US20230203694A1

US20230203694A1 - Alkaline composition for copper electroplating comprising a grain refiner

Info

Publication number: US20230203694A1
Application number: US17/564,979
Authority: US
Inventors: Charlotte Emnet; Lucas Benjamin HENDERSON; Alexander Fluegel; Sathana Kitayaporn; Nadine ENGELHARDT
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2023-06-29
Also published as: CN118451219A

Abstract

Described herein is a composition for depositing copper on a semiconductor substrate, the composition including(a) copper ions;(b) a grain refiner of formula G1or salts thereof(c) a complexing agent; and(d) optionally a buffer or a base capable of adjusting the pH to a pH of from 7 to 13;where the variables are as defined herein; andwhere the pH of the composition is from 7 to 13.

Description

The present invention relates to an alkaline composition for depositing a copper layer onto a semiconductor substrate, its use and a deposition process by using such composition.

BACKGROUND OF THE INVENTION

Filling of small features, such as vias and trenches, by metal electroplating is an essential part of the semiconductor manufacture process. It is well known, that the presence of organic substances as additives in the electroplating bath can be crucial in achieving a uniform metal deposit on a substrate surface and in avoiding defects, such as voids and seams, within the metal lines.
Void-free bottom-up filling of submicrometer-sized interconnect features by using acidic copper electroplating baths on a copper seed is well known in the art.
With further decreasing aperture size of the features like vias or trenches to dimensions of below 5 nanometers and even below 3 nanometers, respectively, the filling of the interconnects with copper becomes especially challenging, also since the copper seed deposition prior to the copper electrodeposition might exhibit inhomogeneity and non-conformity and thus further decreases the aperture sizes particularly at the top of the apertures. The smaller the size of the feature and the higher the aspect ratio of the feature become the more difficult it is to get a continuous seed on the side walls of the feature without significant seed overhang.
To avoid these difficulties a non-copper seed such as cobalt or ruthenium was proposed in WO 2019/199614 A1. An acidic electroplating solution for plating copper on a non-copper liner layer includes a low copper concentration, acidic pH, organic additives, and bromide ions as a copper complexing agent. Also unpublished international patent application No. PCT/EP2021/068001 discloses an acidic bromide containing copper electroplating bath.
However, cobalt is a less noble metal compared to copper and quickly corrodes in the presence of an acid and oxygen, particularly if copper is present, too. On the other hand, alkaline electroplating baths that would show less cobalt corrosion provide bad filling and dirty copper fillings due to the use of complexings agents that are required to keep copper in solution.
Also alkaline compositions for copper electroplating copper on a copper or other metal seeds are generally known in the art. For example, WO 2015/086180 discloses a copper electroplating bath comprising copper ions and a promoter of nucleation of metallic copper on said substrate, characterized in that the promoter of nucleation of copper is a combination of 2,2′-bipyridine, imidazole and an electrochemically inert cation selected from the group consisting of cesium (Cs²⁺), alkylammonium and mixtures thereof to improve the nucleation of copper on the most resistive materials that are a barrier to the diffusion of copper such as ruthenium or cobalt.
There is still a need for a copper electroplating composition that allows a void-free deposition of copper in small recessed features, such as vias or trenches, of semiconductor substrates.
It is therefore an object of the present invention to provide an electroplating composition that is capable of providing a substantially void-free filling of features on the nanometer and/or on the micrometer scale with copper on a non-copper metal seed, particularly a cobalt seed. It is also an object of the present invention to provide an electroplating composition that is capable of depositing a homogeneous, smooth and void-free copper seed layer on a non-copper metal seed, particularly a cobalt seed. For resistivity reasons, this seed layer needs to have a low impurity level.
For resistivity reasons, it is also beneficial that the copper layer deposited on the cobalt seed layer exhibits a low resistivity. A low resistivity of the copper deposit is supported by a low impurity level in the deposited copper film which means that little C, N, S, O, H, Cl, P or other elements than copper are incorporated in the copper film during the copper electrodeposition.

SUMMARY OF THE INVENTION

The present invention provides a copper electroplating bath that may generally be used in two ways:

1. With the bath a copper seed layer is deposited onto the semiconductor substrate to allow using a state-of-the art acidic copper on copper electroplating bath to fill the respective recessed features; and
2. With the bath a direct void-free filling, ideally a bottom-up filling, of the recessed features may also be achieved.

Therefore the present invention provides a composition for depositing copper on a semiconductor substrate, the composition comprising

(a) copper ions;
(b) a grain refiner of formula G1

- or salts thereof
(c) a complexing agent; and
(d) optionally a buffer or a base capable of adjusting the pH to a pH of from 7 to 13;

wherein

R^G1is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN;
R^G2is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN; and
X^G1is selected from C₁to C₆alkanediyl or a group —X^G11—C(O)—O—X^G12—;
X^G11is selected from a chemical bond or C₁to C₄alkandiyl;
X^G12is selected from a chemical bond or C₁to C₄alkandiyl; and
- wherein R^G1or R^G2, comprises at least one C₁to C₄carboxyl group, or group X^G1is —X^G11—C(O)—O—)—X^G12—;

wherein the pH of the composition is from 7 to 13.
The invention further relates to the use of a metal plating bath comprising a composition as defined herein for depositing copper on substrates comprising recessed features having an aperture size of 50 nanometers or less, 15 nm or less, 10 nm or less or even 5 nm or less essentially without forming voids, preferably by bottom. up fill.
The invention further relates to a process for depositing copper on a semiconductor substrate comprising a recessed feature having an aperture size of 50 nm or less, preferably 15 nm or less, the recessed feature comprising a metal seed, the process comprising

(a) bringing a composition as described herein into contact with the metal seed,
(b) applying a current for a time sufficient to deposit a continuous seed of copper onto the surface of the recessed feature or to completely fill the recessed feature with copper.

The alkaline copper electroplating composition according to the invention provides a substantially void-free filling of features on the nanometer and/or on the micrometer scale with copper on a non-copper metal seed, particularly a cobalt seed. It also allows depositing a homogenous, smooth and void-free seed layer on a non-copper metal seed, particularly a cobalt seed. A further advantage of the present invention is that the deposited copper, e.g. a completely filled recessed feature or a continuous seed, has a much lower impurity level.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a FIB/SEM inspected wafer that was used for electrodepositing copper in examples 2c and 3e;

FIG. 2 shows a FIB/SEM inspected wafer that was used for electrodepositing copper in comparative example 3c and examples 3b and 3d;

FIG. 3 shows a FIB/SEM inspected wafer that was electroplated with copper according to comparative example 2a;

FIG. 4 shows a FIB/SEM inspected wafer that was electroplated with copper according to example 2b;

FIG. 5 shows a FIB/SEM inspected wafer that was electroplated with copper according to example 2c;

FIG. 6 shows a FIB/SEM inspected wafer that was electroplated with copper according to example 3a;

FIG. 7 shows a FIB/SEM inspected wafer that was electroplated with copper according to example 3b;

FIG. 8 shows a FIB/SEM inspected wafer that was electroplated with copper according to comparative example 3c;

FIG. 9 shows a FIB/SEM inspected wafer that was electroplated with copper according to example 3d;

FIG. 10 shows a FIB/SEM inspected wafer that was electroplated with copper according to example 3e;

DETAILED DESCRIPTION OF THE INVENTION

The alkaline compositions according to the inventions comprise copper ions, a complexing agent, and an additive of formula G1 as described below.
Grain Refiner
It has been found that the grain refiner of formula G1
or salts thereof are particularly useful additives for alkaline electroplating of copper on semiconductor substrates, particularly those comprising submicrometer-sized recessed features, most particularly those having aperture sizes having nanometer or micrometer scale, preferably aperture sizes having 50 nanometers or less, 15 nm or less, 10 nm or less or even 5 nm or less.
Herein

R^G1is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN;
R^G2is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN; and
X^G1is selected from C₁to C₆alkanediyl or a group —X^G11—C(O)—O—X^G12—;
X^G11is selected from a chemical bond or C₁to C₄alkandiyl; and
X^G12is selected from a chemical bond or C₁to C₄alkandiyl.

Either R^G1or R^G2must comprise (a) at least one C₁to C₄carboxyl group, or (b) group X^G1is —X^G11—C(O)—O—)—X^G12—. This means that a carboxyl group is present in the grain refiner according to the invention.
In a first preferred embodiment the grain refiner is a compound of formula G1 or a salt thereof, wherein

R^G1is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN;
R^G2is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, H and CN; and
X^G1is a C₁to C₄alkanediyl;

and wherein R^G1or R^G2comprises at least one C₁to C₄carboxyl group.
Particularly preferred grain refiners of the first embodiment are those of formula G2a or G2b or a salt thereof
wherein

R^G21 is selected from one or more H, C₁to C₃alkyl, C₁to C₄alkoxy, halogen, and CN;
R^G22is selected from one or more H, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN; and
X^G1is methandiyl, ethanediyl, propanediyl or butanediyl.

A particularly preferred grain refiner of formula G2b is 3-carboxy-1-penylmethylpyridinium (inner salt).
In a second preferred embodiment the grain refiner is a compound of formula G1 or a salt thereof, wherein

R^G1is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN;
R^G2is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN; and
X^G1is a group —X^G11—C(O)—O—)—X^G12—;
X^G11, X^G12are independently selected from C₁to C₄alkandiyl.

Particularly preferred grain refiners of the second embodiment are those of formula G3a, G3b, G3c, or a salt thereof
wherein

R^G31is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN;
R^G32is selected from one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, C₁to C₆carboxy, halogen, and CN; and
X^G32is selected from a chemical bond or C₁to C₄alkandiyl.

Particularly preferred grain refiners of formula G3b are 4-(Methoxycarbonyl)benzyl pyridine-3-carboxylate and benzyl pyridine-3-carboxylate.
In general, the total amount of the grain refiners in the electroplating bath is from 0.5 ppm to 10000 ppm based on the total weight of the plating bath. The grain refiners according to the present invention are typically used in a total amount of from about 0.1 ppm to about 1000 ppm based on the total weight of the plating bath and more typically from 1 to 100 ppm, although greater or lesser amounts may be used.
SIMS measurements of copper films plated with a grain refiner in the plating bath exhibit that the amount of C, N, S, O, H, Cl, P or other elements than copper incorporated in the copper film during the copper electrodeposition is smaller than in copper films plated without grain refiner in the plating bath.
Complexing Agent
The copper electroplating composition also comprises a complexing agent to keep the copper ions in solution and to avoid their precipitation.
The complexing agent may particularly be selected from polyamines, aminocarboxylic acids, aminophosphonic acids, aminoalcohols, polyalcohols, hydroxycarboxylic acids, hydroxyphosphonic acids, thioureas, and polycarboxylic acids.
Without limitation, useful polymines are methylenediamine, ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine, tetraethylenepentamine, pentaethylenehexamine, or hexaethyleneheptamine, or combinations thereof.
Without limitation, useful amino carboxylic acids are ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraaminehexaacetic acid (TTHA), ethylenediaminetetrapropionic acid, nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), Iminodipropionic acid (IDP), metaphenylenediaminetetraacetic acid, 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, diaminopropionic acid, combinations thereof, or salts thereof
Without limitation, useful amino alcohols are monoethanolamine, diethanolamine, triethanolamine, monopropanolamine; Dipropanolamine, tripropanolamine, or combinations thereof.
Without limitation, useful hydroxycarboxylic acids are tartaric acid, citric acid, malic acid, gluconic acid, glycolic acid, lactic acid, glucoheptonic acid, combinations thereof, or salts thereof.
Without limitation, useful hydroxyphosphonic acids are 1-Hydroxyethylidene-1,1-diphosphonic acid (etidronic acid), combinations thereof, or salts thereof.
Thioureas are thiourea and thiourea derivatives.
Without limitation, a useful polyalcohol is sorbitol.
Preferred complexing agents are hydroxycarboxylic acids such as but not limited to citric acid, tartaric acid and hydroxyphosphonic acids such as but not limited to etidronic acid.
The complexing agent may be used alone or in any combination, and the content of the complexing agent in the plating bath is usually from 0.01 to 2 mol/l, preferably from 0.1 to 0.6 mol/l.
Buffer/Base
The composition optionally comprises a buffer or a base (also referred to as “pH adjustor”) that is capable of adjusting the pH to a pH of from 7 to 13.
Without limitation, typical bases are metal, preferably alkaline or alkaline earth metal hydroxides, carbonates, NH₄OH, alkyl ammonium hydroxides, and the like.
Preferred bases are NaOH, KOH, and combinations thereof.
The alkylammonium ions may for example be compounds of formula (N—R^B1R^B2R^B3R^B4)⁺ in which R^B1; R^B2; R^B3; and R^B4independently selected from H and a C₁-C₄alkyl, provided that at least one of R^B1; R^B2; R^B3; and R^B4is a C₁-C₄alkyl.
A C₁-C₄alkyl may be for example methyl, ethyl, n-propyl or n-butyl. Preferred alkylammonium ions are tetra-alkylammonium, for example tetramethylammonium, tetraethylammonium, tetrapropyl-ammonium or tetrabutylammonium, methyltriethylammonium and ethyltrimethylammonium.
The cations are supplied in the form of salts, for example a sulfate salt. The counter-ion of the cation in the salt is preferably the same counter-ion than the counter-ion of the copper(II) salt.
Defect Reducing Agent
The copper electroplating composition may optionally comprise a defect reducing agent.
Preferred defect reducing agents are those of formula S1
or salts thereof,
wherein

R^S1is selected from X^S—Y^S;
R^S2is selected from R^S1and R^S3;
X^Sis selected from linear or branched C₁to C₁₀alkanediyl, linear or branched C₂to C₁₀alkenediyl, linear or branched C₂to C₁₀alkynediyl, and —X^S6—(O—C₂H₃R^S6)_m;
Y^Sis selected from OR^S3, NR^S3R^S4, N⁺R^S3R^S4R^S5and NH—(C═O)—R^S3;
R^S3, R^S4, R^S5are the same or different and are selected from (i) H, (ii) C₅to C₂₀aryl, (iii) C₁to C₁₀alkyl (iv) C₆to C₂₀arylalkyl, (v) C₆to C₂₀alkylaryl, which may be substituted by OH, SO₃H, COOH or a combination thereof, and
- (vi) —(C₂H₃R^S6—O)_n—R^S6, and wherein R^S3and R^S4may together form a ring system, which may be interrupted by O or NR^S7;
X^S6is C₁to C₆alkanediyl;
m, n are integers independently selected from 1 to 30;
R^S6is selected from H and C₁to C₅alkyl;
R^S7is selected from R^S6and

SIMS measurements of copper films plated with a defect reducing agent in the plating bath exhibit that the amount of C, N, S, O, H, Cl, P or other elements than copper incorporated in the copper film during the copper electrodeposition is smaller than in copper films plated without defect reducing agent in the plating bath.
In the defect reducing agents of formula S1, R^S1is selected from X^S—Y^S, wherein X^Sis a divalent spacer group selected from linear or branched C₁to C₁₀alkanediyl, linear or branched C₂to C₁₀alkenediyl, linear or branched C₂to C₁₀alkynediyl, and —X^S6—(O—C₂H₃R^S6)_m—. m is an integer selected from 1 to 30, preferably from 1 to 15, even more preferably from 1 to 10, most preferably from 1 to 5. The spacer X^S6is C₁to C₆alkanediyl, preferably methanediyl, ethandiyl, propanediyl or butanediyl, most preferably methanediyl or ethandiyl.
In a first preferred embodiment X^Sis selected from linear or branched C₁to C₆alkanediyl, preferably from C₁to C₄alkanediyl.
In a second preferred embodiment X^Sis selected from methanediyl, ethane-1,1-diyl and ethane-1,2-diyl. In a third preferred embodiment X^Sis selected from propan-1,1-diyl, butane-1,1-diyl, pentane-1,1-diyl, and hexane-1,1-diyl. In a fourth preferred embodiment X^Sis selected from propane-2-2-diyl, butane-2,2-diyl, pentane-2,2-diyl, and hexane-2,2-diyl.
In a fifth preferred embodiment X^Sis selected from propane-1-2-diyl, butane-1,2-diyl, pentane-1,2-diyl, and hexane-1,2-diyl. In a sixth preferred embodiment X^Sis selected from propane-1-3-diyl, butane-1,3-diyl, pentane-1,3-diyl, and hexane-1,3-diyl.
Y^Sis a monovalent group and may be selected from OR^S3, with R^S3being selected from (i) H, (ii) C₅to C₂₀aryl, preferably C₅, C₆, and C₁₀aryl, (iii) C₁to C₁₀alkyl, preferably C₁to C₆alkyl, most preferably C₁to C₄alkyl (iv) C₆to C₂₀arylalkyl, preferably C₆to C₁₀arylalkyl, (v) C₆to C₂₀alkylaryl, all of which may be substituted by OH, SO₃H, COOH or a combination thereof, and (vi) —(C₂H₃R^S6—O)_n—R^S6. In a preferred embodiment, R^S3may be C₁to C₆alkyl or H. R^S6may independently be selected from H and C₁to C₅alkyl, preferably from H and C₁to C₄alkyl, most preferably H, methyl or ethyl.
As used herein, aryl comprises carbocyclic aromatic groups as well as heterocyclic aromatic groups in which one or more carbon atoms are exchanged by one or more N or O atoms. As used herein, arylalkyl means an alkyl group substituted with one or more aryl groups, such as but not limited to benzyl and methylpyridine. As used herein, alkylaryl means an aryl group substituted with one or more alkyl groups, such as but not limited to toluyl.
In another preferred embodiment, R^S3is selected from H to form a hydroxy group. In another preferred embodiment, R^S3is selected from polyoxyalkylene groups of formula —(C₂H₃R^S6—O)_n—R^S6. R^S6is selected from H and C₁to C₅alkyl, preferably from H and C₁to C₄alkyl, most preferably from H, methyl or ethyl. Generally, n may be an integer from 1 to 30, preferably from 1 to 15, most preferably from 1 to 10. In a particular embodiment polyoxymethylene, polyoxypropylene or a poly(oxymethylene-co-oxypropylene) may be used. In another preferred embodiment, R^S3may be selected from C₁to C₁₀alkyl, preferably from C₁to C₆alkyl, most preferably methyl and ethyl.
Furthermore, Y^Smay be an amine group NR^S3R^S4, wherein R^S3and R^S4are the same or different and may have the meanings of R^S3described for OR^S3above.
In a preferred embodiment, R^S3and R^S4are selected from H to form an NH₂group. In another preferred embodiment, at least one of R^S3and R^S4, preferably both are selected from polyoxyalkylene groups of formula —(C₂H₃R^S6—O)_n—R^S6. R^S6is independently selected from H and C, to C₅alkyl, preferably from H and C₁to C₄alkyl, most preferably H, methyl or ethyl. In yet another preferred embodiment, at least one of R^S3and R^S4, preferably both are selected from C₁to C₁₀alkyl, preferably from C₁to C₆alkyl, most preferably methyl and ethyl.
R^S3and R^S4may also together form a ring system, which may be interrupted by O or NR^S7. R^S7may be selected from R^S6and
Preferably the ring system is formed by two substituents R^S3and R^S4which are bound to the same N atom. Such ring system may preferably comprise 4 or 5 carbon atoms to form a 5 or 6 membered carbocyclic system. In such carbocyclic system one or two of the carbon atoms may be substituted by oxygen atoms.
Furthermore, Y^Smay be a positively charged ammonium group N⁺R^S3R^S4R^S5. R^S3, R^S4, R^S5are the same or different and may have the meanings of R^S3described for OR^S3and NR^S3R^S4above. In a preferred embodiment R^S3, R^S4and R^S5are independently selected from H, methyl or ethyl. In one embodiment at least one of R^S3, R^S4and R^S5, preferably two, most preferably all, are selected from polyoxyalkylene groups of formula —(C₂H₃R^S6—O)_n—R^S6.
m may be an integer selected from 1 to 30, preferably from 1 to 15, even more preferably from 1 to 10, most preferably from 1 to 5.
In the defect reducing agents of formula S1 R^S2may be either R^S1or R^S3as described above. If R^S2is R^S1, R^S1may be selected to form a symmetric compound (both R^S1s are the same) or an asymmetric compound (the two R^S1s are different).
In a preferred embodiment R^S2is H.
Particularly preferred aminoalkynes are those in which

(a) R^S1is X^S—NR^S3R^S4and R^S2is H;
(b) R^S1is X^S—NR^S3R^S4and R^S2is X^S— NR^S3R^S4with X^Sbeing selected from linear C₁to C₄alkanediyl and branched C₃to C₆alkanediyl.

Particularly preferred hydroxyalkynes or alkoxyalkynes are those in which

(a) R^S1is X^S—OR^S3and R^S2is H;
(b) R^S1is X^S—OR^S3and R^S2is X^S—OR^S3with X^Sbeing selected from linear C₁to C₄alkanediyl and branched C₃to C₆alkanediyl.

Particularly preferred alkynes comprising an amino and a hydroxy group are those in which R^S1is X^S—OR^S3, particularly X^S—OH, and R^S2is X^S— NR^S3R^S4with X^Sbeing independently selected from linear C₁to C₄alkanediyl and branched C₃to C₆alkanediyl.
The amine groups in the defect reducing agents may be selected from primary (R^S3, R^S4is H), secondary (R^S3or R^S4is H) and tertiary amine groups (R^S3and R^S4are both not H).
The alkynes may comprise one or more terminal triple bonds or one or more non-terminal triple bonds (alkyne functionalities). Preferably, the alkynes comprise one or more terminal triple bonds, particularly from 1 to 3 triple bonds, most preferably one terminal triple bond.
Particularly preferred specific primary aminoalkynes are:
Particularly preferred specific secondary aminoalkynes are:
Particularly preferred specific tertiary aminoalkynes are:
Other preferred defect reducing agents are those in which the rests R^S3and R^S4may together form a ring system, which is optionally interrupted by O or NR^S3. Preferably, the rests R^S3and R^S4together form a C₅or C₆bivalent group in which one or two, preferably one, carbon atoms may be exchanged by O or NR^S7, with R^S7being selected from hydrogen, methyl or ethyl.
An example of such compounds is:
It may be received by reaction of propargyl amine with formaldehyde and morpholine.
Another preferred defect reducing agent comprising a saturated heterocyclic system is:
In this case R^S3and R^S4together form a ring system which is interrupted by two NR^S3groups, in which R^S3is selected from CH₂—C≡C—H. This defect reducing agent comprises three terminal triple bonds.
The amino groups in the defect reducing agents may further be quaternized by reaction with alkylating agents such as but not limited to dialkyl sulphates like DMS, DES or DPS, benzyl chloride or chlormethylpyridine. Particularly preferred quaternized defect reducing agents are:
Particularly preferred specific pure hydroxyalkynes are:
Particularly preferred specific aminoalkynes comprising OH groups are:
Also in this case the rests R^S3and R^S4may together form a ring system, which is optionally interrupted by O or NR^S3. Preferably, the rests R^S3and R^S4together form a C₅or C₆bivalent group in which one or two, preferably one, carbon atoms may be exchanged by O or NR^S7, with R^S7being selected from hydrogen, methyl or ethyl.
Examples for such compounds are:
These may be received by reaction of propargyl alcohol with formaldehyde and piperidine or morpholine, respectively.
By partial reaction with alkylating agents mixtures of defect reducing agents may be formed. In one embodiment, such mixtures may be received by reaction of 1 mole diethylaminopropyne and 0.5 mole epichlorohydrin, 1 mole diethylaminopropyne and 0.5 mole benzylchloride, 1 mole diethylaminopropyne with 0.9 mole dimethyl sulphate, 1 mole dimethyl propyne amine and 0.33 mole dimethyl sulphate, or 1 mole dimethyl propyne amine and 0.66 mole dimethyl sulphate. In another embodiment such mixtures may be received by reaction of 1 mole dimethyl propyne amine and 1.5, 1.9, or 2.85 mole dimethyl sulphate, 1 mole dimethyl propyne amine and 0.5 mole epichlorohydrin, 1 mole dimethyl propyne amine and 2.85 diethyl sulphate, or 1 mole dimethyl propyne amine and 1.9 mole dipropyl sulphate.
In a further embodiment, the defect reducing agents may be substituted by SO₃H (sulfonate) groups or COOH (carboxy) groups. Specific sulfonated defect reducing agents may be but are not limited to butynoxy ethane sulfonic acid, propynoxy ethane sulfonic acid, 1,4-di-(β-sulfoethoxy)-2-butyne, 3-(β-sulfoethoxy)-propyne.
In one embodiment a single defect reducing agent may be used in the copper electroplating baths. In another embodiment two or more of the defect reducing agents are used in combination.
In general, the defect reducing agents are typically used in an amount of about 0.1 ppm to about 30000 ppm, based on the total weight of the plating bath. Particularly suitable amounts of defect reducing agent useful in the present invention are 1 to 10000 ppm, and more particularly 10 to 1000 ppm.
Other Additives
A large variety of further 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. Advantageously, the electroplating baths may contain one or more of wetting agents or surfactants like Lutensol®, Plurafac® or Pluronic® (available from BASF) to get rid of trapped air or hydrogen bubbles and the like. Further components to be added are stress reducers, levelers and mixtures thereof.
In a further embodiment, surfactants may be present in the electroplating composition in order to improve wetting. Wetting agents may be selected from nonionic surfactants, anionic surfactants and cationic surfactants.
In a preferred embodiment non-ionic surfactants are used. Typical non-ionic surfactants are fluorinated surfactants, polyglycols, or poly oxyethylene and/or oxypropylene containing molecules.
Electrolyte
A wide variety of metal plating baths may be used with the present invention. Metal electroplating baths typically comprise or essentially consist of a copper ion source, an electrolyte, a grain refiner, a complexing agent, optionally a defect reducing agent, optionally a base or a buffer, and optionally further additives as described above.
The plating baths are typically aqueous. The term “aqueous” means that the plating bath is water based. The water may be present in a wide range of amounts. Any type of water may be used, such as distilled, deionized or tap. Preferably the plating bath is a solution of the compounds described herein in water. Preferably the water is electronic grade deionized water. Other solvents besides water may be present in minor amounts but preferably water is the only solvent.
The metal ion source may be any compound capable of releasing copper ions to be deposited in the electroplating bath in sufficient amount, i.e. is at least partially soluble in the electroplating bath.
In a preferred embodiment, no further metals besides copper are present in the electroplating bath. In other preferred embodiment the metal comprises copper and comprise tin in amount of below 0.1 g/l, preferably below 0.01 g/l, most preferably no tin. Most preferably there is no other metal than copper present in the composition.
It is preferred that the copper ion source is soluble in the plating bath to release 100% of the metal ions. Suitable copper ion sources are metal salts and include, but are not limited to, metal sulfates, metal halides, metal acetates, metal nitrates, metal fluoroborates, metal alkylsulfonates, metal arylsulfonates, metal sulfamates, metal gluconates and the like. It is preferred that the metal is copper. It is further preferred that the source of copper ions is copper sulfate, copper chloride, copper acetate, copper citrate, copper nitrate, copper fluoroborate, copper methane sulfonate, copper phenyl sulfonate and copper p-toluene sulfonate. Copper sulfate pentahydrate and copper methane sulfonate are particularly preferred. Such metal salts are generally commercially available and may be used without further purification.
The copper ion source may be used in the present invention in any amount that provides sufficient metal ions for electroplating on a substrate.
Copper is typically present in an amount in the range of from about 0.2 to about 300 g/l of the plating solution. Generally, the defect reducing agent is useful in low copper, medium copper and high copper baths. Low copper means a copper concentration from about 0.3 to about 20 g/l.
The pH of the electroplating composition is in the range of from about 7 to about 13, preferably from about 8 to about 13, more preferably from about 8 to about 12, most preferably from about 9 to about 11.
The electroplating composition is free of any cyanide ions.
In a preferred embodiment the composition is essentially free of chloride ions. Essentially free from chloride means that the chloride content is below 1 ppm, particularly below 0.1 ppm.
Process
According to one embodiment of the present invention an alkaline copper electroplating bath comprising a composition as described herein may be used for depositing copper on substrates comprising recessed features having an aperture size of 50 nanometers or less, which features preferably comprise a seed of cobalt, iridium, osmium, palladium, platinum, rhodium, ruthenium, molybdenum, and alloys thereof, most preferably of cobalt.
An electrolytic bath is prepared comprising copper ions, a complexing agent, and at least one grain refiner according to the invention. A dielectric substrate having the seed layer is placed into the electrolytic bath where the electrolytic bath contacts the at least one outer surface and the three dimensional pattern having a seed layer in the case of a dielectric substrate. A counter electrode is placed into the electrolytic bath and an electrical current is passed through the electrolytic bath between the seed layer on the substrate and the counter electrode. At least a portion of copper is deposited into at least a portion of the three dimensional pattern wherein the deposited copper is substantially void-free.
The present invention is useful for depositing a layer comprising copper on a variety of substrates, particularly those having nanometer and variously sized apertures. For example, the present invention is particularly suitable for depositing copper on integrated circuit substrates, such as semiconductor devices, with small diameter vias, trenches or other recessed features. In one embodiment, semiconductor devices are plated according to the present invention. Such semiconductor devices include, but are not limited to, wafers used in the manufacture of integrated circuits.
In order to allow a deposition of copper on a substrate comprising a dielectric surface a seed layer needs to be applied to the surface. Such seed layer may consist of cobalt, iridium, osmium, palladium, platinum, rhodium, and ruthenium or alloys comprising such metals. Preferred is the deposition of copper on a cobalt seed. The seed layers are described in detail e.g. in US20140183738 A.
The underlying seed layer may be deposited or grown by chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), electroplating, electro less plating or other suitable process that deposits conformal thin films. In an embodiment, the cobalt seed layer is deposited to form a high quality conformal layer that sufficiently and evenly covers all exposed surfaces within the openings and top surfaces. The high quality seed layer may be formed, in one embodiment, by depositing the cobalt seed material at a slow deposition rate to evenly and consistently deposit the conformal seed layer. By forming the seed layer in a conformal manner, compatibility of a subsequently formed fill material with the underlying structure may be improved. Specifically, the seed layer can assist a deposition process by providing appropriate surface energetics for deposition thereon.
In one embodiment the substrate comprises submicrometer sized features and the copper deposition is performed to fill the submicrometer sized features. Most preferably the submicrometer-sized features have an (effective) aperture size of 10 nm or below and/or an aspect ratio of 4 or more. More preferably the features have an aperture size of 7 nanometers or below, most preferably of 5 nanometers or below. Preferably the features bear a cobalt seed layer on which copper is electrodeposited.
In another embodiment a seed of copper is deposited onto the seeded surface of the substrate. Preferably this substrate comprises recessed features having an aperture size of 50 nm or below and/or an aspect ratio of 4 or more. Preferably the substrate bears a cobalt seed layer on which the copper seed layer is electrodeposited.
As used herein, “seed of copper” means a continuous thin layer of copper having a thickness of about 5 nm to about 15 nm.
The aperture size according to the present invention means the smallest diameter or free distance of a feature before plating, i.e. after seed deposition. The terms “aperture” and “opening” are used herein synonymously.
The electrodeposition current density should be chosen to promote the void-free filling behavior. A range of 0.1 to 40 mA/cm²is useful for this purpose. In a particular example, the current density can range from 1 to 10 mA/cm². In another particular example, the current density can range from 0.5 to 5 mA/cm².
Typically, substrates are electroplated by contacting the substrate with the plating baths of the present invention. The substrate typically functions as the cathode. The plating bath contains an anode, which may be soluble or insoluble. Optionally, cathode and anode may be separated by a membrane. Potential is typically applied to the cathode. Sufficient current density is applied and plating performed for a period of time sufficient to deposit a metal layer, such as a copper layer, having a desired thickness on the substrate. Suitable current densities include, but are not limited to, the range of 1 to 250 mA/cm². Typically, the current density is in the range of 1 to 60 mA/cm²when used to deposit copper in the manufacture of integrated circuits. The specific current density depends on the substrate to be plated, the agents and additives selected and the like. Such current density choice is within the abilities of those skilled in the art. The applied current may be a direct current (DC), a pulse current (PC), a pulse reverse current (PRC) or other suitable current. Typical temperatures used for the copper electroplating are from 10° C. to 50° C., preferably 20° C. to 40° C., most preferably from 20° C. to 35° C.
In general, when the present invention is used to deposit metal on a substrate such as a wafer used in the manufacture of an integrated circuit, the plating baths are agitated during use. Any suitable agitation method may be used with the present invention and such methods are well-known in the art. Suitable agitation methods include, but are not limited to, inert gas or air sparging, work piece agitation, impingement and the like. Such methods are known to those skilled in the art. When the present invention is used to plate an integrated circuit substrate, such as a wafer, the wafer may be rotated such as from 1 to 300 RPM and the plating solution contacts the rotating wafer, such as by pumping or spraying. In the alternative, the wafer need not be rotated where the flow of the plating bath is sufficient to provide the desired metal deposit.
In one embodiment copper is deposited in recessed features according to the present invention without substantially forming voids within the metal deposit.
As used herein, void-free fill may either be ensured by an extraordinarily pronounced bottom-up copper growth while perfectly suppressing the sidewall copper growth, both leading to a flat growth front and thus providing substantially defect free trench/via fill (so-called bottom-up-fill) or may be ensured by a so-called V-shaped filling.
As used herein, the term “substantially void-free”, means that at least 95% of the plated apertures are void-free. Preferably that at least 98% of the plated apertures are void-free, mostly preferably all plated apertures are void-free. As used herein, the term “substantially seam-free”, means that at least 95% of the plated apertures are seam-free. Preferably that at least 98% of the plated apertures are seam-free, mostly preferably all plated apertures are seam-free.
Plating equipment for plating semiconductor substrates are well known. Plating equipment comprises an electroplating tank which holds Cu electrolyte 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. The wafer substrate is typically coated with a seed layer of Cu or other metal or a metal containing layer to initiate plating thereon. 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.
These 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.
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 Cu ions in the solution are reduced at the cathode substrate forming plated Cu metal on the cathode surface. An oxidation reaction takes place at the anode. The cathode and anode may be horizontally or vertically disposed in the tank.
While the process of the present invention has been generally described with reference to semiconductor manufacture, it will be appreciated that the present invention may be useful in any electrolytic process where a substantially void-free copper deposit is desired. Such processes include printed wiring board manufacture. For example, the present plating baths may be useful for the plating of vias, pads or traces on a printed wiring board, as well as for bump plating on wafers. Other suitable processes include packaging and interconnect manufacture. Accordingly, suitable substrates include lead frames, interconnects, printed wiring boards, and the like.
All percent, ppm or comparable values refer to the weight with respect to the total weight of the respective composition except where otherwise indicated. All cited documents are incorporated herein by reference.
The following examples shall further illustrate the present invention without restricting the scope of this invention.

EXAMPLES

3-Carboxy-1-phenylmethylpyridinium (inner salt with Na⁺ and Cl⁻) used in the examples is available from BASF SE.

Example 1a: Synthesis of Defect Reducing Agent 1

Propargyl alcohol (280.3 g) and triphenylphosphine (2.0 g) were placed into a 3.5 l autoclave. After nitrogen neutralization, the pressure was adjusted to 1.5 bar and the mixture was homogenized at 60° C. for 1 h. Then ethylene oxide (220.3 g) was added at 60° C. over a period of 4 h, reaching a maximum pressure of 3.5 bar. The reaction mixture was then heated up over 30 min to 80° C., reaching a maximum pressure of 4 bar. To complete the reaction, the mixture post-react for 6 h at 80° C. Then, the temperature was decreased to 40° C. Volatile compounds were re-moved in vacuum at 60° C. Defect Reducing agent 1 was obtained as yellowish liquid (494.4 g), having a hydroxy value of 569 mg/g.

Example 1b: Synthesis of Defect Reducing Agent 2

3-Hexin-2,5-diol (456.6 g) and Imidazol (2.5 g) were placed into a 3.5 l autoclave. After nitrogen neutralization, the pressure was adjusted to 1.0 bar and the mixture was homogenized at 70° C. for 1 h. Then ethylene oxide (176.2 g) was added at 70° C. over a period of 1 h, reaching a maximum pressure of 3.5 bar. To complete the reaction, the mixture post-react for 6 h at 70° C. Then, the temperature was decreased to 60° C. Volatile compounds were removed in vacuum at 60° C. Defect Reducing agent 2 was obtained as orange liquid (630.8 g), having a hydroxy value of 709 mg/g.

Example 1c: Synthesis of Defect Reducing Agent 3

2-Methyl-3-butin-2-ol (420.6 g) and Imidazol (3.4 g) were placed into a 3.5 l autoclave. After nitrogen neutralization, the pressure was adjusted to 1.5 bar and the mixture was homogenized at 70° C. for 1 h. Then ethylene oxide (440.5 g) was added at 70° C. over a period of 8 h, reaching a maximum pressure of 3.5 bar. To complete the reaction, the mixture post-react for 6 h at 70° C. Then, the temperature was decreased to 60° C. Volatile compounds were removed in vacuum at 60° C. Intermediate 1 (=2-Methyl-3-butin-2-ol+2 EO) was obtained as orange liquid (835.3 g), having a hydroxy value of 325 mg/g.
Intermediate 1 (300 g) and Imidazol (0.7 g) were placed into a 3.5 l autoclave. After nitrogen neutralization, the pressure was adjusted to 2.2 bar and the mixture was homogenized at 70° C. for 1 h. Then propylene oxide (202.4 g) was added at 70° C. over a period of 7 h, reaching a maximum pressure of 3.2 bar. To complete the reaction, the mixture post-react for 6 h at 70° C. Then, the temperature was decreased to 60° C. Volatile compounds were removed in vacuum at 60° C. Defect Reducing agent 3 was obtained as dark orange liquid (488.5 g).
Copper Electroplating Experiments
3-Carboxy-1-phenylmethylpyridinium was used as grain refiner either alone or in combination with a defect reducing agent in alkaline Cu electroplating baths. The grain refiner helps to reduce the roughness of the electrodeposited copper layer and thus also prevents the formation of defects in the electrodeposited Cu film.
For some plating experiments a blanket wafer substrate was used bearing a 100 A CVD Co seed on a 30 A TaN layer.
For some plating experiments a patterned wafer substrate was used as shown in FIG. 1 . The wafer substrate was bearing a 100 A Co seed on a 30 A TaN layer and having features with a diameter of 24 nm at the top of the opening, a diameter of 20 nm at half height of the feature. The feature height was about 105 nm which results in an aspect ratio of about 5.25.
For some plating experiments a patterned wafer substrate was used as shown in FIG. 2 . The wafer substrate was bearing a 50 A Co seed on a 30 A TaN layer and having features with a diameter of 18 nm at half height of the feature. The feature height was about 110 nm which results in an aspect ratio of about 6.

Example 2: Cu Electrodeposition with Grain Refiner

Comparative Example 2a

A plating bath was prepared by combining DI water, 0.5 g/l copper as copper sulfate, citric acid in a molar ratio of 2:1 to Cu, and a solution of sodium hydroxide or potassium hydroxide to adjust a pH of 9. A copper layer was electroplated onto a blanket wafer substrate bearing a cobalt seed layer by contacting the wafer substrate with the above described plating bath at 25° C. applying a direct current of −1.0 mA/cm2 for 2000 s. The thus electroplated copper layer was annealed at 400° C. for 5 minutes in forming gas and was investigated by FIB/SEM inspection.
The result is shown in FIG. 3 which provides the SEM image of the electroplated copper film. FIG. 3 shows that the electroplated copper exhibits defects like holes and voids and is uneven.

Example 2b

The experiment as described in Example 2a was repeated with addition of 1 ml/l of a solution in DI water of 0.9 wt % 3-carboxy-1-phenylmethylpyridinium as grain refiner to the plating bath. The result is shown in FIG. 4 which provides the SEM image of the electroplated copper film. FIG. 4 shows significantly less defects in the electroplated copper film and exhibits a smooth Cu surface.

Example 2c

A plating bath was prepared by combining DI water, 0.5 g/l copper as copper sulfate, citric acid in a molar ratio of 2:1 to Cu, and a solution of sodium hydroxide or potassium hydroxide to adjust a pH of 9. 1 ml/l of a solution in DI water of 0.9 wt % 3-Carboxy-1-phenylmethylpyridinium was added to the plating bath. A copper layer was electroplated onto a patterned wafer substrate as shown in FIG. 1 by contacting the wafer substrate with the above described plating bath at 25° C. applying a direct current of −1.0 mA/cm2 for 250 s. The thus electroplated copper layer was investigated by FIB/SEM inspection.
The result is shown in FIG. 5 which provides the SEM image of the electroplated copper film. FIG. 5 shows features that are fully filled with Cu and are mainly free of defects.

Example 3: Cu Electrodeposition with Grain Refiner and Defect Reducing Agent

Example 3a

A plating bath was prepared by combining DI water, 0.5 g/l copper as copper sulfate, citric acid in a molar ratio of 2:1 to Cu, and a solution of sodium hydroxide or potassium hydroxide to adjust a pH of 9. 10 ml/l of a solution in DI water of 0.9 wt % of defect reducing agent 1 and 0.5 ml/l of a solution in DI water of 0.9 wt % 3-carboxy-1-phenylmethylpyridinium were added to the electrolyte. A copper layer was electroplated onto a blanket wafer substrate bearing a cobalt seed layer by contacting the wafer substrate with the above described plating bath at 25° C. applying a direct current of −2.0 mA/cm²for 1000 s. The thus electroplated copper layer was annealed at 400° C. for 5 minutes in forming gas and was investigated by FIB/SEM inspection.
The result is shown in FIG. 6 which provides the SEM image of the electroplated copper film. FIG. 6 shows that the electroplated copper film is mainly free of defects and exhibits a smooth Cu surface.

Example 3b

A plating bath was prepared by combining DI water, 0.5 g/l copper as copper sulfate, citric acid in a molar ratio of 2:1 to Cu, and a solution of sodium hydroxide or potassium hydroxide to adjust a pH of 9. 10 ml/l of a solution in DI water of 0.9 wt % of defect reducing agent 1 and 1.0 ml/l of a solution in DI water of 0.9 wt % 3-carboxy-1-phenylmethylpyridinium were added to the electrolyte. A copper layer was electroplated onto a patterned wafer substrate as shown in FIG. 2 by contacting the wafer substrate with the above described plating bath at 25° C. applying a direct current of −1.0 mA/cm²for 250 s. The thus electroplated copper layer was investigated by FIB/SEM inspection.
The result is shown in FIG. 7 which provides the SEM image of the features filled with Cu. FIG. 7 shows that the electroplated copper film is mainly free of defects.

Comparative Example 3c

A plating bath was prepared by combining DI water, 0.5 g/l copper as copper sulfate, citric acid in a molar ratio of 2:1 to Cu, and a solution of sodium hydroxide or potassium hydroxide to adjust a pH of 9. A copper layer was electroplated onto a patterned wafer substrate as shown in FIG. 2 by contacting the wafer substrate with the above described plating bath at 22° C. applying a direct current of −1.0 mA/cm²for 50 s. The thus electroplated copper layer was investigated by FIB/SEM inspection.
The result is shown in FIG. 8 which provides the SEM image of the electroplated copper film. FIG. 8 shows a nonconformal and rough metal film inside the features.

Example 3d

Example 3d: The experiment as described in Example 3c was repeated with addition of 10 ml/l of a solution in DI water of 0.9 wt % of defect reducing agent 2 and 1.0 ml/l of a solution in DI water of 0.9 wt % 3-carboxy-1-phenylmethylpyridinium to the plating bath. A copper layer was electroplated onto a patterned wafer substrate as shown in FIG. 2 by contacting the wafer substrate with the above described plating bath at 22° C. applying a direct current of −1.0 mA/cm²for 100 s. The thus electroplated copper layer was investigated by FIB/SEM inspection.
The result is shown in FIG. 9 which provides the SEM image of the electroplated copper film. FIG. 9 shows a continuous and smooth metal film inside the features.

Example 3e

A plating bath was prepared by combining DI water, 0.5 g/l copper as copper sulfate, citric acid in a molar ratio of 2:1 to Cu, and a solution of sodium hydroxide or potassium hydroxide to adjust a pH of 9. 10 ml/l of a solution in DI water of 0.9 wt % of defect reducing agent 3 and 1.0 ml/l of a solution in DI water of 0.9 wt % 3-carboxy-1-phenylmethylpyridinium were added to the plating bath. A copper layer was electroplated onto a patterned wafer substrate as shown in FIG. 1 by contacting the wafer substrate with the above described plating bath at 25° C. applying a direct current of −1.0 mA/cm²for 250 s. The thus electroplated copper layer was investigated by FIB/SEM inspection.
The result is shown in FIG. 10 which provides the SEM image of the features filled with Cu. FIG. 10 shows that the features are mainly free of defects.

Claims

1. A composition for depositing copper on a semiconductor substrate, the composition comprising:

(a) copper ions;

(b) a grain refiner of formula G2a, G2b, or salts thereof:

wherein

R^G21is selected from the group consisting of one or more H, C₁to C₃alkyl, C₁to C₄alkoxy, halogen, and CN;

R^G22is selected from the group consisting of one or more H, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN; and

X^G1is methandiyl, ethanediyl, propanediyl or butanediyl;

(c) a complexing agent; and

(d) optionally a buffer or a base capable of adjusting the pH to a pH of from 7 to 13;

wherein the pH of the composition is from 7 to 13;

wherein the composition further comprises a defect reducing agent of formula S1:

or salts thereof,

wherein

R^S1is X^S—Y^S;

R^S2is selected from the group consisting of R^S1and R^S3;

X^Sis selected from the group consisting of linear or branched C₁to C₁₀alkanediyl, linear or branched C₂to C₁₀alkenediyl, linear or branched C₂to C₁₀alkynediyl, and —X^S6—(O—C₂H₃R^S6)_m—;

Y^Sis selected from the group consisting of OR^S3, NR^S3R^S4, N⁺R^S3R^S4R^S5and NH—(C═O)—R^S3;

R^S3, R^S4, R^S5are the same or different and are selected from the group consisting of (i) H, (ii) C₅to C₂₀aryl, (iii) C₁to C₁₀alkyl (iv) C₆to C₂₀arylalkyl, (v) C₆to C₂₀alkylaryl, which may be substituted by OH, SO₃H, COOH or a combination thereof, and

(vi) —(C₂H₃R^S6—O)_n—R^S6, and wherein R^S3and R^S4may together form a ring system, which may be interrupted by O or NR^S7;

X^S6is C₁to C₆alkanediyl;

m, n are integers independently selected from the group consisting of 1 to 30;

R^S6is selected from the group consisting of H and C₁to C₅alkyl;

R^S7is selected from the group consisting of R^S6and

2. (canceled)

3. (canceled)

4. The composition according to claim 1, wherein the grain refiner is 3-carboxy-1-phenylmethylpyridinium.

5. The composition according to claim 1, wherein

R^G1is selected from the group consisting of one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN;

R^G2is selected from the group consisting of one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN; and

X^G1is a group —X^G11—C(O)—O—)—X^G12;

X^G11, X^G12are independently selected from the group consisting of C₁to C₄alkandiyl.

6. The composition according to claim 1, wherein the grain refiners are compounds of formula G3a, G3b, G3c, or salts thereof

wherein

R^G31is selected from the group consisting of one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, halogen, and CN;

R^G32is selected from the group consisting of one or more H, C₁to C₄carboxyl, C₁to C₄alkyl, C₁to C₆alkoxy, C₁to C₆carboxy, halogen, and CN; and

X^G32is selected from the group consisting of a chemical bond or C₁to C₄alkandiyl.

7. The composition according to claim 6, wherein the grain refiners are 4-(Methoxycarbonyl)benzyl pyridine-3-carboxylate and benzyl pyridine-3-carboxylate.

8. (canceled)

9. The composition according to claim 1, wherein the composition is free of any cyanide ions.

10. The composition according to claim 1, which has a pH of 8 to 12.

11. A method of using a composition according to claim 1, the method comprising using the composition for depositing copper on a semiconductor substrate comprising recessed features having an aperture size 50 nanometers or less.

12. The method of use according to claim 11, wherein the recessed features have an aspect ratio of 4 or more.

13. The method of use according to claim 11, wherein the semiconductor substrate is a dielectric substrate onto which a conducting seed layer is placed, wherein the seed layer consists of cobalt, iridium, osmium, palladium, platinum, rhodium, ruthenium, and alloys thereof.

14. A process for depositing copper on a semiconductor substrate comprising a recessed feature having an aperture size of 50 nm or less, the recessed feature comprising a metal seed, the process comprising

(a) bringing a composition according to claim 1 into contact with the metal seed, and

(b) applying a current for a time sufficient to deposit a continuous seed of copper onto the metal seed of the recessed feature or to completely fill the recessed feature.

15. The process according to claim 14, wherein the seed layer consists of cobalt, iridium, osmium, palladium, platinum, rhodium, ruthenium, molybdenum, and alloys thereof.

16. The method of use according to claim 11, wherein the recessed features have an aperture size of 15 nm or less.

17. The process according to claim 14, wherein the recessed feature has an aperture size of 15 nm or less.

18. The process according to claim 14, wherein the seed layer consists of cobalt.