CODEPOSITION OF COPPER NANOPARTICLES IN THROUGH SILICON VIA FILLING

FIELD OF THE INVENTION

[0001 ] The present invention generally relates to via filling with copper metallization and in particular relates to via filling through silicon vias using copper nanoparticles.

BACKGROUND OF THE INVENTION

[ 0002 ] Integrated circuit (IC) devices contain vias that form electrical connections between layers of interconnect structure. In one form, a via may extend from the backside of the IC die to the front, active side of the die. This type of via architecture is known in the art as a "through silicon via" (TSV). In some devices, the through silicon via can form an interconnect between a pair of bonded wafers in a wafer stack.

[ 0003 ] The depth of a TSV is a function of the wafer thickness, which may be about 30 micrometers to about 500 micrometers, such as about 250 micrometers. In the state of the art, via openings in TSV have an entry dimension such as a diameter from about 1 micrometer to about 200 micrometers, such as between about 10 micrometers and about 50 micrometers.

[0004 ] Electrolytic copper metallization is conventionally employed to provide electrical interconnection in the manufacture of semiconductor integrated circuit (IC) devices. Conventional electrolytic copper deposition baths may take as short as half an hour and as long as 20 hours to fill through silicon via. The latter represents a major obstacle to commercial feasibility. Accordingly, there is a need in the art for a faster method of copper metallization of devices containing TSV.

SUMMARY OF THE INVENTION

[0005] It is an object of the invention, therefore, to provide a method for electrolytic Cu filling of TSV which is economical and achieves a high quality fill.

[0006] Briefly, therefore, the present invention is directed to an electrolytic copper plating composition for metallizing a via feature in a semiconductor integrated circuit substrate. The composition comprises coated copper nanoparticles comprising copper nanoparticles and a bi-functional molecule coating, wherein at least about 90% of the copper nanoparticles have at least one transverse dimension that is less than about 500 nm and at least about 90% of the copper nanoparticles have at least one transverse dimension that is greater than about 5 nm.

[ 0007 ] The present invention is further directed to a method for electrolytic deposition of copper into a semiconductor integrated circuit device substrate comprising a via

feature having a bottom, a sidewall, and a top opening having an entry dimension of at least 1 micrometer. The method comprises immersing the semiconductor integrated circuit device substrate into the electrolytic plating composition comprising coated copper nanoparticles comprising copper nanoparticles and a bi-functional molecule coating, wherein at least about 90% of the copper nanoparticles have at least one transverse dimension that is less than about 500 nm and at least about 90% of the copper nanoparticles have at least one transverse dimension that is greater than about 5 nm; and supplying electrical current to the electrolytic composition to deposit copper onto the substrate and into the via feature.

[0008] Other objects and features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

[0009] FIGS. IA through 1C are photographs of copper-metallized through silicon vias illustrating (A) perfect copper metallization resulting from defect- free bottom up filling, (B) copper metallization having a seam therein, typically resulting from conformal filling, and (C) copper metallization having a void therein, typically resulting from pinch off.

[0010] FIG. 2 is a flow chart of the through silicon via preparation process.

DETAILED DESCRIPTION OF THE EMBODIMENT(S) OF THE INVENTION

[0011 ] The present invention is directed to a method of via metallization in the manufacture of semiconductor integrated circuit devices. The method of the present invention is particularly useful for filling through silicon vias at a commercially practicable rate in a defect free via super-filling process. A "defect free" via super-filling process is characterized by good seed layer coverage, adequate wetting of the electrolytic solution down to the bottom of the via, acceptable balance between the action of the suppressor/1 eveler and accelerator to achieve rapid, bottom up filling, and adequate mass transfer. Such a process achieves a completely metallized via. See FIG. IA. Defects resulting from imperfect processes include seams (See FIG. IB) and voids (See FIG. 1C). Seams occur when there is conformal filling, often due to inadequate accelerator in the electrolytic solution and/or the deposition processes uses an incorrect waveform. Voiding occurs due to pinch off, often from non-optimum balance between the action of the suppressor/level er and accelerator and use of an incorrect waveform.

[0012 ] One aspect of the present invention is directed to an electrolytic copper deposition bath comprising copper particles for TSV filling. In particular, the electrolytic

copper deposition bath comprises copper particles having at least one transverse dimension on the order of nanometers. These copper particles are referred to herein as copper nanoparticles. The electrolytic copper plating compositions of the present invention may comprise both a source of copper nanoparticles and a source of copper ions. Preferably, the copper nanoparticles and the source of copper ions are present within a ratio of a concentration of coated copper nanoparticles (in g of copper nanoparticles per Liter) to a concentration of copper ions (in g/L) of between about 0.005 and about 0.4, preferably between about 0.01 and about 0.2. Stated another way, the concentration of copper ions in g/L is typically about 5 to 100 times the concentration of coated copper nanoparticles in g/L.

[0013] Copper nanoparticles refer to copper particles wherein at least about 90% of the particles have at least one transverse dimension that is less than 500 nanometers ("nm") and at least about 90% of the particles have at least one transverse dimension that is greater than 5 nm, preferably at least about 90% of the particles have at least one transverse dimension that is less than 500 nm and at least about 90% of the particles have at least one transverse dimension that is greater than 20 nm. Even more preferably, copper particles for use in the method of the present invention have a particle size distribution wherein at least about 90% of the particles have at least one transverse dimension that is less than 250 nm and at least about 90% of the particles have at least one transverse dimension that is greater than 100 nm. In one preferred embodiment, at least about 90% of the particles are characterized in that all transverse dimensions of such particles are less than 500 nm. All percentages herein are by weight unless stated otherwise.

[0014 ] Copper nanoparticles are available in a wide-variety of shapes, such as spheres, oblate spheroids, prolate spheroids, platelets, flakes, cones, barrels, and rods. With regard to spherical copper nanoparticles, the nanoparticles are generally irregularly-shaped spheres (i.e., comprise divots, protrusions, etc. that cause their shape to deviate from perfectly spherical shape). With regard to irregularly-shaped spherical copper nanoparticles, the at least one transverse dimension on the order of nanometers is essentially the diameter of the nanoparticle.

[0015] Copper nanoparticles shaped roughly as oblate spheroids may be defined by three perpendicular transverse dimensions, two semi-major axes and one semi-minor axis, and at least about 90% of the oblate particles have at least one of these transverse dimension that is less than 500 nm and at least about 90% of the oblate particles have at least one transverse dimension that is greater than 5 nm, preferably at least about 90% of the oblate particles have at

least one of these transverse dimension that is less than 500 nm and at least about 90% of the oblate particles have at least one transverse dimension that is greater than 20 nm. Preferably, at least 90% of the oblate particles have all three transverse dimensions between about 20 nm and about 500 nm, even more preferably all three transverse dimensions are between about 100 nm and about 250 nm.

[0016] Copper nanoparticles shaped roughly as prolate spheroids are also defined by three perpendicular transverse dimensions, one semi-major axis and two semi-minor axes, and at least about 90% of the prolate particles have at least one of these transverse dimension that is less than 500 nm and at least about 90% of the prolate particles have at least one transverse dimension that is greater than 5 nm, preferably at least about 90% of the oblate particles have at least one of these transverse dimension that is less than 500 nm and at least about 90% of the oblate particles have at least one transverse dimension that is greater than 20 nm. Preferably, at least 90% of the prolate spheres have all three transverse dimensions between about 20 nm and about 500 nm, even more preferably all three transverse dimensions are between about 100 nm and about 250 nm.

[0017 ] Platelet, barrels, rods, cones, and flakes may also be defined in terms of transverse dimensions. With regard to each of these shapes, at least about 90% of the particles have at least one transverse dimension that is less than 500 nm and at least about 90% of the particles have at least one transverse that is greater than 5 nm, preferably at least about 90% of the particles have at least one transverse dimension that is less than 500 nm and at least about 90% of the particles have at least one transverse dimension that is greater than 20 nm, even more preferably at least about 90% of the particles have at least one transverse dimension that is less than 250 nm and at least about 90% of the particles have at least one transverse dimension that is greater than 100 nm. Preferably, every transverse dimension for each of the nanoparticle shapes is less than 500 nm and greater than 20 nm.

[0018] In a preferred embodiment, the copper nanoparticles are irregularly-shaped spheres, wherein at least about 90% of the particles have a diameter that is less than 500 nm and at least about 90% of the particles have a diameter that is greater than 20 nm, preferably, at least about 90% of the particles have a diameter that is less than 250 nm and at least about 90% of the particles have a diameter that is greater than 100 nm.

[0019] Copper nanoparticles are available in a range of particle size distributions, and the choice of particle size distribution for a particular application may depend, in part, on the dimensions of the via to be metallized. Larger particles are preferred for filling vias having

larger opening diameters to ensure a commercially practicable fill rate, while smaller particles are preferred for filling vias having smaller opening diameters to ensure void-free filling. For filling vias having smaller opening diameters, such as below about 10 micrometers, copper nanoparticles may be chosen wherein at least about 80% of the particles have at least one dimension between about 20 and about 50 nm. For filling vias having larger opening diameters, such as above about 10 micrometers, copper nanoparticles may be chosen wherein at least about 90% of the particles have at least one dimension between about 50 nm and about 300 nm. It has been discovered that the nanoparticles accelerate the deposition rate both by acting as seed particles around which copper plating may form and as filler particles in the deposited metallization. In both aspects, copper nanoparticles increase the fill rate compared to conventional metallization using electrolytic plating baths in which the source of deposition metal consists of copper atoms. Additionally, the copper deposition method of the present invention yields essentially void-free and defect-free metallized vias.

[0020] Copper nanoparticles that may be used in the method of the present invention are available from many sources. Applicable sources include ND Copper Powder C 1-250 (copper spheres having average diameters of about 250 nm) and ND Copper Powder C 1-500 (copper spheres having average diameters of about 500 nm), both are available from NanoDynamics (Buffalo, NY) and Copper Powder 20-9008, also available from NanoDynamics.

[0021 ] The copper nanoparticles may be prepared prior to adding to the electrolytic copper deposition bath. Nanoparticle preparation may involve both cleaning the particles to remove surface oxides and treating the particles in a surfactant solution to render the particles dispersible in aqueous solution. Cleaning solutions suitable for removing surface oxides are preferably strongly acidic and may comprise organic acids and inorganic acids. Preferably, the pH of the cleaning solution is between about 1.4 and about 3.4, such as between about 1.8 and about 3, such as about 2.4. Applicable inorganic acids include mineral acids, such as hydrofluoric acid, phosphorous acid, and hydrochloric acid. Strong oxidative inorganic acid such as nitric acid should be avoided. Applicable organic acids for inclusion in the cleaning solution include acetic acid, trichloroacetic acid and trifluoroacetic acid. In one embodiment, the copper nanoparticles are washed with a solution comprising concentrated acetic acid and hydrofluoric acid (5%) to remove surface oxides. The particles may be washed by immersing the particles in the cleaning solution or by spraying. Washing typically occurs for between about 1 minute and about 5 minutes to ensure adequate removal of surface oxides. Washing for more than about 5 minutes does not provide further cleaning. The temperature of the wash

solution may be between about 18°C and about 25°C. The particles are not rinsed after washing to avoid surface re-oxidation.

[0022 ] After cleaning, the copper nanoparticles are coated with a bi-functional molecule. The bi-functional molecule comprises a hydrophobic group and a hydrophilic group. During coating of the copper nanoparticles in the solution comprising the bi-functional molecule, the hydrophobic group interacts with the copper nanoparticle while the hydrophilic group interacts with an aqueous solution (typically, a copper-sulfuric acid electrolytic solution with organic additives, for example). By interacting with the copper particle in such a manner, the bi-functional molecule renders the copper nanoparticle dispersible in the aqueous solution, such as by forming a micellar coating of bi-functional molecules around the copper nanoparticle. Further, since the nanoparticles become similarly charged (e.g., positively charged, in the preferred embodiment), the bi-functional coating inhibits copper nanoparticle agglomeration. Accordingly, the particle size distribution of the copper nanoparticles in solution remains essentially the same as the particle size distribution of the dried copper nanoparticles, except for a slight increase in particle size due to the bi-functional coating.

[0023] The bi-functional molecule may be neutral, or positively charged. Preferably, the population of bi-functional molecules has an overall positive charge such that the coated copper nanoparticles bear an overall positive charge. The positive charge is desirable since the wafer substrate comprising through silicon via serves as the cathode (negatively-charged electrode) during electrolytic copper deposition. Accordingly, the coated copper nanoparticles are electrostatically or electrokinetically drawn to the wafer surface when the rectifier (i.e., power supply) is on.

[0024 ] In one embodiment, the bi-functional molecule for use as a coating material comprises an amine and at least one hydrophobic long chain hydrocarbon group. The amine moiety represents the hydrophilic head group and is either rendered cationic in acidic solution (primary, secondary, tertiary amines) or permanently cationic (quaternary amines). Preferably, the amine is a quaternary amine. The long chain hydrocarbon group represents the hydrophobic tail. The hydrocarbon group may be between about six and about 24 carbons long. The hydrocarbon group is preferably at least six carbons long to be sufficiently hydrophobic to form micellar coatings around the copper nanoparticle. The hydrocarbon chain is preferably no more than about 24 carbons long to ensure adequate solubility. Preferably, the hydrocarbon chain is longer than six carbon atoms and shorter than 24 carbon atoms, such as between about eight carbon atoms and about 16 carbon atoms, more preferably between about ten carbon atoms and

about 14 carbon atoms. Exemplary bi-functional molecules comprising an amine and a hydrocarbon group include dodecyltrimethyl quaternary ammonium chloride (such as Arquad 12-35W from Akzo Nobel), dodecyl dimethyl benzyl ammonium chloride; hexadecyl trimethyl ammonium chloride (such as Arquad 16-29 and Arquad 16-29); octadecyl trimethyl ammonium chloride; octadecyl dimethyl benzyl ammonium chloride; tallowbenzyl dimethyl ammonium chloride; cetylpyridinium chloride; benzethonium chloride; and many others. Exemplary bifunctional molecules include surfactants in the Arquad Series and Armeen Series, available from Akzo Nobel. In one embodiment, the bi-functional molecule is dodecyltrimethyl quaternary ammonium chloride, which is available under the trade name PALLADEX ADDITIVE 1, available from Enthone Inc. (West Haven, CT).

[0025] In another embodiment, the bi-functional molecule for use as coatings comprises an amine and at least one polyalkoxylate group. Preferably, the bi-functional molecules comprises an amine, at least one polyalkoxylate group, and at least one hydrophobic long chain hydrocarbon group. The amine moiety is either rendered cationic in acidic solution (primary, secondary, tertiary amines) or permanently cationic (quaternary amines). Preferably, the amine is a quaternary amine. The polyalkoxylate chain may comprise between about two and about 20 alkoxy groups, preferably between about 2 and about 12 alkoxy groups. The alkoxy groups may be ethoxy, propoxy, butoxy, or even combinations thereof. The alkoxy group increases the hydrophilicity of the bi-functional molecule. The hydrocarbon group may be between about six and about 24 carbons long. The hydrocarbon group is preferably at least six carbons long to be sufficiently hydrophobic to form micellar coatings around the copper nanoparticle. The hydrocarbon chain is preferably no more than about 24 carbons long to ensure adequate solubility. Preferably, the hydrocarbon chain is longer than six carbon atoms and shorter than 24 carbon atoms, such as between about eight carbon atoms and about 16 carbon atoms, more preferably between about ten carbon atoms and about 14 carbon atoms.

[0026] Exemplary bi-functional molecules comprising an amine and a polyalkoxylate group include polyethoxylated tallow amine having an average of between about 8 and about 22 ethoxylate groups (e.g., Ethomeen T/20, Ethomeen T/25, and Ethomeen T/30, available from Akzo Nobel), polyethoxylated cocamine having an average of between about 2 and about 16 ethoxylate groups (e.g., Ethomeen C/12, Ethomeen C/15, and Ethomeen C/25, available from Akzo Nobel), polypropoxylated cocoamine (e.g., propomeen C/12), polypropoxylated tallowamine (e.g., propomeen T/12), polyethoxylated tallowdiamine (e.g., ethoduomeen T/13), ethoxylated/propoxylated tallowamine (e.g., Adsee AB557 and Adsee

AB600), coco quaternary ammonium chloride having between about 10 and about 20 ethoxylate groups (e.g., Ethoquad C/15, Ethoquad C/25), and tallow quaternary ammonium chloride having between about 2 and about 15 ethoxylate groups (e.g., Ethoquad T/12, Ethoquad T/15, and Ethoquad T/25).

[0027 ] In yet another embodiment, the bi-functional molecule for use as coatings is a non-ionic EO/PO block co-polymer based on ethylenediamine. These non-ionic polymers are sold under the trade name Tetronic® and are available from BASF Corporation Performance Chemicals (Mount Olive, NJ 07828). Applicable Tetronic® surfacants include Tetronic® 504, Tetronic® 704, Tetronic® 904, Tetronic® 908, Tetronic® 901, Tetronic® 1301, Tetronic® 1307, Tetronic® 304, Tetronic® 701, and Tetronic® 1107. Tetronic® 904 has the structure (1) shown below: H-(OC ₂ H ₄ ) ₁₇ -(OC ₃ H ₆ ) ₁₉ -(C ₃ H ₆ O) ₁₉ -( C ₂ H ₄ O) ₁₇ 'H

\ ^H 2 ^H 2 /

N C C N

H-(OC ₂ H ₄ ) ₁₇ -(OC ₃ H ₆ ) J (C ₃ H ₆ O) ₁₉ -( C ₂ H ₄ O) ₁₇ -H

^ ⁾ .

[0028] The copper nanoparticles are coated with the bi-functional molecule in coating slurry. The slurry typically comprises the copper nanoparticles, the bi-functional molecules, water, and the components of the electrolytic copper deposition composition. Typically, the concentration of copper nanoparticles in the coating slurry is between about 1 g/L and about 10 g/L, such as about 1.0 g/L and about 2.5 g/L. In one embodiment, the concentration of the copper nanoparticles is about 1.4 g/L. Typically, the concentration of bi- functional molecule in the coating slurry is between about 0.05 g/L and about 0.15 g/L. In one embodiment, the concentration of the bi-functional molecules is about 0.1 g/L. The concentrations are chosen in part to ensure adequate coating of the copper nanoparticles and may therefore be expressed as a ratio of concentration of bi-functional molecule to concentration of copper nanoparticle. The nanoparticles are coated with agitation, such as stirring, shaking, etc. and the copper nanoparticles are adequately coated when it is observed that the nanoparticles do not precipitate or agglomerate in the absence of agitation and the color of the composition is stable. Uncoated nanoparticles are particularly susceptible to oxidation if not adequately coated, which can be observed by a color change in solution.

[0029] The coated copper nanoparticles are used in an electrolytic copper deposition bath for metallization of vias and through silicon vias in the manufacture of semiconductor

integrated circuit substrates. The electrolytic copper deposition baths may further comprise a source of copper ions, an acid, and superfilling additives. These superfilling additives typically include a suppressor, a leveler, and an accelerator. The above-listed additives find application in high copper metal/low acid electrolytic plating baths, in low copper metal/high acid electrolytic plating baths, and in mid acid/high copper metal electrolytic plating baths. The compositions can also comprise other additives which are known in the art such as halides, grain refiners, quaternary amines, polysulfide compounds, and others.

[0030] The concentration of copper nanoparticles in the electrolytic copper deposition bath may be between about 1 g/L and about 10 g/L, for example between about 1.5 g/L and about 2.5 g/L.

[0031 ] Applicable suppressors for the Cu plating compositions of the present invention include a group of suppressors comprising polyether groups covalently bonded to primary amines, secondary amines, tertiary amines, and quaternary amines and a group of suppressors comprising polyether groups covalently bonded to primary alcohols, secondary alcohols, and polyols. The polyethers comprise a chain of ethylene oxide repeat units, propylene oxide repeat units, and a combination thereof. Exemplary polyether suppressors covalently bonded to amines are described in U.S. Pat. No. 7,303,992, issued December 4, 2007, the entire disclosure of which is expressly incorporated by reference.

[ 0032 ] The suppressor compounds of the invention have a molecular weight between about 1000 and about 30,000. Exemplary suppressor compounds comprising a polyether group covalently bonded to a cationic species wherein the polyether is covalently bonded to a nitrogen atom are shown by structures (2) through (6) below. It is to be noted that, in one embodiment, the electrolytic copper plating composition of the present invention may comprise coated copper nanoparticles coated with non-ionic EO/PO block co-polymers based on ethylenediamine while further comprising such co-polymers as a suppressor. In this embodiment, non-ionic EO/PO block co-polymers based on ethylenediamine acts as both a suppressor and a bi-functional surfactant for keeping copper nanoparticles dispersed in solution.

[ 0033 ] Structure (2) is a PO/EO block copolymer of ethylenediamine having the structure:

H-(OC ₂ H ₄ ) _n (OC ₃ H ₆ ) _m /C ₃ H ₆ O) _m (C ₂ H ₄ O) _n -H

\ H ₂ H ₂ / N C C N

H-(OC ₂ H ₄ ) _n (OC ₃ H ₆ ) / (C ₃ H ₆ O) _1n (C ₂ H ₄ O) _n -H

( 2 ) and wherein n can be between 1 and about 30 and m can be between 1 and about 30. Accordingly a suppressor compound having the structure (5) comprises between about 4 and about 120 total PO repeat units and between about 4 and about 120 total EO repeat units on the four PO/EO block copolymers. The molecular weight of the PO (hydrophobic unit) block on a single PO/EO block copolymer can be between about 50 g/mol and about 1800 g/mol, and the molecular weight of the EO (hydrophilic unit) block on a single PO/EO block copolymer can be between about 40 g/mol and about 1400 g/mol. The molecular weight of a single PO/EO copolymer can be between about 100 g/mol about 3600 g/mol. An exemplary suppressor compound having the structure (2) is available from BASF Corporation of Mt. Olive, New Jersey under the trade designation Tetronic® 704. This suppressor compound comprises about 13 PO repeat units per PO/EO block copolymer for a total of about 52 PO repeat units on all four PO/EO block copolymers and about 11 EO repeat units per PO/EO block copolymer for a total of about 44 EO repeat units on all four PO/EO block copolymers. Accordingly, the total MW of Tetronic® 704 is between about 5000 g/mol and about 5500 g/mol. Another exemplary block copolymer of structure (2) is also available from BASF Corporation under the trade designation Tetronic® 504. This suppressor compound comprises about 9 PO repeat units per PO/EO block copolymer for a total of about 36 PO repeat units on all four PO/EO block copolymers and about 7.5 EO repeat units per PO/EO block copolymer for a total of about 30 EO repeat units on all four PO/EO block copolymers. Accordingly, the total MW of Tetronic® 504 is between about 3200 g/mol and about 3600 g/mol. The bath composition can comprise a mixture of block copolymers of structure (2).

[0034 ] Structure (3) is an N-methylated PO/EO block copolymer of ethylenediamine having the general structure:

_n -H

(3),

wherein n can be between 1 and about 30 and m can be between 1 and about 30. A source of the suppressor compound having structure (3) is N-methylated Tetronic® 504 or N-methylated Tetronic® 704.

[ 0035 ] Structure (4) is a methyl-capped PO/EO block copolymer of ethylenediamine having the general structure:

CH ₃ ( OC ₂ H ₄

CH ₃ ( OC ₂ H ₄ and wherein n can be between 1 and about 30 and m can be between 1 and about 30. A source of the suppressor compound having structure (4) is methyl-capped Tetronic® 504 or methyl- capped Tetronic® 704. In various alternatives, one of the terminal oxygen atoms can be bonded to a methyl group and the other three terminal oxygen atoms can be bonded to a hydrogen atom; or two of the terminal oxygen atoms can be bonded to a methyl group and two of the terminal oxygen atoms can be bonded to a hydrogen atom; or three of the terminal oxygen atoms can be bonded to a methyl group and one of the terminal oxygen atoms can be bonded to a hydrogen atom; or all of the terminal oxygen atoms can be bonded to a methyl group.

[0036] In yet another alternative, the block copolymer is methylated and capped as described above, as long as the cloud point is such that it is compatible with copper solution.

[ 0037 ] Structure (5) is a PO/EO/PO tri-block copolymer of ethylenediamine having the general structure:

H-( OC ₃ H ₆ J ₀ ( OC ₂ H _{4 6} O) _1n -( C ₂ H ₄ O) _n -( C ₃ H ₆ O) ₀ -H

H-(OC ₃ H ₆ ) ₀ (OC ₂ H _{4 6} O) ,-( C ₂ H ₄ O) ,-( C ₃ H ₆ O) _Q -H

(5), and wherein n can be between 1 and about 30, m can be between 1 and about 30, and 0 can be between about 1 and about 5, or such that the cloud point is compatible with copper solution. Preferably, 0 is 1 or 2. A source of a suppressor compound having structure (5) is PO-capped Tetronic® 504 or PO-capped Tetronic® 704.

[0038] Structure (6) is a PO/EO block copolymer of triethylene glycol diamine having the structure:

and wherein n can be between 1 and about 30 and m can be between 1 and about 30. Triethylene glycol diamine, to which the PO/EO block co-polymers can be covalently bonded, is available from Huntsman LLC of Salt Lake City, Utah under the trade designation Jeffamine XTJ-504. The structure of the PO/EO block copolymer in suppressor compounds having structure (6) can be substantially the same as the PO/EO block copolymers in Tetronic® 504 and Tetronic® 704. Accordingly, the MW of a suppressor compound having structure (6) can be between about 5200 g/mol and about 5800 g/mol.

[0039] The composition of the invention may also include a leveler. An exemplary leveler is disclosed in U.S. Pat. No. 7,316,772, issued January 8, 2008, the entire disclosure of which is expressly incorporated by reference. One such preferred leveler is a reaction product of benzyl chloride and hydroxyethyl polyethyleneimine available from Enthone Inc. of West Haven, Connecticut under the trade designation ViaForm® Leveler. Another suitable leveler is a reaction product of benzyl chloride and polyethyleneimine. A further suitable leveler is the reaction product of 1 -chloromethylnaphthalene and hydroxyethyl polyethyleneimine (available under the tradename Lupasol SC 61B from BASF Corporation of Rensselear, New York). Polyvinylpyridines and their quaternized salts, and polyvinylimidazole and its salts are also suitable. These levelers may be incorporated, for example, in a concentration between about 0.1 mL/L and about 25 mL/L, such as about 4 mL/L. Optionally, additional leveling compounds of other types can be incorporated into the bath.

[0040] Additional levelers are disclosed in U.S. Pat. Pub. No. 2005/0045488, filed October 12, 2004, the entire disclosure of which is expressly incorporated by reference. Levelers disclosed therein include derivatives of 4-vinyl pyridine and 2-vinyl pyridine that are generally alkylated. In some embodiments, these levelers are also pyridyl polymers. Exemplary levelers disclosed therein include a reaction product of 4-vinyl pyridine and methyl sulfate, a reaction product of poly(4-vinyl pyridine) and methyl sulfate, a reaction product of poly(4-vinyl pyridine) with dimethyl sulfate, a reaction product of poly(4-vinyl pyridine) with methyl tosylate, a reaction product of 4-vinyl pyridine with dimethyl sulfate, a reaction product of 4- vinyl pyridine with methyl tosylate, a reaction product of 4-vinyl pyridine with 2-chloroethanol, a reaction product of 4-vinyl pyridine with benzylchloride, a reaction product of 4-vinyl pyridine with allyl chloride, a reaction product of 4-vinyl pyridine with 4-chloromethylpyridine,

a reaction product of 4-vinyl pyridine with 1,3 -propane sultone, a reaction product of 4-vinyl pyridine with methyl tosylate, a reaction product of 4-vinyl pyridine with chloroacetone, a reaction product of 4-vinyl pyridine with 2-methoxyethoxymethylchloride, a reaction product of 4-vinyl pyridine with 2-chloroethylether, a reaction product of 2-vinyl pyridine with methyl tosylate, a reaction product of 2-vinyl pyridine with dimethyl sulfate, poly(2-methyl-5-vinyl pyridine), and 1 -methyl-4-vinylpyridinium trifluoromethyl sulfonate. The leveler is incorporated, for example, in a concentration between about 0.1 mg/L and about 25 mg/L.

[0041 ] The composition may also comprise an accelerator. Exemplary accelerators are bath soluble organic divalent sulfur compounds as disclosed in U.S. Pat. 6,776,893, the entire disclosure of which is expressly incorporated by reference. In one preferred embodiment, the accelerator corresponds to the formula (7)

R ₁ -(S) _n RXO ₃ M (7), wherein

M is hydrogen, alkali metal or ammonium as needed to satisfy the valence;

X is S or P;

R is an alkylene or cyclic alkylene group of 1 to 8 carbon atoms, an aromatic hydrocarbon or an aliphatic aromatic hydrocarbon of 6 to 12 carbon atoms; n is 1 to 6; and

Ri is MO3XR wherein M, X and R are as defined above.

[0042 ] An accelerator which is especially preferred is 1 -propanesulfonic acid, 3,3'- dithiobis, disodium salt ("SPS") according to the following formula (8):

[0043] The accelerator is incorporated typically in a concentration between about 0.5 mL/L and about 1000 mL/L, more typically between about 0.5 mL/L and about 50 mL/L, such as between about 2 mL/L and about 50 mL/L, such as between about 5 mL/L and 30 mL/L. In one embodiment, 10 ml/L SPS is used.

[0044 ] The components of the electrolytic copper plating bath may vary widely depending on the substrate to be plated. The electrolytic baths include acid baths and alkaline baths. A variety of electrolytic copper plating baths are described in the book entitled Modern Electroplating, edited by F. A. Lowenheim, John Reify & Sons, Inc., 1974, pages 183-203. Exemplary electrolytic copper plating baths include copper fluoroborate, copper pyrophosphate, copper cyanide, copper phosphonate, copper acetate, copper sulfate, and other copper metal complexes such as methane sulfonic acid. The most typical copper electrolytic plating bath comprises copper sulfate or copper methanesulfonate in an acid solution.

[0045] Therefore, the concentration of copper ions and acid may vary over wide limits; for example, from about 4 to about 135 g/L copper ions, preferably from about 40 g/L to about 100 g/L, and from about 2 to about 225 g/L acid, preferably from about 10 g/L and about 50 g/L. In one embodiment, the copper source is one of the copper sulfate-based sources, namely, copper sulfate or copper sulfate pentahydrate. In another embodiment, the copper source is copper methane sulfonate. In embodiments wherein the copper source is a sulfate- based source, the concentration of copper typically ranges from about 5 g/L to about 75 g/L, such as between about 5 g/L and about 30 g/L or between about 30 g/L and about 75 g/L. Copper methanesulfonate is a more soluble source of copper, and the copper concentration may range more widely, such as from about 5 g/L to about 135 g/L, such as between about 75 g/L and about 135 g/L copper or between about 40 g/L and about 100 g/L. In low copper systems, the copper ion concentration can be between about 5 g/L and about 30 g/L, such as between about 8 g/L to about 25 g/L. In some high copper systems, the copper ion concentration can be between about 35 g/L and about 135 g/L, such as between about 35 g/L and about 75 g/L, preferably between about 35 g/L and about 60 g/L, or between about 75 g/L and about 135 g/L, preferably between about 100 g/L and about 135 g/L.

[0046] Sources of acid in the electrolytic plating bath include sulfuric acid, methane sulfonic acid, phosphoric acid, acetic acid, and boric acid. The acid concentration may range from about 2 to about 225 g/L acid, preferably from about 10 g/L and about 50 g/L.

[0047 ] Chloride ion may also be used in the bath at a level up to 200 mg/L, preferably about 10 to 90 mg/L. Chloride ion is added in these concentration ranges to enhance the function of other bath additives. These additives system include accelerators, suppressors, and levelers.

[0048] A large variety of additives may typically be used in the bath to provide desired surface finishes for the copper plated metal. Usually more than one additive is used with

each additive forming a desired function. At least two additives are generally used to initiate bottom-up filling of interconnect features as well as for improved metal plated physical (such as brightness), structural, and electrical properties (such as electrical conductivity and reliability). Particular additives (usually organic additives) are used for grain refinement, suppression of dendritic growth, and improved covering and throwing power. A particularly desirable additive system uses a mixture of aromatic or aliphatic quaternary amines, polysulfide compounds, and polyethers. Other additives include items such as selenium, tellurium, and sulfur compounds.

[0049] FIG. 2 is a flow chart of the process steps in preparing a wafer-to-wafer stack or chip-to-wafer stack involving through silicon via metallization. The wafer substrate (i.e., device wafer) for metallization using the electrolytic copper deposition solution of the present invention comprises vias and through silicon vias, which are prepared by photolithography and etching methods as is conventionally known. In a typical process, conventional photoresist material is applied to a cleaned and dried surface of a device wafer by spin coating. The photoresist may be soft-baked to remove excess solvent at a temperature between about 60 ⁰ C and about 100 ⁰ C for about 5 to 30 minutes. After soft-baking, the photoresist is exposed to ultraviolet light in a manner that defines the pattern of copper metallization. Exposed photoresist is then dissolved using a developer solution. The wafer and photoresist defining the copper metallization pattern is then hard-baked, typically between about 120 ⁰ C and about 180 ⁰ C for about 20 to 30 minutes. The exposed wafer is then etched by means known in the art to define a pattern of vias, which are then coated with a barrier layer, which may be titanium nitride, tantalum, tantalum nitride, or ruthenium to inhibit Cu diffusion. Next, the barrier layer is typically seeded with a seed layer of Cu or other metal to initiate Cu superfilling plating thereon. A Cu seed layer may be applied by chemical vapor deposition (CVD), physical vapor deposition (PVD), or the like. The vias having barrier layers and Cu seed layers are then plated using the electrolytic copper deposition composition and method of the present invention.

[0050] Plating equipment for plating semiconductor substrates is well known and is described in, for example, Haydu et al. U.S. Pat. 6,024,856. Plating equipment comprises an electrolytic plating tank which holds the deposition solution and which is made of a suitable material such as plastic or other material inert to the electrolytic plating solution. The tank may be cylindrical, especially for wafer plating. A cathode is horizontally disposed at the upper part of tank and may be any type substrate such as a silicon wafer having openings such as trenches and vias. An anode is also preferably circular for wafer plating and is horizontally disposed at

the lower part of tank forming a space between the anode and cathode. The anode is typically a soluble anode such as copper metal.

[0051 ] The bath additives are useful in combination with membrane technology being developed by various tool manufacturers. In this system, the anode may be isolated from the organic bath additives by a membrane. The purpose of the separation of the anode and the organic bath additives is to minimize the oxidation of the organic bath additives on the anode surface.

[ 0052 ] The cathode substrate and anode are electrically connected by wiring and, respectively, to a rectifier (power supply). The cathode substrate for direct or pulse current has a net negative charge so that copper ions in the solution are reduced at the cathode substrate forming plated copper metal on the cathode surface. Moreover, the net negative charge on the cathode attracts the net positively charged coated copper nanoparticles, which become adhered to the wafer substrate. As copper ion reduction continues during the plating operation, the copper nanoparticles become surrounded by copper metallization that builds around the surfaces of the nanoparticles. An oxidation reaction takes place at the anode. This same oxidation reaction may take place at the cathode if periodic pulse reverse plating is used. The cathode and anode may be horizontally or vertically disposed in the tank.

[0053] During operation of the electrolytic plating system, copper metal is plated on the surface of a cathode substrate when the rectifier is energized. A pulse current, direct current, reverse periodic current, periodic pulse reverse current, or other suitable current may be employed.

[0054 ] It has been discovered that pulse current using cycles between about 50 and about 100 ms long (i.e., applying current for between 25 to 50 ms followed by 25 to 50 ms rest periods) yields a copper deposit having greater mass for the same plating current (as measured by total Coulombs) compared to conventional direct current plating from a bath wherein the source of copper metallization consists of copper ions. Therefore, pulse plating using a bath comprising copper nanoparticles fills the vias with a higher plating efficiency than conventional plating methods. The electrical current density may be up to about 10 A/dm ² , typically between about 0.2 A/dm ² to about 6 A/dm ² . It is preferred to use an anode to cathode ratio of about 1 : 1, but this may also vary widely from about 1 :4 to 4: 1. In a preferred embodiment, plating occurs using a pulsed current profile in which the current density is 0.3 A/dm ² for 25 ms, followed by 25 ms rest. In another preferred embodiment, plating occurs using a pulsed current profile in which the current density is 1 A/dm ² for 25 ms, followed by 25 ms rest.

[0055] The temperature of the electrolytic solution may be maintained using a heater/cooler whereby electrolytic solution is removed from the holding tank and flows through the heater/cooler and then is recycled to the holding tank. For example, the bath temperature is typically about room temperature such as about 20-27 ⁰ C, but may be at elevated temperatures up to about 40 ⁰ C or higher. The process also uses mixing in the electrolytic plating tank which may be supplied by agitation or preferably by the circulating flow of recycle electrolytic solution through the tank. The flow through the electrolytic plating tank provides a typical residence time of electrolytic solution in the tank of less than about 1 minute, more typically less than 30 seconds, e.g., 10-20 seconds.

[0056] With reference again to FIG. 2, after via filling, the wafer surface and exposed copper metallization may be cleaned by chemical mechanical polishing, as is known in the art. The wafer may be thinned by conventional etching techniques to expose the bottom layer of copper metallization, thereby achieving through silicon via wherein copper metallization extends from the backside of the wafer or IC die to the front, active side of the wafer or die. The wafer may be further processed, stacked, and singulated by methods known in the art to achieve a device comprising multiple device levels, each connected electronically using through silicon via.

[ 0057 ] Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Examples

[0058] The following non-limiting examples are provided to further illustrate the present invention. Example 1. Coated Copper Nanoparticles

[0059] Copper nanoparticles were coated with a bi-functional molecule. The copper nanoparticles (200 nm average diameter) were ND copper, available from NanoDymanics Inc. (Buffalo, NY) and had a particle size distribution wherein at least about 80% of the nanoparticles had a diameter between about 100 nm and about 300 nm. The copper nanoparticles were washed in a solution comprising concentrated acetic acid and hydrofluoric acid (5%) to remove surface oxides. The cleaned copper nanoparticles were rinsed in deionized, distilled water.

[0060] The bi-functional molecule was dodecyltrimethyl quaternary ammonium chloride, available under the trade name PALLADEX ADDITIVE 1, from Enthone Inc. (West Haven, CT). The coating slurry was prepared by adding the copper nanoparticles (5.6 g/L) and dodecyltrimethyl quaternary ammonium chloride (2 mL/L) to an aqueous solution. The solution additionally comprises copper ions, sulfuric acid, and chloride ions. The coating slurry was stirred at setting 5 on a Corning Stirrer for about 3 hours at room temperature to achieve a micellar coating surrounding the nanoparticles. Example 2. Electrolytic Copper Deposition Bath Comprising Copper Nanoparticles

[0061 ] An electrolytic copper deposition bath (Bath A, total volume 250 mL) was prepared comprising the following components: coated copper nanoparticles (5.6 g/L); copper sulfate (50 g/L); sulfuric acid (80 g/L); chloride ion (50 ppm); Accelerator (10 mL/L); Suppressor (2 mL/L); Leveler (4 mL/L). This bath was prepared according to the following protocol:

1. Add 250 mL of a base electrolytic copper solution (comprising 50 g/L copper ions, 80 g/L Sulfuric and 50 ppm Chloride) to 400 mL beaker.

2. Add Accelerator (1.25 mL), Suppressor (1.25 mL) and Leveler (1.25 mL) to the beaker using a micropipette (WHEATON 200-1000 μL micropipette).

3. Add ND Copper nano-particles ( 1.4 g) into the beaker.

4. Stir the bath for 3 hours at room temperature.

[0062 ] A comparative electrolytic copper deposition bath (Comparative Bath B, total volume 250 mL) was prepared comprising the following components: copper ions (50 g/L); sulfuric acid (80 g/L); chloride ion (50 ppm); Accelerator (5 mL/L); Suppressor (5 mL/L); Leveler (5 mL/L). Example 3. Electrolytic Copper Deposition From Baths of Example 2

[0063] Baths A and B from Example 2 were used to deposit a layer of copper on Hull Cell Panels. The Baths were plated at a 0.5A current (current density of 2 Amps/dm ) under either direct current or pulse current for duration sufficient to yield 1800 Coulombs.

[0064 ] Deposition from Comparative Bath B at 0.5A direct current (current density = 2 A/dm ² ) for 1 hour deposited 0.58 g of copper onto the Hull Cell panels. The theoretical yield under these conditions is 0.5923 g. Accordingly direct current plating from a conventional bath yielded a 97.9% plating efficiency.

[0065] Bath A comprising copper nanoparticles was used to deposit copper over several panels in several trials. The following TABLE I shows the plating profiles used, the increase in panel weight, and the calculated plating efficiencies:

TABLE I

1 Plating efficiency was calculated by dividing the substrate weight increase by the substrate weight increase using Bath B.

[0066] From TABLE I, it is apparent that pulse current profiles using short cycles increases the plating efficiency above the theoretical limit calculated from a bath wherein the copper metallization sources consists of copper ions. Example 4. Electrolytic Copper Deposition From Baths of Example 2

[0067 ] Baths A and B from Example 2 were used to deposit a layer of copper on Hull Cell Panels. The Baths were plated at a 0.5A current (current density of 2 Amps/dm ² ) under either direct current or pulse current for duration sufficient to yield 1800 Coulombs.

[0068] Deposition from Comparative Bath B at 0.5A direct current (current density =

2 A/dm ) for 1 hour deposited 0.5916 g of copper onto the Hull Cell panels. The theoretical yield under these conditions is 0.5923 g. Accordingly direct current plating from a conventional bath yielded a 99.9% plating efficiency.

[0069] Bath A comprising copper nanoparticles was used to deposit copper over several panels in several trials. The following TABLE II shows the plating profiles used, the increase in panel weight, and the calculated plating efficiencies:

TABLE II

1 Plating efficiency was calculated by dividing the substrate weight increase by the substrate weight increase using Bath B.

[0070] When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the elements. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0071 ] In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

[0072 ] As various changes could be made in the above compositions and processes without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.