Method for manufacturing a laminate structure

Abstract

The present invention relates to a method for manufacturing a laminate structure comprising a receiver substrate and a surface film, the method comprising the steps of: a) providing a carrier substrate and an initial substrate having a front surface and a back surface; b) forming a buried weak surface by implanting light ions through the front surface of one of the substrates; c) bonding the carrier substrate and the initial substrate at their front surfaces; d) thinning the initial substrate at its back surface to form a donor substrate comprising a donor layer obtained from the initial substrate and disposed on the carrier substrate and a buried weak surface; e) providing a receiver substrate having a front surface and a back surface; f) bonding the donor substrate and the receiver substrate at their front surfaces; and g) separating along the buried weak surface to form a laminate structure comprising a receiver substrate and a surface film comprising all or part of the donor layer.

Description

[Technical field]

[0001] Possible applications of the invention are in the fields of microelectronics, microsystems, optoelectronics, photonics and RF filters.The present invention relates to a method for producing a layered structure comprising a surface film disposed on a functionalized substrate. [Background technology]

[0002] In the field of microelectronics, and in particular in the field of MEMS (Microelectromechanical Systems), it is generally useful to transfer thick films (for example with a thickness of more than 5 μm) onto substrates that have previously been subjected to a structuring step in order to integrate various functions. This functionalized substrate can, for example, be provided with cavities and / or nano- or microelectronic devices. The thick films in question can in particular be made of semiconducting, insulating or piezoelectric materials or may exhibit other physical properties depending on the intended application.

[0003] To transfer thick films, it is a known practice to bond the donor substrate from which the film is obtained to a functionalized substrate, and then mechanically and / or chemically thin the donor substrate on its free backside. One drawback of this approach is that the mechanical and chemical processes are limited and tend to degrade the quality of the film and / or the functionalized substrate during transfer. In particular, when the functionalized substrate comprises cavities, the film may show cracks or delamination areas facing the cavities, as well as thickness non-uniformities. When the functionalized substrate comprises microelectronic components, the film may show thickness non-uniformities related to the pattern and topology of the underlying components, and / or the components may suffer degradation.

[0004] The Smart Cut® method, which is well known per se, is particularly suitable for transferring films that can be characterized as "thin", i.e. typically having a thickness of less than 1.5 μm, to a receiver substrate, whether functionalized or not. However, the transfer of thick films, of several μm to tens of μm, cannot be directly realized with conventional ion implantation equipment.

[0005] Other methods are based on detachment by applying mechanical stress or chemical treatment to a weak interface present in a donor substrate, which can then be characterized as a "detachable substrate" since it comprises said weak interface that is the site of detachment, i.e. separation, between the future film and the remainder of the donor substrate.

[0006] This is especially the case for the methods described in FR 2748851, FR 2823599, FR 2823596 or WO 2019110886. One limitation of these approaches may be due to the tendency of the detachment step, which is mainly carried out by inserting a blade between the attached initial substrate and the target substrate, exposing the substrate to substantial tensile stress and / or by prolonged immersion of the substrate in a chemical solution, to adversely affect the quality of the film. Furthermore, the difficulty of precisely localizing the mechanical stress and / or chemical attack at the weak interface may sometimes lead to detachment at interfaces or layers other than the weak interface.

[0007] Yet other methods based on separation at the interface by laser (laser lift-off) require the use of transparent substrates for the functionalized or donor substrate, which limits the scope of application. Summary of the Invention

[0008] The present invention relates to an alternative solution to the prior art solutions and is aimed at overcoming the above mentioned drawbacks in whole or in part.The present invention relates to a method for producing a laminate structure comprising a surface film arranged on a functionalized substrate.

[0009] The present invention relates to a method for manufacturing a laminate structure comprising a receiver substrate and a surface film, the method comprising the steps of: a) providing a carrier substrate and an initial substrate, each having a front surface and a back surface; b) forming a buried weak surface in a carrier substrate or an initial substrate by implanting light ions through the front surface of either of said substrates; c) bonding the carrier substrate and the initial substrate at their front sides; d) mechanically and / or chemically thinning the initial substrate at its back side to form a donor substrate comprising a donor layer derived from the initial substrate and arranged on a carrier substrate and a buried weak surface present in the carrier substrate or in the donor layer, the donor substrate having a front side on the side of the donor layer and a back side on the side of the carrier substrate; e) providing a receiver substrate having a front surface and a back surface; f) bonding the donor substrate and the receiver substrate at their front sides; g) separating along the embedded plane of weakness to form a laminate structure comprising a receiver substrate and a surface film that includes all or a portion of the donor layer; Includes.

[0010] According to other advantageous, non-limiting characteristics of the invention, taken alone or in any technically feasible combination, are the following:

[0011] The method includes a step of forming at least one functionalization layer on the front side of the donor substrate and / or the front side of the receiver substrate prior to the bonding step f), such that the laminated structure comprises the receiver substrate, a surface film and a functionalization layer interposed between the receiver substrate and the surface film.

[0012] The functionalization layer comprises a plurality of micro- or nanostructured regions and / or a plurality of cavities and / or a plurality of micro- or nano-electronic components.

[0013] The components are selected from transistors, MEMS, sensors, resonators, imagers, actuators, radio frequency filters, diodes, and lasers.

[0014] The cavity has lateral dimensions between 1 μm and several hundred μm, and a depth of the order of 0.1 μm to several tens of μm.

[0015] A buried weakened surface is formed in the carrier substrate.

[0016] After completion of step g) the transferred surface film comprises a transferred thin layer obtained from a carrier substrate.

[0017] The transferred thin layer is removed by chemical etching.

[0018] A buried weak surface is formed in the initial substrate.

[0019] After the separation step g) a chemical mechanical polishing, chemical etching and / or cleaning step is performed to at least partially restore the surface quality of the surface film.

[0020] The surface film is formed from at least one semiconductor material selected from silicon, germanium, silicon carbide, III-V compounds, and / or from at least one insulating material selected from sapphire, diamond, and / or from at least one piezoelectric material selected from lithium tantalate, lithium niobate.

[0021] The receiver substrate is formed from at least one semiconducting and / or insulating and / or metallic, monocrystalline, polycrystalline, or amorphous material.

[0022] The receiver substrate has a thickness between a few tens of μm and 1000 μm.

[0023] Other features and advantages of the present invention will become apparent from the following detailed description of the invention which refers to the accompanying drawings. [Brief description of the drawings]

[0024] [Figure 1a] 1 shows an example of a laminate structure obtained using a manufacturing method according to the invention; [Figure 1b] 1 shows an example of a laminate structure obtained using a manufacturing method according to the invention; [Figure 1c] 1 shows an example of a laminate structure obtained using a manufacturing method according to the invention; [Figure 2a] 1A-1D illustrate steps of a method for manufacturing a laminate structure according to a first embodiment of the invention. [Figure 2b] 1A-1D illustrate steps of a method for manufacturing a laminate structure according to a first embodiment of the invention. [Figure 2c] 1A-1D illustrate steps of a method for manufacturing a laminate structure according to a first embodiment of the invention. [Figure 2d] 1A-1D illustrate steps of a method for manufacturing a laminate structure according to a first embodiment of the invention. [Figure 2e] 1A-1D illustrate steps of a method for manufacturing a laminate structure according to a first embodiment of the invention. [Figure 2f] 1A-1D illustrate steps of a method for manufacturing a laminate structure according to a first embodiment of the invention. [Figure 2g] 1A-1D illustrate steps of a method for manufacturing a laminate structure according to a first embodiment of the invention. [Figure 3a] 5A-5D illustrate steps of a method for manufacturing a laminate structure according to a second embodiment of the invention. [Figure 3b] 5A-5D illustrate steps of a method for manufacturing a laminate structure according to a second embodiment of the invention. [Figure 3c] 5A-5D illustrate steps of a method for manufacturing a laminate structure according to a second embodiment of the invention. [Figure 3d] 5A-5D illustrate steps of a method for manufacturing a laminate structure according to a second embodiment of the invention. [Figure 3e]5A-5D illustrate steps of a method for manufacturing a laminate structure according to a second embodiment of the invention. [Figure 3f] 5A-5D illustrate steps of a method for manufacturing a laminate structure according to a second embodiment of the invention. [Figure 3g] 5A-5D illustrate steps of a method for manufacturing a laminate structure according to a second embodiment of the invention. [Figure 4a] FIG. 2 shows a variant of the first embodiment according to the manufacturing method according to the invention. [Figure 4b] FIG. 2 shows a variant of the first embodiment according to the manufacturing method according to the invention. [Figure 5a] FIG. 1 shows a variant of the second embodiment according to the manufacturing method according to the invention. [Figure 5b] FIG. 1 shows a variant of the second embodiment according to the manufacturing method according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] In this specification, the same reference numbers in the figures may be used for the same type of elements. The figures are schematic representations that are not drawn to scale for clarity. In particular, the thickness of layers along the z-axis is not drawn to scale relative to the lateral dimensions along the x- and y-axes. The relative thicknesses of layers with respect to each other are also not taken into account in the figures.

[0026] The laminate structure 100 obtained by the manufacturing method according to the present invention comprises a receiver substrate 70 and surface films 60', 60'', as shown in Figures 1a to 1c.

[0027] The receiver substrate 70 is advantageously in the form of a wafer having a front surface 70a and a back surface 70b (Figures 2e and 3e) and a diameter of more than 100 mm, for example 150 mm, 200 mm, 300 mm or even 450 mm. The thickness of the receiver substrate 70 is typically between a few tens of μm and 1000 μm, for example between 100 μm and 800 μm. The receiver substrate 70 can be made of any semiconducting, insulating or conducting material, whether monocrystalline, polycrystalline or amorphous, depending on the target application.

[0028] According to a first aspect of the invention shown in FIG. 1a, the receiver substrate 70 is not well suited to mechanical thinning techniques or mechanical stress application due to the nature of the material or materials from which it is formed (e.g., fragile materials such as some glasses) or due to its small thickness (e.g., thickness less than 400 μm, less than 250 μm, or even less than 150 μm).

[0029] According to a second aspect of the invention (which can be combined with the first or other aspects), the receiver substrate 70 comprises a functionalization layer 75 (FIGS. 1b, 1c). By functionalization it is meant that the layer 75 comprises micro- or nanostructured areas and / or cavities 71 filled with solid material or free of solid material and / or a plurality of partially or completely formed micro- or nano-electronic components 72. The functionalization layer 75 can be formed in the receiver substrate 70 at the level of its front surface 70a. In general, the functionalization layer 75 can therefore form all types of regular or locally distributed topologies and may comprise an additional material with respect to the material(s) forming the receiver substrate 70. By way of example, the additional material can be an oxide, a nitride or a metal.

[0030] The laminate structure 100 also includes a surface film 60', 60'' disposed on the receiver substrate 70. When present, the functional layer 75 is interposed between the surface film 60', 60'' and the receiver substrate 70.

[0031] The films 60 ′, 60 ″ can have different properties and exhibit different characteristics depending on the intended application for the laminate structure 100 .

[0032] Advantageously, the films 60', 60'' may comprise monocrystalline materials which guarantee the stability and reproducibility of their properties, in contrast to the case of polycrystalline materials, for example, whose mechanical properties are highly dependent on the deposition conditions (grain size and shape, nature of grain boundaries, stresses, etc.). Monocrystalline materials may also enable the formation of micro- or nanoelectronic components on the surface films 60', 60'' of the laminate structure 100. Said components may be connected to a functionalization layer 75 (if present) of the receiver substrate 70.

[0033] The surface film 60', 60'' may be made of at least one semiconducting material, preferably but not exclusively selected from silicon, germanium, silicon carbide, III-V compounds, and / or of at least one insulating material, such as sapphire or diamond, and / or of at least one piezoelectric material, such as lithium tantalate or lithium niobate. The surface film 60', 60'' may have a thickness between 2 μm and 300 μm, advantageously between 5 μm and 80 μm.

[0034] In general, the surface films 60', 60'' may be formed by one or more continuous or discontinuous layers of a variety of materials.

[0035] According to a first option, the surface film 60', 60'' of the laminated structure 100 is raw or continuous, i.e. without any particular structuring (FIGS. 1a, 1b). As mentioned above, deposition, structuring or other device formation steps can be carried out on the free surface, i.e. the front surface 100a, after completion of the manufacturing of the laminated structure 100.

[0036] According to a second option, the surface film 60', 60'' comprises a functionalization layer 75' comprising, for example, micro- or nanostructured areas 73' and / or one or more cavities 71' facing the front side of the receiver substrate 70 (Fig. 1c). The surface film 60', 60'' can form a movable membrane over the cavities 71' and over the predefined metal contacts 73' for the purpose of subsequently manufacturing a MEMS device (Fig. 1c(i)). According to another example, the surface film 60', 60'' can realise an encapsulating cover for components 72 of the functionalization layer 75 of the receiver substrate 70, for example due to the presence of the cavities 71' formed in the surface film 60', 60'', even if the components 72 form a substantial topology on the front side 70a of the receiver substrate 70 (Fig. 1c(ii)).

[0037] Hereinafter, the first functionalization layer 75 and the second functionalization layer 75' refer to the functionalization layers formed, respectively, on the receiver substrate 70 and on the donor substrate 60 from which the surface films 60', 60'' are derived. It is recalled that any combination of the first aspect of the invention, the second aspect of the invention, the first option, and the second option described above is conceivable, although not necessarily a set of combinations is illustrated or specified herein.

[0038] It should be noted that an intermediate layer may also be introduced between the surface film 60', 60'' and the receiver substrate 70, whether placed on the side of the film 60', 60'' or on the side of the receiver substrate 70, in order to promote bonding between the surface film 60', 60'' and the receiver substrate 70, or to achieve the function of electrical or thermal conduction or insulation between the receiver substrate 70 and the film 60', 60''.

[0039] Next, a method for manufacturing the above-mentioned laminate structure 100 will be described with reference to Figures 2a to 2g, 3a to 3g, 4a to 4b, and 5a to 5b.

[0040] The manufacturing method first comprises a step a) of preparing a carrier substrate 30 and an initial substrate 40, each having a front surface 30a, 40a and a rear surface 30b, 40b (Figures 2a, 3a). These two substrates 30, 40 are advantageously in the form of wafers with a diameter greater than 100 mm, for example 150 mm, 200 mm, 300 mm or even 450 mm. Their thickness is typically between 200 and 900 μm.

[0041] As will become clear hereinafter, the initial substrate 40 is the substrate from which the surface films 60', 60'' are primarily taken. Naturally, therefore, the materials mentioned above for the surface films 60', 60'' apply without limitation. The nature and properties of the initial substrate 40 are therefore closely related to the intended application for the laminate structure 100.

[0042] The carrier 30 and the initial substrate 40 may be bare or may comprise one or more layers, the nature of which may possibly differ from that of the substrate.

[0043] Step b) in the method according to the invention comprises the formation of a buried weak surface 32, 42 in the carrier substrate 30 or in the initial substrate 40 by implanting light ions through the front surface of either of said substrates 30, 40 (FIGS. 2b, 3b).

[0044] As is well known for the Smart Cut method mentioned at the beginning, the light ions are advantageously selected from hydrogen, helium or a combination of the two. The implantation energy and dose are defined so as to generate spontaneous separation in the subsequent method step g) by application of a heat treatment at moderate temperatures, typically below 700° C., preferably even below 600° C., below 500° C., below 350° C. or even below 300° C. It is known that depending on the implanted species, the dose introduced, the material from which said surfaces 32, 42 are formed, etc., it is effectively possible to influence the kinetics of coalescence of microcracks present in the buried weak surfaces 32, 42.

[0045] According to a first embodiment shown in Fig. 2b onwards, a buried weak surface 32 is formed in a carrier substrate 30. This substrate is preferably monocrystalline in nature in order to facilitate the formation of the buried weak surface 32 by implantation of light ion species. Optionally, a protective layer 31, for example made of silicon oxide or silicon nitride, may be arranged on the front surface 30a of the carrier substrate 30 in order to protect the substrate during implantation.

[0046] According to a second embodiment, shown in Fig. 3b onwards, a buried weak surface 42 is formed in an initial substrate 40. This substrate is preferably monocrystalline in nature in order to facilitate the formation of the buried weak surface 42 by implantation of light ion species. Optionally, a protective layer 41, for example made of silicon oxide or silicon nitride, may be arranged on the front surface 40a of the carrier substrate 40 in order to protect the substrate during implantation.

[0047] In general, for any embodiment, the carrier substrate 30 is advantageously chosen from an inexpensive material. Examples include low or medium quality monocrystalline or polycrystalline silicon, glass, etc. The initial substrate 40 is advantageously made of one or more materials whose nature and quality (defect density, crystallinity) are defined by the specifications that the surface film 60', 60'' of the target laminate structure 100 must meet. In particular, the initial substrate 40 can comprise at least one semiconducting material and / or at least one insulating material and / or at least one conducting material and / or at least one piezoelectric material.

[0048] In both embodiments, the buried weakened surface 32, 42 is located less than 2 μm from the free surface of the front surface 30a, 40a of the substrate 30, 40. Moreover, it is advantageously located at a depth of less than 1 μm, or even less than 0.5 μm.

[0049] The manufacturing method according to the invention then comprises a step c) of joining the carrier substrate 30 and the initial substrate 40 by their respective front faces 30a, 40a (FIGS. 2c, 3c).

[0050] Various types of bonding are possible, in particular insulating or metallic bonding surfaces making it possible to carry out direct bonding at ambient temperature by molecular adhesion or thermocompression or eutectic bonding at low temperatures (typically below 350° C.). At this stage of the method a bonding interface 50 is thus defined between the two substrates 30, 40 forming a first bonded structure 55.

[0051] The protective layer 31, 41 can be retained or removed before the bonding step c). When the protective layer 31, 41 is retained, it can be used as an intermediate layer in order to improve the mechanical strength of the bonding interface 50. When the protective layer 31, 41 is removed, a conductive or insulating intermediate layer can be deposited on either of the substrates 30, 40 to be bonded in order to improve the bonding quality (low defect density, high bond energy). Alternatively, the initial substrate 40 can be bonded directly to the carrier substrate 30.

[0052] Prior to bonding of the substrates 30, 40, a series of cleaning and plasma surface activations are advantageously applied to the substrates 30, 40 in order to ensure a subsequently good bonding quality. A smoothing treatment, for example chemical mechanical polishing, can also be applied to the front faces 30a, 40a in order to make their surfaces as flat as possible and to reduce the surface roughness at high and low frequencies of the respective front faces 30a, 40a.

[0053] Optionally, a heat treatment is performed to solidify the interface 50 by exposing the first bonded structure 55 to a low temperature, typically below 300° C., or even below 250° C., for a period of a few hours. The thermal budget applied to the bonded structure 55 during this heat treatment must necessarily remain below the thermal budget that would allow spontaneous separation at the level of the embedded weak surfaces 32, 42.

[0054] After bonding, the manufacturing method includes a step d) of mechanically and / or chemically thinning the initial substrate 40 at its back surface 40b to form a donor substrate 60 (FIGS. 2d, 3d). Such thinning can be performed using known techniques of mechanical grinding, chemical-mechanical polishing and / or chemical etching. Since the initial substrate 40 and the carrier substrate 30 are unprocessed or provided with a simple stack of uniform and continuous layers, and the first bonding structure 55 comprises a homogenous bonding interface 50 over its entire surface (typically without cavities or other structuring), the thinning step can be very well controlled, resulting in the formation of a uniform and completely intact donor layer 45.

[0055] The donor substrate 60 is obtained from the initial substrate 40 and comprises a donor layer 45 arranged on a carrier substrate 30. The donor layer 45 may have a thickness between a few μm and 300 μm, advantageously between 5 μm and 80 μm.

[0056] The donor substrate 60 has a front surface 60 a on the side of the donor layer 45 and a back surface 30 b on the side of the carrier substrate 30 , which is also the back surface of the carrier substrate 30 .

[0057] In a first embodiment, the buried weak surface 32 is present in the carrier substrate 30 (FIG. 2d), and in a second embodiment, the buried weak surface 42 is in the donor layer 45 (FIG. 3d). In both cases, the buried weak surface 32, 42 is located less than 1.5 μm, or even less than 0.5 μm, from the bonding interface 50.

[0058] According to the above mentioned second option, in which the surface film 60', 60'' of the laminated structure 100 targeted by the method of the invention comprises a functional layer 75' (second functional layer 75'), the manufacturing method comprises a step d') of forming a second functionalized layer 75' on the front surface 60a of the donor substrate 60. Conventional microelectronic and / or micro- or nanomachining techniques can be implemented to generate the micro- or nanostructured areas and / or cavities 71' (FIGS. 4a, 5a). Assuming the presence of buried weak surfaces 32, 42, the sequence of generating the second functional layer 75' should only require low temperatures, typically below 250° C.

[0059] As shown in Figures 4a (according to a first embodiment) and 5a (according to a second embodiment), the donor substrate 60 may be subjected to local etching, for example on the front side 60a, to define one or more cavities 71' in the donor layer 45.

[0060] The manufacturing method then comprises a step e) of preparing a receiver substrate 70 having a front surface 70a and a back surface 70b (Figures 2e and 3e). As mentioned above, the receiver substrate 70 is advantageously in the form of a wafer with a diameter of more than 100 mm, for example 150 mm, 200 mm, 300 mm or even 450 mm, the thickness of which is typically between a few tens of μm and 1000 μm, and which can be made of any semiconducting, insulating or conducting material, depending on the target application. Since silicon is a material that is available, compatible with all microelectronic processes and has advantageous mechanical and electrical properties, it is preferred that silicon forms the receiver substrate 70 when the functionalization layer 75 defined above according to the second aspect of the invention is provided on the receiver substrate 70.

[0061] The receiver substrate 70 may be fragile or very thin in nature, as described in the first aspect of the invention.

[0062] Thus, according to the second aspect of the invention described above, the method comprises a step e') of forming a functionalization layer 75 on the front side 70a of the receiver substrate 70. Conventional microelectronic and / or micro- or nanomachining techniques can be implemented to produce the partially or completely formed micro- or nanoelectronic components of the micro- or nanostructured areas, cavities 71 and / or functional layer 75. These elements may correspond to passive components (such as resistors or capacitors) or to active components such as transistors. They may also correspond to MEMS, sensors or actuators. These elements are advantageously based on silicon technology, but may also be based, for example, on other semiconductor or piezoelectric technology streams.

[0063] The cavity 71 may have a lateral dimension in the (x,y) plane of the front surface 70a of typically between 1 μm and several hundred μm, for example 200 to 500 μm, and a height (or depth) along a z-axis perpendicular to the front surface 70a of typically on the order of 0.1 μm to several tens of μm.

[0064] The cavity or cavities 71 may be empty, i.e. containing no solid material, or may be filled with a sacrificial solid material, which is subsequently removed in the method for manufacturing the laminated structure 100 or during the manufacture of a device based on said structure 100. Alternatively, the cavity 71 may be filled with a useful material that provides functionality (such as insulation) and is therefore subsequently retained.

[0065] It is noted that it may be more advantageous to have the cavity 71 filled at this stage in order to facilitate the subsequent steps of the manufacturing method. The material placed in the cavity 71 may be silicon oxide, silicon nitride, amorphous or polycrystalline silicon, etc. When the material is a sacrificial material, it is selected depending on the nature of the receiver substrate 70 and possibly the nature of the surface films 60', 60''. In particular, such a material should be capable of being chemically etched with good selectivity with respect to the receiver substrate 70 and to the surface films 60', 60'' placed on the cavity 71, since it is intended to be removed after the laminate structure 100 has been formed.

[0066] The manufacturing method according to the invention then comprises a step f) of bonding the donor substrate 60 and the receiver substrate 70 at their respective front faces 60a, 70a (FIGS. 2f, 3f, 4b, 5b).

[0067] As in the previous bonding step c), various types of bonding are possible, for example direct bonding at ambient temperature by molecular adhesion or thermocompression or eutectic bonding at low temperatures, with insulating or metallic bonding surfaces. Bonding can be performed in ambient atmosphere, in vacuum or in a specific controlled atmosphere. Thus, at this stage of the method, a bonding interface 80 is defined between the two substrates 60, 70 forming a second bonded structure 85.

[0068] Although not shown in the figures, it is also entirely conceivable to form an intermediate layer on the front surface 60a, 70a of one or both of the substrates 60, 70 to be bonded prior to step f). Depending on the needs of the application, a conductive or insulating intermediate layer is suitable to improve the quality and mechanical strength of the bonding interface 80. By way of example, an intermediate layer made of silicon oxide, silicon nitride or polysilicon, or a metal layer such as copper, can be used.

[0069] Prior to bonding of the substrates 60, 70, a series of cleaning, plasma surface activation and / or smoothing treatments (such as chemical mechanical polishing) may be advantageously applied to the substrates 60, 70 in order to ensure continued good bond quality.

[0070] Optionally, a heat treatment is performed to solidify the interface 80 by exposing the second bond structure 85 to a low temperature, typically below 300° C., where the thermal budget applied to the bond structure 85 during this heat treatment remains below the thermal budget that would allow spontaneous separation at the level of the embedded weak surfaces 32, 42.

[0071] Finally, the manufacturing method according to the present invention includes a step g) of separating along the embedded weak surfaces 32, 42 to form a laminated structure 100 including a receiver substrate 70, a surface film 60', 60'' comprising all or part of the donor substrate 45, and, if either or both are present, a first functionalized layer 75 and a second functionalized layer 75' (Figures 2g, 3g, 1a-1c).

[0072] Separation along the buried planes of weakness 32, 42 is achieved by heat treatment which induces splitting in the regions of microcracks under the gas pressure generated by the implanted species.

[0073] For buried weak surfaces 32,42 formed from silicon, the heat treatment is typically carried out at temperatures between 200°C and 600°C for a period of several minutes to several hours to induce spontaneous propagation of the split along the weak surfaces 32,42.

[0074] Naturally, if the first functionalization layer 75 and / or the second functionalization layer 75' comprise materials sensitive to medium and high temperatures, the temperature of the separation heat treatment is selected to be as low as possible, for example between 200°C and 325°C.

[0075] In some cases, the thermal budget can be supplemented by the application of a moderate amount of mechanical stress, where care is taken to apply a high weakening thermal budget to the embedded weakened planes 32, 42 to prevent separation from occurring at interfaces or layers other than the weakened planes 32, 42, requiring only a small mechanical stress just enough to initiate spontaneous propagation of the split.

[0076] According to the embodiment shown in FIG. 2g, the surface film 60' comprises the thick donor layer 45, the intermediate layer 31 (protective or bonding layer) if present, and the thin layer 30' transferred from the carrier substrate 30. In particular, since the buried weak surface 32 is in the carrier substrate 30, the separation results on the one hand in the transferred layer 30' attached to the laminated structure 100, and also in the remaining part of the carrier substrate 30. The transferred layer 30' and possibly the intermediate layer 31 can be easily removed by dry or wet chemical etching. Given the small thickness of those layers, such chemical etching is very well controlled, fast and does not result in an aggressive step that tends to degrade the laminated structure 100. After the completion of this etching, a laminated structure 100 is obtained with a surface film 60' consisting of a thick donor substrate 45 of very high quality, typically between a few μm and 100 μm, or preferably between 5 μm and 50 μm. In particular, the integrity and uniformity of the thickness of the donor layer 45 is guaranteed in step d) of thinning the first bonded structure 55. This step is very well controlled since it is performed on a raw substrate possibly with a simple stack of uniform and continuous layers. The separation step g) applied to the second bonded structure 85 possibly with one or more functionalization layers 75, 75' is much less restrictive than the long and aggressive mechanical and chemical thinning steps (removal of tens of μm of material) or the mechanical separation steps proposed in the prior art to transfer the thick surface film 60' to the receiver substrate 70.

[0077] In a second embodiment shown in FIG. 3g, surface film 60″ consists of the transferred portion of donor layer 45. In particular, since embedded weak surface 42 is located in initial substrate 40, and more particularly in donor layer 45, separation results in transferred portion 60″ attached to laminate structure 100 as one, and in the remaining portion of donor substrate 60.

[0078] A chemical-mechanical polishing, cleaning and / or chemical etching step removing a few hundred nanometers from the surface film 60″ on the side of the front surface 100a of the laminated structure 100 easily allows the recovery of a good surface state of the surface film 60″ (low roughness, low defect density) if this is required in view of the application. As is known for the Smart Cut method, the defect-containing area remaining after the separation of the buried weak surface 42 is thin, so that not much material needs to be removed. In this second embodiment, a laminated structure 100 with a thick surface film 60″ of very high quality, typically between a few μm and 100 μm, or preferably between 5 μm and 50 μm, is likewise obtained, since the completeness and uniformity of the thickness of the donor layer 45 is guaranteed in step d) of thinning the first bonded structure 55.

[0079] Thus, the manufacturing method according to the present invention makes it possible to transfer thick surface films 60', 60'' of high crystalline quality (when the donor layer 45 is single crystalline) and which exhibit completeness and excellent thickness uniformity even when transferred to a functionalization layer 75 comprising components 72, cavities 71, and / or other structured layers.

[0080] When the first functional layer 75 comprises a cavity 71, it is possible, on the basis of the resulting laminated structure 100, to manufacture a device on the basis of a portion of the membrane, i.e. the surface film 60', 60'' movable above the cavity 71. If said cavity 71 is indeed filled at this stage of the method, it is necessary to selectively etch the sacrificial material filling the cavity 71.

[0081] It should be noted that the remainder of the carrier substrate 30 or the remainder of the donor substrate 60 may be processed for reuse in a new manufacturing cycle.

[0082] According to a first embodiment, the mounted substrate is a wafer having a diameter of 300 mm.

[0083] The initial substrate 40 is a bulk substrate made of monocrystalline silicon provided, at least on its front side 40a, with a 0.3 μm thermal silicon oxide layer SiO 2 .

[0084] The carrier substrate 30 is a bulk substrate made of low-grade (low-cost) monocrystalline silicon with a 0.3 μm thermal silicon oxide layer SiO2 on at least its front surface 30a. The initial substrate 40 and the carrier substrate 30 have a standard thickness (around 700-800 μm).

[0085] The initial substrate 40 has, at the level of its front surface 40a, a E 16 / cm 2 The silicon substrate 40 is implanted with H+ hydrogen ions at a conventional dose of about 100 nm and an energy of between 60-120 keV to form a buried weak surface 42 .

[0086] The bonding of the front surfaces 40a, 30a of the initial substrate 40 and the carrier substrate 30 realizes SiO2 / SiO2 direct bonding at ambient temperature. Then, a solidification anneal is applied to the bonded structure 55 at a low temperature between 200°C and 250°C for 1 hour to 2 hours.

[0087] The bond structure 55 is then thinned by mechanical grinding and mechanical trimming at the level of the back surface 40b of the initial substrate 40. These mechanical grinding steps are followed by chemical-mechanical polishing and conventional cleaning sequences (such as SC1 and SC2) to form the donor substrate 60. The donor layer 45 has a thickness of 15 μm and a surface quality (defect density, roughness) compatible with subsequent bonding to a receiver substrate 70 (typically less than 0.5 nm RMS roughness).

[0088] The receiver substrate 70 is a bulk substrate made of monocrystalline silicon having a thickness of less than 400 μm, polished on the backside and provided with a 0.3 μm thermal silicon oxide layer SiO 2 on at least its front side 70a.

[0089] The functionalization layer 75 is formed on the receiver substrate 70, for example by lithography and localized etching. The functionalization layer 75 comprises a plurality of mutually isolated cavities 71 having a depth of 5 μm and a lateral dimension of 350 μm. The cavities 71 may be circular or square in the plane of the front surface 70a, or may have another polygonal shape.

[0090] Bonding of the donor substrate 60 and the receiver substrate 70 is performed by direct bonding at ambient temperature, in ambient atmosphere, or in vacuum.

[0091] A heat treatment at 400° C. is then applied to cause separation along the embedded weak plane 42, resulting in a laminate structure 100 with a surface film 60″ on the one hand and the remaining part of the donor substrate 60 on the other hand.

[0092] To restore the surface roughness and quality of the surface film 60'', heat treatments including sacrificial oxidation or smoothing can be applied. Optionally, chemical mechanical polishing with a low degree of removal (typically less than 0.5 μm) and / or chemical etching can be applied.

[0093] Such a laminate structure 100 can be used, for example, to manufacture a pressure sensor.

[0094] In a second embodiment, the mounted substrate is a wafer having a diameter of 200 mm or 300 mm.

[0095] Carrier substrate 40 is a bulk substrate formed from low-grade (low-cost) single crystal silicon.

[0096] The carrier substrate 30 is a bulk substrate made of low-grade monocrystalline silicon with a 0.4 μm thermal silicon oxide layer SiO2 on at least its front surface 30a. The initial substrate 40 and the carrier substrate 30 have a standard thickness (around 700-800 μm).

[0097] The carrier substrate 30 has, at the level of its front surface 30a, a E 16 / cm 2 The silicon substrate 30 is implanted with H+ hydrogen ions at a conventional dose of about 100 nm and an energy of between 60-120 keV to form a buried weak surface 32.

[0098] The bonding of the front surfaces 40a, 30a of the initial substrate 40 and the carrier substrate 30 realizes SiO2 / SiO2 direct bonding at ambient temperature. Then, a solidification anneal is applied to the bonded structure 55 at a low temperature between 200°C and 250°C for 1 hour to 2 hours.

[0099] The bonded structure 55 is then thinned at the level of the back surface 40b of the initial substrate 40 by mechanical grinding, including mechanical trimming, followed by chemical-mechanical polishing and conventional cleaning sequences (SC1, SC2, etc.) to form the donor substrate 60. The donor layer 45 has a thickness of 30 μm and a surface quality (defect density, roughness) compatible with the subsequent bonding to a receiver substrate 70 (typically a roughness less than 0.5 nm RMS).

[0100] The receiver substrate 70 is made from single crystal silicon and comprises MEMS components such as accelerometers and gyroscopes, which form a first functionalization layer 75 .

[0101] A second functionalization layer 75' is formed in the donor layer 45, for example by lithography and localized etching. The functionalization layer 75' comprises a plurality of cavities 71 having a depth of 3 μm and lateral dimensions of 1.5 mm×1.5 mm.

[0102] The bonding between the donor substrate 60 and the receiver substrate 70 is performed by direct bonding in vacuum at ambient temperature.

[0103] A heat treatment between 350°C and 450°C is then applied to cause separation along the embedded weak surface 32, resulting in a laminate structure 100 with a surface film 60'' on the one hand and the remaining part of the carrier substrate 30 on the other hand.

[0104] A small degree of removal (typically less than 0.5 μm) by chemical etching can be performed to restore the surface roughness and quality of the surface film 60'.

[0105] Such a laminate structure 100 can be used, for example, to manufacture wafer level packaging of inertial sensors.

[0106] Naturally, the invention is not limited to the described embodiments and examples, and alternative embodiments can be introduced without departing from the scope of the invention as defined by the claims.

Claims

1. A method for manufacturing a laminate structure (100) comprising a receiver substrate (70) and a surface film (60', 60''), comprising the steps of: a) providing a carrier substrate (30) and an initial substrate (40), each having a front surface (30a, 40a) and a back surface (30b, 40b); b) forming a buried weak surface (32, 42) in the carrier substrate (30) or the initial substrate (40) by implanting light ions through the front surface (30a, 40a) of either the carrier substrate (30) or the initial substrate (40); c) bonding said carrier substrate (30) and said initial substrate (40) at their front faces (30a, 40a); d) mechanically and / or chemically thinning said initial substrate (40) at its back side (40b) to form a donor substrate (60) comprising a donor layer (45) obtained from said initial substrate (40) and arranged on said carrier substrate (30) and said buried weak surface (32, 42) present in said carrier substrate (30) or in said donor layer (45), said donor substrate (60) having a front side (60a) on the side of said donor layer (45) and a back side (30b) on the side of said carrier substrate (30); e) providing a receiver substrate (70) having a front surface (70a) and a back surface (70b); f) bonding said donor substrate (60) and said receiver substrate (70) at their front faces (60a, 70a); g) separating along said embedded weak planes (32, 42) to form said laminate structure (100) comprising said receiver substrate (70) and said surface film (60', 60'') including all or a portion of said donor layer (45); The method includes:

2. 2. The method according to claim 1, further comprising, prior to the bonding step f), a step of forming at least one functionalization layer (75, 75') on the front surface (60a) of the donor substrate (60) and / or on the front surface (70a) of the receiver substrate (70), such that the laminated structure (100) comprises the receiver substrate (70), the surface film (60', 60'') and the functionalization layer (75, 75') interposed between the receiver substrate (70) and the surface film (60', 60'').

3. 3. The method according to claim 2, wherein the functionalization layer (75, 75') comprises a plurality of micro- or nanostructured regions (73') and / or a plurality of cavities (71, 71') and / or a plurality of micro- or nano-electronic components (72).

4. The method of claim 3, wherein the plurality of micro- or nano-electronic components (72) are selected from transistors, MEMS, sensors, resonators, imagers, actuators, radio frequency filters, diodes, and lasers.

5. A method according to claim 3 or 4, wherein the cavities (71, 71') have lateral dimensions between 1 μm and several hundred μm and a depth of the order of 0.1 μm to several tens of μm.

6. The embedded weakened surface (32) is formed in the carrier substrate (30); After completion of step g), the transferred surface film (60') comprises a transferred thin layer (30') obtained from the carrier substrate (30), The method according to any one of claims 1 to 5.

7. The method of claim 6, wherein the transferred thin layer (30') is removed by chemical etching.

8. The buried weakened surface (42) is formed in the initial substrate (40); After the separation step g), a step of chemical mechanical polishing, chemical etching and / or cleaning is carried out to at least partially restore the surface quality of said surface film (60''). The method according to any one of claims 1 to 5.

9. The method according to any one of the preceding claims, wherein the surface film (60', 60'') is made from at least one semiconducting material selected from silicon, germanium, silicon carbide, III-V compounds, and / or from at least one insulating material selected from sapphire, diamond, and / or from at least one piezoelectric material selected from lithium tantalate, lithium niobate.

10. The method of any one of claims 1 to 9, wherein the receiver substrate (70) is made of a monocrystalline, polycrystalline or amorphous semiconducting, insulating or conducting material.

11. The method according to any one of the preceding claims, wherein the receiver substrate (70) has a thickness between a few tens of μm and 1000 μm.

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