Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2001-04-09
2003-10-28
Barr, Michael (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S098300, C427S123000, C427S304000, C427S305000, C427S306000, C427S240000, C427S346000, C427S347000, C427S437000, C427S438000, C427S443100, C427S427000
Reexamination Certificate
active
06638564
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of electroless plating and an electroless plating apparatus, more particularly relates to a method of electroless plating and an electroless plating apparatus for forming a conductive film having a barrier ability.
2. Description of the Related Art
Aluminum or aluminum alloys have been widely used as materials of miniaturized interconnections in semiconductor devices obtained by forming highly integrated circuits on semiconductor wafers.
In order to further increase the operating speed of semiconductor devices, however, it is necessary to use materials of lower resistivity such as copper, silver, etc, for the interconnections.
Especially, copper has a resistivity as low as 1.8 &mgr;&OHgr;cm, which is advantageous to increase the speed of semiconductor devices, and is 10 times higher in electromigration resistance than aluminum alloys, thus is attracting more and more attention as a next generation material.
Copper, however, is liable to diffuse into the silicon oxide and other insulating materials. The diffusion speed is also high. Thereupon, when using copper for interconnections, as a measure against this problem, usually a barrier metal layer is formed at the boundary between the copper and the insulating material to prevent the diffusion of copper.
Materials frequently used for a barrier metal layer include tantalum, tantalum nitride, titanium, titanium nitride, tungsten, tungsten nitride, etc.
Conventionally, a barrier metal layer was usually formed by a physical vapor deposition (PVD) method such as sputtering or by a chemical vapor deposition (CVD) method.
Together with the increasing compactness and higher integration of semiconductor devices, the interconnection design rule has already been reduced to under the 0.13 &mgr;m. Further, while the silicon oxide or other interlayer insulating films which cover semiconductor elements are becoming thicker along with the increased heights of these elements, the area for opening connection holes (contact holes and via holes for electrical connections between elements or between multi-layer interconnections) is becoming smaller. As a result, the aspect ratio of connection holes is becoming a high ratio of over 1:5. In view of this situation, the coverage provided by a barrier metal layer formed by the PVD or CVD method is becoming poorer. It is extremely difficult to form a uniform film covering up to the inside surfaces of connection holes.
To solve this problem, U.S. Pat. No. 5,695,810 discloses a technique for forming a barrier metal layer of CoWP by means of electroless plating.
In addition, Japanese Unexamined Patent Publication (Kokai) No. 8-83796 discloses another technique of forming a film of cobalt, nickel, etc. by electroless plating.
In the above methods, electroless plating for depositing a CoWP layer was carried out by dipping. In this case, however, the solution for electroless plating (electroless plating processing solution) easily forms Co(OH)
2
precipitates. Furthermore, if a reducing agent is added into the processing solution beforehand, a reduction reaction takes place induced by the reducing agent, resulting in not only a shorter lifetime of the electroless plating processing solution, but also a difference in the rate of film formation because of the aging of the processing solution from the beginning to the end of its lifetime.
Because of the short lifetime, each time an electroless plating processing solution deteriorates, a new solution has to be prepared. This causes increased solution consumption, much extra work in fabrication, and higher fabrication costs. Consequently, application of these techniques is not easy.
Furthermore, when applied to semiconductors, sodium hydroxide containing alkali metal ions cannot be used to adjust the pH value of the electroless plating processing solution. Therefore, ammonia is employed for this purpose. Ammonia is however highly volatile, thus causes the lifetime of the solution to become shorter. In addition, when ammonium tungstate or ammonium molybdate is added into the electroless plating processing solution to improve the barrier ability of the formed barrier metal film, due also to the volatilization of ammonia, tungstic acid or molybdic acid ends up precipitating, so the lifetime of the processing solution again becomes short.
When using processing solutions for pre-processing for the above electroless plating treatment as well, it is desired to reduce the consumption of the processing solution from that when feeding processing solutions to plating surfaces by a spin-coat method.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of electroless plating and an electroless plating apparatus for forming a barrier layer by electroless plating able to stably and uniformly form a film even when interconnections and connection holes are miniaturized and have large aspect ratios and able to reduce the consumption of a processing solution by increasing its lifetime.
To attain the above object, according to a first aspect of the present invention, there is provided a method of electroless plating for processing a plating surface to form a barrier layer, comprising a step of feeding a processing solution used in at least one of the pre-processing steps of the electroless plating and the electroless plating step to the plating surface for puddling treatment.
In the above method of electroless plating of the present invention, preferably puddling treatment is performed by the processing solution used in the electroless plating step.
In addition, preferably, puddling treatment is performed by a processing solution used in at least one of the pre-processing steps of hydrophilization, coupling, catalyzation, and activation. Alternatively, puddling treatment is performed by a processing solution used in at least one of the pre-processing steps of degreasing, acid neutralization, and catalyzation. The catalyzation is a substitution processing induced by palladium, platinum, gold, rhodium, or another catalytic metal.
The above method of electroless plating of the present invention preferably includes a step of removing an unnecessary processing solution after the puddling treatment.
In addition, preferably, the processing solution is fed by a spin-coater, then the spin-coater is stopped for the puddling treatment with the processing solution, then the spin-coated is again operated to remove the unnecessary processing solution.
In addition, preferably, the puddling treatment step and the step of removing an unnecessary processing solution are repeated.
In the above method of electroless plating of the present invention, preferably the puddling treatment is performed by a processing solution including at least a first metallic material supplying a main ingredient of the barrier layer, a completing agent, a reducing agent, and a pH adjusting agent and having a pH value adjusted in a region from neutral to alkali as the processing solution of the electroless plating step.
More preferably, as the processing solution, use is made of a processing solution further including a second metallic material supplying an ingredient enhancing the barrier ability of the barrier layer.
In addition, more preferably, the complexing agent includes a first complexing agent of an amphoteric ion type and a second complexing agent for enhancing a plating reaction.
In the above method of electroless plating of the present invention, preferably the processing solution is prepared divided into a first solution including at least the first metallic material and the complexing agent and a second solution including the reducing agent, and the first and second solutions are mixed to obtain the processing solution before feeding to the plating surface.
More preferably, the second solution includes a second metallic material supplying an ingredient enhancing the barrier ability of the barrier layer.
In addition, more preferably, after the first and second solutions are mixed, the mixe
Sato Shuzo
Segawa Yuji
Suzuki Masatoshi
Watanabe Katsumi
Yoshio Akira
Barr Michael
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
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