Electrolyte and Cobalt Electrodeposition Process

Abstract

Electrolyte and Cobalt Electrodeposition Process The present invention relates to a process for manufacturing cobalt interconnects and to an electrolyte enabling its implementation. The electrolyte, with a pH below 4.0, comprises cobalt ions, chloride ions, and organic additives including an alpha-hydroxylated carboxylic acid and an amine such as polyethyleneimine or benzotriazole. Figure for the abstract: Figure 2

Description

Title of the invention: Electrolyte and Electrodeposition Process for Cobalt Technical Field

[0001] The present invention relates to the electrodeposition of cobalt on a conductive surface. More specifically, it relates to an electrolyte and a cobalt electrodeposition process that can be used to fabricate electrical interconnections in integrated circuits. Previous Art

[0002] Semiconductor devices include different levels of integration and two categories of conductive metallic interconnections: trenches a few tens of nanometers wide, which run on the surface of the device and connect the electronic components, and through-vias which connect the different levels and whose diameter is on the order of several hundred nanometers in diameter.

[0003] The fabrication of the interconnections includes etching cavities on the substrate, followed by the deposition of a metallic germination layer on the surface of the cavities to allow a subsequent step of electrochemically filling the cavities with a conductive metal.

[0004] Conventional processes for filling interconnections with cobalt use electrolytes containing a cobalt salt and numerous organic additives. The combination of these additives is generally necessary to obtain a cobalt mass of good quality, particularly one free of voids and with good conductivity.

[0005] The filling of the cavities can follow two mechanisms depending on the composition of the electrolyte used: bottom-up filling, or conformal filling. Bottom-up filling is distinct from filling in which the cobalt deposit grows at the same rate at the bottom and on the walls of the recessed patterns.

[0006] To achieve bottom-up filling, prior art electrolytes include several additives, including a suppressor and an accelerator. Such a system prevents the formation of voids in the cobalt deposit and the premature closure of the cavity openings during filling. The suppressor limits cobalt deposition to the upper level of the cavities, on their walls as well as on the flat surface of the substrate onto which the cavities open, while the accelerator diffuses to the bottom of the cavities to promote cobalt deposition. The presence of a An accelerator is all the more necessary for cavities of small width and great depth, because it allows to increase the rate of deposition of cobalt at the bottom of the cavities.

[0007] Electrodeposition baths designed for bottom-up filling have several drawbacks that ultimately limit the proper functioning of the manufactured electronic devices and make them too expensive to produce. They generate cobalt interconnections contaminated by the organic additives required to limit the formation of holes in the cobalt during filling. Furthermore, the filling rates obtained with these chemistries are too low and incompatible with industrial-scale production.

[0008] In US application 2016 / 0273117, for example, the electrolyte contains numerous additives, including a suppressor and an accelerator with complementary functions to ensure bottom-up filling. The inventors found that the resistivity of the cobalt deposited with this electrolyte was very high and that holes formed in the cobalt during filling. Therefore, it is necessary to anneal the deposit to remove them.

[0009] The need therefore remains to provide electrolysis baths that lead to cobalt interconnections with improved performance, particularly in terms of their conductivity. To achieve this objective, it is desirable to manufacture cobalt deposits with extremely low impurity content and free of voids, even without an annealing step. It is also desirable to offer electrolytes that, while preventing the formation of holes in the cobalt, allow for a sufficiently high deposition rate to make the manufacturing of the devices cost-effective.

[0010] The inventors found that the combination of an alpha-hydroxylated carboxylic acid and a nitrogenous compound such as polyethyleneimine or benzotriazole meets these expectations.

[0011] Alpha-hydroxylated carboxylic acids have indeed already been used in electrochemical cobalt deposition processes, such as in application WO 2019 / 179897, but these processes follow a conformal filling mechanism at the end of which holes remain in the metal in the absence of annealing of the deposit. General description

[0012] Thus, the invention relates to a method of creating cobalt interconnections by filling cavities from bottom to top (called "bottom-up") which uses an electrolyte with a pH between 1.8 and 4.0, comprising cobalt II, chloride ions, an alpha-hydroxylated carboxylic acid and an additive selected from polyethyleneimines and benzotriazole.

[0013] More specifically, the invention relates to an 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 sufficient quantity to obtain a pH between 1.8 and 4.0, and organic additives of which at least one first additive chosen from alpha-hydroxylated carboxylic acids and their mixtures, and at least one second additive chosen from polyethyleneimines and benzotriazole.

[0014] The electrolyte of the invention makes it possible to obtain continuous and high-purity cobalt deposits whose manufacturing time can be shorter than that of the prior art.

[0015] Indeed, the filling kinetics of conventional processes must be slower to avoid the formation of holes, and the process must include an annealing step when holes have formed. Furthermore, the process may include two distinct cobalt electrodeposition steps: a step to fill the cavities at a relatively slow rate, and a second electrodeposition step using a second electrolyte containing cobalt ions to deposit the overburden layer over the entire surface of the substrate.

[0016] The process of the invention advantageously allows for the filling of cavities and the deposition of the overburden layer in a single electrodeposition step. It also eliminates the need for annealing the cobalt deposit before performing the polishing step, which combines chemical and mechanical etching of the overburden layer.

[0017] Moreover, the cobalt deposits produced within the framework of the invention have the advantage of forming interconnections having a very low impurity rate, preferably less than 1000 atomic ppm.

[0018] The term "electrolyte" means the liquid containing precursors of a metallic coating used in an electrodeposition process.

[0019] By "continuous filling," we mean a mass of cobalt devoid of voids. In the prior art, holes or voids of material can be observed in a cobalt deposit between the walls of the cavities and the cobalt deposit ("sidewall voids"), and holes located equidistant from the walls of the cavities in the form of lines ("seams"). These voids can be observed and quantified by transmission or scanning electron microscopy, by obtaining cross-sections of the structures. The continuous deposit of the invention preferably has an average void percentage of less than 10% by volume, preferably less than or equal to 5% by volume. The void percentage inside the structures to be filled can be measured by scanning electron microscopy with a magnification between 50,000 and 350,000.

[0020] The term "average diameter" or "average width" of the cavities refers to dimensions measured at the opening of the cavities to be filled. The cavities are, for example, in the form of cylinders or flared channels. Brief description of the drawings

[0021] [Fig.1] The [Fig.1] is a transmission electron microscopy image of cavities filled according to a method of the invention of Test 1 of Example 1.

[0022] [Fig.2] The [Fig.2] is a scanning electron microscopy image of cavities filled according to a method of the invention of Test 3 of Example 1.

[0023] [Fig.3] The [Fig.3] is a scanning electron microscopy image of cavities filled according to a prior art electrodeposition process (comparative example 4). Description of the implementation methods

[0024] According to a first embodiment, the invention relates to an electrolyte for the electrodeposition of cobalt characterized in that the electrolyte is 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 sufficient quantity to obtain a pH between 1.8 and 4.0, and organic additives of which at least one first additive selected from alpha-hydroxylated carboxylic acids and their mixtures, and at least one second additive selected from polyethyleneimines and benzotriazole.

[0025] The mass concentration of cobalt II ions can range from 1 g / L to 5 g / L, for example from 2 g / L to 3 g / L. That of chloride ions can range from 1 g / L to 10 g / L.

[0026] Chloride ions can be brought in by dissolving cobalt chloride or one of its hydrates, such as hexahydrated cobalt chloride, in water.

[0027] The electrolyte preferably comprises at most two organic additives, these additives being the first and second additive.

[0028] All organic additives contained in the electrolyte are preferably sulfur-free. For example, alpha-hydroxylated carboxylic acid is preferably sulfur-free.

[0029] The electrolyte preferably does not contain any sulfur compounds. Also, the composition is preferably not obtained by dissolving a cobalt salt such as cobalt sulfate or one of its hydrates, because this generates sulfur contamination of the cobalt deposit, which is to be avoided.

[0030] The total concentration of organic additives in the electrolyte is preferably between 5 ppm and 50 ppm.

[0031] 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.

[0032] The first additive is for example chosen from citric acid, tartaric acid, malic acid, mandelic acid and glyceric acid.

[0033] In a particular embodiment of the invention, the alpha-hydroxylated carboxylic acid is tartaric acid.

[0034] According to one embodiment of the invention, the second amine additive is a linear or branched homopolymer or copolymer of poly(ethyleneimine). The poly(ethyleneimine) is in acid form, with some or all of its amine functions being protonated.

[0035] For example, a linear poly(ethyleneimine) will be chosen having an average number molecular mass Mn between 500 g / mol and 25,000 g / mol.

[0036] It may also be possible to choose a branched poly(ethyleneimine) having an average number molecular mass Mn of between 500 g / mol and 70,000 g / mol which includes both primary amine, secondary amine and tertiary amine functions.

[0037] Thus, the poly(ethyleneimine) can be a polyethyleneimine of CAS number 25987-06-8, having, for example, a number-average molecular weight Mn between 500 g / mol and 700 g / mol, and preferably a weight-average molecular weight Mw between 700 g / mol and 900 g / mol. Such a poly(ethyleneimine) exists under reference 408719, marketed by Sigma-Aldrich.

[0038] Poly(ethyleneimine) may also be a poly(ethyleneimine) of CAS number 9002-98-6, having, for example, a number-average molecular weight (Mn) between 500 and 700 g / mol. Such a poly(ethyleneimine) exists under reference 02371 sold by Polysciences, Inc.

[0039] Number molecular mass and weight molecular mass can be measured independently of each other by a conventional method known to those skilled in the art, such as gel permeable chromatography (GPC) or light scattering (LS).

[0040] According to one embodiment of the invention, the amine is benzotriazole.

[0041] The pH of the electrolyte is preferably between 1.8 and 4.0. In a particular embodiment, the pH is between 1.8 and 2.6.

[0042] The pH of the composition may optionally be adjusted with a base or an acid known to those skilled in the art. The acid used may be hydrochloric acid. The electrolyte may not contain a buffer compound, such as boric acid. Preferably, the electrolyte does not contain boric acid.

[0043] Although there is no restriction in principle on the nature of the solvent (provided that it sufficiently solubilizes the active species in the solution and does not interfere with electrodeposition), it is preferably water. In one embodiment, the solvent consists mainly of water by volume.

[0044] The conductivity of the electrolyte is preferably between 2 mS / cm and 10 mS / cm.

[0045] The invention also relates to an electrochemical deposition process on a substrate having a conductive surface comprising a flat portion and cavities, by filling said cavities from bottom to top, said process comprising:

[0046] - a step of contacting the conductive surface with a conforming electrolyte to the previous description,

[0047] - an electrical step of polarizing the conducting surface for a duration sufficient to create a cobalt deposit on the surface.

[0048] In an advantageous embodiment, the time is sufficient to carry out the filling of the cavities, and the covering of the flat part of the conducting surface by a cobalt deposit having a thickness ranging from 50 nm to 400 nm.

[0049] In an advantageous embodiment, it is not necessary to perform an annealing step on the cobalt deposit obtained after the polarization step, so that the polarization step can be immediately followed by a polishing step combining chemical and mechanical etching (also called "mechanical-chemical") of the cobalt deposit obtained after the polarization step. According to one embodiment, the deposition process of the invention therefore comprises:

[0050] - a step of contacting the conductive surface with a conforming electrolyte to the previous description,

[0051] - a step of polarizing the conductive surface and the electrolyte during a sufficient time to form a cobalt deposit that fills the cavities and eventually covers the flat part of the conductive surface,

[0052] - a polishing step combining chemical and mechanical attack of the deposit cobalt, without carrying out a prior annealing treatment of the deposit at a temperature ranging from 50°C to 500°C.

[0053] The polarization step in the presence of the electrolyte of the invention may last as long as necessary to fill the cavities without coating the flat surface. In this case, the deposition process may include a second polarization step during which a second cobalt deposit is formed using an electrolyte other than that of the invention.

[0054] Alternatively, the polarization step in the presence of the electrolyte of the invention can last for the time necessary to fill the cavities and cover the flat surface, the thickness of the cobalt deposit above the flat surface being at least 20 nm thick.

[0055] The portion of the cobalt deposit that covers the flat surface, also called the overburden layer, can have a thickness between 50 nm and 400 nm. Advantageously, it has a constant thickness over the entire surface of the substrate. The layer is also homogeneous, glossy, and compact.

[0056] Under certain conditions, the process of the invention is a so-called "bottom-up" process, as opposed to the "conformal" processes of the prior art. In this case, the cobalt deposition rate is higher at the bottom of the cavities than on their walls.

[0057] The cobalt deposit obtained after the polarization step advantageously has an impurity content of less than 1000 atomic ppm. The predominant impurities are oxygen, followed by carbon and nitrogen. The total carbon and nitrogen content is preferably less than 300 ppm.

[0058] The cobalt deposit obtained at the end of the electrodeposition step is advantageously continuous, in that it comprises an average void percentage of less than 10% by volume or surface, preferably less than or equal to 5% by volume or surface, without having undergone heat treatment at a temperature ranging from 50°C to 500°C, preferably between 150°C and 500°C.

[0059] The percentage of voids in the cobalt deposit can be measured by electron microscopy, a technique known to those skilled in the art, who will choose the method they deem most appropriate. One such method could be scanning electron microscopy (SEM) or transmission electron microscopy (TEM) using a magnification between 50,000 and 350,000. The void volume can be estimated by measuring the void area observed on one or more cross-sections of the substrate, including the filled cavities. In the case of measuring several areas on several cross-sections, the average of these areas will be calculated to estimate the void volume.

[0060] A low impurity content combined with a very low void percentage makes it possible to obtain a cobalt deposit with lower resistivity. Therefore, the resistivity of the cobalt deposit obtained after the polarization step can be less than 30 μQ.cm without having undergone heat treatment at a temperature ranging from 50°C to 500°C.

[0061] The cobalt deposition rate can be between 0.1 nm / s and 3.0 nm / s, preferably between 1.0 nm / s and 3.0 nm / s, and preferably still between 1 nm / s and 2.5 nm / s.

[0062] The cavities to be filled can be shaped according to a Damascus or Double Damascus process known to those skilled in the art comprising a succession of steps including: - the etching of trenches on the upper part of a silicon wafer; - the deposition of an insulating dielectric layer generally made of silicon oxide on the etched surface; - the deposition of a thin layer of a barrier material used to prevent the migration of cobalt into the silicon; - the possible deposition of a thin metallic layer, called a seed layer.

[0063] The barrier layer and the germination layer generally have, independently of each other, a thickness of between 1 nm and 10 nm.

[0064] The conductive surface which is brought into contact with the electrolyte is a surface of a layer of metal comprising for example at least one compound chosen from the group consisting of cobalt, copper, tungsten, titanium, tantalum, ruthenium, nickel, titanium nitride, and tantalum nitride.

[0065] The conductive surface of the substrate can be the surface of an assembly comprising a tantalum nitride layer of thickness between 1 nm and 6 nm, itself covered and in contact with a metallic cobalt layer of thickness between 1 nm and 10 nm, preferably between 2 nm and 5 nm, on which the cobalt is deposited during the electrical step.

[0066] The substrate can therefore be obtained by successive depositions of SiO2, tantalum nitride and cobalt. The cobalt can be deposited on the tantalum nitride by chemical vapor deposition (CVD) or by atomic thin film (ALD) deposition.

[0067] The resistivity of the assembly including the metallic layer and the cobalt deposit can range from 7 to 10 ohm / cm. It is preferably between 7.5 and 8.5 ohm / cm.

[0068] The cavities intended to be filled with cobalt according to the process of the invention preferably have a width at their opening (i.e., at the surface of the substrate) of less than 100 nm, preferably between 10 and 50 nm. Their depth can range from 50 to 250 nm. According to one embodiment, they have a width between 30 nm and 50 nm, preferably between 35 nm and 45 nm, and a depth between 125 nm and 175 nm.

[0069] The polarization intensity used in the electrical step preferably ranges from 2 mA / cm2 to 20 mA / cm2. The cobalt deposition rate is between 0.1 nm / s and 3.0 nm / s when the polarization current intensity ranges from 8.5 mA / cm2 to 18.5 mA / cm2, which is very advantageous compared to prior art processes for which a much lower rate is observed in this current range.

[0070] The electrical polarization step of the process of the invention may comprise one or more different polarization mode steps.

[0071] The conductive surface can be brought into contact with the electrolyte either before or after polarization. It is preferable that contact with the cavities be made before energizing, so as to limit corrosion of the surface by the electrolyte.

[0072] The electrical step can be carried out using at least one polarization mode chosen from the group consisting of ramp mode, galvano-static mode and galvano-pulsed mode.

[0073] For example, the electrical step includes one or more cathode ramp biasing steps in a current range from 0 mA / cm2 to 10 mA / cm2, for a duration preferably between 10 s and 100 s.

[0074] The electrical stage may also include one or more galvano-static polarization stages with a current ranging from 5 mA / cm2 to 20 mA / cm2.

[0075] According to one example, the electrical step includes at least one cathode polarization step in ramp mode with a current preferably going from 0 mA / cm2 to 10 mA / cm2, followed by a galvano-static mode step imposing a current going from 5 mA / cm2 to 20 mA / cm2.

[0076] The process of the invention may include an annealing step of the cobalt deposit obtained after the filling described above, but advantageously it does not include such a step. Annealing heat treatment is generally carried out at a temperature between 350°C and 550°C, for example around 450°C, preferably under a reducing gas such as 4% H2 in N2.

[0077] The process may include a preliminary step of reducing plasma treatment to reduce the native metal oxide present on the conductive surface of the substrate. The plasma also acts on the surface of the trenches, thereby improving the quality of the interface between the nucleation layer and the electrodeposited cobalt. It is preferred that the electrodeposition step be carried out immediately after the plasma treatment to minimize the reformation of native oxide.

[0078] The process of the invention finds particular application in the manufacture of semiconductor devices during the creation of conductive metallic interconnections such as surface current trenches and vias linking different levels of integration.

[0079] The invention is further illustrated by the following embodiment examples.

[0080] Example 1: Electrodeposition at pH=2.2 for structures 40 nm wide and 150 nm deep, with a solution comprising an alpha-hydroxylated carboxylic acid and polyethylene imine

[0081] Trenches were filled by electrodeposition of cobalt onto a cobalt germination layer. The deposition was carried out using a composition containing cobalt dichloride, an alpha-hydroxylated carboxylic acid and polyethylene imine (PEI) at pH 2.2. A. Materials and Equipment: Substrate:

[0082] The substrate used in this example consisted of a 3.3 x 3.3 cm silicon coupon etched with trenches, which was successively coated with a layer of silicon oxide, a 2 nm thick layer of TaN, and a 3 nm thick layer of metallic cobalt. The resistivity of the substrate is approximately 600 ohms / square. The width the diameter of the cavities to be filled is equal to 40 nm at their opening, and their depth is equal to 150 nm. Electrodeposition solution:

[0083] In this solution, the concentration of Co2+ is 2.3 g / L, obtained from CoC12(H2O)6. Tartaric acid has a concentration of 15 ppm. PEI has a concentration of 5 ppm. The pH of the solution is adjusted to 2.2 by adding hydrochloric acid. Equipment :

[0084] In this example, an electrolytic deposition unit was used, consisting of two parts: the cell for containing the electrodeposition solution, equipped with a fluid recirculation system to control the system's hydrodynamics, and a rotating electrode equipped with a sample holder adapted to the size of the coupons used (3.3 cm x 3.3 cm). The electrolytic deposition cell comprised two electrodes: - A cobalt anode - The structured silicon coupon coated with the layer described above, which constitutes the cathode. - The reference is connected to the anode.

[0085] Connectors allowed electrical contact of the electrodes which were connected by electrical wires to a potentiostat supplying up to 20 V or 2 A. B. Experimental protocol: Electrical process:

[0086] Three tests, designated Test 1, Test 2, and Test 3, were carried out using different electrical processes. The three processes comprised two, three, or five steps from the following: a) "Cold entry": The electrodeposition solution is poured into the electrolytic deposition cell. The various electrodes are positioned and brought into contact in the electrodeposition solution without polarization. Polarization is then applied. b) In the second step, the cathode is biased in galvanodynamic ramp mode within a current range of 0 mA to 30 mA (or 3.8 mA / cm²). This step is carried out at a rotation of 65 rpm for 3 seconds. c) In the third step, the cathode is biased in galvanodynamic ramp mode within a current range of 30 mA (or 3.8 mA / cm2) to 60 mA (or 7.6 mA / cm2). This step was carried out at a rotation of 65 rpm for 55 seconds. d) In the fourth step, the cathode is biased in galvanodynamic ramp mode in a current range of 60 mA (or 7.6 mA / cm2) to 130 mA (16.5 mA / cm2) per For example, a current range of 60 mA (or 3.8 mA / cm2) to 90 mA (11.4 mA / cm2). This step was carried out at a rotation of 65 rpm for 7 seconds. e) In the final step, the cathode is galvanically biased in a current range from 90 mA (11.4 mA / cm²) to 130 mA (16.5 mA / cm²), for example 90 mA (11.4 mA / cm²). This step is carried out at a rotation of 65 rpm or 100 rpm for 40 to 150 seconds.

[0087] The first electrical protocol (Test 1) comprised three steps, steps a), b) and c).

[0088] The second electrical protocol (Test 2) comprised five steps, steps a) to e). During step e), the cathode was polarized in galvanostatic mode at 90 mA (11.4 mA / cm2) under a rotation of 100 rpm for 40 seconds.

[0089] The third electrical protocol (Test 3) comprised two steps, steps a) and e). During step e), the cathode was polarized in galvanostatic mode at 90 mA (11.4 mA / cm2) under a rotation of 65 rpm for 133 seconds. C. Results obtained:

[0090] As can be seen in [Fig. 1], a transmission electron microscopy (TEM) analysis of the metallized substrate obtained in Test 1 reveals the partial filling of the trenches from the bottom, indicating a bottom-up deposition mechanism. Furthermore, there are no gaps in the structures ("seam-voids").

[0091] In Test 2, a scanning electron microscopy (SEM) analysis reveals a flawless filling of holes on the walls of the trenches (“sidewall voids”) indicating good nucleation of the cobalt and no holes in the structures (“seam-voids”) indicating optimal bottom-up filling without annealing.

[0092] Fig. 2 represents a photograph from the scanning electron microscopy (SEM) analysis of Test 3 which reveals a flawless filling of holes on the walls of the trenches ("sidewall voids") indicating good nucleation of cobalt and no holes in the structures ("seam-voids"), indicating optimal bottom-up filling without annealing.

[0093] Example 2: Electrodeposition at pH=2.2 for structures 40 nm wide and 150 nm deep, with a solution comprising an alpha-hydroxylated carboxylic acid and benzotriazole

[0094] Trenches identical to those of Example 1 were filled with a composition containing cobalt dichloride, an alpha-hydroxylated carboxylic acid and benzotriazole at pH 2.2. A. Materials and Equipment: Substrate:

[0095] The substrate used is strictly identical to that of example 1. Electrodeposition solution:

[0096] In this solution, the concentration of Co2+ is 2.3 g / L, obtained from CoC12(H2O)6. Tartaric acid has a concentration of 15 ppm. Benzotriazole has a concentration of 10 ppm. The pH of the solution is adjusted to 2.2 by adding hydrochloric acid. Equipment :

[0097] The equipment is identical to that of example 1. B. Experimental protocol: Electrical process:

[0098] The electrical process was identical to that of Test 2 of Example 1 and comprised the five steps a) to e). C. Results obtained:

[0099] Scanning electron microscopy (SEM) analysis reveals flawless filling of holes on the trench walls (“sidewall voids”) indicating good cobalt nucleation and no holes in the structures (“seam-voids”), indicating optimal bottom-up filling without annealing.

[0100] Example 3 Comparative: Electrodeposition at pH=2.2 for structures 40 nm wide and 150 nm deep with a single organic additive, an alpha-hydroxy carboxylic acid

[0101] Trenches identical to those of Example 1 were filled with a composition containing cobalt dichloride and an alpha-hydroxylated carboxylic acid at pH 2.2. A. Materials and Equipment: Substrate:

[0102] The substrate used is strictly identical to that of Example 1. Electrodeposition solution:

[0103] In this solution, the concentration of Co2+ is 2.3 g / L obtained from CoC12(H2O)6. Tartaric acid has a concentration of 15 ppm. The pH of the solution is adjusted to 2.2 by adding hydrochloric acid. Equipment :

[0104] The equipment is identical to that of example 1. B. Experimental protocol:

[0105] The electrical process was identical to that of Test 2 of Example 1 and comprised the five steps a) to e). C. Results obtained:

[0106] A scanning electron microscopy (SEM) analysis reveals a filling comprising holes in the structures ("seam-voids") which requires an additional annealing step to be able to remove them, reflecting a bottom-up closing growth of the structures, similar to a zipper.

[0107] Example 4 Comparative: Electrodeposition for structures 40 nm wide and 150 nm deep with a prior art electrolyte

[0108] Cobalt electrodeposition was carried out in trenches identical to those of Example 1 using a prior art composition in accordance with the teaching of US application 2016 / 0273117 Al containing cobalt sulfate, boric acid, thiourea and polyethylene imine (PEI) at pH 4. A. Materials and Equipment: Substrate:

[0109] The substrate used is strictly identical to that of Example 1. Electrodeposition solution:

[0110] In this solution, the concentration of Co2+ is 2 g / L, obtained from CoSO4. Boric acid has a concentration of 20 g / L. Thiourea has a concentration of 150 ppm. PEI has a concentration of 10 ppm. The pH of the solution is adjusted to 4 by adding sulfuric acid. Equipment :

[0111] The equipment is identical to that of example 1. B. Experimental protocol:

[0112] The process is identical to that of Test 3 of Example 1 and comprises the two steps a) and e). C. Results obtained:

[0113] As can be seen in [Fig.3], a scanning electron microscopy (SEM) analysis reveals a filling with defects in the structures (“seam-voids”) reflecting a non-optimal bottom-up filling without annealing.

[0114] In parallel, an 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. Film resistance (Ω / square) Thickness (nm) Resistivity (pΩ.cm) Example 1 Test 3 0.52 381 19.8 Example 4 Comparison 23.6 372 878

[0115] The resistivity of the film deposited in Test 3 of Example 1 is better than that of Comparative Example 4, which is more desirable at the industrial level. Lower resistivity means better film quality with fewer impurities.

Claims

Demands

1. Electrolyte for the electrodeposition of cobalt characterized in that the electrolyte is 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 sufficient quantity to obtain a pH between 1.8 and 4.0, and organic additives of which at least one first additive selected from alpha-hydroxylated carboxylic acids and mixtures thereof, and at least one second additive selected from polyethyleneimines and benzotriazole.

2. Electrolyte according to claim 1, characterized in that the total concentration of organic additives in the electrolyte is between 5 ppm and 50 ppm.

3. Electrolyte according to claim 1, characterized in that the concentration of the second additive is between 1 ppm and 10 ppm.

4. Electrolyte according to claim 1, characterized in that it contains no sulfur compounds.

5. Electrolyte according to claim 1, characterized in that its pH is between 1.8 and 2.

6.

6. Electrolyte according to claim 5, characterized in that the first additive is selected from citric acid, tartaric acid, malic acid, mandelic acid and glyceric acid.

7. Electrolyte according to claim 1, characterized in that its conductivity is between 2 mS / cm and 10 mS / cm.

8. Electrolyte according to claim 5, characterized in that it does not contain boric acid.

9. An electrochemical deposition process on a substrate having a conductive surface comprising a flat part and cavities, by filling said cavities from bottom to top, said process comprising: - a step of bringing the conductive surface into contact with an electrolyte according to one of the preceding claims, - an electrical step of polarizing the conductive surface for a sufficient time to effect a cobalt deposit on the surface.

10. An electrochemical cobalt deposition process according to claim 9, characterized in that the duration is sufficient for carry out the filling of the cavities and the covering of the flat part by a cobalt deposit with a thickness ranging from 50 nm to 400 nm.

11. Electrochemical cobalt deposition process according to claim 9, characterized in that the polarization step is immediately followed by a polishing step combining chemical and mechanical attack of the cobalt deposit obtained at the end of the polarization step.

12. A method according to any one of claims 9 to 11, characterized in that the cavities have a width at their opening of less than 100 nm, preferably between 10 nm and 50 nm, and a depth between 50 nm and 250 nm.

13. A process according to any one of claims 9 to 12, characterized in that the cobalt deposit obtained at the end of the polarization step has an impurity content of less than 1000 atomic ppm.

14. A process according to any one of claims 9 to 13, characterized in that the cobalt deposit obtained at the end of the electrodeposition step comprises an average void percentage of less than 10% by volume or surface area, without having undergone heat treatment at a temperature ranging from 50°C to 500°C.

15. A method according to any one of claims 9 to 14, characterized in that the cobalt deposition rate is between 0.1 nm / s and 3.0 nm / s when the bias current intensity is from 8.5 mA / cm2 to 18.5 mA / cm2.

16. A process according to any one of claims 9 to 15, characterized in that the resistivity of the cobalt deposit, obtained at the end of the polarization step, has a resistivity of less than 30 qQ.cm without having undergone heat treatment at a temperature ranging from 50°C to 500°C.

17. A process according to any one of claims 9 to 16, characterized in that the substrate is obtained by successive depositions of SiO2, tantalum nitride and cobalt.

18. A process according to claim 17, characterized in that the cobalt is deposited on the tantalum nitride by chemical vapor deposition (CVD) or by atomic thin film (ALD) deposition.

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