KR20150051926A - Plating bath and method - Google Patents

Abstract

A tin containing electric plating bath having a batch of a specific whitening agent provides a tin containing solder deposit having a reduced void formation and a smooth shape. An electric plating composition comprises: a tin ion source; an acid electrolyte; 0.0001-0.045 g/L of a first crystal growth inhibitor; 0.005-0.75 g/L of an α,β-unsaturated aliphatic carbonyl compound as a second crystal growth inhibitor; a non-ionic surfactant; and water.

Description

{PLATING BATH AND METHOD}

The present invention relates generally to the field of electrolytic metal plating. More particularly, the invention relates to the field of electrolytic tin plating.

Metals and metal-alloys are of particular commercial importance in the electronics industry, where they are often used for electrical contact, final finishing and solder. Tin-lead was once the most common tin-alloy solder, but its use decreased as the limit on lead increased. Lead-free solders are common substitutes for tin-lead solders, such as tin, tin-silver, tin-copper, tin-bismuth, tin-silver-copper and others. These solders are often deposited on a substrate using a plating bath such as an electroplating bath.

A method of electroplating a product with a metal coating generally involves passing current between two electrodes in a plating solution, one of the electrodes (usually a cathode) to be plated. Typical tin plating solutions include dissolved tin ions, water, acid electrolytes such as methane sulfonic acid in an amount sufficient to impart conductivity to the bath, antioxidants, and dedicated additives to improve plating uniformity and metal deposition quality do. Such additives include, in particular, surfactants and crystal growth inhibitors.

Applications for lead-free solder plating present challenges in the electronics industry. For example, when used as a capping layer on a copper pillar, a relatively small amount of lead-free solder, such as tin-silver solder, is deposited on top of the copper pillar. In this small amount of solder plating, it is difficult to uniformly coat the height of the solder composition both on the top of each pillar, both inside the die and across the wafer. The use of known solder electroplating baths also results in deposition with relatively rough surface morphologies, such as an average surface roughness (Ra) of at least about 800 nm as measured by optical profilometry. This relatively rough surface morphology is often associated with void formation in solder after reflow, which ultimately raises concerns about solder joint reliability. Thus, there is an industry interest in pure tin or tin-alloy solder depositions that avoids the problem of relatively rough surface morphology and provides improved in-die uniformity.

Many tin electroplating baths are known. When a glossy surface is required, a polishing agent is generally used in the tin electroplating bath. Typical brighteners include aldehydes, ketones, carboxylic acids, carboxylic acid derivatives, amines or mixtures thereof. For example, U.S. Patent No. 4,582,576 discloses aromatic aldehydes, acetophenones, and the formula Ar-C (H) = C (H) -C (O) -CH 3 (Ar is phenyl, naphthyl, pyridyl, thiophenyl or Furyl), and at least one first brightener selected from the group of lower aliphatic aldehydes and at least one second brightener selected from the group of the formula R ₄ C (R ₃ ) = C (R ₂ ) R _{1 wherein} R ₁ is a carboxy, carboxamide, At least one second polish selected from the group of substituted olefins selected from the group consisting of metal carboxylates, ammonium carboxylates, amine carboxylates or allyl carboxylates, and R ₂ , R ₃ and R ₄ are each independently hydrogen or a lower alkyl group Lead-tin-lead electroplating bath. This patent discloses that each of these first and second brighteners is used in relatively large quantities, i.e., at least 0.1 gram per liter. Such conventional tin electroplating baths, when used in certain electronic applications, for example, when used to form pure tin caps on copper posts, result in tin deposits with voids and / or tin deposits Resulting in deposition with a relatively high level of impurities. Thus, there is a need in the industry for electroplating baths and methods for depositing tin-containing solder layers as cap in an acceptable form and substantially void free, especially on copper posts.

It is an object of the present invention to provide an electroplating bath and method for depositing a tin-containing layer in an acceptable form and substantially void free.

The present invention provides an electroplating composition comprising a tin ion source; Acid electrolytes; 0.0001 to 0.045 g / L of a first crystal growth inhibitor; As the second crystal growth inhibitor, 0.005 to 0.75 g / L of an alpha, beta -unsaturated aliphatic carbonyl compound; Nonionic surfactants; And water, wherein a first crystal growth inhibitor is selected from compounds of formula (1) or (2):

In the formula (1) and (2), each R ¹ is independently (C ₁ - ₆₎ alkyl, (C ₁ - ₆₎ alkoxy, hydroxy, or halo; R ² and R ³ are independently selected from H and (C ₁ - ₆₎ is selected from alkyl; R ⁴ is _{H, OH, (C 1 -} 6) alkyl or O (C ₁ - ₆₎ alkyl; m is an integer from 0 to 2; Each R ⁵ is independently (C ₁ - ₆₎ alkyl; Each R ⁶ is independently _{H, OH, (C 1 -} 6) alkyl, or O (C ₁ - ₆₎ is selected from alkyl; n is 1 or 2; And p is 0, 1 or 2.

The present invention also provides a method of depositing a tin-containing layer on a semiconductor substrate, the method comprising: providing a semiconductor wafer comprising a plurality of conductive bonding features; Contacting the semiconductor wafer with the composition as described above; And applying a sufficient current density to deposit the tin-containing layer in the conductive bonding feature.

The present invention also provides a semiconductor device comprising a plurality of conductive coupling features and a tin-containing layer deposited on a conductive bonding feature, wherein the tin-containing layer substantially voids during plating and after reflow.

The following abbreviations used throughout this specification have the following meanings unless expressly indicated otherwise: ASD = A / dm ² = amps per square decimeter; C = Celsius; g = gram; mg = milligram; L = liters; Å = Angstrom; nm = nanometer; Mu m = micron = micrometer; mm = millimeter; min = min; DI = deionization; And mL = milliliters. Unless otherwise indicated, all contents are percent by weight ("wt%") and all ratios are by weight. All numerical ranges are inclusive and may be combined in any order, except where it is evident that such numerical ranges are limited to a total of 100%.

Throughout this specification, the term "plating" refers to metal electroplating. "Deposition" and "plating" are used interchangeably throughout this specification. "Pure tin" refers to tin deposition rather than tin-alloy, but such deposition can include up to 5 atomic percent impurity. "Halide" refers to chlorine, bromine, iodine, and fluorine. The articles "a "," an "and" the " "Alkyl" refers to linear, branched, and cyclic alkyl. "Aryl" refers to an aromatic carbocycle and an aromatic heterocycle. The term "(meth) acrylic" refers to both "acrylic" and "methacrylic ". When one component is referred to as being " deposited "on another component, it may be present directly on the other component or intervening components may be present therebetween. On the other hand, when one component is referred to as being " deposited directly on another component ", the intervening component is not present. Herein, "and / or" includes any and all combinations of one or more of the related list items.

The composition of the present invention comprises a tin ion source; Acid electrolytes; 0.0001 to 0.045 g / L of a first crystal growth inhibitor; As the second crystal growth inhibitor, 0.005 to 0.75 g / L of an alpha, beta -unsaturated aliphatic carbonyl compound; Nonionic surfactants; And water, wherein the first crystal growth inhibitor is selected from the compounds of formula (1) or (2):

In the formula (1) and (2), each R ¹ is independently (C ₁ - ₆₎ alkyl, (C ₁ - ₆₎ alkoxy, hydroxy, or halo; R ² and R ³ are independently selected from H and (C ₁ - ₆₎ is selected from alkyl; R ⁴ is _{H, OH, (C 1 -} 6) alkyl or O (C ₁ - ₆₎ alkyl; m is an integer from 0 to 2; Each R ⁵ is independently (C ₁ - ₆₎ alkyl; Each R ⁶ is independently _{H, OH, (C 1 -} 6) alkyl, or O (C ₁ - ₆₎ is selected from alkyl; n is 1 or 2; And p is 0, 1 or 2.

Any bath-soluble tribasic salt may suitably be used as a source of tin ions. Examples of such tin salts include tin oxides and salts such as tin halide, tin sulfate, tin alkane sulfonate such as tin methane sulfonate and tin sulfonate, tin aryl sulfonate such as tin phenyl sulfonate, tin phenol sulfonate, tin cresol sulfonate , And tin toluene sulfonate, tin alkanol sulfonate, and the like. When tin halide is used, the halide is preferably chlorine. The tin compound is preferably tin oxide, tin sulfate, tin chloride, tin alkane sulphonate or tin aryl sulphonate. More preferably, the tin salt is selected from the group consisting of methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 2-hydroxyethan-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 1- Phenolsulfonic acid, phenylsulfonic acid, toluenesulfonic acid, phenolsulfonic acid, or cresolsulfonic acid, more preferably methanesulfonic acid, phenylsulfonic acid or tin salts of phenolsulfonic acid. Mixtures of tin salts may also be used. Tin compounds useful in the present invention are generally commercially available from a variety of sources and may be used without further purification. Or tin compounds useful in the present invention may be prepared by methods known in the literature. Typically, the content of tin ions in the composition is in the range of 10 to 300 g / L, preferably 20 to 200 g / L, more preferably 30 to 100 g / L.

Any acid electrolyte that is bath-soluble and does not otherwise adversely affect the electrolyte composition can be used in the present invention. Suitable acid electrolytes include alkanesulfonic acids such as methanesulfonic acid, ethanesulfonic acid and propanesulfonic acid; Aryl sulfonic acids such as phenyl sulfonic acid, toluene sulfonic acid, phenol sulfonic acid, and cresolsulfonic acid; Alkanolsulfonic acid; Sulfuric acid; Sulfamic acid; And inorganic acids such as hydrochloric acid, hydrobromic acid, and fluoroboric acid. Alkanesulfonic acid and arylsulfonic acid are preferred acid electrolytes and alkanesulfonic acid is more preferred. Methanesulfonic acid is particularly preferred. Mixtures of acid electrolytes such as alkanesulfonic acid and sulfuric acid mixtures are particularly useful, but are not limited thereto. Thus, one or more acid electrolytes can be advantageously used in the present invention. Acid electrolytes useful in the present invention are well known and are generally commercially available and can be used without further purification. Alternatively, acid electrolytes can be prepared by methods known in the literature. Generally, the content of acid in the composition is in the range of 10 to 1000 g / L, preferably 20 to 750 g / L, more preferably 30 to 500 g / L.

The composition of the present invention comprises a mixture of a first crystal growth inhibitor and a second crystal growth inhibitor. The first crystal growth inhibitor is selected from the compounds of formula (1) or (2)

In the formula (1) and (2), each R ¹ is independently (C ₁ - ₆₎ alkyl, (C ₁ - ₆₎ alkoxy, hydroxy, or halo; R ² and R ³ are independently selected from H and (C ₁ - ₆₎ is selected from alkyl; R ⁴ is _{H, OH, (C 1 -} 6) alkyl or O (C ₁ - ₆₎ alkyl; m is an integer from 0 to 2; Each R ⁵ is independently (C ₁ - ₆₎ alkyl; Each R ⁶ is independently _{H, OH, (C 1 -} 6) alkyl or O (C ₁ - ₆₎ is selected from alkyl; n is 1 or 2; And p is 0, 1 or 2. Preferably, each R ¹ is independently (C ₁ - ₆₎ alkyl, (C ₁ - ₃₎ alkoxy, or hydroxy, more preferably (C ₁ - ₄₎ alkyl, (C ₁ - ₂₎ alkyl, or Lt; / RTI > Preferably, R ² and R ³ are independently selected from H and - is in the (C _{1 3)} alkyl, more preferably is selected from H and methyl. Preferably, R ⁴ is _{H, OH, (C 1 -} 4) alkyl or a O - - (C _{1 4)} alkyl (C _{1 4)} alkyl, more preferably H, OH, or. Preferably R ⁵ is (C ₁ - ₄₎ alkyl, more preferably (C ₁ - ₃₎ alkyl. Each R ⁶ is preferably H, OH, or is - - ₍₃ C ₁₎ is alkyl, more preferably H or OH (C _{1 6)} is alkyl, more preferably H, OH, or. Preferably m is 0 or 1, more preferably m is 0. Preferably, n is 1. p is 0 or 1, more preferably p is 0. A mixture of a first crystal growth inhibitor, such as two different crystal growth inhibitors of Formula 1, two different crystal growth inhibitors of Formula 2, or a crystal growth inhibitor of Formula 1 and a crystal growth inhibitor of Formula 2, may be used. Preferably, the first crystal growth inhibitor is a compound of formula (1).

Exemplary compounds of the first crystal growth inhibitor include, but are not limited to, cinnamic acid, cinnamaldehyde, benzylidene acetone, picolinic acid, pyridine dicarboxylic acid, pyridine carboxaldehyde, pyridine dicarboxaldehyde, . Preferred first crystal growth inhibitors include cinnamic acid, cinnamic aldehydes and benzylidene acetone.

The first crystal growth inhibitor is present in the plating bath of the present invention in an amount of 0.0001 to 0.045 g / L. Preferably, the first crystal growth inhibitor is present in an amount from 0.0001 to 0.04 g / L, more preferably from 0.0001 to 0.035 g / L, even more preferably from 0.0001 to 0.03 g / L. Compounds useful as the first crystal growth inhibitor are generally commercially available from a variety of sources and can be used as is or further purified.

A second crystal growth inhibitor useful in the plating bath of the present invention is an?,? - unsaturated aliphatic carbonyl compound. Suitable alpha, beta -unsaturated aliphatic carbonyl compounds include, but are not limited to, alpha, beta -unsaturated carboxylic acids, alpha, beta -unsaturated carboxylic acid esters, alpha, beta -unsaturated amides, and alpha, beta -unsaturated aldehydes. Preferably, the second crystal growth inhibitor is selected from alpha, beta -unsaturated carboxylic acids, alpha, beta -unsaturated carboxylic acid esters, and alpha, beta -unsaturated aldehydes, more preferably alpha, beta -unsaturated carboxylic acids, and alpha, beta -unsaturated aldehydes . Exemplary α, β- unsaturated aliphatic carbonyl compounds are (meth) acrylic acid, crotonic acid, (C ₁ - ₆₎ alkyl (meth) acrylate, (meth) acrylamide, (C ₁ - ₆₎ alkyl crotonate, Crotonamide, crotonaldehyde, (meth) acrolein, or mixtures thereof. Preferred?,? - unsaturated aliphatic carbonyl compounds include (meth) acrylic acid, crotonic acid, crotonaldehyde, (meth) acrylic aldehyde or mixtures thereof.

The second crystal grain refiner is present in the plating bath of the invention in an amount of from 0.005 to 0.75 g / L. Preferably, the second crystal growth inhibitor is present in an amount of from 0.005 to 0.5 g / L, more preferably in an amount of from 0.005 to 0.25 g / L, even more preferably from 0.01 to 0.25 g / L ≪ / RTI > Compounds useful as second crystal growth inhibitors are either commercially available from various sources or are used as such or are further purified or further purified.

One or more nonionic surfactants are used in the present compositions. Typically, the nonionic surfactant has an average molecular weight of 200 to 100,000, preferably 500 to 50,000, more preferably 500 to 25,000, still more preferably 750 to 15,000. Such non-ionic surfactants are typically present in the electrolyte composition at a concentration of from 1 to 10,000 ppm, preferably from 5 to 10,000 ppm, based on the weight of the composition. Preferred alkylene oxide compounds include polyalkylene glycols, which include ethylene oxide / propylene oxide ("EO / PO" copolymer alkylene oxide concentrates of one or more hydroxyl groups and organic compounds having up to 20 carbon atoms and other Tetrafunctional polyether derived from an alkylene oxide derived from an ethylene diamine compound prepared by adding oxypropylene to polyoxyethylene glycol.

Typically, polyalkylene glycols useful in the present compositions have an average molecular weight of from 200 to 100,000, and preferably from 900 to 20,000. Preferred polyalkylene glycols are polyethylene glycols, and polypropylene glycols. Such polyalkylene glycols are available commercially from various sources or are used without further purification. Capped polyalkylene glycols wherein at least one terminal hydrogen is substituted with a hydrocarbyl group can be suitably used. Suitable polyalkylene glycols have the formula RO- (CXYCX'Y'O) _n R 'where R and R' are independently selected from H, (C _{2 -20} ) alkyl and (C _{6 -20} ) Selected; Each X, Y, X 'and Y' is independently selected from hydrogen, alkyl such as methyl, ethyl or propyl, aryl such as phenyl, aralkyl such as benzyl; and n is an integer of 5 to 100,000. Typically, at least one of X, Y, X 'and Y' is hydrogen.

Suitable EO / PO copolymers generally have an EO: PO weight ratio of from 10:90 to 90:10, preferably from 10:90 to 80:20. A preferred EO / PO copolymer is a block copolymer having a structure of EO / PO / EO or PO / EO / PO. Such EO / PO copolymers are available from a variety of sources, such as those available from BASF under the Pluronic brand.

Suitable alkylene oxide concentrates of organic compounds having one or more hydroxy groups and up to 20 carbon atoms can be prepared from aliphatic hydrocarbons of 1 to 7 carbon atoms, unsubstituted aromatic compounds, or alkyl moieties such as those described in U.S. Patent No. 5,174,887 Lt; RTI ID = 0.0 > 6 < / RTI > Aliphatic alcohols are saturated or unsaturated. Suitable aromatic compounds have up to two aromatic rings. Aromatic alcohols have up to 20 carbon atoms before being derivatized with ethylene oxide. These aliphatic and aromatic alcohols are further substituted, such as sulfates or sulfonate groups. Such suitable alkylene oxide compounds include, but are not limited to, ethoxylated polystyrene phenols with 12 moles of EO, ethoxylated butanol with 5 moles of EO, ethoxylated with 16 moles of EO Ethoxylated butanol with 8 moles of EO, ethoxylated octanol with 12 moles of EO, ethoxylated beta-naphthol with 13 moles of EO, ethoxylated bisphenol A with 10 moles of EO , Ethoxylated sulfated bisphenol A with 30 moles of EO and ethoxylated bisphenol A. with 8 moles of EO.

(3) and (4) represent nonionic surfactants which are tetrafunctional polyethers derived from the addition of an alkylene oxide to ethylenediamine:

Wherein A and B represent different alkyleneoxy moieties, and x and y each represent the number of repeating units of each alkylene oxide. Preferably, A and B are selected from (C _{2 -4} ) alkylene oxides, preferably propylene oxide and ethylene oxide. The alkyleneoxy moieties in the formulas 1 and 2 are arranged in blocks alternately or randomly. The molar ratio of x: y in formulas 3 and 4 is typically from 10:90 to 90:10, and preferably from 10:90 to 80:20. Such tetrafunctional polyethers are generally available from a variety of sources as available from the Pluronic brand BASF (Ludwigshafen, Germany).

Generally, the present invention includes water. Water can exist in a wide range of amounts. Any type of water can be used, such as distilled water, DI, or tabs.

The compositions may optionally comprise one or more additives such as antioxidants, organic solvents, metal alloys, conductivity acids, complexers, and composites thereof. Additional crystal growth inhibitors may be used in the present plating bath, as discussed above, in which a plating bath containing only first and second crystal growth inhibitors is preferred.

An antioxidant may be optionally added to help keep the tin in a soluble bivalent state. It is preferred that at least one antioxidant is used in the composition. Exemplary antioxidants include, but are not limited to, hydroquinone, and hydroxylated aromatic compounds such as sulfonic acid derivatives of such aromatic compounds, such as: hydroquinone; Methyl hydroquinone; Resorcinol; Catechol; 1,2,3-trihydroxybenzene; 1,2-dihydroxybenzene-4-sulfonic acid; 1,2-dihydroxybenzene-3,5-disulfonic acid; 1,4-dihydroxybenzene-2-sulfonic acid; 1,4-dihydroxybenzene-2,5-disulfonic acid; And 2,4-dihydroxybenzenesulfonic acid. Such antioxidants are described in U.S. Patent No. 4,871,429. Other suitable antioxidants or reducing agents include, but are not limited to, vanadium compounds such as vanadyl acetylacetonate, vanadlydiacetyl acetonate, vanadium halide, vanadium oxyalide, vanadium alkoxide and vanadyl alkoxide. The concentration of such reducing agent is well known in the art, but typically ranges from 0.1 to 10 g / L, preferably from 1 to 5 g / L. Such antioxidants are generally available commercially from a variety of sources.

A selective organic solvent may be added to the tin electroplating composition. Typical solvents useful in the present compositions are aliphatic alcohols. Preferred organic solvents are methanol, ethanol, n-propanol, iso-propanol, n-butanol, and iso-butanol. Such a solvent may be used in the tin electroplating composition in an amount of from 0.05 to 15 g / L, and preferably from 0.05 to 10 g / L.

Alternatively, the plating bath may comprise one or more sources of alloy metal ions. Suitable alloy metals include, but are not limited to, silver, gold, copper, bismuth, indium, zinc, antimony, manganese and mixtures thereof. Preferred alloy metals are silver, copper, bismuth, indium, and mixtures thereof, and more preferably silver. The composition is preferably free of lead. A bath-soluble salt of any alloy metal may suitably be used as a source of the alloy metal ion. Examples of such alloying metal salts include, but are not limited to, metal oxides; Metal halide; Metal fluoroborate; Metal sulfates; Metal alkanesulfonates such as metal methane sulfonate, metal ethane sulfonate and metal propane sulfonate; Metal aryl sulfonates such as metal phenyl sulfonate, metal toluene sulfonate, and metal phenol sulfonate; Metal carboxylates such as metal gluconate and metal acetate; And analogs thereof. Preferred metal alloy salts are metal sulfates; Metal alkanesulfonates; And metal aryl sulfonates. A bivalent alloy deposit is achieved when one alloy metal is added to the composition. When two, three or more other alloying metals are added to the composition, triple, tetrahedral or even more alloy deposition is achieved. The amount of such alloy metal used in the present invention depends on the particular tin-alloy desired. The choice of this amount of alloy metal is within the ability of one skilled in the art. Additional complexing agents may be required in accordance with those skilled in the art when any alloy metal, such as silver, is used. Such complexing agents (or complexing agents) are well known in the art and can be used in any suitable amount.

Conducting acid may optionally be added to the present composition. Such conductivity acids include, but are not limited to, boric acid, alkanoic acids, hydroxyalkanoic acids, and salts of these acids in an amount that is acceptable. Preferred are salts of formic acid, acetic acid, oxalic acid, citric acid, malic acid, tartaric acid, gluconic acid, glucuronic acid, glucuronic acid, and acids thereof. When used, these conductive acids and salts are applied in conventional amounts.

The electroplating compositions of the present invention may be prepared by any suitable method known in the art. Typically, they are prepared by adding an acid electrolyte to a vessel and adding at least one tin compound, at least one surfactant, at least one crystal growth inhibitor, optionally water and other optional compounds. Once the composition is prepared, any undesired material is removed by filtration or the like, and water is added to adjust the final volume of the composition.

The plating bath of the present invention is acidic, i. E., PH < 7. Typically, the pH of the present plating bath is from -1 to < 7, preferably from -1 to 6.5, more preferably from -1 to 5, even more preferably from -1 to 2.

The present electroplating composition is suitable for depositing a tin-containing layer which may be a pure tin layer or a tin-alloy layer. Exemplary tin-alloy layers include tin-silver, tin-silver-copper, tin-silver-copper- antimony, tin- silver- copper- manganese, tin- silver- Zinc-copper, and tin-silver-indium-bismuth. Preferably, the present electroplating composition is selected from the group consisting of pure tin, tin-silver, tin-silver-copper, tin-silver-bismuth, tin-silver- , Tin-silver or tin-silver-copper. The alloy deposited in the present electroplating bath contains a quantity of tin ranging from 0.01 to 99.99 wt% and the at least one alloy metal is selected from the group consisting of electron adsorption spectroscopy (AAS), X-ray fluorescence (XRF) , Inductively coupled plasma (ICP), or differential scanning calorimetry (DSC). Preferably, the tin-silver alloy deposited using the present invention comprises from 75 to 99.99 wt% tin and from 0.01 to 10 wt% silver and other alloying metals. More preferably, the tin-silver alloy comprises from 95 to 99.99 wt% tin and from 0.1 to 5 wt% silver and other alloying metals. Silver alloys are preferably tin-alloy deposits and preferably contain from 90 to 99.9 wt% tin and from 10 to 0.1 wt% silver. More preferably, the tin-silver alloy deposit contains 95 to 99.9 wt% tin and 5 to 0.1 wt% silver. For various applications, eutectic compositions of alloys may be used. The alloy deposited in accordance with the present invention is essentially free of lead, i.e. containing ≤1 wt% lead, more preferably ≤0.5 wt%, and more preferably ≤0.2 wt%, and even more preferably lead .

The plating compositions of the present invention are useful for depositing tin-containing layers on semiconductor wafers, particularly those containing conductive bonding features, in a variety of desired plating methods. Plating methods include horizontal or vertical wafer plating, barrel plating, rack plating, high-speed plating such as reel-to-reel and jet plating, and rackless plating and horizontal or vertical wafer plating But are not limited to. A variety of substrates can be plated into tin-containing deposits in accordance with the present invention. The substrate to be plated is conductive and is a copper, copper alloy, nickel, nickel alloy, nickel-iron containing material. Such substrates include lead frames, connections, chip capacitors, chip resistors, and semiconductor packaging; Plastic, such as circuit boards; And a semiconductor wafer, preferably an electrical compound such as a semiconductor wafer. Therefore, 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 a semiconductor wafer with said composition; And applying a sufficient current density to deposit the tin-containing layer on the conductive bonding features. Preferably, the bonding feature is any interconnect structure, including copper, a copper alloy layer, or copper, which may be in the form of a pure copper layer. Copper pillars are desirable conductive bonding features. Optionally, the copper pillars comprise a metal layer top such as a nickel layer. When the conductive bonding feature has the top of the metal layer, a pure tin solder layer is deposited on the top metal layer of the bonding feature. Features of conductive bonds such as bonding pads, copper pillars, and their analogs are described in U.S. Patent Nos. 7,781,325, and U.S. Patent Nos. 2008/0054459, 2008/0296761, and 2006/0094226 It is well known.

As used herein, the term "semiconductor wafer" refers to various packages for various levels of interconnection such as "electronic device substrate "," semiconductor substrate ", "semiconductor device ", and single chip wafers, Packages for branch levels, or other assemblies that require solder connections. Particularly suitable substrates are patterned wafers such as patterned silicon wafers, patterned sapphire wafers and patterned gallium-arsenide wafers. The wafer may have an appropriate size. The preferred wafer diameter is 200 mm to 300 mm, but wafers having large and small diameters can be suitably used in accordance with the present invention. The term "semiconducting substrate " as used herein includes a substrate having one or more semiconductor layers or a structure comprising an active or operable portion of a semiconductor device. The term "semiconductor substrate" refers to a semiconductor material, such as, but not limited to, an assembly comprising a bulk semiconductor material such as a semiconductor wafer itself or other material thereon, and a semiconductor material layer, Layer &lt; / RTI &gt; A semiconductor device refers to a semiconductor substrate from which at least one microelectronic device is fabricated or manufactured.

The substrate is plated with a tin-containing layer by applying current density for a period of time to contact the substrate with the composition and deposit a tin-containing layer on the substrate. This contact is possible by putting the substrate to be plated into the plating bath composition or by pumping the plating bath composition to the substrate. The substrate is conductive and cathode. The plating bath contains an anode, which may be soluble or insoluble. Displacement is typically applied to the cathode. Plating is performed for a sufficient period of time to deposit a desired thickness of the tin-containing layer on the substrate by applying a sufficient current density. A semiconductor wafer comprising a plurality of bonding features is electroplated by applying a current density for a period of time to contact the wafer with the plating bath of the present invention and deposit the tin containing layer on the plurality of bonding features. The semiconductor wafer acts as a cathode.

The specific current density used to deposit the tin-containing layer depends on the particular plating method, the substrate to be plated, and whether a pure tin or tin alloy layer is deposited. A suitable current density is 0.1 to 200 A / dm &lt; ^{2 &} gt ;. Preferably, the current density is 0.5 to 100 A / dm ² , more preferably 0.5 to 30 A / dm ² , even more preferably 0.5 to 20 A / dm ² , and most preferably 2 to 20 A / dm ² . Other current densities may be useful depending on the particular bonding feature to be plated as well as other considerations known to those skilled in the art. Such current density selection is within the discretion of those skilled in the art.

The tin-containing layer may be deposited at a temperature of 10 ° C or higher, preferably 10 to 65 ° C, more preferably 15 to 40 ° C. Generally, the longer the time the substrate is plated, the thicker the deposition, while the shorter the time, the thinner the deposition at a given temperature and current density. Thus, the length of time the substrate remains in the plating composition can be used to control the thickness of the resulting tin-containing deposit. Typically, the metal deposition rate can be 15 [mu] m / min. Typically, the deposition rate may range from 0.5 to 15 [mu] m / min, preferably from 1 to 10 [mu] m / min.

Although the electrolyte composition of the present invention can be used for a variety of applications as described above, exemplary applications are interconnect bumps (solder bump) formation for wafer level packaging. The method includes providing a semiconductor die (wafer die) having a plurality of conductive bonding features (e.g., interconnect bump pads), forming a seed layer on the bonding feature, contacting the semiconductor die with the electroplating composition of the present invention, Depositing a tin-containing interconnect bump layer, passing current through the electroplating composition to deposit a tin-containing interconnect bump layer on the substrate, and then reflowing the interconnect bump layer to form a solder bump. Conductive interconnect bump pads can be one or more layers of a metal alloy typically formed of a metal, a composite metal or physical vapor deposition (PVD) such as sputtering. Typical conductive bonding features include, but are not limited to, aluminum, copper, titanium nitride, and alloys thereof.

The passivation layer is formed over the bonding features and the openings following the bonding features are formed there by an etching process, typically dry etching. The passivation layer is typically an insulating material, such as silicon nitride, silicon oxynitride or silicon oxide, such as phosphosilicate glass. Such materials may be deposited by chemical vapor deposition (CVD) processes, such as plasma enhanced CVD. An underbump metallization (UBM) structure typically formed from a plurality of metal or metal alloy layers is deposited on the device. The UBM acts as an adhesive layer and an electrical contact base (seed layer) of the interconnect bump to be formed. The layer forming the UBM structure may be deposited by PVD, such as a sputtering or evaporation, or CVD process. The UBM structure may be, for example, but not limited to, a composite structure comprising a lower chromium layer, a copper layer, and an upper tin layer in order. Nickel is a metal used for UBM applications.

Typically, after applying a photoresist layer to a semiconductor wafer, a patterned photoresist layer (or a plating mask) having openings or vias (plating vias) is formed by standard photolithographic exposure and development techniques. The dimensions of the plating mask (the thickness of the plating mask and the size of the opening in the pattern) define the size and location of the tin-silver layer deposited on the I / O pads and UBM. The diameter of such deposits is typically in the range of 5 to 300 [mu] m, preferably 10 to 150 [mu] m. The height of such deposits is typically in the range of 10 to 150 μm, preferably 15 to 150 μm, more preferably 20 to 80 μm. Suitable photoresist materials are commercially available (for example, from Dow Electronic Materials (Marlborough, Mass., USA) and are well known in the art.

The interconnect bump material is deposited in the device by an electroplating process using the electroplating composition described above. The interconnect bump material includes, for example, pure tin or other suitable tin alloy. Exemplary tin alloys are those described above. It is desirable to use such alloys in their process compositions or other suitable compositions. The bump material is electrodeposited in the region defined by the plating vias. For this purpose, horizontal or vertical wafer plating systems, such as fountain plating systems, are typically used in direct current or pulse-plating methods. In the plating process, the interconnect bump material completely fills vias on and over a portion of the top surface of the plating mask to produce a metal deposit in the form of a mushroom. This ensures that a sufficient volume of interconnect bump material is deposited to reliably achieve the desired ball size after reflow. In the via plating process, the photoresist has a sufficient thickness such that a suitable volume of the interconnect bump material is contained within the plating mask vias. A layer of copper or nickel may be electrodeposited to the plating vias before plating the interconnect bump material. This layer can act as a wettability basis for interconnect bumps at reflow.

After deposition of the interconnect bump material, the plating mask is stripped using a suitable solvent or other remover. Such removers are known in the art. The UBM structure is then selectively etched using known techniques to remove all metal around and around the interconnect bumps in the field region.

Alternatively, after the plating vias are formed in the photoresist layer, a tin-free metal interconnect structure, such as a pillar, may be deposited on the coupling features. Copper pillar is common. Typically, such a metal deposition is stopped before the plating via is fully charged. Such an interconnect structure, such as a copper pillar, can then be capped with a tin-containing layer by an electroplating method using the electroplating composition described above. The tin-containing layer is electrodeposited on the area defined by the plating vias. For this purpose, horizontal or vertical wafer plating systems, such as fountain plating systems, are typically used in direct current or pulse-plating methods. A layer of a top metal such as nickel may be electrodeposited to the plating vias at the top of the copper pillar prior to plating the tin containing layer. This top metal layer acts on the pure tin solder layer on a wettability basis and / or provides a barrier layer. The height of such a tin-containing layer may range from 20 to 50 mu m, but other heights may also be suitable and have substantially the same diameter as the interconnect structure to be deposited. After deposition of the tin-containing solder layer, the plating mask is sprinkled using a suitable solvent or other remover. Such removers are known in the art. The UBM structure is then selectively etched using known techniques to remove all metal around and around the interconnect bumps in the field region.

The wafer is optionally fluxed and heated in a reflow oven to a temperature where the tin-containing solder layer melts and flows into a substantially truncated substantially spherical shape. Heating methods are well known in the art and include, for example, infrared, conducting and convection methods and combinations thereof. The reflowed interconnect bumps are generally at the same location as the edge of the UBM structure. The heat treatment step may be performed in an inert gas atmosphere or air, and the specific process temperature and time may vary depending upon the particular composition of the interconnect bump material.

The tin-containing solder electrodeposited in the present composition is substantially free of voids when deposited (or plated), and preferably such solder is one reflow cycle, preferably a repeated reflow cycle, such as a three reflow cycle, There is virtually no void after the reflow cycle. Suitable reflow cycles include 5 heating and 2 cooling, using a temperature of 140/190/230/230/260 占 폚, a 30 second dwell time, a conveyor speed of about 100 cm / min, and a nitrogen flow rate of 40 cubic feet / Lt; RTI ID = 0.0 &gt; Sikama International, &lt; / RTI &gt; Alpha 100-40 flux (Cookson Electronics, Jersey City, New Jersey, USA) is a suitable flux used in this reflow process. As used herein, the term "void" refers to both the interface voids and the voids in the bulk tin containing layer. By "substantially free of voids" is meant using a Cougar microfocus X-ray system (YXLON International GmbH, Hamburg, Germany) that voids with a diameter of 3 μm, preferably 2 μm, more preferably more than 1 μm, are not visible do.

The present electroplating composition also has a relatively smooth surface when plated, i. E., 200 nm, preferably &lt; 150 nm, as measured using an optical roughness meter (Leica DCM3D, Leica Microsystems GmbH, Wetzlar, Germany) , And even more preferably an average surface roughness (R _a ) of? 100 nm.

Example 1 : An electroplating composition for depositing pure tin was prepared by mixing 75 g / L tin (with tin methane sulfonate), 140 g / L methanesulfonic acid, 8.8 g / L ethoxylated beta-naphthol nonionic surfactant , 9.7 g / L ethoxylated bisphenol A nonionic surfactant, 0.0166 g / L benzylidene acetone as a first crystal growth inhibitor, 0.1 g / L second crystal growth inhibitor methacrylic acid, 1.5 g / L alcohol , 1 g / L of commercially available antioxidant, and DI water (balance). The pH of the composition was < 1.

Example 2 : The composition of Example 1 was used to deposit pure tin on the conductive bonding features. A wafer segment of 4 cm x 4 cm with photoresist patterned vias of 75 [mu] m (diameter) x 50 [mu] m (depth) and preformed copper pillars of 37 [mu] m high was immersed in a plating cell containing the composition of Example 1 The pure tin layer was plated. The samples were plated at 8 A / dm &lt; ² &gt; The temperature of the bath was 25 캜. An insoluble gold-plated titanium electrode was used as an anode, and the wafer segment was a cathode. Electroplating was performed until a 23-m high mushroom-shaped tin cap was plated on top of the copper pillar. The shape of the obtained tin layer was examined with a Hitachi S2460 (TM) scanning electron microscope. The pure tin deposits were uniform, smooth, dense, and nodular.

Example 3 : Electroplating compositions for depositing tin-silver alloys were prepared by mixing 75 g / L tin (using tin methane sulfonate), 0.65 g / L (using silver methanesulfonate), 104 g / L methanesulfonic acid, A tetrafunctional block copolymer derived by sequentially adding EO and PO (EO: PO about 40:60, TETRONIC 90R4) to an ethylenediamine nonionic surfactant of 5 g / L, a first crystal growth of 0.0166 g / L Methacrylic acid as a second crystal growth inhibitor of 0.1 g / L, dithiaalkyldiol as a first silver complexing agent of 0.6 g / L, mercaptotetrazole as a second silver complexing agent of 3.1 g / L Derivative, 1.5 g / L alcohol solvent, 1 g / L commercial antioxidant, and DI water (balance). The pH of the composition was < 1.

A 4 cm x 4 cm wafer segment with 75 μm (diameter) x 72 μm (depth) photoresist patterned vias and a copper seed layer were dipped into a plating cell containing a tin-silver electroplating composition to form a tin- . The sample was plated at 8 A / dm ² in the bath. The temperature of the bath was 25 캜. An insoluble gold plated titanium electrode was used as an anode. Electroplating was performed until a 60 μm bump was plated. The resulting tin-silver solder bump deposits were flat and had a smooth shape with an average surface roughness of 150 nm as measured by a Leica DCM3D optical roughness meter. The tin-silver solder deposits were exposed to a Falcon 8500 instrument (Sikama International, Inc.) having 5 heating and 2 cooling zones at a temperature of 140/190/230/230/260 ° C, 30 second dwell time, and about 100 cm / min And a nitrogen flow rate of 40 cubic feet per hour. Solder deposits were added to Alpha 100-40 flux. The reflowed tin-silver deposit was evaluated on a Cougar microfocus X-ray system (YXLON International GmbH, Hamburg, Germany) to confirm that voids were absent.

Example 4 : A variety of tin alloy electroplating compositions were prepared by repeating the process of Example 3 and replacing the silver ion source with the source of the metal ion described in Table 1.

Example 5 : The electroplating compositions of Examples 1 and 3 were repeated except that the crystal growth inhibitor shown in Table 2 was used.

Comparative Example 1 : The procedure of Example 3 was repeated except that the amount of the first crystal growth inhibitor, benzylidene acetone, was 0.166 g / L. The resulting tin-silver bump deposits were considerably concave and warped to one side of the bump. In the evaluation of deposits by microfocus X-ray, formation of voids (> 3 μm) was observed after one reflow of the deposits.

Comparative Example 2 : The method of Example 3 was repeated except that the first crystal growth inhibitor was not used. The obtained tin-silver bump deposits had an average surface roughness (R _a ) of 800 nm or more as measured by a Leica DCM3D optical roughness meter, and the roughness was unacceptable.

Claims (10)

A tin ion source; Acid electrolytes; 0.0001 to 0.045 g / L of a first crystal growth inhibitor; An alpha, beta -unsaturated aliphatic carbonyl compound as a second crystal growth inhibitor selected from 0.005 to 0.75 g / L of a compound of formula (1) or (2); Nonionic surfactants; And water.

In the formula (1) and (2), each R ¹ is independently (C ₁ - ₆₎ alkyl, (C ₁ - ₆₎ alkoxy, hydroxy, or halo; R ² and R ³ are independently selected from H and (C ₁ - ₆₎ is selected from alkyl; R ⁴ is _{H, OH, (C 1 -} 6) alkyl or O (C ₁ - ₆₎ alkyl; m is an integer from 0 to 2; Each R ⁵ is independently (C ₁ - ₆₎ alkyl; Each R ⁶ is independently _{H, OH, (C 1 -} 6) alkyl, or O (C ₁ - ₆₎ is selected from alkyl; n is 1 or 2; And p is 0, 1 or 2. The composition of claim 1, further comprising a source of alloy metal ions. The composition of claim 1 wherein the alpha, beta -unsaturated aliphatic carbonyl compound is selected from an alpha, beta -unsaturated carboxylic acid, an alpha, beta -unsaturated carboxylic acid ester, an alpha, beta -unsaturated amide and an alpha, beta -unsaturated aldehyde. 4. The method of claim 3, α, β- unsaturated aliphatic carbonyl compound is a (meth) acrylic acid, crotonic acid, (C _{1 -6)} alkyl (meth) acrylates, (meth) acrylamide, (C _{1 -6)} alkyl Crotonate, crotonamide, crotonaldehyde or mixtures thereof. The composition of claim 1, wherein the first crystal growth inhibitor is selected from the group consisting of cinnamic acid, cinnamic aldehyde, benzylidene acetone, picolinic acid, pyridine dicarboxylic acid, pyridine carboxaldehyde, pyridine dicarboxaldehyde, or mixtures thereof. The composition of claim 1, wherein the first crystal growth inhibitor is present in an amount of 0.001 to 0.04 g / L. The method of claim 1, wherein the nonionic surfactant comprises an alkoxylated amine moiety. Providing a semiconductor wafer comprising a plurality of conductive bonding features; Contacting a semiconductor wafer with the composition of claim 1; A method for depositing a tin-containing layer on a semiconductor substrate, the method comprising applying a current density sufficient to deposit a tin-containing layer on a conductive bonding feature. 9. The method of claim 8, wherein the bonding feature comprises copper. The method of claim 8, wherein the tin-containing layer on the bonding feature is plated and has substantially no voids after one reflow cycle.