Low temperature bonding process and substrate device thus obtained

Abstract

TITLE: Low temperature bonding method and substrate device thus obtained Method for low temperature bonding of a first substrate (10) and a second substrate (20), having a first bonding surface (11) and a second bonding surface (21), comprising the following steps: - in a first step (101) depositing a first SAM layer (1) on the first bonding surface (11) and / or a second SAM layer on the second bonding surface (21), - in a second step (102), after the first step, bonding at low temperature, using the first SAM layer (1) and / or the second SAM layer developing an adhesive bond between the first bonding surface (11) and the second bonding surface (21). Figure 2b

Description

Title of the invention: Low temperature bonding method and substrate device thus obtained FIELD OF THE INVENTION

[0001] The present invention relates to a method for low-temperature bonding of a first substrate and a second substrate, the first substrate having a first bonding surface and the second substrate having a second bonding surface. The invention also relates to a substrate device thus obtained. STATE OF THE ART

[0002] Semiconductor components such as, for example, MEMS micro-electro-mechanical systems, are subject to often very severe limitations due to the possibilities of materials used, these limitations concerning the possible process temperatures, in particular for the assembly of substrates (bonding of the wafer) so that low-temperature bonding processes are in great demand.

[0003] Document US 2003 / 211705 A1 describes such a low temperature bonding method consisting of carrying out a slight corrosion of a first polished surface and then bonding against a second surface. But this method is limited mainly to flat surfaces having minimal roughness.

[0004] Details of direct bonding processes are, for example, given in the following publication: T. Plach, K. Hingerl, S. Tollabimazraehno, G. Hesser, V. Dragoi, and M. Wimplinger; Mechanisms for room temperature direct wafer bonding; Journal of Applied Physics 113, 094905 (2013).

[0005] PURPOSE OF THE INVENTION

[0006] The aim of the present invention is to develop a low-temperature bonding process making it possible to produce an advantageous bonded connection between a first and a second substrate, so as to protect it.

[0007] DISCLOSURE AND ADVANTAGES OF THE INVENTION

[0008] The subject of the invention is a method for low-temperature bonding of a first substrate and a second substrate, the first substrate having a first bonding surface, the second substrate having a second bonding surface, this method comprising the following steps: in a first step depositing a first SAM layer on the first bonding surface and / or a second SAM layer on the second bonding surface, in a second step, after the first step, bonding at low temperature, using the first SAM layer and / or the second SAM layer, developing an adhesive bond between the first bonding surface and the second bonding surface.

[0009] The method according to the invention for low-temperature bonding of a first substrate and a second substrate has the advantage, compared to the state of the art, of achieving low-temperature bonding, particularly gently, of surfaces, in particular bonding surfaces, accepting greater roughness of the bonding surfaces and which is done selectively according to the surfaces. Thus, the invention makes it possible to produce stable bonded connections which develop locally, with greater tolerance to roughness for lower bonding temperatures.

[0010] According to the invention, it is possible in particular to envisage connecting the first bonding surface and the second bonding surface for low-temperature bonding, preferably directly or indirectly by a first SAM layer and / or a second SAM layer. It is particularly advantageous not to have any other intermediate layer deposited in addition (apart from the first and / or the second SAM layer) between the first and the second bonding surface, in particular at the start of the low-temperature bonding.

[0011] Thus, according to the invention, a substrate bond comprising in particular a MEMS component is produced by proceeding gently. It is possible in particular to envisage bonding substrates produced by the method of the invention or substrate devices in the form of a SIO (silicon on insulator) wafer.

[0012] The first and / or second SAM layer according to the invention are monolayers of self-assembled SAM molecules.

[0013] When directly bonding two surfaces, water molecules play a decisive role. They initiate the bonding of the wafer at low temperatures, in particular at room temperature; they are then diffused into the oxide on the surface of the adjacent bonding surfaces and reacted with the release of water. To have sufficient water molecules at the bonding surface, it is known, according to the state of the art, to carry out an etching step before the bonding step to generate, at the bonding surface, an amorphous layer having a free volume. The amorphous layer thus generated promotes the storage of water molecules and allows a rapid diffusion and displacement process at the boundary surface. However, such methods require direct mechanical contact with the bonding surface so that the chemical bonds can develop above the boundary surface.These known processes therefore do not tolerate any high roughness of the bonding surfaces.

[0014] On the other hand, the invention allows, using the first and / or second SAM layers, better low-temperature bonding of the substrates, by accepting greater roughness of the bonding surfaces and also allowing locally limited bonding or structured bonding.

[0015] Preferably, according to a development, the low temperature bonding is carried out in a second step at a temperature below 100°C, preferably at temperature below 50°C and particularly preferably at room temperature. Room temperature is in particular above 0°C, preferably above 10°C for low-temperature bonding. Room temperature is in particular a temperature between 17°C and 23°C. Thus, low-temperature bonding results in a particularly non-aggressive process, which is advantageous for many applications with different components.

[0016] The fact that in an intermediate step, after the first step and before the second step, the partial or total hydrophilization of the first SAM layer and / or the second SAM layer is carried out, according to a development of the invention it is possible, in a particularly advantageous manner, that the first SAM layer and / or the second SAM layer, at the beginning of the second step, in particular at the beginning of the bonding at low temperature, has hydrophilic properties, which promotes the storage near the surface of the water molecules necessary for bonding.

[0017] In the intermediate step after the first step and before the second step, the first SAM layer and / or the second SAM layer are partially or completely exposed to a reactive oxidizing atmosphere, in particular containing ozone, water vapor and / or reactive oxygen, so that an embodiment of the invention makes it possible to envisage an advantageous hydrophilization of the first and / or second SAM layers. It is also possible to envisage exposing the first SAM layer and / or the second SAM layer, locally or completely to the reactive oxidizing atmosphere.

[0018] In the intermediate step, after the first step and before the second step, electromagnetic radiation is used, in particular for the hydrophilization of the first SAM layer and / or the second SAM layer; this electromagnetic radiation preferably has an energy greater than 6 eV or a wavelength less than 200 nm so that according to one embodiment of the invention, advantageous hydrophilization can be envisaged.

[0019] According to an advantageous characteristic, it is possible to hydrophilize with energetic electromagnetic radiation, in an atmosphere, for example, of water vapor or oxygen. The high-energy electromagnetic radiation preferably has an energy greater than 6 eV or a wavelength less than 20 nm, which develops necessary reactive species by direct photoexcitation. The use of a photomask makes it possible to limit hydrophilization locally to predefined areas of the bonding surfaces.

[0020] As in an additional step after the second step, the first and second bonding surfaces, in particular the first and second bonded substrates, are exposed to a temperature above 150°C. This makes it possible to envisage, according to a development of the invention, that the bond generated in the second step between the first and the second bonding surface will be advantageously reinforced to have a permanent and very strong bonding bond of the plate. At this temperature, the water molecules react with the substrate material on the other side of the surface occupied by the thin oxide layer at the bonding surfaces and develop the bonds through the bonding boundary surface and between the SAM molecules. For example, the temperature of the first and second bonding surfaces exposed in the additional step is between 150°C and 400°C, preferably between 150°C and 300°C, and particularly preferably between 150°C and 200°C.

[0021] Since the first SAM layer and / or the second SAM layer deposited in the first step comprise chains of molecules, the first SAM layer and / or the second SAM layer preferably being formed by and / or using chains of siloxane molecules, one embodiment advantageously uses a SAM layer to achieve the bonding by adhesive bonding between the first and second adhesive surfaces. Preferably, the first and / or second SAM layers are, for example, chains of siloxane molecules, such as 3,3,5,5,7,7,7 Heptamethyl-trasiloxane or 2-Bis-Trimethylsiloxane, the methyl groups of which after deposition in a first step, preferably with a subsequent treatment, carried out in an intermediate step between the first step and the second step, are replaced by hydroxyl groups.To develop temporary adhesive bonds, it is envisaged, as an alternative or in addition, to use a pure hydrocarbon chain whose end terminations are oxidized by treatment, particularly in the intermediate step, so as to develop carboxyl or hydroxyl groups.

[0022] As in the first step, a precursor is used to deposit the first SAM layer or the second SAM layer, the precursor being in particular chain-shaped silane, such as chloro-silane or methoxyl-silane or ethoxy-silane or di-silasane or dimethyl-amine-silane, according to a development of the invention, the first and / or second SAM layer is advantageously deposited. The attachment groups of such chain-shaped SAM precursors react in the first step, preferably with hydroxyl surfaces of the first and / or second bonding surface so that the molecular chains attach to the first or second bonding surface. In particular, it may also happen that the two bonding surfaces have two different SAM layers.

[0023] According to a development of the invention, firstly in a preliminary step, a first and a second bonding surface are developed on the first substrate and on the second substrate, the bonding surfaces having at least thin oxides and / or hydroxyls on the surface. This is done, for example, by thermal oxidation, treatment or oxygen plasma, low pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD) and / or atomic layer deposition ALD). In the first step, at least one SAM layer is deposited on the bonding surface. Examples of precursors are chain-like chlorosiloxanes that react with the surface hydroxyls and thus attach the molecular chains to the bonding surface. In the second step, after the first step, the first and second bonding surfaces are finally bonded to each other at a lower temperature, preferably at room temperature. A particular advantage is that the chain-like SAM molecules, thanks to their mechanical flexibility, can partially compensate for the roughness and free volume left by the SAM layer or the two SAM layers due to their relatively low atomic densities. It is desirable that the first or second layer be hydrophilic to attract water molecules. The hydrophilicity of the molecular chains comes from the polar terminal groups such as, for example, the OH groups on the SAM molecule.If the SAM molecule already had such polar groups as precursors, before deposition (i.e. before or during the first step) there would be a risk of unwanted, anticipated polymerization of the molecules between them because the anchoring groups are also specifically immobilized by the separation of water molecules from the hydroxyls on the surface.

[0024] A direct, particle-free deposition of hydrophilic, OH-terminated SAM layers is not possible for this reason. In a particularly preferred manner according to the invention, however, it is possible, by local or surface exposure of the first and / or second SAM layer before bonding, i.e. before the second step and after the first step, to enrich with a reactive oxidizing atmosphere, for example, having ozone, water vapor and / or reactive oxygen for hydrophilization. Advantageously, this is done by applying energetic electromagnetic radiation to the atmosphere with water vapor or oxygen. The energetic electromagnetic radiation thus preferably has an energy greater than 6 eV or a wavelength less than 200 nm, which allows the necessary reactive species to be developed by direct photoexcitation.Additionally or alternatively, it is also possible to expose the subsequent plate bonding, i.e., in particular after the second step, to a temperature above 150°C (and for example below 400°C or below 300°C and below 200°C) at low temperature, in particular at room temperature, to develop a permanent, very strong plate bond. At such temperatures, the water molecules react with the substrate material on the other side of the upper surface corresponding to a thin oxide layer and the bonds via the bonding boundary surface and between the SAM molecules are then made.

[0025] Another object of the invention is a substrate device comprising a first substrate and a second substrate connected according to an embodiment of the invention, the bonding by adhesive bonding between the first adhesive surface and the second adhesive surface being carried out in particular using the first SAM layer or the second SAM layer.

[0026] According to another characteristic, the first substrate or the second substrate has a micromechanical element, in particular a MEMS element, preferably one or more sensors. The sensor(s) are preferably inertial sensors, in particular rotational speed sensors and / or acceleration sensors, pressure sensors, micro-mirrors, resonators and / or microphones. Other types of micromechanical sensors and actuators are conceivable. Brief description of the drawings

[0027] The present invention will be described below in more detail with the aid of an embodiment shown in the accompanying drawings in which:

[0028] [Fig.l] schematic representation of a method according to an embodiment of the present invention,

[0029] [Fig.2a] schematic representation of a method according to an embodiment of the invention,

[0030] [Fig.2b] schematic representation of a method according to an embodiment of the invention,

[0031] [Fig.3] schematic representation of a bonded connection according to the state of the art,

[0032] [Fig.4] schematic representation of a glued connection according to one embodiment of the present invention.

[0033] DESCRIPTION OF AN EMBODIMENT

[0034] [Fig. 1] is a schematic representation of a method for low-temperature bonding of a first substrate 10 and a second substrate 20 according to an embodiment of the present invention. In the preliminary step 100, which precedes the first step 101, a first bonding surface 11 is provided on the first substrate 10 and a second bonding surface 21 on the second substrate 20. Preferably, the bonding surfaces 11, 21 have, on the surface, an oxide and a hydroxyl. This is done, for example, by the natural development of oxidation, oxidation and LPVD coating, PECVD coating and / or ALD coating.

[0035] In the first step 101, a first SAM layer 1 is deposited on a first bonding surface 11 of the first substrate 10 and / or a second SAM layer on a second bonding surface 21 of the second substrate 20. As a precursor for obtaining the first and / or the second SAM layer 1, it is envisaged, for example, chain chlorosilanes which react with the surface hydroxides and thus attach the molecular chains to the bonding surface and in particular to the first or second bonding surface 11, 21.

[0036] In the second step 102 after the first step 101, the first and second bonding surfaces 11, 21 are bonded to each other at low temperature, preferably at room temperature; a bond is formed by bonding with the first SAM layer 1 or the second SAM layer. A substrate or a combination of wafers is thus developed. A particular advantage is that the chain-shaped SAM molecules can compensate for roughness due to their mechanical flexibility, the free volume left by the first SAM layer or the two SAM layers results from their relatively low atomic density ([Fig.4]).

[0037] It is desirable that the first or second SAM layer 1 be hydrophilic to attract water molecules. The hydrophilicity of the molecular chains is developed by the polar end groups, such as, for example, OH groups on the SAM molecules of the SAM1 layers. If the SAM molecule had such polar groups as precursors before deposition (i.e. before or during the first step 101) there would be a risk of premature, unwanted polymerization of the molecules with each other, because the attachment groups also specifically immobilize their separation of the water molecules from the hydrophilic ones on the surface.

[0038] Thus, it is not possible to have a direct, hydrophilic SAM layer deposition without particles. According to a development, it is however possible in an optional intermediate step 101', before the second step 102 and after the first step 101, to arrive by a local or surface exposure of the first and / or second SAM layer1, with respect to a reactive oxidizing atmosphere, for example, containing ozone, water vapor and / or reactive oxygen, to hydrophilize the first or second SAM layer, 1 as deposited. Advantageously, this is done, for example, by energy-rich electromagnetic radiation in a water vapor or oxygen atmosphere. This energy-rich electromagnetic radiation preferably has an energy greater than 6 eV or a wavelength less than 200 nm, which makes it possible to develop the necessary reactive species by local photoexcitation.

[0039] Additionally or alternatively, it is possible to expose the bonding of plates thus produced at low temperature, in particular at room temperature in an additional step 103 after the second step 102, to a temperature above 150°C to develop a very strong, permanent plate bond. At these temperatures, the water molecules react with the substrate material on the other side of that of the thin layer of oxides existing on the surface and they connect the bonds on the bonding boundary surface and between the SAM molecules.

[0040] The first or second SAM 1 layer are in particular chains of methylated siloxane molecules, for example 3,3,5,5,7,7,7 Heptamethyltetrasiloxane or 2-Bis-Trimethylsiloxane whose methyl groups after coating in the first step 101 with the post-treatment described above in intermediate step 101', are replaced by hydroxyl groups (see also Figures 2a and 2b).

[0041] To develop temporary bonding links, it is possible to consider using a simple hydrocarbon chain whose ends are oxidized by treatment so as to develop carboxyl or hydroxyl groups.

[0042] Figures 2a and 2b are schematic representations of a method according to an embodiment of the present invention. [Fig. 2a] shows the deposition of a first SAM layer 1 on a first bonding surface 11 of a first substrate 10 according to a first step 101 of the present invention. For example, the surface attachment reaction has been represented by the example of 1,1,1-Trichloro-3,3,5,5,7,7,7-heptamethyltetrasiloxane of [Fig. 2a]. In the left part of [Fig. 2b] there is a schematic representation of the hydroxylation, in particular in the intermediate step 101' by the example 1,1,1-Trichloro-3,3,5,5,7,7,7-heptamethyltetrasiloxane. In the right part of [Fig.2b] we have a schematic representation of the bonding operation in the second step 102 with the example of l,l,l-Trichloro-3,3,5,5,7,7,7-heptamethyltetrasiloxane.In the second step 102, the second bonding surface 21 of the second substrate 20 is bonded to the SAM layer 1 to the first bonding surface 11 of the first substrate 10, in particular, at low temperature.

[0043] [Fig. 3] is a schematic representation of a state-of-the-art adhesive bond. The two adhesive surfaces 11', 21' have roughness. The bonding takes place in the vicinity of the direct contact points of the two upper surfaces 11', 21', which, in many cases, results in an adhesive bond which, however, has only low strength.

[0044] On the other hand, [Fig. 4] is a schematic representation of a bonding by adhesive bonding according to an embodiment of the invention. Between the first and second bonding surfaces 11, 12, there is a first SAM layer 1 or a second SAM layer. The SAM layer 1, for a certain roughness, ensures a large contact area through which the chemical bonds between the two bonding surfaces 11, 12 develop. This results in a better bond.

Claims

Claims

1. A method for low-temperature bonding of a first substrate (10) and a second substrate (20), the first substrate (10) having a first bonding surface (11), the second substrate (20) having a second bonding surface (21), the method comprising the following steps: - in a first step (101), - on the first bonding surface (11) of the first substrate (10) which has an oxide or hydroxide surface, a first SAM1 layer is deposited as a chlorosilane precursor in molecular chains which react with the surface hydroxides and attach the molecular chains to the bonding surface (11), - in an intermediate step (101'), by local or surface exposure of the first SAM1 layer in a reactive oxidizing atmosphere, the deposited first SAM1 layer is hydrophilized,formed from chains of methylated siloxane molecules whose methyl groups after coating in the first step (101) are replaced by post-treatment in the intermediate step (101') by hydroxyl groups, - in a second step (102) the bonding is carried out at low temperature using the first hydrophilized SAM1 layer which creates a bonding connection between the first bonding surface (11) and the second bonding surface (21).,

2. Method according to claim 1, according to which the low-temperature bonding is carried out in the second step (102) at a temperature below 100°C, preferably at a temperature below 50°C and particularly preferably at room temperature.

3. Method according to one of the preceding claims, according to which in the first step (101) and in the intermediate step (101'), the second bonding surface (21) on the second surface (20) is treated in the same way as the first bonding surface (11) of the first substrate (10).

4. A method according to claim 3, wherein in the intermediate step (101'), after the first step (101) and before the second step (102), the first layer SAM1 and / or the second layer SAM are exposed in part or in full to an oxidizing reactive atmosphere, in particular comprising ozone, water vapor and / or reactive oxygen.

5. Method according to claim 3 or 4, according to which in the intermediate step (101') after the first step (101) and before the second step (102), the first SAM1 layer and / or the second SAM layer are hydrophilized by electromagnetic radiation, having an energy greater than 6 eV and / or a wavelength less than 200 nm.

6. Method according to one of the preceding claims, according to which in a further step (103), after the second step (102), the first bonded surface and the second bonded surface (11, 21), of the first substrate and the second bonded substrate (10, 20) are exposed to a temperature above 150°C.

7. Method according to any one of the preceding claims, according to which the first SAM1 layer and / or the second SAM layer, deposited in the first step (101) are chains of siloxane molecules.

8. A method according to any preceding claim, wherein in step (101), for the first layer SAM1 and / or the second layer the precursor comprises a chain-like silane such as chlorosilane or methoxysilane or ethoxysilane or disilazane or dimethylamine silane.

9. Substrate device comprising a first substrate (10) and a second substrate (20) bonded by the method according to one of the preceding claims, the bonding between the first bonding surface (11) and the second bonding surface (21) is carried out using the first SAM1 layer and the second SAM layer.

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