Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating process fluid by means other than agitation or...
Reexamination Certificate
2002-06-07
2004-12-28
Wong, Edna (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating process fluid by means other than agitation or...
C205S101000, C205S291000, C205S292000, C205S296000, C205S118000, C205S123000, C205S125000, C205S102000, C205S103000
Reexamination Certificate
active
06835294
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains to an electrolytic copper plating method. More particularly, this invention pertains to an electrolytic copper plating method that does not mar the appearance of plating and is applied to form filled via-holes.
There is a strong demand in the industry for making printed circuit boards thinner and higher-density to achieve high-performance, miniaturized electronic devices, beginning with personal computers. One approach to such demands is to use a multilayer printed circuit board produced using the build-up technique of forming a pattern on each layer and laminating layers in succession (build-up printed circuit board).
In recent years, a method called “via-filling” has been developed for filling the entire via-hole (or “via”) in this type of build-up printed circuit board with a conductor and electrically connecting adjacent build-up printed circuit boards. This method is effective for miniaturizing and increasing the density of printed circuit boards by enabling the effective surface area of printed circuit boards to be increased, and obtaining an adequate electrical connection even for small-diameter vias compared to plating only the via inner wall by the prior art method.
Published via-filling methods include a method for filling vias with conductive paste by the printing method, a method for activating only the conductive layer on the via floor and accumulating electroless copper plating layers, and a method using electrolytic copper plating.
Because it is a mixture of copper and an organic substance, however, conductive paste has lower conductivity than metallic copper, making it difficult to achieve an adequate electrical connection in a small-diameter via, and this cannot be considered an effective method for miniaturizing and increasing the density of printed circuit boards. Furthermore, filling by the printing method requires filling a small-diameter, non-communicating hole with a viscous paste, and the viscosity of the paste makes it difficult to fill this completely leaving no air voids. The method using electroless copper plating is superior to the conductive paste method on the point that the via filling substance is a highly-conductive metallic copper deposit, but has the productivity problem that the plating speed of the deposit is slow. The plating speed of the deposit using a general high-speed electroless copper plating bath is about 3 &mgr;m/hr, but when used to fill a typical blind via measuring 100 &mgr;m in diameter and 100 &mgr;m deep with copper plating, this takes 30 hours or longer and has extremely poor productivity.
By contrast, electrolytic copper plating has a fast plating speed of 10 to 50 &mgr;m/hr, and can greatly shorten time compared to electroless copper plating. As a result, application of electrolytic copper plating to vias is anticipated. However, to fill vias adequately leaving no air voids when plating copper over the entire via inner wall, the plating speed near the floor inside via must be faster than the plating speed at the opening. If the plating speed near the floor is the same or slower than the plating speed at the opening, the via is not adequately filled, or the opening becomes clogged before the filling of the via with plated copper has finished, leaving air inside. Either case is untenable in practice. Therefore, to adequately fill vias, plating conditions must be adjusted carefully such that metal can plate appropriately.
Normally, electrolytic copper plating solutions containing specific sulfated compounds, starting with brighteners, are used for production of printed circuit boards, and generally, electrolysis conditions are direct-current electrolysis using soluble anodes such as phosphated copper anodes. However, plating by a soluble anode has problems such as that the electrolytic copper plating bath is unstable during electrolysis and after stopping electrolysis, and when used thereafter, the electrolytic copper plating solution produces clumps during formation of electrolytic copper deposits, marring the appearance of the plating and destabilizing the via-filling.
In one method for improving via-filling, the method of electrolytic copper plating using an electrolytic copper plating solution containing specific sulfated compounds and a PPR (pulse periodic reverse) current disclosed by Japan Unexamined Patent Application No. 2000-68651 controls adsorption and desorption of the specific sulfated compounds to the substrate by using a PPR current, but does not solve the problems described above caused by using a soluble anode.
Another method for improving via-filling is the method of electrolytic copper plating using an insoluble anode. However, this method has the problem that all the anodes used are insoluble anodes, and because they are expensive, insoluble anodes raise overall system costs. Using insoluble anodes also requires replenishing basic copper carbonates and copper oxides consumed as the plating bath is used, and this leads to the problem that impurities such as chlorine, iron, or nickel contained in the replenished copper salts are mixed into the plating bath.
SUMMARY OF THE INVENTION
Reflecting on this situation, the purpose of this invention is to offer a method for the electrolytic deposition of copper on a substrate using an electrolytic copper plating solution, especially an electrolytic copper plating solution containing specific sulfated compounds, and subjecting the electrolytic copper plating solution to dummy electrolysis using an insoluble anode, whereby the electrolytic copper deposited by continuous electrolytic copper plating using said electrolytic copper plating solution forms a fine deposited film, and the plating has satisfactory appearance and satisfactory via-filling property.
This invention pertains to an electrolytic copper plating method wherein electrolytic copper plating is applied to a substrate, and the electrolytic copper plating solution supplied to said electrolytic copper plating is subjected to dummy electrolysis using an insoluble anode.
This invention also pertains to an electrolytic copper plating method wherein electrolytic copper plating is applied to a substrate using a soluble anode in an electrolytic copper plating bath holding an electrolytic copper plating solution and having said soluble anode or having said soluble anode and an insoluble anode, and after said plating, the electrolytic copper plating solution used in the above-mentioned electrolytic copper plating is subjected to dummy electrolysis using said insoluble anode.
Furthermore, this invention pertains to an electrolytic copper plating method wherein, in a multi-bath electrolytic copper plating apparatus comprised of a main bath having a soluble anode, a dummy electrolysis bath having an insoluble anode, and a circulation pipe connecting said main bath and said dummy electrolysis bath to allow circulation of an electrolytic copper plating solution, the above-mentioned electrolytic copper plating solution is stored in said main bath and said dummy electrolysis bath, and electrolytic copper plating is applied to a substrate in said main bath using said soluble anode, and the electrolytic copper plating solution is subjected to dummy electrolysis simultaneously in said dummy electrolysis bath using said insoluble anode while circulating the above-mentioned electrolytic copper plating solution between said main bath and said dummy electrolysis bath through said circulating pipe, or is subjected to dummy electrolysis in said dummy electrolysis bath using said insoluble anode after said plating.
Also provide by this invention is a method for plating copper comprising the steps of: contacting a substrate to be plated with a copper electroplating solution, applying a current density to the copper electroplating solution to deposit copper on the substrate, and subjecting the copper electroplating solution to dummy electrolysis using an insoluble anode.
In another aspect, this invention provides a method for plating copper comprising the steps of: electrolytically
Hayashi Shinjiro
Kusaka Masaru
Tsuchida Hideki
Cairns S. Matthew
Shipley Company L.L.C.
Wong Edna
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