Abstract:
A method including forming a plurality of dicing channels in a front side of a wafer; the plurality of dicing channels including a depth at least greater than a desired final thickness of the wafer, filling the plurality of dicing channels with a fill material and removing a portion of the wafer from a back side of the wafer until the desired final thickness is achieved, where a portion of the fill material within the plurality of dicing channel is exposed. The method further including depositing a metal layer on the back side of the wafer; removing the fill material from within the plurality of dicing channels to expose the metal layer at a bottom of the plurality of dicing channels, and removing a portion of the metal layer located at the bottom of the plurality of dicing channels.

Description:
BACKGROUND  
       [0001]    The present invention generally relates to semiconductor device manufacturing, and more particularly to chip dicing before backside grinding with the addition of a backside metal. 
         [0002]    Chip dicing is the process of dividing a wafer into multiple individual chips. Typically, chip dicing involves the use of a saw blade, chemicals, a laser, or their combination to cut through and along kerf regions that run between multiple chips arranged on the wafer. The wafer may be diced using a standard dicing technique or a dice-before-grind (DBG) technique, as described in brief below. The standard dicing technique may involve dicing through the entire thickness of a wafer which has previously been ground to a desired final thickness. The dice-before-grind technique typically involves forming shallow dicing channels in a full-thickness wafer before being thinned. 
       SUMMARY  
       [0003]    According to one embodiment of the present invention, a method is provided. The method may include forming a plurality of dicing channels in a front side of a wafer, the plurality of dicing channels including a depth at least greater than a desired final thickness of the wafer; filling the plurality of dicing channels with a fill material; and removing a portion of the wafer from a back side of the wafer until the desired final thickness is achieved, where a portion of the fill material within the plurality of dicing channel is exposed. The method further including depositing a metal layer on the back side of the wafer; removing the fill material from within the plurality of dicing channels to expose the metal layer at a bottom of the plurality of dicing channels; and removing a portion of the metal layer located at the bottom of the plurality of dicing channels. 
         [0004]    According to another embodiment of the present invention, a method is provided. The method may include forming a plurality of dicing channels in a front side of a wafer; the plurality of dicing channels comprising a depth at least less than a desired final thickness of the wafer; removing a portion of the wafer from a back side of the wafer until the desired final thickness is achieved; and depositing a metal layer on the back side of the wafer. The method may further include etching a bottom of the plurality of dicing channels to expose the metal layer; and removing a portion of the metal layer located at the bottom of the plurality of dicing channels. 
         [0005]    According to another embodiment, a structure is provided. The structure may include a chip diced from a wafer; and a metal layer located on a back side of the chip, wherein the edges of the metal layer are offset from the edges of the chip, the edges of the chip being perpendicular to the back side of the chip. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
         [0006]    The following detailed description, given by way of example and not intended to limit the invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, in which: 
           [0007]      FIGS. 1-7  illustrate the steps of a method of dicing a wafer according to an exemplary embodiment. 
           [0008]      FIG. 1A  is a top view of a structure illustrating a plurality of dicing channels in a wafer according to an exemplary embodiment. 
           [0009]      FIG. 1B  is a side view of  FIG. 1A  according to an exemplary embodiment. 
           [0010]      FIG. 2  is a cross section view of  FIG. 1A , along section line A-A, illustrating the formation of a plurality of dicing channels according to an exemplary embodiment. 
           [0011]      FIG. 3  is a cross section view of  FIG. 1A , along section line A-A, illustrating the filling the plurality of dicing channels with a fill material according to an exemplary embodiment. 
           [0012]      FIG. 4  is a cross section view of  FIG. 1A , along section line A-A, illustrating the attachment of a handler followed by a backside grinding technique according to an exemplary embodiment. 
           [0013]      FIG. 5  is a cross section view of  FIG. 1A , along section line A-A, illustrating the deposition of a metal layer followed by the application of a backside tape, and the subsequent removal of the handler according to an exemplary embodiment. 
           [0014]      FIG. 6  is a cross section view of  FIG. 1A , along section line A-A, illustrating the removal of the fill material from within the plurality of dicing channels and the removal of a portion of the metal layer exposed at a bottom of the plurality of dicing channels according to an exemplary embodiment. 
           [0015]      FIG. 7A  is a cross section view of a single chip after dicing according to an exemplary embodiment. 
           [0016]      FIG. 7B  is a bottom view of  FIG. 7A  according to an exemplary embodiment. 
           [0017]      FIGS. 8-13  illustrate the steps of a method of dicing a wafer according to another exemplary embodiment. 
           [0018]      FIG. 8  is a cross section view of  FIG. 1A , along section line A-A, illustrating the formation of a plurality of dicing channels according to an exemplary embodiment. 
           [0019]      FIG. 9  is a cross section view of  FIG. 1A , along section line A-A, illustrating the attachment of a handler followed by a backside grinding technique according to an exemplary embodiment. 
           [0020]      FIG. 10  is a cross section view of  FIG. 1A , along section line A-A, illustrating the deposition of the metal layer followed by the application of a backside tape, and the subsequent removal of the handler according to an exemplary embodiment. 
           [0021]      FIG. 11  is a cross section view of  FIG. 1A , along section line A-A, illustrating etching of the plurality of dicing channels to expose the metal layer and the subsequent removal of a portion of the metal layer exposed at a bottom of the plurality of dicing channels according to an exemplary embodiment. 
           [0022]      FIG. 12A  is a cross section view illustrating a single chip after dicing according to an exemplary embodiment. 
           [0023]      FIG. 12B  is a bottom view of  FIG. 12A  according to an exemplary embodiment. 
       
    
    
       [0024]    The drawings are not necessarily to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention. In the drawings, like numbering represents like elements. 
       DETAILED DESCRIPTION  
       [0025]    Detailed embodiments of the claimed structures and methods are disclosed herein; however, it can be understood that the disclosed embodiments are merely illustrative of the claimed structures and methods that may be embodied in various forms. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this invention to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments. 
         [0026]    References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
         [0027]    For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof shall relate to the disclosed structures and methods, as oriented in the drawing figures. The terms “overlying”, “atop”, “on top”, “positioned on” or “positioned atop” mean that a first element, such as a first structure, is present on a second element, such as a second structure, wherein intervening elements, such as an interface structure may be present between the first element and the second element. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary conducting, insulating or semiconductor layers at the interface of the two elements. 
         [0028]    In the interest of not obscuring the presentation of embodiments of the present invention, in the following detailed description, some processing steps or operations that are known in the art may have been combined together for presentation and for illustration purposes and in some instances may have not been described in detail. In other instances, some processing steps or operations that are known in the art may not be described at all. It should be understood that the following description is rather focused on the distinctive features or elements of various embodiments of the present invention. 
         [0029]    The embodiments of the present invention generally relate to semiconductor device manufacturing, and more particularly to chip dicing before backside grinding with the addition of a backside metal. In one embodiment, a wafer may undergo a partial dicing technique followed by the deposition of a metal layer on a back side of the wafer. 
         [0030]    A metal layer may be deposited on the back side of the wafer, for example, to create a ground plane. During typical dice-before-grind techniques the metal layer may be contaminated by being exposed to an adhesive used to attach a handler. The adhesive may outgas during processing and affect metal adhesion, which may ultimately affect chip yield and performance. Ideally, adding the metal layer without the risk of contamination is preferable. One way to incorporate the metal layer into current dice-before-grind process flows may include filling a plurality of dicing channels with a fill material used to prevent contamination of the metal layer by the adhesive. An embodiment by which to add the metal layer and fill the plurality of dicing channels with the fill material is described in detail below by referring to the accompanying drawings  FIGS. 1-7 . In the present embodiment, the dicing channels are formed to a depth greater than a desired final thickness of the wafer after being thinned. More, specifically, the fill material within the plurality of dicing channels may be in direct contact with the metal layer, and physically separate the metal layer from the adhesive. 
         [0031]    Referring now to  FIGS. 1A and 1B , a structure  100  is shown. The structure  100  may include a wafer  102  having a plurality of dicing channels  104 . The wafer may  102  may also include a front side  106  and a back side  108 . The front side  106  of the wafer  102  may also be referred to as the top side or the device side. The plurality of dicing channels  104  may be formed using any wafer dicing technique known in the art. The chosen dicing technique may include the use of a saw, a laser, chemicals or some combination thereof. In one embodiment, the plurality of dicing channels  104  may have a depth less than the total thickness of the wafer  102  at the present stage before dicing, as described below. For example, a 200 mm diameter silicon wafer may have a thickness ranging from about 705 μm to about 745 μm before backside grinding, and a thickness of about 50 μm to about 200 μm after backside grinding. It should be well understood by a person of ordinary skill in the art that the number and placement of the dicing channels  104  may depend on the placement and size of individual chips formed on the wafer  102 .  FIGS. 2-7  each represent a cross section view of  FIG. 1A  along section line A-A. 
         [0032]    The wafer may include a typical wafer known in the art of which may include multiple layers and materials. The multiple layers may consist of semiconductor materials, dielectric materials, and conductive materials. The semiconductor materials may include any semiconductor materials well known in the art, such as, for example, undoped Si, n-doped Si, p-doped Si, single crystal Si, polycrystalline Si, amorphous Si, Ge, SiGe, SiC, SiGeC, Ga, GaAs, InAs, InP and all other III/V or II/VI compound semiconductors. Non-limiting examples of compound semiconductor materials include gallium arsenide, indium arsenide, and indium phosphide. Typically the wafer  102  may be about, but is not limited to, several hundred microns thick, as described above. 
         [0033]    The dielectric materials may include any of several dielectric materials, for example, oxides, nitrides and oxynitrides of silicon. The dielectric material may also include oxides, nitrides and oxynitrides of elements other than silicon. In addition, the dielectric materials may include crystalline or non-crystalline dielectric material. The conductive materials may include any of several widely used materials, such as, for example, copper, tungsten, and aluminum. 
         [0034]    Referring now to  FIG. 2 , the plurality of dicing channels  104  illustrated in the present figure separate one or more chips, for example the chips  110 . In one embodiment, the wafer  102  may have a total thickness (h 1 ) ranging from about 705 μm to about 745 μm, and a desired final thickness (h 2 ) ranging from about 90 μm to about 110 μm, the total thickness (h 1 ) may be measured before backside grinding and the desired final thickness (h 2 ) may be measured after backside grinding. The desired final thickness (h 2 ) may be indicated in the figures by a reference plane  112 . The wafer  102  may undergo a subsequent backside grinding technique, described in detail below, in which a portion of the back side  108  of the wafer  102  is removed up to the reference plane  112  resulting in the wafer  102  having the desired final thickness (h 2 ). The dicing channels  104  may extend from the front side  106  of the wafer  102  to a depth below the reference plane  112 , or to a depth greater than the desired final thickness (h 2 ). In the present example, the plurality of dicing channels for a wafer with a desired final thickness of 100 μm, may have a depth (d) ranging from about 110 μm to about 150 μm. The dicing channels  104  may preferably be formed to ultimately divide the wafer  102  into individual chips or die. The above dicing technique may also be referred to as a partial dicing technique because the dicing channels do not extend through the total thickness (h 1 ) of the wafer  102 . 
         [0035]    Referring now to  FIG. 3 , a fill material  114  may be deposited within the plurality of dicing channels  104 . The fill material  114  may include any compatible inorganic material and may be deposited using any known method. A compatible inorganic material may be removable selective to the wafer material. In one embodiment, the fill material  114  may include a spin-on material such as, for example, silicon, germanium, or spin-on glass. The fill material  114  may preferably be compatible with any photosensitive soft passivation layer (for example, photosensitive polyimide, PSPI) typically used in known dicing techniques. The fill material  114  may preferably prevent the plurality of dicing channels  104  from being filled with an adhesive used in subsequent steps. In one embodiment, one or more masking layers (not shown) may be deposited above the structure  100  to protect features of the chips  110 , for example, bond pads (not shown) located on the surface of the chips  110 , and which may be susceptible to damage during fabrication. Protecting features of the chips is a well known step of typical dicing techniques. Bond pads may include, for example, aluminum or copper pads located on the front side of an individual chip (e.g.  110 ), and may be used to make electrical connections to the chip or used to join two chips stacked vertically. 
         [0036]    Referring now to  FIG. 4 , an adhesive  116  may be used to attach a handler  118  to the front side  106  of the wafer  102  according to techniques well known in the art. The adhesive  116  may include a solvent based adhesive, a UV sensitive adhesive or a temperature sensitive adhesive. Next, the wafer  102  thickness may be reduced or thinned using backside grinding techniques also well known in the art, as above. The chosen grinding technique may preferably reduce the thickness of the wafer  102  from the total thickness (h 1 ) ( FIG. 3 ) to the desired final thickness (h 2 ). In doing so, the fill material  114  may be exposed on the back side  108  of the wafer  102 . Therefore, the plurality of dicing channels  104  may, now after backside grinding, extend from the front side  106  of the wafer  102  to the back side  108  of the wafer  102 . Typically, in cases in which the plurality of dicing channels  104  are not filled with the fill material  114 , they would otherwise be filled with the adhesive  116  used to attach the handler  118  to the front side  106  of the wafer  102 . In an alternate embodiment, a backside tape (not shown) may be applied to the front side  106  of the wafer  102 , instead of the adhesive  116  and handle wafer  118 , to ensure against wafer surface damage and contamination during the backside grind technique. 
         [0037]    Referring now to  FIG. 5 , a metal layer  120  may be deposited on the back side  108  of the wafer  102 . In one embodiment, the metal layer  120  may be used as a ground plane. The metal layer may include Ti, TiN, Cu, Cr, Au, or any alloy thereof, and may be deposited using any deposition technique known in the art, such as, for example, sputter deposition, evaporation, or chemical vapor deposition. In one embodiment, the metal layer  120  may include Ti/Cu/Ti/Au deposited using a sputter deposition technique. The metal layer  120  may include a thickness ranging from about 10 nm to about 1000 nm. Typically, in cases in which the plurality of dicing channels  104  are not filled with the fill material  114 , the metal layer  120  would directly contact the adhesive  116  within the plurality of dicing channels  104 . Direct contact between the adhesive  116  and the metal layer  120  is undesirable and contamination of the metal layer  120  may occur. Outgasing of the adhesive during deposition of the metal layer  120  and processing, due to its relatively low thermal stability, may contaminate the metal layer  120  and negatively affect adhesion of the metal layer  120  to the back side  108  of the wafer  102 , in turn affecting chip yield and performance. 
         [0038]    Next, in one embodiment, a backside tape  122  maybe applied directly to the metal layer  120 . The backside tape  122  may be applied primarily to hold or secure the individual chips  110  during the remainder of the dicing technique as they are individually separated from one another. 
         [0039]    The adhesive  116  ( FIG. 4 ) may then be deactivated and both the adhesive  116  ( FIG. 4 ) and the handler  118  ( FIG. 4 ) may be removed from the front side  106  of the wafer  102 . Deactivation of the adhesive may depend on the respective adhesive chosen to attach the handler  118  to the front side  106  of the wafer  102 , and is generally well known in the art. In embodiments in which a solvent based adhesive is use, the adhesive may be deactivated with the proper solvent. In embodiment in which a UV sensitive adhesive is used, exposure to UV light may deactivate the adhesive and release the handler  118  form the front side  106  of the wafer  102 . In embodiments in which a temperature sensitive adhesive is used, generally, exposure to heat may deactivate the adhesive. 
         [0040]    Referring now to  FIG. 6 , the fill material  114  within the plurality of dicing channels  104  may be removed using any suitable technique known in the art. The suitable technique may remove the fill material  114  selective to the surrounding features, such as, for example, the wafer  102 , the metal layer  120 , and the bond pads (not shown) located on the surface of the chips  110 . In one embodiment, a wet clean technique using dilute hydrofluoric acid may be used to remove the fill material  114  from within the plurality of dicing channels  104 . It should be noted that removal of the fill material  114  may preferably expose the metal layer  120  at the bottom of the plurality of dicing channels  104 . 
         [0041]    Next, a portion of the metal layer  120  may be removed from the bottom of the dicing channels  104 . Any suitable etching technique known in the art may be used to remove the portion of the metal layer  120  at the bottom of the plurality of dicing channels  104 . At this point in the fabrication process of the present example, the metal layer  120  may be the only physical structure holding the multiple chips (e.g.  110 ) together. By removing the portion of the metal layer  120  from the bottom of the dicing channels  104 , each individual chip  110  may be mechanically separated from one another, while the backside tape  122  remains to hold the chips  110  in some uniform pattern. In one embodiment, a wet etch technique, such as, for example, acid etches based on H 2 SO 4 , HNO 3  or HCl, may be used to remove the portion of the metal layer  120  located at the bottom of the plurality of dicing channels  104 , selective to the wafer  102  and the backside tape  122 . It should be noted that the chosen etching technique used to remove the portion of the metal layer  120  may result in an undercut  124 . The undercut  124  may consist of some amount of the metal layer  120  being removed from directly below the wafer  102  adjacent to the plurality of dicing channels  104 . 
         [0042]    Referring now to  FIGS. 7A and 7B , an individual chip  110  after dicing is shown. After removing the portion of the metal layer  120  from the bottom of the plurality of dicing channels individual chips (e.g.  110 ) may be removed from the backside tape  122  ( FIG. 6 ). The individual chip  110  may include a portion of the wafer  102 , and a portion of the metal layer  120 . As detailed above the portion of the metal layer  120  may be undercut (e.g.  124 ) exposing a portion of the back side  108  of the wafer  102 . Similarly, the edges of the portion of the metal layer  120  may be offset from the edges  126  of the individual chip  110  such that an overall size or footprint of the portion of the metal layer  120  is smaller than an overall size or footprint of the individual chip  110 , as illustrated in  FIG. 7B . Similarly, the offset between the edges of the metal layer  120  and the edges  126  of the chip  110  may correspond to the undercut  124  illustrated in  FIG. 6 . 
         [0043]    According to the present embodiment, the edges  126  of the individual chip  110  formed by the partial dicing technique, described above, may have a noticeably rough surface relative to etched surfaces. In the present embodiment, the entire edge  126 , extending from the front side  106  of the wafer  102  to the back side  108  of the wafer  102  may have the noticeably rough surface. 
         [0044]    Another embodiment by which to prevent the contamination of the metal layer is described in detail below by referring to the accompanying drawings  FIGS. 8-14 . In the present embodiment, the dicing channels are formed to a depth less than a desired final thickness of the wafer after being thinned. More, specifically, the adhesive which typically fills the plurality of dicing channels may not be in direct contact with the metal layer, and as such the metal layer may not be contaminated by the adhesive as it outgases during processing. Like above,  FIGS. 8-12  each represent a cross section view of  FIG. 1A  along section line A-A. In the present embodiment, a structure  200  is shown. The structure  200  may include the wafer  102  having a plurality of dicing channels  128 . 
         [0045]    Referring now to  FIG. 8 , the plurality of dicing channels  128  are substantially similar to those described above; however, the plurality of dicing channels  128  may be formed to a different depth than the plurality of dicing channels  104  described above. Like above, the wafer  102  may have a total thickness (h 1 ) ranging from about 705 μm to about 745 μm, and a desired final thickness (h 2 ) ranging from about 90 μm to about 110 μm, the total thickness (h 1 ) may be measured before backside grinding and the desired final thickness (h 2 ) may be measured after backside grinding. Also, the desired final thickness (h 2 ) may be indicated in the figures by a reference plane  112 . The wafer  102  may undergo the subsequent backside grinding technique according to description above. 
         [0046]    In the present embodiment, the dicing channels  128  may extend from the front side  106  of the wafer  102  to a depth (d) above the reference plane  112 , or to a depth (d) less than the desired final thickness (h 2 ). The dicing technique of the present embodiment may also be referred to as a partial dicing technique because the dicing channels do not extend through the total thickness (h 1 ) of the wafer  102 . In one embodiment, the depth (d) of the plurality of dicing channels may range from about 30 μm to about 80 μm, but in any instance less than the desired final thickness (h 2 ). 
         [0047]    Referring now to  FIG. 9 , the adhesive  116  may be used to attach the handler  118  to the front side  106  of the wafer  102  according to techniques well known in the art. It should be noted that the adhesive  116  may partially occupy or substantially fill the plurality of dicing channels  128  during attachment of the handler  118 . Next, like above, the wafer  102  thickness may be reduced or thinned using a backside grinding technique known in the art. The chosen grinding technique may preferably reduce the thickness of the wafer  102  from the total thickness (h 1 ) ( FIG. 8 ) to the desired final thickness (h 2 ). In doing so, neither the bottom of the plurality of dicing channels  128  nor the adhesive  116  will be exposed by the backside grinding technique. Therefore, after backside grinding, the plurality of dicing channels  128  may partially extend into the wafer  102  from the front side  106  of the wafer  102 . 
         [0048]    Referring now to  FIG. 10 , the metal layer  120  may be deposited on the back side  108  of the wafer  102 , as described above. In one embodiment, as shown, the backside tape  122  maybe applied directly to the metal layer  120 . Lastly, the adhesive  116  ( FIG. 9 ) may then be deactivated and both the adhesive  116  ( FIG. 9 ) and the handler  118  ( FIG. 9 ) may be removed from the front side  106  of the wafer  102 , as described above. 
         [0049]    Referring now to  FIG. 11 , the plurality of dicing channels  128  may be etched deeper using any suitable etching technique known in the art. A suitable etching technique may etch the wafer  102  selective to and stopping on the metal layer  120 . In one embodiment, a wet etching technique (based on KOH alkaline solution), or a reactive ion etching technique (Fluorine-based chemistry) may be used to deepen the plurality of dicing channels  128  and expose the metal layer  120 . 
         [0050]    Next, once the metal layer  120  is exposed, a portion of the metal layer  120  may be removed from a bottom of the plurality of dicing channels  128 . The portion of the metal layer  120  may be etched in accordance with the description above with reference to  FIG. 6  Like above, the chosen etching technique may physically separate individual chips (e.g.  110 ) and result in the undercut  124 . 
         [0051]    Referring now to  FIGS. 12A and 12B , the individual chip  110  is shown, like above. According to the present embodiment, an upper portion of the edges  126  of the individual chip  110  formed by the partial dicing technique may have a noticeably rough surface relative to an etched surface. The noticeably rough portion of the edges  126  may be a direct result of the partial dicing technique described above, and is indicated in the figure by the reference numeral  130 . Conversely, the edges  126  of the present embodiment may also have a noticeably smooth portion relative to a diced surface. The noticeably smooth portion of the edges  126  may be a direct result of the etching technique used to expose the metal layer  120 , and is indicated in the figure by the reference numeral  132 . 
         [0052]    The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiment, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.