Direct bonding process between two substrates

Abstract

The invention relates to a method for direct bonding between two substrates comprising the following steps: (a) providing a first substrate and a second substrate respectively comprising a first bonding surface made of hydrophilic silicon oxide and a second bonding surface made of hydrophilic silicon oxide, (b) depositing a specific compound on the first bonding surface made of hydrophilic silicon oxide, the specific compound being an organic compound consisting of a basic functional group and substituents of said basic functional group, each substituent being a hydrophobic group, (c) bringing the first bonding surface made of hydrophilic silicon oxide on which the specific compound has been deposited into contact with the second bonding surface made of hydrophilic silicon oxide, so as to obtain adhesion of the first substrate with the second substrate. Figure for abstract: Fig 1

Description

Title of the invention: Method for direct bonding between two substrates Technical field

[0001] The invention relates to a method of direct bonding between two substrates. STATE OF THE ART

[0002] Direct bonding is a technique widely used in microelectronics to assemble substrates and form multilayer structures. It consists of directly bringing into contact the two surfaces to be bonded which will spontaneously adhere to each other, without additional material, in particular without the addition of a polymer adhesive. It is possible to have a few monolayers of water adsorbed on the surfaces to be bonded, in particular if they are hydrophilic, but the surfaces to be bonded must be macroscopically dry.

[0003] Spontaneous adhesion between the two surfaces to be bonded occurs under the effect of different attractive forces between the materials, for example under the effect of Van der Waals forces, capillary forces and / or hydrogen bonds involving the water molecules adsorbed on the surfaces to be bonded. Covalent bonds can also be established between the two surfaces to be bonded.

[0004] For example, in the case where the surfaces to be bonded are hydrophilic silicon surfaces or silicon oxide surfaces, the adhesion between the two surfaces results mainly from condensation reactions between the silanols of the first surface to be bonded on the one hand and the silanols of the second surface to be bonded on the other hand. More precisely, each condensation reaction generates a siloxane bond between the two surfaces to be bonded and releases a water molecule according to the following reaction (I):

[0005] SirOH + Si2-OH -> SirO-Si2 + H2O (I)

[0006] The aforementioned attractive forces only act at short range and the formation of covalent bonds requires that the reactants are close enough for their molecular orbitals to overlap. Direct bonding therefore requires that the surfaces to be bonded are clean and flat, and have very low roughness, for example a roughness of less than 0.5 nm. Typically, the aforementioned reaction (I) can only take place at the contact points between the two surfaces to be bonded. Furthermore, such a reaction (I) is very slow and equilibrated (not complete) at room temperature.

[0007] The quality of direct bonding can be evaluated by a quantity called "bonding energy" which corresponds to the energy required to separate the two surfaces once bonded. Due to the difficulties mentioned above, the bonding energy between two surfaces bonded by direct bonding at room temperature is not sufficient to ensure good mechanical strength of the resulting multilayer structure in subsequent applications of said multilayer structure, for example if the multilayer structure is used in a process inducing high mechanical stresses on the bonding interface. Indeed, the bonding energy between two surfaces following direct bonding at room temperature of the two surfaces rarely reaches 200 mJ / m2 when the two surfaces adhere under the effect of the attractive forces previously mentioned. At room temperature, the silanol condensation reaction (I) does not allow it to exceed 0.5 J / m2, even after several days.

[0008] One solution for increasing the bonding energy consists of heating the bonding interface after bringing the two surfaces to be bonded into contact. For example, bringing two surfaces to be bonded of hydrophilic silicon or silicon oxide into contact can be followed by a heat treatment of the bonding interface at 200°C for 2 hours. The condensation reaction of the silanols is then promoted and greatly accelerated.

[0009] However, such high temperatures can induce, at the bonding interface, the formation of gases and bubbles causing bonding defects, as well as significant thermal stress, in particular when the two substrates to be bonded have very different thermal expansion coefficients. Indeed, in the latter case, the difference in behavior of the two substrates under the effect of temperature variations is such that it will induce the opening of the bonding interface before it has had time to strengthen.

[0010] Document FR 3 102 771 B1 advantageously proposes to obtain a high bonding energy at low temperature between two hydrophilic bonding surfaces by depositing a specific molecule on at least one hydrophilic bonding surface prior to bringing the two substrates to be bonded into contact, the at least one hydrophilic bonding surface on which the specific molecule has been deposited being at the bonding interface. Document FR 3 102 771 B1 specifies that the specific molecule is an organic molecule which must comprise a hydrophilic group allowing the specific molecule to chemisorb onto the hydrophilic surface to be bonded, as well as a basic group allowing the pH of the water monolayers adsorbed on the surface to be increased, the hydrophilic group and the basic functional group being separated by at least one carbon atom.The bonding process described by document FR 3 102 771 B1 makes it possible to obtain bonding energies greater than 1 J / m2 with consolidation annealing temperatures of the bond lower than 100°C.

[0011] However, the organic molecules described by FR 3 102 771 B1 are very specific and may not be accessible or expensive. In addition, said organic molecules necessarily remain blocked at the bonding interface in the assembly resulting from the bonding and, as a result, can subsequently lead to electrical and mechanical failures of the components. Finally, they constitute significant sources of pollution in clean rooms since they risk contaminating other stages of the process or other processes carried out in the same clean room. BRIEF DESCRIPTION OF THE INVENTION

[0012] An aim of the invention is to design a low-temperature direct bonding method between two substrates making it possible to obtain bonding energies compatible with use of the assembly resulting from the bonding in conventional microelectronics applications such as the manufacture of silicon-on-insulator substrates or the assembly of hybrid circuits, i.e. typically to obtain energies greater than 1 J / m2. The low-temperature direct bonding method must also be easy to implement, inexpensive and make it possible to manufacture electronic components that fail less than the components manufactured according to the prior art method.

[0013] To this end, the invention proposes a method of direct bonding between two substrates comprising the following steps:

[0014] (a) providing a first substrate and a second substrate comprising respectively a first bonding surface made of hydrophilic silicon oxide and a second bonding surface made of hydrophilic silicon oxide,

[0015] (b) depositing a specific compound on the first bonding surface made of oxide of hydrophilic silicon, the specific compound being an organic compound consisting of a basic functional group and substituents of said basic functional group, each substituent being a hydrophobic group,

[0016] (c) contacting the first hydrophilic silicon oxide bonding surface on which the specific compound has been deposited with the second hydrophilic silicon oxide bonding surface, so as to obtain adhesion of the first substrate with the second substrate.

[0017] Thus, the specific compound deposited on the first hydrophilic bonding surface is an organic compound comprising only a basic functional group. In other words, the specific compound according to the invention does not comprise an additional hydrophilic group. Indeed, the inventors have demonstrated that such a hydrophilic group is not necessary for the presence of the specific compound on at least one bonding surface to significantly increase the bonding energy, so that the implementation of direct bonds at low temperature in the presence of a specific compound according to the invention gives rise to bonding energies sufficient for the aforementioned applications. Typically, the presence of the specific compound according to the invention at the bonding interface makes it possible to achieve bonding energies greater than 1J / m2 after consolidation annealing of only 1 hour at 100°C.

[0018] The invention therefore offers a wide choice of easily accessible organic compounds which may have very low molecular weights. Compared to the specific molecules proposed by FR 3 102 771 B1 for example, the specific compound according to the invention may have the same basic functional group without having the additional hydrophilic group and the intercalary carbon. Finally, the specific compound according to the invention may have a lower molecular mass, in particular a lower carbon molecular mass. Thus, due to this lower carbon molecular mass, the compound according to the invention represents a lesser source of pollution, and will therefore induce fewer electrical and mechanical failures as previously mentioned.

[0019] The inventors assume that the basic functional group is sufficient to allow the chemisorption of the specific compound on the hydrophilic bonding surface. The inventors attribute the obtaining of the previously mentioned high bonding energies at a low thermal budget to a basic catalytic effect of said specific compound which would improve the kinetics of the condensation reactions at the origin of the adhesion between the first substrate and the second substrate and would shift the equilibrium thereof. More precisely, according to a first mechanism represented in [Fig.l], the basic functional group would react with the water adsorbed on the surface to be bonded and thus generate OH- hydroxide ions.Said hydroxide ions would then carry out nucleophilic attacks on the silicon atoms of the surface silanol groups, thus generating pentacoordinated silicon atoms that are very reactive towards the oxygen atoms of the silanol groups of the second hydrophilic silicon oxide bonding surface. The condensation reaction would therefore be greatly facilitated.

[0020] A second mechanism envisaged by the inventors is based on the nucleophilic nature of the basic group of the specific compound: the specific compound could directly implement nucleophilic additions or nucleophilic substitutions on the silicon atoms of the first bonding surface in hydrophilic silicon oxide, thus generating very reactive reaction intermediates, so that the condensation reaction on these reaction intermediates would be facilitated. In this case, we would rather speak of a nucleophilic catalytic effect of the specific compound.

[0021] The two mechanisms probably intervene jointly, one being able to dominate over the other depending on the nature of the specific compound (and its basic character relative to its nucleophilic character) as well as the nature of the first hydrophilic bonding surface and the second hydrophilic bonding surface and other experimental parameters.

[0022] Such a treatment with the specific compound according to the invention is furthermore easier to implement than a treatment with ammonia or ammonium hydroxide, because it makes it easier to control the quantity of catalytic species deposited on the surface and the pH of said surface. Indeed, ammonia and ammonium hydroxide are very volatile compounds and therefore require control of the ammonia vapor in equilibrium with the physisorbed species on the surface.

[0023] According to other optional characteristics of the invention taken alone or in combination when technically possible:

[0024] - the method further comprises depositing the specific compound on the second hydrophilic silicon oxide bonding surface, the adhesion of the first substrate with the second substrate being obtained by bringing into contact the first hydrophilic silicon oxide bonding surface and said second hydrophilic silicon oxide bonding surface on which the specific compound has been previously deposited,

[0025] - the surface concentration of the specific compound on the first surface of hydrophilic bonding prior to bringing the first hydrophilic bonding surface on which said specific compound has been deposited into contact with the second hydrophilic bonding surface is between 1011 molecules / cm2 and 1015 molecules / cm2;

[0026] - the specific compound comprises between 1 and 3 carbon atoms, preferably between 1 and 2 carbon atoms, and / or the specific compound has a molecular mass of less than 200 g / mol, preferably less than 100 g / mol;

[0027] - the specific compound is a primary, secondary or tertiary aliphatic amine, saturated or unsaturated, cyclic or not, preferentially chosen from methylamine CH3NH2, dimethylamine (CH3)2NH, trimethylamine (CH3)3N and piperidine (CH2)5NH;

[0028] - the specific compound is an organic ion, preferably a carboxylate aliphatic, more preferably still an aliphatic carboxylate chosen from the methanoate ion HCOO and the ethanoate ion CH3COO and the counterion of the organic ion is chosen from ammonium NH4+, nitrosonium NO+ and nitronium NO2+.

[0029] - the deposition of the specific compound on the first bonding surface made of oxide of hydrophilic silicon comprises depositing on the first hydrophilic silicon oxide bonding surface a liquid comprising the specific compound;

[0030] - the deposition on the first hydrophilic silicon oxide bonding surface of the liquid comprising the specific compound comprises:

[0031] depositing a volume of the liquid comprising the specific compound in the center of the first hydrophilic silicon oxide bonding surface,

[0032] spreading said volume of liquid comprising the specific compound by rotation of the first hydrophilic silicon oxide bonding surface, said first hydrophilic silicon oxide bonding surface being kept in rotation until ejection and evaporation of the volume of liquid comprising the specific compound;

[0033] - the method further comprises a step of exposing the first surface of bonding hydrophilic silicon oxide to a plasma prior to depositing the volume of liquid comprising the specific compound in the center of the first hydrophilic silicon oxide bonding surface;

[0034] - the liquid comprising the specific compound is obtained from the dissolution of the compound specific in a solvent, preferably in water or in a mixture of water and isopropyl alcohol (IPA), the concentration of the specific compound in the liquid being between 107 mol / L and 10 1 mol / L;

[0035] - the deposition of the specific compound on the first bonding surface made of oxide of hydrophilic silicon comprises exposing said first hydrophilic silicon oxide bonding surface to a gas comprising the specific compound;

[0036] - the first substrate and / or the second substrate are silicon substrates;

[0037] - the first bonding surface made of hydrophilic silicon oxide and / or the second hydrophilic silicon oxide bonding surfaces are deposited oxide, chemical oxide, thermal oxide and / or native oxide;

[0038] - bringing the first silicon oxide bonding surface into contact hydrophilic on which the specific compound has been deposited and the second hydrophilic silicon oxide bonding surface is implemented at a temperature between 0°C and 100°C;

[0039] - the method further comprises a step d) of consolidation annealing implemented after step c) of bringing into contact the first bonding surface made of hydrophilic silicon oxide on which the specific compound has been deposited and the second bonding surface made of hydrophilic silicon oxide, the consolidation annealing being preferably carried out at a temperature below 100°C for a duration of between 1 minute and 5 hours;

[0040] - the first substrate is made of a first material and the second substrate is made of a second material, the difference in coefficient of thermal expansion between the first material and the second material being greater than or equal to 10% in relative value;

[0041] - the first substrate is a multilayer structure comprising a first layer of a first material and a second layer of a second material, the difference in coefficient of thermal expansion between the first material and the second material being greater than or equal to 10% in relative value;

[0042] - the first substrate comprises electronic component elements;

[0043] - the first substrate comprises a weakening zone formed by implantation of atomic or ionic species;

[0044] The invention extends to a method of transferring a layer onto a support substrate, said method comprising the following steps:

[0045] a) providing a donor substrate comprising a first hydrophilic silicon oxide surface and a support substrate comprising a second hydrophilic silicon oxide surface,

[0046] b) the formation of a weakening zone within the donor substrate so as to delimit a layer to be transferred between the first hydrophilic silicon oxide surface and the weakening zone,

[0047] c) bonding between the donor substrate and the support substrate, the first surface made of hydrophilic silicon oxide and the second surface made of hydrophilic silicon oxide being at the bonding interface and the bonding between the donor substrate and the support substrate being implemented by a bonding method as previously described,

[0048] d) detaching the donor substrate along the weakening zone so as to transfer the layer to be transferred onto the support substrate.

[0049] Finally, the invention relates to an assembly comprising a first substrate and a second substrate, the first substrate being covered by a first hydrophilic surface and the second substrate being covered by a second hydrophilic surface, the first hydrophilic surface being bonded with the second hydrophilic surface, a specific compound being disposed between the first hydrophilic bonding surface and the second hydrophilic bonding surface, the specific compound being an organic compound consisting of a basic functional group and substituents of said basic functional group, each substituent being a hydrophobic group. BRIEF DESCRIPTION OF THE FIGURES

[0050] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

[0051] - [Fig.l] illustrates the nucleophilic role of the hydroxide ion in the reaction of condensation of silanols leading to the formation of a Si-O-Si siloxane bond between the two surfaces to be bonded;

[0052] - [Fig.2] illustrates the beneficial effect of two examples of carbon molecules nucleophiles or bases, namely glycine and ethanolamine, on the bonding energy. DETAILED DESCRIPTION OF EMBODIMENTS

[0053] The direct bonding method according to the invention comprises a first step of providing a first substrate comprising a first oxide bonding surface of hydrophilic silicon and a second substrate comprising a second bonding surface of hydrophilic silicon oxide.

[0054] Providing a first substrate comprising a first hydrophilic silicon oxide bonding surface and a second substrate comprising a second hydrophilic silicon oxide bonding surface.

[0055] The first substrate and / or the second substrate may be, for example, made of a material chosen from silicon Si, germanium Ge, indium phosphide InP, gallium arsenide AsGa, alumina Al2O3, silicon oxide SiO2, silicon nitride Si3N4, silicon carbide SiC, gallium nitride GaN, copper, titanium, nickel, lithium niobate LiNbO3 (known to those skilled in the art by the acronym LNO) and lithium tantalate LiTaO3 (known to those skilled in the art by the acronym LTO).

[0056] Alternatively, the first substrate and / or the second substrate may be multilayer structures comprising at least two layers. For example, the first substrate - respectively the second substrate - comprises a first layer made of a first material and a second layer made of a second material. The first material and the second material are for example chosen from the materials mentioned above. According to this embodiment, the step of providing a first substrate comprising a first hydrophilic bonding surface and a second substrate comprising a second hydrophilic bonding surface may comprise one or more sub-steps of assembling said layers, so as to form the first substrate and / or the second substrate.

[0057] The direct bonding method according to the invention is particularly advantageous when the first substrate and / or the second substrate comprise layers made of materials having a large difference in coefficient of thermal expansion. A large difference in coefficient of thermal expansion is understood to mean a difference of 10% or more in relative value between the values of said coefficients of thermal expansion.

[0058] Furthermore, the first substrate and / or the second substrate may comprise one or more electronic component elements. For example, the first substrate and / or the second substrate comprise metal parts such as copper lines and silicon oxide insulating parts (hybrid bonding). Similarly, the step of providing a first substrate comprising a first hydrophilic bonding surface and a second substrate comprising a second hydrophilic bonding surface may in this case comprise one or more sub-steps of forming said electronic component elements.

[0059] The direct bonding method according to the invention is particularly advantageous when the first substrate and / or the second substrate comprise such electronic component elements because during heating, the different elements of such a system expand differently (metals, insulators, semiconductors) and this can generate significant stresses within the device. These stresses can lead to defects such as, for example, delamination. The maximum thermal budget must not exceed the thermal budget generated at the operating temperature of the device, which is generally less than 200°C.

[0060] Finally, the first substrate and / or the second substrate may also comprise a weakening zone formed for example by implantation of atomic and / or ionic species.

[0061] The direct bonding method according to the invention is particularly advantageous when the first substrate and / or the second substrate comprise such a weakened zone because the weakened zone must then be the weakest zone of the material, otherwise controlling the fracture will be difficult. It is therefore necessary for all the other interfaces to have been reinforced at the time of the fracture.

[0062] The first substrate and the second substrate may be of identical nature or they may be different. The direct bonding method according to the invention is particularly advantageous when the first substrate (or the layer of the first substrate at the bonding interface) and the second substrate (or the layer of the second substrate at the bonding interface) are made of materials having a large difference in coefficient of thermal expansion.

[0063] First bonding surface made of hydrophilic silicon oxide and second bonding surface made of hydrophilic silicon oxide

[0064] As previously mentioned, the first substrate and the second substrate respectively comprise a first hydrophilic silicon oxide bonding surface and a second hydrophilic silicon oxide bonding surface. A hydrophilic bonding surface is understood to mean a surface that has a strong affinity with water, such that at least one monolayer of water remains naturally adsorbed on the hydrophilic bonding surface. The contact angle of a hydrophilic surface is typically less than about ten degrees.

[0065] For example, the first hydrophilic silicon oxide bonding surface and / or the second hydrophilic silicon oxide bonding surface may be native silicon oxide surfaces. In other words, if the first substrate and / or the second substrate comprise a material naturally forming an oxide layer on its surface - called a native silicon oxide layer -, the first hydrophilic silicon oxide bonding surface and / or the second hydrophilic silicon oxide bonding surface may be the surface of said native oxide layer. This is why example the case of silicon and silicon carbide which naturally form an oxide layer whose thickness is of the order of 1 nm. If the first substrate and / or the second substrate are made of silicon oxide or comprise a layer of silicon oxide, the first bonding surface made of hydrophilic silicon oxide and / or the second bonding surface made of hydrophilic silicon oxide may be directly the surface of said silicon oxide.

[0066] For example, the first hydrophilic silicon oxide bonding surface and / or the second hydrophilic silicon oxide bonding surface may be thermal silicon oxide surfaces. According to this embodiment, the step of providing a first substrate comprising a first hydrophilic silicon oxide bonding surface and a second substrate comprising a second hydrophilic silicon oxide bonding surface may comprise a sub-step of forming a first thermal silicon oxide layer on the first substrate and / or a sub-step of forming a second thermal silicon oxide layer on the second substrate, a surface of the first, respectively of the second, thermal silicon oxide layer forming the first, respectively the second, hydrophilic silicon oxide bonding surface.

[0067] Thermal oxide is understood to mean an oxide formed by direct oxidation of a material by exposing said material, at high temperature, to dioxygen (dry oxidation), to water (wet oxidation) or possibly to other oxidants (for example N2 O).

[0068] A thermal silicon oxide layer may be formed on the surface of a silicon substrate or a silicon carbide substrate. For this purpose, a silicon substrate is for example heated to a temperature preferably between 800°C and 1200°C and then a surface of said silicon substrate is exposed to an atmosphere of dioxygen or water vapor. The oxidation temperature conditions the growth rate of the thermal silicon oxide layer from the surface of the silicon substrate exposed to the atmosphere of dioxygen or water vapor. In the case of wet thermal oxidation, the formation of the thermal silicon oxide layer may comprise the combustion of dihydrogen by dioxygen in a torch and the exposure of the substrate to the water vapor produced by said combustion, the heat generated by this same combustion reaction being further able to serve to bring the substrate to the temperature chosen for thermal oxidation.

[0069] The thickness of the thermal silicon oxide layer is for example between 1 nm and 1 um.

[0070] For example, the first hydrophilic silicon oxide bonding surface and / or the second hydrophilic silicon oxide bonding surface may be chemical silicon oxide surfaces. According to this embodiment, the step of providing a first substrate comprising a first hydrophilic silicon oxide bonding surface and a second substrate comprising a second hydrophilic silicon oxide bonding surface may comprise a sub-step of forming a first chemical silicon oxide layer on the first substrate and / or a sub-step of forming a second chemical silicon oxide layer on the second substrate, a surface of the first, respectively of the second, chemical silicon oxide layer forming the first, respectively second, hydrophilic silicon oxide bonding surface.

[0071] The term “chemical oxide” means an oxide formed by oxidation of a material at low temperature (preferably at room temperature), in the presence of water or certain oxidants such as hydrogen peroxide H2O2 or ozone O3. A layer of chemical silicon oxide may be formed in this way on the surface of a silicon, silicon carbide or silicon nitride substrate, by exposing said surface at low temperature to water or to an oxidant such as previously mentioned. The thickness of the layer of chemical silicon oxide on the surface of the silicon substrate is, for example, between 0.5 nm and 3 nm.

[0072] For example, the first hydrophilic silicon oxide bonding surface and / or the second hydrophilic silicon oxide bonding surface may be deposited silicon oxide surfaces. According to this embodiment, the step of providing a first substrate comprising a first hydrophilic bonding surface and a second substrate comprising a second hydrophilic bonding surface may comprise a sub-step of depositing a first layer of silicon oxide deposited on the first substrate and / or a sub-step of depositing a second layer of silicon oxide deposited on the second substrate, a surface of the first, respectively of the second, deposited oxide layer forming the first, respectively the second, hydrophilic silicon oxide bonding surface.

[0073] The term “deposited oxide” means an oxide formed by the chemical addition of material, for example in the form of vapor or plasma. A layer of silicon oxide can be deposited on almost any type of material, in particular IV / IV, III / V and II / VI semiconductors as well as oxides of the LiTaO3 or LiNbO3 type. The thickness of the deposited silicon oxide layer is, for example, between 1 nm and 10 pm.

[0074] For the deposition of a silicon oxide layer, the precursor providing the silicon is typically silane (SiH4) while the precursor providing the oxygen is for example N2O or O2. For example, the substrate on which the silicon oxide layer is to be deposited is placed in a plasma chamber. Then, the substrate is introduced into said plasma chamber a carrier gas, for example dihydrogen, comprising precursors of silicon and oxygen, for example SiH4 and N2O. Under the effect of the plasma, the precursors decompose and react, forming on the surface of the substrate exposed to the plasma a layer of silicon oxide.

[0075] The methods for forming the silicon oxide layer previously described are given for illustrative purposes and are in no way limiting of the scope of the invention and may be adapted by a person skilled in the art to the envisaged application case. For example, the method for depositing a silicon oxide layer may comprise the application of magnetic fields or microwaves to accelerate the deposition. Other carrier gases or precursors may be used.

[0076] If the first substrate and / or the second substrate are made of silicon oxide or comprise a silicon oxide layer and / or if the first substrate and / or the second substrate are made of a material naturally forming a silicon oxide layer on the surface or comprise such a material, the provision of the first substrate comprising a first bonding surface of hydrophilic silicon oxide and of the second substrate comprising a second bonding surface of hydrophilic silicon oxide may still comprise the formation of a first thermally or chemically deposited silicon oxide layer on the first substrate and / or the formation of a second thermally or chemically deposited silicon oxide layer on the second substrate such that a surface of the first, respectively of the second, thermally or chemically deposited silicon oxide layer forms the first, respectively the second, hydrophilic silicon oxide bonding surface.

[0077] The first hydrophilic silicon oxide bonding surface and the second hydrophilic silicon oxide bonding surface may be of the same nature or of different nature. For example, the first hydrophilic silicon oxide bonding surface may be a chemical silicon oxide surface and the second hydrophilic silicon oxide bonding surface a native silicon oxide surface. In this case, the step of providing a first substrate comprising a hydrophilic silicon oxide bonding surface and a second substrate comprising a second hydrophilic silicon oxide bonding surface may comprise a sub-step of forming a chemical silicon oxide layer on the first substrate. For example again, the first hydrophilic silicon oxide bonding surface may be a thermal silicon oxide surface and the second hydrophilic silicon oxide bonding surface a deposited silicon oxide surface.In this case, the step of providing a first substrate comprising a hydrophilic silicon oxide bonding surface and a second substrate comprising a second hydrophilic silicon oxide bonding surface may comprise a forming sub-step. of a thermal silicon oxide layer on the first substrate and a sub-step of forming a silicon oxide layer deposited on the second substrate.

[0078] Such combinations are cited as examples and are in no way limiting of the scope of the invention. Any combination between native, chemical, thermal and deposited silicon oxide surfaces of the first substrate and the second substrate remains covered by the present invention.

[0079] Furthermore, depending on the nature of the first, respectively second, substrate that he wishes to obtain (monoblock substrate, or multilayer structure comprising materials having very different thermal expansion coefficients, possibly comprising electronic component elements and / or a weakening zone) and the application envisaged for the assembly resulting from the bonding between the first substrate and the second substrate (for example the manufacture of silicon on insulator or piezoelectric on insulator), the person skilled in the art is able to choose the nature of the silicon oxide most suitable for the first, respectively second, substrate, as well as the order of sequence of the various sub-steps previously mentioned making it possible to provide the expected first, respectively second, substrate.

[0080] Deposition of a specific compound on at least the first hydrophilic silicon oxide bonding surface

[0081] The method further comprises a step of depositing a specific compound on the first hydrophilic silicon oxide bonding surface, or on both the first hydrophilic silicon oxide bonding surface and the second hydrophilic silicon oxide bonding surface.

[0082] The specific compound is an organic compound.

[0083] For the purposes of the present invention, the term organic compound means a compound consisting of several atoms, the atoms being linked together by covalent bonds, and comprising at least one carbon atom with the exception of carbon monoxide CO, carbon dioxide CO2, carbonic acid H2CO3, carbonate ion CO32, bicarbonate ion HCO3 and cyanide ion CN. The term organic compound may refer indifferently to an electrically neutral organic compound, otherwise called an organic molecule, or to a charged organic compound, otherwise called an organic ion. However, carbon monoxide CO, carbon dioxide CO2, carbonic acid H2CO3, carbonate ion CO32, bicarbonate ion HCO3 and cyanide ion CN are excluded from the group of organic compounds for the purposes of the present invention.

[0084] When the specific compound is an organic molecule, said specific compound advantageously makes it possible not to introduce an additional counter-ion which would constitute a significant source of pollution. Thus, the present invention is particularly advantageous compared to treatment with a solution of a hydroxide salt which would make it possible to directly supply hydroxide ions to the hydrophilic silicon oxide bonding surface, but would necessarily induce the joint deposition of such a counter-ion.

[0085] If the specific compound is a basic ion, the counterion is preferably not chosen from alkali and alkaline earth metals. Indeed, alkali and alkaline earth metals are contaminants in microelectronics because they modify the properties of silicon and silicon oxide. For example, the counterion of the organic ion is preferably chosen from ammonium NH4+, nitrosonium NO+ and nitronium NO2+.

[0086] More specifically, the specific compound is an organic compound consisting of a basic functional group and substituents of said basic functional group, each substituent being a hydrophobic group. If the basic functional group comprises two substituents, the substituents may be the same or different from each other. If the basic functional group comprises three or more substituents, the substituents may be all the same, partially the same, or all different from each other. Optionally, the basic functional group forms a first bond with a first atom of a substituent and a second bond with a second atom of the same substituent such that the specific compound is cyclic.

[0087] A functional group is an atom or group of atoms which has similar chemical properties whenever it is present in different compounds. In particular, a basic functional group designates, according to the invention, a functional group capable of protonation. In other words, the basic functional group comprises one or more electron pairs capable of capturing one or more protons.

[0088] A substituent of the basic functional group means an atom or group of atoms linked by a single, double or triple covalent bond to the basic functional group.

[0089] For example, the basic functional group is a monosubstituted amine group H2N-R1, a di-substituted amine group R1-N(H)-R2 or a tri-substituted amine group R1-N(R2)-R3 where RI, R2 and R3 each denotes a substituent of the amine group. In other words, the specific compound is in this case a primary, secondary or tertiary amine respectively.

[0090] For example, the basic functional group is an anionic group derived from the ionization of an acidic functional group. For example, the basic functional group derives from the ionization of the sulfonic group -SO3H, the carboxyl group - COOH or the hydroxyl group -OH. In other words, the specific compound can be a sulfonate R-SO3, a carboxylate R-COO or an alkoxide R-O where R denotes a substituent of the basic functional group.

[0091] For example, the basic functional group is a hydroxylamine group R1-N(OH)-R2 where R1 and R2 each denote a substituent of the hydroxylamine group. In other words, the specific compound is an organic molecule comprising a single bond between a hydroxyl group and a nitrogen atom.

[0092] For example, the basic functional group is a hydrazine group R1-N(R2)-N(R3)-R4 where R1, R2, R3 and R4 each denote a substituent of the hydrazine group. In other words, the specific compound is an organic molecule comprising a single bond between two nitrogen atoms.

[0093] As previously mentioned, each substituent R, RI, R2, R3, R4 of the basic functional group is a hydrophobic group. A hydrophobic group is an atom or group of atoms that does not comprise a hydrophilic functional group. In other words, the hydrophobic group does not comprise a polar functional group or one that is capable of establishing hydrogen bonds with water. In particular, the hydrophobic group does not comprise functional groups such as the hydroxyl group, the ether group, the amide group, the ester group or the oxo group.

[0094] Preferably, the hydrophobic group is a hydrocarbon group comprising exclusively the hydrogen element and / or the carbon element.

[0095] For example and provided that the specific compound also comprises at least one carbon atom (F at least one carbon atom may be included in the basic functional group or in another substituent), the hydrophobic group may designate a single hydrogen atom connected by a single bond to the basic functional group.

[0096] For example, the hydrophobic group may designate an aliphatic chain, preferably a C1-C6 aliphatic chain, the aliphatic chain being connected to the basic functional group by at least one covalent bond between a carbon atom of the aliphatic chain and an atom of the basic functional group. Optionally, the aliphatic chain is connected to the basic functional group by a first bond between a first atom of the aliphatic chain and the basic functional group and by a second bond between a second atom of said aliphatic chain and the basic functional group, so that the specific compound is cyclic.

[0097] For example, the hydrophobic group may designate an aryl group, the aryl group being linked to the basic functional group by at least one bond covalent between a carbon atom of the aryl group and an atom of the basic functional group.

[0098] For the purposes of the present invention, the term "C1-C6 aliphatic chain" means a linear or branched hydrocarbon chain, optionally forming one or more cycles, and comprising in particular 1 to 6 carbon atoms. According to the invention, an aliphatic chain covers linear or branched alkyl, alkenyl or alkynyl groups, optionally comprising one or more cycles. According to the invention, the aliphatic chain may be optionally substituted by one or more, for example 1 to 3, substituents chosen from the group consisting of C1-C6 alkyl or aryl groups.

[0099] For the purposes of the present invention, the term “alkyl” group means a saturated hydrocarbon chain. For example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl or hexyl groups may be mentioned.

[0100] For the purposes of the present invention, the term “alkenyl” group means a hydrocarbon chain comprising at least one double bond. By way of example, mention may be made of ethenyl, propenyl, butenyl, pentenyl or hexenyl groups.

[0101] For the purposes of the present invention, the term “alkynyl” group means a hydrocarbon chain comprising at least one triple bond. By way of example, mention may be made of ethynyl, propynyl, butynyl, pentynyl or hexynyl groups.

[0102] For the purposes of the present invention, the term “aryl” group means an aromatic hydrocarbon group, preferably comprising from 6 to 10 carbon atoms, and comprising one or more fused rings, such as, for example, a phenyl or naphthyl group. According to the invention, the aryl group may optionally be substituted by one or more, for example 1 to 3, substituents chosen from the group consisting of C1-C6 alkyl or aryl groups.

[0103] Preferably, the surface concentration of the specific compound on each hydrophilic silicon oxide bonding surface on which the deposition of the specific compound has been carried out is, prior to bringing the first hydrophilic silicon oxide bonding surface into contact with the second hydrophilic silicon oxide bonding surface, between 1011 molecules / cm2 and 1015 molecules / cm2. A concentration of 1015 molecules / cm2 corresponds to a monolayer and therefore to a saturation of the hydrophilic bonding surface. Below 1011 molecules / cm2 the quantity of molecules becomes difficult to detect, and the catalytic effect is not effective enough.

[0104] The presence of the specific compound and the surface concentration of said specific compound can be characterized by spectroscopic techniques such as X-ray fluorescence, Raman or infrared spectroscopy, or mass spectroscopy assay.

[0105] The specific compound may advantageously comprise between 1 and 3 carbon atoms, even more advantageously between 1 and 2 carbon atoms. Alternatively or additionally, the specific compound may preferentially have a molecular mass of less than 200 g / mol, even more preferentially less than 100 g / mol. The fewer carbon atoms the specific compound comprises, the less risk there is for said specific compound blocked at the bonding interface to induce failures of the components manufactured in the assembly comprising the first substrate and the second substrate. By the same token, the use in a clean room of a specific compound comprising fewer carbon atoms is less risky. In other words, contamination by said specific compound would have fewer harmful consequences on the rest of the manufacturing chain or on the other manufacturing chains.

[0106] For example, the specific compound is a primary, secondary or tertiary aliphatic amine, saturated or unsaturated, cyclic or not, preferably chosen from methylamine CH3NH2, dimethylamine (CH3)2NH, trimethylamine (CH3)3N and piperidine (CH2)5NH. Amines have the advantage of being compounds that are both basic and nucleophilic. In other words, amines can act according to the two mechanisms previously mentioned: either as bases to generate the catalytic hydroxyl ions, or as nucleophiles directly involved in the condensation reactions.

[0107] For example again, the specific compound is an organic ion, preferably an aliphatic carboxylate, even more preferably an aliphatic carboxylate chosen from the methanoate ion HCOO and the ethanoate ion CH3COO. Such compounds have the advantage of being very common, inexpensive and not very dangerous. As previously mentioned, the counterion of the organic ion is preferably chosen from ammonium NH4+, nitrosonium NO+ and nitronium NO2+. These ions are advantageously neither alkali nor alkaline earth and therefore have less contaminating effect than alkali or alkaline earth for microelectronic components.

[0108] Provision of the specific compound in liquid form

[0109] According to a particular embodiment, the deposition of the specific compound comprises the deposition of a liquid comprising the specific compound.

[0110] For example, the liquid comprising the specific compound is a solution resulting from the dissolution of the specific compound in a solvent. The concentration of specific compound in said solution is preferably between 107 mol / L and 10 1 mol / L, even more preferably between 106 mol / L and 103 mol / L. In such a concentration range, the specific compound remains sufficiently soluble, so that the formation of crystals upon evaporation is avoided, while being concentrated enough to bring enough ions to the interface to accelerate the reaction. The solvent is preferably water or a mixture of water and isopropyl alcohol (IPA). IPA is used to improve the plate drying process by modifying the surface tension of the solution.

[0111] The deposition of the liquid comprising the specific compound can be carried out for example by coating, by spraying or by spin-coating (better known to those skilled in the art under the English term “spin-coating”).

[0112] Spraying means the projection of droplets of solutions onto the surface.

[0113] Coating means the dipping of the plates into the solution followed by their removal.

[0114] Preferably, the deposition of the liquid comprising the specific compound is carried out using a spinner. In other words, the deposition of the liquid comprising the specific compound comprises rotating the first hydrophilic silicon oxide bonding surface and depositing a volume of the liquid comprising the specific compound in the center of the rotating first hydrophilic silicon oxide bonding surface, for example using a pipette, the rotation of the first hydrophilic silicon oxide bonding surface making it possible to spread said volume of the liquid comprising the specific compound over the entire first hydrophilic silicon oxide bonding surface.

[0115] The volume of the liquid comprising the specific compound is preferably between 1 cm3 and 100 cm3 for a first substrate with a diameter of 300 mm, while the rotation speed of the first hydrophilic silicon oxide bonding surface during the deposition of said volume is preferably between 100 rpm and 3000 rpm.

[0116] Following the deposition of the volume of liquid comprising the specific compound, the first hydrophilic silicon oxide bonding surface is then kept rotating until the volume of liquid comprising the specific compound is ejected and evaporated.

[0117] Preferably, the first hydrophilic silicon oxide bonding surface is kept rotating at a rotation speed of between 100 rpm and 3000 rpm for a duration of between 1 s and 1 min.

[0118] The deposition of the liquid comprising the specific compound on the spinner is very advantageous insofar as it can be implemented in machines conventionally used for bonding substrates in the microelectronics industry. Indeed, said machines already integrate, for the purposes of cleaning and preparing surfaces for their bonding, the equipment which allows the deposition of the volume of liquid comprising the specific compound and the spreading of said volume as previously described. The person skilled in the art therefore does not need to invest in new equipment to implement the invention according to this embodiment.

[0119] Maintaining rotation of the first hydrophilic silicon oxide bonding surface until ejection and evaporation of the volume of liquid comprising the specific compound makes it possible to dry the first hydrophilic silicon oxide bonding surface, while retaining a sufficient quantity of specific compound on the first hydrophilic silicon oxide bonding surface.

[0120] The choice of rotation speed makes it possible, to a certain extent, to modulate the quantity of specific compound remaining on the surface at the time of bonding by modulating the portion of the volume of liquid comprising the specific compound which is ejected relative to the portion of said volume which is evaporated. If the rotation speed is greater than 3000 rpm, too large a portion of the volume of liquid comprising the specific compound is ejected so that not enough specific compound remains on the surface. Conversely, if the speed is less than 100 rpm, too large a portion of the volume of liquid comprising the specific compound evaporates, so that there is too much specific compound on the surface, which could create defects formed by solid particles (crystals, solid residues).

[0121] Furthermore, said amount of specific compound retained on the surface can be adjusted using different parameters, such as the concentration of specific compound of the liquid comprising the specific compound and the pH of said liquid which influences the surface charge of the oxide.

[0122] According to a particular embodiment of the deposition of the specific compound in liquid form, the deposition of the liquid comprising the specific compound may be preceded by an activation of the hydrophilic silicon oxide bonding surface using a plasma. Indeed, the activation of a silicon oxide bonding surface by plasma is known to those skilled in the art to have a beneficial effect on the bonding energy: the plasma in fact makes it possible to break numerous bonds, in particular Si-O-Si bonds and to generate highly reactive species. Upon exposure of the plasma-activated surface to water or a humid atmosphere, said reactive species will react with the water to form new surface Si-OH silanols. Thus, the plasma activation ultimately makes it possible to increase the number of surface silanol groups which will then be able to react in the condensation reactions when the substrates are brought into contact for bonding.The inventors have demonstrated a beneficial effect of the combination of plasma activation and deposition of the specific compound in liquid form since such a combination, any parameter . otherwise unchanged, allows to increase the bonding energy compared to simple plasma activation or to the sole deposition of the specific compound in liquid form. The inventors attribute this beneficial effect of the combination between plasma and specific compound to the formation of an induced "sponge" surface layer which allows to store a greater quantity of water and specific compound.

[0123] Plasma is for example a plasma formed from a gas such as dioxygen, dinitrogen, helium or argon.

[0124] Each hydrophilic silicon oxide bonding surface on which it is desired to deposit the specific compound can be exposed to said plasma for a period of between 1 s and 1 min.

[0125] Supply in gaseous form

[0126] Alternatively, deposition of the specific compound may comprise exposure to a gas comprising said specific compound.

[0127] The gas comprising the specific compound may for example be chosen from atmospheric air (if the specific compound is volatile), rare gases, hydrogen, helium or possible mixtures including water vapor (for example the 40% humid atmosphere of a clean room). This choice may be dictated for example by the desire to reduce the bonding defects formed at the time of bonding.

[0128] The molar fraction of specific compound in the gas (or the partial pressure of specific compound) is for example between 105 and 102 (i.e. 10 to 10000 ppm).

[0129] Each hydrophilic silicon oxide bonding surface on which it is desired to deposit the specific compound is exposed to said gas for a period of between a few seconds and a few minutes, preferably a period of between 10 s and 10 min.

[0130] The temperature of the gas is very advantageously between -10°C and 50°C. Indeed, the temperature of the gas makes it possible to control the quantity of specific compound which is adsorbed on the surface. A temperature above 50°C would lead to insufficient deposition of specific compound.

[0131] According to a particular embodiment of the deposition of the specific compound in gaseous form, the exposure of the hydrophilic silicon oxide bonding surface to the gas comprising the specific compound may be preceded by an activation of the hydrophilic silicon oxide bonding surface using a plasma. Such plasma activation may be implemented as previously described for the supply in liquid form, and makes it possible to increase the bonding energy compared to simple plasma activation or to the sole deposition of the specific compound in gaseous form.

[0132] Contacting the first hydrophilic silicon oxide bonding surface and the second hydrophilic silicon oxide bonding surface

[0133] The contacting between the first hydrophilic silicon oxide bonding surface and the second hydrophilic silicon oxide bonding surface is carried out so that the specific compound has not been removed or completely removed between the step of depositing said specific compound and the contacting step. In other words, for each hydrophilic silicon oxide bonding surface on which the specific compound has been deposited, the direct bonding method according to the invention does not comprise steps of cleaning and rinsing said surface between the deposition of the specific compound and the contacting of the substrates. In particular, the step of rinsing with ultrapure deionized water conventionally used to remove particles and surface contamination before bonding is limited or very preferably eliminated, so as not to remove the specific compound on the surface.

[0134] The contact between the first hydrophilic silicon oxide bonding surface and the second hydrophilic silicon oxide bonding surface is preferably carried out at a temperature between -10°C and 100°C, even more preferably at room temperature (i.e. typically between 18°C and 25°C) so as to control the quantities of water and molecules present on the surfaces.

[0135] The contacting may comprise the application of localized pressure, so as to generate a point of contact between the first hydrophilic silicon oxide bonding surface and the second hydrophilic silicon oxide bonding surface: the bonding wave propagates from the point of contact in a few seconds over the entire bonding interface. Alternatively, the contacting may be done without applying pressure. According to this embodiment, the first substrate and the second substrate may remain against each other for a few tens of seconds until the evacuation of the air between the two substrates causes the appearance of a point of contact and the start of the propagation of the bonding wave. The vapor pressure during the contacting of the first hydrophilic silicon oxide bonding surface and the second hydrophilic silicon oxide bonding surface is preferably between 1 Pa and 105 Pa.

[0136] The deposition of the specific compound on at least one of the two hydrophilic silicon oxide bonding surfaces followed by bringing the two hydrophilic silicon oxide bonding surfaces into contact and maintaining the assembly resulting from said contact at room temperature (after the end of the propagation of the bonding melt), makes it possible to achieve bonding energies of the order of 1 J / m2 to 2 J / m2 after a few dozen hours. By comparison, such a bonding energy cannot be achieved without deposition of the specific compound and all the other experimental parameters remaining unchanged moreover only after several days, so that it is never actually reached because other phenomena come to disturb the process. Thus, the deposition of the specific compound makes it possible to increase the bonding kinetics and to achieve higher bonding energies.

[0137] To further increase said bonding kinetics, the direct bonding method may further comprise a subsequent step of consolidation annealing of the assembly obtained after bringing the first substrate and the second substrate into contact.

[0138] The consolidation annealing may consist of the application of a temperature preferably between 50°C and 250°C, even more preferably between 50°C and 100°C, for a duration preferably between 15 min and 4 h, even more preferably between 15 min and 2 h. The temperature of the consolidation annealing is chosen according to the nature of the first substrate and the second substrate and their capacity or not to withstand a given temperature.

[0139] For example, annealing at 100°C the assembly resulting from the deposition of the specific compound and the contact between the first substrate and the second substrate makes it possible to achieve the expected bonding energy (of the order of 1 J / m2 or 2 J / m2) after only one hour of implementation of said annealing. Consolidation annealing therefore makes it possible to significantly increase the kinetics of the condensation reactions. Furthermore, it should be noted that such an annealing temperature remains sufficiently low (less than 200°C) so as not to induce the formation of gases and bubbles causing bonding defects at the bonding interface, nor significant thermal stress (which could appear at high temperature if the substrates to be bonded have sufficiently different thermal expansion coefficients), and also remains bearable for substrates having weakened zones and / or electronic component elements.The same bonding process without deposition of the specific compound does not allow to achieve with such consolidation annealing a bonding energy greater than 1 J / m2.

[0140] Method of transferring a layer onto a support substrate

[0141] The invention extends to a method of transferring a layer onto a support substrate.

[0142] The method of transferring a layer onto a support substrate comprises a step of providing a donor substrate comprising a first surface made of hydrophilic silicon oxide and a support substrate comprising a second surface made of hydrophilic silicon oxide.

[0143] The donor substrate and the support substrate are such as the first substrate and the second substrate previously described.

[0144] For example, the donor substrate and / or the support substrate comprise silicon Si, germanium Ge, indium phosphide InP, gallium arsenide AsGa, alumina A12O3, silicon oxide SiO2, silicon nitride Si3N4, silicon carbide SiC, gallium nitride GaN, copper, titanium, nickel, LNO and / or LTO.

[0145] The donor substrate and / or the support substrate may be multilayer structures comprising at least two layers. For example, the donor substrate is a substrate referred to as a pseudo-donor substrate comprising a first layer of LTO and a second layer of silicon. For example, the support substrate is silicon.

[0146] Further, the donor substrate and / or the support substrate may comprise one or more electronic component elements. For example, the donor substrate and / or the support substrate comprise copper connections insulated by silicon oxide portions.

[0147] Thus, the step of providing a donor substrate comprising a first surface of hydrophilic silicon oxide and a support substrate comprising a second surface of hydrophilic silicon oxide may comprise one or more sub-steps of arranging layers and forming electronic component elements as previously described.

[0148] As previously mentioned, the donor substrate and the support substrate respectively comprise a first hydrophilic silicon oxide surface and a second hydrophilic silicon oxide surface. The first hydrophilic surface and / or the second hydrophilic surface are typically native, thermal, chemical or deposited oxide surfaces as previously described. Thus, the step of providing a donor substrate comprising a first hydrophilic silicon oxide surface and a support substrate comprising a second hydrophilic silicon oxide surface may comprise forming said native, thermal, chemical or deposited silicon oxide surfaces according to any of the previously described embodiments.

[0149] The first hydrophilic silicon oxide surface and the second hydrophilic silicon oxide surface may be of the same nature (native, thermal, chemical or deposited). Alternatively, the first hydrophilic silicon oxide surface and the second hydrophilic silicon oxide surface may be of different natures.

[0150] The method for transferring a layer onto a support further comprises a step of forming a weakening zone within the donor substrate so as to delimit a layer to be transferred between the first hydrophilic surface and the weakening zone. According to a preferred embodiment, the weakening zone is formed by implanting atomic species into the donor substrate, the implantation being carried out through the first hydrophilic surface. The atomic species are implanted at a determined depth, this depth fixing the thickness of the layer to be transferred. The implanted atomic species are preferably hydrogen and / or helium.

[0151] Subsequently, the method of transferring a layer onto a support substrate further comprises bonding between the donor substrate and the support substrate, the first hydrophilic silicon oxide surface and the second hydrophilic silicon oxide surface being at the bonding interface and the bonding between the donor substrate and the support substrate being carried out by a direct bonding method according to any of the previously described embodiments. The provision of the specific compound may be carried out on the first hydrophilic silicon oxide surface of the donor substrate, on the second hydrophilic silicon oxide surface of the support substrate or both on the first hydrophilic silicon oxide surface of the donor substrate and on the second hydrophilic silicon oxide surface of the support substrate.

[0152] The layer transfer method finally comprises detaching the donor substrate along the weakening zone so as to transfer the layer to be transferred onto the support substrate. The detachment along the weakening zone can be triggered by a mechanical action and / or a supply of thermal energy. Preferably, the step of detaching along the weakening zone and the consolidation annealing are combined by the application of a temperature ramp, with or without temperature steps, to stabilize the bonding interface.

[0153] Assembly comprising a first substrate and a second substrate

[0154] The invention finally relates to an assembly comprising a first substrate and a second substrate, the first substrate being covered by a first surface of hydrophilic silicon oxide and the second substrate being covered by a second surface of hydrophilic silicon oxide, the first surface of hydrophilic silicon oxide being bonded with the second surface of hydrophilic silicon oxide, a specific compound being arranged between the first bonding surface of hydrophilic silicon oxide and the second bonding surface of hydrophilic silicon oxide, the specific compound being an organic compound consisting of a basic functional group and substituents of said basic functional group, each substituent being a hydrophobic group.

[0155] The first substrate, the second substrate, the first hydrophilic silicon oxide bonding surface and the second hydrophilic silicon oxide bonding surface are as previously described.

[0156] According to a particular embodiment of the assembly, the concentration of specific compound at the bonding interface between the first substrate and the second substrate is preferably between 1011 molecules / cm2 and 1015 molecules / cm2.

[0157] Preferably, the specific compound comprises between 1 and 3 carbon atoms, preferably between 1 and 2 carbon atoms, and / or in which the specific compound has a molecular mass of less than 200 g / mol, preferably less than 100 g / mol.

[0158] For example, the specific compound is a primary, secondary or tertiary aliphatic amine, saturated or unsaturated, preferably chosen from methylamine CH3 NH2, dimethylamine (CH3)2NH, trimethylamine (CH3)3N and piperidine (CH2)5 NH.

[0159] For example again, the specific compound is an organic ion, preferably an aliphatic carboxylate, more preferably still an aliphatic carboxylate chosen from the methanoate ion HCOO and the ethanoate ion CH3COO and in which the counter-ion of the organic ion is chosen from ammonium NH4+, nitrosonium NO+ and nitronium NO2+.

[0160] The presence of the specific compound in the assembly at the bonding interface and its surface concentration can be characterized by characterization techniques well known to those skilled in the art, such as infrared absorption spectroscopy, Raman spectroscopy, X-ray fluorescence techniques if the specific compound comprises heavy elements or mass spectroscopy techniques by opening and then degassing the surfaces (technique known to those skilled in the art under the acronym WOS from the English term "Wafer Outgassing Spectroscopy"). Heavy elements are understood to mean elements with an atomic mass greater than or equal to that of sodium. Example

[0161] 10 mL of a solution of a compound having an amine group (glycine (also called aminoacetic acid) ac-NH2, respectively ethanolamine C2H5O-NH2) at a concentration of 10 4 g / cm3 is dispensed onto a first silicon substrate 200 mm in diameter having a first bonding surface made of hydrophilic silicon oxide of thermal oxide type 100 nm thick. The system is rotated at a speed of 2000 rpm until the thickness of the film formed by the deposited solution is uniform. This uniformization can be classically observed by observing colored Newton fringes, which scroll as the film thins under the combined effect of centrifugal flow and evaporation, until they disappear when the film thickness is below half a wavelength of visible radiation (i.e. typically less than 200 nm). The substrate is then kept rotating for about ten seconds. additional, so as to evacuate the excess aqueous solution of amine compounds and to dry the first hydrophilic silicon oxide bonding surface.

[0162] A second silicon substrate of 200 mm diameter is provided having a second bonding surface made of hydrophilic silicon oxide of thermal oxide type of 100 nm thickness and the same treatment as previously described for the first silicon substrate is applied.

[0163] The first hydrophilic silicon oxide bonding surface is then brought into contact with the second hydrophilic silicon oxide bonding surface at room temperature so as to obtain adhesion by direct bonding between the first substrate and the second substrate. A consolidation annealing of the newly formed structure comprising the first substrate and the second substrate is carried out at a temperature between 100°C and 500°C for a period of 2 hours.

[0164] Finally, the bonding energies obtained are measured as a function of the consolidation annealing temperature and the concentration of the solution of amine compounds deposited by the conventional blade insertion method, known as the "Maszara method", in an anhydrous atmosphere. The results are represented in [Fig.2] in triangle symbols (glycine solution with a concentration of 10 4 g / cm3) and square symbols (ethanolamine solution with a concentration of 10 4 g / cm3).

[0165] Comparative example

[0166] Exactly the same operation as in the example is carried out by replacing the solution of amino compounds with deionized water (DIW). The results are represented in open circle symbols in [Fig.2].

[0167] It is observed that stronger bonding energies are obtained from low annealing temperatures (100 to 200°C) with compounds comprising an amine group compared to the reference exposed to deionized water.

Claims

Claims

1. A method of direct bonding between two substrates comprising the following steps: (a) providing a first substrate and a second substrate respectively comprising a first bonding surface made of hydrophilic silicon oxide and a second bonding surface made of hydrophilic silicon oxide, (b) depositing a specific compound on the first bonding surface made of hydrophilic silicon oxide, the specific compound being an organic compound consisting of a basic functional group and substituents of said basic functional group, each substituent being a hydrophobic group, (c) bringing the first bonding surface made of hydrophilic silicon oxide on which the specific compound has been deposited into contact with the second bonding surface made of hydrophilic silicon oxide, so as to obtain adhesion of the first substrate with the second substrate.

2. The method of claim 1, further comprising depositing the specific compound on the second hydrophilic silicon oxide bonding surface, the adhesion of the first substrate with the second substrate being obtained by bringing into contact the first hydrophilic silicon oxide bonding surface and said second hydrophilic silicon oxide bonding surface on which the specific compound has been previously deposited.

3. Method according to one of claims 1 or 2, in which the surface concentration of the specific compound on the first hydrophilic bonding surface prior to bringing the first hydrophilic bonding surface on which said specific compound has been deposited into contact with the second hydrophilic bonding surface is between 1011 molecules / cm2 and 1015 molecules / cm2

4. cm . Method according to one of claims 1 to 3, in which the specific compound comprises between 1 and 3 carbon atoms, preferably between 1 and 2 carbon atoms, and / or in which the specific compound has a molecular mass of less than 200 g / mol, preferably less than 100 g / mol.

5. Method according to one of claims 1 to 4, in which the specific compound is a primary, secondary or tertiary aliphatic amine, saturated or unsaturated, cyclic or not, preferentially chosen from methylamine CH3NH2, dimethylamine (CH3)2NH, trimethylamine (CH3)3N, and piperidine (CH2)5NH.

6. Method according to one of claims 1 to 4, in which the specific compound is an organic ion, preferably an aliphatic carboxylate, more preferably still an aliphatic carboxylate chosen from the methanoate ion HCOO and the ethanoate ion CH3COO and in which the counter-ion of the organic ion is chosen from ammonium NH4+, nitrosonium NO+ and nitronium NO2+.

7. The method of one of claims 1 to 6, wherein the deposition of the specific compound on the first hydrophilic silicon oxide bonding surface comprises the deposition on the first hydrophilic silicon oxide bonding surface of a liquid comprising the specific compound.

8. The method of claim 7, wherein the deposition on the first hydrophilic silicon oxide bonding surface of the liquid comprising the specific compound comprises: - depositing a volume of the liquid comprising the specific compound in the center of the first hydrophilic silicon oxide bonding surface, - spreading said volume of the liquid comprising the specific compound by rotation of the first hydrophilic silicon oxide bonding surface, said first hydrophilic silicon oxide bonding surface being kept rotating until ejection and evaporation of the volume of liquid comprising the specific compound.

9. The method of claim 8, further comprising a step of exposing the first hydrophilic silicon oxide bonding surface to a plasma prior to depositing the volume of liquid comprising the specific compound in the center of the first hydrophilic silicon oxide bonding surface.

10. Method according to one of claims 7 to 9, in which the liquid comprising the specific compound is obtained by dissolving the specific compound in a solvent, preferably in water or in a mixture of water and isopropyl alcohol (IPA), the concentration of the specific compound in the liquid being between 107 mol / L and 10 1 mol / L.

11. The method of one of claims 1 to 6, wherein depositing the specific compound on the first hydrophilic silicon oxide bonding surface comprises exposing said first hydrophilic silicon oxide bonding surface to a gas comprising the specific compound.

12. Method according to one of claims 1 to 11, wherein the first substrate and / or the second substrate are silicon substrates.

13. Method according to one of claims 1 to 12, in which the first hydrophilic silicon oxide bonding surface and / or the second hydrophilic silicon oxide bonding surface are made of deposited oxide, chemical oxide, thermal oxide and / or native oxide.

14. Method according to one of claims 1 to 13, wherein the contacting of the first hydrophilic silicon oxide bonding surface on which the specific compound has been deposited and the second hydrophilic silicon oxide bonding surface is carried out at a temperature between 0°C and 100°C.

15. Method according to one of claims 1 to 14, further comprising a step d) of consolidation annealing carried out after step c) of bringing into contact the first bonding surface made of hydrophilic silicon oxide on which the specific compound has been deposited and the second bonding surface made of hydrophilic silicon oxide, the consolidation annealing being preferably carried out at a temperature below 100°C for a duration of between 1 minute and 5 hours.

16. Method according to one of claims 1 to 15, in which the first substrate is made of a first material and the second substrate is made of a second material, the difference in coefficient of thermal expansion between the first material and the second material being greater than or equal to 10% in relative value.

17. Method according to one of claims 1 to 15, in which the first substrate is a multilayer structure comprising a first layer of a first material and a second layer of a second material, the difference in coefficient of expansion thermal difference between the first material and the second material being greater than or equal to 10% in relative value.

18. A method according to one of claims 1 to 17, wherein the first substrate comprises electronic component elements.

19. Method according to one of claims 1 to 18, in which the first substrate comprises a weakening zone formed by implantation of atomic or ionic species.

20. A method of transferring a layer onto a support substrate, said method comprising the following steps: a) providing a donor substrate comprising a first surface of hydrophilic silicon oxide and a support substrate comprising a second surface of hydrophilic silicon oxide, b) forming a weakening zone within the donor substrate so as to delimit a layer to be transferred between the first surface of hydrophilic silicon oxide and the weakening zone, c) bonding between the donor substrate and the support substrate, the first surface of hydrophilic silicon oxide and the second surface of hydrophilic silicon oxide being at the bonding interface and the bonding between the donor substrate and the support substrate being carried out by a bonding method according to any one of claims 1 to 18,d) detaching the donor substrate along the weakening zone so as to transfer the layer to be transferred onto the support substrate.,

21. An assembly comprising a first substrate and a second substrate, the first substrate being covered by a first hydrophilic silicon oxide surface and the second substrate being covered by a second hydrophilic silicon oxide surface, the first hydrophilic silicon oxide surface being bonded with the second hydrophilic silicon oxide surface, a specific compound being disposed between the first hydrophilic silicon oxide surface and the second hydrophilic silicon oxide surface, the specific compound being an organic compound consisting of a basic functional group and substituents of said basic functional group, each substituent being a hydrophobic group.

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