Silicon ultrafine self-supporting membrane and associated production method
A controlled ion implantation and separation process with boron doping and stress prevention techniques produce a self-supporting, ultra-thin silicon membrane with high lateral dimensions, addressing mechanical instability and achieving a high lateral-to-thickness ratio.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SOITEC SA
- Filing Date
- 2025-11-21
- Publication Date
- 2026-06-18
AI Technical Summary
Existing methods struggle to produce self-supporting, ultra-thin monocrystalline silicon membranes with large lateral dimensions and high lateral dimension-to-thickness ratios due to issues such as microcavity defects, microcracks, and mechanical instability during separation.
A manufacturing process involving controlled ion implantation of hydrogen and helium, combined with high boron doping, and a separation heat treatment to propagate a fracture wave without allowing perpendicular displacement of the surface layer, using rigid plates or fluids to prevent mechanical stress, resulting in a self-supporting membrane with a thickness less than 2 μm and lateral dimensions greater than 50 mm.
The process achieves a self-supporting silicon membrane with a high lateral dimension-to-thickness ratio, maintaining mechanical integrity and enabling large-area applications.
Smart Images
Figure EP2025083771_18062026_PF_FP_ABST
Abstract
Description
Ultra-thin self-supporting silicon membrane and associated manufacturing process FIELD OF INVENTION
[0001] The present invention relates to the field of semiconductor materials for microelectronic components. It relates in particular to a method for manufacturing a self-supporting, very thin, large-sided monocrystalline silicon membrane. TECHNOLOGICAL BACKGROUND OF THE INVENTION
[0002] The Smart Cut process TMis well known for the fabrication of SOI (silicon-on-insulator) substrates and, more generally, for the production of very thin, high-quality stacks of single-crystal layers, even when the different stacked materials have structures incompatible with epitaxial growth. A buried brittle plane 2, formed by ion implantation of light species (e.g., hydrogen and / or helium) in a donor substrate 1, is the separation point between the surface layer to be transferred 10 and the rest of the donor substrate. It should be noted that ion implantation generates microcavity-type defects in the buried brittle plane, which can develop into microcracks under thermal activation and lead to fracture propagation along the brittle plane.It should also be noted that the buried fragile plane is, in fact, a buried layer in which microcavities and microfissures are found, and whose depth and width depend on the conditions of implantation (light species, doses, energy...).
[0003] In the case of the Smart Cut process, the donor substrate, after ion implantation, is assembled by bonding (preferably by molecular adhesion) onto a support substrate, which acts as a stiffener.
[0004] When developing a self-supporting membrane (without a stiffening substrate), the stiffness of the surface layer to be transferred plays a fundamental role. If this layer is too thin and its material too soft, the microcavities of the buried weak plane 2 will lead to the formation of bubbles 3, which deform the surface layer and eventually cause it to burst locally, preventing any detachment over large dimensions (bubbling regime –(a)). With greater stiffness, particularly due to an increase in the thickness of the surface layer 10 (for example, on the order of 10 μm and more), the layer can be detached intact over larger dimensions (this is called the delamination regime, as opposed to bubbling). However, it is also observed that the surface layer 10 eventually breaks, preventing the creation of a self-supporting, ultra-thin membrane with large lateral dimensions ((b)).
[0005] S. Reboh et al. ("Localized exfoliation versus delamination in H and He coimplanted (001) Si", Journal of Applied Physics 105, 093528, 2009) showed that it is possible to fabricate a self-supporting silicon membrane with a thickness of 1.5 μm and a surface area of 1.5 cm² 2 Even though the lateral dimension-to-thickness ratio is already interesting (on the order of 1.10 4 ), it remains problematic to achieve even higher ratios for a self-supporting membrane. SUBJECT OF THE INVENTION
[0006] The present invention proposes a method for manufacturing a self-supporting, integral monocrystalline silicon membrane with a very thin profile, typically less than 2 μm, or even 1.5 μm, and large lateral dimensions, typically greater than or equal to 50 mm, 100 mm, or even 200 mm. The invention also relates to said self-supporting membrane having a high lateral dimension-to-thickness ratio. BRIEF DESCRIPTION OF THE INVENTION
[0007] The invention relates to a method for manufacturing a self-supporting monocrystalline silicon membrane, comprising the following steps:
[0008] a) the supply of a donor substrate made of monocrystalline silicon, one front face of which extends along a principal plane and has at least one lateral dimension greater than or equal to 50mm,
[0009] b) the formation, by ionic implantation of hydrogen and helium in the donor substrate, with doses respectively between 1 E 16 H / cm 2 and 5 E 16 H / cm 2 and between 2 E 16 He / cm 2 and 1 E 17 He / cm 2 , of a fragile buried plane, parallel to the main plane, defining with the front face of the donor substrate, a surface layer less than 2μm thick,
[0010] c) the application of a separation heat treatment to the donor substrate to propagate a fracture wave in the buried brittle plane and separate the surface layer of the donor substrate, the front face of the donor substrate not being attached to any stiffener.
[0011] Step c) is carried out so that a displacement of the surface layer, perpendicular to the main plane, greater than 200μm, is prevented during the propagation of the fracture wave, said displacement being prevented at least at the level of a peripheral border of the surface layer.
[0012] At the end of step c), a self-supporting membrane (11) corresponding to the separated surface layer (10) is formed and has a thickness of less than 2μm and at least one lateral dimension greater than or equal to 50mm.
[0013] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: the displacement of the surface layer is prevented at its peripheral edge by the presence of a ring-shaped plate placed on the front face of the donor substrate; the ring has a width, in the principal plane, greater than or equal to 1 cm; the displacement of the surface layer is also prevented in a central region of said surface layer; a solid plate with a diameter of less than 5 cm is placed on the front face of the donor substrate, in a central area, to prevent the displacement of the surface layer in its central region; the displacement of the surface layer is prevented over its entire surface; a solid plate, of the same dimensions as the donor substrate, is placed on the front face of the donor substrate to prevent the displacement of the surface layer;the plate(s) have a front face, placed on the front face of the donor substrate, which has a predetermined roughness to avoid any adhesion between the two front faces; in step a), the donor substrate has at least one lateral dimension greater than or equal to 100mm, or even 200mm; in step b), the surface layer has a thickness less than or equal to 1.2μm, or even less than or equal to 1μm; the donor substrate supplied in step a) is doped with boron, with a concentration greater than or equal to 1; E 17 B / cm 3 , or even greater than or equal to 1 E 18 B / cm 3 ;annealing at a temperature greater than or equal to 600°C is applied, during step c) or after step c).
[0014] The invention also relates to a self-supporting monocrystalline silicon membrane having a thickness of less than 2μm and at least one lateral dimension greater than or equal to 50mm. BRIEF DESCRIPTION OF THE FIGURES
[0015] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:
[0016] This presents an illustration of an implanted substrate leading to a bubbling regime (a) or a delamination regime (b) under thermal activation;
[0017] This presents a method for manufacturing a self-supporting membrane according to the present invention;
[0018]
[0019]
[0020] La, laet la present possible embodiments to prevent the displacement perpendicular to the principal plane of the surface layer in an implanted donor substrate, during the propagation of the fracture wave, in accordance with step c) of the process according to the invention;
[0021] [Fig. 3] Shows a diagram and a photo of a self-supporting and integral membrane (from a separate surface layer of a donor substrate), arranged on the donor substrate, according to the present invention.
[0022] The same references in the figures can be used for elements of the same type. Some figures are schematic representations which, for the sake of clarity, are not drawn to scale. In particular, the layer thicknesses along the z-axis are not to scale with respect to the lateral dimensions along the x and y axes; and the relative thicknesses of the layers are not necessarily to scale in the figures. DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention relates to a method for manufacturing a self-supporting membrane made of a single-crystal material, in particular silicon. By self-supporting, we mean a membrane whose two main faces are free, not attached to a supporting substrate (ensuring mechanical support), even temporary.
[0024] The membrane according to the invention has a small thickness, typically less than 2 μm, and at least one large lateral dimension, typically greater than or equal to 50 mm. The lateral dimension-to-thickness ratio of the membrane is therefore particularly high, greater than 2.5 x 10⁻⁶. 4 greater than or equal to 5.10 4 , or even greater than or equal to 1.5.10 5 .
[0025] This manufacturing process is based on the separation of a surface layer 10 along a buried brittle plane 2 created by ion implantation in a donor substrate 1 of single-crystal material, and it is founded on two essential principles. The first is that the ion implantation conditions must allow a delamination regime to be reached in the single-crystal material of interest, specifically in the case of shallow buried brittle planes. The second principle is that, during the propagation of the fracture wave in the buried brittle plane, the surface layer must not be allowed to move perpendicularly to the buried brittle plane.
[0026] The combination of these two principles allows the obtaining of a self-supporting and integral membrane 11 (corresponding to the detached surface layer 10), very thin, with a very large surface area.
[0027] The delamination regime alone is insufficient to ensure the membrane remains intact after separation in the buried fragile plane. The applicant observed that it was crucial to limit the displacement (uplift) of the surface layer 10, perpendicular to the principal plane of said layer, during fracture wave propagation, in order to obtain a perfectly intact membrane.
[0028] The manufacturing process according to the invention comprises a first step a) corresponding to the supply of a donor substrate 1 made of monocrystalline silicon, the front face 1a of which extends along a principal plane (x,y) and has at least one lateral dimension greater than or equal to 50 mm, or even 100 mm ((a)). The lateral dimension(s) may even be greater than or equal to 200 mm.
[0029] In microelectronics, it is common to work with disk-shaped substrates, where the lateral dimensions correspond to the disk diameter. Of course, other substrate shapes are possible, including square or rectangular ones.
[0030] The thickness of the donor substrate 1 is typically between 300μm and 900μm.
[0031] The donor substrate 1 can advantageously be doped with boron, with a concentration greater than or equal to 1 E 15 B / cm 3 Preferably, the concentration of dopant B is greater than or equal to 1 E 17 B / cm 3 , or even greater than or equal to 1 E 18 B / cm 3 These high doping levels allow for a widening of the process window related to the implantation conditions, which will be described in the next step of the process.
[0032] The process includes a second step b) corresponding to the formation, by ion implantation of hydrogen and helium in the donor substrate 1, of a buried fragile plane 2, parallel to the main plane (x,y) ((b)). This buried fragile plane 2 defines, with the front face 1a of the donor substrate 1, a surface layer 10 with a thickness of less than 2 μm, 1.5 μm, or even less than or equal to 1.3 μm, 1.2 μm, 1.1 μm, or even 1 μm. For this, the implantation energy of the hydrogen ions is typically less than 300 keV, in particular between 20 keV and 200 keV, and the implantation energy of the helium ions is typically less than 300 keV, in particular between 30 keV and 250 keV. Advantageously, the hydrogen and helium implantation profiles, particularly the depth of the maxima, are superimposed within + / - 10 nm. It may also be advantageous to implant the helium before the hydrogen.
[0033] The hydrogen implantation dose is between 1E 16 H / cm 2 and 5 E 16 H / cm 2 ; the helium implantation dose is between 2 E 16 He / cm 2 and 1 E 17 He / cm 2 .
[0034] These co-implantation conditions favor the establishment of a delamination regime during thermal separation, meaning they promote the propagation of the fracture wave in the buried brittle layer 2 over long distances, rather than a bubbling regime (localized deformation, normal to the principal plane (x,y), of the surface layer). Indeed, these conditions lead to a high density of microcrack nucleation; at the time of fracture, the microcracks are of a size comparable to or smaller than the implantation depth (i.e., the thickness of the surface layer 10), which is conducive to the delamination phenomenon.
[0035] When these co-implantation conditions are combined with a high doping level of the donor substrate 1 (typically a concentration greater than or equal to 1 E 17 B / cm 3 , or even greater than or equal to 1 E 18 B / cm 3 ), the delamination regime is more effectively established. Indeed, silicon doping promotes the nucleation of microcracks in the buried brittle plane 2, thus resulting in a higher density of microcracks, but with smaller sizes, which is favorable to a delamination regime.
[0036] Note that a protective layer, for example of silicon oxide, can be formed on the front face 1a of the donor substrate 1, prior to ion implantation. Preferably, this layer is removed before carrying out the next step c) of the process.
[0037] Of course, known cleaning sequences can be applied to donor substrate 1, before and / or after step b).
[0038] The implanted donor substrate 1 is then subjected to a third step c) corresponding to the application of a separation heat treatment, in order to propagate the fracture wave in the buried brittle plane 2 and thus separate the surface layer 10 from the donor substrate 1 ((c)).
[0039] During this step c), the front face 1a of the donor substrate 1 is not bonded to any stiffener. In other words, no substrate or plate or thick layer, typically with a thickness greater than or equal to 1, 5, 10, 50 or 300μm, is bonded, assembled or formed by a deposition technique on the front face 1a.
[0040] The temperature experienced by the donor substrate 1 during heat treatment is typically between 250°C and 800°C, preferably between 300°C and 500°C.
[0041] Step c) is carried out so that the surface layer 10 cannot move perpendicular to the principal plane (x,y) by more than 200 μm during the propagation of the fracture wave. Advantageously, the displacement is even limited to less than 100 μm, or even less than 50 μm.
[0042] This displacement is prevented at least at the level of a peripheral boundary 1b of the donor substrate 1 (also peripheral boundary of the surface layer 10). By peripheral boundary 1b, we typically mean a ring extending from the edge of the donor substrate 1 to about 5%-10% of the diameter (or more generally the lateral dimension) of the substrate 1. For example, for a donor substrate 1 having a diameter of 200 mm, the peripheral boundary 1b may have a width in the principal (x,y) plane of 10 to 20 mm.
[0043] The fracture wave can initiate in the buried fragile plane 2, at a point located in the peripheral edge 1b or in a central region 1c of the donor substrate 1, or at any other point. It then propagates over the entire surface of the substrate 1. If no precautions are taken, the fracture wave causes the thin layer 10 to move normally to the principal plane (x,y) as it separates from the donor substrate 1. The end of the wave creates a strong mechanical stress that generally causes cracking, or even explosion, of the thin layer 10 before it can form a self-supporting membrane 11.
[0044] The process according to the invention therefore provides for containing the displacement of the thin layer 10 during the separation, so as to avoid large lifting amplitudes of the layer 10 and sudden releases of stress (at least at the level of the peripheral border 1b), which a very thin released membrane 11 is not able to support mechanically.
[0045] Advantageously, the donor substrate 1 is placed on a horizontal support during heat treatment, to allow the self-supporting membrane 11 to remain lying flat on the rest of the donor substrate 1 after separation.
[0046] Several methods can be considered to prevent the displacement of the surface layer 10 at its peripheral edge 1b. For example, a ring-shaped plate 30', placed on the front face 1a of the donor substrate 1, can fulfill this role (). The ring advantageously has a width L greater than or equal to 1 cm.
[0047] Advantageously, the displacement of the surface layer 10 is also prevented in the central region of said layer 10. For example, if the fracture wave initiates in the central zone 1c of the donor substrate 1, this initiation can create a significant uplift, associated with mechanical stresses, which could damage the surface layer 10. Here again, preventing the displacement (along the z-axis perpendicular to the principal plane (x,y)) of the surface layer 10 from exceeding 200μm, 100μm, or even 50μm, allows for the maintenance of perfect integrity of the self-supporting membrane 11.
[0048] Among the possible means, we can mention the use of a solid 30'' plate with a diameter d less than 50mm, placed in the central area 1c of the front face 1a of the donor substrate 1, allowing the lifting of the surface layer 10 in its central region ().
[0049] According to another advantageous embodiment, the displacement of the surface layer 10 is prevented over its entire surface, namely over the entire surface of the front face 1a of the donor substrate 1. For this, it is possible to place a solid plate 30 of the same dimensions as the donor substrate 1 on the front face 1a of said substrate 1. The displacement of the surface layer 10 is thus limited over its entire surface during the propagation of the fracture wave.
[0050] The plate 30,30',30'' placed on the front face 1a of the donor substrate 1, whatever its shape or size, can in particular be formed of silicon, or of any material sufficiently rigid and capable of preventing the displacement of the surface layer 10, perpendicular to the main plane (x,y), during the propagation of the fracture wave.
[0051] It is important to note that there is no chemical bond between plate 30,30',30'' and donor substrate 1; they are not bonded together. In particular, a layer of air or gas may be present between plate 30,30',30'' and donor substrate 1.
[0052] To ensure that there is no adhesion between the plate 30,30',30'' and the donor substrate 1, said plate 30,30',30'' may have a predetermined roughness or topology on its front face, placed on the front face 1a of the donor substrate 1. For example, the predetermined roughness may be chosen to be greater than or equal to 1 nm RMS (measured by atomic force microscopy (AFM) on a 5x5 μm scan). 2 or more), greater than or equal to 5nm RMS, or even more.
[0053] At the end of step c), a self-supporting membrane 11 corresponding to the separated surface layer 10 is thus formed and has a thickness of less than 2 μm, advantageously less than 1.5 μm, less than or equal to 1.4 μm, 1.3 μm, 1.2 μm, 1.1 μm or even 1 μm, and at least one lateral dimension greater than or equal to 50 mm, 100 mm, or greater than or equal to 200 mm. By way of example, Figure 11 shows a self-supporting membrane 11 having a thickness of approximately 1 μm, with lateral dimensions of 50 x 50 mm. 2 .
[0054] Advantageously, prior to the removal of the plate 30,30',30'' (or other means), the membrane 11, sandwiched (in whole or in part) between the remainder of the donor substrate 1 and the plate 30,30',30'', is annealed so as to relieve the stresses related to ion implantation in said membrane 11. The annealing can be carried out at a temperature typically greater than or equal to 600°C, preferably in the range of 600°C – 900°C. Thus, when the plate 30,30',30'' (or other means) is removed, the self-supporting membrane 11 remains flat, positioned on the remainder of the donor substrate 1.
[0055] This annealing can be carried out simultaneously with the separation heat treatment, or after the separation heat treatment, with or without returning to room temperature (or low temperature) between the two treatments. The means used to prevent displacement of the surface layer 10 during separation remains preferably on the membrane 11 during this annealing, but could optionally be removed.
[0056] Note that an alternative way to prevent vertical displacement of the surface layer 10 is to apply an incompressible fluid to the front face 1a of the donor substrate 1 during fracture wave propagation. For example, this fluid could be water at a pressure of 0.1 MPa.
[0057] The invention also relates to a self-supporting silicon membrane 11 which is characterized by a particularly high lateral dimension to thickness ratio, greater than 2.5 x 10 4greater than or equal to 5.10 4 , or even greater than or equal to 1.5.10 5 The membrane 11 has a thickness of less than 2μm, 1.5μm, or even less than or equal to 1.4μm, 1.3μm, 1.2μm, 1.1μm, or even 1μm. Its lateral dimension(s) is / are greater than or equal to 50mm, 100mm, or even greater than or equal to 200mm.
[0058] Such a membrane is of interest in many fields, particularly in electronics for 3D stacking applications or for the production of sensors. Example of a completed project:
[0059] The donor substrate 1 is monocrystalline silicon, doped with boron at 1 E 19 / cm 3 , with a diameter of 200 mm and a thickness of 725 micrometers. Ion implantation is performed under the following conditions: first, implantation of helium at 220 keV with a dose of 2 E 16 / cm 2 , then implantation of hydrogen at 130keV with a dose of 1E 16 / cm 2 Co-implantation is performed with a current density of 1µA / cm². 2 .
[0060] A 200mm silicon counterplate with a roughness greater than 5nm RMS (measured by AFM on a 10x10 μm scan) 2 ), is deposited on the front face 1a of the donor substrate 1.
[0061] The donor substrate 1 surmounted by the counter plate 30 is placed on a horizontal support in a furnace, and undergoes a separation heat treatment at 500°C (stand) for 1 hour, with a temperature rise from 200°C at 5°C / min, under a nitrogen atmosphere for example.
[0062] Advantageously, an anneal at 650°C, promoting the release of stresses related to implantation, is applied following the separation treatment.
[0063] When the counter plate 30 is removed, a 1.1μm membrane with a diameter of 200mm is placed on the remainder of the donor substrate 1; it is flat and intact, and can be taken for use.
[0064] Of course, the invention is not limited to the embodiments and examples described, and alternative embodiments can be made without departing from the scope of the invention.
Claims
A method for manufacturing a self-supporting monocrystalline silicon membrane (11), comprising the following steps: a) supplying a donor substrate (1) of monocrystalline silicon, a front face (1a) of which extends along a principal plane (x,y) and has at least one lateral dimension greater than or equal to 50 mm, b) forming, by ion implantation of hydrogen and helium in the donor substrate (1), with doses respectively between 1 E 16 H / cm 2 and 5 E 16 H / cm 2 and between 2 E 16 He / cm 2 and 1 E 17 He / cm 2, of a buried brittle plane (2), parallel to the main plane (x,y), defining with the front face (1a) of the donor substrate (1), a surface layer (10) of thickness less than 2μm,c) the application of a separation heat treatment to the donor substrate (1) to propagate a fracture wave in the buried brittle plane (2) and separate the surface layer (10) from the donor substrate (1), the front face (1a) of the donor substrate (1) not being attached to any stiffener, step c) being carried out so that a displacement of the surface layer (10), perpendicular to the main plane (x,y), greater than 200μm, is prevented during the propagation of the fracture wave, said displacement being prevented at least at the level of a peripheral edge (1b) of the surface layer (10), at the end of step c),a self-supporting membrane (11) corresponding to the separated surface layer (10) being formed and having a thickness of less than 2μm and at least one lateral dimension greater than or equal to 50mm. Manufacturing method according to claim 1, wherein the displacement of the surface layer (10) is prevented at its peripheral edge (1b), by the presence of a ring-shaped plate (30') placed on the front face (1a) of the donor substrate (1). Manufacturing method according to the preceding claim, wherein the ring has a width (L), in the principal plane (x,y), greater than or equal to 1cm. A manufacturing method according to any one of the preceding claims, wherein the displacement of the surface layer (10) is also prevented in a central region of said surface layer (10). Manufacturing method according to the preceding claim, wherein a solid plate (30'') of diameter less than 5cm is placed on the front face (1a) of the donor substrate (1), in a central area (1c), to prevent the displacement of the surface layer (10) in its central region. Manufacturing method according to claim 1, wherein the displacement of the surface layer (10) is prevented over its entire surface. Manufacturing method according to the preceding claim, wherein a solid plate (30) of the same dimensions as the donor substrate (1) is placed on the front face (1a) of the donor substrate (1a) to prevent the displacement of the surface layer (10). Manufacturing method according to any one of claims 2, 3, 5 and 7, wherein the plate(s) (30,30',30'') has a front face, placed on the front face (1a) of the donor substrate (1), which has a predetermined roughness to avoid any adhesion between the two front faces. A manufacturing process according to any one of the preceding claims, wherein, in step a), the donor substrate (1) has at least one lateral dimension greater than or equal to 100mm, or even 200mm. A manufacturing process according to any one of the preceding claims, wherein, in step b), the surface layer (10) has a thickness less than or equal to 1.2μm, or even less than or equal to 1μm. A manufacturing process according to any one of the preceding claims, wherein the donor substrate (1) supplied in step a) is doped with boron, with a concentration greater than or equal to 1 E 17 B / cm 3 , or even greater than or equal to 1 E18 B / cm 3 . A manufacturing process according to any one of the preceding claims, wherein annealing at a temperature greater than or equal to 600°C is applied, during step c) or after step c). Self-supporting monocrystalline silicon membrane (11) having a thickness of less than 2μm and at least one lateral dimension greater than or equal to 50mm.