]     In another aspect of the invention, additional intermediate stud bumps, intermediate RDL patterns, and intermediate insulating layers may be formed to make a three (or more) layer RDL pattern rather than the two layer RDL pattern illustrated in  FIG. 11 .  
         [0041]     In the aspects of the invention described above, it is possible to reduce or prevent an inclined portion of a RDL pattern in the art between a solder bump and a chip pad. Such a configuration suppresses cracks in the RDL pattern, even where an underlying insulating layer has a large thickness. Further, a stud bump can be easily and inexpensively formed using a capillary.  
         [0042]     In another aspect of the invention, the wafer level chip scale package is manufactured in the manner depicted in  FIGS. 12-17  so as to not contain a UBM between the chip pad the RDL pattern and to contain a single non-polymeric insulating layer. In this aspect of the invention, and as depicted in  FIG. 17 , the bond pads are first redistributed (as depicted in more detail in  FIGS. 12-15 ). Then, the stud bumps are formed on the wafer (as depicted in more detail in  FIG. 16 ). The solder balls are then attached to the stud bumps, either directly or by using solder paste, and the solder balls are re-flowed. The resulting packaged semiconductor device can then be mounted on a circuit board as known in the art.  
         [0043]     In this aspect of the invention, and as illustrated in  FIGS. 12-13 , a substrate  300  (substantially similar to substrate  100 ) containing IC  305  is obtained. A passivation layer  310  (substantially similar to passivation layer  110 ) is then formed on substrate  300 . A portion of the passivation layer is then removed and a chip pad  315  (substantially similar to chip pad  115 ) is formed in that exposed portion. The methods used for these processes are substantially similar to those described above.  
         [0044]     Next, as depicted in  FIG. 14 , a re-distributed (RDL) pattern  340  is formed directly on the chip pad  315  and the passivation layer  310 . The RDL pattern  340  electrically connects the chip pad  315  and the solder bump  365  that is formed during subsequent processing (as described below). The RDL pattern  340  is formed by blanket depositing a metal layer and then removing—typically by masking and etching—the portions of the metal layer not needed for the RDL pattern  340 . The RDL pattern  340  can contain any electrically conductive material, such as metals and metal alloys. Examples of such metal and metal alloys include Cu, Al, Cr, NiV, and Ti. In one aspect of the invention, the RDL pattern comprises Al.  
         [0045]     Next, as shown in  FIG. 15 , an insulating layer  350  is formed to cover the RDL pattern  340 . In this aspect of the invention, the material for the insulating layer is blanket deposited on the RDL pattern  340 . A masking and etching process is then used to remove a portion of this insulating material in the area of region  375  (where stud bumps  365  will later be formed).  
         [0046]     The material for the insulating layer  350  does not comprise a polymer material like BCB, PI, and EMC. As described above, such materials are often used in conventional WLCSP. To form such layers, however, the structure containing the material is subjected to a high temperature heating process. This heating is necessary to cure the polymer material. Unfortunately, such a high temperature heating process damages the structure underlying the polymeric material including the IC  305  in substrate  300 .  
         [0047]     In this aspect of the invention, the insulating layer  350  is not made of polymeric materials. Rather, the insulating layer  350  is made of dielectric non-polymeric materials. Examples of such non-polymeric dielectric materials include silicon nitride, silicon oxide, and silicon oxynitride. Such materials can be deposited by any known method in the art.  
         [0048]     In this aspect of the invention, only a single layer is used as the redistribution layer. In the aspect of the invention shown in  FIGS. 4-10 , a UBM and a metal layer are used to redistribute the electrical signal from the chip pad  115  to the stud bump  160 . By using only a metal layer in this aspect of the invention, the cost of the manufacturing the UBM can be eliminated. Thus, this aspect of the invention uses only a single conductive layer as the RDL pattern in the WLSCP.  
         [0049]     As depicted in  FIG. 16 , the stud bumps are then formed on the exposed portion of the RDL pattern  340  (in the area  375 ). The stud bumps  365 A can be formed by electroplating the material for the stud bumps with a cladding as known in the art. In this aspect of the invention, the material for the study bumps is Cu and the cladding is a Ni/Au alloy.  
         [0050]     Alternatively, the stud bumps  365 B can be formed by a wire bonding process. In this aspect of the invention, a coated wire  380  is attached to the RDL pattern  340  using a capillary  385 . As shown in  FIG. 16 , the bottom of the wire  380  is first bonded to the metal of the RDL pattern  340 . Then a coining process is performed to press the wire  380  under a predetermined pressure to form a coined stud bump  365 B. By using the capillary, the coined stud bump  365 B can be formed with a simple structure and with a simple manufacturing process. In one aspect of the invention, the material for the wire comprises Cu and the coating comprises Pd.  
         [0051]     Finally, as shown in  FIG. 17 , the solder balls are then attached to the stud bumps, either directly or by using solder paste, and the solder balls are re-flowed. Both of these processes are performed using conventional processing that is known in the art.  
         [0052]     Having described these aspects of the invention, it is understood that the invention defined by the appended claims is not to be limited by particular details set forth in the above description, as many apparent variations thereof are possible without departing from the spirit or scope thereof.