Nickel electroplating bath and method of using the same

Abstract

A nickel electroplating bath and a method of using the same to deposit nickel onto a substrate. The nickel deposit exhibits low co-planarity and bump height uniformity. The nickel electroplating bath comprises (a) a source of nickel ions; (b) a conducting salt; (c) a first plating additive; (d) a second plating additive; and (e) at least one of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers.

Description

FIELD OF THE INVENTION

[0001] The invention relates generally to a ECD (electrochemical deposition) nickel bath capable of producing a nickel deposits that exhibits low co-planarity for wafer level packaging applications.BACKGROUND OF THE INVENTION

[0002] Wafer bumping technology is well known and understood by those skilled in the art of wafer level packaging. The purpose of wafer bumping is to establish mechanical and electrical connections between the die and the substrate or printed circuit board within the IC device. The material and size of these bumps depend on various factors such as the device's cost, form factor, and electrical, mechanical, and thermal performance specifications. Typically, the bumps are cylindrical-shaped multilayer raised structures that are formed by ECD. A metal stack typically comprises a copper conductor, which is protected from oxidation by a diffusion barrier that also has a function of preventing copper interdiffusion into a subsequently deposited solder layer used for bonding. The solder may be tin-silver alloy, which can form brittle intermetallic with copper on thermal exposure if it is not protected by the diffusion barrier.

[0003] The diffusion barrier is typically ECD nickel or nickel alloy. It is critically important for the bumps to be of at least substantially uniform height so that the surface that is bonded thereto and attached to the bumps is parallel to the substrate.

[0004] Making sure that all of the bumps have a consistent height (i.e., low co-planarity) can be a challenge and it is desirable that the difference in bump height across the wafer be kept to a minimum. If co-planarity of bumps is high, the adhesion of a surface being attached might be compromised, which can reduce yield or can cause reliability problems.

[0005] Nickel electroplating baths typically include a source of nickel ions, a halide as nickel anode corrosion aid, boric acid as a buffer, one or more surfactants, one or more organic a additives, and other proprietary ingredients. However, these traditional baths have been found to be incapable of producing a nickel deposit that exhibits low co-planarity and high bump height uniformity. As well, boric acid is increasingly regulated and there is a desire for a boric acid free bath.SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a nickel electroplating bath for use in integrated circuit packaging applications, including wafer level packaging (WLP) applications.

[0007] It is another object of the present invention to provide a nickel plating bath for use as a diffusion barrier layer.

[0008] It is another object of the present invention to provide a nickel bath capable of producing a nickel deposit that exhibits low co-planarity.

[0009] It is another object of the present invention to provide a nickel plating bath that exhibits increased conductivity.

[0010] It is another object of the present invention to provide a nickel plating bath is configured to produce a nickel deposit that exhibits low co-planarity and bump height uniformity.

[0011] It is still another object of the present invention to provide a nickel electroplating bath that contains a low metal concentration, high electrolyte conductivity and that includes an alkene sulfonate additive to produce a nickel deposit that exhibits low co-planarity and bump height uniformity.

[0012] To that end, in one embodiment, the present invention relates generally to a metal electroplating bath comprising:

[0013] a. a source of nickel ions;

[0014] b. a conducting salt;

[0015] c. a first plating additive; and

[0016] d. a second plating additive; and

[0017] e. one or more of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers;

[0018] wherein the nickel electroplating bath is configured to deposit nickel exhibiting low co-planarity and high bump height uniformity.

[0019] In addition, the present invention also relates generally to a method of depositing a nickel layer on a substrate that is capable of achieving low co-planarity and bump height uniformity, the method comprises the steps of:

[0020] a. bringing the substrate and at least one counter electrode into contact with the nickel plating bath described above, which nickel plating bath comprises a source of nickel ions to be plated; and

[0021] b. applying an electrical current to the nickel plating bath to electroplate the nickel ions from the nickel plating bath onto the substrate.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention relates generally to a metal plating bath capable of / configured to provide a nickel deposit that exhibits low co-planarity and bump height uniformity.

[0023] As used herein, “a,”“an,” and “the” refer to both singular and plural referents unless the context clearly dictates otherwise.

[0024] As used herein, the term “about” refers to a measurable value such as a parameter, an amount, a temporal duration, and the like and is meant to include variations of + / −15% or less, preferably variations of + / −10% or less, more preferably variations of + / −5% or less, even more preferably variations of + / −1% or less, and still more preferably variations of + / −0.1% or less of and from the particularly recited value, in so far as such variations are appropriate to perform in the invention described herein. Furthermore, it is also to be understood that the value to which the modifier “about” refers is itself specifically disclosed herein.

[0025] As used herein, spatially relative terms, such as “beneath,”“below,”“lower,”“above,”“upper,”“front,”“back,” and the like, are used for ease of description to describe one element or feature's relationship to another element(s) or feature(s). It is further understood that the terms “front” and “back” are not intended to be limiting and are intended to be interchangeable where appropriate.

[0026] As used herein, the terms “comprises” and / or “comprising,” specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0027] In one embodiment, the present invention relates generally to a metal electroplating bath comprising:

[0028] a. a source of nickel ions;

[0029] b. a conducting salt;

[0030] c. a first plating additive; and

[0031] d. a second plating additive; and

[0032] e. one or more of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers;

[0033] wherein the nickel electroplating bath is configured to deposit nickel exhibiting low co-planarity and bump height uniformity.

[0034] In one embodiment, the metal plating bath is a nickel plating bath, preferably a nickel plating bath that is at least substantially free of boric acid. By “at least substantially free of boric acid” what is meant is that the metal plating bath contains less than 1 ppm boric acid, more preferably less than 0.5 ppm boric acid, most preferably less than 0.1 ppm boric acid. In a preferred embodiment, the metal plating bath is free of boric acid except for minor traces that may be caused by contamination.

[0035] In one embodiment, the source of nickel ions comprises a soluble nickel salt including, for example, a nickel salt selected from the group consisting of nickel carboxylate, nickel chloride, nickel bromide, nickel sulfate, nickel sulfamate, nickel fluoroborate, and combinations of the foregoing. In one embodiment, the soluble nickel salt comprises nickel sulfamate.

[0036] In one embodiment, the concentration of nickel ions of less than about 35 g / L, preferably less than about 30 g / L, even more preferably less than about 25 g / L. In one embodiment, the concentration of nickel ions in the nickel plating bath is between about 10 and about 35 g / L, preferably about 15 to about 25 g / L.

[0037] The inventors of the present invention have surprisingly discovered that the synergy in a nickel plating bath that has a low concentration of nickel ions in combination with an alkene sulfonate and that is highly conductive produces a nickel deposit with low co-planarity and bump height uniformity as further described herein.

[0038] In one embodiment, the one or more conducting salts are of the type and added to the plating bath of the invention in an amount sufficient to achieve a high solution conductivity, preferably a solution conductivity of at least 5.6 S / m or a solution conductivity of at least 5.8 S / M or a solution conductivity of at least 6 S / m. Examples of suitable conducting salts include, for example, sulfamate salts such as sodium sulfamate, ammonium sulfamate, or potassium sulfamate, which may be used alone or in combination. Other conducting salts including, for example, sulfate salts and chloride salts that have a high solubility, including sodium, potassium, lithium, and ammonium salts and that are easily soluble in the nickel plating composition. In one embodiment, the conducting salt comprises sodium sulfamate. In another embodiment, the conducting salt comprises ammonium sulfamate. The concentration of the conducting salt depends on the solubility of the conducting salt in the solution and is preferably within the range of about 20 to about 500 g / L, more preferably within the range of about 50 to about 300 g / L, more preferably within the range of about 75 to about 275 g / L, more preferably within the range of about 100 to about 250 g / L.

[0039] In one embodiment, the first plating additive is a Class 1 Brightener. Examples of Class 1 brighteners are brighteners are aromatic or unsaturated aliphatic sulfonic acids, sulfonamides, sulfonimides, sulfimides, and salts thereof, which may be used alone or in combination. Class I brighteners typically incorporate sulfur into the deposit, which reduces the internal tensile stress of the deposit and provides grain refinement. In one embodiment, the first plating additive comprises saccharine, preferably sodium saccharine. Examples of other Class 1 brighteners that can be used in the practice of the invention include, but are not limited to benzene sulfonic acid, 1,3,6-naphthalene sulphonic acid (sodium salt), and p-toluene sulfonamide. Combinations of these Class I brighteners may also be used. The concentration of the first plating additive is preferably within the range of about 20 mg / L to about 2 g / L, more preferably in the range of about 30 mg / L to about 1.7 g / L, or about 0.10 g / L to about 1.3 g / L or about 0.3 g / L to about 0.8 g / L.

[0040] The second plating additive is preferably an alkene sulfonate which may be, for example, sodium allyl sulfonate, vinyl sulfonate, or a combination thereof, by way of example and not limitation. The concentration of the second plating additive will depend in part on the particular unsaturated sulfonate that is used in the nickel electroplating bath. The concentration of the second plating additive is preferably within the range of about 0.2 to about 15 g / L, more preferably about 0.3 to about 11 g / L, more preferably about 1.5 to about 7 g / L.

[0041] While the inventors of the present invention have determined that the use of an alkene sulfonate as a second plating additive produces a good result, the inventors of the present invention have also discovered that the use of other sulfonates, including saturated sulfonates and alkyne sulfonates do not perform as well as alkene sulfonates. For example, the inventors of the present invention discovered that the use of propargyl sulfonate produced a nickel deposit that showed an increase in co-planarity. Therefore, in one embodiment, it is desirable that the nickel electroplating bath be at least substantially free of any saturated sulfonates such as sodium benzene sulfonate and bis-(3-sulfopropyl)-disulfide (SPS) and at least substantially free of any alkyne sulfonates. By at least substantially free what is meant is that nickel electroplating composition contains less than 1 ppm of any of these other sulfonates, preferably less than 0.1 ppm, and is most preferably free of any of these other sulfonates.

[0042] As discussed above, the nickel electroplating bath preferably also includes other additives that are suitable for use in a nickel, including at least one of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers. Other additives that are suitable for including in a nickel electroplating bath and that do not have a detrimental effect on the ability of the plating bath to achieve low co-planarity and bump height uniformity would also be usable in the nickel electroplating bath described herein.

[0043] The nickel electroplating bath of the present invention is mildly acidic and the pH can, preferably, range from about 2 to about 5. Various pH buffers can be added to the nickel electroplating bath to buffer the solution including one or more weak inorganic acids, and weak organic acids, inorganic bases and / or organic bases. Such acids may include, but are not limited to, inorganic acids such as phosphoric acid and boric acid. Organic acids such as acetic acid, amino acetic acid, oxalic, tartaric, citric and phthalic acid can be used. While boric acid can be used as a buffer, in one embodiment, the nickel electroplating bath is at least substantially free of boric acid. The buffers can be added in amounts as needed to maintain a desired pH range.

[0044] In one embodiment, the one or more surfactants include ionic surfactants such as anionic surfactants. Surfactants can be used in conventional amounts such as 0.05 g / L to 10 g / L, preferably about 0.1 to about 5 g / L, more preferably about 0.3 to about 1.0 g / L. Examples of suitable surfactants include, but are not limited to sodium, potassium or ammonium alkyl sulfates, alkyl sulfonates, alkyl sulfosuccinates and mixtures thereof.

[0045] In addition, in one embodiment, the nickel electroplating bath is also at least substantially free of any catalytic poisons such as lead, mercury, antimony, chromium, bismuth, thallium, cadmium, tellurium, arsenic, selenium, and other similar metals and metalloids.

[0046] In one embodiment, the nickel electroplating bath of the present invention comprises:

[0047] a. about 10 to about 35 g / L, preferably about 15 to about 25 g / L nickel ions;

[0048] b. about 20 to about 500 g / L, preferably about 50 to about 300 g / L, more preferably about 75 to about 225 g / L of a conducting salt;

[0049] c. about 20 mg / L to about 2 g / L, more preferably in the range of about 30 mg / L to about 1.7 g / L, or about 0.10 g / L to about 1.3 g / L or about 0.3 g / L to about 0.8 g / L of a first plating additive, preferably wherein the first plating additive comprises a Class 1 brightener;

[0050] d. about 0.2 to about 15 g / L, more preferably about 0.3 to about 11 g / L, more preferably about 1.5 to about 7 g / L of a second plating additive, preferably wherein the second plating additive comprises an alkene sulfonate; and

[0051] e. at least one of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers.

[0052] In one embodiment, the nickel electroplating bath of the present invention consists essentially of:

[0053] a. about 10 to about 35 g / L, preferably about 15 to about 25 g / L nickel ions;

[0054] b. about 20 to about 500 g / L, preferably about 50 to about 300 g / L, more preferably about 75 to about 225 g / L of a conducting salt;

[0055] c. about 20 mg / L to about 2 g / L, more preferably in the range of about 30 mg / L to about 1.7 g / L, or about 0.10 g / L to about 1.3 g / L or about 0.3 g / L to about 0.8 g / L of a first plating additive, preferably wherein the first plating additive comprises a Class 1 brightener;

[0056] d. about 0.2 to about 15 g / L, more preferably about 0.3 to about 11 g / L, more preferably about 1.5 to about 7 g / L of a second plating additive, preferably wherein the second plating additive comprises an alkene sulfonate;

[0057] e. at least one of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers; and

[0058] f. balance water.

[0059] By “consisting essentially of” what is meant is that the nickel electroplating bath is free of any ingredient that would result in a nickel deposit that does not exhibit low co-planarity and / or excellent bump height uniformity. For example, the nickel electroplating bath must be at least substantially free (i.e., less than 1 ppm or less than 0.5 ppm or less than 0.1 ppm) of any strong suppressors, including Class II brighteners such as N,N-diethyl-2-propyne-1-amine, propargyl alcohol, propargyl alcohol ethoxylate, propargyl alcohol propoxylate, 1-(3-sulfopropyl)-2-vinylpyridinium betaine, 1-(3-sulfopropyl)-pyridinium betaine, and 2-butyne-1,4-diol.

[0060] In one embodiment, the nickel electroplating bath of the present invention consists of:

[0061] a. about 10 to about 35 g / L, preferably about 15 to about 25 g / L nickel ions;

[0062] b. about 20 to about 500 g / L, preferably about 50 to about 300 g / L, more preferably about 75 to about 225 g / L of a conducting salt;

[0063] c. about 20 mg / L to about 2 g / L, more preferably in the range of about 30 mg / L to about 1.7 g / L, or about 0.10 g / L to about 1.3 g / L or about 0.3 g / L to about 0.8 g / L of a first plating additive, preferably wherein the first plating additive comprises a Class 1 brightener;

[0064] d. about 0.2 to about 15 g / L, more preferably about 0.3 to about 11 g / L, more preferably about 1.5 to about 7 g / L of a second plating additive, preferably wherein the second plating additive comprises an alkene sulfonate;

[0065] e. at least one of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers; and

[0066] f. balance water.

[0067] The present invention provides an improved nickel electroplating solution that is configured to deposit a nickel layer that exhibits low co-planarity and that exhibits the following properties:

[0068] a. Within feature (WIF) uniformity of <10%;

[0069] b. Within die (WID) uniformity of <15%;

[0070] c. Surface morphology (Ra) of <20 nm;

[0071] d. No pinholes or voids; and

[0072] e. Internal stress that is low compressive to neutral.

[0073] It is important that the nickel deposit exhibits low co-planarity without sacrificing deposit ductility and internal stress. The internal stress of the planted nickel deposit can be compressive stress or tensile stress. Compressive stress is where the deposit contracts to relieve the stress. In contrast, tensile stress is where the deposit expands. Highly stressed deposits can result in blisters, warping, or cause the deposit to separate from the substrate, and deposits with high tensile stress can also cause warping in addition to cracking and reduction in fatigue strength, resulting in loss of adhesion. Therefore, it is also desirable that an internal stress of the nickel deposit internal stress is low compressive to neutral. For example, the internal stress may be in the range of about 0 to about −70 MPa, preferably about 0 to about −50 MPa.

[0074] The inventors of the present invention have surprisingly discovered that good results in terms of low co-planarity can be achieved when using the metal plating bath described herein to deposit nickel onto an underlying substrate.

[0075] In one embodiment, the present invention relates generally to a method of depositing nickel on a substrate, wherein the nickel deposit exhibits low co-planarity. In one embodiment, the nickel is deposited on bumps of a wafer or other integrated circuit substrate. As described above, these “bumps” connect the die to the substrate and become part of the package

[0076] Co-planarity (COP) is a function of the bump height (BH) of a plated nickel bump as measured from a midpoint of a bump to its base. To determine co-planarity, the bump height of each bump on a die is measured and co-planarity is defined as the difference between the maximum BH and the minimum BH on the die. COP % can be calculated from COP and average BH as further described herein. In one embodiment, the COP % is less than about 6.0%, preferably less than about 5.0%, more preferably less than about 4.0%, more preferably less than about 3.5%.

[0077] Another desirable property of the plated nickel bumps is bump height uniformity which can be calculated as Within Die % (WID %) uniformity and it is typically desirable that the value for WID % uniformity to be less than about 15%. The WID % uniformity is determined by the following calculation:WID⁢ %⁢ uniformity=(Max⁢ BH-Min⁢ BH⁢ in⁢ a⁢ die) / (2⋆BH⁢ average).

[0078] In one embodiment, the WID % uniformity achieved using the nickel electroplating bath described herein is less than about 4.00%, preferably less than about 3.50%, more preferably less than about 3.20%, more preferably less than about 2.60%, more preferably less than about 2.20%.

[0079] In one embodiment, the method comprises the steps of:

[0080] a. Bringing the substrate and at least one counter electrode into contact with the nickel plating bath described above, which nickel plating bath comprises a source of nickel ions to be plated; and

[0081] b. Applying an electrical current to the nickel plating bath to electroplate the nickel ions from the nickel plating bath onto the substrate.

[0082] In one embodiment, the substrate is a semiconductor die or wafer and the nickel is deposited on bumps on the substrate. In one embodiment, the bumps comprise copper and the nickel is deposited on the copper. In one embodiment, the substrate comprises copper and the nickel is deposited on the copper substrate. In one embodiment, a conductive layer, such as a copper conductive layer is deposited on the nickel deposit. In another embodiment, a solder cap or other layer is deposited over the nickel deposit.

[0083] In one embodiment, the nickel plating bath is maintained at a temperature within the range of about 40° C. to about 60° C. In some embodiments, the electrolyte may be agitated by stirring or other methods known to those skilled in the art.

[0084] The current density during plating is preferably within the range of about 0.5 to about 10 ASD, more preferably about 2 to about 5 ASD.

[0085] In one embodiment, the counter electrode is a soluble nickel anode although insoluble anodes can also be used.

[0086] In some embodiments, the pH of the electrodeposition composition is within the range of 2 to 5, preferably in the range of 3.5 to 4.5.

[0087] In some embodiments, the plating time may be from 10 seconds to about 60 minutes for some applications. More preferably, the plating time may be from 30 seconds to about 10 minutes depending on the application requirements. One of skill in the art would recognize that the plating time and the current density may be tuned in order to achieve a target thickness. In one embodiment, the nickel layer is plated to a thickness of between about 1 μm to about 50 μm, preferably about 2 μm to about 25 μm.

[0088] In one embodiment, the present invention also relates generally to a semiconductor wafer comprising a plurality of bumps, wherein the plurality of bumps are metallized with a nickel electrodeposition layer and where the nickel layer exhibits low co-planarity and bump height uniformity.

[0089] The invention will now be described in reference to the following non-limiting examples.

[0090] In these examples, it was a goal to have a minimal difference between the highest plated and lowest plated bumps on a wafer, i.e., low coplanarity.

[0091] In each of the examples, a nickel electroplating bath was prepared and used to plate a nickel deposit on a plurality of bumps on a semiconductor wafer. Measurements of the nickel deposit on the semiconductor wafer were determined as follows:

[0092] a. Minimum, maximum, and midpoints of the plated nickel deposit were generated by microscope software.

[0093] b. Bump Within Feature uniformity (WIF)=maximum point to the minimum point of the plated nickel deposit.

[0094] c. Bump Height (BH)=midpoint to base

[0095] d. Average BH=average of a representative sampling of total bumps across a die.

[0096] e. WID (%) uniformity=(Max BH-Min BH in a die) / (2*BH average)

[0097] f. WIF (%) uniformity=(average WIF / Average BH)*100

[0098] g. Co-planarity (COP)=Max BH-Min BH in a die

[0099] h. Co-planarity (COP %)=(COP / Avg BH)*100

[0100] Table 1 describes the parameters of two different nickel plating baths. The first bath (Bath 1) is a conventional nickel plating bath and the second bath (Bath 2) is an improved nickel plating bath in accordance with the present invention.TABLE 1Nickel plating bath parametersConventional NiLow COP NiAlternativeBathBathConventional BathParameter(Bath 1)(Bath 2)(Bath 3)Ni (g / L)502075Conducting salt (g / L)020001st Additive (g / L)0.320.320.482nd Additive (g / L)070Buffer (g / L)303030Anti-pitting surfactant (g / L)0.50.50.5Anode corrosion additive (g / L)101010Temperature (° C.)404040-60Current density (ASD)2-5Example 1

[0101] Nickel plating Baths 1, 2, and 3 were prepared as described in Table 1. Each of these plating compositions was used to deposit a nickel layer on a copper substrate to a thickness of 6 μm. Electroplating was conducted at a current density of 3 ASD. No conducting salt was used in any of the baths and 0.5 g / L of the first additive was used in all of the compositions. The results obtained are presented in Table 2.TABLE 2PlatingAvg.ThicknessRaBHCOPCOPBathComposition(μm)WID %WIF %(nm)(μm)(μm)%Bath 13 ASD66.3341.489125.2800.66912.67Bath 2*No conducting salt63.9982.45695.5270.4417.98Bath 30.5 g / L 1st Additive65.2371.901155.6530.59210.47Bath 4*63.46210.837115.5090.3826.93

[0102] In each of Baths 2 and 4, 7 g / L of the 2nd Additive were added to the composition. The composition of Bath 2 is described above in Table 1. The composition of Bath 4 was the composition of Bath 3 with the addition of the 2nd Additive.

[0103] As shown in Table 2, Baths 2 and 4 exhibited much lower WID % uniformity demonstrating bump height uniformity. In addition, the COP was also reduced in each deposit as compared with the use of Bath 1 and Bath 3. Table 2 demonstrates the improved effects in terms of WID % uniformity and low co-planarity that can be achieved when using a bath in which the 2nd Additive has been added.Example 2

[0104] Nickel plating Baths 1 and 2 were prepared as described in Table 1. Each of these plating compositions was used to deposit a nickel layer on a copper substrate to a thickness of 6 μm. Electroplating was conducted at a current density of 3 ASD. The results obtained are presented in Table 3.

[0105] As seen in Table 3, Bath 2 (with the 2nd Additive) provided the best results in terms of WID % uniformity and low-coplanarity. Bath 2 as compared with Bath 1 contained a lower concentration of nickel with an increased concentration of the conducting salt.

[0106] Based on the results of Tables 2 and 3, it can be seen that both the presence of the 2nd Additive and the conducting salt contribute to a nickel deposit that exhibits low co-planarity along with good results in terms of WID % uniformity.

[0107] Bath 2 was then electrolyzed to 50 Amp*hour / liter (Ah / L). As seen in Table 3, the aged baths still exhibited low co-planarity and the co-planarity was lower than the co-planarity of Bath 1 or Bath 2 without the 2nd Additive. The results for WID % uniformity were also good.TABLE 3PlatingThicknessRaAvg. BHCOPBath(μm)WID %WIF %(nm)(μm)(μm)COP %Bath 164.9670.73985.3060.5279.93Bath 2 without 2nd63.4791.01395.2490.3656.95AdditiveBath 261.6942.167115.5860.1893.38Bath 2, 25 Ah / L Aged62.1850.96175.2440.2294.37Bath 2, 50 Ah / L Aged62.5501.916105.4340.2775.10

[0108] Table 4 provides the results for film resistivity, solution resistivity and conductivity for Bath 1 and Bath 2.TABLE 4Film Resistivity, Solution Resistivity, and ConductivityCurrentFilmSheetSolutionSolutionDensityThicknessResistanceTemperatureResistivityConductivityBath(ASD)(μm)(mΩ / sq)(° C.)(Ω-cm)(S / m)Bath 15338.739RT (25° C.)18.065.537Bath 25339.201RT (25° C.)15.316.532

[0109] Table 5 provides the results for film impurities for Bath 1, Bath 2 and the aged Bath 2 and Table 6 provides the results for stress and current efficiency.TABLE 5Film Impurities -- SIMSImpurity (ppmw)COSClNNaTotalBath 119.319.6109.30.11.80.03150.1Bath 2, Fresh bath220.1463.89162.20.085.920.08452.3Bath 2, 25 Ah / L Aged74.5829.0171.430.082.610.05177.8Bath 2, 50 Ah / L Aged138.8335.3681.640.062.120.06258.1TABLE 6Stress and Current EfficiencyBathStress (MPa)CommentsCurrent EfficiencyBath 1−51.2Compressive97.26%Bath 2, Fresh bath−48.7Compressive95.85%Bath 2, 25 Ah / L Aged−71.4Compressive95.85%Bath 2, 50 Ah / L Aged−64.3Compressive96.79%Table 7 presents a summary of the results for the nickel deposit obtained using Bath 2.TABLE 7Summary of ResultsGoalCriteriaLow COP Results with Bath 2Reduce COP<0.53μm0.189μmWithin Feature (WIF)<10%2.167%Within Die (WID)<15%1.694%Surface Morphology (Ra)<20nm11nmTemperature<45°C.40°C.No pinholes / voidsNoneNoneInternal StressCompressive−48.7 MPa CompressiveExample 3Nickel plating baths 1, 2, and 3 were prepared as described in Table 1. Each of these plating compositions was used to deposit a nickel layer on a copper substrate to a thickness of 6 μm. Electroplating was conducted at a current density of 3 ASD.

[0112] As shown in Table 8, several different compounds were used as the second additive, including sodium ally sulfonate, vinyl sulfonate, and propargyl sulfonate. Of these, propargyl sulfonate did not work at all and the values for WID % uniformity and co-planarity were much worse even then the baseline results obtained with Bath 1. Thus, it can be seen that propargyl sulfonate had a detrimental effect.

[0113] In addition, the concentration of the second additive was varied and it can be seen that the concentration of the second additive also had an effect. That is, while increasing the concentration of sodium allyl sulfonate from 3500 ppm to 7000 ppm had a positive effect on WID % uniformity, roughness and co-planarity, once the concentration was doubled to 14000 ppm, the values for roughness were higher than at lower concentrations.

[0114] As also shown in Table 8, a nickel plating bath prepared with 7000 ppm sodium allyl sulfonate as the 2nd Additive but without a conducting salt performed poorly. Thus, it can be seen that the best results are achieved when using a conducting salt in combination with the 2nd Additive and other ingredients of the nickel plating bath.

[0115] Thus it can be seen that the present disclosure advantageously provides an improved nickel electroplating composition that includes a variety of additives that contribute to a nickel deposit that exhibits low co-planarity and has good WID % uniformity and good WIF % uniformity.TABLE 8PlatingConc.ThicknessRoughnessChemistry2nd Additive(ppm)(μm)WID %WIF %(nm)Bath 1 - 50 g / LNone064.9670.7398Ni, noconducting salt,0.32 g / L 1stAdditiveBath 2 - 20 g / LNone063.4791.0139nickel, 200 g / Lconducting salt,0.32 g / L 1stAdditiveBath 3 - 75 g / LNone065.2371.90116nickel, noconducting salt,0.48 g / L 1stAdditiveBath 2 - 20 g / LSodium allyl700066.0124.0865nickel, nosulfonateconducting salt,0.32 g / L 1stAdditiveBath 2 - 20 g / LSodium Allyl350062.0952.16711nickel, 200 g / LSulfonate700061.6942.16711conducting salt,1400061.9191.942280.32 g / L 1stVinyl Sulfonate200063.1296.49134Additive400063.0233.56515Propargyl564.0282.17725Sulfonate73610.8081.18523AvgSolutionSolutionBHCOPCOPConductivityResistivityChemistry2nd Additive(μm)(μm)%(S / m)(Ω· cm)Bath 1 - 50 g / LNone5.3060.5279.935.53718.06Ni, noconducting salt,0.32 g / L 1stAdditiveBath 2 - 20 g / LNone5.2490.3656.956.66115.00nickel, 200 g / Lconducting salt,0.32 g / L 1stAdditiveBath 3 - 75 g / LNone5.6530.59210.475.34418.82nickel, noconducting salt,0.48 g / L 1stAdditiveBath 2 - 20 g / LSodium allyl5.9250.71312.034.35722.88nickel, nosulfonateconducting salt,0.32 g / L 1stAdditiveBath 2 - 20 g / LSodium Allyl5.4990.234.18nickel, 200 g / LSulfonate5.5860.1893.386.53215.31conducting salt,5.4730.213.840.32 g / L 1stVinyl Sulfonate5.4630.3426.26Additive5.4310.3286.04Propargyl5.3860.4348.06Sulfonate5.3661.15921.60Additional EmbodimentsClause 1: A nickel electroplating bath comprising:a. a source of nickel ions;b. a conducting salt;

[0118] c. a first plating additive; and

[0119] d. a second plating additive,

[0120] e. at least one or more of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers;

[0121] wherein the nickel electroplating bath is configured to deposit nickel exhibiting low co-planarity.Clause 2: The nickel electroplating bath according to Clause 1, wherein the source of nickel ions is selected from the group consisting of nickel carboxylates, nickel chloride, nickel bromide, nickel sulfate, nickel sulfamate, nickel fluoroborate, and combinations of the foregoing.Clause 3: The nickel electroplating bath according to Clause 1 or Clause 2, wherein the source of nickel ions comprises nickel sulfamate.Clause 4: The nickel electroplating bath according to any of Clauses 1 to 3, wherein the conducting salt comprises a sulfamate salt, wherein the sulfamate salt is selected from the group consisting of sodium sulfamate, ammonium sulfamate, potassium sulfamate, and combinations of the foregoing.Clause 5: The nickel electroplating bath according to any of Clauses 1 to 4, wherein the first plating additive comprises a brightener comprising an aromatic or unsaturated sulfonic acid, sulfonamide, sulfonimide, sulfimide, or salt thereof.Clause 6: The nickel electroplating bath according to any of Clauses 1 to 5, wherein the second plating additive is selected from the group consisting of sodium allyl sulfonate, vinyl sulfonate, and combinations thereof.Clause 7: The nickel electroplating bath according to any of Clauses 1 to 6, wherein the nickel electroplating bath comprises:

[0122] a. about 10 to about 30 g / L nickel ions;

[0123] b. about 20 g / L to about 500 g / L of a conducting salt, wherein the conducting salt comprises a sulfamate salt;

[0124] c. about 20 mg / L to about 2 g / L, more preferably in the range of about 30 mg / L to about 1.7 g / L, or about 0.10 g / L to about 1.3 g / L or about 0.3 g / L to about 0.8 g / L of a first plating additive, wherein the first additive comprises a Class 1 brightener; and

[0125] d. about 0.2 to about 15 g / L, more preferably about 0.3 to about 11 g / L, more preferably about 1.5 to about 7 g / L of a second plating additive, preferably wherein the second additive comprises an alkene sulfonate.Clause 8: A method of a method of depositing a nickel layer on a substrate that is capable of achieving low coplanarity, the method comprises the steps of:

[0126] a. bringing the substrate and at least one counter electrode into contact with the nickel plating bath of any of Clauses 1 to 7; and

[0127] b. applying an electrical current to the nickel plating bath to electroplate the nickel ions from the nickel plating bath onto the substrate.Clause 9: The method of Clause 8, wherein the substrate is a semiconductor wafer and the nickel layer is deposited on bumps disposed on the semiconductor wafer.Clause 10: The method any of Clauses 8 to 9, wherein a within die % (WID %) uniformity of the nickel deposit is less than about 3.50%, optionally wherein the WID % is less than about 2.20%, wherein the WID % uniformity is determined by the following calculation:WID⁢ %⁢ uniformity=(Max⁢ BH-Min⁢ BH⁢ in⁢ a⁢ die) / (2⋆BH⁢ average).

Claims

1. A nickel electroplating bath comprising:a. a source of nickel ions;b. a conducting salt;c. a first plating additive;d. a second plating additive, ande. at least one of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers;wherein the nickel electroplating bath contains less than 1 ppm of any ingredient that would result in a nickel deposit that does not exhibit low co-planarity or hump height uniformity, andwherein the nickel electroplating bath is configured to deposit nickel exhibiting low co-planarity and bump height uniformity.

2. The nickel electroplating bath according to claim 1, wherein the source of nickel ions is selected from the group consisting of nickel carboxylates, nickel chloride, nickel bromide, nickel sulfate, nickel sulfamate, nickel fluoroborate, and combinations of the foregoing.

3. The nickel electroplating bath according to claim 2, wherein the source of nickel ions comprises nickel sulfamate.

4. The nickel electroplating bath according to claim 1, wherein the conducting salt comprises a sulfamate salt, wherein the sulfamate salt is selected from the group consisting of sodium sulfamate, ammonium sulfamate, potassium sulfamate, and combinations of the foregoing.

5. The nickel electroplating bath according to claim 1, wherein the first plating additive comprises a brightener comprising an aromatic or unsaturated sulfonic acid, sulfonamide, sulfonimide, sulfimide, or salt thereof.

6. The nickel electroplating bath according to claim 1, wherein the second plating additive is an alkene sulfonate.

7. The nickel electroplating bath according to claim 6, wherein the alkene sulfonate is selected from the group consisting of sodium allyl sulfonate, vinyl sulfonate, and combinations thereof.

8. The nickel electroplating bath according to claim 1, wherein the nickel electroplating bath comprises:a. about 10 to about 30 g / L nickel ions;b. about 20 to about 500 g / L of the conducting salt, wherein the conducting salt comprises a sulfamate salt;c. about 20 mg / L to about 2 g / L of the first plating additive, wherein the first additive comprises a Class 1 brightener; andd. about 0.2 to about 15 g / L of the second plating additive, wherein the second additive comprises an unsaturated sulfonate.

9. A method of a method of depositing a nickel layer on a substrate, the method comprises the steps of:a. bringing the substrate and at least one counter electrode into contact with the nickel electroplating bath of claim 1; andb. applying an electrical current to the nickel plating bath to electroplate the nickel ions from the nickel electroplating bath onto the substratewherein the nickel layer deposited on the substrate exhibits low co-planarity and bump height uniformity.

10. The method of claim 9, wherein a within die % (WID %) uniformity of the nickel layer is less than about 3.50%, wherein the WID % uniformity is determined by the following calculation:WID %=(Max BH−Min BH in a die) / (2*BH average).

11. The method of claim 10, wherein the WID % uniformity is less than about 2.20%.

12. The method of claim 9, wherein the solution conductivity of the nickel plating bath is at least about 5.6 S / m.

13. The method of claim 12, wherein the solution conductivity of the nickel plating bath is at least about 6.0 S / m.

14. The nickel electroplating bath according to claim 1, wherein the nickel electroplating bath contains less than 1 ppm of a strong suppressor.

15. The nickel plating bath according to claim 14, wherein the strong suppressor is selected from the group consisting of saturated sulfonates, alkyne sulfonates, N,N-diethyl-2-propyne-1-amine, propargyl alcohol, propargyl alcohol ethoxylate, propargyl alcohol propoxylate, 1-(3-sulfopropyl)-2-vinylpyridinium betaine, 1-(3-sulfopropyl)-pyridinium betaine, and 2-butyne-1,4-diol.

16. A nickel electroplating bath consisting essentially of:a. about 10 to about 35 g / L nickel ions;b. about 20 to about 500 g / L of a conducting salt;c. about 20 mg / L to about 2 g / L of a first plating additive comprising a Class 1 brightener;d. about 0.2 to about 15 g / L of a second plating additive comprising an alkene sulfonate;e. at least one of one or more nickel anode corrosion additives, one or more surfactants, and one or more pH buffers; andf. balance water.

17. The method of claim 9, wherein the substrate comprises an integrated circuit substrate or a wafer, wherein the substrate comprises a plurality of bumps and the nickel layer is electroplated on the plurality of bumps.

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