Patent Publication Number: US-2020294930-A1

Title: Package structure and method of fabricating the same

Description:
BACKGROUND 
     The semiconductor industry has experienced rapid growth due to continuous improvements in the integration density of various electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, which allows more of the smaller components to be integrated into a given area. These smaller electronic components also require smaller packages that utilize less area than previous packages. Currently, integrated fan-out packages are becoming increasingly popular for their compactness. However, there are many challenges related to integrated fan-out packages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the critical dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1A  and  FIG. 1B  are schematic sectional views of various stages in a method of fabricating a semiconductor die in accordance with some embodiments of the present disclosure. 
         FIG. 2A  to  FIG. 2G  are schematic sectional views of various stages in a method of fabricating a package structure in accordance with some embodiments of the present disclosure. 
         FIG. 3  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. 
         FIG. 4A  to  FIG. 4D  are schematic top views illustrating various configurations of an alignment mark in accordance with some embodiments of the present disclosure. 
         FIG. 5A  and  FIG. 5B  are schematic sectional views of various stages in a method of fabricating semiconductor dies in accordance with some alternative embodiments of the present disclosure. 
         FIG. 6A  to  FIG. 6C  are schematic sectional views of various stages in a method of fabricating a package structure in accordance with some alternative embodiments of the present disclosure. 
         FIG. 7A  and  FIG. 7B  are schematic sectional views of various stages in a method of fabricating semiconductor dies in accordance with some alternative embodiments of the present disclosure. 
         FIG. 8A  and  FIG. 8B  are schematic top views illustrating various configurations of a bulk alignment mark in accordance with some embodiments of the present disclosure. 
         FIG. 9  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. 
         FIG. 10A  and  FIG. 10B  are schematic sectional views of various stages in a method of fabricating semiconductor dies in accordance with some alternative embodiments of the present disclosure. 
         FIG. 11  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. 
         FIG. 12  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. 
         FIG. 13A  to  FIG. 13C  are schematic sectional views of various stages in a method of fabricating a package structure in accordance with some alternative embodiments of the present disclosure. 
         FIG. 14  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. 
         FIG. 15  is a schematic top view illustrating the arrangement of package structures on a semiconductor wafer in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a second feature over or on a first feature in the description that follows may include embodiments in which the second and first features are formed in direct contact, and may also include embodiments in which additional features may be formed between the second and first features, such that the second and first features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath”, “below”, “lower”, “on”, “over”, “overlying”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     Other features and processes may also be included. For example, testing structures may be included to aid in the verification testing of the 3D packaging or 3DIC devices. The testing structures may include, for example, test pads formed in a redistribution layer or on a substrate that allows the testing of the 3D packaging or 3DIC, the use of probes and/or probe cards, and the like. The verification testing may be performed on intermediate structures as well as the final structure. Additionally, the structures and methods disclosed herein may be used in conjunction with testing methodologies that incorporate intermediate verification of known good dies to increase the yield and decrease costs. 
       FIG. 1A  and  FIG. 1B  are schematic sectional views of various stages in a method of fabricating a semiconductor die in accordance with some embodiments of the present disclosure. Referring to  FIG. 1A , in some embodiments, a first semiconductor die D 1  may be formed by the following steps. For example, a first semiconductor substrate D 1   a  is provided. The first semiconductor substrate D 1   a  may be a bulk silicon substrate or a silicon-on-insulator (SOI) substrate, and further includes active components (e.g., transistors or the like) and optionally passive components (e.g., resistors, capacitors, inductors or the like) formed therein. 
     After providing the first semiconductor substrate D 1   a,  first conductive pads D 1   b  are formed on the first semiconductor substrate D 1   a.  Although only one first conductive pad D 1   b  is illustrated, it is noted that the number of first conductive pads D 1   b  located on the first semiconductor substrate D 1   a  should be more than one. In some embodiments, the first conductive pads D 1   b  may be aluminum pads, copper pads or other suitable metal pads. After forming the first conductive pads D 1   b,  a first passivation layer D 1   c  is formed over the first semiconductor substrate D 1   a,  wherein the first passivation layer D 1   c  has first openings that partially expose the first conductive pads D 1   b  located on the first semiconductor substrate D 1   a.  In some embodiments, the passivation layer D 1   c  may be a silicon oxide layer, a silicon nitride layer, a silicon oxy-nitride layer or a dielectric layer formed of any suitable dielectric materials. The disclosure is not limited thereto. 
     In some embodiments, after forming the first passivation layer D 1   c,  first conductive posts D 1   d  are formed on the first conductive pads D 1   b  by plating. For example, the first conductive posts D 1   d  may be formed by forming a seed layer SD over the first passivation layer D 1   c;  forming a mask pattern with openings exposing portions of the seed layer SD; forming a metallic material on the exposed portions of the seed layer SD to form the first conductive posts D 1   d  by plating; removing the mask pattern; and then removing portions of the seed layer SD exposed by the first conductive posts D 1   d.  The remaining seed layer SD will exist in between the first conductive posts D 1   d  and the first conductive pads D 1   b.    
     In some embodiments, a first alignment mark AM 1  is formed in the same step as forming the first conductive posts D 1   d.  For example, the first alignment mark AM 1  is formed with a seed layer SX 1  and a conductive body CB 1 . In some embodiments, the seed layer SX 1  and the seed layer SD are formed together in the same steps. In certain embodiments, the conductive body CB 1  and the first conductive posts D 1   d  are formed together in the same steps. In some embodiments, the first alignment mark AM 1  and the first conductive posts D 1   d  are located at the same level on the first semiconductor substrate D 1   a.  Furthermore, the first alignment mark AM 1  and the first conductive posts D 1   d  are made of the same materials. In the exemplary embodiment, the first alignment mark AM 1  is formed with a plurality of stripe patterns. For example, the alignment mark AM 1  includes a plurality of stripe patterns when observed from a top view. The configuration and design of the stripe patterns will be described in detail later. 
     Referring to  FIG. 1B , in a next step, a first protection layer D 1   e  is optionally formed on the first passivation layer D 1   c.  In some embodiments, the first protection layer D 1   e  covers the first conductive posts D 1   d  and the first alignment mark AM 1  so as to protect the first conductive posts D 1   d  and the first alignment mark AM 1 . Dicing may then be performed to obtain a plurality of the first semiconductor die D 1 . In the exemplary embodiment, the first semiconductor die D 1  may be selected from application-specific integrated circuit (ASIC) chips, analog chips (for example, wireless and radio frequency chips), digital chips (for example, a baseboard chip), integrated passive devices (ISP), voltage regulator chips, sensor chips, memory chips, or the like. The disclosure is not limited thereto. 
       FIG. 2A  to  FIG. 2G  are schematic sectional views of various stages in a method of fabricating a package structure in accordance with some embodiments of the present disclosure. Referring to  FIG. 2A , a carrier  102  with a de-bonding layer  104  coated thereon is provided. In some embodiments, the carrier  102  may be a glass carrier or any suitable carrier for carrying a semiconductor wafer or a reconstituted wafer used for the manufacturing method of the package-on-package structure. In some embodiments, the de-bonding layer  104  may be any material suitable for bonding and de-bonding the carrier  102  from the above layer(s) or any wafer(s) disposed thereon. 
     In some embodiments, the de-bonding layer  104  may include a dielectric material layer made of a dielectric material including any suitable polymer-based dielectric material (such as benzocyclobutene (“BCB”), polybenzoxazole (“PBO”)). In an alternative embodiment, the de-bonding layer  104  may include a dielectric material layer made of an epoxy-based thermal-release material, which loses its adhesive property when heated, such as a light-to-heat-conversion (LTHC) release coating film. In a further alternative embodiment, the de-bonding layer  104  may include a dielectric material layer made of an ultra-violet (UV) glue, which loses its adhesive property when exposed to UV lights. In certain embodiments, the de-bonding layer  104  may be dispensed as a liquid and cured, or may be a laminate film laminated onto the carrier  102 . In certain embodiments, the de-bonding layer  104  is, for example, a LTHC layer with good chemical resistance, and such layer enables room temperature de-bonding from the carrier  102  by applying laser irradiation. 
     After providing the carrier  102  and the de-bonding layer  104 , a backside redistribution layer  106  is formed on the de-bonding layer  104 . In some embodiments, the backside redistribution layer  106  includes a conductive layer  106   a  embedded within a dielectric layer  106   b.  For example, the conductive layer  106   a  may be constituted by a plurality of redistribution conductive patterns. In some embodiments, the dielectric layer  106   b  further includes via openings Vx revealing the conductive layer  106   a.  For simplicity, the dielectric layer  106   b  is illustrated as one single layer of dielectric layer and the conductive layer  106   a  is illustrated as embedded in the dielectric layer  106   b.  However, from the perspective of the manufacturing process, the dielectric layer  106   b  is constituted by two dielectric layers, and the redistribution conductive layer  106   a  is sandwiched between the two adjacent dielectric layers. In some embodiments, materials of the conductive layer  106   a  include aluminum, titanium, copper, nickel, tungsten, and/or alloys thereof. The conductive layer  106   a  may be formed by, for example, electroplating, deposition, and/or photolithography and etching. In some embodiments, the material of the dielectric layer  106   b  includes polyimide, epoxy resin, acrylic resin, phenol resin, benzocyclobutene (BCB), polybenzooxazole (PBO), or any other suitable polymer-based dielectric material. The dielectric layer  106   b,  for example, may be formed by suitable fabrication techniques such as spin-on coating, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), or the like. 
     It should be noted that the number of the conductive layers  106   a  and the number of the dielectric layers  106   b  illustrated in  FIG. 2A  are merely for illustrative purposes, and the disclosure is not limited thereto. In some alternative embodiments, more layers of the conductive layer and more layers of the dielectric layer may be formed depending on the design requirement. When more layers of conductive layer and more layers of the dielectric layer are adapted, these conductive layers and these dielectric layers are stacked alternately, and the conductive layers are interconnected with one another by the conductive vias. 
     As illustrated in  FIG. 2A , after forming the backside redistribution layer  106 , a plurality of the first semiconductor die D 1  prepared in  FIG. 1B , and a plurality of through insulator vias  108  are provided on the backside redistribution layer  106  over the carrier  102 . In some embodiments, the through insulator vias  108  are through integrated fan-out (“InFO”) vias. In one embodiment, the formation of the through insulator vias  108  includes forming a mask pattern (not shown) with openings, then forming a metallic material (not shown) filling up the openings by electroplating or deposition, and removing the mask pattern to form the through insulator vias  108  on the backside redistribution layer  106  and within the via openings Vx. In one embodiment, the material of the through insulator vias  108  may include a metal material such as copper or copper alloys, or the like. However, the disclosure is not limited thereto. In an alternative embodiment, the through insulator vias  108  may be formed by forming a seed layer (not shown) on the backside redistribution layer  106 ; forming the mask pattern with openings exposing portions of the seed layer; forming the metallic material on the exposed portions of the seed layer to form the through insulator vias  108  by plating; removing the mask pattern; and then removing portions of the seed layer exposed by the through insulator vias  108 . For example, the seed layer may be a titanium/copper composited layer. 
     Furthermore, as illustrated in  FIG. 2A , a plurality of the first semiconductor dies D 1  is placed on the backside redistribution layer  106 . Although only two semiconductor dies are illustrated, it should be noted that the number of semiconductor dies placed on the backside redistribution layer  106  is not limited thereto, and this can be adjusted based on design requirement. In some embodiments, the first semiconductor dies D 1  are attached or adhered on the backside redistribution layer  106  through a die attach film (DAF), an adhesion paste (not shown) or the like. In certain embodiments, the first semiconductor die D 1  is placed onto the carrier  102 , and an alignment process is performed using the first alignment mark AM 1  for alignment. Since each of the first semiconductor dies D 1  includes at least one alignment mark (first alignment mark AM 1 ), the relative positions of each of the first semiconductor dies D 1  can be appropriately controlled, and the overlay accuracy of the package structure can be improved. 
     In the exemplary embodiment, the plurality of first semiconductor dies D 1  placed on the backside redistribution layer  106  may be arranged in an array, and when the first semiconductor dies D 1  are arranged in an array, the through insulator vias  108  may be classified into groups. The number of the first semiconductor dies D 1  may correspond to the number of the groups of the through insulator vias  108 . In the illustrated embodiment, the first semiconductor dies D 1  may be picked and placed on the backside redistribution layer  106  after the formation of the through insulator vias  108 . However, the disclosure is not limited thereto. In some alternative embodiments, the first semiconductor dies D 1  may be picked and placed on the backside redistribution layer  106  before the formation of the through insulator vias  108 . 
     Referring to  FIG. 2B , after forming the through insulator vias  108  and providing the first semiconductor dies D 1 , an insulating material  110  is formed on the backside redistribution layer  106  covering the through insulator vias  108  and the first semiconductor dies D 1 . In some embodiments, the insulating material  110  is formed through, for example, a compression molding process, filling up the gaps between the first semiconductor dies D 1  and adjacent through insulator vias  108  to encapsulate the first semiconductor dies D 1 . The insulating material  110  also encapsulates the through insulator vias  108 . In some embodiments, the first conductive posts D 1   d  and the first protection layer D 1   e  of the first semiconductor dies D 1  are encapsulated by and well protected by the insulating material  110 . In other words, the first conductive posts D 1   d  and the first protection layer D 1   e  are not revealed and are well protected by the insulating material  110 . 
     In some embodiments, the insulating material  110  includes polymers (such as epoxy resins, phenolic resins, silicon-containing resins, or other suitable resins), dielectric materials having low permittivity (Dk) and low loss tangent (DO properties, or other suitable materials. In an alternative embodiment, the insulating material  110  may include an acceptable insulating encapsulation material. In some embodiments, the insulating material  110  may further include inorganic filler or inorganic compound (e.g. silica, clay, and so on) which can be added therein to optimize coefficient of thermal expansion (CTE) of the insulating material  110 . The disclosure is not limited thereto. 
     Referring to  FIG. 2C , in a next step, the insulating material  110  and the first protection layer D 1   e  of the first semiconductor dies D 1  are ground or polished by a mechanical grinding process and/or a chemical mechanical polishing (CMP) process until the top surfaces D 1   d -TS of the first conductive posts D 1   d  and the top surfaces AM1-TS of the first alignment mark AM 1  are revealed. In some embodiments, the through insulator vias  108 , the first conductive posts D 1   d  and the first alignment mark AM 1  may be partially polished so that the top surface  108 -TS of the through insulator vias  108  are levelled with the top surfaces D 1   d -TS of the first conductive posts D  1   d  and the top surfaces AM 1 -TS of the first alignment mark AM 1 . The insulating material  110  is polished to form an insulating encapsulant  110 ′. In some embodiments, after the polishing process, a top surface  110 -TS of the insulating encapsulant  110 ′ is coplanar with the top surface  108 -TS of through insulator vias  108 , the top surface D 1   d -TS of the first conductive posts Dld and the top surface AM 1 -TS of the first alignment mark AM 1 . 
     Referring to  FIG. 2D , after forming the insulating encapsulant  110 ′, a redistribution layer  112  is formed on the first semiconductor die DE on the through insulator vias  108 , and on the insulating encapsulant  110 ′. In some embodiments, the redistribution layer  112  is formed on the top surface  108 -TS of the through insulator vias  108 , on the top surface D  1   d -TS of the first conductive posts D 1   d,  and on the top surface  110 -TS of the insulating encapsulant  110 ′. In some embodiments, the redistribution layer  112  is electrically connected to the through insulator vias  108 , and is electrically connected to the first semiconductor dies D 1  through the first conductive posts D 1   d.  In certain embodiments, the first semiconductor dies D 1  are electrically connected to the through insulator vias  108  through the redistribution layer  112 . 
     In some embodiments, the formation of the redistribution layer  112  includes sequentially forming one or more dielectric layers  112   a,  and one or more conductive layers  112   b  in alternation. In certain embodiments, the conductive layers  112   b  are sandwiched between the dielectric layers  112   a.  For example, a first dielectric layer  112   a - 1  is formed over the insulating encapsulant  110 ′, and the first dielectric layer  112   a - 1  has contact openings revealing the first conductive posts D 1   d.  Subsequently, a first conductive layer  112   b - 1  is formed within the contact openings and over the first dielectric layer  112   a - 1 . Thereafter, a second dielectric layer  112   a - 2 , a second conductive layer  112   b - 2  and a third dielectric layer  112   a - 3  are sequentially formed in the same way. Although only two layers of the conductive layers  112   b  and three layers of dielectric layers  112   a  are illustrated herein, however, the scope of the disclose is not limited by the embodiments of the disclosure. In other embodiments, the number of conductive layers  112   b  and the dielectric layers  112   a  may be adjusted based on product requirement. In some embodiments, seed layers SY are formed prior to forming the conductive layers  112   b.  In other words, the first conductive layer  112   b - 1  and the second conductive layer  112   b - 2  are respectively formed on a seed layer SY. In some embodiments, the conductive layers  112   b  are electrically connected to the conductive posts D 1   d  of the first semiconductor dies D  1 . Furthermore, the conductive layers  112   b  are electrically connected to the through insulator vias  108 . 
     In certain embodiments, the material of the dielectric layers  112   a  may be polyimide, polybenzoxazole (PBO), benzocyclobutene (BCB), a nitride such as silicon nitride, an oxide such as silicon oxide, phosphosilicate glass (PSG), borosilicate glass (BSG), boron-doped phosphosilicate glass (BPSG), a combination thereof or the like, which may be patterned using a photolithography and/or etching process. In some embodiments, the dielectric layers  112   a  are formed by suitable fabrication techniques such as spin-on coating, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) or the like. The disclosure is not limited thereto. 
     In some embodiments, the material of the conductive layer  112   b  may be made of conductive materials formed by electroplating or deposition, such as aluminum, titanium, copper, nickel, tungsten, and/or alloys thereof, which may be patterned using a photolithography and etching process. In some embodiments, the conductive layer  112   b  may be patterned copper layers or other suitable patterned metal layers. Throughout the description, the term “copper” is intended to include substantially pure elemental copper, copper containing unavoidable impurities, and copper alloys containing minor amounts of elements such as tantalum, indium, tin, zinc, manganese, chromium, titanium, germanium, strontium, platinum, magnesium, aluminum or zirconium, etc. 
     After forming the redistribution layer  112 , a plurality of conductive pads  112   c  may be disposed on an exposed top surface of the topmost layer of the conductive layers  112   b  (second conductive layer  112   b - 2 ) for electrically connecting with conductive balls. In certain embodiments, the conductive pads  112   c  are for example, under-ball metallurgy (UBM) patterns used for ball mount. As shown in  FIG. 2D , the conductive pads  112   c  are formed on and electrically connected to the redistribution layer  112 . In some embodiments, the materials of the conductive pads  112   c  may include copper, nickel, titanium, tungsten, or alloys thereof or the like, and may be formed by an electroplating process, for example. The number of conductive pads  112   c  are not limited in this disclosure, and may be selected based on the design layout. In some alternative embodiments, the conductive pads  112   c  may be omitted. In other words, conductive balls  114  formed in subsequent steps may be directly disposed on the redistribution layer  112 . 
     As illustrated in  FIG. 2D , after forming the conductive pads  112   c,  a plurality of conductive balls  114  is disposed on the conductive pads  112   c  and over the redistribution layer  112 . In some embodiments, the conductive balls  114  may be disposed on the conductive pads  112   c  by a ball placement process or reflow process. In some embodiments, the conductive balls  114  are, for example, solder balls or ball grid array (BGA) balls. In some embodiments, the conductive balls  114  are connected to the redistribution layer  112  through the conductive pads  112   c.  In certain embodiments, some of the conductive balls  114  may be electrically connected to the first semiconductor dies D 1  through the redistribution layer  112 . Furthermore, some of the conductive balls  114  may be electrically connected to the through insulator vias  108  through the redistribution layer  112 . The number of the conductive balls  114  is not limited to the disclosure, and may be designated and selected based on the number of the conductive pads  112   c.  In some alternative embodiments, an integrated passive device (IPD) (not shown) may optionally be disposed on the redistribution layer  112  and be electrically connected to the redistribution layer  112 . 
     Referring to  FIG. 2E , in a next step, after forming the redistribution layer  112  and the conductive balls  114 , the structure shown in  FIG. 2E  may be turned upside down and attached to a tape  201  supported by a frame  202 . Subsequently, the carrier  102  is debonded so as to separate the de-bonding layer  104  and the other elements formed thereon from the carrier  102 . In the exemplary embodiment, the de-bonding process includes projecting a light such as a laser light or an UV light on the de-bonding layer  104  (e.g., the LTHC release layer), such that the carrier  102  can be easily removed. In certain embodiments, the de-bonding layer  104  may be further removed or peeled off to reveal the backside redistribution layer  106 . 
     Referring to  FIG. 2F , in a next step, the dielectric layer  106   b  of the backside redistribution layer  106  may be patterned to form a plurality of openings that expose the conductive layers  106   a.  Thereafter, a plurality of conductive balls  120  may be placed on the surface of the conductive layers  106   a  exposed by the openings. The conductive balls  120  are, for example, reflowed to bond with the surfaces of the conductive layers  106   a.  Referring to  FIG. 2G , the structure illustrated in  FIG. 2F  is diced or singulated along the dicing lanes DL to form a plurality of package structures PK 1 . In some embodiments, the dicing process or the singulation process typically involves dicing with a rotating blade or a laser beam. In other words, the dicing or singulation process is, for example, a laser cutting process, a mechanical cutting process, or other suitable processes. Up to here, a package structure PK 1  having dual side terminals is accomplished. 
       FIG. 3  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. The package structure PK 2  illustrated in  FIG. 3  is similar to the package structure PK 1  illustrated in  FIG. 2G , hence the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference between the embodiment shown in  FIG. 3  and the embodiment of  FIG. 2G  is that the first protection layer D 1   e  is omitted from some of the first semiconductor dies D 1 . In other words, the insulating encapsulant  110 ′ is in direct contact with the first alignment mark AM 1  and the first conductive posts D 1   d.  Similar to the embodiment above, since each of the first semiconductor dies D 1  includes at least one alignment mark (first alignment mark AM 1 ), the relative positions of each of the first semiconductor dies D 1  can be appropriately controlled, and the overlay accuracy of the package structure can be improved. 
       FIG. 4A  to  FIG. 4D  are schematic top views illustrating various configurations of an alignment mark in accordance with some embodiments of the present disclosure. In the embodiments of the present disclosure, the alignment mark having stripe patterns may be any one of the designs shown in  FIG. 4A  to  FIG. 4D . In other words, the first alignment mark AM 1  illustrated in the package structure PK 1  and the package structure PK 2  may be designed to have the stripe patterns shown in  FIG. 4A  to  FIG. 4D . Referring to  FIG. 4A , the stripe patterns  301  may have stripes of different lengths, and the stripe patterns  301  are extending along a first direction X 1  and sequentially arranged along a second direction X 2  that is perpendicular to the first direction X 1 . In some embodiments, the stripe patterns  301  are arranged to form an alignment mark AM with a L-shaped grid pattern. In some embodiments, the alignment mark AM has a dimension of 1 μm to 20 μm. Herein, the dimension refers to the length or the width of the alignment mark AM from the top view. By adapting the alignment mark AM with the stripe patterns, the signal noise on the alignment mark AM may be sufficiently reduced. That is, the machinery is able to precisely detect the alignment mark AM, thereby enhancing the overlay accuracy and reducing the alignment failure rate. For example, in some embodiments, an overlay accuracy within 0.5 μm may be achieved through the adaption of the stripe patterns. 
     In some alternative embodiments, the alignment mark AM may have other shapes from the top view. For example, referring to  FIG. 4B , the stripe patterns  301  together form a square-shaped grid pattern. The square-shaped grid pattern has an L-shaped hollow portion therein. In some embodiments, the machinery may detect the contour of the L-shaped hollow portion based on the stripe patterns  301  for alignment.  FIG. 4A  and  FIG. 4B  illustrated that all of the stripe patterns  301  in the alignment mark AM are separated from each other, but the disclosure is not limited thereto. For example, referring to  FIG. 4C , the stripe patterns  301  having stripes of different lengths may be connected to form a hollow polygonal shape. In some embodiments, the stripe patterns  301  may be connected to each other to form a L-shaped pattern. Furthermore, referring to  FIG. 4D , in some embodiments, a portion of the stripe patterns  301  may be connected to each other to form a first L-shaped pattern. On the other hand, another portion of the stripe patterns  301  are connected to each other to form a second L-shaped pattern encircling the first L-shaped pattern. As illustrated in  FIG. 4D , the stripe patterns  301  in the first L-shaped pattern are separated from the stripe patterns  301  in the second L-shaped pattern. By adapting the alignment marks AM of the present disclosure with the stripe patterns, the signal noise on the alignment mark AM may be sufficiently reduced and the overlay accuracy may be sufficiently enhanced. 
       FIG. 5A  and  FIG. 5B  are schematic sectional views of various stages in a method of fabricating semiconductor dies in accordance with some alternative embodiments of the present disclosure. Referring to  FIG. 5A  and  FIG. 5B , a first semiconductor die D 1  and a second semiconductor die D 2  is fabricated. The first semiconductor die D 1  is fabricated in the same way as described in  FIG. 1A  and  FIG. 1B , hence its detailed description will be omitted herein. In the exemplary embodiment, the first semiconductor die D 1  and the second semiconductor die D 2  are different types of semiconductor dies. For example, in some embodiments, the first semiconductor die D 1  may be an application-specific integrated circuit (“ASIC”) die, and the second semiconductor die D 2  may be a high bandwidth memory (HBM) die, the disclosure is not limited thereto. 
     The method of fabricating the second semiconductor die D 2  is as follows. For example, a second semiconductor substrate D 2   a  is provided. The second semiconductor substrate D 2   a  may be a bulk silicon substrate or a silicon-on-insulator (SOI) substrate, and further includes active components (e.g., transistors or the like) and optionally passive components (e.g., resistors, capacitors, inductors or the like) formed therein. 
     After providing the second semiconductor substrate D 2   a,  second conductive pads D 2   b  are formed on the second semiconductor substrate D 2   a.  Although only one second conductive pad D 2   b  is illustrated, it is noted that the number of second conductive pads D 2   b  located on the second semiconductor substrate D 2   a  should be more than one. In some embodiments, the second conductive pads D 2   b  may be aluminum pads, copper pads or other suitable metal pads. After forming the second conductive pads D 2   b,  a second passivation layer D 2   c  is formed over the second semiconductor substrate D 2   a,  wherein the second passivation layer D 2   c  has second openings that partially expose the second conductive pads D 2   b  located on the second semiconductor substrate D 2   a.  In some embodiments, the second passivation layer D 2   c  may be a silicon oxide layer, a silicon nitride layer, a silicon oxy-nitride layer or a dielectric layer formed of any suitable dielectric materials. The disclosure is not limited thereto. 
     In some embodiments, after forming the second passivation layer D 2   c,  second conductive posts D 2   d  are formed on the second conductive pads D 2   b  by plating. For example, the second conductive posts D 2   d  may be formed by forming a seed layer SD over the second passivation layer D 2   c;  forming a mask pattern with openings exposing portions of the seed layer SD; forming a metallic material on the exposed portions of the seed layer SD to form the second conductive posts D 2   d  by plating; removing the mask pattern; and then removing portions of the seed layer SD exposed by the second conductive posts D 2   d.  The remaining seed layer SD will exist in between the second conductive posts D 2   d  and the second conductive pads D 2   b.    
     In some embodiments, a second alignment mark AM 2  is formed in the same step of forming the second conductive posts D 2   d.  For example, the second alignment mark AM 2  is formed with a seed layer SX 2  and a conductive body CB 2 . In some embodiments, the seed layer SX 2  and the seed layer SD are formed together in the same steps. In certain embodiments, the conductive body CB 2  and the second conductive posts D 2   d  are formed together in the same steps. In some embodiments, the second alignment mark AM 2  and the second conductive posts D 2   d  are located at the same level on the second semiconductor substrate D 2   a.  Furthermore, the second alignment mark AM 2  and the second conductive posts D 2   d  are made of the same materials. In the exemplary embodiment, the second alignment mark AM 2  is formed with a plurality of stripe patterns. For example, the second alignment mark AM 2  includes a plurality of stripe patterns when observed from a top view. In certain embodiments, the first alignment mark AM 1  and the second alignment mark AM 2  may be any one of the designs shown in  FIG. 4A  to  FIG. 4D . In one embodiment, the first alignment mark AM 1  and the second alignment mark AM 2  may have the same design or configuration. In an alternative embodiment, the first alignment mark AM 1  and the second alignment mark AM 2  may have different design or configuration. 
     Referring to  FIG. 5B , in a next step, a first protection layer D 1   e  is optionally formed on the first passivation layer D 1   c,  wherein the first protection layer D 1   e  covers the first conductive posts D 1   d  and the first alignment mark AM 1  in the first semiconductor die D 1 . On the other hand, the second conductive posts D 1   d  and the second alignment mark AM 2  in the second semiconductor die D 2  are not covered by any protection layer. That is, the second conductive posts D 1   d  and the second alignment mark AM 2  are revealed. Dicing may then be performed to obtain a plurality of the first semiconductor dies D 1  and a plurality of second semiconductor dies D 2   
       FIG. 6A  to  FIG. 6C  are schematic sectional views of various stages in a method of fabricating a package structure in accordance with some alternative embodiments of the present disclosure. The method of fabricating the package structure shown in  FIG. 6A  to  FIG. 6C  is similar to the method shown in  FIG. 2A  to  FIG. 2G , hence the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference between the embodiments is that the first semiconductor die D 1  and the second semiconductor die D 2  prepared in  FIG. 5B  are used instead. 
     Referring to  FIG. 6A , at least one first semiconductor die D 1  and one second semiconductor die D 2  prepared in  FIG. 5B , and a plurality of through insulator vias  108  are provided on the backside redistribution layer  106  over the carrier  102 . In some embodiments, a plurality of through insulator vias  108  are provided on the backside redistribution layer  106  to surround the first semiconductor die D 1  and the second semiconductor die D 2 . Although only two semiconductor dies are illustrated herein, it should be noted that the number of semiconductor dies placed on the backside redistribution layer  106  is not limited thereto, and this can be adjusted based on design requirement. In some embodiments, the first semiconductor die D 1  and the second semiconductor die D 2  are attached or adhered on the backside redistribution layer  106  through a die attach film (DAF), an adhesion paste (not shown) or the like. In some embodiments, the first semiconductor die D 1  is placed onto the carrier  102 , and a first alignment process is performed using the first alignment mark AM 1  for alignment. In certain embodiments, the second semiconductor die D 2  is placed onto the carrier  102 , and a second alignment process is performed using the second alignment mark AM 2  for alignment. 
     After forming the through insulator vias  108  and providing the first semiconductor die D 1  and the second semiconductor die D 2 , an insulating material  110  is formed on the backside redistribution layer  106  to cover the through insulator vias  108 , the first semiconductor die D 1  and the second semiconductor die D 2 . In some embodiments, the insulating material  110  is formed to encapsulate the first semiconductor die D 1  and the second semiconductor die D 2 . Since a protection layer is omitted from the second semiconductor die D 2 , the insulating material  110  is formed to be in direct contact with the second conductive posts D 2   d  and the second alignment mark AM 2 . Furthermore, the insulating material  110  also encapsulates the through insulator vias  108 . 
     Referring to  FIG. 6B , after forming the insulating material  110 , the insulating material  110  is polished to form an insulating encapsulant  110 ′. Thereafter, the same steps described in  FIG. 2D  may be performed to form the redistribution layer  112 , the conductive pads  112   c  and the conductive balls  114 . In some embodiments, the redistribution layer  112  is electrically connected to the first conductive posts D 1   d  of the first semiconductor die D 1 , and electrically connected to the second conductive posts D 2   d  of the second semiconductor die D 2 . Furthermore, the redistribution layer  112  may be electrically connected to the through insulator vias  108  by the conductive layers  112   b.    
     Referring to  FIG. 6C , in a next step, the carrier  102  is debonded so as to separate the de-bonding layer  104  and the other elements formed thereon from the carrier  102 . Subsequently, the dielectric layer  106   b  of the backside redistribution layer  106  may be patterned to form a plurality of openings that expose the conductive layers  106   a,  and a plurality of conductive balls  120  may be placed on the surface of the conductive layers  106   a  exposed by the openings. The structure may then be diced or singulated to form a plurality of package structures PK 3 . Similar to the embodiments above, since each of the first semiconductor die D 1  and the second semiconductor die D 2  includes at least one alignment mark (first alignment mark AM 1  and second alignment mark AM 2 ) used for the alignment process, the relative positions of the first semiconductor die D 1  to the second semiconductor die D 2  can be appropriately controlled, and the overlay accuracy of the package structure can be improved. 
       FIG. 7A  and  FIG. 7B  are schematic sectional views of various stages in a method of fabricating semiconductor dies in accordance with some alternative embodiments of the present disclosure. Referring to  FIG. 7A  and  FIG. 7B , a first semiconductor die Dl and a second semiconductor die D 2  is fabricated. The method of fabricating the first semiconductor die D 1  and the second semiconductor D 2  is similar to the method described in  FIG. 5A  and  FIG. 5B , hence the same reference numerals will be used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference being that the second semiconductor die D 2  of  FIG. 7A  and  FIG. 7B  is fabricated with a bulk alignment mark BAM. 
     The method of fabricating the second semiconductor die D 2  is as follows. Referring to  FIG. 7A , a second semiconductor substrate D 2   a  is provided. After providing the second semiconductor substrate D 2   a,  second conductive pads D 2   b  are formed on the second semiconductor substrate D 2   a.  Subsequently, a second passivation layer D 2   c  is formed over the second semiconductor substrate D 2   a,  wherein the second passivation layer D 2   c  has second openings that partially expose the second conductive pads D 2   b  located on the second semiconductor substrate D 2   a.    
     In some embodiments, after forming the second passivation layer D 2   c,  second conductive posts D 2   d  are formed on the second conductive pads D 2   b  by plating. Furthermore, in some embodiments, a bulk alignment mark BAM is formed in the same step of forming the second conductive posts D 2   d  on the second passivation layer D 2   c.  For example, the bulk alignment mark BAM is formed with a seed layer SX 3  and a conductive body CB 3 . In some embodiments, the seed layer SX 3  and the seed layer SD are formed together in the same steps. In certain embodiments, the conductive body CB 3  and the second conductive posts D 2   d  are formed together in the same steps. In some embodiments, the bulk alignment mark BAM and the second conductive posts D 2   d  are located at the same level on the second semiconductor substrate D 2   a.  Furthermore, the bulk alignment mark BAM and the second conductive posts D 2   d  are made of the same materials. In the exemplary embodiment, a “bulk” alignment mark tends to mean that the alignment mark can be viewed primarily as a single mass of material, and it does not have stripe patterns. 
     Referring to  FIG. 7B , in a next step, a second alignment mark AM 2  having a plurality of stripe patterns is formed on the second passivation layer D 2   c.  In some embodiments, the second alignment mark AM 2  is formed after forming the second conductive posts D 2   c  and the bulk alignment mark BAM. In certain embodiments, the second alignment mark AM 2  is formed with a seed layer SX 2  and a conductive body CB 2 . Furthermore, the second alignment mark AM 2 , the bulk alignment mark BAM and the second conductive posts D 2   d  are located at the same level on the second semiconductor substrate D 2   a.  In some embodiments, during the formation of the second alignment mark AM 2 , the bulk alignment mark BAM is further etched to form an undercut Ux. In certain embodiments, the seed layer SX 3  of the bulk alignment mark BAM is etched to form the undercut Ux. After forming the second alignment mark AM 2 , dicing may then be performed to form a plurality of the second semiconductor die D 2 . 
       FIG. 8A  and  FIG. 8B  are schematic top views illustrating various configurations of a bulk alignment mark in accordance with some embodiments of the present disclosure. The design of the bulk alignment mark BAM illustrated in  FIG. 7A  and  FIG. 7B  is not particularly limited, and can be for example, any one of the designs shown in  FIG. 8A  and  FIG. 8B . Referring to  FIG. 8A , the bulk alignment mark BAM is formed with a L-shaped pattern. Referring to  FIG. 8B , the bulk alignment mark BAM is formed with a polygonal shape. However, the bulk alignment marks BAM of  FIG. 8A  and  FIG. 8B  are formed as a single mass of material, and does not contain any stripe patterns. 
       FIG. 9  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. The package structure PK 4  illustrated in  FIG. 9  is similar to the package structure PK 3  illustrated in  FIG. 6C , hence the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference between the embodiments is that the first semiconductor die Dl and the second semiconductor die D 2  prepared in  FIG. 7B  are used instead. In other words, the second semiconductor die D 2  further contains the bulk alignment mark BAM with the undercut Ux. Similar to the embodiments above, since each of the first semiconductor die D 1  and the second semiconductor die D 2  includes at least one alignment mark (first alignment mark AM 1  and second alignment mark AM 2 ) used for the alignment process, the relative positions of the first semiconductor die D 1  to the second semiconductor die D 2  can be appropriately controlled, and the overlay accuracy of the package structure can be improved. 
       FIG. 10A  and  FIG. 10B  are schematic sectional views of various stages in a method of fabricating semiconductor dies in accordance with some alternative embodiments of the present disclosure. Referring to  FIG. 10A  and  FIG. 10B , a first semiconductor die D 1  and a second semiconductor die D 2  is fabricated. The method of fabricating the first semiconductor die D 1  and the second semiconductor D 2  is similar to the method described in  FIG. 5A  and  FIG. 5B , hence the same reference numerals will be used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference between the embodiments is in the position of the first alignment mark AM 1  and the second alignment mark AM 2 . 
     Referring to  FIG. 10A , in the first semiconductor die D 1 , the first alignment mark AM 1  and the first conductive pads D 1   b  are formed together in the same steps. In some embodiments, the first alignment mark AM 1  and the first conductive pads D 1   b  are located at the same level on the first semiconductor substrate D  1  a. Furthermore, the first alignment mark AM 1  and the first conductive pads D 1   b  are made of the same materials. Similarly, in the second semiconductor die D 2 , the second alignment mark AM 2  and the second conductive pads D 2   b  are formed together in the same steps. In some embodiments, the second alignment mark AM 2  and the second conductive pads D 2   b  are located at the same level on the second semiconductor substrate D 2   a.  Furthermore, the second alignment mark AM 2  and the second conductive pads D 2   b  are made of the same materials. In the exemplary embodiment, the first alignment mark AM 1  and the second alignment mark AM 2  are formed with a plurality of stripe patterns. For example, the first alignment mark AM 1  and the second alignment mark AM 2  may be any one of the designs shown in  FIG. 4A  to  FIG. 4D . 
     Referring to  FIG. 10B , in a next step, a first protection layer D 1   e  and a second protection layer D 2   e  are optionally formed on the first passivation layer D 1   c  and the second passivation layer D 2   c  respectively. In some embodiments, the first protection layer D 1   e  covers the first conductive posts D 1   d  and the first alignment mark AM 1  in the first semiconductor die D 1 . In certain embodiments, the second protection layer D 2   e  covers the second conductive posts D 2   d  and the second alignment mark AM 2  in the second semiconductor die D 2 . In some embodiments, since the first protection layer D 1   e  and the second protection layer D 2   e  are made of transparent materials, the first alignment mark AM 1  covered by the first protection layer D 1   e,  and the second alignment mark AM 2  covered by the second protection layer D 2 e can still be observed, detected and used for alignment. After forming the first protection layer D 1   e  and the second protection layer D 2   e,  dicing may then be performed to form a plurality of the first semiconductor dies D 1  and a plurality of the second semiconductor dies D 2 . 
       FIG. 11  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. The package structure PK 5  illustrated in  FIG. 11  is similar to the package structure PK 3  illustrated in  FIG. 6C , hence the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference between the embodiments is that the first semiconductor die D 1  and the second semiconductor die D 2  prepared in  FIG. 10B  are used instead. In other words, the first alignment mark AM 1  and the first conductive pads D 1   b  are located at the same level on the first semiconductor substrate D 1   a.  Furthermore, the second alignment mark AM 2  and the second conductive pads D 2   b  are located at the same level on the second semiconductor substrate D 2   a.  Similar to the embodiments above, since each of the first semiconductor die D 1  and the second semiconductor die D 2  includes at least one alignment mark (first alignment mark AM 1  and second alignment mark AM 2 ) used for the alignment process, the relative positions of the first semiconductor die D 1  to the second semiconductor die D 2  can be appropriately controlled, and the overlay accuracy of the package structure can be improved. 
       FIG. 12  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. The package structure PK 6  illustrated in  FIG. 12  is similar to the package structure PK 5  illustrated in  FIG. 11 , hence the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference between the embodiments is in the position of the second alignment mark AM 2 . In the above embodiments, the position of the alignment mark (AM 1 /AM 2 ) on the semiconductor substrate is the same for the first semiconductor die D 1  and the second semiconductor die D 2 . However, the disclosure is not limited thereto. Referring to  FIG. 12 , in the first semiconductor die D 1 , the first alignment mark AM 1  and the first conductive pads D 1   b  are located at the same level on the first semiconductor substrate D 1   a,  whereas in the second semiconductor die D 2 , the second alignment mark AM 2  and the second conductive posts D 2   d  are located at the same level on the second semiconductor substrate D 2   a.  In other words, the alignment marks (AM 1 /AM 2 ) may be located at the pad-level or at the post-level depending on actual design requirements. Similar to the embodiments above, since each of the first semiconductor die D 1  and the second semiconductor die D 2  includes at least one alignment mark (first alignment mark AM 1  and second alignment mark AM 2 ) used for the alignment process, the relative positions of the first semiconductor die D 1  to the second semiconductor die D 2  can be appropriately controlled, and the overlay accuracy of the package structure can be improved. 
       FIG. 13A  to  FIG. 13C  are schematic sectional views of various stages in a method of fabricating a package structure in accordance with some alternative embodiments of the present disclosure. The method of fabricating the package structure PK 7  shown in  FIG. 13C  is similar to the method of fabricating the package structure PK 3  as described in  FIG. 6A  to  FIG. 6C . Therefore, the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference between the embodiments is that auxiliary alignment marks AAM are further formed on the redistribution layer  112 . 
     Referring to  FIG. 13A , the redistribution layer  112  is formed by first forming a first dielectric layer  112   a - 1  having contact openings revealing the first conductive posts D 1   d  and the second conductive posts D 2   d.  Subsequently, a first conductive layer  112   b - 1  is formed within the contact openings and over the first dielectric layer  112   a - 1 . In the exemplary embodiment, auxiliary alignment marks AAM are formed in the same steps of forming the first conductive layer  112   b - 1 . In certain embodiments, the auxiliary alignment marks AAM are formed with a seed layer SZ and a conductive body CX. In some embodiments, the seed layer SZ and the seed layer SY are formed together in the same steps. Furthermore, the conductive body CX and the first conductive layer  112   b - 1  are formed together in the same steps, and the conductive body CX and the first conductive layer  112   b - 1  are made of the same materials. In the exemplary embodiment, the auxiliary alignment marks AAM are formed with a plurality of stripe patterns. For example, the auxiliary alignment marks AAM may be any one of the designs shown in  FIG. 4A  to  FIG. 4D . 
     Referring to  FIG. 13B , in a next step, a second dielectric layer  112   a - 2 , a second conductive layer  112   b - 2  and a third dielectric layer  112   a - 3  are sequentially formed in the same way as in  FIG. 6B . Thereafter, the same steps described in  FIG. 2D  may be performed to form the conductive pads  112   c  and the conductive balls  114  on the redistribution layer  112 . In the exemplary embodiment, the auxiliary alignment marks AAM are only formed on the first dielectric layer  112   a - 1 . However, the disclosure is not limited thereto, in some other embodiments, the auxiliary alignment marks AAM may be formed on any of the first dielectric layer  112   a - 1 , the second dielectric layer  112   a - 2  and/or the third dielectric layer  112   a - 3 . 
     Referring to  FIG. 13C , in a next step, the carrier  102  is debonded so as to separate the de-bonding layer  104  and the other elements formed thereon from the carrier  102 . Subsequently, the dielectric layer  106   b  of the backside redistribution layer  106  may be patterned to form a plurality of openings that expose the conductive layers  106   a,  and a plurality of conductive balls  120  may be placed on the surface of the conductive layers  106   a  exposed by the openings. The structure may then be diced or singulated to form a plurality of package structures PK 7 . Similar to the embodiments above, since each of the first semiconductor die D 1  and the second semiconductor die D 2  includes at least one alignment mark (first alignment mark AM 1  and second alignment mark AM 2 ), the relative positions of the first semiconductor die D 1  to the second semiconductor die D 2  can be appropriately controlled, and the overlay accuracy of the package structure can be improved. Furthermore, by forming the redistribution layer  112  having the auxiliary alignment marks AAM, the subsequently formed elements may be accurately formed on the designated location with high overlay accuracy, thereby enhancing the reliability of the package structure. 
       FIG. 14  is a schematic sectional view of a package structure in accordance with some alternative embodiments of the present disclosure. The package structure PK 8  illustrated in  FIG. 14  is similar to the package structure PK 7  illustrated in  FIG. 13C , hence the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. The difference between the embodiments is that the backside redistribution layer  106  is omitted from  FIG. 14 . In the above embodiments, all of the first semiconductor dies D 1  and the second semiconductor dies D 2  are bonded onto the backside redistribution layer  106 . However, the disclosure is not limited thereto. Referring to  FIG. 14 , the first semiconductor die D 1  and the second semiconductor die D 2  are bonded onto a dielectric layer  104 . In some embodiments, the dielectric layer  104  may be patterned to form a plurality of openings that expose the through insulator vias  108 . Thereafter, a plurality of conductive balls  120  may be placed on the surface of the through insulator vias  108  exposed by the openings. As such, a package structure PK 8  having dual side terminals is accomplished. 
     As illustrated in  FIG. 14 , since each of the first semiconductor die D 1  and the second semiconductor die D 2  includes at least one alignment mark (first alignment mark AM 1  and second alignment mark AM 2 ) used for the alignment process, the relative positions of the first semiconductor die D 1  to the second semiconductor die D 2  can be appropriately controlled, and the overlay accuracy of the package structure can be improved. Furthermore, by forming the redistribution layer  112  having the auxiliary alignment marks AAM, the subsequently formed elements may be accurately formed on the designated location with high overlay accuracy, thereby enhancing the reliability of the package structure. 
       FIG. 15  is a schematic top view illustrating the arrangement of package structures on a semiconductor wafer in accordance with some embodiments of the present disclosure. Referring to  FIG. 15 , each of the package structures prepared in the above embodiments may be fabricated on a semiconductor wafer. For example, the semiconductor wafer may be diced to form a plurality of package structures PK. In the exemplary embodiment, the number of semiconductor dies disposed on each of the package structure PK is not limited thereto, and this can be adjusted based on design requirement. For instance, in one embodiment, a package structure PK may contain two semiconductor dies Dx being the same type of semiconductor dies. In another embodiment, a package structure PK may contain a first semiconductor die Dx, a second semiconductor die Dy and a third semiconductor die Dz, wherein these semiconductor dies are different types of semiconductor dies. Since each of the semiconductor dies (Dx, Dy or Dz) in the package structure PK respectively includes at least one alignment mark AM used for alignment, the semiconductor dies Dx may be picked and placed on the semiconductor wafer with high overlay accuracy and reduced field shift error. 
     In the above-mentioned embodiments, each of semiconductor dies in the package structure includes at least one alignment mark, therefore, the relative positions of the semiconductor dies (die to die position) can be appropriately controlled, and the overlay accuracy of the package structure can be improved. As such, the semiconductor dies may be picked and placed on the semiconductor wafer with high overlay accuracy and reduced field shift error. 
     In some embodiments of the present disclosure, a package structure includes a plurality of semiconductor die, an insulating encapsulant and a redistribution layer. Each of the plurality of semiconductor dies includes a semiconductor substrate, conductive pads disposed on the semiconductor substrate, conductive posts disposed on the conductive pads, and at least one alignment mark located on the semiconductor substrate. The insulating encapsulant is encapsulating the plurality of semiconductor dies. The redistribution layer is disposed on the insulating encapsulant and electrically connected to the plurality of semiconductor dies. 
     In another embodiment of the present disclosure, a package structure includes a first semiconductor die, a second semiconductor die, an insulating encapsulant and a redistribution layer. The first semiconductor die includes a first semiconductor substrate, first conductive pads disposed on the first semiconductor substrate, first conductive posts disposed on the first conductive pads, and a first alignment mark located on the first semiconductor substrate, the first alignment mark includes first stripe patterns. The second semiconductor die includes a second semiconductor substrate, second conductive pads disposed on the semiconductor substrate, second conductive posts disposed on the second conductive pads, and a second alignment mark located on the second semiconductor substrate, the second alignment mark of the second semiconductor die includes second stipe patterns. The insulating encapsulant is encapsulating the first semiconductor die and the second semiconductor die. The redistribution layer is disposed on the insulating encapsulant and electrically connected to the first semiconductor die and the second semiconductor die. 
     In yet another embodiment of the present disclosure, a method of fabricating a package structure is described. The method includes the following steps. A first semiconductor substrate having first conductive pads formed thereon is provided. A first passivation layer with first openings is formed over the first conductive pads. First conductive posts are formed within the first openings and over the first conductive pads. First alignment mark is formed to be located on the first passivation layer. Dicing is performed to obtain first semiconductor dies. A second semiconductor die is provided. The second semiconductor die has a second semiconductor substrate having second conductive pads formed thereon, a second passivation layer covering the second conductive pad and having a second opening exposing the second conductive pads, second conductive posts disposed on the second conductive pads within the second opening, and a bulk alignment mark located on the second passivation layer. A second alignment mark is formed on the second passivation layer, wherein the bulk alignment mark is etched to form an undercut during forming the second alignment mark. The first semiconductor die is placed onto a carrier, and a first alignment process is performed using the first alignment mark for alignment. The second semiconductor die is placed beside the first semiconductor die, and a second alignment process is performed using the second alignment mark for alignment. An insulating encapsulant is formed over the carrier and encapsulating the first semiconductor die and the second semiconductor die. A redistribution layer is formed on the insulating encapsulant, wherein the redistribution layer is electrically connected to the first semiconductor die and the second semiconductor die. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.