WO2022243462A1 - Electrolyte and method for copper and graphene electrodeposition - Google Patents

Electrolyte and method for copper and graphene electrodeposition Download PDF

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Publication number
WO2022243462A1
WO2022243462A1 PCT/EP2022/063623 EP2022063623W WO2022243462A1 WO 2022243462 A1 WO2022243462 A1 WO 2022243462A1 EP 2022063623 W EP2022063623 W EP 2022063623W WO 2022243462 A1 WO2022243462 A1 WO 2022243462A1
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Prior art keywords
copper
graphene
electrolyte
comprised
graphene oxide
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PCT/EP2022/063623
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French (fr)
Inventor
Vincent Mevellec
Céline Pascale DOUSSOT
Louis CAILLARD
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Aveni
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/38—Electroplating: Baths therefor from solutions of copper
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D7/00—Electroplating characterised by the article coated
    • C25D7/12—Semiconductors

Definitions

  • the present invention concerns an electrolyte and its use in a method for electrodepositing copper onto the surface of a conductor or semiconductor substrate. This method is part of a scheme of steps aimed at creating a conductive network of interconnections for the manufacture of semiconductor devices.
  • An 3D integrated circuit (3D IC) is fabricated by stacking silicon wafers comprising active components, connected by vertical conductive interconnections called "through-silicon vias” (TSV) or “through wafer vias” or “through wafer interconnects” which make it possible to connect the devices by a copper conductive network.
  • TSV through-silicon vias
  • through wafer vias through wafer interconnects
  • the thickness of the silicon wafers must be increased to limit the deformations created by the devices, which requires increasing the height/width ratio of the TSVs.
  • the design of the 3D integrated circuits must take into account the constraints created by the TSVs on the resonator. Indeed, the denser the 3D integrated circuit is, the more the optical performances of the device risk being impaired.
  • Some authors have defined a so-called keep out zone (KOZ) as a function of the TSV diameter and the distance between the TSV and the waveguide. The smaller the distance between the waveguide and the TSV, the smaller the diameter of the TSV needs to be so that the resonance wavelength remains stable. The need to respect the keep out zones therefore imposes a maximum TSV value in the device.
  • the present invention precisely meets the needs presented above by proposing an electrolyte for filling TSVs in a 3D integration method, the electrolyte having a pH greater than or equal to 7.0 and containing copper ions and graphene.
  • graphene into the electrolyte advantageously makes it possible to reduce the thermal expansion of the copper deposited and, consequently, to increase the density of TSVs in the 3D integrated circuit.
  • the addition of graphene also allows improving the electrical performances of the devices by reducing the temperature increase points in the copper.
  • graphene oxide is easily dispersed in alkaline medium, which allows a more homogeneous dispersion of graphene without the use of a stabilizer and leads to a more homogeneous distribution of graphene in the electrodeposited copper.
  • the present invention relates to an electrolyte for electrodeposition of copper on a semiconductor substrate, the electrolyte comprising copper ions, a solvent, an amine that complexes the copper ions and graphene, the electrolyte having a pH ranging from 7.0 to 11.0.
  • the present invention also concerns a manufacturing method for a 3D semiconductor device comprising at least one step of fabricating through-silicon vias (TSV), said step comprising an electrodeposition method implementing the electrolyte described above.
  • TSV through-silicon vias
  • Electrodeposition here means a method that makes it possible to cover a substrate surface by a metallic or organometallic coating, in which the substrate is electrically polarized and contacted with a liquid containing precursors of said metallic or organometallic coating, so as to form said coating.
  • the electrodeposition is, for example, performed by passing a current between the substrate to be coated constituting an electrode (the cathode in the case of a metallic or organometallic coating) and a second electrode (the anode) in an electrolyte containing a source of coating material precursors (for example metal ions in the case of a metallic coating) and optionally various agents intended to improve the properties of the coating formed (regularity and thinness of the deposit, resistivity), optionally in the presence of a reference electrode.
  • a source of coating material precursors for example metal ions in the case of a metallic coating
  • agents intended to improve the properties of the coating formed optionally in the presence of a reference electrode.
  • Electrode also called “electrodeposition bath”, “electrolytic solution” or “electrodeposition composition” means, in the present description, a solution or suspension containing precursors of said metallic or organometallic coating which is used in an electrodeposition method such as defined previously.
  • the electrolyte, the electrodeposition method implementing this electrolyte and the method for manufacturing a semiconductor device of the invention can advantageously be used to deposit the copper in contact with a material endowed with a copper-diffusion barrier property, or in contact with a thin conductive layer of copper (seed layer).
  • the surface contacted with the electrolyte to deposit the copper is advantageously that of cavities whose opening width is greater than or equal to 0.5 micron.
  • the invention therefore concerns an electrolyte for electrodepositing copper onto a semiconductor substrate, the electrolyte having a pH ranging from 7.0 to 11.0, comprising copper ions at a concentration ranging from 0.1 mM to 2000 mM, at least one amine present at a concentration comprised between 0.5 mM and 5000 mM, from 0.1 g/L to 10 g/L of graphene or graphene oxide and a solvent.
  • the pH of the electrolyte ranges from 7.0 to 11.0.
  • the pH of the electrolyte of the invention is, for example, comprised between 7.5 and 8.5 and more preferentially of the order of 8.0, the expression "of the order of" taking measurement uncertainties into account.
  • the pH of the electrolyte of the invention is, for example, comprised between 7.0 and 7.5 and more preferentially of the order of 7.2.
  • the pH of the electrolyte of the invention is, for example, comprised between 9.5 and 10.5 and more preferentially of the order of 10.0.
  • the pH can optionally be adjusted by means of one or more pH modifying compounds (so-called buffer compounds) such as those described in the "Handbook of Chemistry and Physics - 84th Edition" by David R. Lide published by CRC Press.
  • the electrolyte can contain a buffer compound, for example, such as ammonium sulfate, which limits pH fluctuations during an electrodeposition process.
  • the electrodeposition composition according to the invention comprises copper ions, in particular cupric ions Cu 2+ .
  • the electrolyte is prepared from a copper salt such as, in particular, copper sulphate, copper chloride, copper nitrate, copper acetate, preferably copper sulphate and more preferably copper sulphate pentahydrate.
  • a copper salt such as, in particular, copper sulphate, copper chloride, copper nitrate, copper acetate, preferably copper sulphate and more preferably copper sulphate pentahydrate.
  • the copper ions are present in the electrolyte of the invention at a concentration ranging from 0.1 mM to 2000 mM.
  • the copper ions are at a concentration comprised between 10 mM and 150 mM, for example comprised between 10 mM and 20 mM.
  • copper ions are present at a concentration comprised between 45 mM and 1500 mM, preferably between 50 mM and 150 mM.
  • the electrolyte also contains copper ions, graphene and/or graphene oxide.
  • the graphene or graphene oxide are preferably in the form of a sheet (so called mono-sheet graphene or graphene oxide) or a stack of several sheets (so called multi-sheet graphene or graphene oxide).
  • the number of sheets in multi sheets can vary from 2 to 100, preferably from 10 to 15.
  • the sheets preferably have a length comprised between 200 nm and 1 pm, for example between 300 nm and 600 nm. They preferably have a thickness of 10 nm to 15 nm.
  • the graphene or graphene oxide are multi-sheets comprising 10 to 15 sheets and having a length comprised between 300 nm and 600 nm.
  • the graphene or graphene oxide which is used to prepare the electrolyte of the invention can be in the mono-sheet or multi-sheet form previously dispersed in aqueous solution or in organic solution.
  • the graphene or graphene oxide which is used to prepare the electrolyte of the invention can alternatively be in powder.
  • the degree of oxidation of the terminal functions can vary from 5% to 30%, preferably from 10% to 15%.
  • the graphene or graphene oxide which is mixed with other electrolyte compounds can be in the form of a dispersion in solvent, a solution or a powder.
  • the skilled person will know how to prepare a dispersion on the basis of their general knowledge, or find this dispersion commercially.
  • the concentration of graphene or graphene oxide in the electrolyte can be comprised between 0.1 g/L and 1 g/L.
  • the electrolyte comprises molecules of at least one amine which can advantageously complex with copper ions.
  • the amine may also be called “complexing agent” or “copper-ion complexing agent” in the present description.
  • the amine can be chosen from aliphatic polyamines having 2 to 4 amino - NH 2 groups. These aliphatic polyamines include ethylenediamine, diethylenetriamine, triethylenetetramine and dipropylene triamine.
  • the amine concentration can vary from 0.5 mM to 5000 mM, for example from 5 mM to 50 mM, or from 100 mM to 500 mM.
  • the molar ratio between the copper ions and the amine can be comprised between 0.1 and 5, preferably between 0.1 and 1, for example between 0.2 and 0.6.
  • the amine is ethylenediamine
  • the concentration of the copper ions is comprised between 10 mM and 120 mM
  • the molar ratio between the copper ions and the ethylenediamine is comprised between 0.4 and 0.6
  • the pH is comprised between 7.0 and 7.5.
  • the amine is ethylenediamine
  • the concentration of the copper ions is comprised between 45 mM and 1500 mM
  • the molar ratio between the copper ions and the ethylenediamine is comprised between 0.2 and 0.4
  • the pH is comprised between 9.5 and 10.5.
  • the solvent preferably be water.
  • the electrolyte solvent predominantly comprises water by volume.
  • the electrolyte according to the invention can optionally contain one or more other compounds chosen from suppressors, accelerators, levelers and/or brighteners known in the prior art.
  • the electrolyte can contain thiodiglycolic acid in a concentration comprised between 1 mg/L and 500 mg/L, preferably comprised between 1 mg/L and 100 mg/L.
  • the electrolyte of the invention can be used in a copper electrodeposition method comprising the steps of:
  • the invention also relates to a method for manufacturing through vias (TSVs) in a semiconductor device by implementing an electrodeposition step on a surface having a flat part and an assembly of at least one cavity of opening width greater than 0.5 micron, the method being characterized in that it comprises the steps of:
  • a step can be performed of annealing the copper deposit containing the graphene oxide at a temperature ranging from 200°C to 400°C, in order to reduce the graphene oxide and obtain a copper deposit containing the graphene.
  • the copper deposit containing the graphene or graphene oxide can be a seed layer or can completely fill the volume of the cavity.
  • 3D circuits are produced by thinning a silicon wafer either before fabricating the through vias or after fabricating the through vias.
  • the method of the invention can therefore be implemented with cavities that have been previously made in a silicon wafer without piercing through it, or with cavities that have been previously made through a silicon wafer.
  • the method for fabricating through vias comprises the following succession of steps: a step of etching cavities in a silicon wafer, a step of depositing a dielectric layer (generally consisting of silicon oxide or nitride) on the surface of the cavities, a step of depositing a barrier layer or liner serving to prevent the migration of copper into the dielectric layer, an optional step of depositing a thin layer of metallic copper on the dielectric layer, called a seed layer, a step of filling the cavities by electrodeposition of graphene-doped copper using the electrolyte described above, then a step of mechanical-chemical polishing of the graphene-doped copper that has been deposited in excess (overburden), outside the cavities on the flat surface of the substrate.
  • a step of etching cavities in a silicon wafer a step of depositing a dielectric layer (generally consisting of silicon oxide or nitride) on the surface of the cavities, a step of depositing a barrier layer or liner serving to prevent the migration of
  • the method for fabricating through vias comprises the following succession of steps: a step of etching cavities in a silicon wafer, a step of depositing a dielectric layer on the surface of the cavities, a step of depositing a barrier layer or liner serving to prevent the migration of copper into the dielectric layer, a step of depositing a thin layer of graphene-doped copper on the dielectric layer by electrodeposition, by using the electrolyte described previously, a step of filling cavities with copper according to a method known to the skilled person, and then a step of mechanical-chemical polishing of the graphene-doped copper that has been deposited in excess outside the cavities on the flat surface of the substrate.
  • the electrodeposition of the method of the invention can lead to complete filling of the cavity or, alternatively, to the formation of a seed layer of copper on the surface of the cavities.
  • the method of the invention makes it possible to deposit a seed layer of graphene-doped copper which has a thickness that can be of the order of 50 nm to 5 pm, preferably 100 nm to 3 pm, for example of the order of 300 nm.
  • the electrolyte and the method of the invention can be used to create through-silicon vias (TSV) from cavities whose opening width generally exceeds half a micron.
  • TSV through-silicon vias
  • the cavities have a cylindrical or frustoconical form. Their opening width (or diameter) is greater than or equal to 0.5 micron.
  • the cavities have an opening diameter, for example, ranging from 500 nm to 200 microns, for example ranging from 1 to 75 microns, or from 1 to 10 microns.
  • the depth of the cavitis varies according to the position and function of the through via in the silicon wafer. It can thus vary from 1 micron to 500 microns, typically from 10 microns to 250 microns or from 10 microns to 50 microns.
  • the opening diameter of the cavities ranges from 1 micron to 10 microns while their depth ranges from 10 microns to 50 microns.
  • the copper and the graphene or, alternatively, the copper and the graphene oxide are co-deposited during the same electrodeposition step on a surface which can be that of a copper diffusion barrier layer, that of a copper seed layer, or that of a copper diffusion barrier layer at least partially covered with a copper seed layer.
  • the surface which is polarized in the context of the implementation of the method of the invention can therefore be the surface of a copper seed layer or a barrier layer which have been produced by a method known to the skilled person such as, for example physical vapour deposition (PVD) or chemical vapour deposition (CVD), a method in accordance with the teaching of document WO 2012/15013, or a method in accordance with the teaching of document WO 2007/034116.
  • PVD physical vapour deposition
  • CVD chemical vapour deposition
  • the surface that is polarized is that of a barrier layer.
  • the method in accordance with the invention can be implemented to fill a cavity whose surface is that of a material forming a copper diffusion barrier which is not covered with copper.
  • the barrier layer comprises at least one of the materials chosen from cobalt (Co), ruthenium (Ru), tantalum (Ta), titanium (Ti), tantalum nitride (TaN), titanium nitride (TiN), tungsten (W), tungsten titanate (TiW) and tungsten nitride or carbide (WCN).
  • a copper diffusion barrier layer can be, for example, made up of several underlayers and comprise several different materials.
  • Such a layer comprises, for example, a tantalum/tantalum nitride/tantalum stack of the order of 100 nm thick or a tantalum/tantalum nitride stack of the order of 30 nm thick.
  • the surface can be polarized, either in galvanostatic mode (imposed fixed current), or in potentiostatic mode (imposed and fixed potential, possibly relative to a reference electrode), or even in pulsed mode (current or voltage).
  • the electrolytes according to the invention can be implemented by following a method comprising an initial "hot entry” step, or an initial “cold entry” step, during which the surface to be coated is contacted with the electrodeposition bath without electrical polarization and maintained in this state for the desired duration.
  • the method in accordance with the invention can comprise, prior to surface polarization, a cold entry step during which the surface is contacted with the electrodeposition composition according to the invention without electrical polarization and maintained in this state for a duration of at least 1 second, even at least 3 seconds, before polarizing the surface.
  • the electrolytes according to the invention will preferably be implemented in an electrodeposition method comprising: - a so called cold entry step during which the surface to be coated is contacted with the electrolyte without electrical polarization and preferably maintained for the desired duration;
  • the duration of the polarization step can be comprised between 10 seconds and 10 minutes, depending on the quantity of graphene-doped copper that one wishes to deposit and depending on the current density chosen.
  • the method according to the invention can be implemented at a temperature comprised between 20°C and 30°C, i.e., at ambient temperature. It is therefore not necessary to heat the electrodeposition bath.
  • the polarization step of the method of the invention can be performed by maintaining in rotation a silicon wafer having a surface in contact with the electrolyte.
  • the rotation speed will preferably range from 20 to 240 RPM or from 20 to 100 RPM.
  • the polarization is produced by imposing current pulses corresponding to a maximum current per unit area in a range of - 0.6 mA/cm2 to -10 mA/cm2, and a minimum current per unit area in a range of 0 mA/cm2 to -5 mA/cm2.
  • the duration of polarization with maximum current can be comprised between 0.1 and 1.5 seconds, while the duration of polarization with minimum current can be comprised between 0.1 and 1.5 seconds.
  • the number of cycles to perform during the polarization step depends on the thickness of doped copper desired.
  • the cathode is polarized in galvano-pulsed (PC) mode with successive cathode pulses for a time Ton followed by a period Toff where the system is in open circuit.
  • the amplitude of the cathode pulses is kept constant and can be chosen in a range from 5 to 80 mA or 20 to 160 mA for the system used (this corresponds to a current density of 0.6 to 10 mA/cm2 and 2.5 to 20 mA/cm2, respectively).
  • the polarization time Ton can be comprised between 2 ms and 1.6 s and the time Toff can be comprised between 10 ms and 1.6 s. The duration of this step depends, as is understood, on the desired copper thickness.
  • the surface is polarized in continuous mode by imposing a current per area unit comprised in a range from 0.2 mA/cm2 to 50 mA/cm2, preferably from 0.5 mA/cm2 to 5 mA/cm2.
  • the step of polarization and electrodeposition of the graphene-oxide doped copper can be followed by a step of annealing the deposit in an oven at a temperature comprised between 200°C and 400°C under a reducing gas so as to reduce the graphene oxide into graphene.
  • a silicon substrate in a first step, is obtained which has been etched with cylindrical or frustoconical patterns, the surface of which has been covered with a layer of silica, which has itself been coated either with a layer of a copper diffusion barrier material, or with a copper seed layer, or with a layer of copper diffusion barrier material partially covered with at least one a copper seed layer, to obtain cavities.
  • an electrolyte in accordance with the previous description is prepared.
  • the electrolyte can be prepared by first producing an aqueous solution containing the copper ions and amine, to which is the added an aqueous colloidal suspension of graphene or graphene oxide. The mixture is then stirred until the graphene or graphene oxide are well dispersed.
  • the silicon substrate comprising the cavities is mounted onto a rotating electrode, then the assembly is introduced into the electrolyte prepared beforehand, before putting the whole thing into rotation.
  • the cathode is then polarized for a sufficient duration to obtain the desired quantity of doped copper deposit.
  • the deposit can be either a seed layer of doped copper deposited on the walls of the cavities or a deposit of doped copper that fills the cavities.
  • a fourth step is performed which consists of a step of annealing the graphene-oxide doped copper deposit obtained at the end of the third step.
  • the annealing can be done at a temperature ranging from 200°C to 400°C, in order to reduce the graphene oxide into graphene and obtain a graphene-doped copper deposit.
  • the method in accordance with the invention makes it possible to produce graphene or graphene oxide-doped copper deposits, which are of excellent quality, with no defects in the material.
  • EXAMPLE 1 Preparation of a araphene-doped copper seed layer on a barrier layer based on tantalum using an electrolyte according to the invention based on a mixture of copper ions, ethylenediamine and graphene
  • the substrate used in this example is made up of a square coupon of silicon measuring 4 cm x 4 cm etched with cylindrical patterns of the "through via" type with a depth of 25 pm and a diameter of 5 pm. These patterns are covered with a layer of silica having a thickness of 400 nm, itself coated by a tantalum-based layer deposited by physical vapour deposition (PVD) which breaks down into two underlayers of tantalum nitride (15 nm) and tantalum (10 nm) and which constitutes a copper diffusion barrier.
  • PVD physical vapour deposition
  • Electrodeposition solution is an aqueous solution containing 2.1 mL/L (or 32 mM) of ethylenediamine and 4 g/L (or 16 mM) of CuS0 4 (H 2 0) 5 .
  • To this solution is added 0.2 g/L of an aqueous colloidal suspension of graphene multi-sheets (comprising 10-15 sheets) of a length comprised between 300 nm and 600 nm for a thickness of 10 nm to 15 nm.
  • the solution is then vigorously stirred for 5 min in order to allow good dispersion of the graphene.
  • a cell intended to contain the electrodeposition solution equipped with a system for recirculating the fluid in order to control the system's hydrodynamics.
  • the electrolytic deposition cell comprises two electrodes: an inert circular platinum anode (connected to the reference) and the coated structured silicon coupon of the layer that constitutes the cathode. Connectors allow the electrical contact of the electrodes that are connected by electrical wires (insulated from the solution) to a potentiostat providing up to 20 V or 2 A.
  • Preliminary steps The silicon sample is mounted on the sample holder which is then mounted on the rotating electrode. After being rotated at a speed of 60 RPM, for example, the sample is introduced into the electrolyte solution while the device is still not powered. After a short time of 3 seconds, the system is powered and the electrical protocol is started.
  • the cathode is polarized in galvano-pulsed (PC) mode with successive cathode pulses for a time Ton followed by a period Toff where the system is in open circuit.
  • the amplitude of the cathode pulses is kept constant and equal to 25 mA in this example (3.1 mA/cm2).
  • the polarization time Ton is 0.35 s
  • the time Toff is equal to 0.25 s.
  • a duration of 10 minutes gives a coating having a thickness of 200 nm.
  • the rotation is interrupted and the sample is removed from the electrolyte solution in order to be rinsed with deionized water and dried with a nitrogen flow.
  • EXAMPLE 2 Preparation of a araphene-doped copper seed layer on a barrier layer based on tantalum using an electrolyte according to the invention based on a mixture of copper ions, ethylenediamine and graphene oxide
  • Substrate The substrate used is the same as that of Example 1.
  • Electrodeposition solution is an aqueous solution containing 2.1 mL/L (or 32 mM) of ethylenediamine and 4 g/L (or 16 mM) of CuS0 4 (H 2 0) 5 .
  • a suspension of graphene oxide multi-sheets comprising 10-15 sheets of a length comprised between 300 nm and 600 nm for a thickness of 10 nm to 15 nm.
  • the oxidation rate of the terminal functions of the graphene oxide sheets is 10%.
  • the solution is then vigorously stirred for 5 min in order to allow good dispersion of the graphene oxide.
  • the electrical protocol is the same as that in Example 1.
  • Annealing Once the protocol is completed, the rotation is interrupted and the sample is removed from the electrolyte solution in order to be rinsed with deionized water and dried with a nitrogen flow. The sample is then put in an oven to perform annealing at a temperature of 300°C under reducing gas.
  • EXAMPLE 3 Filling the through vias with araphene-doped copper on a copper seed layer using a composition according to the invention based on a mixture of copper ions, ethylenediamine and graphene.
  • the substrate used in this example is made up of a square coupon of silicon measuring 4 cm x 4 cm etched with cylindrical patterns of the "through via" type with a depth of 25 pm and a diameter of 5 pm. These patterns are covered with a layer of silica having a thickness of 400 nm, itself coated with a layer based on a nickel-boron alloy 80 nm thick which has been deposited by an electroless method, (without electrodes) in accordance with the teaching of document WO 2012/15013, and which constitutes a copper diffusion barrier.
  • a copper seed layer of 200 nm is deposited on the barrier electrolytically using an alkaline copper solution, for example according to the teaching of document WO 2007/034116.
  • Electrodeposition solution is an aqueous solution containing 18 g/L (or 0.3 M) of ethylenediamine, 198 g/L (or 1.5 M) of ammonium sulfate, 10 mg/L of thiodiglycolic acid and 25 g/L (or 0.1 M) of CuS0 4 (H 2 0) 5 .
  • the pH of this solution is 10.
  • To this solution is added 0.2 g/L of an aqueous colloidal suspension of graphene multi-sheets (comprising 10-15 sheets) of a length comprised between 300 nm and 600 nm for a thickness of 10 nm to 15 nm. The solution is then vigorously stirred for 5 min in order to allow good dispersion of the graphene.
  • Preliminary steps The silicon sample is mounted on the sample holder which is then mounted on the rotating electrode. After being rotated at a speed of 160 RPM, the sample is introduced into the electrolyte solution while the device is still not powered. After a short time of 3 seconds, the system is powered and the electrical protocol is started.
  • the cathode is polarized in galvano-pulsed (PC) mode with successive cathode pulses for a time Ton followed by a period Toff where the system is in open circuit.
  • the amplitude of the cathode pulses is kept constant at 60 mA (7.5 mA/cm2).
  • the polarization time Ton is equal to 0.35 s and the time Toff is equal to 0.25 s.
  • a deposition time of 2 hours is required.
  • the vias are completely filled by the copper.
  • Sheets of graphene are co-deposited during the deposition and uniformly dope the copper layer. This doping makes it possible to modify certain physical and mechanical properties of the deposited layer.
  • EXAMPLE 4 Filling the through vias with araphene-doped copper on a copper seed layer using a composition according to the invention based on a mixture of copper, ethylenediamine and graphene oxide.
  • Substrate The substrate used is the same as that of Example 3.
  • Electrodeposition solution is an aqueous solution containing 18 g/L (or 0.3 M) of ethylenediamine, 198 g/L (or 1.5 M) of ammonium sulfate, 10 mg/L of thiodiglycolic acid and 25 g/L (or 0.1 M) of CuS0 4 (H 2 0) 5 .
  • the pH of this solution is 10.
  • To this solution is added 0.2 g/L of a suspension of graphene oxide multi-sheets (comprising 10- 15 sheets) of a length comprised between 300 nm and 600 nm for a thickness of 10 nm to 15 nm.
  • the oxidation rate of the terminal functions of the graphene oxide sheets is 10%.
  • the solution is then vigorously stirred for 5 min in order to allow good dispersion of the graphene oxide.
  • the vias are completely filled by the copper.
  • Sheets of graphene oxide are co-deposited and uniformly dope the copper layer before being reduced during the final annealing. This reduced graphene doping makes it possible to modify certain physical and mechanical properties of the deposited layer.

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Abstract

The present invention relates to an electrolyte composition for depositing graphene–doped copper onto semiconductor substrates. This electrolyte has a pH ranging from 7.0 to 11.0 and comprises copper ions at a concentration ranging from 0.1 mM to 2000 mM, at least one amine present at a concentration comprised between 0.5 mM and 5000 mM, from 0.1 g/L to 10 g/L of graphene or graphene oxide and a solvent.

Description

Description
Title of the invention: Electrolyte and method for copper and graphene electrodeposition Technical field
The present invention concerns an electrolyte and its use in a method for electrodepositing copper onto the surface of a conductor or semiconductor substrate. This method is part of a scheme of steps aimed at creating a conductive network of interconnections for the manufacture of semiconductor devices.
An 3D integrated circuit (3D IC) is fabricated by stacking silicon wafers comprising active components, connected by vertical conductive interconnections called "through-silicon vias" (TSV) or "through wafer vias" or "through wafer interconnects" which make it possible to connect the devices by a copper conductive network.
In particularly dense 3D integration schemes, the thickness of the silicon wafers must be increased to limit the deformations created by the devices, which requires increasing the height/width ratio of the TSVs.
Moreover, in the case of photonic devices integrated on an insulating platform of the Si-on-insulator (SOI) interposer type, the design of the 3D integrated circuits must take into account the constraints created by the TSVs on the resonator. Indeed, the denser the 3D integrated circuit is, the more the optical performances of the device risk being impaired. Some authors have defined a so-called keep out zone (KOZ) as a function of the TSV diameter and the distance between the TSV and the waveguide. The smaller the distance between the waveguide and the TSV, the smaller the diameter of the TSV needs to be so that the resonance wavelength remains stable. The need to respect the keep out zones therefore imposes a maximum TSV value in the device.
Consequently, there is a need to increase the number of TSVs in a 3D integrated circuit. It is particularly desirable to reduce the keep out zone in an interposer.
There is also a need to reduce the electrical failures that occur in small semiconductor devices with high current densities. Indeed, the thermal management of 3D ICs is often difficult due to lack of access to intermediate levels. However, the more the electrical current density increases in the device, the greater the number of heating points in the copper and the greater the risk of failure. Copper electrodeposition methods implementing an electrolyte containing copper ions and graphene have been proposed in the prior art. However, the dispersion of graphene in acid medium requires the addition of a polymer to stabilize the graphene sheets. This polymer remains trapped in the electrodeposited copper layer, which has the disadvantage of affecting the electrical properties of the copper deposit.
The present invention precisely meets the needs presented above by proposing an electrolyte for filling TSVs in a 3D integration method, the electrolyte having a pH greater than or equal to 7.0 and containing copper ions and graphene.
The addition of graphene into the electrolyte advantageously makes it possible to reduce the thermal expansion of the copper deposited and, consequently, to increase the density of TSVs in the 3D integrated circuit. The addition of graphene also allows improving the electrical performances of the devices by reducing the temperature increase points in the copper. Finally, graphene oxide is easily dispersed in alkaline medium, which allows a more homogeneous dispersion of graphene without the use of a stabilizer and leads to a more homogeneous distribution of graphene in the electrodeposited copper.
General description of the invention
Thus, the present invention relates to an electrolyte for electrodeposition of copper on a semiconductor substrate, the electrolyte comprising copper ions, a solvent, an amine that complexes the copper ions and graphene, the electrolyte having a pH ranging from 7.0 to 11.0.
The present invention also concerns a manufacturing method for a 3D semiconductor device comprising at least one step of fabricating through-silicon vias (TSV), said step comprising an electrodeposition method implementing the electrolyte described above.
"Electrodeposition" here means a method that makes it possible to cover a substrate surface by a metallic or organometallic coating, in which the substrate is electrically polarized and contacted with a liquid containing precursors of said metallic or organometallic coating, so as to form said coating. When the substrate is electrically conductive, the electrodeposition is, for example, performed by passing a current between the substrate to be coated constituting an electrode (the cathode in the case of a metallic or organometallic coating) and a second electrode (the anode) in an electrolyte containing a source of coating material precursors (for example metal ions in the case of a metallic coating) and optionally various agents intended to improve the properties of the coating formed (regularity and thinness of the deposit, resistivity), optionally in the presence of a reference electrode. By international convention, the current and voltage applied to the substrate of interest, i.e., the cathode of the electrochemical circuit, are negative. Throughout this text, when these currents and voltages are mentioned with a positive value, it is implicit that this value represents the absolute value of said current or said voltage.
"Electrolyte", also called "electrodeposition bath", "electrolytic solution" or "electrodeposition composition" means, in the present description, a solution or suspension containing precursors of said metallic or organometallic coating which is used in an electrodeposition method such as defined previously.
The electrolyte, the electrodeposition method implementing this electrolyte and the method for manufacturing a semiconductor device of the invention can advantageously be used to deposit the copper in contact with a material endowed with a copper-diffusion barrier property, or in contact with a thin conductive layer of copper (seed layer). The surface contacted with the electrolyte to deposit the copper is advantageously that of cavities whose opening width is greater than or equal to 0.5 micron.
Description of embodiments
The invention therefore concerns an electrolyte for electrodepositing copper onto a semiconductor substrate, the electrolyte having a pH ranging from 7.0 to 11.0, comprising copper ions at a concentration ranging from 0.1 mM to 2000 mM, at least one amine present at a concentration comprised between 0.5 mM and 5000 mM, from 0.1 g/L to 10 g/L of graphene or graphene oxide and a solvent.
The pH of the electrolyte ranges from 7.0 to 11.0. In one embodiment, the pH of the electrolyte of the invention is, for example, comprised between 7.5 and 8.5 and more preferentially of the order of 8.0, the expression "of the order of" taking measurement uncertainties into account.
In another embodiment, the pH of the electrolyte of the invention is, for example, comprised between 7.0 and 7.5 and more preferentially of the order of 7.2.
In another embodiment, the pH of the electrolyte of the invention is, for example, comprised between 9.5 and 10.5 and more preferentially of the order of 10.0.
The pH can optionally be adjusted by means of one or more pH modifying compounds (so-called buffer compounds) such as those described in the "Handbook of Chemistry and Physics - 84th Edition" by David R. Lide published by CRC Press. The electrolyte can contain a buffer compound, for example, such as ammonium sulfate, which limits pH fluctuations during an electrodeposition process.
Generally, the electrodeposition composition according to the invention comprises copper ions, in particular cupric ions Cu2+.
Advantageously, the electrolyte is prepared from a copper salt such as, in particular, copper sulphate, copper chloride, copper nitrate, copper acetate, preferably copper sulphate and more preferably copper sulphate pentahydrate.
The copper ions are present in the electrolyte of the invention at a concentration ranging from 0.1 mM to 2000 mM.
In a first embodiment, for example when one wishes to deposit a graphene-doped copper seed layer on the surface of TSV precursor cavities using the electrolyte of the invention, the copper ions are at a concentration comprised between 10 mM and 150 mM, for example comprised between 10 mM and 20 mM.
In a second embodiment, for example when it is desired to create TSVs by filling cavities with graphene-doped copper by using the electrolyte of the invention, copper ions are present at a concentration comprised between 45 mM and 1500 mM, preferably between 50 mM and 150 mM.
The electrolyte also contains copper ions, graphene and/or graphene oxide.
The graphene or graphene oxide are preferably in the form of a sheet (so called mono-sheet graphene or graphene oxide) or a stack of several sheets (so called multi-sheet graphene or graphene oxide). The number of sheets in multi sheets can vary from 2 to 100, preferably from 10 to 15. The sheets preferably have a length comprised between 200 nm and 1 pm, for example between 300 nm and 600 nm. They preferably have a thickness of 10 nm to 15 nm. In a particular embodiment, the graphene or graphene oxide are multi-sheets comprising 10 to 15 sheets and having a length comprised between 300 nm and 600 nm.
The graphene or graphene oxide which is used to prepare the electrolyte of the invention can be in the mono-sheet or multi-sheet form previously dispersed in aqueous solution or in organic solution. The graphene or graphene oxide which is used to prepare the electrolyte of the invention can alternatively be in powder.
In the case of graphene oxide, the degree of oxidation of the terminal functions can vary from 5% to 30%, preferably from 10% to 15%.
In a method for preparing the electrolyte of the invention, the graphene or graphene oxide which is mixed with other electrolyte compounds can be in the form of a dispersion in solvent, a solution or a powder. The skilled person will know how to prepare a dispersion on the basis of their general knowledge, or find this dispersion commercially.
It is not necessary to pre-disperse the graphene oxide in a solvent before introducing it into a solution containing copper ions and amine to prepare the electrolyte of the invention.
The concentration of graphene or graphene oxide in the electrolyte can be comprised between 0.1 g/L and 1 g/L.
The electrolyte comprises molecules of at least one amine which can advantageously complex with copper ions. The amine may also be called "complexing agent" or "copper-ion complexing agent" in the present description.
The amine can be chosen from aliphatic polyamines having 2 to 4 amino - NH2 groups. These aliphatic polyamines include ethylenediamine, diethylenetriamine, triethylenetetramine and dipropylene triamine.
The amine concentration can vary from 0.5 mM to 5000 mM, for example from 5 mM to 50 mM, or from 100 mM to 500 mM.
The molar ratio between the copper ions and the amine can be comprised between 0.1 and 5, preferably between 0.1 and 1, for example between 0.2 and 0.6.
In one embodiment, the amine is ethylenediamine, the concentration of the copper ions is comprised between 10 mM and 120 mM, the molar ratio between the copper ions and the ethylenediamine is comprised between 0.4 and 0.6 and the pH is comprised between 7.0 and 7.5.
In another particular embodiment, the amine is ethylenediamine, the concentration of the copper ions is comprised between 45 mM and 1500 mM, the molar ratio between the copper ions and the ethylenediamine is comprised between 0.2 and 0.4 and the pH is comprised between 9.5 and 10.5.
Although there is no restriction in principle regarding the nature of the solvent (provided that it sufficiently solubilizes or disperses the active species of the electrolyte and does not interfere during the electrodeposition process), it will preferably be water. According to one embodiment, the electrolyte solvent predominantly comprises water by volume.
The electrolyte according to the invention can optionally contain one or more other compounds chosen from suppressors, accelerators, levelers and/or brighteners known in the prior art. For example, the electrolyte can contain thiodiglycolic acid in a concentration comprised between 1 mg/L and 500 mg/L, preferably comprised between 1 mg/L and 100 mg/L. The electrolyte of the invention can be used in a copper electrodeposition method comprising the steps of:
- contacting a surface of a copper diffusion barrier material or a copper surface, and
- polarizing said surface at a sufficient electrical potential and for a sufficient time to form a copper deposit containing graphene or graphene oxide.
The invention also relates to a method for manufacturing through vias (TSVs) in a semiconductor device by implementing an electrodeposition step on a surface having a flat part and an assembly of at least one cavity of opening width greater than 0.5 micron, the method being characterized in that it comprises the steps of:
- contacting said surface with an electrolyte such as described previously, and
- polarizing said surface at an electrical potential so as to form a copper deposit containing graphene or graphene oxide.
When the electrolyte contains graphene oxide, following a polarization, a step can be performed of annealing the copper deposit containing the graphene oxide at a temperature ranging from 200°C to 400°C, in order to reduce the graphene oxide and obtain a copper deposit containing the graphene.
The copper deposit containing the graphene or graphene oxide can be a seed layer or can completely fill the volume of the cavity.
In accordance with the general knowledge of the skilled person, 3D circuits are produced by thinning a silicon wafer either before fabricating the through vias or after fabricating the through vias. In a second case, the cavities etched in the silicon and then metallized form vias which have a bottom: they are called "blind vias". The method of the invention can therefore be implemented with cavities that have been previously made in a silicon wafer without piercing through it, or with cavities that have been previously made through a silicon wafer.
According to a first embodiment of the invention, the method for fabricating through vias comprises the following succession of steps: a step of etching cavities in a silicon wafer, a step of depositing a dielectric layer (generally consisting of silicon oxide or nitride) on the surface of the cavities, a step of depositing a barrier layer or liner serving to prevent the migration of copper into the dielectric layer, an optional step of depositing a thin layer of metallic copper on the dielectric layer, called a seed layer, a step of filling the cavities by electrodeposition of graphene-doped copper using the electrolyte described above, then a step of mechanical-chemical polishing of the graphene-doped copper that has been deposited in excess (overburden), outside the cavities on the flat surface of the substrate.
According to a second embodiment of the invention, the method for fabricating through vias comprises the following succession of steps: a step of etching cavities in a silicon wafer, a step of depositing a dielectric layer on the surface of the cavities, a step of depositing a barrier layer or liner serving to prevent the migration of copper into the dielectric layer, a step of depositing a thin layer of graphene-doped copper on the dielectric layer by electrodeposition, by using the electrolyte described previously, a step of filling cavities with copper according to a method known to the skilled person, and then a step of mechanical-chemical polishing of the graphene-doped copper that has been deposited in excess outside the cavities on the flat surface of the substrate.
The electrodeposition of the method of the invention can lead to complete filling of the cavity or, alternatively, to the formation of a seed layer of copper on the surface of the cavities.
The method of the invention makes it possible to deposit a seed layer of graphene-doped copper which has a thickness that can be of the order of 50 nm to 5 pm, preferably 100 nm to 3 pm, for example of the order of 300 nm.
The electrolyte and the method of the invention can be used to create through-silicon vias (TSV) from cavities whose opening width generally exceeds half a micron.
The cavities have a cylindrical or frustoconical form. Their opening width (or diameter) is greater than or equal to 0.5 micron. The cavities have an opening diameter, for example, ranging from 500 nm to 200 microns, for example ranging from 1 to 75 microns, or from 1 to 10 microns. The depth of the cavitis varies according to the position and function of the through via in the silicon wafer. It can thus vary from 1 micron to 500 microns, typically from 10 microns to 250 microns or from 10 microns to 50 microns.
According to one embodiment of the invention, the opening diameter of the cavities ranges from 1 micron to 10 microns while their depth ranges from 10 microns to 50 microns.
The copper and the graphene or, alternatively, the copper and the graphene oxide, are co-deposited during the same electrodeposition step on a surface which can be that of a copper diffusion barrier layer, that of a copper seed layer, or that of a copper diffusion barrier layer at least partially covered with a copper seed layer.
The surface which is polarized in the context of the implementation of the method of the invention can therefore be the surface of a copper seed layer or a barrier layer which have been produced by a method known to the skilled person such as, for example physical vapour deposition (PVD) or chemical vapour deposition (CVD), a method in accordance with the teaching of document WO 2012/15013, or a method in accordance with the teaching of document WO 2007/034116.
In an advantageous embodiment of the invention, the surface that is polarized is that of a barrier layer. The method in accordance with the invention can be implemented to fill a cavity whose surface is that of a material forming a copper diffusion barrier which is not covered with copper.
The barrier layer comprises at least one of the materials chosen from cobalt (Co), ruthenium (Ru), tantalum (Ta), titanium (Ti), tantalum nitride (TaN), titanium nitride (TiN), tungsten (W), tungsten titanate (TiW) and tungsten nitride or carbide (WCN).
A copper diffusion barrier layer can be, for example, made up of several underlayers and comprise several different materials. Such a layer comprises, for example, a tantalum/tantalum nitride/tantalum stack of the order of 100 nm thick or a tantalum/tantalum nitride stack of the order of 30 nm thick.
The surface can be polarized, either in galvanostatic mode (imposed fixed current), or in potentiostatic mode (imposed and fixed potential, possibly relative to a reference electrode), or even in pulsed mode (current or voltage).
The electrolytes according to the invention can be implemented by following a method comprising an initial "hot entry" step, or an initial "cold entry" step, during which the surface to be coated is contacted with the electrodeposition bath without electrical polarization and maintained in this state for the desired duration.
Thus, the method in accordance with the invention can comprise, prior to surface polarization, a cold entry step during which the surface is contacted with the electrodeposition composition according to the invention without electrical polarization and maintained in this state for a duration of at least 1 second, even at least 3 seconds, before polarizing the surface.
The electrolytes according to the invention will preferably be implemented in an electrodeposition method comprising: - a so called cold entry step during which the surface to be coated is contacted with the electrolyte without electrical polarization and preferably maintained for the desired duration;
- a step of polarizing the surface for a sufficient duration to form a deposit of graphene-doped copper on the surface;
- a so-called hot entry step during which the surface covered with the graphene-doped copper deposit is separated from the electrolyte while it is still under electrical polarization.
The duration of the polarization step can be comprised between 10 seconds and 10 minutes, depending on the quantity of graphene-doped copper that one wishes to deposit and depending on the current density chosen.
The method according to the invention can be implemented at a temperature comprised between 20°C and 30°C, i.e., at ambient temperature. It is therefore not necessary to heat the electrodeposition bath.
The polarization step of the method of the invention can be performed by maintaining in rotation a silicon wafer having a surface in contact with the electrolyte. The rotation speed will preferably range from 20 to 240 RPM or from 20 to 100 RPM.
In a particular embodiment, the polarization is produced by imposing current pulses corresponding to a maximum current per unit area in a range of - 0.6 mA/cm2 to -10 mA/cm2, and a minimum current per unit area in a range of 0 mA/cm2 to -5 mA/cm2. The duration of polarization with maximum current can be comprised between 0.1 and 1.5 seconds, while the duration of polarization with minimum current can be comprised between 0.1 and 1.5 seconds. The number of cycles to perform during the polarization step depends on the thickness of doped copper desired.
In another embodiment, the cathode is polarized in galvano-pulsed (PC) mode with successive cathode pulses for a time Ton followed by a period Toff where the system is in open circuit. The amplitude of the cathode pulses is kept constant and can be chosen in a range from 5 to 80 mA or 20 to 160 mA for the system used (this corresponds to a current density of 0.6 to 10 mA/cm2 and 2.5 to 20 mA/cm2, respectively). The polarization time Ton can be comprised between 2 ms and 1.6 s and the time Toff can be comprised between 10 ms and 1.6 s. The duration of this step depends, as is understood, on the desired copper thickness. This duration can be easily determined by the skilled person, the film growth being a function of the charge passed into the circuit. In a variant of the method of the invention, the surface is polarized in continuous mode by imposing a current per area unit comprised in a range from 0.2 mA/cm2 to 50 mA/cm2, preferably from 0.5 mA/cm2 to 5 mA/cm2.
The step of polarization and electrodeposition of the graphene-oxide doped copper can be followed by a step of annealing the deposit in an oven at a temperature comprised between 200°C and 400°C under a reducing gas so as to reduce the graphene oxide into graphene.
In one embodiment of the method of the invention, in a first step, a silicon substrate is obtained which has been etched with cylindrical or frustoconical patterns, the surface of which has been covered with a layer of silica, which has itself been coated either with a layer of a copper diffusion barrier material, or with a copper seed layer, or with a layer of copper diffusion barrier material partially covered with at least one a copper seed layer, to obtain cavities.
In a second step, an electrolyte in accordance with the previous description is prepared. The electrolyte can be prepared by first producing an aqueous solution containing the copper ions and amine, to which is the added an aqueous colloidal suspension of graphene or graphene oxide. The mixture is then stirred until the graphene or graphene oxide are well dispersed.
In a third step, the silicon substrate comprising the cavities is mounted onto a rotating electrode, then the assembly is introduced into the electrolyte prepared beforehand, before putting the whole thing into rotation. The cathode is then polarized for a sufficient duration to obtain the desired quantity of doped copper deposit. The deposit can be either a seed layer of doped copper deposited on the walls of the cavities or a deposit of doped copper that fills the cavities. Once the deposition is done, the polarization and rotation are interrupted and the assembly is removed from the electrolyte for the silicon substrate to then be rinsed and dried.
When an electrolyte is used comprising graphene oxide, preferably a fourth step is performed which consists of a step of annealing the graphene-oxide doped copper deposit obtained at the end of the third step. The annealing can be done at a temperature ranging from 200°C to 400°C, in order to reduce the graphene oxide into graphene and obtain a graphene-doped copper deposit.
The method in accordance with the invention makes it possible to produce graphene or graphene oxide-doped copper deposits, which are of excellent quality, with no defects in the material.
EXAMPLE 1: Preparation of a araphene-doped copper seed layer on a barrier layer based on tantalum using an electrolyte according to the invention based on a mixture of copper ions, ethylenediamine and graphene
A. Material and equipment
Substrate: The substrate used in this example is made up of a square coupon of silicon measuring 4 cm x 4 cm etched with cylindrical patterns of the "through via" type with a depth of 25 pm and a diameter of 5 pm. These patterns are covered with a layer of silica having a thickness of 400 nm, itself coated by a tantalum-based layer deposited by physical vapour deposition (PVD) which breaks down into two underlayers of tantalum nitride (15 nm) and tantalum (10 nm) and which constitutes a copper diffusion barrier.
Electrodeposition solution: The electrodeposition solution implemented in this example is an aqueous solution containing 2.1 mL/L (or 32 mM) of ethylenediamine and 4 g/L (or 16 mM) of CuS04(H20)5. To this solution is added 0.2 g/L of an aqueous colloidal suspension of graphene multi-sheets (comprising 10-15 sheets) of a length comprised between 300 nm and 600 nm for a thickness of 10 nm to 15 nm. The solution is then vigorously stirred for 5 min in order to allow good dispersion of the graphene.
Equipment: In this example, a piece of equipment for electrolytic deposition was used made up of two parts:
- A cell intended to contain the electrodeposition solution equipped with a system for recirculating the fluid in order to control the system's hydrodynamics.
- A rotating electrode equipped with a sample holder appropriate for the coupons used (4 cm x 4 cm).
The electrolytic deposition cell comprises two electrodes: an inert circular platinum anode (connected to the reference) and the coated structured silicon coupon of the layer that constitutes the cathode. Connectors allow the electrical contact of the electrodes that are connected by electrical wires (insulated from the solution) to a potentiostat providing up to 20 V or 2 A.
B. Experimental protocol
Preliminary steps: The silicon sample is mounted on the sample holder which is then mounted on the rotating electrode. After being rotated at a speed of 60 RPM, for example, the sample is introduced into the electrolyte solution while the device is still not powered. After a short time of 3 seconds, the system is powered and the electrical protocol is started.
Electrical method: The cathode is polarized in galvano-pulsed (PC) mode with successive cathode pulses for a time Ton followed by a period Toff where the system is in open circuit. The amplitude of the cathode pulses is kept constant and equal to 25 mA in this example (3.1 mA/cm2). The polarization time Ton is 0.35 s, the time Toff is equal to 0.25 s. Under the abovementioned conditions, a duration of 10 minutes gives a coating having a thickness of 200 nm.
Final steps:
Once the protocol is completed, the rotation is interrupted and the sample is removed from the electrolyte solution in order to be rinsed with deionized water and dried with a nitrogen flow.
C. Results obtained
By applying the experimental protocol disclosed above, a uniform copper layer of 200 nm is obtained. The graphene sheets which were co-deposited uniformly dope the copper layer. This doping makes it possible to modify certain physical and mechanical properties of the copper layer.
EXAMPLE 2: Preparation of a araphene-doped copper seed layer on a barrier layer based on tantalum using an electrolyte according to the invention based on a mixture of copper ions, ethylenediamine and graphene oxide
A. Material and Equipment
Substrate: The substrate used is the same as that of Example 1.
Electrodeposition solution: The electrodeposition solution implemented in this example is an aqueous solution containing 2.1 mL/L (or 32 mM) of ethylenediamine and 4 g/L (or 16 mM) of CuS04(H20)5. To this solution is added 0.2 g/L of a suspension of graphene oxide multi-sheets (comprising 10-15 sheets) of a length comprised between 300 nm and 600 nm for a thickness of 10 nm to 15 nm. The oxidation rate of the terminal functions of the graphene oxide sheets is 10%. The solution is then vigorously stirred for 5 min in order to allow good dispersion of the graphene oxide.
Equipment: The equipment used is the same as that in Example 1.
B. Experimental protocol
Preliminary steps: The preliminary steps are the same as in Example 1.
Electrical method: The electrical protocol is the same as that in Example 1. Annealing: Once the protocol is completed, the rotation is interrupted and the sample is removed from the electrolyte solution in order to be rinsed with deionized water and dried with a nitrogen flow. The sample is then put in an oven to perform annealing at a temperature of 300°C under reducing gas.
C. Results obtained
By applying the experimental protocol disclosed above, a uniform copper layer of 200 nm is obtained. Sheets of graphene oxide are co-deposited during the deposition and uniformly dope the copper layer before being reduced during the final annealing. This graphene doping makes it possible to modify certain physical and mechanical properties of the deposited layer.
EXAMPLE 3: Filling the through vias with araphene-doped copper on a copper seed layer using a composition according to the invention based on a mixture of copper ions, ethylenediamine and graphene.
A. Material and Equipment
Substrate: The substrate used in this example is made up of a square coupon of silicon measuring 4 cm x 4 cm etched with cylindrical patterns of the "through via" type with a depth of 25 pm and a diameter of 5 pm. These patterns are covered with a layer of silica having a thickness of 400 nm, itself coated with a layer based on a nickel-boron alloy 80 nm thick which has been deposited by an electroless method, (without electrodes) in accordance with the teaching of document WO 2012/15013, and which constitutes a copper diffusion barrier. A copper seed layer of 200 nm is deposited on the barrier electrolytically using an alkaline copper solution, for example according to the teaching of document WO 2007/034116.
Electrodeposition solution: The electrodeposition solution implemented in this example is an aqueous solution containing 18 g/L (or 0.3 M) of ethylenediamine, 198 g/L (or 1.5 M) of ammonium sulfate, 10 mg/L of thiodiglycolic acid and 25 g/L (or 0.1 M) of CuS04(H20)5. The pH of this solution is 10. To this solution is added 0.2 g/L of an aqueous colloidal suspension of graphene multi-sheets (comprising 10-15 sheets) of a length comprised between 300 nm and 600 nm for a thickness of 10 nm to 15 nm. The solution is then vigorously stirred for 5 min in order to allow good dispersion of the graphene.
Equipment: The equipment is the same as that used in Example 1.
B. Experimental protocol
Preliminary steps: The silicon sample is mounted on the sample holder which is then mounted on the rotating electrode. After being rotated at a speed of 160 RPM, the sample is introduced into the electrolyte solution while the device is still not powered. After a short time of 3 seconds, the system is powered and the electrical protocol is started.
Electrical method: The cathode is polarized in galvano-pulsed (PC) mode with successive cathode pulses for a time Ton followed by a period Toff where the system is in open circuit. The amplitude of the cathode pulses is kept constant at 60 mA (7.5 mA/cm2). The polarization time Ton is equal to 0.35 s and the time Toff is equal to 0.25 s. To completely fill vias of 5 pm in diameter and a depth of 25 pm, a deposition time of 2 hours is required.
Final steps: Once the protocol is completed, the rotation is interrupted and the sample is removed from the electrolyte solution in order to be rinsed with deionized water and dried with a nitrogen flow.
C. Results obtained
By applying the experimental protocol disclosed above, the vias are completely filled by the copper. Sheets of graphene are co-deposited during the deposition and uniformly dope the copper layer. This doping makes it possible to modify certain physical and mechanical properties of the deposited layer.
EXAMPLE 4: Filling the through vias with araphene-doped copper on a copper seed layer using a composition according to the invention based on a mixture of copper, ethylenediamine and graphene oxide.
A. Material and Equipment
Substrate: The substrate used is the same as that of Example 3.
Electrodeposition solution: The electrodeposition solution implemented in this example is an aqueous solution containing 18 g/L (or 0.3 M) of ethylenediamine, 198 g/L (or 1.5 M) of ammonium sulfate, 10 mg/L of thiodiglycolic acid and 25 g/L (or 0.1 M) of CuS04(H20)5. The pH of this solution is 10. To this solution is added 0.2 g/L of a suspension of graphene oxide multi-sheets (comprising 10- 15 sheets) of a length comprised between 300 nm and 600 nm for a thickness of 10 nm to 15 nm. The oxidation rate of the terminal functions of the graphene oxide sheets is 10%. The solution is then vigorously stirred for 5 min in order to allow good dispersion of the graphene oxide.
Equipment: The equipment is the same as that used in Example 1.
B. Experimental protocol
Preliminary steps: The preliminary steps are the same as in Example 3.
Electrical method: The electrical method is the same as that in Example 3.
Final steps: The final steps comprising annealing the copper layer to reduce the graphene oxide that it contains into graphene are the same as those of Example 2.
C. Results obtained
By applying the experimental protocol disclosed above, the vias are completely filled by the copper. Sheets of graphene oxide are co-deposited and uniformly dope the copper layer before being reduced during the final annealing. This reduced graphene doping makes it possible to modify certain physical and mechanical properties of the deposited layer.

Claims

1. An electrolyte for electrodepositing copper onto a semiconductor substrate, the electrolyte having a pH ranging from 7.0 to 11.0 and comprising copper ions having a concentration ranging from 0.1 mM to 2000 mM, at least one amine present having a concentration comprised between 0.5 mM and 5000 mM, from 0.1 g/L to 10 g/L of a graphene or a graphene oxide and a solvent.
2. The electrolyte according to claim 1, wherein the pH is comprised between 7.5 and 8.5 or between 9.5 and 10.5.
3. The electrolyte according to claim 1 oro 2, wherein the amine is selected in the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine and dipropylene triamine.
4. The electrolyte according to claim 1 or 3, wherein the amine is ethylenediamine, the concentration of the copper ions is comprised between 10 mM and 120 mM, the molar ratio between the copper ions and the ethylenediamine is comprised between 0.4 and 0.6 and the pH is comprised between 7.0 and 7.5.
5. The electrolyte according to one of claims 1 to 3, wherein the amine is ethylenediamine, the concentration of the copper ions is comprised between 45 mM and 1500 mM, the molar ratio between the copper ions and the ethylenediamine is comprised between 0.2 and 0.4 and the pH is comprised between 9.5 and 10.5.
6. The electrolyte according to one of the preceding claims, wherein the graphene or the graphene oxide are multi-sheets comprising 10 to 15 sheets and having a length comprised between 300 nm and 600 nm.
7. A method for manufacturing through vias (TSVs) in a semiconductor device by implementing an electrodeposition step on a surface having a flat part and an assembly of at least one cavity of opening width greater than 0.5 micron, the method being characterized in that it comprises the steps of:
- contacting said surface with an electrolyte according to one of claims 1 to 6, and
- polarizing said surface at an electrical potential so as to form a copper deposit containing the graphene or the graphene oxide.
8. The method according to claim 7, wherein the electrolyte contains graphene oxide and wherein a step of annealing the copper deposit containing the graphene oxide is performed, following a polarization at a temperature ranging from 200°C to 400°C, in order to reduce the graphene oxide and to obtain a copper deposit containing a graphene.
9. The method according to claim 7 or 8, wherein the copper deposit containing the graphene or the graphene oxide is a seed layer.
10. The method according to claim 7 or 8, wherein the copper deposit containing the graphene or the graphene oxide completely fills the volume of the cavity.
11. The method according to claim 7, wherein the surface is a surface of a copper diffusion barrier layer, a surface of a copper seed layer, or a surface of a copper diffusion barrier layer that is at least partially covered with a copper seed layer.
12. The method according to claim 11, wherein the barrier layer comprises at least one of the materials chosen from cobalt (Co), ruthenium (Ru), tantalum (Ta), titanium (Ti), tantalum nitride (TaN), titanium nitride (TiN), tungsten (W), tungsten titanate (TiW) and tungsten nitride or carbide (WCN).
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