Microelectronic device comprising an enclosing grid and method of fabrication

Abstract

Title: Microelectronic Device Comprising an Encapsulating Grid and Method of Embedding The invention relates to a device comprising: • channels (41) stacked along (z), • an enclosing grid (50) completely surrounding several channels (41), • a source (42) and a drain (43) on either side of each channel (41), and source and drain contacts (60S, 60, 60D). Advantageously, the source and drain contacts form, respectively, a first comb and a second comb facing each other, separated by dielectric plugs (70), the electrical contact between the fingers of each of the combs and the sources and / or drains being made along (z). Figure for the abstract: Fig. 15A

Description

Title of the invention: Microelectronic device comprising an enclosing grid and method of implementation. Technical field

[0001] The invention relates to the field of microelectronic technologies. It finds a particularly advantageous application in the manufacture of advanced FET (Field-Effect Transistor) type devices with encapsulated gate and channel based on two-dimensional (2D) materials or semiconductor oxides. STATE OF THE ART

[0002] The constant increase in transistor performance was first made possible by reducing the dimensions of transistors, for a classic MOSFET (“Metal-Oxide-Semiconductor Field-Effect Transistor” meaning Metal-Oxide-Semiconductor field-effect transistor) architecture based on silicon.

[0003] This classic architecture has since given way to other types of architectures better suited to the performance specified in technology nodes below 12 nm. The so-called "finFET" architecture, for example, makes it possible to meet the performance requirements set by the 7 nm technology node.

[0004] For the next technological nodes, particularly from 2 nm onwards, other architectures offering improved gate confinement are needed. One architecture considered to address the challenges of these next technological nodes includes gate-around transistors, known as GAA transistors (acronym for Gate Around), stacked one on top of the other.

[0005] In parallel with the development of new architectures, materials other than silicon are being considered for the fabrication of transistor channels. Recently, 2D materials, which can consist of a single layer of atoms, have emerged as promising candidates for use in electronic and optoelectronic devices comprising one or more very thin elements.

[0006] US2023 / 0093343 discloses a method for manufacturing stacked GAA transistors comprising a 2D material-based channel. In this method, the 2D materials considered include transition metal dichalcogenides in monolayer form. These 2D materials degrade easily when subjected to the typical conditions of deposition and etching processes. However, the various steps of the method disclosed by this document involve such conditions, which are likely to degrade the 2D material monolayers. It also appears that the drain-source contacts obtained by this method are weak reliable and / or inefficient. Low-resistive drain and source contacts are difficult to achieve on 2D materials.

[0007] A high-performance architecture and reliable industrial manufacturing, meeting the required quality standards, are important issues for the development of GAA transistor technologies based on 2D materials.

[0008] One objective of the invention is to provide a device and a manufacturing process that addresses these challenges. Another objective of the invention is to overcome, at least in part, the drawbacks of known processes. SUMMARY

[0009] To achieve these objectives, according to one embodiment, a microelectronic device is provided comprising: - At least two channels stacked along a principal z-direction, each channel being based on a semiconductor material, - a so-called enveloping grid, surrounding at least one of the channels along one entire perimeter of said channel, and preferably several channels, - a source and a drain on either side of each channel, and source and drain contacts connected respectively to the source and the drain, - a dielectric grid layer separating each channel and the surrounding grid, - spacers on either side of the grid, configured to electrically isolate the grid from the source and drain contacts.

[0010] Advantageously, the source and drain contacts each comprise a so-called main part extending along the main direction z, and secondary parts connected to the main part and extending along a sequential direction x to the main direction z, and extending at least partially vertically above the spacers flanking the enclosing grid, so that the main part and the secondary parts of the source contact form a first comb and the main part and the secondary parts of the drain contact form a second comb opposite the first comb, along the sequential direction x. The sequential direction x is, for example, transverse or perpendicular to the main direction z.

[0011] Thus, the source and drain contacts extend beneath the spacers flanking the enclosing grid. This prevents contact from occurring solely "from the side" of the sources and drains. The secondary parts of the source contact, i.e., the fingers of the first comb, are typically interposed between two sources stacked successively along the principal z direction. Similarly, the secondary parts of the drain contact, i.e., the fingers of the second comb, are typically interposed between two drains stacked successively along the principal z direction. The quality of the source / drain contact is improved.

[0012] The secondary sections extending between the sources and drains, respectively, further reduce the effective gate length Lg for the stacked channels. This improves the transistor characteristics of the device. In particular, the device can operate at higher currents. It is thus possible to physically modulate, by the effective gate length Lg, the figures of merit of the device, especially the lon / Ioff ratio of the drain currents in the on and off states. This modulation can be performed locally, on certain areas of a microelectronic chip comprising a plurality of devices according to the invention.

[0013] Another aspect of the invention relates to a method for manufacturing such a device, the method comprising: - To provide on a substrate S a stacking E along the principal direction z comprising first layers of a first material alternating with second layers of a second material, the first and second materials being different from the semiconductor material of the device channels, - To form, within this stacking E, the first openings defining the first patterns, - To form sacrificial grids straddling the initial motifs and partly within the initial openings, - Form initial spacers on the initial patterns and bordering the sacrificial grids, - To form second openings within the initial patterns, defining further second patterns. - Partially remove, from the second openings, the first material of the first layers selectively to the second material of the second layers, so as to form first spaces under the first spacers, and preferably partly under the sacrificial grids, - Fill the initial spaces with a dielectric material to form internal spacers, - Completely remove, starting from the second openings, the second material from the second layers, so as to form second spaces, - To deposit a layer based on a semiconductor material onto exposed surfaces of the second spaces, without completely filling the second spaces, said layer being intended to form the channels based on the semiconductor material, and the sources and drains based on the semiconductor material, - Fill the second spaces with a dielectric material to form dielectric plugs occupying the second spaces, - Partially engrave the dielectric plugs from the second openings, on either side of the second motifs, so as to reduce a dimension l70 of said dielectric plugs along the sequential direction x, the second spaces being obstructed in their centers by the dielectric plugs, - Fill the second spaces and openings with a metallic material, so as to form the source and drain contacts in the form of the first and second opposing combs, - Remove the sacrificial grids to create third openings, - Completely remove, from the third openings, the first material from the remaining parts of the first layers, to create third spaces, - To form a dielectric layer, called the gate dielectric layer, in the third spaces, - Fill the third spaces with a material, called grid material, so as to form the surrounding grids.

[0014] Thus, the layer based on the semiconductor material has a thickness less than that of the second layers of the initial stack.

[0015] Partial etching of the dielectric plugs subsequently allows the fingers of the first and second combs to be formed in the remaining empty spaces. The fingers of the first and second combs can thus extend along the sequential x direction under the sources and drains, respectively. In one possibility, the termination of the partial etching is time-controlled. Advantageously, the partial etching is configured to significantly reduce the dimension l70 along the sequential x direction of the dielectric plugs. The final dimension l70 of the dielectric plugs, after partial etching, is preferably less than at least 80% of the initial dimension l70 of the dielectric plugs before partial etching. Time-controlled termination of the etching is thus facilitated. This improves the dimensional control of the dielectric plugs.The final dimension l70 of the dielectric plugs determines the effective grid length Lg of the device. Dimensional control of the effective grid length Lg is also improved.

[0016] It is possible to configure different partial etching times on different areas of the same chip. This makes it possible to ultimately form devices with physically different effective gate lengths Lg.

[0017] The other objects, features and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated. BRIEF DESCRIPTION OF THE FIGURES

[0018] [Fig.1A] [Fig.2A] [Fig.3A] [Fig.4A] [Fig.5A] [Fig.0A] [Fig.7A] [Fig.8A] [Fig.9A] [Fig.1OA] [Fig.11A] [Fig.12A] [Fig.13A] [Fig.14A] [Fig.15A] Figures nA (n=l... 15) schematically illustrate, according to transverse sections xz, the manufacturing steps of a superimposed transistor device, according to a first embodiment of the present invention.

[0019] [Fig.1B] [Fig.2B] [Fig.3B] [Fig.4B] [Fig.5B] [Fig.0B] [Fig.7B] [Fig.8B] [Fig.9B] [Fig.1OB] [Fig.11B] [Fig.12B] [Fig.13B] [Fig.14B] [Fig.15B] Figures nB (n=1... 15) schematically illustrate, according to transverse sections yz indicated on the corresponding figures nA, the same manufacturing steps of the device, according to a first embodiment of the present invention.

[0020] [Fig.16A] [Fig.16B] Figures 16A and 16B schematically illustrate a manufacturing variant according to an embodiment of the present invention.

[0021] [Fig.17A] [Fig.18A] [Fig.19A] [Fig.20A] [Fig.21A] [Fig.22A] [Fig.23A] [Fig.24A] [Fig.25A] Figures nA (n=17...25) schematically illustrate, according to transverse sections xz, the manufacturing steps of a superimposed transistor device, according to a second embodiment of the present invention.

[0022] [Fig.17B] [Fig.18B] [Fig.19B] [Fig.20B] [Fig.21B] [Fig.22B] [Fig.23B] [Fig.24B] [Fig.25B] Figures nB (n=17...25) schematically illustrate, according to transverse sections yz indicated on the corresponding figures nA, the same manufacturing steps of the device, according to a second embodiment of the present invention.

[0023] Figures 22A and 22B illustrate in particular alternative steps to the step illustrated in Figures 21A, 21B.

[0024] In the cross-sectional figures, cutting planes are indicated (A-A', B-B', ..., P-P') with cross-references to the cutting planes of the corresponding figures. The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale for practical applications. In particular, in the schematic diagrams, the thicknesses and / or dimensions of the various layers, patterns, and reliefs are not representative of reality. For clarity, all alphanumeric references are not systematically repeated from one figure to another. It is understood that elements already described and referenced, when reproduced in another figure, typically bear the same alphanumeric references, even if these are not explicitly mentioned.A person skilled in the art will easily identify the same element reproduced in different figures. DETAILED DESCRIPTION

[0025] Before proceeding with a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:

[0026] According to one example, the secondary parts of the source contact and the secondary parts of the drain contact facing each other, along the sequential direction x, are separated by dielectric plugs. The source and drain contacts are insulated from each other. The dielectric plugs also facilitate the formation of the secondary parts of the source and drain contacts.

[0027] According to one example, the dielectric plugs further separate two successive stacked channels, along the main direction z.

[0028] According to one example, the dielectric plugs have a dimension l70, along the sequential direction x, smaller than a dimension l50 of the enclosing grid at the level of said successive stacked channels, so that the dielectric plugs define an effective grid length Lg shorter than the dimension l50 of the enclosing grid, for the successive stacked channels. This makes it possible to physically define the effective grid length Lg of the channels.

[0029] By way of example, each source comprises at least one so-called horizontal portion in contact with a secondary part of the source contact, and each drain comprises at least one so-called horizontal portion in contact with a secondary part of the drain contact. This improves the quality of the electrical contact between the source (drain) contacts and the sources (the drains).

[0030] By way of example, each source comprises a so-called vertical portion in contact with the main part of the source contact, and a so-called horizontal portion in contact with a secondary part of the source contact, and each drain comprises a so-called vertical portion in contact with the main part of the drain contact, and a so-called horizontal portion in contact with a secondary part of the drain contact. This improves the quality of the electrical contact between the source (drain) contacts and the sources (the drains).

[0031] According to one example, each source comprises only a so-called horizontal portion in contact with a secondary part of the source contact, and in which each drain comprises only a so-called horizontal portion in contact with a secondary part of the drain contact. This avoids a delamination phenomenon of the source and drain contacts.

[0032] According to one example, the device comprises a single source common to all channels and a single drain common to all channels.

[0033] According to one example, the semiconductor material of the channels is taken from: - the transition metal dichalcogenides MX2 with M taken from molybdenum (Mo) or tungsten (W), and X taken from sulfur (S), selenium (Se) or tellurium (Te), or - a semiconductor oxide, for example IGZO (Indium Gallium Zinc Oxide), In2O3, IWO (tungsten doped indium oxide), ITO (Indium Tin Oxide), IAZO (Indium Aluminium Zinc Oxide), InGaZnO, InGaO, InZnO or an amorphous semiconductor oxide, - graphene, hexagonal boron nitride or phosphorene.

[0034] According to one example, the method comprises, after deposition of the semiconductor material-based layer, a partial removal of said layer on flanks of the second motif substantially parallel to the principal z-direction, in particular on flanks of the first spacers and on flanks of the internal spacers, so that the source and drain contacts are directly in contact with the flanks of the first spacers and the flanks of the internal spacers. This avoids delamination of the source and drain contacts.

[0035] According to one example, the partial etching of the dielectric plugs is configured so that the dimension l70 of the dielectric plugs is less than a dimension ho of the remaining parts of the first layers, or a dimension l50 of the enclosing grids, according to the sequential direction x. This makes it possible to define a shorter effective grid length Lg for the channels.

[0036] According to one example, the formation of the encapsulating grids is carried out before the deposition of the semiconductor-based layer. This type of process, called "Gate-Last and Channel-Last," where the functional grid is formed in place of a sacrificial grid before the semiconductor-based layer is depositioned, preserves the dimensional and structural characteristics of the semiconductor-based layer. The thermal budget associated with the formation of the functional grid does not affect the properties of the semiconductor-based layer.

[0037] According to an example, the process comprises the following steps linked together in the following order: - To provide on a substrate S a stacking E along the principal direction z comprising first layers of a first material alternating with second layers of a second material, the first and second materials being different from the semiconductor material of the device channels, - To form, within this stacking E, the first openings defining the first patterns, To create sacrificial grids straddling the initial motifs and partly within the initial openings, Forming initial spacers on the initial patterns and bordering the sacrificial grids, Forming second openings within the initial patterns, which in turn define further second patterns. Partially remove, from the second openings, the first material of the first layers selectively to the second material of the second layers, so as to form first spaces under the first spacers, and preferably partly under the sacrificial grids, Fill the first spacers with a dielectric material to form internal spacers. Fill the second set of openings with a layer of masking material. Remove the sacrificial grids to form third openings; completely remove, from the third openings, the first material from the remaining parts of the first layers, so as to form third spaces. To form a dielectric layer, called the gate dielectric layer, in the third spacers, Fill the third spaces with a material, called grid material, so as to form the surrounding grids. Remove at least part of the masking layer, so as to recreate the second openings. Completely remove the second layer of material from the second openings, so as to form second spaces. Depositing a layer based on a semiconductor material onto exposed surfaces of the second spaces, without completely filling the second spaces, said layer being intended to form the channels based on the semiconductor material, and the sources and drains based on the semiconductor material, Fill the second spaces with a dielectric material to form dielectric plugs occupying the second spaces. Partially engrave the dielectric plugs from the second openings, on either side of the second motifs, so as to reduce a dimension l70 of said dielectric plugs along the sequential direction x, the second spaces being obstructed in their centers by the dielectric plugs, - Fill the second spaces and the second openings with at least one metallic material, so as to form the source and drain contacts in the form of the first and second combs facing each other.

[0038] According to one example, the stacking E comprises at least four first layers of the first material alternating with three second layers of the second material. This makes it possible to obtain an enclosing grid for all the stacked channels of the device.

[0039] In one example, the stack comprises an alternation of a first layer with a second layer. Preferably, said first layer and said second layer are in contact. In one example, the final device comprises transistor channels formed after selective removal of the second layers of the initial stack. In another example, the final device comprises encapsulating gates formed after selective removal of the first layers of the initial stack. The initial stack typically does not include the semiconductor material of the transistor channels or the material of the encapsulating gates.

[0040] According to one example, the internal spacers are silicon nitride-based. Before the internal spacers are formed, the partial removal of the first material from the first layers is configured to retain portions of the first layers between the first spaces. These portions are called residual portions. The residual portions of the first layers are thus located between the first spaces. The internal spacers are preferably in contact with the residual portions of the first layers before the formation of the surrounding grids.

[0041] According to one example, the formation of the first spaces is configured so that the first spaces extend under the sacrificial grids. The width of the internal spacers is thus increased. This makes it possible to reduce the parasitic capacitance due to the proximity of the source and drain contacts.

[0042] According to one example, the secondary parts of the source and drain contacts are made of a metallic material different from the primary parts of the source and drain contacts. Such materials engineering in the source and drain contacts makes it possible, for example, to optimize the access resistance of the contacts. It also makes it possible to use a "non-planarizable" material at the fingers of the source and drain contacts. This increases the possibilities for using materials of interest.

[0043] According to one possibility, secondary parts made of a metallic material different from the main parts can also locally introduce a state of stress at the sources and drains. The transport properties of the sources and drains can be improved. The channels can also be mechanically constrained via the sources and drains. Transport at the channel level can also be advantageously modified.

[0044] According to one example, after partially etching the dielectric plugs and before filling the second cavities, a second semiconductor material, preferably a two-dimensional (2D) material, is deposited in the second cavities without completely filling them. This thickens the sources and drains of the device. This improves electrical contact with the source and drain contacts. This compensates for any potential damage to the semiconductor material at the sources and drains of the device.

[0045] According to one example, the formation of the encapsulating grids is carried out after the deposition of the semiconductor material base layer. This type of process, called "Channel First and Gate Last," where the functional grid is formed at the end of the process, replacing a sacrificial grid, preserves the dimensional characteristics of the grid. The thermal budget associated with the deposition of the semiconductor material does not affect the equivalent thickness of the grid oxide at the interface with the grid. The structural and electrical characteristics of the functional grid are better controlled.

[0046] According to one example, the deposition of the semiconductor material base layer is carried out by chemical vapor deposition or by atomic layer deposition. Chemical vapor deposition is easy to implement. Atomic layer deposition allows for precise control of the thickness of the semiconductor material base layer.

[0047] According to one example, the semiconductor material is chosen from the transition metal dichalcogenides MX2 with M taken from molybdenum (Mo) or tungsten (W), and X taken from sulfur (S), selenium (Se) or tellurium (Te).

[0048] According to another example, the semiconductor material is chosen based on a semiconductor oxide, for example based on IGZO (Indium Gallium Zinc Oxide), In2O3, IWO (tungsten doped indium oxide), ITO (Indium Tin Oxide), IAZO (Indium Aluminium Zinc Oxide), InGaZnO, InGaO, InZnO or an amorphous semiconductor oxide.

[0049] For example, the first material is chosen to be SiGe and the second material to be Si, or vice versa. These materials can be easily epitaxially grown using conventional microelectronics processes. This allows for the use of existing technologies. The cost of the process is reduced.

[0050] According to one example, the sacrificial grids are formed in such a way that they extend over the entire height of the first openings. According to another example, the first openings extend along the entire height of the stack of the first and second layers. The sacrificial grids extend over the entire height of the stack. The sacrificial grids take Typically, support is provided on the substrate. This allows access to all layers of the stack via the third openings.

[0051] According to one example, the substrate is a bulk silicon-based substrate.

[0052] According to one example, the stack comprises as many first layers as the first material than second layers of the second material.

[0053] According to one example, the removal of the first material from the first layers selectively to the second material from the second layers is carried out by a first selective etching having a selectivity Si0:20 of at least 5:1, preferably at least 10:1. This first selective etching is typically stopped at time.

[0054] According to one example, the removal of the second material from the second layers selectively from the first material from the first layers is carried out by a second selective etching having a selectivity S2 o: 10 of at least 5:1, preferably at least 10:1.

[0055] Except in cases of incompatibility, it is understood that all the above optional features can be combined to form an embodiment that is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention. The features and advantages of one aspect of the invention, for example, the device or the method, can be adapted mutatis mutandis to the other aspect of the invention.

[0056] The invention relates generally to a GAA transistor microelectronic device and a method for manufacturing such a device. This microelectronic device may have a "GAA stacked nanosheet" architecture, i.e., with stacked nanosheets and a fully enclosing grid. A stacked nanowire architecture with a fully enclosing grid is also possible.

[0057] Nanowires or nanosheets typically each comprise a conduction channel of a transistor. These channels are stacked along a z-direction. This means that they each occupy a specific elevation level along the z-direction. A level can be defined between two planes perpendicular to the z-direction.

[0058] Advantageously, the process according to the invention can be implemented for the production of GAA MOS transistors for the 2 nm and sub-2 nm technology nodes.

[0059] A microelectronic device comprising stacked GAA transistors can be advantageously integrated into logic systems with 3D architectures. These transistors can, in particular, be associated with other structural or functional elements in order to design complex systems.

[0060] A particular aspect of the invention relates to the implementation of 2D materials to produce the nanowires or nanosheets of the device.

[0061] 2D materials typically correspond to compounds with a lamellar structure made up of two-dimensional sheets stacked along the c-axis. The atomic bonds within each sheet are strong and covalent. The bonds between sheets are much weaker and of the Van der Waals type. These two-dimensional sheets are also called monolayers.

[0062] In the context of the present invention, the monolayers are preferably MX2 type semiconductor monolayers where M is molybdenum (Mo) or tungsten (W) and X is sulfur (S) or selenium (Se). Each monolayer is composed of a plane of metal cations M sandwiched between two planes of anions X. A monolayer thus typically comprises three atomic planes: the transition metal atoms (Mo or W) form a plane sandwiched between two chalcogen planes (S, Se, or Te, for example). Each transition metal atom is bonded to six chalcogen atoms. These anions are in prismatic trigonal coordination with respect to the metal atoms. The MX2 transition metal dichalcogenide monolayers exhibit a hexagonal atomic lattice.

[0063] The monolayers of transition metal dichalcogenides MX2 are preferably based on molybdenum disulfide MoS2, MoSe2, MoTe2, WS2, WSe2.

[0064] An alternative possibility involves using semiconductor oxides to fabricate the nanowires or nanosheets of the device. These semiconductor oxides are preferably based on IGZO (Indium Gallium Zinc Oxide), In2O3, IWO (tungsten-doped indium oxide), InGaZnO, InGaO, InZnO, IAZO, or ITO (Indium Tin Oxide). Another possibility involves using graphene, hexagonal boron nitride (h-BN), or phosphorene (also known as Black Phosphorous, BP), particularly in monolayer form.

[0065] It is specified that, within the framework of the present invention, the terms "on", "overcomes", "covers", "underlying", "opposite" and their equivalents do not necessarily mean "in contact with". Thus, for example, the deposit or application of a first layer on a second layer does not necessarily mean that the two layers are directly in contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it, or by being separated from it by at least one other layer or at least one other element.

[0066] A substrate, film, or layer "based" on a material A is understood to mean a substrate, film, or layer comprising only that material A or that material A and possibly other materials, for example, dopant elements or alloying elements. Thus, a spacer based on silicon nitride (SiN) may, for example, comprise non-stoichiometric silicon nitride (SiN), or stoichiometric silicon nitride (Si3N4), or even silicon oxynitride (SiON).

[0067] A "continuous" layer is understood to be a layer exhibiting continuity of material. Typically, a continuous layer can encase the second layers of the second motifs, or line the second spaces of the second motifs.

[0068] The term "dielectric" describes a material whose electrical conductivity is sufficiently low in the given application to serve as an insulator. In the present invention, a dielectric material preferably has a dielectric constant less than 20, and preferably a dielectric constant less than 7.

[0069] Several embodiments of the invention implementing successive steps of the manufacturing process are described below. Unless explicitly stated, the adjective "successive" does not necessarily imply, although this is generally preferred, that the steps follow each other immediately; intermediate steps may separate them.

[0070] Furthermore, the term "step" refers to the execution of a part of the process, and can designate a set of sub-steps.

[0071] Furthermore, the term "step" does not necessarily mean that the actions carried out during a step are simultaneous or immediately successive. Certain actions of a first step may, in particular, be followed by actions related to a different step, and other actions from the first step may be repeated later. Thus, the term "step" does not necessarily imply unitary actions that are inseparable in time and in the sequence of phases of the process.

[0072] The term "selective etching with respect to" or "etching exhibiting selectivity with respect to" refers to etching configured to remove a material A or a layer A with respect to a material B or a layer B, and exhibiting an etching speed of material A greater than the etching speed of material B. Selectivity is the ratio of the etching speed of material A to the etching speed of material B. It is denoted SA:B. A selectivity SA:B of 10:1 means that the etching speed of material A is ten times greater than the etching speed of material B.

[0073] The various patterns formed during the manufacturing steps typically have a structure designed to evolve during the process steps. Thus, the patterns may include sacrificial layers of the initial stacking, layers based on 2D material or semiconductor oxide, and dielectric layers, whether continuous or discontinuous.

[0074] A preferably orthonormal coordinate system, comprising the x, y, z axes, is shown in the accompanying figures.

[0075] In this patent application, the term thickness will preferably be used for a layer or film, and height for a device or structure. The thickness is measured in a direction normal to the principal plane of extension of the layer or film. Thus, a surface layer of silicon (topSi) typically has a Thickness along z. A grid pattern formed on such a surface layer has a height along z. The relative terms "on," "overlies," "under," and "sub-" refer to positions taken along the z-direction. A "lateral" dimension corresponds to a dimension along a direction of the xy plane. A "lateral" or "lateral" extension is understood to be an extension along one or more directions of the xy plane.

[0076] An element located "in line with" or "directly above" another element means that these two elements are both located on the same line perpendicular to a plane in which extends mainly a lower or upper face of a substrate, that is to say on the same line oriented vertically on the cross-sectional figures.

[0077] The terms "approximately", "around", "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the bounds are inclusive, unless otherwise stated.

[0078] The following description presents examples of implementation of the method according to the invention in the context of developing a complex 3D device. The scope of this description is obviously not limiting to the invention.

[0079] Figures IA, IB to 15A, 15B schematically illustrate manufacturing steps of a device comprising stacked GAA transistors, according to a so-called "Gate-Last and Channel-Last" embodiment. Figures nA (n=l... 15) correspond to cross-sections along xz, each illustrating a different step of the manufacturing process. Figures nB (n=l... 15) correspond to cross-sections along yz, each illustrating the same step as the corresponding figure nA.

[0080] As illustrated in Figures IA and IB, a first step consists of creating a stack E of layers 10, 20 on a substrate S. The substrate S can be a SOI (Silicon On Insulator), GeOI (Germanium On Insulator), or SGOI (Silicon-Germanium On Insulator) type substrate. These known substrates comprise, according to the terminology commonly used by those skilled in the art, a thick silicon SI layer called "Si bulk," a silicon oxide S2 layer called "BOX" (Burn Oxide), and a thin surface layer, respectively based on silicon, germanium, or silicon-germanium. This thin surface layer can advantageously correspond to the first layer 10 of the stack E.

[0081] Alternatively, the substrate S can be a bulk substrate “Si bulk”.

[0082] The stack E comprises, according to one example, an alternation of first layers 10 in silicon-germanium (SiGe) and second layers 20 in silicon (Si).

[0083] The concentration of Ge in the SiGe alloy can be 20%, 30%, or 45%, for example. This germanium concentration is chosen to ensure good selectivity of the SiGe etching with respect to Si during the selective etching steps. The higher the Ge concentration, the greater the selectivity for Si during the Subsequent removal of the SiGe. This E-stack is advantageously formed by epitaxy of the SiGe 10 and Si 20 layers. This E-stack formation step is inexpensive and well known to those skilled in the art. The thicknesses of the Si and SiGe layers can typically be on the order of 10 nm, and more generally range from 5 nm to 20 nm, for example. As is known, to avoid the formation of structural defects, the maximum permissible thicknesses for the SiGe 10 layers depend, in particular, on the chosen Ge concentration.

[0084] In the example illustrated in Figures IA, IB, four layers 10 of Si are alternated with three epitaxial layers 20 of SiGe. A Si / SiGe superlattice is thus obtained. The number of Si and SiGe layers can naturally be increased. This ultimately allows for an increase in the number of transistors stacked in the final device.

[0085] Generally, the first material of the first layers 10 and the second material of the second layers 20 are chosen so that one can be selectively etched with respect to the other. Thus, other pairs of first and second materials are possible. Subject to this condition of selectivity in etching, the first and second materials can be chosen from among dielectric materials (oxides and nitrides, for example), semiconductor materials, and metallic materials. For example, the first material of the first layers 10 is an oxide-based dielectric, and the second material of the second layers 20 is amorphous silicon. In this case, the dielectric material of the subsequently formed internal spacers is typically nitride-based. Other combinations are possible.

[0086] As illustrated in Figures 2A and 2B, a conventional lithography / etching step is performed to define the first 101M motifs and the first 100 apertures. The etching is anisotropic and z-directed. It is configured to etch the stack E, here the Si / SiGe superlattice, over its entire height, stopping at the substrate S, here the BOX S2. It can be performed by plasma using HBr / O2 etching chemistry. The first 101M motifs can have a length Li along x between 100 nm and 500 nm. They preferably have a width h along y between 10 nm and 120 nm, for example, on the order of 40 nm. This first structuring of the E stack in the form of fins or "fins" according to the common Anglo-Saxon terminology, makes it possible to define a plurality of superimposed nanowires or nanosheets.

[0087] For the sake of clarity, the following figures iB (i=3... 15) illustrate only one "end" motif 101M.

[0088] As illustrated in Figures 3A, 3B, sacrificial grids 150 are then formed on the "end" motifs 101M. The formation of these sacrificial grids 150 is typically done by lithography / engraving. The formation of the sacrificial grids 150 is configured so that the sacrificial grids 150 straddle the "end" patterns 101M, as illustrated in [Fig. 3B]. The sacrificial grids 150 typically comprise a top portion located on the "end" pattern 101M, and side portions located on the lateral flanks of the "end" pattern 101M. The sacrificial grids 150 typically rest on the substrate S. At this stage, the sacrificial grids 150 are typically topped by an etching mask 160, called a hard mask, implemented in the structuring of the sacrificial grids 150. The sacrificial grids 150 are, for example, based on polycrystalline silicon or amorphous silicon, or even on polycrystalline SiGe or amorphous SiGe.

[0089] As illustrated in Figures 4A and 4B, first spacers 170 are then formed on the yz-oriented flanks of the sacrificial grids 150. In general, in z-projection, these spacers form a continuous ring around each sacrificial grid 150, with a closed contour. In cross-section, however, along the xz plane illustrated in [Fig. 4A], the first spacer 170 has two opposing parts on each flank of the sacrificial grid 150. These two parts are generally referred to as the first spacers 170, even though they can be considered as belonging to a single spacer. The first spacers 170 typically extend to an upper face of the hard masks 160.The first 170 spacers are typically based on silicon nitride SiN (dielectric constant k~7.5) or a dielectric material with a low dielectric constant, for example SiOCN (k~5.2), SiBCN (k~5.5), SiOC, SiCN, SICO (k~4.5), SiO2 (k~3.9).

[0090] As illustrated in Figures 5A, 5B, after the formation of the first spacers 170 by lithography / etching, the anisotropic etching along z is extended in order to define second motifs 102M, and second apertures 200. The etching is configured to etch the stack E over its entire height, stopping on the substrate S. It can be carried out by plasma using an HBr / O2 etching chemistry.

[0091] As illustrated in Figures 6A, 6B, after the formation of the second openings 200, the first layers 10 are partially etched selectively to the second layers 20, the substrate S, the sacrificial grids 150, and the first spacers 170. The etching of the first material of the first layers 10 typically exhibits a selectivity of Si0:20 with respect to the second material of the second layers 20 of at least 5:1, preferably at least 10:1. This partial etching aims to form first spaces 111 under the first spacers 170, and preferably under the sacrificial grids 150. This partial etching is typically stopped at time. The partial etching has an isotropic character and can be carried out by wet or dry means, from the second openings 200. At the end of this partial etching, central parts of the first layers 10 are preserved under the sacrificial grids 150.These central parts typically have a dimension. The lio is less than the x-dimension of the sacrificial grids 150 (also called "false grids" or "dummy-gate"). This reduces parasitic capacitances by increasing the thickness of the internal spacers (which can penetrate under the metal grid).

[0092] As illustrated in Figures 7A, 7B, the first spaces 111 are then filled with a dielectric material to form internal spacers 171. These "internal" spacers 171 are integrated into the stack E. They are in contact with the central parts of the first layers 10. The formation of the internal spacers 171 typically takes place from the second openings 200. As before, the internal spacers 171 can be based on silicon nitride SiN (dielectric constant k~7.5) or on a dielectric material with a low dielectric constant, for example SiOCN (k~5.2), SiBCN (k~5.5), SiOC, SiCN, SICO (k~4.5), SiO2 (k~3.9). The material of these internal spacers 171 may be different from that of the first spacers 170. The internal spacers 171 typically have a dimension along x greater than or equal to 3 nm, preferably greater than or equal to 5 nm.Since the dimension ho of the central parts of the first layers 10 is less than the dimension along x of the sacrificial grids 150, the internal spacers 171 extend under the sacrificial grids 150 (later replaced by functional metallic grids). This reduces parasitic capacitances in the device.

[0093] As illustrated in Figures 8A, 8B, the second openings 200 are first filled with a masking layer 80. This layer 80 helps to better mechanically hold the second layers 20. The hard masks 160 and sacrificial grids 150 are then removed to form the third openings 300. The first material from the remaining parts of the first layers 10 is then completely removed from the third openings 300 by selective etching with respect to the second layers 20. This forms the third spaces 112. The third spaces 112 and the third openings 300 surround the exposed central parts of the second layers 20, as illustrated in [Fig. 8B].

[0094] As illustrated in Figures 9A, 9B, a gate dielectric layer 30 is deposited in the third openings 300 and in the third spaces 112, so as to form a continuous layer lining the third openings 300 and the third spaces 112. This dielectric layer 30 is typically based on a high permittivity material, for example, based on HfO2, HfSiO4, La2O3, LaAlO3, ZrO2, ZrSiO4, Ta2O5, TiO2, SrTiO3, AlO2O3. It is intended to form the gate dielectric layer between the channels of the GAA transistors and their surrounding gates. It can be formed by chemical vapor deposition (CVD) or by low-pressure chemical vapor deposition (LPCVD). (acronym for "Low Pressure Chemical Vapor Deposition"), by atmospheric pressure chemical vapor deposition (APCVD), by plasma-enhanced chemical vapor deposition (PECVD), or by atomic layer deposition (ALD). The dielectric layer 30 typically has a thickness between 1 nm and 5 nm.

[0095] The third openings 300 and the third spaces 112 are then filled with one or more metallic layers, for example based on W, Al, Ni, Ti, TiN, TaN, TiC, TaC, Ru, in order to form the encapsulating gates 50 of the GAA transistors. These metallic layers can be formed by CVD, LPCVD, APCVD, PECVD, or ALD. A chemical-mechanical polishing (CMP) is typically performed to remove excess metal deposited on the motifs 102M. The CMP typically stops on the masking layer 80.

[0096] As illustrated in Figures 10A, 10B, the masking layer 80 is then partially removed to reform the second openings 200b. The second material of the second layers 20 is then completely removed by selective etching from the second openings 200b to form the second spaces 21. This complete etching can be stopped at a specific time, possibly after an over-etching time intended to ensure the complete removal of the second material from the second layers 20. This complete etching is isotropic and can be carried out wet or dry. During the complete etching of the second layers 20, the exposed surfaces of the enclosing grids 50 can be protected by a protective cap, for example, a nitride-based cap, to prevent damage related to the complete etching of the second layers 20.

[0097] As illustrated in Figures 1 IA, 1 IB, optionally only, a dielectric layer 73 may be deposited in the second spaces 21. This dielectric layer 73 is typically based on a high permittivity material, for example, based on HfO2. It allows the dielectric gate barrier formed by the dielectric layer 30 to be thickened, or to compensate for any consumption of the dielectric layer 30 during the complete etching of the second layers 20. The dielectric layer 73 can be deposited as before, by CVD, LPCVD, APCVD, PECVD or ALD.

[0098] As illustrated in Figures 12A, 12B, a layer 40 based on a semiconductor material is then deposited on the dielectric layer 73, or directly on the gate dielectric layer 30 in the second spaces 21. The layer 40 is also typically deposited outside the second spaces 21, on the flanks of the first spacers 170 and the inner spacers 171. The deposition of the layer 40 is configured so that said layer 40 does not completely fill the second spaces 21. The thickness of the layer 40 located in the second spaces 21 can be significantly thinner than the thickness of the initial second layers. The layer 40 may have a thickness corresponding to only a few atomic layers, for example between 1 and 5 atomic layers of semiconductor material.

[0099] This layer 40 is intended to form the channels of the GAA transistors substantially directly above the enclosing gates 50, and the sources and drains of these transistors substantially directly above the internal spacers 171.

[0100] The semiconductor material of layer 40 is advantageously a two-dimensional material selected from among the MX2 transition metal dichalcogenides, with M being molybdenum (Mo) or tungsten (W), and X being sulfur (S), selenium (Se), or tellurium (Te). Such a 2D material can advantageously be deposited as a thin film comprising 1 to 5 atomic layers. The deposition of this 2D material can be carried out by CVD, MOCVD, or ALD. Alternatively, the semiconductor material of layer 40 is a semiconductor oxide such as TITO (Indium Tin Oxide), 1TGZO (Indium Gallium Zinc Oxide), IWO (tungsten-doped indium oxide), or indium oxide In2O3.

[0101] As illustrated in Figures 13A, 13B, a dielectric plug 70 is then formed between the horizontal portions of the layer 40, in the second spaces 21. This dielectric plug 70 can be formed by CVD or ALD or PEALD deposition (acronym for "Plasma Enhanced Atomic Layer Deposition"), followed by etching, in a conventional manner.

[0102] As illustrated in Figures 14A, 14B, the isotropic etching of the dielectric plug 70 is typically extended so as to reduce the x-dimension l70 of the dielectric plug 70. This etching is typically stopped at time. The etching is performed from both sides of the motif 102M, so that the "reduced" dielectric plug 70 is located substantially in the middle of the second x-spaces 21. The x-dimension l70 of the dielectric plug 70 is typically less than 10 nm, preferably less than 5 nm. Advantageously, the x-dimension l70 of the dielectric plug 70 effectively defines the channel lengths of the GAA transistors. The etching of the dielectric plug 70 is typically extended so that the dimension l70 is less than the dimension 15 0 of the enveloping grid 50. Extending the etching under the enveloping grids 50 facilitates the control of the etching stop over time.The dimensional control along x of the dielectric plug 70 is improved. The dimensional control over the effective grid length of the GAA channels is thus advantageously improved.

[0103] As illustrated in Figures 15A, 15B, the second openings 200b can then be filled with one or more metallic layers, for example based on Ti, TiN, W, in order to form the source and drain contacts 60S, 60, 60D. A chemical-mechanical polishing (CMP) is typically carried out to remove the excess metal deposited on the patterns 102M. Advantageously, the second spaces left vacant after the reduction in size of the dielectric plug 70 are filled during the formation of the source and drain contacts 60S, 60, 60D. The source and drain contacts 60S, 60, 60D thus have fingers 62 extending under the internal spacers 171. These fingers 62 are in direct contact with the sources 42 and the drains 43 based on the material of the layer 40, along z. This improves electrical contact with the sources 42 and the drains 43.The source and drain contacts 60S, 60, 60D are thus arranged in the form of opposing combs on either side of the dielectric plugs 70. According to a possible configuration not shown, the fingers 62 are made of a different material than the main part 61 of the contact 60S, 60, 60D. The main part 61 is, for example, based on TiN and W, or on NbN, and the fingers are, for example, based on Nb. This optimizes the access resistance of the source and drain contacts 60S, 60, 60D. It also allows the use of a non-planarizable material for the fingers 62 and a planarizable material for the main part 61.

[0104] A microelectronic device comprising six transistors stacked along z, with encapsulating gate 50, is thus advantageously obtained. The channels 41, the sources 42 and the drains 43 are preferably made of a two-dimensional material. Source and drain contacts 60S, 60, 60D in the form of combs electrically connect these z-stacked GAA transistors.

[0105] Figures 16A, 16B illustrate an alternative embodiment in which layer 40 is etched anisotropically along z, prior to the formation of contacts 60S, 60, 60D, so as to retain only the horizontal portions of layer 40 in the second spaces 21. The vertical portions of layer 40 are thus eliminated. This avoids "side" contact between the main parts 61 of contacts 60S, 60, 60D and the horizontal portions of layer 40. The mechanical strength of contacts 60S, 60, 60D is improved. In particular, the removal of the vertical portions of layer 40 on the sides of the spacers 170, 171 limits or eliminates a delamination phenomenon of the contacts 60S, 60, 60D, especially during the planarization of these contacts 60S, 60, 60D. The contact with the sources 42 and drains 43 is here made solely or predominantly via the fingers 62 of the contacts 60S, 60, 60D.

[0106] Figures 17A, 17B to 25A, 25B schematically illustrate manufacturing steps of a device comprising GAA transistors according to a "Channel First and Gate Last" embodiment. Figures nA (n=17...25) Figures nB (n=17...25) correspond to cross-sections along the xz axis, each illustrating a different step in the manufacturing process. Figures nB (n=17...25) correspond to cross-sections along the yz axis, each illustrating the same step as the corresponding figure nA.

[0107] Only the features that differ from those of this second embodiment compared to the first embodiment are described below. The other features are deemed to be identical to those of the first embodiment, with reference to the foregoing.

[0108] Figures 17A, 17B illustrate the structures obtained at the end of the formation of the internal spacers 171, in a manner similar to what has been described previously with reference to Figures IA, IB to 7A, 7B.

[0109] As illustrated in Figures 18A, 18B, the second layers 20 are fully etched selectively to the first layers 10, the substrate S, and the internal spacers 171. The etching of the second material of the second layers 20 typically exhibits a selectivity S2 0:1 with respect to the first material of the first layers 10 of at least 5:1, preferably at least 10:1. This full etching is intended to form the second spaces 21. The full etching typically exhibits isotropic character and can be carried out by wet or dry method, starting from the second openings 200.

[0110] As illustrated in Figures 19A, 19B, after the formation of the second spaces 21, the layer 40, based on a semiconductor material, is deposited on the remaining portions of the first layers 10 and on the internal spacers 171, within the second spaces 21. The layer 40 is deposited as before and has the same characteristics. Optionally, a dielectric layer, known as an interlayer, can be deposited prior to the deposition of the layer 40. This allows the layer 40 to be protected later during the removal of the remaining portions of the first layers 10.

[0111] As illustrated in Figures 20A, 20B, the dielectric plug 70 is then formed between the horizontal portions of the layer 40, in the second spaces 21, as before.

[0112] As illustrated in Figures 21A, 21B, the isotropic etching of the dielectric plug 70 is extended so as to reduce the x-dimension l70 of the dielectric plug 70, as before. In the example illustrated in Figures 21A, 21B, the x-dimension l70 of the dielectric plug 70 is greater than the x-dimension l10 of the remaining portions of the first layers 10. The edges of the dielectric plug 70 are located here below the internal spacers 171.

[0113] Figures 22A, 22B illustrate another example where the isotropic etching is extended so that the dimension l70 along x of the dielectric plug 70 is less than the dimension li 0 along x of the remaining parts of the first layers 10. The edges of the dielectric plug 70 are here located under the remaining parts of the first layers 10.

[0114] By adjusting the parameters of the isotropic etching, in particular by adjusting the etching time, the x-axis dimension l70 of the dielectric plug 70 can be precisely controlled, for example, according to requirements or the intended applications. It is possible to create different zones on the same chip comprising devices with different dimensions l70 of dielectric plugs 70. This allows the effective gate length of these devices to be physically modulated, depending on the chip zones.

[0115] As illustrated in Figures 23A, 23B, the second openings 200 are then filled with one or more metallic layers, for example based on Ti, TiN, W, in order to form the source and drain contacts 60S, 60, 60D, as before. The fingers 62 of the contacts 60S, 60, 60D may be based on a different material than the main parts 61 of the contacts 60S, 60, 60D. According to one possibility, the vertical portions of the layer 40 may be removed before the formation of the contacts 60S, 60, 60D, to avoid a "side contact" as described previously with reference to Figures 16A, 16B.

[0116] As illustrated in Figures 24A, 24B, after the formation of the source and drain contacts 60S, 60, 60D, the hard masks 160, sacrificial grids 150, and the remaining portions of the first layers 10 are successively removed by selective etching to form the third openings 300 and the third spaces 112, as before. The etching exhibits, in particular, selectivity with respect to the first spacers 170, the internal spacers 171, the layer 40, and / or the intercalated dielectric layer.

[0117] As illustrated in Figures 25A, 25B, the gate dielectric layer 30 is first deposited in the third openings 300 and in the third spaces 112, then the enclosing gates 50 of the GAA transistors are formed, as before.

[0118] In view of the foregoing description, it is clear that the proposed method offers a particularly efficient solution for forming stacked GAA transistors based on 2D material, comprising comb-shaped source and drain contacts. This solution is also advantageously compatible with standard microelectronic processes. However, the invention is not limited to the embodiments described above.

Claims

Demands

1. A microelectronic device comprising: • At least two channels (41) stacked along a principal direction (z), each channel being based on a semiconductor material, • a so-called encapsulating grid (50) surrounding at least one of the channels (41) around one periphery of said channel (41), and preferably several channels (41), • a source (42) and a drain (43) on either side of each channel (41), and source and drain contacts (60S, 60, 60D) connected respectively to the source (42) and the drain (43), • a dielectric grid layer (30) separating each channel (41) from the encapsulating grid (50), • spacers (170, 171) on either side of the grid (50), configured to electrically isolate the grid (50) from the source and drain contacts (60S, 60, 60D). drain,the device being characterized in that the source and drain contacts each comprise a so-called main part (61) extending along the main direction (z), and secondary parts (62) connected to the main part (61) and extending along a sequential direction (x) to the main direction (z) and extending at least partially to the vertical alignment of the spacers (170, 171) flanking the surrounding grid (50), such that the main part (61) and the secondary parts (62) of the source contact (60S, 60) form a first comb and the main part (61) and the secondary parts (62) of the drain contact (60D, 60) form a second comb opposite the first comb, along the sequential direction (x).

2. Device according to the preceding claim wherein the secondary parts (62) of the source contact and the secondary parts (62) of the drain contact opposite each other, along the sequential direction (x), are separated by dielectric plugs (70).

3. Device according to the preceding claim in which the dielectric plugs (70) further separate two successive stacked channels (41) along the principal direction (z).

4. Device according to the preceding claim wherein the dielectric plugs (70) have a dimension l70, along the sequential direction (x), less than a dimension 15 0 of the enclosing grid (50) at the level of said successive stacked channels (41), so that the dielectric plugs (70) define an effective grid length Lg shorter than the dimension 15 0 of the enclosing grid (50), for the successive stacked channels (41).

5. Device according to any one of the preceding claims wherein each source (42) comprises at least a so-called horizontal portion in contact with a secondary part (62) of the source contact (60S, 60), and wherein each drain (43) comprises at least a so-called horizontal portion in contact with a secondary part (62) of the drain contact (60D, 60).

6. Device according to any one of the preceding claims wherein each source (42) comprises a so-called vertical portion in contact with the main part (61) of the source contact (60S, 60), and a so-called horizontal portion in contact with a secondary part (62) of the source contact, and wherein each drain (43) comprises a so-called vertical portion in contact with the main part (61) of the drain contact (60D, 60), and a so-called horizontal portion in contact with a secondary part (62) of the drain contact.

7. Device according to any one of claims 1 to 5 wherein each source (42) comprises only a so-called horizontal portion in contact with a secondary part (62) of the source contact (60S, 60), and wherein each drain (43) comprises only a so-called horizontal portion in contact with a secondary part (62) of the drain contact (60D, 60).

8. A device according to any one of the preceding claims, wherein the semiconductor material of the channels (41) is taken from: - the transition metal dichalcogenides MX2 with M taken from molybdenum (Mo) or tungsten (W), and X taken from sulfur (S), selenium (Se) or tellurium (Te), or - a semiconductor oxide, for example IGZO (Indium Gallium Zinc Oxide), In2O3, IWO (tungsten doped indium oxide), ITO (Indium Tin Oxide), IAZO (Indium

9.

10. Aluminium Zinc Oxide), InGaZnO, InGaO, InZnO or an amorphous semiconductor oxide, - graphene, hexagonal boron nitride or phosphorene. Device according to any one of the preceding claims wherein the secondary parts (62) of the source and drain contacts (60S, 60, 60D) are made of a metallic material different from the main parts (61) of the source and drain contacts (60S, 60, 60D). A method for manufacturing a microelectronic device according to any one of the preceding claims, said method comprising the following steps: • Provide on a substrate (S) a stacking (E) along the principal direction (z) comprising first layers (10) of a first material alternating with second layers (20) of a second material, the first and second materials being different from the semiconductor material of the channels (41) of the device, • Form in this stacking (E) the first openings (100) defining the first patterns (101M), • Form sacrificial grids (150) straddling the first motifs (101M) and partly within the first openings (100), • Form initial spacers (170) on the initial motifs (101M) and bordering the sacrificial grids (150), • Forming in the first motifs (101M) second openings (200) defining second motifs (102M), • Partially remove, from the second openings (200), the first material of the first layers (10) selectively to the second material of the second layers (20), so as to form first spaces (111) under the first spacers (170), and preferably partly under the sacrificial grids (150), • Fill the first spaces (111) with a dielectric material to form internal spacers (171), • Completely remove, from the second openings (200), the second material from the second layers (20), so as to form second spaces (21),

11. • Depositing a layer (40) based on a semiconductor material onto exposed surfaces of the second spaces (21), without completely filling the second spaces (21), said layer (40) being intended to form the channels (41) based on the semiconductor material, and the sources (42) and drains (43) based on the semiconductor material, • Fill the second spaces (21) with a dielectric material so as to form dielectric plugs (70) occupying the second spaces (21), • Partially etch the dielectric plugs (70) from the second openings (200, 200b), on either side of the second motifs (102M), so as to reduce a dimension l70 of said dielectric plugs (70) along the sequential direction (x), the second spaces (21) being obstructed in their centers by the dielectric plugs (70), • Fill the second spaces (21) and the second openings (200, 200b) with at least one metallic material, so as to form the source and drain contacts (60S, 60, 60D) in the form of the first and second facing combs, • Remove the sacrificial grids (150) to form third openings (300), • Completely remove, from the third openings (300), the first material from the remaining parts of the first layers (10), so as to form third spaces (112), • Form a dielectric layer (30), called the gate dielectric layer, in the third spaces (112), • Fill the third spaces (112) with a material, called grid material, so as to form the surrounding grids (50). A method according to the preceding claim comprising, after deposition of the layer (40) based on the semiconductor material, a partial removal of said layer (40) on flanks of the second motif (102M) substantially parallel to the principal direction (z), in particularly on the flanks of the first spacers (170) and on the flanks of the internal spacers (171).

12. A method according to any one of claims 10 to 11 wherein the partial etching of the dielectric plugs (70) is configured so that the dimension l70 of the dielectric plugs (70) is less than a dimension h0 of the remaining parts of the first layers (10), or a dimension 150 of the enclosing grids (50), along the sequential direction (x).

13. A method according to any one of claims 10 to 12 wherein the formation of the encapsulating grids (50) is carried out before the deposition of the layer (40) based on the semiconductor material.

14. A method according to any one of claims 10 to 13, said method comprising the following steps in the following order: • Providing on a substrate (S) a stack (E) along the principal direction (z) comprising first layers (10) of a first material alternating with second layers (20) of a second material, the first and second materials being different from the semiconductor material of the channels (41) of the device, • Forming in this stack (E) first openings (100) defining first patterns (101M), • Forming sacrificial grids (150) straddling the first patterns (101M) and partly within the first openings (100), • Forming first spacers (170) on the first patterns (101M) and bordering the sacrificial grids (150), • Forming in the first patterns (101M) second openings (200) defining second patterns (102M)• Partially remove, from the second openings (200), the first material from the first layers (10) selectively to the second material from the second layers (20), so as to form first spaces (111) under the first spacers (170), and preferably partly under the sacrificial grids (150), • Fill the first spaces (111) with a dielectric material to form internal spacers (171), Fill the second openings (200) with a masking layer (80), Remove the sacrificial grids (150) so as to form third openings (300), Completely remove, from the third openings (300), the first material from the remaining parts of the first layers (10), so as to form third spaces (112), To form a dielectric layer (30), called the grid dielectric layer, in the third spaces (112), To fill the third spaces (112) with a material, called the grid material, so as to form the surrounding grids (50), Remove at least part of the masking layer (80), so as to re-form the second openings (200b), Completely remove, from the second openings (200b), the second material from the second layers (20), so as to form second spaces (21), Deposit a layer (40) based on a semiconductor material on exposed surfaces of the second spaces (21), without completely filling the second spaces (21), said layer (40) being intended to form the channels (41) based on the semiconductor material, and the sources (42) and drains (43) based on the semiconductor material, Fill the second spaces (21) with a dielectric material so as to form dielectric plugs (70) occupying the second spaces (21), Partially etch the dielectric plugs (70) from the second openings (200, 200b), on either side of the second motifs (102M), so as to reduce a dimension l70 of said dielectric plugs (70) along the sequential direction (x), the second spaces (21) being obstructed in their centers by the dielectric plugs (70), Fill the second spaces (21) and the second openings (200b) with at least one metallic material, of

15. so as to form the source and drain contacts (60S, 60, 60D) in the form of the first and second combs facing each other. A method according to any one of claims 10 to 14 in which the deposition of the layer (40) based on the semiconductor material is carried out by chemical vapor deposition or by atomic layer deposition.

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