METHOD FOR DIRECT BONDING USING A BASIC MOLECULE

Description

[0001] The present invention relates to the field of direct bonding. It relates in particular to a method for manufacturing a multilayer structure by direct bonding.

[0002] Direct bonding is a technique now well known and used for industrial applications such as the manufacturing of SOI by SOITEC or STMicroelectronics for the production of imagers for example. As understood in this document, direct bonding is a spontaneous bonding between two surfaces without adding material to the interface between the bonded surfaces, and in particular without a thick layer of liquid. It is nevertheless possible to have some monolayers of water adsorbed on the surfaces, which represents between 0.25 nm and 1.25 nm of thickness, so that these surfaces are macroscopically dry.

[0003] Direct bonding is typically performed at room temperature and pressure, but this is not a requirement.

[0004] An important characteristic of direct bonding is its adhesion energy, i.e. the energy available to achieve spontaneous bonding. This is the energy that allows the two surfaces to be deformed to bring them into contact at the atomic scale so that the Van der Waals forces can be implemented. This adhesion energy partly governs the duration of the bonding wave propagation; for example, the bonding wave typically propagates in 9 seconds for the direct bonding of two 200 mm silicon substrates. For example, for two hydrophilic silicon or silicon oxide surfaces, the adhesion energy typically ranges from 30 to 100 mJ / m 2 < .

[0005] Another important characteristic of direct bonding is its adhesion energy or otherwise called its bonding energy. This is the energy that must be used to separate the two bonded surfaces. In the context of bonding two silicon substrates covered with thermal oxide of around 145 nm, this adhesion typically varies between 0.14 J / m 2 < and 6 J / m 2 < .

[0006] To achieve spontaneous bonding, surfaces are generally cleaned of organic and particulate contamination, which is very detrimental to direct bonding. For example, cleaning is carried out beforehand on the surfaces to be bonded with a Caro acid-based solution obtained with a mixture of 96% sulfuric acid and 30% hydrogen peroxide (3:1) at 180°C and SC1 (mixture of 30% ammonia, 30% hydrogen peroxide and deionized water (1:1:5)) at 70°C. Alternatively, other highly oxidizing cleaning solutions can be used, such as aqueous solutions containing ozone or with a treatment using exposure to UV light in the presence of ozone gas.The adhesion energy of a SiO 2 -SiO 2 bond (two silicon substrates covered with approximately 145 nm of thermal oxide for example), in a clean room environment, with chemical cleaning based on Caro and SC1 at 70°C, is approximately 140 mJ / m 2 < just after bonding, without heat treatment.

[0007] The bonding energy also changes depending on the heat treatment applied after bonding at room temperature. The adhesion energy increases depending on the temperature of the heat treatments. For example, the SiO 2 -SiO 2 bonding energy increases slowly to reach, depending on the surface treatments, 3J / m 2 < at 500°C and then stagnates up to 800°C.

[0008] To further increase the bonding energy, another lever is to carry out a plasma treatment prior to contact. With a nitrogen plasma (N 2 ), for oxide-oxide bonding, the bonding energy increases rapidly to around 5 J / m 2 < for a treatment temperature of 300°C.

[0009] However, the use of plasma may be incompatible with certain substrates and / or its use increases the time and / or costs of the processes, making them more difficult to industrialize. Plasma treatment also modifies the surface over a thickness of a few nanometers (between 1 and 10 nm). This modification can disrupt future devices. For example, with a silicon wafer, the plasma creates an oxide layer that is difficult to control in terms of thickness and quality. With a silicon oxide surface, certain plasmas such as N2 plasma create interfacial charge problems that can disrupt the electrical operation of future devices.

[0010] It has also been shown in patent FR1912269 that the exposure of the Si and / or SiO2 surfaces to a specific molecule comprising a hydrophilic functional group and a basic functional group, before bringing the two surfaces into contact during the direct bonding process, provided a significant increase in the adhesion energy of the bonded assembly after heat treatment in the range 100-500°C. The exposure of the surface(s) before bonding can be done by liquid or gaseous means.Other relevant prior art is US 2006 / 273068 A1, which describes a method for directly bonding two substrates, comprising, before the direct bonding step, a step of treating an oxidized surface of the first wafer with a NH4OH / H2O2 solution to increase the bond strength; and US 2006 / 141746 A1, which describes a method for directly bonding two substrates comprising, before the direct bonding step, a step of activating at least one of the bonding surfaces by applying an activating solution comprising a solution of ammonia (NH4OH) in water.

[0011] One of the aims of the present invention is to propose a direct bonding method that is simple to implement and makes it possible to overcome the aforementioned drawbacks. To this end, the present invention proposes a method for manufacturing a multilayer structure by direct bonding between a first substrate and a second substrate, the method comprising the steps of: a) providing a first substrate and a second substrate respectively comprising a first bonding surface and a second bonding surface, b) bringing the first bonding surface and the second bonding surface into contact so as to create a direct bonding interface between the first substrate and the second substrate, c) providing at least the direct bonding interface in a basic environment, and d) applying a heat treatment at a temperature between 20°C and 1000°C, in particular between 100°C and 500°C, for example between 150 and 250°C, so as to obtain the multilayer structure.

[0012] This direct bonding process thus carried out makes it possible to obtain a multilayer structure having a bonding energy greater than that of a multilayer structure obtained by a direct bonding process without step c) of treatment in a basic environment. A high bonding energy is then obtained at low temperature, that is to say at temperatures below 1000°C, preferably less than or equal to 500°C and more preferably a temperature of 200°C.

[0013] These bonding temperatures are compatible with many applications and / or with many substrates, whose nature and / or presence of electronic and / or optoelectronic components require low thermal budgets. In addition, the process is applicable to many materials and is inexpensive. The process leads to multilayer structures with good mechanical strength after bonding, compatible with subsequent processes such as Smart Cut™ and / or any process generating mechanical stresses on the assembly, such as mechanical thinning. In addition, this process does not affect the adhesion energy since the use of a basic environment is only carried out after the surfaces have been brought into direct contact. For example, the bonding wave always propagates in 9 seconds for silicon substrates of approximately 200 mm.

[0014] Post-bonding heat treatment is also known to those skilled in the art as 'bonding annealing'.

[0015] According to one possibility, the heat treatment according to step d) is carried out by a temperature increase, from ambient temperature to a final temperature, the temperature increase being carried out with a slope of 0.1 to 10°C / min for example and more specifically of 0.5 to 5°C / min to then reach a plateau lasting a few hours, for example 2 hours, at a final temperature between 200 and 300°C.

[0016] According to one possibility, step c) of arranging the direct bonding interface in a basic environment is carried out for a duration of approximately 1 h to 80 days. The duration of this step increases with the diameter of the first and second substrates. It is indeed necessary that the basic molecules of the environment of step c) have time to move over the entire direct bonding interface to obtain a homogeneous and uniform bonding energy. Also, the larger the diameter of the multilayer structure, the longer the duration of step c).

[0017] According to one arrangement, the first bonding surface and / or the second bonding surface is formed at least in part by a hydrophilic film of a material selected from a native oxide, a thermal or deposited silicon oxide, a silicon nitride, a copper oxide and a combination of these materials.

[0018] Typically, the hydrophilic copper oxide film is a hybrid film composed of copper pads separated by SiO2. The copper pads are almost instantly covered in air with native copper oxide.

[0019] When the hydrophilic film is made of oxide, it is for example formed by a deposited oxide, a thin oxide film obtained by heat treatment (also called thermal oxide) and / or a thin oxide film obtained by chemical treatment (also called native oxide or chemical oxide).

[0020] According to a variant, the first and / or second substrate are made of oxidized material(s), such as alumina, so that the first bonding surface and / or the second bonding surface are formed by the material of the first and / or second substrate respectively because it is an intrinsically hydrophilic material. This does not prevent the presence of a hydrophilic film in addition.

[0021] According to a particular example, the first bonding surface is hydrophobic (for example made of hydrophobic silicon obtained by passivation of the silicon surface and grafting of hydrogen onto the silicon) and the second bonding surface is hydrophilic. The second bonding surface is formed at least in part by a hydrophilic film chosen from a native oxide (of silicon, AsGa, InP, etc. depending on the material of the second substrate), a thermal oxide (of silicon), a deposited oxide, a silicon nitride, a copper oxide, and a combination of these compounds, or the second bonding surface is constituted by the material of the second substrate, which is an oxide and therefore hydrophilic. Bringing the second hydrophilic surface into contact with the hydrophobic surface changes the initial hydrophobic character of the latter into a hydrophilic character, which allows direct bonding.

[0022] Specifically, the first bonding surface and the second bonding surface are completely flat. In other words, the first and second bonding surfaces are free of recesses or patterns forming plateaus on a microscopic scale. The first bonding surface and / or the second bonding surface have a roughness of the order of angstrom RMS, typically less than 5 angstrom RMS.

[0023] The first bonding surface and / or the second bonding surface has a peak-valley roughness of less than 5 nm.

[0024] According to one possibility, the first substrate and the second substrate have a diameter strictly greater than 2.5 cm.

[0025] Advantageously, step a) further comprises drying the first bonding surface and the second bonding surface before carrying out step b) of bringing them into contact. After drying, the first bonding surface and the second bonding surface each have a face on which resides at most one to five monoatomic layers of H 2 O, so that the first bonding surface and the second bonding surface are dry on a macroscopic scale.

[0026] Concretely, the basic environment is an aqueous basic solution. Therefore, step c) consists of immersing at least the direct bonding interface in said aqueous basic solution. In other words, the multilayer assembly obtained in step b) is totally or partially immersed in the aqueous basic solution to the extent that the direct bonding interface is immersed in said basic solution.

[0027] According to one provision, the aqueous basic solution has a pH strictly greater than 7.5, in particular greater than 8 and for example greater than 9.

[0028] According to one possibility, the aqueous basic solution is formed, by dissolving in deionized water, a basic compound chosen from NaOH, KOH, Na 2 CO 3 , NH 4 OH, an amino alcohol and a mixture of these compounds; the amino alcohol being selected in particular from dimethylaminoethanol (or DMAE, CAS: 108-01-0), N,N-Diethyl-2-aminoethanol (or DEAE, CAS: 100-37-8), monoethanolamine (CAS: 141-43-5), N-methyldiethanolamine (or MDEA, CAS: 105-59-9), aminomethanol (CAS: 3088-27-5), N-methylhydroxylamine (CAS: 593-77-1), diethanolamine (or DEA, CAS: 111-42-2), dimethanolamine (CAS: 7487-32-3), triethanolamine (CAS: 102-71-6), trimethanolamine (CAS: 14002-32-5) and a mixture of these amino alcohols.

[0029] According to one characteristic, the aqueous basic solution has a molar concentration of 10 -7 < mol / l and 5 mol / l, in particular between 10 --6 < mol / l and 1 mol / l and in particular between 0.01 mol / l and 0.5 mol / l in basic compound. A small amount of base is sufficient to ensure strong bonding, which allows for an inexpensive step. Of course, a higher molar concentration is possible but without improvement in the results obtained.

[0030] According to an alternative embodiment, the basic environment is an atmosphere saturated with basic molecules in the vapor phase by evaporation in a hermetic enclosure of a basic mother solution comprising deionized water and a basic compound chosen from N,N-diethylethanolamine, N,N-dimethylethanolamine, 2-aminoethanol, N-methyldiethanolamine, aminomethanol, N-methylhydroxylamine, diethanolamine, dimethanolamine, triethanolamine, trimethanolamine, ethalonamine, diethyl-NN-ethanol, ammonia and a mixture of these compounds.

[0031] According to one possibility, the basic mother solution comprises a molar concentration of between 10 -7< mol / l and 5 mol / l of an amino alcohol dissolved in deionized water. The basic mother solution is placed in a hermetic enclosure for one hour so as to obtain a gaseous environment saturated with gaseous amino alcohol. The multilayer assembly obtained in step b) is then placed in the hermetic enclosure to subject the direct bonding interface to the atmosphere saturated with basic molecules in the vapor phase.

[0032] According to one arrangement, the temperature of the heat treatment applied in step d) is between 20°C and 1000°C, in particular between 100°C and 500°C, in particular between 150°C and 250°C.

[0033] According to one possibility, the first substrate and the second substrate are each formed by a material independently selected from semiconductors, such as Si, Ge, InP, AsGa, SiC, GaN; LNO (acronym for lanthanum nickel oxide LaNiO3), LTO (acronym for lithium titanate Li2TiO3) and their combination.

[0034] The first substrate and the second may be of the same or different nature.

[0035] According to a particular embodiment, the first substrate and the second substrate provided in step a) each comprise a silicon substrate having a diameter of between 25 mm and 300 mm, for example between 100 and 300 mm and in particular 200 mm or 300 mm, and the first bonding surface and the second bonding surface are each formed by a silicon oxide film, step c) comprises the arrangement of the direct bonding interface, obtained in step b), in the basic environment for a period of between 21 and 40 days, in particular 30 days, the basic environment being an aqueous basic solution, formed by dissolving NaOH and having a molar concentration of between 10 -7< mol / l and 0.01 mol.l and in particular a molar concentration of approximately 10 -3< mol / l, and step d) comprises the application of a heat treatment at approximately 300°C, so as to obtain a direct bond between the first substrate and the second substrate having a bonding energy greater than 5J / m 2< .

[0036] The bonding energy is measured for example with the double lever method with imposed displacement in an anhydrous atmosphere as described in the article by F. Fournel, L. Continni, C. Morales, J. Da Fonseca, H. Moriceau, F. Rieutord, A. Barthelemy, and I. Radu, Journal of Applied Physics 111, 104907 (2012).

[0037] According to an alternative embodiment, the first substrate provided in step a) comprises one or more first vignettes originating from the vignetting of the first substrate so as to obtain direct bonding of one or more first vignettes to the second substrate.

[0038] The first bonding surface is delimited by the exposed face of one or more first vignettes.

[0039] According to another variant, the second substrate provided in step a) comprises one or more second vignettes originating from the vignetting of the second substrate so as to obtain direct bonding between one or more first vignettes and one or more second vignettes.

[0040] The second bonding surface is delimited by the exposed face of one or more second vignettes.

[0041] According to other characteristics, the method of manufacturing the multilayer structure of the invention comprises one or more of the following optional characteristics considered alone or in combination: The first substrate and / or the second substrate have a thickness greater than 50 micrometers, preferably greater than 100 micrometers, and for example a thickness of approximately 725 micrometers. The first substrate and / or the second substrate may be layers thick enough to be self-supporting. The first substrate and the second substrate are stacks of at least two layers of material of different nature. The first bonding surface and the second bonding surface respectively of the first and second substrates are each formed at least in part by a hydrophilic film made of a native oxide, a silicon oxide, a silicon nitride, a copper oxide or a combination of these materials. The first bonding surface and / or the second bonding surface respectively of the first and second substrates are each completely formed by a continuous hydrophilic film made of a native oxide, a silicon oxide, a silicon nitride or a copper oxide.Only the first bonding surface or the second bonding surface has a hydrophilic character before contacting. The first substrate and / or the second substrate comprise recesses opening respectively onto the first and / or the second bonding surface. The first bonding surface and the second bonding surface are free of any added material before contacting in step b). The method comprises, before step b) of contacting the bonding surfaces, a step consisting of applying a plasma treatment to the bonding surfaces of the first and second substrates. It is thus possible to significantly reduce the temperature of the thermal budget while maintaining a high bonding energy. The drying of the first bonding surface and the second bonding surface comprises centrifugation of the first and second substrates, in particular at 2000 rpm for 45 s.The drying of the first bonding surface and the second bonding surface comprises drying using the Marangoni effect. The first bonding surface and / or the second bonding surface are cleaned with ozonated water before step b). The first bonding surface and / or the second bonding surface are cleaned by SC1 stripping and / or SC2 treatment before step b). The contacting according to step b) is preferably carried out at room temperature under an atmosphere having a relative humidity of approximately 75% or a lower humidity value or under vacuum (<5.10 -2< mbar) or under an anhydrous atmosphere (<0.5 ppm).The first substrate and the second substrate provided in step a) each comprise a silicon substrate having a diameter of between 50 mm and 300 mm, for example between 100 mm and 200 mm, and the first bonding surface and the second bonding surface are each formed by a silicon oxide film, step c) comprises the arrangement of the direct bonding interface, obtained in step b), in the basic environment for a period of between 1 and 40 days, in particular the basic environment is an aqueous basic solution of NaOH having a molar concentration of between 10 -7< mol / l and 5 mol / l, in particular between 10 -7< mol / l and 10 -2< mol / l and for example 10 -3< mol / l, and step d) comprises the application of a heat treatment at 300°C, so as to obtain a direct bond between the first substrate and the second substrate, the direct bond having a bonding energy greater than 5J / m 2< .The first and second substrates have a diameter of 50 mm and the duration of step c) is between approximately 1 and 2 days. The first and second substrates have a diameter of 100 mm and the duration of step c) is between approximately 4 and 6 days. The first and second substrates have a diameter of 200 mm and the duration of step c) is between approximately 15 and 20 days. Step c) of providing at least the direct bonding interface is carried out in a basic environment having a temperature between room temperature and 100°C at atmospheric pressure and for example between approximately 50°C and 60°C. The first and second substrates have a diameter of 300 mm and the duration of step c) is between approximately 35 and 40 days. Step d) of applying the heat treatment is carried out concomitantly with step c).Step d) of applying the heat treatment is carried out during step c) for a shorter period than that of step c).

[0042] Other aspects, aims and advantages of the present invention will appear more clearly on reading the following description of different variant embodiments thereof, given by way of non-limiting example and with reference to the appended drawings. In the remainder of the description, for the sake of simplification, identical, similar or equivalent elements of the different embodiments bear the same numerical references. The figures do not necessarily respect the scale of all the elements represented so as to improve their readability and in which: There figure 1 represents a schematic view of steps a) and b) of the method according to a first embodiment of the invention. The figure 2 represents a schematic view of step c) of the method according to the first embodiment of the invention. The figure 3 represents a schematic view of step d) of the method according to the first embodiment of the invention. The figure 4 represents a schematic view of steps a) and b) of the method according to a second embodiment of the invention. The figure 5 represents a schematic view of step c) of the method according to the second embodiment of the invention. The figure 6 represents a schematic view of step d) of the method according to the second embodiment of the invention. The figure 7 represents a schematic view of step c) of the method according to an alternative embodiment of the invention.

[0043] As illustrated in figures 1 à 3 , the direct bonding method of the present invention comprises the steps of bringing a first substrate 1 and a second substrate 2 ( figure 1 steps a and b), a step of arrangement in a basic environment, namely a basic aqueous solution 8 whose pH is strictly greater than 7.5 ( figure 2 step c) and a bonding annealing heat treatment step so as to obtain a multilayer structure 100 having a greater bonding energy than that obtained without step c) of arrangement in a basic environment ( figure 3 step d). The first and second substrates 1, 2 are made of silicon and have a diameter of 200 mm and a thickness of 725 micrometers. These two substrates 1, 2 respectively comprise a first bonding surface 3 made of a native silicon oxide (not visible in the figures) and a second bonding surface 4 formed of thermal silicon oxide (hydrophilic film 5 of oxide 145 nm thick). The first and second surfaces 3, 4 are prepared before contact by cleaning with ozonated water, SC1 (mixture of 30% ammonia, 30% hydrogen peroxide and deionized water in the respective volume proportions 1:1:5) followed by SC2 (mixture of 30% hydrochloric acid, 30% hydrogen peroxide and water in the respective volume proportions 1:1:5). These cleanings make it possible to remove organic and particulate contamination which is very detrimental to direct bonding.According to a variant not illustrated, the step of preparing the surfaces before contacting includes a conventional plasma treatment.

[0044] The first and second bonding surfaces 3, 4 are then brought into contact for spontaneous direct bonding (step b). The direct bonding interface 6 of the multilayer assembly 7 thus obtained is arranged in a basic environment consisting of a basic aqueous solution 8 of NaOH in deionized water with a molar concentration of approximately 10 -3 < mol / I (step c).

[0045] The immersion of the multilayer assembly 7 in the basic aqueous solution 8 is maintained for 30 days at the end of which the multilayer assembly 7 is subjected to a bonding annealing heat treatment at 300°C (step d - the temperature rise from room temperature at 1°C / min to 300°C for 2 hours). The measurement of the bonding energy to the multilayer structure 100 obtained leads to the breakage of the silicon substrates 1,2 and not to the detachment of the substrates 1,2. This indicates that the bonding energy obtained is greater than 5J / m2 which is the fracture energy of silicon. The same process carried out without step c) of immersion in a basic environment leads to a bonding energy of 4J / m2 after annealing at 500°C.

[0046] According to an alternative not illustrated, one of the two substrates 1,2 provided in step a) has a weakening plane. The bonding annealing heat treatment contributes to the thermal budget allowing a fracture at the weakening plane. The multilayer structure 100 obtained then comprises one of the two substrates 1,2 bonded to a transferred thin layer originating from the fracture and a negative of the other of the substrates 1,2.

[0047] According to a variant not illustrated, the immersion time of the direct bonding interface 6 in the basic environment is approximately 5 hours for substrates of 25 mm / l (15 days for substrates of 200 mm in diameter). The duration of the immersion is also variable depending on the nature of the substrates 1,2.

[0048] As illustrated in the figure 4 , a silicon oxide film 5 can also form the bonding surfaces 3,4 of the first and second substrates 1,2. The figure 4 illustrates the two bonding surfaces 3,4 brought into contact so as to form the direct bonding interface 6. The figure 5 illustrates step c) of the method which consists of placing the multilayer assembly 7 obtained in step b) in a basic environment formed by an aqueous basic solution 8 comprising the amino alcohol DMAE (acronym for 2-(dimethylamino) ethanol) having a molar concentration of 10 -2< mol / l. The basic environment 8 covers the level of the direct bonding interface 6 and the immersion is maintained for 20 days. Then, the bond strengthening heat treatment is applied at 200°C to the multilayer assembly 7 for 3 hours according to step d) of the method.

[0049] These operations make it possible to obtain a reinforced bonding energy, in particular of more than 5 J / m2 at any point of the direct bonding interface 6 (value obtained by observing the rupture of the silicon during the application of the double lever method). When the same direct bonding process is carried out without step c), it is possible to separate the first and second substrates during the application of the double lever method.

[0050] According to an embodiment variant illustrated in the figure 7, the assembly 7 obtained in step b) is placed in a basic environment formed by an atmosphere saturated with basic molecules in the vapor phase 8'. For this purpose, the method provides for the preparation of a hermetic enclosure 9 saturated with basic molecules in the vapor phase by evaporation of a basic mother solution 11 of ethalonamine having a concentration of 10 -4< mol / I for one hour. Then the assembly is placed in the enclosure 9 for twice as long as with immersion (step c). After immersion of the direct bonding interface 6 in this atmosphere saturated with basic molecules in the vapor phase 8', the assembly 7 is subjected to a heat treatment at 300°C for 2 hours (step d) to strengthen the bonding energy. At the end, the bonding energy measured by the double lever method is greater than 5 J / m 2< .

[0051] According to another possibility not illustrated, the two bonding surfaces 3,4 are plasma treated before contacting according to step b) of the method and the thermal annealing according to step d) is applied at a temperature between approximately 20 and 250°C, for example at 50°C, for a few hours.

[0052] According to a variant not illustrated in the figures, the first and / or second substrates 1 and 2 are made of a material chosen from Ge, InP, AsGa, SiC, GaN, which have a bonding surface in a hydrophilic film such as a native oxide of the material considered, LNO and LTO which intrinsically have a hydrophilic bonding surface.

[0053] According to yet another variant not illustrated, the first substrate 1 provided in step a) is vignetted into several first vignettes whose exposed faces are first bonding surfaces 3. The first vignettes are bonded according to the method previously described on the second substrate 2 (full wafer) according to a chip-wafer bonding also known in English terminology by the expression 'chip to wafer'. According to yet another variant not illustrated, the second substrate 2 is also vignetted into several second vignettes and the method of the invention allows the direct bonding of the first vignettes and the second vignettes.

[0054] According to a non-illustrated alternative, the first bonding surface 3 and the second bonding surface 4 are prepared so as to have copper-oxide hybrid surfaces that can be bonded in direct bonding. These first and second hydrophilic bonding surfaces 3, 4 are typically composed of copper pads with sides of 2.5 micrometers separated by 2.5 micrometers of SiO2. This is then referred to as a hybrid surface with a “pitch” of 5 micrometers. Then steps b) to d) of the method are reproduced as previously described.

[0055] Thus, the present invention proposes a method for manufacturing a multilayer structure 100 comprising direct bonding between two substrates 1, 2 having a high bonding energy, and making it possible to limit the temperature of the post-bonding thermal annealing. The preparation of a basic environment is inexpensive and the immersion step c) is applicable to many materials. It is in particular possible to bond substrates (or thick layers) of materials having a significant difference in thermal expansion coefficient. In addition, when the materials of the first and second substrates 1, 2 comprise devices, these are not damaged by the temperatures used.

[0056] It goes without saying that the invention is not limited to the embodiment variants described above by way of example but that the scope of the invention is defined by the appended claims.

Claims

1. A method for manufacturing a multilayer structure (100) by direct bonding between a first substrate (1) and a second substrate (2), the method comprising the steps of: a) providing a first substrate (1) and a second substrate (2) respectively comprising a first bonding surface (3) and a second bonding surface (4), b) bringing the first bonding surface (3) and the second bonding surface (4) into contact so as to create a direct bonding interface (6) between the first substrate (1) and the second substrate (2), c) disposing at least the direct bonding interface (6) in a basic environment, and d) applying a thermal treatment at a temperature of between 20°C and 1000°C so as to obtain the multilayer structure (100).

2. The manufacturing method according to claim 1, wherein step c) of disposing the direct bonding interface (6) in the basic environment is carried out for a duration of approximately 1 hour to 80 days.

3. The manufacturing method according to claim 1 or 2, wherein the first bonding surface (3) and / or the second bonding surface (4) are / is formed at least in part by a hydrophilic film (5) made of a material chosen from a native oxide, a thermal or deposited silicon oxide, a silicon nitride, a copper oxide and a combination of these materials.

4. The manufacturing method according to any of claims 1 to 3, wherein the first bonding surface (3) and the second bonding surface (4) are completely flat.

5. The manufacturing method according to any of claims 1 to 4, wherein the basic environment is an aqueous basic solution (8).

6. The manufacturing method according to claim 5, wherein the aqueous basic solution (8) is formed, by dissolving in deionized water, a basic compound chosen from NaOH, KOH, Na2CO3, NH4OH, an amino alcohol and an mixture of these basic compounds; the amino alcohol being selected notably from 2-(dimethylamino)ethanol DMAE, N,N-diethyl-2-amino-ethanol, monoethanolamine, N-methyldiethanolamine, aminomethanol, N-methylhydroxylamine, diethanolamine, dimethanolamine, triethanolamine, trimethanolamine and a mixture of these amino alcohols.

7. The manufacturing method according to claim 5 or 6, wherein the aqueous basic solution (8) has a molar concentration of between 10-7 mol / l and 5 mol / l, notably between 10--6 mol / l and 1 mol / l and in particular between 0.01 mol / l and 0.5 mol / l of basic compound.

8. The manufacturing method according to any of claims 1 to 4, wherein the basic environment is an atmosphere saturated with basic molecules in the vapor phase (8'), by evaporation in a hermetic enclosure (9) of a basic stock solution (11) comprising deionized water and a basic compound chosen from N,N-diethylethanolamine, dimethylaminoethanol, aminoethanol, N-methyldiethanolamine, aminomethanol, N-methylhydroxylamine, diethanolamine, dimethanolamine, triethanolamine, trimethanolamine, ethalonamine, diethyl-N-N-ethanol, ammonia and their combination.

9. The manufacturing method according to any of claims 1 to 8, wherein the first substrate (1) and the second substrate (2) are each formed by a material chosen from semiconductors, such as Si, Ge, InP, AsGa, SiC and GaN; the LNO, the LTO and their combination.

10. The manufacturing method according to any of claims 1 to 9, wherein: the first substrate (1) and the second substrate (2) provided in step a) each comprise a silicon substrate having a diameter of between 25 mm and 300 mm, in particular 200 mm or 300 mm, and in which the first bonding surface (3) and the second bonding surface (4) are each completely formed by a continuous hydrophilic film (5) made of silicon oxide, step c) comprises disposing the direct bonding interface (6), obtained in step b), in the basic environment over a duration of between 21 and 40 days, the basic environment being an aqueous basic solution (8) formed by dissolution of NaOH and having a molar concentration of between 10-7 mol / l and 0.01 mol / l and for example a molar concentration of approximately 10-3 mol / l, and step d) comprises applying a thermal treatment at approximately 300°C, so as to obtain a direct bonding between the first substrate (1) and the second substrate (2) having a bonding energy greater than 5 J / m2.