Abstract:
A semiconductor wafer having a multi-layer wiring structure is disclosed. The wafer comprises a plurality of chip die areas arranged on the wafer in an array and scribe line areas between the chip die areas. The scribe lines of a semiconductor wafer having USG top-level wiring layers above ELK wiring layers have at least one metal film structures substantially covering corner regions where two scribe lines intersect to inhibit delamination at the USG/ELK interface during wafer dicing operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. non-provisional application claiming the benefit of U.S. provisional patent application Ser. No. 60/991,074 filed on Nov. 29, 2007, the entire disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This disclosure is generally related to a semiconductor wafer including one or more inter-metal-dielectric (IMD) layers of extremely-low dielectric constant (ELK) dielectric and one or more IMD layers of undoped silica glass (USG) layers for the top layer wiring layers and the wafer&#39;s scribe structure. 
       BACKGROUND 
       [0003]    Integrated circuit (IC) devices are formed in multiples on semiconductor wafers and then diced into individual IC devices. The IC devices generally have rectilinear shapes and are formed in a matrix array on semiconductor wafers. Once the formation of IC devices are completed, the semiconductor wafers are diced into individual IC devices. The dicing operation involves scribing between the rows and columns of the IC devices on the semiconductor wafers using a dicing saw. The area between the IC devices that get scribed are called scribe lines. 
         [0004]    The scribing is carried out on the active side of the semiconductor wafers where the integrated circuits and the multi-layer wiring layers of the IC devices are formed and the scribe lines are defined in the areas of the wafer between each individual IC devices (die patterns). The scribe line areas do not have circuit elements of the die areas and because each die is an independent device, the metal features for interconnect wiring conductors are also confined to the die areas and do not extend into or across the scribe lines where the die saw will cut through the wiring layers. However, some wafer-level reliability and functionality test pads are located in the scribe line areas to facilitate wafer-level testing. In such wafers, the die sawing across the test pads generally results in severe dielectric peeling and cracking. These delaminations easily become sources of defects that detrimentally affect reliability of the diced chips. 
         [0005]    In semiconductor wafers for advanced 45 nm dimension IC devices, the lower level wiring layers, also known as IMD layers, use ELK dielectric materials as the insulator material between the wiring conductor features. An example of an ELK dielectric material is a trimethylsilane-based organosilicate glass with a dielectric constant as low as about 2.1. In these wafers, one or more top-level wiring layers above the ELK layers are formed of undoped silicate glass (USG) as the insulator material between the wiring conductor features. In these wafers, the interface between the ELK layers and the USG layers suffer high level of delamination at the corner areas during scribing of the scribe lines by the dicing saw, regardless of whether there are metal features in the corner areas. The delamination is believed to be caused by high level of residual stress at the ELK/USG interface attributed to the substantial difference in the coefficient of thermal expansion (CTE) and Young&#39;s modulus between the ELK and the USG insulators. The CTE and Young&#39;s modulus of the ELK material is substantially different from those of the USG. The typical CTE and Young&#39;s modulus of ELK dielectric is about 0.7 ppm/° C. and 10 GPa, respectively. The typical CTE and Young&#39;s modulus of USG material is about 0.5 ppm/° C. and 70 GPa. 
         [0006]    The peeling defects cause reliability problems with the IC devices and are not desired. Thus, there is a need for improved scribe line structures especially for IC devices utilizing ELK dielectric for IMD layers and USG dielectric for top-level wiring layers. 
       SUMMARY 
       [0007]    According to an embodiment of the present disclosure, a semiconductor wafer having a multi-layer wiring structure is disclosed. The wafer comprises a plurality of chip die areas arranged on the wafer in an array and scribe line areas between the chip die areas. The chip die areas have a structure comprising a first set of one or more wiring layers comprising conductor metal features and a first dielectric material providing insulation between the first set of conductor metal features. A second set of one or more wiring layers overly the first set of wiring layers and comprise a second set of conductor metal features and a second dielectric material providing insulation between the second set of conductor metal features, wherein the first dielectric material has lower dielectric constant than the second dielectric material. The first and second set of conductor metal features do not extend into the scribe line areas. A top-level passivation layer overlies the second set of one or more wiring layers. 
         [0008]    The scribe line areas comprise a plurality of metal film structures are provided on top of the top-level passivation layer, wherein each of the metal film structures substantially occupy a corner region in the scribe line areas, whereby the presence of the metal film structures in the corner regions inhibit the occurrence of delamination between the first dielectric material and the second dielectric material in the corner region during wafer dicing operation. The corner region is defined by the intersection of two scribe lines. 
         [0009]    According to another embodiment, the plurality of metal film structures in the scribe line areas are provided within the top-level passivation layer, wherein each of the metal film structures substantially occupy a corner region in the scribe line areas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1A  is a plan view of a wafer whose scribe lines have structures according to an embodiment of the present disclosure. 
           [0011]      FIG. 1B  is a plan view illustration of a detailed view of a corner region of the scribe lines on the wafer of  FIG. 1A  according to one embodiment. 
           [0012]      FIGS. 1C-1F  are cross-sectional views taken along the line B-B shown in  FIG. 1B  showing the interim stages in forming the structure of the scribe line area according to an embodiment of the present disclosure. 
           [0013]      FIG. 2A  is a plan view illustration of a detailed view of a corner region of the scribe lines on the wafer of  FIG. 1A  according to another embodiment. 
           [0014]      FIGS. 2B-2E  are cross-sectional views taken along the line C-C shown in  FIG. 2A  showing the interim stages in forming the structure of the scribe line area according to an embodiment of the present disclosure. 
           [0015]      FIG. 3  is a plan view illustration of a portion of a wafer whose scribe lines have structures according to another embodiment of the present disclosure. 
           [0016]      FIGS. 4A-4D  are illustrations of variations of metal film structures that can be provided in the scribe lines of a wafer according to the present disclosure. 
       
    
    
       [0017]    The features shown in the above referenced drawings are illustrated schematically and are not intended to be drawn to scale nor are they intended to be shown in precise positional relationship. Like reference numbers indicate like elements. 
       DETAILED DESCRIPTION 
       [0018]    This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. 
         [0019]      FIG. 1A  is a plan view of a semiconductor wafer  10  with dies separated by scribe lines according to one embodiment is illustrated. The semiconductor wafer  10  comprises an array of dies (or chips)  16  separated from each other by two sets of intersecting scribe lines  14 . One set of scribe lines  14  extend along a first direction and a second set of scribe lines  14  extend along a second direction. The intersections of the two sets of scribe lines define corner regions  15  that are substantially covered with metal film structures  18 . For illustrative purposes only some of the metal film structures  18  are shown in  FIG. 1A  but according to the present disclosure, the metal film structures  18  are provided in every corner region  15  on the wafer  10 . 
         [0020]      FIG. 1B  is a detailed view of a corner region of the wafer  10  shown in  FIG. 1A . A metal film structure  18  substantially occupies the corner region defined by the two intersecting scribe lines  14 . Each of the dies  16  is surrounded by a sealing ring structure  20  that protect the circuitry area of the dies  16  from an damage such as dicing saw induced cracks and moisture. According to an aspect of the present disclosure, the spacing S between the metal film structure  18  and the neighboring sealing rings  20  is no more than 6 μm to insure that substantial portion of the corner region is covered by the metal film structure  18 . The width of the scribe lines  14  is 30-100 μm. 
         [0021]      FIGS. 1C-1F  are cross-sectional views of the semiconductor wafer  10  taken along the line B-B shown in  FIG. 1B  showing the interim structures as the metal film structures are formed in the scribe line areas according to an embodiment of the present disclosure.  FIG. 1C  shows plurality of wiring layers  52  and  54  formed on top of a silicon substrate  50  in the die areas  16 . The scribe line  14  is between the two die areas  16 . On top of the active devices (not shown) of the silicon substrate  50  is generally formed an insulation layer  51  formed of phosphorous silicate glass (PSG). The PSG layer  51  is provided with through via conductors  71  connecting the active devices on the silicon substrate  50  to the interconnecting wiring layers above. 
         [0022]    The plurality of wiring layers comprise a first set of one or more wiring layers  52 . Each of the first set of one or more wiring layers  52  includes a plurality of first set of conductor metal features  72  and first dielectric material providing insulation between the first set of conductor metal features  72 . These conductor metal features provide electrical interconnection of the active devices (not shown) on the semiconductor substrate  50  within a given die  16 . As shown, the scribe line area  14  in these wiring layers  52  is free of the first set of interconnecting conductor metal features  72 . 
         [0023]    A second set of one or more wiring layers  54 , also called the top-level wiring layers, are provided above the first set of wiring layers  52 . Each of the second set of one or more wiring layers  54  includes a plurality of second set of conductor metal features  74  and second dielectric material providing insulation between the second set of conductor metal features  74 . These conductor metal features  74  provide further electrical interconnection of the active devices (not shown) on the semiconductor substrate  50  within a given die  16 . The scribe line area  14  in the second set of wiring layers  54  is also free of the second set of interconnecting conductor metal features  74 . The first and second set of conductor metal features  72 ,  74  are usually formed of copper metal. 
         [0024]    The first dielectric material forming the insulation layers in the first set of wiring layers  52  has lower dielectric constant than the second dielectric material and can be a low-k (LK) dielectric material or an extremely-low-k (ELK) dielectric material. LK dielectric materials are those having dielectric constant between about 3.0 to 2.6. ELK dielectric material are those having dielectric constant of about 2.6 or lower. The second dielectric material forming the insulation layers in the second set of one or more wiring layers  54  are usually formed with dielectric material having higher Young&#39;s modulus (i.e. higher mechanical strength) than the first dielectric material and can be undoped silicate glass (USG), fluorine-doped silica glass (FSG) or silicon nitride (NIT). The second dielectric material has a dielectric constant greater than about 3.4. 
         [0025]    Referring to  FIG. 1C , a top-level passivation layer  56  is deposited over the second set of wiring layers  54 . The top-level passivation layer  56  can be formed of USG, FSG or NIT and can be deposited by a chemical vapor deposition (CVD) process. Referring to  FIG. 1D , the top-level passivation layer  56  is patterned by photolithography to form openings  55  over the conductor metal features  74  of the wiring layers  54 . Referring to  FIG. 1E , a blanket layer of aluminum metal  120  is deposited over the patterned top-level passivation layer  56 . The blanket aluminum metal  120  fills the openings  55  and contacts the second set of conductor metal features  74 . Referring to  FIG. 1F , the aluminum metal layer  120  is then patterned by photolithography forming the sealing rings  20  in the die areas  16  and the metal film structures  18  in the scribe lines  14 . A spacing S is maintained between the metal film structure  18  and the neighboring seal ring structures  20  so that the metal film structure  18  does not contact the seal ring structures  20 . 
         [0026]    The provision of the metal film structures  18  in the corner regions of the scribe lines  14  on top of the top-level passivation layer  56  minimizes or eliminates delamination at the interface  99  between the first dielectric material and the second dielectric material. The provision of the metal film structures  18  reduces the residual stress at the interface  99  caused by the CTE and Young&#39;s modulus mismatch between the lower dielectric constant first dielectric material layers and the higher dielectric constant second dielectric material layers. 
         [0027]      FIGS. 2A-2E  show the structure of the scribe line  14  for the wafer  10  according to another embodiment.  FIG. 2A  is a detailed view of a corner region of the wafer  10 . As in the embodiment of  FIGS. 1B-1F , the metal film structure  18  substantially occupies the corner region defined by the two intersecting scribe lines  14  as seen in this plan view. Each of the dies  16  is surrounded by a sealing ring structure  20  that protect the circuitry area of the dies  16  from an damage such as dicing saw induced cracks and moisture. The spacing S between the metal film structure  18  and the neighboring sealing rings  20  is no more than 6 μm to insure that substantial portion of the corner region is covered by the metal film structure  18 . The width of the scribe lines  14  is 30-80 μm. 
         [0028]      FIGS. 2B-2E  are cross-sectional views of the semiconductor wafer  10  taken along the line C-C shown in  FIG. 2A  showing the interim structures as the metal film structures are formed in the scribe line areas according to another embodiment of the present disclosure. Referring to  FIG. 2B , a top-level passivation layer  56  is deposited over the second set of wiring layers  54  of the wafer  10 . The top-level passivation layer  56  can be formed of USG, FSG or NIT and can be deposited by a chemical vapor deposition (CVD) process. Referring to  FIG. 2C , the top-level passivation layer  56  is patterned by photolithography to form openings  55  over the conductor metal features  74  of the wiring layers  54  and openings  57  in the scribe line areas  14 . Referring to  FIG. 2D , a blanket layer of aluminum metal  120  is deposited over the patterned top-level passivation layer  56 . The blanket aluminum metal  120  fills the openings  55  and  57 . Referring to  FIG. 2E , the aluminum metal layer  120  is then patterned by photolithography forming the sealing rings  20  in the die areas  16  and the metal film structures  18  in the scribe lines  14 . In this embodiment, because the metal film structure  18  is formed within the opening  57  in the top-level passivation layer  56 , the metal film structure  18  sits directly on the wiring layer structure rather than on the top-level passivation layer  56 . 
         [0029]    As in the previous embodiment, a spacing S is maintained between the metal film structure  18  and the neighboring seal ring structures  20  so that the metal film structure  18  does not contact the seal ring structures  20 . The provision of the metal film structures  18  in the scribe lines&#39; corner regions minimizes or eliminates delamination at the interface  99  between the first dielectric material and the second dielectric material. The provision of the metal film structures  18  reduces the residual stress at the interface  99  caused by the CTE and Young&#39;s modulus mismatch between the lower dielectric constant first dielectric material layers and the higher dielectric constant second dielectric material layers. 
         [0030]    The inventors have discovered that the provision of the metal film structures  18  reduces or eliminates delamination at the ELK/USG interface  99  is caused by the substantially different CTE and Young&#39;s modulus between ELK and USG material. From the simulation results, the residual stress between ELK/USG interfaces can be lowered as much as 30% after placing the dummy metal film structures  18  in the corner regions of the scribe line areas  14 . The average latent energy of the USG/metal composite structure is brought closer to the latent energy of the ELK layers. This reduces the residual stress at the ELK/USG interface and inhibits delamination of the ELK/USG interface during the wafer dicing process. 
         [0031]    Referring to  FIG. 3 , according to another embodiment, the metal film structures  18  need not be limited to the corner regions of the scribe line areas  14 . As shown, the metal film structure  18  can extend the full length of the scribe lines  14  on the wafer out to the wafer edges so that the metal film structure  18  occupies substantially all scribe lines in one continuous film. The spacing S between the metal film structure  18  and the seal rings  20  is maintained as in the previous embodiments. If there are other metal features  110 , such as test pads, etc. in the scribe lines  14 , the metal film structure  18  can be configured to have windows or holes  120  to accommodate such other metal features. 
         [0032]    Referring to  FIGS. 4A-4D , the metal film structures  18  need not be limited to the substantially solid film configuration as shown in the previous embodiment and shown again in  FIG. 4A . The metal film structure can have a variety of patterns as shown in the films  18   a ,  18   b  and  18   c  of  FIGS. 4B-4D  as long as the resulting metal film structure has somewhat uniform and symmetric surface coverage in the X-Y plane. In  FIG. 4B , the areas marked as  18   a  are solid metal film and the areas marked as  180  are holes. In  FIG. 4C , the area marked as  18   b  is a solid metal film and the areas marked as  180  are holes. In  FIG. 4D , the area marked as  18   c  is a solid metal film and the areas marked as  180  are holes. 
         [0033]    Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.