EP2898121A1

EP2898121A1 - Electrolyte and method for electrodepositing copper onto a barrier layer

Info

Publication number: EP2898121A1
Application number: EP13767028.7A
Authority: EP
Inventors: Vincent Mevellec; Dominique Suhr; Laurianne RELIGIEUX
Original assignee: Alchimer SA
Current assignee: Aveni SA
Priority date: 2012-09-24
Filing date: 2013-08-28
Publication date: 2015-07-29
Anticipated expiration: 2033-08-28
Also published as: KR20150056655A; JP2015533946A; US20150218724A1; CN104685107A; TWI592522B; FR2995912B1; FR2995912A1; CN104685107B; IL237731B; TW201418528A; EP2898121B8; US10472726B2; CA2885231A1; SG11201502044VA; EP2898121B1; WO2014044942A1; JP6218837B2; KR102206291B1

Abstract

The present invention concerns an electrolyte composition for depositing copper onto semi-conductive substrates covered with a barrier layer. This electrolyte contains a combination of imidazole and 2,2'-bipyridine, used as a suppressor, and thiodiglycolic acid, used as an accelerator. The combination of these additives makes it possible to obtain bottom-up filling on very narrow trenches, typically narrower than 100 nm.

Description

Electrolyte and copper electroplating process on a barrier layer

The present invention relates to the electroplating of copper on a semiconductor substrate. More specifically, it relates to a method of electroplating copper on the surface of a semiconductor substrate having an etching, the surface being covered with a copper diffusion barrier layer.

Integrated circuits are generally manufactured by forming active semiconductor devices, in particular transistors, on the surface of silicon wafers (called "wafers" in English), said semiconductor devices being interconnected by a system of metal interconnects. submicron obtained by filling "trenches" hollowed out in the dielectric layers. The width of these lines is generally of the order of one to several hundreds of nanometers.

The submicron interconnect elements are generally formed using the Damascene method (see, for example, S. Wolf, "Silicon Processing for the VLSI Era", Vol. 4, (2002), p.671-687) in a succession of steps comprising: etching the lines on the silicon surface; depositing an insulating dielectric layer (generally consisting of oxide or silicon nitride); depositing a barrier layer for preventing migration of the copper; depositing a thin layer of metallic copper, called the seed layer; the filling of the trenches by copper electrodeposition in an acidic medium; and - removing the excess copper by polishing.

The barrier layer is generally too high in resistance to electrochemically homogeneous or uniform copper deposition on the trench scale, mainly because of the ohmic drop phenomenon. The high strength of the barrier layer results from the high resistivity of the material and its low thickness. It is therefore generally necessary, prior to the step of electroplating the copper, to cover the barrier layer with a thin layer of metallic copper, called the seed layer, in order to improve the conductivity of the substrate to be coated during the electroplating filling step. In fact, copper electroplating techniques, traditionally used for trench filling with copper, after the step of forming a copper seed layer, can not be implemented on resistive substrates such as barrier layers.

The demand for manufacturing semiconductor integrated circuits such as computer chips of high power, high storage density and low dissipation requires the reduction of the size of the structures. Decreasing the size of the chips and increasing the density of the circuits in turn require miniaturization of the interconnection devices.

When the trenches reach a size too small, it becomes difficult or impossible to deposit a copper sprouting layer prior to filling, due to insufficient space in the device. For example, if the trench has a width of 20 nm, the thickness of the seed layer can not exceed 5 nm. However, copper vapor deposition processes do not allow the deposition of layers as thin and regular thickness (deposit compliant).

In order to fill more and more thin interconnection structures, there is therefore a need for electrolytes which allow the conformal deposition of very thin copper seed layers on barrier substrates. There is also the need to overcome the prior deposition of the seed layer, by providing an electrolyte that allows the filling of copper on an irregular or discontinuous sprouting layer, or even filling the copper directly on the barrier layer. Indeed, the decrease in the thickness of the copper seed layer deposited on the barrier layer is imposed by the miniaturization of the interconnection elements. However, the regularity of the thickness of the seed layer is generally necessary to ensure a constant current density over the entire surface to be metallized during the filling step, so that the deposition of copper is of good quality.

The invention finds particular application in the field of integrated circuits for the manufacture of interconnection elements whose size does not exceed one micron. The invention finds particular application for the electroplating of copper in trenches and other small elements such as small vias whose surface width (also called aperture diameter) of the semiconductor is less than 200 nm.

In the prior art there are electrolytes for the metallization of "vias traverses" (called "through silicon vias" or TSV in English) necessary for the integration of electronic chips in three dimensions. These structures are much larger than the submicron structures targeted by the present invention: the TSVs generally have an opening diameter of the order of 10 to 250 microns. The electrolytes used to fill the TSVs have specific chemistries and are not suitable for filling much smaller structures such as interconnection lines.

It has furthermore been found that conventional electrolytes used for the electroplating of copper in trenches do not work on finer patterns and patterns with a higher form factor, typically greater than 2/1 (remember that the shape factor is the ratio of the depth of the pattern to the width of its opening at the surface of the substrate). In particular, it is observed at the end of the filling step that voids can form in the copper deposited in such trenches, which tends to increase the resistance or even to cause a break in the conductive line for be formed by the copper deposited in the patterns. The voids may be between the substrate and the copper deposit, or in the copper deposit itself, generally in the form of a line equidistant from the edges of the trench.

The desire to combine process efficiency and cost price has always pushed the industry to constantly improve the formulations of electrolytes. Thus, the Applicant has filed several patent applications concerning copper electroplating compositions for producing seed layers on barrier layers in interconnection elements or TSVs.

WO 2007/034116 discloses electrodeposition compositions which make it possible to produce adherent, uniform and uniform deposits of copper germination layers on resistive barriers. The formulations described in this document are designed for the production of ultra-thin deposits, usually of a thickness of less than 20 nm, on substrates having resistivities of the order of a few tens of ohms / square. It has been found that such formulations can not be used during the subsequent step of filling the trenches with copper: voids ("voids") or vacuum lines ("seams") appear in fact in the copper deposit with this type of electrolyte.

In the patent application FR 2 930 785, the Applicant has described an electroplating process specifically provided for the deposition of a seed layer in through vias. This technology, which is specific to through vias, can not be transferred to the metallization of very thin interconnection lines. Finally, WO 2007/096390 discloses electrodeposition compositions which make it possible to fill lines and vias with copper in a single step on the copper barrier. The formulations described in this prior art are specifically designed to address the problem of filling lines and low volume vias. However, it has been found that the compositions illustrated by the examples mentioned in WO 2007/096390 do not allow the filling of trenches in a time compatible with industrial production.

Under these conditions, the present invention aims to solve the technical problem of providing a new electrolyte meeting both the filling constraints generated by the fineness of certain trenches, and the profitability requirements of the industry. on the filling times.

To date, the traditional electroplating of copper comprises the application of a current to a wafer previously covered with a seed layer and immersed in an acid bath of copper sulphate containing additives, mainly accelerator, suppressor type, leveler or brightener. The prior art suggests that, in order to perform the filling of the patterns, it is preferable to employ an accelerator and a suppressor in combination, and in some cases a three-component system consisting of an accelerator, a suppressor and a leveler.

According to the known methods of electroplating, copper tends to grow faster at the opening of the trench than at the bottom thereof. A gradient of copper filling rates in the trenches is observed, which generally results in the formation of an empty line ("seam") located equidistant from the walls of the trench. It is therefore desirable to accelerate the growth of copper at the bottom of the trench to limit the appearance of voids in the copper deposit.

On the other hand, a continuous copper layer will generally have a greater thickness at the top of the trench on the surface of the substrate. It is desirable to limit the thickness of the layer at the plane portion because the electroplating step is followed by a polishing step necessary to remove the excess copper present on the planar portion.

Thus, the thickness decrease of the copper present on the flat part of the semiconductor substrates and the absence of defects in the copper deposit in trenches are very important elements in the manufacture of integrated circuits.

Suppressors and accelerators are therefore incorporated in electrolytic baths, to respectively slow down and / or accelerate the deposition of copper at the desired locations of the trench.

Once the electrodes are polarized, a suppressor can adsorb to the surface to be coated (a barrier layer or a copper seed layer for example), and begin to slow the growth of copper. The adsorption of the suppressor on the surface causes a partial masking of the surface, which has the effect of slowing the growth of the copper locally.

Typical suppressors are, for example, polymers of high molecular weight, generally of the order of 2000 g / mol to 8000 g / mol, such as polypropylenes glycols, polyethylenes glycols and polyethers. They are usually added to electroplating solutions to be specifically adsorbed on a copper seed layer, previously deposited on the surface of the wafer, to slow the growth kinetics of copper at the entrance of the structures of lines of interconnection (opening of trenches).

Suppressors that slow the growth of copper on the surface of trenches may be associated with smaller molecules, accelerators, which will have the property of catalysing the growth of copper at the bottom of the etched patterns. The accelerator is chosen to adsorb on a copper seed layer or on a layer of barrier material. For example, a copper-specific accelerator acts on the modification of copper reduction mechanisms, which results in an increase in kinetics. The accelerator generally comprises small molecules with a high diffusion rate that reach the bottom of the structures faster than the suppressors, which are large molecules. The most commonly used accelerator is bis (3-sulfopropyl) disulfide (also called SPS).

It has been discovered that the combination of imidazole and bipyridine can serve as a suppressor, particularly a suppressor suitable for adsorbing on a barrier layer or on copper.

Biprydine is already known as a complexing agent for copper to stabilize copper ions in plating baths (WO 2007/034116). It is also known as a brightener for the metallization of steel with copper when it is used at a very high concentration, of the order of 100 mM. (US 3,617,451). However, its suppressor properties have never been described.

Without being bound by any theory, it is believed that imidazole and bipyridine are active as soon as the substrate is polarized and begin to slow copper growth from the beginning of the process.

It has also been discovered in the context of the present invention that imidazole combined with bipyridine makes it possible, quite unexpectedly, to increase the number of nucleation grains on the surface of the substrate to be coated, so that the substrate is covered very quickly over the entire surface with a very small thickness of copper and continuous at a time. The electrical continuity of the substrate is thus guaranteed in the very first instants of the electrodeposition reaction, which allows, according to the variant of the method chosen, i) to overcome a preliminary step of deposition of a seed coat. copper, or ii) to deposit a continuous and consistent thickening of very thin layer allowing space saving in trenches of very small dimensions.

It has also been discovered that it is possible to solve the above technical problem using electrodeposition compositions comprising the combination of a suppressor with a particular accelerator. This particular accelerator makes it possible to cancel the suppressor effect in the bottom of the trenches because it accumulates strongly at this point and competes with the suppressive effect of the imidazole / bipyridine pair. The inventors have discovered that other accelerators do not make it possible to cancel the suppressive effect of the imidazole / bipyridine pair in the background of the patterns.

The combination of bipyridine, imidazole and thiodiglycolic acid according to the invention makes it possible to fill the trenches without any defects being observed. The trenches thus filled do not have voids or void lines: the filling is optimal from the bottom to the top of the trenches (so-called bottom-up effect).

The combination of bipyridine, imidazole and thiodiglycolic acid according to the invention also makes it possible to stabilize the electrolyte over time, in particular during the storage of the electrolyte.

This unexpected effect can not be observed with another accelerator of the prior art. Indeed, the inefficiency of another accelerator, SPS, has been demonstrated experimentally in a comparative example, when used in combination with imidazole and bipyridine. The SPS disrupts the action of the other two compounds, and renders them ineffective. This effect can not be observed either with another suppressor such as the combination of bipyridine with another aromatic amine of structure close to that of imidazole, such as pyridine, which reinforces the unexpectedness of the present invention.

Thus, according to one of its aspects, the present invention relates to an electrolyte for electroplating copper on a copper diffusion barrier layer, the electrolyte comprising a source of copper ions, a solvent, and the combination of bipyridine, imidazole and thiodiglycolic acid.

According to a second aspect, the present invention relates to an electrolyte for electroplating copper on a copper diffusion barrier layer, the electrolyte comprising a source of copper ions, a solvent, and the combination of a suppressor. and an accelerator, characterized in that the suppressor comprises the combination of bipyridine and imidazole, and the accelerator is thiodiglycolic acid.

The pH of the electrolyte is preferably greater than 6.7. This is all the more surprising since the electrolytes of the prior art used for filling cavities generally have a much lower pH to guarantee a sufficient conductivity of the solution thanks to the presence of H ⁺ ions, and consequently to obtain sufficient kinetics. The pH of the electrolyte of the invention is preferably greater than 6.7, more preferably greater than 6.8, more preferably between 7.5 and 8.5, and even more preferably of the order of 8. .

It has furthermore been shown that the electrolyte of the invention makes it possible to fill, without defect of material, very fine trenches having high form factors, of 2: 1 and beyond, for example greater than 3: 1.

By "electroplating" is meant here a process which makes it possible to cover a surface of a substrate with a metal or organometallic coating, in which the substrate is electrically polarized and brought into contact with a liquid containing precursors of said metallic or organometallic coating. , so as to form said coating. When the substrate is electrically conductive, the electroplating is for example carried out by passing a current between the substrate to be coated constituting an electrode (the cathode in the case of a metal or organometallic coating) and a second electrode ( the anode) in a bath containing a source of precursors of the coating material (for example metal ions in the case of a metal coating) and optionally various agents intended to improve the properties of the coating formed (regularity and fineness of the deposit, resistivity, etc.), optionally in the presence of a reference electrode. By international convention the current and the voltage applied to the substrate of interest, that is to say to the cathode of the electrochemical circuit, are negative. Throughout this text, when these currents and voltages are mentioned by a positive value, it is implicit that this value represents the absolute value of said current or of said voltage.

The term "electrolyte" means the liquid containing precursors of said metal coating used in an electroplating process as defined above.

The term "suppressor" means a substance adapted to adsorb on the surface of the barrier layer or on the surface of the copper which has been deposited on the barrier layer at the beginning and during the electroplating process, which has the effect of function to partially mask the surface to be coated so as to slow down the reaction taking place at this surface.

The term "accelerator" is understood to mean a substance adapted to accelerate the growth of copper at the bottom of the trench. The accelerator acts on the modification of copper reduction mechanisms, which has the effect of increasing the deposition kinetics of the metal.

The interaction between copper ions, imidazole, bipyridine and thiodiglycolic acid makes it possible to fill trenches of very small widths in times compatible with industrial application.

In general, the electrodeposition composition according to the invention comprises a source of copper ions, in particular Cu ²⁺ cupric ions.

Advantageously, the copper ion source is a copper salt such as in particular copper sulphate, copper chloride, copper nitrate, copper acetate, preferably copper sulphate, and preferably still copper sulphate pentahydrate.

According to one particular characteristic, the source of copper ions is present within the electroplating composition in a concentration of between 0.4 and 40 mM, for example between 1 and 25 mM, and more preferably between 3 and 6 mM.

Bipyridine is preferably in the form of 2,2'-bipyridine.

The bipyridine may be optionally replaced by or used in combination with an amine chosen from aromatic amines - in particular 1,2-diaminobenzene or 3,5-dimethylaniline - and nitrogenous heterocycles, in particular pyridine, 8-hydroxyquinoline sulfonate, the 1, 10- phenanthroline, 3,5-dimethylpyridine, 2,2'-bipyrimidine or 2-methylamino-pyridine.

The concentration of bipyridine is preferably between 0.4 and 40 mM, preferably between 1 and 25 mM, for example between 3 and 6 mM. The bipyridine is preferably 0.5 to 2, more preferably 0.75 to 1.25 molar equivalents, more preferably in the order of 1 molar equivalent of the copper ion concentration.

Advantageously, the thiodiglycolic acid is present, within the electrodeposition compositions according to the invention, in a concentration of between 1 and 500 mg / l, preferably between 2 and 100 mg / l.

The concentration of the imidazole is preferably between 1.2 and 120 mM, preferably between 3 and 75 mM, for example between 9 and 18 mM.

The imidazole preferably represents 1 to 5, more preferably 2 to 4 molar equivalents, more preferably in the order of 3 molar equivalents of the copper ion concentration.

The electrolyte may further comprise a copper complexing agent which may function to prevent the precipitation of copper hydroxide in a neutral or basic medium. Moreover, the complexing agent may also have the effect of modifying the electrochemical properties of the copper in order to optimize the growth mechanisms and to stabilize the electrolyte. The electrolyte may be free of pyridine.

Although there is no principled restriction on the nature of the solvent (provided it sufficiently solubilises the active species of the solution and does not interfere with electrodeposition), it will preferably be water. According to one mode of implementation, the solvent mainly comprises water by volume.

Advantageously, the electrolyte of the invention comprises less than 50 ppm of chlorine ions. In the prior art a source of chlorine ions is generally introduced into the electrolyte to stabilize a suppressor. In the context of the present invention, it has been found on the contrary that it is not necessary to add chlorine ions for the effectiveness of the solution. The electrolyte of the invention is preferably free of chlorine ions.

According to a variant of the invention, the electrolyte comprises, in addition to imidazole and bipyridine, another copper-specific complementary suppressor known from the prior art, such as polyethylene glycol polymers. Advantageously, the electrolyte may comprise a leveler (leveler in English terminology) and / or a brightener known from the prior art, such as for example a polypyridine.

According to a particular embodiment, the electrolyte comprises, in aqueous solution:

- copper sulphate, in a concentration of between 0.4 and

40 mM;

a mixture of imidazole and thiodiglycolic acid

- 2,2'-bipyridine

the pH of said composition being between 7.5 and 8.5.

The electrolyte described in this variant makes it possible, by implementing the method according to the second aspect of the invention, to fill the trenches without forming holes ("voids") translating an optimum filling from the bottom to the top of the trenches (bottom-up).

According to a particular embodiment, the concentration of the copper ions is between 0.4 and 40 mM, the concentration of bipyridine is between 0.4 and 40 mM, the concentration of imidazole is between 1.2 and 120 mM, and the concentration of thiodiglycolic acid is between 1 and 500 mg / l.

The invention also proposes, according to a third aspect, a method of electroplating copper on a copper diffusion barrier layer, optionally covered with a seed layer, the barrier layer covering a surface of a semiconductor substrate the surface of the substrate having a planar portion and an assembly of at least one trench of width less than 200 nm, the method comprising the steps of:

contacting the barrier layer with an electrolyte according to the first or second aspect of the invention,

- Polarizing the surface of said barrier layer to an electrical potential for electroplating copper on the barrier layer or the copper seed layer, so as to form a copper deposit on said barrier layer.

All the features that have been described in connection with the first and second aspects of the invention apply electroplating process.

This method may consist in the deposition of a copper seed layer on the barrier layer, or alternatively, if the duration of polarization is prolonged, in a complete filling of the said trench with the said deposit of copper by copper deposit directly on the barrier layer not previously covered with a copper seed layer.

The deposited seed layer preferably has a thickness of between 1 and 30 nm, for example between 2 and 20 nm.

The method of the invention makes it possible to fill trenches of very small width. Thus, the width of the trenches may be less than an upper limit selected from the group consisting of 150 nm, 100 nm, 75 nm, 35 nm, 25 nm and 10 nm. The trench width may be 32 nm, 22 nm, 14 nm, 10 nm or even 7 nm.

During the filling step, the surface of the cavity to be filled can be polarized, either in galvanostatic mode (fixed imposed current), or in potentiostatic mode (imposed and fixed potential, possibly with respect to a reference electrode) , still in pulsed mode (current or voltage).

According to one embodiment of the invention, the polarization of the surface of the cavity to be filled is carried out in continuous mode by imposing a current per unit area in a range of 0.2 mA / cm ² to 50 mA / cm ² , preferably from 0.5 mA / cm ² to 5 mA / cm ² , and preferably from 0.5 to 1.5 mA / cm ² .

According to another embodiment of the invention, the polarization of the surface of the cavity to be filled is performed in galvano-pulsed or potentiopulsed mode at medium or high frequency.

The polarization of the surface can be carried out for example in galvano-pulsed mode by imposing an alternation of polarization periods and rest periods without polarization. The frequency of the polarization periods can be between 0.1 kHz and 50 kHz (ie a polarization time of between 0.02 ms and 10 ms), preferably between 1 kHz and 20 kHz, for example between 5 kHz and 15 kHz. kHz, while the frequency of the rest periods can be between 0.1 kHz and 50 kHz, preferably between 1 kHz and 10 kHz, for example 5 kHz. The polarization of the surface can be achieved by applying a current of maximum intensity of between 0.01 and 10 mA / cm ² , for example of the order of 4 to 5 mA / cm ² .

The filling time of the trenches of width less than 150 nm is advantageously between 30 seconds and 10 minutes to obtain a complete filling of the trenches. In one embodiment, the duration of the electroplating step is less than 5 minutes to obtain a filling trenches of width less than 100 nm wide and less than 200 nm deep.

The electrolytes according to the invention can be implemented by following a process comprising an initial "hot-entry" step, but in a particularly advantageous manner, they can also be implemented by following a method comprising an initial step. "Cold inlet", during which the surface to be coated is brought into contact without electrical polarization with the electroplating bath, and maintained in this state for the desired duration. Thus, according to a particular characteristic, the process according to the invention comprises, prior to electroplating, a "cold-entry" step during which the surface of the cavity to be filled is brought into contact with the composition of the electroplating according to the invention without electrical bias, and optionally maintained in this state for a period of at least 30 seconds.

The electrolytes according to the invention will preferably be used in an electroplating process comprising:

a so-called "cold-entry" step during which said surface to be coated is brought into contact without electrical polarization with an electroplating bath and preferably maintained in this state for a period of at least 5 seconds, preferably between 10 and 60 seconds, and more preferably from about 10 to 30 seconds;

a step of forming the coating during which said surface is polarized for a time sufficient to form said coating;

a so-called "hot exit" step during which said surface is separated from the electrodeposition bath while it is still under electrical polarization.

The combination of a cold-entry step and a hot-exit step in this process makes it possible, under easier and reproducible conditions, to obtain a better adhesion of the copper deposited on the substrate.

During the coating forming step, the surface is polarized for a time sufficient to form said coating. This duration is at least 5 seconds, preferably between 10 seconds and 10 minutes.

According to another particularly advantageous characteristic, the filling method according to the invention can be implemented at a temperature between 20 and 30 ° C, that is to say at room temperature. he it is therefore not necessary to heat the electrodeposition bath which is an advantage from the point of view of the simplicity of the process.

The process according to the invention has made it possible to achieve copper fills of excellent quality, without defect of material.

This method can be implemented to fill a cavity in which the surface of the barrier layer is at least partially covered with a copper seed layer.

Advantageously, the method according to the invention can also be used to fill a cavity whose surface is made of a material forming a copper diffusion barrier, which is not covered with a seed layer of copper.

A layer forming a copper diffusion barrier may comprise at least one of the materials selected from cobalt (Co), ruthenium (Ru), tantalum (Ta), titanium (Ti), tantalum nitride (TaN) ), titanium nitride (TiN), tungsten (W), tungsten titanate (TiW) and nitride or tungsten carbide (WCN). The copper diffusion barrier layer is preferably made of ruthenium or cobalt. The thickness of the barrier layer is generally between 1 and 30 nm.

If a support coated with a tantalum barrier layer is available, it will be preferred to cover the support with a copper seed layer before carrying out the process of the invention.

The invention is further illustrated by the following figures and examples.

Figure 1 shows the trench fill of 140 nm wide and 380 nm deep with copper with an electroplating solution of the invention.

Figure 2 shows the trench fill of 140 nm wide and 380 nm deep with an electrolyte containing the combination of imidazole and SPS. Vacuum lines can be seen in the trenches.

EXAMPLE 1

A copper seed layer was prepared in nm trenches of width and 202 nm depth directly on a layer Ruthenium barrier using a composition according to the invention based on 2,2 'bipyridine, imidazole and thiodiglycolic acid.

A. Material and equipment

Substrate:

The substrate used in this example consisted of a silicon coupon having a length of 4 cm and a width of 4 cm, covered with a layer of structured silicon oxide having trenches of 55 nm in width and 202 nm in diameter. depth and itself coated with a layer of ruthenium (Ru) 3 nm thick deposited by reactive sputtering. The resistivity of the ruthenium layer was 250 ohm / square.

This ruthenium layer constitutes a copper diffusion barrier as used in so-called "double damascene" structures in the fabrication of copper interconnections of integrated circuits.

Electroplating solution:

The electroplating solution used in this example was an aqueous solution containing CuSO ₄ (H ₂ O) ₅ , 2,2 'bipyridine, imidazole and thiodiglycolic acid.

In this solution, the concentration of 2,2-bipyridine was 4.5 mM and the concentration of imidazole was 13.5 mM. The concentration of CuSO ₄ (H ₂ O) ₅ was 1.14 g / l which equals 4.5 mM. The concentration of thiodiglycolic acid could vary from 5 to 200 ppm, for example equal to 100 ppm. The pH of the solution was between 7.8 and 8.2.

Equipment :

In this example, an electrolytic deposition equipment composed of two parts was used: the cell intended to contain the electroplating solution equipped with a fluid recirculation system in order to control the hydrodynamics of the system, and an equipped rotary electrode a sample holder adapted to the size of the coupons used (4 cm * 4 cm). The electrolytic deposition cell had two electrodes:

A copper anode

- The structured silicon coupon coated with the ruthenium layer which constitutes the cathode. Connectors allowed electrical contacting of the electrodes which were connected by electrical wires to a potentiostat providing up to 20 V and 2 AB.

The electroplating process used in this example included the following consecutive steps:

Step 1: "Cold entry"

The electroplating solution was poured into the cell.

The various electrodes which were brought into contact without polarization with the electroplating solution were put in place. The polarization was then applied.

Step 2: Cuiyre coating formation

The cathode was polarized in galvanostatic mode in a range of current of 5 mA (or 0.63 mA / cm ²⁾ at 15 mA (or 1.88 mA / cm ^z), for example 7.5 m (or 0, 94 mA / cm ² ).

The duration of this step was generally between 15 sec and 1 minute in order to obtain a conformal layer of copper over the entire structure.

In this example, the duration of the electroplating step was 30 seconds to obtain a conformal copper layer with a thickness of 5 nm.

Step 3: "hot exit"

The cathode was removed from the electrodeposition bath under polarization. The cathode was then disconnected, and thoroughly rinsed with deionized water 18.2 ΜΩ, then dried with a gun delivering nitrogen at a pressure of about 2 bar.

C. Results achieved

Applying the experimental protocol described above, a continuous and conformal copper layer (observation under a scanning electron microscope) of 5 nm thickness was obtained. The copper seed layer thus obtained has a square resistance of 72 ohm / square measured using a device of the type "4-point" measurement well known to those skilled in the art. EXAMPLE 2

Trenches 55 nm wide and 202 nm deep were filled with copper directly onto a Ruthenium barrier layer using a composition according to the invention, based on 2,2 'bipyridine, imidazole and thiodiglycolic acid.

A. Material and equipment

Substrate:

The substrate used in this example was identical to that of the example

1.

Electroplating solution:

The electroplating solution used in this example was identical to that of Example 1.

No suppressor molecules, such as certain high molecular weight polymers, have been added to the solution.

Equipment :

The equipment used in this example was identical to that of Example 1.

B. Experimental protocol

Step 1: "Cold entry"

The electroplating solution was poured into the cell.

Step 2: Cuiyre coating formation

The cathode was galvanostatically biased in a current range of 5 mA (or 0.63 mA / cm ² ) to 15 mA (or 1.88 mA / cm ² ), for example 7.5 m A (or 0, 94 mA / cm ² ).

The duration of this step was generally between 1 minutes and 10 minutes in order to obtain a complete filling of the trenches. In this example, the duration of the electroplating step was 3 min to obtain a complete filling of the trenches 55 nm wide and 202 nm deep.

Step 3: "hot exit"

The cathode was removed from the electrodeposition bath under polarization. The cathode was then disconnected and thoroughly rinsed with deionized water 18.2 Ω, and then dried using a gun delivering nitrogen at a pressure of about 2 bar.

C. Results achieved

Applying the experimental protocol described above, a complete filling of trenches 55 nm wide and 202 nm deep was obtained. The trenches thus filled do not have holes ("voids") translating an optimal filling from the bottom to the top of the trenches ("bottom-up").

Surprisingly, an optimal "bottom up" filling has been obtained in very thin trenches of 55 nm width without the need to add a suppressor as described in the literature.

EXAMPLE 3

Trenches 140 nm wide and 380 nm deep were filled with copper on a Tn / Ti barrier layer coated with a 20 nm PVD copper layer using a composition according to the invention with based on 2,2 'bipyridine, imidazole and thiodiglycolic acid.

A. Material and equipment

Substrate:

The substrate used in this example consisted of a silicon coupon having a length of 4 cm and a width of 4 cm, covered with a layer of structured silicon oxide having trenches of 140 nm in width and 380 nm in diameter. depth, itself coated with a 15 nm thick TilM / Ti bi-layer and a 20 nm copper layer deposited by reactive spraying. The resistivity of the copper layer was 2.5 ohm / square.

Electroplating solution:

Equipment :

The equipment used in this example was identical to that used in Example 1.

B. Experimental protocol

Step 1: "Cold entry"

The electroplating solution was poured into the cell.

Step 2: Cuiyre coating formation

The cathode was galvanostatically biased in a current range of 5 mA (or 0.63 mA / cm ² ) to 15 mA (or 1.88 mA / cm ² ), for example 10 mA (or 1.25 mA / cm ² ).

The duration of this step was generally between 1 minute and 10 minutes in order to obtain a complete filling of the trenches.

In this example, the duration of the electrodeposition step was 9 min to obtain a complete filling of the trenches 140 nm wide and 380 nm deep.

Step 3: "hot exit"

The cathode was removed from the electrodeposition bath under polarization. The cathode was then disconnected, and thoroughly rinsed with deionized water 18.2 Ω, and then dried with a gun delivering nitrogen at a pressure of about 2 bar.

Results obtained Applying the experimental protocol described above, a complete filling of trenches 140 nm wide and 380 nm deep was obtained. The trenches thus filled do not have holes ("voids") translating an optimal filling from the bottom to the top of the trenches ("bottom-up"). Optimum trench filling has been demonstrated by the formation of a copper outgrowth above the trenches as shown on the micrograph reproduced in Figure 1.

EXAMPLE 4 Comparative

Trenches 140 nm wide and 380 nm deep were filled with copper on a TiN / Ti barrier layer coated with a PVD copper layer using a 2,2 'bipyridine composition. imidazole and bis (3-sulfopropyl) disulfide (SPS).

A. Material and equipment

Substrate:

The substrate used in this example was identical to that of the example

3.

Electroplating solution:

The electrodeposition solution used in this example was an aqueous solution containing CuSO ₄ (H ₂ O) ₅ , 2,2 'bipyridine, imidazole and bis (3-sulphopropyl) disulphide (SPS). .

In this solution, the concentration of 2,2'-bipyridine was 4.5 mM and the concentration of imidazole was 13.5 mM. The concentration of CuSO ₄ (H ₂ O) ₅ was 1.14 g / l (equivalent to 4.5 mM). The concentration of SPS could vary from 5 to 200 ppm, for example equal to 14 ppm. The pH of the solution was between 7.8 and 8.2.

Equipment :

The equipment used in this example was identical to that used in Example 1.

B. Experimental Protocol The electroplating process implemented in this example included the following consecutive steps: Step 1: "Cold entry"

The electroplating solution was poured into the cell.

Step 2: Cuiyre coating formation

The cathode was galvanostatically polarized in a current range of 5 mA (or 0.44 mA / cm ² ) to 15 mA (or 1.3 mA / cm ² ), for example 10 mA (or 1.25 mA / cm ²⁾ ).

Step 3; "Hot exit"

The cathode was removed from the electrodeposition bath under polarization. The cathode was then disconnected, and thoroughly rinsed with deionized water 10 Ω, and then dried using a gun delivering nitrogen at a pressure of the order of 2 bars.

Results obtained

By applying the experimental protocol described above, inhomogeneous growth of copper in the trenches has been observed. The morphology of the copper obtained was found to be very poor (very small grains of inhomogeneous form) reflecting a non-compatibility of the SPS with the formulation and the pH of the solution according to the invention. Figure 2 shows the poor filling obtained with this comparative electrodeposition solution.

EXAMPLE 5

Trenches 55 nm wide and 165 nm deep were filled with copper on a TiN / Ti barrier layer coated with a 10 nm copper PVD layer using a composition according to the invention containing 2,2 'bipyridine, imidazole and thiodiglycolic acid. A. Material and equipment

Substrate:

The substrate used in this example consisted of a silicon coupon having a length of 4 cm and a width of 4 cm, covered with a layer of structured silicon oxide having trenches 55 nm wide and 165 nm in diameter. depth, itself coated with a 10 nm thick Ti / Ti layer and a 10 nm copper layer deposited by reactive sputtering. The resistivity of the copper layer was 8 ohm / square.

Electroplating solution:

Equipment :

The equipment used in this example was identical to that used in Example 1.

B. Experimental protocol.

The electroplating protocol implemented in this example included the following consecutive steps:

Step 1: "Cold entry"

The electroplating solution was poured into the cell.

The various electrodes which were in contact without polarization with the electroplating solution were put in place. The polarization was then applied.

Step 2: Formation of the cuiyre coating.

The cathode was polarized in galvano-pulsed mode so that the frequency of cathode pulses is very high between 0.1 and 50 kHz, for example 10 kHz. The current range used was between 5 mA (1.88 mA / cm 2) and 60 mA (7.52 mA / cm 2), for example 35 mA (4.38 mA / cm 2). The cathode pulses were spaced by idle times (without current) of frequency between 0.1 and 50 kHz, for example 5 kHz.

The duration of this step was generally between 30 seconds and 10 minutes in order to obtain a complete filling of the trenches.

The duration of the electroplating step was 4 minutes to obtain a complete filling of the trenches 55 nm wide and 165 nm deep. Step 3: "Hot Exit"

Results obtained

Applying the experimental protocol described above, a complete filling of the trenches 55 nm wide and 165 nm deep was obtained. The trenches thus filled do not have holes ("voids") translating an optimal filling from the bottom to the top of the trenches ("bottom-up").

COMPARATIVE EXAMPLE 6

Copper trenches 55 nm wide and 202 nm deep were filled with copper over a ruthenium barrier layer using a composition of 2,2'-bipyridine, pyridine and thiodiglycolic acid. .

A. Material and equipment

Substrate:

The substrate used in this example was identical to that of Example 1.

Electroplating solution:

The electrodeposition solution used in this example was identical to that of Example 1, except for the replacement of imidazole with pyridine in an identical concentration of 13.5 mM. The pH of the solution was between 5.8 and 6.0.

Equipment :

The equipment used in this example was identical to that of Example 1. B. Experimental protocol

Step 1: "Cold entry"

The electroplating solution was poured into the cell.

Step 2: Cuiyre coating formation

The cathode was galvanostatically polarized in a current range of 5 mA (or 0.63 mA / cm ² ) to 15 mA (or 1.88 mA / cm ² ), for example 14.4 mA (or 1.80 mA). mA / cm ² ).

The duration of this step was generally between 1 minutes and 10 minutes in order to obtain a complete filling of the trenches.

In this example, the duration of the electroplating step was 1 minute and 35 seconds to obtain a complete filling of the trenches 55 nm wide and 202 nm deep.

Step 3: "hot exit"

The cathode was removed from the bath of electroplating under polarization.

The cathode was disconnected and thoroughly rinsed with deionized water 18.2 ΜΩ, then dried with a gun delivering nitrogen at a pressure of 2 bar. Results obtained

Applying the experimental protocol described above, 55 nm wide and 202 nm deep trenches with small holes on the sidewall voids were obtained. In addition, a thorough study of the surface of the copper thus electrodeposited shows a roughness greater than that of the electroplating solution with imidazole as described in Example 2, reflecting a poorer nucleation of copper in the presence of pyridine by compared to imidazole. These observations may be even more unfavorable for smaller trenches where nucleation density is a crucial parameter. The electroplating solution with imidazole is therefore preferred.

Claims

An electrolyte for electroplating copper on a copper diffusion barrier layer, the electrolyte comprising a source of copper ions, a solvent, and a combination of a suppressor and an accelerator, characterized in that the suppressor comprises the combination of bipyridine and imidazole, and the accelerator is thiodiglycolic acid.

2. Electrolyte according to claim 1, characterized in that its pH greater than 6.7, preferably between 7.5 and 8.5, and more preferably of the order of 8.

3. Electrolyte according to one of the preceding claims, characterized in that the copper ions are derived from a compound selected from copper sulfate, copper chloride, copper nitrate and copper acetate.

4. Electrolyte according to one of the preceding claims, characterized in that it comprises less than 50 ppm of chlorine ions, and is preferably free of chlorine ions.

5. Electrolyte according to one of the preceding claims, characterized in that the bipyridine is in the form of 2,2'-bipyridine.

6. Electrolyte according to one of the preceding claims, further comprising a leveler and / or a brightener, such as a polypyridine.

7. Electrolyte according to one of the preceding claims, characterized in that the concentration of copper ions is between 0.4 and 40 mM, the bipyridine concentration is between 0.4 and 40 mM, the concentration of imidazole is between 1.2 and 120 mM, and the concentration of thiodiglycolic acid is between 1 and 500 mg / l.

8. Electrolyte according to one of the preceding claims, characterized in that the solvent comprises predominantly water.

9. A method of electroplating copper on a copper diffusion barrier layer, optionally covered with a copper seed layer, said barrier layer covering a surface of a semiconductor substrate, the surface of the substrate having a flat portion and an assembly of at least one trench of width less than 200 nm, the method being characterized in that it comprises the steps of:

contacting the barrier layer with an electrolyte according to one of claims 1 to 8,

polarization of the surface of the barrier layer to an electrical potential allowing the electroplating of copper on the barrier layer or copper seed layer, so as to form a copper deposit on said barrier layer.

10. The method of claim 9, characterized in that the polarization step is conducted so as to form on said barrier layer a copper seed layer.

11. The method of claim 9, characterized in that the polarization step is conducted so as to completely fill the volume of the copper trench.

12. Method according to any one of claims 9 to 11, characterized in that the barrier layer comprises at least one of the materials selected from cobalt (Co), ruthenium (Ru), tantalum (Ta), titanium (Ti), tantalum nitride (TaN), titanium nitride (TiN), tungsten (W), tungsten titanate (TiW) and nitride or tungsten carbide (WCN).

13. Method according to any one of claims 9 to 12, characterized in that, during filling of the cavity, the substrate is rotated at a speed between 20 and 600 revolutions per minute, preferably at a speed of rotation between 30 and 240 rpm.

14. Method according to any one of claims 9 to 13, characterized in that the trench has a form factor greater than 2/1, preferably greater than 3/1.

15. Method according to any one of claims 9 to 14, characterized in that the polarization of the surface is carried out in continuous mode by imposing a current per unit area in a range of 0.2 mA / cm ² to 50 mA / cm ² , preferably from 0.5 mA / cm ² to 5 mA / cm ² , and in that the polarization time is at least 5 seconds, preferably between 10 seconds and 10 minutes.

16. Method according to any one of claims 9 to 14, characterized in that the polarization of the surface is carried out in galvano-pulsed mode such that the frequency of the polarization periods is between 0.1 kHz and 50 kHz, by example between 5 kHz and 15 kHz.

17. The method of claim 16, characterized in that the polarization periods are spaced by zero-current dwell times whose frequency is between 0.1 kHz and 50 kHz, for example between 1 kHz and 10 kHz.

18. The method of claim 17, characterized in that the frequency of the polarization periods is equal to about 10 kHz, and the frequency of the rest periods is equal to about 5 kHz.

19. Method according to one of claims 16 to 18, characterized in that the polarization of the surface is carried out with a current of maximum intensity of between 0.01 and 10 mA / cm ² .