Patent Application
20240055366
The present disclosure generally relates to semiconductor devices, and more particularly relates to spacers for chips on wafer (CoW) semiconductor device assemblies.
Semiconductor packages typically include a semiconductor die (e.g., memory chip, microprocessor chip, imager chip) mounted on a substrate or an interface wafer and encased in a protective covering (e.g., an encapsulating material). The semiconductor die may include functional features, such as memory cells, processor circuits, or imager devices, as well as bond pads electrically connected to the functional features. The process of attaching semiconductor dies on a semiconductor wafer in general refers as chips on wafer (CoW) process, which can increase throughput and reduce difficulties in handling individual semiconductor dies as they continue to shrink in size. Individual semiconductor dies can further be stacked in the semiconductor assemblies.
The drawings illustrate only example embodiments and are therefore not to be considered limiting in scope. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the example embodiments. Additionally, certain dimensions or placements may be exaggerated to help visually convey such principles. In the drawings, the same reference numerals used in different embodiments designate like or corresponding, but not necessarily identical, elements.
CoW assembly is a promising technology for high-density package application to overcome the limitations of Wafer-to-Wafer (WoW) bonding and improve die stacking process yield and bonding placement accuracy. Conventional CoW assembly includes encapsulant material filling for mechanical support and electrical isolation of the semiconductor device assemblies. The filling of encapsulant materials in general is followed by a post mold cure (PMC) process at an elevated temperature so as to cross-link the encapsulant materials for stiffness.
Wafer level molding and post mold cure (PMC) are important process steps in the CoW approach, in which molding materials are applied on the semiconductor assemblies and are cured to fully cross-link the mold compound for stiffness, respectively. The PMC process is generally implemented in the CoW process to ensure suitable levels of mechanical strength are reached through accelerating the molding material curing process and optimizing some physical properties of the molding material by raising ambient temperature. However, there is always a coefficient of thermal expansion (CTE) mismatch between the molding materials and the silicon wafer. During the PMC process, microstructure of the molding materials, e.g., Epoxy molding compound (EMC), can be changed and warpage of the semiconductor assemblies can be formed due to the CTE mismatch. Moreover, the PMC process may cause a high warpage on the CoW assemblies and delaminate the device wafer from the carrier wafer, also affecting downstream packaging process, e.g., packages singulation. The warpage issue may be raised from the CTE mismatch between encapsulant material and semiconductor dies in the CoW assemblies. By adding underfill between these two components to enhance solder joint reliability and encapsulating the CoW device and substrate with EMC to protect the CoW package can make the package warpage even worse, depending on the mechanical and thermo-mechanical properties of the underfill and encapsulant materials, and the relative thickness of each of the components of the CoW assemblies.
To address these challenges and others, the present technology applies a spacer assembly to the CoW assemblies. The spacer assembly includes a grid spacer with a higher CTE and a conductive package perimeter material with a lower CTE. The spacer assembly may be attached to a carrier wafer and the conductive package perimeter can be pressure fitted within the spacer grid of the spacer assembly. In the CoW packaging process, once a plurality of semiconductor dies or die stacks are attached to a device wafer, and the spacer assembly can be disposed on the device wafer and between the plurality of semiconductor dies. After encapsulant material being filled into the CoW assemblies, a stealth dicing process can be conducted, i.e., forming dislocations on the device wafer and aligning to the dislocations to the grid spacer. At an elevated temperature, the spacer grid will expand faster than the conductive package perimeter material, interacting with the semiconductor wafer to break it into semiconductor dies each corresponding to an upper semiconductor die stack. Moreover, the spacer grid can be removed through heating the CoW assemblies and stretching a mount tape on which the CoW assemblies are disposed. These operations create gaps between adjacent semiconductor device assemblies in the CoW packaging in order to relieve stress generated in the PMC process for hardening the encapsulant material and to control the CoW assemblies warpage.
In some embodiments, the spacer assembly 110 may be in a grid shape and include a spacer 112 and a conductive package perimeter material 114. The spacer 112 may be made of at least one of polytetrafluoroethylene (PTFE), organic materials, water-soluble materials, and/or molding materials. In addition, the conductive package perimeter material 114 may be made of conductive metals including copper, tungsten, molybdenum, nickel, titanium, tantalum, platinum, silver, gold, ruthenium, iridium, rhenium, rhodium, or alloys thereof.
As shown in
In some embodiments, the semiconductor wafer 102 includes different types of semiconductor dies (e.g., logic dies, controller dies) than the plurality of semiconductor die stacks 104 (e.g., memory dies, DRAM products) of the stacks. The logic dies of the semiconductor wafer 102 can be configured to exchange electrical signals with the semiconductor dies 104 and with higher level circuitry (e.g., a host device external to the semiconductor device assembly) coupled with the logic dies. In some embodiments, the semiconductor wafer 102 includes interposer dies having various conductive structures (e.g., redistribution layers, vias, interconnects) configured to route electrical signals between the plurality of semiconductor die stacks 104 and higher-level circuitry—e.g., a central processing unit (CPU) coupled with the semiconductor die stacks 104 through the interposer die.
In some embodiments, each of the plurality of semiconductor die stacks 104 may include semiconductor dies stacked on top of each other. Each semiconductor die of the stack has a frontside facing toward the semiconductor wafer 102, which may be referred to as an active side of the semiconductor die having memory arrays, integrated circuits coupled to the memory arrays, bond pads coupled to the integrated circuits, etc., and a backside opposite to the frontside. In some embodiments, the semiconductor dies 104 may be stacked through a non-conductive film (NCF) underfill process. For example, solder bumps of an upper semiconductor die can be aligned with and attached to a through silicon via (TSV) of a lower semiconductor die for the solder-TSV bonding in each of the plurality of semiconductor die stacks 104. In this example, NCF underfill materials can be further flowed into the interface between the stacked semiconductor dies in a later process to provide electric isolation between the solder bumps and mechanical support between the stacked dies.
In some other embodiments, each of the plurality of semiconductor die stacks 104 may be stacked and processed through a non-NCF underfill process, e.g., direct bonding technologies including fusion bonding, covalent bonding, diffusion bonding, and/or thermal compression bonding (TCB). For example, a dielectric layer of the upper semiconductor die can be attached to a dielectric layer of the lower semiconductor die through forming covalent dielectric-dielectric bonds between the stacked semiconductor dies. Further, a metal bond pad of the upper semiconductor die can be attached to a metal bond pad of the lower semiconductor die through forming metal-metal diffusion bonds between the stacked semiconductor dies. In this example, the semiconductor dies of each of the semiconductor die stacks 104 are directly bonded to each other, without flowing NCF materials therebetween.
As shown in
In the present technology, the spacer assembly 110 may be formed on a carrier wafer (not shown) and then implemented into the CoW assembly shown in
In some embodiments, the plurality of semiconductor die stacks 104 are processed in a mold underfill (MUF) process, i.e., flowing mold encapsulating material into bond line thickness (BLT) between adjacent semiconductor die. In this example, the mold compound material 116 can flow vertically into the spaces between the spacer assembly 110 and the plurality of the semiconductor die stacks 104, and then laterally flow into the BLT between each of the stacked semiconductor dies 104. In addition, the mold encapsulating material may flow into the space between bottom dies of the plurality of semiconductor die stacks 104 and the semiconductor wafer 102. Here, the conductive package perimeter material 114 performs as a barrier to restrict the mold compound material from flowing out of the edge of the semiconductor wafer 102 and isolate the mold compound from the spacer 112.
In some other embodiments and as described earlier, the plurality of semiconductor die stacks 104 can be processed in a NCF underfill process. In this example, the BLT between each die of the stack of semiconductor dies 104 can be filled by nonconductive fill material. Moreover, the conductive package perimeter material 114 can perform as a stop to the non-conductive underfill material, which may horizontally squeeze out of the stack of semiconductor dies 104 during a thermal bonding process. In this example, the spacer assembly 100 including the conductive package perimeter material 114 may be attached on the semiconductor wafer 102 before the bonding of the plurality of semiconductor die stacks 104 there on.
As shown in
Turning to
Once the carrier wafer 106 is removed, the semiconductor device assemblies can be flipped upside down and processed by the stealth dicing technique. Specifically, a stealth laser can be applied on the semiconductor wafer 102 by aligning the laser spot to the spacer assembly 110. The stealth laser may be an infrared laser which could generate defects 118 through laser ablation within the semiconductor wafer 102 and above the spacer assembly 110. The defects 118 may include silicon dislocations, cracks, or a combination thereof. Further, the defects 118 may be through the thickness of the semiconductor wafer 102. In this process, the stealth laser can be controlled and focused through a conventional stealth dicing tool.
Additionally, and as described in
In some embodiments, the semiconductor device assemblies may be mounted on the tape 120 before the stealth dicing process. For example, after the carrier wafer 106 is debonded and removed from the semiconductor wafer 102, the semiconductor device assemblies 100 may be mounted on the tape 120 by attaching the semiconductor wafer 102 and the mount tape 120 through the adhesive layer 108. After that, the stealth laser may be applied on the semiconductor wafer 102 through the mount tape 120. The stealth laser can be focused on the semiconductor wafer 102 and form defects therein through laser ablation. As described, the defects 118 can be aligned to and disposed above the spacer assembly 110. In addition, the defects 118 may be through the thickness of the semiconductor wafer 102.
During the heating process and as shown in
In some embodiments, the spacer 112 can be lifted up from the semiconductor device assemblies 100. For example, after the semiconductor wafer 102 is broken into semiconductor dies 126 due to the expansion of the spacer 112, the spacer 112 is exposed while the semiconductor dies 126 are being separated from the stretching of the mount tape 120. The spacer 112 can be then removed in a needle peeling process. In some other embodiments, the spacer 112 can be removed from the edge of the mount tape 112. For example, at the edge of the semiconductor wafer 102, there are no semiconductor dies 114 and the spacer 112 is in direct contact with the mold compound 116. After the separation of semiconductor device assemblies, the spacer 112 can be pulled out from the edge of the semiconductor wafer 102. In some other embodiments, the semiconductor device assemblies can be flipped upside down, having the plurality of semiconductor die stacks 114 and the spacer 112 disposed there between all face down. This way, the spacer 114 can fall off the semiconductor devise assemblies 100 automatically by the gravity.
In some embodiments, the spacer 112 can be removed in a plasma treatment or a wet cleaning process. For example, the spacer 112 may be made of an organic material. Once the semiconductor wafer 102 is broken into semiconductor dies 126 and each of the semiconductor device assemblies are separated, the spacer 112 can be removed in a plasma cleaning process. Specifically, oxygen plasma can be used to remove the organic spacer material through chemical reactions or physical sputtering of hydrocarbons. In another example, the spacer 112 can be made of water-soluble materials such as polymers, surfactants, or fibers. The water-soluble spacer material can be removed from the semiconductor device assemblies in a wet cleaning process using deionized water. Further, the spacer 112 can be made of a mold material. At the edge of the semiconductor wafer 102, the mold spacer may be attached with the mold encapsulating material 116. Once the semiconductor device assemblies are horizontally separated through stretching the mount tape, the spacer 112 maybe pulled out of the conductive package perimeter ring from the edge of the semiconductor wafer 102. Here, the gaps between the conductive package perimeter materials 114 that surround adjacent semiconductor die stacks 104 can relieve stresses formed in the PMC process to reduce the CoW assembly warpage, and further allow for an easy package separation between each of the semiconductor device assemblies 100.
In some embodiments and after the separation of the plurality of semiconductor die stacks 104 (including corresponding lower semiconductor dies 126), the semiconductor device assemblies 100 may go through the PMC process at an elevated temperature, in which the molding material 116 are cured to have the mold compound fully cross-linked for stiffness. Here, the gaps between the adjacent conductive package perimeter materials 114 of each of the semiconductor device assemblies 100 can relieve stress that is generated in the PMC process and reduce the CoW assembly warpage.
In the present technology, the CoW assembly warpage post encapsulation or the PMC process can be effectively controlled to be lower than a semiconductor manufacturing equipment tolerance on wafer warpage, e.g., below 1.0 mm, so that the CoW assembly wafers can be handled on equipments in downstream processes. The present technology may also eliminate the risk of polymer or encapsulation voids on the edge of each of the CoW assemblies. For example, encapsulate material can be filled to encapsulate the semiconductor die stack 104 and corresponding semiconductor die 126 of the CoW assembly. Specifically, encapsulate material can flow into the edge of each of the CoW assemblies to fill empty spaces that are available after the spacer 112 being removed.
Once the semiconductor wafer 102 is broken into semiconductor dies 126 and the spacer 112 are removed, the semiconductor wafer 102 can be processed in a singulation process to form separated semiconductor device assemblies 100. Specifically, the semiconductor wafer 102 can be sliced into individual semiconductor die for each of the semiconductor device assemblies 100 by singulating the semiconductor wafer 102 along gaps between the adjacent plurality of semiconductor die stacks 104. In some embodiment, the conductive package perimeter material 114 may form a conductive rectangular annulus that surrounds sidewalls of each of the semiconductor die stacks 104. Additionally, the conductive rectangular annulus of the conductive package perimeter material 114 may be disposed within each of the lower semiconductor dies 126 and has a footprint within a footprint of each of the lower semiconductor dies 126.
Turning to
In some embodiments, the spacer material 112 may be attached to the carrier wafer 202 by a water-soluble resin. Moreover, the spacer material 112 may have a low surface energy that prevents molding compounds or epoxy encapsulants from sticking on the spacer for reusage. Further, the spacer grid may have a thickness ranging from 20 μm to 340 μm, depending on the dicing scribe width. As described, the spacer 112 may be made of at least one of polytetrafluoroethylene (PTFE), organic materials, water-soluble materials, and/or molding materials.
In some embodiments, the conductive package perimeter material 114 may have a thickness ranging from 100 μm to 200 μm. As shown in
Turning to
In some other embodiments, the spacer material 112 and the conductive package perimeter material 114 are not coplanar in the spacer assembly 200. For example and as shown in
In this example, mold compound material 314 can flow into the semiconductor device assembly 310 through the gap between the stack of semiconductor dies 312 and the conductive package perimeter material 313. Specifically, the mold compound 314 can flow into the BLT between each die of the stack of semiconductor dies 312. Moreover, the mold compound material 314 can horizontally flow into the gap 316 disposed between the conductive package perimeter material 313 and the lower semiconductor die 311. The gap 316 is formed due to a height variance h between the conductive package perimeter material 313 and a spacer used to form the semiconductor device assembly 310. In this example, the spacer assembly, specifically the package perimeter material 313 can be bonded on the lower semiconductor die 311 after the stack of semiconductor dies 312 being attached on the lower semiconductor die 311.
In some embodiments, the semiconductor device assembly 320 is processed through the NCF underfill process. For example, each of the semiconductor dies 322 may be vertically stacked through solder-TSV bonds and the BLT is filled by the nonconductive fill material 324. In this example, the stack of semiconductor dies 322, together with nonconductive fill material 324 disposed in the BLT between the semiconductor dies 322, can be attached on the lower semiconductor die 321 after the spacer assembly (e.g., the package perimeter material 323) being bonded on the lower semiconductor die 321. During the thermal bonding of the semiconductor dies 322 to the lower semiconductor die 321, the nonconductive fill material may horizontally squeeze out of the BLT regions, as shown in
The gaps 316 and 326 of the semiconductor device assemblies 310 and 320 can mechanically separate the conductive package perimeter materials 313 and 323 from the lower semiconductor dies 311 and 321, respectively. At an elevated temperature during the processing and operating of the semiconductor device assemblies, there is a risk of breaking the interface dies by the conductive package perimeter material due to different CTEs there between. The gaps 316 and 326 included in the semiconductor device assemblies 310 and 320 may effectively reduce the risk of interface dies cracking due the CTE mismatch. Further, the gaps 316 and 326 can provide electrical isolation between the conductive package perimeter materials (e.g., 313 and 323) and the interface dies (e.g., 311 and 321), respectively.
In this example, a mold compound material 414 can flow into the semiconductor device assembly 410 through a gap between the stack of semiconductor dies 412 and the conductive package perimeter material 413. Additionally, the mold compound material 414 can flow into the BLT between each of the stack of semiconductor dies 412. As shown, the conductive package perimeter material 413 directly contacts the lower semiconductor die 411 and the mold compound material 414 is limited in the BLT and gaps between the semiconductor dies 412 and the conductive package perimeter material 413.
In the present technology, the heat transfer of the CoW assemblies can be enhanced through the conductive package perimeter material. For example, heat generated from the semiconductor die stacks 322 and 422 can be respectively transferred out through the conductive package perimeter material 323 and 423 disposed at the edge of the CoW assemblies. In addition, the heat generated from the semiconductor dies (interface dies) 411 and 421 can be transferred out through the conductive package perimeter materials 413 and 423, respectively as they are directly contacted as shown in
The method 500 also includes disposing a pre-formed conductive package conductive package perimeter structure around each of the plurality of semiconductor die stacks, at 504. For example, the pre-formed spacer assembly 110 can be disposed on the semiconductor wafer 102 and around each of the plurality of semiconductor die stacks 104. In particular, the spacer assembly 110 includes the package conductive package perimeter material 114 that is disposed around each of the semiconductor die stacks 104, as shown in
Further, the method 500 includes disposing an encapsulant material between each conductive package perimeter structure and the corresponding semiconductor die stack, at 506. For example, mold compound material 116 can flow into a gap between each of the plurality of semiconductor die stacks 104 and adjacent package conductive package perimeter mater 114 of the spacer assembly 110. For semiconductor die stacks 104 having empty interfaces between vertically stacked semiconductor dies, the mold compound material 116 can further flow into the interface between stacked semiconductor dies.
Lastly, the method 500 includes singulating the device wafer to form the plurality of semiconductor device assemblies, at 508. For example, after the semiconductor wafer 102 is broken into semiconductor dies 126, the spacer 112 of the spacer assembly is lifted out, as shown in
Turning now to
The method 600 also includes expanding the plurality of spacer grids at an elevated temperature, at 604. For example, once the spacer grid 112 is attached to the carrier wafer 202, it may be processed at an elevated temperature ranging from 200° C. to 500° C. Here, the spacer grid 112 will expand at the elevated temperature due to its high CTE.
In addition, the method 600 includes disposing the conductive package perimeter material in each of the plurality of the spacer grids, at 606. For example, the conductive package perimeter material 114 can be disposed into the spacer grid 112, e.g., on the sidewall of the spacer grid 112. Here, the conductive package perimeter material 114 may be made of materials having a lower CTE, e.g., copper.
Further, the method 600 includes holding the conductive package perimeter material in the plurality of spacer grids through pressure fitting at a cooled down temperature, at 608. For example, as described in
Any one of the semiconductor structures described above with reference to
Specific details of several embodiments of semiconductor devices, and associated systems and methods, are described below. A person skilled in the relevant art will recognize that suitable stages of the methods described herein can be performed at the wafer level or at the die level. Therefore, depending upon the context in which it is used, the term “substrate” can refer to a wafer-level substrate or to a singulated, die-level substrate. Furthermore, unless the context indicates otherwise, structures disclosed herein can be formed using conventional semiconductor-manufacturing techniques. Materials can be deposited, for example, using chemical vapor deposition, physical vapor deposition, atomic layer deposition, plating, electroless plating, spin coating, and/or other suitable techniques. Similarly, materials can be removed, for example, using plasma etching, wet etching, chemical-mechanical planarization, or other suitable techniques.
In accordance with one aspect of the present disclosure, the semiconductor devices illustrated above could be memory dice, such as dynamic random access memory (DRAM) dice, NOT-AND (NAND) memory dice, NOT-OR (NOR) memory dice, magnetic random access memory (MRAM) dice, phase change memory (PCM) dice, ferroelectric random access memory (Fe RAM) dice, static random access memory (SRAM) dice, or the like. In an embodiment in which multiple dice are provided in a single assembly, the semiconductor devices could be memory dice of a same kind (e.g., both NAND, both DRAM, etc.) or memory dice of different kinds (e.g., one DRAM and one NAND, etc.). In accordance with another aspect of the present disclosure, the semiconductor dice of the assemblies illustrated and described above could be logic dice (e.g., controller dice, processor dice, etc.), or a mix of logic and memory dice (e.g., a memory controller die and a memory die controlled thereby).
The devices discussed herein, including a memory device, may be formed on a semiconductor substrate or die, such as silicon, germanium, silicon-germanium alloy, gallium arsenide, gallium nitride, etc. In some cases, the substrate is a semiconductor wafer. In other cases, the substrate may be a silicon-on-insulator (SOI) substrate, such as silicon-on-glass (SOG) or silicon-on-sapphire (SOP), or epitaxial layers of semiconductor materials on another substrate. The conductivity of the substrate, or sub-regions of the substrate, may be controlled through doping using various chemical species including, but not limited to, phosphorous, boron, or arsenic. Doping may be performed during the initial formation or growth of the substrate, by ion-implantation, or by any other doping means.
The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. Other examples and implementations are within the scope of the disclosure and appended claims. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.
As used herein, including in the claims, “or” as used in a list of items (for example, a list of items prefaced by a phrase such as “at least one of” or “one or more of”) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an exemplary step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on.”
As used herein, the terms “top,” “bottom,” “over,” “under,” “above,” and “below” can refer to relative directions or positions of features in the semiconductor devices in view of the orientation shown in the Figures. These terms, however, should be construed broadly to include semiconductor devices having other orientations, such as inverted or inclined orientations where top/bottom, over/under, above/below, up/down, and left/right can be interchanged depending on the orientation.
It should be noted that the methods described above describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Furthermore, embodiments from two or more of the methods may be combined.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Rather, in the foregoing description, numerous specific details are discussed to provide a thorough and enabling description for embodiments of the present technology. One skilled in the relevant art, however, will recognize that the disclosure can be practiced without one or more of the specific details. In other instances, well-known structures or operations often associated with memory systems and devices are not shown, or are not described in detail, to avoid obscuring other aspects of the technology. In general, it should be understood that various other devices, systems, and methods in addition to those specific embodiments disclosed herein may be within the scope of the present technology.
