TWI850331B - Electrodeposition of a cobalt or copper alloy, and use in microelectronics - Google Patents

Abstract

The present invention relates to a process for fabricating cobalt or copper interconnects, and to an electrolyte enabling implementation of said process. The electrolyte, with a pH of less than 4.0, comprises cobalt or copper ions, chloride ions, manganese or zinc ions, and at most two organic additives of low molecular mass. One of these additives may be an alpha-hydroxy carboxylic acid.

Description

Electroplating of cobalt or copper alloys and their use in microelectronics

The invention relates to an electrolyte and its use for electroplating an alloy of a first metal selected from cobalt, copper and mixtures thereof and a second metal selected from manganese, zinc and mixtures thereof on a conductive surface. The invention also relates to a manufacturing method employing the electrolyte and which can be used to produce cobalt or copper interconnects in integrated circuits. The invention finally relates to a device comprising a layer of a first metal in contact with a layer of a second metal.

The known methods for filling interconnects with cobalt employ an electrolyte containing a cobalt salt and a number of organic additives, including inhibitors and accelerators, with complementary functions, in order to obtain what is known as bottom-up filling. The incorporation of these additives is usually necessary to obtain a cobalt nugget of good quality, more specifically without material voids. The inhibitor controls the deposition of cobalt at the opening of the cavity and on the flat surface of the substrate surrounding the cavity, either by absorption onto the cobalt surface or by complexing with the cobalt ions. Thus, this compound may be a molecule with a high molecular mass, such as a polymer that cannot diffuse inside the cavity or a reagent that complexes the cobalt ions. For its part, the accelerator diffuses to the bottom of the cavities and its presence is more necessary in cavities with greater depth. It allows increasing the deposition rate of cobalt at the bottom of the cavities and also on their walls. The filling method via the bottom-up mechanism is contrasted with the filling method called "conformal" or "continuous", in which the cobalt deposit grows at the same rate at the bottom and on the walls of the hollow pattern.

These electroplating baths and their use have a number of defects that ultimately limit the good operation of the electronic devices produced and make them too expensive to produce. The reason is that these defects produce cobalt interconnects that are contaminated with the required organic additives, thereby limiting the formation of filled holes in the cobalt. In addition, the filling rates obtained with these chemistries are too slow and not compatible with industrial scale production.

Patent application US 2015/0179579 describes the use of manganese for enhancing the adhesion of cobalt in interconnects, more specifically on mixed cobalt/dielectric substrates, for the purpose of manufacturing photogates for MOSFET transistors. However, in the method described, manganese and cobalt are deposited during two sequential, separate material deposition steps: a step of vapor phase chemical deposition of manganese followed by a step of electroplating cobalt.

There is therefore still a need to provide electrolytic baths which produce cobalt deposits with enhanced performance, i.e. cobalt deposits with very low impurity content, whose formation rate is high enough to be advantageous for the manufacture of electronic devices and/or which allow reducing the thickness of a layer of cobalt diffusion barrier material, such as tantalum nitride, between an insulating substrate based on, for example, silicon dioxide and the cobalt or even avoiding the deposition of such a layer of cobalt diffusion barrier material.

The inventors have found that a solution containing cobalt II ions and metal ions selected from manganese II ions and zinc II ions at a pH between 1.8 and 4.0 allows to achieve this goal.

The possibility of depositing cobalt alloys in a conformal electroplating process, in particular using α-hydroxycarboxylic acids, at a pH of less than 4 has never been suggested, which makes the results of the present invention even more surprising. In addition, the possibility of forming a thin layer based on manganese or zinc without the need for a chemical or physical deposition step before the deposition of cobalt has never been suggested.

The inventors have discovered that replacing cobalt II ions with copper II ions achieves the same result, enabling the invention to produce copper deposits with enhanced performance, i.e., copper deposits with very low impurity content, whose formation rate is high enough to be advantageous for the manufacture of electronic devices and/or to allow the thickness of a layer of cobalt diffusion barrier material, such as tantalum nitride, between an insulating substrate such as silicon dioxide and the copper to be reduced or even to avoid deposition of such a layer of cobalt diffusion barrier material.

Therefore, the present invention relates to an electrolyte for electroplating an alloy of a first metal and a second metal, wherein the first metal is selected from cobalt, copper and mixtures thereof, and the second metal is selected from manganese, zinc and mixtures thereof, and is characterized in that the electrolyte is an aqueous solution comprising: - cobalt II ions or copper II ions in a mass concentration of 1 g/L to 5 g/L, - chlorine ions in a mass concentration of 1 g/L to 10 g/L, - metal ions selected from manganese II ions and zinc II ions, the metal ions being present in a mass concentration such that the ratio between the mass concentration of cobalt II ions or copper II ions and the mass concentration of metal ions is 1/10 to 25/1, - an organic or inorganic acid, present in a sufficient amount to obtain a pH of the electrolyte between an amount between 1.8 and 4.0, and -only one or at most two organic additives which are not polymers, wherein the organic additive, one of the two organic additives or the two organic additives when present in the composition may be the organic acid, and wherein the concentration of the organic additive or the sum of the concentrations of the two organic additives is between 5 mg/L and 200 mg/L.

The ratio between the mass concentration of cobalt II ions (or copper II ions) and the mass concentration of metal ions may be higher than a value selected from the group consisting of 1/10, 1/5, 1/3, 1/2, 1/1, 2/1, 3/1, 5/1, 10/1, 15/1, and 20/1. The ratio between the mass concentration of cobalt II ions (or copper II ions) and the mass concentration of metal ions may be lower than a value selected from the group consisting of 1/5, 1/3, 1/2, 1/1, 2/1, 3/1, 5/1, 10/1, 15/1, 20/1, and 25/1.

The invention also relates to a method for filling a cavity with cobalt or copper, comprising a first step of conformally depositing the alloy using the above electrolyte and a second step of annealing the alloy to obtain a cobalt or copper deposit.

The electrolyte and method of the present invention provide a means of obtaining continuous deposits of cobalt or copper having high purity and within a manufacturing time compatible with industrial applications.

The advantage of cobalt or copper deposits is that they are of extremely high purity for essentially three reasons.

One of the goals pursued in the prior art is to slow down the metal deposition at the entrance of the cavity without passing through the hollow space to be filled by the conductive metal, using inhibitors that are specifically absorbed on the flat surface of the substrate (surface inhibitors). These organic additives, which are used in the prior art in large quantities and are required to ensure quality filling, cause contamination of the cobalt or copper deposits. However, the electroplating method used with the electrolyte of the invention follows a conformal and cavity filling method that does not require the use of these additives.

Thus, the electrolyte and method of the invention make it possible to considerably limit the contamination of cobalt or copper deposits by limiting the concentration of organic molecules, the presence of buffer substances in high concentrations and the formation of cobalt hydroxide or copper hydroxide during electroplating.

Additionally, the electrolyte and method of the present invention provide a means of obtaining cobalt or copper interconnects having extremely low impurity levels, preferably less than 1000 ppm atomic, while being formed at a high deposition rate.

Finally, the electrolyte and the method of the invention make it possible to form a thin layer containing manganese or zinc by annealing an alloy of cobalt and manganese, an alloy of cobalt and zinc, an alloy of copper and manganese or an alloy of copper and zinc, which alloy is deposited by electroplating in a single step.

In a particular embodiment, a cobalt-manganese or copper-manganese alloy is deposited on the surface of a seed layer made of a metallic material, this layer covering an insulating material. The alloy is then subjected to a heat treatment, allowing separation of cobalt and manganese or copper and manganese and producing a layer containing cobalt or copper on the one hand and a manganese layer on the other hand. During the annealing of the alloy, the manganese atoms distributed in the alloy migrate to the interface between the metallic layer and the insulating material to form a thin manganese layer inserted between the metallic layer and the insulating material. The result is a stack of insulating substrates covered with a thin manganese layer, a thin metallic layer and a deposit of cobalt or copper. Annealing enhances the manufacturing profitability and reliability of electronic devices containing cobalt or copper interconnects.

Finally, in the case of cobalt, the method of the invention allows reducing the thickness of a cobalt diffusion barrier material layer such as tantalum nitride between a silicon dioxide-based insulating substrate and the cobalt or even not depositing the same. The same result is obtained in the case of copper.

Definition “Electrolyte” means a liquid containing a precursor to metal coating used in an electroplating process.

"Continuous filling" refers to a cobalt or copper block that does not contain voids. In the prior art, holes or voids in the material can be observed in the cobalt or copper deposit between the wall of the pattern and the metal deposit ("sidewall voids"). There are also observable voids that are located at equal distances from the wall of the pattern in the form of holes or lines ("slots"). These voids can be observed and quantified by transmission or scanning electron microscopy by making cross-sections of the deposit. The continuous deposit of the present invention preferably has an average void percentage of less than 10 volume %, preferably less than or equal to 5 volume %. The measurement of the percentage of voids within the structure to be filled can be achieved by electron microscopy at a magnification between 50 000 and 350 000 or by TEM.

The "average diameter" or "average width" of a cavity refers to the dimension measured at the opening of the cavity to be filled. The cavity is, for example, in the form of a wedge-shaped channel or a cylinder.

"Conformal filling" refers to a filling pattern in which the deposit of the alloy of cobalt and manganese, the alloy of cobalt and zinc, the alloy of copper and manganese, or the alloy of copper and zinc grows at the same rate at the bottom and on the walls of the hollow pattern. This filling pattern is contrasted with bottom-to-top filling ("bottom-up" filling), in which the alloy deposition rate is higher at the bottom of the cavity.

The present invention relates to an electrolyte for electroplating an alloy of a first metal and a second metal, wherein the first metal is selected from cobalt, copper and mixtures thereof, the second metal is selected from manganese, zinc and mixtures thereof, the alloy comprises a metal selected from manganese and zinc, and the electrolyte is an aqueous solution comprising: - cobalt II or copper II ions in a mass concentration of 1 g/L to 5 g/L, - chlorine ions in a mass concentration of 1 g/L to 10 g/L, - metal ions selected from manganese II ions and zinc II ions, said metal ions being present in such a mass concentration that the ratio between the mass concentration of cobalt II ions or copper II ions and the mass concentration of metal ions is from 1/10 to 10/1, - an organic or inorganic acid, present in an amount sufficient to obtain a pH between 1.8 and 4.0, and - only one or at most two organic additives, which are not polymers, one of which may be an acid; when this acid is an organic acid, the concentration of the additive or the sum of the concentrations of the two additives is between 5 mg/L and 200 mg/L.

The organic additives are preferably sulfur-free additives, wherein at least one or even two of the organic additives are preferably α-hydroxycarboxylic acids. The electrolyte preferably comprises a single organic additive.

The one or more organic additives preferably have a molecular weight of less than 250 g/mol, more preferably less than 200 g/mol and greater than 50 g/mol, more preferably greater than 100 g/mol.

The concentration of the additive or the sum of the concentrations of the two additives is preferably between 5 mg/L and 200 mg/L. In this embodiment, the additives may each be a sulfur-free α-hydroxycarboxylic acid.

At least one of the organic additives may be selected from citric acid, tartaric acid, malic acid, mandelic acid, maleic acid, fumaric acid, glyceric acid, orotic acid, malonic acid, L-alanine, acetylsalicylic acid and salicylic acid.

The mass concentration of cobalt II or copper II ions may be 1 g/L to 5 g/L, such as 2 g/L to 3 g/L. The mass concentration of chloride ions may be 1 g/L to 10 g/L.

The relatively high concentration of cobalt or copper ions at a highly acidic pH has several advantages over prior art electrolytic baths having an alkaline or slightly acidic pH and lower cobalt or copper ion concentrations.

The reason is that the inventors have found that it is not necessary to operate at a pH greater than 4 in order to limit the corrosion of the cobalt or copper in the deposit. By increasing the concentration of cobalt or copper ions and by lowering the pH value, it seems possible to stabilize the metallic cobalt or copper by substantially increasing the concentration of ions present in the aqueous solution. The inventors have thus observed deposition rates greater than those of the prior art, and also larger sizes of the cobalt or copper grains in the deposit after the annealing step, typically greater than 20 nm.

The metal ions are selected from manganese II ions and zinc II ions, and their mass concentration is such that the ratio between the mass concentration of cobalt ions or copper ions and the mass concentration of metal ions is 1/10 to 25/1 or 1/10 to 10/1.

Chloride ions may be provided by dissolving i) cobalt chloride or cupric chloride or one of their hydrates (such as cobalt chloride hexahydrate) and ii) manganese chloride or zinc chloride in water.

The composition is preferably not obtained by dissolving salts including sulfates, which results in undesirable sulfur contamination of the cobalt or copper deposits.

The one or more organic additives are preferably free of sulfur and are preferably selected from α-hydroxycarboxylic acids, such as compounds citric acid, tartaric acid, glycolic acid, lactic acid, malic acid, mandelic acid, maleic acid, oxalic acid and 2-hydroxybutyric acid.

The electrolyte may contain organic additives other than α-hydroxycarboxylic acids, such as glycine or ethylenediamine. The electrolyte may be of any type, provided that it does not produce a bottom-up filling effect. The electrolyte of the present invention is preferably free of surface inhibitor polymers, such as polyethylene glycol, polypropylene glycol, polyvinyl pyrrolidone or polyethyleneimine.

The cobalt II or copper II ions and the metal ions (manganese II or zinc II) are advantageously in free form, meaning that they are not complexed with one or more organic additives, more particularly when the pH is less than 3, either in the absence of polarization or during polarization of the conductive surface.

The absence of substantial amounts of cobalt or copper complexes or other metal complexes with organic molecules presents numerous advantages: it makes it possible to reduce the organic contamination of the metal deposits, since the concentration of organic molecules in the bath can be very low; it also makes it possible to avoid any uncontrolled changes in pH, which tend to destabilize the solution, during the period of time during which the cobalt or copper is deposited in the structure. Furthermore, the cobalt or copper ions are not stabilized by the complex and can be reduced more easily, and therefore the deposition rate of cobalt or copper is greater. Finally, the very high concentration of cobalt or copper ions protects the conductive surfaces of the cavity from corrosion. This effect is determined when the substrate is covered with a layer with very low thickness (seed layer) which acts as a conductive surface during electroplating.

The electrolyte of the invention advantageously comprises one of the following characteristics, taken alone or in combination: - it does not comprise an accelerator of the growth of cobalt or copper at the bottom of the pattern, - the electrolyte does not contain organic inhibitor molecules capable of slowing down the growth of cobalt or copper on the flat part of the substrate at the opening of the cavity by adsorption specifically on cobalt or on copper, said cobalt or said copper being deposited at this site during electroplating, - it does not comprise a combination of additives that produces a bottom-up filling mechanism, in particular a combination of inhibitor and accelerator, or a combination of inhibitor, accelerator and leveler, - it does not comprise a polymer, where a polymer means a molecule having at least four repeating units, - it does not comprise a sulphur-containing compound.

Surface inhibitors include the following compounds: carboxymethyl cellulose, nonylphenol polyglycol ether, polyethylene glycol dimethyl ether, octanol bis(polyalkylene glycol ether), octanol polyalkylene glycol ether, polyglycol esters of oleic acid, polyethylene glycol-propylene glycol, polyethylene glycol, polyethyleneimine, polyethylene glycol dimethyl ether, polyoxypropylene glycol, polypropylene glycol, polyvinyl alcohol, polyglycol esters of stearic acid, polyglycol ethers of octadecyl alcohol, butanol-ethylene oxide-propylene oxide copolymer, 2-butyl-5-benzimidazole sulfonic acid, 2-butylbenzimidazole.

The accelerator is usually a compound containing a sulfur atom, such as 3-sulfopropyl ester of N,N-dimethyldisulfidecarbamate; 3-sulfopropyl ester of 3-butylenesulfonic acid, 3-sulfo-1-propanesulfonate; ester of s-ethyl dithiocarbonate with the potassium salt of 3-butyl-1-propanesulfonic acid, bissulfopropyl disulfide; 3-(benzothiazolyl-s-thio)propylsulfonic acid, pyridinium propylsulfonic acid betaine, sodium salt of 1-sodium 3-butylpropane-1-sulfonate; 3-sulfoethyl ester of N,N-dimethyldisulfidecarbamate; 3-sulfoethyl ester of 3-butylenesulfonic acid; sodium salt of 3-butylenesulfonic acid, pyridinium ethylsulfonic acid betaine or thiourea.

In a first embodiment, the pH of the electrolyte is preferably between 1.8 and 4.0. In a particular embodiment, the pH is between 2.0 and 3.5 or between 2.0 and 2.4.

The pH of the composition can be adjusted as appropriate with bases or acids known to those skilled in the art. The acid can be organic or inorganic. Strong inorganic acids such as hydrochloric acid are preferably contemplated.

Although there is in principle no restriction on the nature of the solvent (the limitation is that the solvent fully dissolves the active species of the solution and does not interfere with the electroplating), the solvent will preferably be water. According to one embodiment, the solvent mainly comprises water (by volume).

According to one variant, the electrolyte of the invention has a pH between 1.8 and 4.0, for example between 2.0 and 4.0, and comprises in aqueous solution ions of cobalt II or copper II, metal ions of manganese II or zinc II, chlorine ions and between 5 mg/L and 200 mg/L of one or more compounds having a pKa of from 1.8 to 3.5, preferably from 2.0 to 3.5 and more preferably from 2.2 to 3.0.

The compound preferably has a molecular weight of less than 250 g/mol, preferably less than 200 g/mol and greater than 50 g/mol, preferably greater than 100 g/mol.

In some cases, the compound having a pKa value of 1.8 to 3.5 may be the same as at least one of the organic additives used in the first embodiment. More specifically, the compound may be selected from citric acid, tartaric acid, malic acid, maleic acid and mandelic acid.

The compound can also be selected from the compounds fumaric acid (pKa = 3.03), glyceric acid (pKa = 3.52), orotic acid (pKa = 2.83), malonic acid (pKa = 2.85), L-alanine (pKa = 2.34), phosphoric acid (pKa = 2.15), acetylsalicylic acid (pKa = 3.5) and salicylic acid (pKa = 2.98).

Prior art methods of cobalt filling employ alkaline electrolytes, e.g., pH greater than 4, when applying very low current density and inhibitor compounds specific for cobalt, and thus the pH inside the trench is maintained greater than 4 throughout the filling step, thereby causing the formation of significant amounts of cobalt hydroxide in the resulting cobalt deposit, wherein the cobalt hydroxide reduces the conductivity of the cobalt interconnect and degrades the performance level of the integrated circuit.

The electrolyte of the invention and the method of the invention specifically aim to solve this problem by significantly limiting the formation of cobalt hydroxide so that it is present only in trace amounts in the deposited cobalt. The solution to this problem involves using an electrolyte with a pH between 1.8 and 4.0, for example between 2.0 and 4.0, to which an additive is added, which preferably exhibits at least one or even all of the following characteristics: - Local buffering capacity in grooves on its surface, which allows to maintain the pH of the electrolyte at a pH greater than 1.8 during the entire substrate polarization time. 8 or 2.0 and less than 3.5 and preferably less than 2.5, - low molecular weight, so that the additive can diffuse into structures with low average diameter at the openings or with low average width, and - very low concentration in the electrolyte, so that the amount of additive present in the electrolyte before the start of polarization is almost completely diffused into the cavities of the structure and the additive has local buffering capacity.

An electrolyte comprising an additive of this type can selectively limit the increase in pH, for example, to values less than 4.0, preferably less than 3.0 and more preferably selectively to values between 2.0 and 2.5, only in the cavities of the structure and not at the flat surface of the substrate. The additive can thus advantageously fulfil the function of a buffer by exerting its effect locally, i.e. only in the cavities. Organic additives or compounds with a pKa of 1.8 to 3.5 or 2.0 to 3.5 can act as a local buffer, the effect of which is observed only in the cavities.

According to a first embodiment, the first metal is cobalt and the second metal is manganese. According to a second embodiment, the first metal is cobalt and the second metal is zinc. According to a third embodiment, the first metal is copper and the second metal is manganese. According to a fourth embodiment, the first metal is copper and the second metal is zinc.

For example, the electrolyte is an aqueous solution comprising: - cobalt II ions in a mass concentration of 1 g/L to 5 g/L, - chlorine ions in a mass concentration of 1 g/L to 5 g/L, - zinc II ions in a mass concentration such that the ratio between the mass concentration of cobalt II ions and the mass concentration of zinc II ions is 15/1 to 20/1, - an inorganic acid in an amount sufficient to obtain a pH between 2.0 and 2.4, and - only one organic additive, the concentration of which is between 10 mg/L and 20 mg/L.

In this example, the organic additive may be tartaric acid.

The invention also relates to an electrochemical method for filling cavities having an average width or average diameter at the opening of between 15 nm and 100 nm and a diameter of between 50 nm and 250 nm. nm, the method comprising: - a step of contacting the conductive surface of the cavities with an electrolyte as described above, - a step of polarizing the conductive surface for a period of time sufficient to carry out conformal and complete filling of the cavities by depositing an alloy of a first metal and a second metal, the first metal being chosen from cobalt, copper and mixtures thereof, the second metal being chosen from manganese, zinc and mixtures thereof, and - a step of annealing the deposit of the alloy obtained at the end of the polarization step, the annealing being carried out at a temperature allowing the metals to migrate to form a first layer and a second layer, the first layer mainly containing metal, the layer having a thickness of between 0.5 nm and 2 nm, the second layer essentially containing cobalt or copper.

The annealing step can also improve the crystallinity of the cobalt or copper and suppress any material voids in the deposit.

In a specific embodiment, the conductive surface is a first surface of a metal seed layer having a thickness of 1 to 10 nanometers, the seed layer having a second surface in contact with a dielectric material comprising silicon dioxide. The metal seed layer may include a metal selected from the group consisting of cobalt, copper, tungsten, titanium, tantalum, ruthenium, nickel, titanium nitride, and tantalum nitride.

In a specific embodiment, the seed layer is a cobalt seed layer. The method of the invention can be implemented by one of the electrolytes described above, which electrolytes contain one or two non-polymeric organic additives or contain between 5 mg/L and 200 mg/L of one or more compounds with a pKa of 1.8 to 3.5, preferably 2.0 to 3.5 and more preferably 2.2 to 3.0.

During the entire time of the filling step of the method of the invention, the pH inside the cavity is advantageously kept less than 3.5 or even less than 3.0, depending on the type of electrolyte used.

The cavity can be designed in the case of metallization or dual metallization. The cavity can be obtained in particular by performing the following steps: - a step of etching the structure into a silicon substrate, - a step of forming a silicon oxide layer on the silicon surface of the structure to obtain a silicon oxide surface, - a step of depositing a metal layer on the silicon oxide layer to obtain a cavity conductive surface.

The metal layer is preferably a metal seed layer with a thickness between 1 nm and 10 nm. The metal layer is preferably deposited on a silicon oxide layer, which is in contact with silicon. The metal may include at least one compound selected from the group consisting of: cobalt, copper, tungsten, titanium, tantalum, ruthenium, nickel, titanium nitride and tantalum nitride. The metal layer preferably includes a cobalt layer. In a first embodiment, the metal layer is composed of a cobalt layer. In a second embodiment, the metal layer includes a cobalt layer and a material layer having cobalt diffusion barrier properties. The metal layer can be deposited by any suitable method known to those skilled in the art.

The method of the present invention is a "conformal" method, as opposed to the "bottom-up" or "super-conformal" methods of the prior art. In the conformal filling method of the present invention, the cobalt alloy or copper alloy deposit grows at the same rate at the bottom and on the walls of the hollow pattern to be filled. This filling pattern is compared to other methods of the prior art, in which the deposition rate of the cobalt alloy is higher at the bottom of the cavity than on the walls of the cavity.

The manganese or zinc content of the alloy deposited at the end of the electroplating step is preferably between 0.5 and 10 atom %, for example between 1.0 and 5.0 atom % or between 1.5 and 2.5 atom %.

The polarization intensity used in the electrochemical step is preferably 2 mA/cm ² to 50 mA/cm ² , whereas the polarization intensity in the prior art method using an alkaline electrolyte is typically 0.2 mA/cm ² to 1 mA/cm ² .

The electrochemical step of the method of the present invention may include only one or several polarization steps, wherein a person skilled in the art will know how to select the variables based on his general knowledge.

The electrical step may be performed using at least one polarization mode selected from the group consisting of: a ramp mode, a galvano-static mode, and a galvano-pulsed mode.

The electroplating step may thus comprise at least one step of electroplating in pulsed current mode and at least one step of electroplating in constant current mode, the electroplating step in constant current mode preferably following the electroplating step in pulsed current mode.

For example, the electrical step comprises a first step of polarizing the cathode in a pulsed current mode so that the current is preferably alternating from ³ mA/cm2 to 20 mA/ ^cm2 , such as from 12 mA/ ^cm2 to 16 mA/ ^cm2 for a time ( _Ton ) preferably between 5 ms and 50 ms and zero polarization for a time ( _Toff ) preferably between 50 ms and 150 ms.

In this first step, the substrate can be brought into contact with the electrolyte either before polarization or after polarization. The contact with the cavity is preferably performed before applying the voltage in order to limit corrosion of the metal layer in contact with the electrolyte.

In a second step, the cathode can be polarized in constant current mode, wherein the current ranges from 3 mA/cm ² to 50 mA/cm ^2. Both steps preferably have substantially the same duration.

The second step in the constant current mode may itself comprise two steps: a first step in which the intensity of the current is 3 mA/cm ² to 8 mA/cm ² , and a second step in which the current is applied with an intensity of 9 mA/cm ² to 50 mA/cm ² .

This electrochemical step can be used especially when the pH of the electrolyte is between 2.5 and 3.5.

In another example, the electrochemical step comprises a first step of polarizing the cathode in a ramp mode, wherein the current is preferably 0 mA/cm ² to 15 mA/cm ² , preferably 0 mA/cm ² to 10 mA/cm ² , followed by a step in a constant current mode, wherein a current of 10 mA/cm ² to 50 mA/cm ² , preferably 8 mA/cm ² to 20 mA/cm ² is applied. This electrochemical step can be used especially when the pH of the electrolyte is between 2.0 and 2.5.

The electroplating step is usually stopped when the alloy deposit covers the flat surface of the substrate: in this case, the deposit includes material inside the cavity and material covering the surface of the substrate in which the cavity has been hollowed out. The thickness of the alloy layer covering the surface can be between 50 nm and 400 nm, and can be, for example, between 125 nm and 200 nm.

The deposition rate of the cobalt alloy or the copper alloy is between 0.1 nm/s and 3.0 nm/s, preferably between 1.0 nm/s and 3.0 nm/s, and more preferably between 1 nm/s and 2.5 nm/s.

The method of the present invention comprises a step of annealing the alloy deposit obtained at the end of the filling as described above.

This annealing heat treatment can be carried out at a temperature between 50°C and 550°C, preferably in a reducing gas such as 4% _H2 in _N2 .

The combination of low impurity content and a very low percentage of voids provides a path to obtaining cobalt or copper deposits with relatively low resistivity.

During the annealing step, the manganese or zinc atoms present in the alloy migrate towards the surface of the conductive substrate, thus causing the formation of two layers: a first layer, which essentially comprises cobalt or copper; and a second layer, which essentially comprises manganese or zinc. A layer "essentially" comprising cobalt may be a layer comprising up to 100% cobalt and a minimum amount of cobalt selected from the group consisting of: 95%, 96%, 97%, 98%, 99%, 99.5%, 99.8% and 99.9%. A layer "essentially" comprising copper may be a layer comprising up to 100% copper and a minimum amount of copper selected from the group consisting of: 95%, 96%, 97%, 98%, 99%, 99.5%, 99.8% and 99.9%. A layer "substantially" comprising manganese may be a layer comprising up to 100% manganese and a minimum amount of manganese selected from the group consisting of: 95%, 96%, 97%, 98%, 99%, 99.5%, 99.8% and 99.9%. A layer "substantially" comprising zinc may be a layer comprising up to 100% zinc and a minimum amount of zinc selected from the group consisting of: 95%, 96%, 97%, 98%, 99%, 99.5%, 99.8% and 99.9%. These percentages are atomic % and may be measured by any method known to those skilled in the art.

In one embodiment, the conductive surface is the surface of a cobalt seed layer that covers an insulating substrate comprising silicon dioxide. In this embodiment, manganese or zinc atoms migrate through the cobalt seed layer during the annealing step to reach the interface between the first seed layer and the insulating substrate comprising silicon dioxide.

The total impurity content of the cobalt or copper deposit obtained by the electroplating and annealing method of the present invention is less than 1000 ppm atomic, without considering manganese or zinc as impurities. The impurities mainly include oxygen, followed by carbon and nitrogen. The total carbon and nitrogen content is less than 300 ppm. The cobalt or copper deposit is advantageously continuous. The cobalt or copper deposit preferably has an average void percentage of less than 10 volume % or surface area, preferably less than or equal to 5 volume % or surface area. The void percentage of the cobalt or copper deposits can be measured by observation using electron microscopy, which is known to those skilled in the art, who will choose the method that seems most appropriate to them. One of these methods can be scanning electron microscopy (SEM) or transmission electron microscopy (TEM) using a magnification between 50,000 and 350,000. The void volume can be evaluated by measuring the void surface area observed on one or more cross-sections of the substrate containing the filled cavities. When two or more surface areas are measured on two or more cross-sections, the average of these surface areas will be calculated in order to evaluate the void volume.

The layer substantially comprising manganese or zinc is preferably a continuous layer with an average thickness of 0.5 nm to 2 nm. "Continuous" means that the layer covers the entire surface of the dielectric substrate without the latter penetrating. The thickness of the layer preferably varies by +/- 10% relative to the average thickness.

The method may comprise a basic step of treatment by means of a reducing plasma in order to reduce the native metal oxide present at the surface of the substrate. The plasma also acts on the surface of the trenches, thereby being able to improve the quality of the interface between the conductive surface and the alloy. The subsequent electroplating step is preferably carried out immediately after the plasma treatment in order to minimize the reformation of the native oxide.

The method of the invention finds application in particular in the manufacture of semiconductor devices, during the production of conductive metal interconnects such as trenches extending along a surface or vias connecting different integration levels.

Finally, the invention relates to a semiconductor device provided with a metal interconnect comprising a layer of dielectric material covered by and in contact with a layer substantially comprising manganese or zinc, the layer being covered by a layer of cobalt or copper.

The metal seed layer may be inserted between the layer substantially comprising manganese or zinc and the cobalt or copper layer and may be in contact with each of these two layers.

The interconnects consist essentially of cobalt or copper and can be obtained by the method described above. In this case, they correspond to cobalt or copper deposits filling the cavities. The interconnects can have an average width between 15 nm and 100 nm and an average depth between 50 nm and 250 nm.

The layer substantially comprising manganese or zinc advantageously has a thickness between 0.5 nm and 2 nm and is in contact with a dielectric material such as silicon dioxide.

The present specification also relates to a method for forming a metal interconnect structure, which includes an adhesion layer material and a metal filler material, the adhesion layer material is manganese or zinc, and the metal filler material is cobalt or copper, wherein the adhesion layer is formed by at most two steps: a first step of electrodelessly depositing an alloy including the metal filler material and the adhesion layer material, and a second step of thermally annealing the alloy deposit to separate the adhesion layer material from the metal filler material to form two separated regions (adhesion layer and metal filler layer). The method comprises: forming an opening in a dielectric layer in a substrate, wherein the opening exposes a conductive surface; filling the opening with an alloy electrodeless comprising a first metal and a second metal, wherein the first metal is cobalt or copper and the second metal is manganese or zinc; and thermally annealing the alloy. According to this embodiment, the method does not comprise the step of forming an adhesion layer comprising manganese before filling the opening with the alloy electrodeless.

The features described above in relation to the electrolyte and method may be applied to the semiconductor device of the present invention where appropriate.

Example 1 : Electroplating of a Cobalt and Zinc Alloy from a pH 2.2 Solution on a Substrate Containing a Cobalt Seed Layer An alloy of cobalt and zinc is electroplated onto a flat substrate comprising a cobalt seed layer. The deposition is carried out with the aid of a composition containing a chloride-containing salt of cobalt (II) ions and a chloride-containing salt of zinc (II) ions in the presence of tartaric acid (pH 2.2).

A.- Materials and Equipment : Substrate : The substrate used in this example consisted of a 4×4 cm silicon coupon. The silicon was capped with silicon oxide in contact with a 3 nm thick tantalum layer, which itself was capped with a 3 nm thick cobalt layer and deposited by CVD. The measured resistivity of the substrate was about 168 ohms/square.

Plating solution : The Co ²⁺ concentration in this solution is 2.35 g/L, obtained from CoCl ₂ (H ₂ O) ₆ . The Zn ²⁺ concentration is 0.136 g/L, obtained from ZnCl ₂ . Tartaric acid is present at 15 mg/L. The pH of the solution is adjusted to pH=2.2 by adding hydrochloric acid.

Equipment : In this example, the electrolytic deposition equipment used consists of two parts: a cell for containing the plating solution, equipped with a fluid recirculation system in order to control the fluid dynamics of the system; and a rotating electrode, equipped with a sample holder adapted to the size of the sample used (4 cm × 4 cm). The electrolytic deposition cell consists of two electrodes: - a cobalt anode - a silicon sample coated with the layers described above, which constitutes the cathode, reference connected to the anode.

The connectors enable electrical contact to the electrodes which are connected by wires to a voltage regulator supplying up to 20 V or 2 A.

B.- Experimental plan : Basic steps : Due to the age of the wafer or the fact that it has been stored poorly, substrates usually only require special treatment when the native cobalt oxide layer is too large. This storage usually takes place under nitrogen. In this case, it is necessary to generate a plasma containing hydrogen, which is either pure hydrogen or a mixture containing 4% hydrogen in nitrogen.

Electrical method : The method is performed as follows: In continuous current mode at 50 mA (or 11 mA/cm² ) to 120 mA (or 26 mA/cm² ) (For example, 100 mA (or 22.1 mA/cm² ) to polarize the cathode. This step was performed for 1 hour with rotation at 60 rpm. The electrolyte was in contact with the substrate for 5 seconds before applying the voltage. The alloy was deposited at a rate of 3.3 nm/s. In another embodiment, the cathode was polarized at 80 mA (or 17.6 mA/cm² ) to 160 mA (or 35.2 mA/cm² ) (For example, 130 mA (or 28.6 mA/cm² )) with a pulse duration of 5 ms to 1000 ms in cathode polarization and 5 ms to 1000 ms in zero polarization between two cathode pulses.

annealing :Annealing was performed at 400°C for 30 minutes in a hydrogen atmosphere (4% hydrogen in nitrogen) to allow zinc to migrate to SiO₂ The interface between and cobalt.

C.- Results obtained : Profile analysis by scanning electron microscopy shows an alloy thickness close to 200 nm. This thickness decreases slightly to 190 nm after annealing. XPS analysis before annealing shows the presence of about 2 atomic % of zinc in the alloy. On the one hand, after annealing, this same form of analysis shows a migration of zinc both towards the SiO ₂ -cobalt interface and towards the outermost surface. On the other hand, the total contamination of oxygen, carbon and nitrogen does not exceed 600 ppm atomic.

Claims (11)

An electrolyte for electroplating an alloy of a first metal and a second metal, characterized in that the first metal is cobalt and the second metal is manganese, the first metal is copper and the second metal is manganese, or the first metal is copper and the second metal is zinc, characterized in that the electrolyte is an aqueous solution, the aqueous solution comprising: cobalt II ions or copper II ions, which are present in a mass concentration of 1g/L to 5g/L, chlorine ions, which are present in a mass concentration of 1g/L to 10g/L, metal ions, which are selected from manganese II ions and zinc II ions, Metal ions are present in a mass concentration such that the ratio between the mass concentration of cobalt II ions or copper II ions and the mass concentration of metal ions is 1/10 to 25/1, an organic acid or a strong inorganic acid in an amount sufficient to maintain a pH between 1.8 and 4.0, and no more than two organic additives which are not polymers, wherein at least one of the no more than two organic additives is present in the aqueous solution as the organic acid, and wherein the concentration of the no more than two organic additives is between 5 mg/L and 200 mg/L. The electrolyte of claim 1, wherein the strong inorganic acid is hydrochloric acid, wherein the no more than two organic additives include only one organic additive, and wherein the only one organic additive is selected from organic compounds having a pKa between 1.8 and 3.5. The electrolyte of claim 1, wherein the organic acid is an α-hydroxycarboxylic acid, and the α-hydroxycarboxylic acid is selected from the group consisting of: citric acid, tartaric acid, glycolic acid, lactic acid, apple acid, mandelic acid, oxalic acid and 2-hydroxybutyric acid. The electrolyte of claim 1, wherein the pH thereof is between 2.0 and 3.5. The electrolyte of claim 1, wherein the first metal is cobalt and the second metal is manganese. The electrolyte of claim 1, wherein the first metal is copper and the second metal is manganese. The electrolyte of claim 1, wherein the first metal is copper and the second metal is zinc. For example, the electrolyte in claim 1, wherein the organic acid is tartaric acid. An electrochemical method for filling cavities having an average width or average diameter at the opening between 15 nm and 100 nm and a depth between 50 nm and 250 nm, the method comprising: a step of contacting the conductive surfaces of the cavities with an electrolyte as claimed in any one of claims 1 to 8, a step of polarizing the conductive surfaces for a period of time sufficient to perform conformal and complete filling of the cavities by depositing an alloy of a first metal and a second metal, the first metal being selected from cobalt, copper, or a mixture thereof, the second metal being selected from manganese, zinc or a mixture thereof, and a step of annealing the deposit of the alloy obtained at the end of the polarization step, the annealing being carried out at a temperature allowing the second metal to migrate to form a first layer and a second layer, the first layer mainly containing the second metal and in contact with the conductive surface, the first layer having a thickness between 0.5 nm and 2 nm, the second layer essentially containing cobalt or copper and covering the surface of the first layer, the second layer not in contact with the conductive surface. The method of claim 9, wherein the conductive surface is a first surface of a metal seed layer, the metal seed layer is composed of a third metal different from the second metal, the metal seed layer has a thickness of 1 nm to 10 nm, and the metal seed layer has a second surface in contact with a dielectric material comprising silicon dioxide. The method of claim 10, wherein the third metal is selected from the group consisting of: cobalt, copper, tungsten, titanium, tantalum, ruthenium, nickel, titanium nitride, tantalum nitride, and mixtures thereof.