This application claims priority to Taiwan Application No. 092114226, filed May 27, 2003.
(1) Field of the Invention
The invention relates to the manufacturing of high performance Integrated Circuit (IC's), and, more specifically, to a wafer structure and fabrication method to form both gold and solder bumps on the same wafer.
(2) Description of the Related Art
Integrated circuit (IC) packaging techniques must be able to accommodate the developing trends of electronic devices, including digitization, networking, localization, and user friendliness. In order to meet these requirements, electronic devices must be functional, highly integrated, miniaturized, lightweight, inexpensive, and high speed. There is a soaring demand for incorporating many more functions on one chip while still having few bonding pads to link the chip to other substrates. High-density IC packages such as ball grid arrays (BGA), chip scale packages (CSP), flip chips, and multi-chip modules (MCM) have been developed. For high-density IC packaging, the speed of signal transmission increases as the wiring length decreases. Thus, the application of bumps has become a major trend in high-density packaging.
Having solder bonding and wirebonding capabilities simultaneously on a same wafer is desirable for applications of chip-on-chip or chip-on-silicon-substrate assembly. Currently, solder bonding is provided by creating solder bumps on a subset of the bonding pads, while wirebonding is performed on the remainder of the original bonding pads; that is, on the aluminum surface. However, the process of creating solder bumps on the wafer will often damage the aluminum bonding pads, making it impossible to perform wirebonding on the original aluminum bonding pads.
In our invention, we create gold bumps or gold pads to protect the aluminum pads before performing the solder bumping process. The gold bumps or gold pads can be used for the wirebonding or TAB (Tape-Automated-Bonding). Having both solder bumps and gold bumps placed on one wafer enables the possibility of chip-on-chip or chip-on-silicon-substrate packages. A process to form both solder bumps and gold bumps on the same wafer will allow a large chip to be solder bonded face-to-face with one or several smaller chips and later wirebonded or TAB (Tape-Automated-Bonding) to the next layer of an assembly (for example, organic, ceramic or glass substrate).
U.S. Pat. No. 6,492,692 to Ishii et al describes solder and gold bumps together, but gives no details about how these two types of bumps are to be formed on a same wafer. A barrier metal layer of TiW and Au is disclosed for gold bumps. U.S. Pat. No. 6,228,689 (Liu), U.S. Pat. No. 5,655,639 (Seppala et al), and U.S. Pat. No. 5,532,612 (Liang) teach diffusion/barrier layers of TiW and Au under gold bumps. The last patent teaches that formation of solder and gold bumps differs in many details. U.S. Pat. No. 6,383,916 to Lin et al, assigned to the same assignee as the present invention, adds, in a post passivation processing sequence, a thick layer of dielectric over a layer of passivation and layers of wide and thick metal lines on top of the thick layer of dielectric.
It is the primary objective of the invention to provide a chip structure and a manufacturing method thereof wherein a wire bonding (or TAB bonding) pad and a solder pad are concurrently fabricated on a same wafer.
Another-objective of the invention is to provide a wafer structure having both a wire (or TAB) bonding pad and a solder pad thereon.
Yet another objective of the invention is to provide a connection structure of a chip and an external circuit wherein a bonding wire (or TAB lead) connects a wire (or a TAB) bonding pad to a circuit board or next level of assembly and a solder bump connects a solder pad on the same chip to other chips.
A further objective of the invention is to provide a chip structure having a post-passivation interconnection scheme wherein wire (or TAB) bonding pads are formed of the same material as the post-passivation interconnection lines.
A still further objective of the invention to provide a method of fabricating both wire (or TAB) bonding pads and solder pads on a same wafer.
According to the objectives of the invention, a chip structure having both wire (or TAB) bonding pads and solder pads thereon is achieved. The chip structure comprises a substrate comprising a plurality of bonding pads and a passivation layer overlying the bonding pads wherein the passivation layer comprises a plurality of openings through which are exposed the bonding pads. A plurality of wire bonding (or TAB) pads comprising gold are disposed on a first subset of the plurality of bonding pads exposed through the openings and a plurality of solder pads are disposed on a second subset of the plurality of bonding pads not covered by the wire (or TAB) bonding pads.
Also according to the objectives of the invention, a connection between a chip structure and an external circuit are achieved. The chip structure comprises a substrate comprising a plurality of bonding pads and a passivation layer overlying the bonding pads wherein the passivation layer comprises a plurality of openings through which the bonding pads are exposed. A plurality of wire (or TAB) bonding pads comprising gold are disposed on a first subset of the plurality of bonding pads exposed through the openings. A plurality of bond wires (or TAB leads) electrically connect between the wire (or TAB) bonding pads and the external circuit. A plurality of solder pads are disposed on a second subset of the plurality of bonding pads not covered by the wire (or TAB) bonding pads. A plurality of solders are disposed on the solder pads to electrically connect to the external circuit.
Also in accordance with the objectives of the invention, a fabrication process for forming a chip structure having wire (or TAB) bonding pads and solder pads on the same wafer is achieved. A substrate is provided comprising a plurality of bonding pads and a passivation layer overlying the bonding pads wherein the passivation layer comprises a plurality of openings through which the bonding pads are exposed. A plurality of wire (or TAB) bonding pads are formed, disposed on a first subset of the plurality of bonding pads exposed through the openings. A plurality of solder pads are formed, disposed on a second subset of the plurality of bonding pads not covered by the wire (or TAB) bonding pads. Then, the substrate is diced to form a plurality of chips.
Referring now more specifically to
A plurality of bonding pads 20 and 21 are provided in a top layer on the wafer as shown. The bonding pads can be made of copper, aluminum, an aluminum alloy, and so on, and have a thickness from about 0.1 to 3 microns. The bonding pads can be used for inputting/outputting of signal and power sources and for interconnection to other devices in a package.
A passivation layer 22, formed of, for example, a single or a composite layer of silicon oxide, silicon nitride, and silicon oxynitride, is provided over the surface of the wafer and over the bonding pads 20 and 21 and functions to prevent the penetration of mobile ions (such as sodium ions), moisture, transition metal (such as gold, copper, silver), and other contamination. The passivation layer is used to protect the underlying devices and metal interconnecting lines. A plurality of openings 23 in the passivation layer expose the surface of the bonding pads 20 and 21.
Referring now to
Now, a mask layer 30 is formed over the seed layer 26, as shown in
Referring now to
Referring now to
Now, a second adhesion layer 38 is formed over the surface of the wafer as shown in
Now, a mask layer 45 is formed over the wafer having openings 46 to expose the seed layer 40 over the bonding pads 21 that are not covered by wire (or TAB) bonding pads 34/24, as shown in
Now, solder bumps are to be formed as illustrated in
Furthermore, a solder wettable layer 50 may be formed on the UBM layer 48 to increase bonding ability between the subsequently formed solder and the UBM layer 48. For example, the solder wettable layer 50 comprises gold, copper, tin, a tin-lead alloy, or an unleaded solder. The solder wettable layer 50 may have a thickness of between about 500 and 10,000 Angstroms.
Now, solder 52 is formed on the solder wettable layer 50. The solder 52 may be tin, a tin-lead alloy, a tin-silver alloy, or a tin-silver-copper alloy, or any other unleaded solder material.
For example, solder 52 can be electroplated into the openings 46. Alternatively, in a printing method, a solder paste is pushed into the openings 46. Referring to
The solder 52 is reflowed to form the solder bump 54 shown in
After completion of wafer fabrication, the wafer can be diced into a plurality of chips. After dicing, a chip typically includes a substrate comprising a plurality of electronic devices, covered by a passivation layer. Connections to external circuitry positioned over another substrate are made after dicing. The connection to external circuits are achieved through wire bonding or TAB bonding on the gold bumps, and through solder bonding on the solder bumps.
For example, refer to
In another aspect of the invention, a redistribution layer may be formed on the wafer. With the redistribution layer, the original positions of the bonding pads can be redistributed to specific positions. The redistribution layer may be formed of the same material as the gold bumps and may be formed by the same process, as shown in
In another aspect of the invention, a post-passivation metal interconnect structure can be fabricated on the passivation layer, as shown in
The post-passivation layer metal interconnect structure 76 connects one circuit to another circuit under the passivation layer 22 through openings in the passivation layer 22, as shown. For example, the post passivation layer metal interconnect structure 76 and the gold pads 26 are formed of the same type of material and may be formed by the same process. The openings in the passivation layer 22 can be, for example, greater than 0.1 micron in width. In
The post passivation metal interconnect structure 76 may be a circuit that includes power bus, signal bus, and ground bus connected to power lines, signal lines, and ground lines under the passivation layer 22 through the openings in the passivation layer 22.
Active devices, passive devices, and/or metal interconnects may underlie the bonding pads connected to the gold bumps or gold pads.
In an alternative to the method of the present invention, gold bonding pads will be formed instead of gold bumps. This alternative is illustrated in
Now, as illustrated in
The solder bump 54 can now be fabricated as described above with reference to
In a second alternative to the present invention, an unreflowed solder 60 can be formed on the solder bonding pad 38/40/48/50 rather than forming the reflowed solder bump 54. This alternative will be presented with reference to
In another alternative illustrated in
The present invention permits modification of the wafer required by the packaging process.
A second preferred embodiment of the present invention will be described with reference to
In certain applications of IC design, it is not necessary to decide ahead of time which wire bonding pad is for wire bonding and which solder bonding pad is for soldering. The lifetime and area of application of the IC are expanded in this embodiment of the invention. For example, if an IC is originally designed for wiring, but is not used due to changes in packaging, the use of this IC will not be limited if the IC comprises the dual functional bonding pad of the invention.
The present invention has been described with respect to the structure and fabrication of a wafer. However, it will be understood by those skilled in the art that the invention is applicable to the wire bonding process or to the fabrication of solder conducted on a wafer structure to form a connection between the IC chip and an external circuit. The wire bonding pad and the solder pad are fabricated concurrently on the same wafer. Various chips on the wafer can be electrically connected with other chips, carriers, passive devices, and so on, through soldering or wire bonding. Furthermore, the gold bonding pads can be used as testing pads.
Although the preferred embodiment of the present invention has been illustrated, and that form has been described in detail, it will be readily understood by those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.
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