Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-02-22
2002-01-01
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C427S125000, C427S437000, C427S438000, C428S637000, C428S641000, C428S655000, C428S656000, C428S670000, C428S672000, C428S673000, C428S674000, C428S675000, C428S680000, C428S686000, C428S926000, C428S936000
Reexamination Certificate
active
06335104
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method for forming a conductive pad for electrical connection and pad formed and more particularly, relates to a method for forming a conductive copper pad surface for electrical connection to a wirebond or solder bump and conductive copper pad formed.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor devices, an integrated circuit (IC) chip may be assembled in a package in a final process step. The assembled package can then be connected to a printed circuit board as part of a large circuit. To establish electrical communication with the integrated circuit chip, a wire bonding process or a solder bumping process can be used to connect a multiplicity of bond pads on the IC chip to the outside circuitry.
In a typical IC chip, active circuit elements such as transistors, resistors, etc., are positioned in the central portion, i.e. the active region, of the chip while the bond pads are arranged around the periphery of the active region such that active circuit elements could not be damaged during a subsequent bonding process. When a wire bonding process is performed, the process entails the bonding of a gold or aluminum wire to a bond pad on the chip by fusing the two together with ultrasonic energy. The wire is then pulled away from the bond pad after the bond is formed. The wire pulling process frequently causes a defect known as bond pad lift-off. It occurs since during the process of attaching a gold wire to a bond pad, a high level of stress is placed on the bond pad, i.e. a relatively large, heavy bond is placed on layers which may have poor adhesion to the underlying layers.
For instance, one factor that affects adhesion between the layers is the common usage of a diffusion barrier layer formed of TiN for preventing aluminum diffusion into underlying conductive layers during subsequent high temperature processes. The diffusion barrier layer utilized, i.e. TiN, TiW or other suitable alloys, does not have a strong adhesion to the underlying oxide layer in the bond pad. This is one reason that leads to the bond pad lift-off defect. Other reasons such as the high bonding stress and the high pull force further contribute to the lift-off problem. Most lift-off problems occur at an interface between a sili conductive layer and an insulating (i.e. SiO
2
) layer. “In addition to the wirebond process by aluminum or gold wires to form electrical connections, the solder bump (a.k.a. “C4”) process has also been used for attaching a chip to a package for the transmission of electronic signals from the bond pads to the second level packaging or a circuit board. The solder bump process has been used more exclusively by IBM Corporation, while most of the IC industry has used the wirebond technology. In a conventional wirebond process, the bond pad on the chip surface is formed of aluminum which readily lends itself to the attachments of aluminum or gold wires by standard and highly automated tools. However, with the recent introduction of the copper technology where all the wiring of an IC chip back-end-of-line (BEOL) is copper wiring, both the solder bump and the aluminum or gold wirebond have been performed by direct processing on the copper bond pads, or by the addition of a suitable Al cap patterned on the Cu pad, with a suitable thin film barrier metal in-between the Al and Cu, to prevent their inter-diffusion (i.e. incorporated herein by reference, entitled “Robust Interconnect Structure”, filed May 19, 1999).”
A direct wirebond on copper pads cannot be easily performed, since a wirebond formed on pure copper by either aluminum or gold wires is subjected to corrosion, oxidation and thermal diffusion problems. A direct wirebond to copper pads is unreliable and subject to fail. The Al pad cap technique adds significant cost, as it adds a lithographic pattern (mask) and etch cycle, in addition to the depositions. It is therefore of great commercial significance to offer a maskless solution to wirebond of copper bond pads, i.e. bond pads on copper chips that can be used in the IC industry.
It is therefore an object of the present invention to provide a method for preparing a conductive pad surface for electrical connection that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for preparing a conductive pad surface for electrical connection by either a wirebond or a solder bumping process. “It is a further object of the present invention to provide a method for preparing a copper pad surface for electrical connection by first forming a protection layer and then an adhesion layer on the copper pad surface, both being done without requiring additional photomask and etching steps. (Incorporated herein by reference, entitled “Self-Aligned Corrosion Stop for Copper C4 and Wirebond”, filed May 14, 1999.)”
It is another further object of the present invention to provide a method for preparing a copper pad surface for electrical connection by first depositing a protection film layer of a phosphorus or boron-containing metal alloy on the copper pad surface.
It is still another object of the present invention to provide a method for preparing a copper pad surface for electrical connection by depositing an adhesion layer of a noble metal on top of a protection layer previously formed on the copper pad surface.
It is yet another object of the present invention to provide a method for preparing a copper pad surface for electrical connection which further includes a step of depositing a nucleation layer of a noble metal on the copper pad surface prior to the deposition of the protection layer.
It is still another further object of the present invention to provide a conductive pad for forming an electrical connection thereon which includes a copper pad surface, a protection layer on the copper pad surface and an adhesion layer on top of the protection layer for providing electrical connection with a wirebond or a solder bump.
It is yet another further object of the present invention to provide an electrical structure for providing electrical connection which includes a copper pad surface, a protection layer on the copper pad surface, an adhesion layer on top of the protection layer, and an electrical connection of a wirebond or solder bump integrally formed with the adhesion layer.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method for preparing a copper pad surface for electrical connection with a wirebond or a solder bump and devices formed by the method are provided.
In a preferred embodiment, a method for preparing a copper pad surface for electrical connection can be carried out by the operating steps of first providing a copper pad surface, depositing a protection layer of phosphorus or boron-containing metal alloy on the copper pad surface, and depositing an adhesion layer of a noble metal on top of the protection layer.
The method for preparing a copper pad surface for electrical connection may further include the step of depositing a nucleation layer of a noble metal on the copper pad surface prior to the deposition of the protection layer. The method may further include the steps of cleaning the copper pad surface in an acid solution, and depositing a nucleation layer of a noble metal on the copper pad surface. The nucleation layer may be deposited of palladium, or palladium nanoparticles. Pd nanoparticles are most commonly used although other nanoparticles of noble metals such as ruthenium and rhenium can be used. The method may further include the step of rinsing the copper pad surface with water after the nucleation layer is deposited, or the step of depositing the protection layer by an electroless plating technique. The step of depositing a protection layer may further include the steps of contacting the copper pad surface with a heated, buffered solution of an electroless bath that contains cobalt ions, tungstate ions, boric acid, citrate ions, lead acetate and hypophosphite; and then contacti
Edelstein Daniel C.
Gaudiello John G.
Rubino Judith M.
Sambucetti Carlos J.
Walker George
Koehler Robert R.
Trepp Robert M.
Tung Randy W.
LandOfFree
Method for preparing a conductive pad for electrical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for preparing a conductive pad for electrical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for preparing a conductive pad for electrical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2818914