Patent Publication Number: US-2019181019-A1

Title: Method of reconstituted substrate formation for advanced packaging applications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 15/840,900, filed on Dec. 13, 2017, which will issue on Feb. 19, 2019 as U.S. Pat. No. 10,211,072, which claims benefit of U.S. Provisional Patent Application Ser. No. 62/524,298, filed on Jun. 23, 2017, each of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     Embodiments described herein generally relate to the field of semiconductor device manufacturing, and more specifically, to methods of packaging semiconductor devices. 
     Description of the Related Art 
     As circuit densities increase and device sizes decrease for next generation semiconductor devices, providing the external connections, i.e., wiring, to these devices requires advanced packaging technologies. One such advanced packaging technology is wafer level packaging. 
     Wafer level packaging streamlines the manufacturing and packaging processes of semiconductor devices by integrating device manufacturing, package assembly (packaging), electrical testing, and reliability testing (burn-in) at the wafer level, where forming of the top and bottom layers of the packaging, creating the I/O connections, and testing the packaged device are all performed before the devices are singulated into individual packaged components. The advantages of wafer level packaging include reduced overall manufacturing costs of the resulting device, reduced package size, and improved electrical and thermal performance. However, typical wafer level packaging schemes limit the number of I/O connections that can be made from the semiconductor device to the number of I/O terminals that can be spread over the surface of the die. Fan-out wafer level packaging retains the advantages of wafer level packaging while increasing the area available for I/O terminals by redistributing the I/O terminals to areas exterior of the surface of the die, using one or more redistribution layers. 
     Fan-out wafer level packaging processes require that the surface area of the I/O terminal redistribution layer for each individual die be larger than the surface area of the individual die itself. However, because it is desirable to maximize the number of devices (dies) on a wafer in order to minimize costs during manufacturing of the device, the spaces between individual devices (dice lines) are usually only large enough to accommodate the width of the dicing saw used to dice the wafer into its individual dies. One method of creating the desired additional surface area external of the die surface is to form a new wafer with dies redistributed in a spaced apart pattern, known as a reconstituted substrate. 
     Typically, to form a reconstituted substrate, a wafer is singulated into individual die which are then positioned on a molding plate (carrier substrate) spaced apart from one another and temporarily secured thereto by an adhesion layer. A molding compound is dispensed onto the carrier substrate, and the dies secured thereto, and subsequently cured, which embeds the spaced apart dies in the molding compound to form the reconstituted substrate. The terminal sides of the dies are then exposed by removing the adhesion layer, and redistribution layers, having interconnects disposed therein, are subsequently formed on the reconstituted substrate, to redistribute a portion, or all, of the device&#39;s I/O terminals to areas exterior of the surface of the die, which increases the area available for I/O connections and thus the number of possible I/O terminals. 
     Process defects associated with forming the reconstituted substrate, such as undesirable repositioning of the dies within the reconstituted substrate from their original placement location on the adhesion layer, also known as die shift, cause misalignment between the via interconnects in the subsequently formed redistribution layer and the electrical contacts on the dies. Accordingly, there is a need in the art for improved methods of forming reconstituted substrates for fan-out wafer level packaging schemes. 
     SUMMARY 
     Embodiments herein generally relate to device packaging processes, and in particular, relate to methods of forming a reconstituted substrate in a fan-out wafer level packaging process. 
     In one embodiment, a method of forming a reconstituted substrate is provided. The method includes positioning a plurality of devices on a carrier substrate. Herein, the carrier substrate comprises a structural base and an adhesion layer disposed on a major surface thereof, where the active surfaces of the plurality of singular devices are temporarily secured to the structural base by the adhesion layer. The method further includes depositing a device immobilization layer onto the plurality of singular devices and onto at least a portion of the carrier substrate adjacent thereto and extending laterally outward therefrom, wherein depositing the device immobilization layer comprises a HWCVD process, a PECVD process, a controlled dispense process, a spray process, an additive manufacturing process, or a combination thereof. 
     In another embodiment, another method of forming a reconstituted substrate is provided. The method includes positioning a plurality of devices on a carrier substrate. Herein, the carrier substrate comprises a structural base and an adhesion layer disposed on a major surface thereof, where the active surfaces of the plurality of singular devices are temporarily secured to the structural base by the adhesion layer. The method further includes dispensing a plurality of droplets of a precursor composition onto the carrier substrate at locations adjacent to each of the plurality of devices, and at least partially curing each of the plurality of dispensed droplets to form a plurality of device immobilization beads. 
     In another embodiment, a reconstituted substrate is provided. The reconstituted substrate comprises a plurality of devices disposed in a molding compound, wherein an immobilization layer or a plurality of immobilization beads is interposed between each of the plurality of devices and the molding compound, and wherein the immobilization layer or the plurality of immobilization beads comprises parylene, urethane acrylate, epoxy acrylate, thermal and/or UV curable modifications thereof, or combinations thereof. In some embodiments, the reconstituted substrate further comprises a polymer layer disposed on the plurality of devices, the polymer layer having a plurality of metal interconnect structures disposed therethrough. In some embodiments, the reconstituted substrate further comprises an electrostatic discharge layer interposed between the mold layer and the device. In some embodiments, the immobilization layer has a thickness between about 0.5 μm and 100 μm. In some embodiments, the polymer layer comprises polyimide. 
     In another embodiment, a packaged device is provided. The packaged device comprises a first layer including a mold layer, a device disposed in the mold layer, an second layer interposed between at least a portion of the mold layer and at least a portion of the device, and a first surface defined by an active surface of the device and a surface or surfaces of the second layer. The packaged device further comprises one or more redistribution layers disposed on the first surface, each redistribution layer comprising at least a dielectric layer and a plurality of interconnect structures disposed therethrough. In some embodiments, the second layer comprises parylene, urethane acrylate, epoxy acrylate, modifications thereof (e.g. thermal and/or UV curable), or combinations thereof. In some embodiments, the second layer has a thickness of between about 0.5 μm and about 100 μm. In some embodiments, the mold layer comprises an epoxy. In some embodiments, the dielectric layer comprises a polyimide. In some embodiments, the packaged device further comprises a conductive layer interposed between the mold layer and the device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1A  is a schematic cross-sectional view of an example processing chamber, herein a hot-wire chemical vapor deposition (HWCVD) chamber, used to practice some of methods described herein, according to one embodiment. 
         FIG. 1B  is a flowchart illustrating a method for forming a reconstituted substrate, according to one embodiment. 
         FIGS. 2A-2E  illustrate the formation of a reconstituted substrate, according to the method of  FIG. 1B . 
         FIG. 2F  is a schematic plan view of an electrostatic discharge layer, formed according to further embodiments of  FIG. 1B . 
         FIGS. 2G-2H  illustrate the formation or more redistribution layers on the reconstituted substrate, according to further embodiments of  FIG. 1B . 
         FIG. 2I  is a schematic cross-sectional view of a singulated packaged device, formed according to further embodiments of  FIG. 1B . 
         FIG. 3A  is a schematic cross-sectional view of an example additive manufacturing system used to practice the method of  FIG. 4  according to one embodiment. 
         FIG. 3B  is a close up cross-sectional view of a portion of the carrier substrate shown in  FIG. 3A . 
         FIG. 4  is a flow diagram illustrating a method of forming a reconstituted substrate using the additive manufacturing system described in  FIG. 3A . 
         FIG. 5A  is a schematic plan view of a device disposed on a carrier substrate, according to one embodiment. 
         FIG. 5B  is a side view of the device shown in  FIG. 5B . 
         FIG. 5C  is a schematic plan view of a device disposed on a carrier substrate, according to one embodiment. 
         FIG. 5D  is a side view of the device  204  shown in  FIG. 5C . 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure generally describe methods for minimizing the occurrence and extent of die shift during the formation of a reconstituted substrate in fan-out wafer level packaging processes. 
     Die shift is a process defect that occurs when a die (device) moves from its intended position within a reconstituted substrate during the formation thereof. Generally, the methods disclosed herein include depositing a device immobilization layer and/or a plurality of device immobilization beads over and/or adjacent to a plurality of singulated dies (individual dies), and the carrier substrate they are positioned on, before forming a reconstituted substrate with an epoxy molding compound. The device immobilization layer and/or the plurality of device immobilization beads immobilize the plurality of singular devices and prevent them from shifting on the carrier substrate during the molding process. 
     Typically, some tolerance in alignment between the interconnects in the redistribution layers and the device contact pads in a fan-out wafer level packaging scheme must be built into the manufacturing process to account for die shift. For example, die shift can cause a die to deviate from its intended position in a reconstituted substrate by 20 μm to 140 μm or more which causes misalignment between via interconnects in a subsequently formed redistribution layer and the contact sites on the die. One contributing factor to die shift is the drag force the molding compound exerts on the die as the molding compound is dispensed onto the molding plate (carrier) and/or into a mold, such as a compression mold. Additional factors contributing to die shift are deformation of the molding compound during curing, warping of the reconstituted substrate, and thermal expansion/contraction of the molding compound and/or reconstituted substrate. By immobilizing the plurality of singular devices on a carrier substrate using the methods described herein, die shift is eliminated or substantially reduced. Eliminating or substantially reducing die shift desirably enables precise alignment of interconnect layers and scaling of via/pitch dimensions which desirably allows for a reduction in the final package size of a device. 
       FIG. 1A  is a schematic cross-sectional view of an example processing chamber, herein a hot-wire chemical vapor deposition (HWCVD) chamber, used to practice some of methods described herein, according to one embodiment. 
     The processing chamber  100  includes a chamber lid  102 , one or more sidewalls  104 , and a chamber bottom  106 , which define a processing volume  108 . The processing volume  108  is in fluid communication with a vacuum source  116 , such as one or more dedicated vacuum pumps, through a vacuum outlet  118 , which maintains the processing volume  108  at sub-atmospheric conditions and evacuates processing gases, and other gases, therefrom. A carrier substrate support  120 , disposed on a support shaft  132  sealingly extending through the chamber bottom  106 , is disposed in the processing volume  108  and a carrier substrate  210  is transferred thereto and therefrom through an opening  124  formed through the sidewall  104 , which is sealed with a door or a valve (not shown) during the deposition process. Typically, the carrier substrate  210  is positioned on, and removed from, the carrier substrate support  120  using a conventional lift pin system (not shown). In some embodiments, the carrier substrate support  120  is configured to heat, cool, and/or to maintain the carrier substrate  210  at a desired processing temperature using a resistive heater  126  embedded in and or disposed on the carrier substrate support  120  and/or cooling conduits  130  disposed in the carrier substrate support  120 . Typically the resistive heater  126  is coupled to a DC power supply which provides current thereto and the cooling conduits  130  are fluidly coupled to a cooling source (not shown), such as a water or refrigerant source. 
     The processing chamber  100  further includes a plurality of heating elements, herein a plurality of wires  128 , disposed in the processing volume  108  between the carrier substrate support  120 , and the carrier substrate  210  disposed thereon, and the chamber lid  102 . The plurality of wires  128  are formed of a conductive material, such as a steel alloy, and are electrically coupled to a power supply (not shown). Herein, the processing volume  108  is fluidly coupled to one or more gas supplies, such as gas supply  110 , which provides processing gases to the processing volume  108  through one or more gas inlets, such as gas inlet  112  disposed through a sidewall  104  at a location between a horizontal plane of the plurality of wires  128  and the chamber lid  102 . In other embodiments, the gas inlet  112  is disposed through the chamber lid  102 . In some embodiments, the processing chamber  100  further includes a gas distributor (not shown), such as a showerhead, disposed between the gas inlet  112  and the carrier substrate support  120  and the carrier substrate  210  disposed thereon. In embodiments herein, the processing gases include one or more monomers and one or more initiator gases. During the HWCVD deposition process the plurality of wires  128  are resistively heated by electrical current flowing therethrough to a desired temperature sufficient to catalytically dissociate the initiator gases into their reactive species, e.g. radicals. The monomer gas(es), absorbed onto a surface of the carrier substrate  210 , react with the dissociated reactive species of the initiator gas(es) to deposit and/or form a polymer layer, herein an immobilization layer  206 , on the surface of the carrier substrate  210 . Typically, a pressure in the processing volume  108  is maintained at less than about 1 Torr, such as less than about 700 mTorr, such as between about 400 mTorr and about 1 Torr, or between about 400 mTorr and about 700 mTorr. 
       FIG. 1B  is a flowchart illustrating a method  150  for forming a reconstituted substrate, according to one embodiment.  FIGS. 2A-2E  illustrate the formation of a reconstituted substrate  212 , according to the method of  FIG. 1B . 
     The method  150  begins at activity  155  with the positioning of a plurality of devices, i.e., individual singular devices, on a carrier substrate. A carrier substrate  210  is illustrated in  FIG. 2A  and it includes a structural base  200  having an adhesion layer  202  disposed on a major surface thereof. Herein, the structural base  200  is a rigid substrate, such as a silicon wafer or a metal plate. In other embodiments, the structural base  200  is a rectangular panel made from a material having sufficient rigidity to act as a mold plate, such as glass or a rigid polymer. In some embodiments, the structural base  200  is made from glass or a rigid polymer. Herein, the adhesion layer  202  is a double sided tape, a temporary adhesive bonding film, a thermally releasable adhesive, a photo-releasable adhesive, or any suitable adhesive layer for temporarily securing the active surfaces of a plurality of devices  204  to the structural base  200 . Herein, each of the plurality of devices  204  has a thickness T( 1 ) of between about 50 μm and about 800 μm, such as between about 50 μm and about 760 μm, between about 50 μm and about 400 μm, or between about 50 μm and about 300 μm, such as between about 100 μm and about 300 μm. Typically, each of the plurality of devices  204  are spaced apart from one another by a distance X so that a portion of the structural base  200  associated with each device  204  has a redistribution surface area that is greater than the surface area of the device  204 . The size of the redistribution surface determines the surface area available for the formation of redistribution layers on the to be formed reconstituted substrate. The method  150  continues at activity  160  with depositing an immobilization layer  206  over the plurality of devices  204  and the adhesion layer  202 , as shown in  FIG. 2B . Herein, the immobilization layer  206  is a polymer, such as parylene, urethane acrylate, epoxy acrylate, modifications thereof, or combinations thereof, deposited using a chemical vapor deposition (CVD) process, a hot wire CVD process, a plasma enhanced CVD process (PECVD), or a controlled dispense and/or spray process. In some embodiments, the immobilization layer  206  is formed by depositing a UV curable polymer precursor (using a controlled dispense and/or spray process) over the plurality of devices  204  and the carrier substrate  210  and exposing the deposited UV curable polymer precursor, or portions thereof, to UV radiation from a UV radiation source. 
     In one embodiment, the immobilization layer  206  is deposited and/or formed using a HWCVD process in a HWCVD processing chamber, such as the processing chamber  100  described in  FIG. 1A . Typically, the HWCVD process comprises flowing a processing gas comprising one or more monomers and one or more initiators into the processing volume of a processing chamber. The one or more monomers are absorbed onto surfaces of the carrier substrate  210  and the plurality of devices  204  disposed thereon. The one or more initiators are dissociated into their reactive species by a plurality of heated wires maintained at a temperature less than about 600° C., such as less than about 450° C., for example between about 100° C. and about 450° C. The absorbed monomers react with the dissociated reactive species of the initiator precursor to deposit or form the immobilization layer  206  over the carrier substrate  210  and the plurality of devices  204  disposed thereon. Immobilization layers  206  deposited using the HWCVD methods described herein comprise the polymerized reaction product of the one or more monomer gases and the dissociated reactive species of one or more initiator precursors. 
     Monomer gases herein include ethyleneglycol diacrylate, t-butylacrylate, N,N-dimethylacrylamide, vinylimidazole, 1-3-diethynylbenzene, 4-vinyl pyridine, poly vinyl pyridine, poly 4-vinyl pyridine, polyphenylacetylene, N, N-dimethylaminoethylmethacrylate, divinylbenzene, poly divinylbenzene, glycidyl methacrylate, poly thiophene, ethyleneglycol dimethacrylate, tetrafluoroethylene, dimethylaminomethylstyrene, perfluoroalkyl ethylmethacrylate, trivinyltrimethoxy-cyclotrisiloxane, furfuryl methacrylate, cyclohexyl methacrylate-co-ethylene glycol dimethacrylate, pentafluorophenyl methacrylate-co-ethylene glycol diacrylate, 2-hydroxyethyl methacrylate, methacrylic acid, 3,4-ethylenedioxythiophene, and combinations thereof. In some embodiments, the monomer gas further include a cross-linker source gas to facilitate the cross-linking of the to be formed immobilization layer  206 . Cross-linker source gases here include 2-ethyl-2(hydroxymethyl)propane-trimethyacrylate (TRIM), acrylic acid, methacrylic acid, trifluoro-methacrylic acid, 2-vinylpyridine, 4-vinylpyridine, 3(5)-vinylpyridine, p-methylbenzoic acid, itaconic acid, 1-vinylimidazole, ethylene glycol dimethacrylate, and combinations thereof. 
     Initiator precursors herein include, hydrogen peroxide, alkyl peroxides, aryl peroxides, hydroperoxides, halogens, azo compounds, and combinations thereof. In some embodiments, the initiator source gas is selected from the group including perfluorooctane sulfonyl fluoride (PFOS), perfluorobutane-1-sulfonyl fluoride (PFBS), triethylamine (TEA), tert-butyl peroxide (TBPO), 2,2′-azobis (2-methylpropane), tert-amyl peroxide (TAPO), di-tert-amyl peroxide, antimony pentachloride and benzophenone, and combinations thereof. Typically, a ratio of initiator precursor to monomer gas is between about 1:10 and about 1:1. 
     The polymerized reaction products herein include poly(glycidyl methacrylate-co-divinylbenzene), poly(glycidyl methacrylate-co-methacrylamide), poly(ethyleneglycol diacrylate), poly(t-butylacrylate), poly N,N-dimethylacrylamide, poly(vinylimidazole), poly(1-3-diethynylbenzene), poly(phenylacetylene), poly(N,N-dimethylaminoethylmethacrylate) (p(DMAM), poly (divinylbenzene), poly(glycidyl methacrylate) (p(GMA)), poly (ethyleneglycol dimethacrylate), poly (tetrafluoroethylene), poly(tetrafluoroethylene) (PTFE), poly(dimethylaminomethylstyrene) (p(DMAMS), poly(thiophene), poly(vinylpyridine), poly(perfluoroalkyl ethylmethacrylate), poly(trivinyltrimethoxy-cyclotrisiloxane), poly(furfuryl methacrylate), poly(cyclohexyl methacrylate-co-ethylene glycol dimethacrylate), poly(pentafluorophenyl methacrylate-co-ethylene glycol diacrylate), poly(2-hydroxyethyl methacrylate-co-ethylene glycol diacrylate), poly(methacrylic acid-co-ethylene glycol dimethacrylate), poly(3,4-ethylenedioxythiophene), and combinations thereof. 
     In one embodiment, the immobilization layer  206  comprises HWCVD deposited poly(glycidyl methacrylate) (p(GMA)) having a thickness T( 2 ) of more than about 1 μm, such as between about 1 μm and about 20 μm, or more than about 8 μm for a device  204  having a thickness T( 1 ) of more than about 700 μm and less than about 8 μm for a singulated die having a thickness T( 1 ) of less than about 700 μm. 
     In some embodiments, the processing gas further includes a carrier gas or a diluent gas, such as one or more inert gases, for example helium (He), neon (Ne), argon (Ar), or combinations thereof. In some embodiments, the one or more monomer gases and the one or more initiator precursor gases are provided separately to the processing volume of the processing chamber and allowed to mix therein. 
     In some embodiments, the immobilization layer  206  forms a continuous closed surface over the plurality of devices  204  and the adhesion layer  202  exposed therebetween. Herein, the immobilization layer  206  has a thickness of between about 0.5 μm and 100 μm, such as between about 0.5 μm and about 50 μm, between about 0.5 μm and 20 μm, between about 0.5 μm and about 10 μm, or between about 0.5 μm and 5 μm. In other embodiments, the immobilization layer  206  has a thickness of more than about 100 μm or less than about 0.5 μm. 
     In other embodiments, the immobilization layer  206  forms a discontinuous surface comprising a plurality of immobilization layer regions, herein immobilization patches  207  (shown in phantom in  FIG. 2F ), each disposed over a respective device  204  and portions of the respective adhesion layer  202  adjacent thereto. In some embodiments, the discontinuous surface of the immobilization layer  206  is formed using a physical mask (i.e. a shadow mask) during the deposition thereof, by a subsequent photolithography/etch process, or by any other suitable means. In some embodiments, the discontinuous surface of the immobilization layer  206  is formed by selectively curing portions of the UV curable polymer precursor to form the plurality of immobilization layer regions and removing the uncured polymer precursor from surfaces of the structural base  200  and/or portions of the adhesion layer  202 . 
     In some other embodiments, the immobilization layer  206  forms a continuous surface over the plurality of devices  204  and over portions of the adhesion layer  202  exposed therebetween but has openings (not shown) in the continuous surface between the portions of the adhesion layer  202  covered by the immobilization layer  206 . 
     In some embodiments, the method  150  continues at activity  165  with dispensing a molding compound, such as an epoxy, to form a mold layer  208  over the immobilization layer  206  as shown in  FIG. 2C . Herein, the molding compound is dispensed using a spin application wherein the molding compound is distributed over the immobilization layer  206  and underlying carrier substrate  210  by spinning the carrier substrate  210  while the molding compound is dispensed thereover and/or thereon. In other embodiments the molding compound is applied to the carrier substrate  210  and the plurality of devices  204  disposed thereon by any conventional molding process, such as pressure/compression molding, injection molding, film assisted molding, or combinations thereof. 
     The method  150  continues at activity  175  with curing the molding compound by exposing the molding compound to a UV source  209  as shown in  FIG. 2D , by heating the molding compound, by applying curing agents, by vacuum curing, or by a combination thereof, to form a reconstituted substrate  212 , as shown in  FIG. 2E . In some embodiments the reconstituted substrate  212  is planarized using a back grind process. 
     The method  150  continues at activity  180  with debonding the reconstituted substrate  212  from the adhesion layer  202  of the carrier substrate  210 . In some embodiments, the method  150  further includes forming an electrostatic discharge layer  205  on the carrier substrate  210  and the plurality of devices  204  disposed thereon before or after depositing the immobilization layer  206  thereover, as shown in  FIG. 2F . 
       FIG. 2F  is a schematic plan view of a carrier substrate, such as the carrier substrate  210  described in  FIG. 2A , having a plurality of devices  204  disposed thereon, and further having an electrostatic discharge layer  205  disposed over the plurality of devices  204  and the exposed regions of the carrier substrate  210 , according to one embodiment. Herein, the electrostatic discharge layer  205  is formed of a conductive polymer, a metal, or a plastic with electrically conducting particles disposed therein. The electrostatic discharge layer  205  is typically formed by printing a conductive polymer or conductive ink, vapor deposition, such as sputtering or evaporative deposition, or by placing a metal mesh netting or gauze like fabric of conductive material on the surface of the carrier substrate  210  and the plurality of devices  204  disposed thereon. Herein, the electrostatic discharge layer  205  comprises a plurality of parallel columns  205   a  and a plurality of parallel rows  205   b  that are perpendicular to the plurality of parallel columns  205   a . During the formation of the reconstituted substrate and the subsequent formation of redistribution layers thereon, the electrostatic discharge layer  205  is used to dissipate and/or prevent electrostatic charging of the carrier substrate and/or the plurality of devices  204  disposed thereon. 
     In some embodiments, the method  150  further includes forming one or more redistribution layers  214  on the reconstituted substrate  212 , as described in  FIGS. 2G-2H . 
       FIG. 2G  shows a reconstituted substrate  212  with one or more redistribution layers  214  disposed thereon. Herein, the reconstituted substrate  212  includes an electrostatic discharge layer  205  interposed between the immobilization layer  206  and the plurality of devices  204  and interposed between the immobilization layer  206  and the one or more redistribution layers  214  in regions between the devices  204 . Typically, the electrostatic discharge layer  205  has a thickness T( 3 ) of less than about 100 μm, such as between about 20 μm and about 50 μm. In some embodiments, the electrostatic discharge layer  205  is a metal layer having thickness T( 3 ) of less than about 20 μm, such as between about 0.1 μm and about 2 μm. Each of the one or more redistribution layers  214  comprises a dielectric layer  217 , such as an oxide layer, a nitride layer, or a polymer layer, for example a polyimide layer, having a plurality of metal interconnect structures  215  disposed therethrough. Herein, the metal interconnect structures  215  include wire interconnects and/or via interconnects that alone or in combination enable electrical coupling of bond pads  225  of the device  204  to circuits external to the device  204  and the redistribution layers  214 . The reconstituted substrate  212  includes the plurality of devices  204  embedded in the cured mold layer  208  with the immobilization layer interposed between each of the plurality of devices  204  and the cured mold layer  208 . Herein, the immobilization layer  206  forms a continuous layer over the cured mold layer  208  of the reconstituted substrate  212 . In other embodiments, the immobilization layer  206  comprises a discontinuous layer comprising a plurality of immobilization patches  207  (shown in phantom in  FIG. 2F ) disposed between portions of the cured mold layer  208  and portions of the redistribution layer  214  in locations adjacent to each of the plurality of devices  204  and extending laterally outward therefrom. 
     In some embodiments, the method  150  further comprises electrically coupling a plurality of solder balls  216  to the metal interconnect structures  215  and singulating the reconstituted substrate  212  and the layers and features formed thereon, into singulated packaged devices  218  such as shown in  FIGS. 2H-2I .  FIG. 2H  shows the reconstituted substrate  212  of  FIG. 2E  further comprising an electrostatic discharge layer  205  and further comprising the plurality of solder balls  216  electrically coupled to the plurality of metal interconnect structures  215  of the redistribution layer  214 .  FIG. 2I  shows a singulated packaged device  218  where a first layer of the packaged device, herein a portion of the reconstituted substrate  212 , includes the mold layer  208 , the immobilization layer  206  (second layer), the electrostatic discharge layer  205  (third layer), and the device  204 . Herein, an active surface of the device  204 , having bond pads  225  disposed therein, a surface of the electrostatic discharge layer  205  and/or a surface of the immobilization layer  206  disposed between surfaces of the electrostatic discharge layer  205  define a planer surface  230 , the redistribution layer  214  disposed thereon. In other embodiments, an active surface of the device  204 , having bond pads  225  disposed therein, and a surface of the immobilization layer  206  (second layer) define a planer surface  230 , the redistribution layer  214  disposed thereon. Herein, the redistribution layer  214  is separated from the mold layer  208  by the electrostatic discharge layer  205  (third layer) and/or the immobilization layer  206  (second layer) and does not make contact therewith. In other embodiments, at least portions of the redistribution layer  214  are separated from the mold layer  208  by the electrostatic discharge layer  205  (third layer) and/or the immobilization layer  206  (second layer) in regions adjacent to the device  204  and extending laterally outward therefrom. 
     The method  150  described above immobilizes the device during the molding process of forming the reconstituted substrate, which prevents die shift and reduces process defects related to misalignment of subsequently formed redistribution layers and the contact pads of the device. 
       FIG. 3A  is a schematic view of an example additive manufacturing system  300  used to practice some of the methods described herein, according to one embodiment. Herein the additive manufacturing system  300  comprises a manufacturing support  301 , one or more dispense heads, such as dispense head  303 , for dispensing droplets  305  of a precursor composition  307 , and an electromagnetic radiation source, such as UV source  309 . Typically, each of the one or more dispense heads  303  further comprises one or more nozzles  311 . The carrier substrate  210 , and the plurality of devices  204  disposed thereon, are positioned on the manufacturing support  301  which moves independently of the dispense head  303  to enable dispensing of the droplets  305  on selected locations on the carrier substrate  210  and the plurality of devices  204 . 
     Herein, the precursor composition  307  comprises a mixture of one or more functional polymers, functional oligomers, functional monomers, and/or reactive diluents that are at least monofunctional and undergo polymerization when exposed to free radicals; photoacids, Lewis acids, and/or electromagnetic radiation. 
     Examples of functional polymers herein include multifunctional acrylates including di, tri, tetra, and higher functionality acrylates, such as 1,3,5-triacryloylhexahydro-1,3,5-triazine or trimethylolpropane triacrylate. 
     Examples of functional oligomers include monofunctional and multifunctional oligomers, acrylate oligomers, such as aliphatic urethane acrylate oligomers, aliphatic hexafunctional urethane acrylate oligomers, diacrylate, aliphatic hexafunctional acrylate oligomers, multifunctional urethane acrylate oligomers, aliphatic urethane diacrylate oligomers, aliphatic urethane acrylate oligomers, aliphatic polyester urethane diacrylate blends with aliphatic diacrylate oligomers, or combinations thereof, for example bisphenol-A ethoxylate diacrylate or polybutadiene diacrylate. In one embodiment, the functional oligomer comprises tetrafunctional acrylated polyester oligomer available from Allnex Corp. of Alpharetta, Ga. as EB40® and the functional oligomer comprises an aliphatic polyester based urethane diacrylate oligomer available from Sartomer USA of Exton, Pa. as CN991. 
     Examples of monomers used in the precursor composition include tetrahydrofurfuryl acrylate (e.g. SR285 from Sartomer®), tetrahydrofurfuryl methacrylate, vinyl caprolactam, isobornyl acrylate, isobornyl methacrylate, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, 2-(2-ethoxyethoxy)ethyl acrylate, isooctyl acrylate, isodecyl acrylate, isodecyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, cyclic trimethylolpropane formal acrylate, 2-[[(Butylamino) carbonyl]oxy]ethyl acrylate (e.g. Genomer 1122 from RAHN USA Corporation), 3,3,5-trimethylcyclohexane acrylate, or mono-functional methoxylated PEG (350) acrylate. Multifunctional monomers include diacrylates or dimethacrylates of diols and polyether diols, such as propoxylated neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, alkoxylated aliphatic diacrylate (e.g., SR9209A from Sartomer®), diethylene glycol diacrylate, diethylene glycol dimethacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, triethylene glycol dimethacrylate, alkoxylated hexanediol diacrylates, or combinations thereof, for example SR562, SR563, SR564 from Sartomer®. 
     Examples of reactive diluents used in the precursor composition include monoacrylate, 2-ethylhexyl acrylate, octyldecyl acrylate, cyclic trimethylolpropane formal acrylate, caprolactone acrylate, isobornyl acrylate (IBOA), or alkoxylated lauryl methacrylate. 
     Examples of photoacids used in the precursor composition include onium salts such as Omnicat 250, Omnicat 440, and Omnicat 550, manufactured by manufactured by IGM Resins USA Inc. of Charlotte N.C. and compositional equivalents thereof, triphenylsulfonium triflate, and triarylsulfonium salt type photo acid generators such as CPI-210S available from San-Apro Ltd. of Tokyo, Japan, and compositional equivalents thereof. 
     In some embodiments, the precursor composition  307  further comprises one or more photoinitiators. Photoinitiators used herein include polymeric photoinitiators and/or oligomer photoinitiators, such as benzoin ethers, benzyl ketals, acetyl phenones, alkyl phenones, phosphine oxides, benzophenone compounds and thioxanthone compounds that include an amine synergist, combinations thereof, and equivalents thereof. For example, in some embodiments photoinitiators include Irgacure® products manufactured by BASF of Ludwigshafen, Germany, or equivalent compositions. 
     Typically, the precursor composition  307  is formulated to have a viscosity between about 80 cP and about 110 cP at about 25° C., between about 12 cP and about 30 cP at about 70° C., or between 10 cP and about 40 cP for temperatures between about 50° C. and about 150° C. so that the precursor compositions  307  may be effectively dispensed through the nozzles  311  of the one or more dispense heads  303 . 
     Herein, each of the droplets  305  is at least partially cured using electromagnetic radiation, such as the UV radiation  315  provided by the UV source  309 , before the droplet  305  reaches its equilibrium size as described further in  FIG. 3B . 
       FIG. 3B  is a close up cross-sectional view of a portion of the carrier substrate  210  shown in  FIG. 3A . Herein, each of the plurality of devices  204  includes a horizontal surface  204   a  and a one or more vertical surfaces  204   b  substantially normal to the horizontal surface  204   a  and substantially normal to the carrier substrate  210  including the adhesion layer  202  thereof. An immobilization bead  305   a , of a plurality of immobilization beads  305   a  (shown in  FIG. 5A ) formed of an at least partially cured droplet  305  of the precursor composition  307  secures (tacks) the device  204  to the carrier substrate  210  to prevent lateral movement of the device  204  relative to the surface of the carrier substrate  210 , or in other words to prevent/and or substantially reduce die shift during the formation of a reconstituted substrate. 
     Typically, an uncured dispensed droplet, such as the example uncured dispensed droplet  305   b , will spread to an equilibrium size having an equilibrium contact angle α within a very short period of time, such as less than about 1 second, from the moment the droplet  305  first comes into contact with a surface of the carrier substrate  210  and/or a surface of one of the plurality of devices  204  disposed thereon. Therefore, herein, the droplets  305  are at least partially cured (fixed) by exposure thereof to UV radiation  315  from the UV source  309  to form the immobilization bead  305   a  having a fixed contact angle θ that is greater than the equilibrium contact angle α. Herein, the fixed contact angle θ of the immobilization bead  305   a  is desirably controlled to a value of greater than about 50°, such as greater than about 55°, greater than about 60°, or greater than about 70°, or even greater than about 80°. The immobilization bead  305   a  herein covers at least a portion of the vertical surface  204   b  of the device  204  and a portion of the carrier substrate  210 , including the adhesion layer  202  thereof, adjacent to the device  204  and extending laterally outward therefrom. 
       FIG. 4  is a flow diagram illustrating a method of forming a reconstituted substrate using the additive manufacturing system  300  described in  FIG. 3A . 
     The method  400  begins at activity  410  with the positioning of a plurality of devices, i.e., individual singulated dies, on a carrier substrate, such as the carrier substrate  210  illustrated in  FIG. 2A . In some embodiments, the method further includes forming an electrostatic discharge layer, such as the electrostatic discharge layer  205  described in  FIG. 2F  or other embodiments of the electrostatic discharge layer  205  described herein, on the carrier substrate  210  and the plurality of devices  204  disposed thereon. 
     The method  400  continues at activity  420  with dispensing a plurality of droplets of a precursor composition onto the carrier substrate at a location adjacent to a vertical portion of a device  204  and at least partially curing each of the plurality of dispensed droplets at activity  430  to form a plurality of immobilization beads, as shown in  FIGS. 5A-5B . 
       FIG. 5A  is a schematic plan view of a device  204  disposed on a carrier substrate  210 , according to one embodiment.  FIG. 5B  is a side view of the device  204  shown in  FIG. 5A  further showing (in phantom) an electrostatic discharge layer  205  and the mold layer  208  disposed thereon. Herein, a plurality of immobilization beads  305   a  prevent lateral movement of the device  204  in relation to the carrier substrate  210  during the formation of the mold layer  208  (as shown in  FIGS. 2C-2E ). Typically, the immobilization beads  305   a  are located at the corners of the device  204 , are located between the corners of the device  204 , or a combination thereof. Each of the immobilization beads  305   a  covers at least a portion of the one or more vertical surfaces  204   b  (shown in  FIG. 3B ) of the device  204  and at least a portion of the carrier substrate  210  adjacent to the vertical surface  204   b  and extending laterally outward therefrom. In some embodiments, an electrostatic discharge layer  205  (shown in phantom in  FIG. 5B ), such as the electrostatic discharge layer  205  described in  FIG. 2F , is interposed between each of the immobilization beads  305   a  and the device  204  and/or the carrier substrate  210 . In some other embodiments, the electrostatic discharge layer is interposed between portions of the immobilization beads  305   a  and/or some of the immobilization beads  305   a  and the device  204  and/or the carrier substrate. 
     In other embodiments, the droplets  305  are dispensed to form an immobilization patch over the device  204  and portions of the carrier substrate  210  adjacent thereto and extending laterally outward therefrom. 
     In some embodiments, a plurality of droplets  305  are dispensed and at least partially cured to form a continuous immobilization bead layer  305   d  about the perimeter of the device  204  as shown in  FIGS. 5C and 5D .  FIG. 5C  is a schematic plan view of a device  204  disposed on a carrier substrate  210 , according to one embodiment.  FIG. 5D  is a side view of the device  204  shown in  FIG. 5C  further showing (in phantom) the electrostatic discharge layer  205  and the mold layer  208  disposed thereon. Herein, the immobilization bead layer  305   d  forms a continuous surface about the perimeter of the device  204  and prevents lateral movement of the device  204  in relation to the carrier substrate  210  during the formation of the mold layer  208  (as shown in  FIGS. 2C-2E ). 
     In some embodiments, the method  400  further includes UV curing the immobilization beads  305   a , and or immobilization bead layers  305   d  in a UV furnace for between about 5 minutes and about 2 hours, such as between about 5 minutes and about 90 minutes, or about 1 hour, at a curing temperature between about 50° C. and about 200° C., such as between about 50° C. and about 150° C., or less than about 150° C. 
     The method  400  continues at activity  440  with dispensing a molding compound over the carrier substrate, the plurality of singular devices, and the immobilization layer thereon, at activity  450  with curing the molding compound to form a reconstituted substrate  512   a  (shown in  FIG. 5C ) or  512   b  (shown in  FIG. 5D , and activity  460  with debonding the reconstituted substrate from the carrier, which correspond to activities  165 ,  175 , and  180  respectively of method  150  described in  FIG. 1B . 
     In some embodiments, the method  400  further includes forming one or more redistribution layers on the reconstituted substrate  212 , as described above in  FIG. 2G . 
     The method  400  described above immobilizes the device during the molding process of forming the reconstituted substrate, which prevents die shift and reduces process defects related to misalignment of subsequently formed redistribution layers and the contact pads of the device. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.