KR102562159B1 - Electrodeposition of cobalt or copper alloys and their use in microelectronics - Google Patents

Abstract

The present invention relates to a process for manufacturing cobalt or copper interconnects, and to an electrolyte enabling implementation of the process. An electrolyte having a pH less than 4.0 contains cobalt or copper ions, chloride ions, manganese or zinc ions and up to two low molecular weight organic additives. One of these additives may be an alpha-hydroxy carboxylic acid.

Description

Electrodeposition of cobalt or copper alloys and their use in microelectronics

The present invention relates to electrolytes and their use for the electrodeposition of an alloy of a first metal selected from cobalt, copper and mixtures thereof and a second metal selected from manganese, zinc and mixtures thereof onto a conductive surface. The invention likewise relates to a fabrication process that uses this electrolyte and can be used to create electrical cobalt or copper interconnects in integrated circuits. The present invention finally relates to a device comprising a first metal layer in contact with a second metal layer.

Existing processes for filling interconnects with cobalt use cobalt salts and numerous organic additives, including suppressors and accelerators with complementary functions, to achieve what is called bottom-up filling. Use an electrolyte containing In order to obtain a cobalt mass of good quality, especially free from material voids, it is usually necessary to combine these additives. The inhibitor controls the deposition of cobalt on the openings of the cavities and on the flat surface of the substrate surrounding the cavities by adsorbing on the cobalt surface or complexing with the cobalt ions. Thus, the compound may be a high molecular weight molecule such as a polymer that cannot diffuse into the cavity or an agent that complexes cobalt ions. The accelerator partially diffuses to the bottom of the cavity and its presence is more necessary in very deep cavities. It increases the rate of deposition of cobalt at the bottom of the cavity and also at the walls. Filling methods via a bottom-up mechanism contrast with filling methods called "conformal" or "continuous" where cobalt deposits grow at the same rate at the bottom and at the walls of a hollow pattern.

These electrodeposition baths and their use have a number of drawbacks that ultimately limit the good operation of manufactured electronic devices and make them too expensive to manufacture. The reason for this is that it creates cobalt interconnects that are contaminated with organic additives needed to limit cobalt fill hole formation. Moreover, these chemicals obtain filling speeds that are too slow and incompatible with industrial scale production.

Patent application US 2015/0179579 describes the use of manganese to improve the adhesion of cobalt in interconnects, more specifically on mixed cobalt/dielectric substrates, for the purpose of fabricating the lattice of a MOSFET transistor. However, in the described process manganese and cobalt are deposited during two successive and independent material deposition steps: a chemical deposition of manganese in the vapor phase followed by an electrodeposition of cobalt.

Accordingly, there is still a need to provide an electrolysis bath that leads to cobalt deposits that are characterized by improved performance, i.e., with an extremely reduced impurity content, and the rate of formation is high enough to be used for manufacturing electronic devices. It may advantageously and/or allow a thickness reduction or even prevent the deposition of a layer of cobalt diffusion barrier material, such as tantalum nitride, between cobalt and an insulating substrate based on, for example, silicon dioxide.

The inventors have found that a solution containing cobalt II ions and metal ions selected from manganese II ions and zinc II ions and having a pH of 1.8 to 4.0 can achieve this purpose.

The possibility of depositing cobalt alloys at a pH less than 4 using alpha-hydroxy carboxylic acids in an equidistant electrodeposition process, in particular, has never been suggested, making the results of the present invention all the more surprising. Moreover, the possibility of forming a thin layer based on manganese or zinc without involving a chemical or physical deposition step prior to depositing cobalt has not yet been suggested.

The inventors have found that the same results can be achieved by using copper II ions instead of cobalt II ions, which allows the production of copper deposits characterized by improved performance, i.e., extremely reduced impurity content, and , the rate of formation is sufficiently high, which is advantageous for manufacturing electronic devices and/or allows a reduction in the thickness of a layer of cobalt diffusion barrier material, such as tantalum nitride, between copper and an insulating substrate, for example based on silicon dioxide, or even deposition can be prevented.

Accordingly, the present invention relates to an electrolyte for electrodeposition of an alloy of a first metal selected from cobalt, copper and mixtures thereof and a second metal selected from manganese, zinc and mixtures thereof, wherein the electrolyte is an aqueous solution comprising Features:

- cobalt II ions or copper II ions in a mass concentration of 1 g/L to 5 g/L,

- chloride ion in a mass concentration of 1 g/L to 10 g/L,

- a metal ion selected from manganese II ion and zinc II ion, said metal ion in a mass concentration such that the ratio between the mass concentration of cobalt II ion or copper II ion and the mass concentration of metal ion is from 1/10 to 25/1. present, the metal ion,

- an organic or inorganic acid in an amount sufficient to obtain a pH for the electrolyte between 1.8 and 4.0, and

- only one or at most two organic additives that are not polymers, said organic additive, one of said two organic additives or said two organic additives, if present in the composition, may be an organic acid, the concentration of said organic additive or said two organic additives The sum of the concentrations of 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 is 1/10, 1/5, 1/3, 1/2, 1/1, 2/1, 3/1, 5 may be higher than a value selected from the group consisting of /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 is 1/5, 1/3, 1/2, 1/1, 2/1, 3/1, 5/1, 10 may be lower than a value selected from the group consisting of /1, 15/1, 20/1 and 25/1.

The present invention likewise relates to a method for filling a cavity with cobalt or copper, comprising the first step of iso-dispersively depositing an alloy using said electrolyte and the second step of annealing the alloy to provide a cobalt or copper deposit. include

The electrolyte and method of the present invention provides access to continuous deposits of high purity cobalt or copper within manufacturing times compatible with industrial applications.

The advantage of cobalt or copper deposits is that they are inherently very pure for three reasons.

One of the objectives pursued in the prior art is to slow down metal deposition upon entry into the cavities by using inhibitors (surface inhibitors) that specifically adsorb onto the flat surface of the substrate without penetrating the cavities that the conductive metal is supposed to fill. These organic additives, which are used in large quantities in the prior art and are necessary to ensure good filling, cause contamination of cobalt or copper deposits. However, the electrodeposition process used by the electrolyte of the present invention follows a cavity filling method that is iso-dispersible and does not require the use of such additives.

Thus, the electrolyte and process of the present invention enable significant limitations on contamination of cobalt or copper deposits by limiting the concentration of organic molecules, the presence of high concentrations of buffer substances, and the formation of cobalt or copper hydroxide during electrodeposition. let it

Furthermore, the electrolyte and process of the present invention provides access to cobalt or copper interconnects with very low impurity rates, preferably less than 1000 ppm atoms, while forming at greater deposition rates.

The electrolyte and process of the present invention make it possible to form thin layers comprising 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, and finally , this alloy is deposited in a single step by electrodeposition.

In one particular embodiment, a cobalt-manganese or copper-manganese alloy is deposited on the surface of a seed layer made of a metallic material, which layer covers the insulating material. The alloy is then subjected to a heat treatment to separate cobalt and manganese or copper and manganese and produce a layer containing cobalt or copper on the one hand and a manganese layer on the other hand. During annealing of the alloy, manganese atoms distributed in the alloy migrate to the interface between the metal layer and the insulating material to form a thin manganese layer interposed between the metal layer and the insulating material. The result is a stack of insulating substrates covered with a thin layer of manganese, a thin metal layer and deposits of cobalt or copper. Annealing improves manufacturing profitability and reliability of electronic devices containing cobalt or copper interconnects.

Finally, the method of the present invention allows, in the case of cobalt, a thickness reduction or even non-deposition of a layer of cobalt diffusion barrier material, such as tantalum nitride, between the insulating substrate based on cobalt and silicon dioxide. The same result is obtained in the case of copper.

Justice

"Electrolyte" means a liquid containing a precursor to a metal coating used in an electrodeposition process.

"Continuous filling" means a cobalt mass or a copper mass without voids. In the prior art, holes or voids in the material may be observed in the cobalt or copper deposits between the walls of the pattern and the metal deposits ("sidewall voids"). There are also observable voids located equidistant from the walls of the pattern in the form of holes or lines ("seams"). These voids can be observed and quantified by transmission or scanning electron microscopy by making cross-sections of the deposit. The continuous deposits of the present invention preferably have an average void percentage of less than 10% by volume, preferably less than 5% by volume. Measurement of the percent voids in the structure to be filled can be performed with an electron microscope 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 tapered channel or cylinder.

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

The present invention relates to an electrolyte for electrodeposition of an alloy of a first metal selected from cobalt, copper, and mixtures thereof, and a second metal selected from manganese, zinc, and mixtures thereof, wherein the alloy comprises a metal selected from manganese and zinc. And, the electrolyte is characterized in that it is an aqueous solution containing:

- cobalt II or copper II ions in a mass concentration of 1 g/L to 5 g/L,

- chloride ion in a mass concentration of 1 g/L to 10 g/L,

- a metal ion selected from manganese II ion and zinc II ion, said metal ion in a mass concentration such that the ratio between the mass concentration of cobalt II ion or copper II ion and the mass concentration of metal ion is between 1/10 and 10/1. present, the metal ion,

- an organic or inorganic acid in an amount sufficient to obtain a pH of 1.8 to 4.0, and

- only one or at most two organic additives that are not polymers, one of the two additives being 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 am.

The organic additives are preferably not sulfur-containing additives, and one or both of them are preferably alpha-hydroxy carboxylic acids. The electrolyte preferably contains a single organic additive.

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

The concentration of additives or the sum of the concentrations of two additives is preferably 5 mg/L to 200 mg/L. In this embodiment, the additives may each be a sulfur-free alpha-hydroxy carboxylic acid.

At least one of the organic additives is 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, for example 2 g/L to 3 g/L. The mass concentration of chloride ion may be 1 g/L to 10 g/L.

A relatively high concentration of cobalt or copper ions at a highly acidic pH has a number of advantages over prior art electrolyzers having basic or slightly acidic pHs and lower cobalt or copper ion concentrations.

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

The metal ion is selected from manganese II ion and zinc II ion. 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 can be provided by dissolving i) cobalt chloride or copper chloride, or one of their hydrates, such as cobalt chloride hexahydrate, and ii) manganese chloride or zinc chloride in water.

It is preferred that the composition not be obtained by dissolving salts comprising sulfates which cause sulfur contamination of cobalt or copper deposits, an undesirable phenomenon.

The organic additive or additives are preferably sulfur-free and are preferably selected from alpha-hydroxy carboxylic acids such as the compounds citric acid, tartaric acid, glycolic acid, lactic acid, malic acid, mandelic acid, maleic acid, oxalic acid and 2 hydroxy acids. hydroxybutyric acid.

The electrolyte may contain organic additives other than alpha-hydroxy carboxylic acids such as glycine or ethylenediamine. It can be of any kind as long as it doesn't cause a bottom-up filling effect. Indeed, the electrolyte of the present invention is preferably free of surface suppressor polymers such as polyethylene glycol, polypropylene glycol, polyvinylpyrrolidone or polyethyleneimine.

The cobalt II or copper II ions and the metal ions (manganese II or zinc II) are advantageously in free form, since they are organic additives or additives in the absence of polarization or during polarization of the conductive surface, especially when the pH is less than 3. It means that it does not get along with the field.

There are numerous advantages to not having significant amounts of cobalt or copper complexes or other metal complexes with organic molecules: it can reduce organic contamination of metal deposits, since the concentration of organic molecules in the bath can be very low. Because; Similarly, uncontrolled changes in pH that could destabilize the solution during the period during which cobalt or copper is deposited on the structure are avoided. Also, cobalt or copper ions are not stabilized by complexes and can be more easily reduced, so the deposition rate of cobalt or copper is faster. Finally, very high concentrations of cobalt or copper ions protect the conductive surfaces of the cavity from corrosion. This effect determines when the substrate is covered with a very low thickness layer (seed layer) that serves as a conductive surface during electrodeposition.

The electrolyte of the present invention advantageously comprises one of the following features, alone or in combination:

- does not contain cobalt or copper growth promoters at the bottom of the pattern;

- the electrolyte does not contain organic inhibitor molecules which can slow down the growth of cobalt or copper on the flat parts of the substrate at the openings of the cavities by adsorbing specifically to the cobalt or copper deposited in these areas during electrodeposition,

- It does not contain a combination of additives that results in a bottom-up filling mechanism, in particular a combination of an inhibitor and an accelerator, or a combination of an inhibitor, an accelerator and a leveler.

- does not contain a polymer - a polymer means a molecule having at least 4 repeating units,

- Does not contain sulfur-containing compounds.

Surface inhibitors include the following compounds: carboxymethylcellulose, nonylphenol polyglycol ethers, polyethylene glycol dimethyl ether, octanediolbis (polyalkylene glycol ethers), octanol polyalkylene glycol ethers, polyglycol esters of oleic acid, polyethylene Glycols - Propylene glycol, polyethylene glycol, polyethyleneimine, polyethylene glycol dimethyl ether, polyoxypropylene glycol, polypropylene glycol, polyvinyl alcohol, polyglycol esters of stearic acid, polyglycol ethers of stearyl alcohol, butyl alcohol - ethylene oxide - Propylene oxide copolymer, 2-mercapto-5-benzimidazolesulfonic acid, 2-mercaptobenzimidazole.

The accelerator is usually a compound containing a sulfur atom, e.g., 3-sulfopropyl ester of N,N-dimethyldithiocarbamic acid, 3-sulfopropyl ester of 3-mercaptopropylsulfonic acid, 3-sulfanyl-1 -Propane sulfonate, potassium salt of 3-mercapto-1-propanesulfonic acid and ester of dithiocarbonic acid o-ethyl ester s-ester, bissulfopropyl disulfide, 3-(benzothiazolyl-s-thio)propylsulfonic acid Sodium salt of pyridinium propylsulfobetaine, 1-sodium 3-mercaptopropane-1-sulfonate, 3-sulfoethyl ester of N,N-dimethyldithiocarbamic acid, 3-mercapto-ethylpropylsulfonic acid 3-sulfoethyl ester, sodium salt of 3-mercaptoethylsulfonic acid, pyridinium ethylsulfobetaine or thiourea.

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

The pH of the composition can optionally be adjusted with bases or acids known to those skilled in the art. Acids can be organic or inorganic. Preference is given to using strong mineral acids such as hydrochloric acid.

The nature of the solvent is in principle not limited (as long as it sufficiently dissolves the active species in the solution and does not interfere with electrodeposition), but is preferably water. According to one embodiment, the solvent comprises primarily water by volume.

According to one variant, the electrolyte of the present invention has a pH of 1.8 to 4.0, for example 2.0 to 4.0, in an aqueous solution containing cobalt II or copper II ions, manganese II or zinc II metal ions, chloride ions, and 1.8 to 4.0 pH. 5 to 200 mg/L of one or more compounds with a pKa of 3.5, preferably 2.0 to 3.5, more preferably 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 certain 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, it may be selected from citric acid, tartaric acid, malic acid, maleic acid and mandelic acid.

In addition, 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 processes for cobalt filling, for example, use an alkaline electrolyte with a pH above 4 while applying very low current densities and inhibitor compounds that are unique to cobalt so that the pH inside the trench is maintained above 4 throughout the filling step so that Causes substantial formation of cobalt hydroxide in the resulting cobalt deposit, which reduces the conductivity of the cobalt interconnect and reduces the performance level of the integrated circuit.

The electrolyte of the present invention and the process of the present invention aim to solve this problem, in particular by significantly limiting the formation of cobalt hydroxide so that it is only present in trace amounts in the deposited cobalt. A solution to this problem involves using an electrolyte having a pH between 1.8 and 4.0, for example between 2.0 and 4.0, wherein an additive exhibiting preferably one or more or even all of the following characteristics: is added:

- local buffering capacity in the trenches on the surface such that the pH of the electrolyte is maintained at a value above 1.8 or 2.0 and below 3.5, preferably below 2.5, throughout the time of substrate polarization;

- a low molecular weight that allows the additive to diffuse into structures with a low average diameter or low average width at the apertures, and

- a very low concentration of electrolyte such that the amount of additive present in the electrolyte before polarization begins diffuses almost completely into the cavities of the structure and the additive has a local buffering capacity.

Electrolytes comprising additives of this kind are selectively limited to increasing pH to a value less than 4.0, preferably less than 3.0, more preferably to a value between 2.0 and 2.5 - e.g. not on a flat surface of a substrate. Only in the cavities of the structure - makes it possible. Thus, the additive can advantageously perform the function of a buffer by exerting its effect locally, ie only in the cavity. Organic additives or compounds with a pKa of 1.8 to 3.5 or 2.0 to 3.5 can act as local buffers, the effect of which is observed only in the cavity.

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, an electrolyte is an aqueous solution comprising:

- cobalt II ions in a mass concentration of 1 g/L to 5 g/L,

- chloride ion 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 between 15/1 and 20/1,

- mineral acids in an amount sufficient to obtain a pH of 2.0 to 2.4, and

- Only one organic additive with a concentration between 10 mg/L and 20 mg/L.

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

The present invention likewise relates to an electrochemical process for filling cavities, said cavities having an average width or average diameter at an aperture of 15 nm to 100 nm and a depth of 50 nm to 250 nm, said process comprising:

- contacting the conductive surface of the cavity with an electrolyte according to the above description;

- a conductive surface for a period of time sufficient to effect a uniform and complete filling of the cavities by deposition of an alloy of a first metal selected from cobalt, copper and mixtures thereof and a second metal selected from manganese, zinc and mixtures thereof; polarizing, and

- annealing the deposit of the alloy obtained at the end of the polarization step, said annealing being carried out at a temperature which causes the metal to migrate to form a first layer and a second layer, said first layer containing predominantly metal , the layer has a thickness of 0.5 and 2 nm, and the second layer essentially comprises cobalt or copper.

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

In one specific embodiment, the conductive surface is a first surface of a metallic 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 metallic 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 one particular embodiment, the seed layer is a cobalt seed layer. The process of the present invention comprises one or two non-polymeric organic additives, or 5 mg/L to 200 mg/L with a Ka of 1.8 to 3.5, preferably 2.0 to 3.5, more preferably 2.2 to 3.0. It can be implemented with one of the above-mentioned electrolytes comprising one or more compounds of

Throughout the implementation of the filling step of the process of the present invention, the pH inside the cavity is advantageously maintained below 3.5, or even below 3.0, depending on the type of electrolyte used.

The cavity may be designed with respect to the implementation of a damascene or dual damascene process. The cavity can be obtained in particular by the implementation of the following steps:

- etching the structure into the silicon substrate,

- forming a silicon oxide layer on the silicon surface of the structure to provide a silicon oxide surface;

- depositing a metal layer on the silicon oxide layer to provide a conductive surface to the cavity.

The metal layer is preferably a metallic seed layer with a thickness of 1 nm to 10 nm. It is preferably deposited on a silicon oxide layer in contact with the 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 the 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 may be deposited by any suitable method known to those skilled in the art.

The process of the present invention is a "conformal" process as opposed to the "bottom up" or "super-conformal" processes of the prior art. In the isostatic filling process of the present invention, the cobalt alloy or copper alloy deposits grow at the same rate on the bottom and walls of the hollow pattern to be filled. This filling mode contrasts with other processes of the prior art where the deposition rate of the cobalt alloy is higher at the bottom of the cavity than at the walls of the cavity.

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

The intensity of polarization used in the electrical step is preferably between 2 mA/cm 2 and 50 mA/cm 2 , whereas in prior art processes where alkaline electrolytes are used, it is typically between 0.2 mA/cm 2 and 1 mA/cm 2 .

The electrical step of the process of the present invention may include only one or several polarization steps, and those skilled in the art will know how to select the parameters based on their 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. .

Thus, the electrical step may comprise at least one electrodeposition step in galvano-pulse mode and at least one electrodeposition step in galvano-static mode, the electrodeposition step in galvano-static mode preferably being galvano-static. This is followed by an electrodeposition step in no-pulse mode.

For example, the electrical step is the first step of polarization of the cathode in galvano-pulse mode, preferably a time (T _on ) of 5 to 50 ms, 3 mA/cm 2 to 20 mA/cm 2 , for example 12 mA/cm 2 to 16 mA /cm 2 of current, preferably between 50 ms and 150 ms of time (T _off ) alternating zero polarization.

In this first step, the substrate may be contacted with an electrolyte either before polarization or after polarization. Contacting the cavity is preferably performed prior to application of the voltage to limit corrosion of the metal layer coming into contact with the electrolyte.

In a second step, the cathode may be polarized in galvano-static mode with a current ranging from 3 mA/cm2 to 50 mA/cm2. The two steps are preferably of substantially the same duration.

The second stage of the galvano-static mode may itself include two stages: in the first stage, the current has an intensity of 3 mA/cm 2 to 8 mA/cm 2 and in the second stage 9 mA/cm 2 to 50 A current having an intensity of mA/cm 2 is applied.

This electrical step can be used especially when the electrolyte has a pH between 2.5 and 3.5.

In another example, the electrical step comprises a first step of polarization of the cathode in a lamp mode where the current preferably lies between 0 mA/cm 2 and 15 mA/cm 2 , preferably between 0 mA/cm 2 and 10 mA/cm 2 , and /cm 2 to 50 mA/cm 2 , preferably 8 mA/cm 2 to 20 mA/cm 2 , followed by a step in galvano-static mode. This electrical step can be used especially when the electrolyte has a pH between 2.0 and 2.5.

The electrodeposition step is usually stopped when the alloy deposit covers the flat surface of the substrate: in this case, the deposit includes the material inside the cavities and the material covering the substrate surface where the cavities are empty. The thickness of the alloy layer covering the surface may be 50 nm to 400 nm, for example 125 nm to 200 nm.

The deposition rate of the cobalt alloy or copper alloy is 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 process of the present invention includes annealing the obtained alloy deposit at the end of filling as described above.

This annealing heat treatment may be performed at a temperature of 50° C. to 550° C., preferably under a reducing gas such as 4% H ₂ in N ₂ .

The low impurity content combined with a very low percentage of voids provides access to cobalt deposits or copper deposits with low resistivities.

During the annealing step, the manganese or zinc atoms present in the alloy migrate towards the surface of the conducting substrate to form two layers: a first layer comprising essentially cobalt or copper and a second layer essentially comprising manganese or zinc. floor. A layer comprising "essentially" cobalt contains 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%. It may be a layer containing A layer comprising "essentially" copper is 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%. can A layer comprising “essentially” manganese contains 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%. can be layered. A layer containing “essentially” zinc is a layer containing 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%. can These percentages are atomic percent and can be determined by any method known to those skilled in the art.

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

The total impurity content of cobalt deposits or copper deposits obtained by the electrodeposition and annealing process of the present invention is less than 1000 ppm atomic, and manganese or zinc are not considered impurities. Impurities mainly include oxygen, followed by carbon and nitrogen. The total carbon and nitrogen content is less than 300 ppm. Cobalt or copper deposits are preferably continuous. It preferably has an average void percentage of less than 10% by volume or surface area, preferably less than or equal to 5% by volume or surface area. The percent voids of cobalt or copper deposits can be determined by electron microscopy, and it is known to those skilled in the art to select the method that seems most appropriate. One such method may be scanning electron microscopy (SEM) or transmission electron microscopy (TEM) using magnifications between 50,000 and 350,000. Void volume can be evaluated by measuring the void surface area observed on a cross-section of at least one substrate containing filled cavities. If two or more surface areas are measured in two or more cross sections, an average of these surface areas will be calculated to estimate the void volume.

The layer comprising essentially 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 dielectric substrate being visible. The thickness of the layer preferably varies by +/- 10% relative to the average thickness.

The process may include a preliminary step of treatment with a reductive plasma to reduce native metal oxides present on the surface of the substrate. Plasma can also act on the surface of the trench to improve the interface quality between the conductive surface and the alloy. The subsequent electrodeposition step is preferably performed immediately after the plasma treatment to minimize modification of the native oxide.

The process of the present invention finds application in the fabrication of semiconductor devices, especially during the fabrication of conductive metal interconnects such as vias connecting different levels of integration or trenches running along a surface.

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

A metal seed layer may be inserted between the layer comprising essentially manganese or zinc and the layer of cobalt or copper 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 process described above. In this case, they correspond to cobalt or copper deposits filling the cavities. The interconnects may have an average width between 15 nm and 100 nm and an average depth between 50 nm and 250 nm.

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

The present description also covers a method of forming a metal interconnection structure comprising an adhesive layer material and a metal filler, wherein the adhesive layer material is manganese or zinc, the metal filler is cobalt or copper, and the adhesive layer is formed in up to two steps. In the first step of the electroless deposition of an alloy comprising a metal filler and an adhesive layer material, the heat of the alloy deposit causes separation of the adhesive layer material and the metal filler to form two separate regions, the adhesive layer and the metal filler. Second step of annealing. The method comprises forming an opening in a dielectric layer of a substrate, the opening exposing a conductive surface, and electroless filling the opening with an alloy comprising a first metal that is cobalt or copper, and a second metal that is manganese or zinc. and thermal annealing of the alloy. According to this embodiment, the method does not include forming an adhesive layer comprising manganese prior to electrolessly filling the opening with the alloy.

The electrolyte and process features described above can be applied to the semiconductor device of the present invention when appropriate.

Example 1: Electrodeposition of a cobalt and zinc alloy from a solution at pH=2.2 on a substrate containing a cobalt seed layer.

An alloy of cobalt and zinc was electrodeposited on a flat substrate containing a cobalt seed layer. Deposition takes place with a composition at pH 2.2 containing a chloride containing cobalt(II) ion salt and a chloride containing zinc(II) ion salt in the presence of tartaric acid.

A. - Materials and Equipment:

Board:

The substrate used in this example consists of a 4x4 cm silicon coupon. Silicon is deposited by CVD and covered with silicon oxide in contact with a 3 nm thick layer of tantalum which itself is covered with a 3 nm thick layer of cobalt. The measured substrate resistance is about 168 ohm/square.

Electrodeposition solution:

The Co ²⁺ concentration of 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 was adjusted to pH=2.2 by adding hydrochloric acid.

equipment:

In this example, the electrolytic deposition equipment used consisted of two parts: a cell containing the electrodeposition solution, equipped with a fluid recirculation system to control the fluid dynamics of the system, and a sample appropriate to the size of the coupon used (4 cm x 4 cm). Rotating electrode with holder. The electrolytic deposition cell consisted of two electrodes:

- Cobalt Anode

A silicon coupon is coated with the layer described above constituting the cathode.

The reference is connected to the anode.

The connectors allowed electrical contact of wired electrodes to a potentiostat that supplied up to 20V or 2A.

B. - Experimental protocol:

Preliminary steps:

Substrates usually only require special handling when they have too many layers of native cobalt oxide, due to aging or poorly stored wafers. This storage usually takes place under nitrogen. In this case, it is necessary to create a plasma containing hydrogen, such as pure hydrogen or a gas mixture containing 4% hydrogen in nitrogen.

Electrical process:

The process was carried out as follows: the cathode was polarized in continuous galvanic mode in the current range of 50 mA (or 11 mA/cm 2 ) to 120 mA (or 26 mA/cm 2 ), for example 100 mA (or 22.1 mA/cm 2 ). This step was performed at 60 rpm rotation for 1 hour. The electrolyte is brought into contact with the substrate for a period of 5 seconds before voltage is applied. The deposition rate of the alloy is 3.3 nm/s. In another embodiment, the cathode can deliver between 80 mA (or 17.6 mA/cm 2 ) and 160 mA (or 35.2 mA) with a pulse duration between 5 and 1000 ms at cathodic polarization and between 5 and 1000 ms at zero polarization between the two cathode pulses. /cm 2 ), for example, 130 mA (or 28.6 mA/cm 2 ) was polarized in galvano pulse mode.

Annealing:

Annealing is performed for 30 minutes in a hydrogen containing atmosphere (4% hydrogen in nitrogen) at a temperature of 400° C. to allow zinc to migrate to the interface between SiO ₂ 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 that there is about 2 atomic percent zinc present in the alloy. The same type of analysis after annealing shows migration of zinc towards the SiO ₂ -cobalt interface on the one hand and the outermost surface. On the other hand, total contamination by oxygen, carbon and nitrogen does not exceed 600 ppm atomically.

Claims (13)

An electrolyte for electrodeposition of an alloy of a first metal and a second metal, wherein the electrolyte is wherein the first metal is cobalt and the second metal is manganese or the first metal is copper and the second metal is manganese or wherein the first metal is copper and the second metal is zinc, the electrolyte is an aqueous solution, the aqueous solution comprising:
- cobalt II ions or copper II ions in a mass concentration of 1 g/L to 5 g/L,
- chloride ion in a mass concentration of 1 g/L to 10 g/L,
- a metal ion selected from manganese II ion and zinc II ion, said metal ion present in a mass concentration such that the ratio between the mass concentration of cobalt II ion or copper II ion and the mass concentration of metal ion is from 1/10 to 25/1 To, the metal ion,
- an organic or inorganic acid in an amount sufficient to obtain a pH for said electrolyte between 1.8 and 4.0, and
- at most two organic additives that are not polymers, wherein at least one of the at most two organic additives is present as the organic acid in the aqueous solution, and the concentration of the two organic additives is from 5 mg/L to 200 mg/L Saiin, the organic additive; characterized in that it comprises, the electrolyte. 2. Electrolyte according to claim 1, characterized in that the acid is a strong inorganic acid and the electrolyte contains a single organic additive selected from organic compounds having a pKa between 1.8 and 3.5. 3. The method of claim 2, wherein at least one of the at most two organic additives is 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. Characterized in that selected from the group consisting of, electrolyte. The electrolyte according to claim 1, characterized in that the pH is 2.0 to 3.5. The electrolyte according to claim 1, wherein the first metal is cobalt and the second metal is manganese. delete The electrolyte according to claim 1, wherein the first metal is copper and the second metal is manganese. The electrolyte according to claim 1, characterized in that the first metal is copper and the second metal is zinc. delete 4. The electrolyte according to claim 3, characterized in that the organic additive is tartaric acid. An electrochemical process for filling a cavity, wherein the cavity has an average width or average diameter at the aperture of 15 nm to 100 nm and a depth of 50 nm to 250 nm, the process comprising:
- contacting the conductive surface of the cavity with an electrolyte, wherein the electrolyte is an aqueous solution, the aqueous solution comprising:
a) cobalt II ions or copper II ions at a mass concentration of 1 g/L to 5 g/L,
b) chloride ions at a mass concentration of 1 g/L to 10 g/L;
c) a metal ion selected from manganese II ion and zinc II ion, the metal ion being at a mass concentration such that the ratio between the mass concentration of cobalt II ion or copper II ion and the mass concentration of metal ion is from 1/10 to 25/1. present, the metal ion,
d) an organic or inorganic acid in an amount sufficient to obtain a pH for the electrolyte between 1.8 and 4.0, and
e) at most two organic additives that are not polymers, wherein at least one of the at most two organic additives is present as the organic acid in the aqueous solution, and the concentration of the two organic additives is from 5 mg/L to 200 mg/L between L, the organic additive;
- a period of time sufficient to effect a conformal and complete filling of the cavity by deposition of an alloy of a first metal selected from cobalt, copper and mixtures thereof and a second metal selected from manganese, zinc and mixtures thereof; polarizing the conductive surface during
- annealing the deposit of the alloy obtained at the end of the polarization step, the annealing being at a temperature at which the second metal migrates to form a first layer and a second layer. wherein the first layer contains a second metal and is in contact with the conductive surface, the first layer has a thickness of 0.5 nm to 2 nm, and the second layer contains cobalt or copper and annealing, wherein the annealing covers a surface of the first layer and the second layer is not in contact with the conductive surface. 12. The method of claim 11, wherein the conductive surface is a first surface of a metallic seed layer, the metallic seed layer comprised of a third metal different from the second metal, the metallic seed layer having a thickness of 1 nanometer to 1 nanometer. Having a thickness of 10 nanometers, characterized in that the metallic seed layer has a second surface in contact with a dielectric material comprising silicon dioxide. 13. The process of claim 12, 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.