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 xcexcxcexa9cm, 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 xcexcm. 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.
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 mixed solution is immediately fed to the plating surface.
In addition, more preferably, the first and second solutions are stored in an atmosphere of a nitrogen gas or other inert gases or ammonia gas or alternatively in a pressurized atmosphere of an inert gas or ammonia gas until feeding said processing solution to the plating surface.
In the above method of electroless plating of the present invention, preferably the processing solution is prepared divided into a first solution including the first metallic material and the complexing agent, a second solution including the reducing agent, and a third solution including the second metallic material, and the first, second, and third solutions are mixed to obtain the processing solution before feeding to the plating surface.
More preferably, the first, second, and third solutions are stored in an atmosphere of an inert gas or ammonia gas or alternatively in a pressurized atmosphere of an inert gas or ammonia gas until feeding said processing solution to the plating surface.
In the above method of electroless plating of the present invention, the first metallic material includes at least a compound of nickel or cobalt.
In addition, preferably the second metallic material includes at least a compound of tungsten or molybdenum, more preferably the atomic weight concentration of the tungsten or molybdenum is 0.2% to 2%.
In addition, preferably the first complexing agent is an amino acid.
In addition, preferably, the second complexing agent is an organic acid.
In addition, preferably the complexing agent, the reducing agent, and the pH adjusting agent substantially do not contain a metal in their chemical formulae.
In the above method of electroless plating of the present invention, the pH value of the processing solution is adjusted to 7 to 12. If the processing solution includes the second metallic material, the pH value of the processing solution is adjusted to 8 to 12.
More preferably, when the processing solution is prepared divided among several tanks, the pH value is adjusted to 7 to 12 in each tank. If the processing solution includes the second metallic material, the pH value is adjusted to 8 to 12 in each tank.
In addition, preferably the temperature of the processing solution is adjusted to 50xc2x0 C. to 95xc2x0 C.
More preferably, when the processing solution is prepared divided among several tanks, the temperature is adjusted to 50xc2x0 C. to 95xc2x0 C. in each tank.
In addition, preferably the processing solution is sprayed onto the plating surface by a spray nozzle.
In the above method of electroless plating of the present invention, preferably, as the processing solution of the electroless plating step, use is made of a processing solution containing, with respect to one mole of the first metallic material, three or more moles of the complexing agent and three or more moles of the reducing agent.
More preferably, as the processing solution of the electroless plating step, use is made of a processing solution of a pH value adjusted to 9 or more.
In addition, more preferably, the pH value of the processing solution of the electroless plating step is monitored and, when the pH value is less than 9, the pH adjusting agent is further added to increase the pH value to 9 or more.
In the above method of electroless plating of the present invention, since a barrier film is formed by electroless plating, the barrier film can be stably and uniformly formed even when interconnections and connection holes are miniaturized and have large aspect ratios. Further, because a processing solution is fed to the plating surface for puddling treatment in at least one of the pre-processing steps of electroless plating and the electroless plating step, the consumption of the processing solution can be reduced.
In particular, a processing solution is shortened in lifetime due to precipitation of Co(OH)2, occurrence of reduction reactions induced by an addition of a reducing agent into the processing solution, or volatilization of ammonia. In the method of electroless plating of the present invention, however, up until immediately before feeding the processing solution to the plating surface, the processing solution is divided into the first solution including a first metallic material and a complexing agent and the second solution including a reducing agent. These are stored in an atmosphere of a nitrogen gas or another inert gas or ammonia gas to prevent volatilization of ammonia and oxidation in the solution. By mixing the first and second solutions and immediately feeding the resultant processing solution to the plating surface, the lifetime of the processing solution can be extended and the consumption can be reduced.
Dividing and storing the processing solution in this way up until just before use becomes possible by adoption of the above puddling treatment of the processing solution.
Particularly, by making the molar ratio of the electroless plating processing solution three or more moles of complexing agent and three or more moles of reducing agent to one mole of the first metallic material, a film is able to be formed stably and uniformly by electroless plating. Further, with the pH value not less than 9, a dense and high quality plating film giving a lustrous surface can be formed.
In addition, by controlling the pH value to 9 or more at the above composition, fluctuation of the composition of the processing solution due to precipitation is prevented and therefore the lifetime of the processing solution can be extended. Furthermore, the amount of waste of the processing solution and therefore the consumption of the processing solution can be reduced.
In addition, to achieve the above object, according to a second aspect of the present invention, there is provided a method of electroless plating for processing a plating surface to form a barrier layer, wherein a processing solution of an electroless plating step contains, with respect to one mole of a first metallic material, three or more moles of a complexing agent, three or more moles of a reducing agent, and a pH adjusting agent, and the pH value of the processing solution is adjusted in the region from neutral to alkali.
In the above method of electroless plating of the present invention, preferably, as the processing solution of the electroless plating step, use is made of a processing solution of a pH value adjusted to 9 or more.
More preferably, the pH value of the processing solution of the electroless plating step is monitored and the pH adjusting agent is further added to increase the pH value to 9 or more when the pH value becomes less than 9.
In the above method of electroless plating of the present invention, as the pre-processing of the electroless plating, hydrophilization, coupling, catalyzation, and activation are performed.
Alternatively, preferably, as the pre-processing of the electroless plating, degreasing, acid neutralization, and catalyzation are performed.
In the above method of electroless plating of the present invention, 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, the completing agent preferably 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 stored in an atmosphere of a nitrogen gas or other inert gases or ammonia gas until feeding said processing solution to the plating surface.
In addition, preferably the processing solution is fed to the plating surface in a pressurized atmosphere of an inert gas or ammonia gas.
In the above method of electroless plating of the present invention, more preferably the first metallic material includes at least a compound of nickel or cobalt.
In addition, the second metallic material includes at least a compound comprising 0.2% to 2% tungsten or molybdenum by atomic weight concentration.
In addition, preferably the first complexing agent is an amino acid.
In addition, preferably the second complexing agent is an organic acid.
In addition, preferably the completing agent, the reducing agent, and the pH adjusting agent substantially do not contain a metal in their chemical formulae.
In the above method of electroless plating of the present invention, the temperature of the processing solution is adjusted to 50xc2x0 C. to 95xc2x0 C.
In the above method of electroless plating of the present invention, by setting the molar ratio of the processing solution for the electroless plating to three or more moles of complexing agent and three or more moles of reducing agent to one mole of the first metallic material, a film is able to be formed stably and uniformly by electroless plating. Furthermore, with a pH value not less than 9, a dense and high quality plating film giving a lustrous surface can be formed.
In addition, by controlling the pH value to 9 or more at the above composition, storing the processing solution in an atmosphere of a nitrogen or other inert gas or ammonia gas, and feeding the processing solution to the plating surface in a pressurized atmosphere of an inert gas or ammonia gas, the fluctuation of the composition of the processing solution due to precipitation is prevented, the lifetime of the processing solution can be extended, and the waste of the processing solution and therefore the consumption of the processing solution can be reduced.
In addition, to achieve the above object, according to a third aspect of the present invention, there is provided an electroless plating apparatus for processing a plating surface to form a barrier layer, comprising a table for fixing a plating object having a plating surface and a feeding means for feeding a processing solution to the plating surface in at least one of the pre-processing steps of electroless plating and the electroless plating step, wherein stopping the table enables puddling treatment by the processing solution.
In the above electroless plating apparatus of the present invention, preferably the feeding means feeds a processing solution used for the electroless plating step.
Alternatively, the feeding means feeds a processing solution used in at least one of the pre-processing steps of hydrophilization, coupling, catalyzation, and activation or the feeding means feeds a processing solution used in at least one of the pre-processing steps of degreasing, acid neutralization, and catalyzation.
The above electroless plating apparatus of the present invention preferably further comprises a means for removing an unnecessary processing solution.
More preferably, the table, feeding means, and removing means are comprised by a spin-coater. The spin-coater feeds the processing solution, is stopped to allow the puddling treatment by the processing solution, then is operated to remove unnecessary processing solution.
In addition, more preferably, the puddling treatment step and the step of removing an unnecessary processing solution are repeated.
In the above electroless plating apparatus of the present invention, preferably, as the processing solution of electroless plating step, a processing solution including at least a first metallic material supplying a main ingredient of the barrier layer, a complexing agent, a reducing agent, and a pH adjusting agent and having a pH value adjusted in a region from neutral to alkali is fed.
More preferably, as the processing solution, a processing solution further including a second metallic material supplying an ingredient enhancing the barrier ability of the barrier layer is fed.
Further, more preferably, a processing solution containing a completing agent including a first completing agent of an amphoteric ion type and a second complexing agent for enhancing a plating reaction is fed.
The above electroless plating apparatus of the present invention preferably further comprises at least a first tank containing a first solution including the first metallic material and the complexing agent and a second tank containing a second solution including the reducing agent, wherein the processing solution can be prepared divided into at least the first and second solutions, a pipe system is provided for merging the first and second solutions before feeding them to the plating surface, and the first and second solutions are mixed there and fed as the processing solution.
More preferably, the second solution is prepared to include a second metallic material supplying an ingredient enhancing the barrier ability of the barrier layer.
Further more preferably, after the first and second solutions are mixed, the mixed solution is immediately fed to the plating surface.
In the above electroless plating apparatus of the present invention, preferably, the first and second tanks are connected to a merging tank by a pipe, and a pipe system is provided for mixing the first and second solutions in the merging tank.
In addition, preferably, a static mixer is connected downstream of a merging portion of a pipe from the first and second tanks, and a pipe system is provided for mixing the first and second solutions by the static mixer.
In addition, preferably the first and second solutions are stored in an atmosphere of an inert gas or ammonia gas in the first and second tanks. Alternatively, the first and second solutions are stored in a pressurized atmosphere of an inert gas or ammonia gas in the first and second tanks, and due to the pressurized atmosphere, the first and second solutions flow to pipes connected to the first and second tanks.
The above electroless plating apparatus of the present invention may alternatively comprise a first tank containing a first solution including the first metallic material and the complexing agent, a second tank containing a second solution including the reducing agent, and a third tank containing a third solution including the second metallic material, wherein the processing solution can be divided into at least the first, second, and third solutions, a pipe system is provided for merging the first, second, and third solutions before feeding them to the plating surface, and the first, second, and third solutions are mixed there and fed as the processing solution.
More preferably, after the first, second, and third solutions are mixed, the mixed solution is immediately fed to the plating surface.
In the above electroless plating apparatus of the present invention, preferably the first, second, and third tanks are connected to a merging tank by pipes, and a pipe system is provided for merging the first, second, and third solutions in the merging tank.
Alternatively, preferably, a static mixer is connected downstream of a merging portion of a pipe from the first, second, and third tanks, and a pipe system is provided for merging the first, second, and third solutions by the static mixer.
In addition, preferably the first, second, and third solutions are stored in an atmosphere of an inert gas or ammonia gas in the first, second, and third tanks. Alternatively, the first, second, and third solutions are stored in a pressurized atmosphere of an inert gas or ammonia gas in the first, second, and third tanks, and due to the pressurized atmosphere, the first, second, and third solutions flow to pipes connected to the first, second, and third tanks.
In the above electroless plating apparatus of the present invention, preferably, a processing solution containing a first metallic material including at least a compound of nickel or cobalt is fed.
In addition, preferably, a processing solution containing a second metallic material including at least a compound of tungsten or molybdenum is fed.
Further preferably, a processing solution containing 0.2% to 2% tungsten or molybdenum by atomic weight concentration is fed.
In addition, preferably a processing solution containing an amino acid as the first complexing agent is fed.
In addition, preferably a processing solution containing an organic acid as the second complexing agent is fed.
In addition, preferably a processing solution in which the complexing agent, the reducing agent, and the pH adjusting agent substantially do not contain a metal in their chemical formulae is fed.
In the above electroless plating apparatus of the present invention, a processing solution of a pH value adjusted to 7 to 12 is fed as the processing solution. If the processing solution includes the second metallic material, a processing solution of a pH value adjusted to 8 to 12 is fed.
More preferably, when the processing solution is prepared divided among several tanks, the pH value is adjusted to 7 to 12 in each tank. If the processing solution includes the second metallic material, the pH value is adjusted to 8 to 12 in each tank.
In addition, preferably, a heater is further provided for adjusting the temperature of the processing solution to 50xc2x0 C. to 95xc2x0 C.
More preferably, when the processing solution is prepared divided among several tanks, a heater is provided in each tank for adjusting the temperature in each tank to 50xc2x0 C. to 95xc2x0 C.
In the above electroless plating apparatus of the present invention, preferably a heater is included in the table for adjusting the temperature of the plating object.
In addition, preferably, there is further provided a heater able to be arranged to face the plating surface of the plating object. In the apparatus, the heater is arranged to face the plating surface to adjust the temperature of the processing solution in the puddling treatment step.
In addition, preferably the portion for feeding the processing solution is a spray nozzle, and the processing solution is fed by being sprayed onto the plating surface.
In the above electroless plating apparatus of the present invention, a processing solution containing, with respect to one mole the first metallic material, three or more moles of completing agent and three or more moles of reducing agent is fed by the feeding means as the processing solution in the electroless plating step.
More preferably, a processing solution of a pH value adjusted to 9 or more is fed by the feeding means as the processing solution.
In addition, more preferably, the electroless plating apparatus further comprises a processing solution tank for storing the processing solution, a measuring means for measuring the pH value of the processing solution in the processing solution tank, a pH adjusting agent tank for storing the pH adjusting agent, and a control means for adding the pH adjusting agent from the pH adjusting agent tank to the processing solution tank to increase the pH value to 9 or more when the pH value of the processing solution in the processing solution tank is less than 9.
In the above method of electroless plating of the present invention, since a barrier film is formed by electroless plating, a barrier film can be stably and uniformly formed even when interconnections and connection holes are miniaturized and have large aspect ratios. Further, by fixing a plating object having a plating surface on a table and feeding a processing solution by a feeding means to the plating surface in at least one of the pre-processing steps of electroless plating and the electroless plating step, puddling treatment by the processing solution can be performed, so the consumption of the processing solution can be reduced.
In particular, a processing solution is shortened in lifetime due to precipitation of Co(OH)2, occurrence of reduction reactions induced by an addition of a reducing agent into the processing solution, or volatilization of ammonia. In the apparatus of electroless plating of the present invention, however, up until immediately before feeding the processing solution to the plating surface, the processing solution is divided into the first solution including a first metallic material and a complexing agent and the second solution including a reducing agent. These are stored in an atmosphere of a nitrogen gas or another inert gas or ammonia gas to prevent volatilization of ammonia and oxidation in the solution. By mixing the first and second solutions and immediately feeding the resultant processing solution to the plating surface, the lifetime of the processing solution can be extended and the consumption can be reduced.
Dividing and storing the processing solution in this way up until just before use becomes possible by adoption of the above puddling treatment of the processing solution.
Particularly, by making the molar ratio of the electroless plating processing solution three or more moles of complexing agent and three or more moles of reducing agent to one mole of the first metallic material, a film is able to be formed stably and uniformly by electroless plating. Further, with the pH value not less than 9, a dense and high quality plating film giving a lustrous surface can be formed.
In addition, by controlling the pH value to 9 or more at the above composition, by adding the pH adjusting agent to the processing solution tank from the pH adjusting agent tank when the pH value of the processing solution in the processing solution tank is less than 9, fluctuation of the composition of the processing solution due to precipitation is prevented and therefore the lifetime of the processing solution can be extended. Furthermore, the amount of waste of the processing solution and therefore the consumption of the processing solution can be reduced.
In addition, to achieve the above object, according to a fourth aspect of the present invention, there is provided an electroless plating apparatus for processing a plating surface to form a barrier layer comprising a means for feeding to the plating surface a processing solution at least including, with respect to one mole of a first metallic material supplying a main ingredient of the barrier layer, three or more moles of a complexing agent and three or more moles of a reducing agent, and a pH adjusting agent and having a pH value adjusted in a region from neutral to alkali.
In the above electroless plating apparatus of the present invention, preferably an electroless plating bath filled with the processing solution is provided as the plating solution feeding means, and the plating object having the plating surface is immersed in the electroless plating bath for electroless plating.
More preferably, the above electroless plating apparatus further comprises a lid provided on the electroless plating bath and a means for feeding a gas including at least an inert gas or ammonia gas to the electroless plating bath sealed by the lid.
Alternatively, preferably the above electroless plating apparatus comprises a plating cell arranged to allow its inside surface to be seen by the plating surface and separating at least the plating surface from the outside atmosphere and a means for feeding a gas including at least an inert gas or ammonia gas to the plating cell, wherein a plating solution is fed to the plating surface seen from the inside surface of the plating cell by the plating solution feeding means.
In the above electroless plating apparatus, preferably a processing solution of a pH value adjusted to 9 or more is fed by the plating solution feeding means as the processing solution.
More preferably, the above electroless plating apparatus further comprises a processing solution tank for storing the processing solution, a measuring means for measuring the pH value of the processing solution in the processing solution tank, a pH adjusting agent tank for storing the pH adjusting agent, and a control means for adding the pH adjusting agent from the pH adjusting agent tank to the processing solution tank to increase the pH value to 9 or more when the pH value of the processing solution in the processing solution tank is less than 9.
In the above electroless plating apparatus, preferably, as the processing solution, a processing solution further including a second metallic material supplying an ingredient enhancing the barrier ability of the barrier layer is fed.
In addition, preferably, a processing solution containing a complexing agent including a first completing agent of an amphoteric ion type and a second completing agent for enhancing a plating reaction is fed.
In addition, preferably, a processing solution containing a first metallic material including at least a compound of nickel or cobalt is fed.
In addition, preferably, a processing solution containing a second metallic material including at least a compound of tungsten or molybdenum is fed.
In addition, preferably, a processing solution containing 0.2% to 2% of the tungsten or molybdenum by atomic weight concentration is fed.
In addition, preferably, a processing solution containing an amino acid as the first completing agent is fed.
In addition, preferably, a processing solution containing an organic acid as the second complexing agent is fed.
In addition, preferably, a processing solution in which the complexing agent, the reducing agent, and the pH adjusting agent substantially do not contain a metal in their chemical formulae is fed.
In addition, preferably, the above electroless plating apparatus further comprises a heater for adjusting the temperature of the processing solution to 50xc2x0 C. to 95xc2x0 C.
In the above electroless plating apparatus, by adjusting the molar ratio in the processing solution for the electroless plating to three or more moles of complexing agent and three or more moles of reducing agent to one mole of the first metallic material, a film is able to be formed stably and uniformly by electroless plating. Furthermore, with the pH value not less than 9, a dense and high quality plating film giving a lustrous surface can be formed.
In addition, by controlling of the pH value to 9 or more at the above composition, using an electroless plating bath closed by a lid and a plating cell arranged so that its inside surface is seen by the plating surface and separating the plating surface from the outside atmosphere, storing the processing solution in an atmosphere of nitrogen gas or an other inert gas or ammonia gas, and feeding it to the plating surface in a pressurized atmosphere of an inert gas or ammonia gas, the fluctuation of the composition of the processing solution due to precipitation is prevented, the lifetime of the processing solution can be increased, and the waste of the processing solution and therefore the consumption of the processing solution can be reduced.