US20110180412A1

US20110180412A1 - Plating method and plating apparatus

Info

Publication number: US20110180412A1
Application number: US13/014,931
Authority: US
Inventors: Masashi Shimoyama; Fumio Kuriyama; Masanori Hayase
Original assignee: Individual
Current assignee: Ebara Corp; Tokyo University of Science
Priority date: 2010-01-27
Filing date: 2011-01-27
Publication date: 2011-07-28
Also published as: JP5780496B2; TWI487815B; TW201139760A; JP2011174177A

Abstract

A plating method can fill a plated metal into interconnect recesses at a higher rate without forming voids in the plated metal embedded in the interconnect recesses. The plating method includes: preparing a substrate having interconnect recesses in a surface; carrying out first pretreatment of the substrate by immersing the substrate in a first pretreatment solution containing an accelerator, a metal ion and an acid; carrying out second pretreatment of the substrate by immersing the substrate in a second pretreatment solution containing an additive which inhibits the effect of the accelerator contained in the first pretreatment solution, and not containing an accelerator; and then carrying out electroplating of the substrate surface by using a plating solution containing at least a metal ion, an acid and a suppressor, and not containing an accelerator, thereby filling the plated metal into the interconnect recesses.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a technique for forming interconnects in a semiconductor device, and more particularly to a plating method and a plating apparatus which can fill a plated metal for interconnects, such as copper, into interconnect recesses such as trenches and via holes, formed in a surface of a substrate such as a semiconductor wafer, at a high rate.
2. Description of the Related Art
In order to fill a plated metal for interconnects into interconnect recesses such as trenches and via holes, formed in a surface of a substrate such as a semiconductor wafer, at a high rate, the following points are of importance: suppression of the deposition rate of the plated metal in a surface of a field area of the substrate; and promotion of the deposition rate of the plated metal in the bottoms of the interconnect recesses. It is therefore common practice to use three types of additives, an accelerator for accelerating the deposition of a plated metal, a suppressor for suppressing the deposition of the plated metal, and a leveler (leveling agent), in a plating solution for use in recess-filling plating.
When plating of a substrate is carried out by using a plating solution containing a leveler which, while being consumed, suppresses the deposition of a plated metal, the plated metal deposition-suppressing effect differs depending on a thickness of a diffusion layer formed in the vicinity of a surface of the substrate. In this case, when the plating is carried out while stirring the plating solution, the deposition of the plated metal is significantly suppressed in a surface of a field area of the substrate where the plating solution flows at a fast speed, whereas because of insufficient supply of the leveler, the deposition of the plated metal is not suppressed in bottoms of interconnect recesses where the plating solution flows at a slow speed. Thus, by carrying out the plating while stirring the plating solution, it becomes possible to fill the plated metal into the interconnect recesses from the bottoms at a high rate while fully maintaining the plated metal deposition-accelerating effect of an accelerator in the interconnect recesses, and preventing blocking of the openings of the interconnect recesses due to the deposition of the plated metal in the vicinities of the openings.
When filling of a plated metal into interconnect recesses is performed by utilizing the synergistic effect of the above-described additives present in a plating solution, a repetition of plating operations can cause an alteration of an additive(s), leading to an unstable process. Especially when a long plating time is necessary for one wafer as in plating to fill a plated metal into through-silicon via holes, a large amount of an additive(s) will be consumed during plating of one wafer. This can cause a quality change of the plating solution after processing of several wafers, resulting in poor filling of the plated metal.
A method is therefore conceivable in which an accelerator, one of the above-described common additives, is allowed to adsorb only onto surfaces of interconnect recesses in advance, and thereafter plating is carried out by using a plating solution, such as a copper sulfate plating solution, containing only a suppressor as an additive. This method is expected to suppress the deposition of a plated metal in a surface of a field area of a substrate by the effect of the suppressor while accelerating the deposition of the plated metal from the bottoms of the interconnect recesses by the effect of the adsorbed accelerator. It is generally impossible to allow an accelerator to adsorb only onto surfaces of interconnect recesses by one treatment operation. The applicant has proposed a method comprising: carrying out first plating of a substrate surface in a plating solution containing a plating accelerator; carrying out a plating accelerator removal treatment by bringing an accelerator remover, capable of removing or reducing the accelerator, into contact with the substrate surface; and then carrying out second plating (recess-filling plating) of the substrate surface (see Japanese Patent Laid-Open Publications No. 2007-262486, patent document 1, and No. 2006-131961, patent document 2).
The applicant has also proposed a method which involves applying a plating suppressing material (plating suppressor) to a substrate surface except surfaces of interconnect recesses prior to plating (see Japanese Patent Laid-Open Publications No. 2006-274369, patent document 3, No. 2006-307279, patent document 4, and No. 2007-9247, patent document 5). Further, a method has been proposed which comprises after filling a plated metal into interconnect recesses formed in a substrate surface, removing an accelerator in surfaces of the interconnect recesses in the vicinities of their openings, and then forming a plated metal film in the surface of the field area of the substrate (see Japanese Patent Laid-Open Publication No. 2003-268590, patent document 6).

SUMMARY OF THE INVENTION

An accelerator is an additive essential for depositing a plated metal on surfaces of interconnect recesses in a bottom-up manner. In the case of interconnect recesses having a high aspect ratio, it is likely that when an accelerator is adsorbed onto an entire surface of a substrate, including the surfaces of the interconnect recesses, the deposition of a plated metal will be accelerated also in the surfaces of the interconnect recesses in the vicinities of their openings and the openings will be blocked with the plated metal before the interconnect recesses are completely filled with the plated metal that grows in a bottom-up manner. To solve the problem, the method disclosed in the patent documents 1 and 2 performs the accelerator removal treatment using an accelerator remover, e.g., containing a chloride ion, to reduce or remove an accelerator from a substrate surface by utilizing competitive adsorption of the chloride ion on the accelerator. This treatment is preferably carried out while performing reverse electrolysis. Recess-filling plating is carried out after the accelerator removal treatment. However, it has been found that despite the accelerator removal treatment, in some cases, voids are formed in the plated metal embedded in interconnect recesses because of insufficient removal (desorption) of accelerator. A considerably longer plating time will be necessary to prevent the formation of such voids. In addition, the use of reverse electrolysis makes the power feeding system of the plating apparatus complicated.
The present invention has been made in view of the above situation. It is therefore an object of the present invention to provide a plating method and a plating apparatus which can fill a plated metal into interconnect recesses at a higher rate without forming voids in the plated metal embedded in the interconnect recesses.
In order to achieve the above object, the present invention provides a plating method comprising: preparing a substrate having interconnect recesses in a surface; carrying out first pretreatment of the substrate by immersing the substrate in a first pretreatment solution containing an accelerator, a metal ion and an acid; carrying out second pretreatment of the substrate by immersing the substrate in a second pretreatment solution containing an additive which inhibits the effect of the accelerator contained in the first pretreatment solution, and not containing an accelerator; and then carrying out electroplating of the surface of the substrate by using a plating solution containing at least a metal ion, an acid and a suppressor, and not containing an accelerator, thereby filling the plated metal into the interconnect recesses.
By thus carrying out the second pretreatment by immersing a substrate in the second pretreatment solution containing an additive which inhibits the effect of the accelerator contained in the first pretreatment solution, and not containing an accelerator, the accelerator existing in a surface of a field area of the substrate can be more securely deactivated. It therefore becomes possible to fill a plated metal into interconnect recesses at a higher rate without forming voids in the embedded plated metal.
In a preferred aspect of the present invention, the first pretreatment is a preliminary electrolytic treatment carried out by electrolytically treating the surface of the substrate while immersing the substrate in the first pretreatment solution.
In the first pretreatment, by immersing the substrate in the first pretreatment solution containing an accelerator, a metal ion and an acid, the accelerator is allowed to adsorb onto an entire surface of the substrate, including surfaces of the interconnect recesses. This accelerator adsorption process can be stabilized by electrolytically treating the surface of the substrate.
The preliminary electrolytic treatment may be carried out at a current density of 50 to 250 A/m².
A sulfur compound, such as SPS (bis(3-sulfopropyl)disulfide), may preferably be used as the accelerator contained in the first pretreatment solution.
The concentration of the accelerator contained in the first pretreatment solution may generally be 5 to 500 μM/L, preferably 50 to 500 μM/L.
The additive contained in the second pretreatment solution and which inhibits the effect of the accelerator contained in the first pretreatment solution may be a leveler.
An ethyleneimine polymer or a derivative thereof, such as polyethyleneimine (PEI), may preferably be used as the leveler.
PEI has a high accelerator deactivating effect as a leveler. Accordingly, by immersing a substrate, onto which an accelerator has been adsorbed, e.g., in an aqueous sulfuric acid solution containing PEI, the adsorbed accelerator existing in the surface of the field area of the substrate can be selectively deactivated.
Preferably, at least one of the first pretreatment, the second pretreatment and the electroplating is carried out while stirring the treatment solution.
In a preferred aspect of the present invention, the second pretreatment is carried out while stirring the second pretreatment solution, and the electroplating is carried out while stirring the plating solution with a stirring intensity equal to or higher than the stirring intensity in the second pretreatment.
In a preferred aspect of the present invention, the surface of the substrate is cleaned with dilute sulfuric acid after the first pretreatment, and the surface of the substrate is cleaned with dilute sulfuric acid after the second pretreatment.
Compared to the case where the substrate surface is cleaned with pure water, the process stability and uniformity can be enhanced by cleaning the substrate surface with dilute sulfuric acid after the first pretreatment and after the second pretreatment.
The present invention also provides a plating apparatus for carrying out plating of a surface of a substrate having interconnect recesses in the surface, the plating apparatus comprising: a first pretreatment unit for carrying out first pretreatment of the substrate by immersing the substrate in a first pretreatment solution containing an accelerator, a metal ion and an acid; a second pretreatment unit for carrying out second pretreatment of the substrate by immersing the substrate in a second pretreatment solution containing an additive which inhibits the effect of the accelerator contained in the first pretreatment solution, and not containing an accelerator; and a plating unit for carrying out electroplating of the surface of the substrate after the second pretreatment by using a plating solution containing at least a metal ion, an acid and a suppressor, and not containing an accelerator, thereby filling the plated metal into the interconnect recesses.
In a preferred aspect of the present invention, the first pretreatment unit is configured to carry out an electrolytic treatment of the surface of the substrate while immersing the substrate in the first pretreatment solution.
In a preferred aspect of the present invention, the plating apparatus further comprises a first cleaning unit for cleaning with dilute sulfuric acid the surface of the substrate which has undergone the first pretreatment in the first pretreatment unit, and a second cleaning unit for cleaning with dilute sulfuric acid the surface of the substrate which has undergone the second pretreatment in the second pretreatment unit.
In a preferred aspect of the present invention, at least one of the first pretreatment unit, the second pretreatment unit and the plating unit is provided with a stirring device for stirring the treatment solution; and the plating apparatus includes a control section for controlling the stirring speed of the stirring device, the first pretreatment time in the first pretreatment unit, the second pretreatment time in the second pretreatment unit, and the electroplating time in the plating unit.
In a preferred aspect of the present invention, the second pretreatment unit is provided with a stirring device for stirring the second treatment solution; and the control section, based on the width or diameter and the depth of the interconnect recesses, determines the substrate immersion time in the second pretreatment and the stirring intensity of the second pretreatment solution.
According to the present invention, plating of a surface of a substrate can be carried out in the presence of an accelerator which has been adsorbed onto the surface of the substrate and which is active surfaces of interconnect recesses but has been fully deactivated in a surface of a field area of the substrate. This makes it possible to fill a plated metal into the interconnect recesses at a higher rate without forming voids in the embedded plated metal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall plan view of a plating apparatus according to an embodiment of the present invention;

FIG. 2 is a schematic view of a first pretreatment unit provided in the plating apparatus shown in FIG. 1;

FIG. 3 is a schematic view of a second pretreatment unit provided in the plating apparatus shown in FIG. 1;

FIG. 4 is a schematic view of a plating unit provided in the plating apparatus shown in FIG. 1;

FIGS. 5A through 5C are diagrams illustrating a sequence of process steps for filling a plated metal into interconnect recesses by the plating apparatus shown in FIG. 1;

FIG. 6 is a series of cross-sectional photomicrographs of a test chip after electroplating, showing the results of a verification experiment on preliminary electrolysis conditions in the first pretreatment;

FIG. 7 is a series of cross-sectional photomicrographs of a test chip after electroplating, showing the results of a verification experiment on the concentration of an accelerator in a first pretreatment solution in the first pretreatment;

FIG. 8 is a series of cross-sectional photomicrographs of a test chip after electroplating, showing the results of a verification experiment on the concentration of an additive (leveler) in a second pretreatment solution in the second pretreatment;

FIG. 9 is a series of cross-sectional photomicrographs of a test chip after electroplating, showing the results of a verification experiment on the chip immersion time in the second pretreatment;

FIG. 10 is a series of cross-sectional photomicrographs of a test chip after electroplating, showing the results of a verification experiment on plating overvoltage in electroplating;

FIG. 11 is a series of cross-sectional photomicrographs of a test chip after electroplating, showing the results of a verification experiment on desorption of an accelerator by reverse electrolysis in a high-concentration chloride ion-containing solution, conducted as a reference experiment;

FIG. 12 is a graph showing the relationship between the rotational speed of a rotational circular plate and a thickness of a diffusion layer formed over a substrate surface in a copper sulfate plating solution;

FIG. 13 is a graph showing the relationship between the depth from an upper surface of a diffusion layer and the normalized concentration of a chemical species; and

FIG. 14 is a graph showing the relationship between the diameter of a via hole and the intrusion depth of the flow of a treatment solution into the via hole.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described with reference to the drawings. The following description illustrates an exemplary case in which a substrate W having interconnect recesses 12, such as trenches and via holes, formed in a surface and covered with a seed layer 10, as shown in FIG. 5A, is prepared; and a metal plated film 14 of copper is filled into the interconnect recesses 12 to form interconnects of copper, as shown in FIG. 5C.
FIG. 1 shows an overall plan view of a plating apparatus according to an embodiment of the present invention. As shown in FIG. 1, the plating apparatus 20 includes three loading/unloading sections 22 each for mounting therein a substrate cassette in which a plurality of substrates W are housed, a first pretreatment unit 24 for carrying out first pretreatment of a substrate W by immersing the substrate W in a first pretreatment solution containing an accelerator, a metal ion and an acid, a second pretreatment unit 26 for carrying out second pretreatment of the substrate W by immersing the substrate W in a second pretreatment solution containing an additive which inhibits the effect of the accelerator contained in the first pretreatment solution, and not containing an accelerator, and two plating units 28 for carrying out electroplating of the surface of the substrate W by using a plating solution containing at least a metal ion, an acid and a suppressor, and not containing an accelerator.
The plating apparatus 20 also includes three cleaning units 30 a, 30 b, 30 c each for cleaning (rinsing) the surface of the substrate W with dilute sulfuric acid, a cleaning/drying unit 32 for cleaning and drying the substrate W after electroplating, and a substrate stage 34 for temporarily placing thereon the substrate W before or after processing. A first substrate transport device 36 is disposed movably between the loading/unloading sections 22 and the substrate stage 34, and a second substrate transport device 38 is disposed movably between the substrate stage 34 and the units. All the units, including the first pretreatment unit 24, the second pretreatment unit 26 and the plating units 28, are controlled by a control section 40 provided in an exterior panel of the plating apparatus 20.
In this embodiment, an electrolytic treatment unit for carrying out electrolytic treatment (plating) of a surface of a substrate W is used as the first pretreatment unit 24. Thus, as shown in FIG. 2, the first pretreatment unit 24 includes a treatment tank 44 for holding therein a first pretreatment solution 42 containing an accelerator, e.g., a sulfur compound such as SPS (bis (3-sulfopropyl)disulfide), a metal ion (copper ion) and an acid. The concentration of the accelerator (SPS) in the first pretreatment solution 42 is generally 5 to 500 μM/L, preferably 50 to 500 μM/L.
The first pretreatment unit 24 also includes a vertically movable substrate holder 46 for detachably holding a substrate W and immersing the substrate W in the first pretreatment solution 42 at a predetermined position in the treatment tank 44, an anode 50, e.g., made of phosphorus-containing copper, held by an anode holder 48 and to be immersed in the first pretreatment solution 42 at a predetermined position in the treatment tank 44, and stirring paddles 54 as a stirring device, which reciprocate by actuation of a stirring mechanism 52 to stir the first pretreatment solution 42 between the anode 50 and the substrate W.
In operation, the substrate W held by the substrate holder 46 is immersed in the first pretreatment solution 42 at a predetermined position, facing the anode 50, in the treatment tank 44. The negative pole of a power source 58 is connected via a conducting wire 56 a to the substrate W, and the positive pole of the power source 58 is connected via a conducting wire 56 b to the anode 50 to carry out preliminary electrolytic treatment (plating) of the surface of the substrate Was the first pretreatment. During this treatment, the stirring paddles 54 of the stirring mechanism 52 are reciprocated to stir the first pretreatment solution 42 as necessary. The current density in the preliminary electrolytic treatment is, for example, 50 to 250 A/m². The time for immersion of the substrate W in the first pretreatment solution 42, the stirring speed of the stirring paddles 54, the current density, etc. during this treatment are controlled by the control section 40.
As shown in FIG. 3, the second pretreatment unit 26 includes a treatment tank 62 for holding therein a second pretreatment solution 60 containing an additive, e.g., PEI (polyethyleneimine) as a leveler, which inhibits the effect of the accelerator, e.g., a sulfur compound such as SPS (bis(3-sulfopropyl)disulfide), and not containing an accelerator. The second pretreatment unit 26 also includes a vertically movable substrate holder 64 for detachably holding a substrate W and immersing the substrate W in the second pretreatment solution 60 at a predetermined position in the treatment tank 62, and stirring paddles 68 as a stirring device, which reciprocate by actuation of a stirring mechanism 66 to stir the second pretreatment solution 60 in front of the substrate W.
In operation, the substrate W held by the substrate holder 64 is immersed in the second pretreatment solution 60 at a predetermined position in the treatment tank 62 to carry out second pretreatment of the surface of the substrate W. During this treatment, the stirring paddles 68 of the stirring mechanism 66 are reciprocated to stir the second pretreatment solution 60 as necessary. The time for immersion of the substrate W in the second pretreatment solution 60, the stirring speed of the stirring paddles 68, etc. during this treatment are controlled by the control section 40.
As shown in FIG. 4, the plating unit 28 includes a plating tank 72 for holding therein a plating solution 70 containing a suppressor, e.g., PEG (polyethylene glycol), a metal ion (copper ion) and an acid. The concentration of the suppressor (PEG) in the plating solution 70 is, for example, 1 mM/L.
The plating unit 28 also includes a vertically movable substrate holder 74 for detachably holding a substrate W and immersing the substrate W in the plating solution 70 at a predetermined position in the plating tank 72, an anode 78, e.g., made of phosphorus-containing copper, held by an anode holder 76 and to be immersed in the plating solution 70 at a predetermined position in the plating tank 72, and stirring paddles 82 as a stirring device, which reciprocate by actuation of a stirring mechanism 80 to stir the plating solution 70 between the anode 78 and the substrate W.
In operation, the substrate W held by the substrate holder 74 is immersed in the plating solution 70 at a predetermined position, facing the anode 78, in the plating tank 72. The negative pole of a plating power source 86 is connected via a conducting wire 84 a to the substrate W, and the positive pole of the plating power source 86 is connected via a conducting wire 84 b to the anode 78 to carry out electroplating of the surface of the substrate W. During this plating, the stirring paddles 82 of the stirring mechanism 80 are reciprocated to stir the plating solution 70 as necessary. The plating conditions, the stirring speed of the stirring paddles 82, etc. during this plating are controlled by the control section 40.
The operation of the plating apparatus shown in FIG. 1 will now be described with reference also to FIGS. 5A to 5C.
First, an unprocessed substrate W is taken by the first substrate transport device 36 out of a substrate cassette mounted in one of the loading/unloading units 22, and the substrate W is transported to the substrate stage 34. The substrate W on the substrate stage 34 is then transported by the second substrate transport device 38 to the cleaning unit 30 a, where a surface of the substrate W is cleaned (rinsed) with dilute sulfuric acid. The substrate W after cleaning is then transferred to the substrate holder 46 of the first pretreatment unit 24.
In the first pretreatment unit 24, as shown in FIG. 2, the substrate W is immersed in the first pretreatment solution 42 at a predetermined position in the treatment tank 44, and a voltage is applied between the substrate W and the anode 50, disposed opposite each other, to carry out preliminary electrolytic treatment (plating) of the surface of the substrate W as the first pretreatment. By the first pretreatment, the accelerator 90, such as SPS, is adsorbed onto the entire surface of the substrate W, including surfaces of the interconnect recesses 12, as shown in FIG. 5A. During this treatment, the first pretreatment solution 42 in the treatment tank 44 is stirred with the stirring paddles 54 as necessary. The first pretreatment conditions, the stirring speed of the stirring paddles 54, etc. are controlled by the control section 40.
The substrate W after the first pretreatment is then transported by the second substrate transport device 38 to the cleaning unit 30 b, where the surface of the substrate W is cleaned (rinsed) with dilute sulfuric acid. The substrate W after cleaning is transferred to the substrate holder 64 of the second pretreatment unit 26.
In the second pretreatment unit 26, as shown in FIG. 3, second pretreatment of the surface of the substrate W is carried out by immersing the substrate W in the second pretreatment solution 60 in the treatment tank 62. By the second pretreatment, the additive (leveler) 92, such as PEI, is adsorbed onto the surfaces of the interconnect recesses 12 in the vicinities of their openings and onto the surface of the field area of the substrate, as shown in FIG. 5B. During this treatment, the second pretreatment solution 60 in the treatment tank 62 is stirred with the stirring paddles 68 as necessary. The second pretreatment conditions, the stirring speed of the stirring paddles 68, etc. are controlled by the control section 40.
By thus allowing the additive (leveler) 92, such as PEI, to adsorb onto the surfaces of the interconnect recesses 12 in the vicinities of their openings and onto the surface of the field area of the substrate, the accelerator 90 such as SPS, which has been adsorbed onto the surfaces of the interconnect recesses 12 in the vicinities of their openings and onto the surface of the field area of the substrate, can be deactivated by the additive 92 while maintaining the effect of the accelerator 90 existing in the interconnect recesses 12. In particular, it has been confirmed that PEI has a high SPS deactivating effect as a leveler, and SPS, existing in a surface of a field area of a substrate, can be selectively deactivated by immersing the substrate, onto which SPS has been adsorbed in the entire surface area, in an aqueous sulfuric acid solution containing PEI.
The substrate W after the second pretreatment is transported by the second substrate transport device 38 to the cleaning unit 30 c, where the surface of the substrate W is cleaned (rinsed) with dilute sulfuric acid. The substrate W after cleaning is transferred to the substrate holder 74 of the plating unit 28.
In the plating unit 28, as shown in FIG. 4, the substrate W is immersed in the plating solution 70 at a predetermined position in the plating tank 72, and a voltage is applied between the substrate W and the anode 78, disposed opposite each other, to carry out electroplating of the surface of the substrate W. During this plating, the plating solution 70 in the plating tank 72 is stirred with the stirring paddles 82 as necessary. The plating conditions and the stirring speed of the stirring paddles 82 are controlled by the control section 40.
By thus carrying out electroplating of the substrate W after deactivating with the additive (leveler) 92 the accelerator 90 such as SPS, which has been adsorbed onto the surfaces of the interconnect recesses 12 in the vicinities of their openings and onto the surface in the field area of the substrate, while maintaining the effect of the accelerator 90 existing in the interconnect recesses 12, the (bottom-up) deposition of the plated metal (copper) 14 on the bottoms of the interconnect recesses 12 can be accelerated by the action of the accelerator 90 while suppressing the deposition of the plated metal 14 on the surface of the field area of the substrate W by the action of the suppressor contained in the plating solution, as shown in FIG. 5C.
The substrate W after plating is transported by the second substrate transport device 38 to the cleaning/drying unit 32, where the surface of the substrate W is cleaned (rinsed), e.g., with pure water and dried. The substrate W after drying is transported by the second substrate transport device 38 to the substrate stage 34. The first substrate transport device 36 takes up the substrate W from the substrate stage 34 and returns it to the substrate cassette of the loading/unloading section 22.
An accelerator, such as SPS, is an additive essential for depositing a plated metal from bottoms of interconnect recesses such as trenches and via holes, i.e., in a bottom-up manner. In the case of interconnect recesses having a high aspect ratio, it is likely that when an accelerator is adsorbed onto an entire surface of a substrate, including surfaces of the interconnect recesses, and the effect of the accelerator is exerted, the deposition of a plated metal will be accelerated also the surfaces of the interconnect recesses 12 in the vicinities of their openings and the openings will be blocked with the plated metal before the interconnect recesses are completely filled with the plated metal that grows in a bottom-up manner.
To solve the problem, according to the present invention, a substrate is first subjected to the first pretreatment in which the substrate is immersed in a first pretreatment solution containing an accelerator, a metal ion and an acid, e.g., an aqueous copper sulfate solution containing an accelerator such as SPS, and a chloride ion, while electrolytically treating a surface of the substrate as necessary, thereby allowing the accelerator to adsorb onto the entire surface of the substrate, including surfaces of interconnect recesses. The substrate is then subjected to the second pretreatment in which the substrate is immersed in a second pretreatment solution containing an additive (leveler), such as PEI, which inhibits the effect of the accelerator, to deactivate the accelerator existing in the surface of the field area of the substrate and the surfaces of the interconnect recesses in the vicinities of their openings. The additive (leveler) can diffuse to the surfaces of the interconnect recesses only in a small amount and, therefore, the accelerator remains active in the surfaces of the interconnect recesses. The substrate is then subjected to electroplating in the presence of the accelerator in such a state, using a plating solution containing a metal ion, an acid and a suppressor. Thus, bottom-up deposition of a plated metal progresses from the bottoms of the interconnect recesses where the effect of the accelerator is maintained, whereas deposition of the plated metal is suppressed by the effect of the suppressor in the surface of the field area of the substrate where the accelerator has been deactivated. It is not likely that the openings of the interconnect recesses will be blocked with the plated metal before the interconnect recesses are filled with the bottom-up grown plated metal even when a high plating current is employed to achieve a high plating rate. It therefore becomes possible to fill the plated metal into the interconnect recesses at a higher rate.
In order to determine the optimum treatment conditions for the first pretreatment, the second pretreatment and the electroplating, the effects of various treatment conditions on the filling of plated metal into interconnect recesses were examined by chip testing. The results are described below. A patterned chip, having a pattern of via holes (interconnect recesses) with varying diameters of 20, 30, 40 and 50 μm and a depth of 60 μm, was used as a test chip. Electroplating of the test chip after pretreatment was carried out in a 6-mm diameter area centered on the pattern, using a masking tape. A three electrode-type cell was fabricated using the test chip, a reference electrode (mercury/mercury sulfate electrode), a platinum anode and a 200-mL beaker, and first pretreatment and electroplating were carried out in the cell under control of the electric potential by a potentiostat.
An aqueous sulfuric acid/copper sulfate solution (0.9 M CuSO₄.5H₂O/0.56 M H₂SO₄) was used as a basic plating bath, and an aqueous 1M H₂SO₄solution was used for cleaning (rinsing) between treatment steps. For cleaning (rinsing) between treatment steps, the use of dilute sulfuric acid is preferred to the use of pure water from the viewpoint of ensuring process stability and uniformity.
A solution, obtained by adding to the basic bath PEG (polyethylene glycol) as a suppressor at a concentration of 0.1 mM, a chloride ion at a concentration of 1 mM, and SPS (bis(3-sulfopropyl)disulfide) as an accelerator at a predetermined concentration, was used as a first pretreatment solution. In the first pretreatment, the test chip was immersed in the first pretreatment solution, and electric current was applied to allow the accelerator (SPS) to adsorb onto the entire surface of the chip, including surfaces of the via holes. In the second pretreatment, the test chip was immersed in a second pretreatment solution obtained by adding PEI (polyethyleneimine) at a predetermined concentration to an aqueous sulfuric acid solution. In the electroplating, using a plating solution obtained by adding only PEG (polyethylene glycol) as a suppressor at a concentration of 0.1 mM and a chloride ion at a concentration of 1 mM to the basic bath, the plated metal (copper) was deposited on the surface of the test chip at a predetermined electric potential, thereby filling the plated metal (copper) into the via holes.
In each treatment, the treatment solution was stirred by means of a stirrer chip at a rotational speed of 200 rpm. Cleaning (rinsing) of the test chip with the aqueous sulfuric acid solution was carried out for 30 seconds before the first pretreatment, and for 20 seconds between treatments. During the cleaning, the cell was kept in its open circuit state. After the plating, a cross-section of the test chip was polished to observe the state of copper embedded in the via holes.
Evaluations were made of the effects of the following treatment conditions: the preliminary electrolysis current during immersion of the substrate (chip) in the first pretreatment solution and the concentration of the accelerator in the first pretreatment solution in the first pretreatment; the concentration of the additive (leveler) in the second pretreatment solution and the substrate immersion time in the second pretreatment; and the overvoltage upon plating in the electroplating. The detailed descriptions are described below.

A. Preliminary Electrolysis Conditions in the First Pretreatment

An experiment was conducted to examine the effect of preliminary electrolysis conditions (current conditions) in the first pretreatment. 50 A/m², 100 A/m²and 250 A/m²were selected as a current density for use during immersion of the substrate (chip) in the first treatment solution in the first pretreatment. In order to make electric charge, applied for adsorption of the accelerator, constant in total (3000 Q/m²) for all the selected current densities, the preliminary electrolysis time was varied as follows: 600 sec, 300 sec and 120 sec. The concentration of the accelerator in the first pretreatment solution was 50 μM. The other process conditions are shown in Table 1 below. The results of the experiment are shown in FIG. 6 which is a series of cross-sectional photomicrographs of the test chip after the process. As can be seen from FIG. 6, the plating growth rate is the highest in the case of 300 sec-100 A/m². FIG. 6 also indicates that the increase in the current causes no increase in the plating growth rate. In this regard, it is conceivable that diffusion of the accelerator may also affect preliminary adsorption of the accelerator.

TABLE 1

Additives	Potential/	Current density/

Process	Basis	PEG/mM	Cl/mM	SPS/μM	PEI/μM	Time/s	mV. vs MSE	A/m²

Rinse

H₂SO₄

—

30

Open Circuit

1st bath

Plating Bath

0.1

1

50

—

600, 300, 120

—

−50, −100, −250

Rinse	H₂SO₄	—	—	—	—	25	Open Circuit
2nd bath	H₂SO₄	—	—	—	1	30	Open Circuit
Rinse	H₂SO₄	—	—	—	—	25	Open Circuit

3rd bath	Plating Bath	0.1	1	—	—	1800	−575	—

Though adsorption of an accelerator onto a surface of a substrate is possible merely by immersing the substrate in a first pretreatment solution containing the accelerator, a metal ion and an acid, it is preferred to use electrolysis in order to stabilize the process.

B. The Concentration of the Accelerator in the First Pretreatment Solution in the First Pretreatment

An experiment was conducted to examine the effect of the concentration of the accelerator in the first pretreatment solution in the first pretreatment. 5 μM, 50 μM and 500 μM were selected as the concentration of the accelerator in the first pretreatment solution. The preliminary electrolysis was carried out under the conditions of 300 sec-100 A/m². The other process conditions are shown in Table 2 below. The results of the experiment are shown in FIG. 7 which is a series of cross-sectional photomicrographs of the test chip after the process. As can be seen from FIG. 7, with reference to the 20-μm via hole, the plating growth rate is the highest when the concentration of the accelerator in the first pretreatment solution is 50 μM. With reference to the via holes having a diameter of 30-50 μm, the plating growth rate increases with the increase in the accelerator concentration. The optimum concentration of the accelerator in the first pretreatment is therefore considered to lie between 50 μM and 500 μM.

TABLE 2

Additives	Potential/	Current density/

Process	Basis	PEG/mM	Cl/mM	SPS/μM	PEI/μM	Time/s	mV. vs MSE	A/m²

Rinse

H₂SO₄

—

30

Open Circuit

1st bath

Plating Bath

0.1

1

5, 50, 500

—

300

—

−100

3rd bath	Plating Bath	0.1	1	—	—	1800	−575	—

C. The Concentration of the Additive (Leveler) in the Second Pretreatment Solution in the Second Pretreatment

An experiment was conducted to examine the effect of the concentration of the additive (leveler) in the second pretreatment solution in the second pretreatment. 0.1 μM, 1 μM and 10 μM were selected as the concentration of the additive in the second pretreatment solution. The time for immersion of the chip in the second pretreatment solution was 30 seconds. The other process conditions are shown in Table 3 below. The results of the experiment are shown in FIG. 8 which is a series of cross-sectional photomicrographs of the test chip after the process. As can be seen from FIG. 8, when the second pretreatment of the chip was carried out by immersing the chip in the second pretreatment solution having the additive concentration of 0.1 μM for 30 seconds, the openings of the via holes were blocked with the copper plated upon the electroplating and voids were formed in the copper embedded in the via holes. This indicates that the effect of the additive to deactivate the accelerator, existing in the surface of the field area of the chip and the surfaces of the via holes in the vicinities of their openings, is insufficient. From the growth of the plated metal in the via holes, 1 μM is considered appropriate as the concentration of the additive in the second pretreatment solution. FIG. 8 also demonstrates that the accelerator is fully deactivated in the entire surface of the chip and plating progresses uniformly when the second pretreatment is carried out by immersing the chip in the second pretreatment solution having the additive concentration of 10 μM for 30 seconds.

TABLE 3

Additives	Potential/	Current density/

Process	Basis	PEG/mM	Cl/mM	SPS/μM	PEI/μM	Time/s	mV. vs MSE	A/m²

Rinse

H₂SO₄

—

30

Open Circuit

1^stbath

Plating Bath

0.1

1

50

—

300

—

−50, −100, −250

Rinse	H₂SO₄	—	—	—	—	25	Open Circuit
2^ndbath	H₂SO₄	—	—	—	0.1, 1, 10	30	Open Circuit
Rinse	H₂SO₄	—	—	—	—	25	Open Circuit

3^rdbath	Plating Bath	0.1	1	—	—	1800	−575	—

D. The Substrate Immersion Time in the Second Pretreatment

An experiment was conducted to examine the effect of the time for immersion of the substrate (chip) in the second pretreatment solution in the second pretreatment. 1 μM was selected as the concentration of the additive in the second pretreatment solution. The chip immersion time was varied as follows: 5 sec, 30 sec and 60 sec. The other conditions are shown in Table 4 below. The results of the experiment are shown in FIG. 9 which is a series of cross-sectional photomicrographs of the test chip after the process. As can be seen from FIG. 9, the plated metal can be filled into the via holes at the highest rate when the second pretreatment is carried out by immersing the chip in the second pretreatment solution for 5 seconds. This is considered to be due to the fact that compared to the case where the chip is immersed in the second pretreatment solution for 30 seconds, the deactivated accelerator is more limited to that existing in a top area of the via holes. As will be appreciated from the effect of the additive concentration of the second pretreatment solution and the effect of the chip immersion time, the consumption and the diffusion of the additive (leveler) are important factors in the second pretreatment.

TABLE 4

Additives	Potential/	Current density/

Process	Basis	PEG/mM	Cl/mM	SPS/μM	PEI/μM	Time/s	mV. vs MSE	A/m²

rinse

H₂SO₄

—

30

Open Circuit

1st bath

Plating Bath

0.1

1

50

—

300

—

−100

rinse	H₂SO₄	—	—	—	—	25	Open Circuit
2nd bath	H₂SO₄	—	—	—	1	5, 30, 60	Open Circuit
rinse	H₂SO₄	—	—	—	—	25	Open Circuit

3rd bath	Plating Bath	0.1	1	—	—	1800	−575	—

E. Plating Overvoltage in the Electroplating

An experiment was conducted to examine the effect of the electric potential during the electroplating. Because the accelerator, existing in the surface of the field area of the chip and the surfaces of the via holes in the vicinities of their openings, is deactivated by the second pretreatment, it is considered possible to use a high plating current. In order to verify this, electroplating was conducted at the following varying electric potentials: −550 mV, −575 mV and −600 mV. The other process conditions are shown in Table 5 below. The results of the experiment are shown in FIG. 10 which is a series of cross-sectional photomicrographs of the test chip after the process. As can be seen from FIG. 10, when the electroplating was carried out at the highly negative potential −600 mV, the plated metal (copper) was completely filled into the 20-μm via hole in 30 minutes without forming voids in the embedded plated metal. Further, an adverse effect of the deposition of the plated metal in the surface of the field area of the chip on the filling of the plated metal into the via holes, which is a concern associated with the change of electric potential, was not observed.

TABLE 5

Additives	Potential/	Current density/

Process	Basis	PEG/mM	Cl/mM	SPS/μM	PEI/μM	Time/s	mV. vs MSE	A/m²

Rinse

H₂SO₄

—

30

Open Circuit

1st bath

Plating Bath

0.1

1

50

—

300

—

−100

3rd bath	Plating Bath	0.1	1	—	—	1800	−550, −575, −600	—

A reference experiment was conducted to examine desorption of the accelerator by reverse electrolysis in a high-concentration chloride ion-containing solution.

F. Desorption of the Accelerator by Reverse Electrolysis in a High-Concentration Chloride Ion-Containing Solution (Reference Experiment)

The same basic bath as used in the above experiments was used in this reference experiment. Preliminary electrolytic treatment (first pretreatment) was first carried out at a current density of 100 A/m²for 300 seconds while immersing the above-described test chip in the same first pretreatment solution as described above, containing the accelerator at a concentration of 100 μM. Next, in order to desorb the accelerator from the surface of the field area of the chip, the chip was immersed in a treatment solution containing a chloride ion at a high concentration, and the system was subjected to reverse electrolysis. After this treatment, copper electroplating of the surface of the chip was carried out. The details of the process conditions are shown in Table 6 below. The results of the experiment are shown in FIG. 11 which is a series of cross-sectional photomicrographs of the test chip after the process.

	TABLE 6

	Additives		Current

		PEG/	Cl/	SPS/		Potential/	density/
Process	Basis	mM	mM	μM	Time/s	mV	A/m²

1st bath	Standard	0.1	1	100	300	—	−100
2nd	Standard	0.1	1	—	20	—	100
bath
3rd bath	Standard	0.1	1	—	3000	−575	—

As can be seen from FIG. 11, when the electroplating was carried out for 3000 seconds to fill the plated metal (copper) into the via holes, a void was formed centrally in the plated metal (copper) embedded in the 20-μm via hole. This indicates that the main copper plating must be carried out at least for 3000 seconds if the chip is pretreated by the accelerator desorbing method in which the chip is immersed in the treatment solution containing a chloride ion at a high concentration while carrying out reverse electrolysis in order to remove the accelerator from the surface of the field area of the chip. Regarding this pretreatment method, the reverse electrolysis promotes desorption of the accelerator. Thus, if the accelerator desorbing pretreatment is carried out without the reverse electrolysis, i.e., merely by immersing the chip in the treatment solution, the accelerator desorbing effect will be insufficient, whereby deposition of the plated metal will not be sufficiently suppressed in the surface of the field area of the chip and the surfaces of the via holes in the vicinities of their openings.
The results of the above experiments thus demonstrate that a plated metal can be filled into interconnect recesses of a substrate at a high rate by carrying out the first pretreatment of the substrate by immersing the substrate in a first pretreatment solution containing an accelerator such as SPS, a metal ion and an acid, carrying out the second pretreatment of the substrate by immersing the substrate in a second pretreatment solution containing an additive (leveler), such as PEI, which inhibits the effect of the accelerator contained in the first pretreatment solution, and then carrying out electroplating of the substrate by using a plating solution containing at least a metal ion, an acid and a suppressor, and not containing an accelerator. In particular, PEI as an additive (leveler) has a high SPS deactivating effect. SPS, which has been adsorbed onto a substrate surface, can be deactivated by immersing the substrate in an aqueous sulfuric acid solution containing PEI.
According to the present invention, by carrying out the second pretreatment of a substrate by immersing the substrate in a second pretreatment solution containing an additive (leveler), such as PEI, an accelerator such as SPS, which has been adsorbed onto the substrate surface, can be selectively deactivated in the surface of the field area of the substrate, i.e., the surface area other than surfaces of interconnect recesses. This enables selective growth of plated metal from the bottoms of the interconnect recesses. Therefore, for a via hole having a diameter of 20 μm and a depth of 60 μm, for example, void-free via-filling plating can be completed in 30 minutes, and in the total treatment time, including the pretreatment time, of no more than 40 minutes.
The above-described experimental results also indicate the capability of controlling the depth in interconnect recesses, to which the accelerator deactivating effect can be exerted effectively, by controlling the amount of adsorption of an accelerator, such as SPS, in the first pretreatment and the accelerator deactivating effect in the second pretreatment. This in turn indicates the capability of void-free high-rate filling of plated metal into interconnect recesses, such as trenches and via holes, of various depths through adjustment of the pre-plating treatment conditions. In particular, the intended recess-filling plating can be achieved by changing the concentration of an additive (leveler) in a second pretreatment solution, the substrate immersion time, etc. in the second pretreatment depending on the aspect ratio of interconnect recesses. The solution stirring conditions also affect the depth in interconnect recesses to which an accelerator is deactivated.
When a flow of a treatment solution is produced over a substrate surface, e.g., by stirring, a thickness of a diffusion layer, formed in the vicinity of the substrate surface, generally is inversely proportional to the velocity of the flow. A method to control the flow velocity of a treatment solution, flowing over a substrate surface, is to use a rotational circular plate. In this method, the rotational speed of a rotational circular plate is proportional to the flow velocity of a treatment solution flowing over the surface of the rotational circular plate. With reference to a thickness of a diffusion layer formed over a surface of a rotating circular plate, the relationship between the rotational speed ω of the circular plate and the thickness δ of the diffusion layer can be analytically determined by the following formula (V. G. Levich et al., “Physicochemical Hydrodynamics”, Prentice-Hall, Englewood Cliffs, N.J. (1962)): δ=1.61D^1/3ν^1/6ω^−1/2(wherein D represents diffusion coefficient, and ν represents kinetic viscosity).
FIG. 12 is a graph showing the relationship, calculated according to the above formula, between the rotational speed of a rotational circular plate and a thickness of a diffusion layer formed over a substrate surface in an aqueous copper sulfate/sulfuric acid solution (copper sulfate plating solution) as a copper plating solution.
In the case where because of small width or diameter of interconnect recesses, such as trenches and via holes, no flow of a treatment solution is produced in the interconnect recesses, a thickness of a diffusion layer, formed over the substrate surface depending on the flow velocity of the treatment solution flowing over the substrate surface, determines the time it takes for a substance to move from a point in the solution to the substrate surface. In the diffusion layer, a substance moves mainly by diffusion. Taking a one-dimensional model as an example for simplicity, change with time in the concentration of a chemical species, which diffuses from an upper surface of a diffusion layer, can be determined as shown in FIG. 13 by solving the diffusion equation. The diffusion coefficient of copper ions in a copper sulfate plating solution is used as the diffusion coefficient in the diffusion equation.
As can be seen from FIG. 13, the longer the distance of a point from the upper surface of the diffusion layer, the more time it takes for the chemical species to reach that point.
Further, it is apparent from FIG. 12 that the thickness of the diffusion layer depends on the flow velocity of the treatment solution. These data suggest that in the first pretreatment the stirring intensity of a first pretreatment solution should be strong so that a large amount of chemical species (accelerator) will be supplied and adsorbed onto bottoms of interconnect recesses, such as via holes and trenches, of a substrate, whereas in the second pretreatment stirring of a second pretreatment solution should be performed gently so that a chemical species (additive (leveler)) will reach only to the surface in the field area of the substrate and the surfaces of the interconnect recesses in the vicinities of their openings.
On the other hand, in the case where because of large width or diameter of interconnect recesses, such as trenches and via holes, a flow of a treatment solution is produced also in the interconnect recesses by stirring of the solution, the flow of the treatment solution affects the movement distance of a substance which moves in the depth direction of the interconnect recesses.
For example, consider now three types of via holes having diameters of 10 μm, 30 μm and 50 μm, respectively, which are expected to allow a treatment solution to intrude into the via holes when the treatment solution is stirred. On the assumption that all the via holes have a depth of 70 μm, and the treatment solution is stirred by means of paddles at a paddle movement speed of 0.3 m/sec or 1.3 m/sec, a numerical analysis is made to determine the flow state of the treatment solution in the via holes and the surfaces of the via holes in the vicinities of their openings. Based on the analytical results, evaluations can be made of the intrusion of the flow of the pretreatment solution into a via hole in relation to the stirring intensity and the diameter of the via hole, as follows. FIG. 14 shows the relationship between the diameter of a via hole and the intrusion depth of the flow of the treatment solution into the via hole. In FIG. 14, the intrusion depth is defined as the depth which is reached by the flow of the treatment solution at a flow velocity of 1 mm/sec.
As can be seen from FIG. 14, the intrusion depth increases with increase in the via hole diameter when the treatment solution is stirred at the same paddle movement speed. In order to obtain in the 50-μm via hole the same intrusion depth of the flow of a second pretreatment solution as that obtained in the 10-μm via hole when the solution is stirred at a paddle movement speed of 1.3 mm/sec, it is necessary to stir the solution at a paddle movement speed of 0.3 m/sec. Thus, the flow velocity distribution in a larger diameter via hole in the depth direction of the via hole can be made similar to that in a smaller diameter via hole by using a lower stirring intensity. Accordingly, by controlling the stirring intensity (movement speed) of stirring paddles during the second pretreatment, the effect of an additive (leveler) in the depth direction of interconnect recesses can be equalized for interconnect recesses of various diameters or widths.
As described above, in the second pretreatment, the depth range in interconnect recesses in which the effect of an additive (leveler) is exerted can be controlled by controlling the stirring intensity of a second pretreatment solution whether the interconnect recesses are narrow ones in which no flow of the solution is produced upon stirring of the solution or wide ones in which a flow of the solution is produced upon stirring of the solution. Therefore, for a substrate having any size of interconnect recesses, the effect of an accelerator can be inhibited in the surface of the field area of the substrate and the surfaces of the interconnect recesses in the vicinities of their openings, whereas the effect of the accelerator can be maintained in the interconnect recesses, especially in their bottoms. This enables bottom-up growth of plating.
A depth of the surfaces of the interconnect recesses in the vicinities of their openings, to which the effect of the accelerator can be suppressed, is preferably ranging about from a half to one-third of a depth from the surface of the field area of the substrate to the bottoms of the interconnect recesses. An additive (leveler) for suppressing the effect of the accelerator is transported by diffusion from the upper surface of the diffusion layer formed over the substrate surface to the bottoms of the interconnect recesses. Therefore, the effect for suppressing the accelerator is inversely proportional to the distance from the closest upper surface of the diffusion layer.
In the electroplating, it is necessary to quickly supply metal ions to bottoms of interconnect recesses, and therefore strong stirring of a plating solution is required. Accordingly, a plating solution should preferably be stirred in the electroplating with a stirring intensity equal to or higher than that in the second pretreatment.
Though SPS has been described as an accelerator, it is possible to use other sulfur compounds as an accelerator. Examples of other usable sulfur compounds include an isomer of SPS, bis(3-sulfo-2-hydroxypropyl)disulfide and its sodium salt, 3-(benzothiazolyl-2-thio)propylsulfonic acid and its sodium salt, 3-sulfopropyl N,N-dimethyldithiocarbamate and its sodium salt, O-ethyl-S-(3-sulfopropyl)-diethylcarbonate and its potassium salt, thiourea and its derivatives, etc.
Though PEI has been described as an additive (leveler), it is possible to use other compounds which inhibit the effect of the accelerator used. Examples of such compounds include nitrogen-containing polymers, e.g., cationic polymers such as polyvinyl pyrrolidone or its derivatives, and Janus Green B which has conventionally been used as a leveler; amide compounds; thioamide compounds; compounds having an aniline or pyridine ring; heterocyclic compounds; condensed heterocyclic compounds; and aminocarboxylic acids.
Though polyethylene glycol has been described as a suppressor for use in plating, it is possible to use other suppressors. Examples of other usable suppressors include polypropylene glycol, a copolymer of ethylene glycol and propylene glycol, and its derivatives, polyvinyl alcohol, carboxymethyl cellulose, etc.
A via hole having a diameter of 20 μm and a depth of 60 μm, for example, is used in the above-described experiments. For a via hole of the same diameter, but having a larger depth, void-free via-filling plating can be performed by increasing the concentration of the additive (leveler) in the second pretreatment solution in the second pretreatment, or prolonging the substrate immersion time. In the experimental examples, the time for immersion of a substrate in the second pretreatment solution is, for example, 5 seconds. Such a short substrate immersion time may be inappropriate in view of low reproducibility in a practical apparatus. Thus, it is preferred to set a longer substrate immersion time. The substrate immersion time can be prolonged suitably by decreasing the concentration of the additive (leveler) in the second pretreatment solution for a via hole having the same diameter and the same depth.
For a substrate having via holes with various diameters and depths or having trenches with various widths and depths, an appropriate additive (leveler) concentration in a second pretreatment solution and an appropriate substrate immersion time in the second pretreatment can be determined by performing a plating test of the same substrate in advance. An appropriate additive (leveler) concentration in a second pretreatment solution and an appropriate substrate immersion time in the second pretreatment of a substrate, having via holes or trenches with various widths or diameters and various depths, can also be determined based on comparison of the results of such a test with the results of a diffusion analysis. It is possible to provide a plating apparatus which, by using a database that stores data on such test results and analytical results, can automatically control the substrate immersion time and the additive (leveler) concentration of a second pretreatment solution in the second pretreatment.
While the present invention has been described with reference to preferred embodiments, it is understood that the present invention is not limited to the embodiments described above, but is capable of various changes and modifications within the scope of the inventive concept as expressed herein.

Claims

1. A plating method comprising:

preparing a substrate having interconnect recesses in a surface;

carrying out first pretreatment of the substrate by immersing the substrate in a first pretreatment solution containing an accelerator, a metal ion and an acid;

carrying out second pretreatment of the substrate by immersing the substrate in a second pretreatment solution containing an additive which inhibits the effect of the accelerator contained in the first pretreatment solution, and not containing an accelerator; and then

carrying out electroplating of the surface of the substrate by using a plating solution containing at least a metal ion, an acid and a suppressor, and not containing an accelerator, thereby filling the plated metal into the interconnect recesses.

2. The plating method according to claim 1, wherein the first pretreatment is a preliminary electrolytic treatment carried out by electrolytically treating the surface of the substrate while immersing the substrate in the first pretreatment solution.

3. The plating method according to claim 2, wherein the preliminary electrolytic treatment is carried out at a current density of 50 to 250 A/m².

4. The plating method according to claim 1, wherein a sulfur compound is used as the accelerator contained in the first pretreatment solution.

5. The plating method according to claim 4, wherein the concentration of the accelerator contained in the first pretreatment solution is 5 to 500 μM/L.

6. The plating method according to claim 1, wherein the additive contained in the second pretreatment solution and which inhibits the effect of the accelerator contained in the first pretreatment solution is a leveler.

7. The plating method according to claim 6, wherein the leveler is an ethyleneimine polymer or a derivative thereof.

8. The plating method according to claim 1, wherein at least one of the first pretreatment, the second pretreatment and the electroplating is carried out while stirring the treatment solution.

9. The plating method according to claim 1, wherein the second pretreatment is carried out while stirring the second pretreatment solution, and the electroplating is carried out while stirring the plating solution with a stirring intensity equal to or higher than the stirring intensity in the second pretreatment.

10. The plating method according to claim 1, wherein the surface of the substrate is cleaned with dilute sulfuric acid after the first pretreatment, and the surface of the substrate is cleaned with dilute sulfuric acid after the second pretreatment.

11. A plating apparatus for carrying out plating of a surface of a substrate having interconnect recesses in the surface, the plating apparatus comprising:

a first pretreatment unit for carrying out first pretreatment of the substrate by immersing the substrate in a first pretreatment solution containing an accelerator, a metal ion and an acid;

a second pretreatment unit for carrying out second pretreatment of the substrate by immersing the substrate in a second pretreatment solution containing an additive which inhibits the effect of the accelerator contained in the first pretreatment solution, and not containing an accelerator; and

a plating unit for carrying out electroplating of the surface of the substrate after the second pretreatment by using a plating solution containing at least a metal ion, an acid and a suppressor, and not containing an accelerator, thereby filling the plated metal into the interconnect recesses.

12. The plating apparatus according to claim 11, wherein the first pretreatment unit is configured to carry out an electrolytic treatment of the surface of the substrate while immersing the substrate in the first pretreatment solution.

13. The plating apparatus according to claim 11, further comprising a first cleaning unit for cleaning with dilute sulfuric acid the surface of the substrate which has undergone the first pretreatment in the first pretreatment unit, and a second cleaning unit for cleaning with dilute sulfuric acid the surface of the substrate which has undergone the second pretreatment in the second pretreatment unit.

14. The plating apparatus according to claim 11, wherein at least one of the first pretreatment unit, the second pretreatment unit and the plating unit is provided with a stirring device for stirring the treatment solution, and wherein the plating apparatus includes a control section for controlling the stirring speed of the stirring device, the first pretreatment time in the first pretreatment unit, the second pretreatment time in the second pretreatment unit, and the electroplating time in the plating unit.

15. The plating apparatus according to claim 14, wherein the second pretreatment unit is provided with a stirring device for stirring the second treatment solution; and the control section, based on the width or diameter and the depth of the interconnect recesses, determines the substrate immersion time in the second pretreatment and the stirring intensity of the second pretreatment solution.