Abstract:
A semiconductor wafer ( 10 ) and associated methods are disclosed in which a plurality of semiconductor dice ( 14 ) include a semiconductor substrate ( 12 ) overlain by a plurality of upper layers ( 13 ) are provided with encompassing scribe streets ( 20 ) at the top surface ( 16 ) of the wafer ( 10 ) defined by inactive areas ( 18 ) between and circumscribing the dice ( 14 ). Ditches ( 22 ) in the scribe streets ( 20 ) extend from the top surface ( 16 ) to the substrate ( 12 ) for facilitating saw singulation of the dice ( 14 ).

Description:
TECHNICAL FIELD  
       [0001]     The invention relates in general to semiconductors devices and to semiconductor devices manufacturing. More particularly, it relates to semiconductor wafers with ditched scribe streets for facilitating chip singulation, and methods for manufacturing the same.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is common to form semiconductor devices, or chips, in large quantities arrayed on the upper surface of a semiconductor wafer. The chips are fashioned with multiple layers of conductive and non-conductive materials interconnected to form circuitry. The completed chips are typically singulated for final packaging by cutting the wafer at gaps of inactive area left between and around the active areas of the chips for that purpose. Mechanical sawing is the process generally used for singulation.  
         [0003]     Mechanically sawing through a multi-layered semiconductor wafer presents certain problems. For example, instances of chipping, cracking, or peeling of the multiple layers of the completed wafer are not uncommon. This type of damage is often caused by the stresses induced by sawing the inactive areas and can cause damage to the adjacent active areas. The result may be reduced yield, defective devices, increased inspection and testing requirements, and increased expense. Examples of efforts to minimize such problems include: Providing wider inactive areas, at the expense of smaller active areas, and; laser cutting, often in combination with mechanical sawing, with the expense of additional equipment and additional processing time. These examples of problems encountered in wafer sawing may be particularly acute with the fabrication of devices employing copper film as a conductive interconnect material and low-k or ultra low-k dielectric materials.  
         [0004]     Due to these and other problems, improved wafers and methods for facilitating the avoidance of damage to devices upon singulation would be useful and desirable in the arts.  
       SUMMARY OF THE INVENTION  
       [0005]     In carrying out the principles of the present invention, in accordance with preferred embodiments thereof, methods and devices are provided in which the chips on a semiconductor wafer are circumscribed by ditched scribe streets to facilitate sawing.  
         [0006]     According to one aspect of the invention, a method for manufacturing a semiconductor wafer having a plurality of semiconductor chips includes steps of applying photo resist material to the top surface of the wafer to protect the chips, and forming a pattern of scribe streets adjacent to the chip edges. In a further step, ditches are etched into the scribe streets extending from the wafer surface down to the substrate below the multiple layers of conductive and non-conductive materials.  
         [0007]     According to another aspect of the invention, a method for singulating semiconductor chips from a wafer includes steps for applying photo resist material to the top surface of the wafer to protect the chips. A pattern of scribe streets is formed adjacent to the chip edges by removing selected portions of the photo resist. The scribe streets are etched to form ditches extending from the wafer surface to the substrate below the multiple layers of conductive and non-conductive materials. In a further step, the wafer is sawn in alignment with the ditches in order to singulate the semiconductor chips.  
         [0008]     According to additional aspects of the invention, examples of preferred embodiments of semiconductor wafers of the invention include a semiconductor wafer with numerous semiconductor chips arranged thereon. The wafer has a semiconductor substrate overlain by a series of upper layers. A scribe street at the top surface of the wafer is defined by inactive areas between and surrounding the edges of the chips. A ditch in the scribe street extends from the top surface of the wafer to the semiconductor substrate below the multiple layers of conductive and non-conductive materials.  
         [0009]     According to still another aspect of the invention, examples of specific embodiments include wafers and associated manufacturing methods of the invention for providing a scribe street ditch within the range of approximately 40 to 90 um in width in inactive areas circumscribing the chips on the wafer.  
         [0010]     According to yet another aspect of the invention, examples of specific embodiments include wafers and associated methods of the invention providing a scribe street ditch within the range of approximately 10 to 40 um in depth in the inactive areas bordering the chips on the wafer.  
         [0011]     The invention provides technical advantages including but not limited to higher yield of devices undamaged by the sawing operation, savings of time providing improved throughput for reduced-damage singulation methods, lower manufacturing costs, and advantageous extension of existing manufacturing processes. These and other features, advantages, and benefits of the present invention can be understood by one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will be more clearly understood from consideration of the following detailed description and drawings in which:  
         [0013]      FIG. 1  is a top perspective view of a semiconductor wafer illustrating an example of an embodiment of the invention having semiconductor chips with ditched scribe streets;  
         [0014]      FIG. 2A  is a partial cross section view of a semiconductor wafer showing an example of steps in preferred method embodiments of the invention;  
         [0015]      FIG. 2B  is a partial cross section view of a semiconductor wafer showing an example of preferred embodiments of the invention; and  
         [0016]      FIG. 3  is a process flow diagram showing an alternative view of steps in an example of preferred methods according to the invention. 
     
    
       [0017]     References in the detailed description correspond to like references in the figures unless otherwise noted. Descriptive and directional terms used in the written description such as first, second, top, bottom, upper, side, etc., refer to the drawings themselves as laid out on the paper and not to physical limitations of the invention unless specifically noted. The drawings are not to scale, and some features of embodiments shown and discussed are simplified or amplified for illustrating the principles, features, and advantages of the invention.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]     In general, the methods and devices of the invention provide improved semiconductor wafers providing features for improving singulation of individual devices. An example of a preferred embodiment of a semiconductor wafer of the invention is illustrated in the top perspective view of  FIG. 1 . The wafer  10 , preferably has a semiconductor substrate  12  such as silicon, although other materials are sometimes used. The substrate  12  is typically overlain by various layers  13  of interconnected conductive and non-conductive materials in order to implement microelectronic circuitry in numerous chips  14  arranged on the top surface  16  of the wafer  10 . Typically, semiconductor wafers  10  with chips  14  formed thereon have inactive areas  18  around the edges of the chips  14  in order to provide a margin for manufacturing purposes. The inactive area  18  preferably more or less defines the boundaries of a scribe street  20 . The wafer  10  may be sawn along the scribe street  20  in order to separate the chips  14  for individual packaging and use. The scribe street  20  on wafers  10  of the invention includes a ditch  22 , along which the wafer  10  may be sawn. Preferably, the scribe street  20  extends from the top surface  16  of the wafer to the substrate layer  12  below the multiple layers of conductive and non-conductive materials. It has been found that the scribe street ditch  22  is effective in preventing damage such as chipping and cracking to the chip  14  edges. Preferably, the sides of the ditch  22  are approximately 10 um from the edge of the inactive area  18  of the chips  14 , permitting the edges of the ditch  22  to be relatively coarse without detriment to the functioning of the chips  14 .  
         [0019]     The ditches  22  are preferably formed using traditional manufacturing processes. Close-up views of the inactive areas  18  of the wafer  10  are shown and further described referring primarily to  FIGS. 2A and 2B . The wafer  10  is preferably manufactured according to ordinary manufacturing methods known in the arts up to a point approaching the singulation process. The new steps for implementing the invention are preferably performed after the chips are substantially completed, and prior to singulation. Preferably, ordinary manufacturing processes and equipment are used to add the new steps according to the invention. Now referring primarily to  FIG. 2A , the top surface  16  of the wafer  10  is covered with a photo resist material  30 . The photo resist  30  is developed and patterned to define scribe streets  20  on the inactive areas  18  adjacent to the chip  14  edges. The exposed scribe streets  20  are then etched, preferably using common wet or dry etching techniques, in order to form ditches  22  as shown in  FIG. 2B . Preferably, the ditches  22  are formed leaving about 10 um of inactive area material  18  between the sides of the ditches  22  and the active areas of the chips  14 . Accordingly, the width of the ditches  22  may generally be between about 50 um and 90 um, although other widths may also be used without departure from the invention. Preferably the ditch  22  is of a width greater than the width of the saw blade to ultimately be used for singulation of the individual chips  14 . The ditch  22  preferably extends down from the wafer surface  16  to the wafer substrate  12  below the multiple layers of conductive and non-conductive materials, thus providing maximum assurance that the devices  14  will not subjected to potential damage by the stresses induced by singulation. A ditch  22  depth of approximately 10 um to 40 um is generally sufficient, although a greater or lesser depth may be used according to specific application requirements.  
         [0020]     Ultimately, the individual chips  14  are singulated by aligning a cutting tool, such as a mechanical saw, with the ditches  22  and sawing through the exposed substrate  12 .  FIG. 3  presents an alterative depiction of the process flow of steps of preferred embodiments of the invention. A wafer  10 , preferably prepared by conventional processes, has substantially completed processing the chips thereon, typically with a passivation overcoat in preparation for chip singulation and packaging. As shown at step  40 , photo-resist material is applied, preferably using conventional spin-coating techniques. The photo-resist is developed  42  and the desired pattern for the scribe street ditches is determined and transferred to the photo-resist material, shown in step  44 . The ditches are etched  46  into the wafer, preferably using wet or dry etching techniques familiar in the arts. Subsequently, chip singulation is performed  48 , preferably using common mechanical sawing processes, by slicing the wafer in alignment with the ditches. It will be appreciated by those skilled in the arts that other steps may be interposed between the etching step  46  and chip singulation  48 , such as for example, cleaning, ashing, or transferring the wafer to a packaging facility.  
         [0021]     Thus, the invention provides new semiconductor wafers and methods for making the same, as well as methods for chip singulation. Ditched scribe streets are provided for improved singulation of individual chips. The methods and devices of the invention provide advantages including but not limited to a higher yield of devices undamaged by sawing, improved throughput for reduced-damage singulation methods, lower manufacturing costs, and extension of existing manufacturing processes. While the invention has been described with reference to certain illustrative embodiments, the methods and apparatus described are not intended to be construed in a limited sense. Various modifications and combinations of the illustrative embodiments as well as other advantages and embodiments of the invention will be apparent to persons skilled in the art upon reference to the description and claims.