# Patent

## Title
Semiconductor packages and methods of packaging semiconductor devices

## Abstract

Semiconductor packages and methods of forming a semiconductor package are disclosed. The method includes providing at least one die having first and second surfaces. The second surface of the die includes a plurality of conductive pads. A support carrier is provided and the at least one die is attached to the support carrier. The first surface of the at least one die is facing the support carrier. A cap having first and second surfaces is formed to encapsulate the at least one die. The second surface of the cap is disposed at a different plane than the second surface of the die.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of U.S. Provisional Application No. 61/413,577 entitled “Embedded Die Fan-Out Packaging Structures and Processes” filed on Nov. 15, 2010, which is herein incorporated by reference for all purposes.


BACKGROUND
Industry fan-out solutions involve high capital investment costs for new wafer redistribution layer (RDL) and bumping facilities. Furthermore, new equipment for compression molding system and retrofit kits are required to enable wafer handling in the pick and place system for fan-out solutions.
To minimize or avoid the above mentioned expenses, it is desirable to improve fan-out semiconductor packaging processes which are able to utilize existing equipment tools and process associated with current wafer level fan out solutions. Additionally, it is desirable to produce fan-out semiconductor packages having very thin package profile, higher I/O counts for wafer level chip scale packaging, with multi-level redistribution layers and possibly system in package applications.
SUMMARY
Embodiments relate generally to semiconductor packages. In one embodiment, a method for forming a semiconductor package is presented. The method includes providing at least one die having first and second surfaces, wherein the second surface of the die includes a plurality of conductive pads. The method also includes providing a support carrier and attaching the at least one die to the support carrier. The first surface of the at least one die is facing the support carrier. A cap having first and second surfaces is formed to encapsulate the at least one die. The second surface of the cap is disposed at a different plane than the second surface of the die.
In another embodiment, a method for forming a semiconductor package is disclosed. The method includes providing at least one die stack having first and second surfaces. The second surface of the die stack includes a plurality of conductive pads. A cap having first and second surfaces is provided to encapsulate the at least one die stack. The second surface of the cap is disposed at a different plane than the second surface of the die stack. The method also includes forming a built-up package substrate having an interconnect on the second surface of the die stack. The interconnect couples to the conductive pads of the same die stack.
In another embodiment, a semiconductor package is disclosed. The semiconductor package includes at least one die having first and second surfaces. The second surface of the die includes a plurality of conductive pads. The semiconductor package includes a cap having first and second surfaces to encapsulate the at least one die. The second surface of the cap is disposed at a different plane than the second surface of the die. The package further includes a built-up package substrate having an interconnect on the second surface of the at least one die. The interconnect couples to the conductive pads of the same die.
In yet another embodiment, a semiconductor package is presented. The semiconductor package includes at least one die stack having first and second surfaces. The second surface of the die stack includes a plurality of conductive pads. The semiconductor package includes a cap having first and second surfaces to encapsulate the at least one die stack. The second surface of the cap is disposed at a different plane than the second surface of the die stack. The package further includes a built-up package substrate having an interconnect on the second surface of the at least one die stack. The interconnect couples to the conductive pads of the same die stack.
These embodiments, along with other advantages and features herein disclosed, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations.



BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
FIGS. 1a-b and FIG. 2 show various embodiments of a semiconductor package; and
FIGS. 3a-k, FIGS. 4a-d, FIGS. 5a-b, FIGS. 6a-e, FIG. 7 and FIGS. 8a-b show various embodiments of a method for forming a semiconductor package.



DESCRIPTION
Embodiments relate to semiconductor packages and methods for forming a semiconductor package. The packages are used to package one or more semiconductor dies or chips. For the case of more than one die, the dies may be arranged in a planar arrangement, vertical arrangement, or a combination thereof. The dies, for example, may include memory devices, logic devices, communication devices, optoelectronic devices, digital signal processors (DSPs), microcontrollers, system-on-chips (SOCs) as well as other types of devices or a combination thereof. Such packages may be incorporated into electronic products or equipment, such as phones, computers as well as mobile and mobile smart products. Incorporating the packages into other types of products may also be useful.
FIGS. 1a-b show simplified cross-sectional views of different embodiments of a semiconductor package 100 with a portion A′ in greater detail. The package includes a built-up or integrated wiring substrate 110. The wiring substrate includes first and second major surfaces 111 and 112. The first major surface, for example, may be referred to as the top surface and the second major surface, for example, may be referred to as the bottom surface. Other designations for the surfaces may also be useful. In one embodiment, the first major surface of the wiring substrate includes first and second regions 111a-b. The first region, for example, is a die or chip region on which a die 150 is mounted and the second region, for example, is a non-die region. In one embodiment, the non-die region surrounds the die region. The die region, for example, may be disposed in a central portion of which the die 150 is mounted and a non-die region 111b which is outside of the die attach region. The die region, for example, may be concentrically disposed within the periphery of the wiring substrate. Other configurations of die and non-die region may also be useful.
The die can be a semiconductor die or chip. The die, for example, may be any type of integrated circuit (IC), such as a memory device such as a dynamic random access memory (DRAM), a static random access memory (SRAM) and various types of non-volatile memories including programmable read-only memories (PROM) and flash memories, an optoelectronic device, a logic device, a communication device, a digital signal processor (DSP), a microcontroller, a system-on-chip, as well as other types of devices.
The die includes a first surface 150a and a second major surface 150b. The first surface, for example, is an inactive or backside of the die and the second surface is an active surface of the die. Other designations for the surfaces of the die may also be useful. The active surface of the die contacts the die region of the wiring substrate. The active surface, for example, includes openings in a final passivation layer to expose conductive die pads 155. The surfaces of the conductive die pads, for example, are substantially coplanar with the second major surface 150b of the die. Providing surfaces of the conductive pads which are not coplanar with the second major surface of the die may also be useful. The die pads provide connections to the circuitry of the die. The die pads, for example, are formed of a conductive material, such as copper, aluminum, gold, nickel or alloys thereof. Other types of conductive material may also be used for the die pads. The pattern of the die pads may be one or more rows disposed at a center or at opposing sides of the active surface. Other pad patterns, such as grid or matrix arrangements, may also be useful.
In one embodiment, the wiring substrate includes a multi-layered substrate. The multi-layered substrate, in one embodiment, includes first and second insulating substrate layers 113 and 117. The first layer includes first 113a and second surfaces 113b. The first surface may be referred to as the top surface and the second surface may be referred to as the bottom surface. Other designations for the surfaces of the first layer may also be useful. The first surface contacts the die. In one embodiment, the first layer includes through via contacts 130 which extend from the first surface to the second surface of the first layer. The via contacts are formed of a conductive material. For example, the via contacts may be formed of copper, aluminum, gold, nickel or alloys thereof. Other types of conductive materials may also be useful. The via contacts are isolated from each other by the first insulating substrate layer.
Conductive traces 140 are disposed on the second surface of the first insulating substrate layer. The conductive traces are formed of a conductive material, such as copper, aluminum, gold, nickel or alloys thereof. Other types of conductive material may also be useful. The conductive traces are coupled to the substrate via contacts forming interconnects which are coupled to the die pads of the same die. The conductive traces may include conductive pads 168.
The first substrate layer may be a dielectric layer. The dielectric layer, for example, is disposed on the second surface of the die. Other types of first substrate layers may also be useful. In other embodiments, the substrate layer may be patterned to provide vias in which substrate via contacts are disposed. Formation of the vias in the first substrate layer may be achieved by any suitable techniques, including and not limited to laser and mechanical drilling.
The second insulating substrate layer includes first 117a and second surfaces 117b. The first surface may be referred to as the top surface and the second surface may be referred to as the bottom surface. Other designations for the surfaces of the second insulating substrate layer may also be useful. The first surface of the second insulating layer is disposed on the second surface of the first substrate layer and the conductive traces; the second surface serves as a bottom surface of the package. The second substrate layer isolates the conductive traces from each other. The second substrate layer may be formed of solder mask or other dielectric materials. Other types of second substrate layers may also be useful.
Openings are provided in the second substrate layer in which package contacts 170 are disposed. The openings, for example, expose conductive pads on the conductive traces. The pattern of the openings may be designed to provide the desired package contact pattern. For example, the contact openings may be arranged in a grid pattern to form a BGA type package. Other contact opening patterns may also be useful. The conductive pads, for example, are coplanar with the conductive traces. In other embodiments, the conductive pads may include protruding conductive pads. The conductive pads may be further covered with a surface protection material, such as OSP or a metallic coating or plating.
The external package contacts 170 are disposed on the second substrate layer in the openings. The package contacts, for example, are spherical shaped structures or balls. The package contacts protrude from the bottom surface of the second substrate layer. Providing package contacts which do not protrude from the bottom surface of the second substrate layer, such as solder lands, may also be useful. The package contact is formed of a conductive material. The package contacts, for example, can be formed from solder. Various types of solder can be used to form the package contacts. For example, the solder can be a lead-based or non lead-based solder. Other types of conductive materials may also be used to form the package contacts.
The package contacts provide external access to the die via the conductive traces, substrate via contacts and die pads. The package may be electrically coupled to an external device (not shown), such as a circuit board, by the package contacts.
In one embodiment, the built-up wiring substrate is an integrated package substrate. As described, the package substrate directly contacts the die in the die region, with the conductive traces and via contacts coupled to the die pads of the same die. In one embodiment, the integrated package substrate includes via contacts which are directly coupled to the die pads of the same die. The wiring substrate serves as a fan out redistribution structure for the die, enabling redistributed, fanned-out external package connections.
As described, the first substrate layer is a single layer. In other embodiments, the first substrate layer 113 may include a plurality of first sub-layers. For example, the first substrate layer may include first and second first sub-layers. Providing a first substrate layer with other numbers of first sub-layers may also be useful. The first and second first sub-layers, for example, may include the same material. Providing the first sub-layer having a different material than the second sub-layer may also be useful. A first sub-layer is similar to the first substrate layer. For example, a first sub-layer includes first and second surfaces and substrate via contacts extending through the surfaces and conductive traces on the second surface. The first surface of a sub-layer either contacts the die or the second surface of an adjacent first sub-layer. This produces a first substrate layer or layered stack with multiple conductive layers. Providing a first substrate layer having multiple built-up conductive layers may facilitate a package for a die with a higher density of the die contacts and package contacts.
In one embodiment, a cap 190 is formed over the second region 111b of the first major surface 111 of the package substrate. The cap serves to protect the die from the environment. For example, the cap may protect the die from moisture. The cap, for example, is formed of an encapsulation material. The encapsulation material, for example, may be molding epoxy resin material. Other types of encapsulation materials may also be useful
The cap includes first and second major surfaces 190a-b. The first surface, for example, may be the top surface and the second surface may be the bottom surface. Other designations for the surfaces of the cap may also be useful. In one embodiment, the cap at least surrounds the die. For example, the bottom surface 190b is disposed on the package substrate on the non-die region of the package substrate. The cap, by surrounding the die, protects the die.
In one embodiment, the non-die region is disposed in a different plane than the die region. For example, as shown by portion A′, the die and non-die region forms a step 187 in the package substrate. In one embodiment, the die region is disposed or recessed into the encapsulation material with respect to first major surface 190a of the cap. For example, the die region 111a has a greater distance from the bottom 117b of the package substrate than the non-die region 111b. The non-die region, for example, is above the die region or the conductive die pads with respect to the first major surface 190a of the cap. Referring to FIG. 1a, the second surface of the die is disposed in a different plane than the second surface of the cap. Providing the bottom surface of the cap at a different plane than the die advantageously relieves the mechanical stress on the die due to the thermal mismatch of the package materials.
In one embodiment, the cap leaves the backside or first surface of the die exposed, as shown in FIG. 1a. For example, the top surface 190a of the cap is about co-planar with the backside surface 150a of the die. In another embodiment, the cap surrounds and covers the die, as shown in FIG. 1b. For example, the first surface 190a of the cap is above the backside surface 150a of the die. The cap protects the sides and backside of the die.
FIG. 2 shows another embodiment of a semiconductor package 200. The semiconductor package is similar to that described in FIGS. 1a-b. As such, common elements may not be described or described in detail.
The semiconductor package 200 includes a die stack 210 being mounted on a die region 111a of a wiring substrate 110. The die stack includes n number of dies, where n is ≧2. The bottom die, for example, may be referred to as the first (e.g., n=1) and the top die is equal to n. Designating the dies of the die stacks using other conventions may also be useful. The die stack, for example, may be formed by any suitable types of die stacking methods. As shown, the die stack includes first and second dies 2501 and 2502. The second die 2502 is attached onto the first die 2501, and the first die is attached to the die region 111a of the wiring substrate 110. Dies used for the die stack may be TSV or non-TSV dies. In one embodiment, both top and bottom die may be TSV dies. In yet another embodiment, the bottom die may include a TSV die and the top die may include a non-TSV die. Non-TSV die, for example, may include wire bonded, direct connection, flip chip die, etc. For die stacks having more than 2 dies, the lower dies (bottom and intermediate dies except the top die) are usually TSV dies while the top die is a non-TSV die. Other configurations or types of dies of a die stack may also be useful.
A TSV die includes first and second major surfaces 250a-b. The first surface includes first die contacts 233 and the second major surface includes second die contacts 235. The die contacts, for example, are die contact pads which have top surfaces co-planar with the first 250a and second 250b major surfaces of the die. Providing surfaces of the contact pads which are not coplanar with the surfaces of the die may also be useful. Other configurations of die contacts or die contact pads may also be useful. The first and second die contacts are interconnected by through via contacts 230. Other configurations of the TSV dies may also be useful. The via contacts and the contact pads, for example, are formed of a conductive material. The conductive material, for example, may include copper. Other types of conductive material may also be used for the via contacts and contact pads.
As shown, the second die contacts 235 of the bottom die are mounted onto the die region 111a of the wiring substrate. The first die contacts 233 are mated with the top die of the die stack. In one embodiment, a die attach film or an underfill 217 can be provided in the cavity formed between the dies to facilitate stacking and to protect bonding contacts 240 which couple the conductive die pads 155 of the second die with the first die contacts 233 of the first die. Redistribution layer may also be provided Similar to FIGS. 1a-b, the die and non-die region of the semiconductor package 200 forms a step 187 in the package substrate. For the case where more than two dies are used to form the die stack, the bottom and intermediate dies may include TSV dies. Providing the bottom and intermediate dies with non-TSV dies may also be useful. The second die contacts of the nth+1 die above is connected to the first die contacts of the nth die below.
A cap 190 is provided to encapsulate the die stack 210. In one embodiment, the cap surrounds and covers the die. For example, the top surface 190a of the cap covers a top surface 150a of the top die 2502. The cap protects the sides and backside of the second die of the die stack. As discussed, the die region is disposed or recessed into the encapsulation material with respect to first major surface 190a of the cap 190. In other embodiments, the top surface of the cap may be coplanar with the top surface of the top die (not shown). This, for example, leaves the top surface of the die exposed, similar to the device or package described in FIG. 1a. 
FIGS. 3a-k show an embodiment of a method for forming a semiconductor package 300. FIG. 3a shows a wafer 301 having a first surface 301a and a second surface 301b. The wafer serves as a substrate for forming a die 350. The first surface, for example, is an inactive surface 350a while the second surface is an active surface 350b. Other designations of the surfaces may also be useful. The wafer, for example, may be a silicon wafer. Other types of semiconductor wafers may also be useful. In one embodiment, the wafer is processed to include a plurality of dies or chips. For example, a plurality of dies are processed in parallel on the wafer.
A die 350 includes circuit components formed on the wafer or substrate. The circuit components include, for example, transistors, resistors, capacitors and interconnections to form an IC. A final passivation layer may be formed over the die. The final passivation layer includes openings to expose die pads 355. The surface of the wafer or substrate which includes the openings to the die pads may be referred to as the active surface of the wafer.
In one embodiment, a sacrificial layer 377 is formed over the active surface of the wafer 301b. The sacrificial layer is a temporary layer which will subsequently be removed. The sacrificial layer, for example, is an adhesive material. Other types of sacrificial layer may also be useful. The sacrificial layer may be formed on the substrate using various techniques. For example, the sacrificial layer may be provided by spin coating or lamination. Other techniques for forming the sacrificial layer may also be useful. The technique, for example, may depend on the type of sacrificial layer. In one embodiment, the sacrificial layer may be half-cured to be less tacky during the encapsulation process. In other embodiments, the sacrificial layer remains tacky to improve adhesion to a support carrier, if used.
The process continues by dicing the wafer processed with the dies and sacrificial layer over the active surface of the wafer. Dicing the wafer separates the dies into individual dies with the sacrificial layer over the active surface. In another embodiment, the sacrificial layer 377 may be formed over the active surfaces of the dies after dicing the wafer into individual dies.
Referring to FIG. 3b, a support carrier 380 is provided. The support carrier, for example, is a temporary carrier for processing chip packages. The carrier should be sufficiently rigid to serve as a support and withstand further processing steps. For example, the carrier should be sufficiently rigid to reduce or prevent warpage of chip assemblies during the assembly process. By way of a non-limiting example, the carrier may be a mold plate adapted for molding of chip assemblies. Various types of materials may be used to form the support carrier. For example, the carrier may be formed of metal, glass, semiconductor, reinforced materials or any other suitable materials.
The carrier includes a first surface on which dies are processed to form packages. The carrier can be configured in a strip format to process a row of dies. In other embodiments, the carrier is configured to process a plurality of rows of dies. For example, the carrier may have a panel format to form a 2 dimensional array of packages. Providing a carrier configured in a wafer format to form a plurality of packages may also be useful. In some embodiments, the carrier may be configured to form one package, for example, a single format. The type of format selected may depend on, for example, the requirements of the process, available equipment or cost considerations.
Illustratively, the carrier is configured in a strip format with four package regions or zones 380a-d for forming four packages. Providing a carrier with other number of package regions or formats may also be useful. A package region includes a die region and a non-die region. The size of the package region is equal to about the size of a package. A die 350 coated with the sacrificial layer 377 on the active surface 350b is attached to the die region. For example, four dies 3501-4 are attached to the die regions on the carrier.
In one embodiment, an adhesive 375 is provided on a first surface of the carrier to facilitate temporary die attachment. Other temporary bonding techniques may also be useful for attaching the dies. The adhesive, for example, is provided in at least the die regions on the support carrier for temporarily holding a chip assembly thereto. In one embodiment, the adhesive is provided on the whole first surface. In other embodiments, the adhesive is provided only in the die regions. The adhesive can be any type of adhesive that provides temporary bonding of a chip assembly to the chip assembly surface. The adhesive 375, for example, may include the same material as the sacrificial layer 377. In other embodiments, the adhesive 375 may include different material than the sacrificial layer. The adhesive may be in different forms. For example, the adhesive may be a tape, a liquid or a paste. The adhesive may be provided on the substrate using various techniques. The technique employed may depend on the type or form of the adhesive. For example, a tape adhesive may be provided on the substrate by lamination, a paste adhesive may be provided on the substrate by printing while a liquid adhesive may be provided on the substrate by spin-coating. Providing the adhesive on the substrate using other techniques may also be useful.
In one embodiment, the inactive surface 350a or backside of the dies are attached to the die regions of the carrier. The dies are attached to the die regions using any suitable techniques according to the equipment and the type of the adhesive used.
Referring to FIG. 3c, a cap 390 is formed to encapsulate the dies. The cap, in one embodiment, is disposed in the non-die region. For example, an encapsulation material is dispensed to fill the spaces between the dies. In one embodiment, the encapsulation is a mold compound, such as molding epoxy resin material. Providing other types of encapsulation materials may also be useful.
The cap, in one embodiment, is formed by transfer molding techniques. In one embodiment, the cap is formed by a film assisted transfer molding technique. For example, a film 393 is placed against contours of a mold (not shown). In one embodiment, when the carrier and the dies are placed against the mold, the film contacts the sacrificial layer on the active surface of the dies, leaving spaces therebetween in the non-die regions. Encapsulation material, such as a mold compound, is dispensed into the mold assembly, filling the spaces in the non-die regions to form the cap. The sacrificial layer protects the active surface of the dies from the encapsulation material. After molding, the molded panel of dies is separated from the mold. The sacrificial layer also facilitates release of the molded panel from the molding tool. Other techniques for forming the cap may also be useful. For example, the cap may also be formed by printing or compression molding.
Referring to FIG. 3d, the support carrier 380 and the adhesive 375 are separated from the dies after forming the cap. In one embodiment, a de-bonding treatment is employed to separate the chip assemblies from the chip assembly surface. The de-bonding treatment may, for example, cause the adhesive to lose or reduce its adhesive strength to allow separation of a chip assembly from the substrate. In one embodiment, the de-bonding treatment includes a temperature or heating treatment. When heated to the de-bonding temperature, the adhesive loses or reduces its adhesive strength. Other types of de-bonding treatments may also be useful. The de-bonding treatment may depend on the type of adhesive used. The de-bonding treatment, for example, may include chemical treatment such as applying a solvent to dissolve the adhesive or a mechanical treatment, such as pulling or twisting to separate the chip from the base carrier.
Removal of the carrier and adhesive leaves the plurality of dies attached to each other by the cap. The cap provides mechanical support for the chips for further processing. The surfaces of the cap, in one embodiment, are coplanar with the surfaces of the dies. For example, a first surface 390a of the cap is coplanar with the backside or first surface 350a of the dies and a second surface 390b is coplanar with the sacrificial layer 377 on the active or second surface 350b of the dies. By providing a cap which does not cover the backside of the die helps improves the heat dissipation from the dies. External heat sink may also be attached to the backside of the die to further improve heat dissipation.
Referring to FIG. 3e, the sacrificial layer 377 is removed. In one embodiment, the sacrificial layer is removed by dissolving the layer with chemicals. For example, chemical which preferably does not cause any damage to the second or active surface of the dies is used to remove the sacrificial layer. Other techniques may also be used to remove the sacrificial layer. The removal of the sacrificial layer exposes the active or second surface of the dies and the die contact pads 355.
In one embodiment, the second surface 390b of the cap is non-coplanar with the active surface 350b of the dies. For example, the active surface of the die and the second surface of the cap form a step 387. In one embodiment, the active surface of the dies is recessed below the surface of the cap. The height of the step, for example, may be about the thickness of the sacrificial layer. Other step heights may also be useful.
Providing a step between the active surface of the dies and cap surface alleviates mechanical stress due to the difference between the thermal coefficient of the die and the mold compound in the subsequently formed packages.
The process continues to form a package substrate. The process, for example, continues to form a built-up or integrated wiring substrate. The package substrate, for example, includes a multi-layered substrate. In one embodiment, a first insulating substrate layer 313 is provided on the second surface of the cap and active surface of the dies. For example, a first surface 313a of the first substrate layer contacts the second surface of the cap and fills the recesses over the dies.
In one embodiment, the first substrate layer may be a dielectric layer. The dielectric layer, for example, is disposed on the active surface of the die. Other types of first substrate layers may also be useful. The dielectric materials may be deposited via suitable techniques such as wafer processing technologies, spin coating, printing, etc. Other techniques for depositing the first substrate layer may also be useful.
Vias 315 are formed in the first substrate layer. The vias extend from a second surface 313b through the first surface 313a to expose the die contact pads of the dies. In one embodiment, the vias are formed by laser drilling. Other techniques, such as mechanical drilling or RIE, are also useful. The vias may have tapered or straight profiles, depending on process requirements and type of via formation method used. In one embodiment, the vias are formed with a tapered profile. Tapering of the sidewalls facilitates filling of the vias. For example, the tapered sidewall facilitates uniform material coverage of the sidewalls and base of the via which reduces formation of voids. Providing vias with a non-tapered sidewall profile is also useful.
Referring to FIG. 3f, the process continues to form conductive via contacts 330 and traces 340 of the package substrate. In one embodiment, a conductive layer is formed on the first substrate layer, covering the second surface thereof and filling the vias. The conductive layer, for example, may be copper or a copper alloy. Other types of conductive materials may also be useful. For example, other types of conductive materials may include aluminum, gold, nickel or a combination or an alloy thereof. The conductive layer may be formed by plating. For example, electrochemical or electroless plating may be employed to form the conductive layer. Other suitable methods of forming the conductive layer may also be used. In some embodiments, seed layers may be used prior to forming the conductive layer.
The patterning of the conductive layer may be formed with the help of a patterned masked layer prior to the plating process. Alternatively, the conductive layer may be patterned to form conductive traces 340 coupled to the substrate via contacts 330 in the vias which are coupled to the die pads of the same die. The conductive traces and the via contacts form interconnect. Patterning of the conductive layer can be achieved by any suitable etching techniques. For example, a patterned etch mask, such as photoresist, is provided over the conductive. An etch may be performed using the etch mask to remove portions of the conductive layer unprotected by the etch mask. The etch, for example, may be an isotropic etch, such as a wet etch. An anisotropic etch, such as reactive ion etch (RIE) may be used. Other techniques for patterning the conductive layer may also be useful.
After patterning the conductive layer, the mask is removed. The mask, for example, may be removed by ashing. Other techniques for removing the mask may also be useful.
As shown in FIG. 3g, a second insulating substrate layer 317 is deposited on the first substrate layer, covering and filling the spaces between conductive traces. The second substrate layer provides insulation between conductive traces. A first surface 317a of the second substrate layer contacts the first substrate layer. The second substrate layer serves as a contact mask. In one embodiment, the second substrate is formed of a polymer. The second substrate layer, for example, may be formed by spin-coating. Other types of dielectric materials and deposition techniques may also be useful for forming the second substrate layer.
The second substrate layer is patterned to form contact openings 319 to expose portions of the conductive traces. The contact openings correspond to locations of package contacts of the semiconductor package. For example, the contact openings may be arranged in a grid pattern to form a BGA type package. Other contact opening patterns may also be useful.
In one embodiment, package or conductive pads 368 are formed on the exposed portions of the conductive traces 340, as shown in FIG. 3h. In one embodiment, the package pads include a conductive material. In one embodiment, the package pads are selectively formed in the openings of the dielectric layer by coating or plating techniques. Other types of conductive materials or techniques may be used to form the contact pads. The conductive pads, for example, are coplanar with the conductive traces. In other embodiments, the conductive pads may include protruding conductive pads. The conductive pads may be further covered with a surface protection material, such as OSP or a metallic coating or plating.
The process continues by forming package contacts 370 in the openings of the package mask, as shown in FIG. 3i. For example, the package contacts are formed on the package pads 368 in the openings of the package mask. The package contacts, for example, may include spherical shaped structures or balls arranged in grid pattern to form a BGA type package. The package contacts are formed of a conductive material. The package contacts, for example, can be formed from solder. Various types of solder can be used to form the package contacts. For example, the solder can be a lead-based or non lead-based solder.
In some embodiments, other types of package contacts are formed in the openings. For example, the package contacts may include contacts which do not protrude from the bottom surface of the second substrate layer. Providing package contacts which do not protrude from the bottom surface of the second substrate layer, such as solder lands, may also be useful. The package contacts may be formed of materials other than solder or using other techniques.
Referring to FIG. 3j, the structure formed is singulated to form individual semiconductor packages, as indicated by dotted lines 395. As such, a semiconductor package such as that shown in FIG. 3k or FIG. 1a is formed.
The process, as described, results in advantages. For example, the sacrificial layer is used to protect the second major surface or active surface of the die from contamination during molding. Furthermore, the sacrificial layer serves as a temporary coating which is removed after molding such that a recess is created over the second surface of the die to alleviate mechanical stress arising from the thermal mismatch between the mold compound and the die. Also, the process allows various molding techniques such as printing, transfer and compression molding to be used to form the cap. The process also reduces processing steps and time since the first major surfaces of the dies are exposed upon removal of the base carrier. Additionally, the exposed first major surfaces of the die improve thermal dissipation.
Although only one conductive via and trace level is formed and coupled to the die pads of the same die in the package substrate, it is understood that additional conductive via and trace levels may be included. For example, the first substrate layer may include a plurality of first sub-layers. The process therefore enables multiple wiring structures to be built up in the package substrate as compared to existing wafer based fan-out processes that are limited to only a single metal layer fan-out structures. Furthermore, since the cap serves as a mechanical support for the dies to form package substrate thereon and the resultant structure is in the form of a panel or strip, substrate processes may be used to form the redistribution structures on the active surfaces of the dies. As such, conventional wafer redistribution layers forming processes are not necessarily required. This avoids the need for capital investment in new wafer-based process equipment.
FIGS. 4a-d show another embodiment of a process 400 for forming a semiconductor package. The process is similar to that described in FIGS. 3a-k. As such, common elements may not be described or described in detail.
Referring to FIG. 4a, a wafer 301 having a plurality of dies or chips, similar to the one described with respect to FIG. 3a, is provided. The wafer includes a first surface 301a and a second surface 301b. The second surface, for example, is an active surface 350b for the dies. The second surface of the wafer is coated with a sacrificial layer 377, covering the wafer and contact openings which expose the die pads 355. The wafer is diced, providing individual dies with a sacrificial layer on the active surface.
Referring to FIG. 4b, a support carrier 380 having an adhesive 375 on a first surface of the support carrier. The carrier, for example, includes a plurality package regions 380a-d. Individual dies are temporarily attached to the die regions on the carrier. In one embodiment, the surface 350b of the dies with the sacrificial layer 377 is attached to and contacts the die regions of the carrier. The dies are attached to the die regions using any suitable techniques according to the equipment and the type of the adhesive used.
Referring to FIG. 4c, a cap 390 is formed to encapsulate the dies. The cap, in one embodiment, is disposed in the non-die region. For example, an encapsulation material is dispensed to fill the spaces between the dies. In one embodiment, the encapsulation is a mold compound, such as molding epoxy resin material. Providing other types of encapsulation materials may also be useful.
The cap, in one embodiment, is formed by transfer molding techniques. In one embodiment, the cap is formed by a film assisted transfer molding technique. For example, a film 393 is placed against contours of a mold (not shown). In one embodiment, when the carrier and the dies are placed against the mold, the film contacts the backsides or first surfaces 350a of the dies, leaving spaces therebetween the non-die regions. Encapsulation material, such as a mold compound, is dispensed into the mold assembly, filling spaces in the non-die regions to form the cap. Other types of techniques for forming the cap may also be useful. For example, the cap may be formed by printing or compression molding.
Referring to FIG. 4d, the support carrier and the adhesive 375 are separated from the dies after forming the cap. Removal of the carrier and adhesive leaves the plurality of dies attached to each other by the cap. The cap provides mechanical support for the chips for further processing. The surfaces of the cap, in one embodiment, are coplanar with the surfaces of the dies. For example, a first surface 390a of the cap is coplanar with the first or backside of the dies and a second surface 390b is coplanar with the sacrificial layer 377 on the second or active surface of the dies. The process continues, for example, as described in FIG. 3e and onwards.
FIGS. 5a-b show yet another embodiment of a process 500 for forming a semiconductor package 500. The process is similar to that described in FIGS. 3a-k and 4a-d. As such, common elements may not be described or described in detail. Referring to FIG. 5a, the process is at a similar stage as that described in FIG. 4b. For example, a support carrier 380 having an adhesive 375 on a first surface of the support carrier is provided with dies 350 temporarily attached to the die regions on the carrier. As shown, the surface 350b of the dies with the sacrificial layer 377 is attached to and contacts the die regions of the carrier.
Referring to FIG. 5b, the process continues to form a cap 590. In one embodiment, the cap is formed of an encapsulation material. In one embodiment, the encapsulation is a mold compound, such as molding epoxy resin material. Providing other types of encapsulation materials may also be useful. The cap may be formed by various molding techniques. For example, the cap may be formed by compression or transfer molding. Other techniques may also be useful to form the cap. In one embodiment, the cap 590 encapsulates the dies. As shown in FIG. 5b, the cap covers the first surfaces 350a and sides of the dies.
After forming the cap, the process continues, as similarly described in FIG. 3d and onwards. For example, the process forms a package as described in FIG. 1b. 
FIGS. 6a-e show another embodiment of a process for forming a semiconductor package 600. The process is similar to that described in FIGS. 3a-k, 4a-d and 5a-b. As such, common elements may not be described or described in detail. Referring to FIG. 6a, a wafer 601 having a die stack arrangement is provided. In one embodiment, the wafer is processed to include a plurality of die stacks 610.
A die stack includes n number of dies, where n is ≧2. The bottom die, for example, may be referred to as the first (e.g., n=1) and the top die is equal to n. Designating the dies of the die stacks using other conventions may also be useful. The die stack, for example, may be formed by any suitable types of die stacking methods. As shown, the die stack includes first and second dies 6501 and 6502. The second die 6502 is attached onto the first die 6501, and the first die is attached to the die region of a wiring substrate. Dies used for the die stack may be TSV or non-TSV dies. In one embodiment, both the top and bottom dies may be TSV dies. In yet another embodiment, the bottom die may include a TSV die and top die may include a non-TSV die. Non-TSV die, for example, may include wire bonded, direct connection, flip chip die, etc. For die stacks having more than 2 dies, the lower dies (bottom and intermediate dies except the top die) are usually TSV dies while the top die may be a non-TSV die. Other configurations or types of dies of a die stack may also be useful.
A TSV die includes first and second major surfaces 650a-b. The first surface includes first die contacts 633 and the second major surface includes second die contacts 635. The die contacts, for example, are die contact pads which have top surfaces co-planar with the first and second major surfaces of the TSV die. Providing surfaces of the contact pads which are not co-planar with the surfaces of the die may also be useful. Other configurations of die contacts or die contact pads may also be useful. The first and second die contacts are interconnected by through via contacts 630. Other configurations of TSV dies may also be useful. The via contacts and the contact pads, for example, are formed of a conductive material. The conductive material, for example, may include copper. Other types of conductive material may also be used for the via contacts and contact pads.
As shown in FIG. 6a, the first die contacts 633 are mated with the second die of the die stack. In one embodiment, a die attach film or an underfill 617 can be provided in the cavity formed between the dies to facilitate stacking and to protect bonding contacts 640 which couple the conductive die pads 355 of the second die with the first die contacts 633 of the first die. For the case where more than two dies are used to form the die stack, the bottom and intermediate dies may be TSV dies. Other types of dies may also be used for the bottom and intermediate dies. The second die contacts of the nth+1 die above is connected to the first die contacts of the nth die below.
In one embodiment, a sacrificial layer 377 is formed over the second major surface 650b of the first die 6501 of the die stack or the wafer 601.
The process continues by dicing the wafer processed with the die stacks and sacrificial layer over the second surface of the wafer. Dicing the wafer separates the die stack into individual die stacks 6101-3. Although three die stacks are shown in FIG. 6b, it is understood that other number of die stacks may also be provided with the sacrificial layer over the second surface 650b. In another embodiment, the sacrificial layer 377 may be provided after dicing the wafer into individual die stacks.
Referring to FIG. 6b, the process is at a similar stage as that described in FIG. 4b and FIG. 5a. For example, a support carrier 380 having an adhesive on a first surface of the support carrier is provided with the die stacks 6101-3 temporarily attached to the die regions on the carrier. As shown, the surface 650b of the die stacks with the sacrificial layer 377 is attached to and contacts the die regions having the adhesive 375 of the carrier 380.
Referring to FIG. 6c, the process continues to form a cap 590. In one embodiment, the cap is formed of an encapsulation material. The encapsulation, for example, is a mold compound. Providing other types of encapsulation materials may also be useful. The cap may be formed by various molding techniques. For example, the cap may be formed by compression molding for a wafer or transfer molding for strip or panel. Other techniques may also be useful to form the cap. In one embodiment, the cap 590 covers the sides and first or backside 350a of the die stacks as shown in FIG. 6c. 
After forming the cap, the process continues, as similarly described in FIG. 3d and onwards. For example, the support carrier and the adhesive 375 are separated from the die stacks by a de-bonding treatment after forming the cap as shown in FIG. 6d. Referring to FIG. 6e, the sacrificial layer 377 of the die stacks is removed. In one embodiment, the sacrificial layer is removed by dissolving the layer with chemicals, which preferably do not cause any damage to the surface 650b of the first dies of the die stacks. Other techniques for removing the sacrificial layer may also be used. The removal of the sacrificial layer exposes the second surface 650b and the second die contact 635 of the first dies of the die stacks. In addition, the second surface 650b of the first die of the die stack is recessed into the encapsulation material with respect to the first surface 590a of the cap, forming a step 387 as shown in FIG. 6e. The process continues, for example, as described in FIG. 3e and onwards. For example, the process continues to form a semiconductor package as described in FIG. 2.
FIG. 7 shows another embodiment of a method for forming a semiconductor package 700. Referring to FIG. 7, the process is at a similar stage as that described in FIG. 6b. As such, common elements may not be described or described in detail.
A cap 390 is formed to encapsulate the die stacks. The cap, for example, is disposed in the non-die region of the support carrier. The cap, in one embodiment, is formed by transfer molding technique. In one embodiment, the cap is formed by a film assisted transfer molding technique, similar to that described in FIG. 4c. For example, a film 393 is placed against contours of a mold (not shown). In one embodiment, when the carrier and the die stacks are placed against the mold, the film contacts the backside or first surface 350a of the second dies of the die stacks, leaving spaces therebetween in the non-die regions. Encapsulant material, such as a mold compound, is dispensed into the mold assembly, filling spaces in the non-die regions to form the cap. This enables top surface 390a of the cap to be coplanar with first surfaces 350a of first dies of the die stacks. For example, a first surface 390a of the cap is coplanar with the first or backsides of the first dies of the die stacks and a second surface 390b of the cap is coplanar with the sacrificial layer 377 on the second surface 650b of the first die of the die stacks. This allows a semiconductor package with exposed backsides of the die stacks to be formed later. The process continues, for example, as described in FIG. 4d and onwards.
FIG. 8a-b show another embodiment of a method for forming a semiconductor package 800. Referring to FIG. 8a, the process is at a similar stage as that described in FIG. 6b, except that the backsides or first surfaces 350a of the second dies of the die stacks are attached to and contact the die regions having the adhesive 375 of the carrier 380. As such, common elements may not be described or described in detail.
A cap 390 is formed to encapsulate the die stacks as shown in FIG. 8b. The cap, in one embodiment, is formed by transfer molding technique. In one embodiment, the cap is formed by a film assisted transfer molding technique, similar to that described in FIG. 3c. For example, a film 393 is placed against contours of a mold (not shown). In one embodiment, when the carrier and the die stacks are placed against the mold, the film contacts the sacrificial layers 377 over the second surfaces 650b of the first dies of the die stacks, leaving spaces therebetween in the non-die regions. Encapsulant material, such as a mold compound, is dispensed into the mold assembly, filling spaces in the non-die regions to form the cap. This enables first surface 390a of the cap to be coplanar with first surfaces 350a of the second dies of the die stacks, allowing a semiconductor package with exposed backside of the die stacks to be formed later. The process continues, for example, as described in FIG. 3d and onwards to complete the package.
The embodiments described with respect to FIGS. 4a-d, FIGS. 5a-b, FIGS. 6a-e, FIG. 7 and FIGS. 8a-b include some or all advantages as described with respect to FIG. 3a-k. As such, these advantages will not be described or described in detail.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments, therefore, are to be considered in all respects illustrative rather than limiting the invention described herein.

## Claims

1. A semiconductor package comprising:
at least one die stack having first and second surfaces, the second surface of the die stack includes a plurality of conductive die pads;
an integrated package substrate having first and second major surfaces, wherein the package substrate includes a first patterned substrate layer comprising
first and second major surfaces, the first major surface of the package substrate includes a die attach region and a non-die attach region, the die attach and non-die attach regions are defined by the first major surface of the same first patterned substrate layer, wherein the die attach region is disposed in a different plane than the non-die attach region and the second surface of the die stack directly contacts the first major surface of the first patterned substrate layer in the die attach region, and
substrate via contacts disposed therein, wherein a top surface of the via contacts is coplanar with the first major surface of the package substrate, the via contacts are directly coupled to and contact the die pads; and

a cap having first and second surfaces to encapsulate the at least one die stack, wherein the second surface of the cap is disposed at a different plane than the second surface of the die stack, such that a cavity is enclosed by the second surface of the die stack and sidewalls of the cap in between the die attach and non-die attach regions, wherein the substrate via contacts are disposed within the cavity and extend from a plane below the second surface of the die stack to the second major surface of the first patterned substrate layer, and wherein the first surface of the cap is substantially coplanar with the first surface of the die stack which is opposite the second surface of the die stack such that the first surface of the die stack is exposed and not covered by the cap.

2. The semiconductor package of claim 1 wherein:
the first patterned substrate layer comprises conductive traces disposed over the second major surface of the first patterned substrate layer; and
the package substrate further comprises a second substrate layer disposed on the first patterned substrate layer and conductive traces, the second substrate layer isolates the conductive traces.

3. The semiconductor package of claim 2 wherein the second substrate layer comprises openings to expose the conductive traces.

4. The semiconductor package of claim 1 wherein the die stack comprises n dies, each having first die contacts on a first surface and second die contacts on a second surface, wherein the second die contacts of the nth+1 die above is interconnected to the first die contacts of the nth die below by through via contacts.

5. The semiconductor package of claim 4 wherein the top die of the die stack comprises a non-TSV die.

6. The semiconductor package of claim 1 wherein the die stack comprises at least a first die and a second die, a second surface of the first die forms the second surface of the die stack.

7. The semiconductor package of claim 1 wherein
the substrate via contacts which are directly coupled to and contacts the conductive die pads comprise the same material.

8. The semiconductor package of claim 1 wherein the first patterned substrate layer comprises conductive traces disposed over the second major surface of the first patterned substrate layer and wherein the conductive traces and the substrate via contacts are single unitary interconnect structures having no seams therebetween.

9. The semiconductor package of claim 8 wherein the die attach region is recessed into the cap with respect to the first surface of the cap.

10. The semiconductor package of claim 6 wherein the conductive die pads of the first die are substantially coplanar with the second surface of the first die.

11. The semiconductor package of claim 4 wherein the first patterned substrate layer comprises conductive traces disposed over the second major surface of the first patterned substrate layer.

12. The semiconductor package of claim 11 wherein the package substrate further comprises a second substrate layer disposed on the first patterned substrate layer and conductive traces, the second substrate layer isolates the conductive traces.

13. The semiconductor package of claim 12 wherein the second substrate layer comprises openings to expose the conductive traces.

14. The semiconductor package of claim 13 comprising package contacts disposed in the openings of the second substrate layer.

15. The semiconductor package of claim 11 wherein the conductive traces and the substrate via contacts are single unitary interconnect structures having no seams therebetween.

16. The semiconductor package of claim 11 wherein the conductive traces and the substrate via contacts comprise the same material.

17. The semiconductor package of claim 5 wherein the non-TSV die comprises wire bonded, direct connection or flip chip die.

18. The semiconductor package of claim 5 wherein the first patterned substrate layer comprises conductive traces disposed over the second major surface of the first patterned substrate layer.

19. The semiconductor package of claim 18 wherein the package substrate further comprises a second substrate layer disposed on the first patterned substrate layer and conductive traces, the second substrate layer isolates the conductive traces.

20. The semiconductor package of claim 18 wherein the conductive traces and the substrate via contacts are single unitary interconnect structures having no seams therebetween.