KR20230146586A - Electrolyte and Cobalt Electrodeposition Method - Google Patents

Abstract

The present invention relates to a method for manufacturing cobalt interconnections and an electrolyte capable of implementing the same. The electrolyte below pH 4.0 includes cobalt ions, chloride ions, and organic additives including alpha-hydroxy carboxylic acids and amines selected from polyethyleneimine or benzotriazole.

Description

Electrolyte and Cobalt Electrodeposition Method

The present invention relates to cobalt electrodeposition on conductive surfaces. More precisely, it relates to electrolytic and cobalt electrodeposition methods that can be used to fabricate electrical interconnections in integrated circuits.

Prior art

Semiconductor devices contain conductive metal interconnects at different integration levels and in two categories: trenches tens of nanometers wide that run on the surface of the device and connect electronic components, and through vias that connect the different levels and are on the order of hundreds of nanometers in diameter. do.

Fabrication of the interconnect involves etching a cavity in the substrate and the subsequent steps of electrochemically filling the cavity with a conductive metal by depositing a metal seed layer on the cavity surface.

Conventional methods for filling interconnects with cobalt use an electrolyte containing a cobalt salt and numerous organic additives. This combination of additives is necessary to obtain a cobalt mass of good quality in general, especially void-free material and good conductivity.

Charging of the cavity can follow two mechanisms, depending on the composition of the electrolyte used: bottom-up charging or conformal charging. The charging method by the bottom-up mechanism is the opposite of the charging method in which cobalt deposits grow at the same rate on the bottom and walls of the hollow pattern.

To achieve bottom-up charging, prior art electrolytes contain several additives, including inhibitors and accelerators. This system prevents voids from forming in the cobalt deposit during charging and prevents premature closure of void openings. The inhibitor limits the deposition of cobalt at the top level of the cavity, the walls and the flat surface of the substrate where the cavity opens, while the accelerator diffuses at the bottom of the cavity and promotes the deposition of cobalt. The presence of an accelerator is more necessary in narrow and deep cavities because it can increase the rate of cobalt deposition at the bottom of the cavity.

Electrodeposition baths designed for bottom-up charging have several drawbacks that ultimately limit the smooth operation of the fabricated electronic devices and make them too expensive to manufacture. These actually create cobalt interconnects contaminated with organic additives needed to limit the formation of holes in the cobalt during charging. Moreover, the charging rates achieved with these chemicals are too slow and incompatible with industrial-scale production.

For example, in application US 2016/0273117 the electrolyte contains numerous additives including inhibitors and accelerators with complementary functions to ensure upward charging. The inventors discovered that cobalt deposited with this electrolyte had a very high resistivity and that holes formed in the cobalt during charging. This is why it is necessary to anneal the deposits to remove them.

Accordingly, there is a need to provide an electrolyzer that leads to cobalt interconnects with improved performance, particularly with regard to conductivity. To achieve this goal, it is desirable to produce a cobalt deposit with very low impurity content and no material voids, even without an annealing step. It would also be desirable to propose an electrolyte that could reach sufficiently high deposition rates to make device fabrication profitable while preventing the formation of holes in the cobalt.

The inventors have discovered that a combination of an alpha-hydroxy carboxylic acid and a nitrogen compound such as polyethyleneimine or benzotriazole meets this need.

Alpha-hydroxy carboxylic acids have certainly already been used in electrochemical methods for cobalt deposition, as for example in application WO 2019/179897, but this method involves forming a conformal process at the ends leaving pores in the metal in the absence of annealing of the deposit. A charging mechanism follows.

Accordingly, the present invention relates to the bottom-up filling of cavities using an electrolyte with a pH comprised between 1.8 and 4.0, comprising cobalt II, chloride ions, alpha-hydroxy carboxylic acid, and additives selected from polyethyleneimine and benzotriazole. A method of creating a cobalt interconnect is provided.

More precisely, the present invention relates to 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 consisting of 1.8 to 4.0, and alpha-hydroxy carboxyl It relates to an electrolyte for cobalt electrodeposition in the form of an aqueous solution comprising an organic additive including at least one first additive selected from acids and mixtures thereof and at least one second additive selected from polyethyleneimine and benzotriazole.

The electrolyte of the present invention allows obtaining high purity, continuous cobalt deposits whose production duration can be shorter than that of the prior art.

In practice, the filling kinetics of conventional methods must be slower to prevent the formation of holes, and the method must include an annealing step when holes are formed. Moreover, this method involves two distinct steps of cobalt electrodeposition: performing charging of the cavities at a fairly slow rate and using a second electrolyte containing cobalt ions to deposit a so-called “overload layer” over the entire substrate surface. It may include a second step of electrodeposition.

The method of the invention has the advantage of making it possible to carry out the filling of the cavities and the deposition of the overburden layer in a single electrodeposition step. This also makes it possible to avoid annealing the cobalt deposit before performing the polishing step, which combines chemical and mechanical attack of the overburden layer.

Additionally, the cobalt deposits produced in the context of the present invention have the advantage of forming interconnects with very low amounts of impurities, preferably less than 1000 atomic ppm.

“Electrolyte” means a liquid containing the precursor of a metal coating used in an electrodeposition process.

“Continuous charge” means a mass of cobalt without voids. In the prior art, material pores or voids can be observed in the cobalt deposit between the walls of the cavity and the cobalt deposit (side wall voids) and the pores located at a distance from the wall of the cavity in the form of a seam. These voids can be observed and quantified using transmission or scanning electron microscopy by creating a cross-section of the structure. The continuous deposit of the present invention has an average porosity of less than 10% by volume, preferably less than 5% by volume. The porosity within the structure to be filled can be measured with a scanning electron microscope at a magnification of 50,000 to 350,000.

“Average diameter” or “average width” of a cavity means the dimension measured at the opening of the cavity to be filled. The cavity is for example in the form of a cylindrical or flared channel.

Figure 1 is a transmission electron microscope slide of a cavity filled according to the method of Test 1 of Example 1 of the present invention.
Figure 2 is a scanning electron microscope slide of a cavity filled according to the method of Test 3 of Example 1 of the present invention.
Figure 3 is a scanning electron microscope slide of a cavity filled according to a prior art electrodeposition method (Comparative Example 4).

According to a first embodiment, the present invention provides an electrolyte 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 of 1.8 to 4.0, and A cobalt solution comprising an organic additive comprising at least one first additive selected from alpha-hydroxy carboxylic acids and mixtures thereof and at least one second additive selected from polyethyleneimine and benzotriazole. It's about wearing electrolytes.

The mass concentration of cobalt II ions may range from 1 g/L to 5 g/L, for example from 2 g/L to 3 g/L. The mass concentration of chloride ions may range from 1 g/L to 10 g/L.

Chloride ions can be introduced by dissolving cobalt chloride or one of the hydrate salts, such as cobalt chloride hexahydrate, in water.

The electrolyte preferably contains at most two organic additives, these additives being the first and second additives.

All organic additives included in the electrolyte are preferably sulfur-free. For example, alpha-hydroxy carboxylic acids are preferably sulfur-free.

It is preferred that the electrolyte does not contain any sulfur compounds. Additionally, the composition is preferably not obtained by dissolving cobalt salts, such as cobalt sulfate, or one of its hydrates, since sulfur compounds produce sulfur contamination of the cobalt deposits, which we wish to avoid.

The total concentration of organic additives in the electrolyte preferably consists of 5 ppm to 50 ppm.

The concentration of the first additive is preferably 5 to 200 ppm, and the concentration of the second additive is preferably 1 to 10 ppm.

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

In certain embodiments of the invention, the alpha-hydroxy carboxylic acid is tartaric acid.

According to one embodiment of the invention, the secondary amine additive is a linear or branched poly(ethyleneimine) homopolymer or copolymer. Poly(ethyleneimine) exists in acid form, and some or all of the amine functional groups are protonated.

For example, a linear poly(ethyleneimine) with a number average molecular weight Mn consisting of 500 g/mol to 25,000 g/mol would be selected.

Branched poly(ethyleneimines) with a number average molecular weight Mn consisting of 500 g/mol to 70,000 g/L comprising primary amine, secondary amine and tertiary amine functionalities may also be selected.

Thus, the poly(ethyleneimine) has, for example, a number average molecular weight Mn consisting of 500 g/mol to 700 g/mol, preferably a weight average molecular weight Mw consisting of 700 g/mol to 900 g/mol. It may be poly(ethyleneimine) with number 25987-06-8.

This poly(ethyleneimine) is sold by the Sigma-Aldrich company under reference number 408719.

The poly(ethyleneimine) may also be, for example, poly(ethyleneimine) of CAS number 9002-98-6, with a number average molecular weight Mn consisting of 500 to 700 g/mol. This poly(ethyleneimine) is sold by Polysciences, Inc. under reference number 02371.

Number average molecular weight and weight average molecular weight can be measured independently of each other by conventional methods known to those skilled in the art, such as gel permeation chromatography (GPC) or light scattering (LS).

According to one embodiment of the present invention, the amine is benzotriazole.

The pH of the electrolyte is preferably comprised between 1.8 and 4.0.

In certain embodiments, the pH consists of 1.8 and 2.6.

The pH of the composition can optionally be adjusted with bases or acids known to those skilled in the art. The acid used may be hydrochloric acid. The electrolyte may not contain buffering compounds, such as boric acid, for example. Preferably, the electrolyte does not contain boric acid.

There is no limitation in principle as to the nature of the solvent (provided it sufficiently dissolves the active species in the solution and does not interfere with electrodeposition), but the electrolyte will preferably be water. According to one embodiment, the solvent comprises mostly water by volume.

The conductivity of the electrolyte is preferably comprised between 2 mS/cm and 10 mS/cm.

The invention also relates to an electrochemical method for depositing a substrate provided with a conductive surface comprising flat portions and cavities by filling the cavities from the bottom up, the method comprising:

- contacting the conductive surface with an electrolyte according to the preceding description;

- and an electrical step of polarizing the conductive surface for a period of time sufficient to effect cobalt deposition on the surface.

In one advantageous embodiment, the duration is sufficient to effect coating of flat parts of the conductive surface and filling of the cavities with a cobalt deposit having a thickness ranging from 50 nm to 400 nm.

In one advantageous variant, there is no need to perform a step of annealing the cobalt deposits obtained at the end of the polarization step, so that the polarization step combines chemical and mechanical attack (also called mechanochemical) of the cobalt deposits obtained at the end of the polarization step. ) immediately follows the polishing step. Therefore, according to one embodiment, the deposition method of the present invention

- contacting the conductive surface with an electrolyte according to the preceding description;

- polarizing the conductive surface and the electrolyte for a period of time sufficient to form a cobalt deposit that fills the cavities and optionally coats flat portions of the conductive surface;

- A polishing step that combines chemical and mechanical attack on the cobalt deposit without performing a prior annealing treatment of the deposit at a temperature ranging from 50° C. to 500° C.

Includes.

The polarization step in the presence of the electrolyte of the present invention can last 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 while the second cobalt deposit is formed using an electrolyte other than the electrolyte of the present invention.

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 cavities and coat the flat surface, with the thickness of the cobalt deposit on the flat surface being at least 20 nm.

The portion of the cobalt deposit that coats the flat surface (also referred to as the overburden layer) may have a thickness comprised between 50 nm and 400 nm. It is advantageous to have a consistent thickness across the entire substrate surface. The layer is also homogeneous, shiny and compact.

Under certain conditions, the method of the present invention is a so-called “bottom-up” method, in contrast to the “conformal” methods of the prior art. In this case, the cobalt deposition rate is higher at the bottom of the cavity than at the walls.

The cobalt deposit obtained at the end of the polarization step advantageously has an impurity content of less than 1000 atomic ppm. The main impurity is oxygen, followed by carbon and nitrogen. The total carbon and nitrogen content is preferably less than 300 ppm.

The cobalt deposit obtained at the end of the electrodeposition step is less than 10% by volume or area, preferably by volume or area, without undergoing heat treatment at a temperature in the range of 50° C. to 500° C., preferably 150° C. to 500° C. It is advantageously continuous in that it contains a porosity of 5% or less.

The porosity of the cobalt deposit can be measured by electron microscopy as is known to those skilled in the art, and the skilled person will select the method that seems most appropriate. One of these methods can be scanning electron microscopy (SEM) or transmission electron microscopy (TEM) using magnifications ranging from 50,000 to 350,000. Pore volume can be assessed by measuring the observed void area across one or more cross-sections of the substrate containing filled cavities. When measuring multiple areas across multiple cross sections, calculate the average of these areas to estimate the void volume.

Low impurity content combined with very low porosity makes it possible to obtain cobalt deposits with reduced resistivity. Additionally, the resistivity of the cobalt deposit obtained at the end of the polarization step may be less than 30 μΩ.cm without heat treatment at a temperature ranging from 50° C. to 500° C.

The cobalt deposition rate may be 0.1 nm/s to 3.0 nm/s, preferably 1.0 nm/s to 3.0 nm/s, more preferably 1 nm/s to 2.5 nm/s.

The cavity to be filled can be formed according to the damascene or dual damascene method known to the person skilled in the art, comprising a series of steps: etching a trench in the upper part of the silicon wafer; - depositing on the etched surface an insulating dielectric layer, generally consisting of silicon oxide; - depositing a thin layer of barrier material used to prevent cobalt from migrating into the silicon; - optionally depositing a thin metal layer called a seed layer.

The barrier layer and the seed layer generally, independently of each other, have a thickness comprised of 1 nm to 10 nm.

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

The conductive surface of the substrate is the surface of the assembly comprising a layer of tantalum nitride with a thickness of 1 nm to 6 nm, covered with itself, and 1 nm to 10 nm, preferably 2 nm to 2 nm, onto which cobalt will be deposited during the electrical step. It can be contacted with a layer of metallic cobalt consisting of 5 nm.

Therefore, the substrate can be obtained by sequential deposition of SiO ₂ , tantalum nitride, and cobalt. Cobalt can be deposited on tantalum nitride via chemical vapor deposition (CVD) or atomic layer deposition (ALD).

The resistivity of the assembly including the metal layer and cobalt deposit may range from 7 to 10 ohm/cm. The resistivity is preferably comprised between 7.5 and 8.5 ohm/cm.

Cavities designed to be filled with cobalt according to the method of the invention preferably have a width at the opening (i.e. at the substrate surface) of less than 100 nm, preferably between 10 and 50 nm. The depth may range from 50 to 250 nm. According to one embodiment, they have a width comprised between 30 nm and 50 nm, preferably between 35 nm and 45 nm, and a depth comprised between 125 nm and 175 nm.

The intensity of polarization used in the electrical step preferably ranges from 2 mA/cm ² to 20 mA/cm ² . Cobalt deposition rates range from 0.1 nm/s to 3.0 nm/s when the intensity of the polarization current ranges from 8.5 mA/cm ² to 18.5 mA/cm ² , compared to the prior art where much lower rates are observed in this current range. It is very advantageous compared to the method of.

The electrical polarization step of the method of the present invention may comprise a single or several different polarization mode steps.

The conductive surface may be in contact with the electrolyte before or after polarization. To limit surface corrosion by the electrolyte, it is desirable to complete contact with the cavity before applying power.

The electrical step may be performed using at least one polarization mode selected from the group consisting of ramp mode, constant current mode, and galvano pulse mode.

For example, the electrical step preferably comprises one or more cathode polarization steps in ramp mode with a current ranging from 0 mA/cm ² to 10 mA/cm ² for a duration consisting of 10 seconds to 100 seconds.

The electrical step may include one or more polarization steps in constant current mode using currents ranging from 5 mA/cm ² to 20 mA/cm ² .

According to one embodiment, the electrical step preferably includes at least one step of polarizing the cathode in ramp mode using a current in the range of 0 mA/cm ² to 10 mA/cm ² , followed by 5 mA/cm ² to 20 mA/cm 2 It involves the step of constant current mode by imposing a current of cm ² .

The method of the invention may, but advantageously does not have, a step of annealing the cobalt deposit obtained at the end of the charge described above. The annealing heat treatment is generally carried out at a temperature comprised between 350° C. and 550° C., for example about 450° C., preferably under a reducing gas such as 4% H ₂ in N ₂ .

The method may include a preliminary step of treatment with a reducing plasma to reduce native metal oxides present on the conductive surface of the substrate. The plasma also acts on the trench surface to improve the quality of the interface between the seed layer and the electrodeposited cobalt. It is desirable to perform the electrodeposition step immediately after plasma treatment to minimize reformation of native oxide.

The method of the present invention has particular application in the fabrication of semiconductor devices when creating conductive metal interconnects such as trenches extending on the surface and vias connecting different integration levels.

The invention is further illustrated by the following examples.

Example 1: Electrodeposition at pH=2.2 on a 40 nm wide, 150 nm deep structure with a solution containing alpha-hydroxy carboxylic acid and polyethyleneimine.

The trench is filled by electrodepositing cobalt on the cobalt seed layer. Deposition is carried out using a composition comprising cobalt dichloride, alpha-hydroxy carboxylic acid and polyethyleneimine (PEI) at pH 2.2.

A. Materials and Equipment

Board

The substrate used in this example consisted of a trench-etched silicon coupon measuring 3.3 x 3.3 cm, 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 ohm per square. The width of the cavity to be filled is 40 nm and the depth is 150 nm at the opening.

Electrodeposition solution:

In this solution, the Co ²⁺ concentration is 2.3 g/L, obtained in CoCl ₂ (H ₂ O) 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:

In this example, the electrolytic deposition equipment was designed to accommodate two components: a cell designed to contain an electrodeposition solution equipment equipped with a fluid recirculation system to control the hydrodynamics of the system, and tailored to the coupon size used (3.3 cm x 3.3 cm). It consists of a rotating electrode equipment equipped with a sample holder. The electrolytic deposition cell consists of two electrodes, viz.

- cobalt anode

- Structured silicon coupon coated with the above-described layer, constituting the cathode

had

- The reference is connected to the anode.

The connector allowed electrical contact of electrodes connected by wires to a potentiostat providing up to 20 V or 2 A.

B. Experimental Protocol:

Electrical method:

Three tests, named Test 1, Test 2, and Test 3, are performed by applying different electrical methods. The three methods included two, three, or five of the following steps.

a) “Cold Input”: Electrodeposition solution is poured into the electrolytic deposition cell. The different electrodes are placed in place and brought into contact with the electrodeposition solution without polarization. Polarization is then applied.

b) In the second stage, the cathode is polarized in galvanodynamic ramp mode in the current range from 0 mA to 30 mA (or 3.8 mA/cm ² ). This step is performed for 3 seconds with a rotation of 65 rpm.

c) In the third step, the cathode is polarized in galvanodynamic ramp mode in the current range from 30 mA (or 3.8 mA/cm ² ) to 60 mA (or 7.6 mA/cm ² ). This step is performed for 55 seconds with a rotation of 65 rpm.

d) In the fourth stage, the cathode is subjected to a current ranging from 60 mA (or 7.6 mA/cm ² ) to 130 mA (16.5 mA/cm²), for example from 60 mA (or 3.8 mA/cm ² ) to 90 mA (11.4 mA). It is polarized in a galvanodynamic ramp mode in the current range of mA/cm²). This step is performed for 7 seconds with a rotation of 65 rpm.

e) In the final step, the cathode is polarized in constant current mode in the current range from 90 mA (11.4 mA/cm ² ) to 130 mA (16.5 mA/cm²), for example 90 mA (11.4 mA/cm²). This step is performed at a rotation of 65 rpm or 100 rpm and lasts between 40 and 150 seconds.

The first electrical protocol (Test 1) included three steps: step a), step b) and step c).

The second electrical protocol (Test 2) included five steps: steps a) through e). During step e), the cathode was polarized in constant current mode at 90 mA (11.4 mA/cm²) for 40 s with a rotation of 100 rpm.

The third electrical protocol (Test 3) included two steps: step a) and step e). During step e), the cathode was polarized in constant current mode at 90 mA (11.4 mA/cm²) for 133 seconds with a rotation of 65 rpm.

C. Results obtained:

As can be seen in Figure 1, analysis by transmission electron microscopy (TEM) of the metallized substrate obtained in Test 1 shows partial filling of the trench starting from the bottom, reflecting a bottom-up deposition mechanism. Moreover, there are no holes (seam gaps) in the structure.

In Test 2, analysis by scanning electron microscopy (SEM) showed that there were no holes (sidewall voids) in the trench walls, reflecting good cobalt seeding, and no holes (seam voids) in the structure, reflecting optimal bottom-up filling without annealing. Indicates charging.

Figure 2 shows a slide of the scanning electron microscopy (SEM) analysis results from Trial 3, showing that there are no holes (sidewall voids) in the trench walls, reflecting good cobalt seeding, and in the structure reflecting optimal bottom-up filling without annealing. Indicates filling without holes (seam voids).

Example 2: Electrodeposition at pH=2.2 on structures 40 nm wide and 150 nm deep with solutions containing alpha-hydroxy carboxylic acid and benzotriazole

A trench identical to that of Example 1 was filled using a composition comprising cobalt dichloride, alpha-hydroxy carboxylic acid, and benzotriazole at pH 2.2.

A. materials and equipment

Board

The substrate used was exactly the same as that of Example 1.

Electrodeposition solution:

In this solution, the Co ²⁺ concentration is 2.3 g/L, obtained in CoCl ₂ (H ₂ O) 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:

The equipment is the same as that of Example 1.

B. Experimental Protocol:

Electrical method:

The electrical method is the same as that of Test 2 of Example 1 and consists of five steps, namely steps a) to steps e).

C. Results obtained:

Analysis by scanning electron microscopy (SEM) shows filling with no holes (sidewall voids) in the trench walls, reflecting good cobalt nucleation, and no holes (seam voids) in the structure, reflecting optimal bottom-up filling without annealing.

Comparative Example 3: Electrodeposition at pH=2.2 on structures 40 nm wide and 150 nm deep with alpha-hydroxy carboxylic acid as the single organic additive.

A trench identical to that of Example 1 was filled using a composition comprising cobalt dichloride and alpha-hydroxy carboxylic acid at pH 2.2.

A. materials and equipment

Board

The substrate used was exactly the same as that of Example 1. Electrodeposition solution:

In this solution, the Co ²⁺ concentration is 2.3 g/L, obtained in CoCl ₂ (H ₂ O) ₆ . Tartaric acid has a concentration of 15 ppm. The pH of the solution is adjusted to 2.2 by adding hydrochloric acid.

equipment:

The equipment is the same as that of Example 1.

B. Experimental Protocol:

The electrical method is the same as that of Test 2 of Example 1 and consists of five steps, namely steps a) to steps e).

C. Results obtained:

Analysis by scanning electron microscopy (SEM) reveals fillings containing pores (seam voids) in the structure, which, similar to a zipper, eliminate cavities reflecting growth by closing the structure from bottom to top. It requires an additional annealing step.

Comparative Example 4: Electrodeposition of structures 40 nm wide and 150 nm deep with prior art electrolytes

Electrodeposition of cobalt in the same trench as that of Example 1 was carried out using a prior art composition according to the teachings of application US 2016/0273117 A1 comprising cobalt sulfate, boric acid, thiourea and polyethyleneimine (PEI) at pH 4. do.

A. materials and equipment

Board

The substrate used was exactly the same as that of Example 1.

Electrodeposition solution:

In this solution, the Co ²⁺ concentration is 2 g/L, obtained in CoSO ₄ . 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 hydrochloric acid.

equipment:

The equipment is the same as that of Example 1.

B. Experimental Protocol:

This method is identical to the method of Test 3 of Example 1 and consists of two steps, namely step a) and step e).

C. Results obtained:

As can be seen in Figure 3, analysis by scanning electron microscopy (SEM) shows filling with structural defects (seam voids) reflecting non-optimal bottom-up filling without annealing.

At the same time, the resistivity could be compared through analysis of the film obtained in Test 3 of Example 1 and the film obtained in this Example. The results are reported in Table 1 below.

The resistivity of the film deposited in Test 3 of Example 1 was superior to that of Comparative Example 4, making it more desirable at the industrial level. Lower resistivity equates to better film quality with fewer impurities.

Claims (18)

An electrolyte for electrodeposition of cobalt, the electrolyte 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 consisting of 1.8 to 4.0, and alpha-hydroxy An electrolyte for electrodeposition of cobalt, characterized in that it is an aqueous solution containing an organic additive including at least one first additive selected from carboxylic acids and mixtures thereof and at least one second additive selected from polyethyleneimine and benzotriazole. . Electrolyte according to claim 1, characterized in that the total concentration of organic additives in the electrolyte consists of 5 ppm to 50 ppm. The electrolyte according to claim 1, wherein the concentration of the second additive is 1 ppm to 10 ppm. 2. Electrolyte according to claim 1, characterized in that the electrolyte does not contain any sulfur compounds. The electrolyte according to claim 1, wherein the pH is comprised between 1.8 and 2.6. The electrolyte according to claim 5, wherein the first additive is selected from citric acid, tartaric acid, malic acid, mandelic acid and glyceric acid. The electrolyte according to claim 1, characterized in that the conductivity consists of 2 mS/cm to 10 mS/cm. 6. Electrolyte according to claim 5, characterized in that the electrolyte does not contain boric acid. An electrochemical method for deposition on a substrate provided with a conductive surface including flat portions and cavities by filling the cavities from the bottom up, the method comprising:
- contacting the conductive surface with an electrolyte according to any one of claims 1 to 8,
- An electrochemical method for deposition, comprising an electrical step of polarizing the conductive surface for a period of time sufficient to effect cobalt deposition on the surface. The method of claim 9, wherein the duration is
An electrochemical method for depositing cobalt, characterized in that it is sufficient to effect filling of the cavity and coating of the flat part with a cobalt deposit having a thickness in the range from 50 nm to 400 nm. 10. The electrochemical method of depositing cobalt according to claim 9, wherein 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. Method according to claim 9 , wherein the cavity has a width at the opening of less than 100 nm, preferably between 10 and 50 nm, and a depth between 50 nm and 250 nm. . 13. Method according to any one of claims 9 to 12, wherein the cobalt deposit obtained at the end of the polarization step has an impurity content of less than 1000 atomic ppm. 14. The method of any one of claims 9 to 13, wherein the cobalt deposit obtained at the end of the electrodeposition step has an average density of less than 10% by volume or area without undergoing heat treatment at a temperature in the range of 50° C. to 500° C. A method, characterized in that it includes porosity. 15. The method of any one of claims 9 to 14, wherein when the intensity of the polarization current is in the range of 8.5 mA/cm ² to 18.5 mA/cm ² , the cobalt deposition rate is 0.1 nm/s to 3.0 nm/s. A method, characterized in that consisting of. 16. The method of any one of claims 9 to 15, wherein the resistivity of the cobalt deposit obtained at the end of the polarization step is less than 30 μΩ.cm without heat treatment at a temperature in the range of 50° C. to 500° C. How to. 17. Method according to any one of claims 9 to 16, characterized in that the substrate is obtained by sequential deposition of SiO ₂ , tantalum nitride and cobalt. 18. The method of claim 17, wherein the cobalt is deposited on tantalum nitride by chemical vapor deposition (CVD) or atomic layer deposition (ALD).