Patent Application
20210193522
The present invention generally relates to a semiconductor package. More specifically, the present invention is directed to a semiconductor package being free of metal debris.
The recent rapid dissemination of smartphones and other mobile and wearable electronic terminals reflects the demand for faster and smaller products. The growing demand for faster and smaller products concomitantly requires semiconductor packages to have smaller footprints. With Wafer Level Chip Scale Package (WLCSP), semiconductor packages have the smallest possible package footprint and superior electrical and thermal performance. WLCSP refers to the technology of packaging an integrated circuit (IC) at the wafer level, instead of the traditional process of assembling individual units in packages after dicing them from a wafer. After the wafer level packaging of ICs is completed, a singulation process is conducted to separate the wafer to individual semiconductor packages.
A wafer may include backside metallization (BSM). For example, a metal stack may be formed on the backside of the wafer. BSM is employed to meet power, speed, reliability as well as improved circuit performance. BSM enables the semiconductor package to be optimized for electrical, mechanical, and thermal requirements. For example, the wafer with dies may be thinned to improve circuit performance. The BSM improves the mechanical strength of the thinned wafer and thermal dissipation.
However, one problem with conventional singulation process of a wafer with BSM is that metal debris from the BSM remains on the packages. The debris can cause failures such as poor reliability due to short circuiting when the package is being used.
From the foregoing discussion, there is a desire to provide a package free of debris for a reliable and functional product.
Embodiments of the present disclosure generally relate to semiconductor packages.
An embodiment related to a method of forming a device is disclosed. The method includes providing a wafer with a front surface and a back surface, the front surface including a plurality of dies, wherein the wafer includes defined saw streets in first and second orthogonal directions between rows and columns of dies. Saw street openings are formed on the front surface of the wafer on the saw streets. Backside metallization (BSM) is formed over the back surface of the wafer. The method further includes etching the wafer from the back surface of the wafer to completely singulate the dies, wherein singulating the wafer into dies avoids metal debris on sides of the dies.
Another embodiment related to a semiconductor package is disclosed. The semiconductor package includes a substrate with a first surface, a second surface and sidewalls. The package also includes backside metallization (BSM) over the second surface of the substrate. A sidewall profile of the semiconductor package includes an etched surface with a first edge and a second edge. The first edge of the etched surface is located within the second surface of the substrate.
In yet another embodiment, a semiconductor package disclosed herein includes a die with a front die surface, a back die surface, and side die surfaces, wherein an upper portion of the die includes a second passivation layer over a first passivation layer, a top surface of the second passivation layer serves as the front die surface and a top package surface. The package also includes backside metallization (BSM) on the back die surface, wherein a bottom BSM surface which opposes a top BSM surface on the back die surface serves as the bottom package surface. A package side profile of the semiconductor package comprises an upper side package profile portion defined by vertical sidewalls of the second passivation layer, an intermediate side package profile portion defined by the first passivation layer and die portion of the die below the first passivation layer, wherein the intermediate side package profile portion is slanted and includes plasma etched intermediate side package profile surfaces, the upper side package profile portion is recessed from the intermediate side package profile portion, and a lower side package profile portion defined by vertical sidewalls of the BSM, wherein the lower side package profile portion is aligned with the back die surface.
These and other advantages and features of the embodiments 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.
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:
Embodiments relate to semiconductor packages and methods for forming semiconductor packages. More particularly, embodiments relate to singulated semiconductor packages and methods for singulating semiconductor packages. In one embodiment, the semiconductor package includes a WLP, such as a WLCSP. A WLCSP may be formed by packaging semiconductor chips at wafer level followed by separation of individual chip packages from the wafer.
The semiconductor package, for example, may include one or more semiconductor dies or chips such as integrated circuits (ICs). The die in the WLCSP may include interconnects containing layers of metal traces and dielectric materials on one major surface of the die, such as the top or active surface. The die in the WLCSP may be electrically connected to an external circuit, such as a printed circuit board (PCB), by a plurality of solder balls extending between the interconnects and the external circuit.
In one embodiment, the WLCSP includes a BSM on a back or inactive surface of the wafer. The backside metallization may include a single layer of metal or a BSM stack having a plurality of metal layers. The backside metallization, for example, may include various types of metal layers, such as gold, silver, nickel, chromium, titanium, tungsten, vanadium, other metals and alloys thereof. The backside metallization, for example, may serve to improve mechanical strength and heat dissipation. Other types of packages may also be useful. Such packages may be incorporated into electronic products or equipment, including vehicles.
Referring to
A back-end-of-line (BEOL) dielectric with interconnects is formed over the active surface of the substrate. For example, the BEOL may cover the active components. The BEOL includes multiple metal or interconnect levels of metal lines and via contacts separated by dielectric material or layers for interconnecting the circuit components. The top interconnect level may serve as the pad level with contact pads for providing external connections.
A passivation stack may be provided over the BEOL dielectric. The passivation stack, for example, may include a combination of dielectric layers, such as silicon oxide and silicon nitride layers. Other types of dielectric layers may also be useful. As shown, the dielectric stack includes first and second passivation layers 140 and 150. The first passivation layer may be the bottom passivation layer on the BEOL and the second passivation layer may be the top passivation layer. The first passivation layer 140 may be about 2 μm thick. The second passivation layer 150 may be about 5 μm thick. Providing a passivation stack with other numbers of passivation layers or thicknesses may also be useful. Pad openings are formed in the passivation stack to expose die contact pads on the top interconnect level for external die connections. The passivation stack, for example, may serve as a protective stack, protecting the die from moisture and corrosion.
In one embodiment, the bottom or inactive surface of the die 110 includes a BSM 160. The BSM may include a single layer of metal or a metal stack having a plurality of metal layers. The BSM may include, for example, gold, silver, chromium, titanium, tungsten, vanadium, nickel, other metals and alloys thereof. The BSM may be formed by chemical vapor deposition, sputter deposition, e-beam evaporation or plating. Other techniques may also be useful.
As shown, the BSM includes first and second metal layers 120 and 130. The first metal layer 120 is disposed on the inactive surface of the wafer and the second metal layer 130 is disposed on the first metal layer 120. The first metal layer is a silver layer, while the second metal layer is a nickel layer. The first metal layer may be about 50 μm while the second metal layer may be about 30 μm thick. Other numbers, types, thicknesses or configurations of metal layers of the BSM may also be useful.
The top surface of the passivation stack may be referred to as the top or active package surface 151 and the bottom surface of the BSM may be referred to as the bottom or inactive package surface. In one embodiment, the dicing streets are defined using laser etching from the frontside of the wafer. Laser etching, for example, employs a protective coating. As for the final singulation, it is performed using plasma etching from the backside of the wafer. For example, a dry etch may be employed. Other types or configurations of the singulation process may also be useful.
A sidewall profile of an embodiment of a packaged die 200 is shown. The sidewall profile may include vertical and slanted portions. As shown, the sidewall profiles of the four sides of the die package are the same or about the same. Slight variations or differences may occur due to process variations.
As shown, a sidewall profile of a side of the package includes a top portion 178 with a vertical or substantially vertical sidewall, an intermediate portion 174 with a slanted sidewall, and a bottom portion 170 with a vertical or substantially vertical sidewall. As shown, the top portion is recessed from the intermediate portion and the intermediate portion slants inwardly from the bottom portion or outwardly from the top portion.
In one embodiment, the top portion 178 of the sidewall profile is created with an open process. The open process, in one embodiment, is performed on the second or top passivation layer 150. The open process, for example, may be a reactive-ion etching (RIE) using a photoresist mask. The RIE patterns the top passivation layer to form openings along the x and y dicing streets of the wafer. The RIE forms trenches at the dicing street in the second passivation layer. The RIE stops at the first or bottom passivation layer 140. For example, the first passivation layer may serve as an etch stop for the RIE. The RIE forms trenches with vertical or substantially vertical sidewalls 155 in the top passivation layer. In the case of multiple top passivation layers, the RIE may etch the top passivation layers, forming a vertical or substantially vertical sidewall profile. The vertical or substantially vertical sidewalls of the second passivation layers serve as the top portion of the sidewall profiles.
The bottom portion 170 of the sidewall profile is generated by the formation of BSM 160. For example, the BSM is formed by a plating process, such as electroplating. The plating process is performed selectively on a seed layer (not shown) over the inactive die surface 132. The seed layer may be deposited by sputtering or evaporating. Other techniques may also be useful. The seed layer may be patterned or selectively exposed in regions with the BSM to be formed. For example, an etch using a mask may be performed to remove the seed layer from the saw street region or having the saw street region covered by a plating mask, such as a resist layer. The BSM is formed on exposed portions of the seed layer.
In one embodiment, the plating process forms the first and second metal layers 120 and 130 on the seed layer over the inactive die surface 132. The plating process forms the first and second metal layers with vertical or substantially vertical sidewalls 125 and 135. The first metal layer sidewall 125 and the second metal layer sidewall 135 serve as the bottom portion 170 of the sidewall profile. Due to selective deposition of the BSM, the sidewalls of the BSM are unetched surfaces.
As for the intermediate portion 174, it is created by a cutting or dicing process. In one embodiment, the dicing process cuts the wafer and the first passivation layer 140 to singulate the die packages. The dicing process is performed from the wafer backside. In one embodiment, the dicing process is performed using a dry etch, such as a Bosch Process. The dry etch employs the selectively formed BSM as an etch mask. The dry etch creates a slanted profile in the die and first passivation layer sidewalls, for example, due to an overetch to ensure complete separation.
In one embodiment, a grooving process is performed after the open process. The grooving process, for example, may be a laser grooving process, such as laser etching. After the open process, a laser etching protective layer is formed over the wafer. In one embodiment, the laser etches the protective layer, first passivation layer 140 and an interface portion of the wafer with the BEOL dielectric. The wafer with the BEOL dielectric may be collectively referred to as the wafer.
The grooving process forms grooves along the x and y dicing streets within the trenches of the second passivation layer. The grooves, in one embodiment, include vertical or substantially vertical sidewalls. The grooves are narrower than the trench openings of the second passivation layer. This results in the sidewalls of the second passivation layer being recessed from the sidewalls of the first passivation layer and wafer. The laser etching protective layer is removed after the grooving process.
After the grooving process, the wafer is thinned, for example, by backside grinding. Other techniques for thinning the wafer is also useful. The BSM is then selectively formed on the backside of the thinned wafer. After forming the BSM, the wafer is diced by, for example, a dry etch. This results in slanted sidewalls in the intermediate portion of the die, as described.
Referring to
A passivation stack may be provided over the BEOL dielectrics. The passivation stack, for example, may include a combination of dielectric layers, such as silicon oxide and silicon nitride layers. Other types of dielectric layers may also be useful. As shown, the dielectric stack may include first and second passivation layers 140 and 150. The first passivation layer 140 may be the bottom passivation layer on the BEOL and the second passivation layer 150 may be the top passivation layer. The first passivation layer 140 may be about 2 μm thick. The second passivation layer 150 may be about 5 μm thick. Providing a passivation stack with other numbers of passivation layers may also be useful. The first passivation layer 140 may include a SiN layer, and the second passivation layer 150 may include a SiO2 layer. Other types of material or configurations for the passivation stack may also be useful. Pad openings (not shown) are formed in the passivation stack to expose die contact pads on the top interconnect level for external die connections. The passivation stack, for example, may serve as a protective stack, protecting the die from moisture.
In one embodiment, an open process is employed. In one embodiment, the open process patterns the second or top passivation layer 150. The open process forms openings or trenches 385 in the top passivation layer along the dicing streets of the wafer. The open process, for example, may be a chemical etch, such as RIE using a patterned resist mask as an etch mask (not shown). Portions of the top passivation layer exposed by the etch mask are removed. The etch selectively, removes the top passivation layer and stops at the first or bottom passivation layer 140. For example, the first passivation layer may serve as an etch stop for the open process. The RIE is an anisotropic etch, forming a patterned top passivation layer with vertical or substantially vertical sidewalls 155. It is understood that process variations may cause slight variances from vertical. The vertical sidewalls or substantially vertical of the top passivation layer serve as the top passivation portion 178 of the sidewall profiles of the singulated packages.
As shown in
The grooving process, for example, may be a laser grooving process, such as laser etching. In one embodiment, the laser etches through the protective layer 370, the first passivation layer 140 and an interface or upper portion of the wafer 110 with the first passivation layer to form grooves or trenches 390 in the dicing lines of the wafer. In other words, the grooving process overetches the first passivation layer to ensure it is completely removed. The grooving process results in the sidewall of the protective layer 370, sidewall 141 of the first passivation layer 140 and sidewall 111 of the upper portion of the wafer 110 being vertical or substantially vertical. In addition, a width of the groove 390 is less than the width of the trenches 385 of the second passivation layer 150 from the open process. This results in the top passivation layer being recessed from the sidewalls of the second passivation layer and the wafer.
After the grooving process, the protective layer 370 is removed, for example, by a clean process using deionized water. Other removal processes may also be useful. After the clean process, the semiconductor wafer 110 with the passivation layers is reversed and attached to a temporary carrier 165 with the second or top passivation layer abut against the top surface of the support carrier.
As shown in
Referring to
As shown, the BSM 160 includes first and second metal layers 120 and 130. The first metal layer is disposed on the inactive wafer surface and the second metal layer 130 is disposed on the first metal layer 120. In one embodiment, the first metal layer is a silver layer while the second metal layer is a nickel layer. The thickness of the first metal layer may be about 50 μm while the second metal layer may be about 30 μm thick. Other numbers, types, thicknesses or configurations of metal layers may also be useful. The metal layers may be formed by sputtering or electroplating. Other techniques may also be used to form the BSM.
In one embodiment, the BSM 160 is formed by selectively plating the first and second metal layers 120 and 130 on a seed layer (not shown) over the inactive die surface. The seed layer, for example, may be deposited by sputtering or evaporating. Other techniques, such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), may also be useful. The seed layer may be patterned for selective plating. For example, the seed layer may be patterned using mask and etch techniques. For example, an etch using a mask may be performed to remove the seed layer from the saw street region or having the saw street region covered by a plating mask, such as a resist layer. The BSM is formed on exposed portions of the seed layer. Other techniques for preparing the seed layer for selective plating may also be useful. The plating process selectively forms a patterned BSM with saw streets. In one embodiment, the plating process selectively forms a patterned BSM with saw streets using a resist plating mask. The plating mask is removed after forming the patterned BSM, exposing the saw streets.
As described, the patterned BSM is achieved without an etch process performed on the BSM. For example, the BSM includes unetched sidewalls. The sidewalls of the BSM may be vertical or substantially vertical. For example, the first metal layer sidewall 125 and second metal layer sidewall 135 may have vertical or substantially vertical sidewalls. The BSM sidewalls, such as the first metal layer sidewall 125 and the second metal layer sidewall 135, serve as the bottom portion 170 of the sidewall profile.
Referring to
After the dicing process, the packages are singulated. In one embodiment, the singulated dies may be reversed mounted on another carrier or tape 175 for further processing. For example, the back surface of the wafer is mounted onto another carrier or tape and the initial carrier wafer on the active surface is removed.
The present disclosure 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. Scope of the invention is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.
This application claims the benefit of U.S. Provisional Application Ser. No. 62/949,459, filed on Dec. 18, 2019, which is herein incorporated by reference in its entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 62949459 | Dec 2019 | US |
