Methods for hydrophilic bonding of substrates

Abstract

The present invention relates to a method for hydrophilically bonding a first substrate (S1) to a second substrate (S2), the method comprising: bringing the first substrate (S1) into contact with the second substrate (S2) to form a bonding interface between the main surface of the first substrate and the main surface of the second substrate, applying a heat treatment suitable for sealing the bonding interface, the method being characterized in that it comprises: before the step of contacting, depositing a bonding layer (12) made of a non-metallic material on the main surface of the first substrate and / or the second substrate, the non-metallic material being permeable to hydrogen and having a yield strength at the temperature of the heat treatment lower than at least one of the materials of the first substrate (S1) and the second substrate (S2) located at the bonding interface, the thickness of the layer being 1 nm to 6 nm, and the heat treatment being carried out at a temperature lower than or equal to 900° C., and preferably lower than or equal to 600° C.

Description

Technical Field

[0001] The present invention relates to methods for hydrophilic bonding of substrates for applications in microelectronic, optoelectronic or optical devices. Background Art

[0002] It is known to bond substrates, particularly semiconductor substrates, to form structures suitable for forming devices for use in microelectronic, optoelectronic or optical devices.

[0003] For example, a semiconductor-on-insulator structure includes, in sequence, a carrier substrate, an electrically insulating layer, and a thin semiconductor layer (called an active layer). When the active layer is made of silicon, the structure is called a silicon-on-insulator (SOI) structure. The electrically insulating layer is typically a silicon oxide layer and is typically called a buried oxide or BOX layer.

[0004] A particularly advantageous method for forming such a structure is Smart Cut TM Method. This method generally includes the following steps:

[0005] - providing a carrier substrate;

[0006] - providing a silicon donor substrate covered with a silicon oxide layer formed by thermal oxidation;

[0007] - implanting ionic species (e.g. hydrogen and / or helium) into the donor substrate through the silicon oxide layer to form weakened areas delineating the thin layer to be transferred;

[0008] - bonding the donor substrate to the carrier substrate, with the silicon oxide layer being located at the bonding interface;

[0009] - Splitting the donor substrate along the weakened areas and detaching the remaining donor substrate to transfer the thin silicon layer to the donor substrate.

[0010] Preferably, the bonding is hydrophilic, ie the adhesion between the donor substrate and the carrier substrate is obtained via water molecules present at the bonding interface. The water is subsequently removed by subjecting the substrate to a heat treatment.

[0011] To ensure high-quality bonding, the surface of the carrier substrate in contact with the donor substrate must have very low roughness. Therefore, before bonding, the substrates usually undergo a treatment aimed at obtaining the required roughness.

[0012] However, even if the surface has a suitable roughness, due to the high hardness and rigidity of the substrate, contact will always be made via several asperities.

[0013] As can be seen in Figure 1In the left part, the protrusions present on the surfaces of the substrates S1 and S2 create cavities C at the interface between the two substrates; the bonding interface is therefore not completely closed. However, when a high temperature heat treatment is applied, the contact surface grows until the protrusions are flattened, which removes the cavities; the bonding interface I is then closed ( Figure 1 on the right side of the ).

[0014] Figure 2 3 is a high-resolution transmission electron microscope (HRTEM) micrograph of a cross section of the bonding interface I between the silicon oxide (SiO2) layer and the silicon (Si) substrate at the end of such a heat treatment. The interface I is continuous and does not exhibit cavities, making it perfectly closed.

[0015] However, such sealing of the bonding interface can only be obtained at the expense of a high thermal budget. Thus, for bonding between two thermal oxide layers, the temperature to be applied is at least 1200° C. for several hours. For bonding between a thermal oxide layer and a silicon substrate (potentially covered with a native oxide), the temperature to be applied is 1100° C. for 2 hours; this temperature can be reduced to 1050° C. for 2 hours when a plasma treatment is previously applied to the oxide layer.

[0016] Such high-temperature thermal treatments are usually very expensive, since semiconductors are very susceptible to damage at high temperatures. They must therefore be carried out with a slow temperature ramp to avoid the risk of deformation of the substrate, which results in long treatment times, or else with extremely controlled heating, which requires complex parts of the equipment. Furthermore, the thermal treatment for sealing the bonding interface is usually the only step in the process for manufacturing structures requiring such high temperatures.

[0017] Therefore, it is desirable to minimize the temperature of the heat treatment used to seal the interface while still ensuring sealing of the interface.

[0018] Specifically, interfacial enclosed defects can be extremely detrimental to the integrity and performance of the bonded structure.

[0019] The first consequence of an imperfect closure of the interface is localized detachment, especially at the edges of the bonded structures. The areas that detach at the edge of the wafer are locally redeposited on the surface of the substrate, thus forming areas that are unsuitable for the subsequent manufacture of electronic devices. These defects are called flakes. Therefore, Figure 3 A top view image showing the locations of defects on the SOI structure associated with incomplete closure of the bonding interface, identified by black dots. Figure 3 The three insets on the left part of are scanning electron microscope (SEM) micrographs of three flake-type defects F having different shapes and sizes.

[0020] A second consequence of the imperfect closure of the interface is that the cavities present at the interface, in particular on the edges of the structure, are areas that are susceptible to being etched preferably by chemical etchants. Specifically, the etchant is able to wet the interface through such cavities and preferably etches the material present at the interface. Therefore, Figure 4 A cross-sectional view showing the interface between two silicon oxide layers (SiO2(1), SiO2(2)) belonging to one substrate S1, S2 respectively. The image on the right is an enlarged view of the image on the left. In these images, the lighter area at the interface I corresponds to the silicon oxide that has been etched.

[0021] Adding a metal layer (e.g., a copper or tungsten layer) to the bonding interface or indeed to the polymer deposit allows low interface sealing temperatures to be achieved, typically below 500° C. However, they are not compatible with a large number of microelectronic applications because they are conductive or create impurities in the semiconductor substrate. In addition, polymers are unstable at circuit fabrication temperatures.

[0022] Furthermore, non-hydrophilic bonding techniques (e.g. ultra-high vacuum bonding) do exist, where the surfaces of the substrates in contact are mechanically activated beforehand by ion bombardment. In this case, interface sealing occurs at room temperature. This technique is called surface activated bonding (SAB). However, this technique is incompatible with the presence of oxides at the bonding interface. Summary of the invention

[0023] It is therefore an object of the present invention to devise a method for the hydrophilic bonding of two substrates, wherein the bonding interface is sealed by heat treatment at lower temperatures than in prior art methods.

[0024] To this end, the present invention provides a method for hydrophilically bonding a first substrate to a second substrate, the method comprising:

[0025] - contacting a first substrate with a second substrate to form a bonding interface between a major surface of the first substrate and a major surface of the second substrate,

[0026] - applying a heat treatment suitable for closing said bonding interface,

[0027] The method is characterized in that it includes: before the contacting step, depositing a bonding layer made of a non-metallic material on the main surface of the first substrate and / or the second substrate, the non-metallic material being permeable to hydrogen and having a yield strength (yield stress) at the temperature of the heat treatment lower than the yield strength of at least one of the materials of the first substrate and the second substrate located at the bonding interface, the thickness of the layer being 1 nm to 6 nm.

[0028] Furthermore, the bonding heat treatment is performed at a temperature lower than or equal to 900°C, and preferably lower than or equal to 600°C.

[0029] The yield strength is the stress at which the ductile material in question begins to deform plastically. The yield strength is a well-known property of materials and its variation as a function of temperature is determinable; therefore, a comparison of the yield strengths of two materials at a given temperature is within the capabilities of one skilled in the art.

[0030] Thus, for example, at a temperature of about 900° C., the yield strength of amorphous silicon is lower than that of crystalline silicon or polycrystalline silicon (usually covered with a native oxide) and silicon oxide. The same applies to amorphous germanium.

[0031] The yield strength quantifies the ability of the material present at the bonding interface to deform plastically at the temperature at which the heat treatment is performed.

[0032] Thus, the bonding layer is more able to conform to the major surface of the opposing substrate to close the interface, and is performed at a lower temperature.

[0033] Furthermore, this very thin bonding layer is compatible with hydrophilic bonding chemistries. Specifically, the layer is sufficiently porous to allow the transfer of hydrogen produced by the reaction of water with the silicon of the second substrate to the silicon oxide layer, which avoids defect-related problems encountered during silicon-to-silicon bonding.

[0034] According to other advantageous features, when this is technically appropriate, the following are considered, alone or in combination:

[0035] - the first substrate and the second substrate are semiconductor substrates;

[0036] - the first substrate comprises a silicon oxide surface layer different from a native oxide, and the bonding layer is deposited on said silicon oxide layer;

[0037] - the silicon oxide surface layer is formed by thermal oxidation of the first substrate;

[0038] - the second substrate comprises a silicon oxide surface layer different from a native oxide, and the bonding layer is also deposited on said silicon oxide layer;

[0039] - after applying a heat treatment for closing the bonding interface, the method comprises a step of thinning the first substrate to transfer the thin silicon layer of the first substrate to the second substrate;

[0040] - between the steps of depositing the bonding layer and bringing the first substrate into contact with the second substrate, the method comprises forming a silicon oxide surface layer on the first substrate and implanting ionic species into the first substrate through the silicon oxide layer to form a weakened area delineating the semiconductor layer to be transferred;

[0041] - between the steps of depositing the bonding layer and bringing the first substrate into contact with the second substrate, the method comprises subjecting the major surfaces of these substrates to a hydrophilic treatment, applying water to the major surfaces of the substrates to form a water film on said major surfaces;

[0042] - before depositing the bonding layer, the method comprises a step of cleaning the main surface on which said layer must be deposited with an oxidizing solution;

[0043] - the second substrate is a silicon substrate, said substrate being covered with a native silicon oxide layer;

[0044] - during the heat treatment for closing the bonding interface, the method comprises oxidizing a surface section of the silicon of the second substrate through the native oxide layer;

[0045] - the material of the bonding layer is selected from: amorphous silicon and amorphous germanium;

[0046] - the material of the bonding layer is amorphous silicon, and the amorphous silicon layer is formed in an epitaxial reactor at a temperature below 550° C.;

[0047] - The amorphous silicon layer is formed from a precursor selected from the following: disilane (Si2H6), silane (SiH4) or a precursor of formula Si n H 2n+2 A liquid precursor of wherein n is an integer greater than 2;

[0048] - during the heat treatment for closing the bonding interface, the method comprises oxidizing at least a portion of the bonding layer;

[0049] The thickness of the bonding layer is chosen so that the entire layer is oxidized during the heat treatment for sealing the bonding interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Other features and advantages of the present invention will become apparent from the following embodiments with reference to the accompanying drawings, in which:

[0051] - Figure 1 Schematically showing the closure of the bonding interface;

[0052] - Figure 2 is a high-resolution transmission electron microscopy (HRTEM) micrograph of a cross section of a completely closed bonding interface between silicon oxide and silicon;

[0053] - Figure 3 An image of an SOI substrate covered with flake-type defects and a scanning electron microscope (SEM) micrograph of such defects are shown;

[0054] - Figure 4 is a cross-sectional image of an imperfectly closed bonding interface that undergoes preferred chemical etching;

[0055] - Figure 5A is a schematic cross-sectional view of a step before contacting the substrates in a first embodiment of the method according to the present invention;

[0056] - Figure 5B yes Figure 5A A schematic cross-sectional view of the substrates after they have been contacted but before the bonding interface is closed;

[0057] - Figure 5C After heat treatment, Figure 5B A schematic cross-sectional view of the substrate when the bonding interface is closed;

[0058] - Fig. 6A shows a top view image above a structure combined with an amorphous silicon layer having a thickness greater than or equal to 8 nm;

[0059] - Figure 6B A top view image above the structure is shown in combination with an amorphous silicon layer having a thickness of 2.5 nm to 6 nm;

[0060] - Figure 7 is a transmission electron microscope (TEM) micrograph of a cross section of a bonding interface between a silicon substrate and a silicon oxide layer on which an amorphous silicon layer with a thickness of 6 nm has been deposited after heat treatment at 500° C.;

[0061] - Fig. 8A is a schematic cross-sectional view of a step before contacting the substrates in a second embodiment of the method according to the present invention;

[0062] - Figure 8B yes Fig. 8A A schematic cross-sectional view of the substrates after they have been contacted but before the bonding interface is closed;

[0063] - Figure 8C After heat treatment, Figure 8B A schematic cross-sectional view of the substrate when the bonding interface is closed;

[0064] - Fig. 9 is a graph showing the (unitless) ratio R between the horizontal etch rate and the vertical etch rate as a function of the interface sealing temperature T (° C.) for the standard bonding method (a) and the bonding method of the present invention (b).

[0065] For the sake of legibility of the drawings, the thickness of the various layers shown are not necessarily shown to scale. DETAILED DESCRIPTION

[0066] Overview of the method

[0067] FIG. 5A to FIG. 5C Successive steps of a method according to a first embodiment of the invention are shown.

[0068] Reference Figure 5A , a first substrate S1 and a second substrate S2 to be bonded along one of their main surfaces are provided.

[0069] According to one embodiment, the first substrate and the second substrate are semiconductor substrates, i.e. substrates comprising at least one semiconductor (e.g. silicon) layer. The substrates may optionally include other materials, such as electrical insulators (e.g. silicon oxide (SiO2)) layers.

[0070] In general, the present invention is applicable to any substrate that is compatible with hydrophilic bonding. Certain substrates are naturally hydrophilic; those that are not hydrophilic can be treated to render their surfaces hydrophilic, as described below.

[0071] Before the substrates are brought into contact, a layer 12 of material having both low yield strength and a certain permeability to hydrogen is deposited at low temperature (200° C. to 600° C.) on the substrates S1 and / or S2. In the example shown, the bonding layer is deposited on the substrate S1, but alternatively or additionally, it can also be deposited on the substrate S2.

[0072] In practice, the bonding layer is preferably deposited on a substrate whose material present at the bonding interface has the highest yield strength at the temperature at which the heat treatment for closing the interface is performed. Thus, the negative effects of the material with a high yield strength are minimized. For example, in the case of an oxide bonded to silicon, the bonding layer is preferably deposited on a substrate comprising an oxide layer.

[0073] The thickness of the bonding layer is selected to be thin enough to provide some porosity to the layer. The thickness is typically less than 10 nm, and preferably between 1 nm and 6 nm.

[0074] According to an advantageous embodiment, in particular when the material present on the main surface of the substrate S1, S2 is silicon or silicon oxide, the material of the bonding layer is amorphous silicon or amorphous germanium. Amorphous silicon is a particularly advantageous choice for the bonding layer, because at high temperatures (typically above 900° C.), the yield strength of amorphous silicon is lower than the yield strength of crystalline silicon and silicon oxide. Alternatively, amorphous germanium is also suitable for the present application, because its yield strength is lower than the yield strength of these materials.

[0075] In contrast, the bonding layer does not include metal, particularly due to the disadvantages pointed out above.

[0076] Figure 5B Substrates S1 and S2 are shown contacting via a bonding layer 12 .

[0077] Hydrophilic bonding usually requires that the substrate face undergo a hydrophilic treatment, such as SC1 cleaning, followed by rinsing in water. At the end of this step, the substrate surface is covered with a thin film (about 2 or 3 monolayers) of water that is hydrogen-bonded to the major face.

[0078] Before the heat treatment for closing the interface, the main surfaces of the substrates S1 and S2, although smooth, contain protrusions where contact between the substrates occurs. Cavities extend between such protrusions; therefore, the interface I is not closed.

[0079] Figure 5C The structure at the end of the heat treatment for sealing the bonding interface is shown. The heat treatment lasts for several hours, preferably about 2 hours, and includes a relatively slowed temperature ramp so as not to damage the substrate. The temperature of the heat treatment can be defined by any person skilled in the art, for example based on tests of interfaces of multiple identical structures treated at different temperatures where they are sealed. The lowest temperature among the temperatures that cause the complete sealing of the bonding interface is preferably selected.

[0080] Under the action of temperature and the mutual attraction of the contact surfaces, the protrusions of the bonding layer become flat, thereby removing the gap cavity and closing the interface I.

[0081] In addition to this mechanical action, a chemical reaction occurs between water present at the bonding interface and the semiconductor during the heat treatment, thereby releasing hydrogen.

[0082] In the case of oxide combined with the hydrophilicity of silicon, the chemical reaction is written as:

[0083] 2H2O+Si→SiO2+2H2

[0084] In other words, the water present at the bonding interface passes through the native oxide present on the silicon and oxidizes the silicon. This action occurs at 150° C. and causes the release of hydrogen, which diffuses into the oxide layer on the other side of the bonding interface and is stored therein. If the oxide layer is too thin or there is a diffusion barrier between the bonding interface and the oxide layer, the hydrogen reopens the bonding interface by forming bubbles. In this regard, reference may be made to the publication [Vincent et al.].

[0085] Therefore, there may be concern that the bonding layer will form such a barrier and will cause the bonded structure to exhibit a high defect density.

[0086] therefore, Fig. 6A Top view images of buried oxide layers of structures bonded to amorphous silicon layers having a thickness greater than or equal to 8 nm (i.e., from left to right; 8 nm, 14 nm, and 28 nm) are shown. White patches represent hydrogen bubbles formed at the bonding interface. It can be seen that these three structures exhibit high defect density.

[0087] In contrast, surprisingly, no such high defect density is produced for structures combined with amorphous silicon layers having a thickness of 1 nm to 6 nm. Figure 6B A top view image of a structure showing a buried oxide layer combined with an amorphous silicon layer having a thickness of 2.5 nm to 6 nm; Fig. 6A The absence of white patches observed in shows the absence of hydrogen bubbles. Therefore, the amorphous silicon layer can be considered thin enough to allow hydrogen to diffuse into the buried oxide layer, thereby ensuring a high-quality bond.

[0088] Exemplary Embodiments

[0089] According to reference FIG. 5A to FIG. 5C In one specific application of the method described, substrate S1 is a silicon substrate 10 covered with a silicon oxide layer 11. The silicon oxide layer is preferably formed by thermal oxidation of silicon. Substrate S2 is a silicon substrate, which typically has a native silicon oxide layer (not shown) on its surface.

[0090] It will be recalled that the native oxide layer differs from the thermal oxide layer in its thickness (the native oxide layer is much thinner than the thermal oxide layer) and in its stoichiometry. The native oxide layer is naturally present on the substrate surface and is not intended to perform a specific function. In contrast, the thermal oxide layer is generally intended to perform an electrical insulation function within the structure obtained by bonding two substrates. Thus, in the case of an SOI wafer, the thermal oxide layer is intended to form the buried oxide (BOX) layer of the SOI wafer.

[0091] The bonding layer 12 made of amorphous silicon may be deposited as follows.

[0092] The surface of the substrate intended to receive the amorphous silicon layer is cleaned by an oxidizing solution, for example a solution such as O3 / HF / O3 or O3 / HF / SCl.

[0093] To ensure the amorphous and smooth characteristics of amorphous silicon, the substrate is placed in an epitaxial reactor raised to a relatively low temperature. According to one embodiment, the precursor used is disilane (Si2H6); the optimal deposition temperature is 475°C to 550°C. The growth rate is then 5 to 10 nm / mn. According to another embodiment, the precursor used is silane (SiH4); the growth rate is lower. According to other embodiments, the precursor is a compound of the formula Si n H 2n+2 A liquid precursor, wherein n is an integer greater than 2, requires the use of a bubbler; the deposition temperature is about 425°C to 450°C.

[0094] Figure 7is a transmission electron microscope (TEM) micrograph of a cross-section of a bonding interface between a substrate S2 and a substrate S1 after heat treatment at 500° C., wherein the substrate S2 includes a silicon substrate 20 covered with a native silicon oxide layer 20 b, and the substrate S1 includes a silicon substrate (not shown) covered with a silicon oxide layer 11 on which an amorphous silicon layer with a thickness of 6 nm has been deposited.

[0095] The amorphous silicon layer has been partially converted to silicon oxide by reaction with bound water on its surface, thereby forming a bonding interface I. The remaining portion of the amorphous silicon is designated by 12a, while the portion of the bonding layer converted to silicon oxide is designated by 12b. This portion 12b combines with the native silicon oxide layer 20b of the substrate S2 to form a silicon oxide layer extending on either side of the bonding interface I.

[0096] This effect can optionally be exploited to convert the entire amorphous silicon layer into silicon oxide during the heat treatment for sealing the bonding interface.For this purpose, the thickness of the deposited amorphous silicon layer is chosen to be small enough to react with the bound water to consume it completely.

[0097] FIG. 8A to FIG. 8C Successive steps of a method according to a second embodiment of the invention are shown.

[0098] FIG. 8A to FIG. 8C The steps shown in the reference FIG. 5A to FIG. 5C The steps described are of the same nature, the difference between the two embodiments of the method being that, in the second embodiment, a bonding layer is deposited on each of the substrates S1 and S2. The steps common to both methods will therefore not be described again.

[0099] exist FIG. 8A to FIG. 8C In the case of , substrate S1 comprises a layer 10 (eg, a silicon layer) covered with a silicon oxide layer 11. Similarly, substrate S2 comprises a layer 20 (eg, a silicon layer) covered with a silicon oxide layer 21. The silicon oxide layers 11, 21 may be formed by thermal oxidation of silicon.

[0100] In this case, therefore, there is the problem of oxide-oxide bonding. This type of bonding allows the use of hydrophilic bonding (which is standard in the microelectronics industry) and therefore allows bonding of any material even if it is not compatible with this type of bonding (specifically, it is sufficient to cover them with a thin oxide layer to make them hydrophilic for bonding). For the manufacture of SOI structures, oxide-oxide bonding allows obtaining thick buried oxide layers, or encapsulating the bonding interface in oxide when it is prone to interacting with silicon.

[0101] For Smart Cut TM Application of the method

[0102] Advantageously but not limitingly, this combination method can be used for Smart Cut TMThe method is used to manufacture an SOI structure.

[0103] By applying the present invention, during the implementation of this method, an amorphous silicon layer is deposited on a donor substrate (which corresponds to FIG. 5A to FIG. 5C On the oxide layer of the substrate S1) in the embodiment, the thickness is 1 to 6 nm, and then ion implantation for weakening the donor substrate is performed.

[0104] Since the yield strength of amorphous silicon is lower than that of silicon and silicon oxide, it allows heat treatment at about 900°C for 2 hours to close the bonding interface. However, in standard Smart Cut TM In the process, if the oxide layer is activated by plasma before contacting the substrate, the temperature to be applied to obtain complete sealing is 1100° C. for 2 hours, or even 1050° C. for 2 hours.

[0105] As Smart Cut TM As an alternative to this approach, the thin semiconductor layer may be transferred via another thinning method, such as etching the donor substrate from its side opposite to the bonding interface.

[0106] Experimental Results

[0107] The closure of the bonding interface can also be evaluated by the ratio between the horizontal etching rate (i.e., in the plane of the bonding interface) and the vertical etching rate (i.e., in the direction perpendicular to the bonding interface) of the bonded structure exposed to the etching solution. When the bonding interface is properly closed, the ratio is close to 1, which indicates the fact that the etching solution etches all structures uniformly. In contrast, when the bonding interface is not closed, the etching solution penetrates into the cavity of the bonding interface, thereby etching the interface faster than the rest of the structure. Thus, the ratio is higher than 1.

[0108] Fig. 9 The ratio R is shown as a function of the sealing temperature T of the interface for the standard bonding method (a) and the bonding method of the present invention (b).

[0109] Using standard bonding methods, multiple structures were formed by hydrophilic bonding of a first substrate including a silicon substrate covered with a silicon oxide layer with a second silicon substrate. Thus, the materials present at the bonding interface were silicon oxide of the first substrate (previously activated by plasma) and silicon of the second substrate. Each bonded structure was subjected to heat treatment at different temperatures (500° C. to 1050° C.). After the heat treatment, each bonded structure was exposed to an etchant solution consisting of hydrofluoric acid (HF) diluted to 10%, and the etching rate was measured both vertically and horizontally.

[0110] Using the bonding method of the present invention, multiple structures are formed by hydrophilic bonding of a first substrate S1 with a second silicon substrate, wherein the first substrate S1 includes a silicon substrate covered with a silicon oxide layer on which an amorphous silicon layer with a thickness of 1 nm to 6 nm has been deposited. Therefore, the materials present at the bonding interface are the amorphous silicon deposited on the first substrate and the silicon of the second substrate. Each bonded structure is subjected to heat treatment at different temperatures (500° C. to 900° C.). After the heat treatment, each bonded structure is exposed to the aforementioned etchant solution, and the etching rate is measured in both the vertical direction and the horizontal direction.

[0111] Comparison of curves (a) and (b) shows that, in the case of standard bonding, the bonding interface is closed only by heat treatment at 1050°C (R is approximately equal to 1), and any reduction in the temperature of the heat treatment causes a significant increase in the ratio R, i.e., the sealing of the bonding interface deteriorates. In contrast, using the bonding method of the present invention, the interface is closed from 900°C; moreover, the slope of curve (b) is much smaller than that of curve (a), and therefore the reduction in the heat treatment temperature has less adverse effects on the quality of the interface sealing. In particular, a temperature of about 600°C allows to obtain almost complete sealing.

[0112] References

[0113] [Vincent et al.]: A model of interface defect formation in silicon waferbonding, S. Vincent et al., Applied Physics Letters 94, 101914 (2009)

Claims

1. A method for hydrophilically bonding a first substrate (S1) to a second substrate (S2), the method comprising: - bringing the first substrate (S1) into contact with the second substrate (S2) to form a bonding interface (I) between the main surface of the first substrate and the main surface of the second substrate, - applying a heat treatment suitable for closing said bonding interface, The method is characterized in that it comprises: before the contacting step, depositing a bonding layer (12, 22) made of a non-metallic material on the main surface of the first substrate and / or the second substrate, the non-metallic material being permeable to hydrogen and having a yield strength at the temperature of the heat treatment lower than the yield strength of at least one of the materials of the first substrate (S1) and the second substrate (S2) located at the bonding interface, the material of the bonding layer being selected from amorphous silicon and amorphous germanium, the thickness of the bonding layer being 1 nm to 6 nm, and The method is characterized in that the heat treatment is performed at a temperature lower than or equal to 900°C.

2. The method of claim 1, wherein the first substrate (S1) comprises a silicon oxide surface layer (11) different from a native oxide, and the bonding layer is deposited on the silicon oxide surface layer.

3. The method of claim 2, wherein the silicon oxide surface layer is formed by thermal oxidation of the first substrate (S1).

4. A method as claimed in claim 2 or 3, wherein the second substrate (S2) comprises a silicon oxide surface layer (21) different from a native oxide, and the bonding layer is also deposited on the silicon oxide surface layer.

5. The method according to any one of claims 1 to 3, comprising: After applying the heat treatment for sealing the bonding interface, a step of thinning the first substrate to transfer a thin layer of the first substrate to the second substrate.

6. The method of claim 5, further comprising: Between the steps of depositing the bonding layer and contacting the first substrate with the second substrate, a silicon oxide surface layer is formed on the first substrate, and ionic species are implanted into the first substrate through the silicon oxide surface layer to form a weakened area of ​​the semiconductor layer to be transferred.

7. The method according to any one of claims 1 to 3, comprising: Between the steps of depositing the bonding layer and contacting the first substrate with the second substrate, the major surface of the substrate is subjected to a hydrophilic treatment, and water is applied to the major surface of the substrate to form a water film on the major surface.

8. The method according to any one of claims 1 to 3, comprising: Prior to depositing the bonding layer, a step of cleaning the main surface is performed, the bonding layer having to be deposited on the main surface with an oxidizing solution.

9. The method according to any one of claims 1 to 3, wherein the second substrate (S2) is a silicon substrate, and the substrate is covered with a native silicon oxide layer (20b).

10. The method of claim 9, comprising: During the heat treatment for sealing the bonding interface, a surface section of silicon of the second substrate is oxidized through the native silicon oxide layer.

11. The method according to any one of claims 1 to 3, wherein the bonding layer is an amorphous silicon layer formed in an epitaxial reactor at a temperature below 550°C.

12. The method of claim 11, wherein the amorphous silicon layer is formed from a precursor selected from the group consisting of disilane (Si2H6), silane (SiH4), or a precursor of the formula Si n H 2n+2 A liquid precursor wherein n is an integer greater than 2.

13. The method of claim 10, comprising: During the heat treatment for sealing the bonding interface, at least a portion (12b) of the bonding layer (12) is oxidized.

14. The method of claim 13, wherein the thickness of the bonding layer (12) is selected such that the entire bonding layer is oxidized during the heat treatment for sealing the bonding interface.

15. The method according to any one of claims 1 to 3, wherein the temperature of the heat treatment is lower than or equal to 600°C.

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