Method for manufacturing a microelectronic device comprising a membrane suspended above a cavity - Patent Application 20070122997

Abstract

To provide a method for manufacturing a device which can adjust cavity dimension, and on the other hand, maintains membrane integrity, and comprising the membrane suspended above the cavity.SOLUTION: A method for manufacturing a microelectronic device comprising a membrane 20' suspended above at least one final cavity provides a support substrate 1 having at least one basic cavity 110, and a donor substrate. The method includes a step at which the support substrate and the donor substrate are assembled, and then, a step at which the donor substrate is thinned in a way that forms a membrane. The method further includes a step at which at least one mooring column 3 of the membrane is formed. The method includes a step at which a surface layer of the support substrate is etched in a way that expands at least one basic cavity in order to form the final cavity after forming at least one mooring column 3 and after assembling.SELECTED DRAWING: Figure 9A

Description

[Technical Field]

[0001] The present invention relates to the field of microelectronic devices comprising a membrane suspended over a cavity. The invention finds particularly advantageous application in the field of transducers known as micromachined ultrasonic transducers (MUTs). [Background technology]

[0002] The development of MEMS and NEMS has popularized the opportunities of microelectronics for many applications, especially for applications based on membrane devices.

[0003] These devices are, for example, acoustic transducers. Transducers can use different techniques to actuate or measure the actuation of a membrane. One of these techniques uses piezoelectricity. Such transducers, known by the name "piezoelectric micromachined ultrasonic transducer" or its acronym pMUT (Piezoelectric Micromachined Ultrasonic Transducer), generate and / or detect ultrasound waves by using a membrane that is deposited as a thin layer on a piezoelectric actuator and moved by the piezoelectric actuator to generate waves, generating an electric charge in the piezoelectric layer during detection.

[0004] Other transducers rely on capacitive control: known under the name "capacitive micromachined ultrasonic transducer" or its acronym cMUT (Capacitive Micromachined Ultrasonic Transducer), these transducers generate and / or detect ultrasound waves using a membrane that is moved by the capacitive effect between the membrane and the bottom of the cMUT's cavity.

[0005] These MEMS devices include one or more membranes that form the vibrating mechanical portion of the device. The membrane is typically suspended above a cavity. The membrane thus creates a structure that is inherently deformable when flexed. During operation of the device in reception, the bending of the membrane can be converted into an electrical signal, and vice versa for operation in transmission.

[0006] The proper operation of these devices depends in particular on the condition of the membrane. The fabrication of these membranes is itself a technical challenge related to the dimensions considered, with membrane thicknesses often exceeding 10 μm (10 -6 The cavity size is much smaller than the diameter (μm) of the membrane, typically less than 1 μm. One of the difficulties is maintaining the mechanical reliability of the membrane suspension during the steps of fabricating the device. Furthermore, depending on the type of device, the shape of the cavity can vary.

[0007] There are methods for manufacturing microelectronic devices with membranes suspended above cavities, in which a support substrate with a cavity opening at its surface and a donor substrate are provided. The support substrate and the donor substrate are then assembled by attaching the surface of the support substrate to the surface of the donor substrate. The donor substrate is then thinned in such a way as to form a membrane, which is then suspended above the cavity formed in the support substrate. In practice, these methods are limited in terms of the shape of the cavity that can be obtained. In practice, it remains difficult to obtain a membrane of small thickness suspended over a cavity of large dimensions. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is therefore to propose a method for manufacturing a device comprising a membrane suspended above a cavity in a substrate, which makes it possible to overcome the aforementioned drawbacks. In particular, the object of the present invention can be to propose a method for manufacturing a device comprising a membrane suspended above a cavity in a substrate, which makes it possible to adjust the dimensions of the cavity while still preserving the integrity of the membrane.

[0009] Other objects, features, and advantages of the present invention will become apparent upon review of the following description and accompanying drawings, and it is understood that other advantages may be incorporated. [Means for solving the problem]

[0010] To this end, an embodiment provides a method for manufacturing a microelectronic device comprising a membrane suspended above at least one final cavity, the method comprising: - providing a support substrate comprising a surface layer having a first surface; - forming at least one elementary cavity in a surface layer of a support substrate, the at least one elementary cavity being open at said first face; - providing a donor substrate having a first surface; - forming at least one membrane suspended above at least one final cavity, assembling the support substrate and the donor substrate by attaching a first surface of the support substrate to a first surface of the donor substrate in such a way that the donor substrate at least partially covers the at least one elementary cavity; and Thinning the donor substrate in such a way as to form a membrane and Includes:

[0011] Advantageously, before or after forming the membrane, the method further comprises the step of forming at least one anchoring post of the membrane, the at least one anchoring post comprising: - made from or based on at least one material different from the material forming the surface layer, - configured to support at least one underside of the membrane at least at the edge of the membrane.

[0012] After the formation of the at least one anchoring post and after assembly, the method advantageously comprises a step of etching the surface layer of the support substrate in such a way as to extend the at least one basic cavity in at least one direction parallel to the main plane of extension of the first face of the surface layer of the support substrate to form the final cavity.

[0013] Said etching is configured in such a way as to selectively etch a surface layer with respect to at least one material of at least one mooring post.

[0014] Thus, etching the surface layer of the support substrate allows the at least one basic cavity to be enlarged after the membrane has been transferred from the donor substrate to the support substrate. The risk of damaging the membrane during the process is limited or even avoided. As a result, it is possible to obtain a membrane suspended above at least one final cavity that is even more enlarged than in existing solutions.

[0015] By forming the tethering posts to be more resistant to etching than the surface layer, the etching can propagate within the surface layer of the support substrate until it reaches the tethering posts, which are to be left behind. Thus, according to contemplated embodiments, the tethering posts can form a physical constraint to the etching of the surface layer of the support substrate.

[0016] In practice, etching of the surface layer of the support substrate can be difficult to control to obtain a final cavity with a defined and reproducible shape. The use of anchoring posts as physical constraints to the etching makes it possible to obtain a final cavity that is better defined and now with better reproducibility.

[0017] Furthermore, the use of tethering posts as physical constraints to the etch allows for customization of the size and / or shape of the final cavity through placement of the tethering posts, specifically, the resulting final cavity does not necessarily depend on the shape of the base cavity.

[0018] The aims, objects, features and advantages of the present invention will become better apparent in the following detailed description of embodiments of the invention as illustrated in the accompanying drawings. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a cross-sectional view of an upper portion of a support substrate performed in a method according to an embodiment. [Figure 2] 2 is a cross-sectional view illustrating the formation of at least one elementary cavity in a support substrate from the substrate shown in FIG. 1; [Figure 3A] 2 is a cross-sectional view illustrating the formation of at least one elementary cavity in a support substrate from the substrate shown in FIG. 1; [Figure 3B] 2 is a top view illustrating the formation of at least one basic cavity in a support substrate from the substrate shown in FIG. 1. [Figure 4] 1 is a cross-sectional view of a surface layer of a donor substrate performed in a method according to an embodiment. [Figure 5] 3B is a cross-sectional view illustrating the assembly of the support substrate shown in FIG. 3A and the donor substrate shown in FIG. 4. [Figure 6A] 6 is a cross-sectional view illustrating thinning of the donor substrate to form a membrane from the assembly shown in FIG. 5 for an embodiment of the method. [Figure 6B] 6 is a cross-sectional view illustrating thinning of the donor substrate to form a membrane from the assembly shown in FIG. 5 for an embodiment of the method. [Figure 7A] 6 is a cross-sectional view of another embodiment of the method, showing thinning of the donor substrate from the assembly shown in FIG. 5 to form a membrane. [Figure 7B]6 is a cross-sectional view of another embodiment of the method, showing thinning of the donor substrate from the assembly shown in FIG. 5 to form a membrane. [Figure 7C] 6 is a cross-sectional view of another embodiment of the method, showing thinning of the donor substrate from the assembly shown in FIG. 5 to form a membrane. [Figure 7D] 6 is a cross-sectional view of another embodiment of the method, showing thinning of the donor substrate from the assembly shown in FIG. 5 to form a membrane. [Figure 8A] 1A-1C are cross-sectional views illustrating etching of a donor substrate following membrane formation for different embodiments of the method. [Figure 8B] 1A-1C are cross-sectional views illustrating etching of a donor substrate following membrane formation for different embodiments of the method. [Figure 8C] 1A-1C are cross-sectional views illustrating etching of a donor substrate following membrane formation for different embodiments of the method. [Figure 9A] 9C showing the formation of a mooring post from the assembly shown in FIG. 8A for an embodiment of a method according to the plane BB shown in FIG. 9C. [Figure 9B] 8B is a top view illustrating the formation of a mooring post from the assembly shown in FIG. 8A for an embodiment of the method. [Figure 9C] 9B is a cross-sectional view taken along plane CC shown in FIG. 9A. [Figure 9D] 8B and 8C are cross-sectional views illustrating the formation of a mooring post from the assembly shown in FIGS. 8B and 8C, respectively, for an embodiment of a method. [Figure 9E] 8B and 8C are cross-sectional views illustrating the formation of a mooring post from the assembly shown in FIGS. 8B and 8C, respectively, for an embodiment of a method. [Figure 10A] 10C is a cross-sectional view according to plane DD shown in FIG. 10B illustrating the formation of an opening in the membrane from the assembly shown in FIG. 9A for an embodiment of the method. [Figure 10B] 9B is a top view illustrating the formation of an opening in the membrane from the assembly shown in FIG. 9A for an embodiment of the method. [Figure 11A] 11C is a cross-sectional view according to the plane EE shown in FIG. 11C illustrating the device after etching of the surface layer of the support substrate from the assembly shown in FIG. 10A for an embodiment of the method. [Figure 11B] 10B is a top view of a device from the assembly shown in FIG. 10A after etching of a surface layer of the support substrate for an embodiment of the method. [Figure 11C] FIG. 11B is a cross-sectional view along plane FF shown in FIG. 11A. [Figure 12A] 10A and 10B are top views of the device after etching of the surface layer of the support substrate for another embodiment of the method. [Figure 12B] 12B is a cross-sectional view of the device shown in FIG. 12A along a cutting plane equivalent to plane FF shown in FIG. 11A. DETAILED DESCRIPTION OF THE INVENTION

[0020] The drawings are provided as examples and are not intended to limit the present invention. The drawings form schematic block diagrams intended to facilitate understanding of the present invention and are not necessarily drawn to scale in actual applications. In particular, the thicknesses and relative dimensions of substrates, layers, or portions do not represent reality.

[0021] Before proceeding with the detailed description of embodiments of the present invention, reference is made below to optional features which may be used in combination or as alternatives. the material of the at least one anchoring post has a resistance to etching of the surface layer of the support substrate that is greater than the resistance of the surface layer to said etching; The material of the membrane also has a greater resistance to etching of the surface layer of the support substrate than the resistance of the surface layer to said etching. Etching of the surface layer of the support substrate is carried out after the thinning. - widening at least one elementary cavity includes merging at least one elementary cavity with at least one adjacent, even neighboring, elementary cavity; The formation of the at least one anchoring post is carried out before assembling the support substrate and the donor substrate. The formation of the at least one anchoring post is carried out after assembly of the support substrate and the donor substrate. - the formation of the at least one anchoring post is configured in such a way that the at least one anchoring post is continuous and extends along at least one edge of the membrane. According to an example, the anchoring post is continuous and extends along at least one edge of the membrane by forming a closed perimeter. - the formation of the at least one anchoring post is configured in such a way that the at least one anchoring post is point-like and a plurality of anchoring posts are distributed along at least one edge of the membrane, for example, the anchoring post is point-like and a plurality of anchoring posts are regularly distributed along at least one edge of the membrane. The formation of the at least one mooring post is configured in such a way that the at least one mooring post is configured to surround at least the lower and upper surfaces of the membrane. The at least one basic cavity is defined by a sidewall and a bottom. - the formation of the at least one anchoring post is carried out after assembly of the support substrate and the donor substrate, Etching at least a portion of the assembly formed by the donor substrate and the support substrate from one of the second side of the donor substrate or the top surface of the membrane to a depth in the support substrate equal to a depth of a bottom of the at least one basic cavity; At least one material deposit on at least one mooring pole; Includes: The deposition of at least one material of the at least one anchoring pillar is by atomic layer deposition, abbreviated as ALD (Atomic Layer Deposition). - Etching the surface layer of the support substrate forming at least one opening through one of the donor substrate and the membrane; injecting an etching compound through the at least one opening; Includes: The at least one opening is formed perpendicular to the at least one basic cavity. The openings are formed perpendicular to each basic cavity. In projection in a plane parallel to the main surface of the extension of the surface layer of the support substrate, the surface of the opening is included in the surface of the basic cavity. During the formation of at least one elementary cavity in the surface layer of the support substrate, several elementary cavities are formed. The elementary cavities form a preferably periodic arrangement in the main plane of the extent of the first face of the surface layer of the support substrate. - the method comprises a step of defining a group of elementary cavities prior to etching of the surface layer of the support substrate, the etching of the surface layer of the support substrate being configured to merge the elementary cavities of said group together to form the final cavity. The elementary cavities are each defined by a sidewall and a bottom, and the elementary cavities of a group are separated in pairs by a common sidewall. The final cavity can be formed by etching the common sidewall of the group of elementary cavities. Thinning the donor substrate comprises oxidizing the donor substrate to form an oxidized portion that extends to a first portion of the donor substrate intended to form a membrane, and then etching the oxidized portion of the donor substrate. - providing the donor substrate comprises ion implantation in a buried portion of the donor substrate, the buried portion being located at an interface between a first portion of the donor substrate intended to form the membrane and a second portion of the donor substrate intended to form the remainder of the donor substrate, and thinning the donor substrate comprises fracturing the donor substrate in the buried portion. Thinning the donor substrate comprises, for example after fracturing, at least one mechanical modification, at least one mechanical-chemical polishing, at least one etching, and / or at least one plasma etching on its rear surface. Assembling the support substrate and the donor substrate comprises directly bonding a first surface of the donor substrate to a first surface of the support substrate. The thinning of the donor substrate is configured in such a way as to obtain a film with a thickness between 0.05 μm and 20 μm, preferably between 0.1 μm and 2 μm. - at least one anchoring post is made from or based on at least one of monocrystalline silicon, polycrystalline silicon, silicon nitride, alumina and a polymer such as parylene. At least one of the upper part of the support substrate and the surface layer of the donor substrate is made from or based on at least one of silicon, silicon carbide and silicon semiconductor alloys such as silicon germanium alloys. More preferably, at least one of the upper part of the support substrate and the surface layer of the donor substrate is made from or based on monocrystalline silicon. According to an example, the upper part below the surface layer is made from silicon and the surface layer is made from silicon oxide.

[0022] Within the scope of the present invention, it is specified that "on", "resting on", or their equivalent expressions do not necessarily mean "in contact". Thus, for example, depositing a layer on another layer does not necessarily mean that the two layers are in direct contact with each other, but it does mean that one of the layers at least partially covers the other, either in direct contact or separated by a thin film, yet another layer, or another element. Furthermore, a layer may consist of several sublayers of the same or different materials.

[0023] In the following description, the thickness and depth of a layer, region, or portion are generally measured along a vertical direction parallel to the stacking direction and perpendicular to the main surface of the extent of the substrate, layer, sublayer, or portion.

[0024] A substrate, layer, area or part "based on" material A means a substrate, layer, area or part that comprises this material A, e.g., at least 50%, and possibly other materials, e.g., doping elements.

[0025] In the following, the following designations are used where the longitudinal or front / back direction corresponds to the x-axis, the transverse or left / right direction corresponds to the y-axis, and the vertical or down / up direction corresponds to the z-axis.

[0026] A parameter that is "substantially equal to / greater than / less than" a given value means that the parameter is equal to / greater than / less than the given value by approximately 10%, or even approximately 5%.

[0027] "Direct bonding" refers to bonding performed, for example, at ambient temperature and in ambient atmosphere, on a relatively smooth surface (typically less than 5 Å roughness, where 1 Å is 10 -10 It means bonding without the addition of adhesive materials (specifically of the adhesive or polymer type), consisting in bringing their surfaces into contact so as to create an intimate contact between them (equal to m). By way of example, direct bonding of two substrates means that the bond is obtained by molecular adhesion, that is to say by a chemical bond established between the two surfaces in contact.

[0028] Microelectronic devices refer to any type of device implemented by microelectronic means, and in particular cover micromechanical or electromechanical devices (MEMS: microelectromechanical systems), NEMS (nanoelectromechanical systems), and optical or optoelectronic devices (MOEMS: microoptoelectromechanical systems), in addition to devices with purely electronic purposes.

[0029] A method for manufacturing a microelectronic device comprising a membrane 20' suspended above at least one final cavity 110' will now be described, according to an embodiment, with reference to Figures 1 to 12B. Within the scope of this application, the term "membrane" does not imply any specific limiting feature. The term "membrane" equally designates a thin film or layer of any thickness. "Suspension" above at least one cavity means that the membrane overhangs at least one cavity, at least partially covering it, or even completely covering it. As will be seen in more detail later, the membrane may be suspended by at least one anchoring point, also called anchoring post.

[0030] As will be explained in more detail below, the method comprises several etching steps, each of which can be a dry etch, more preferably a wet etch. Each of the etching steps can be preceded by the application of a mask, e.g., from positive or negative lithography, followed by the removal of this mask. This mask can be, for example, a resin, e.g., a photosensitive resin.

[0031] As shown in Figure 1, the method comprises providing a support substrate 1. The support substrate 1 comprises an upper part 10 made from or based on, for example, a monocrystalline semiconductor material. By way of example, the semiconductor material can be selected from silicon or a semiconducting silicon alloy, such as silicon carbide of the chemical formula SiC and a silicon germanium alloy of the chemical formula Si-Ge. In the following, reference will be made to the case where the semiconductor material is made from or based on silicon.

[0032] In the figure, only the upper part 10 of the support substrate 1 is shown. Nevertheless, the support substrate 1 can be, for example, made of different materials or in the form of a stack of several layers based on different materials. The upper part 10 can also consist solely of monocrystalline silicon, ignoring impurities related to the refining of silicon. The support substrate 1 can be, for example, a silicon wafer. By way of example, the support substrate 1 can be 200 mm (10 -3The silicon wafer has a diameter of 1 / 4 inch (m).

[0033] As shown in Fig. 2, the support substrate 1 comprises a surface layer 11 located on the surface of the support substrate 1 and having a first surface 1a. The surface layer 11 may more particularly rest on the upper part 10. The surface layer 11 is more particularly based on or made of a material different from the material forming the upper part 10. More preferably, the surface layer 11 is based on or made of an oxide. By way of example, the surface layer 11 is an oxide of the material of the upper part 10.

[0034] The method then comprises the formation of at least one elementary cavity 110 in the surface layer 11 of the support substrate 1. In the following, reference will be made to an example in which several elementary cavities are formed in the surface layer 11. The elementary cavities 110 are open on the first side 1a of the support substrate 1. As shown, when passing from FIG. 1 to FIG. 2, the formation of the elementary cavities 110 may comprise the oxidation of a part of the upper part 10 in order to form a surface layer 11 on at least the first side 1a of the support substrate 1. This oxidation may be thermal oxidation. The surface layer 11 may extend according to a plane parallel to the main plane of extension (x, y) of the upper part 10. The thickness of the surface layer 11 may be several hundred nm (10 -9 m), for example, the thickness is comprised between 100 nm and 3 μm.

[0035] 3A, the elementary cavity 110 may be etched in the surface layer 11. The elementary cavity 110 may be defined by sidewalls 110a and a bottom 110b parallel to the main plane (x, y) of extent of the surface layer 11 and may even be confused with the surface 10a at the interface between the surface layer 11 and the upper part 10. The elementary cavity 110 may extend vertically through substantially the entire thickness of the surface layer 11.

[0036] The basic cavity 110 can be of various shapes and dimensions depending on the target device 4 shown in Figures 11 to 12B, which will be described later. The basic cavity 110 can be, for example, square, rectangular, circular, or polygonal. The lateral dimensions of the basic cavity 110 in the plane (x, y) are substantially 1 μm (10 -6 The depth of the basic cavity 110 may be between several tens of nanometers (nm) and several micrometers, preferably between several tens of nanometers and several hundreds of nanometers, along the z-axis shown in FIG. 3A. Specifically, the depth of the basic cavity 110 may be smaller than the thickness of the surface layer 11, or more preferably, may be equal to the thickness of the surface layer 11.

[0037] The elementary cavities 110 may be separated from one another by portions 111 of the surface layer 11. These portions 111 may be larger in the plane (x, y) than the lateral dimensions of the elementary cavities 110, for example three times larger. These elementary cavities 110 may be shown, for example, in FIGS. 8C and 9D. According to an alternative example, the elementary cavities 110 may be separated from one another by portions 111 of the surface layer 11 with lateral dimensions of the same order of magnitude as the lateral dimensions of the elementary cavities. The portions 111 separating the elementary cavities are designated by the term "pillars." Each pillar 111 may have lateral dimensions in the plane (x, y) between a few μm and several hundred μm, or even a few mm. It will be seen below that at least some of these pillars 111 may be considered "temporary."

[0038] The elementary cavities 110 may form a periodic arrangement in the main plane of the extent (x, y) of the surface layer 11, as shown, for example, in FIG. 3B. The planar distribution of the elementary cavities 110, i.e., the distribution of the elementary cavities 110 in the plane (x, y), also depends on the target device and determines the dimensions of the pillars 111. The elementary cavities 110 may be substantially identical to one another and are uniformly distributed in the surface layer 11 of the support substrate 1. It should be noted that the support substrate 1 may have elementary cavities 110 with different shapes, lateral dimensions, depths, and / or planar distribution depending on the area of ​​the surface layer 11, in particular if it is planned to incorporate different types of devices 4 together in the support substrate 1.

[0039] The elementary cavities 110 can be pre-formed by the provider of the support substrate 1. Typically, the provided support substrate 1 therefore has elementary cavities with lateral dimensions of a few tens of μm, for example 10 μm and 20 μm. In the case of a common substrate, the elementary cavities 110 are typically substantially identical to one another and are uniformly distributed in the surface layer 11. As will be seen below, the method makes it possible in practice to obtain final cavities 110′ with customized dimensions and / or shape from elementary cavities 110 coming from a substrate available, for example, at a supplier.

[0040] As shown in FIG. 4 , the method includes providing a donor substrate 2. The donor substrate 2 may comprise a surface layer 20 made of, or based on, a monocrystalline semiconductor material, for example. By way of example, the semiconductor material can be selected from silicon or a semiconducting silicon alloy, such as silicon carbide with the formula SiC and a silicon germanium alloy with the formula Si-Ge. In the following, reference will be made to the case where the semiconductor material is made of or based on silicon. The surface layer 20 may also consist solely of monocrystalline silicon, ignoring impurities associated with the refining of silicon.

[0041] In the figure, only the surface layer 20 of the donor substrate 2 is shown. Nevertheless, with respect to the support substrate 1, the donor substrate 2 can be, for example, made of different materials or in the form of a stack of multiple layers based on different materials. The surface layer 20 is located on the surface of the donor substrate 2 and has a first surface 2 a.

[0042] The donor substrate 2 can be, for example, a semiconductor-on-insulator type substrate, more specifically, a silicon-on-insulator (commonly abbreviated SOI) type substrate with a buried oxide layer (commonly designated BOX (buried oxide layer)). By way of example, the donor substrate 2 is an SOI substrate with a diameter of 200 mm. The BOX layer can typically have a thickness of several hundred nanometers, and the silicon surface layer 20 can typically have a thickness comprised between several hundred nanometers and several micrometers. In particular, when considering the thickness of the surface layer 20, providing the donor substrate 2 can include oxidizing a portion of the surface layer 20 from the surface 2a to form an oxide portion (not shown) that is subsequently etched. It should be noted that it can be provided that the surface layer 20 is covered with a thin oxide film. By way of example, the donor substrate 2 is, for example, a silicon wafer with a diameter of 200 mm.

[0043] Next, the method includes assembling the support substrate 1 and the donor substrate 2. During this assembly, the first surface 1a of the support substrate 1 is bonded to the first surface 2a of the donor substrate 2. The first surface 1a of the support substrate 1 and the first surface 2a of the donor substrate 2 may be in direct contact. As shown in FIG. 5, the donor substrate 2 at least partially covers, and more preferably entirely covers, the basic cavity 110. According to an example, the support substrate 1 and the donor substrate 2 are assembled by direct bonding, more specifically, by molecular adhesion between their first surfaces 1a, 2a. The direct bonding is obtained without the need for application of substantial pressure to the substrates being assembled. Only a slight pressure needs to be applied to initiate bonding. Thermal annealing may further be performed to initiate bonding.

[0044] To form the suspended membrane 20', the donor substrate 2 is thinned after assembly. The donor substrate 2 can be thinned, more particularly, to retain only the part intended to form the membrane 20' with a thickness comprised between 0.05 μm and 20 μm, preferably between 0.1 μm and 2 μm.

[0045] According to a first example shown in FIGS. 6A and 6B, thinning the donor substrate 2 can include oxidizing the donor substrate 2 to form an oxidized portion 21. The oxidized portion 21 can extend from the rear surface of the donor substrate 2, i.e., the surface opposite the first surface 2a of the donor substrate 2, to the first portion of the donor substrate 2 intended to form the membrane 20′. Thus, the oxidized portion 21 can be etched, for example, in the direction of the arrow shown in FIG. 6B. As shown in FIG. 6B, it is possible to leave only the first portion of the donor substrate 2 intended to form the membrane 20′. Prior to oxidation of the donor substrate 2, the donor substrate 2 can be further thinned, for example, by mechanical modification of its rear surface. This embodiment is particularly adapted to form a membrane 20′ having a thickness comprised between 2 μm and 20 μm.

[0046] According to a more specific example, when the donor substrate 2 is a semiconductor-on-insulator type substrate, more specifically a silicon-on-insulator substrate with a buried oxide layer, the donor substrate can be thinned from its rear surface down to the buried oxide layer, more specifically down to the upper surface of the buried oxide layer, for example, by mechanical modification, mechanical-chemical polishing, chemical etching, and / or plasma etching. The buried oxide layer can thus form an etching barrier. The buried oxide layer can then be removed, for example, by wet etching with hydrofluoric acid. Thus, only the first portion of the donor substrate 2, which initially extends between the surface 2a and the lower surface of the buried oxide layer and is intended to form the membrane 20′, remains. This embodiment is particularly adapted to form the membrane 20′ with a thickness comprised between 0.1 μm and 2 μm.

[0047] According to an alternative example, providing the donor substrate 2 may include implanting, for example, light ion species in an implanted portion 22 of the donor substrate 2. As shown in FIG. 7B, the implanted portion 22 may be located at the interface between a first portion of the donor substrate 2 intended to form the membrane 20′ and a second portion of the donor substrate 2, also called a sacrificial portion, intended to form the remainder of the donor substrate 2 and to be subsequently removed. The implantation may be of light ions, for example hydrogen ions, with an implantation depth comprised between several hundred nanometers and several micrometers, for example between 0.2 μm and 2 μm. This embodiment is particularly adapted for forming a membrane 20′ with a thickness comprised between 0.1 μm and 2 μm.

[0048] According to this example, thinning the donor substrate 2 may involve fracturing the donor substrate into fracture zones 22′ at the embedded portions 22, or separating them in an equivalent manner. Following this fracturing, a first portion of the donor substrate 2 intended to form the membrane 20′ may remain in contact with the support substrate 1, while a second portion of the donor substrate 2 may be removed, as shown in FIG. 7C. This fracturing may be performed, for example, mechanically and / or by a fracture anneal performed at a temperature of about several hundred degrees Celsius, for example substantially 500° C.

[0049] Therefore, regardless of the implemented embodiment, thinning the donor substrate 2 can include chemical, mechanical, or chemical-mechanical polishing of the rear surface 2b of the donor substrate 2, as shown by way of example when going from Figure 7C to Figure 7D. The film 20' obtained after thinning the donor substrate 2 can have a thickness comprised between several hundred nanometers and several micrometers, for example between 0.2 μm and 2 μm.

[0050] During the development of the present invention, it became apparent that, regardless of the method used for depositing the membrane 20' in the basic cavity(ies) 110, it is difficult to keep the membrane 20' intact beyond the cavity size limit. According to the first two examples described above, this size limit is substantially 200 μm. According to a second example, where thinning of the donor substrate 2 is performed by ion implantation rather than by spalling of the donor substrate 2, this size limit is substantially 50 μm.

[0051] To exceed this size limit, the formation of the membrane 20' is carried out in the elementary cavities 110. The elementary cavities 110 are then extended in at least one direction, even in a plane parallel to the main plane (x, y) of extension of the surface layer 11 of the support substrate 1, to form at least one final cavity 110'. One or more groups of elementary cavities 110 can be defined to correspond to one or more final cavities 110'. As will be explained in more detail hereinafter, the extension of the elementary cavities 110 can be carried out by etching the surface layer 11 of the support substrate 1. Thus, the pillars 111 between the elementary cavities 110 allow the donor substrate 2 and thus the membrane 20' to be supported during the formation of the membrane 20'. The elementary cavities 110, from which the membrane 20' is suspended, are then extended and consolidated to form the final cavity 110'. The method thus allows the risk of damaging the membrane 20' during the manufacture of the membrane 20' of the device to be minimized. Furthermore, by widening the basic cavity 110 after manufacturing the membrane 20', it is possible to obtain a membrane 20' suspended above one or more final cavities 110' that are wider than in existing solutions.

[0052] Depending on the type of device intended, the shape of the final cavity 110' can vary. The method makes it possible to start with a support substrate 1 having a basic cavity of a given lateral shape, regardless of the desired shape of the final cavity 110'. Following the fabrication of the membrane 20', the basic cavity 110 can be widened as desired depending on the type of target device. The method of fabrication is therefore versatile and simplified with respect to existing solutions.

[0053] In addition to widening the basic cavity 110 to form the final cavity 110', the method further comprises forming at least one tethering post 3 configured to support the membrane 20'. The widening etch of the basic cavity 110 is further configured to selectively etch the surface layer 11 with respect to the material of the tethering posts 3. For this purpose, the tethering posts 3 may be based on or even made from a material that is hereinafter designated as "etch-resistant", i.e., having a greater resistance to etching than the resistance of the surface layer 11 to etching during widening of the basic cavity 110. More preferably, under the etching conditions of the surface layer 11 of the support substrate 1, the etching rate of the tethering posts 3 is less than or negligible compared to the etching rate of the surface layer 11.

[0054] Preferably, at least one anchoring post 3 is arranged in such a way that it at least partially defines the final cavity 110' to be obtained. During etching of the surface layer 11 aimed at widening the basic cavity 110, the anchoring parts form a physical limit to this etching, since they are more resistant to etching than the surface layer 11. During this etching, the posts 111 supporting the membrane can be removed, resulting in their role as "temporary". As the membrane 20' is supported by the anchoring posts 3, its integrity can be ensured despite the removal of the temporary posts 111.

[0055] Because the anchoring posts 3 form a physical constraint on this etching, the anchoring posts 3 allow customization of the shape and dimensions of the final resulting cavity 110' depending on their placement. Furthermore, by constraining the etching to the shape of the final resulting cavity 110', the anchoring posts 3 allow for increased reproducibility of the method.

[0056] The formation of the anchoring posts 3 will now be described with reference to FIGS. 8A to 9B. The formation of the anchoring posts 3 may involve etching a portion of the assembly formed by the support substrate 1 and the membrane 20′, as indicated by the arrows in FIGS. 8A to 8C. The etching may be carried out from the rear face 20b′ of the membrane to a level of the support substrate 1 corresponding to the bottom of the basic cavity 110. It may be provided that this etching step is carried out before thinning the donor substrate 2. This etching step may then be carried out from the rear face of the donor substrate 2, i.e., from the face opposite its first face 2a, to a level of the support substrate 1 corresponding to the bottom of the basic cavity 110.

[0057] As shown in FIG. 8A, the support substrate 1 can be etched until the surface layer 11 is removed. The etched portions correspond to the locations of the anchoring posts 3 and thus define the resulting final cavities 110′ in the plane (x, y). This etching step can further be used to define the membrane 20′ in the plane (x, y), providing it with a desired shape. The group of elementary cavities 110 defined to correspond to the final cavities 110′ can include any cavities located inside the periphery 20d′ of the membrane 20′. The unetched portions of the donor substrate 2 and the membrane 20′ can typically extend laterally up to 1 mm, more preferably up to several hundred μm.

[0058] The mooring posts 3 can then be formed by deposition of an etching-resistant material in the etched portion of the assembly formed by the support substrate 1 and the membrane 20′. The mooring posts 3 can extend vertically from the surface layer 11 of the support substrate 1 to the membrane 20′ and even vertically beyond the membrane 20′. More preferably, this material deposition is configured in such a way that the mooring posts 3 follow the vertical contour of the edge 20a′ of the membrane 20′. The resulting mooring posts 3 at least support the lower surface 20c′ of the membrane 20′ at least at its edge 20a′, as shown in FIG. 9A. Thus, the mooring posts 3 support the membrane 20′ at least at its edge 20a′. According to an example, the mooring posts 3 are arranged facing the membrane 20′ and are provided with a contour in the form of jaws 30 configured to surround the membrane 20′ at the edge 20a′ via the upper surface 20b′ and the lower surface 20c′. The jaw-shaped profile 30 more particularly allows the membrane 20' to engage with the support substrate 1 in all of its degrees of freedom.

[0059] As shown in Figures 8B, 8C, and 9D and 9E, the formation of the anchoring posts 3 can be configured to define adjacent films 20' on the donor substrate 2, and these films 20' can be supported by only one anchoring post 3 at one of the adjacent edges 20a' therebetween.

[0060] As shown in Figure 9B, the formation of the mooring posts 3 can be configured in such a way that the mooring posts 3 are continuous and extend along at least one edge of the membrane 20'. According to an example, the mooring posts 3 are continuous and extend along at least 80%, even 90%, even 99% or even 100% of the periphery 20d' of the membrane 20'. The mooring posts 3 therefore provide the membrane 20' with good mechanical support along the periphery 20d'. The mooring posts 3 can form a closed periphery of the membrane 20'.

[0061] The deposition of etch-resistant material may be configured in such a way that the anchoring posts 3 follow the vertical contour of the membrane 20'. The material may at least partially penetrate the basic cavities 110 at the periphery 20d' of the membrane 20', as shown in Figure 9C.

[0062] The formed tethering posts 3 can extend laterally over several μm, up to the maximum desired dimension of the final cavity 110, for example, up to several mm. The etch-resistant material can be deposited by chemical vapor deposition, more specifically by atomic layer deposition (ALD). The etch-resistant material can be a semiconductor or a dielectric. The etch-resistant material can be monocrystalline silicon, polycrystalline silicon, silicon nitride, alumina, and polymers such as parylene. If the etch-resistant material is a polymer, the deposition can be carried out by chemical vapor deposition (abbreviated as CVD). The tethering posts 3 can be formed from several materials, for example in the form of a stack of multiple layers made from or based on different materials.

[0063] In order to perform etching of the surface layer 11 of the support substrate 1 in such a way as to widen the basic cavity 110, at least one opening 23 is formed through the membrane 20'. This opening 23 can then be used as an access to the basic cavity 110 for injecting an etching compound for the surface layer 11 through this opening 23. The opening 23 is described with reference to FIG. 10A. The opening 23 can extend vertically between the upper surface 20b' and the lower surface 20c' of the membrane 20'. It can be provided that the formation of the opening 23 is performed before thinning the donor substrate 2. Thus, the formation of the opening 23 can be performed from the rear surface to the first surface 2a of the donor substrate 2.

[0064] The openings 23 can be formed perpendicular to the basic cavities 110. An etching compound can then be injected into the basic cavities 110 in order to etch the pillars 111 surrounding the basic cavities 110. A plurality of openings 23 can be formed in the membrane 20′, for example perpendicular to several basic cavities 110, or even perpendicular to each basic cavity 110 as shown in FIG. 10B. Alternatively or additionally, the openings 23 can be formed perpendicular to the pillars 111. In projection in a plane parallel to the main plane (x, y) of extension of the surface layer 11 of the support substrate 1, the surface of the openings 23, and even the surface of each opening 23, can be included in the surface of the basic cavities 110. By way of example, the openings 23 are circular and have a diameter of about a few μm, for example comprised between 1 μm and 10 μm.

[0065] Next, an etching compound for the pillars 111 can be injected through the formed openings 23 to remove the pillars 111. The etching of the surface layer 11 is preferably wet etching. Wet etching has the advantage of being easier to perform, reducing the cost of the method. This etching compound can be hydrofluoric acid in vapor or liquid form, or even in solution. Thus, when the surface layer 11 is oxide-based or made of oxide, the oxide that constitutes the pillars 111 can be removed. During the injection of the etching compound through the openings 23, the pillars are gradually removed starting from the injection location. Depending on the etching time and the amount of etching compound used, portions of the pillars 111 can be removed over the extent of the final cavities 110' in the plane (x, y). Thus, the pillars 111 may remain at the edges of the etching, for example, in the center of the membrane in the plane (x, y). The remaining pillars 111 can define several final cavities 110' below the membrane 20'. By way of example, all the pillars 111 can be removed over the extent of the final cavity 110' in the plane (x,y), as shown in Figures 11A, 11B and 11C.

[0066] During etching of the pillars 111 by injecting an etching compound, preferred paths may appear, for example depending on a preferred orientation in the plane (x, y). Since the anchoring pillars 3 are made of a material that is resistant to etching, and more particularly to the etching compound, etching can be carried out in such a way as to remove the pillars 111 up to reaching the anchoring pillars 3. It is therefore possible to overcome the appearance of preferred etching paths and obtain a final cavity 110' of a defined and reproducible shape. For example, the etching time may be selected to allow complete removal of the pillars 111 over the extent of the final cavity 110'.

[0067] The openings 23 can then be plugged if necessary, for example to complete the device 4 .

[0068] The method may further include mechanical modification, at least one mechanical-chemical polishing, and / or at least one chemical etching on the rear surface 1b of the support substrate 1, for example as shown in FIG. 11A, to adjust the thickness of the support substrate 1.

[0069] Thus, a device 4 is obtained, which comprises a membrane 110' suspended above at least one final cavity 110'. It is understood that multiple devices 4 can be obtained depending on the shape of the elementary cavities 110, their distribution on the surface of the support substrate 1, the dimensions of the membrane 20', and the arrangement of the anchoring posts 3. Final cavities 110' of any shape can be obtained in a reproducible manner. Final cavities 110' with large dimensions, for example, larger than 200 × 200 μm, can be obtained. It is possible to obtain final cavities 110' with shapes that have substantially equal dimensions relative to one another in the plane (x, y), such as circles or squares as shown in FIGS. 11B and 11C. Alternatively, it is possible to obtain final cavities 110' with shapes that have different dimensions relative to one another in the plane (x, y), such as rectangles or "L" shapes as shown in FIGS. 12A and 12B.

[0070] An alternative method for manufacturing a microelectronic device 4 comprising a membrane 20' suspended above at least one final cavity 110' will now be described by way of example.

[0071] The method can be configured in such a way that the membrane 20' has any geometric shape in the plane (x, y). For example, the membrane 20' can be in the shape of a ring, i.e. a disk extending in the plane (x, y) and provided with a central opening. A step of etching the membrane 20' prior to the deposition of the material of the anchoring posts 3 can be used, for example, to give the membrane 20' a geometric shape in the plane (x, y).

[0072] The anchoring posts 3 may be discontinuous, or in an equivalent manner, may be formed as a plurality of point-like anchoring posts 3. The anchoring posts 3 may be distributed along at least one edge 20a' of the membrane 20' and also along its periphery 20d'. The anchoring posts 3 may form a discontinuous periphery of the membrane 20' so as to provide the membrane 20' with good mechanical support along its periphery 20d'.

[0073] The formation of the tethering posts 3 can be performed before assembling the support substrate 1 and the donor substrate 2. For example, the tethering posts 3 can be formed before or simultaneously with the formation of the basic cavities 110. The tethering posts 3 can be deposited into the already formed basic cavities 110. Thus, after assembling the support substrate 1 and the donor substrate 2 and following the formation of the membrane 20′, at least one tethering post 3 can be separated from the periphery 20d′ of the membrane 20′. For example, this tethering post 3 can be positioned in the center of the membrane 20′. The tethering posts 3 can therefore define at least two final cavities 110′ below the membrane 20′, or equivalently, two membranes 20′, one for each final cavity 110′, the two membranes being continuous with each other.

[0074] In view of the foregoing, it is clearly evident that the present invention proposes a method for manufacturing a device comprising a membrane suspended above at least one final cavity, which is an improvement over existing solutions: in particular, the method of manufacturing makes it possible to adjust the dimensions of the final cavity, while still preserving the integrity of the membrane.

[0075] The invention is not limited to the embodiments described above, but extends to all embodiments covered by the claims. [Explanation of symbols]

[0076] 1 Support substrate 1a First Side 10 Upper part 10a Boundary with surface layer 11 Surface layer 110 Basic cavity 110' final cavity 110a side wall 110b bottom 111 pillars 2. Donor Substrate 2a First side 20 Surface layer 20' membrane 20a' Edge 20b' top surface 20c' bottom surface Around 20d' 21 Oxidized part 2b Rear 22 Embedded Part 22' Crushing Area 23 Aperture 3 Mooring poles 30 Jaw-Shaped Contour

Claims

1. A method for manufacturing a microelectronic device (4) comprising a membrane (20') suspended above at least one final cavity (110'), comprising: providing a support substrate (1) comprising a surface layer (11) having a first surface (1a); forming at least one elementary cavity (110) in the surface layer (11) of the support substrate (1), said at least one elementary cavity (110) being open at said first face (1a); Providing a donor substrate (2) having a first surface (2a); forming at least one membrane (20') suspended above at least one final cavity (110'), assembling the support substrate (1) and the donor substrate (2) by attaching the first surface (1 a) of the support substrate (1) to the first surface (2 a) of the donor substrate (2) in such a way that the donor substrate (2) at least partially covers the at least one elementary cavity (110); and thinning said donor substrate (2) in such a way as to form said membrane (20'); Including steps and Including, forming at least one anchoring post (3) for said membrane (20') before or after said formation of said membrane (20'), said at least one anchoring post (3) comprising: based on at least one material different from the material forming the surface layer (11), configured to support at least one lower surface (20c') of the membrane (20') at least at an edge (20a') of the membrane (20'); Steps and after the formation of the at least one anchoring post (3) and after the assembly, etching the surface layer (11) of the support substrate (1) so as to extend the at least one elementary cavity (110) in at least one direction parallel to the main plane (x, y) of extension of the first face (1a) of the surface layer (11) of the support substrate (1) to form the final cavity (110'), the etching being configured to selectively etch the surface layer (11) with respect to the at least one material of the at least one anchoring post (3); The method further comprising:

2. 2. The method of claim 1, wherein the formation of the at least one anchoring post (3) is configured so that the at least one anchoring post (3) is continuous and extends along at least one edge (20a') of the membrane (20').

3. 2. The method according to claim 1, wherein the formation of the at least one mooring post (3) is configured so that the at least one mooring post (3) is point-like, and a plurality of mooring posts (3) are distributed along at least one edge (20a') of the membrane (20').

4. 4. The method according to claim 1, wherein the formation of the at least one mooring post (3) is performed after the formation of the membrane (20'), and the at least one mooring post (3) is configured to surround at least the lower surface (20c') and the upper surface (20b') of the membrane (20').

5. said at least one basic cavity (110) being defined by a sidewall (110a) and a bottom (110b), and said forming of said at least one anchoring post (3) being carried out after said assembly of said support substrate (1) and said donor substrate (2), Etching at least a portion of the assembly formed by the donor substrate (2) and the support substrate (1) from either the second side (2b) of the donor substrate (2) or the top side (20b') of the membrane (20') to a depth in the support substrate (1) equal to the depth of the bottom (110b) of the at least one elementary cavity (110); depositing the at least one material on the at least one mooring post; 5. The method of claim 1, comprising:

6. The method of claim 5 , wherein the deposition of the at least one material of the at least one tethering post is atomic layer deposition.

7. The etching of the surface layer (11) of the support substrate (1) comprises: forming at least one opening (23) through one of the donor substrate (2) and the membrane (20'); injecting an etching compound through said at least one opening (23); 7. The method of claim 1, comprising:

8. 8. The method according to claim 1, wherein during the step of forming the at least one elementary cavity (110) in the surface layer (11) of the support substrate (1), several elementary cavities (110) are formed, the elementary cavities (110) forming an arrangement, preferably periodic, in the main plane (x, y) of the extent of the first face (1 a) of the surface layer (11) of the support substrate (1).

9. During the step of forming the at least one elementary cavity (110) in the surface layer (11) of the support substrate (1), several elementary cavities (110) are formed, The method comprises the step of defining a group of elementary cavities (110) before the etching of the surface layer (11) of the support substrate (1), 9. The method according to any one of claims 1 to 8, wherein the etching of the surface layer (11) of the support substrate (1) is configured to merge the elementary cavities (110) of the group together to form the final cavity (110').

10. 10. The method according to claim 1, wherein thinning the donor substrate (2) comprises oxidizing the donor substrate (2) to form an oxidized portion (21) extending to a first portion of the donor substrate (2) intended to form the membrane (20'), and then etching the oxidized portion (21) of the donor substrate (2).

11. the step of providing the donor substrate (2) comprises ion implantation in a buried portion (22) of the donor substrate (2), the buried portion (22) being located at an interface between a first portion of the donor substrate intended to form the membrane (20') and a second portion of the donor substrate (2) intended to form the remainder of the donor substrate (2); The method of any one of claims 1 to 9, wherein thinning the donor substrate (2) comprises fracturing the donor substrate (2) at the buried portion (22).

12. 12. The method according to claim 1, wherein assembling the support substrate (1) and the donor substrate (2) comprises directly bonding the first surface (1 a) of the donor substrate (1) to the first surface (2 a) of the support substrate (2).

13. 13. The method according to any one of claims 1 to 12, wherein thinning the donor substrate (2) is configured to obtain a film (20') with a thickness between 0.05 μm and 20 μm.

14. 14. The method according to any one of the preceding claims, wherein the at least one mooring post (3) is made from or based on at least one of monocrystalline silicon, polycrystalline silicon, silicon nitride, alumina and polymer.

15. 15. The method according to any one of claims 1 to 14, wherein at least one of the upper part (10) of the support substrate (1) and the surface layer (20) of the donor substrate (2) is made from or based on at least one of silicon, silicon carbide and silicon semiconductor alloys such as silicon germanium alloys.

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