Abstract:
A method and system for dicing a wafer is disclosed. One illustrative method includes forming a layer of frozen material above a plurality of integrated circuit die on a substrate and performing a cutting process to cut through the layer of frozen material and the substrate to singulate the plurality of die. Another method includes performing a cutting process to singulate a plurality of integrated circuit die having a layer of frozen material formed above the plurality of die. One illustrative system comprises a substrate having a plurality of integrated circuit die, a cooled layer of material attached to the substrate and a dicing saw for singulating the plurality of die. Another illustrative system comprises a semiconducting substrate comprising a backside and a plurality of integrated circuit die, a layer of material attached to the backside of the substrate, the layer of material being at a temperature of 10° C. or less and a dicing saw for singulating the plurality of die.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is generally directed to the field of manufacturing integrated circuit devices, and, more particularly, to systems and methods for dicing a wafer. 
         [0003]    2. Description of the Related Art 
         [0004]    The manufacturing of semiconductor devices may involve many process steps. For example, semiconductor fabrication typically involves processes such as deposition processes, etching processes, thermal growth processes, various heat treatment processes, ion implantation, photolithography, etc. Such processes may be performed in any of a variety of different combinations to produce semiconductor devices that are useful in a wide variety of applications. 
         [0005]    Integrated circuit devices are formed in regions of a semiconducting substrate known as die. The number of die on a particular substrate depends upon the particular type of integrated circuit device and the size of the substrate. Typically, a substrate may have hundreds of die formed thereon. 
         [0006]    After the integrated circuit devices are manufactured and tested, they must be packaged for sale. This packaging process typically involves coupling the die to another structure, such as a leadframe, so that electrical connections can be made between the die and other electrical components or devices, e.g., a printed circuit board. Packaging also typically involves encapsulating all or a portion of the die within an encapsulant material, e.g., mold compound. A vast number of techniques and structure have been and continue to be employed in packaging the vast number of integrated circuit devices on the market. 
         [0007]    Typically, each of the individual die on a substrate are separated or singulated by cutting the substrate with a dicing saw. The saw blades used during the wafer dicing operation are typically made of diamond particles that are embedded or bonded in a metal matrix. Such saw blades are well-suited for cutting relatively hard, brittle materials, such as silicon. During dicing operations, the saw blade is rotated at a very high rate of speed, and the diamonds make small chips in the silicon substrate. 
         [0008]    In some cases, various relatively soft materials are applied to the substrate, e.g., die attach tape attached to the backside of the substrate, protective polymeric films or layers on the active side (front side) of the substrate, etc. Typically, these layers are applied to the substrate prior to performing the saw-cutting or dicing process. In some cases, these layers of material are intended to remain in place as part of the finished product. For example, laminated layers of material may be applied to the backside of the substrate to protect the die in direct flip chip packaging applications, adhesive films may be attached for use as die attach materials, particularly in die stacking applications, and optical films may be applied to control or manage light penetration and/or reflection in optical devices, e.g., CMOS imager devices. 
         [0009]    The chips generated during the dicing process may cause several problems. For example, the functional circuitry and structures on the die may be damaged by impact impingement with the chips or particles created during dicing operations. In later process operations, such particles or chips may be inadvertently pressed into the functional circuitry on the die. For example, this may occur in subsequent processes such as die picking, die stacking and/or encapsulation. Particles that adhere to the surface of the die may also cause the integrated circuit device to fail or underperform during later operations. For example, the particles that adhere to the surface of the die can create a stress point on the die without causing a detectable failure when the device is first made. However, over time, such a stress point may lead to fatigue failure during the operational life of the integrated circuit device. For optical devices, the presence of such particles can interfere with or prevent the transmission of light for emitting devices or they can prevent or limit the collection of light for sensing devices. 
         [0010]    The attachment of various relatively soft films or layers to the substrate, which are subsequently cut during dicing operations, may also cause several problems. One such problem is that the saw blade may become “loaded” with such materials. Blade loading occurs when resin builds up on the surface of the blade or flows into the pores of the blade matrix. Blade loading may decrease cutting efficiency, increase blade heating, decrease blade life, increase blade breakage and/or cause an increase in chipping of the substrate. Additionally, as the blade cuts through soft polymeric material, it tends to melt that material. As the blade spins, this material may be cast off and may be deposited on the surface of the dies. Such particles may lead to functional failure or yield loss of the integrated circuit devices. For example, polymeric particulars that are deposited on wire bond pads are known to cause so-called wire bond “no sticks,” which may result in significant yield loss in semiconductor assembly operations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
           [0012]      FIG. 1  depicts one illustrative embodiment of a system described herein; 
           [0013]      FIGS. 2-4  depict an illustrative technique of dicing a substrate as described herein; and 
           [0014]      FIGS. 5-7  depict another illustrative technique of dicing a substrate as described herein. 
       
    
    
       [0015]    While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Illustrative embodiments are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0017]    The present subject matter will now be described with reference to the attached figures. Various structures and systems for performing during operations are schematically depicted in the drawings. For purposes of clarity and explanation, the relative sizes of the various features depicted in the drawings may be exaggerated or reduced as compared to the size of those features or structures on real-world devices and systems. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present subject matter. 
         [0018]      FIG. 1  depicts one illustrative embodiment of a system  10  as described herein. The system  10  generally comprises a substrate chuck  12 , a dicing saw  14 , a saw blade  15 , a chiller  16 , a source or reservoir  18  of process fluid, e.g., water, a chiller  20 , a temperature meter  22 , a flow meter  24 , a temperature meter  26 , a flow meter  28 , a mixing valve  30  and a nozzle  32 . As depicted in  FIG. 1 , a substrate  100  is positioned on the chuck  12 . The chiller  16  is adapted to supply a cooling fluid (liquid or gas), e.g., water or some other medium, to the chuck  12 . 
         [0019]    It should be noted that the system  10  depicted in  FIG. 1  is schematic in nature. That is, various components that might be present in an actual operational system, e.g., circulating pumps, valves, etc., are not depicted so as not to obscure the present disclosure with details that will be readily apparent to those skilled in the art after a complete reading of the present application. Additionally, in many applications, a wafer dicing tape  110  is applied to the backside  100 B of the substrate  100  prior to beginning dicing operations. 
         [0020]    In one particular example, the chiller  16  supplies sufficient cooling fluid to the chuck  12  such that the substrate  100  is cooled to at least the approximate freezing temperature of a fluid to be directed to the top surface  100 A of the substrate  100 . In the illustrative case where the fluid to be applied to the substrate  100  is water, the chuck  12  may be cooled to a temperature of at least about 0° C. Thereafter, a fluid, e.g., water, is directed toward the surface  100 A of the substrate  100 , via nozzle  32 , such that a frozen layer of material  104  is formed above the substrate  100 .  FIG. 2  is an enlarged view of the substrate  100  comprised of a plurality of schematically depicted die  102  having the frozen layer of material  104  formed thereabove. The fluid supplied via the nozzle  32  may be chilled by the chiller  20  to any desired temperature. The layer of frozen material  104  may be formed to any desired thickness. For example, the layer of frozen material  104  may have a thickness ranging from approximately 100-500 micron. In one particularly illustrative embodiment, the fluid supplied via the nozzle  32  is water that, when frozen, results in a layer of ice  104 . 
         [0021]    Thereafter, as shown in  FIG. 3 , dicing operations are performed using the dicing saw  14  to dice the substrate  100  as is commonly done in typical semiconductor dicing operations. During the actual cutting process, additional fluid may be continuously or intermittently supplied to the surface  100 A of the substrate  100  via the nozzle  32  or by some other means. Using the methods described herein, particles resulting from the cutting operation may be either trapped in the layer of frozen material  104  or flow away with the fluid that is directed toward the surface of the substrate  100  during the cutting process. 
         [0022]    After the substrate  100  is completely diced, the chuck  12  may be warmed by stopping the flow of chilled fluid from the chiller  16  and/or supplying a warm fluid, e.g., warm water, to the chuck  12 . The warming of the chuck  12  should tend to cause the layer of frozen material  104  to thaw. During this process, if desired, relatively warm fluid may also be supplied from the reservoir  18  or another source to the substrate  100  via the nozzle  32  or by some other means. This relatively warm fluid may be flowed over the substrate  100  to remove the layer of frozen material  104  and any captured or loose particles resulting from the dicing process. Alternatively, the diced substrate  100  with the layer of frozen material  104  intact may be transferred to a separate station for thawing the layer of frozen material  104  and removing the particles. In another illustrative example, as shown in  FIG. 4 , the substrate  100  may be flipped upside down and sprayed with a relatively warm fluid, e.g., water, via nozzle  33 . In that orientation, the particles would naturally fall away from the diced substrate  100 . 
         [0023]    In yet another illustrative variation of this process, after the layer of frozen material  104  is fully formed, the substrate  100  may be diced without applying any additional fluid, e.g., water, to the surface of the substrate  100 . The layer of frozen material  104  and the chilled chuck  12  would then absorb the heat generated during the dicing process. As the layer of frozen material  104  melts, it would act as a lubricant for the cutting surface of the saw blade  15 . As with the other variations, the layer of frozen material  104  would provide protection for the surface  100 A of the substrate  100  during the dicing operation. 
         [0024]    It should be understood that the various components depicted in  FIG. 1  are illustrative and intended to be schematic in nature. For example, the dicing saw  14  may be any type of dicing saw commonly employed in semiconductor manufacturing operations to dice semiconducting substrates. Similarly, the particular configuration of the illustrative system components, e.g., chillers  16 ,  20 , temperature meters  22 ,  26 , flow meters  24 ,  28 , the mixing valve  30  and the nozzle  32 , is provided by way of example only. After a complete reading of the present application, those skilled in the art will readily understand that a variety of arrangements may be employed to supply chilled water and/or warm water to the surface of the substrate. Similarly, the chuck  12  may be of traditional configuration. Thus, the particular illustrative arrangement depicted in  FIG. 1  should not be considered a limitation of the present invention. Although not depicted in  FIGS. 2-4 , the substrate  100  may have a film or layer attached to the backside  100 B of the substrate  100 , e.g., a die attach film. However, such an additional film may or may not be present depending upon the particular application. 
         [0025]    As indicated in the background section of the application, one problem encountered in dicing operations is that the blade  15  of the saw  14  may engage relatively soft layers of material attached to the front side  100 A or backside  100 B of the substrate  100 . For example, die attach tape is commonly attached to the backside  100 B of a substrate  100  prior to beginning dicing operations. The die attach tape is cut during dicing operations along with the substrates and the tape is used to attach the individual die to a package. 
         [0026]      FIG. 5  depicts such an illustrative layer  105  attached to the backside  100 B of the substrate  100 . In accordance with one aspect of the present disclosure, any such layer(s)  105  attached to the front side  100 A or the backside  100 B of the substrate  100  may be cooled to facilitate cutting the cooled layer of material. In stating that the layer  105  is attached to the substrate  100 , it should be understood that the layer(s)  105  may be directly attached to the backside  100 B of the substrate  100  or the front side  100 A, or there may be an intermediate layer of material between the layer  105  and the actual front side  100 A or backside  100 B of the substrate  100 . Nevertheless, by stating that the layer(s)  105  are attached to the substrate  100  is intended to cover all such variations. 
         [0027]    In general, the layer  105  may be cooled to a temperature that is less than the ambient temperature of the environment where dicing operations will be performed. The exact cooled temperature of the layer  105  may vary depending upon the particular application. Many materials that comprise the layers  105 , e.g., polymeric materials, generally become harder and more brittle as their temperature is decreased. For example, Ablestik ATB  240 , a common die attach film, has a dynamic tensile modulus of 4 MPa at 150° C., 630 MPa at 25° C. and 3130 MPa at −65° C. Thus, cooling such a layer  105  and making it harder would make it easier to cut using the saw blade  15 . 
         [0028]    Various techniques may be employed to cool the layer(s)  105 . For example, as indicated in  FIG. 5 , the substrate  100  has a polymeric film or layer  105  laminated to the backside  100 B. In this embodiment, a chilling fluid (liquid or gas) is circulated through the cooling chuck  12  to cool the layer  105  to a desired temperature, e.g., below 10° C., below 0° C., etc., to thereby make the layer  105  harder and easier to cut. In this illustrative example, the primary objective is to improve the dicing characteristics of the layer  105 . Thus, it is not essential to form a layer of frozen material  104  on the top surface  100 A of the substrate  100  as previously described. However, such a layer of frozen material  104  may be formed if desired. 
         [0029]    Another technique for cooling the layer  105  would be to direct or spray a cooled fluid  113  (liquid or gas) onto the layers  105  shown in  FIG. 7 . In this particular example, the substrate  100  has layers  105  attached to both the front side  100 A and backside  100 B of the substrate  100 . The cooled fluid  113  may be applied to the layers  105  via illustrative nozzles  37 . The cooled fluid  113  may be any type of fluid that may be used to reduce the temperature of the layers  105 , e.g., liquid nitrogen, a refrigerant, a chilled liquid, etc. 
         [0030]    Additionally, the layer(s)  105  may be cooled by placing the substrate  100  in a refrigerated environment, e.g., a freezer, for a sufficient period such that the layer(s)  105  reach the desired temperature. Such a refrigerated environment may be a stand-alone freezer or it may be a portion of a dicing system. 
         [0031]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.