Accelerator-containing electrolyte for bottom-up copper electroplating

Abstract

The present invention relates to an electrolyte composition for depositing copper on an electrically conductive surface. The composition contains a combination of two aromatic amines, a complexing agent for copper (II) ions and an accelerator such as dithiodiglycolic acid, mercaptoacetic acid, thiourea, ammonium thiocyanate, thiocyanic acid or a combination of the foregoing. The invention also relates to a method for producing a copper interconnect, comprising the step of electroplating copper into a cavity with said electrolyte. The electrolyte enables the fabrication of copper interconnects with improved bottom-up effects during a copper filling electroplating step.

Description

Technical Field

[0001] The present invention relates to a copper electrodeposition solution for electroplating copper on a metal surface. The solution can be used in a method for filling etched lines and etched holes in a semiconductor substrate to manufacture interconnects in an integrated circuit. Background Art

[0002] The demand for semiconductor integrated circuit (IC) devices such as computer chips with high circuit speeds and high circuit density requires miniaturization of feature size. The trend toward smaller device size and increasing circuit density requires reducing the size of interconnect features and increasing their density. Interconnect features are features such as vias or trenches formed in a dielectric substrate that are then filled with metal, usually copper, to create conductive interconnects. Copper, which has better conductivity than any metal except silver, is the metal of choice because copper metallization allows for smaller features and uses less energy to pass current. In damascene processing, electrolytic copper deposition is used to metallize the interconnect features of semiconductor IC devices.

[0003] In recent years, new copper plating processes have been evaluated to address the miniaturization and integration requirements of advanced and portable electronic products.

[0004] The miniaturization of devices such as high-power computer chips with high storage density and low dissipation also requires smaller sizes of interconnects such as through silicon vias (TSVs). Therefore, technology semiconductor device manufacturing nodes below 30 nm are being developed for chip manufacturing.

[0005] Interconnects form a conductive copper metal network used to connect various electrical devices within a dielectric material (usually silicon oxide). Fabricating interconnects involves etching trenches in a layer of dielectric material, as well as etching blind vias that connect two different layers of dielectric material. The resulting cavities are then filled with copper.

[0006] There is a need to increase production rates without any deleterious defects, particularly voids or seam lines in copper interconnects which tend to increase resistance or even cause breaks in the copper conductors.

[0007] It has been found that many known electrolytes cannot be used on an industrial scale to fill trenches and vias having low opening dimensions and / or high depth dimensions. That is, defects (including voids) in the copper volume can form during copper filling with conventional acidic copper ion baths.

[0008] During interconnect fabrication, copper plating techniques are often used to fill patterns with copper in order to form conductive lines. Copper electroplating can also be performed before the copper filling step when a very thin layer of copper (called a copper seed layer) is required on the pattern surface. However, the electrolyte used for copper seed plating is generally not suitable for copper filling plating.

[0009] Solutions containing bipyridine and pyridine are described, for example, in U.S. Pat. No. 9,133,560 to Daviot et al., the subject matter of which is incorporated herein by reference in its entirety. These solutions are designed to produce a copper seed layer on a substrate having a high resistivity. However, it was found that the aqueous solutions of copper (II) ions described therein could not be used to fill trenches with copper, particularly because the copper plating speed was too low.

[0010] There remains a need in the art for improved copper electrodeposition compositions that avoid deleterious defects in copper interconnects, particularly voids or seam lines that tend to increase resistance or even lead to fracture.

[0011] Additionally, there remains a need in the art for electrolytic plating solutions and electrodeposition methods for defect-free copper filling of recessed features according to a bottom-up filling mechanism. Summary of the invention

[0012] According to a first aspect, the present invention relates to an electrolyte for copper electrodeposition, the electrolyte comprising copper ions, at least two aromatic amines and a complexing agent for copper ions and at least one accelerator in aqueous solution, the accelerator being selected from the group consisting of dithiodiglycolic acid, thioglycolic acid, thiourea, ammonium thiocyanate, thiocyanic acid and combinations thereof.

[0013] According to a second aspect, the invention relates to a method for electrochemical copper deposition on a substrate comprising at least one electrically conductive exposed surface, the method comprising the following steps:

[0014] - contacting the conductive exposed surface with the electrolyte for copper electrodeposition of the present invention, and

[0015] - polarizing the conductive exposed surface with a cathodic current and electrodepositing copper onto the conductive exposed surface for a time sufficient to form a copper deposit on the conductive exposed surface that is free of voids and other defects.

[0016] It has been surprisingly found that the use of dithiodiglycolic acid, thioglycolic acid, thiourea and thiocyanic acid in the electrolyte provides a promoter effect much higher than that observed using prior art promoters such as thiodiglycolic acid. Such promoter effect is a key phenomenon for void-free filling of mosaic structures by a bottom-up mechanism.

[0017] In one embodiment, the present invention is generally directed to an electrolyte having a pH of 8.5 to 9.5, the electrolyte being intended for use in electrodeposition of copper on a conductive substrate, the electrolyte comprising in aqueous solution:

[0018] - 0.4 mM to 50 mM copper (II) ions,

[0019] - 0.4 mM to 50 mM of a mixture consisting of a first aromatic amine, a second aromatic amine and a complexing agent for copper(II) ions, and

[0020] - at least one accelerator, wherein the at least one accelerator is selected from the group consisting of:

[0021] dithiodiglycolic acid, thioglycolic acid, thiourea, ammonium thiocyanate, thiocyanic acid, and combinations of the foregoing. DETAILED DESCRIPTION

[0022] The inventors of the present invention have surprisingly found that the addition of specific molecules to a copper electrodeposition composition can improve the quality of bottom-up filling by promoting copper deposition.

[0023] As used herein, the term "promoter" refers to an organic molecule selected from the group consisting of dithiodiglycolic acid, thioglycolic acid, thiourea, ammonium thiocyanate, and thiocyanic acid. According to a specific embodiment, the promoter improves the quality of the copper deposit in the cavity when the electrolyte is used to fill the cavity via an electrochemical method.

[0024] As used herein, the term "electrodeposition" refers to a method in which a substrate surface can be covered with a metal or organometallic coating, wherein the substrate is electrically polarized and contacted with a liquid containing a precursor of the metal or organometallic coating (called an electrolyte) so as to form the coating. Electrodeposition is optionally carried out in the presence of a reference electrode, for example by passing an electric current between the substrate to be coated, which constitutes one electrode (the cathode in the case of a metal coating) and a second electrode (the anode) in a bath containing a precursor source of the coating material (for example, metal ions in the case of a metal coating) and various reagents that are optionally intended to improve the properties of the formed coating (uniformity and fineness of the deposit, resistivity, etc.). According to international convention, the current and voltage applied to the substrate of interest (i.e., applied to the cathode of the electrochemical circuit) are negative. Throughout this article, when these currents and voltages are mentioned as positive values, it is implied that the value represents the absolute value of the current or the voltage.

[0025] As used herein, the term "electrolyte" refers to a liquid containing the precursors of the metal coating used in the electrodeposition process as defined above.

[0026] As used herein, the term "opening size" of a pattern (such as a through hole or a trench) refers to the average diameter or average width of a pattern previously hollowed out in a dielectric substrate and covered with a metal seed layer, wherein the average diameter is measured at the pattern opening. These dimensions are measured at the surface of the dielectric material, because the average diameter of a trench at its bottom or the average diameter of a blind hole at its bottom may be different from the opening size, especially when the pattern wall is not perpendicular to the substrate surface.

[0027] As used herein, the term "continuous filling" refers to a large amount of void-free copper resulting from optimal filling of the entire empty volume of a hollow pattern (also referred to as a cavity or recessed feature structure) that has been etched in a dielectric substrate. According to the present invention, optimal filling is obtained from the bottom of the pattern to the opening ("bottom-up"). In the prior art, holes or voids ("sidewall voids") can be observed in the copper deposit between the sidewalls of the pattern and the copper deposit. Voids in the form of holes or lines ("seams") equidistant from the sidewalls of the pattern can also be observed, which is usually because the copper growth rate at the bottom of the pattern is slower than the copper growth rate on the sidewalls of the pattern and at the opening. These voids can be quantified on a cross-section of the copper deposit, which is observed by transmission electron microscopy (TEM) at a magnification of 100,000 to 150,000. The continuous copper deposit of the present invention preferably has an average void volume percentage of less than 10% by volume, preferably less than or equal to 5% by volume. The average void percentage is preferably 0% by volume. The voids can be located in the copper deposit itself. In some cases, such voids are formed in the upper region of the cavity because the copper growth rate is higher in the pattern opening region than in the pattern bottom region.

[0028] As used herein, the term "about" refers to a measurable value, such as a parameter, amount, duration, etc., and is intended to include variations of + / -15% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1% or less relative to the specifically stated value, as long as such variations are suitable for performing in the invention described herein. In addition, it should also be understood that the value to which the modifier "about" refers is itself specifically disclosed herein.

[0029] As used herein, for ease of description, spatially relative terms such as "below," "below," "lower," "above," "upper," etc. are used to describe the relationship of one element or feature structure to another or more elements or features, as shown in the figures. Spatially relative terms may be intended to cover different orientations of the device in use or operation other than the orientation shown in the figures. For example, if the device in the figure is flipped, the elements described as being "below" or "below" other elements or features will be oriented to be "above" other elements or features. Therefore, the exemplary term "below" may cover both orientations of above and below. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein are interpreted accordingly. It should also be understood that the terms "front" and "rear" are not intended to be limiting and are intended to be interchangeable where appropriate.

[0030] As used herein, if not otherwise defined herein for a particular element or compound, the term "substantially free" or "substantially free" means that the given element or compound cannot be detected by ordinary analytical means of bath analysis well known to those skilled in the art of metal plating. Such methods typically include atomic absorption spectroscopy, titration, UV-visible analysis, secondary ion mass spectrometry, and other commonly used analytical methods.

[0031] As used herein, the term "includes and / or comprises" specifies the presence of the described characteristic structures, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other characteristic structures, integers, steps, operations, elements, components and / or groups thereof. As used herein, the term "between ... and ..." does not include a cutoff value, while the term "from ... to ..." includes the described lower limit and upper limit.

[0032] In a first embodiment, the present invention is generally directed to an electrolyte having a pH of 8.5 to 9.5, the electrolyte being intended for use in electrodeposition of copper on a metal substrate, the electrolyte comprising in aqueous solution:

[0033] - 0.4 mM to 50 mM copper (II) ions,

[0034] - 0.4 mM to 50 mM of a mixture consisting of a first aromatic amine, a second aromatic amine and a complexing agent for copper(II) ions, and

[0035] - at least one accelerator selected from the group consisting of dithiodiglycolic acid, thioglycolic acid, thiourea, ammonium thiocyanate, thiocyanic acid, and combinations thereof.

[0036] The complex constant (constant K) of the complex consisting of copper (II) ions and the complexing agent differs by a factor greater than 10 and preferably greater than 100 from the complex constant of copper (II) and a ligand selected from the group consisting of a first aromatic amine, a second aromatic amine and mixtures thereof.

[0037] The copper ions are preferably in the form of a complex with the first aromatic amine, with the second aromatic amine and with the complexing agent.

[0038] The electrolyte comprises at least one first copper (II) ion complex selected from the group consisting of:

[0039] - a complex of a copper(II) ion with a first aromatic amine and a second aromatic amine;

[0040] - a combination of a complex of copper(II) ions with a first aromatic amine and a complex of copper(II) ions with a second aromatic amine;

[0041] - a combination of a complex of a copper(II) ion with a first aromatic amine and a complex of a copper(II) ion with a first aromatic amine and a second aromatic amine;

[0042] - a combination of a complex of a copper(II) ion with a second aromatic amine and a complex of a copper(II) ion with a first aromatic amine and a second aromatic amine; and

[0043] - A combination of a complex of a copper(II) ion with 2,2'-bipyridine, a complex of a copper(II) ion with a second aromatic amine, and a complex of a copper(II) ion with a first aromatic amine and a second aromatic amine.

[0044] The electrolyte preferably comprises at least one second copper (II) ion complex comprising a complexing agent as described herein.

[0045] The complex of the copper(II) ion and the complexing agent may have a logarithmic complex constant (log K) greater than 7.

[0046] The molar ratio between the first aromatic amine concentration and the second aromatic amine concentration may be 1 / 2 to 2 / 1, more preferably 4 / 5 to 6 / 5, and the molar ratio between the first amine concentration and the complexing agent concentration may be 1 / 4 to 4 / 1, such as 1 / 3 to 3 / 1, or 1 / 2 to 2 / 1 ± 10%.

[0047] The complex of copper (II) ions may include a single first aromatic amine, a single second aromatic amine, or two aromatic amines. In the electrolyte solution, the molar concentration of the copper (II) ion complex comprising the first aromatic amine and the second aromatic amine is preferably higher than the molar concentration of the copper complex comprising the first aromatic amine, and higher than the molar concentration of the copper complex comprising the second aromatic amine. More preferably, the electrolyte does not contain a copper complex comprising a single first aromatic amine, and does not contain a copper complex comprising a single second aromatic amine.

[0048] In a preferred embodiment, the first amine may be 2,2'-bipyridine and the second amine may be imidazole.

[0049] Typically, the electrodeposition composition according to the present invention comprises copper ions Cu 2+ The copper(II) ion source (copper(II) in salt form) is preferably a copper(II) salt such as copper(II) sulfate, a copper(II) alkylsulfonate such as copper(II) methanesulfonate, a copper(II) chloride, copper(II) nitrate, copper(II) citrate, copper(II) oxide, copper(II) carbonate or copper(II) acetate. In one embodiment, the copper(II) ion source is copper(II) sulfate, and more preferably copper(II) sulfate pentahydrate.

[0050] According to a particular feature, the copper(II) ions in complex form are present in the electrodeposition composition in a concentration between 0.4 mM and 50 mM, preferably between 0.4 mM and 40 mM, for example between 1.0 mM and 25 mM, for example between 4.0 mM and 15 mM.

[0051] The electrolyte advantageously comprises a first complex of copper(II) ions comprising a 2,2'-bipyridine ligand and an imidazole ligand, and a second complex of copper(II) ions with a copper complexing agent.

[0052] In the electrolyte, the molar ratio between the first copper (II) complex and the second copper (II) complex can be advantageously selected according to the complexing agent chemical formula and pattern dimensions (such as opening size and depth). The molar ratio between the first copper (II) complex and the second copper (II) complex can be 0.1 to 4.0, such as 0.2 to 3.0, and preferably 0.5 to 1.5.

[0053] The ratio of the 2,2′-bipyridine molar concentration to the imidazole molar concentration is preferably 1:2 to 2:1, more preferably 4:5 to 6:5, and still more preferably 0.95 to 1.05.

[0054] The ratio of the molar concentration of the complexing agent to the molar concentration of the copper(II) ions is preferably between 0.15 and 6.0, more preferably between 0.2 and 4.0 or 0.3 and 2.5, for example 0.5 and 2.0.

[0055] The electrolyte of the present invention further comprises at least one accelerator selected from the group consisting of dithiodiglycolic acid, thioglycolic acid, thiourea, ammonium thiocyanate, thiocyanic acid, and combinations of the foregoing. In one embodiment, the electrolyte is at least substantially free of thiodiglycolic acid.

[0056] Depending on the accelerator chosen, the concentration of the at least one accelerator may range from 0.05 ppm to 200 ppm, advantageously from 0.1 ppm to 20 ppm.

[0057] When the accelerators used in accordance with the present invention are used at mass concentrations or molar concentrations equal to or lower than the mass concentrations of accelerators (such as thiodiglycolic acid) used in prior art compositions such as those described in U.S. Pat. No. 10,883,185, the subject matter of which is incorporated herein by reference in its entirety, improved acceleration can be provided. By "improved acceleration" is meant a lower percentage of voids in the copper deposit, or a higher rate of void filling, than when prior art accelerators are used.

[0058] Without being bound by theory, it is believed that the reason why the promoting effect of the compounds described herein is greater than that of thiodiglycolic acid is due to the higher mass percentage of sulfur in the compounds. In alkaline environments, it has been observed that promoting materials containing a higher mass percentage of sulfur (total compound mass) have a better bottom-up effect. This trend is not observed in acid copper electroplating. In one embodiment, the accelerator is dithiodiglycolic acid, preferably used in a concentration ranging from 2ppm to 20ppm, more preferably 5ppm to 15ppm.

[0059] In one embodiment, the accelerator is thioglycolic acid, preferably used in a concentration ranging from 0.1 ppm to 20 ppm, more preferably from 1 ppm to 10 ppm.

[0060] In one embodiment, the accelerator is thiourea, preferably used in a concentration of 0.01 ppm to 5 ppm, more preferably 0.1 ppm to 2 ppm.

[0061] In one embodiment, the accelerator is ammonium thiocyanate, preferably used in a concentration ranging from 0.01 ppm to 5 ppm, more preferably from 0.1 ppm to 2 ppm.

[0062] In one embodiment, the accelerator is thiocyanic acid, preferably used in a concentration of 0.01 ppm to 5 ppm, more preferably 0.1 ppm to 2 ppm.

[0063] In one embodiment, the present invention also relates to an electrolyte having a pH of 8.5 to 9.5, which is intended for electrodeposition of copper on a metal substrate, said electrolyte comprising in aqueous solution:

[0064] - 0.4 mM to 50 mM, for example 0.4 mM to 40 mM, of copper(II) ions,

[0065] - 0.8 mM to 80 mM of a mixture of 2,2'-bipyridine and imidazole, the ratio of the molar concentration of copper(II) ions to the molar concentration of the second aromatic amine mixture being preferably 1 / 5 to 10 / 1,

[0066] For example, 1 / 4 to 5 / 1, 1 / 3 to 3 / 1, 1 / 2 to 2 / 1 or 2 / 3 to 1 / 1,

[0067] - a complexing agent for copper(II) ions, preferably wherein the complexing agent for copper(II) ions preferably forms a complex having a logarithmic complex constant (log K) of greater than 7 with the copper(II) ions in the electrolyte.

[0068] - 0.05 mg / l to 200 mg / l (ppm) of at least one accelerator as described herein,

[0069] The electrolyte has a pH of 8.5 to 9.5.

[0070] In a specific embodiment of the electrolyte, the ratio of the molar concentration of copper (II) ions to the molar concentration of the mixture of imidazole and 2,2'-bipyridine is 1 / 4 to 2 / 1.

[0071] Features as described herein apply to any of the foregoing electrolytes, as appropriate.

[0072] The complexing agent for copper (II) as part of the electrolyte of the present invention or as part of the process of the present invention for preparing the electrolyte can be selected from the group consisting of: citric acid, tartaric acid, phenanthroline, ethylenediaminetetraacetic acid (EDTA), N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA), ethylenediamine, 1,6-diamino-cyclohexane, diethylene-triamine, triethylene-tetraamine, N,N,N,N-tetramethyl-ethylenediamine, N,N-bis(2-hydroxyethyl)ethylenediamine, N,N,N,N-tetrakis(2-hydroxyethyl)ethylenediamine, glycine, 2-amino-ethyl-phosphonic acid, salicylic acid, salicylhydroxamic acid, catechol, 1,2-dihydroxybenzene-4-sulfonic acid, acetylacetone, acetylacetone, dimethylglyoxime and 1,3-diamino-propane. The complexing agent can be used in any of its acidic or basic forms when complexing with copper.

[0073] In a particular embodiment, the complexing agent is ethylenediamine.

[0074] In another specific embodiment, the complexing agent is a tartrate ion.

[0075] The electrolyte of the present invention may advantageously be free of polymer inhibitors such as polyethylene glycol. In addition, previously, a chloride ion source was typically added to the electrolyte to synergize with the polymer inhibitor. However, in the context of the present invention, it was found that chloride ions do not need to be added to ensure the efficacy of the solution. Therefore, the electrolyte of the present invention preferably contains less than 50ppm of chloride ions. More preferably, the electrolyte is at least substantially free of chloride ions.

[0076] Although surfactants are usually required in prior art electrolytes for improving the wettability of the barrier material surface to be coated with copper, according to the present invention, no surfactants need to be incorporated into the electrolyte. Therefore, the electrolyte of the present invention may be substantially free of any surfactants or wetting agents.

[0077] The electrolyte may contain levelers and / or brighteners as known in the art. However, the use of levelers and / or brighteners is not required, and good results can be achieved even in the absence of levelers and / or brighteners.

[0078] The pH of the electrolyte is preferably above 8.5. This is all the more surprising since prior art electrolytes used to fill cavities typically have a much lower pH to ensure that the electrolyte is free of H. + The electrolyte of the present invention preferably has a pH between 9.0 and 9.5, more preferably 9.2 ± 10%. One or more pH adjusting compounds, including, for example, tetraalkylammonium salts such as tetramethylammonium salts or tetraethylammonium salts, can be used to adjust the pH of the electrolyte to the desired range. In one embodiment, the pH adjusting agent includes tetramethylammonium hydroxide or tetraethylammonium hydroxide.

[0079] According to a particular embodiment, the concentration of copper(II) ions is between 0.4 mM and 50 mM, for example between 0.4 mM and 40 mM, the concentration of 2,2'-bipyridine is between 0.4 mM and 40 mM, and the concentration of the complexing agent is between 1 mM and 100 mM.

[0080] In case the complexing agent is ethylenediamine, the concentration of copper(II) ions may be between 4 mM and 20 mM, the concentration of the mixture consisting of 2,2'-bipyridine and imidazole may be between 5 mM and 20 mM, and the concentration of the complexing agent may be between 1 mM and 60 mM.

[0081] In the case where the complexing agent is tartrate ion, the molar concentration of copper (II) ion may be 4 to 20 mM, the molar concentration of the mixture of 2,2'-bipyridine and imidazole may be 5 to 20 mM, and the molar concentration of the complexing agent of copper (II) ion may be 3 to 50 mM.

[0082] In the electrolyte, the first aromatic amine concentration (such as 2,2'-bipyridine concentration) preferably accounts for 0.05 to 1 molar equivalents of the copper (II) ion concentration, more preferably 0.1 to 0.8 molar equivalents, more preferably 0.4 to 0.7 molar equivalents.

[0083] In the electrolyte, the second aromatic amine concentration (such as imidazole concentration) is preferably 0.05 to 1 molar equivalent, more preferably 0.1 to 0.8 molar equivalent, more preferably 0.4 to 0.7 molar equivalent to the copper (II) ion concentration.

[0084] This electrolyte can be obtained by mixing:

[0085] - a first solution comprising a first copper (II) ion complex is mixed with a second solution comprising a second copper (II) ion complex, wherein the first solution is obtained by mixing copper (II) ions, 2,2'-bipyridine and imidazole, wherein the molar ratio between the concentration of 2,2'-bipyridine and the concentration of imidazole is in the range of 4 / 1 to 1 / 4, and

[0086] - A second solution obtained by mixing copper(II) ions with complexing molecules.

[0087] The concentration of the complexing molecule in the second solution may be 0.15 to 6.0 molar equivalents of the copper (II) ion concentration in the second solution. In the first solution, the ratio of the molar concentration of the copper (II) ion to the molar concentration obtained by the sum of the molar concentration of imidazole and the molar concentration of 2,2'-bipyridine may be 1 / 5 to 10 / 1.

[0088] The first solution and the second solution may be mixed by selecting a volume ratio between the second solution and the first solution of 5 volume % to 35 volume %, more preferably 10 volume % to 25 volume %.

[0089] The invention also relates to a method for preparing one of the electrolytes described above.

[0090] Such a method may include the steps of preparing a first solution of a complex of copper(II) with 2,2'-bipyridine and imidazole, preparing a second solution of a complex of copper(II) with a complexing agent for copper(II) ions, the complexing agent forming a complex with copper(II) ions having a logarithmic complex constant (log K) higher than 7, mixing the first solution and the second solution in a specific volume ratio, and obtaining an electrolyte comprising at least two complexes: a complex of copper(II) with 2,2'-bipyridine and imidazole, and a complex of copper(II) with a complexing agent.

[0091] Another method may include the steps of preparing a first solution comprising copper (II) ions, a first aromatic amine and a second aromatic amine so as to advantageously prepare a complex of copper (II) ions with the first aromatic amine and / or the second aromatic amine, preparing a second solution comprising copper (II) ions and a complexing agent so as to advantageously prepare a complex of copper (II) ions with the complexing agent, and mixing the first solution and the second solution.

[0092] In the first solution, the molar concentration of copper(II) ions is preferably between 0.3 mM and 60 mM or between 0.8 mM and 50 mM, preferably between 1 mM and 10 mM, more preferably between 3 mM and 9 mM.

[0093] In the first solution, the first aromatic amine concentration (such as 2,2'-bipyridine concentration) and the copper (II) molar concentration are preferably equal to the second aromatic amine concentration (such as imidazole concentration) within a possible variation range of ±10%.

[0094] After mixing the aromatic amine with the copper (II) ions, the pH of the first solution may optionally be adjusted with a base or acid known to those skilled in the art. The pH adjuster may be, for example, sulfuric acid or a tetraalkylammonium salt such as a tetramethylammonium salt or a tetraethylammonium salt (e.g., tetramethylammonium hydroxide or tetraethylammonium hydroxide). The first solution may have a pH value between 8 and 10, for example 8.85 to 9.25.

[0095] Once adjusted, the pH of the first solution may optionally be stabilized within the aforementioned pH range by buffers known to those skilled in the art.

[0096] In the second solution, the molar concentration of copper(II) ions is preferably between 30 mM and 100 mM or between 40 mM and 80 mM, preferably between 60 mM and 70 mM.

[0097] In the second solution, the concentration of the complexing agent is generally selected relative to the copper (II) concentration in the electrolyte so that a large amount of copper complexes with the complexing agent are formed. The complexing agent concentration is preferably 0.5 to 3 molar equivalents to the copper (II) ion concentration.

[0098] In the case where the complexing agent is a tartrate, the concentration of the complexing agent is preferably 0.5 to 2 molar equivalents, more preferably 0.65 to 1.25 molar equivalents, more preferably 0.75 to 1.15 molar equivalents, and still more preferably 0.95 to 1.05 molar equivalents of the copper (II) ion concentration. After mixing the aromatic amine with the copper (II) ions, the pH of the second solution may optionally be adjusted with a base or acid known to those skilled in the art.

[0099] The second solution may contain a pH adjusting agent so as to have a pH value between 7 and 11. The pH is preferably adjusted so as to form a complex of copper ions and the complexing agent.

[0100] Once adjusted, the pH of the second solution may optionally be stabilized within the aforementioned pH range by buffers known to those skilled in the art.

[0101] The volume ratio between the second solution and the first solution may be between 5% and 35% by volume, more preferably between 10% and 25% by volume.

[0102] Additional ingredients may be incorporated into the first solution and / or the second solution prior to mixing the first solution and / or the second solution.

[0103] Alternatively, the additional ingredients may be added in another step after the step of mixing the first solution and the second solution.

[0104] Although there is no restriction on the solvent in principle (provided that the solvent fully dissolves the active material of the solution and does not interfere with the electrodeposition), water is preferred as the solvent for the electrolyte, the first solution and the second solution. According to one embodiment, the solvent substantially comprises water, i.e. comprises more than 90% by volume.

[0105] The first solution and the second solution can be prepared by dissolving a salt selected from the group consisting of copper (II) sulfate, copper (II) chloride, copper (II) nitrate, copper (II) acetate, preferably copper (II) sulfate, more preferably copper (II) sulfate pentahydrate, or a hydrate thereof in a solvent.

[0106] The present invention also relates to a method for electrochemical copper deposition on a substrate comprising at least one conductive exposed surface, the method comprising the following steps:

[0107] - contacting the conductive exposed surface with an electrolyte as described above, and

[0108] - polarizing the conductive exposed surface with a cathodic current and electrodepositing copper onto the conductive exposed surface for a sufficient time to form a copper deposit.

[0109] The cavities (also referred to as patterns) may have an average diameter or average width of 10 nm to 30 nm at their openings, and a depth of 1 à to 150 micrometers.

[0110] In one embodiment, the method of the present invention can be used to fill a pattern that has been hollowed out in a dielectric substrate, the pattern having a size less than 45 nm, preferably less than 25 nm, and a shape factor higher than 2:1, preferably higher than 3:1.

[0111] In a preferred embodiment, the pattern has an opening size less than 25 nm and a form factor higher than 3:1.

[0112] The method may be an electrochemical method for copper filling of a pattern hollowed out in a dielectric substrate and having at least one exposed surface of a metal seed layer, wherein the pattern has an opening size of less than 45 nm and a form factor higher than 2, the method comprising the steps of:

[0113] - contacting the exposed surface with one of the electrolytes as described herein, and

[0114] - polarizing the exposed surface with a cathodic current and electrodepositing copper onto the exposed surface for a time sufficient to completely fill the pattern with a copper deposit that contains no voids.

[0115] All features that have been described with respect to the electrolyte of the present invention and the method for preparing the electrolyte are applicable to the electrodeposition method.

[0116] The electrolyte is used by applying an electric current. Reducing agents for copper(II) oxide, such as dimethylamine borane or hypophosphorous acid, are not indicated in the electroless method and for this reason are not included.

[0117] The electrochemical process of the present invention has the advantage of providing a copper filling rate that is at least twice or at least three times the copper filling rate obtained with the same electrochemical process except that the electrolyte does not contain a complex of copper (II) ions with a complexing agent as described herein.

[0118] In this embodiment, the pattern preferably has an opening size of less than 25 nm and a form factor greater than 3.

[0119] The copper fill rate is determined by the time required to fill the entire volume of the trench or via. The copper fill rate is the percentage of the volume of the pattern cavity filled with copper at the end of a predetermined time (e.g., 1 minute or 3 minutes). The copper fill rate can be expressed as the time required to fill the entire volume of the predetermined pattern cavity.

[0120] The present invention also describes a semiconductor manufacturing method similar to a copper damascene system or a copper dual damascene system.

[0121] The main first step consists of etching the dielectric substrate. The architecture consists of a combination of the above patterns which can be trenches and vias. Next, a diffusion barrier layer is placed on the free surface of the dielectric substrate including the etched pattern in order to prevent the subsequently applied copper layer from diffusing into the junctions of the substrate.

[0122] The electrochemical deposition method of the present invention may include a step of forming a thin metal seed layer made of copper (Cu), cobalt (Co) or ruthenium (Ru) before the copper filling step. The metal seed layer may include at least two materials selected from the group consisting of copper (Cu), cobalt (Co) or ruthenium (Ru). In a specific embodiment, the metal seed layer includes a ruthenium layer and a copper layer. In another embodiment, the metal seed layer includes a cobalt layer and a copper layer, and the cobalt layer is stacked on the diffusion barrier layer.

[0123] The thin metal seed layer may be deposited onto the diffusion barrier layer using techniques known to those skilled in the art, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), electroless deposition, or electrochemical deposition.

[0124] Therefore, the method of the present invention may include the step of forming a metal seed layer using chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), electroless deposition or electrochemical deposition, provided that both the electroless deposition and the electrolytic deposition use an electrolyte different from that described with respect to the first embodiment of the present invention.

[0125] In a preferred embodiment of the present invention, the metal seed layer is formed via a PVD route.

[0126] The thickness of the metal seed layer is preferably between 0.5 nm and 20 nm, preferably between 1 nm and 10 nm, for example between 2 nm and 5 nm. Such thickness values ​​are preferably measured on the inner wall of the pattern. In practice, the metal seed layer can have different thickness values ​​on the dielectric substrate field; at the pattern opening, as well as on the pattern sidewalls and at the pattern bottom.

[0127] The diffusion barrier layer may comprise at least one material selected from the group consisting of tantalum (Ta), titanium (Ti), tantalum nitride (TaN), titanium nitride (TiN), manganese (Mn) and tungsten (W). The thickness of the diffusion barrier layer is typically between 0.5 nm and 20 nm. The layer may be deposited using techniques known to those skilled in the art, such as chemical vapor deposition (CVD), physical vapor deposition (PVD) or atomic layer deposition (ALD). The diffusion barrier layer may be formed of two layers, each layer consisting of one of the materials disclosed above.

[0128] According to one embodiment of the present invention, the dielectric substrate is covered successively with at least two layers of two different materials and a conductive layer as described above on the pattern sidewalls, on the pattern bottom and on the dielectric substrate field, and the at least two layers of two different materials form a copper diffusion barrier as disclosed above.

[0129] The method of the present invention makes it possible to deposit copper in a pattern with a small opening size, in particular a groove of very small width. Therefore, the opening size of the pattern can be lower than the upper limit corresponding to the technology node selected from the group consisting of 45nm, 40nm, 35nm, 30nm, 25nm, 20nm, 15nm and 10nm. The opening size of the pattern can be selected from the group consisting of 45nm, 32nm, 22nm, 14nm, 10nm, 7nm and 5nm. The pattern preferably has an opening size greater than or equal to 5nm.

[0130] The form factor, expressed as the ratio of the depth of the pattern to the size of the opening, may vary from 2: 1 to 20: 1, e.g., 3: 1 to 10: 1. The method according to the invention advantageously allows void-free deposition of copper in cavities having particularly high form factors, e.g., greater than 2: 1, greater than 3: 1, greater than 4: 1, greater than 5: 1, greater than 6: 1, or even greater than 7: 1 and above, preferably less than 20: 1 or less than 15: 1.

[0131] According to a specific embodiment, the pattern has an opening size of 5 to 45 nm and a form factor of 3:1 to 10:1.

[0132] The patterned surface of conductive material includes three main regions: (1) the field shared by all cavities of the pattern, (2) each cavity including the sidewalls, and (3) the bottom.

[0133] During the deposition step, the surface of the cavity to be filled can be polarized in constant current mode (fixed applied current) or in constant voltage mode (applied and fixed potential, optionally relative to a reference electrode) or in pulse mode (with current or with voltage) or in ramp mode (with current or with voltage).

[0134] According to one embodiment of the present invention, the polarization of the surface of the patterned cavities is performed in ramp mode, applying a voltage from open circuit potential to -1.5 V / SCE (calomel saturated electrode) and from -1.5 V / SCE (calomel saturated electrode) to open circuit potential, with a scan rate equal to 5 mV / s.

[0135] The electrolytes according to the invention can be used after a procedure comprising an initial step of "hot entry", but they can also be used, particularly advantageously, after a procedure comprising an initial step of "cold entry", during which the surface to be coated is brought into contact with the electrodeposition bath without being electrically polarized and is maintained in this state for the desired time. Thus, according to a particular feature, the method according to the invention comprises, before the electrodeposition, a "cold entry" step, during which the surface of the cavity to be filled is brought into contact with the electrodeposition composition according to the invention without being electrically polarized and is optionally maintained in this state for at least 30 seconds.

[0136] The electrodeposition method according to the invention can be carried out at room temperature. The room temperature may be between 20° C. and 35° C. Therefore, it is usually not necessary to heat the electrodeposition bath.

[0137] The method according to the invention provides copper deposits of excellent quality, for example without material defects such as seams or voids.

[0138] The invention finally relates to a semiconductor device obtainable or obtained by the method that has just been described.

[0139] The present invention is illustrated in more detail in the following examples. Unless otherwise stated, the temperature in each example is room temperature.

[0140] Example 1 Comparison: Characterization of Thiodiglycolic Acid Promotion Effect Using Copper Electrochemical Deposition

[0141] Electrochemical Characterization of the Effect of Thiodiglycolic Acid on Copper Deposition Deposition was performed using a composition containing copper (II) sulfate, 2,2'-bipyridine, imidazole, tetraethylammonium hydroxide, and tartaric acid according to the teachings of US Patent No. 10,883,185, the subject matter of which is incorporated herein by reference in its entirety.

[0142] Materials and Equipment :

[0143] Substrate :

[0144] The substrate used in this example was a bulk pure cobalt having a thickness of 10 micrometers and a diameter of 5 mm.

[0145] Electrolyte solution :

[0146] A first solution was prepared containing 6.05 mM 2,2'-bipyridine, 6.05 mM imidazole, and 6.05 mM CuSO4(H2O)5. A second solution was prepared containing 65.4 mM tartaric acid and 64.1 mM CuSO4(H2O)5. The first and second solutions were mixed in a selected ratio, thiodiglycolic acid was added, and the pH was adjusted to obtain an electrolyte solution.

[0147] In the resulting solution, the concentration of 2,2'-bipyridine was 5.44 mM and the concentration of imidazole was 5.44 mM. The concentration of CuSO4(H2O)5 was equal to 11.85 mM and the concentration of tartrate was 6.54 mM. The concentration of thiodiglycolic acid was 25 ppm. The pH of the solution was adjusted to 9.2 with tetraethylammonium hydroxide.

[0148] Add 0.1M K2SO4 salt carrier to ignore Cu 2+ Current migration contribution.

[0149] equipment :

[0150] In this example, the electrolytic deposition apparatus consists of two parts: (1) an electrolytic cell designed to contain the electrodeposition solution, which is equipped with a fluid recirculation system for controlling the fluid dynamics of the system; and (2) a rotating electrode equipped with a sample holder suitable for the size of the part used (4 cm×4 cm).

[0151] The electrowinning cell has two electrodes :

[0152] - Working electrode: rotating disk Co electrode (D = 5mm)

[0153] - Counter electrode: Platinum

[0154] - Reference electrode: Calomel saturated electrode (CSE)

[0155] The connector provides electrical contact for the electrodes, which are connected via electrical leads to a potentiostat supplying up to 20 V or 2 A.

[0156] Electricity Solution :

[0157] Cathodic polarization was performed from open circuit potential to -1.5 V / ECS and to -1.5 V / ECS to open circuit potential. The scan rate was 5 mV / s and the duration of the electrodeposition step was sufficient to measure the current response to assess the deposition rate.

[0158] Reference :

[0159] A comparison has been made in order to evaluate the accelerator effect of thiodiglycolic acid.The above protocol was repeated except that the electrolyte solution did not contain thiodiglycolic acid.

[0160] Evaluation of the effect of accelerator

[0161] Low current was observed during the first scan (from open circuit potential to -1.5 V / SCE), while hysteresis was observed during the reverse scan (from -1.5 V / SCE to open circuit potential) once the passivation of the bulk cobalt surface was broken.

[0162] Hysteresis is characterized by ΔE, which is the difference in potential when deposition occurs when passivation is intact (forward scan) and when passivation is degraded (reverse scan). The hysteresis surface area is a good indicator of the effect of the promoter and can be extrapolated to be a good indicator of the bottom-up effect of the promoter during the electroplating deposition process on substrates etched with recessed features rather than flat bulk cobalt substrates. High ΔE means that the promoter makes copper reduction thermodynamically easier after passivation is broken.

[0163] Results :

[0164] The ratio of the prior art (ΔE value of the electrolyte comprising thiodiglycolic acid) to the reference (ΔE value of the electrolyte comprising no promoter molecules) was found to be 1.1.

[0165] The same ratio was also measured using the hysteresis surface area as a parameter.

[0166] in conclusion :

[0167] Comparable ΔE and hysteresis surface areas were obtained using thiodiglycolic acid as accelerator and reference. This means that thiodiglycolic acid has a very weak accelerator effect.

[0168] Example 2: Characterization of the effect of dithiodiglycolic acid promotion using copper electrochemical deposition

[0169] Example 1 was repeated except that thiodiglycolic acid was replaced by dithiodiglycolic acid at different concentrations (i.e., 1 ppm to 30 ppm) in the electrolyte solution. The best ΔE was obtained at a concentration of 10 ppm, resulting in a 3-fold increase in ΔE and hysteresis surface area. This value is much higher than that obtained in Example 1 under similar conditions, which means that dithiodiglycolic acid has a stronger accelerator effect than thiodiglycolic acid.

[0170] Example 3: Characterization of Thioglycolic Acid Promotion Effect Using Copper Electrochemical Deposition

[0171] Example 1 was repeated except that thiodiglycolic acid was replaced by thioglycolic acid at various concentrations (e.g., 1 ppm to 30 ppm) in the electrolyte solution. The highest ΔE was obtained at a concentration of 5 ppm, resulting in a 2.5-fold increase in ΔE and a 2.5-fold increase in hysteresis surface area.

[0172] This value is much higher than the value obtained under similar conditions in Example 1, which means that thioglycolic acid has a stronger accelerator effect than thiodiglycolic acid.

[0173] Example 4 Comparison: Characterization of Thiourea Promotion Effect Using Copper Electrochemical Deposition

[0174] Example 1 was repeated except that thiodiglycolic acid was replaced with thiourea at concentrations ranging from 0.2 ppm to 2 ppm, and the highest ΔE was obtained at a concentration of 1 ppm, resulting in a 1.5-fold increase in ΔE and hysteresis surface area over the reference.

[0175] Example 5: Characterization of the effect of ammonium thiocyanate on copper electrochemical deposition

[0176] Example 1 was repeated except that ammonium thiocyanate at a concentration less than 1 ppm was used instead of thiodiglycolic acid, and the highest ΔE was obtained at a concentration of 0.5 ppm.

[0177] In this case, ΔE and hysteresis surface area have been increased 2.0 times based on the reference.

[0178] The results of Examples 1 to 5 are summarized below in Table 1. The concentration of each accelerator was varied due to different stabilities and ΔE changes with concentration.

[0179] Table 1

[0180]

[0181] The examples demonstrate that the use of one of these promoters in a copper electrolyte produces copper deposits that are free of voids, seams, and other defects.

Claims

1. An electrolyte having a pH of 8.5 to 9.5, the electrolyte being intended for use in the electrodeposition of copper on a conductive substrate, the electrolyte comprising in aqueous solution: - 0.4 mM to 50 mM copper (II) ions, - 0.4 mM to 50 mM of a mixture consisting of a first aromatic amine, a second aromatic amine and a complexing agent for copper(II) ions, and - at least one accelerator, wherein the at least one accelerator is selected from the group consisting of dithiodiglycolic acid, thioglycolic acid, thiourea, ammonium thiocyanate, thiocyanic acid, and combinations of the foregoing. 2 . The electrolyte of claim 1 , wherein the first aromatic amine is 2,2′-bipyridine and the second aromatic amine is imidazole. 3 . The electrolyte according to claim 2 , wherein the ratio between the molar concentration of 2,2′-bipyridine and the molar concentration of imidazole is 1:2 to 2:

1.

4. The electrolyte according to any one of the preceding claims, wherein the complexing agent for copper(II) ions is a tartrate or ethylenediamine.

5. The electrolyte according to any one of the preceding claims, wherein the molar ratio between the first amine concentration and the complexing agent concentration can be 1 / 4 to 4 / 1, such as 1 / 3 to 3 / 1, or 1 / 2 to 2 / 1 ± 10%.

6. The electrolyte according to any one of the preceding claims, wherein the concentration of the at least one promoter is from 0.05 ppm to 200 ppm, preferably from 0.1 ppm to 20 ppm.

7. The electrolyte of claim 6, wherein the promoter is dithiodiglycolic acid and is present at a concentration of 5 ppm to 15 ppm.

8. The electrolyte of claim 6, wherein the promoter is thioglycolic acid and is present at a concentration of 1 ppm to 10 ppm.

9. The electrolyte of claim 6, wherein the promoter is thiourea and is present at a concentration of 0.1 ppm to 2 ppm.

10. The electrolyte of claim 6, wherein the promoter is ammonium thiocyanate and is present at a concentration of 0.1 ppm to 2 ppm.

11. A method for electrochemical copper deposition on a substrate comprising at least one conductive exposed surface, the method comprising the steps of: - contacting the electrically conductive exposed surface with an electrolyte according to any one of claims 1 to 10, and - polarizing the conductive exposed surface with a cathodic current and electrodepositing copper onto the conductive exposed surface for a sufficient time to form a copper deposit.

12. The electrochemical process of claim 11, wherein the electrically conductive exposed surface is a surface of a material comprising essentially cobalt, copper or ruthenium.

13. The electrochemical process according to claim 12, wherein the material is in the form of a layer having a thickness of 1 nm to 10 nm.

14. The electrochemical method of claim 11, wherein the conductive exposed surface is a surface of a pattern that has been hollowed out in a dielectric substrate.

15. Electrochemical method according to the preceding claim, wherein polarizing the electrically conductive exposed surface is performed for a time sufficient to completely fill the pattern with a copper deposit free of voids. 16 . The electrochemical method according to claim 14 , wherein the pattern has an opening size of 5 nm to 45 nm and a shape factor higher than 2, preferably 3 to 10, and also preferably 4 to 10.

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