Method for Copper Electrodeposition

Abstract

The present invention is related to a method for electroplating a copper deposit onto a substrate, wherein the method comprises the steps of: a) immersing the substrate into an electroplating bath having a copper ion concentration comprised between 0.5 mmol·l−1 and 50 mmol·l−1, and an acid concentration comprised between 0.05% and 10% per volume of said electroplating bath; and wherein the method further comprises the step of b) electroplating the copper deposit from the electroplating bath onto the substrate. In particular, the present invention is directed to an improved method for the manufacture of semiconductor integrated circuit (IC) devices provided with sub-100 nm features.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to the field of semiconductor processing, and in particular the field of semiconductor integrated circuit (IC) device manufacturing. More specifically, the present invention is directed to a method for copper electrodeposition onto a substrate provided with sub-100 nm features.

2. Description of Related Art

The demand for manufacturing semiconductor integrated circuit (IC) devices such as computer chips with high circuit speed, high packing density and low power dissipation requires the downward scaling of feature sizes in ultra-large-scale integration (ULSI) and very-large-scale integration (VLSI) structures. The trend to smaller chip sizes and increased circuit density requires the miniaturization of interconnect features which severely penalizes the overall performance of the structure because of increasing interconnect resistance and reliability concerns such as electromigration.

Traditionally, such structures had used aluminum and aluminum alloys as the metallization on silicon wafers with silicon dioxide being the dielectric material. In general, openings are formed in the dielectric layer in the shape of vias and trenches after metallization to form interconnects. Increased miniaturization is reducing the openings to submicron, and even sub-100 nm sizes.

To achieve further miniaturization of the device, copper has been introduced instead of aluminum as the metal to form the connection lines and interconnects in the chip. Copper has a lower resistivity than aluminum and the thickness of a copper line for the same resistance can be thinner than that of an aluminum line. Also, copper has excellent electromigration resistance.

Copper can be deposited on substrates by plating (electroless or electrolytic), sputtering, physical vapor deposition (PVD), and chemical vapor deposition (CVD). It is generally recognized that electrochemical deposition is the most suitable method to apply copper to semiconductor devices since high deposition rates are typically achieved and the associated tool costs may be kept to a minimum. However, plating methods shall meet the stringent requirements of the semiconductor industry. As a way of example, the copper deposits shall be uniform and capable of flawlessly filling the extremely small trenches and vias of the device.

The deposition of copper from acid cooper baths is recognized in the electronics industry as the leading candidate to copper plate integrated circuit devices. The integration of copper into the IC manufacturing process may be e.g. implemented by damascene plating techniques where electrodeposition is used for fabricating the wiring structures. In that context, a successful integration of the copper into the wiring structures requires depositing a continuous copper seed layer as a conductive layer on top of a highly resistive barrier liner which covers the underlying substrate such as a patterned wafer, and which is aimed at preventing copper from diffusing into the underlying substrate. The copper seed layer is deposited to ensure good electrical contact and improved adhesion to the diffusion barrier layer.

As the feature sizes of interconnects decrease and aspect ratios increase, copper electrodeposition becomes even more challenging. Due to the dimensional shrinkage, the thickness of the barrier/copper seed layers becomes significantly bigger with respect to the trench/via opening. As a result, the available space for copper deposition decreases dramatically which can lead to pinch off of the feature openings and void formation in the inlaid trench and via features. In order to compensate for the dimensional shrinkage, the thicknesses of the barrier and copper seed layers have to be scaled down as well.

However, scaling down of the copper seed layer thickness is stringently limited due to the so-called terminal effect. The terminal effect, which is particularly severe for very thin copper seeds, leads to the applied current or voltage dropping off drastically within a short distance from the edge of the wafer, where the electrical contact is made (as described below). As a result of this severe terminal effect, copper deposition will only occur near the edge of the substrate and copper plating will only take place at the edge of the substrate. At most, a delay in plating of the center of the processed wafer is observed. As a result of this “non-instant plating”, corrosion of the copper seed occurs in the center of the wafer. The terminal effect is therefore a key limitation for the integration of copper plating performed on very thin copper seed (having thicknesses typically below 20 nm) in the manufacture of chip semiconductor integrated circuit (IC) devices comprising very narrow interconnect features (having typically a width below 100 nm).

Conventional methods for overcoming the terminal effects for these seed layers include low platting current, segmented anode configuration, high copper concentration and low conductivity (low acid concentration) copper plating baths which improve the current distribution and result in a more uniform film thickness. However, these techniques may not be applicable for very thin seed layers having thicknesses typically below 20 nm or in the absence of seed layer due to the extreme severity of the terminal effect.

One partial solution to problem of achieving acceptable filling of very narrow feature openings (trench or via) throughout the entire processed wafer is allegedly disclosed in US-A1-2004/0069648 which describes a method for electroplating an electrically conductive material onto a platable resistive metal barrier layer located on a substrate, which method comprises contacting the substrate with a plating bath and applying changing current or voltage as a function of the area of plated metal, and wherein the method does not require the pre-deposition of a seed layer.

Another partial solution to have very narrow features filled with standard copper electrochemical deposition (ECD) techniques is allegedly disclosed in US-A1-2002/0153259 which describes a method of forming a copper-containing layer on a substrate, wherein the method comprises electroplating the substrate in an electroplating bath comprising a source of copper ions and a specific complexing agent for complexing the copper ions. However no enabling teaching of narrow features filling is described whatsoever.

US-A1-2003/0168343 discloses a method for electroplating a copper deposit onto a semiconductor integrated circuit device substrate having submicron-sized features with allegedly fewer defects and improved surface morphology. The disclosed method involves immersing the substrate into an electroplating bath including ionic copper and an effective amount of a defect reducing agent.

Despite the progress in the art, there is still need for an efficient method for the integration of copper plating onto a substrate provided with very narrow feature openings (such as trenches or vias), in particular sub-100 nm feature openings.

Advantageously, the method of the present invention may be performed on a substrate provided with very thin copper seeds which typically have thicknesses below 20 nm.

Advantageously still, the method of the invention is applicable to direct (seedless) copper plating with direct (super) filling of very narrow feature openings.

Other advantages of the invention will be immediately apparent to those skilled in the art from the following description.

SUMMARY OF THE INVENTION

It is against the above background that the present invention provides certain advantages and advancements over the prior art.

According to one aspect of the present invention, it is provided a method for electroplating a copper deposit onto a substrate, wherein the method comprises (or consists of) the steps of:

immersing the substrate into an electroplating bath having a copper ion concentration comprised between about 0.5 mmol·l⁻¹ and about 50 mmol·l⁻¹, and an acid concentration comprised between about 0.05% and about 10% per volume of the electroplating bath solution; and

electroplating the copper deposit from the electroplating bath onto the substrate.

Preferably, in the method of the invention as described above, the copper ion is a copper (II) cation.

Preferably, in the method of the invention as described above, the pH of the electroplating bath is acidic. Preferably, the pH is below about 6, more preferably below about 4, even more preferably below about 3, still more preferably below about 2. Still more preferably, the pH of the electroplating bath is comprised between about −0.3 and about 3.0, more preferably between about −0.25 and about 2.0, even more preferably between about −0.25 and about 2.0.

Preferably, in the method of the invention as described above, the electroplating bath has a chloride ion concentration comprised between about 0.1 ppm and about 10 ppm, preferably between about 0.5 ppm and about 8 ppm, more preferably between about 1 ppm and about 5 ppm, even more preferably between about 1 ppm and about 3 ppm, still more preferably between about 1.5 ppm and about 2.5 ppm, still more preferably between about 1.8 ppm and about 2.2 ppm, most preferably the electroplating bath has a chloride ion concentration of about 2.0 ppm.

Preferably, in the method of the invention as described above, the source of chloride ion in the electroplating bath is selected from the group consisting of hydrochloric acid, potassium chloride, sodium chloride, and any combinations or mixtures thereof. Preferably, the source of chloride ion in the electroplating bath is selected to comprise hydrochloric acid.

Preferably, in the method of the invention as described above, the substrate comprises a semiconductor material which is preferably selected from the group consisting of silicon, germanium, silicon on insulator (SOI), and any combinations or mixtures thereof. More preferably, in the method according to the invention, the substrate is a silicon wafer.

Preferably, in the method of the invention as described above, the substrate is provided with at least one feature opening, preferably selected from the group of trenches and vias, wherein the feature opening has a width below about 100 nm, preferably below about 70 nm, more preferably below about 50 nm, even more preferably below about 35 nm.

According to one preferred aspect, in the method of the invention as described above, the substrate is provided with a copper seed having a thickness below about 60 nm, preferably below about 50 nm, more preferably below about 30 nm, even more preferably below about 20 nm, still more preferably below about 10 nm, most preferably below about 8 nm.

Preferably, in the method of the invention as described above, the copper seed layer at least partly covers the sidewalls and the bottom of the feature opening. More preferably, the copper seed layer fully covers the sidewalls and the bottom of the feature opening, without fully filling the feature opening.

Preferably, the method of the invention as described above further comprises the step of providing the substrate with a copper seed layer having a thickness preferably below about 60 nm, more preferably below about 50 nm, even more preferably below about 20 nm, still more preferably below about 10 nm, most preferably below about 8 nm. Preferably, the copper seed layer is deposited using Physical Vapor Deposition (PVD) techniques.

Preferably, in the method of the invention as described above, the substrate is further provided with a diffusion barrier layer, whereby the copper seed layer is preferably deposited onto the diffusion barrier layer.

Preferably, in the method of the invention as described above, the source of acid concentration in the electroplating bath is selected to comprise sulfuric acid.

According to one preferred aspect of the method of the invention, whereby the substrate is provided with a copper seed, the electroplating bath preferably has an acid concentration comprised between about 0.05% and about 1%, more preferably between about 0.05% and about 0.7%, even more preferably between about 0.05% and about 0.5%, still more preferably between about 0.05% and about 0.3%, most preferably between about 0.05% and about 0.15% per volume of the electroplating bath.

Still according to the preferred aspect of the method of the invention, whereby the substrate is provided with a copper seed, the electroplating bath preferably comprises sulfuric acid, more preferably in a concentration comprised between about 10 mmol·l⁻¹ and about 200 mmol·l⁻¹, more preferably between about 10 mmol·l⁻¹ and about 100 mmol·l⁻¹, even more preferably between about 15 mmol·l⁻¹ and about 50 mmol·l⁻¹, most preferably between about 15 mmol·l⁻¹ and about 25 mmol·l⁻¹.

According to another preferred aspect of the method of the invention, the substrate is provided with a seed layer made from a seed material not comprising copper. In a preferred aspect, the seed material comprises a metal selected from the group consisting of ruthenium, tantalum, cobalt, and any combinations or mixtures thereof. More preferably, the seed material comprises ruthenium.

According to another aspect of the invention, the seed layer not comprising copper may also further act as a diffusion barrier layer.

According to one preferred aspect of the method of the invention, whereby the substrate is provided with a seed layer made from a seed material not comprising copper, the electroplating bath preferably has an acid concentration comprised between about 5% and about 10%, more preferably between about 6% and about 9.5%, even more preferably between about 7% and about 9%, most preferably between about 8% and about 9%, per volume of said electroplating bath.

Still according to the preferred aspect of the method of the invention, whereby the substrate is provided with a seed layer made from a seed material not comprising copper, the electroplating bath preferably comprises sulfuric acid, more preferably in a concentration comprised between about 1 mol·l⁻¹ and about 2 mol·l⁻¹, more preferably between about 12 mol·l⁻¹ and about 1.9 mol·l⁻¹, even more preferably between about 1.4 mol·l⁻¹ and about 1.8 mol·l⁻¹, most preferably between about 1.0 mol·l⁻¹ and about 1.8 mol·l⁻¹.

Preferably, in the method of the invention as described above, the electroplating bath has a copper ion concentration comprised between about 0.5 mmol·l⁻¹ and about 30 mmol·l⁻¹, preferably between about 0.5 mmol·l⁻¹ and about 20 mmol·l⁻¹, more preferably between about 1.0 mmol·l⁻¹ and about 20 mmol·l⁻¹, even more preferably between about 1.0 mmol·l⁻¹ and about 10 mmol·l⁻¹.

Preferably, in the method of the invention as described above, the source of copper ion concentration in the electroplating bath is selected from the group consisting of copper sulfate, copper nitrate, copper carbonate, copper phosphate, and any combinations or mixtures thereof. More preferably, the source of copper ion concentration in the electroplating bath is selected to comprise copper sulfate.

Preferably, in the method of the invention as described above, the electroplating bath further comprises an organic additive system comprising a suppressor of copper deposition on copper and an accelerator of copper deposition on copper.

Preferably, in the method of the invention as described above, the suppressor of copper deposition is selected from the group consisting of polyethylene glycol, polypropylene glycol, block copolymer of polyethylene glycol-polypropylene glycol-polyethylene glycol, and any combinations or mixtures thereof; and the accelerator of copper deposition is preferably selected to comprise (or consist of) bis-(sodium sulfopropyl)-disulfide.

Preferably, in the method of the invention as described above, the electroplating bath comprises a suppressor of copper deposition, which is preferably polyethylene glycol, in a concentration preferably comprised between about 20 ppm and about 500 ppm, more preferably between about 50 ppm and about 120 ppm, even more preferably between about 70 ppm and about 115 ppm, still more preferably between about 90 ppm and about 110 ppm; most preferably the electroplating bath comprises a suppressor of copper deposition in a concentration of about 100 ppm.

Preferably, in the Method of the invention as described above, the electroplating bath further comprises an accelerator of copper deposition, which is preferably bis-(sodium sulfopropyl)-disulfide, in a concentration preferably comprised between about 0.02 ppm and about 2 ppm, more preferably between about 0.1 ppm and about 1.5 ppm, even more preferably between about 0.5 ppm and about 1.3 ppm, most preferably between about 0.7 ppm and about 1.0 ppm.

Preferably still, the method of the invention further comprises the step of performing a surface pre-treatment of the substrate before the step of electroplating the copper deposit, more preferably before the step of immersing the substrate into the electroplating bath. More preferably, the surface pre-treatment consists of an electrochemical clean.

According to another aspect, the present invention is directed to a method for the preparation of a electroplating bath suitable for electroplating a copper deposit onto a substrate, wherein the method comprises the step of:

providing a concentrate composition comprising a source of copper ion and a source of acid; and

diluting the concentrate composition into a solution comprising deionized water, thereby forming an electroplating bath having a copper ion concentration comprised between about 0.5 mmol·l⁻¹ and about 50 mmol·l⁻¹, and an acid concentration comprised between about 0.05% and about 10% per volume of the electroplating bath.

According to still another aspect, the present invention is directed to a method for the preparation of a electroplating bath suitable for electroplating a copper deposit onto a substrate, wherein the method comprises the step of:

providing a concentrate composition comprising a source of copper ion and a source of acid; and

diluting the concentrate composition into a solution comprising deionized water, thereby forming an electroplating bath as described above.

According to still another aspect, the present invention is directed to a concentrate composition as defined above. Preferably, the concentrate composition further comprises a source of chloride ion, preferably in such an amount as to form an electroplating bath having a chloride ion concentration comprised between about 0.1 ppm and about 10 ppm, more preferably between about 0.5 ppm and about 8 ppm, even more preferably between about 1 ppm and about 5 ppm, still more preferably between about 1 ppm and about 3 ppm, still more preferably between about 1.5 ppm and about 2.5 ppm, still more preferably between about 1.8 ppm and about 2.2 ppm, most preferably of about 2.0 ppm, when the concentrate composition is diluted into a solution comprising deionized water.

According to yet another aspect, the present invention is directed to the use of the method as described above for the manufacture of a semiconducting device, preferably a semiconductor integrated circuit (IC) device.

According to a preferred aspect, the present invention is directed to the use of the method as described above for the manufacture of semiconducting devices features, preferably for the manufacture of interconnections having a width which is preferably below about 100 nm, more preferably below about 70 nm, even more preferably below about 50 nm, most preferably below about 35 nm.

Accordingly, the present invention is further directed to a method for the superfilling of a feature opening provided in a substrate, wherein the feature opening is preferably selected from the group of trenches and vias, and wherein the feature opening has a width below about 100 nm, preferably below about 70 nm, more preferably below about 50 nm, even more preferably below about 35 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

All figures/drawings are intended to illustrate some aspects and embodiments of the present invention. Devices are depicted in a simplified way for reason of clarity. Not all alternatives and options are shown and therefore the invention is not limited to the content of the given drawings.

FIG. 1 graphically represents the radial profiles of substrates containing copper deposits with increasing thicknesses plated on a 5 nm thin copper seed with an ultra-high copper ion concentrated electroplating bath.

FIG. 2 graphically represents semi-logarithmic plot of the measured current density vs. the sample's potential measured with respect to saturated mercurous sulphate electrode (SMSE) for:

• • i. a highly concentrated copper-acid electroplating bath (250 mmol·l⁻¹ CuSO₄) (▪) (full square); and
  • ii. an ultra-lowly concentrated copper-acid electroplating bath (10 mmol·l⁻¹ CuSO₄) (▴) (full triangle).

FIG. 3 graphically represents a simulated comparative current distribution over a wafer while using ultra-lowly concentrated copper-acid electroplating bath (10 mmol·l⁻¹ CuSO₄+0.1% H₂SO₄) and highly copper ion and acid concentrated electroplating bath (160 mmol·l⁻¹ CuSO₄+0.5% H₂SO₄).

FIG. 4 shows SEM images of copper islands electrodeposited on a Ru based substrate from solutions containing 1.8 M H₂SO₄, 50 ppm HCl and different copper concentrations (10 mM to 600 mM CuSO₄.5H₂O) at different current densities.

FIG. 5 shows the respective island density values as obtained from the SEM images shown in FIG. 4.

FIG. 6 shows top-down SEM images of copper islands deposited from solutions containing 1.8 mol·l⁻¹ H₂SO₄, 50 ppm HCl and different CuSO₄.5H₂O concentrations (50 to 600 mM) with and without the addition of 300 ppm PEG. The depositions are performed at current density of −2.5 mAcm⁻² for 4 seconds.

FIG. 7 shows top-down SEM images of copper islands deposited on a Ru based substrate from solutions containing 10 mmol·l⁻¹ CuSO₄.5H₂O, 1.8 mmol·l⁻¹ H₂SO₄, 2 ppm HCl and different PEG concentrations (0 ppm to 1000 ppm).

FIG. 8 shows top-down SEM images of copper islands deposited on a Ru based substrate from solutions containing 10 mmol·l⁻¹ CuSO₄.5H₂O, 1.8 mol·l⁻¹ H₂SO₄, 500 ppm PEG and different HCl concentrations (0 ppm to 50 ppm).

FIG. 9 shows the chloride concentration as a function of the normalized charge (Q/Q_o) calculated from data for the measured current density after copper depositions on Cu-seed layers from two electroplating baths according to the invention, and comprising ultra-low copper ion concentration (10 mmol·l⁻¹ CuSO₄), 2 ppm HCl, 100 ppm PEG 4000, 1 pmm SPS and H₂SO₄. A comparison between () 18 mmol·l⁻¹ H₂SO₄ and (♦) 1.8 mol·l⁻¹ H₂SO₄ is made and the most appropriate chloride concentrations for each of the two electrolytes are indicated in the graph. The smallest normalized charge indicates the strongest suppression; hence, the optimum working condition.

FIG. 10 represents schematically a profile of a damascene structure (trench) in a silicon substrate, with a diffusion barrier (1.5 nm TaN/Ta) and a copper seed layer.

FIG. 11 is a cross-sectional SEM image of 90 nm wide trenches, with 60 nm thick initial copper seed layer, filled with copper according to the method of the invention using electroplating baths comprising various ultra-low copper ion concentrations and adjusted additives concentrations.

DETAILED DESCRIPTION OF THE INVENTION

According to one aspect of the present invention, it is provided a method for electroplating a copper deposit onto a substrate, wherein the method comprises the steps of:

immersing the substrate into an electroplating bath solution having a copper ion concentration comprised between 0.5 mmol·l⁻¹ and 50 mmol·l⁻¹, and an acid concentration comprised between 0.05% and 10% per volume of the electroplating bath solution; and

electroplating the copper deposit from the electroplating bath onto the substrate.

In the context of the present invention, it has been surprisingly discovered while performing the method of the invention, efficient integration of copper plating onto a substrate provided with very narrow feature openings (such as trenches or vias) may be achieved. More specifically, efficient (e.g. void free) filling of narrow feature openings, having typically a width which is below 100 nm, preferably below 70 nm, more preferably below 50 nm, even more preferably below 35 nm may be unexpectedly achieved. This is surprising result in view of the ultra low copper ion concentration of the electroplating bath for use in the method of the invention.

Without wishing to be bound by theory, it is believed that the low copper ion concentration of the electrolytic bath provides the following effects: 1) the relative potential drop over the thin seed layer is considerably reduced by lowering the deposition current (and exchange current density); 2) the potential window for copper plating is enlarged by the presence of a diffusion limited current region, which further counters the terminal effect; 3) improvement in current distribution over the substrate during electroplating.

FIG. 1 graphically represents the radial profiles (on a 300 mm wafer) of substrates containing copper deposits with increasing thicknesses electroplated on a 5 nm thin copper seed with an ultra-high copper ion concentrated electroplating bath, and thereby depicts the severe terminal effect experienced by very thin copper seeds. For the first 10 to 20 nm of electroplated copper, the plating rate is near zero in the center and fast around the edge of the wafer.

FIG. 2 graphically represents semi-logarithmic plot of the measured current density vs. the sample's potential measured with respect to saturated mercurous sulfate electrode (SMSE) for:

• • i. a highly concentrated copper-acid electroplating bath (250 mmol·l⁻¹ CuSO₄) (▪) (full square); and
  • ii. an ultra-lowly concentrated copper-acid electroplating bath (10 mmol·l⁻¹ CuSO₄) (▴) (full triangle).

FIG. 2 clearly shows that by lowering the copper concentration, the relative potential drop over the thin seed layer is considerably reduced by lowering the deposition current (and exchange current density).

FIG. 3 graphically represents a simulated comparative current distribution over a wafer while using ultra-lowly concentrated copper-acid electroplating bath (10 mmol·l⁻¹ CuSO₄+0.1% H₂SO₄) and highly copper ion and acid concentrated electroplating bath (160 mmol·l⁻¹ CuSO₄+0.5% H₂SO₄). FIG. 3 clearly shows the drastic improvement in current distribution for ultra-low copper concentrations.

Advantageously and no less surprisingly, the method of the present invention may be performed on a substrate provided with very thin copper seeds which typically have thicknesses below 20 nm.

Preferably, in the method of the invention as described above, the copper ion is a copper (II) cation.

Preferably, in the method of the invention as described above, the pH of the electroplating bath is acidic. Preferably, the pH is below 6, more preferably below 4, even more preferably below 3, still more preferably below 2. Still more preferably, the pH of the electroplating bath is comprised between −0.3 and 3.0, more preferably between −0.25 and 2.0, even more preferably between −0.25 and 2.0.

Preferably, in the method of the invention as described above, the electroplating bath comprises chloride ion, preferably in a concentration comprised between 0.1 ppm and 10 ppm, more preferably between 0.5 ppm and 8 ppm, even more preferably between 1 ppm and 5 ppm, still more preferably between 1 ppm and 3 ppm, still more preferably between about 1.5 ppm and about 2.5 ppm, still more preferably between about 1.8 ppm and about 2.2 ppm, most preferably the electroplating bath has a chloride ion concentration of about 2.0 ppm.

As will be easily apparent to those skilled in the art of electrochemistry in the light of the present description, the optimum value for the pH and the chloride ion concentration of the electroplating bath will depend on the particular composition of the electroplating bath.

Preferably, in the method of the invention as described above, the source of chloride ion in the electroplating bath is selected from the group consisting of hydrochloric acid, potassium chloride, sodium chloride, and any combinations or mixtures thereof. Preferably, the source of chloride ion in the electroplating bath is selected to comprise hydrochloric acid. Advantageously, according to the preferred aspect of the invention where hydrochloric acid is used as the source of chloride ion in the electroplating bath, the latter is typically used in such a very low concentration that the addition of hydrochloric acid does not substantially affect the pH of the resulting electroplating bath.

Preferably, in the method of the invention as described above, the substrate comprises a semiconductor material which is preferably selected from the group consisting of silicon, germanium, silicon on insulator (SOI), and any combinations or mixtures thereof. More preferably, in the method according to the invention, the substrate is a silicon wafer.

Preferably, in the method a of the invention as described above, the substrate is provided with at least one feature opening, preferably selected from the group of trenches and vias, wherein the feature opening has a width below 100 nm, preferably below 70 nm, more preferably below 50 nm, even more preferably below 35 nm.

According to one preferred aspect, in the method of the invention as described above, the substrate is provided with a copper seed having a thickness below about 60 nm, preferably below about 50 nm, more preferably below about 30 nm, even more preferably below about 20 nm, still more preferably below about 10 nm, most preferably below about 8 nm.

Preferably, in the method of the invention as described above, the copper seed layer at least partly covers the sidewalls and the bottom of the feature opening. More preferably, the copper seed layer fully covers the sidewalls and the bottom of the feature opening, without fully filling the feature opening.

Preferably, the method of the invention as described above further comprises the step of providing the substrate with a copper seed layer having a thickness preferably below 60 nm, more preferably below 50 nm, even more preferably below 20 nm, still more preferably below 10 nm, most preferably below 8 nm. Preferably, the copper seed layer is deposited using Physical Vapor Deposition (PVD) techniques.

Preferably, in the method of the invention as described above, the substrate is further provided with a diffusion barrier layer, whereby the copper seed layer is preferably deposited onto the diffusion barrier layer.

Preferably, in the method of the invention as described above, the source of acid concentration in the electroplating bath is selected to comprise or consist of sulfuric acid. However, the invention is not that limited as other suitable sources of acid concentration in the electroplating bath will be easily identified by those skilled in the art in the light of the present description.

According to one preferred aspect of the method of the invention, whereby the substrate is provided with a copper seed, the electroplating bath preferably has an acid concentration comprised between 0.05% and 1%, more preferably between 0.05% and 0.7%, even more preferably between 0.05% and 0.5%, still more preferably between 0.05% and 0.3%, most preferably between 0.05% and 0.15% per volume of the electroplating bath.

Still according to the preferred aspect of the method of the invention, whereby the substrate is provided with a copper seed, the electroplating bath preferably comprises sulfuric acid, more preferably in a concentration comprised between 10 mmol·l⁻¹ and 200 mmol·l⁻¹, more preferably between 10 mmol·l⁻¹ and 100 mmol·l⁻¹, even more preferably between 15 mmol·l⁻¹ and 50 mmol·l⁻¹, most preferably between 15 mmol·l⁻¹ and 25 mmol·l⁻¹.

According to another preferred aspect of the method of the invention, the substrate is provided with a seed layer made from a seed material not comprising copper. In a preferred aspect, the seed material comprises a metal selected from the group consisting of ruthenium, tantalum, cobalt, and any combinations or mixtures thereof. More preferably, the seed material comprises ruthenium. Exemplary seed materials for use herein include, but are not limited to, Ru-containing alloys, such as e.g. RuTa. In one preferred aspect, the seed material comprises or consists of RuTa.

In the context of the present invention, it has been surprisingly discovered that the method of the invention is advantageously applicable to direct (seedless) copper plating with direct (super)filling of very narrow feature openings. In the context of the present invention, the term “seedless or direct plating” is meant to refer to copper plating and filling on a seed material not comprising copper, which may also be referred to throughout the description as alternative seed layer. According to this particular aspect, the need for a copper seed layer, and as a consequence the problem of copper seed corrosion due to terminal effect in acid copper electroplating bath, may be advantageously obviated.

In another aspect of the invention, the seed layer not comprising copper may also further act as a diffusion barrier layer. According to this particular aspect of the invention, it derives that the method of the invention is also applicable to direct plating and filling directly onto the diffusion barrier layer.

According to one preferred aspect of the method of the invention, whereby the substrate is provided with a seed layer made from a seed material not comprising copper, the electroplating bath preferably has an acid concentration comprised between 5% and 10%, more preferably between 6% and 9.5%, even more preferably between 7% and 9%, most preferably between 8% and 9%, per volume of said electroplating bath.

Still according to the preferred aspect of the method of the invention, whereby the substrate is provided with a seed layer made from a seed material not comprising copper, the electroplating bath preferably comprises sulfuric acid, more preferably in a concentration comprised between 1 mol·l⁻¹ and 2 mol·l⁻¹, more preferably between 1.2 mol·l⁻¹ and 1.9 mol·l⁻¹, even more preferably between 1.4 mol·l⁻¹ and 1.8 mol·l⁻¹, most preferably between 1.6 mol·l⁻¹ and 1.8 mol·l⁻¹.

While electrodeposition of copper on copper typically follows layer-by-layer type of growth, copper electrodeposition on seed layer made from a seed material not comprising copper proceeds through nucleation and specific growth process. Accordingly, in the context of the particular aspect of the invention whereby the substrate is provided with a seed layer made from a seed material not comprising copper, the present invention has required extensive experiments so as to achieve a profound understanding of the nucleation and growth mechanism. In that context, the Applicant has found that the copper growth process proceeds through forming and growing of three dimensional (3D) islands until they coalesce into a continuous film. Since the coalescence thickness is determined by the island density, it alters according to the shape of the islands (sphere to hemisphere and disk), i.e. quasi 2D growth leads to a thinner coalescence thickness. In order to fill small features, the coalescence shall be fast and followed by preferably by bottom-up superfilling, which is indistinguishable from growth on a conventional copper seed layer. In order to achieve the first copper layer in the small features, high island density shall be achieved with consequently fast coalescence in the features with thickness smaller than the features size. In the context of the invention, the critical importance of achieving high enough island density while trying to achieve efficient (i.e. void- and defect-free) filling of small features has been identified. In order to achieve high island density of copper electrodeposition, the nucleation and growth mechanism has been elucidated at a fundamental level and the influence of each component of the electroplating bath has been extensively studied.

Preferably, in the method of the invention as described above, the electroplating bath has a copper ion concentration comprised between 0.5 mmol·l⁻¹ and 30 mmol·l⁻¹, preferably between 0.5 mmol·l⁻¹ and 20 mmol·l⁻¹, more preferably between 1.0 mmol·l⁻¹ and 20 mmol·l⁻¹, even more preferably between 1.0 mmol·l⁻¹ and 10 mmol·l⁻¹.

In the context of the present invention, it has been surprisingly discovered that copper island density directly increases with lower copper concentration. Also, it has been no less surprisingly discovered that copper island density directly increases with higher applied deposition current.

FIG. 4 shows SEM images of copper islands electrodeposited on a Ru based substrate from solutions containing 1.8 M H₂SO₄, 50 ppm HCl and different copper concentrations (10 mM to 600 mM CuSO₄.5H₂O) at different current densities. The experiments were terminated at the same charge, Q=0.01 C cm⁻².

FIG. 5 shows the respective island density values as obtained from the SEM images shown in FIG. 4.

In the context of the present invention still, it has been unexpectedly found that copper islands coalesce faster with decreasing copper concentration.

Preferably, in the method of the invention as described above, the source of copper ion concentration in the electroplating bath is selected from the group consisting of copper sulfate, copper nitrate, copper carbonate, copper phosphate, and any combinations or mixtures thereof. More preferably, the source of copper ion concentration in the electroplating bath is selected to comprise or consist of copper sulfate.

Preferably, in the method of the invention as described above, the electroplating bath further comprises an organic additive system comprising a suppressor of copper deposition on copper and an accelerator of copper deposition on copper.

Preferably, in the method of the invention as described above, the suppressor of copper deposition is selected from the group consisting of polyethylene glycol, polypropylene glycol, block copolymer of polyethylene glycol-polypropylene glycol-polyethylene glycol, and any combinations or mixtures thereof; and the accelerator of copper deposition is preferably selected to comprise or consist of bis-(sodium sulfopropyl)-disulfide. More preferably, the suppressor of copper deposition for use herein is selected from the group consisting of PEG8000, PEG4000, EPE2000, and any combinations or mixtures thereof. Even more preferably, the suppressor of copper deposition for use herein is selected to comprise or to consist of PEG4000.

Preferably, in the method of the invention as described above, the electroplating bath comprises a suppressor of copper deposition, which is preferably polyethylene glycol, in a concentration preferably comprised between about 20 ppm and about 500 ppm, more preferably between about 50 ppm and about 120 ppm, even more preferably between about 70 ppm and about 115 ppm, still more preferably between about 90 ppm and about 110 ppm; most preferably the electroplating bath comprises a suppressor of copper deposition in a concentration of about 100 ppm.

In the context of the present invention, it has been surprisingly discovered that the addition of a suppressor, such as e.g. polyethylene glycol, in the electroplating bath having a low copper concentration, increases the copper island density.

FIG. 6 shows top-down SEM images of copper islands deposited from solutions containing 1.8 mol·l⁻¹ H₂SO₄, 50 ppm HCl and different CuSO₄.5H₂O concentrations (50 to 600 mM) with and without the addition of 300 ppm PEG. The depositions are performed at current density of −2.5 mAcm⁻² for 4 seconds.

FIG. 7 shows top-down SEM images of copper islands deposited on a Ru based substrate from solutions containing 10 mmol·l⁻¹ CuSO₄.5H₂O, 1.8 mol·l⁻¹ H₂SO₄, 2 ppm HCl and different PEG concentrations (0 ppm to 1000 ppm). The depositions are performed at current density of −0.5 mAcm⁻² for 20 seconds.

It has also been discovered that the addition of chloride ion may, in some selected conditions, participate in increasing the copper island density.

FIG. 8 shows top-down SEM images of copper islands deposited on a Ru based substrate from solutions containing 10 mmol·l⁻¹ CuSO₄.5H₂O, 1.8 mol·l⁻¹ H₂SO₄, 500 ppm PEG and different HCl concentrations (0 ppm to 50 ppm). The depositions are performed at current density of −0.5 mAcm-2 for 20 seconds.

FIG. 9 represents the chloride concentration as a function of the normalized charge (Q/Q_o) calculated from data for the measured current density after copper depositions on Cu-seed layers from two different electroplating baths according to the invention, and comprising ultra-low copper ion concentrations (10 mmol·l⁻¹ CuSO₄), 2 ppm HCl, 100 ppm PEG 4000, 1 pmm SPS and H₂SO₄. A comparison between () 18 mmol·l⁻¹ H₂SO₄ and (♦) 1.8 mol·l⁻¹ H₂SO₄ is made and the most appropriate chloride concentrations for each of the two electrolytes are indicated in the graph. The smallest normalized charge indicates the strongest suppression, and therefore the optimum working condition.

Preferably, in the method of the invention as described above, the electroplating bath further comprises an accelerator of copper deposition, which is preferably bis-(sodium sulfopropyl)-disulfide, in a concentration preferably comprised between 0.02 ppm and 2 ppm, more preferably between 0.1 ppm and 1.5 ppm, even more preferably between 0.5 ppm and 1.3 ppm, most preferably between 0.7 ppm and 1.0 ppm.

According to another preferred aspect, the method of the invention further comprises the step of performing a surface pre-treatment of the substrate before the step of electroplating the copper deposit, more preferably before the step of immersing the substrate into the electroplating bath. More preferably, the surface pre-treatment consists of an electrochemical clean.

According to another aspect, the present invention is directed to a method for the preparation of a electroplating bath suitable for electroplating a copper deposit onto a substrate, wherein the method comprises the step of:

providing a concentrate composition comprising a source of copper ion and a source of acid; and

diluting the concentrate composition into a solution comprising deionized water, thereby forming an electroplating bath having a copper ion concentration comprised between 0.5 mmol·l⁻¹ and 50 mmol·l⁻¹, and an acid concentration comprised between 0.05% and 10% per volume of the electroplating bath.

According to still another aspect, the present invention is directed to a method for the preparation of a electroplating bath suitable for electroplating a copper deposit onto a substrate, wherein the method comprises the step of:

providing a concentrate composition comprising a source of copper ion and a source of acid; and

diluting the concentrate composition into a solution comprising deionized water, thereby forming an electroplating bath as described above.

According to still another aspect, the present invention is directed to a concentrate composition as defined above. Preferably, the concentrate composition further comprises a source of chloride ion, preferably in such an amount as to form an electroplating bath having a chloride ion concentration comprised between 0.1 ppm and 10 ppm, more preferably between 0.5 ppm and 8 ppm, even more preferably between 1 ppm and 5 ppm, still more preferably between 1 ppm and 3 ppm, still more preferably between 1.5 ppm and 2.5 ppm, still more preferably between 1.8 ppm and 2.2 ppm, most preferably of about 2.0 ppm, when the concentrate composition is diluted into a solution comprising deionized water.

The methods and concentrate composition according to the present invention may find particular use in the manufacture of a semiconducting device. Accordingly, the present invention is further directed to the use of the method as described above for the manufacture of a semiconducting device, preferably a semiconductor integrated circuit (IC) device.

According to a preferred aspect, the present invention is directed to the use of the method as described above for the manufacture of semiconducting devices features, preferably for the manufacture of interconnections having a width which is preferably below 100 nm, more preferably below 70 nm, even more preferably below 50 nm, most preferably below 35 nm. FIG. 10 represents schematically a profile of a damascene structure (trench) in a silicon substrate, with a diffusion barrier (1.5 nm TaN/Ta) and a copper seed layer.

Accordingly, the present invention is further directed to a method for the (super)filling of a feature opening provided in a substrate, wherein the feature opening is preferably selected from the group of trenches and vias, and wherein the feature opening has a width below 100 nm, preferably below 70 nm, more preferably below 50 nm, even more preferably below 35 nm.

FIG. 11 is a cross-sectional SEM image of 90 nm wide trenches, with 60 nm thick initial copper seed layer, filled with copper from an electroplating bath according to the invention, and comprising ultra-low copper ion concentrations (10 mmol·l⁻¹ or 1 mmol·l⁻¹ CuSO₄) and adjusted additives concentrations, as follows:

• • a. 10 mmol·l⁻¹ CuSO₄+18 mmol·l⁻¹ H₂SO₄+2 ppm HCl+100 ppm PEG4000+1 ppm SPS, where PEG4000 is polyethylene glycol with average molecular weight Mw=4000 g·mol⁻¹,
  • b. 10 mmol·l⁻¹ CuSO₄+18 mmol·l⁻¹ H₂SO₄+2 ppm HCl+200 ppm EPE2000+0.04 ppm SPS, where EPE2000 is a block copolymer of polyethylene glycol-polypropylene glycol-polyethylene glycol with average molecular weight MW=2000 g·mol⁻¹, and
  • c. 1 mmol·l⁻¹ CuSO₄+18 mmol·l⁻¹ H₂SO₄+0.7 ppm HCl+200 ppm EPE2000+0.02 ppm SPS.

With all three electroplating baths, very good quality trench-filling with copper are obtained, i.e. without any voids or defects.

While the present invention has been described and illustrated with reference to specific illustrative embodiments thereof, it will be recognized by those skilled in the art that variations and modifications may be made without departing from the spirit and scope of the present invention. It is therefore intended to include within the present invention all such variations and modifications that fall within the scope of the appended claims and equivalents thereof.

EXAMPLES

One exemplary method of the invention is described below with full details. The examples herein are meant to exemplify the present invention but are not necessarily used to limit or otherwise define the scope of the present invention.

Example 1

Preparation of the Make-Up Solutions

The make-up solutions are prepared from CuSO₄.5H₂O (>98%, Sigma Aldrich), H₂SO₄ (96%, Assay, Baker), and deionized water (DI water). HCl (Assay, Baker) is added to vary the chloride ions concentration between 0 and 10 ppm (10 ppm=10 mg·l⁻¹ Cl⁻). The suppressor, polyethylene glycol with molecular weight 4000 (PEG 4000; Sigma Aldrich), is added to the make-up solutions in concentrations between 10 and 1000 ppm (1000 ppm=1000 mg·l⁻¹=1 g·l⁻¹ PEG). The accelerator, bis-(3-sodiumsulfopropyl) disulfide (SPS) is added in concentrations between 0.02 and 2.0 ppm (0.02 ppm=20 ppb=0.02 mg·l⁻¹ SPS).

The steps for preparing 1.0 liter of copper plating solution (electrolyte) with a composition 10 mmol·l⁻¹ CuSO₄+18 mmol·l⁻¹ H₂SO₄+2 ppm+300 ppm PEG+1 ppm SPS are as follows:

• • a. Measuring on analytical scale the amount of CuSO₄.5H₂O needed. The amount needed is calculated according to the formula: m(g)=c(mol·l⁻¹)·Mm(g·mol⁻¹)·V(I). Hence, m(g)=0.01(mol·l⁻¹)·249.684(g·mol¹)·1(l)=2.4968 g.
  • b. Quantitative transfer of the proper amount of CuSO₄.5H₂O measured on the analytical scale into a measuring glass with exact volume of 1 liter. Quantitative transfer means that the transfer of all the quantity of a chemical compound is assisted by 2-3 portions of deionized water (DI water) in small quantities.
  • c. Addition of H₂SO₄ in a quantity found according to the formula: V_initial(l)=V_needed(l)·c_needed(mol·l⁻¹)/c_initial(mol·l⁻¹). As the initial concentration of 96% H₂SO₄ corresponds to 18 mol·l⁻¹, the formula is expressed as: V_initial(l)=1(l)·0.018(mol·l⁻¹)/18(mol·l⁻¹)=1.10⁻⁴ l=1000 μl.
  • d. Filling the measuring glass with DI water until volume of 1 liter is obtained.
  • e. Chloride ions are added to the make-up electrolyte in micro-liter amounts of 0.14 mol·l⁻¹ HCl previously prepared. For example, to obtain a concentration of 2 ppm Cl⁻ in the electrolyte, 400 μl of 0.14 ml·l¹HCl is added.
  • f. PEG is measured on analytical scale and added in the amount needed prior to each experiment. For example, to obtain a concentration of 300 ppm PEG in the electrolyte, 0.3 g of PEG is added to 1 L of electrolyte.
  • g. As a source of SPS, a solution of 1 g SPS in 100 ml DI water (10000 ppm SPS) is used. For example, to obtain a concentration of 1 ppm SPS in the electrolyte, 100 μl of SPS solution (10000 ppm) were added to 1 L of electrolyte.

The different solution compositions tested are listed in Table 1 below:

TABLE 1
Composition of the make-up solutions tested.
[CuSO4],	[H2SO4],
mmol · l−1	mmol · l−1	[Cl], ppm	[PEG], ppm	[SPS], ppm
10.0,	18	0.0, 0.2, 0.4,	10, 100, 200,	0.02, 0.04, 0.06,
1.0,	1800	0.6, 1.0, 1.5,	300, 500,	0.1, 0.2, 0.4,
0.5		2.0, 4.0	1000	0.6, 1.0, 2.0

Example 2

Substrate

The substrate is a patterned wafer (wafer with trenches) with a diameter of 300 mm. Two types of structures (trenches) are examined, i.e. trenches with width 90 nm and depth of about 208 nm and trenches with width 35 nm and depth of about 80 nm.

The aspect ratio, which is the ratio between depth and width, is 2.3 for both structures. The aspect ratio is obtained after patterning the wafer to achieve the required shape and size of the trenches and deposition of a barrier layer made of a low-k dielectric material. In the case of Damascene copper plating with copper seed, the barrier layer is 1.5 nm of tantalum nitride/tantalum (TaN/Ta).

At the surface of the wafer, including both the surface between the trenches and the surface of the trench bottom and side walls, a thin copper seed layer is previously deposited by means of physical vapor deposition (PVD) as schematically shown in FIG. 10. The thickness of the copper seed layer is 60 nm for 90 nm wide trenches and 20 nm for 35 nm wide trenches. Coupons with size about 2×2 cm are cut manually from the wafer with a diamond tip.

Alternatively, on other samples, an alternative seed layer (such as e.g. Ru, RuTa, Co, etc.) may be deposited instead of the copper seed layer.

Example 3

Electrochemical Step

All tests are performed at room temperature using a glass three-electrode electrochemical cell wherein the three electrodes and the plating bath are placed. The counter electrode is separated from the working electrode compartment with a porous glass frit. The working electrode is a coupon of a patterned wafer (a sample) with dimensions around 2×2 cm, placed in a sample holder. The area of the sample exposed therefore to the plating bath (working area) was of 1.54 cm². All tests are performed keeping the working electrode at a rotation rate of 500 rpm. Before each test, a copper tape is placed at the edges of the sample connecting the front and the back side of the sample in order to ensure an electrical contact between the working sample area (front part) and the electrode connection at the back side of the sample.

As a reference electrode a saturated mercurous sulfate electrode (SMSE) is used to avoid leakage of chloride ions into the electrolyte, which can be the case when using silver/silver chloride or calomel electrodes. This is important since the [Cl⁻] concentration is always in the range of few ppm. The potential of the SMSE is measured with respect to a silver/silver chloride standard reference electrode (3 mmol·l⁻¹ KCl, 0.210 V vs. SHE) in a solution of 5 wt. % H₂SO₄ (0.94 mol·l⁻¹) and 10 vol. % HCl (1.20 mol·l⁻¹). A stable and reproducible value of 0.485 V for the potential of the SMSE is observed. Considering the potential of silver/silver chloride standard reference electrode vs. SHE, the potential of SMSE vs. SHE is calculated to be 0.695 V.

The SMSE is connected to the plating cell via a Luggin capillary placed about 0.5 cm from the working electrode. All potentials are referred to the SMSE. The counter electrode consisted of a platinum rod cleaned in a solution of hydrogen peroxide and sulfuric acid in range H₂O₂:H₂SO₄=1:3 before the tests.

Cyclic voltammetry measurements are performed at a step potential of 0.001 V and a scan rate of 0.020 V·s⁻¹ for the different solution compositions examined. In this case, potential is applied between the working electrode (blanket copper sample) and the counter electrode (Pt). This potential is the driving force of the electrodeposition process. In order to obtain the range when copper deposition occurs, the applied potential is changed to more negative values with a step of 0.001 V as described above. The change in the potential of the working electrode (blanket copper sample) is monitored with respect to the reference electrode (SMSE) and recorded versus the measured current, flowing between the working electrode (blanket copper sample) and the counter electrode (Pt). The results of these measurements are represented in the current-voltage curve shown in FIG. 2.

Apart from the cyclic voltammetry measurements, electrochemical copper depositions at patterned samples (coupons of patterned wafers) are performed. For this goal, a constant current or a constant potential, chosen from the current-voltage curves, is applied for a time long enough to obtain surface charge of Q=0.830 C which corresponds to a copper deposit with thickness about 200 nm.

All electrochemical steps are performed using a potentiostat from Metrohm Ltd., which controls the applied current or voltage, in the case of copper electrodeposition, or applies potential and measures the current, in the case of cyclic voltammetry measurements.

Example 4

Quality of the Deposits

After electrochemical deposition of copper, the patterned samples are examined using a scanning electron microscope (SEM). For this purpose, a FIB tool with a beam of Ga⁺ ions is first used to provide with uniform cut through the middle of the trenches ensuring that the deposited copper will not be pulled out of the trenches during a mechanical cleaving. After the FIB cut, the samples are examined by SEM and images of the samples at different magnification are recorded. The appearance or absence of voids (defects in the copper deposit) is observed. Copper deposit with a good quality is the one without voids (defects).

Claims

1. A method for electroplating a copper deposit onto a substrate, wherein the method comprises the steps of:

a. immersing said substrate into an electroplating bath having a copper ion concentration comprised between about 0.5 mmol·l−1 and about 50 mmol·l−1, and an acid concentration comprised between about 0.05% and about 10% per volume of said electroplating bath; and

b. electroplating the copper deposit from said electroplating bath onto said substrate.

2. A method according to claim 1, wherein the pH of the electroplating bath is acidic, preferably the pH is comprised between about −0.3 and about 3.0, more preferably between about −0.2 and about 2.0.

3. A method according to claim 1, wherein the electroplating bath has a chloride ion concentration comprised between about 0.1 ppm and about 10 ppm, preferably between about 0.5 ppm and about 8 ppm, more preferably between about 1 ppm and about 5 ppm, even more preferably between about 1 ppm and about 3 ppm, still more preferably between about 1.5 ppm and about 2.5 ppm, most preferably between about 1.8 ppm and about 2.2 ppm.

4. A method according to claim 1, wherein the substrate is provided with at least one feature opening, preferably selected from the group of trenches and vias, wherein said feature opening has a width below about 100 nm, preferably below about 70 nm, more preferably below about 50 nm, even more preferably below about 35 nm.

5. A method according to claim 1, wherein the substrate is provided with a copper seed having a thickness below about 60 nm, preferably below about 50 nm, more preferably below about 30 nm, even more preferably below about 20 nm, still more preferably below about 10 nm, most preferably below about 8 nm.

6. A method according to claim 5, wherein the electroplating bath has an acid concentration comprised between about 0.05% and about 1%, preferably between about 0.05% and about 0.7%, more preferably between about 0.05% and about 0.5%, even more preferably between about 0.05% and about 0.3%, most preferably between about 0.05% and about 0.15% per volume of said electroplating bath.

7. A method according to claim 5, wherein the electroplating bath comprises sulfuric acid, preferably in a concentration comprised between about 10 mmol·l−1 and about 200 mmol·l−1, more preferably between about 10 mmol·l−1 and about 100 mmol·l−1, even more preferably between about 15 mmol·l−1 and about 50 mmol·l−1, most preferably between about 15 mmol·l−1 and about 25 mmol·l−1.

8. A method according to any of claim 1, wherein the substrate is provided with a seed layer made from a seed material not comprising copper; and wherein the seed material preferably comprises ruthenium.

9. A method according to claim 8, wherein the electroplating bath has an acid concentration comprised between about 5% and about 10%, preferably between about 6% and about 9.5%, even more preferably between about 7% and about 9%, most preferably between about 8% and about 9% per volume of said electroplating bath.

10. A method according to claim 8, wherein the electroplating bath comprises sulfuric acid, preferably in a concentration comprised between about 1 mol·l−1 and about 2 mol·l−1, more preferably between about 1.2 mol·l−1 and about 1.9 mol·l−1, even more preferably between about 1.4 mol·l−1 and about 1.8 mol·l−1, most preferably between about 1.6 mol·l−1 and about 1.8 mmol·l−1.

11. A method according to claim 1, wherein the electroplating bath has a copper ion concentration comprised between about 0.5 mmol·l−1 and about 30 mmol·l−1, preferably between about 0.5 mmol·l−1 and about 20 mmol·l−1, more preferably between about 1.0 mmol·l−1 and about 20 mmol·l−1, even more preferably between about 1.0 mmol·l−1 and about 10 mmol·l−1.

12. A method according to claim 1, wherein the electroplating bath further comprises an organic additive system comprising a suppressor of copper deposition on copper and/or an accelerator of copper deposition on copper.

13. A method according to claim 12, wherein the electroplating bath comprises a suppressor of copper deposition, which is preferably polyethylene glycol, in a concentration comprised between about 20 ppm and about 500 ppm, more preferably between about 50 ppm and about 120 ppm, even more preferably between about 70 ppm and about 115 ppm, still more preferably between about 90 ppm and about 110 ppm; most preferably in a concentration of about 100 ppm; and wherein the electroplating bath comprises an accelerator of copper deposition, which is preferably bis-(sodium sulfopropyl)-disulfide, in a concentration comprised between about 0.02 ppm and about 2 ppm, preferably between about 0.1 ppm and about 1.5 ppm, more preferably between about 0.5 ppm and about 1.3 ppm, most preferably between about 0.7 ppm and about 1.0 ppm.

14. A method for the preparation of an electroplating bath suitable for electroplating a copper deposit onto a substrate, wherein the method comprises the step of:

a. providing a concentrate composition comprising a source of copper ion and a source of acid; and

b. diluting said concentrate composition into a solution comprising deionized water, thereby forming an electroplating bath as described in claim 1.

15. The concentrate composition as defined in claim 14.

16. The concentrate composition according to claim 15, which further comprises a source of chloride ion, preferably in such an amount as to form an electroplating bath having a chloride ion concentration comprised between about 0.1 ppm and about 10 ppm, preferably between about 0.5 ppm and about 8 ppm, more preferably between about 1 ppm and about 5 ppm, even more preferably between about 1 ppm and about 3 ppm, still more preferably between about 1.5 ppm and about 2.5 ppm, most preferably between about 1.8 ppm and about 2.2 ppm, when said concentrate composition is diluted into a solution comprising deionized water.

17. The method of use according to claim 1 for the manufacture of a semiconducting device, preferably a semiconductor integrated circuit (IC) device.

18. The method of use according to claim 17 for the manufacture of semiconducting devices features, preferably for the manufacture of interconnections having a width which is preferably below about 100 nm, more preferably below about 70 nm, even more preferably below about 50 nm, most preferably below about 35 nm.