WO2024022979A1

WO2024022979A1 - Composition for tin or tin alloy electroplating comprising leveling agent

Info

Publication number: WO2024022979A1
Application number: PCT/EP2023/070322
Authority: WO
Inventors: Sabine FRISCHHUT; Jan Niclas GORGES; Soichi Watanabe; Marco Arnold
Original assignee: Basf Se
Priority date: 2022-07-26
Filing date: 2023-07-21
Publication date: 2024-02-01
Also published as: TW202409352A

Abstract

The present invention provides an aqueous composition comprising tin ions, optionally alloy metal ions selected from silver, copper, indium, and bismuth ions and at least one additive of formula L1 (L1) wherein RL1 is, for each group RL1 independently, selected from C1 to C6 alkyl, C1 to C6 alkenyl, C1 to C6 alkoxy, halogen, CN, and OH; RL2 is a C1 to C6 alkyl, C1 to C6 alkenyl, C5 to C12 aryl, C6 to C15 alkylaryl, C6 to C15 arylalkyl, all of which may be substituted by CN, OH, C1 to C6 alkoxy or halogen; RL3 is selected from C1 to C6 alkyl; RL4 is H; n is the number of substituents RL1 selected from 0 to 5 wherein the amount of organic solvents in the composition is below 0.1 g/l, and wherein the composition does not contain any electrolytically depositable metal ions besodes tin ions and the alloying metal ions.

Description

Composition for tin or tin alloy electroplating comprising leveling agent

Background of the Invention

The invention relates to tin or tin alloy electroplating compositions comprising a leveling agent, their use and processes for tin or tin alloy electroplating.

Metals and metal-alloys are commercially important, particularly in the electronics industry where they are often used as electrical contacts, final finishes and solders.

Leadfree solders, such as tin, tin-silver, tin-copper, tin-bismuth, tin-silver-copper, and others, are common metals used in solders. These solders are often deposited on semiconductor substrates by means of metal electroplating plating baths.

A typical tin plating solution comprises dissolved tin ions, water, an acid electrolyte such as methanesulfonic acid in an amount sufficient to impart conductivity to the bath, an antioxidant, and additives to improve the uniformity of the plating and the quality of the metal deposit in terms of surface roughness and void formation. Such additives usually include surfactants and grain refiners, among others.

Certain applications for lead-free solder plating present challenges in the electronics industry. For example, when used as a capping layer on copper pillars, a relatively small amount of lead- free solder, such as tin-silver solder, is deposited on top of a copper pillar. In plating such small amounts of solder, it is often difficult to plate a uniform height of solder composition on top of each pillar, both within a die and across the wafer. The use of known solder electroplating baths also often results in deposits having a relatively rough surface morphology.

US 3 361 652 discloses an acidic tin electroplating composition comprising primary brightener of the formula X-CH=CH-Y, in which X is phenyl, furfuryl, or pyridyl and Y may be hydrogen, formyl, carboxyl, alkyl, hydroxyalkyl, formylalkyl, or the acyl radical of a carboxylic acid. One of the mentioned brighteners is 4-hydroxy-3-methoxy-benzylideneacetone.

In a preferred embodiment, US 4 582 576 discloses an acidic tin electroplating composition comprising a carbonyl compound of the following formula

wherein Xi and X2 may be hydrogen, hydroxyl, alkoxy, chlorine or bromine, and the alkyl group of the alkoxy group may contain from about 1 to about 5 carbon atoms. Examples of such compounds include benzylidene acetone and 3'-chlorobenzylidine acetone.

US 2014/183 050 A1 discloses a tin or tin alloy electroplating liquid which is suitable for via filling which deposits tin or a tin alloy selectively in a via, and a method for via filling using the liquid, which can form a column-like deposit which practically does not have voids. The plating liquid comprises a specific a, p-unsaturated carbonyl compound is added into the tin or tin alloy plating liquid. Such carbonyl compound may specifically be substituted by alkyl groups with 1-9 carbon atoms, alkenyl groups, alkoxy groups, amino groups, halogen atoms, hydroxyl groups, carbonyl groups, and cyano groups. 3-chloro acetophenone, crotonyl chloride, butenoyl chloride, and 4-chloro-2-butenal are mentioned.

JP H10 102279 A discloses an electroplated tin-zinc gradient alloy film, the zinc content on the lower layer side of the plating film is 0.1 % or more and 15% or less, and the zinc content on the surface layer side of the plating film is higher than that of the lower film. Standard tin-zinc electroplaing baths may be used.

JP 2000 080493 A discloses a composition for tin or tin alloy electroplating comprising (A) at least one or more kinds of tin salt or tin complex, or at least one or more kinds of tin salt or tin complex and at least one or more kinds of metal salt or complex of a metal other than tin, (B) at least one or more kinds of acid, base and/or complexing agent, (C) at least one or more kinds of surfactant, (D) at least one or more kinds of 1C-6C saturated lower aliphatic water-soluble alcohol, ketone or ether, and (E) at least one or more kinds of mono (or poly) hydroxy benzene or mono (or poly) hydroxy naphthalene obtained by further introducing a carboxyl group or a sulfonic acid group.

However, the prior art does neither solve nor even address the problem to get a uniform height of the deposited solder, both within a die and across the wafer. Therefore, there is still a need in the electronic industry for a pure tin or tin-alloy electroplating bath which leads to solder deposit with an improved uniformity in height, also called coplanarity (COP). WO 2022/129238 discloses aqueous compositions comprising tin ions, optionally alloy metal ions selected from silver, indium, and bismuth ions and a fluorine substituted a,p-unsaturated aliphatic carbonyl compound. However, it would be desirable not to use fluorinated or perfluorinated compounds in the plating bath.

It is an object of the present invention to provide a tin or tin alloy electroplating additive having good leveling properties, in particular leveling agents capable of providing a substantially planar tin or tin alloy layer and filling features on the micrometer scale without substantially forming defects, such as but not limited to voids, with a tin or tin alloy electroplating bath. It is further an object of the invention to provide a tin or tin alloy electroplating bath that provides a uniform and planar tin or tin alloy deposit, in particular in features of 1 micrometer to 200 micrometer width. It is a further object of the invention to provide levelers that have a reduced environmental impact.

Summary of the Invention

The present invention provides an aqueous composition comprising tin ions, optionally alloy metal ions selected from silver, copper, indium, and bismuth ions and at least one additive of formula L1

wherein

R^L1 is, for each group R^L1 independently, selected from Ci to Ce alkyl, Ci to Ce alkenyl, Ci to Ce alkoxy, halogen, CN, and OH;

R^L2 is a Ci to Ce alkyl, Ci to Ce alkenyl, Cs to C12 aryl, Ce to C15 alkylaryl, Ce to C15 arylalkyl, all of which may be substituted by CN, OH, Ci to Ce alkoxy or halogen;

R^L3 is selected from Ci to Ce alkyl;

R^L4 is H; n is the number of substituents R^L1 selected from 0 to 5, wherein the amount of organic solvents in the composition is below 0.1 g/l, and wherein the composition does not contain any electrolytically depositable metal ions besodes tin ions and the alloying metal ions. A further embodiment of the present invention is the use of the additives as described herein in a bath for electrodepositing tin or tin alloy containing layers, wherein the tin alloy containing layers comprise an alloy metal selected from silver, copper, indium, and bismuth in an amount of 0.01 to 10 % by weight.

Yet another embodiment of the present invention is a process for depositing a tin or tin alloy layer on a substrate by a) contacting a tin alloy electroplating bath comprising a composition as described herein with the substrate, and b) applying a current density to the substrate for a time sufficient to deposit a tin alloy layer onto the substrate.

The additives according to the present invention can advantageously be used in bonding technologies such as the manufacture of tin or tin alloy bumps of typically 1 to 200, preferably 3 to 100, most preferably 5 to 50 micrometers height and width for the bumping process, in circuit board technologies or in packaging processes for electronic circuits. In one particular embodiment, the substrate comprises micrometer sized features and the deposition is performed to fill the micrometer sized features, wherein the micrometer-sized features have a size from 1 to 200 micrometers, preferably 3 to 100 micrometers.

The additives according to the invention lead to tin or tin alloy, particularly tin-silver deposits that show a better coplanarity (COP) compared to unsubstituted a,p-unsaturated carbonyl compounds or a,p-unsaturated carbonyl compounds that have a substitution other than the a- substituents described herein. The additives according to the invention also lead to tin or tin alloy deposits that show a good or even better roughness.

Detailed Description of the Invention

Levelers according to the invention

In the following, the terms “additive”, “leveler”, and “a-substituted carbonyl compound” are used herein synonymously.

In a first embodiment, besides tin ions and optional alloy metal ions selected from silver, indium, copper, and bismuth ions, the electroplating composition comprises at least one a-substituted carbonyl compound of formula L1

R^L1 may be, for each group R^L1 independently, selected from Ci to Ce alkyl, Ci to Ce alkenyl, Ci to Ce alkoxy, halogen, CN, and OH. Preferably R^L1 may be, for each group R^L1 independently, selected from Ci to C4 alkyl or Ci to C4 alkoxy. Most preferred group(s) R^L1 are methyl, ethyl, 1- propyl, 2-propyl, methoxy, ethoxy, 1 -propoxy or 2-propoxy. n is the number of substituents R^L1 selected from 0 to 5, preferably 0, 1 or 2, most preferably 1 or 2.

R^L2 may be a Ci to Ce alkyl, Ci to Ce alkenyl, C5 to C12 aryl, Ce to C15 alkylaryl, Ce to C15 arylalkyl, all of which may be substituted by CN, OH, Ci to Ce alkoxy or halogen. Preferably R^L2 is a Ci to C4 alkyl, all of which may be substituted by CN, OH, or Ci to C3 alkoxy. Most preferably R^L2 is methyl, ethyl or propyl, particularly methyl.

R^L3 may be Ci to Ce alkyl, preferably Ci to C4 alkyl, most preferably methyl, ethyl, 1 -propyl and 2-propyl. The inventors surprisingly found that the alkyl substitution in the a position to the carbonyl functional group leads to a significantly higher coplanarity compared to levelers that are not substituted in this position.

R^L4 is H. The inventors surprisingly found that any alkyl substituent negatively influences the performance of the leveling agent.

As used herein, “alkyl” and “alkanediyl” mean a linear, branched or cyclic alkyl or alkanediyl group, respectively. As used herein, “aromatic” or “aryl” means a mono or bicyclic, carbocyclic aromatic group that may be unsubstituted or substituted by substituents R^L1 selected from one or more Cl, Ci to Ce alkyl groups, particularly one or more Ci to C4 alkyl groups, more particularly one or more methyl, ethyl or propyl groups, most particularly one or two methyl or ethyl groups. As used herein, “alkenyl” and “alkenediyl” mean a linear, branched or cyclic alkenyl or alkenediyl group, respectively. As used herein, “arylalkyl” means an alkyl group that is substituted by one or more aryl groups, particularly one or more phenyl groups, most particularly one phenyl group. As used herein, “alkylaryl” means an aryl group that is substituted by one or more Ci to Ce alkyl groups, particularly one or more Ci to C4 alkyl groups, more particularly one or more methyl, ethyl or propyl groups, most particularly one or two methyl or ethyl groups. In formula 1 , two configuations of the double bond E and Z are possible. The E configuration (or trans-configuration of the phenyl and the carbonyl substituent) is preferred.

Particularly preferred levelers may be a compound of formula L2

wherein R^L2 d R^L3 may have the meanings described above. Preferably R^L2 is selected from methyl, ethyl, and propyl, most preferably from methyl. Preferably R^L3 is selected from methyl, ethyl, and propyl, most preferably from methyl.

Most preferred levelers of formula L2 are (E)-3-methyl-4-phenyl-but-3-en-2-one, (E)-3-ethyl-4- phenyl-but-3-en-2-one, (E)-4-methyl-5-phenyl-pent-4-en-3-one, and (E)-4-ethyl-5-phenyl-pent-4- en-3-one.

Further particularly preferred levelers may be a compound of formula L3

wherein R^L1, R^L2, and R^L3 may have the meanings described above. Preferably R^L1 is selected from methyl, ethyl, and propyl, methoxy, most preferably from methyl and methoxy. Preferably R^L2 is selected from methyl, ethyl, and propyl, most preferably methyl. Preferably R^L3 is selected from methyl, ethyl, and propyl, most preferably from methyl.

Most preferred levelers of formula L3 are selected from (E)-3-methyl-4-(4-methylphenyl)-but-3- en-2-one, (E)-3-ethyl-4-(4-methylphenyl)-but-3-en-2-one, (E)-4-methyl-5-(4-methylphenyl)-pent- 4-en-3-one, (E)-4-ethyl-5-(4-methylphenyl)-pent-4-en-3-one, (E)-3-methyl-4-(4-methoxyphenyl)- but-3-en-2-one, (E)-3-ethyl-4-(4-methoxyphenyl)-but-3-en-2-one, (E)-4-methyl-5-(4-methoxy- phenyl)-pent-4-en-3-one, and (E)-4-ethyl-5-(4-methoxyphenyl)-pent-4-en-3-one, all of which may be unsubstituted or further phenylsubstituted by one or two methyl or methoxy.

The additives according to the present invention may be prepared by any preparation method.

Preferred preparation processes are described in the following. 3-Methyl-4-aryl-but-3-en-2-ones may be synthesized according to a literature procedure (Org.

Lett. 2021, 23, 242-246) using the corresponding aldehyde, 2-butanone, sulfuric acid and acetic acid (procedure 1).

4-Methyl-5-aryl-pent-4-en-3-ones may be synthesized according to the literature procedure (Org. Lett. 2021, 23, 242-246) using the corresponding aldehyde, 3-pentanone, sodium hydroxide solution and ethanol (procedure 2).

(E)-4-phenylpent-3-en-2-one may be synthesized according to a literature procedure (J. Am. Chem. Soc. 2006, 128, 13368-13369) using acetoacetone, phenylmagnesium bromide and THF, followed by ammonium chloride and oxalic acid (procedure 3).

4-Aryl-but-3-en-2-ones may be synthesized according to a literature procedure (J. Am. Chem. Soc. 2013, 135, 1891-1894) using the corresponding aldehyde, diethyl(2- oxopropyl)phosphonate, cesium carbonate, dioxane and water (procedure 4).

In the process of preparing the a-substituted carbonyl compounds, it is possible to use further compounds, e.g. in order to introduce specific substituents into the leveler, to set defined properties or to make further reactions on the resulting leveler at a later point in time possible.

Due to limited solubility of most of the a-substituted carbonyl compounds in the aqueous plating bath, it may be advantageous to dissolve them in a water-miscible solvent, such as but not limited to isopropanol, ethanol, glycols, etc., before mixing them with the rest of the plating composition.

The composition as described herein may comprise further additives, particularly one or more surfactants and one or more grain refiners different from the a-substituted carbonyl compounds described above.

Usually, the total amount of the leveling agents in the electroplating bath is from 0.5 ppm to 10000 ppm based on the total weight of the plating bath. The leveling agents according to the present invention are typically used in a total amount of from about 100 ppm to about 10000 ppm based on the total weight of the plating bath, although greater or lesser amounts may be used. Further Levelers

It will be appreciated by those skilled in the art that more than one leveling agent may be used. When two or more leveling agents are used, at least one of the leveling agents is an a- substituted carbonyl compound or a derivative thereof as described herein. It is preferred to use only one or more a-substituted carbonyl compound as leveling agents in the plating bath composition.

Suitable additional leveling agents include, but are not limited to, polyaminoamide and derivatives thereof, polyalkanolamine and derivatives thereof, polyethylene imine and derivatives thereof, quaternized polyethylene imine, polyglycine, poly(allylamine), polyaniline, polyurea, polyacrylamide, poly(melamine-co-formaldehyde), reaction products of amines with epichlorohydrin, reaction products of an amine, epichlorohydrin, and polyalkylene oxide, reaction products of an amine with a polyepoxide, polyvinylpyridine, polyvinylimidazole, polyvinylpyrrolidone, or copolymers thereof, nigrosines, pentamethyl-para-rosaniline hydrohalide, hexamethyl-pararosaniline hydrohalide, or compounds containing a functional group of the formula N-R-S, where R is a substituted alkyl, unsubstituted alkyl, substituted aryl or unsubstituted aryl. Typically, the alkyl groups are Ci-Ce alkyl and preferably C1-C4 alkyl. In general, the aryl groups include C6-C20 aryl, preferably Ce-C^ aryl. Such aryl groups may further include heteroatoms, such as sulfur, nitrogen and oxygen. It is preferred that the aryl group is phenyl or napthyl. The compounds containing a functional group of the formula N-R-S are generally known, are generally commercially available and may be used without further purification.

In such compounds containing the N-R-S functional group, the sulfur ("S") and/or the nitrogen ("N") may be attached to such compounds with single or double bonds. When the sulfur is attached to such compounds with a single bond, the sulfur will have another substituent group, such as but not limited to hydrogen, C1-C12 alkyl, C2-C12 alkenyl, C6-C20 aryl, C1-C12 alkylthio, C2- C12 alkenylthio, C6-C20 arylthio and the like. Likewise, the nitrogen will have one or more substituent groups, such as but not limited to hydrogen, C1-C12 alkyl, C2-C12 alkenyl, C7-C10 aryl, and the like. The N-R-S functional group may be acyclic or cyclic. Compounds containing cyclic N-R-S functional groups include those having either the nitrogen or the sulfur or both the nitrogen and the sulfur within the ring system.

Further leveling agents are triethanolamine condensates as described in unpublished international Patent Application No. PCT/EP2009/066581. In general, the total amount of further leveling agents in the electroplating bath is from 0.5 ppm to 10000 ppm based on the total weight of the plating bath.

A large variety of additives may typically be used in the bath to provide desired surface finishes for the plated tin or tin alloy bump. Usually more than one additive is used with each additive forming a desired function. Advantageously, the electroplating baths may contain one or more of surfactants, grain refiners, complexing agents in case of alloy deposition, antioxidants, and mixtures thereof. Most preferably the electroplating bath comprises a surfactant and optionally a grain refiner in addition to the leveling agent according to the present invention. Other additives may also be suitably used in the present electroplating baths.

Surfactants

One or more nonionic surfactants may be used in the present compositions. Typically, the nonionic surfactants have an average molecular weight from 200 to 100,000, preferably from 500 to 50,000, more preferably from 500 to 25,000, and yet more preferably from 750 to 15,000. Such nonionic surfactants are typically present in the electrolyte compositions in a concentration from 1 to 10,000 ppm, based on the weight of the composition, and preferably from 5 to 10,000 ppm. Preferred alkylene oxide compounds include polyalkylene glycols, such as but not limited to alkylene oxide addition products of a C2 to C20 organic compound having at least one hydroxy group and multi-functional, particularly tetra-, penta-, or hexa-functional polyethers derived from the addition of different alkylene oxides to C2 to C20 polyamine compounds.

Preferred polyalkylene glycols are polyethylene glycol and polypropylene glycol. Such polyalkylene glycols are generally commercially available from a variety of sources and may be used without further purification. Capped polyalkylene glycols where one or more of the terminal hydrogens are replaced with a hydrocarbyl group may also be suitably used. Examples of suitable polyalkylene glycols are those of the formula R-O-(CXYCX'Y'O)_nR' where R and R' are independently chosen from H, C2 - C20 alkyl group and C6-C20 aryl group; each of X, Y, X' and Y' is independently selected from hydrogen, alkyl such as methyl, ethyl or propyl, aryl such as phenyl, or aralkyl such as benzyl; and n is an integer from 5 to 100,000. Typically, one or more of X, Y, X' and Y' is hydrogen.

Suitable EO/PO copolymers generally have a weight ratio of EO:PO of from 10:90 to 90:10, and preferably from 10:90 to 80:20. Such EO/PO copolymers preferably have an average molecular weight of from 750 to 15,000. Such EO/PO copolymers are available from a variety of sources, such as those available from BASF under the tradename “PLURONIC” or TETRONIC. Suitable alkylene oxide condensation products of an organic compound having at least one hydroxy group and 20 carbon atoms or less include those having an aliphatic hydrocarbon from one to seven carbon atoms, an unsubstituted aromatic compound or an alkylated aromatic compound having six carbons or less in the alkyl moiety, such as those disclosed in US 5 174 887. The aliphatic alcohols may be saturated or unsaturated. Suitable aromatic compounds are those having up to two aromatic rings. The aromatic alcohols have up to 20 carbon atoms prior to derivatization with ethylene oxide. Such aliphatic and aromatic alcohols may be further substituted, such as with sulfate or sulfonate groups.

Antioxidants

Antioxidants may optionally be added to the present composition to assist in keeping the tin in a soluble, divalent state. It is preferred that one or more antioxidants are used in the present compositions. Exemplary antioxidants include, but are not limited to, hydroquinone, and hydroxylated and/or alkoxylated aromatic compounds, including sulfonic acid derivatives of such aromatic compounds, and preferably are: hydroquinone; methylhydroquinone; resorcinol; catechol; 1 ,2,3-trihydroxybenzene; 1,2-dihydroxybenzene-4-sulfonic acid; 1,2-dihydroxy- benzene-3, 5-disulfonic acid; 1,4-dihydroxybenzene-2-sulfonic acid; 1,4-dihydroxybenzene-2, 5- disulfonic acid; 2,4-dihyroxybenzene sulfonic acid, and p-Methoxyphenol. Such antioxidants are disclosed in US 4 871 429. Other suitable antioxidants or reducing agents include, but are not limited to, vanadium compounds, such as vanadylacetylacetonate, vanadium triacetylacetonate, vanadium halides, vanadium oxyhalides, vanadium alkoxides and vanadyl alkoxides. The concentration of such reducing agent is well known to those skilled in the art, but is typically in the range of from 0.1 to 10 g/l, and preferably from 1 to 5 g/l. Such antioxidants are generally commercially available from a variety of sources. It is particularly preferred to use the prescribed antioxidants in pure tin electroplating compositions.

Complexing Agents

The tin or tin alloy electroplating bath may further contain complexing agents for complexing tin and/or any other metal present in the composition. A typical complexing agent is 3,6-Dithia-1 ,8- octanediol. Further useful complexing agents are described in WO 2019/185468 and WO2021/052817.

Typical complexing agents are polyoxy monocarboxylic acids, polycarboxylic acids, aminocarboxylic acids, lactone compounds, and salts thereof. Other complexing agents are organic thiocompounds like thiourea, thiols or thioethers as disclosed in US 7628903, JP 4296358 B2, EP 0854206 A and US 8980077 B2.

Electrolyte

In general, as used herein “aqueous” means that the present electroplating compositions comprises water and optionally organic solvents below 0.1 g/l, preferably below 0.05 g/l, most preferably below 0.01 g/l. Any type of water may be used, such as distilled, deinonized or tap. Preferably the electroplating composition does not contain any organic solvents or even lower amounts of organic solvents as described above since, due to the limited solubility of most of the a-substituted carbonyl compounds in the aqueous plating bath, it may be necessary to dissolve them in a water-miscible solvent before mixing them with the rest of the plating composition.

The present electroplating compositions are suitable for depositing a tin-containing layer, which may be a pure tin layer or a tin-alloy layer.

Tin

The tin ion source may be any compound capable of releasing metal ions to be deposited in the electroplating bath in sufficient amount, i.e is at least partially soluble in the electroplating bath. It is preferred that the metal ion source is soluble in the plating bath. Suitable metal 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.

The metal ion source may be used in the present invention in any amount that provides sufficient metal ions for electroplating on a substrate. The tin salt is typically present in an amount in the range of from about 1 to about 300 g/l of plating solution. If no alloying metal ions are present, The composition does not contain any metals that can be electrolytically deposited from an aqueous solution besides tin. For the evoidance of doublt, alkaline or alkaline earch metal ions may be present since they do not interact with the electroplating.

In a preferred embodiment the tin ions are present plating composition in an amount of from 20 to 200 g/l, particularly from 40 to 120 g/l, most particularly from 60 to 90 g/l. Alloying metals

Optionally, the plating baths according to the invention may contain one or more alloying metal ions. Suitable alloying metals include, without limitation, silver, gold, copper, bismuth, indium, zinc, antimony, manganese and mixtures thereof. Preferred alloying metals are silver, copper, bismuth, indium, and mixtures thereof, and more preferably silver. It is preferred that the present compositions are free of lead. Any bath-soluble salt of the alloying metal may suitably be used as the source of alloying metal ions. Examples of such alloying metal salts include, but are not limited to: metal oxides; metal halides; metal fluoroborate; metal sulfates; metal alkanesulfonates such as metal methanesulfonate, metal ethanesulfonate and metal propanesulfonate; metal arylsulfonates such as metal phenylsulfonate, metal toluenesulfonate, and metal phenolsulfonate; metal carboxylates such as metal gluconate and metal acetate; and the like. Preferred alloying metal salts are metal sulfates; metal alkanesulfonates; and metal arylsulfonates. When one alloying metal is added to the present compositions, a binary alloy deposit is achieved. When 2, 3 or more different alloying metals are added to the present compositions, tertiary, quaternary or higher order alloy deposits are achieved. The amount of such alloying metal used in the present compositions will depend upon the particular tin-alloy desired. The selection of such amounts of alloying metals is within the ability of those skilled in the art. It will be appreciated by those skilled in the art that when certain alloying metals, such as silver, are used, an additional complexing agent may be required. Such complexing agents (or complexers) are well-known in the art and may be used in any suitable amount.

If alloying metals are present, the composition does not contain any metals that can be electrolytically deposited from an aqueous solution besides tin and the one or more of the alloying metals mentioned above. For the evoidance of doublt, alkaline or alkaline earch metal ions may be present since they do not interact with the electroplating.

Most preferably the composition does not comprise any metals that can be electrolytically deposited from an aqueous solution besides (a) tin and silver, (b) tin and copper, (c) tin and indium, or (d) tin and bismuth.

Exemplary tin-alloy layers include, without limitation, tin-silver, tin-copper, tin-indium, tinbismuth, tin-silver-copper, tin-silver-bismuth, tin-silver-indium, and tin-silver-indium-bismuth. Preferably, the present electroplating compositions deposit pure tin, tin-silver, tin-silver-copper, tin-silver-bismuth, tin-silver-indium, and tin-silver-indium-bismuth, and more preferably pure tin, tin-silver or tin-copper. Alloys deposited from the present electroplating bath contain an amount of tin ranging from 0.01 to 99.99 wt %, and an amount of one or more alloying metals ranging from 99.99 to 0.01 wt %, based on the weight of the alloy, as measured by either atomic adsorption spectroscopy (AAS), X-ray fluorescence (XRF), inductively coupled plasma (ICP) or differential scanning calorimetry (DSC). Preferably, the tin-silver alloys deposited using the present invention contain from 90 to 99.99 wt % tin and 0.01 to 10 wt % of silver and any other alloying metal. More preferably, the tin-silver alloy deposits contain from 95 to 99.9 wt % tin and 0.1 to 5 wt % of silver and any other alloying metal. Tin-silver alloy is the preferred tin-alloy deposit, and preferably contains from 90 to 99.9 wt % tin and from 10 to 0.1 wt % silver. More preferably, the tin-silver alloy deposits contain from 95 to 99.9 wt % tin and from 5 to 0.1 wt % silver. For many applications, the eutectic composition of an alloy may be used. Alloys deposited according to the present invention are substantially free of lead, that is, they contain 1 wt % lead, more preferably below 0.5 wt %, and yet more preferably below 0.2 wt%, and still more preferably are free of lead.

The alloy metal ions are present in the plating composition in an amount of from 0.1 to 5 % by weight, particularly from 0.2 to 3 % by weight, most particularly from 0.3 to 2.0 % by weight. Bath

In general, besides the metal ion source and at least one of the leveling agents according to the invention the present metal electroplating compositions preferably include electrolyte, i. e. acidic or alkaline electrolyte, one or more sources of metal ions, optionally halide ions, and optionally other additives like surfactants and grain refiners. Such baths are typically aqueous. 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 compositions of the invention are acidic, that is, they have a pH below 7. Typically, the pH of the tin or tin alloy electroplating composition is below 4, preferably below 3, most preferably below 2.

The electroplating baths of the present invention may be prepared by combining the components in any order. It is preferred that the inorganic components such as metal salts, water, electrolyte and optional halide ion source, are first added to the bath vessel followed by the organic components such as surfactants, grain refiners, levelers and the like.

Typically, the plating baths of the present invention may be used at any temperature from 10 to 65 degrees C or higher. It is preferred that the temperature of the plating baths is from 10 to 35 degrees C and more preferably from 15 degrees to 30 degrees C. Suitable electrolytes include such as, but not limited to, sulfuric acid, acetic acid, fluoroboric acid, alkylsulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid and trifluoromethane sulfonic acid, arylsulfonic acids such as phenyl sulfonic acid and toluenesulfonic acid, sulfamic acid, hydrochloric acid, phosphoric acid, tetraalkylammonium hydroxide, preferably tetramethylammonium hydroxide, sodium hydroxide, potassium hydroxide and the like. Acids are typically present in an amount in the range of from about 1 to about 300 g/l.

Such electrolytes may optionally contain a source of halide ions, such as chloride ions as in tin chloride or hydrochloric acid. A wide range of halide ion concentrations may be used in the present invention such as from about 0 to about 500 ppm. Typically, the halide ion concentration is in the range of from about 10 to about 100 ppm based on the plating bath. It is preferred that the electrolyte is sulfuric acid or methanesulfonic acid, and preferably a mixture of sulfuric acid or methanesulfonic acid and a source of chloride ions. The acids and sources of halide ions useful in the present invention are generally commercially available and may be used without further purification.

A preferred composition essentially consists of or consists of:

(a) 20 to 200 g/l tin ions, particularly tin methanesulfonate;

(b) the additive of formula L1, particularly of formula L2 or L3, including all preferred embodiments described above;

(c) 1 to about 300 g/l acid, particularly an acid selected from sulfuric acid, acetic acid, fluoroboric acid, alkylsulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid and trifluoromethane sulfonic acid, arylsulfonic acids such as phenyl sulfonic acid and toluenesulfonic acid, sulfamic acid, hydrochloric acid, and phosphoric acid, most particularly sulfuric acid and methansulfonic acid;

(d) optionally further levelers, particularly levelers selected from polyaminoamide and derivatives thereof, polyalkanolamine and derivatives thereof, polyethylene imine and derivatives thereof, quaternized polyethylene imine, polyglycine, poly(allylamine), polyaniline, polyurea, polyacrylamide, poly(melamine-co-formaldehyde), reaction products of amines with epichlorohydrin, reaction products of an amine, epichlorohydrin, and polyalkylene oxide, reaction products of an amine with a polyepoxide, polyvinylpyridine, polyvinylimidazole, polyvinylpyrrolidone, or copolymers thereof, nigrosines, pentamethyl- para-rosaniline hydrohalide, hexamethyl-pararosaniline hydrohalide, and compounds containing a functional group of the formula N-R-S, where R is a substituted alkyl, unsubstituted alkyl, substituted aryl or unsubstituted aryl; (e) optionally a surfactant, particularly a polyalkylene glycol, most particularly analkylene oxide addition products of a C2 to C20 organic compound having at least one hydroxy group and 20 carbon atoms or less and tetra-, penta-, hexa, or more functional polyethers derived from the addition of different alkylene oxides to C2 to C20 polyamine compounds;

(f) optionally an antioxidant, particularly hydroquinone; methylhydroquinone; resorcinol; catechol; 1 ,2,3-trihydroxybenzene; 1,2-dihydroxybenzene-4-sulfonic acid; 1,2-dihydroxy- benzene-3, 5-disulfonic acid; 1,4-dihydroxybenzene-2-sulfonic acid; 1,4-dihydroxybenzene- 2, 5-disulfonic acid; 2,4-dihyroxybenzene sulfonic acid, and p-Methoxyphenol;

(g) optionally a complexing agent, particularly a sulfur-containing complexing agent.

(h) optionally an organic solvent in an amount below 0.1 g/l.

A particularly preferred composition essentially consists of or consists of:

(a) 20 to 200 g/l tin ions, particularly tin methanesulfonate;

(b) the additive of formula L1 , particularly of formula L2 or L3, including all preferred embodiments described above;

(d) optionally an antioxidant, particularly hydroquinone; methylhydroquinone; resorcinol; catechol; 1 ,2,3-trihydroxybenzene; 1,2-dihydroxybenzene-4-sulfonic acid; 1,2-dihydroxy- benzene-3, 5-disulfonic acid; 1,4-dihydroxybenzene-2-sulfonic acid; 1,4-dihydroxybenzene- 2, 5-disulfonic acid; 2,4-dihyroxybenzene sulfonic acid, and p-Methoxyphenol;

(e) optionally a complexing agent, particularly a sulfur-containing complexing agent.

(f) optionally an organic solvent in an amount below 0.1 g/l.

Another preferred composition essentially consists of or consists of:

(a) 20 to 200 g/l tin ions, particularly tin methanesulfonate;

(b) 0.2 to 3 % by weight, particularly from 0.3 to 2.0 % by weight of the alloy metal ions, most particularly silver or indium.

(c) the additive of formula L1 , particularly of formula L2 or L3, including all preferred embodiments described above;

(d) 1 to about 300 g/l acid, particularly an acid selected from sulfuric acid, acetic acid, fluoroboric acid, alkylsulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid and trifluoromethane sulfonic acid, arylsulfonic acids such as phenyl sulfonic acid and toluenesulfonic acid, sulfamic acid, hydrochloric acid, and phosphoric acid, most particularly sulfuric acid and methansulfonic acid;

(e) optionally further levelers, particularly levelers selected from polyaminoamide and derivatives thereof, polyalkanolamine and derivatives thereof, polyethylene imine and derivatives thereof, quaternized polyethylene imine, polyglycine, poly(allylamine), polyaniline, polyurea, polyacrylamide, poly(melamine-co-formaldehyde), reaction products of amines with epichlorohydrin, reaction products of an amine, epichlorohydrin, and polyalkylene oxide, reaction products of an amine with a polyepoxide, polyvinylpyridine, polyvinylimidazole, polyvinylpyrrolidone, or copolymers thereof, nigrosines, pentamethyl- para-rosaniline hydrohalide, hexamethyl-pararosaniline hydrohalide, and compounds containing a functional group of the formula N-R-S, where R is a substituted alkyl, unsubstituted alkyl, substituted aryl or unsubstituted aryl;

(f) optionally a surfactant, particularly a polyalkylene glycol, most particularly analkylene oxide addition products of a C2 to C20 organic compound having at least one hydroxy group and 20 carbon atoms or less and tetra-, penta-, hexa, or more functional polyethers derived from the addition of different alkylene oxides to C2 to C20 polyamine compounds;

(g) optionally an antioxidant, particularly hydroquinone; methylhydroquinone; resorcinol; catechol; 1 ,2,3-trihydroxybenzene; 1,2-dihydroxybenzene-4-sulfonic acid; 1,2-dihydroxy- benzene-3, 5-disulfonic acid; 1,4-dihydroxybenzene-2-sulfonic acid; 1,4-dihydroxybenzene- 2, 5-disulfonic acid; 2,4-dihyroxybenzene sulfonic acid, and p-Methoxyphenol;

(h) optionally a complexing agent, particularly a sulfur-containing complexing agent.

(i) optionally an organic solvent in an amount below 0.1 g/l, particularly an organic solvent selected from isopropanol, ethanol, and a glycol.

A particularly preferred composition essentially consists of or consists of:

(a) 20 to 200 g/l tin ions, particularly tin methanesulfonate;

(d) 1 to about 300 g/l acid, particularly an acid selected from sulfuric acid, acetic acid, fluoroboric acid, alkylsulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid and trifluoromethane sulfonic acid, arylsulfonic acids such as phenyl sulfonic acid and toluenesulfonic acid, sulfamic acid, hydrochloric acid, and phosphoric acid, most particularly sulfuric acid and methansulfonic acid; (e) optionally an antioxidant, particularly hydroquinone; methylhydroquinone; resorcinol; catechol; 1 ,2,3-trihydroxybenzene; 1,2-dihydroxybenzene-4-sulfonic acid; 1,2-dihydroxy- benzene-3, 5-disulfonic acid; 1,4-dihydroxybenzene-2-sulfonic acid; 1,4-dihydroxybenzene- 2, 5-disulfonic acid; 2,4-dihyroxybenzene sulfonic acid, and p-Methoxyphenol;

(f) optionally a complexing agent, particularly a sulfur-containing complexing agent.

(g) optionally an organic solvent in an amount below 0.1 g/l, particularly an organic solvent selected from isopropanol, ethanol, and a glycol.

Application

The plating compositions of the present invention are useful in various plating methods where a tin-containing layer is desired, and particularly for depositing a tin-containing solder layer on a semiconductor wafer comprising a plurality of conductive bonding features. Plating methods include, but are not limited to, horizontal or vertical wafer plating, barrel plating, rack plating, high speed plating such as reel-to-reel and jet plating, and rackless plating, and preferably horizontal or vertical wafer plating. A wide variety of substrates may be plated with a tin- containing deposit according to the present invention. Substrates to be plated are conductive and may comprise copper, copper alloys, nickel, nickel alloys, nickel-iron containing materials. Such substrates may be in the form of electronic components such as (a) lead frames, connectors, chip capacitors, chip resistors, and semiconductor packages, (b) plastics such as circuit boards, and (c) semiconductor wafers. Preferably the substrates are semiconductor wafers. Accordingly, the present invention also provides a method of depositing a tin-containing layer on a semiconductor wafer comprising: providing a semiconductor wafer comprising a plurality of conductive bonding features; contacting the semiconductor wafer with the composition described above; and applying sufficient current density to deposit a tin-containing layer on the conductive bonding features. Preferably, the bonding features comprise copper, which may be in the form of a pure copper layer, a copper alloy layer, or any interconnect structure comprising copper. Copper pillars are one preferred conductive bonding feature. Optionally, the copper pillars may comprise a top metal layer, such as a nickel layer. When the conductive bonding features have a top metal layer, then the tin or tin alloy solder layer is deposited on the top metal layer of the bonding feature. Conductive bonding features, such as bonding pads, copper pillars, and the like, are well-known in the art, such as described in US 7,781 ,325, US 2008/0054459 A, US 2008/0296761 A, and US 2006/0094226 A. Process

One embodiment of the present invention is the use of an additive of formula L1 and any other leveler described herein in a bath for depositing tin or tin alloy containing layers, wherein the tin alloy containing layers comprise an alloy metal selected from silver, copper, indium, and bismuth in an amount of 0.01 to 10 % by weight. Preferably the deposited tin alloy layer has an alloy metal content of 0.1 to 5 % by weight.

Another embodiment of the present invention is a process for depositing a tin or tin alloy layer on a substrate by

A process for depositing a tin or tin alloy layer on a substrate by a) contacting a tin alloy electroplating bath comprising a composition described herein with the substrate, and b) applying a current density to the substrate for a time sufficient to deposit the tin or tin alloy layer onto the substrate.

As used herein, “recessed feature” means a via, trench or any other opening in the substrate, particularly openings for depositing solder bumps. As used herein, “aperture size” means the shortest distance in the opening of the recessed feature.

Preferably the substrate comprises recessed features having an aperture size from 1 to 1000 micrometers and the deposition is performed to at least partially fill the micrometer sized recessed features. Most preferably the recessed features have an aperture size from 1 to 200 micrometers, preferably 3 to 100 micrometers.

In general, when the present invention is used to deposit tin or tin alloys on a substrate the plating baths are agitated during use. Preferably a tin alloy is deposited and the alloy metal content of the deposited tin alloy is from 0.01 to 10 % by weight. 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 150 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. The tin or tin alloy is deposited in recesses according to the present invention without substantially forming voids within the metal deposit. By the term "without substantially forming voids", it is meant that there are no voids in the metal deposit which are bigger than 1000 nm, preferably 500 nm, most preferably 100 nm.

Plating equipment for plating semiconductor substrates are well known. Plating equipment comprises an electroplating tank which holds tin or tin alloy 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.

These additives can be used with soluble and insoluble anodes in the presence or absence of a membrane or membranes separating the catholyte from the anolyte.

The cathode substrate and anode are electrically connected by wiring and, respectively, to a power supply. The cathode substrate for direct or pulse current has a net negative charge so that the metal ions in the solution are reduced at the cathode substrate forming plated 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.

In general, when preparing tin or tin alloy bumps, a photoresist layer is applied to a semiconductor wafer, followed by standard photolithographic exposure and development techniques to form a patterned photoresist layer (or plating mask) having openings or vias therein. The dimensions of the plating mask (thickness of the plating mask and the size of the openings in the pattern) defines the size and location of the tin or tin alloy layer deposited over the I/O pad and UBM.

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. Methods used herein

The molecular weight of the polymeric ionic compounds was determined by size-exclusion chromatography (SEC).

Coplanarity and morphology (roughness) was determined by measuring the height of the substrate by laser scanning microscopy.

The patterned photoresist contained vias of 8 pm diameter and 15 pm depth and pre-formed copper p-bump of 5 pm height. The isolated (iso)-area consists of a 3 x 6 array of pillars with a center to center distance (pitch) of 32 pm. The dense area consists of an 8 x 16 array of pillars with a center to center distance (pitch) of 16 pm. For the calculation of the within die coplanarity 3 bumps of the iso-area and 3 bumps from the center of the dense area are taken.

The Within Die (WID) coplanarity (COP) was determined by using formula

COP ⁼ (Hjso - Hdense)/HAv

Herein Hj_S0 and Hdense are the average heights of the bumps in the iso/dense area and HA_V is the overall average height of all bumps in the iso and dense area as described above.

For leveler screening experiments a double-walled tempered beaker was used equipped with a rotating disc electrode (platinum surface), platinum counter-electrode and Ag/AgCI reference electrode and a potentiostat. The platinum disc electrode was chemically and electrochemically cleaned before each measurement. The measurements were performed in galvanostatic mode. The plating solution was tempered to 25 °C. A current density of 4 A/dm² was applied and the potential was measured over time. The rotation speed of the rotating disc electrode was varied over time throughout one measurement in the following way: 800 rpm from 0 to 60s, 50 rpm from 61 to 120s and 400 rpm from 121 to 180 s. The step height between 800 and 50 rpm was calculated substituting the potential at 60 s from the potential at 120 s. Each experiment was repeated at least one time to verify the result. The average of the step height of two experiments was used to compare different levelers.

The inventors found that the coplanarity of the deposited copper layers correlates with the step high determined as described above. Usually, with increasing step height, the leveling performance increases. Examples

The following levelers were used for the following Examples:

Leveler 1 (comparative): (E)-4-phenyl-but-3-en-2-one, benzalacetone;

Leveler 2: (E)-3-methyl-4-phenyl-but-3-en-2-one;

Leveler 3 (comparative): (E)-4-methyl-4-phenyl-but-3-en-2-one;

Leveler 4 (comparative): (E)-4-(4-methoxyphenyl)-but-3-en-2-one;

Leveler 5: (E)-3-methyl-4-(4-methoxyphenyl)-but-3-en-2-one;

Leveler 6: (E)-1-(4-methoxyphenyl)-2-methylpent-1-en-3-one.

Leveler Source/Preparation

Leveler 1: available from Sigma-Aldrich;

Leveler 2: according to procedure 1 using benzaldehyde;

Leveler 3: according to procedure 3;

Leveler 4: according to procedure 4 using 4-methoxybenzaldehyde;

Leveler 5: according to procedure 1 using 4-methoxybenzaldehyde;

Leveler 6: according to procedure 2 using 4-methoxybenzaldehyde.

Procedure 1: Synthesis of 3-methyl-4-aryl-but-3-en-2-ones:

rt, 20 h

Under nitrogen to 20 ml acetic acid, benzaldehyde (2.65 g, 25 mmol, 1.0 equiv) and 2-butanone (3.61 g, 50 mmol, 2.0 equiv) were added. To the colorless solution, concentrated sulfuric acid (2.40 g, 25 mmol, 1.0 equiv) was added over a period of 5 minutes at room temperature, leading to a color change from yellow to brown. After stirring at room temperature for 20 h, 100 mL water was added, followed by pH adjusting with 25% aqueous NaOH solution to pH = 5. The mixture was extracted twice with ethyl acetate (50 ml, 30 ml). The combined organic layers were washed with saturated NaHCCh-solution followed by washing with saturated NaCI-solution. After drying of the organic layer (Na2SO4) followed by filtration, the solvent was removed in vacuo. The crude product was purified using column chromatography (silica, cyclohexane I ethyl acetate gradient) the desired product (2.20 g, GC-FID 96.7 area-%, 13.3 mmol, 53% yield) was isolated as a yellow oil.

Procedure 2: Synthesis of 4-methyl-5-aryl-pent-4-en-3-ones:

Under nitrogen, 4-methoxybenzaldehyde (2.72 g, 20 mmol, 1.0 equiv) was dissolved in 20 ml ethanol. Diethylketone (6.89 g, 80 mmol, 4.0 equiv) was added, followed by the addition of aqueous sodium hydroxide solution (10%, 2.5 ml, 6.93 mmol, 0.35 equiv) over 3 minutes. The reaction mixture was stirred at room temperature overnight. After pH adjustment mit aqueous HCI (37%) to pH ~2, 70 mL of water was added. The aqueous mixture was extracted with DCM (2 x 30 ml). The combined organic layers were dried (MgSC ) followed by filtration and the solvent was removed in vacuo. The crude product was purified using column chromatography (silica, cyclohexane I ethyl acetate gradient) giving access to the desired product (2.50 g, GC- FID 98.2 area-%, 12.0 mmol, 60% yield) as white crystals.

Procedure 3: Synthesis of 4-aryl-pent-3-en-2-ones (comparative):

1) THF

2) NH₄Cl_aq 3) oxalic acid _A MgBr ₊ - _

Under nitrogen, to phenylmagnesium bromide (3 M in Et20, 25.7 ml, 77.1 mmol, 1.6 equiv) was added a solution of acetylacetone (4.85 g, 48.4 mmol, 1 .0 equiv) in 50 ml THF at room temperature over a period of 30 minutes. After stirring at room temperature for 20 h, 200 ml of saturated NH4CI-solution was added at room temperature. The layers were separated, and the aqueous layer was extracted three times with MTBE (3 x 100 ml). The combined organic layers were dried (MgSC ) followed by filtration and the solvent was removed in vacuo. The residue was added to 100 ml of water followed by the addition of oxalic acid dihydrate (8.41 g, 66.7 mmol, 1.4 equiv) and the mixture was heated to reflux for 30 min. After cooling to room temperature, 100 mL DCM were added. The layers were separated, and the aqueous layer was extracted twice with DCM (2 x 100 ml). The combined organic layers were dried (MgSC ) followed by filtration and the solvent was removed in vacuo. The crude product was purified using column chromatography (silica, cyclohexane I ethyl acetate gradient) giving access to the desired product (1.10 g, GC-FID 92.1 area-%, 5.84 mmol, 12% yield) as a yellow oil. The product contained acetophenone as an impurity.

Procedure 4: Horner-Wadsworth-Emmons route:

O O

Under nitrogen atmosphere 20 ml dioxane and 3.6 mL water were mixed, followed by the addition of diethyl (2-oxopropyl)phosphonate (5.01 g, 25.8 mmol, 1.25 equiv), 2- methylbenzaldehyde (2,48 g, 20.6 mmol, 1.0 equiv) and CS2CO3 (6.73 g, 20.6 mmol, 1.0 equiv). The reaction mixture was stirred at room temperature overnight. The solvent was removed in vacuo and the crude product was purified using column chromatography (silica, hexane I DCM gradient). The desired unsaturated ketone (2.5 g, 15.6 mmol, 76%) was isolated as pale-yellow liquid.

Step hight measurements

Compositions containing 75 g/l tin as tin methanesulfonate, 180 g/l methanesulfonic acid, 0.3 g/l of a commercial anti-oxidant, and 0.04 g/l of the respective levelers 1 to 6 in isopropanol were prepared.

The step heights as described above were measured. The results are depicted in Table 1.

Table 1

Table 1 shows that levelers Nos. 2, 5, and 6 that are substituted in the a position to the carbonyl functional group have significantly higher step heights indicating a better coplanarity compared to levelers Nos. 1 and 4 that are not substituted in this position. Surprisingly, example C3 shows that a substitution in position to the carbonyl functional group even leads to a reduced step height indicating a reduced leveling function compared to prior art leveler No. 1.

Claims

1 . An aqueous composition comprising tin ions, optionally alloy metal ions selected from silver, copper, indium, and bismuth ions and at least one additive of formula L1

wherein

R^L2 is a Ci to Ce alkyl, Ci to Ce alkenyl, C5 to C12 aryl, Ce to C15 alkylaryl, Ce to C15 arylalkyl, all of which may be substituted by CN, OH, Ci to Ce alkoxy or halogen;

R^L3 is selected from Ci to Ce alkyl;

R^L4 is H; n is the number of substituents R^L1 selected from 0 to 5 wherein the amount of organic solvents in the composition is below 0.1 g/l, and wherein the composition does not contain any electrolytically depositable metal ions besides tin ions and the alloying metal ions.

2. The composition according to claim 1 , wherein R^L3 is selected from Ci to C4 alkyl.

3. The composition according to claim 2, wherein R^L3 is methyl.

4. The composition according to anyone of claims 1 to 3, wherein n is 0.

5. The composition according to anyone of claims 1 to 3, wherein n is 1 or 2 and R^L1 _n, for each group R^L1 independently, selected from Ci to C4 alkyl and Ci to C4 alkoxy.

6. The composition according to anyone of the preceding claims, wherein R^L2 is selected from methyl, ethyl, 1 -propyl, and 2-propyl, preferably from methyl and ethyl.

7. The composition according to anyone of the preceding claims, wherein the tin ions are present in an amount of from 40 to 120 g/l, particularly from 60 to 90 g/l.

8. The composition according to anyone of the preceding claims, wherein the alloy metal ions are present in an amount of from 0.2 to 3 % by weight, particularly from 0.3 to 2.0 % by weight.

9. The composition according to claim 8, wherein the alloy metal ions comprise silver ions, preferably consist of silver ions.

10. The composition according to anyone of the preceding claims, wherein the pH of the composition is below 4, preferably below 3, most preferably below 2.

11. Use of an additive of formula L1

in a composition for electrodepositing tin or tin alloy containing layers, wherein the tin alloy containing layers comprise an alloy metal selected from silver, copper, indium, and bismuth in an amount of 0.01 to 10 % by weight, wherein

R^L3 is selected from Ci to Ce alkyl;

R^L4 is H; n is the number of substituents R^L1 selected from 0 to 5 wherein the amount of organic solvents in the composition is below 0.1 g/l, and wherein the composition does not contain any electrolytically depositable metal ions besides tin ions and the alloying metal ions..

12. The use according to claim 11 , wherein the deposited tin alloy layer has an alloy metal content of 0.1 to 5 % by weight.

13. A process for depositing a tin or tin alloy layer onto a substrate by a) contacting a tin alloy electroplating bath comprising a composition according to anyone of claims 1 to 10 with the substrate, and b) applying a current density to the substrate for a time sufficient to deposit the tin or tin alloy layer onto the substrate. The process according to claim 13, wherein the substrate comprises recessed features having an aperture size from 1 to 1000 micrometers, preferably from 1 to 200 micrometers, most preferably from 3 to 100 micrometers, and the deposition is performed to at least partially fill the micrometer sized recessed features. A compound selected from (E)-4-ethyl-5-(4-methylphenyl)-pent-4-en-3-one and (E)-4-ethyl- 5-(4-methoxyphenyl)-pent-4-en-3-one.