Process for manufacturing removable substrates

Abstract

Method for manufacturing removable substrates (1, 2), comprising the steps: a) providing: - a first substrate (1), comprising implanted species (10) forming a flat implantation zone (100) and a proximal surface (S); - a second substrate (2), comprising a surface (20) b) forming a set of cavities (200) on the proximal surface (S) of the first substrate (1) and / or on the surface (20) of the second substrate (2); c) assembling the first and second substrates (1, 2) by direct bonding; d) applying a heat treatment according to a to weaken the flat implantation zone (100); the set of cavities (200) being arranged so as to: - allow direct bonding between the first and second substrates (1, 2) during step c); - prohibit thermal initiation of the fracture of the flat implantation zone (100) weakened at the end of step d). Figure 1

Description

Title of the invention: Method for manufacturing removable substrates Technical field

[0001] The invention relates to the technical field of manufacturing removable substrates. These are also referred to as temporary handles.

[0002] The invention is particularly useful in transferring a useful layer onto a support substrate to manufacture a device (or component) for any type of application (electronic, mechanical, optical, etc.). State of the art

[0003] Temporary handles of the prior art are mainly of two types. Temporary handles of a first type are made from a polymer material, and are compatible only with low temperatures (typically below 300°C). Temporary handles of a second type are compatible with higher temperatures (typically of the order of 500°C to 600°C). Temporary handles known from the prior art are conventionally manufactured using a weakened bonding interface between two substrates. The weakened bonding interface can be obtained with rough surfaces, or with materials of the two substrates chosen so as to be physicochemically poorly compatible. The disassembly of the two substrates can be carried out subsequently using a heat treatment, or mechanically by inserting a blade following the bonding interface.

[0004] Such state-of-the-art solutions are not entirely satisfactory, due to the complexity of their implementation. Statement of the invention

[0005] The invention aims to remedy all or part of the aforementioned drawbacks. To this end, the invention relates to a method for manufacturing removable substrates, comprising the steps: (a) provide: - a first substrate, comprising implanted species forming a flat implantation zone, the first substrate comprising a surface proximal to the flat implantation zone; - a second substrate, comprising a surface; b) forming a set of cavities on the proximal surface of the first substrate and / or on the surface of the second substrate; c) joining the first and second substrates by direct bonding between the surface proximal of the first substrate and the surface of the second substrate; d) applying a heat treatment to the assembly obtained at the end of step c), according to a thermal budget adapted to weaken the flat implantation zone; the set of cavities being arranged during step b) so as to: - allow direct bonding between the first and second substrates during step c); - prohibit thermal initiation of the fracture of the weakened flat implantation zone at the end of step d).

[0006] Thus, such a method according to the invention makes it possible to obtain temporary handles by using a flat implantation zone formed by implanted species, then weakened by a heat treatment to subsequently dismantle the first and second substrates by applying a mechanical stress (e.g. insertion of a blade at the bonding interface). The heat treatment of step d) makes it possible to mature the implanted defects, which can generate microcrack or blister type defects which will grow and thereby weaken the flat implantation zone.

[0007] The arrangement (for example the dimensioning and / or the distribution) of the set of cavities on the proximal surface of the first substrate and / or on the surface of the second substrate during step b) is adapted to delimit, at the end of step c): - bonding zones, facing the walls separating the cavities and occupying the inter-cavity space, the bonding zones therefore being subject to a stiffening effect; - free areas, facing the cavities.

[0008] More specifically, the set of cavities is arranged on the proximal surface of the first substrate and / or on the surface of the second substrate during step b) so that: - the bonding areas have a surface area suitable for allowing direct bonding between the first and second substrates during step c); - the free zones have a spatial distribution adapted to prevent thermal initiation of the fracture of the weakened flat implantation zone at the end of step d).

[0009] The triggering of the fracture (splitting in English) of the flat implantation zone is mainly due to the maturation of microcracks. The maturation of microcracks is linked to the implanted species (conventionally ionized gaseous species) undergoing a heat treatment (for example at 500°C for several tens of minutes), in the presence of a stiffening effect. The inventors noted that the presence of cavities in the free zones, adjacent to the bonding zones, limited the development of microcracks at the bonding regions.

[0010] Furthermore, when the cavities extend to the proximal surface of the first substrate, below the flat implantation zone, the free zones are not subject to a stiffening effect, and can therefore deform inside the cavity(ies). facing during the maturation of blister-type defects. The maturation of blister-type defects is in fact linked to the implanted species (classically ionized gaseous species) undergoing heat treatment (for example at 500°C for several tens of minutes), in the absence of a stiffening effect. The growth of blister-type defects is limited by the exfoliation phenomenon corresponding to their decapsulation. The presence of cavities allows a vertical expansion of blister-type defects.

[0011] The flat implantation zone thus resists thermal energy provided by the heat treatment of step d), i.e. the flat implantation zone is not fractured by the heat treatment of step d), but is sufficiently weakened (by the presence of microcracks and, where appropriate, blisters) to be fractured subsequently by mechanical stress to dismantle the first and second substrates, for example by inserting a blade between the first and second substrates or by peeling.

[0012] The method according to the invention may comprise one or more of the following characteristics.

[0013] According to a characteristic of the invention, the method comprises a step e) consisting of carrying out a mechanical fracture of the weakened planar implantation zone after step d), so as to dismantle the first and second substrates.

[0014] Thus, one advantage provided is the simplicity of disassembly of the first and second substrates, for example by inserting a blade between the first and second substrates.

[0015] According to a characteristic of the invention, the set of cavities is arranged during step b) so that each pair of adjacent cavities is spaced apart by a distance between: - a first threshold, beyond which direct bonding between the first and second substrates is authorized during step c); - a second threshold, strictly higher than the first threshold, below which thermal initiation of the fracture of the weakened flat implantation zone is prohibited at the end of step d).

[0016] Thus, an advantage provided is to obtain: (i) bonding areas having a sufficient surface area to allow direct bonding between the first and second substrates during step c); (ii) free zones, arranged between the bonding zones to prevent thermal initiation of the fracture of the weakened flat implantation zone at the end of step d).

[0017] According to a characteristic of the invention, the first threshold is between 500 nm and 3 pm, preferably between 1 pm and 2 pm.

[0018] According to a characteristic of the invention, the second threshold is between 5 pm and 200 pm, preferably between 5 pm and 100 pm, more preferably between 5 pm and 10 pm.

[0019] According to a characteristic of the invention, the first and second substrates have a bonding surface at the end of step c); and the set of cavities is arranged during step b) so as to occupy between 50% and 85% of the bonding surface, preferably between 60% and 80% of the bonding surface.

[0020] Thus, an advantage provided is to obtain: (i) bonding areas having a sufficient surface area to allow direct bonding between the first and second substrates during step c); (ii) free zones, arranged between the bonding zones to prevent thermal initiation of the fracture of the weakened flat implantation zone at the end of step d).

[0021] According to a characteristic of the invention: - the set of cavities is formed during step b) on the proximal surface of the first substrate so as to extend below the flat implantation zone; - the set of cavities is arranged during step b) so that each cavity has at least one dimension, in the plane of the proximal surface of the first substrate, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0022] Thus, an advantage provided is to limit the lateral expansion of the blisters inside the cavities in order to avoid the phenomenon of exfoliation.

[0023] According to a characteristic of the invention: - the set of cavities is formed during step b) on the surface of the second substrate; - the set of cavities is arranged during step b) so that each cavity has at least one dimension, in the plane of the surface of the second substrate, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0024] Thus, an advantage provided is to limit the lateral expansion of the blisters inside the cavities in order to avoid the phenomenon of exfoliation.

[0025] According to a characteristic of the invention: - the set of cavities is formed during step b): to the proximal surface of the first substrate so as to extend below the flat implantation zone, and on the surface of the second substrate; - the set of cavities is arranged during step b) so that each cavity has at least one dimension, in the plane of the proximal surface of the first substrate and in the plane of the surface of the second substrate, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0026] Thus, an advantage provided is to limit the lateral expansion of the blisters inside the cavities in order to avoid the phenomenon of exfoliation.

[0027] According to a characteristic of the invention, the set of cavities is formed during step b) on the proximal surface of the first substrate so as to extend beyond the flat implantation zone.

[0028] Thus, an advantage provided is to avoid the presence of blisters, which allows greater tolerance on the lateral dimension of the cavities in the plane of the proximal surface of the first substrate. The set of cavities is arranged to prevent the lateral propagation of microcracks and thereby the fracture of the weakened flat implantation zone.

[0029] According to a characteristic of the invention, each cavity of the assembly occupies the proximal surface of the first substrate and / or the surface of the second substrate so as to delimit an opening having a shape chosen from a rectangular, square, triangular or circular shape.

[0030] According to a characteristic of the invention, the thermal budget of step d) is defined by: - a heat treatment temperature between 200°C and 900°C, - a heat treatment duration between a few minutes and a few tens of minutes.

[0031] Thus, an advantage provided is to obtain a flat implantation zone resistant to thermal energy provided by a fracturing heat treatment or by a heat treatment for strengthening the bonding interface. The flat implantation zone is not fractured by such a thermal budget, but is sufficiently weakened (by the presence of microcracks and blisters) to be fractured subsequently by mechanical stress to disassemble the first and second substrates, for example by inserting a blade between the first and second substrates. Such a thermal budget would be sufficient to fracture the flat implantation zone in the absence of such a set of cavities on the proximal surface of the first substrate and / or on the surface of the second substrate.

[0032] According to a characteristic of the invention, step a) comprises a prior step consisting of determining an average exfoliation radius and / or a minimum exfoliation radius by a statistical analysis of microscopic observations, after having applied to the first substrate a heat treatment for fracturing the flat implantation zone.

[0033] This heat treatment is applied directly to the first substrate to de complete the exfoliation radius in the case where the cavities are formed on the surface of the second substrate. If the cavities are formed on the proximal surface of the first substrate, this heat treatment will be applied to the first substrate after thinning over its entire surface and to a thickness corresponding to the depth of the cavities.

[0034] Thus, an advantage provided is to improve the reliability of the dimensioning of the cavities during step b) in order to obtain free zones, not subject to a stiffening effect, which can deform inside the cavity or cavities facing them during the maturation of blister-type defects during step d), while limiting the lateral expansion of the blisters inside the cavities in order to avoid the exfoliation phenomenon.

[0035] According to a characteristic of the invention, the first substrate provided during step a) is made from a material chosen from: - a semiconductor material, preferably selected from Si, Ge, Si-Ge, SiC, a III-V material; - lithium tantalate LiTaO3, lithium niobate LiNbO3.

[0036] The invention also relates to an assembly for manufacturing removable substrates, comprising: - a first substrate, comprising implanted species forming a flat implantation zone, the first substrate comprising a surface proximal to the flat implantation zone; - a second substrate, comprising a surface; - a set of cavities, arranged on the proximal surface of the first substrate and / or on the surface of the second substrate so as to: allow direct bonding between the proximal surface of the first substrate and the surface of the second substrate; prohibit thermal initiation of fracture of the flat implantation zone, after a heat treatment applied to the first and second bonded substrates, according to a thermal budget adapted to weaken the flat implantation zone.

[0037] Thus, as mentioned previously, the arrangement (for example the dimensioning and / or the distribution) of the set of cavities on the proximal surface of the first substrate and / or on the surface of the second substrate is adapted to delimit: - bonding zones, facing the walls separating the cavities and occupying the inter-cavity space, the bonding zones therefore being subject to a stiffening effect; - free areas, facing the cavities.

[0038] More specifically, the set of cavities is arranged on the proximal surface of the first substrate and / or on the surface of the second substrate so that: - the bonding areas have a surface area suitable for allowing direct bonding between the first and second substrates; - the free zones have a spatial distribution adapted to prevent thermal initiation of the fracture of the weakened flat implantation zone after the heat treatment applied to the first and second bonded substrates.

[0039] The triggering of the fracture (splitting in English) of the flat implantation zone is mainly due to the maturation of microcracks. The maturation of microcracks is linked to the implanted species (conventionally ionized gaseous species) undergoing a heat treatment (for example at 500°C for several tens of minutes), in the presence of a stiffening effect. The inventors have noted that the presence of cavities in the free zones, adjacent to the bonding zones, limits the development of microcracks at the bonding regions.

[0040] Furthermore, when the cavities extend to the proximal surface of the first substrate, below the flat implantation zone, the free zones are not subject to a stiffening effect, and can therefore deform inside the cavity(ies) facing them during the maturation of blister-type defects. The maturation of blister-type defects is in fact linked to the implanted species (conventionally ionized gaseous species) undergoing a heat treatment (for example at 500°C for several tens of minutes), in the absence of a stiffening effect. The growth of blister-type defects is limited by the exfoliation phenomenon corresponding to their decapsulation. The presence of cavities allows vertical expansion of blister-type defects.

[0041] The flat implantation zone thus resists thermal energy provided by the heat treatment applied to the first and second bonded substrates, that is to say that the flat implantation zone is not fractured by the heat treatment, but is sufficiently weakened (by the presence of microcracks and, where appropriate, blisters) to be fractured subsequently by mechanical stress to dismantle the first and second substrates, for example by inserting a blade between the first and second substrates or by peeling.

[0042] According to a characteristic of the invention, the set of cavities is arranged on the proximal surface of the first substrate and / or on the surface of the second substrate so that each pair of adjacent cavities is spaced apart by a distance between: - a first threshold, beyond which direct bonding between the first and second substrates is authorized; - a second threshold, strictly higher than the first threshold, below which thermal initiation of fracture of the flat implantation zone is prohibited after the heat treatment applied to the first and second bonded substrates.

[0043] Thus, an advantage provided is to obtain: (i) bonding areas having sufficient surface area to permit bonding direct between the first and second substrates; (ii) free zones, arranged between the bonding zones to prevent thermal initiation of fracture of the weakened flat implantation zone after the heat treatment applied to the first and second bonded substrates.

[0044] According to a characteristic of the invention, the first and second substrates are intended to have a bonding surface; and the set of cavities is arranged on the proximal surface of the first substrate and / or on the surface of the second substrate so as to occupy between 50% and 85% of the bonding surface, preferably between 60% and 80% of the bonding surface.

[0045] Thus, an advantage provided is to obtain: (i) bonding areas having sufficient surface area to allow direct bonding between the first and second substrates; (ii) free zones, arranged between the bonding zones to prevent thermal initiation of fracture of the weakened flat implantation zone after the heat treatment applied to the first and second bonded substrates.

[0046] According to a characteristic of the invention: - the set of cavities is arranged on the proximal surface of the first substrate so as to extend below the flat implantation zone; - the set of cavities is arranged on the proximal surface of the first substrate such that each cavity has at least one dimension, in the plane of the proximal surface of the first substrate, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0047] Thus, an advantage provided is to limit the lateral expansion of the blisters inside the cavities in order to avoid the phenomenon of exfoliation.

[0048] According to a characteristic of the invention, the set of cavities is arranged on the surface of the second substrate so that each cavity has at least one dimension, in the plane of the surface of the second substrate, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0049] Thus, an advantage provided is to limit the lateral expansion of the blisters inside the cavities in order to avoid the phenomenon of exfoliation.

[0050] According to a characteristic of the invention: - the set of cavities is arranged: to the proximal surface of the first substrate so as to extend below the flat implantation zone, and on the surface of the second substrate; - the set of cavities is arranged so that each cavity has at least one dimension, in the plane of the proximal surface of the first substrate and in the plane of the surface of the second substrate, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0051] Thus, an advantage provided is to limit the lateral expansion of the blisters inside the cavities in order to avoid the phenomenon of exfoliation.

[0052] According to a characteristic of the invention, the set of cavities is arranged on the proximal surface of the first substrate so as to extend beyond the flat implantation zone.

[0053] Thus, an advantage provided is to avoid the presence of blisters, which allows greater tolerance on the lateral dimension of the cavities in the plane of the proximal surface of the first substrate. The set of cavities is arranged to prevent the lateral propagation of microcracks and thereby the fracture of the weakened flat implantation zone.

[0054] Definitions

[0055] - By "substrate" is meant a self-supporting physical support, made of a material base from which a device (or component) can be formed for any type of application, including electronic, mechanical, optical. A substrate can be a "slice" (also called a "wafer") which generally takes the form of a disc cut from an ingot of a crystalline material.

[0056] - By "flat area" we mean a flatness within the usual tolerances linked to experimental manufacturing conditions, and not perfect flatness in the mathematical sense of the term.

[0057] - By "exfoliation radius" we mean a parameter, noted Rexfo, defined by the equation: Rexfo = x Ek^TX axD XX where "v" denotes the Poisson's ratio of the thin layer, "E" denotes the Young's modulus of the thin layer, "kB" is the Boltzmann constant, "T" is the temperature (in K) to which the thin layer is subjected, "a" is the effective dose fraction (in %) of the implanted species, "D" is the implanted dose (in at. / cm2) of the species, "o" is the ultimate shear stress, "e" is the thickness of the thin layer, and "x" is the multiplication operator. The thin layer is the part of the first substrate extending between the flat implantation zone and the surface of the first substrate through which the implantation of the species has taken place (surface proximal to the flat implantation zone). Exfoliation corresponds to a partial (local) detachment of the thin layer at the level of the flat implantation zone. It is difficult to theoretically determine the exfoliation radius due to physical quantities that are difficult to quantify, in particular the shear stress limit. The exfoliation radius is specific to the implantation carried out in the first substrate.

[0058] - By "mean exfoliation radius" is meant an arithmetic mean of the radii of exfoliation obtained experimentally.

[0059] - By "predetermined" is meant that the average exfoliation radius is determined before designing the set of cavities formed on the proximal surface of the first substrate and / or on the surface of the second substrate.

[0060] - The term "cavity" designates a superficial, open cavity extending to the surface proximal to the first substrate and / or on the surface of the second substrate, and obtainable by etching.

[0061] - By "distributed on the surface" we mean a spatial distribution of the whole of cavities on the proximal surface of the first substrate and / or on the surface of the second substrate.

[0062] - By "direct bonding" we mean a bonding (preferably spontaneous) resulting from the direct contact of two surfaces, i.e. in the absence of an additional element such as glue, wax or solder. Adhesion comes mainly from van der Waals forces resulting from the electronic interaction between the atoms or molecules of two surfaces, hydrogen bonds due to surface preparations or covalent bonds established between the two surfaces. Direct bonding is advantageously carried out at ambient temperature and pressure. Direct bonding can cover thermocompression bonding or eutectic bonding depending on the nature of the two surfaces brought into contact.

[0063] - By "thermal initiation" is meant an initiation of the fracture of the plane zone implantation obtained by thermal energy.

[0064] - By "mechanical fracture" is meant a fracture of the flat implantation zone (weakened) obtained by mechanical energy.

[0065] - By "allow direct pasting" we mean that the pasting interface (limited mainly by the entire surface of the walls separating the cavities) has sufficient adhesion energy to bond the first and second substrates together.

[0066] - By "prohibiting thermal initiation" we mean that thermal energy (for example provided by a heat treatment applied to the assembly of the first and second substrates) is not sufficient to initiate a fracture of the flat implantation zone which would have the effect of separating the first and second substrates.

[0067] - By “type IILV material” is meant a binary alloy between elements located respectively in column III and in column V of the periodic table of elements.

[0068] - By "semiconductor material" is meant a material having a electrical conductivity at 300 K between 108 S / cm and 103 S / cm.

[0069] - The expression “occupy a percentage of the bonding surface” by the set of cavities can be described by an occupancy rate defined by the formula (a + b)2 - a2 (a + b)2 when each cavity delimits an opening having a square shape with side “a”, each pair of adjacent cavities being spaced by a distance “b” from the proximal surface of the first substrate and / or from the surface of the second substrate.

[0070] - By “thermal budget” we mean an energy input of a thermal nature, determined by the choice of a value for the heat treatment temperature and the choice of a value for the duration of the heat treatment.

[0071] - The values ​​X and Y expressed using the expressions "between X and Y" or "included between X and Y” are included in the defined range of values.

[0072] - By "facing" we mean that an element A faces an element B when the elements A and B are opposite each other along the normal to the bonding surface of the first and second substrates.

[0073] - By "extending below" is meant that the cavities extend below the zone implantation plane when the depth of the cavities is strictly less than the implantation depth of the implanted species.

[0074] - By "extending beyond" is meant that the cavities extend beyond the area implantation plane when the depth of the cavities is strictly greater than the implantation depth of the implanted species. Brief description of the drawings

[0075] Other characteristics and advantages will appear in the detailed description of different embodiments of the invention, the description being accompanied by examples and references to the attached drawings.

[0076] [Fig-1] is a schematic sectional view illustrating the first and second substrates before bonding according to a first embodiment where the set of cavities is formed on the surface of the second substrate.

[0077] [Fig.2] is a schematic sectional view, illustrating the direct bonding of the first and second substrates according to the first embodiment.

[0078] [Fig.3] is a schematic sectional view, illustrating the presence of blister-type defects after bonding of the first and second substrates according to the first embodiment, when the assembly undergoes a heat treatment leading to maturation of the defects.

[0079] [Fig.4] is a schematic sectional view, illustrating the insertion of a blade at the bonding interface to disassemble the first and second substrates according to the first embodiment.

[0080] [Fig.5] is a graph representing on the abscissa the implantation depth (in pm) and on the ordinate an exfoliation radius (in pm) obtained experimentally.

[0081] [Fig.6] is an illustration of a microscopic observation of localized tearing (or exfoliation) of the surface of the first substrate (i.e. the surface proximal to the flat implantation zone), the first substrate being subjected to a thermal fracturing treatment without stiffening effect.

[0082] [Fig.7] is a schematic sectional view illustrating the first and second substrates before bonding according to a second embodiment where the set of cavities is formed on the proximal surface of the first substrate.

[0083] [Fig.8] is a schematic sectional view illustrating the first and second substrates before bonding according to a third embodiment where the set of cavities is formed on the proximal surface of the first substrate and on the surface of the second substrate.

[0084] [Fig.9] is a schematic sectional view, illustrating the first and second substrates before bonding according to a fourth embodiment where the set of cavities is formed on the proximal surface of the first substrate so as to extend beyond the flat implantation zone.

[0085] It should be noted that figures 1 to 4, 7 to 9 described above are schematic, and are not to scale for the sake of readability and to simplify their understanding. The sections are made along the normal to the bonding surface. Detailed description of the implementation methods

[0086] Elements that are identical or provide the same function will have the same references for the different embodiments, for the sake of simplification. Manufacturing method

[0087] An object of the invention is a method for manufacturing removable substrates 1, 2, comprising the steps: (a) provide: - a first substrate 1, comprising implanted species 10 forming a flat implantation zone 100, the first substrate 1 comprising a surface S proximal to the flat implantation zone 100; - a second substrate 2, comprising a surface 20; b) forming a set of cavities 200 on the proximal surface S of the first substrate 1 and / or on the surface 20 of the second substrate 2; c) assembling the first and second substrates 1, 2 by direct bonding between the proximal surface S of the first substrate 1 and the surface 20 of the second substrate 2; d) applying a heat treatment to the assembly obtained at the end of step c), according to a thermal budget adapted to weaken the flat implantation zone 100; the set of cavities 200 being arranged during step b) so as to: - allow direct bonding between the first and second substrates 1, 2 during step c); - prohibit thermal initiation of the fracture of the weakened flat implantation zone 100 at the end of step d).

[0088] Step a)

[0089] Step a) is illustrated in Figures 1, 7 to 9.

[0090] The implanted species 10 are advantageously gaseous species, preferably comprising ionized hydrogen atoms and / or ionized helium atoms. It is possible to carry out co-implantation between these species and / or with other gaseous species, or even to carry out multi-implantation of the same gaseous species.

[0091] The first substrate 1 provided during step a) is advantageously made from a material chosen from: - a semiconductor material, preferably selected from Si, Ge, Si-Ge, SiC, an IILV material; - lithium tantalate LiTaO3, lithium niobate LiNbO3.

[0092] By way of non-limiting example, when the first substrate 1 is made of silicon, it is possible to implant ionized hydrogen atoms according to the following parameters: - an energy between 120 keV and 200 keV; - a dose between 6.1016 at.cm2 and 7.1016 at.cm2.

[0093] As illustrated in Figures 5 and 6, step a) advantageously comprises a prior step consisting of determining an average exfoliation radius and / or a minimum exfoliation radius by a statistical analysis of microscopic observations, after having applied to the first substrate 1 (comprising the implanted species 10) a heat treatment for fracturing the flat implantation zone 100 (for example 1 h at 500°C when the first substrate 1 is made of silicon). This heat treatment is applied directly to the first substrate 1 to determine the exfoliation radius in the case where the cavities 200 are formed on the surface 20 of the second substrate 2. If the cavities 200 are formed on the proximal surface S of the first substrate 1, this heat treatment will be applied to the first substrate 1 after thinning over its entire surface and over a thickness corresponding to the depth of the cavities 200.

[0094] The fracturing heat treatment of the flat implantation zone 100 is carried out according to a thermal budget similar to the thermal budget of step d). In the absence of a stiffening effect, this heat treatment leads to the formation of blisters 3 and localized tears 3' (exfoliations). As illustrated in [Fig. 6], optical microscopy observations of the surface S (proximal to the flat implantation zone 100) of the first substrate 1 make it possible to observe these blisters 3 and these exfoliations 3', the exfoliations 3' being easily identifiable by the presence of a dark border on their outline. An image analysis makes it possible to measure the surface of these ex 3' foliations. The surfaces thus measured are converted into radius (considering the defects as circular). The dimensions thus extracted, in sufficient number to allow a statistical analysis (i.e. typically a population of several dozen exfoliations), then make it possible to define their minimum, average, and maximum size. [Fig.5] illustrates in this respect the radius of the 3' exfoliations observed according to this experimental protocol for first silicon substrates 1, implanted at a fixed dose, as a function of the implantation energy here translated into implantation depth.

[0095] Step b)

[0096] Step b) is illustrated in Figures 1, 7 to 9.

[0097] According to a first embodiment illustrated in [Fig. 1], the set of cavities 200 is formed during step b) on the surface 20 of the second substrate 2. The set of cavities 200 is sized and distributed during step b) so as to: - allow direct bonding between the first and second substrates 1, 2 during step c); - prohibit thermal initiation of the fracture of the flat implantation zone 100 weakened at the end of step d).

[0098] According to a second embodiment illustrated in [Fig.7], the set of cavities 200 is formed during step b) on the proximal surface S of the first substrate 1 so as to extend below the flat implantation zone 100. Step b) is carried out after the formation of the flat implantation zone 100. The set of cavities 200 is sized and distributed during step b) so as to: - allow direct bonding between the first and second substrates 1, 2 during step c); - prohibit thermal initiation of the fracture of the flat implantation zone 100 weakened at the end of step d).

[0099] According to a third embodiment illustrated in [Fig.8], the set of cavities 200 is formed during step b) on the proximal surface S of the first substrate 1, so as to extend below the flat implantation zone 100, and on the surface 20 of the second substrate 2. Step b) is carried out after the formation of the flat implantation zone 100. The set of cavities 200 is sized and distributed during step b) so as to: - allow direct bonding between the first and second substrates 1, 2 during step c); - prohibit thermal initiation of the fracture of the flat implantation zone 100 weakened at the end of step d).

[0100] According to a fourth embodiment illustrated in [Fig.9], the set of cavities 200 is formed during step b) on the proximal surface S of the first substrate 1 of so as to extend beyond the flat implantation zone 100. Step b) is carried out after the formation of the flat implantation zone 100. The set of cavities 200 is spaced during step b) so as to: - allow direct bonding between the first and second substrates 1, 2 during step c); - prohibit thermal initiation of the fracture of the weakened flat implantation zone 100 at the end of step d).

[0101] The set of cavities 200 is advantageously arranged during step b) so that each pair of adjacent cavities 200 is spaced apart by a distance between: - a first threshold, beyond which direct bonding between the first and second substrates 1, 2 is authorized during step c); - a second threshold, strictly higher than the first threshold, below which thermal initiation of the fracture of the weakened flat implantation zone 100 is prohibited at the end of step d).

[0102] The first threshold is advantageously between 500 nm and 3 pm, preferably between 1 pm and 2 pm. The second threshold is advantageously between 5 pm and 200 pm, preferably between 5 pm and 100 pm, more preferably between 5 pm and 10 pm.

[0103] The first and second substrates 1, 2 have a bonding surface at the end of step c). The set of cavities 200 is advantageously arranged during step b) so as to occupy between 50% and 85% of the bonding surface, preferably between 60% and 80% of the bonding surface.

[0104] The set of cavities 200 is advantageously arranged during step b) so that each cavity 200 has at least one dimension, in the plane of the proximal surface S of the first substrate 1 and / or in the plane of the surface 20 of the second substrate 2, less than or equal to twice the predetermined average exfoliation radius, preferably less than or equal to twice the predetermined minimum exfoliation radius. According to the first embodiment illustrated in [Fig.l], the lateral dimension of the cavities 200 is in the plane of the surface 20 of the second substrate 2. According to the second embodiment illustrated in [Fig.7], the lateral dimension of the cavities 200 is in the plane of the proximal surface S of the first substrate 1. According to the third embodiment illustrated in [Fig.8], the lateral dimension of the cavities 200 is in the plane of the proximal surface S of the first substrate 1 and in the plane of the surface 20 of the second substrate 2.According to the fourth embodiment illustrated in [Fig.9], the lateral dimension of the cavities, in the plane of the proximal surface S of the first substrate 1, is not a critical parameter in the absence of blisters 3. .

[0105] Each cavity 200 of the assembly occupies the proximal surface S of the first substrate 1 and / or the surface 20 of the second substrate 2 so as to delimit an opening having a shape advantageously chosen from a rectangular, square, triangular or circular. By way of non-limiting example, each cavity 200 may delimit an opening having a square shape, each side of which is between 10 pm and 30 pm, preferably between 15 pm and 20 pm. If the predetermined minimum exfoliation radius is 15 pm, the cavities 200 may advantageously take the form of squares with a side of 30 pm, circles with a diameter of 30 pm, or lines with a width of 30 pm.

[0106] The cavities 200 can be obtained by etching the second substrate 2. By way of non-limiting example, the second substrate 2 can be made of a semiconductor material, such as silicon.

[0107] In the presence of blisters 3, the set of cavities 200 is advantageously dimensioned so that each cavity 200 has a depth, along the normal to the surface 20 of the second substrate 2 (and / or along the normal to the proximal surface S of the first substrate 1), greater than the maximum deflection of the blisters 3, noted Hmax. The value of Hmax can be approximated according to the theory of elasticity of plates and blisters, developed by Timoshenko, by the formula: = 16 xx P< x Or : - “v” denotes the Poisson’s ratio of the transferred thin layer, - “E” denotes the Young’s modulus of the thin layer, - “e” is the thickness of the thin layer, - “Pi” is the pressure in a blister 3 (dependent on the implantation dose), - “R” is the radius of a blister 3, - “x” is the multiplication operator.

[0108] The thin layer is the part of the first substrate 1 extending between the flat implantation zone 100 and the surface S of the first substrate 1 through which the implantation of the species 10 has taken place (proximal to the flat implantation zone 100) when the cavities 200 are formed on the surface 20 of the second substrate 2.

[0109] However, the depth of each cavity 200 may be less than the maximum deflection of the blisters 3 (i.e. the blisters 3 may 'touch the bottom of the cavities 200') without this affecting the proper implementation of a method according to the invention.

[0110] Step c)

[0111] Step c) is illustrated in [Fig.2].

[0112] Step c) is advantageously preceded by a step consisting of cleaning the surfaces to be bonded of the first and second substrates 1, 2, for example to avoid contamination of the surfaces by hydrocarbons, particles or metallic elements. By way of non-limiting example, it is possible to clean the surfaces to be bonded using a dilute SCI solution (mixture of NH4OH and H2O2).

[0113] Step c) is advantageously preceded by a step consisting of activating the surfaces to be bonded of the first and second substrates 1, 2, for example by plasma treatment or by ion beam sputtering (IBS). Activating the surfaces to be bonded makes it possible to reduce the first threshold.

[0114] Step c) is preferably carried out in a controlled atmosphere environment. By way of non-limiting example, step c) may be carried out under high vacuum such as a secondary vacuum of less than 102 mbar.

[0115] Step d)

[0116] The heat treatment is applied to the assembly of the first and second substrates 1, 2 obtained at the end of step c). The heat treatment is applied during step d) according to a thermal budget adapted to weaken the flat implantation zone 100. More precisely, in the first, second and third embodiments illustrated respectively in FIGS. 1, 7 and 8, the implanted species 10 generate microcracks or blisters 3 in response to the heat treatment applied during step d) which weaken the flat implantation zone 100. The blisters 3 generated during step d) extend inside the set of cavities 200. One or more blisters 3 may extend inside a cavity 200 of the set. The heat treatment of step d) allows the implanted defects to mature, generating microcracks and blisters 3 which will grow and thereby weaken the flat implantation zone 100.

[0117] As illustrated in [Fig. 3], blister-type defects 3 appear during step d), when the assembly is subjected to a heat treatment. The free zones ZL, extending to the surface S of the first substrate 1 (i.e. the surface proximal to the flat implantation zone 100), facing the cavities 200, are not subjected to a stiffening effect. The free zones ZL, not subjected to a stiffening effect, can then deform inside the cavity(ies) 200 facing them, after the maturation of blister-type defects 3, so as to prevent thermal initiation of the fracture of the flat implantation zone 100 weakened at the end of step d). This mechanism is identical for the second and third embodiments illustrated respectively in figures 7 and 8. The free zones ZL, extending to the proximal surface S of the first substrate 1, facing the cavities 200, are not subject to a stiffening effect.The free zones ZL, not subject to a stiffening effect, can then deform inside the cavity(ies) 200 facing them, after the maturation of blister-type defects 3, so as to prevent thermal initiation of the fracture of the flat implantation zone 100 weakened at the end of step d).

[0118] In the fourth embodiment illustrated in [Fig.9], the implanted species 10 only generate microcracks at the bonding zones in response to the heat treatment applied during step d) which weaken the flat zone of implantation 100.

[0119] The thermal budget of step d) is advantageously adapted to fracture the flat implantation zone 100, in the absence of the set of cavities 200 on the proximal surface S of the first substrate 1 and / or on the surface 20 of the second substrate 2. However, in the invention, that is to say in the presence of such a set of cavities 200 on the proximal surface S of the first substrate and / or on the surface 20 of the second substrate 2, such a thermal budget of step d) weakens the flat implantation zone 100 but does not allow thermally initiating the fracture of the flat implantation zone 100.

[0120] As a non-limiting example, the thermal budget of step d) can be defined by: - a heat treatment temperature between 200°C and 900°C, - a heat treatment duration between a few minutes and a few tens of minutes.

[0121] The thermal budget of step d) depends in particular on the material of the first substrate 1 and the implantation conditions of the implanted species 10. When the first substrate 1 is made of silicon Si, the temperature of the heat treatment can be between 300°C and 600°C, for example of the order of 500°C. When the first substrate 1 is made of lithium tantalate LiTaO3, the temperature of the heat treatment can be of the order of 200°C. When the first substrate 1 is made of indium phosphide InP, the temperature of the heat treatment can be of the order of 150°C.

[0122] The heat treatment of step d) is advantageously thermal annealing.

[0123] Step e)

[0124] The method may comprise a step e) consisting of carrying out a mechanical fracture of the flat implantation zone 100 weakened after step d), so as to dismantle the first and second substrates 1, 2.

[0125] As illustrated in [Fig.4], step e) can be carried out by inserting a blade L between the first and second substrates 1, 2, at the bonding interface, from an edge of the assembly of the first and second substrates 1, 2. As a variant, it is possible to provide for laminating on the thin layer a peeling layer (for example made of a polymer material) which will then be used to mechanically peel the thin layer.

[0126] After performing step e), the first disassembled substrate 1 can be recycled and reused. Furthermore, after performing step e), the thin layer transferred onto the second substrate 2 can be subjected to chemical and / or mechanical treatments to cover a flat surface, and obtain a useful layer from which a component can be formed for any type of application, in particular electronic, mechanical, optical.

[0127] Technological steps

[0128] The first substrate 1 and / or the second substrate 2 may be subjected to technological steps, carried out between steps d) and e), in order to form all or part of a component. By way of non-limiting examples, the technological steps may consist of thinning, layer transfer, layer deposition, photolithography, etching, etc. It should be noted that the thinning of the first substrate 1 is advantageously carried out between steps c) and d). The assembly of the first and second substrates 1, 2 may be secured to a receiving substrate for the implementation of certain technological steps. Manufacturing set

[0129] An object of the invention is an assembly for manufacturing removable substrates 1, 2, comprising: - a first substrate 1, comprising implanted species 10 forming a flat implantation zone 100, the first substrate 1 comprising a surface S proximal to the flat implantation zone 100; - a second substrate 2, comprising a surface 20; - a set of cavities 200, arranged on the proximal surface S of the first substrate 1 and / or on the surface 20 of the second substrate 2 so as to: allow direct bonding between the proximal surface S of the first substrate 1 and the surface 20 of the second substrate 2; prohibiting thermal initiation of the fracture of the flat implantation zone 100 after a heat treatment applied to the first and second bonded substrates 1, 2, according to a thermal budget adapted to weaken the flat implantation zone 100.

[0130] The set of cavities 200 is advantageously arranged on the proximal surface S of the first substrate 1 and / or on the surface 20 of the second substrate 2 so that each pair of adjacent cavities 200 is spaced apart by a distance between: - a first threshold, beyond which direct bonding between the first and second substrates 1, 2 is authorized; - a second threshold, strictly higher than the first threshold, below which thermal initiation of the fracture of the weakened flat implantation zone 100 is prohibited after the heat treatment applied to the first and second bonded substrates 1, 2.

[0131] The first and second substrates 1, 2 are intended to have a bonding surface. The set of cavities 200 is advantageously arranged on the proximal surface S of the first substrate 1 and / or on the surface 20 of the second substrate 2 so as to occupy between 50% and 85% of the bonding surface, preferably between 60% and 80% of the bonding surface.

[0132] The set of cavities 200 is advantageously arranged so that each cavity 200 has at least one dimension, in the plane of the proximal surface S of the first substrate 1 and / or in the plane of the surface 20 of the second substrate 2, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0133] According to the first embodiment illustrated in [Fig. 1], the lateral dimension of the cavities 200 is in the plane of the surface 20 of the second substrate 2. According to the second embodiment illustrated in [Fig.7], the lateral dimension of the cavities 200 is in the plane of the proximal surface S of the first substrate 1. According to the third embodiment illustrated in [Fig.8], the lateral dimension of the cavities 200 is in the plane of the proximal surface S of the first substrate 1 and in the plane of the surface 20 of the second substrate 2. According to the fourth embodiment illustrated in [Fig.9], the lateral dimension of the cavities, in the plane of the proximal surface S of the first substrate 1, is not a critical parameter in the absence of blisters 3.

[0134] According to the first embodiment illustrated in [Fig. 1], the set of cavities 200 is arranged on the surface 20 of the second substrate 2 so that each cavity 200 has at least one dimension, in the plane of the surface 20 of the second substrate 2, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0135] According to the second embodiment illustrated in [Fig.7]: - the set of cavities 200 is arranged on the proximal surface S of the first substrate 1 so as to extend below the flat implantation zone 100; - the set of cavities 200 is arranged on the proximal surface S of the first substrate 1 so that each cavity 200 has at least one dimension, in the plane of the proximal surface S of the first substrate 1, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0136] According to the third embodiment illustrated in [Fig.8]: - the set of cavities 200 is arranged: to the proximal surface S of the first substrate 1 so as to extend below the flat implantation zone 100, and on the surface 20 of the second substrate 2; - the set of cavities 200 is arranged so that each cavity 200 has at least one dimension, in the plane of the proximal surface S of the first substrate 1 and in the plane of the surface 20 of the second substrate 2, less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

[0137] According to the fourth embodiment illustrated in [Fig.9], the set of cavities 200 is arranged on the proximal surface S of the first substrate 1 so as to extend beyond beyond the flat installation zone 100.

[0138] The technical characteristics described above (first and second substrates 1, 2, implanted species 10, average exfoliation radius, shape of the cavities 200) apply to this subject of the invention.

[0139] The invention is not limited to the embodiments disclosed. Those skilled in the art are able to consider their technically effective combinations and to substitute equivalents for them.

Claims

Claims

1. Method for manufacturing removable substrates (1, 2), comprising the steps: a) providing: - a first substrate (1), comprising implanted species (10) forming a flat implantation zone (100), the first substrate (1) comprising a surface (S) proximal to the flat implantation zone (100); - a second substrate (2), comprising a surface (20); b) forming a set of cavities (200) on the proximal surface (S) of the first substrate (1) and / or on the surface (20) of the second substrate (2); c) assembling the first and second substrates (1, 2) by direct bonding between the proximal surface (S) of the first substrate (1) and the surface (20) of the second substrate (2); d) applying a heat treatment to the assembly obtained at the end of step c), according to a thermal budget adapted to weaken the flat implantation zone (100);the set of cavities (200) being arranged during step b) so as to: - allow direct bonding between the first and second substrates (1, 2) during step c); - prevent thermal initiation of the fracture of the flat implantation zone (100) weakened at the end of step d).;

2. Method according to claim 1, comprising a step e) consisting of carrying out a mechanical fracture of the flat implantation zone (100) weakened after step d), so as to dismantle the first and second substrates (1, 2).

3. Method according to claim 1 or 2, in which the set of cavities (200) is arranged during step b) so that each pair of adjacent cavities (200) is spaced apart by a distance between: - a first threshold, beyond which direct bonding between the first and second substrates (1, 2) is authorized during step c); - a second threshold, strictly greater than the first threshold, below which thermal initiation of the fracture of the weakened flat implantation zone (100) is prohibited at the end of step d).

4. Method according to claim 3, wherein the first threshold is between 500 nm and 3 pm, preferably between 1 pm and 2 pm.

5. Method according to claim 3 or 4, wherein the second threshold is between 5 pm and 200 pm, preferably between 5 pm and 100 pm, more preferably between 5 pm and 10 pm.

6. Method according to one of claims 1 to 5, in which the first and second substrates (1, 2) have a bonding surface at the end of step c); and the set of cavities (200) is arranged during step b) so as to occupy between 50% and 85% of the bonding surface, preferably between 60% and 80% of the bonding surface.

7. Method according to one of claims 1 to 6, in which: - the set of cavities (200) is formed during step b) on the proximal surface (S) of the first substrate (1) so as to extend below the flat implantation zone (100); - the set of cavities (200) is arranged during step b) so that each cavity (200) has at least one dimension, in the plane of the proximal surface (S) of the first substrate (1), less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

8. Method according to one of claims 1 to 6, in which: - the set of cavities (200) is formed during step b) on the surface (20) of the second substrate (2); - the set of cavities (200) is arranged during step b) so that each cavity (200) has at least one dimension, in the plane of the surface (20) of the second substrate (2), less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

9. Method according to one of claims 1 to 6, in which: - the set of cavities (200) is formed during step b): on the proximal surface (S) of the first substrate (1) so as to extend below the flat implantation zone (100), and on the surface (20) of the second substrate (2); - the set of cavities (200) is arranged during step b) so that each cavity (200) has at least one dimension, in the plane of the proximal surface (S) of the first substrate (1) and in the plane of the surface (20) of the second substrate (2), less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

10. Method according to one of claims 1 to 6, in which the set of cavities (200) are formed during step b) on the proximal surface (S) of the first substrate (1) so as to extend beyond the flat implantation zone (100).

11. Method according to one of claims 1 to 9, in which step a) comprises a prior step consisting of determining an average exfoliation radius and / or a minimum exfoliation radius by a statistical analysis of microscopic observations, after having applied to the first substrate (1) a heat treatment for fracturing the flat implantation zone (100).

12. Assembly for manufacturing removable substrates (1, 2), comprising: - a first substrate (1), comprising implanted species (10) forming a flat implantation zone (100), the first substrate (1) comprising a surface (S) proximal to the flat implantation zone (100); - a second substrate (2), comprising a surface (20); - a set of cavities (200), arranged on the proximal surface (S) of the first substrate (1) and / or on the surface (20) of the second substrate (2) so as to: allow direct bonding between the proximal surface (S) of the first substrate (1) and the surface (20) of the second substrate (2); prevent thermal initiation of the fracture of the flat implantation zone (100), after a heat treatment applied to the first and second bonded substrates (1, 2), according to a thermal budget adapted to weaken the flat implantation zone (100).

13. Assembly according to claim 12, in which the set of cavities (200) is arranged on the proximal surface (S) of the first substrate (1) and / or on the surface (20) of the second substrate (2) so that each pair of adjacent cavities (200) is spaced apart by a distance between: - a first threshold, beyond which direct bonding between the first and second substrates (1, 2) is permitted; - a second threshold, strictly greater than the first threshold, below which thermal initiation of the fracture of the flat implantation zone (100) is prohibited after the heat treatment applied to the bonded first and second substrates (1, 2).

14. An assembly according to claim 12 or 13, wherein the first and second substrates (1, 2) are intended to have a bonding surface; and the set of cavities (200) is arranged at the proximal surface (S) of the first substrate (1) and / or at the surface (20) of the second substrate (2) of so as to occupy between 50% and 85% of the bonding surface, preferably between 60% and 80% of the bonding surface.

15. Assembly according to one of claims 12 to 14, wherein: - the set of cavities (200) is arranged on the proximal surface (S) of the first substrate (1) so as to extend below the flat implantation zone (100); - the set of cavities (200) is arranged on the proximal surface (S) of the first substrate (1) so that each cavity (200) has at least one dimension, in the plane of the proximal surface (S) of the first substrate (1), less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

16. Assembly according to one of claims 12 to 14, in which the set of cavities (200) is arranged on the surface (20) of the second substrate (2) so that each cavity (200) has at least one dimension, in the plane of the surface (20) of the second substrate (2), less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

17. Assembly according to one of claims 12 to 14, wherein: - the set of cavities (200) is arranged: on the proximal surface (S) of the first substrate (1) so as to extend below the flat implantation zone (100), and on the surface (20) of the second substrate (2); - the set of cavities (200) is arranged so that each cavity (200) has at least one dimension, in the plane of the proximal surface (S) of the first substrate (1) and in the plane of the surface (20) of the second substrate (2), less than or equal to twice a predetermined average exfoliation radius, preferably less than or equal to twice a predetermined minimum exfoliation radius.

18. Assembly according to one of claims 12 to 14, in which the set of cavities (200) is arranged on the proximal surface (S) of the first substrate (1) so as to extend beyond the flat implantation zone (100).

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