Abstract:
A semiconductor wafer ( 100 ) having a regular pattern of predetermined separation lanes ( 102 ) is provided, wherein the predetermined separation lanes ( 102 ) are configured in such a way that the semiconductor wafer is singularizable along the regular pattern.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority under 35 U.S.C. §119 of European patent application no. 11168688.7, filed on Jun. 3, 2011, the contents of which are incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to a semiconductor wafer having a regular pattern of predetermined separation lanes, in particular to a semiconductor wafer which can be used for creation of ultrathin and ultrarobust silicon chips. 
     Beyond this, the invention relates to a method of producing a wafer having a regular pattern of predetermined separation lanes. 
     BACKGROUND OF THE INVENTION 
     In the field of ultrathin integrated circuit or semiconductor wafers, the separation of such ultrathin integrated circuit wafers may result in back side and front side chipping. In particular, a mechanical robustness and flexibility of a die may be reduced due to the low thickness of the wafers. Back end of line layers of advanced semiconductor device wafers, e.g. of advanced CMOS devices, are covered with metals, e.g. copper, dielectric materials, e.g. low k materials, and other materials like silicon nitride as a passivation material and/or aluminum for chip finishing, and/or bond pads. The design rules for advanced semiconductor device wafers require a dense coverage of metal (e.g. copper, aluminum, etc) tiles in order to fulfill homogeneity and planarization demands. The ubiquitous metal coverage dominates the mechanical behavior of the semiconductor wafer and/or chip when a thickness of a substrate, e.g. silicon, reduced to a thickness smaller than 150 micrometers. The semiconductor wafer and/or chip behave like composite of a flexible silicon spring with a ductile metal multi layer on top of it. For ultrathin semiconductor wafers, in particular, when a thickness of the metal/dielectrical layers approaches a thickness of a remaining silicon substrate, a mechanical blade dicing process may not reach a high process capability. The reason may be a strong clogging or strong coverage of the dicing blade with metal, e.g. copper. 
     Alternative laser separation or even dry (trench) etching processes that could overcome the issue of mechanical chip weakness may not be applied on the wafer front side, because the metal structures may shield laser separation or even dry (trench) etching processes. 
     OBJECT AND SUMMARY OF THE INVENTION 
     There may be a need to provide a semiconductor wafer having a regular pattern of predetermined separation lanes, and method of producing a wafer having a regular pattern of predetermined separation lanes that allow for an easy separation of a semiconductor wafer while at the same time maintaining a mechanical robustness and flexibility of a separated die. 
     In order to meet the need defined above, a method and a device according to the independent claims are provided. Further embodiments are described in the dependent claims. 
     According to an exemplary aspect, a semiconductor wafer having a regular pattern of predetermined separation lanes, wherein the predetermined separation lanes are configured in such a way that the semiconductor wafer is singularizable along the regular pattern. 
     In particular, the predetermined separation lanes may have a predetermined width which is adapted in such a way that it enables the singularization or dicing but at the same time is narrow enough that an area density across the wafer is of suitable homogeneity that the processing of the wafer can be performed, in particular without restriction. In particular, the predetermined separation lane may adjoin or may be arranged adjacent to a standard saw lane which may have test structures and/or mask alignment structures (e.g. wafer release modules (PCM), mask alignment and special processing structures (OCM/T-Boxes). A semiconductor wafer may be in particular a raw substrate, e.g. a silicon substrate, a partly processed, or a fully processed semiconductor wafer already comprising chips and/or integrated circuits and/or semiconductor devices. In particular, the regular pattern of predetermined separation lanes may be formed by unpatterned or unprocessed lanes, e.g. lanes which may be metal free and/or polycrystalline silicon free, and/or trenches between partly or fully processed chips or dies. 
     The term “unpatterned lanes” may particularly denote lanes or areas on the wafer without semiconductor devices or chips or integrated circuits or parts thereof. In other words, the predetermined separation lines may form a regular pattern of areas which are free of metal or polycrystalline silicon forming parts of semiconductor devices. The unpatterned lanes or areas may be formed either by sparing these lanes from deposition of metal or components with metal-like characteristics during the processing of the wafer or substrate or by removing substantially all deposited metal or polycrystalline silicon layers during the processing of the wafer or substrate. More particularly, the unpatterned lanes may be formed by areas which may not comprise any metal components and/or components with metal-like characteristics, e.g. polycrystalline silicone. In this context “free of metal or metal free” may particularly denote areas in which substantially no metal or conductor lanes, e.g. polycrystalline silicone lanes, are formed. However, small amounts of metal and/or polycrystalline silicon may be present in the metal free lanes. 
     In particular, the predetermined separation lanes may form areas which may allow for easy separating or singularizing the processed semiconductor wafer into individual chips. For example, the dies of the processed semiconductor wafer may be singularized by cutting and/or laser dicing and/or etching and/or breaking. In particular, a final passivation layer, e.g. silicon nitride, may be removed in the area of the predetermined separation lane. In particular, a delamination on the front side of the semiconductor wafer may be avoided during die separation due to the providing of predetermined separation lanes having a suitable width, for example. 
     According to a further exemplary aspect, a method of producing a wafer having a regular pattern of predetermined separation lanes is provided. The method comprises providing an unpatterned or unprocessed semiconductor wafer, leaving a regular pattern of unpatterned lanes between chip areas during the further processing of the semiconductor wafer, from a wafer front side and/or back side, and/or forming regular pattern of predetermined separation lanes by implanting ions between chip areas during the processing of the unpatterned or unprocessed semiconductor wafer. 
     In particular, the unpatterned lanes may be formed by areas on which no processing, structuring or patterning took place during the forming of the integrated circuits of the chips. 
     The term “chip areas” or “functional chip areas” may denote areas or portion of a semiconductor wafer on which semiconductor devices or integrated circuits or chips or active elements or parts thereof are formed. 
     In particular, the regular pattern of predetermined separation lanes may be formed by deep oxygen implantation from a wafer front side and/or a wafer back side. In particular the ion implantation may take place prior the processing of the semiconductor wafer, i.e. before electronic or integrated circuits of a chip are formed, intermittently or subsequently to the processing of the semiconductor wafer. In particular, an implantation depth and/or implantation direction may be adjusted to a thickness of a final semiconductor wafer. 
     The provision of semiconductor wafers already having a pattern of predetermined separation lanes formed thereon may in particular enable to avoid a delamination on a front side of the semiconductor wafer, in particular on a chip, due to imperfect die separation. In particular, a delamination of metal layers and/or polycrystalline silicon layers or an incomplete separation due to ductile metal fillings may not occur. Also, a chipping on a back side of the semiconductor wafer, in particular in case of thin semiconductor wafers, e.g. smaller than 150 micrometers, may be avoidable, which may result in a significant improvement of mechanical chip strength. Moreover, delamination of brittle and low adhesion dielectric materials, e.g. low k materials, even into an active chip area beyond a chip seal ring may be avoidable. Furthermore, a semiconductor wafer having a pattern of predetermined separation lanes formed thereon may in particular allow for a manufacturing of chips with defect free chip edges. A risk of mechanical damages that may propagate to functional chip areas may be reduced. Moreover, a risk of mechanical breakage of a chip in assembly and/or field application may be reduced. In case of ion implantation from a wafer front side the provision of semiconductor wafers having a pattern of predetermined separation lanes formed thereon may not require major changes in front end product design since a layout may be fully implementable into a default product mask set. For example, test patterns, e.g. OCM and/or PCM, may still be used as in state of the art wafers with default saw lane layout or reticle drop-in. In addition, in the case of small sized chips subsequent laser dicing and/or blade dicing processes may be skipped. Furthermore, the die separation may be less depending on overall thickness to thickness variations of the semiconductor wafer. 
     In the following, further exemplary embodiments of the semiconductor wafer will be explained. However, these embodiments also apply to the method of producing a wafer. 
     According to another exemplary embodiment, a semiconductor wafer is provided, wherein the predetermined separation lanes have a width between 1 micrometer and 50 micrometer. 
     The width of the predetermined separation lanes may in particular be between 1 micrometer and 50 micrometer or smaller than 50 micrometer, more particularly between 5 micrometer and 25 micrometer. 
     According to another exemplary embodiment a semiconductor wafer is provided, wherein the regular pattern of predetermined separation lanes is a rectangular pattern of predetermined separation lanes. 
     In particular, the rectangular pattern of predetermined separation lanes may be formed by lanes between rectangular shaped dies which may be comprised in or may form the semiconductor wafer. 
     According to another exemplary embodiment a semiconductor wafer is provided, wherein the predetermined separation lanes are formed by implantation of ions into the semiconductor wafer. 
     In particular, the implantation of ions may take place prior the processing of the semiconductor wafer, i.e. before electronic or integrated circuits of a chip are formed, or intermittently or subsequently to the processing of the semiconductor wafer. In particular, an implantation depth may be adjusted to a thickness of a final semiconductor wafer. 
     According to another exemplary embodiment a semiconductor wafer is provided, wherein the predetermined separation lanes are formed by implantation of ions into the semiconductor wafer, wherein the implanted ions are oxygen ions. 
     More particularly, the predetermined separation lanes may be formed by deep oxygen implantation. In particular, a mask patterned oxide layer may induce a defined stress layer in the predetermined separation lane. For example, when using a silicon substrate, the implanted oxygen ions may form vertical lanes, areas, or portions of silicon oxide within the silicon substrate of the semiconductor wafer. In particular, the vertical silicon oxide lanes of predetermined separation lanes may allow for separating the semiconductor wafer along the predetermined separation lanes by expansion of the semiconductor wafer since the vertical silicon oxide lanes form lanes of weakened spots or weakened areas that may allow for easy breaking of the semiconductor wafer. More particularly, the deep oxygen ion implantation may exactly define a location and a plane where the silicon lattice may fracture. 
     According to another exemplary embodiment a semiconductor wafer is provided, wherein the predetermined separation lanes are formed by metal free lanes and/or polycrystalline silicon free lanes between chip areas. 
     In particular, the metal free and/or polycrystalline silicon free lanes may be in accordance with back-end-of-line design rules based on dual damascene process technology. 
     The regular pattern of predetermined separation lanes formed by metal free and/or polycrystalline silicon free lanes may allow avoiding a clogging of dicing blades with metal components during a chip separation, in particular die separation by cutting. This may have the advantage that a back side chipping may be avoidable. In particular, the metal free and/or polycrystalline silicon free lanes of the regular pattern of predetermined separation lanes may allow for easy laser dicing on a front side and/or back side of the wafer along the predetermined separation lanes, since the predetermined separation lanes may not comprise any components that will substantially reduce an efficiency of a laser beam during a laser dicing process. 
     According to another exemplary embodiment the method may comprise singularizing or dicing the chips produced on the semiconductor wafer by etching. 
     In particular, the etching may be wet chemical etching and/or a dry etching on a front side and/or back side of the semiconductor wafer. An etching process may in particular be suitable to separate chips formed on the wafer in case the predetermined separation lanes are formed by implanting ions, e.g. oxygen ions. For example, the etching agent may have a high etch selectivity between silicon and silicon oxide so that the chips may be separable along lanes of silicon oxide within the semiconductor wafer. In particular, an etching agent may be diluted HF. 
     According to another exemplary embodiment the method may comprise singularizing or dicing the chips produced on the semiconductor wafer by expansion. 
     In particular, the expansion may be implemented by applying a sticky tape, e.g. an adhesive tape, on the back side of the semiconductor wafer, placing the sticky tape with the semiconductor wafer thereon into a supporting frame, e.g. a film frame carrier, and stretching the sticky tape with aid of the supporting frame in an outward direction. This causes the sticky tape to expand and with it expands the semiconductor wafer. An expansion process may in particular be suitable to separate chips formed on the wafer in case the predetermined separation lanes are formed by implanting ions, e.g. oxygen ions. 
     In another exemplary embodiment the predetermined separation lanes are predetermined weak lanes produced by implantation of ions and/or etching, the method may further comprise singularizing the chips produced on the semiconductor wafer by expansion and subsequent breakage along predetermined weak lanes. 
     For example, silicon oxide lanes may form weakened lanes or weakened areas in the crystal structure of a silicon so that the chips may be separable along lanes of silicon oxide within the semiconductor wafer. In particular, a breakage mechanism may be build-in compressive stress which may be off-loaded during expansion of the semiconductor wafer, in particular a thinned semiconductor wafer. 
     In another exemplary embodiment the method may further comprise singularizing or dicing the chips produced on the semiconductor wafer by cutting. 
     In particular, the cutting may be performed on a back side of the semiconductor wafer. A cutting process may in particular be suitable to separate chips formed on the wafer in case the predetermined separation lanes are formed by unpatterned lanes. 
     According to another exemplary embodiment the method may further comprise singularizing or dicing the chips produced on the semiconductor wafer by laser separation. 
     In particular, the laser separation may be performed by using a laser beam on a back side or on a front side of the semiconductor wafer. A laser separation process may in particular be suitable to separate chips formed on the wafer in case the predetermined separation lanes are formed by unpatterned lanes. Due to the fact that the predetermined separation lanes may be formed by metal free and/or polycrystalline silicon free lanes laser separation may be performable also on the front side of the semiconductor wafer because the separation process may no longer be shielded by metal structures. In particular, due to the predetermined separation lanes, a laser separation or laser dicing processes may not damage the crystal lattice close to the die edge. Thereby mechanical die robustness may be maintained. Moreover, the predetermined separation lanes may reduce a dependence of the laser dicing process on the wafer thickness, in particular a negative effect of wafer thickness variations on a separation process may be reduced. In the case of a semiconductor wafer with a silicon substrate thickness lower than 20 micrometer, predetermined separation lanes may prevent imperfect die edges during laser separation. Imperfect die edges may lead to fragile chips. Furthermore, additional alignment markers may not be required in the case of front side laser separation or laser dicing. A further aspect when using a method according to an exemplary embodiment may be the enabling of easier die separation in case of wafer back side coating (WBC) required for standard package applications. 
     The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. 
         FIG. 1  schematically illustrates a semiconductor wafer according to an exemplary embodiment. 
         FIG. 2  schematically illustrates a cross section through the semiconductor wafer illustrated in  FIG. 1  along the line A-A. 
         FIG. 3  schematically illustrates a semiconductor wafer prior to a separation by expansion. 
         FIG. 4  schematically illustrates a semiconductor wafer after a separation by expansion. 
         FIG. 5  schematically illustrates a semiconductor wafer after etching and prior to a separation by expansion. 
         FIG. 6  schematically illustrates a semiconductor wafer after etching and after a separation by expansion. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The illustration in the drawing is schematically. In different drawings, similar or identical elements are provided with the same reference signs. 
       FIG. 1  schematically illustrates a semiconductor wafer  100  having a silicon substrate. The wafer comprises a number of chips  101  arranged in an array on a front side  107  of the semiconductor wafer. Metal free and/or polycrystalline silicon free lanes  102  are arranged between the individual chips  101 . A width of the metal free and/or polycrystalline silicon free lanes  102  may be between 1 micrometer and 50 micrometer or less than 50 micrometer. In an exemplary embodiment the width of the metal free and/or polycrystalline silicon free lanes  102  may be 20 micrometer. Each chip  101  comprises an active area  103 , whose border is formed by a seal ring  104 . The area  103  may comprise semiconductor devices such as integrated circuits and/or active elements. Adjacent to the seal ring  104  each chip  101  comprises an area  105 , which is covered with metal tiles and/or polycrystalline silicon tiles and comprises test structures  106 . A width of the area  105  is between 15 micrometers and 150 micrometer. In an exemplary embodiment the width of area  105  may be 60 micrometers. 
       FIG. 2  schematically illustrates a cross section through the semiconductor wafer  100  illustrated in  FIG. 1  along the line A-A. The semiconductor wafer  100  comprises a silicone substrate  201  and a final passivation layer of silicon nitride  202  on top of the semiconductor wafer. The cross section shown in  FIG. 2  further shows an area  205  with active elements, whose border is formed by a seal ring  204 . On top of the seal ring the passivation layer may be open or alternatively the passivation layer may cover the seal ring as well. The alternatives may be chosen depending on different process options or silicon foundries. Adjacent to the seal ring  204  a test structure  206  is shown. The area  205  as well as the seal ring  204  and the test structure  206  comprise metal layers and/or polycrystalline silicon layers  208  and dielectric material layers  203 . Between the test structure  206  and the seal ring  204  of another active area  209  the semiconductor wafer  100  comprises a metal free and/or polycrystalline silicon free lane or portion  207  which consist only or substantially only of dielectric materials. The final passivation silicon nitride layer  202  may be removed in the area of the metal free and/or polycrystalline silicon free lane  207 . This metal free and/or polycrystalline silicon free lane  207  may in particular be suited to separate the active areas  205  and  209  formed on the semiconductor wafer  100  from each other by laser separation. Due to the fact that the metal free and/or polycrystalline silicon free lane  207  does neither comprise metal and/or polycrystalline silicon on a front side  210  of the semiconductor wafer  100  nor on a back side  211  of the semiconductor wafer  100  the laser separation may be performable on the front side  210  of the semiconductor wafer  100  as well as on the back side  211  of the semiconductor wafer  100 . 
       FIG. 3  schematically illustrates a semiconductor wafer  300  prior to a separation by expansion. The semiconductor wafer  300  comprises a final passivation layer of silicon nitride  302  on top of the semiconductor wafer. The cross section showed in  FIG. 3  further shows an active area  305  the border of which is formed by a seal ring  304 . The active area  305  as well as the seal ring  304  comprises metal layers and/or polycrystalline silicon layers  308  and dielectric material layers  303 . Between the seal ring  304  of the active area  305  and the seal ring  304  of another area  309  the semiconductor wafer  300  comprises a metal free and/or polycrystalline silicon free lane  307  which consist only of dielectric materials, in particular the final passivation silicon nitride layer  302  may be removed in the area of the metal free and/or polycrystalline silicon free lane  307 . Furthermore, the metal free and/or polycrystalline silicon free lane  307  comprises a lane of silicon oxide  306  within the silicon substrate  301 . The lane of silicon oxide  306  is formed by implanting oxygen ions into the silicon substrate  301  prior and/or subsequent to a processing of the semiconductor wafer  300 . The oxygen ions may be implanted across the whole thickness of the silicon substrate  301  or only across parts thereof. Consequently the depth of the silicon oxide lane  306  may either extend along a part of the thickness of a silicon substrate  301  or along the entire thickness of the silicon substrate  301 . For a separation of the semiconductor wafer  300  into individual chips, a sticky tape  312  is applied to a back side  311  of the semiconductor wafer  300 . Alternatively, the sticky tape may also be appliable to a front side  310  of the semiconductor wafer  300 . The sticky tape  312  is mounted in a film frame carrier  313 . In order to separate the individual chips of the semiconductor wafer  300 , the sticky tape  312  is expanded, in particular isotropically extended or expanded, in an outward direction by the aid of the film frame carrier  313  as indicated by the arrows in  FIG. 3 . This causes the semiconductor wafer  300  to separate along the lanes of silicon oxide  306 . The result of such a separation is illustrated in  FIG. 4 . 
       FIG. 4  schematically illustrates the semiconductor wafer  300  after a separation by expansion. Since the lane of silicon oxide  306  within the semiconductor wafer  300  forms a weakened lane in the silicon crystal structure, the semiconductor wafer  300  is separated along the metal free and/or polycrystalline silicon free lane  307  having below the weakened lane of silicon oxide. 
       FIG. 5  schematically illustrates a semiconductor wafer  500  after etching and prior to a separation by expansion. The semiconductor wafer  500  comprises a final passivation layer of silicon nitride  502  on top of the semiconductor wafer formed on a silicon substrate  501 . The cross section shown in  FIG. 5  further shows an area  505  the border of which is formed by a seal ring  504 . The area  505  as well as the seal ring  504  comprises metal layers and/or polycrystalline silicon layers  508  and dielectric material layers  503 . Between the seal ring  504  of the area  505  and the seal ring  504  of another area  509  the semiconductor wafer  500  comprises a metal free and/or polycrystalline silicon free lane  507  which consist only of dielectric materials, in particular the final passivation silicon nitride layer  502  may be in the area of the metal free and/or polycrystalline silicon free lane  507 . Furthermore, the metal free and/or polycrystalline silicon free lane  507  comprises a lane of silicon oxide  506  within the silicon substrate  501 . The lane of silicon oxide  506  is formed by implanting oxygen ions into the silicon substrate  501  prior to a processing of the semiconductor wafer  500 . Prior to the separation an etching agent, e.g. HF, is applied to a back end side  511  of the semiconductor wafer  500 . The etching agent etches with a high etch selectivity between silicon and silicon oxide so that mainly the silicon oxide in the lane of silicon oxide  506  is removed by the etching agent. This etching process leaves a trench  514  in the back end side  511  of the semiconductor wafer  500 . For a separation of the semiconductor wafer  500  into individual chips, a sticky tape  512  is applied to a front side  510  of the semiconductor wafer  500 . The sticky tape  512  is mounted in a film frame carrier  513  which is then expanded. 
       FIG. 6  schematically illustrates the semiconductor wafer  500  after etching and after a separation by expansion. The semiconductor wafer  500  is separated by expanding, in particular isotropically expanding, the sticky tape  512  in an outward direction by the aid of the film frame carrier  513 . This causes the semiconductor wafer  500  to separate along the trench  514 . 
     It should be noted that the term “comprising” does not exclude other elements or features and the “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined. 
     It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.