COMPOSITIONS FOR GOLD ELECTRODEPOSITION AND METHOD OF USING THE SAME

Abstract

A gold electroplating bath comprising (a) a source of gold ions, (b) a sulfite compound, (c) a chelating agent, (d) an organic accelerator, (e) a suppressor, (f) optionally, a pH adjuster, and (g) balance water. The gold electroplating bath can be used for electroplating a gold deposit onto a substrate comprising one or more features.

Description

FIELD OF THE INVENTION

The present invention relates generally to a gold electroplating bath and a method for gold electrodeposition.

BACKGROUND OF THE INVENTION

Electrolytic copper metallization is commonly used to provide electrical interconnection by filling interconnects in a wide variety of applications, including semiconductor integrated circuit (IC) devices and microelectromechanical systems (MEMS).

Radio frequency (RF) technology, such as smartphones, wireless base stations, wearable devices (e.g., smartwatches), medical devices (e.g., hearing aids), and other devices requiring wireless connectivity, include these semiconductor IC devices. RF technology relies on filters to convert an input signal to an output signal according to its frequency and permit desirable frequencies to pass and block all other frequencies.

Bulk acoustic wave (BAW) filters provide good performance and act at frequencies above 1.5 GHZ as needed for 4G and 5G telecommunication applications. A critical component of the BAW filter is the acoustic resonator, which amplifies or absorbs acoustic energy at specific frequencies to trap acoustic energy in the resonator, and each BAW filter may include an array of acoustic resonators.

An example of a resonator is a film bulk acoustic resonator (FBAR). An FBAR filter (i.e., a BAW filter comprising at least one FBAR) typically comprises of a piezoelectric thin film disposed between two electrodes and acoustically isolated from the surrounding medium. The thickness of the piezoelectric thin film determines the resonant frequency due to the FBAR filter resonating in the vertical direction. Development of the FBAR filter framework involves carving out an air cavity using reactive ion etching (RIE) to isolate the resonator. The air cavity acts as an insulator for the resonator by trapping acoustic energy. This provides for low insertion loss (which is desirable for applications where signal strength is important), a high quality (Q) factor, and a compact size necessary for the next generation of devices. The “Q factor” is a dimensionless parameter that describes how under-damped a resonator is and characterizes a bandwidth of the resonator relative to its center frequency (i.e., the ratio of the acoustic energy stored to the power dissipated).

RF technology generally requires high efficiency and reliability and the trend towards smaller/more compact sizes and increased circuit density necessitates decreasing the dimensions of semiconductor IC devices and therefore the interconnect features contained therein. In addition, these interconnect features need to have comparable thermal and electrical conductivities but superior resistance to corrosion compared to the performance of a traditional copper fill.

As semiconductor IC device architecture gets smaller, there is a need to increase the bottom-up growth speed for filling interconnect features. That is, the metal must fill “faster” in the sense that the rate of growth in the vertical direction must be substantially greater (e.g., 50%, 75%, or more) than the rate of growth in the horizontal direction. The extraordinary speed of bottom-up growth on these fine structures generates a significantly large dimension of overplating humps that require a higher concentration of leveler in copper electroplating baths used to fill interconnect features in order to provide the desired leveling effect. However, further increasing the leveler concentration may reduce the superfilling speed which is especially critical for filling interconnect features.

As an alternative metal to improve performance, gold may be used to fill interconnect features. However, in addition to superfilling and overplating issues, micro-defects may form to include, for example, the formation of internal voids and microvoids inside the interconnect features. As gold is deposited on the walls and top entry of an interconnect feature, “pinch off” may occur and thereby close access to the depths of the interconnect feature. An internal void can form in the interconnect feature if gold solution is prevented from flowing into the interconnect feature during the electrolytic process. This is significant because an internal void may interfere with electrical connectivity through the interconnect feature. Microvoids can form during or after electrolytic gold deposition due to uneven gold growth or grain recrystallization that happens after gold electroplating. Other defects include surface protrusions, which are isolated deposition peaks that occur at localized high current density sites and localized impurity sites.

Due in part to the miniaturization of semiconductor IC devices, the gold electroplating bath chemistry of the prior art often fails to provide for the bottom-up filling of interconnect features required to form defect free or substantially defect-free interconnects.

U.S. Pat. No. 12,173,424 to Inoue et al., the subject matter of which is herein incorporated by reference in its entirety, describes an electroplating solution that includes thallium and bismuth as crystal modifiers, used in an electrolytic deposition reaction to fill vias with a gold deposit.

U.S. Pat. No. 10,889,908 to Josell et al., the subject matter of which is herein incorporated by reference in its entirety, describes an electrolyte that includes lead, thallium, bismuth, and antimony as an accelerator to superconformally fill gold in recessed features.

There remains a need in the art for an improved gold electroplating bath that can suppress sidewall growth and enable the bottom-up filling of interconnect features to form defect-free or substantially defect-free interconnects. In addition, there remains a need in the art for an improved gold electroplating bath that does not include heavy metals (i.e., lead, arsenic, mercury, cadmium, bismuth, thallium, and antimony).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved gold electroplating bath.

It is another object of the present invention to provide an improved gold electroplating bath for the filling of vias and trenches.

It is still another object of the present invention to provide an improved gold electroplating bath that is free of cyanide.

It is still another object of the present invention to provide an improved gold electroplating bath that is free of heavy metals such as lead, arsenic, mercury, cadmium, bismuth, thallium, and antimony.

It is still another object of the present invention to provide an improved gold electroplating bath that prevents defects such as void formation.

It is still another object of the present invention to provide an improved gold electroplating bath that suppresses sidewall growth.

It is still another object of the present invention to provide an improved gold electroplating bath that enables the rapid and complete bottom-up filling of interconnect features.

It is still another object of the present invention to provide an improved gold electroplating bath that enables gold filling with high thermal conductivity.

It is still another object of the present invention to provide an improved gold electroplating bath that enables gold filling with good electrical conductivity.

It is still another object of the present invention to provide an improved gold electroplating bath that enables gold filling with excellent resistance to corrosion.

To that end, in one embodiment, the present invention relates generally to a gold electroplating bath comprising:

• • a source of gold ions;
  • a complexing agent;
  • an organic accelerator;
  • a suppressor;
  • optionally, a pH adjuster; and
  • balance water.

Additionally, the present invention also relates generally to a method for electroplating a gold deposit onto a substrate, wherein the substrate comprises one or more features, the method comprising:

• • a) bringing the substrate into contact with the gold electroplating bath described herein, and
  • b) supplying electrical current to the gold electroplating bath to deposit gold onto the substrate and fill the one or more features by bottom-up deposition.

BRIEF DESCRIPTION OF THE FIGURES

For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying figures, in which:

FIG. 1 depicts a SEM of a gold deposit produced in accordance with Comparative Example 1, showing at least one partially filled interconnect feature.

FIGS. 2A and 2B depict a SEM of a gold deposit produced in accordance with Comparative Example 2. FIG. 2A shows at least one partially filled interconnect feature and FIG. 2B shows at least one fully filled interconnect feature.

FIG. 3 depicts a SEM of a gold deposit produced in accordance with Comparative Example 3, showing at least one partially filled interconnect feature.

FIGS. 4A and 4B depict a SEM of a gold deposit produced in accordance with Example 4. FIG. 4A shows at least one partially filled interconnect feature and FIG. 4B shows at least one fully filled interconnect feature.

FIGS. 5A and 5B depict a SEM of a gold deposit produced in accordance with Example 5. FIG. 5A shows at least one partially filled interconnect feature and FIG. 5B shows at least one fully filled interconnect feature.

FIG. 6 depicts a SEM of a gold deposit produced in accordance with Example 6, showing at least one fully filled interconnect feature.

FIG. 7 depicts a SEM of a gold deposit produced in accordance with Example 7, showing at least one fully filled interconnect feature.

FIG. 8 depicts a SEM of a gold deposit produced in accordance with Example 8, showing at least one fully filled interconnect feature.

FIG. 9 depicts a SEM of a gold deposit produced in accordance with Example 9, showing at least one partially filled interconnect feature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors of the present invention have discovered that a gold electroplating bath as described herein can promote bottom-up filling of interconnect features in semiconductor IC devices while preventing void formation. The gold plating baths of the present invention generally include one or more suppressors that have been traditionally used as levelers in copper electroplating baths. The inventors of the present invention have discovered that these suppressors can also have a beneficial effect when used in a gold electroplating bath.

It should be understood that the disclosed embodiments are merely illustrative of the present disclosure, which may be embodied in various forms.

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

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.

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.

As used herein, the terms “comprise(s)” 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.

As used herein, the term “substantially free” or “essentially free” if not otherwise defined herein for a particular element or compound means that a given element or compound is not detectable by ordinary analytical means that are well known to those skilled in the art of metal plating for bath analysis. Such methods typically include atomic absorption spectrometry, titration, UV-Vis analysis, secondary ion mass spectrometry, and other commonly available analytical techniques.

As used herein, the term “features” refers to vias, through-silicon vias (TSV), trenches, pillars, pads, bumps, etc. that may be present on or in a microelectronic (i.e., semiconductor) substrate.

As used herein, the term “interconnect feature” refers to a feature such as a via or trench formed in a dielectric substrate which is then filled with metal to yield an electrically (and/or thermally) conductive interconnect.

All amounts are percent by weight unless otherwise noted. All numerical ranges are inclusive and combinable in any order except where it is local that such numerical ranges are constrained to add up to 100%. The term “average” is equivalent to the mean value of a sample.

As used herein, the terms “composition,” “bath,” “electrolyte,” and “solution” are used interchangeably throughout this specification.

As used herein, the terms “bottom-up filling,” “super filling,” and “superconformal filling” are used interchangeably throughout this specification.

The present invention is directed to a composition and a method for depositing gold or gold alloys. The inventors of the present invention have found, in some instances, it is favorable to replace copper with gold to form interconnects in semiconductor substrates because while gold has slightly lower thermal and electrical conductivity than copper, it also has superior resistance to corrosion compared to copper.

In one embodiment, the present invention relates generally to a gold electroplating bath comprising:

• • a source of gold ions;
  • a complexing agent;
  • an organic accelerator;
  • a suppressor;
  • optionally, a pH adjuster; and
  • balance water.

The source of gold ions used in the gold electroplating bath may be selected from sources of gold(I) ions and sources of gold(III) ions. Suitable sources of gold(I) ions include, for example, gold(I) salts comprising gold thiosulfate compounds, gold sulfite compounds, and gold(I) halides. Gold thiosulfate compounds may include alkali gold thiosulfates such as trisodium gold thiosulfate or tripotassium gold thiosulfate. Gold sulfite compounds may include alkali gold sulfites such as sodium gold sulfite and potassium gold sulfite, as well as ammonium gold sulfite. Gold(I) halides may include gold(I) chloride. Suitable sources of gold(III) ions include gold(III) halides such as gold(III) trichloride. In one embodiment, the source of gold(I) ions comprises a gold sulfite compound.

In one embodiment, the concentration of the gold compound (i.e., the source of gold ions) in the gold electroplating bath preferably ranges from about 1 g/L to about 100 g/L, preferably from about 10 g/L to about 70 g/L, even more preferably from about 15 to about 45 g/L. In one embodiment, the concentration of gold ions in the gold electroplating bath is generally in the range of about 8 g/L to about 24 g/L, preferably about 12 g/L to about 20 g/L, even more preferably about 16 g/L. In one embodiment, the concentration of sulfite ions added to the gold electroplating bath is generally in the range of about 30 g/L to about 70 g/L, preferably about 40 g/L to about 60 g/L, even more preferably about 50 g/L.

The complexing agent used in the gold electroplating bath may be selected from the group consisting of citric acid, potassium citrate, sodium citrate, tartaric acid, oxalic acid, succinic acid, amino trimethylene phosphonic acid, 1-hydroxyethylidene-1,1-di-phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylenetriamine pentamethylene phosphonic acid, ammonia, ethylenediamine, triethanolamine, a salt thereof, and combinations of one or more of the foregoing. In one embodiment, the complexing agent may comprise nitrogen compounds such as ammonia, ethylenediamine or triethanolamine may be used together with a carboxyl group-containing compound. In one embodiment, the complexing agent comprises ethylenediamine.

The amount of complexing agent to be added to the gold electroplating bath is generally within the range of about 0.1 g/L to about 300 g/L, preferably about 1 g/L to about 200 g/L, even more preferably about 1 g/L to about 9 g/L. The concentration of the complexing agent depends in-part on the amount of gold (i.e., molar concentration) added to the gold electroplating bath.

The gold electroplating bath also contains an accelerator selected from the group consisting of pyridine compounds, quinoline compounds, polyethyleneimine, sulphonic acid derivatives, substituted pyridine, and combinations of one or more of the foregoing. In one embodiment, the pyridine compounds and quinoline compounds are selected from the group consisting of pyridine-3-carboxylic acid (i.e., nicotinic acid), quinoline-3-carboxylic acid, 4-pyridine carboxylic acids, nicotinic acid methyl ester, nicotinamide, nicotinic acid diethyl amide, pyridine-2,3-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, pyridine-4-thioacetic acid, pyridine sulfonic acid, and combinations of one or more of the foregoing. The accelerator advantageously causes deposition of a bright gold layer or layers over a wide current density range, such as in the range of about 0.1 A/dm² to about 20 A/dm², preferably in the range of about 0.1 A/dm² to about 6 A/dm².

The accelerator to be added to the gold electroplating bath should be generally in the range of about 1 mg/L to about 5,000 mg/L, preferably in the range of about 10 mg/L to about 2,000 mg/L, even more preferably in the range of about 50 mg/L to about 600 mg/L.

The method of the present invention is accomplished by the incorporation of a suppressor compound previously used as a leveler in copper electroplating baths. The inventors of the present invention surprisingly found that the use of these suppressor compounds at an appropriate concentration can enhance deposition of a highly pure gold layer, agnostic to the size of interconnect features. The suppressors comprise, for example, quaternized pyridyl compounds, quaternized polyethyleneimine compounds, quaternized dipyridyl compounds, quaternized aliphatic compounds, and combinations of one or more of the foregoing.

1. Quaternized Pyridyl Suppressor Compounds

In one embodiment, a quaternized pyridyl suppressor compound is added to the gold electroplating bath. In general, quaternized pyridyl compounds are derived from the reaction between a pyridyl compound and an alkylating agent, as described, for example, in U.S. Pat. No. 8,608,933 to Paneccasio, Jr. et al., the subject matter of which is herein incorporated by reference in its entirety. In one embodiment, the quaternized pyridyl compounds are prepared by reacting 4-vinyl pyridine, a polymer comprising repeating units of 4-vinyl pyridine, or derivatives thereof with an alkylating agent selected from the group consisting of dimethyl sulfate, methyl tosylate, dimethyl sulfate, methyl tosylate, 2-chloroethanol, benzyl chloride, allyl chloride, chloromethylpyridine, 1,3-propane sultone, chloroacetone, methoxyethoxymethylchloride, 2-chloroethylether, poly(2-methyl-5-vinyl pyridine), and 1-methyl-4-vinylpyridinium trifluoromethyl sulfonate.

2. Quaternized Polyethyleneimine Suppressor Compounds

In one embodiment, a quaternized polyethyleneimine suppressor compound is added to the gold electroplating bath. In general, the quaternized polyethyleneimine compounds are derived from the reaction between polyethyleneimine or a derivative thereof, and an alkylating agent. In one embodiment, the quaternized polyethyleneimine compounds are prepared by reacting polyethylenimine and benzyl chloride as described, for example, in U.S. Pat. Pub. No. 2007/0178697 to Paneccasio et al., the subject matter of which is herein incorporated by reference in its entirety.

3. Quaternized Dipyridyl Suppressor Compounds

In one embodiment, a quaternized dipyridyl suppressor compound is added to the gold electroplating bath. In general, quaternized dipyridyl compounds are derived from the reaction between a dipyridyl compound and an alkylating agent, as described, for example, in U.S. Pat. No. 11,124,888 to Richardson et al., the subject matter of which is herein incorporated by reference in its entirety.

Particularly preferred suppressor compounds of this type include:

• • where the value of n is preferably between about 5 and about 20, such as between 6 and 9 in a low molecular weight embodiment or between 10 and 15 in a higher molecular weight embodiment, and/or is such that the polymer or oligomer has a number average molecular weight between about 1,000 and about 5,000.

In one embodiment, the dipyridyl compounds comprise 2,2′-dipyridyl compounds, 3,3′-dipyridyl compounds, 4,4′-dipyridyl compounds, and one or more of the foregoing.

In one embodiment, the 2,2′-dipyridyl compounds comprise 2,2′-dipyridyl, 2,2′-ethylenedipyridine (1,2-Bis(2-pyridyl)ethane), Bis(2-pyridyl)methane, 1,3-Bis(2-pyridyl)propane, 1,4-Bis(2-pyridyl)butane, 1,5-Bis(2-pyridyl)pentane, and 1,6-Bis(2-pyridyl)hexane.

3,3′-dipyridyl compounds include 3,3′-dipyridyl, 3,3′-ethylenedipyridine (1,2-Bis(3-pyridyl)ethane), Bis(3-pyridyl)methane, 1,3-Bis(3-pyridyl)propane, 1,4-Bis(3-pyridyl)butane, 1,5-Bis(3-pyridyl)pentane, 1,6-Bis(3-pyridyl)hexane, and one or more of the foregoing.

In one embodiment, the 4,4′-dipyridyl compounds comprise 4,4′-dipyridyl, 4,4′-ethylenedipyridine (1,2-Bis(4-pyridyl)ethane), Bis(4-pyridyl)methane, 1,3-Bis(4-pyridyl)propane, 1,4-Bis(4-pyridyl)butane, 1,5-Bis(4-pyridyl)pentane, 1,6-Bis(4-pyridyl)hexane, and one or more of the foregoing.

In one embodiment, the alkylating agents comprise 2-chloroethylether, benzyl chloride, 2-(2-chloroethoxy)ethanol, chloroethanol, 1-(chloromethyl)-4-vinylbenzene, and 1-(chloromethyl)naphthalene, 1-chloro-2-(2-chloroethoxy)ethane, 1,2-bis(2-chloroethoxy)ethane, 1,3-dichloropropan-2-one, 1,3-dichloropropan-2-ol, 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane, 1,8-dichlorooctane, 1,2-di(2-chloroethyl)ether, 1,4-bis(chloromethyl)benzene, m-di(chloromethyl)benzene, o-di(chloromethyl)benzene, epichlorohydrin, and one or more of the foregoing.

4. Quaternized Aliphatic Suppressor Compounds

In one embodiment, a quaternized aliphatic suppressor compound is added to the gold electroplating bath. In general, the quaternized aliphatic compounds are derived from the reaction between an aliphatic di(t-amine) and an alkylating agent as described, for example, in U.S. Pat. No. 10,294,574 to Whitten et al., the subject matter of which is herein incorporated by reference in its entirety.

In one embodiment, the aliphatic di(t-amine)s comprise N,N,N′,N′-tetramethyl-1,2-diaminoethane, N,N,N′,N′-tetramethyl-1,3-diaminopropane, bis(N,N-dimethyl-2-amino)ethyl ether, N,N,N′,N′-tetramethyl-1,6-diaminohexane, N,N,N′,N′-tetramethyl-1,4-diaminobutane, N,N,N′,N′-tetramethyl-1,4-Bis(aminomethyl)cyclohexane, N,N,N′,N′-tetramethyl-1,2-Bis(2-aminoethoxy)ethane, and one or more of the foregoing.

In one embodiment, the alkylating agents comprise bis(2-chloroethyl) ether (i.e., 2-chloroethylether), bis(2-chloroethoxy)ethane, 1,6-dichlorohexane, bis[2-(2-chloroethoxy)ethyl]ether, 1,3-dichloro-2-propanol, bis(4-chlorobutyl) ether, 1,3-dichloropropan-2-one, 1,2-di(2-chloroethyl)ether, 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichlorobutane, 1,8-dichlorooctane, analogs of these compounds which comprise bromide or other leaving groups, and one or more of the foregoing.

In another embodiment, the alkylating agents comprise 2-(2-hydroxyethoxy)ethyl chloride, 2-methoxyethyl chloride, 1-chloro-4-butanol, 1-chloro-4-hexanol, 1-chloro-4-octanol, (3-chloro-2-hydroxypropyl)trimethyl-ammonium chloride, (2-chloroethyl)trimethylammonium chloride, (2-chloroethoxy)benzene, Benzyl chloride, 4-Methylbenzyl chloride, allyl chloride, and one or more of the foregoing.

The suppressor may be added to the gold electroplating bath at a concentration from about 0.01 mg/L to about 10 g/L, preferably from about 0.2 mg/L to about 7 g/L, and more preferably from about 0.25 mg/L to about 5 g/L. The concentration of the suppressor depends on the particular suppressor being utilized and particularly preferred suppressors include, but are not limited to, a suppressor made from a reaction of 4,4′-dipyridyl and 2-chloroethylether and a suppressor made from a reaction of polyethyleneimine and benzyl chloride.

The suppressors are typically prepared in a reaction solvent comprising a large concentration of high boiling glycol. Examples of high boiling glycols include, for example, ethylene glycol or propylene glycol. The solution is then diluted to a final volume with distilled water. A subsample comprising the suppressor may be used to add the suppressor to the gold electroplating bath in the concentrations indicated above. Advantageously, gold electroplating baths, compared to copper electroplating baths, have been discovered to be tolerant to relatively higher concentrations of the suppressors of the present invention. That is, a gold electroplating bath may be tolerant of higher concentrations of the suppressors of the present invention without negatively impacting gapfill or inhibiting superfilling, such that compositions comprising relatively high concentrations of the suppressors of the present invention are able to superfill features without the formation of voids and seams.

Without wishing to be bound by theory, it is believed that the suppressor works in combination with the other gold electroplating bath ingredients to advantageously enhance bottom-up filling of interconnect features and inhibit conformal and sub-conformal filling. Conformal plating is characterized by a deposit of equal thickness at all points of an interconnect feature, which may lead to formation of a seam. Conformal plating results from relatively equal gold deposition suppression along the sidewalls and via or trench bottom, resulting in a relatively equal rate of gold deposition on both the sidewalls and the bottom of the interconnect feature. Gold growth along the sidewalls converges at some point towards the center of the via or trench, undesirably forming a seam.

To achieve defect-free filling, i.e., void-free and seam-free, the deposition rate at the bottom of interconnect features should greatly exceed the deposition rate on the sidewalls. For example, during gold metallization, the gold deposition rate along the bottom of interconnect features (i.e., bottom-up or vertical growth rate) is preferably at least one order of magnitude faster than the gold deposition rate along the sidewalls (i.e. lateral or horizontal growth rate).

The pH of the gold electroplating bath of the present invention is preferably alkaline. In one embodiment, the pH is within the range of about 7 to about 9, preferably about 8. The pH can optionally be adjusted by adding one or more pH adjusters. In one embodiment, the pH adjuster is as alkali metal hydroxide such as one or more of sodium hydroxide, potassium hydroxide, and other alkali hydroxides. In another embodiment, the pH adjuster is an acidic compound such as one or more of citric acid, phosphoric acid, tartaric acid, oxalic acid, succinic acid, sulfuric acid, and salts thereof. By adding a pH adjuster, the pH of the gold electroplating bath can be maintained uniform, and the plating operation can be performed for a long period of time.

In one embodiment, the present invention also relates generally to a method for electroplating a gold deposit onto a substrate comprising one or more features, the method comprising:

• • a) bringing the substrate into contact with the gold electroplating bath described herein, and
  • b) supplying electrical current to the gold electroplating bath to deposit gold onto the substrate to fill the one or more features by bottom-up deposition.

In one embodiment, the one or more features may include for example vias, through-silicon vias (TSV), trenches, pillars, pads, bumps, etc. that may be present on or in a microelectronic (i.e., semiconductor) substrate. In one embodiment, these features may be tapered or have a slope.

In one embodiment, the substrate is brought into contact with the gold electroplating bath by immersing the substrate in the bath. The substrate may also be brought into contract with the gold electroplating bath by other means known in the art such as spraying.

In one embodiment, the electrical current is supplied to the gold electroplating bath for a time ranging from about 1 minute to about 20 minutes, while the gold electroplating bath is maintained at a temperature within the range of about 35 to about 75° C., preferably about 45 to about 65° C., in order to completely fill the interconnect features. The electroplating time will depend on various factors including, but not limited to, the gold electroplating bath composition and temperature, the current density, the dimensions of the features, and the desired thickness of the gold filling.

In one embodiment, a source of alloying metal ions may optionally be added to the gold electroplating bath. Sources of alloying metal ions include, for example, one or more sources of tin ions, manganese ions, zirconium ions, copper ions, nickel ions, zinc ions, iron ions, aluminum ions, silver ions, platinum ions, palladium ions, and combinations of one or more thereof. If used, the source of alloying metal ions is added in concentrations ranging from about 0.001 g/L to about 5 g/L, preferably ranging from about 0.05 g/L to about 2 g/L, more preferably ranging from about 0.05 g/L to about 1 g/L. The concentration of the source of alloying metal ions may vary depending upon the desired alloying metal content in the deposited gold alloy.

Various additives and combinations of additives may be included in the electroplating bath to provide desired surface finishes. In one embodiment, at least two additives or at least three additives may be used in combination to initiate bottom-up filling of interconnect features and to improve metal metallurgical, physical and electrical properties (e.g., electrical conductivity and reliability). These additives (usually organic additives) include, but are not limited to, additional suppressors and accelerators, primary brighteners (e.g., saccharin), wetting agents, grain refiners, and secondary brighteners.

The inventors of the present invention have discovered a gold electroplating bath that is free of heavy metals such as lead, arsenic, mercury, cadmium, bismuth, thallium, and antimony and capable of filling interconnect features to produce a gold deposit by bottom-up filling.

The gold electroplating bath of the present invention is suitable for plating semiconductor IC device substrates (i.e., semiconductor substrate, wafer, or die) having challenging fill characteristics, including interconnect features that are poorly seeded or not substantially seeded, interconnect features having a complex geometry, and large diameter interconnect features as well as nano-sized interconnect features.

In one embodiment, the gold electroplating bath described herein is capable of superfilling large interconnect features having an opening dimension (i.e., via opening diameter or trench width) ranging from about 0.1 micrometer (μm) to about 30 μm, preferably from about 1 μm to about 10 μm, more preferably from about 2 μm to about 8 μm and having a depth ranging from about 0.1 μm to about 30 μm, preferably from about 1 μm to about 10 μm, more preferably from about 2 μm to about 8 μm. The gold electroplating bath of the present invention is also capable of superfilling large interconnect features having various aspect ratios ranging from about 1:10 to about 10:1, preferably from about 1:4 to about 4:1.

In another embodiment, the gold electroplating bath described herein is also believed to be capable of superfilling nano-sized interconnect features having an opening dimension ranging from about 10 nm to about 500 nm, a depth ranging from about 200 nm to about 2,000 nm, and an aspect ratio ranging from about 1:5 to about 20:1, preferably from about 1:1 to about 10:1.

An important aspect of the invention described herein is that it is desirable for the gold electroplating bath to comprise an accelerator and thus be at least substantially free of cyanide and at least substantially free of heavy metals, including lead, arsenic, mercury, cadmium, bismuth, thallium, and antimony. Due to the toxic nature of cyanides and select heavy metals, as well as environmental policy considerations, the inventors of the present invention have discovered that it is preferred that the gold electroplating bath is at least substantially free, and preferably completely free of these compounds.

In another embodiment, the present invention relates generally to a gold electroplating bath comprising:

• • a) about 1 g/L to about 100 g/L, preferably about 10 g/L to about 70 g/L, even more preferably about 15 to about 45 g/L of a source of gold ions;
  • b) about 0.1 g/L to about 300 g/L, preferably about 1 g/L to about 200 g/L, even more preferably about 1 g/L to about 9 g/L of a complexing agent;
  • c) about 1 mg/L to about 5,000 mg/L, preferably about 10 mg/L to about 2,000 mg/L, even more preferably about 50 mg/L to about 600 mg/L of an organic accelerator;
  • d) about 0.01 mg/L to about 10 g/L, preferably about 0.2 mg/L to about 7 g/L, and more preferably about 0.25 mg/L to about 5 g/L of a suppressor;
  • e) optionally, a pH adjuster; and
  • f) balance water.

In another embodiment, the present invention relates generally to a gold electroplating bath consisting essentially of:

• • a source of gold ions;
  • a complexing agent;
  • an accelerator;
  • a suppressor;
  • optionally, a pH adjuster; and
  • balance water.

As used herein, the term “consisting essentially of,” refers to a gold electroplating bath that is free of any additive that would have a detrimental effect on the ability of the gold electroplating bath to produce a gold deposit by bottom-up filling.

In still another embodiment, the present invention relates generally to a gold electroplating bath consisting of:

• • a source of gold ions;
  • a complexing agent;
  • an accelerator;
  • a suppressor;
  • optionally, a pH adjuster; and
  • balance water.

In some embodiments, the present invention is directed to a composition and a method for metallizing an interconnect feature in a semiconductor IC device substrate. The semiconductor wafer may be a silicon wafer or silicon chip, or another semiconductor material, such as germanium, silicon germanium, silicon carbide, silicon germanium carbide, and gallium arsenide.

The semiconductor substrate may have deposited thereon a dielectric (insulative) film, such as, SiO₂, silicon nitride, silicon oxynitride, carbon-doped silicon oxides, low-κ, or ultra low-κ dielectrics.

The dielectric film is typically deposited on the surface of the semiconductor wafer or chip and then patterned by lithography, to achieve the circuitry pattern comprising the interconnect features. Low-κ dielectric refers to a material having a smaller dielectric constant than silicon dioxide (dielectric constant=3.9), such as about 3.5, about 3, about 2.5, about 2.2, or even about 2.0.

As applicable to radio frequency (RF) technologies, high purity gold interconnect metallization is desired to decrease resistivity, particularly as device sizes and density continue to decrease. Highly pure gold traces are capable of carrying more current in a smaller cross-section than gold traces with high impurities. A highly pure gold layer also has lesser tendency to form voids as the individual grains coalesce during high temperature processing steps, e.g., post-deposition anneals. In a low purity deposit, there is a greater tendency to form voids as the grains coalesce and condense, grain boundaries are eliminated and empty space, i.e., a void, is formed within the volume of the feature.

Therefore, the present invention is also directed to a method of depositing a highly pure gold layer in which coalescence of individual grains in the deposit is limited and void formation is inhibited.

Such a highly pure gold film has been found to exhibit improved corrosion resistance, rapid room temperature crystallization, lower resistivity, improved electromigration resistance, and lower microvoid formation in the post-anneal processing. Additionally, the gold electroplating bath and the method for electroplating a gold deposit can be used to electroplate features with significantly improved underplating characteristics. In view of the advantages obtained by more productive gold superfilling and suppressing of interconnect features, the overplate and underplate of deposited gold has been significantly reduced, which alleviates non-uniformity and decreases the chemical mechanical policing (CMP) challenges which include high overburden removal and underplate causing CMP erosion.

EXAMPLES

The following non-limiting examples are provided to further illustrate the present invention. In each of the examples described herein, the substrates comprising a 4.5×4.5 μm via were plated in a gold electroplating bath. The line roughness of the resulting gold deposit was measured at five different locations on the surface of the gold deposit using a Keyence™ microscope and then averaged. A gold deposit with an average line roughness of less than about 50 nm has a bright finish and is considered to be smooth. A gold deposit with an average line roughness of about 50 nm or greater has a matte-finish and is considered to be rough.

Comparative Example 1

A gold electroplating bath was prepared comprising 16 g/L gold, 50 g/L sodium sulfite, 500 mg/L pyridine sulfonic acid, and 4.88 g/L ethylenediamine. The solution was heated to 55° C. in a water bath and the pH was adjusted to 8.0 using either dilute sulfuric acid or dilute aqueous sodium hydroxide solution. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 13 minutes. Results of the electroplating are shown in FIG. 1.

As seen in FIG. 1, a via partially filled with the gold electroplating bath of Comparative Example 1 (i.e., without the disclosed suppressor) resulted in a smooth gold deposit possessing an average line roughness of 23.0 nm and large grains. However, it is seen that this partial fill result is conformal with the growth from the sidewalls (1.810 μm), from the bottom (1.530 μm) of the vias, and overburden (1.480 μm) being similar.

Comparative Example 2

The same electroplating bath from Comparative Example 1 was prepared except that 7.5 mg/L of a suppressor made from a reaction of epichlorohydrin and 1-benzylimidazole (i.e., a quaternized polyepichlorohydrin (QPECH) suppressor) was added to the composition. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 8 to 13 minutes. Results of the electroplating are shown in FIGS. 2A and 2B.

FIGS. 2A and 2B show the partial fill and full fill and demonstrate that when a QPECH suppressor was added, the fill was conformal, denoting that adding a QPECH suppressor to the gold electroplating bath produced a conformal deposit and not a bottom-up fill. As seen in FIGS. 2A and 2B, a via filled with the gold electroplating bath of Comparative Example 2 formed a gold deposit with a large dimple. In both instances, the growth from the bottom of the via (0.843 μm), sidewalls (0.961 μm), and overburden (0.631 μm) of the partial fill (FIG. 2A) and the growth from the bottom of the via (1.970 μm), sidewalls (1.680 μm), and overburden (1.440 μm) of the full fill (FIG. 2B) were roughly similar in height, indicative of conformal fill. The rough gold deposit of FIG. 2A possessed an average line roughness of 206.2 nm and the rough gold deposit of FIG. 2B possessed an average line roughness of 226.6 nm, each consistent with a brown, matte-finish.

Comparative Example 3

The same electroplating bath from Comparative Example 1 was prepared except that 100 mg/L of saccharin was added to the solution. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 13 minutes. Results of the electroplating are shown in FIG. 3.

As seen in FIG. 3, a via partially filled with the gold electroplating bath of Comparative Example 3 (i.e., adding saccharin without the disclosed suppressor) resulted in a smooth gold deposit possessing an average line roughness of 20.0 nm, consistent with a bright finish. The saccharin acted as a grain refiner decreasing the size of the grains, therefore brightening the gold finish. However, it is seen that this partial fill result is conformal with the growth from the bottom of the via (1.820 μm), sidewalls (1.860 μm), and overburden (1.580 μm) being roughly similar.

Example 4

The same electroplating bath from Comparative Example 1 was prepared except that 4 mg/L of a suppressor made from a reaction of 4,4′-dipyridyl and 2-chloroethylether (i.e., quaternized dipyridyl suppressor compound) was added to the composition. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 8 to 13 minutes. Results of the electroplating are shown in FIGS. 4A and 4B.

FIGS. 4A and 4B show the partial fill and full fill results when adding the suppressor of this example. As seen in FIGS. 4A and 4B, a via filled using a gold electroplating bath containing the disclosed suppressor, exhibited a reduced dimple when electroplated as compared to a gold electroplating bath without the disclosed suppressor. The overburden (0.432 μm) compared to the fill height of the via (3.210 μm) of the partial fill (FIG. 4A) and the overburden (1.170 μm) compared to the fill height of the via (5.540 μm) of the full fill (FIG. 4B), demonstrate that the suppressor provided good suppression of the overburden, while facilitating bottom-up growth in each via. The smooth gold deposit of FIG. 4A possessed an average line roughness of 30.6 nm and the smooth gold deposit of FIG. 4B possessed an average line roughness of 48.4 nm, each consistent with a bright finish.

Example 5

The same electroplating bath from Comparative Example 1 was prepared except that 4 mg/L of a suppressor made from a reaction of polyethyleneimine and benzyl chloride (i.e., a quaternized polyethyleneimine suppressor compound) was added to the composition. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 8 to 13 minutes. Results of the electroplating are shown in FIGS. 5A and 5B.

FIGS. 5A and 5B show the partial fill and full fill results when adding the suppressor of this example. As seen in FIGS. 5A and 5B, a via filled using a gold electroplating bath containing the disclosed suppressor, a reduced dimple when electroplated as compared to a gold electroplating bath without the disclosed suppressor. The overburden (0.691 μm) compared to the fill height of the via (3.000 μm) of the partial fill (FIG. 5A) and the overburden (1.230 μm) compared to the fill height of the via (4.750 μm) of the full fill (FIG. 5B), demonstrate that the suppressor provided good suppression of the overburden, while facilitating growth from the bottom of each via. The gold deposit of FIG. 5A possessed an average line roughness of 89.4 nm and the gold deposit of FIG. 5B possessed an average line roughness of 68.2 nm, each consistent with a matte finish.

Example 6

The same electroplating bath from Comparative Example 1 was prepared except that 0.4 mg/L of a suppressor made from a reaction of 4,4′-dipyridyl and 2-chloroethylether was added to the composition. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 13 minutes. Results of the electroplating are shown in FIG. 6.

As seen in FIG. 6, a fully filled via using a gold electroplating bath containing the disclosed suppressor, exhibited a reduced dimple when electroplated as compared to a gold electroplating bath without the disclosed suppressor. The addition of the suppressor showed significantly more growth from the bottom of the via (4.670 μm) while maintaining similar overburden height (1.550 μm) to Comparative Example 1 (1.480 μm), exemplifying bottom-up filling. The smooth gold deposit possessed an average line roughness of 17.0 nm, consistent with a bright finish.

Example 7

A gold electroplating bath was prepared comprising 16 g/L gold, 50 g/L sodium sulfite, 400 mg/L pyridine sulfonic acid, 0.4 mg/L of a suppressor made from a reaction of 4,4′-dipyridyl and 2-chloroethylether, 100 mg/L of saccharin, and 4.88 g/L ethylenediamine. The solution was heated to 55° C. in a water bath and the pH was adjusted to 8.0 using aqueous sulfuric acid or dilute aqueous sodium hydroxide solution. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 13 minutes. Results of the electroplating are shown in FIG. 7.

As seen in FIG. 7, a via filled using a gold electroplating bath containing the disclosed suppressor, exhibited a reduced dimple when electroplated as compared to a gold electroplating bath without the disclosed suppressor. The overburden (1.660 μm) compared to the fill height of the via (5.350 μm) demonstrates that the suppressor provided good suppression of the overburden, while facilitating growth from the bottom of the via. The smooth gold deposit possessed an average line roughness of 18.0 nm, consistent with a bright finish.

Example 8

The same electroplating bath from Comparative Example 1 was prepared except that 4.2 mg/L of an aliphatic suppressor made from a reaction of N,N,N′N′-tetramethyl-1,3-diaminopropane and 2-chloroethylether was added to the composition. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 13 minutes. Results of the electroplating are shown in FIG. 8.

As seen in FIG. 8, a via filled using a gold electroplating bath containing the disclosed aliphatic suppressor exhibited a reduced (yet still moderate) dimple when electroplated, compared to a gold electroplating bath without the disclosed suppressor. The sidewall growth and overburden growth (1.270 μm) were suppressed while growth from the bottom (4.220 m) was accelerated which produced a smooth gold deposit. The smooth gold deposit possessed an average line roughness of 52.0 nm, consistent with a yellow, matte finish.

The same electroplating bath from Comparative Example 1 was prepared except that 6 mg/L of an aliphatic suppressor made from a reaction of N,N,N′N′-tetramethyl-1,6-diaminohexane and 2-chloroethylether was added. The substrates were immersed in the gold electroplating bath and electroplated at 0.3 ASD for 13 minutes. Results of the electroplating are shown in FIG. 9.

As seen in FIG. 9, a via filled with the gold electroplating bath containing the disclosed aliphatic suppressor formed a large dimple when electroplated. However, the partial fill result demonstrated the bottom-up fill capabilities of the gold electroplating bath. Growth is accelerated from the bottom (2.510 m), while sidewall and overburden (0.850 μm) growth were suppressed. The rough gold deposit possessed an average line roughness of 220.0 nm, consistent with a brown, matte-finish.

Table 1 provides a summary of the bottom-up filling and surface roughness results based on the examples:

TABLE 1
			Over-			Average
		Bottom	burden	Sidewall	Bottom-	Line
	Fill	Growth	Growth	Growth	up	Roughness
Example	Level	(μm)	(μm)	(μm)	Filling	(nm)
Comparative	Partial	1.530	1.480	1.810	N	23.0
Example 1
Comparative	Partial	0.843	0.631	0.961	N	206.2
Example 2	Full	1.970	1.440	1.680	N	226.6
Comparative	Partial	1.820	1.580	1.860	N	20.0
Example 3
Example 4	Partial	3.210	0.432	NA	Y	30.6
Example 4	Full	5.540	1.170	NA	Y	48.4
Example 5	Partial	3.000	0.691	NA	Y	89.4
Example 5	Full	4.750	1.230	NA	Y	68.2
Example 6	Full	4.670	1.550	NA	Y	17.0
Example 7	Full	5.350	1.660	NA	Y	18.0
Example 8	Full	4.220	1.270	NA	Y	52.0
Example 9	Partial	2.510	0.850	NA	Y	220.0

As shown in Table 1, the use of quaternized polyethyleneimine compounds and quaternized dipyridyl compounds as suppressors (e.g., Examples 4-7) resulted in the bottom-up fill of the vias with a gold deposit having a reduced dimple. Examples 8 and 9 demonstrate that aliphatic suppressors can also result in bottom-up filling. However certain aliphatic suppressors (e.g., Example 8) demonstrate an improved bottom-up fill performance compared to others (e.g., Example 9). As shown in Comparative Example 2, a large dimple in the gold deposit will form when the via is conformally plated such that the growth at the bottom, top (i.e., overburden), and sides occurs at roughly the same degree. Additionally, a gold electroplating bath that does not contain a suppressor (e.g., Comparative Example 1) or that uses a QPECH suppressor (e.g., Comparative Example 2), does not result in bottom-up filling. Furthermore, adding a primary brightener (e.g., Comparative Example 3) to a gold electroplating bath without the disclosed suppressor will not result in bottom-up filling.

Also as shown in Table 1, the use of a QPECH suppressor (e.g., Comparative Example 2) and aliphatic suppressors (e.g., Examples 8 and 9) will result in a rough gold deposit, consistent with a brown or yellow, matte-finish. Furthermore, a gold electroplating bath comprising an accelerator and either having no suppressor (e.g., Comparative Example 1) or using a suppressor as disclosed (e.g., Examples 4-7) will result in a smoother gold deposit with a brighter finish.

As various changes could be made in the above compositions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Additional Embodiments

Clause 1: A gold electroplating bath comprising:

• • a. a source of gold ions;
  • b. a complexing agent;
  • c. an organic accelerator;
  • d. a suppressor;
  • e. optionally, a pH adjuster; and
  • f. balance water.

Clause 2: A gold electroplating bath comprising:

• • a. about 1 g/L to about 100 g/L, preferably about 10 g/L to about 70 g/L, even more preferably about 15 to about 45 g/L of a source of gold ions;
  • b. about 0.1 g/L to about 300 g/L, preferably about 1 g/L to about 200 g/L, even more preferably about 1 g/L to about 9 g/L of a complexing agent;
  • c. about 1 mg/L to about 5,000 mg/L, preferably about 10 mg/L to about 2,000 mg/L, even more preferably about 50 mg/L to about 600 mg/L of an organic accelerator;
  • d. about 0.01 mg/L to about 10 g/L, preferably about 0.2 mg/L to about 7 g/L, and more preferably about 0.25 mg/L to about 5 g/L of a suppressor;
  • e. optionally, a pH adjuster; and
  • f. balance water.

Clause 3: the gold electroplating bath of Clause 1 or Clause 2, wherein the source of gold ions is selected from the group consisting of gold thiosulfate compounds, gold sulfite compounds, and gold(I) halides, gold(III) halides, and combinations of one or more of the foregoing.

Clause 4: the gold electroplating bath of Clauses 1 to 3, wherein the source of gold ions is selected from the group consisting of trisodium gold thiosulfate, tripotassium gold thiosulfate, sodium gold sulfite, potassium gold sulfite, ammonium gold sulfite, gold(I) chloride, gold(III) trichloride, and combinations of one or more of the foregoing.

Clause 5: the gold electroplating bath of Clauses 1 to 4, wherein the complexing agent is selected from the group consisting of citric acid, potassium citrate, sodium citrate, tartaric acid, oxalic acid, succinic acid, amino trimethylene phosphonic acid, 1-hydroxyethylidene-1,1-di-phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylenetriamine pentamethylene phosphonic acid, ammonia, ethylenediamine, triethanolamine, a salt thereof, and combinations of one or more of the foregoing.

Clause 6: the gold electroplating bath of Clauses 1 to 5, wherein the organic accelerator is selected from the group consisting of pyridine compounds, quinoline compounds, polyethyleneimine, sulphonic acid derivatives, substituted pyridine, and combinations of one or more of the foregoing, wherein the pyridine compounds and quinoline compounds are selected from the group consisting of pyridine-3-carboxylic acid, quinoline-3-carboxylic acid, 4-pyridine carboxylic acid, nicotinic acid methyl ester, nicotinamide, nicotinic acid diethyl amide, pyridine-2,3-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, pyridine-4-thioacetic acid, pyridine sulfonic acid, and combinations of one or more of the foregoing.

Clause 7: the gold electroplating bath of Clauses 1 to 6, wherein the suppressor is selected from the group consisting of quaternized dipyridyl compounds, quaternized pyridyl compounds, quaternized polyethyleneimine compounds, quaternized aliphatic compounds, and combinations of one or more of the foregoing.

Clause 8: the gold electroplating bath of Clause 7, wherein the quaternized pyridyl compounds comprise a reaction product of pyridyl and an alkylating agent or wherein the quaternized dipyridyl compounds comprise a reaction product of dipyridyl and an alkylating agent.

Clause 9: the gold electroplating bath of Clauses 1 to 8, wherein the bath is maintained at a pH in the range of about 6 to about 10.

Clause 10: the gold electroplating bath of Clauses 1 to 9, wherein the bath is maintained at a temperature in the range of about 35 to about 75° C.

Clause 11: the gold electroplating bath of Clauses 1 to 10, wherein the bath is at least substantially free of cyanide ions.

Clause 12: the gold electroplating bath of Clauses 1 to 11, wherein the bath is at least substantially free of heavy metals selected from the group consisting of lead, arsenic, mercury, cadmium, bismuth, thallium, and antimony.

Clause 13: the gold electroplating bath of Clauses 1 to 12, wherein the bath comprises one or more source of alloying metal ions selected from the group consisting of a source of tin ions, a source of manganese ions, a source of zirconium ions, a source of copper ions, a source of nickel ions, a source of zinc ions, a source of iron ions, a source of aluminum ions, a source of silver ions, a source of platinum ions, a source of palladium ions, and combinations of one or more thereof.

Clause 14: A method for electroplating a gold deposit onto a substrate comprising one or more features, the method comprising:

• • a) bringing the substrate into contact with the gold electroplating bath of Clause 1 or Clause 2, and
  • b) supplying electrical current to the gold electroplating bath to deposit gold onto the substrate to fill the one or more features by bottom-up deposition.

Clause 15: the method of Clause 14, wherein the current density during filling of the one or more features is from about 0.1 A/dm² to about 6 A/dm².

Clause 16: the method of Clause 14 or Clause 15, wherein the one or more features have an opening dimension ranging from about 0.1 μm to about 30 μm and have a depth ranging from about 0.1 μm to about 30 μm.

Clause 17: the method of Clauses 14 to 16, wherein the one or more features have an aspect ratio ranging from about 1:4 to about 4:1.

Clause 18: the method of Clauses 14 to 17, wherein the suppressor is selected from the group consisting of quaternized dipyridyl compounds, quaternized pyridyl compounds, quaternized polyethyleneimine compounds, quaternized aliphatic compounds, and combinations of one or more of the foregoing.

Clause 19: the method of Clause 18, wherein the quaternized pyridyl compounds comprise a reaction product of pyridyl and an alkylating agent or wherein the quaternized dipyridyl compounds comprise a reaction product of dipyridyl and an alkylating agent.

Claims

1. A gold electroplating bath comprising:

a. a source of gold ions;

b. a complexing agent;

c. an organic accelerator;

d. a suppressor;

e. optionally, a pH adjuster; and

f. balance water.

2. The gold electroplating bath according to claim 1, wherein the source of gold ions is selected from the group consisting of gold thiosulfate compounds, gold sulfite compounds, and gold(I) halides, gold(III) halides, and combinations of one or more of the foregoing.

3. The gold electroplating bath according to claim 2, wherein the source of gold ions is selected from the group consisting of trisodium gold thiosulfate, tripotassium gold thiosulfate, sodium gold sulfite, potassium gold sulfite, ammonium gold sulfite, gold(I) chloride, gold(III) trichloride, and combinations of one or more of the foregoing.

4. The gold electroplating bath according to claim 1, wherein the complexing agent is selected from the group consisting of citric acid, potassium citrate, sodium citrate, tartaric acid, oxalic acid, succinic acid, amino trimethylene phosphonic acid, 1-hydroxyethylidene-1,1-di-phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylenetriamine pentamethylene phosphonic acid, ammonia, ethylenediamine, triethanolamine, a salt thereof, and combinations of one or more of the foregoing.

5. The gold electroplating bath according to claim 1, wherein the organic accelerator is selected from the group consisting of pyridine compounds, quinoline compounds, polyethyleneimine, sulphonic acid derivatives, substituted pyridine, and combinations of one or more of the foregoing, wherein the pyridine compounds and quinoline compounds are selected from the group consisting of pyridine-3-carboxylic acid, quinoline-3-carboxylic acid, 4-pyridine carboxylic acid, nicotinic acid methyl ester, nicotinamide, nicotinic acid diethyl amide, pyridine-2,3-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, pyridine-4-thioacetic acid, pyridine sulfonic acid, and combinations of one or more of the foregoing.

6. The gold electroplating bath according to claim 1, wherein the suppressor is selected from the group consisting of quaternized dipyridyl compounds, quaternized pyridyl compounds, quaternized polyethyleneimine compounds, quaternized aliphatic compounds, and combinations of one or more of the foregoing.

7. The gold electroplating bath according to claim 1, wherein the quaternized pyridyl compounds comprise a reaction product of pyridyl and an alkylating agent or wherein the quaternized dipyridyl compounds comprise a reaction product of dipyridyl and an alkylating agent.

8. The gold electroplating bath according to claim 1, wherein the bath is maintained at a pH in the range of about 6 to about 10.

9. The gold electroplating bath according to claim 1, wherein the bath is maintained at a temperature in the range of about 35 to about 75° C.

10. The gold electroplating bath according to claim 1, wherein the bath is at least substantially free of cyanide ions.

11. The gold electroplating bath according to claim 1, wherein the bath is at least substantially free of heavy metals selected from the group consisting of lead, arsenic, mercury, cadmium, bismuth, thallium, and antimony.

12. The gold electroplating bath according to claim 1, wherein the bath comprises one or more source of alloying metal ions selected from the group consisting of a source of tin ions, a source of manganese ions, a source of zirconium ions, a source of copper ions, a source of nickel ions, a source of zinc ions, a source of iron ions, a source of aluminum ions, a source of silver ions, a source of platinum ions, a source of palladium ions, and combinations of one or more thereof.

13. A method for electroplating a gold deposit onto a substrate comprising one or more features, the method comprising:

a) bringing the substrate into contact with the gold electroplating bath of claim 1, and

b) supplying electrical current to the gold electroplating bath to deposit gold onto the substrate and fill the one or more features by bottom-up deposition.

14. The method according to claim 13, wherein the current density during filling of the one or more features is from about 0.1 A/dm2 to about 6 A/dm2.

15. The method according to claim 13, wherein the one or more features have an opening dimension ranging from about 0.1 μm to about 30 μm and have a depth ranging from about 0.1 μm to about 30 μm.

16. The method according to claim 13, wherein the one or more features have an aspect ratio ranging from about 1:4 to about 4:1.

17. The method according to claim 13, wherein the suppressor is selected from the group consisting of quaternized dipyridyl compounds, quaternized pyridyl compounds, quaternized polyethyleneimine compounds, quaternized aliphatic compounds, and combinations of one or more of the foregoing.

18. The method according to claim 13, wherein the quaternized pyridyl compounds comprise a reaction product of pyridyl and an alkylating agent or wherein the quaternized dipyridyl compounds comprise a reaction product of dipyridyl and an alkylating agent.