KR102022926B1 - Indium electroplating compositions and methods for electroplating indium - Google Patents

Abstract

Indium electroplating compositions electroplat a substantially defect free uniform layer with smooth surface morphology on the metal layer. The indium electroplating composition can be used for electroplating indium metal on metal layers of various substrates such as semiconductor wafers and as a thermal interface material.

Description

Indium electroplating composition and method for electroplating indium {INDIUM ELECTROPLATING COMPOSITIONS AND METHODS FOR ELECTROPLATING INDIUM}

The present invention relates to an indium electroplating composition and a method of electroplating indium metal on a metal layer. More specifically, the present invention relates to a method of electroplating indium metal on a metal layer wherein the indium electroplating composition and the indium metal deposit are uniform, substantially void free and have smooth surface morphology.

The ability to reproducibly plate uniform indium without voids of target thickness and smooth surface morphology on metal layers is challenging. Indium reduction occurs at cathodic potentials greater than that of proton reduction, and significant hydrogen frothing at the cathode results in increased surface roughness. Stabilized indium ( ¹⁺ ) ions, formed during the process of indium deposition, stabilize the indium ( ¹⁺ ) ions to participate in the disproportionation reaction to catalyze proton reduction and to regenerate indium ( ³⁺ ) ions. In the absence of complexing agents, indium ions begin to precipitate from solutions>pH> 3. Plating indium on metals such as nickel, tin, copper and gold is tricky because these metals are good catalysts for reducing protons and are stronger than indium and thus they can cause corrosion of indium in the interaction of direct current electricity. Indium can also form unwanted intermetallic compounds with these metals. Finally, indium chemistry and electrochemistry have not been well studied, and therefore no interaction with compounds that can act as additives is known.

In general, conventional indium electroplating baths were unable to electroplate indium deposits compatible with many under bump metals (UBM) such as nickel, copper, gold and tin. More importantly, conventional indium electroplating baths could not electroplate indium with high coplanarity and high surface planarity on substrates containing nickel. However, indium is a very desirable metal in many industries because of its unique physical properties. For example, it is easily deformed and filled into the microstructure between the two junctions, and has a low melting temperature (156 ° C.) and high thermal conductivity (~ 82 W / m ° K), good electrical conductivity, with other metals in the stack. This is soft enough to have an excellent ability to alloy and form intermetallic compounds. It can be used as a low temperature solder bump material, which is a preferred process for 3D stack assembly to reduce damage to the assembled chip due to thermal stress induced during the reflow process. This property enables indium in a variety of applications in electronics and related industries, including semiconductors and polycrystalline thin film solar cells.

Indium can also be used as thermal interface materials (TIM). TIMs are important for protecting electronic devices such as integrated circuits (ICs) and active semiconductor devices such as microprocessors from exceeding their operating temperature limits. They enable the coupling of heat generating devices (eg, silicon semiconductors) to heat sinks or heat spreaders (eg, copper and aluminum components) without creating excessive thermal barriers. The TIM can also be used to assemble other components of the heat sink or heat spreader stack that make up the entire thermal impedance path.

Several classes of materials are used as TIMs, such as thermal greases, thermal gels, adhesives, elastomers, thermal pads, and phase change materials. Although the aforementioned TIMs are suitable for many semiconductor devices, the increased performance of semiconductor devices makes these TIMs inadequate. Many current TIMs do not exceed 5W / m ° K and most are less than 1W / m ° K. However, there is currently a need for a TIM that forms a thermal interface with an effective thermal conductivity exceeding 15 W / m ° K.

Thus, indium is a very preferred metal for electronic devices, and there is a need for an improved indium composition for electroplating indium metal, especially indium metal layers on metal substrates.

The composition comprises one or more indium ion sources, one or more thiourea and thiourea derivatives, and citric acid, salts thereof, or mixtures thereof.

The method includes providing a substrate comprising a metal layer; Contacting the substrate with an indium electroplating composition comprising at least one source of indium ions, at least one thiourea and thiourea derivatives, and citric acid, salts of citric acid, or mixtures thereof; And electroplating an indium metal layer on the metal layer of the substrate with the indium electroplating composition.

The indium electroplating composition can provide a deposit of indium metal on a metal layer that is substantially void free and has a uniform and smooth morphology. The target thickness and the ability to reproducibly plate uniform indium without voids of smooth surface morphology allow for the expanded use of indium in the electronics industry, including semiconductors and polycrystalline thin film solar cells. Indium deposited from the electroplating compositions of the present invention can be used as a preferred low temperature solder material for 3D stack assembly to reduce damage to the assembled chip by thermal stress induced during the reflow process. Indium can also be used as a thermal interface material to protect electronic devices such as microprocessors and integrated circuits. The present invention solves a number of problems of the prior art that are electroplated with indium of sufficient properties to meet the requirements for applications in advanced electronic devices.

1A is an optical microscope image of nickel plated vias having a diameter of 75 μm.
1B is an optical microscope image of an indium layer on a nickel plated via having a diameter of 75 μm.
FIG. 2 is an optical microscopic image of an indium layer on a nickel plated via having a diameter of 75 μm where indium was electroplated from an indium composition containing guanylthiourea.
FIG. 3 is an optical microscopic image of an indium layer on a nickel plated via having a diameter of 75 μm where indium was electroplated from an indium composition containing tetramethyl-2-thiourea.
FIG. 4 is an optical microscopic image of an indium layer on a nickel plated rectangular via having a length of 50 μm indium where the indium was electroplated from an indium composition containing 1-allyl-2-thiourea.
FIG. 5 is an optical microscopic image of an indium layer on a nickel plated via having a diameter of 75 μm indium in which an indium was electroplated from an indium composition containing guanylthiourea and sodium chloride.

As used throughout this specification, the following abbreviations have the following meanings unless the context clearly indicates otherwise: ° C = degrees Celsius; K = Kelvin temperature; g = grams; mg = milligrams; L = liter; A = amps; dm = decimeter; ASD = A / dm 2 = current density; Μm = micron = micrometer; ppm = parts per million; ppb = billions; ppm = mg / L; In indium ion = ^{3 +; +} Li = Li-ion; Na ⁺ = sodium ion; K ⁺ = potassium ion; NH ₄ ⁺ = ammonium ion; nm = nanometers = 10 ^-9 meters; Μm = micrometer = 10 ⁻⁶ meters; M = mole; MEMS = micro-electro-mechanical system; TIM = thermal interface material; IC = integrated circuit; EO = ethylene oxide and PO = propylene oxide.

The terms "deposition", "plating" and "electroplating" are used interchangeably throughout this specification. The term "copolymer" is a compound composed of two or more different monomers. The term "dendritic" refers to branched spike-like metal crystals. Unless otherwise indicated, all plating baths are aqueous solvent based, ie water based plating baths. Unless otherwise indicated, all amounts are weight percent and all ratios are molar ratios. All numerical ranges are inclusive and combinable in any order, but it is logical that such numerical ranges are limited to a sum of up to 100%.

The composition includes one or more sources of indium ions that are soluble in an aqueous environment. The indium composition is free of alloy metals. Such sources include, but are not limited to, indium salts of alkanesulfonic acids and aromatic sulfonic acids, such as methanesulfonic acid, ethanesulfonic acid, butane sulfonic acid, benzenesulfonic acid and toluenesulfonic acid, indium salts of sulfamic acid, sulfate salts of indium, Chloride and bromide salts, nitrate salts, hydroxide salts, indium oxides, fluoroborate salts, citric acid, acetoacetic acid, glyoxylic acid, pyruvic acid, glycolic acid, malonic acid, hydroxamic acid, iminodiacetic acid Indium salts of carboxylic acids such as salicylic acid, glyceric acid, succinic acid, malic acid, tartaric acid, hydroxybutyric acid, arginine, aspartic acid, asparagine, glutamic acid, glycine, glutamine, leucine, lysine, threonine, isoleucine, and valine Indium salts. Typically, the source of indium ions is an indium salt of at least one sulfuric acid, sulfamic acid, alkane sulfonic acid, aromatic sulfonic acid and carboxylic acid. More typically, the source of indium ions is an indium salt of at least one sulfuric acid and sulfamic acid.

A water soluble salt of indium is included in the composition in an amount sufficient to provide an indium deposit of the desired thickness. Preferably, the indium (3 ⁺⁾ in the water-soluble indium salts are 2g / L to 70g / L, more preferably from 2g / L to 60g / L, and most preferably the composition in an amount of 2g / L to 30g / L It is included in the composition to provide.

Citric acid, salts thereof or mixtures thereof are included in the indium composition. Citric acid salts include but are not limited to sodium citrate dihydrate, monosodium citrate, potassium citrate and diammonium citrate. Citric acid, salts thereof or mixtures thereof may be included in amounts of 5 g / L to 300 g / L, preferably 50 g / L to 200 g / L. Preferably the mixture of citric acid and salts thereof is included in the indium composition in the amounts described above.

At least one of thiourea and thiourea derivatives are included in the indium composition. Thiourea derivatives include, but are not limited to, guanylthiourea, 1-allyl-2-thiourea, 1-acetyl-2-thiourea, 1-benzoyl-2-thiourea, 1-benzyl-2-thiourea, 1- Butyl-3-phenyl-2-thiourea, 1,1-dimethyl-2-thiourea, tetramethyl-2-thiourea, 1,3-dimethyl thiourea, 1-methyl thiourea, 1,3-diethyl Thiourea, 1,1-diphenyl-2-thiourea, 1,3-diphenyl-2-thiourea, 1,1-dipropyl-2-thiourea, 1,3-dipropyl-2-thiourea , 1,3-diisopropyl-2-thiourea, 1,3-di (2-tolyl) -2-thiourea, 1-methyl-3-phenyl-2-thiourea, 1 (1-naphthyl) -3-phenyl-2-thiourea, 1 (1-naphthyl) -2-thiourea, 1 (2-naphthyl) -2-thiourea, 1-phenyl-2-thiourea, 1,1,3 , 3-tetramethyl-2-thiourea and 1,1,3,3-tetraphenyl-2-thiourea. Preferably the thiourea derivative is selected from guanylthiourea, 1-allyl-2-thiourea and tetramethyl-2-thiourea. More preferably the thiourea derivative is selected from guanylthioureas. Thiourea and thiourea derivatives are included in amounts of 0.01 g / L to 50 g / L, preferably 0.1 g / L to 35 g / L, more preferably 0.1 g / L to 5 g / L.

Optionally, but preferably, at least one source of chloride ions is included in the indium electroplating composition. Sources of chloride ions include, but are not limited to sodium chloride, potassium chloride, hydrogen chloride or mixtures thereof. Preferably the source of chloride ions is sodium chloride, potassium chloride or mixtures thereof. More preferably the source of chloride ions is sodium chloride. One or more sources of chloride ions are included in the indium composition such that the molar ratio of chloride ions to indium ions is at least 2: 1, preferably 2: 1 to 7: 1, more preferably 4: 1 to 6: 1. .

Optionally, in addition to citric acid, salts thereof, or mixtures thereof, one or more additional buffers may be included in the indium composition to provide a pH of 1-4, preferably 2-3. The buffer includes salts of acids and their base salts. Acids are amino acids, carboxylic acids, glyoxylic acid, pyruvic acid, hydroxamic acid, iminodiacetic acid, salicylic acid, succinic acid, hydroxybutyric acid, acetic acid, acetoacetic acid, tartaric acid, phosphoric acid, oxalic acid, carbonic acid, ascorbic acid, boric acid, butanoic acid , Thioacetic acid, glycolic acid, malic acid, formic acid, heptanoic acid, hexanoic acid, hydrofluoric acid, lactic acid, nitrous acid, octanoic acid, pentanic acid, uric acid, nonanoic acid, decanoic acid, sulfurous acid, sulfuric acid, alkane sulfonic acid and aryl sulfonic acid Such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, sulfamic acid. The acid is combined with Li ⁺ , Na ⁺ , K ⁺ , NH ₄ ⁺ or (C _n H _{(2n + 1)} ) ₄ N ⁺ salt of a base, where n is an integer from 1 to 6.

Optionally, one or more surfactants may be included in the indium composition. In one embodiment, the one or more surfactants are amine surfactants, ethoxylated naphthols, sulfonated naphthol polyethers, (alkyl) phenol ethoxylates, sulfonated alkylalkoxylates, alkylene glycol alkyls Ether and sulfopropylated polyalkoxylated beta-naphthol alkali salts. Such surfactants include, but are not limited to quaternary amines commercially available as amine surfactants such as TOMAMINE®-QC-15 surfactants, amine oxides commercially available as TOMAMINE®-AO-455 surfactants, both from Air Products Available; Hydrophilic polyether monoamines commercially available from Huntsman as SURFONAMINE® L-207 amine surfactants; Polyethylene glycol octyl (3-sulfopropyl) diether commercially available as RALUFON® EA 15-90 surfactant; [(3-Sulfopropoxy) -polyalkoxy] -β-naphthyl ether, commercially available as RALUFON® NAPE 14-90 surfactant, Octa commercially available as RALUFON® EN 16-80 surfactant Ethyleneglycol octyl ether, polyethyleneglycol alkyl (3-sulfopropyl) diether, potassium salt, commercially available as RALUFON® F 11-3 surfactants, all of which can be obtained from Rasich GmbH; EO / PO block copolymers commercially available as TETRONIC®-304 surfactant, available from BASF; Ethoxylated β-naphthols from Schaerer & Schlaepfer AG such as ADUXOL ™ NAP-08, ADUXOL ™ NAP-03, ADUXOL ™ NAP-06 ; SURFYNOL® 484 surfactant from ethoxylated 2,4,7,9-tetramethyl-5-decine-4,7-diol such as Air Products and Chemicals Corporation; LUX ™ BN-13 surfactants, ethoxylated β-naphthols such as TIB Chemicals LUX ™ NPS surfactants; Ethoxylated-β-naphthol such as POLYMAX® PA-31 surfactants available from PCC Kemax Inc. Such surfactants are included in amounts of 1 ppm to 10 g / L, preferably 5 ppm to 5 g / L.

Optionally, the indium composition may comprise one or more crystal growth inhibitors. Such crystal growth inhibitors include, but are not limited to, 2-picolinic acid, sodium 2-naphthol-7-sulfonate, 3- (benzothiazol-2-ylthio) propane-1-sulfonic acid (ZPS), 3- ( Carbamimidoylthio) propane-1-sulfonic acid (UPS), bis (sulfopropyl) disulfide (SPS), mercaptopropane sulfonic acid (MPS), 3- N , N -dimethylaminodithiocarbamoyl-1-propane Sulfonic acid (DPS), and (O-ethyldithiocarbonato) -S- (3-sulfopropyl) -ester (OPX). Preferably such crystal growth inhibitor is included in the indium composition in an amount of 0.1 ppm to 5 g / L, more preferably 0.5 ppm to 1 g / L.

Optionally, one or more inhibitors may be included in the indium composition. Inhibitors include, but are not limited to, phenanthroline and derivatives thereof such as 1,10-phenanthroline, triethanolamine and derivatives thereof such as triethanolamine lauryl sulfate, sodium lauryl sulfate and ethoxylated ammonium lauryl sulfate , Polyethylenimine and derivatives thereof such as hydroxypropylpolyenimine (HPPEI-200), and alkoxylated polymers. Such inhibitors are included in the indium composition in conventional amounts. Typically, inhibitors are included in amounts of 1 ppm to 5 g / L.

Optionally, one or more leveling agents can be included in the indium composition. Leveling agents include, but are not limited to, polyalkylene glycol ethers. Such ethers include, but are not limited to, dimethyl polyethylene glycol ether, di-tertiary butyl polyethylene glycol ether, polyethylene / polypropylene dimethyl ether (mixed or block copolymer), and octyl monomethyl polyalkylene ether ( Mixed or block copolymers). Such leveling agents are included in conventional amounts. Generally, such leveling agents are included in amounts of 100 ppb to 500 ppb.

Optionally, one or more hydrogen inhibitors may be included in the indium composition to inhibit hydrogen gas formation during indium metal electroplating. Hydrogen inhibitors include epihalohydrin copolymers. Epihalohydrin includes epichlorohydrin and epibromohydrin. Typically, copolymers of epichlorohydrin are used. Such copolymers are water soluble polymerization products of epichlorohydrin or epibromohydrin and at least one organic compound comprising nitrogen, sulfur, oxygen atoms or combinations thereof.

Nitrogen-containing organic compounds copolymerizable with epihalohydrin include, but are not limited to:

1) aliphatic chain amines;

2) unsubstituted heterocyclic nitrogen compounds having at least two reactive nitrogen moieties; And,

3) substituted heterocyclic nitrogen compounds having at least two reactive nitrogen moieties and having 1-2 substituents selected from alkyl groups, aryl groups, nitro groups, halogens and amino groups.

Aliphatic chain amines include, but are not limited to, dimethylamine, ethylamine, methylamine, diethylamine, triethyl amine, ethylene diamine, diethylenetriamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octyl Amines, 2-ethylhexylamine, isooctylamine, nonylamine, isononylamine, decylamine, undecylamine, dodecylamine, tridecylamine and alkanol amines.

Unsubstituted heterocyclic nitrogen compounds having at least two reactive nitrogen moieties include, but are not limited to, imidazole, imidazoline, pyrazole, 1,2,3-triazole, tetrazole, pyrazine, 1, 2,4-triazole, 1,2,3-oxadiazole, 1,2,4-thiadiazole and 1,3,4-thiadiazole.

Substituted heterocyclic nitrogen compounds having at least two reactive nitrogen moieties and having 1-2 substituents include, but are not limited to, benzimidazole, 1-methylimidazole, 2-methylimidazole, 1,3 -Dimethylimidazole, 4-hydroxy-2-amino imidazole, 5-ethyl-4-hydroxyimidazole, 2-phenylimidazoline and 2-tolylimidazolin.

Preferably, imidazole, pyrazole, imidazoline, 1,2,3-triazole, tetrazole, pyridazine, 1,2,4-triazole, 1,2,3-oxadiazole, 1, One or more compounds selected from 2,4-thiadiazole and 1,3,4-thiadiazole and its derivatives incorporating one or two substituents selected from methyl, ethyl, phenyl and amino groups are known as epihalohydrin co- Used to form polymers.

Some epihalohydrin copolymers are commercially available, such as Rashee GmbH, Ludwigshafen, Germany, and BASF, Wyundo, Michigan, USA, or can be prepared by methods disclosed in the literature. An example of a commercially available imidazole / epichlorohydrin copolymer is the LUGALVAN® IZE copolymer obtainable from BASF.

Epihalohydrin copolymers may be formed by reacting epihalohydrin with the nitrogen, sulfur or oxygen containing compounds described above under any suitable reaction conditions. For example, in one method, both materials are dissolved at a suitable concentration in the body of the mutual solvent and reacted therein, for example, for 45 to 240 minutes. The aqueous chemical product of the reaction is isolated by distilling off the solvent and then added to the body of water, which acts as an electroplating solution once the indium salt is dissolved. Alternatively, these two materials are placed in water and heated to 60 ° C. with constant vigorous stirring until they react and dissolve in water.

A wide ratio of reaction compounds to epihalohydrin is used, such as from 0.5: 1 to 2: 1 moles. Typically the molar ratio is 0.6: 1 to 2: 1 moles, more typically the molar ratio is 0.7 to 1: 1 and most typically the molar ratio is 1: 1.

In addition, the reaction product may be further reacted with one or more reagents before the electroplating composition is completed by addition of the indium salt. Thus, the described products can be further reacted with reagents that are at least one of ammonia, aliphatic amines, polyamines, and polyimines. Typically, the reagent is at least one of ammonia, ethylenediamine, tetraethylene pentamine and polyethyleneimine having a molecular weight of at least 150, although other species that meet the definitions set forth herein may be used. The reaction can take place with stirring in water.

For example, a reaction may occur between the reaction product of epichlorohydrin and a nitrogen-containing organic compound as described above and a reagent selected from one or more of ammonia, aliphatic amines, and arylamines or polyimines, and For example, it may be carried out at a temperature of 30 ℃ to 60 ℃, for example for 45 to 240 minutes. The molar ratio between the reaction product and the reagent of the nitrogen containing compound-epichlorohydrin reaction is typically 1: 0.3-1.

Epihalohydrin copolymer is included in the composition in an amount of 0.01 g / L to 100 g / L. Preferably, the epihalohydrin copolymer is included in an amount of 0.1 g / L to 80 g / L, more preferably they are in an amount of 0.1 g / L to 50 g / L, most preferably 1 g / L to 30 g / L.

The indium composition can be used to deposit a substantially uniform, void-free layer of indium metal on metal layers of various substrates. The indium layer is also substantially free of dendritic tissue. The indium layer is preferably in the range of 10 nm to 100 μm, more preferably 100 nm to 75 μm in thickness.

The apparatus used to deposit indium metal on the metal layer is conventional. Preferably a conventional soluble indium electrode is used as the anode. Any suitable reference electrode can be used. Typically, the reference electrode is a silver chloride / silver electrode. The current density may range from 0.1 ASD to 10 ASD, preferably 0.1 to 5 ASD, more preferably 1 to 4 ASD.

The temperature of the indium composition during indium metal electroplating can range from room temperature to 80 ° C. Preferably, the temperature is from room temperature to 65 ° C, more preferably from room temperature to 60 ° C. Most preferably the temperature is room temperature.

Indium compositions can be used to electroplat indium metal on nickel, copper, gold and tin layers of various substrates, including components for electronic devices, magnetic field devices and superconducting MRI. Preferably indium is electroplated on nickel. The metal layer is preferably in the range of 10 nm to 100 μm, more preferably 100 nm to 75 μm. Indium compositions can also be used in conventional photoimaging methods for electroplating indium metal small diameter solder bumps on a variety of substrates, such as silicon wafers. The small diameter bumps preferably have an aspect ratio of 1 to 3, and have a diameter of 1 µm to 100 µm, more preferably 2 µm to 50 µm.

For example, the indium composition can be used for electroplating indium metal on electrical devices that function as TIMs, such as, but not limited to, ICs, microprocessors in semiconductor devices, parts for MEMS, and parts for optoelectronic devices. . Such electronic components can be included in printed circuit boards and melt-sealed chip-scale and wafer-level packages. Such a package typically includes an electronic device disposed within the enclosed volume and a melt-sealed enclosed volume formed between the base substrate and the lid. The package provides for the containment and protection of the enclosed device from contamination and water vapor in the atmosphere outside the package. Contamination and the presence of water vapor in the package can cause problems such as corrosion of metal parts as well as optical losses in the case of optoelectronic devices and other optical parts. Low melting temperatures (156 ° C.) and high thermal conductivity (˜82 W / m ° K) are properties that make indium metals very desirable for use as TIMs.

In addition to the TIM, the indium composition can be used to electroplat an underlayer on a substrate to prevent whisker formation in electronic devices. The substrate may include, but is not limited to, electrical or electronics such as film carriers for mounting semiconductor chips, printed circuit boards, lead frames, contact elements such as contacts or ends, and plated structural members that require good appearance and high operational reliability. Contains ingredients or parts.

The following examples further illustrate the invention but are not intended to limit the scope of the invention.

Example  1 (comparative)

A photoresist patterned silicon wafer with a plurality of vias having a diameter of 75 μm from Silicon Valley Microelectronics and a copper seed layer on the base of each via was fabricated using NIKAL ™ BP nickel electroplating baths available from Dow Advanced Materials. Electroplating with a nickel layer. Nickel electroplating was performed at 55 ° C. with a cathode current density of 1 ASD for 120 seconds. The conventional rectifier supplied the current. The anode was a soluble nickel electrode. After plating, the silicon wafer was removed from the plating bath and the photoresist was stripped from the wafer and rinsed with water with a SHIPLEY BPR ™ photo stripper available from Dow Advanced Materials. Nickel deposits looked substantially soft and there were no observable dendritic tissues on the surface. 1A is an optical image of one of the nickel plated copper seed layers taken with a LEICA ™ optical microscope.

The following aqueous indium electrolytic composition was prepared:

ingredient sheep Indium sulfate 45 g / L Citric acid 96 g / L Sodium citrate dihydrate 59 g / L

After the electroplating of the nickel layer, the nickel layer electroplating process described above was patterned in another set, except that the nickel plated silicon wafer was immersed in the indium electroplating composition and the indium metal layer was electroplated on nickel. For repeated wafers. Indium electroplating was performed at 25 ° C. for 30 seconds at a current density of 4ASD. The pH of the indium electroplating composition was 2.4. The anode was an indium soluble electrode. After plating indium on nickel, the photoresist was stripped from the wafer and the morphology of the indium deposit was observed. All indium deposits appeared rough.

1B is an optical image of one of the indium metal deposits electroplated on a nickel layer. Indium deposits were very rough compared to nickel deposits as shown in FIG. 1A.

Example  2

The method described in Example 1 above was repeated except that the indium electroplating composition contained the following components:

ingredient sheep Indium sulfate 45 g / L Citric acid 96 g / L Sodium citrate dihydrate 59 g / L Guanylthiourea 0.75 g / L

The nickel plated silicon wafer is immersed in the indium electroplating composition and the indium metal is electroplated onto nickel. Indium electroplating was performed at 25 ° C. for 30 seconds at a current density of 4ASD. The pH of the composition was 2.4. The anode was an indium soluble electrode. After indium was electroplated onto the nickel layer, the photoresist was stripped from the wafer and indium morphology was observed. All indium deposits appeared uniform and smooth.

2 is an optical microscope image of one of the indium metal deposits electroplated on a nickel layer. Indium deposits appeared smooth compared to the indium deposit of FIG. 1B.

Example 3

The method described in Example 1 above was repeated except that the indium electroplating composition contained the following components:

ingredient sheep Indium sulfate 45 g / L Citric acid 96 g / L Sodium citrate dihydrate 59 g / L Tetramethyl-2-thiourea 0.5 g / L

The nickel plated silicon wafer is immersed in the indium electroplating composition and the indium metal is electroplated onto nickel. Indium electroplating was performed at 25 ° C. for 30 seconds at a current density of 4ASD. The pH of the composition was 2.4. After indium was electroplated onto nickel, the photoresist was stripped from the wafer and indium morphology was observed. All indium deposits appeared uniform and smooth.

3 is an optical microscope image of one of the indium metal deposits electroplated on nickel. Indium deposits appeared smooth compared to the indium deposit of FIG. 1B.

Example 4

The method described in Example 1 above was repeated except that the silicon wafer was patterned with photoresist to have rectangular vias having a length of 50 μm and the indium electroplating composition included the following components:

ingredient sheep Indium sulfate 45 g / L Citric acid 96 g / L Sodium citrate dihydrate 59 g / L 1-allyl-2-thiourea ¹ 1 g / L

¹ Synonym = N-allyl-thiourea

The nickel plated silicon wafer is immersed in the indium electroplating composition and the indium metal is electroplated onto nickel. Indium electroplating was performed at 25 ° C. for 11 seconds at a current density of 4ASD. The pH of the composition was 2.4. After indium was electroplated onto nickel, the photoresist was stripped from the wafer and indium morphology was observed. All indium deposits appeared uniform and smooth.

4 is an optical microscope image of one of the indium metal deposits electroplated on a nickel layer. Indium deposits appeared smooth compared to the indium deposit of FIG. 1B.

Example  5

 The method described in Example 1 above was repeated except that the indium electroplating composition contained the following components:

ingredient sheep Indium sulfate 45 g / L Citric acid 96 g / L Sodium citrate dihydrate 59 g / L Guanylthiourea 0.75 g / L Quaternary Amine Surfactants ² 5 ppm

² TOMAMINE® QC-15 Surfactant Available from Air Products

The nickel plated silicon wafer is immersed in the indium electroplating composition and the indium metal is electroplated onto nickel. Indium electroplating was performed at 25 ° C. for 11 seconds at a current density of 4ASD. The pH of the composition was 2.4. After indium was electroplated onto nickel, the photoresist was stripped from the wafer and indium morphology was observed. All indium deposits appeared uniform and smooth substantially the same as shown in FIGS. 2-4.

Example  6

The method described in Example 1 above was repeated except that the indium electroplating composition contained the following components:

ingredient sheep Indium sulfate 45 g / L Citric acid 96 g / L Sodium citrate dihydrate 59 g / L Guanylthiourea 0.75 g / L Polyethyleneglycol octyl (3-sulfopropyl) diether ³ 10 ppm

³ RALUFON® EA 15-90 Surfactant Available from Lassihi

The nickel plated silicon wafer is immersed in the indium electroplating composition and the indium metal is electroplated onto nickel. Indium electroplating was performed at 25 ° C. for 11 seconds at a current density of 4ASD. The pH of the composition was 2.4. After indium was electroplated onto nickel, the photoresist was stripped from the wafer and indium morphology was observed. All indium deposits appeared uniform and smooth substantially the same as shown in FIGS. 2-4.

Example  7

The method described in Example 1 above was repeated except that the indium electroplating composition contained the following components:

ingredient sheep Indium sulfate 45 g / L Citric acid 96 g / L Sodium citrate dihydrate 59 g / L Guanylthiourea 0.75 g / L Quaternary Amine Surfactants ⁴ 5 ppm Sodium 2-naphthol-7-sulfonate 100 ppm

⁴ TOMAMINE® QC-15 Surfactant Available from Air Products

The nickel plated silicon wafer is immersed in the indium electroplating composition and the indium metal is electroplated onto nickel. Indium electroplating was performed at 25 ° C. for 11 seconds at a current density of 4ASD. The pH of the composition was 2.4. After indium was electroplated onto nickel, the photoresist was stripped from the wafer and indium morphology was observed. All indium deposits appeared uniform and smooth substantially the same as shown in FIGS. 2-4.

Example  8

The method described in Example 1 above was repeated except that the indium electroplating composition contained the following components:

ingredient sheep Indium sulfate 45 g / L Citric acid 96 g / L Sodium citrate dihydrate 59 g / L Guanylthiourea 0.15 g / L Sodium chloride ⁵ 50 g / L

Molar ratio of ⁵ chloride: indium ions = 5: 1

The nickel plated silicon wafer is immersed in the indium electroplating composition and the indium metal is electroplated onto nickel. Indium electroplating was performed at 25 ° C. for 30 seconds at a current density of 4ASD. The pH of the composition was 2.4. After indium was electroplated onto the nickel layer, the photoresist was stripped from the wafer and indium morphology was observed. All indium deposits appeared uniform and smooth. FIG. 5 is an optical microscope image of indium electroplated from the bath of Table 8. FIG. As shown in FIG. 5, the indium deposit was uniform and smooth.

Claims (16)

As a method of electroplating indium metal on nickel,
a) providing a substrate comprising a nickel layer;
b) contacting the substrate with an indium electroplating composition comprising at least one source of indium ions, one or more of thiourea and thiourea derivatives, and salts of citric acid, citric acid or mixtures thereof; And
c) electroplating an indium metal layer on the nickel layer of the substrate with the indium electroplating composition;
Wherein the indium electroplating composition does not contain an alloy metal. The method of claim 1, wherein at least one of the thiourea and thiourea derivatives is included in the indium electroplating composition in an amount of 0.01 g / L to 50 g / L. The method of claim 1, wherein the indium electroplating composition further comprises at least one source of chloride ions, wherein the molar ratio of chloride ions to indium ions is at least 2: 1. 4. The method of claim 3, wherein the molar ratio of chloride ions to indium ions is from 2: 1 to 7: 1. 5. The method of claim 4, wherein the molar ratio of chloride ions to indium ions is 4: 1 to 6: 1. The method of claim 1, wherein the nickel layer is 10 nm to 100 μm thick. The method of claim 1, wherein the indium metal layer is 10 nm to 100 μm thick. The method of claim 1, wherein the thiourea derivative is guanylthiourea, 1-allyl-2-thiourea, 1-acetyl-2-thiourea, 1-benzoyl-2-thiourea, 1-benzyl-2-thio Urea, 1-butyl-3-phenyl-2-thiourea, 1,1-dimethyl-2-thiourea, tetramethyl-2-thiourea, 1,3-dimethyl thiourea, 1-methyl thiourea, 1, 3-diethyl thiourea, 1,1-diphenyl-2-thiourea, 1,3-diphenyl-2-thiourea, 1,1-dipropyl-2-thiourea, 1,3-dipropyl- 2-thiourea, 1,3-diisopropyl-2-thiourea, 1,3-di (2-tolyl) -2-thiourea, 1-methyl-3-phenyl-2-thiourea, 1 (1 -Naphthyl) -3-phenyl-2-thiourea, 1 (1-naphthyl) -2-thiourea, 1 (2-naphthyl) -2-thiourea, 1-phenyl-2-thiourea, 1 A method of electroplating indium metal on nickel, selected from 1,3,3-tetramethyl-2-thiourea and 1,1,3,3-tetraphenyl-2-thiourea. The method of claim 8, wherein the thiourea derivative is selected from guanylthiourea, 1-allyl-2-thiourea, and tetramethyl-2-thiourea. The method of claim 1 wherein the indium electroplating composition is an amine surfactant, ethoxylated naphthol, sulfonated naphthol polyether, (alkyl) phenol ethoxylate, sulfonated alkylalkoxylate, alkylene glycol alkyl A method of electroplating indium metal on nickel, further comprising at least one surfactant selected from ethers and sulfopropylated polyalkoxylated beta-naphthol alkali salts. The method of claim 1, wherein the indium electroplating composition further comprises one or more copolymers of the reaction product of epihalohydrin and one or more nitrogen-containing organic compounds. . delete delete delete delete delete

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