Patent Publication Number: US-2023154897-A1

Title: High bandwidth die to die interconnect with package area reduction

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 16/991,908, filed Aug. 12, 2020, which is a continuation of U.S. patent application Ser. No. 16/287,635, filed on Feb. 27, 2019, now U.S. Pat. No. 10,770,433 which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Field 
     Embodiments described herein relate to semiconductor packaging, and more particularly to folded die package structures. 
     Background Information 
     The current market demand for portable and mobile electronic devices such as mobile phones, personal digital assistants (PDAs), digital cameras, portable players, gaming, and other mobile devices requires the integration of more performance and features into increasingly smaller spaces. While the form factor (e.g. thickness) and footprint (e.g. area) for semiconductor die packaging is decreasing, system on chip (SoC) designs are becoming more complex. 
     Scaling of features to lower technology nodes in a monolithic die has typically been the way forward for both accommodating higher SoC demands and area reduction. This in turn has placed significantly higher demands on design verification, which has led to partitioning of the hardware and/or software of certain SoC cores (also referred to as IP blocks) within the chip (also referred to as die) such as the central processing unit (CPU), GPU (graphics processing unit), memory-application processor (MEM/AP), voltage regulation, passives integration, etc. 
     More recently, industry has begun to look at die splitting of SoC cores into separate dies. Several advanced packaging solutions have emerged as potential candidates to accommodate SoC die splitting such as fan-out packaging with a redistribution layer (RDL), 2.5D packaging with dies mounted side-by-side on an interposer, or 3D packaging with stacked dies. 
     SUMMARY 
     Embodiments describe package structures that include a folded die arrangement. In particular, such folded die arrangements may be used to split SoC cores into separate dies. In an embodiment, the folded die arrangement is accomplished with the combination of a vertical interposer and local interposer to electrically connect the split dies. The vertical interposer provides vertical interconnection, while the local interposer provides lateral interconnection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional side view illustration of a package on package structure in accordance with an embodiment. 
         FIG.  2    is a schematic top view layout illustration of various package components in accordance with an embodiment. 
         FIG.  3    is a flow chart illustrating a sequence of forming a package structure in accordance with an embodiment. 
         FIGS.  4 A- 4 F  are cross-sectional side view illustrations of a sequence of forming a package structure in accordance with an embodiment. 
         FIG.  5    is a cross-sectional side view illustration of a package on package structure in accordance with an embodiment. 
         FIG.  6    is a cross-sectional side view illustration of a flip chip ball grid array package structure in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe package structures that include a folded die arrangement. In particular, such folded die arrangements may be used to split SoC cores into separate dies. In an embodiment, a package structure includes a first wiring layer including a first side and a second side opposite the first side. A first die and a vertical interposer may be located side-by-side on the first side of the first wiring layer. The vertical interposer includes electrical interconnects from a first side of the vertical interposer coupled with the first side of the first wiring layer to a second side of the vertical interposer opposite the first side of the vertical interposer. A second die is located face down on and electrically connected with the second side of the vertical interposer, and a local interposer is located on the second side of the first wiring layer and in electrical connection with the first die and the vertical interposer. 
     In one aspect, the folded die package structures in accordance with embodiments can leverage both vertical stacking and a local interposer to simultaneously achieve both high bandwidth die-to-die interconnects and package footprint (area) reduction. Such a stacked arrangement may reduce footprint compared to a fan-out RDL or 2.5D packaging solution. Furthermore, such a stacked arrangement may provide significant cost savings compared to a 3D packaging solution in which face-to-face die interconnections formed using techniques such as through-silicon vias (TSVs) can be expensive. 
     In various embodiments description is made with reference to figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions and processes, etc., in order to provide a thorough understanding of the embodiments. In other instances, well-known semiconductor processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the embodiments. Reference throughout this specification to “one embodiment” means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The terms “over”, “to”, “between”, “span” and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “over”, “spanning” or “on” another layer or bonded “to” or in “contact” with another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers. 
     Referring now to  FIG.  1    a cross-sectional side view illustration is provided of a package on package (PoP) structure in accordance with embodiments. As shown, the PoP structure  300  may include a lower package structure  100  with a folded die arrangement in accordance with embodiments, and a top package structure  200  mounted on the lower package structure  100 . As shown, the lower package structure  100  may include a first package level  111  and second package level  171  beneath the first package level  111 . The first package level may include a first die  140  that is stacked on, and offset with, a first die  110 . For example, this may be accomplished by stacking the first die  140  on the second die  110  and a mechanical chiplet  120  (e.g. silicon). A vertical interposer  130  is also stacked on the second die  110 , and electrically connected with the second die. A wiring layer  160  spans across terminals  146  of the first die  140  and terminals  136  of the vertical interposer  130 . In accordance with embodiments, the wiring layer  160  may fan out, or fan in, connections with the vertical interposer  130  and first die  140 . While the wiring layer  160  may form some electrical connections between the vertical interposer  130  and first die  140 , in accordance with embodiments the wiring layer  160  does not form all electrical connections between the vertical interposer  130  and the first die  140 . In some embodiments, the wiring layer  160  does not include any electrical connections between the vertical interposer and the first die. As shown in  FIG.  1   , a local interposer  170  located within the second package level  171  may be used to complete electrical connections between the first die  140  and vertical interposer  130 , which in turn connects to the second die  110  completing an electrical path from the first die  140 , to wiring layer  160  (optional), to local interposer  170 , to wiring layer  160  (optional), to vertical interposer  130 , to second die  110 . Accordingly, this approach leveraged both vertical stacking of (first die  140 , second die  110 , vertical interposer  130 ) as well as local interposer  170  to achieve both high bandwidth die-to-die interconnects and package area reduction. 
     In accordance with embodiments, the first die  140  may be a main chip including higher performance cores (e.g. CPU, GPU) or cores fabricated with smaller node technology, while the second die  110  may be a daughter chip including lower performance cores (e.g. RF, memory) or cores fabricated with a larger node technology, for example. A variety of potential reasons are contemplated for die splitting. 
     In an embodiment, a package structure includes a first wiring layer  160  including a first side  162  and a second side  164  opposite the first side. A first die  140  and a vertical interposer  130  are located side-by-side (and laterally adjacent) on the first side  162  of the first wiring layer  160 . The vertical interposer  130  include electrical interconnects  130  from a first side  132  of the vertical interposer coupled with the first side  162  of the first wiring layer  160  to a second side  164  of the vertical interposer opposite the first side of the vertical interposer. The electrical interconnects  130  may be, or include, pillars or through silicon vias (TSVs) through a bulk silicon chiplet for example. A second die  110  is face down on and electrically connected with the second side  134  of the vertical interposer  130 . In accordance with embodiments, a local interposer  170  is mounted on the second side  164  of the first wiring layer  160  and in electrical connection with the first die  140  and the vertical interposer  130 . In an embodiment, the local interposer  170  includes a plurality of terminals  176  on a first side  172  of the local interposer that is coupled with the second side  164  of the first wiring layer  160 , and the local interposer  170  does not include a terminal on a second side  174  of the local interposer opposite the first side  172  of the local interposer. Thus, the local interposer  170  may function for lateral routing between the first die  140  and vertical interposer  130  as opposed to vertical routing of the vertical interposer  130 . 
     Still referring to  FIG.  1   , a first molding compound  150  may encapsulate the first die  140 , the vertical interposer  130 , and the second die  110 . Additionally, a mechanical chiplet  120  may be attached to the first die  140  laterally adjacent to the second die  110 . More specifically, the first die  140  may be attached to the second die  110  and mechanical chiplet  120 , for example, with an adhesive layer  148 . A first plurality of conductive pillars  104  can extend from the first wiring layer  160  and through the first molding compound  150 . 
     A second molding compound  180  may encapsulate the local interposer  170  on the second side  164  of the first wiring layer  160 . Additionally, a second plurality of conductive pillars  185  can extend from the first wiring layer  160  and through the second molding compound  180 . As illustrated, a second wiring layer  190  may be formed on the second molding compound  180  and connected to the second plurality of conductive pillars  185 . In an embodiment, the second wiring layer  190  is on a planarized surface including the second molding compound  180 , the second plurality of conductive pillars  185 , and the local interposer  170 . Solder bumps  199  may be placed on landing pads  196  of the second wiring layer  190 . For example, solder bumps  199  may be used for mounting onto a circuit board. 
     In the particular package-on-package (PoP) embodiment illustrated in  FIG.  1   , a second package  200  can be mounted on the lower package  100 . For example, the second package  200  can be mounted on an in electrical connection with the first plurality of conductive pillars  104 . In an embodiment, the second package includes a chip  210  connected with a wiring substrate  220 , and encapsulated within a molding compound  230 . In an embodiment the chip  210  is a memory chip, such as dynamic random-access memory (DRAM) or NAND. Chip  210  may be connected with the wiring substrate  220  by a variety of methods, including wire bonds  212 . 
       FIG.  2    is a schematic top view layout illustration of various package components in accordance with an embodiment. While embodiments are not limited to the particular configuration provided,  FIG.  2    is to be understood as a particularly graceful implementation of a folded die structure in accordance with embodiments. As shown, the first die  140  may occupy the largest area within the package structure. The first die  140  is also located beneath the second die  110 . This location may facilitate closest routing to a circuit board within the package structure. 
     As shown, the first die  140  and vertical interposer  130  are laterally adjacent to one another, or side-by-side. The second die  110 , or daughter chip, may be sized as necessary depending on the cores it contains. The relative widths (W) of the components are illustrated in the direction of lateral overlap illustrated in  FIG.  1   . The relative depths (D) of the components are illustrated in a direction orthogonal to widths. In an embodiment, the second die  110  overlaps the vertical interposer  130 , and may completely overlap the area of the vertical interposer  130 . The second die  110  may partially or completely overlap the first die  140 . In the embodiment illustrated, the second die  110  has a smaller area than the first die  140  and only partially overlaps the first die  140 . In such an embodiment, a mechanical chiplet  120  may overlap some remaining area of the first die  140 . This may provide mechanical stability and thermal expansion matching for the package structure. The mechanical chiplet  120  may additionally help thermal performance. As shown, the local interposer  170  overlaps the first die  140  and the vertical interposer  130 . As illustrated, comparative depths (D) of the components may only be as deep as necessary for lateral and vertical routing. For example, local interposer depth (D) may be less than with the first chip  140  and optionally the vertical interposer  130 . The vertical interposer  130  may have a smaller depth than the second die  110 , and optionally the local interposer  170 . 
     In an embodiment, the first die  140  occupies a larger area than the second die  110 . The first die  140  and the second die  110  may include split logic. For example, one IP logic block (e.g. CPU) may be in one die, with another IP logic block (GPU) in another die. In another example, one IP logic block (e.g. higher performance block, with optional smaller processing node) is in one die, with another IP logic block (e.g. lower performance block, with optional larger processing node) in the second die. In an embodiment, first transistors of the first die  140  are formed with a smaller processing node than second transistors of the second die  110 . 
     Referring now to  FIG.  3    and  FIGS.  4 A- 4 F ,  FIG.  3    is a flow chart illustrating a sequence of forming a package structure in accordance with an embodiment;  FIGS.  4 A- 4 F  are cross-sectional side view illustrations of a sequence of forming a package structure in accordance with an embodiment. In interest of clarity and conciseness, the flow chart of  FIG.  3    is described with reference to the features illustrated in  FIGS.  4 A- 4 F . In the following description, the processing sequence may be used to form the package structure, and in particular, the first and second package level structures described with regard to  FIG.  1   , as well as the structural variations provided in  FIG.  5    and  FIG.  6   . 
     As shown in  FIG.  4 A , at operation  3010  a second die  110  and a mechanical chiplet  120  are placed onto a carrier substrate  102 . The second die  110  may include a first side  112  and second side  114  opposite the first side. Likewise, the mechanical chiplet  120  may include a first side  122  opposite a second side  124 . In the embodiment illustrated, the second die  110  is attached to the carrier substrate  102  face up. In an embodiment, the first side  112  of the second die  110  includes exposed terminals  116  (e.g. copper pads) and a passivation material  117 . In some embodiments passivation material  117  may be an oxide material (e.g. silicon oxide) for hybrid-bonding. The second die  110  and mechanical chiplet  120  may optionally be secured on the carrier substrate  102  with adhesive layers  118 ,  128 , respectively. In an embodiment, the mechanical chiplet  120  is formed of silicon for thermal expansion matching. 
     In the embodiment illustrated in  FIG.  4 A  a first plurality of conductive pillars  104  are located on the carrier substrate  102 . The first plurality of conductive pillars  104  may be formed prior to placement of the second die  110  and mechanical chiplet  120 . For example, the first plurality of conductive pillars  104  may be plated. Alternatively, the first plurality of conductive pillars  104  can be placed on the substrate. This may occur prior to placement of the second die  110  and mechanical chiplet  120 , or at a later time. In an embodiment, the second die  110  and mechanical chiplet  120  are placed within a periphery, or between rows of the first plurality of conductive pillars  104 . 
     At operation  3020  a vertical interposer  130  is bonded to the second die  110  as illustrated in  FIG.  4 B . The vertical interposer  130  may be bonded using a technique such as hybrid bonding to achieve a high density terminal pitch (e.g. less than 15 μm), or use of micro (solder) bumps to achieve a terminal pitch density of less than 40 μm. The vertical interposer  130  may include terminals  136  on a first side  132  of the vertical interposer, electrical interconnects  135  that extend from the terminals  136  to terminals  138  on a second side  134  of the vertical interposer opposite the first side of the vertical interposer. Terminals  138  are bonded to the terminals  116  of the second die  110 . In the particular embodiment illustrated, terminals  138  and passivation layer  137  (e.g. oxide) on the second side  134  of the vertical interposer  130  are hybrid bonded (metal-metal and oxide-oxide) with the terminals  116  and passivation layer  117  of the second die  110 . 
     Still referring to  FIG.  4 B , at operation  3030  a first die  140  is placed on the second die  110 , and optionally, a mechanical chiplet  120 . The first die  140  may be placed face up and secured with an adhesive  148 . As illustrated, the first die  140  includes a first side  142  including terminals  146  and a second side  144  opposite the first side  142 . The second die  110  and mechanical chiplet  120  may be approximately the same height to facilitate attaching the first die  140 . 
     It is to be appreciated that variations may exist in the processing sequence. For example, the first die  140  may be placed prior to bonding the vertical interposer  130 . In another variation, the vertical interposer  130  and second die  110  are bonded prior to placement on the carrier substrate  102 . Furthermore, the first plurality of conductive pillars  104  may be formed, or placed at various times. 
     Referring now to  FIG.  4 C , at operation  3040  the second die  110 , the optional mechanical chiplet  120 , the vertical interposer  130 , the first die  140 , and optionally the first plurality of conductive pillars  104  are encapsulated in a molding compound  150 . This may be followed by additional planarization and/or etching to expose terminals  146 ,  136  and the first plurality of conductive pillars  104 , which may extend between a first side  152  and second side  154  of the molding compound  150 . In an alternative processing sequence, the first plurality of conductive pillars  104  are formed in the molding compound  150  after the molding operation. 
     A wiring layer  160  is then optionally formed on the first side  152  of the molding compound, first side  142  of the first die  140 , first side  132  of the vertical interposer  130  and in electrical connection with the terminals  146  of the first die  140  and terminals  136  of the vertical interposer  130  as illustrated in  FIG.  4 D . Wiring layer  160  may also be referred to as a redistribution layer (RDL). For example, wiring layer  160  may be formed with dielectric layer  166  deposition and patterning, and metal seed deposition, patterning and plating (e.g. copper) to form redistribution lines  168 . Contact pads may also be formed as a part of or in addition to redistribution lines in the wiring layer  160 . 
     Referring now to  FIG.  4 E , at operation  3050  a local interposer  170  is mounted on an in electrical connection with the first die  140  and the vertical interposer  130 . In an embodiment the local interposer  170  includes a single face and is mounted face down. For example, local interposer  170  includes a first side  172 , a second side opposite the first side  174 . The first side includes a plurality of terminals  176  bonded to terminals  146 ,  136  of the first die  140  and vertical interposer  130 , respectively. In an embodiment, bonding is accomplished with solder bumps  179 . As shown, the local interposer  170  includes routing  173  to electrically connect the vertical interposer  130  and first die  140 . 
     Similarly, as with the first plurality of conductive pillars  104 , a second plurality of conductive pillars  185  may be formed on the wiring layer  160 . The second plurality of conductive pillars  185  may be formed prior to placement of the local interposer  170 . For example, the second plurality of conductive pillars  185  may be plated. Alternatively, the second plurality of conductive pillars  185  can be placed on the underlying structure. This may occur prior to placement of the local interposer  170 , or at a later time. In an embodiment, the local interposer  170  is placed within a periphery, or between rows of the second plurality of conductive pillars  185 . 
     Referring now to  FIG.  4 F , at operation  3060  the local interposer  170  and optionally second plurality of conductive pillars  185  are encapsulated in a second molding compound  180 . This may be followed by additional planarization and/or etching to expose a second side  174  of the local interposer  170  and the second plurality of conductive pillars  185 , which may extend between a first side  182  and second side  184  of the second molding compound  180 . In an alternative processing sequence, the second plurality of conductive pillars  185  are formed in the molding compound  180  after the molding operation. 
     Various processing sequences may then be performed depending upon the final package structure to be formed. In the exemplary embodiment illustrated in  FIG.  4 F  a second wiring layer  190  including one or more insulation layers  192  and wiring layers  194  is formed on the first side  182  of the second molding compound  180 , the exposed second plurality of pillars  185 , and optionally directly on the second side  174  of the local interposer  170 . The second wiring layer  190  may include landing pads  196 , and solder bumps  199  may be placed on the landing pads  196  for further integration, followed by removal of the carrier substrate  102 . 
       FIG.  5    is a cross-sectional side view illustration of a package on package structure in accordance with an embodiment.  FIG.  5    is substantially similar to the structure provided in  FIG.  1   , with except the vertical interposer  130  is bonded to the second die  110  using micro (solder) bumps  139 . 
       FIG.  6    is a cross-sectional side view illustration of a flip chip ball grid array (FCBGA) package structure in accordance with an embodiment. As previously described, the package structure including the first and second package levels  111 ,  171  may be integrated into a variety of package configurations including PoP and flip chip FCBGA. In an embodiment illustrated in  FIG.  6   , landing pads  196  may be on studs  197 . The package structure  100  may be bonded to a package substrate  402  with solder bumps  199 . An underfill material  195  may then be applied between the package  100  and the package substrate  402 . Package (solder) bumps  404  may then be applied to the opposite side of the package substrate  402  for mounting onto a circuit board, etc. 
     In utilizing the various aspects of the embodiments, it would become apparent to one skilled in the art that combinations or variations of the above embodiments are possible for forming a folded die package structure. Although the embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the appended claims are not necessarily limited to the specific features or acts described. The specific features and acts disclosed are instead to be understood as embodiments of the claims useful for illustration.