DE102021200230A1 - Low temperature bonding method, substrate assembly - Google Patents

Abstract

A method of low temperature bonding of a first substrate and a second substrate, the first substrate having a first bonding pad, the second substrate having a second bonding pad, the method comprising the steps of:-- in a first step, a first SAM layer is deposited the first bonding surface and/or a second SAM layer deposited on the second bonding surface,-- in a second step, after the first step, the low-temperature bonding is carried out, with the low-temperature bonding using the first SAM layer and/or the second SAM Layer a bond between the first bonding pad and the second bonding pad is formed.

Description

State of the art

The 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, the second substrate having a second bonding surface. Furthermore, the invention relates to a substrate arrangement.

Semiconductor components such as MEMS (microelectromechanical systems) are often subject to severe limitations in terms of the permissible process temperatures due to the functional materials used. Low-temperature bonding processes are therefore in demand, especially when joining two substrates - wafer bonding.

In the U.S. 2003/211705 A1 describes such a low-temperature bonding method in which a first polished surface is slightly etched and then bonded against a second surface. However, the method is essentially limited to planar surfaces with minimal roughness.

Further details on the processes involved in direct bonding are disclosed, for example, 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).

Disclosure of Invention

It is an object of the present invention to provide a method for low-temperature bonding with which an advantageous bond connection between a first and a second substrate can be formed in a gentle manner.

The method according to the invention for low-temperature bonding of a first substrate and a second substrate according to the main claim has the advantage over the prior art that a particularly gentle low-temperature bonding of two surfaces, in particular bonding surfaces, can be achieved, which tolerates a higher roughness of the bonding surfaces and can be surface-selective. It is thus possible according to the invention to achieve stable bond connections that can be formed locally and have a high roughness tolerance at low bonding temperatures.

It is particularly conceivable according to the invention that the first bonding surface and the second bonding surface are preferably connected directly or directly by a first SAM layer and/or a second SAM layer during low-temperature bonding. In this case, it is particularly preferably possible for no further additionally deposited intermediate layers (apart from the first and/or second SAM layer) to be present between the first and second bonding surface, in particular at the beginning of the low-temperature bonding.

Thus, according to the invention, a substrate assembly, in particular comprising a MEMS component, can be produced particularly gently. In particular, it is conceivable that the composite substrate or the substrate arrangement produced with the aid of the method according to the invention is an SOI (silicon on insulator) wafer.

According to the invention, the first and/or second SAM layer is to be understood as meaning self-organizing monolayer layers (self-assembled monolayer, SAM).

Water molecules play a crucial role in direct bonding of two surfaces. They initiate the wafer bond at low temperatures, particularly at room temperature, then diffuse into the superficial oxides of the adjoining bonding surfaces and react there with the elimination of hydrogen. In order to provide sufficient water molecules on the bonding surface, it is known from the prior art to carry out an etching step before the bonding step, which creates an amorphous layer with a free volume on the bonding surface. The amorphous layer created in this way promotes the storage of water molecules and enables rapid diffusion and rearrangement processes at the interface. However, such known methods require direct mechanical contact of the bonding surfaces so that chemical bonds can form across the interface. Therefore, these known methods do not tolerate any great roughness of the bonding surfaces.

According to the invention, on the other hand, it is possible for the first and/or second SAM layer to enable improved low-temperature bonding of substrates, with greater surface roughness of the bonding surfaces being tolerable and moreover locally limited bonding or structured bonding being made possible.

Advantageous developments and embodiments result from the dependent claims.

According to one embodiment, it is preferably conceivable for the low-temperature bonding in the second step to take place at a temperature below of 100°C, preferably at a temperature below 50°C, particularly preferably at room temperature. In particular, a temperature above 0° C., preferably above 10° C., is conceivable for low-temperature bonding. The room temperature is understood in particular as a temperature between 17°C and 23°C inclusive. It is thus possible to provide a particularly gentle method by bonding at low temperatures, which is advantageous for a large number of different components and applications.

The fact that hydrophilization is carried out partially or completely for the first SAM layer and/or the second SAM layer in an intermediate step, after the first step and before the second step, makes it particularly advantageous according to one embodiment of the present invention Way possible 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 low-temperature bonding, has hydrophilic properties, which promotes the near-surface storage of the water molecules necessary for bonding.

Because in the intermediate step, after the first step and before the second step, the first SAM layer and/or the second SAM layer is partially or completely exposed to a reactive-oxidizing atmosphere, in particular comprising ozone, water vapor and/or reactive oxygen it is conceivable according to one embodiment of the present invention that an advantageous hydrophilization of the first and/or second SAM layer is carried out. It is conceivable for the first SAM layer and/or the second SAM layer to be exposed locally or over the entire surface to the reactive-oxidizing atmosphere.

Because electromagnetic radiation is used in the intermediate step, after the first step and before the second step, in particular for making the first SAM layer and/or the second SAM layer hydrophilic, the electromagnetic radiation preferably having an energy of greater than 6 eV and/or has a wavelength of less than 200 nm, it is conceivable according to one embodiment of the present invention that an advantageous hydrophilization is carried out. Hydrophilization can thus advantageously take place by means of high-energy electromagnetic radiation in an atmosphere, for example with water vapor and/or oxygen. The high-energy electromagnetic radiation preferably has an energy greater than 6 eV or a wavelength less than 200 nm, as a result of which necessary reactive species can arise through direct photoexcitation. By using a photomask, the hydrophilization can be limited locally to the intended areas of the bonding surface(s).

Due to the fact that in an additional step, after the second step, the bonded first and second bonding surface, and in particular the bonded first and second substrate, are exposed to a temperature of greater than 150° C., it is conceivable according to one embodiment of the present invention that the bond connection produced in the second step between the first and second bonding surface can be particularly advantageously strengthened in order to form a permanent and high-strength wafer bond connection. At this temperature, the water molecules react with the substrate material beyond the thin oxide layer present on the surface of the bonding surfaces and the bonds across the bonding interface and between the SAM molecules continue to crosslink. It is conceivable, for example, that the temperature to which the first and second bonding surfaces are exposed in the additional step is between 150° C. and 400° C., preferably between 150° C. and 300° C., more preferably between 150° C. and 200° C. lies.

Because the first SAM layer deposited in the first step and/or the second SAM layer comprises chain molecules, the first SAM layer and/or the second SAM layer preferably being formed by and/or with the aid of siloxane chain molecules, it is conceivable according to an embodiment of the present invention that an advantageous SAM layer is used to produce the bond connection between the first and second bonding surface. It is preferably possible for the first and/or second SAM layer to be, for example, methylated siloxane chain molecules, such as 3,3,5,5,7,7,7-heptamethyltetrasiloxane or 2-BIS-TRIMETHYLSILOXANE, whose methyl groups are replaced by hydroxyl groups after the deposition in the first step, preferably by means of a post-treatment in the intermediate step, after the first step and before the second step. For the formation of temporary bonded connections, it is alternatively or additionally conceivable to use pure hydrocarbon chains whose terminal termination is oxidized by the treatment, in particular in the intermediate step, so that carboxyl or hydroxyl groups are formed.

Because a precursor is used in the first step for depositing the first SAM layer and/or the second SAM layer, the precursor being in particular chain-shaped silanes such as chlorosilanes and/or methoxysilanes and/or ethoxysilanes and/or disilazanes , and/or dimethylaminosilane, it is conceivable according to one embodiment of the present invention to advantageously coat the first and/or second SAM layer divorce In the first step, the anchor groups of these chain-like SAM precursors preferably react with the surface hydroxyls of the first and/or second bonding surface, so that the molecular chains are anchored to the bonding surface or surfaces. In particular, it can also be the case that two different SAM layers are applied to the two bonding surfaces.

According to one embodiment of the present invention, it is conceivable that a first and a second bonding surface are initially formed on the first substrate and second substrate in a preliminary step, the bonding surfaces having thin oxides and/or hydroxyls at least on the surface. This is done, for example, by thermal oxidation, oxygen plasma treatment, LPCVD (low pressure chemical vapor deposition), PECVD (plasma-enhanced chemical vapor deposition) and/or ALD (atomic layer deposition) coating. In the first step, a SAM layer is then deposited on at least one of the bonding surfaces. For example, chain-like chlorosilanes are used as precursors, which react with the surface hydroxyls and thus anchor the molecular chains to the bond surface. In the second step, after the first step, the first and second bonding surfaces are finally bonded to one another at a low temperature, preferably at room temperature. A particular advantage is that the chain-like SAM molecules can partially compensate for roughness due to their mechanical flexibility and the SAM layer or the two SAM layers provide free volume due to their comparatively lower atomic densities. It is desirable here that the first and/or second SAM layer is hydrophilic in order to attract water molecules. Hydrophilicity of molecular chains is caused by terminating polar end groups such as OH groups on the SAM molecule. If the SAM molecule already had these polar groups as a precursor before the deposition (i.e. before or in the first step), there would be a risk of unwanted premature polymerization of the molecules among themselves, since the anchor groups are also specifically formed by splitting off water molecules on hydroxyls on the surface be immobilized. A direct and particle-free deposition of hydrophilic, OH-terminated SAM layers is therefore not possible. However, it is particularly preferably possible according to the invention to expose the first and/or second SAM layer to a reactive-oxidizing atmosphere, for example containing ozone, water vapor and / or reactive oxygen to achieve hydrophilization. This can advantageously be done, for example, by high-energy electromagnetic radiation in an atmosphere with water vapor and/or oxygen. The high-energy electromagnetic radiation preferably has an energy of more than 6 eV or a wavelength of less than 200 nm, as a result of which necessary reactive species can arise locally through direct photoexcitation. It is additionally or alternatively possible to subject the wafer assembly bonded at a low temperature, in particular at room temperature, subsequently, i.e. in particular after the second step, to a temperature of greater than 150°C (and for example below 400°C or below 300°C or below 200°C) to form a high strength permanent wafer bond. At this temperature, the water molecules react with the substrate material beyond the thin oxide layer present on the surface and the bonds across the bonding interface and between the SAM molecules continue to crosslink.

Another subject matter of the present invention is a substrate arrangement, comprising a first substrate and a second substrate bonded using a method according to an embodiment of the present invention, the bond connection between the first bonding surface and the second bonding surface being made in particular using the first SAM layer and/or the second SAM layer is formed.

In particular, it is conceivable that the first substrate and/or the second substrate has a micromechanical element, in particular a MEMS (microelectromechanical element), preferably one or more sensors. The sensor or sensors can preferably be inertial sensors, in particular yaw rate sensors and/or acceleration sensors, pressure sensors, micromirrors, resonators and/or microphones. Other micromechanical sensor types or actuators are also conceivable.

Exemplary embodiments of the present invention are illustrated in the drawings and explained in more detail in the following description.

character list

• 1 shows a schematic representation of a method according to an embodiment of the present invention.
• 2a and 2 B FIG. 12 shows schematic representations of a method according to an embodiment of the present invention.
• 3 shows a schematic representation of a bond according to the prior art.
• 4 12 shows a schematic representation of a bond connection according to an embodiment of the present invention.

Embodiments of the invention

In the various figures, the same parts are always provided with the same reference symbols and are therefore usually named or mentioned only once.

In 1 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 a preliminary step 100, before a first step 101, a first bonding pad 11 on the first substrate 10 and a second bonding pad 21 on the second substrate 20 are provided. The bonding surfaces 11, 21 preferably have oxides and hydroxyls at least on the surface. This is done, for example, by natural oxide formation, thermal oxidation, LPCVD, PECVD and/or ALD coating. 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 is deposited on a second bonding surface 21 of the second substrate 20 . As a precursor for producing the first and/or second SAM layer 1, chain-like chlorosilanes are used, for example, which react with the surface hydroxyls and thus anchor the molecular chains on the bonding surface, i.e. in particular on the first and/or second bonding surface 11, 21 . In the second step 102, after the first step 101, the first and second bonding pads 11, 21 are bonded to one another at low temperature, preferably at room temperature, a bond connection being formed with the aid of the first SAM layer 1 and/or the second SAM layer becomes. A substrate arrangement or a wafer assembly is thus created. A particular advantage is that the chain-like SAM molecules can compensate for roughness due to their mechanical flexibility and that the SAM layer or the two SAM layers provide free volume due to their comparatively lower atomic density (cf. 4 ). It is desirable here that the first and/or second SAM layer 1 is hydrophilic in order to attract water molecules. Hydrophilicity of molecular chains is caused by terminating polar end groups such as OH groups on the SAM molecules of the SAM layer(s) 1. If the SAM molecule already had these polar groups as a precursor before the deposition (i.e. before or in the first step 101 ). A direct particle-free deposition of hydrophilic SAM layers is therefore not possible. According to the illustrated embodiment, however, it is possible in an optional intermediate step 101', before the second step 102 and after the first step 101, by exposing the first and/or second SAM layer 1 locally or over a large area to a reactive-oxidizing atmosphere, for example comprising ozone, water vapor and/or reactive oxygen, to achieve hydrophilization of the deposited first and/or second SAM layer 1. This can advantageously be done, for example, by high-energy electromagnetic radiation in an atmosphere with water vapor and/or oxygen. The high-energy electromagnetic radiation preferably has an energy of more than 6 eV or a wavelength of less than 200 nm, as a result of which necessary reactive species can arise locally as a result of direct photoexcitation.

It is additionally or alternatively possible to expose the wafer assembly bonded at low temperature, in particular at room temperature, to a temperature of greater than 150° C. in an additional step 103 after the second step 102 in order to form a high-strength permanent wafer bond. At this temperature, the water molecules react with the substrate material beyond the thin oxide layer present on the surface and the bonds across the bonding interface and between the SAM molecules continue to crosslink.

The first and/or second SAM layer 1 can be, in particular, methylated siloxane chain molecules, such as 3,3,5,5,7,7,7-heptamethyltetrasiloxane or 2-BIS-TRIMETHYLSILOXANE, whose methyl groups follow of the coating in the first step 101 by means of the previously described post-treatment in the intermediate step 101' are replaced by hydroxyl groups (cf. also 2a and 2 B) .

To form temporary bonds, it is conceivable to use pure hydrocarbon chains whose terminal termination is oxidized by the treatment, so that carboxyl or hydroxyl groups are formed.

In the 2a and 2 B Schematic representations of a method according to an embodiment of the present invention are shown. In 2a 1 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. Here, the surface anchoring reaction using the example of 1,1,1-trichloro-3,3,5,5,7,7,7-heptamethyltetrasiloxane in 2a shown. In the left part of 2 B is a schematic representation of the hydroxylation, in particular in the intermediate step 101', using the example of 1,1,1-trichloro-3,3,5,5,7,7,7-heptamethyltetrasiloxane. In the right part of 2 B a schematic representation of the bonding process in the second step 102 is shown using the example of 1,1,1-trichloro-3,3,5,5,7,7,7-heptamethyltetrasiloxane. In the second step 102, the second bonding pad 21 of the second substrate 20 is bonded to the first bonding pad 11 of the first substrate 10 via the SAM layer 1, in particular at a low temperature.

In 3 a schematic representation of a bond connection according to the prior art is shown. The two bonding surfaces 11', 21' have roughness. A chemical bond only occurs in the vicinity of the direct contact points of the two surfaces 11', 21', which in many cases leads to a bonded connection that at best has little strength.

In 4 on the other hand, a schematic representation of a bond connection according to an embodiment of the present invention is shown. A first SAM layer 1 and/or a second SAM layer is arranged between the first and second bonding surface 11, 12. For a given roughness, the flexible SAM layer 1 provides a larger contact area over which chemical bonds can form between the two bonding surfaces 11, 12. This results in an improved connection.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US2003211705A1 [0003]

Claims (9)

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 includes the following steps: -- in a first step (101) a first SAM layer (1) is deposited 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, the low-temperature bonding is carried out, with low-temperature bonding using the first SAM layer (1) and/or the second SAM layer to create a bond between the first bonding surface (11) and the second bonding surface (21) is formed. procedure after claim 1 , wherein the low-temperature bonding in the second step (102) is carried out at a temperature below 100° C., preferably at a temperature below 50° C., particularly preferably at room temperature. Method according to one of the preceding claims, wherein in an intermediate step (101'), after the first step (101) and before the second step (102), for the first SAM layer (1) and/or the second SAM layer partially or complete hydrophilization is carried out. procedure after claim 3 , wherein in the intermediate step (101 '), after the first step (101) and before the second step (102), the first SAM layer (1) and / or the second SAM layer partially or completely a reactive-oxidizing atmosphere , in particular comprising ozone, water vapor and/or reactive oxygen, is or are exposed. Procedure according to one of claims 3 or 4 , wherein electromagnetic radiation is used in the intermediate step (101'), after the first step (101) and before the second step (102), in particular for making the first SAM layer (1) and/or the second SAM layer hydrophilic, wherein the electromagnetic radiation preferably has an energy of greater than 6 eV and/or a wavelength of less than 200 nm. Method according to one of the preceding claims, wherein in an additional step (103), after the second step (102), the bonded first and second bonding surface (11, 21), and in particular the bonded first and second substrate (10, 20), one exposed to temperatures in excess of 150°C. Method according to one of the preceding claims, wherein the first SAM layer (1) and/or the second SAM layer deposited in the first step (101) comprises chain molecules, wherein the first SAM layer (1) and/or the second SAM Layer is preferably formed by and / or with the help of siloxane chain molecules. Method according to one of the preceding claims, wherein in the first step (101) for the deposition of the first SAM layer (1) and / or the second SAM layer, a precursor is used, wherein the precursor in particular chain-shaped silanes, such as chlorosilanes, and / or methoxysilanes, and/or ethoxysilanes, and/or disilazanes, and/or dimethylaminosilanes. Substrate arrangement, comprising a first substrate (10) and a second substrate (20) bonded using a method according to one of the preceding claims, wherein the bonding connection between the first bonding surface (11) and the second bonding surface (21) in particular using the first SAM layer ( 1) and/or the second SAM layer is formed.

Images