Permanent bonding method for wafers

Abstract

To find out a method of carefully providing permanent bonding having bonding strength which is as high as possible.SOLUTION: A method comprises a step of forming a storage portion (5) in a surface layer (6) on a first contact surface (3), a step of at least partially filling the storage portion (5) with a first raw material or a first raw material group, a step of bringing the first contact surface (3) into contact with the second contact surface (4) to form temporary bonding connection, and a step that forms permanent bonding between the first contact surface (3) and the second contact surface (4) and reacts the first raw material with a second raw material contained in a reaction layer (7) of the second substrate (2) to at least partially strengthen the permanent bonding, thereby bonding the first contact surface (3) of the first substrate (1) to the second contact surface (4) of the second substrate (2).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for joining a first contact surface of a first substrate to a second contact surface of a second substrate, as described in Embodiment 1. [Background technology]

[0002] The objective in permanent or irreversible bonding of substrates is to create the strongest possible, and especially irreversible, interconnection between two contact surfaces of the substrates, and thus a high bonding force. In the prior art, there are various methods and manufacturing processes for such bonding.

[0003] Known manufacturing methods and techniques used to date often fail to reproduce results, or fail to reproduce them sufficiently, and are largely unapplicable when conditions change. In particular, currently used manufacturing methods often employ high temperatures, especially above 400°C, to ensure reproducible results.

[0004] Technical problems such as high energy consumption and the risk of damaging structures on the substrate are a result of the high temperatures, some far exceeding 300°C, that have been required to achieve high bonding strength until now. Patent Document 1 below describes a low-temperature bonding method. Further bonding methods are shown in Patent Documents 1 to 8 below.

[0005] Other requirements include the following: - Interoperability of front-end processes This is defined as process compatibility during the manufacturing of electrically active components. Therefore, the bonding process must be designed so that active components, such as transistors, already present on the structural wafer are not adversely affected or damaged during processing. Criteria for determining compatibility include (primarily in CMOS structures) the purity of chemical elements and the mechanical load-bearing capacity, primarily due to thermal stress. - Low pollution - No added force

[0006] A decrease in bonding strength necessitates more careful handling of the structural wafer, thus reducing the probability of failure due to direct mechanical load. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 01 / 61743 Pamphlet [Patent Document 2] U.S. Patent Application Publication No. 2003 / 0089950 [Patent Document 3] U.S. Patent Application Publication No. 2002 / 0048900 Specification [Patent Document 4] U.S. Patent Application Publication No. 2008 / 0006369 [Patent Document 5] U.S. Patent No. 5451547 [Patent Document 6] European Patent Application Publication No. 0584778 [Patent Document 7] U.S. Patent No. 5,427,638 [Patent Document 8] Japanese Patent Application Publication No. 5-166690 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Therefore, the objective of the present invention is to devise a method for carefully manufacturing permanent bonds that have the highest possible bonding strength. [Means for solving the problem]

[0009] This object is achieved by the features described in embodiment 1. Advantageous developments of the invention are described in the dependent embodiments. Any combination of at least two of the features described in at least one of the present specification, the claims and the drawings is also included within the scope of the framework of the invention. In a given range of values, the values within the indicated limits are also disclosed as boundary values and are claimed in any combination.

[0010] The idea underlying the present invention is to devise a reservoir for holding a first raw material on at least one of the substrates, and after bringing the first raw material into contact or temporarily bonding it between the substrates having a second raw material present in the other substrate, to react it, thereby forming an irreversible or permanent bond between the substrates. Cleaning of the substrates is generally carried out, particularly by a flushing step, before or after forming the reservoir in a surface layer on one surface of the first contact surface. This cleaning generally has to ensure that there are no particles on the surface, as the presence of such particles would result in unbonded areas. The reservoir and the raw material contained therein enable a reaction that strengthens the permanent bond directly on the contact surface and increases it in a controlled manner in terms of the bonding rate after forming a temporary or reversible bond, and there is a technical possibility that this reaction is induced, particularly by deforming at least one of the contact surfaces, preferably the contact surface facing the reservoir, by said reaction.

[0011] As a temporary bonding step for forming a temporary or reversible bond between the substrates, there are various possibilities for the purpose of generating a weak interaction between the contact surfaces of the substrates. The strength of the temporary bond is lower than the strength of the permanent bond, at least 1 / 2 to 1 / 3, particularly 1 / 5, preferably 1 / 15, more preferably 1 / 25 lower. As a reference value, the temporary bonding strength of pure non-activated hydrophilic silicon is about 100 mJ / m 2 , and the temporary bonding strength of pure plasma-activated hydrophilic silicon is about 200 - 300 mJ / m 2It is. The temporary bonding between molecule-wetted substrates is realized by the van der Waals interaction between molecules on different sides of the substrates. Therefore, molecules mainly having a permanent dipole moment are suitable for enabling the temporary bonding between wafers. The following chemical compounds are given as examples of interconnecting agents, but are not limited thereto. - Water - Thiol - AP3000 - Silane, and / or - Silanol

[0012] A suitable substrate according to the present invention is a substrate whose material can react with separately supplied raw materials as raw materials to form a product having a higher molar volume, and as a result, a growth layer is formed on the substrate. The following combinations are particularly advantageous. The left side of the arrow lists the raw materials, and the right side of the arrow lists the products. However, the supplied raw materials or by-products that react with the listed raw materials are not listed individually. - Si → SiO2, Si3N4, SiN x O y - Ge → GeO2, Ge3N4 - α-Sn → SnO2 - B → B2O3, BN - Se → SeO2 - Te → TeO2, TeO3 - Mg → MgO, Mg3N2 - Al → Al2O3, AlN - Ti → TiO2, TiN - V → V2O5 - Mn → MnO, MnO2, Mn2O3, Mn2O7, Mn3O4 - Fe → FeO, Fe2O3, Fe3O4 - Co → CoO, Co3O4 - Ni → NiO, Ni2O3 - Cu → CuO, Cu2O, Cu3N - Zn → ZnO - Cr → CrN, Cr 23C6, Cr3C, Cr7C3, Cr3C2 - Mo → Mo3C2 - Ti → TiC - Nb → Nb4C3 - Ta → Ta4C3 - Zr → ZrC - Hf → HfC - V → V4C3, VC - W → W2C, WC - Fe → Fe3C, Fe7C3, Fe2C

[0013] As a substrate, the following semiconductor hybrid forms are also conceivable. - III-V: GaP, GaAs, InP, InSb, InAs, GaSb, GaN, AlN, InN, Al x Ga 1-x As, In x Ga 1-x N - IV-IV: SiC, SiGe - III-IV: InAlP - Nonlinear optical systems: LiNbO3, LiTaO3, KDP (KH2PO4) - Solar cells: CdS, CdSe, CdTe, CuInSe2, CuInGaSe2, CuInS2, CuInGaS2 - Conductive oxides: In 2-x Sn x O 3-y

[0014] As claimed in this invention, there is a reservoir on at least one of the wafers, and directly on each contact surface, capable of storing a certain amount of at least one of the raw materials supplied for the volume expansion reaction. The raw materials may be, for example, O2, O3, H2O, N2, NH3, H2O2, etc. Due to the expansion caused in particular by oxide growth, based on the tendency of reaction partners to reduce the energy of the system, possible gaps, pores, and cavities between the contact surfaces are minimized, and thus the bonding force is increased by narrowing the distance between the substrates in these regions. In the best-case scenario, existing gaps, pores, and cavities are completely closed, resulting in an increase in the overall bonding area and, accordingly, an increase in the bonding force as claimed in this invention.

[0015] The contact surface typically exhibits a root mean square roughness (Rq) of 0.2 nm. This corresponds to a peak-to-peak value on a surface in the 1 nm range. These empirical values ​​were obtained using atomic force microscopy (AFM).

[0016] The reaction claimed in this invention is suitable for enabling the growth of a growth layer to a depth of only 0.1 to 0.3 nm on the wafer surface of a conventional circular wafer having a diameter of 200 to 300 mm and a single layer of water monolayers (ML).

[0017] Therefore, as claimed in the present invention, at least 2 ml, preferably at least 5 ml, and more preferably 10 ml of fluid, particularly water, is stored in the reservoir.

[0018] It is particularly preferable to form reservoirs by plasma exposure, because plasma exposure synergistically produces smoothing and hydrophilicity of the contact surface. The surface is smoothed by plasma activation, mainly by the viscous flow of the surface layer material. The increase in hydrophilicity occurs particularly by an increase in silicon hydroxyl group bonds, preferably by the decomposition of Si-O bonds present on the surface, such as Si-O-Si, according to the reaction shown in chemical formula (1) below.

[0019] [ka]

[0020] In particular, another side effect resulting from the above-mentioned effects is that the temporary joint strength is improved by a factor of 2 to 3.

[0021] The reservoir in the surface layer on the first contact surface of the first substrate is formed by plasma activation of the first substrate, which is coated with, for example, a thermal oxide. Plasma activation is performed in a vacuum chamber so that the conditions required for the plasma can be adjusted. As claimed in this invention, as the plasma discharge, N2 gas, O2 gas, or argon gas is used with an ion energy in the range of 0 to 2000 eV, and as a result, the reservoir is formed to a depth of 20 nm, preferably 15 nm, more preferably 10 nm, and most preferably 5 nm, on the processed surface, in this case the first contact surface. As claimed in this invention, at least one of each particle type, atom, and molecule suitable for forming the reservoir can be used. Preferably, atoms or molecules, or both, that can be formed so that the reservoir has the required properties are used. Relevant properties mainly include pore size, pore distribution, and pore density. Alternatively, as claimed in this invention, a mixed gas such as air or a forming gas consisting of 95% Ar and 5% H2 can be used. Depending on the gas used, N2 is particularly present in the reservoir during plasma processing. + , N2 + , O + , O2 + Ar + The ions are present. The first raw material can be contained in the unoccupied free space.

[0022] The reservoir is formed based on the following considerations: The pore size is less than 10 nm, preferably less than 5 nm, more preferably less than 1 nm, even more preferably less than 0.5 nm, and most preferably less than 0.2 nm.

[0023] The pore density is preferably directly proportional to the density of particles that create pores through collision action, and most preferably can be varied depending on the partial pressure of the collision species, as well as the processing time and, in particular, the parameters of the plasma system used.

[0024] The pore distribution preferably has at least one region with the highest pore density below the surface, and by varying the parameters of several such regions, these regions overlap, preferably forming a flat region (see Figure 7). The pore distribution decreases to zero as the thickness increases. The region near the surface during impact has approximately the same pore density as the region near the surface. After the completion of plasma treatment, the pore density on the surface may be reduced as a result of the stress relaxation mechanism. The pore distribution in the thickness direction has steep sides relative to the surface and rather flatter sides relative to the bulk, but with continuously decreasing sides (see Figure 7).

[0025] The same considerations regarding pore size, pore distribution, and pore density apply to all methods that do not involve the use of plasma.

[0026] The reservoir can be designed by controlling and combining process parameters. Figure 7 shows the concentration of nitrogen atoms injected by the plasma as a function of the penetration depth into the silicon oxide layer. By varying the physical parameters, it was possible to obtain two profiles. The first profile 11 was formed when atoms accelerated at a higher speed penetrated deeper into the silicon oxide, while profile 12 was formed after changing the process parameters to a lower density. When the two profiles are superimposed, a sum of curves 13 is obtained, and this curve represents the characteristics of the reservoir. The relationship between the concentrations of injected atomic species, molecular species, or both is clear. Higher concentrations indicate regions of more defective structures, and therefore more space to accommodate subsequent raw materials. By continuously changing the process parameters in a dedicated manner during plasma activation, it is possible to realize a reservoir in which the added ions are distributed as uniformly as possible over depth.

[0027] As a reservoir, or as a substitute for a reservoir formed by plasma, a TEOS (tetraethyl orthosilicate) oxide layer may be used on at least one of the substrates, at least on the first substrate. This oxide is generally less dense than thermal oxides, and for this reason, it is advantageous for compression as claimed in the present invention. Compression is carried out by heat treatment to adjust the porosity of the reservoir to a specified level.

[0028] According to one embodiment of the present invention, the filling of the reservoir can be carried out at the same time as the formation of the reservoir, particularly advantageously by applying the reservoir as a coating to the first substrate, and the coating already contains the first raw material.

[0029] The storage portion can be considered as a porous layer having porosity in the nanometer range, or as a layer having channels with a channel width of less than 10 nm, more preferably less than 5 nm, even more preferably less than 2 nm, most preferably less than 1 nm, and most preferably less than 0.5 nm.

[0030] With regard to the step of filling the storage section with a first raw material or a group of first raw materials, the following embodiments and combinations thereof are possible, as claimed in the present invention. - Step to expose the storage area to the surrounding atmosphere - In particular, the step of flushing with deionized water. - A step of flushing with a fluid containing raw materials, particularly H2O, H2O2, NH4OH, or a fluid consisting of these raw materials. - A step of exposing the storage area to any gas atmosphere, particularly atomic gas, molecular gas, or gas mixture. - The step of exposing the storage section to an atmosphere containing water vapor or hydrogen peroxide vapor, and - A step of depositing a storage section already filled with raw materials onto a first substrate as a surface layer.

[0031] At least one of the compounds O2, O3, N2, NH3, H2O, H2O2, and NH4OH can be considered as a starting material.

[0032] The use of hydrogen peroxide vapor, as described above, is considered a preferred version in addition to the use of water. Hydrogen peroxide has the further advantage of having a higher oxygen-to-hydrogen ratio. Furthermore, hydrogen peroxide dissociates into hydrogen and oxygen when heated above a certain temperature and / or when a high-frequency electromagnetic field in the MHz range is used.

[0033] According to one advantageous embodiment of the present invention, the formation of the growth layer and the strengthening of the irreversible bond are carried out by the diffusion of the first raw material into the reaction layer.

[0034] According to another advantageous embodiment of the present invention, the formation of an irreversible bond is intended to take place typically at a temperature below 300°C, preferably below 200°C, more preferably below 150°C, even more preferably below 100°C, most preferably at room temperature, particularly for a maximum of 12 days, more preferably a maximum of 1 day, even more preferably a maximum of 1 hour, most preferably a maximum of 15 minutes.

[0035] In this specification, irreversible bonding is defined as 1.5 J / m 2 Ultra, especially 2J / m 2 More preferably 2.5 J / m 2 Having superior bonding strength is particularly advantageous.

[0036] The bonding strength can be particularly advantageously increased by the formation of a product in the reaction layer during the reaction, having a molar volume greater than that of the second raw material, as claimed in this invention. In this way, growth is induced on the second substrate, and as a result, the gap between the contact surfaces can be closed by the chemical reaction claimed in this invention. As a result, the distance between the contact surfaces, and therefore the average distance, is reduced, and dead space is minimized.

[0037] The reservoir is formed by plasma activation, particularly at activation frequencies between 10 and 600 kHz and / or 0.075 to 0.2 watts / cm². 2 As long as the pressurization is performed at an output density between and / or at a pressure between 0.1 and 0.6 mbar, additional effects such as smoothing of the contact surface and even a significant increase in the hydrophilicity of the contact surface can be obtained.

[0038] Alternatively, the formation of the reservoir claimed in this invention can also be carried out by using a tetraethoxysilane oxide layer as a surface layer, which is compressed in a manner that controls the porosity to a certain degree.

[0039] According to another advantageous embodiment of the present invention, the surface layer is intended to consist mainly of silicon dioxide produced by thermal oxidation, particularly amorphous silicon dioxide, especially silicon dioxide produced by thermal oxidation, and the reaction layer is intended to consist mainly of an oxidizable material, particularly Si, Ge, InP, GaP, or GaN, preferably essentially entirely. Particularly stable reactions that effectively close existing gaps are made possible by oxidation.

[0040] In this specification, it is particularly advantageous to have a growth layer, mainly of native silicon dioxide, between the second contact surface and the reaction layer, as claimed in the present invention. This growth layer undergoes growth resulting from the reaction claimed in the present invention. This growth proceeds by the reformation of amorphous SiO2 from transition Si-SiO2(7), thereby causing deformation, particularly blistering, of the growth layer, especially on the interface with the reaction layer and especially in the gap region between the first and second contact surfaces. This reduces the distance between the two contact surfaces or reduces dead space, resulting in increased bonding strength between the two substrates. Temperatures between 200 and 400°C, preferably about 200°C to 150°C, more preferably between 150°C and 100°C, and most preferably between 100°C and room temperature are particularly advantageous.

[0041] In this specification, it is particularly advantageous if the growth layer has an average thickness A between 0.1 nm and 5 nm before forming an irreversible bond. The thinner the growth layer, the more rapidly and easily the reaction between the first and second raw materials via the growth layer proceeds, particularly by the diffusion of the first raw material through the growth layer into the reaction layer.

[0042] According to one embodiment of the present invention, it is advantageous to perform the formation of the reservoir in a vacuum. Therefore, contamination of the reservoir by undesirable materials or compounds can be avoided.

[0043] In another embodiment of the present invention, the filling of the storage section is - A step of exposing the first contact surface to the atmosphere in order to fill the reservoir with moisture in the atmosphere, oxygen contained in the air, or both. - The first contact surface is brought into contact with a fluid, particularly mainly, preferably almost completely, consisting of deionized H2O or H2O2, or both. - The first contact surface is exposed to at least one of N2 gas, O2 gas, Ar gas, and a forming gas, particularly a forming gas consisting of 95% Ar and 5% H2, in particular, with an ionic energy in the range of 0 to 2000 eV. - A step of evaporating one of the previously mentioned raw materials in order to fill the storage section. This is carried out by one or more of the following steps.

[0044] The storage portion is preferably formed with a thickness R between 0.1 nm and 25 nm, more preferably between 0.1 nm and 15 nm, even more preferably between 0.1 nm and 10 nm, and most preferably between 0.1 nm and 5 nm, which is particularly effective for process sequence. Furthermore, according to one embodiment of the present invention, it is advantageous if the average distance B between the storage portion and the reaction layer immediately before the formation of an irreversible bond is between 0.1 nm and 15 nm, particularly between 0.5 nm and 5 nm, preferably between 0.5 nm and 3 nm.

[0045] An apparatus for carrying out the method claimed in the present invention comprises a chamber for forming a reservoir, a separate chamber specifically provided for filling the reservoir, and a separate chamber specifically provided for forming a temporary joint, all of which are directly connected to one another via a vacuum system.

[0046] In another embodiment, filling of the storage unit can also be done directly by atmosphere, and thus in a chamber that can be opened to the atmosphere, or simply on a structure that does not have an outer covering but can handle wafers semi-automatically and / or fully automatically.

[0047] Other advantages, features, and details of the present invention will become apparent by using the following description and drawings of exemplary preferred embodiments. [Brief explanation of the drawing]

[0048] [Figure 1] This figure shows the first step of the method claimed in this invention, immediately after the first substrate is brought into contact with the second substrate. [Figure 2a] This figure shows other steps of the method claimed in the present invention for forming a higher joint strength. [Figure 2b] This figure shows other steps of the method claimed in the present invention for forming a higher joint strength. [Figure 3] This figure shows another step of the claimed method, following the steps described in Figures 1, 2a, and 2b, in which the contact surfaces of the substrate are in contact. [Figure 4] This figure shows the steps claimed in this invention for forming an irreversible / permanent bond between substrates. [Figure 5] Figures 3 and 4 show enlarged views of the chemical / physical processes taking place on the two contact surfaces during the steps described. [Figure 6] Figures 3 and 4 show another enlarged view of the chemical / physical processes taking place on the interface between the two contact surfaces during the steps described. [Figure 7] This graph shows the manufacturing process of the storage unit claimed in this invention. [Modes for carrying out the invention]

[0049] In the diagram, identical components / mechanisms and components / mechanisms having the same function are identified by the same reference number.

[0050] The situation shown in Figure 1 illustrates only a portion of the chemical reaction that takes place between the first contact surface 3 of the first substrate 1 and the second contact surface 4 of the second substrate 2 during or immediately after the temporary bonding step. This surface is hydrophilic because its terminology consists of polar OH groups. The first substrate 1 and the second substrate 2 are held together by the attractive forces of hydrogen bonding between the OH groups present on the surface and H2O molecules, and by the attractive forces of hydrogen bonding between individual H2O molecules. At least the hydrophilicity of the first contact surface 3 is increased by the plasma treatment of the first contact surface 3 in the preceding step.

[0051] The reservoir 5 in the surface layer 6, which is made of thermal silicon dioxide, is formed by plasma treatment as claimed in this invention. By plasma treatment using O2 ions with an ion energy in the range of 0 to 2000 eV, the average thickness R of the reservoir 5 becomes approximately 15 nm, and channels or pores are formed in the surface layer 6 by the ions.

[0052] Similarly, prior to the steps shown in Figure 1 and after the plasma treatment, H2O is filled into the reservoir 5 as the first raw material. Reduced species of ions present during the plasma process, particularly O2, N2, H2, and Ar, can also be present in the reservoir.

[0053] Therefore, the contact surfaces 3 and 4 still have a relatively wide gap, which is mainly occupied by water present between the contact surfaces 3 and 4. Consequently, the existing joint strength is relatively low, approximately 100 mJ / cm². 2 From 300 mJ / cm 2 During this period, especially at 200 mJ / cm² 2 This is excellent. In this regard, prior plasma activation plays a crucial role, particularly because it increases the hydrophilicity of the first contact surface 3 and provides a smoothing effect.

[0054] The process called pre-bonding, shown in Figure 1, can preferably proceed at ambient temperature or at a maximum of 50°C. Figures 2a and 2b show hydrophilic bonding, where Si-O-Si bridges are formed as a result of water desorption by the -OH-terminated surface. The processes in Figures 2a and 2b last for approximately 300 hours at room temperature, and approximately 60 hours at 50°C. The state in Figure 2b occurs at the indicated temperature without the formation of a reservoir.

[0055] H2O molecules are formed between contact surfaces 3 and 4, and at least some of the H2O molecules are supplied to further fill the reservoir 5 as long as free space still exists. Other H2O molecules are removed. In the steps shown in Figure 1, there are approximately 3 to 5 individual OH base layers or H2O layers, and from the steps shown in Figure 1 to the steps shown in Figure 2a, 1 to 3 H2O monolayers are removed or contained within the reservoir 5.

[0056] In the step shown in Figure 2a, hydrogen crosslinking bonds are directly formed between siloxane groups, resulting in a higher bonding force. This bonding force causes contact surfaces 3 and 4 to attract each other more strongly, reducing the distance between them. Therefore, there are only one or two individual OH group layers between contact surfaces 3 and 4.

[0057] In the step shown in Figure 2b, the separation of H2O molecules according to the reaction shown in chemical formula (2) below forms a covalent bond in the form of a silanol group between contact surfaces 3 and 4, resulting in a much stronger bonding force and requiring less space. Consequently, the distance between contact surfaces 3 and 4 is further reduced, eventually reaching the minimum distance at which contact surfaces 3 and 4 touch each other, as shown in Figure 3.

[0058] [ka]

[0059] Up to step 3, since the storage section 5 is formed, there is no need to excessively increase the temperature; in fact, the process can proceed at room temperature. This allows the process steps shown in Figures 1 to 3 to be carried out with particular care.

[0060] In the method steps shown in Figure 4, the temperature is raised to preferably up to 500°C, more preferably up to 300°C, even more preferably up to 200°C, most preferably up to 100°C, and most preferably not above room temperature, in order to form an irreversible or permanent bond between the first and second contact surfaces. These temperatures are relatively low, unlike in the prior art, and are only possible if the reservoir 5 contains the first raw materials for the reaction shown in chemical formula (3) below, as shown in Figures 5 and 6.

[0061] [ka]

[0062] Due to the slight temperature increase described above, H2O molecules diffuse from the reservoir 5 to the reaction layer 7 as the first raw material. This diffusion can occur through direct contact between the surface layer 6, which is formed as an oxide layer, and the growth layer, or through or from the gaps 9 present between the oxide layers. There, silicon dioxide, a chemical compound having a larger molar volume than pure silicon, is formed from the reaction layer 7 as the reaction product 10 of the above reaction. This silicon dioxide grows at the interface between the reaction layer 7 and the growth layer 8, and therefore deforms the growth layer 8, which is formed as a native oxide, in the direction of the gaps 9. Here again, H2O molecules from the reservoir are required.

[0063] Because of the nanometer-range gaps, the native oxide layer 8 may bulge, which in turn reduces the stress on the contact surfaces 3 and 4. This reduces the distance between contact surfaces 3 and 4, resulting in a greater effective contact surface and thus a stronger bond. In this type of welded joint, unlike conventional products which are not partially welded, all holes are closed, and the welded joint is formed across the entire wafer, thus contributing to a greater bond strength. The type of joint between two amorphous silicon oxide surfaces welded to each other is a hybrid of covalent and ionic bonding.

[0064] The above-described reaction between the first raw material (H2O) and the second raw material (Si) in the reaction layer 7 proceeds particularly rapidly or at the lowest possible temperature when the average distance B between the first contact surface 3 and the reaction layer 7 is as small as possible.

[0065] Therefore, the pretreatment of the first substrate 1, and the selection of the second substrate 2, which consists of a silicon reaction layer 7 and a native oxide layer as thin as possible as a growth layer 8, are crucial. The native oxide layer as thin as possible, as claimed in this invention, is provided for the following two reasons: Because the growth layer 8 is very thin, the reaction products 10 newly formed on the reaction layer 7 can cause the growth layer 8 to expand toward the surface layer 6, which is formed as an oxide layer on the opposing substrate 1, and mainly within the region of nano-gaps 9. Furthermore, the shortest possible diffusion path is desirable in order to achieve the desired effect as quickly as possible and at the lowest possible temperature. Similarly, the first substrate 1 consists of a silicon layer and an oxide layer formed thereon as a surface layer 6, and the reservoir 5 is formed at least partially or completely within this surface layer 6.

[0066] Therefore, the storage section 5 claimed in the present invention is filled with at least the amount of the first raw material necessary to close the nano-gaps 9, and thus the growth layer 8 can be optimally grown to close the nano-gaps 9 in the shortest possible time and / or at the lowest possible temperature.

[0067] Embodiments of the present invention are described below. ·Aspect 1 A method for joining the first contact surface (3) of a first substrate (1) to the second contact surface (4) of a second substrate (2), The steps include forming a reservoir (5) in the surface layer (6) on the first contact surface (3), The steps include filling the storage section (5) with at least a portion of the first raw material or the first group of raw materials, The steps include bringing the first contact surface (3) into contact with the second contact surface (4) in order to form a temporary joint, A step of forming a permanent bond between the first contact surface (3) and the second contact surface (4), comprising the step of at least partially strengthening the permanent bond by reacting the first raw material with the second raw material contained in the reaction layer (7) of the second substrate (2), A method that includes the above in particular order. • Feature 2 The method according to embodiment 1, wherein the formation or strengthening of the permanent bond, or both, is carried out by the diffusion of the first raw material into the reaction layer (7). ·Aspect 3 The method according to embodiment 1 or 2, wherein the formation of the permanent bond is carried out at a temperature between room temperature and 200°C, particularly for up to 12 days, more preferably up to 1 day, even more preferably up to 1 hour, and most preferably up to 15 minutes. • Feature 4 The irreversible junction is 1.5J / m 2 Larger, especially 2 J / m 2 Larger, preferably 2.5 J / m 2 The method according to any one of embodiments 1 to 3, which has greater bonding strength. • Phenomenon 5 The method according to any one of embodiments 1 to 4, wherein during the reaction, a reaction product (10) having a molar volume greater than the molar volume of the second raw material is formed in the reaction layer (7). ·Aspect 6 The method according to any one of embodiments 1 to 5, wherein the storage portion (5) is formed by plasma activation. • Phenomenon 7 The method according to any one of embodiments 1 to 6, wherein the formation of the storage portion (5) is carried out using a particularly compressed tetraethoxysilane oxide layer as the surface layer (6). • Aspect 8 The method according to any one of embodiments 1 to 7, wherein the surface layer (6) is mainly, in particular essentially completely, particularly amorphous, silicon dioxide produced by thermal oxidation, and the reaction layer (7) is mainly, preferably essentially completely Si, Ge, InP, GaP, or GaN. • 9th aspect The method according to any one of embodiments 1 to 8, wherein a growth layer (8) mainly consisting of native silicon dioxide is provided between the second contact surface (4) and the reaction layer (7). ·Aspect 10 The method according to embodiment 9, wherein, before forming a permanent bond, the growth layer (8) has an average thickness A between 1 angstrom and 10 nm. ·Aspect 11 The method according to any one of the embodiments 1 to 10, wherein the storage portion is formed in a vacuum. ·Aspect 12 The storage section is, The first contact surface (3) is exposed to an atmosphere that has a particularly high content of oxygen, water, or both. The first contact surface (3) is brought into contact with a fluid consisting mainly, preferably almost completely, of deionized H2O or H2O2, or both. The first contact surface (3) is exposed to at least one of N2 gas, O2 gas, Ar gas, and a forming gas, particularly a forming gas consisting of 95% Ar and 5% H2, in particular, with an ion energy in the range of 0 to 2000 eV. The method according to any one of embodiments 1 to 11, wherein the filling is performed by one or more of the steps described above. ·Aspect 13 The method according to any one of embodiments 1 to 12, wherein the storage portion (5) is formed with an average thickness (R) between 0.1 nm and 25 nm, particularly between 0.1 nm and 20 nm. ·Aspect 14 The method according to any one of embodiments 1 to 13, wherein the average distance (B) between the storage portion (5) and the reaction layer (7) immediately before the formation of the permanent bond is between 0.1 nm and 15 nm, particularly between 0.5 nm and 5 nm, preferably between 0.5 nm and 3 nm. Appearance 15 The method according to any one of embodiments 1 to 14, wherein the irreversible joint has a joint strength twice, preferably four times, more preferably ten times, and most preferably twenty-five times, the strength of the temporary joint. [Explanation of Symbols]

[0068] 1. First substrate 2. Second substrate 3. First contact surface 4. Second contact surface 5 Storage section 6 Surface layer 7 Reaction layer 8 growth layer 9 nanometer gaps 10 Reaction Products 11. First Profile 12. Second Profile 13. Sum of curves A Average thickness B Average distance R average thickness

Claims

1. A method for joining a first contact surface of a first substrate to a second contact surface of a second substrate, The steps include smoothing the first contact surface to form a reservoir in the surface layer on the first contact surface, The steps include filling the storage section with at least a portion of the first raw material or the first group of raw materials, The steps include bringing the first contact surface into contact with the second contact surface in order to form a temporary joint, A step of forming a permanent bond between the first contact surface and the second contact surface, comprising the step of at least partially strengthening the permanent bond by reacting the first raw material with the second raw material contained in the reaction layer of the second substrate, Methods that include...

2. The method according to claim 1, wherein the first contact surface is smoothed by plasma exposure.

3. The plasma has an activation frequency between 10 and 600 kHz and / or 0.075 to 0.2 watts / cm². 2 The method according to claim 2, which is produced at an output density between the two.

4. The method according to any one of claims 1 to 3, wherein the first contact surface is smoothed by the viscous flow of the material of the surface layer.

5. The method according to any one of claims 1 to 4, wherein during the reaction, a reaction product having a molar volume greater than the molar volume of the second raw material is formed in the reaction layer.

6. The method according to any one of claims 1 to 5, wherein the increase in hydrophilicity is caused by an increase in silicon hydroxyl group bonds in the surface layer.

7. The method according to any one of claims 1 to 6, wherein the formation or strengthening of the permanent bond, or both, is carried out by diffusing the first raw material into the reaction layer.

8. The method according to any one of claims 1 to 7, wherein the surface layer is made of an amorphous material and the reaction layer is made of an oxidizable material.

9. The method according to any one of claims 1 to 8, wherein a growth layer of native silicon dioxide is provided between the second contact surface and the reaction layer.

10. The method according to claim 9, wherein, before forming a permanent bond, the growth layer has an average thickness A between 1 angstrom and 5 nm.

11. The method according to any one of claims 1 to 10, wherein the storage section is formed in a vacuum.

12. The method according to any one of claims 1 to 11, wherein the storage portion is formed with an average thickness (R) between 0.1 nm and 25 nm.

13. The method according to any one of claims 1 to 12, wherein the average distance (B) between the storage portion and the reaction layer immediately before the formation of the permanent bond is between 0.1 nm and 15 nm.

14. The method according to any one of claims 1 to 13, wherein the permanent joint has a joint strength twice that of the temporary joint.

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