Electroless ruthenium plating bath

Abstract

To provide an electroless ruthenium plating bath capable of improving a bath stability and providing an excellent precipitation ability of ruthenium, the electroless plating bath using a general reducer of an amine borane compound or a sodium hypophosphite.SOLUTION: An electroless ruthenium plating bath contains at least a ruthenium compound, a reducer, and a stabilizer. The reducer is at least either of an amine borane compound or sodium hypophosphite. The stabilizer is composed of a hydroxylamine compound and an amine-base compound, the hydroxylamine compound being at least either of hydroxylamine sulfate or hydroxyl amine chloride.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an electroless ruthenium plating bath. [Background technology]

[0002] Traditionally, copper has been widely used in the electronics industry for wiring in printed circuit board circuits, mounting parts and terminals of IC packages, etc., because it has high electrical conductivity and excellent physical properties, such as connectability by thermocompression bonding, as well as excellent chemical properties, such as oxidation resistance and chemical resistance.

[0003] As semiconductor circuits become finer, copper wiring is also becoming finer. However, as this miniaturization progresses, the current density flowing through the copper wiring increases, which causes problems such as electromigration (the phenomenon in which copper atoms move due to a high density current flowing through copper wiring), which leads to the formation of voids and resulting in disconnections.

[0004] In recent years, ruthenium has been attracting attention as a next-generation wiring material to replace copper. Ruthenium has a higher current density tolerance and higher electromigration resistance than copper, so in addition to the wiring of the above-mentioned semiconductor circuits, it is expected to be used as a material to form a thin film (cap metal) formed on copper wiring, and a liner layer formed on a barrier metal when forming a copper wiring film by electrolytic plating to grow a copper seed film uniformly.

[0005] If it were possible to use electroless ruthenium plating in the process of forming wiring and the like for this semiconductor circuit, an external power source would not be required, and ruthenium could be selectively deposited by immersion alone, and therefore electroless plating baths containing ruthenium have been proposed.

[0006] For example, an electroless ruthenium plating bath containing a ruthenium source, a polyaminopolycarboxylic acid as a complexing agent, sodium borohydride (NaBH4) as a reducing agent, and hydroxylamine sulfate as a stabilizer has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2012-508819 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, since ruthenium has multiple valences, it is difficult to deposit as a metal, and there is a problem in that it has poor depositability.

[0009] In addition, in the above-mentioned conventional plating baths, sodium borohydride is used as a reducing agent. However, this sodium borohydride is highly reactive and prone to bath decomposition and deposition of patterns other than the desired pattern, and therefore has the problem of being difficult to handle.

[0010] In view of the above problems, the present invention has an object to provide an electroless ruthenium plating bath that uses an amine borane compound or sodium hypophosphite, which is a general reducing agent, and that can improve bath stability and has excellent ruthenium deposition properties. [Means for solving the problem]

[0011] In order to achieve the above object, the electroless ruthenium plating bath of the present invention is an electroless ruthenium plating bath containing at least a ruthenium compound, a reducing agent, and a stabilizer, characterized in that the reducing agent is at least one of an amine borane compound and sodium hypophosphite, the stabilizer is composed of a hydroxylamine compound and an amine compound, and the hydroxylamine compound is at least one of hydroxylamine sulfate and hydroxylamine chloride. Effect of the Invention

[0012] According to the present invention, in an electroless ruthenium plating bath using an amine borane compound or sodium hypophosphite, which are general reducing agents, it is possible to improve bath stability and also improve the deposition properties of ruthenium. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The electroless ruthenium plating bath of the present invention will now be described.

[0014] <Electroless ruthenium plating bath> The electroless ruthenium plating bath of the present invention is a plating bath containing at least a ruthenium compound, a reducing agent, and a stabilizer.

[0015] (Ruthenium Compounds) The ruthenium compound is a source of ruthenium ions for obtaining ruthenium plating. The ruthenium compound may be water-soluble, and examples thereof include inorganic water-soluble ruthenium salts such as ruthenium chloride, ruthenium sulfate, and ruthenium nitrate. These ruthenium compounds may be used alone or in combination of two or more.

[0016] Ruthenium exists in a variety of valences, and the amount of ruthenium precipitated in the plating bath varies depending on the valence of ruthenium. From the viewpoint of ensuring the stability of the plating bath, however, the valence of ruthenium is preferably trivalent or tetravalent.

[0017] Therefore, it is preferable to use, as the ruthenium compound, for example, ruthenium chloride (III) or ruthenium nitrate (III) which are composed of trivalent ruthenium, or ruthenium chloride (IV) or ruthenium sulfate (IV) which are composed of tetravalent ruthenium.

[0018] The ruthenium ion concentration in the electroless ruthenium plating bath is not particularly limited, but if the ruthenium ion concentration is too low, the deposition rate of the plating film may be significantly reduced, so it is preferably more than 0.01 g / L, more preferably 1 g / L or more. Also, if the ruthenium ion concentration is too high, the bath may be decomposed due to an excessive reaction, so it is preferably 20 g / L or less, more preferably 10 g / L or less.

[0019] The ruthenium ion concentration can be measured by atomic absorption spectrometry (AAS) using an atomic absorption spectrophotometer.

[0020] (reducing agent) The reducing agent has the effect of precipitating ruthenium in the electroless ruthenium plating bath. In the electroless ruthenium plating bath of the present invention, at least one of an amine borane compound and sodium hypophosphite is used as the reducing agent.

[0021] Examples of the amine borane compound include dimethylamine borane (DMAB), trimethylamine borane (TMAB), morpholine borane, picoline borane, pyridine borane, diethylaniline borane, etc., and from the viewpoint of large distribution volume and easy availability, dimethylamine borane, trimethylamine borane, and morpholine borane are particularly preferred. These amine borane compounds may be used alone or in combination of two or more.

[0022] The content of the reducing agent in the electroless ruthenium plating bath is preferably 0.2 g / L or more, more preferably 1 g / L or more, since if the concentration of the reducing agent is too low, the deposition rate of the plating film may be significantly reduced, and if the concentration of the reducing agent is too high, the bath may be decomposed due to an overreaction, so the content is preferably 30 g / L or less, more preferably 15 g / L or less.

[0023] (Stabilizer) The stabilizer acts mainly as a complexing agent that stabilizes the solubility of ruthenium in the electroless ruthenium plating bath. In the electroless ruthenium plating bath of the present invention, a hydroxylamine compound and an amine compound are used in combination as the stabilizer.

[0024] Hydroxylamine compounds contribute to bath stability by forming metal complexes with ruthenium ions in electroless ruthenium plating baths. Examples of the hydroxylamine compounds include hydroxylamine sulfate and hydroxylamine chloride. These hydroxylamine compounds may be used alone or in combination of two or more.

[0025] The content of the hydroxylamine compound in the electroless ruthenium plating bath is preferably 1 g / L or more, more preferably 2 g / L or more, because if the concentration of the hydroxylamine compound is too low, the bath stability may decrease and the bath may decompose. Also, if the concentration of the hydroxylamine compound is too high, the bath stability may become excessive and the precipitation property of ruthenium may decrease, so the content is preferably 10 g / L or less, more preferably 8 g / L or less.

[0026] In addition, the amine compound functions as a second complexing agent by being used in combination with the above-mentioned hydroxylamine compound in the electroless ruthenium plating bath, and contributes to bath stability by forming a metal complex with ruthenium ions. Examples of the amine compound include amino acids such as glycine, glycylglycine, sodium aspartate, sodium glutamate, aspartic acid, glutamic acid, iminodiacetic acid, L-arginine, alanine, β-alanine, serine, threonine, tyrosine, asparagine, glutamine, lysine, leucine, isoleucine, lysine, tryptophan, valine, histidine, and arginine, taurine, and ethylenediamine, and are particularly preferred, including glycine, glycylglycine, sodium aspartate, sodium glutamate, L-arginine, β-alanine, serine, threonine, tyrosine, asparagine, glutamine, and lysine. These amine compounds may be used alone or in combination of two or more.

[0027] The content of the amine compound in the electroless ruthenium plating bath is preferably 1 g / L or more, more preferably 2 g / L or more, because if the concentration of the amine compound is too low, the bath stability may decrease and the bath may decompose. Also, if the concentration of the amine compound is too high, the bath stability may become excessive and the precipitation property of ruthenium may decrease, so the content is preferably 15 g / L or less, more preferably 10 g / L or less.

[0028] Here, since the hydroxylamine compound contributes more to the bath stability than the amine compound, if only the hydroxylamine compound is used as a stabilizer, the bath stability becomes excessive, and the precipitation property of ruthenium may be reduced. Therefore, in the electroless ruthenium plating bath of the present invention, by using a hydroxylamine compound and an amine compound that contributes less to the bath stability than the hydroxylamine compound in combination as a stabilizer, the bath stability is improved (i.e., the bath stability is prevented from becoming excessive) in the electroless ruthenium plating bath using the general reducing agent, amine borane compound or sodium hypophosphite, and it is possible to obtain an electroless ruthenium plating bath with excellent precipitation property.

[0029] Furthermore, it becomes possible to obtain an electroless ruthenium plating bath with excellent deposition properties, even in fine areas where plating reactions are difficult to occur (for example, areas to be plated with plating areas on the order of several tens of nanometers squared).

[0030] (Deposition rate regulator) The deposition rate adjuster is added to facilitate the removal of oxides and the like from the base layer, and has the effect of improving the deposition rate of ruthenium.

[0031] As the deposition rate regulator, various chelating agents can be used, including nitrogen-containing phosphorus compounds such as EDTA (ethylenediaminetetraacetic acid), NTA (nitrilotriacetic acid), DTPA (diethylenetriaminepentaacetic acid), HEDTA (hydroxyethylethylenediaminetriacetic acid), TTHA (triethylenetetraminehexaacetic acid), CyDTA (trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid), and EDTMP (ethylenediaminetetramethylenephosphonic acid), as well as citric acid, malic acid, gluconic acid, lactic acid, malonic acid, and fumaric acid. These deposition rate regulators may be used alone or in combination of two or more.

[0032] The content of the deposition rate modifier in the electroless ruthenium plating bath is preferably 1 g / L or more, more preferably 2 g / L or more, because if the concentration of the deposition rate modifier is too low, the deposition rate of ruthenium decreases and the plating process may take a long time. On the other hand, if the concentration of the deposition rate modifier is too high, the cost increases due to excessive addition, so the content is preferably 60 g / L or less, more preferably 20 g / L or less.

[0033] (Other Ingredients) In addition to the above-mentioned components, the electroless ruthenium plating bath of the present invention may contain various additives that are commonly used in the field of plating baths. Examples of such additives include a deposition rate inhibitor for suppressing the deposition rate of ruthenium (for fine-tuning the deposition rate of ruthenium).

[0034] Examples of the deposition rate inhibitor include unsaturated carboxylic acids such as maleic acid, 1,4-butynediol, and itaconic acid. These deposition rate inhibitors may be used alone or in combination of two or more.

[0035] (pH) The pH of the electroless ruthenium plating bath of the present invention is preferably 10 to 14, more preferably 11 to 14, and even more preferably 12 to 14. If the pH is less than 10, ruthenium may not be sufficiently precipitated, and if the pH is greater than 14, ruthenium salts may be generated and precipitated.

[0036] The pH of the plating bath can be adjusted with a pH adjuster such as sodium hydroxide, potassium hydroxide, ammonia water, tetramethylammonium hydroxide, sulfuric acid, hydrochloric acid, citric acid, boric acid, phosphoric acid, monocarboxylic acid, dicarboxylic acid, etc. These pH adjusters may be used alone or in combination of two or more.

[0037] (Plating bath temperature) The temperature of the plating bath is not particularly limited, but is preferably 60 to 90° C., more preferably 65 to 90° C., and even more preferably 70 to 85° C. If the temperature of the plating bath is less than 60° C., the plating bath may be inactivated, resulting in insufficient ruthenium deposition, whereas if the temperature exceeds 90° C., the bath may be excessively activated, resulting in bath decomposition.

[0038] (Item to be plated) There are no particular limitations on the type of object to be plated using the electroless ruthenium plating bath of the present invention, and the object to be treated with conventional ruthenium plating (for example, wiring in a printed circuit board circuit, mounting parts and terminal parts of an IC package, etc.) can be used as the object to be plated.

[0039] Furthermore, the electroless ruthenium plating bath of the present invention can be particularly suitably used when forming a liner layer from ruthenium on the wiring portion of a semiconductor circuit, on a thin film (cap metal) formed on copper wiring, or on a barrier metal when copper wiring is formed by electrolytic plating to ensure uniform growth of a copper seed film.

[0040] (Electroless ruthenium plating) By contacting the above-mentioned object to be plated with the electroless ruthenium plating bath of the present invention and subjecting the object to electroless ruthenium plating treatment, for example, a ruthenium plating film constituting the above-mentioned wiring portion, thin film (cap metal), or liner layer can be formed. Note that the temperature during the electroless ruthenium plating treatment is controlled to the bath temperature of the above-mentioned electroless ruthenium plating bath.

[0041] The processing time for the electroless ruthenium plating is not particularly limited and may be appropriately set so as to obtain a desired film thickness. More specifically, it may be, for example, about 30 seconds to 15 hours.

[0042] The thickness of the ruthenium plating film may be appropriately set depending on the required characteristics, and is usually about 0.001 to 1.0 μm. EXAMPLES

[0043] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples in any way.

[0044] (Examples 1 to 48, Comparative Examples 1 to 17) (Preparation of plating bath) Each of the plating baths of Examples 1 to 48 and Comparative Examples 1 to 17 was prepared by adding a ruthenium compound (ruthenium salt), a hydroxylamine compound and an amine compound serving as stabilizers, a reducing agent, a deposition rate regulator, a pH adjuster, and a deposition rate inhibitor to 200 ml of deionized water so as to obtain the concentrations shown in Tables 2 to 8, mixing and stirring the mixture.

[0045] As shown in Tables 2 to 8, the temperature of each plating bath (temperature for plating treatment) was set to 50 to 90° C., and the pH was set to 10 to 14.

[0046] (Pretreatment) Before carrying out the electroless plating treatment, the substrate was subjected to the pretreatment steps 1 and 2 shown in Table 1 in order. Note that between each step, washing with deionized water was carried out.

[0047] Step 1: Using MCL-12 (manufactured by Uemura Kogyo Co., Ltd., product name: Epitas (registered trademark) MCL-12), a degreasing and cleaning process was performed on a substrate (a Si wafer having a thin film of ruthenium (5 nm) applied as a base by a CVD method).

[0048] Step 2: Next, the surface of the substrate was activated using MRU-30 (manufactured by Uemura Kogyo Co., Ltd., product name: Epitas (registered trademark) MRU-30).

[0049] [Table 1]

[0050] (Electroless ruthenium plating) Next, the substrate that had been subjected to the above-mentioned pretreatment was immersed for 10 minutes in each of the plating baths of Examples 1 to 48 and Comparative Examples 1 to 17 shown in Tables 2 to 8 to form a ruthenium plating film on the surface of the substrate (on the thin ruthenium film).

[0051] (Calculation of the thickness of the formed ruthenium plating film and calculation of the deposition rate of ruthenium) Next, the thickness [nm] of the ruthenium plating film formed on the surface of the substrate was calculated using a fluorescent X-ray film thickness meter (manufactured by Fisher Instruments, product name: XDV-μ).

[0052] More specifically, a fluorescent X-ray thickness meter was used to measure the thickness [nm] of the ruthenium plating film on the surface of the substrate, and the thickness [nm] of the formed ruthenium plating film was determined by subtracting the thickness (5 nm) of the ruthenium thin film applied as a base to the above-mentioned substrate from this measured thickness.

[0053] The deposition rate [nm / 10 min] of ruthenium in the above-mentioned 10-minute plating treatment was calculated using the calculated thickness of the ruthenium plating film. The results are shown in Tables 2 to 8.

[0054] (Evaluation of Ruthenium Precipitation) The appearance of the substrate that had been subjected to the above-mentioned electroless ruthenium plating treatment was visually observed, and the deposition properties of the ruthenium plating formed by the electroless ruthenium plating treatment were evaluated according to the following criteria. The results are shown in Tables 2 to 8.

[0055] Ruthenium is deposited uniformly on the substrate: ◎ Although some color unevenness was observed on the substrate, ruthenium was deposited almost uniformly on the substrate: 〇 Ruthenium was not deposited in some areas of the substrate: △ Ruthenium is not deposited on the substrate: ×

[0056] (Evaluation of plating bath stability) After the electroless ruthenium plating process, the ruthenium plating bath was visually inspected for the presence or absence of precipitation of ruthenium particles, and the stability of the plating bath was evaluated according to the following criteria. The results are shown in Tables 2 to 8.

[0057] No precipitation of ruthenium particles was observed even after 3 hours had passed since plating: ◎ Three hours after plating, very small amounts of ruthenium particles were generated: Yes Three hours after plating, a small amount of ruthenium particles were generated: △ Three hours after plating, a large amount of ruthenium particles were generated: ×

[0058] (Measurement of resistivity of ruthenium plating film after annealing) The substrate that had been subjected to the above-mentioned electroless ruthenium plating treatment was subjected to an annealing treatment in a formic acid atmosphere at 400° C. for 10 minutes using a reduction reflow device (manufactured by Unitemp, product name: VSS-300-EP).

[0059] Next, the sheet resistance of the ruthenium film after the annealing treatment was measured using a four-probe measuring device (manufactured by Napson Corporation, product name: Napson RT-70V), and the resistivity [μΩcm] of the ruthenium plating film after the annealing treatment was calculated using the following formula (1) based on this sheet resistance value and the thickness of the ruthenium plating film measured by the above-mentioned fluorescent X-ray thickness meter. The results are shown in Tables 2 to 8.

[0060] [Number 1] Resistivity of ruthenium plating film [μΩcm] = (sheet resistance value [Ω / □] × film thickness [nm]) / 10 (1)

[0061] Incidentally, since the resistivity of a pure ruthenium plating film is approximately 7.6 [μΩcm], when the resistivity after annealing is 10 [μΩcm] to 60 [μΩcm], it is believed that almost no boron (boron derived from the amine borane compound, which is a reducing agent) is co-deposited in the ruthenium plating film formed on the surface of the substrate, and it can be said that a low resistance equivalent to that of a pure ruthenium plating film has been achieved.

[0062] Moreover, in Comparative Examples 1 to 2 and 5 to 17, since ruthenium was not deposited on the surface of the substrate, it was not possible to measure the resistivity of the ruthenium film after the annealing treatment.

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

[0066] [Table 5]

[0067] [Table 6]

[0068] [Table 7]

[0069] [Table 8]

[0070] As shown in Tables 2 to 6, in the electroless ruthenium plating baths of Examples 1 to 48, which use a hydroxylamine compound (at least one of hydroxylamine sulfate and hydroxylamine chloride) in combination with an amine compound (at least one selected from the group consisting of glycine, glycylglycine, sodium aspartate, sodium glutamate, L-arginine, β-alanine, serine, threonine, tyrosine, asparagine, glutamine, and lysine) as a stabilizer, it is found that even when an amine borane compound or sodium hypophosphite, which is a common reducing agent, is used, the bath stability can be improved and the deposition properties of ruthenium can be improved.

[0071] On the other hand, as shown in Table 7, the electroless ruthenium plating baths of Comparative Examples 1 to 4 do not use a hydroxylamine compound and an amine compound in combination as a stabilizer, and therefore the bath stability is poor. In particular, the electroless ruthenium plating baths of Comparative Examples 1 and 2, in which a hydroxylamine compound is not used, also show poor ruthenium deposition properties.

[0072] Furthermore, as shown in Tables 7 to 8, in the electroless ruthenium plating baths of Comparative Examples 5 to 17, an amine borane compound or sodium hypophosphite was not used as a reducing agent, and therefore the deposition properties of ruthenium were poor even when a hydroxylamine compound and an amine compound were used in combination as stabilizers. [Industrial Applicability]

[0073] The electroless ruthenium plating bath of the present invention can be particularly suitably used as a plating bath for forming a ruthenium plating film that constitutes a liner layer for uniformly growing a copper seed film and is formed on a barrier metal when forming a copper wiring by electrolytic plating, or a thin film (cap metal) formed on the wiring portion of a semiconductor circuit or on a copper wiring.

Claims

1. An electroless ruthenium plating bath containing at least a ruthenium compound, a reducing agent, and a stabilizer, the reducing agent is at least one of an amine borane compound and sodium hypophosphite; The stabilizer comprises a hydroxylamine compound and an amine compound, the hydroxylamine compound is at least one of hydroxylamine sulfate and hydroxylamine chloride, The amine compound is at least one selected from the group consisting of glycylglycine, sodium aspartate, sodium glutamate, L-arginine, β-alanine, serine, threonine, tyrosine, asparagine, glutamine, and lysine. Electroless ruthenium plating bath characterized by:

2. 2. The electroless ruthenium plating bath according to claim 1, wherein the concentration of the ruthenium compound is more than 0.01 g / L and not more than 10 g / L, and the concentration of the reducing agent is 0.2 g / L or more and 15 g / L or less.

3. 2. The electroless ruthenium plating bath according to claim 1, wherein the concentration of the hydroxylamine compound is from 1 g / L to 10 g / L, and the concentration of the amine compound is from 1 g / L to 15 g / L.

4. 2. The electroless ruthenium plating bath according to claim 1, further comprising a deposition rate adjuster.

5. 5. The electroless ruthenium plating bath according to claim 4, further comprising a deposition rate inhibitor.

Images