Electrolyte and method for cobalt electrodeposition

Abstract

The present invention relates to a method for producing cobalt interconnects and to an electrolyte making it possible to achieve this, the electrolyte having a pH of less than 4.0, comprising cobalt ions, chloride ions and an organic additive, the organic additive comprising an α-hydroxycarboxylic acid and an amine chosen from polyethyleneimine or benzotriazole.

Description

[Technical Field]

[0001] This invention relates to the electrodeposition of cobalt onto a conductive surface. More precisely, this invention relates to an electrolyte and method for cobalt electrodeposition that can be used to create electrical interconnections in integrated circuits. [Background technology]

[0002] Semiconductor devices include different levels of integration and two categories of conductive metal interconnects. These two categories of conductive metal interconnects are trenches, tens of nanometers wide, that extend across the surface of the device and connect electronic components, and through vias, which connect different levels and have a diameter of approximately several hundred nanometers.

[0003] The fabrication of the interconnection includes etching a cavity onto a substrate, subsequently depositing a metal seed layer on the surface of the cavity, thereby enabling a subsequent step of electrochemically filling the cavity with a conductive metal.

[0004] Conventional methods for filling interconnects with cobalt involve using an electrolyte containing cobalt salts and numerous organic additives. These combinations of additives are generally necessary to obtain high-quality cobalt ingots, particularly those free of material voids and exhibiting good conductivity.

[0005] Cavity filling can be carried out according to two mechanisms, namely bottom-up filling or conformal filling, depending on the electrolyte used. The bottom-up filling method is in contrast to a filling method in which cobalt precipitates grow at the same rate at the bottom and walls of the hollow pattern.

[0006] To achieve bottom-up filling, conventional electrolytes include several cleaning additives (e.g., inhibitors and accelerators). Such systems prevent the formation of cobalt precipitate voids and thus prevent premature blockage of the cavity opening. Inhibitors limit cobalt deposition at the upper level of the cavity, on the cavity walls, and on the flat surface of the substrate through which the cavity opens, while accelerators diffuse to the bottom of the cavity to promote cobalt deposition. The presence of accelerators is even more necessary for narrow and deep cavities because their diffusion can increase the rate of cobalt deposition at the bottom of the cavity.

[0007] Electrodeposition baths designed for bottom-up filling have several drawbacks that ultimately limit the smooth operation of the manufactured electronic devices and make them too expensive to produce. They actually generate cobalt interconnects contaminated by the organic additives required to limit hole formation during filling. Furthermore, the filling rates achieved with these chemicals are far too slow to be suitable for industrial-scale production.

[0008] For example, in U.S. Patent Application Publication 2016 / 0273117, the electrolyte contains numerous additives, including inhibitors and accelerators that have complementary functions to ensure reliable bottom-up filling. The inventors found that the cobalt precipitated using this electrolyte has a very high resistivity and that holes are formed in the cobalt during filling. This is why the precipitate needs to be annealed to eliminate the holes.

[0009] Therefore, there is a need to provide an electrolytic bath that results in cobalt interconnection with particularly improved conductivity. To achieve this goal, it is desirable to produce cobalt precipitates that contain very small amounts of impurities and have no material voids, even without the use of an annealing step. It is also desirable to propose an electrolyte that avoids the formation of holes in the cobalt while achieving a deposition rate high enough to make device manufacturing profitable.

[0010] The inventors found that a combination of α-hydroxycarboxylic acid and a nitrogen compound (e.g., polyethyleneimine or benzotriazole) satisfies these needs.

[0011] While α-hydroxycarboxylic acids have indeed been used in electrochemical methods for cobalt deposition (e.g., International Patent Application Publication No. 2019 / 179897), these methods follow a conformal packing mechanism, and once that mechanism is complete, holes remain in the metal unless the precipitate is annealed. [Overview of the project]

[0012] Accordingly, the present invention relates to a method for creating cobalt interconnects by bottom-up filling of a cavity using an electrolyte with a pH in the range of 1.8 to 4.0, which contains an additive selected from cobalt(II) ions, chloride ions, α-hydroxycarboxylic acid, polyethyleneimine ions, and benzotriazole.

[0013] More precisely, the present invention relates to an aqueous electrolyte for the electrodeposition of cobalt, in the form of an aqueous solution comprising 1 to 5 g / L of cobalt(II) ions, 1 to 10 g / L of chloride ions, a strong acid in an amount sufficient to obtain a pH in the range of 1.8 to 4.0, and an organic additive, wherein the organic additive comprises at least one first additive selected from α-hydroxycarboxylic acids and mixtures thereof, and at least one second additive selected from polyethyleneimine and benzotriazole.

[0014] The electrolyte of the present invention makes it possible to continuously obtain high-purity cobalt precipitates, and the duration of their formation can be shortened compared to the conventional technology.

[0015] In fact, the filling speed of conventional techniques must be slower to prevent hole formation, and if holes are formed, an annealing step must be included. Furthermore, the method may include two separate steps of cobalt electrodeposition: a step of filling the cavity at a considerably slow speed, and a second step of electrodeposition using a second electrolyte containing cobalt ions to deposit a so-called "over-baden layer" onto the entire surface of the substrate.

[0016] The method of the present invention is advantageous in that it allows for cavity filling and deposition of the overbaden layer in a single electrodeposition step. The method of the present invention also makes it possible to avoid annealing the cobalt precipitate before performing a polishing step that combines chemical and mechanical attack on the overbaden layer.

[0017] In addition, the cobalt precipitate produced in the context of the present invention has the advantage of forming interconnections that contain only very small amounts of impurities, preferably less than 1000 atoms ppm.

[0018] "Electrolyte" refers to the liquid containing the precursor for the metal coating used in the electrodeposition process.

[0019] "Continuous filling" means a cobalt mass without voids. In the prior art, all or voids of the material are observed between the cavity wall and the cobalt precipitate in the cobalt precipitate (sidewall voids), and holes are located in the form of seams at a distance from the cavity wall. These voids can be observed by taking a cross-section of the structure and quantified by transmission or scanning electron microscopy. The continuous precipitate of the present invention preferably has an average porosity of less than 10% on a volume basis, and more preferably has an average porosity of 5% or less on a volume basis. The porosity in the structure to be filled can be measured using a scanning electron microscope at a magnification in the range of 50,000 to 350,000.

[0020] The "average diameter" or "average width" of the cavity means the dimension measured at the filled cavity opening. The cavity is, for example, in the form of a cylindrical or flared channel.

Brief Description of the Drawings

[0021] [Figure 1] A transmission electron microscope slide of a cavity filled by the method of the present invention in Test 1 of Example 1. [Figure 2] A scanning electron microscope slide of a cavity filled by the method of the present invention in Test 3 of Example 1. [Figure 3] A scanning electron microscope slide of a cavity filled by the method of the prior art (Comparative Example 4).

Modes for Carrying Out the Invention

[0022] According to Embodiment 1, the present invention relates to an electrolyte for cobalt electrodeposition, the electrolyte being an aqueous solution comprising 1 to 5 g / L of cobalt(II) ions, 1 to 10 g / L of chloride ions, a strong acid in an amount sufficient to obtain a pH in the range of 1.8 to 4.0, and an organic additive, wherein the organic additive comprises at least one first additive selected from α-hydroxycarboxylic acids and mixtures thereof, and at least one second additive selected from polyethyleneimine and benzotriazole.

[0023] The mass concentration of cobalt(II) ions may be in the range of 1 g / L to 5 g / L, for example, 2 g / L to 3 g / L. The chloride ion concentration may be in the range of 1 g / L to 10 g / L.

[0024] Chloride ions can be introduced by dissolving a type of cobalt chloride or its hydrated salt (e.g., cobalt chloride hexahydrate) in water.

[0025] The electrolyte preferably contains at most two organic additives, which are a first additive and a second additive.

[0026] All organic additives contained in the electrolyte are preferably sulfur-free. For example, α-hydroxycarboxylic acid is preferably sulfur-free.

[0027] The electrolyte preferably does not contain any sulfur compounds. Furthermore, the composition is preferably not obtained by dissolving a cobalt salt, such as cobalt sulfate or a hydrate thereof, because this would generate sulfur contamination of cobalt precipitates, which the inventors wish to avoid.

[0028] The total concentration of organic additives in the electrolyte is preferably in the range of 5 ppm to 50 ppm.

[0029] The concentration of the first additive is preferably between 5 and 200 ppm, and the concentration of the second additive is preferably between 1 and 10 ppm.

[0030] The first additive is selected from, for example, citric acid, tartaric acid, malic acid, mandelic acid, and glyceric acid.

[0031] In a particular embodiment of the present invention, the α-hydroxycarboxylic acid is tartaric acid.

[0032] According to one embodiment of the present invention, the second amine additive is a linear or branched poly(ethyleneimine) homopolymer or copolymer. The poly(ethyleneimine) is in the form of an acid, and some or all of its amine functional groups are protonated.

[0033] For example, a linear poly(ethyleneimine) with a number-average molecular weight (Mn) between 500 g / mol and 25,000 g / mol would likely be selected.

[0034] Branched poly(ethyleneimines) having a number-average molecular weight Mn ranging from 500 g / mol to 70,000 g / L may also be selected, which may contain primary amine functional groups, secondary amine functional groups, and tertiary amine functional groups.

[0035] Thus, the poly(ethyleneimine) may be, for example, the poly(ethyleneimine) of CAS number 25987-06-8, having a number-average molecular weight Mn in the range of 500 g / mol to 700 g / mol and a weight-average molecular weight Mw preferably in the range of 700 g / mol to 900 g / mol. Such poly(ethyleneimine) is available and sold by Sigma-Aldrich under reference number 408719.

[0036] Poly(ethyleneimine) can also be, for example, poly(ethyleneimine) of CAS number 9002-98-6, having a number-average molecular weight Mn in the range of 500 g / mol to 700 g / mol. Such poly(ethyleneimine) is available and sold by Polysciences, Inc. under reference number 02371.

[0037] The number-average molecular weight and weight-average molecular weight can be measured independently by conventional methods known to those skilled in the art, such as gel permeation chromatography (GPC) or light scattering (LS).

[0038] According to one embodiment of the present invention, the amine is a benzotriazole.

[0039] The pH of the electrolyte is preferably in the range of 1.8 to 4.0. In a particular embodiment, the pH is in the range of 1.8 to 2.6.

[0040] The pH of the composition may be optionally adjusted with a base or acid known to those skilled in the art. The acid used may be hydrochloric acid. The electrolyte does not necessarily have to contain a buffer compound such as boric acid. Preferably, the electrolyte does not contain boric acid.

[0041] In principle, there are no restrictions on the properties of the solvent (provided that the solvent sufficiently solubilizes the active species in the solution and does not hinder electrodeposition), but preferably the solvent is water. In one embodiment, the solvent mainly consists of water by volume.

[0042] The conductivity of the electrolyte is preferably in the range of 2 mS / cm to 10 mS / cm.

[0043] The present invention also relates to an electrochemical method for depositing materials on a substrate having a conductive surface including flat portions and cavities, by filling the cavities from the bottom up, wherein the method is: - The step of bringing the conductive surface into contact with the electrolyte in accordance with the above description, - The process includes an electrical step of polarizing the conductive surface for a sufficient duration to carry out the deposition of cobalt onto the conductive surface.

[0044] In one advantageous embodiment, the above duration is sufficient time to perform cavity filling and coating of the flat portions of the conductive surface with cobalt precipitates with a thickness in the range of 50 nm to 400 nm.

[0045] In one advantageous modification, it is not necessary to perform an annealing step on the cobalt precipitate obtained at the end of the polarization step. Therefore, immediately after the polarization step, a polishing step can be performed that combines chemical and mechanical attack (which can also be called a mechanochemical attack) on the cobalt precipitate obtained at the end of the polarization step. Thus, according to one embodiment, the precipitation method of the present invention is: - The step of bringing the conductive surface into contact with the electrolyte, as described above, - A step of polarizing the conductive surface and the electrolyte for a duration sufficient to fill the cavity and form cobalt precipitates that optionally coat the flat portions of the conductive surface, The process includes a polishing step that combines chemical and mechanical attack on cobalt precipitates at a temperature in the range of -50°C to 500°C, without performing a preceding annealing treatment.

[0046] The polarization step in the presence of the electrolyte of the present invention can be continued for as long as necessary to fill the cavity without covering a flat surface. In this case, the deposition method may include a second polarization step, during which a second cobalt precipitate is formed using an electrolyte other than the electrolyte of the present invention.

[0047] Alternatively, the polarization step in the presence of the electrolyte of the present invention can be continued for as long as necessary to fill the cavity and coat the flat surface (the thickness of the cobalt precipitate on the flat surface is at least 20 nm).

[0048] The portion of cobalt precipitate covering a flat surface, also known as the overbaden layer, can have a thickness ranging from approximately 50 nm to 400 nm. Advantageously, this cobalt precipitate portion has a uniform thickness across the entire substrate surface. This layer is also homogeneous, glossy, and dense.

[0049] Under certain conditions, the method of the present invention is a so-called "bottom-up" method, in contrast to the "conformal" method of the prior art. In this case, the rate of cobalt precipitation is faster at the bottom of the cavity than at the rate of precipitation on the walls.

[0050] The cobalt precipitate obtained at the end of the polarization step is advantageous in that it contains less than 1000 ppm of impurities. The main impurity is oxygen, followed by carbon and nitrogen. The total content of carbon and nitrogen is preferably less than 300 ppm.

[0051] The cobalt precipitate obtained at the end of the electrodeposition process is advantageously continuous in the sense that it contains a void ratio of less than 10% by volume or area, preferably 5% or less by volume or area, without undergoing heat treatment at temperatures in the range of 50°C to 500°C, preferably in the range of 150°C to 500°C.

[0052] The proportion of voids in cobalt precipitates can be measured by electron microscopy, a method known to those skilled in the art, and a suitable method will be selected as deemed most appropriate. One such method may be scanning electron microscopy (SEM) or transmission electron microscopy (TEM) using magnifications ranging from 50,000x to 350,000x. The volume of the voids can be assessed by measuring the void area observed over one or more cross-sections of the substrate containing the filled cavities. Once several areas are measured over several cross-sections, the average of these areas is calculated to estimate the volume of the voids.

[0053] When a low impurity content is combined with a very low void ratio, it becomes possible to obtain cobalt precipitates with reduced resistivity. Furthermore, the resistivity of the cobalt precipitate obtained at the end of the polarization step can be less than 30 μΩ·cm without heat treatment at temperatures in the range of 50°C to 500°C.

[0054] The cobalt deposition rate may be in the range of 0.1 nm / sec to 3.0 nm / sec, preferably in the range of 1.0 nm / sec to 3.0 nm / sec, and more preferably in the range of 1 nm / sec to 2.5 nm / sec.

[0055] The cavity to be filled may be formed according to a damascene or dual damascene method known to those skilled in the art, the method comprising the following sequence of steps: - etching a trench onto the top of a silicon wafer; depositing an insulating dielectric layer, generally made of silicon oxide, on the etched surface; - depositing a thin layer of barrier material used to prevent the migration of cobalt into silicon; and - optionally depositing a thin metal layer called a seed layer.

[0056] The barrier layer and seed layer generally have a thickness ranging from 1 nm to 10 nm, independently of each other.

[0057] The conductive surface in contact with the electrolyte is, for example, the surface of a metal layer containing at least one compound selected from the group consisting of cobalt, copper, tungsten, titanium, tantalum, ruthenium, nickel, titanium nitride, and tantalum nitride.

[0058] The conductive surface of the substrate may be the surface of an assembly comprising a tantalum nitride layer having a thickness of 1 nm to 6 nm, which is covered by and in contact with a layer of metallic cobalt having a thickness of 1 nm to 10 nm, preferably 2 nm to 5 nm, on which cobalt is deposited during electrical steps.

[0059] Therefore, the substrate can be obtained by the continuous deposition of SiO2, tantalum nitride, and cobalt. Cobalt can be deposited on the tantalum nitride by chemical vapor deposition (CVD) or atomic layer deposition (ALD).

[0060] The resistivity of the assembly containing the metal layer and cobalt precipitate may be in the range of 7 Ω / cm to 10 Ω / cm. Preferably, the resistivity is in the range of 7.5 to 8.5 Ω / cm.

[0061] Cavities designed to be filled with cobalt by the method of the present invention preferably have a width of less than 100 nm at their openings (i.e., on the surface of the substrate), and preferably in the range of 10 nm to 50 nm. The depth may be in the range of 50 nm to 250 nm. According to one embodiment, the cavity has a width in the range of 30 nm to 50 nm, preferably in the range of 35 nm to 45 nm, and a depth in the range of 125 nm to 175 nm.

[0062] The polarization intensity used in the electrical step is preferably about 2 mA / cm². 2 ~about 20mA / cm 2 It is within this range. The polarization current strength is 8.5 mA / cm². 2 ~18.5mA / cm 2 In this range, the cobalt deposition rate is in the range of 0.1 nm / sec to 3.0 nm / sec, which is very advantageous compared to conventional methods (where much slower rates are observed in this current range).

[0063] The electrical polarization step of the method of the present invention may include a step of a single polarization mode or a step of several different polarization modes.

[0064] The conductive surface may come into contact with the electrolyte either before or after polarization. Contact with the cavity is preferably made before current is applied in order to limit corrosion of the surface by the electrolyte.

[0065] The electrical step can be performed by using at least one polarization mode selected from the group consisting of a lamp mode, a galvanostat mode, and a galvanopulse mode.

[0066] For example, the electrical step comprises one or more steps of cathode polarization in lamp mode over a duration preferably in the range of 10 seconds to 100 seconds, at a current range of 0 mA / cm 2 ~10 mA / cm 2

[0067] The electrical step can also include one or more steps of polarization in galvanostat mode using a current in the range of 5 mA / cm 2 ~20 mA / cm 2

[0068] According to one example, the electrical step preferably comprises at least one or more steps of polarizing the cathode in lamp mode using a current in the range of about 0 mA / cm 2 ~ about 10 mA / cm 2 followed by a step in galvanostat mode by applying a current of about 5 mA / cm 2 ~ about 20 mA / cm 2

[0069] The method of the present invention can include a step of annealing the cobalt precipitate obtained at the end of the filling described above, but the method preferably does not have this step. The annealing heat treatment is generally carried out at a temperature in the range of about 350 °C to about 550 °C, for example at a temperature near about 450 °C, preferably under a reducing gas such as 4% H2 in N2.

[0070] This method may include a preliminary step, which may include treatment with a reducing plasma, thereby reducing natural metal oxides present on the conductive surface of the substrate. The plasma also acts on the surface of the trench, thereby improving the quality of the interface between the seed layer and the electrodeposited cobalt. To minimize the reformation of natural oxides, the electrodeposition process is preferably performed immediately after the plasma treatment.

[0071] The method of the present invention is particularly applicable to the manufacturing of semiconductor devices, when creating metal interconnects (trenches provided on the surface or vias connecting integrated parts at different levels).

[0072] The present invention will be further explained by the following examples. [Examples]

[0073] Example 1: Electrodeposition of a structure with a width of 40 nm and a depth of 150 nm using a solution containing α-hydroxycarboxylic acid and polyethyleneimine at pH = 2.2 The trenches are filled by electrodeposition of cobalt onto the cobalt seed layer. Precipitation is carried out using a composition containing cobalt dichloride, α-hydroxycarboxylic acid, and polyethyleneimine (PEI) at pH=2.2.

[0074] A. Materials and equipment substrate The substrate used in this embodiment was made from a silicon test specimen prepared by etching trenches, which was continuously coated with a 3.3 × 3.3 cm silicon oxide layer, a 2 nm thick TaN layer, and a 3 nm thick metallic cobalt layer. The resistivity of the substrate is approximately 600 Ω per square meter. The width of the filled cavities is equal to 40 nm at their openings, and their depth is equal to 150 nm.

[0075] Electrodeposition solution: In this solution, Co 2+The concentration of is equal to 2.3 g / L obtained from CoCl2(H2O)6. The concentration of tartaric acid is equal to 15 ppm. The concentration of PEI is equal to 5 ppm. The pH of the solution is adjusted to 2.2 by adding hydrochloric acid.

[0076] Device: The electrodeposition apparatus used in this embodiment consists of two parts: a cell designed to contain the electrodeposition solution, equipped with a recirculation system for controlling the fluid dynamics of the system, and a rotating electrode equipped with a sample holder adapted to the size of the test specimen used (3.3 cm × 3.3 cm). The electrodeposition cell is - Cobalt anode and, -It had two electrodes, a structured silicon specimen coated with the layer described above, which constituted the cathode. - The reference electrode is connected to the anode.

[0077] The connector enabled electrical contact between electrodes connected by wires to a potentiostat providing up to 20V or 2A.

[0078] B. Experimental protocol: Electrical methods Three tests (referred to as Test 1, Test 2, and Test 3) were performed by applying different electrical methods. Each of the three methods included two, three, or five of the following steps: a) "Cold input": The electrodeposition solution is injected into the electrodeposition cell. Different electrodes are placed in their designated positions and brought into contact with the electrodeposition solution without polarization. Polarization is then applied. b) In the second step, the cathode is set to 0mA to 30mA (or 3.8mA / cm²) in galvanodynamic ramp mode. 2 Polarize within the current range. Perform this step for 3 seconds at a rotation of 65 rpm. c) In the third step, the cathode is set to 30mA (or 3.8mA / cm²) in galvanodynamic ramp mode. 2)~60mA (or 7.6mA / cm²) 2 Polarize within the current range of ). This step is performed for 55 seconds at a rotation of 65 rpm. d) In the fourth step, the cathode is set to 60mA (or 7.6mA / cm²) in galvanodynamic ramp mode. 2 )~130mA (16.5mA / cm²) 2 Up to, for example, 60mA (or 3.8mA / cm²). 2 )~90mA (11.4mA / cm²) 2 Polarize within the current range of ). This step is performed for 7 seconds at a rotation of 65 rpm. e) In the final step, the cathode is set to constant current mode at 90mA (11.4mA / cm²). 2 )~130mA (16.5mA / cm²) 2 For example, 90mA (11.4mA / cm²). 2 Polarize within the current range of ). This step is performed at a rotation speed of 65 rpm or 100 rpm and continued for a period of 40 to 150 seconds.

[0079] The first electrical protocol (Test 1) consisted of three steps: step a), step b), and step c).

[0080] The second electrical protocol (Test 2) consisted of five steps, namely steps a) to e). During step e), the cathode was set to 90 mA (11.4 mA / cm²) in galvanostat mode. 2 The material was then polarized at a rotation speed of 100 rpm for 40 seconds.

[0081] The third electrical protocol (Test 3) consisted of two steps, namely step a) and step e). During step e), the cathode was set to 90 mA (11.4 mA / cm²) in galvanostat mode. 2 The material was then polarized at a rotation speed of 65 rpm for 133 seconds.

[0082] C. Results obtained: As can be seen in Figure 1, transmission electron microscopy (TEM) analysis of the metallized substrate obtained in Test 1 shows a bottom-up deposition mechanism, with filling starting from the bottom and partially filling trenches. Furthermore, the structure does not contain holes (seam voids).

[0083] In Test 2, scanning electron microscopy (SEM) analysis revealed that the trench walls were free of hole defects (sidewall voids) (reflecting good cobalt nucleation) and the structure was free of holes (seam voids), reflecting optimal bottom-up filling without annealing.

[0084] Figure 2 shows a slide obtained from the scanning electron microscopy (SEM) analysis of Experiment 3. This slide shows no hole defects (sidewall voids) in the trench walls (reflecting good cobalt nucleation) and a hole-free (seam void) filling structure, reflecting optimal bottom-up filling without annealing.

[0085] Example 2: Electrodeposition of a structure with a width of 40 nm and a depth of 150 nm using a solution containing α-hydroxycarboxylic acid and benzotriazole at pH = 2.2 The same trench as in Example 1 was filled with a composition containing cobalt dichloride, α-hydroxycarboxylic acid, and benzotriazole at pH 2.2.

[0086] A. Materials and equipment substrate The substrate used is exactly the same as the substrate used in Example 1.

[0087] Electrodeposition solution: In this solution, Co 2+ The concentration of is equal to 2.3 g / L obtained from CoCl2(H2O)6. The concentration of tartaric acid is equal to 15 ppm. The concentration of benzotriazole is equal to 10 ppm. The pH of the solution is adjusted to 2.2 by adding hydrochloric acid.

[0088] Device: The apparatus is identical to that of Example 1.

[0089] B. Experimental protocol: Electrical methods: The electrical method was identical to the electrical method of Test 2 in Example 1 and consisted of five steps a) to e).

[0090] C. Results obtained: Scanning electron microscopy (SEM) analysis shows that the trench walls are free of hole defects (sidewall voids) (reflecting good cobalt nucleation) and the structure is free of holes (seam voids), reflecting optimal bottom-up filling without annealing.

[0091] Comparative Example 3: Electrodeposition of a structure with a width of 40 nm and a depth of 150 nm using a single organic additive, i.e., α-hydroxycarboxylic acid, at pH = 2.2. The same trench as in Example 1 was filled with a composition containing cobalt dichloride and α-hydroxycarboxylic acid at a pH of 2.2.

[0092] A. Materials and equipment substrate The substrate used is exactly the same as the substrate used in Example 1.

[0093] Electrodeposition solution: In this solution, Co 2+ The concentration of is equal to 2.3 g / L obtained from CoCl2(H2O)6. The concentration of tartaric acid is equal to 15 ppm. The pH of the solution is adjusted to 2.2 by adding hydrochloric acid.

[0094] Device: The apparatus is identical to that of Example 1.

[0095] B. Experimental protocol: The electrical method was identical to the electrical method of Test 2 in Example 1 and consisted of five steps a) to e).

[0096] C. Results obtained: Scanning electron microscopy (SEM) analysis reveals that the structure contains holes (seam voids) (which would require an additional annealing step to remove), and shows filling that reflects growth due to the structure closing up from bottom to top, similar to a zipper.

[0097] Comparative Example 4: Electrodeposition of a structure with a width of 40 nm and a depth of 150 nm using a conventional electrolyte. Cobalt electrodeposition in the same trench as in Example 1 is carried out at pH=4 using a prior art composition containing cobalt sulfate, boric acid, thiourea, and polyethyleneimine (PEI), as taught in U.S. Patent Application Publication No. 2016 / 0273117A1.

[0098] A. Materials and equipment substrate The substrate used is exactly the same as the substrate used in Example 1.

[0099] Electrodeposition solution: In this solution, Co 2+ The concentration of is equal to 2 g / L obtained from CoSO4. The concentration of boric acid is equal to 20 g / L. The concentration of thiourea is equal to 150 ppm. The concentration of PEI is equal to 10 ppm. The pH of the solution is adjusted to 4 by adding sulfuric acid.

[0100] Device: The apparatus is identical to that of Example 1.

[0101] B. Experimental protocol: The method was identical to that of Test 3 in Example 1 and included two steps a) and e).

[0102] C. Results obtained: As can be seen in Figure 3, scanning electron microscopy (SEM) analysis reveals structurally defective (seam voids) filling, reflecting suboptimal bottom-up filling without annealing.

[0103] Simultaneously, analysis of the film obtained in Test 3 of Example 1 and the film obtained in this example made it possible to compare their resistivities. The results are reported in Table 1 below.

[0104] [Table 1]

[0105] The resistivity of the film deposited in Test 3 of Example 1 was better than that of Comparative Example 4, which is more desirable at an industrial level. Lower resistivity is synonymous with better film quality, meaning fewer impurities.

Claims

1. An electrolyte for cobalt electrodeposition, The electrolyte is an aqueous solution containing 1 to 5 g / L of cobalt(II) ions, 1 to 10 g / L of chloride ions, a strong acid in an amount sufficient to obtain a pH in the range of 1.8 to 4.0, and an organic additive, wherein the organic additive comprises at least one first additive selected from α-hydroxycarboxylic acids and mixtures thereof, and at least one second additive selected from polyethyleneimine and benzotriazole. The total concentration of the organic additive in the electrolyte is in the range of 5 ppm to 50 ppm. The electrolyte does not contain any sulfur-containing compounds. The aforementioned electrolyte is an electrolyte that does not contain boric acid.

2. The electrolyte according to claim 1, characterized in that the concentration of the second additive is in the range of 1 ppm to 10 ppm.

3. The electrolyte according to claim 1, characterized in that the pH is in the range of 1.8 to 2.

6.

4. The electrolyte according to claim 3, characterized in that the first additive is selected from citric acid, tartaric acid, malic acid, mandelic acid, and glyceric acid.

5. The electrolyte according to claim 1, characterized in that its conductivity is in the range of 2 mS / cm to 10 mS / cm.

6. An electrochemical method for depositing a material on a substrate having a conductive surface including a flat portion and a cavity, by filling the cavity from the bottom up, - An electrodeposition step of bringing the conductive surface into contact with the electrolyte according to any one of claims 1 to 5, - An electrical step of polarizing the conductive surface for a sufficient duration in order to carry out cobalt deposition on the surface, Methods that include...

7. The electrochemical method for depositing cobalt according to claim 6, characterized in that the duration is sufficient to fill the cavity of the conductive surface and coat the flat portion with a cobalt precipitate having a thickness in the range of 50 nm to 400 nm.

8. The electrochemical method for depositing cobalt according to claim 6, wherein immediately after the electrical step of polarizing the conductive surface, a polishing step is performed which combines chemical attack and mechanical attack on the cobalt precipitate obtained at the end of the electrical step of polarizing the conductive surface.

9. The method according to any one of claims 6 to 8, wherein the cavity has an opening with a width of less than 100 nm and a depth in the range of 50 nm to 250 nm.

10. The method according to any one of claims 6 to 9, wherein the cobalt precipitate obtained at the end of the electrical step of polarization of the conductive surface has an impurity content of less than 1,000 atomic ppm.

11. The method according to any one of claims 6 to 10, wherein the cobalt precipitate obtained at the end of the electrodeposition step has an average porosity of less than 10% by volume or by area, without undergoing heat treatment at a temperature in the range of 50°C to 500°C.

12. The polarization current intensity is 8.5 mA / cm². ２ ~18.5mA / cm ２ The method according to any one of claims 6 to 11, characterized in that, when within the range, the precipitation rate of cobalt is in the range of 0.1 nm / second to 3.0 nm / second.

13. The method according to any one of claims 6 to 12, characterized in that the resistivity of the cobalt precipitate obtained at the end of the electrical step of polarization of the conductive surface is less than 30 μΩ·cm without heat treatment at a temperature in the range of 50°C to 500°C.

14. The aforementioned substrate is SiO ２ The method according to any one of claims 6 to 13, characterized in that it is obtained by the continuous precipitation of tantalum nitride and cobalt.

15. The method according to claim 14, wherein the cobalt is deposited on the tantalum nitride by chemical vapor deposition (CVD) or atomic layer deposition (ALD).

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