QUANTUM DEVICE WITH SUPERIMPOSED AND LATERALLY CONTROLLED QBITS

Abstract

Quantum electronic device provided with: - a first set of semiconductor regions (102L, 104L) comprising a first lower semiconductor region (102L) and a first upper semiconductor region (104L), superimposed on, and separated from, the first lower semiconductor region by means of a first dielectric separation zone (ZS1), - a second set of semiconductor regions (102R, 104R) comprising a second lower semiconductor region (102R) and a second upper semiconductor region (104R), superimposed on, and separated from, the first lower semiconductor region by means of a second dielectric separation zone (ZS2), the first set of semiconductor regions (102L, 104L) being arranged opposite the second set of semiconductor regions (102R, 104R), at least one dielectric region (RD) separating the first set of semiconductor regions (102R,104R) of the second set of semiconductor regions (102R, 104R). Figure for the abstract: 1,

Description

Title of the invention: Quantum device with superimposed and laterally controlled Qbits

[0001] TECHNICAL FIELD AND STATE OF THE PRIOR ART

[0002] The present application relates to the field of quantum devices in in which at least one quantum computing based on a given quantum state among at least two measurable levels is used as an information vector. This quantum state is called a qubit or quantum bit or "quantum bit" in English.

[0003] A special type of qubit is the spin qubit when the intrinsic degree of freedom of the spin of individual electrons is used to encode quantum information.

[0004] Qubits can be formed in a semiconductor material within confinement structures of nanometric size and defined electrostatically and / or physically. These confinement structures are typically called "quantum dots" or "quantum boxes".

[0005] A quantum dot behaves like a potential well confining one or more elementary charges (electrons or holes) in a semiconductor region.

[0006] To measure the state of a qubit, it is known to carry out a spin / charge conversion which makes it possible to convert the spin state of the charged particles into a charge state of the quantum dots containing said particles. It is then necessary to measure this charge state in order to deduce the spin state of the charged particles before conversion. For this, a means for measuring the charge state is generally arranged opposite or close to each quantum dot.

[0007] Reading a qubit can for example be carried out using another quantum box called a "reading island" or "detection island" coupled to that of the qubit intended to be read. These two elements form two potential wells separated by a potential barrier.

[0008] Devices in which the detection islands and quantum dots are arranged opposite and in the same plane parallel to the main plane of a substrate on which the quantum dots and the detection islands are formed are known.

[0009] The document by R Pillarisetty “High Volume Electrical Characterization of Semiconductor Qubits”, 2019 IEEE International Electron Devices Meeting (IEDM) proposes for example a device with quantum dots formed in a first semiconductor block of elongated shape (“thin” according to Anglo-Saxon terminology ”) and detection islands formed in a second elongated semiconductor block parallel to the first block.

[0010] The problem arises of producing a new quantum device which is improved in terms of integration density while preferably retaining good detection sensitivity. Statement of the invention

[0011] According to one aspect, an embodiment of the present invention relates to a quantum electronic device having a substrate and on this substrate °:

[0012] - of a set of superimposed semiconductor bars comprising at least one lower semiconductor rod and at least one upper semiconductor rod, the lower semiconductor rod and the upper semiconductor rod being arranged one above the other,

[0013] - a first group of superimposed grids comprising at least one first grid lower and a first upper grid superimposed on, and separated from the first lower grid by an insulation zone, the first lower grid being arranged opposite, and capable of being coupled by capacitive coupling to, a first region of the lower semiconductor bar forming a first quantum dot, the first upper grid being arranged opposite, and capable of being coupled by capacitive coupling to, a first region of the upper semiconductor bar forming a second quantum dot,

[0014] - a second group of superimposed grids comprising a second grid lower and a second upper grid superimposed on, and separated from the second lower grid by an insulation zone, the first lower grid being arranged opposite a second region of the lower semiconductor bar opposite the first region of the lower semiconductor bar, the second upper grid being arranged opposite a second region of the upper semiconductor bar opposite the first region of the upper semiconductor bar, the first group and the second group of grids being arranged so that said set of semiconductor bars is arranged between the first group of superimposed grids and the second group of superimposed grids.

[0015] Such an arrangement with superimposed semiconductor bars and lateral grids makes it possible to obtain a density of quantum dots arranged on several distinct planes in a direction orthogonal to the main plane and improved lateral control of these quantum dots.

[0016] Advantageously, the device may further comprise:

[0017] - a third group of superimposed grids juxtaposed with said first group of grids, the third group of superimposed grids comprising at least a third lower grid separated from a third upper grid superimposed on, and separated from the third lower grid by an insulation zone, the third lower grid and the third upper grid being arranged opposite, respectively, a third lower semiconductor region of the lower semiconductor bar and a third upper semiconductor region of the upper semiconductor bar,

[0018] - a fourth group of superimposed grids juxtaposed with said second group of grids, the fourth group of superimposed grids comprising a fourth lower grid and a fourth upper grid superimposed on, and separated from, the fourth lower grid by an insulation zone, the fourth lower grid and the fourth upper grid being arranged facing respectively a fourth lower semiconductor region of the lower semiconductor bar and a fourth upper semiconductor region of the upper semiconductor bar.

[0019] Thus, superimposed rows of quantum dots can be advantageously implemented, each row being controlled by a set of juxtaposed grids and typically extending orthogonally to the semiconductor bars.

[0020] According to one possible implementation, between neighboring or juxtaposed grids, and in particular between the first group of grids and said third group of grids: - at least one exchange electrode or exchange electrodes superimposed and separated from each other by at least one insulating separation layer can be provided. This makes it possible to carry out an exchange of charges between quantum dots. Alternatively, between neighboring or juxtaposed grids, and in particular between the first group of grids and said third group of grids, an area of ​​insulating material can be provided.

[0021] According to a particular embodiment of the device, the latter may be further provided with a doped semiconductor block forming a first charge reservoir, the doped semiconductor block being arranged at a first end of the upper semiconductor bar and the first lower semiconductor bar. The device may advantageously comprise another doped semiconductor block, forming a second charge reservoir, the other doped semiconductor block being arranged at a second end of the upper semiconductor bar and the lower semiconductor bar.

[0022] According to a possible implementation of the quantum device, the latter can be provided with a dielectric region arranged between the first group of superimposed grids, and the second group of superimposed grids, this dielectric region encapsulating the superimposed semiconductor bars.

[0023] The quantum device is particularly suitable for detection by reflectometry. Thus, the lower and upper grids of said second group of grids and / or of the first group are coupled or capable of being coupled to a reflectometry measurement circuit, said circuit being in particular configured to:

[0024] - transmit an RF signal to the second lower grid or the second upper grid;

[0025] - detect an impedance variation following the reception of a reflected signal by said second semiconductor region of the lower semiconductor rod or by said second upper semiconductor region of the semiconductor rod following the emission of said RF signal.

[0026] According to a first possible implementation, the lower semiconductor bar and the upper semiconductor bar have a width W1 less than a predetermined width, the second lower gate and the second upper gate being configured to control respectively the chemical potential of the first quantum box and the chemical potential of the second quantum box. Thus, it is possible to provide a pair of gates arranged laterally on either side of a quantum box to enable this box to be controlled.

[0027] Alternatively, and according to a second possible implementation, the lower semiconductor bar and the upper semiconductor bar have a width W1 greater than a predetermined width, the second lower gate and the second upper gate being configured to control respectively, the chemical potential of a third quantum box formed in said second region of the lower bar, the chemical potential of a fourth quantum box formed in said second region of the upper bar.

[0028] According to a particular embodiment, the grids of said groups of grids extend orthogonally to said superimposed semiconductor bars and are arranged against lateral zones of the bars.

[0029] Advantageously, in a plane orthogonal to a main plane of the substrate and passing through said superimposed semiconductor bars, the device is devoid of an electrode overhanging the bars. The device here therefore does not comprise an electrode for controlling or reading the quantum dots above the structure enclosing these quantum dots. Here, only lateral control of the bars in which the quantum dots are provided is advantageously carried out.

[0030] According to another aspect, the present invention relates to a method of manufacturing a quantum device as defined above.

[0031] Thus, according to one possible implementation, this method may comprise steps of:

[0032] - production on said substrate of a structure formed from a stack of bars semiconductor formed from an alternation of bars based on a first material, and bars based on a second material, the second material being semiconducting, then,

[0033] - formation of grid patterns on either side and against said structure stacking, then,

[0034] - release in said structure of the bars based on the second material by withdrawal selective bars based on the first material.

[0035] Advantageously, the release of the bars based on the second material leads to the release of a space between said grid patterns and around the bars based on the second material, the method further comprising: a step of filling said space using at least one dielectric material.

[0036] According to one possible implementation, the method may further comprise, prior to the formation of the grid patterns on either side and against said structure, steps of:

[0037] - partial etching of the bars based on the second material by selective etching relative to the first material so as to form recesses on either side of the lateral sides of said structure, then

[0038] - formation of dielectric plugs in said recesses.

[0039] According to a particular implementation, the method may further comprise, after formation of said structure and prior to the release in said structure of the bars based on the second material, a formation of charge reservoirs at ends of said structure, the formation of the charge reservoirs comprising:

[0040] - carry out a partial selective etching of the first material with respect to the second material in order to create recesses at said ends of said stacking structure,

[0041] - filling said recesses with an insulating material in order to form plugs insulators in said recesses,

[0042] - carry out epitaxy of semiconductor material from exposed ends bars made from the second material, while the bars made from the first material are protected by the insulating caps.

[0043] Advantageously, the grid patterns on either side and against said structure are formed from a grid material, the method further comprising, after release of the bars based on the second material, steps of:

[0044] - formation of an insulating encapsulation between and around the grid patterns,

[0045] - partial removal of said grid material so as to retain a lower block of grid material and release cavities above this lower block of grid material and surrounded by the encapsulation,

[0046] - filling the cavities with at least one insulating layer so as to form a zone insulation on the lower block of grid material then,

[0047] - filling the cavities with at least one layer of grid material, so as to form a top block of grid material over the insulation area.

[0048] According to one possible implementation, after the formation of the grid patterns and before formation of the encapsulation, the method may further comprise:

[0049] - formation of an insulating spacer distributed in a conformal manner on the patterns of grids and between the grid patterns and arranged on a central area of ​​said stacking structure.

[0050] Advantageously, the method may further comprise steps of:

[0051] - removal of the insulating encapsulation between the grid patterns or between the blocks of grid, so as to free up one or more spaces,

[0052] - formation of exchange grids in the space(s). Brief description of the drawings

[0053] The present invention will be better understood upon reading the description of exemplary embodiments given, for purely indicative and non-limiting purposes, with reference to the appended drawings in which:

[0054] [Fig.lA]

[0055] [Fig. IB] illustrate an example of a quantum device according to the invention with several levels of superimposed semiconductor bars and, respectively, a first pair of superimposed grids and a second pair of superimposed grids distributed along the semiconductor bars.

[0056] [Fig.2] illustrates an example of a quantum device comprising a superposition of semiconductor bars and pairs of grids superimposed along the bars, the pairs here being isolated from each other.

[0057] [Fig.3] illustrates an example of embodiment of the quantum device with charge reservoirs at the ends of the bars.

[0058] [Fig.4] illustrates an example of a quantum device comprising a superposition of semiconductor bars and pairs of grids superimposed along the bars, one or more exchange grids being provided here between each pair.

[0059] [Fig.5]

[0060] [Fig.6A]

[0061] [Fig.6B] illustrate an exemplary embodiment of a semiconductor structure of active zone with stacked semiconductor bars to form a quantum device.

[0062] [Fig.7A]

[0063] [Fig.7B]

[0064] [Fig.8A]

[0065] [Fig.8B] illustrate an example of the lateral removal of certain semiconductor bars from the structure to form recesses and to be able to produce dielectric plugs in these recesses.

[0066] [Fig.9]

[0067] [Fig. 10]

[0068] [Fig. 11] illustrate an example of the production of grid patterns.

[0069] [Fig. 12]

[0070] [Fig. 13]

[0071] [Fig. 14] illustrate an example of the production of charge tanks.

[0072] [Fig. 15] illustrates an example of the embodiment of an insulating encapsulation between and around the grid patterns.

[0073] [Fig. 16]

[0074] [Fig. 17] illustrate an example of selective removal of bars based on a first material to release semiconductor bars intended to each typically accommodate a row of quantum dots.

[0075] [Fig. 18]

[0076] [Fig. 19] illustrate an example of the production of a dielectric region between the gate patterns and around the semiconductor bars.

[0077] [Fig.20]

[0078] [Fig.21]

[0079] [Fig.22]

[0080] [Fig.23] illustrate a particular example of the production of superimposed grids according to a method with replacement grid.

[0081] [Fig.24] are used to illustrate insulating regions in a neighboring or adjacent inter-grid space.

[0082] [Fig.25]

[0083] [Fig.26]

[0084] [Fig.27] illustrate an alternative embodiment with the implementation of exchange grids in an inter-grid space.

[0085] Identical, similar or equivalent parts of the different figures bear the same numerical references so as to facilitate the transition from one figure to another.

[0086] The different parts represented in the figures are not necessarily on a uniform scale, in order to make the figures more readable.

[0087] Furthermore, in the following description, terms that depend on the orientation of the structure such as "above", "below", "lower", "upper", "juxtaposed", "superimposed" apply considering that the structure is oriented in the manner illustrated in the figures.

[0088] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0089] We first refer to figures 1A, 1B, 2, 3 which give an example of embodiment of a quantum device (respectively illustrated according to a first cross-sectional view A'A, according to a second cross-sectional view B'B, according to a partial perspective view, and according to a top view).

[0090] The device is arranged on a substrate 5 which may in particular be of the semiconductor on insulator type, for example of the SOI type (SOI for “Silicon On Insulator” or silicon on insulator) or SiGeOI (for “Silicon Germanium On Insulator” or Silicon Germanium on insulator) or of the bulk type, for example made of silicon.

[0091] The device here comprises quantum dots QD1, QD2, QD3, QD4 formed in semiconductor regions of superimposed semiconductor rods 102, 104 and for example made of silicon, in particular Si28, or germanium. By “rod” is meant a layer or a strip comprising at least one semiconductor material.

[0092] By “superimposed” is meant here that the bars are arranged one above the other, a so-called “upper” semiconductor bar 104 of the assembly being arranged here above a so-called “lower” semiconductor bar 102 without being in contact with the latter.

[0093] The semiconductor bars 102, 104 have a shape which can advantageously be parallelepiped or substantially parallelepiped, and extend mainly in a direction called the “first direction” which is parallel to the main plane of the substrate 5 (i.e. a plane defined throughout the description as a plane passing through the substrate 5 and which is parallel to the plane [0; x; y] of an orthogonal reference frame [0; x; y; z]).

[0094] In the particular embodiment illustrated, the semiconductor bars 102, 104 have a width W1 greater than their thickness el in particular so as to give them a flat or strip-like appearance.

[0095] The semiconductor bars 102, 104 can thus be provided with a width W1 (i.e. dimension measured parallel to the x axis of the orthogonal reference frame [0; x; y; z] given in [Fig. 1A]) of for example between 20nm and 100nm, advantageously between 40nm and 80nm. The thickness el (i.e. dimension measured parallel to the z axis of the orthogonal reference frame [0; x; y; z]) of the semiconductor bars 102A, 102B can for example be between 5nm and 20nm, advantageously between 10nm and 15nm.

[0096] As can be seen in FIGS. 1A, 1B, the bars 102, 104 are typically surrounded by at least one dielectric material 58, for example chosen from one of the following materials: SiO2, SiN, HfO2. An insulating zone 158 is thus provided between the bars 102, 104 in order preferably to prevent electrostatic coupling between the bars 102, 104.

[0097] The quantum device is also provided with different superimposed grids GI1, GSI, GI2, GS2, GI3, GS3, GI4, GS4 of oblong shape, advantageously parallelepiped or substantially parallelepiped, and which extend mainly in a second direction which is parallel to the main plane of the substrate 5 and orthogonal to the first direction. Each grid GI1, GSI, GI2, GS2 may be formed from a conductive or semiconductive block of gate material 22, for example polysilicon, against a gate dielectric layer disposed between the gate block and the semiconducting bars. According to one possible implementation, this gate dielectric layer may be based on the same dielectric material 58 as that of the insulating zone 158.

[0098] In this embodiment, there is advantageously an alignment of the lower gates GI1, GI2, GI3, GI4 and of the lower semiconductor block 102 in the same plane PI and an alignment of the upper gates GSI, GS2, GS3, GS4 and of the upper semiconductor block 104 in the same upper plane P2 distinct from the plane PI, the planes PI and P2 typically being planes parallel or substantially parallel to the main plane of the substrate 5.

[0099] The operation of the device is based on a capacitive coupling between each quantum box QD1 (respectively QD2, QD3, QD4) and an associated control gate GI1 (respectively GSI, GI2, GS2) arranged opposite or in front of this box. In this example, due to a sufficient width W1 of each of the semiconductor rods 102, 104, typically with W1 greater than 40 nm, each rod 102 (resp. 104) can be, in a sectional view (the section being in a direction orthogonal to that of the rods 102, 104 and typically parallel to that of the gates (in other words a direction parallel to the x axis)), be intended to accommodate two quantum boxes QD1, QD3 (resp. QD2, QD4). According to an alternative embodiment, each bar 102, 104 is intended to accommodate, in a sectional view, a single quantum box. In this case, the width W1 of each of the semiconductor bars 102, 104 is typically 20nm.Generally, the width W1 of each of the semiconductor bars 102, 104 is adapted according to the desired number of quantum dots.

[0100] A first group of gates GI1, GSI superimposed with a first so-called "lower" gate GI1 is provided for the control respectively of a first semiconductor region 102A of the lower semiconductor bar 102 in which the quantum dot QD1 is formed while a first so-called "upper" gate GS1 is provided for the control of the first upper semiconductor region 104A of the upper semiconductor bar 104 and in which the quantum dot QD2 is formed. The gate GI1 controls, as a function of an electrostatic potential applied to it, the chemical potential of the first quantum dot QD1, while the gate GSI, independent of the gate of GI1, controls as a function of an electrostatic potential applied to it, the chemical potential of the second quantum dot QD2.

[0101] The first upper grid GSI is superimposed on, and separated from, the first lower grid GI1 by means of a first insulation zone ZIL. This first zone insulation zone ZI1 of the lower grids GI1 and upper grids GSI between them is typically made of insulating material and preferably of thickness e0 sufficient to electrically insulate the grids GI1, GSI from each other. For example, the first insulation zone ZI1 is formed from SiO2 and has a thickness e0 which can be for example between 5 nm and 20 nm.

[0102] To enable control of the quantum boxes QD3, QD4, a second group of grids GI2, GS2 is typically provided.

[0103] A gate GI2 of the second group can thus be provided opposite a second semiconductor region 102B of the lower semiconductor bar 102 in which the quantum dot QD3 is formed while a gate GS2 independent of the gate GI2 can be arranged opposite a semiconductor region 104B of the upper semiconductor bar 104 and in which the quantum dot QD4 is formed. The gate GI2 controls, as a function of an electrostatic potential applied to it, the chemical potential of the third quantum dot QD3, while the gate GS2 controls, as a function of an electrostatic potential applied to it, the chemical potential of the fourth quantum dot QD4. A second insulation zone ZI2, for example also based on SiO2 and of thickness e0 is also provided between the lower gate GI2 and upper gate GS2 of the second group.

[0104] As can be seen in Figures 1B, 2 and 3, another lower gate GI3 may be provided to control another quantum dot of the same lower row as the first quantum dot QD1 and formed in the lower bar 102, while another upper gate GS3 may be provided to control a quantum dot of the same upper row as the second quantum dot QD2 and formed in the upper bar 104. The lower gate GI3 and the upper gate GS3 are thus arranged opposite, respectively, a lower semiconductor region 102C of the lower semiconductor bar 102 and an upper semiconductor region 104C of the upper semiconductor bar 104. The lower gate GI3 is here also separated from the upper gate GS3 superimposed on, and separated from the third lower gate by an isolation zone ZI3.

[0105] A lower gate GI4 may be provided to control a quantum dot of the same lower row as the third quantum dot QD3, while another upper gate GS4 may be provided to control a quantum dot of the same upper row as the fourth quantum dot QD4. Thus, a group of superimposed gates GI4, GS4 comprises a lower gate GI4 and an upper gate GS4 superimposed on, and separated from, the fourth lower gate by an isolation zone ZI4. The lower gate GI4 and the upper gate GS4 are arranged facing respectively a lower semiconductor region 102D of the semi-conductor bar lower conductor 102 and a fourth upper semiconductor region 104D of the upper semiconductor rod 104.

[0106] Thus, the quantum device is here advantageously provided with a plurality of lower gates GI1, GI3 on ​​a first side of the lower semiconductor bar 102 to control a first row of quantum dots. The device may also be provided with a plurality of lower gates GI2, GI4 arranged on a side opposite the first side of the lower semiconductor bar 102 to control a second row of quantum dots opposite the first row.

[0107] Similarly, the device may be provided with a plurality of upper gates GSI, GS3 on a first side of the upper semiconductor bar 104 to control a third row of quantum dots as well as a plurality of upper gates GS2, GS4 arranged on a side opposite the first side of the upper semiconductor bar 104 to control a fourth row of quantum dots opposite the third row.

[0108] The quantum boxes QD1, QD2, QD3, QD4 each ensure the confinement of at least one elementary charge (electron(s) or hole(s)). Preferably, each quantum box QD1, QD2, QD3, QD4 here comprises a single elementary charge. The spin of this charge, in particular an electron, makes it possible to code the quantum information. In this case, the qubits associated with the quantum boxes QD1, QD2, QD3, QD4 are spin qubits.

[0109] To enable the detection of a quantum state also called “charge state” of the quantum boxes QD1, QD2, QD3, QD4, a reflectometry detection device may in particular be provided.

[0110] The state of a quantum box QD1 (resp. QD2, QD3, QD4) can be read by coupling a reflectometry circuit 350 to the grid GI1 (resp. GS2, GI2, GS2) located in its immediate vicinity and opposite or facing this box QD1.

[0111] The detection of the charge state of a quantum box QD1 can be implemented here by applying an RF SE signal to the gate GI1 and receiving a reflected RF SR signal following the emission of the RF SE signal. The RF SE signal is typically a high-frequency signal (for example between 100 MHz and 1 GHz) sent to the region 104A. The RF signal reflected by this region 104A is then demodulated by the reflectometry circuit 350. An inductor 352 is used to create an LC resonator composed of this inductor 352 and which depends on a quantum capacitance Cq formed by the quantum box BQ1 and the gate GIL. When the value of Cq varies, the phase and the amplitude of the reflected signal vary, which can be detected by measuring means. It is thus possible to know the relative charge state of the quantum box QD1 of the qubit intended to be read.

[0112] In the particular embodiment illustrated in [Fig.2], the intergrid spaces are filled with an insulating material 53. Thus, the grid GI1 is here isolated from the grid GI3 which controls a quantum box of the same row of quantum boxes as the grid GI1. Similarly, the adjacent upper grids GSI and GS3 are here isolated from each other, by means of a zone of insulating material 53, for example SiO2.

[0113] As can be seen in the top view of [Fig. 3], the device can also be provided with charge reservoirs, in particular DTI and DT2 doped regions at the ends of the lower and upper bars 102, 104. These DTI, DT2 doped regions can be in the form of blocks, typically made of doped semiconductor material, for example phosphorus-doped silicon or boron-doped silicon germanium. In the particular embodiment illustrated, each block forming a DTI, DT2 doped region is connected to one end of the set of semiconductor bars 102, 104 (the bars not being visible in [Fig. 3]).

[0114] According to a variant of the embodiment illustrated in [Fig.2] exchange electrodes GE1, GE2, GE3, GE4 also called “exchange grids” can be provided in inter-grid spaces. In the particular embodiment of [Fig.4], a single exchange electrode in the same inter-grid space.

[0115] The exchange electrodes GE1, GE2, GE3, GE4 extend mainly in a direction parallel to that in which the gates GI1, GSI, GI3, GS3 extend and which is preferably orthogonal to the first direction, in other words to the direction in which the host semiconductor bars 102, 104 of the quantum dots extend. Each exchange electrode is typically separated from the adjacent gates by means of an insulating spacer layer 33.

[0116] The exchange electrodes allow charge exchanges to be carried out between neighboring quantum dots or between neighboring detection islands distributed along the same semiconductor bar. Thus, an exchange electrode can allow charge exchange between a first lower semiconductor region 102A controlled by a gate GI1 and another lower semiconductor region 102C controlled by a gate GI3 adjacent to the gate GI1 and located on the same semiconductor bar 102 as the first lower semiconductor region 102A.

[0117] An arrangement of exchange electrodes similar to that of the grids GS3, GI3 or GSI, GI1 may be provided such that an upper exchange electrode is arranged above a lower exchange electrode and insulated from this lower exchange electrode by the insulating layer an insulating separation layer.

[0118] The implementation of exchange electrodes is optional, in particular when the pitch A of the grid distribution ("pitch according to English terminology") is low and for example less than 40 nm. In this case, it is some of the grids which can- be used to control the exchange between adjacent quantum dots or detection islands of the same semiconductor bar.

[0119] In either of the exemplary embodiments which have just been given, the device comprises two levels or stages of quantum dots. However, the quantum device is not limited to this number and can integrate a higher number k (with k>2) of stages. Thus, more generally, a quantum device as implemented according to the invention can comprise a number k of stages of superimposed semiconductor blocks greater than two, with k for example between 3 and 10).

[0120] As a variant of one or other of the examples described previously, a single row of quantum dots can be provided per semiconductor rod 102, 104.

[0121] In this case, the superimposed semiconductor bars 102, 104 are provided with a smaller width W1, and in particular a higher ratio el / Wl of its thickness to its width. It is still possible to keep one or more pairs of gates GI1, GI2 (resp. GSI, GS2) on either side of each bar 102, 104. In this case, the gates GI1, GI2 arranged respectively opposite a region 102A located on a lateral portion of the bar 102 and opposite another region 102B located on an opposite lateral portion of the bar 102 are associated with the same quantum box. The gates GI1, GI2 can in particular be connected to each other and provided to control the chemical potential of the same quantum box.Alternatively, the grids GI1, GI2 can be independent and thus disconnected from each other, one grid being provided to control the chemical potential of the quantum dot, the other being dedicated to measuring and conveying the reflectometry RF signal.

[0122] In either of the examples of quantum devices described above, the superposition of bars is only controlled laterally by the groups of gates GI1, GI2, GS1, GS2, GI3, GS3, GI4, GS4. Preferably, no control electrode is provided located above the bars or between them. Thus, in a plane orthogonal to the substrate 5 and passing through the bars 102, 105, no additional electrode for controlling the bars is preferably provided in order to avoid an untimely screening phenomenon.

[0123] A quantum device as provided according to one or more of the previously described modes can be implemented using a thin-film microelectronic manufacturing method.

[0124] We first refer to [Fig.5] which gives an example of a possible starting structure for the production of a quantum device according to the invention and which here comprises a substrate 5, this substrate 5 being able to be of the semiconductor on insulator type, for example SOI, or of the massive type (“bulk”) and for example made of silicon.

[0125] A stack of layers formed of an alternation of layers 10i, 103, 105 in a first material 12 and of layers 102, 104, in a second material 14, semiconductor, is first of all formed on the substrate 5.

[0126] The materials 12, 14 are typically semiconductor materials different from one another, the first material 12 being capable of being etched selectively with respect to the second material 14. The stacking is in this case typically carried out by successive epitaxies. The particular embodiment illustrated in [Fig. 5] provides an odd number of layers, in particular five layers, but the method can be carried out with a different and in particular higher number of layers.

[0127] The layers 10i, 103, 105 based on the first material 12 may advantageously be produced with a thickness eA greater than that of the layers 102, 104, based on the second material 14, and which may be, for example, more than twice that of the layers 102, 104. The layers 10i, 103, 105 based on the first material 12 may have a thickness eA of, for example, between 10 nm and 50 nm, while the layers 102, 104 have a thickness eB of, for example, between 5 nm and 20 nm. For example, the first material 12 is made of silicon, in particular Si28, while the second material 14 is made of Sii_xGex, with x > 0, x being, for example, of the order of 30%. The layers 10i, 103, 105, 102, 104 can be produced by successive epitaxies.

[0128] When the first layer 10i is made of SiGe, this layer can optionally be formed from a surface layer of silicon of an SOI substrate by a Germanium enrichment method known to those skilled in the art and which consists of carrying out silicon epitaxy and then carrying out oxidation in order to diffuse the germanium. An etching is then carried out so as to remove the oxide formed. The layer 10i can alternatively be the surface layer of a SiGeOI substrate

[0129] Then (Figures 6A and 6B), an active zone structure 16 is defined by etching the stack of layers, here in the form of a block, typically of oblong shape, for example parallelepiped, and which extends mainly in a first direction (direction orthogonal to the plane of [Fig.6A] and parallel to the y axis of the orthogonal reference frame [0;x;y;°z]). This can be achieved by photolithography and etching of the stack.A dry etching using fluorocarbon chemistry and carried out through while a part of the stack is protected by a lithography mask (not shown) can be carried out for this.

[0130] The structure 16 produced by etching from the layers 10i, 102, 103, 104>105 is formed from a stack of semiconductor rods comprising an alternation of rods 101, 103, 105 based on the first material 12, and rods 102, 104 based on the second material 14.

[0131] A partial etching of the bars 102, 104 based on the second material 14 is then carried out by selective etching relative to the first material 12 so as to form lateral recesses 17 on either side of lateral flanks 16L, 16R of the stacking structure 16 (FIGS. 7A and 7B). This lateral etching can be carried out by wet chemical etching, for example using a solution of NH4OH, or of TMAH (tetramethylammonium hydroxide) or of TEAH (tetraethylammonium hydroxide), when Si is etched selectively relative to SiGe. A removal of lateral portions of the bars 102, 104, for example of at least 5 nm, can be in particular when the latter have a width typically between 40 nm and 80 nm.

[0132] Then, dielectric plugs 19 are formed in the lateral recesses 17 (FIGS. 8A and 8B). For this, a deposit is typically made on the stacking structure 16, advantageously conformal, of dielectric material for example SiN, SiO2 or HfO2, according to a thickness chosen so as to fill the recesses 17.

[0133] This deposition is followed by at least one etching, typically a dry etching or a combination of dry etching and wet etching of the previously deposited dielectric, so as to remove this dielectric material and to keep it only in the form of the dielectric plugs 19 against, and masking the lateral flanks of the blocks 102, 104 based on the second material 14.

[0134] Grid patterns 25 are then formed from grid material 22 on either side of the structure 16.

[0135] For this, it is possible to first deposit at least one layer 21 of gate dielectric, for example silicon oxide (SiO2) or formed from a stack of silicon oxide and a high-k material such as for example HfO2. This deposition is followed by that of at least one layer of conductive gate material 22, such as doped polysilicon ([Fig.9]).

[0136] Preferably, after deposition and possible planarization by CMP (“Chemical mechanical polishing”) or chemical-mechanical polishing, a non-zero thickness e', for example of the order of 50 nm, of conductive material 22 is left to protrude above the active zone structure 16.

[0137] Hard masks 31, typically dielectric and for example formed from a stack of SiN and SiO2 are then produced ([Fig. 10]).

[0138] We then carry out ([Fig. 11] giving a sectional view along the first sectional plane parallel to the reference [0;y;°z]) a lithography and an etching of the grid stack to form a network of patterns 25 of parallel grids and of elongated shape. The patterns 25 may, for example, be in the form of parallelepiped blocks, and typically extend orthogonally to the bars of the structure 16.

[0139] The grid patterns 25 can be distributed according to a small pitch Pg, for example of the order of 100 nm, or even smaller, for example 40 nm, to form a dense network of patterns 25.

[0140] After the formation of the grid patterns 25, it is advantageous to form reservoirs of DTI, DT2 dopants (figures 12 to 14).

[0141] According to one method, a thin insulating spacer layer 33 is firstly deposited in a conformal manner on the gate patterns 25, for example made of silicon nitride and with a thickness which may be for example between 5 nm and 10 nm. The thin insulating spacer layer 33 is arranged on and between the gate patterns 25, for example by an ALD (Atomic Layer Deposition) type technique in order to fill the inter-gate pattern spaces without creating a filling defect.

[0142] Lithography is then carried out so as to remove portions of the thin insulating spacer layer 33 and extend this etching into parts of the active zone structure 16 located around another part 161 in line with all of the grid patterns 25 ([Fig. 12] giving a sectional view along a section plane parallel to the reference [0;y;°z]). To carry out this removal, an example method comprises the formation of a lithographic stack, for example a tri-layer formed of a SOC layer, an anti-reflective layer, a photosensitive resin, which is deposited and then exposed. The lithography stack protects the areas where the dielectric of the thin insulating spacer layer 33 must be preserved. A fluorocarbon type dry etch can be provided to remove the thin insulating SiN-based spacer layer 33 outside the protected areas.

[0143] To form the dopant reservoirs in contact with the ends of the semiconductor bars 102, 104 without bringing these reservoirs into contact with the other bars 101, 103, 105 of the structure, it is advantageous to carry out a partial selective etching of the first material 12 with respect to the second material 14 in order to remove end portions of the bars 102, 104 and to create recesses 41 ([Fig. 13]) at the ends of the structure 16.

[0144] For example, when the first material 12 is made of SiGe, this etching is carried out, for example, by wet chemical etching, or using HCl or a HF:H2O2:CH3COOH mixture. It is advantageous to provide a ratio close to or equal to 1:1 between the etched depth and the thickness of the etched layer. A withdrawal, for example, of at least 5 nm can be provided to produce these recesses 4L. The recesses 41 are then filled by insulating plugs 43, also called “internal spacers”. This can be achieved, for example, by means of a conformal deposition. of dielectric material, for example SiN or SiO2. This deposition is typically followed by dry etching or a combination of dry and wet etching of the deposited dielectric, so as to form insulating plugs 43 blocking access to the bars 101, 103, 105 based on the first material 12.

[0145] Once the insulating plugs 43 have been produced, selective epitaxy ([Fig. 14]) of semiconductor material 48 can be carried out from the exposed ends of the bars 102, 104, based on the second material 14. The epitaxy can provide in situ doping. For example, reservoirs of DTI, DT2 dopants in Si:P or in SiGe:B can be formed by epitaxy from the ends of the silicon bars 102, 104. The epitaxy formed may or may not follow preferential crystalline orientations, and the epitaxy fronts from the different Si layers can possibly join together as in the embodiment shown in [Fig. 13] to form semiconductor blocks or clusters.

[0146] An insulating encapsulation 52 is then produced around the gate patterns. The insulating encapsulation 52 can be produced for example by depositing a PMD (for “Pre Metal Dielectric”) type material such as for example SiO2 on the entire structure 16 followed by a CMP planarization step. This step is preferably carried out so that the polishing front stops at the top of the active zone structure 16. This makes it possible to reveal the material 22 of the gate patterns, typically made of conductive gate material such as polysilicon ([Fig. 15]).

[0147] The final structure intended to accommodate the quantum boxes is here provided in the form of suspended and superimposed semiconductor bars 102, 104, the bars 102, 104 being spaced from one another.

[0148] To do this, a release is then carried out (figures 16 and 17) in said structure of the semiconductor bars 102, 104 based on the second material 14 by removing the bars based on the first material 12 by selective etching with respect to the second material 14. Such a step is shown in figures 16 and 17. This release is typically accompanied by the removal of the dielectric plugs 19 arranged along the bars based on the second material 14. This release is advantageously implemented using several etching sub-steps, in particular selective wet etching.

[0149] Typically, a method is implemented in which, first of all, a layer-by-layer removal is carried out from the top of the structure 16. The upper layer 105 of first semiconductor material 12 is thus etched, then the sacrificial plugs 19 on either side of the layer 104 of second material 14, then the layer 103 of first semiconductor material 12, then the plugs 19 on either side of the layer 102 of second material 14, then the upper layer 101 of first semiconductor material 12.

[0150] Selective etching of SiGe relative to Si can be carried out, for example, using HCl or a HF:H2O2:CH3COOH mixture. As many etching sequences as there are stages of bars based on the first material 12 can be provided.

[0151] The release of the bars 102, 104 based on the second material leads to the formation of a space 55, in other words a cavity, which extends around and between the bars 102, 104 and is located between the grid patterns 25.

[0152] Then (figures 18 and 19), this space 55 is filled using at least one dielectric material 58, for example such as SiO2, or SiN, or HfO2, in order to form a dielectric region RD coating the bars 102, 104.

[0153] Typically, for this purpose, a conformal deposition of the dielectric material 58 is carried out, followed by a planarization step, for example by CMP.

[0154] In a case where the dielectric plugs 19 have been removed or partially etched previously during the step of releasing the semiconductor rods 102, 104 previously described, the dielectric material 58 acts as a gate dielectric or forms a thickness of gate dielectric in locations 551 located between the semiconductor rods 102, 104 and the gate patterns 25. A volume 552 separating the semiconductor rods 102, 104 and an area 553 around all of the rods 102, 104 are also filled.

[0155] The formation of superimposed grids is then completed. For this, a partial etching of the material 22 of the grid patterns is carried out ([Fig.20]). The partial removal of the grid material 22 is carried out so as to retain a lower block 24 of grid material and to produce cavities 64 surrounded by the encapsulation 52 and arranged above this lower block 24 of grid material. A dry etching or a chemical etching, in particular a wet etching using TMAH is in particular implemented when the material 22 is polySi.

[0156] The etching is carried out so as to control the height of the lower block 24 of gate material relative to that of the semiconductor layers of the active zone structure 16. Partial removal is implemented so that this block 24 intended to form lower gates GI is opposite only the lower semiconductor bar 102.

[0157] These cavities 64 are then filled ([Fig. 21]) with at least one layer of insulating material 66, for example SiO2. This deposition is optionally followed by planarization and etching ([Fig. 22]) to partially remove the deposited insulating material 66. The insulating material 66 is used to form an insulation zone ZI making it possible to insulate the lower stage gates GI from the upper stage gates GS. A new layer of conductive material, advantageously based on the same conductive material 22 as the lower gate GI, for example polysilicon, is then deposited so as to fill the cavities 64. A planarization is then typically carried out by CMP to thus form upper grids GS opposite the upper bar 104 ([Fig.23]).

[0158] In the example of the production method which has just been given, for the implementation of the superimposed grids GI, GS, lower grids GI are provided formed from the same material 22 as the upper grids GS. It is however possible, as a variant, to provide different materials between the lower grids GI on the one hand and the upper grids GS on the other hand.

[0159] Similarly, in the embodiment example which has just been given, the grids formed against the portion 16R of active zone dedicated for example to receiving the quantum boxes are based on the same material as those located against the portion 16L of active zone which faces it and which is dedicated for example to receiving the detection islands.

[0160] It is however possible as a variant to provide different materials between, on the one hand, the grids located against the portion 16R and, on the other hand, the grids located against the portion 16L. Such a variant can be carried out to obtain output work and consequently different operating regimes between, for example, grids controlling the quantum dots and grids controlling the detection islands. To carry out such a variant, it is possible to provide for adding one or more lithography steps and one or more additional deposition steps.

[0161] As a variant of the example of the production method which has just been given, the implementation of the superimposed grids GI, GS, which describes an approach of the type commonly called “gate-last” (with replacement grid) where at least partial replacement of grid patterns is carried out by a stack with grids separated from an isolation zone, it is possible to provide for directly producing grid patterns composed of this stack.

[0162] Thus, according to this variant of the gates, an approach of the type called "gate-first" can be provided. In this case, directly after the step of forming the active zone structure 16 described previously in connection with FIGS. 6A-6B, it is possible to provide for the production of a stack of layers to form the lower gate, the insulation zone, then the upper gate. The thicknesses of the conductive or semiconductive layers of gate material(s) and of the intercalated insulating layer are then preferably adjusted according to those of the layers of first material 12 and second material 14 of the structure 16 so that each layer of gate material is arranged opposite and in the same plane parallel to the main plane of the substrate as a layer based on the second semiconductor material 14 and in which quantum dots or detection islands are provided.

[0163] In either of the embodiments which have just been described, making contact on different grid levels as well as on different grid levels different semiconductor layers, can be achieved for example by providing, at the ends of the grid structures or portions of active zone, a staircase shape.

[0164] In the embodiment illustrated in [Fig.24], the so-called “intergrid” space(s) between neighboring or adjacent grids distributed along bars 102, 104 are filled with insulating material, here encapsulation 52.

[0165] Alternatively, it is possible to provide exchange electrodes in the inter-grid space(s).

[0166] For this, a method illustrated in Figures 25 to 27 consists of starting from a structure such as obtained at the end of the production of the grids. A masking 82 is then produced, typically in photosensitive resin, in an area located above the grid block assembly and which comprises openings 84 facing inter-grid spaces ([Fig.25]). The encapsulation insulating material 52, for example SiO2, located in the inter-grid spaces selectively relative to the thin spacer layer 33, for example in SiN, is then selectively etched in order to form holes 86. A fluorocarbon dry etching process can be used in particular.

[0167] After removal of the masking 82, a deposition of conductive material 89, for example a TiN / W type stack, is carried out to fill the holes 414 thus defined ([Fig.26]). This deposition is typically followed by a CMP planarization step. The planarization is preferably stopped when the top of the active zone structure is reached (not visible in FIGS. 26 and 27). In this exemplary embodiment, a single GE exchange electrode is produced per inter-grid space.

[0168] However, it is alternatively possible to form superimposed exchange grids which follow an arrangement similar to that of the grid electrodes between which these exchange grids are inter-calated. It is thus possible to form in each inter-grid space pairs of superimposed exchange grids separated from each other by an insulator. For this, it is possible to follow a method similar to that used to produce the grids and described previously in connection with Figures 11 to 20-22.

Claims

1. Claims Quantum electronic device provided with a substrate (5) and comprising on this substrate: - a set of superimposed semiconductor rods (102, 104) comprising at least one lower semiconductor rod (102) and at least one upper semiconductor rod (104), the lower semiconductor rod and the upper semiconductor rod (104) being arranged one above the other, - a first group of gates (GI1, GSI) comprising a first lower gate (GI1) and a first upper gate (GSI), the first upper gate (GSI) being superimposed on the first lower gate (GI1) and separated from the first lower gate by an insulation zone (ZI1), the first lower gate (GI1) being arranged opposite a first region (102A) of the lower semiconductor bar (102) and is capable of being coupled by capacitive coupling to the first region (102A), so as to form a first quantum dot (QD1) in the first region (102A) of the lower semiconductor bar (102), the first upper gate (GSI) being arranged opposite a first region (104A) of the upper semiconductor bar (104) and capable of being coupled by capacitive coupling to the first region (102A) so as to form a second quantum dot (QD2) in the first region (104A) of the upper semiconductor bar (104), - a second group of gates (GI2, GS2) comprising a second lower gate (GI2) and a second upper gate (GS2), the second upper gate (GS2) being superimposed on the second lower gate and separated from the second lower gate (GI2) by an insulation zone (ZI2), the first lower gate (GI2) being arranged opposite, and capable of being coupled by capacitive coupling to, a second region (102B) of the lower semiconductor bar (102) opposite the first region (102A) of the lower semiconductor bar, the second upper gate (GS2) being arranged opposite, and capable of being coupled by capacitive coupling to a second region (104B) of the upper semiconductor bar (104) opposite the first region (104A) of the upper semiconductor bar, said set of semi- conductors (102A, 104A) is arranged between the first group of grids (GI1, GSI) and the second group of grids (GI2, GS2).

2. Quantum electronic device according to claim 1, further comprising: - a third group of superimposed gates (GI3, GS3) juxtaposed with said first group of gates (GI1, GS1), the third group of gates (GI3, GS3) comprising at least a third upper gate (GS3) superimposed on a third lower gate (GI3), the third upper gate (GS3) being separated from the third lower gate by an insulation zone, the third lower gate (GI3) and the third upper gate (GS3) being arranged opposite, respectively, a third lower semiconductor region (102C) of the lower semiconductor rod (102) and a third upper semiconductor region (104C) of the upper semiconductor rod (104), - a fourth group of superimposed gates (GI4, GS4) juxtaposed with said second group of gates (GI2, GS2), the fourth group of gates (GI4,GS4) comprising a fourth upper gate (GS4) superimposed on a fourth lower gate (GI4), the fourth upper gate (GS4) being separated from the fourth lower gate by an insulation zone, the fourth lower gate (GI4) and the fourth upper gate (GS4) being arranged facing respectively a fourth lower semiconductor region (102D) of the lower semiconductor bar (102) and a fourth upper semiconductor region (104D) of the upper semiconductor bar (104).,

3. Device according to claim 2, further comprising, between said first group of grids (GI1, GSI) and said third group of grids (GI3, GS3): - at least one exchange electrode (GE) or - superimposed exchange electrodes (GE11, GE12) separated from each other by at least one insulating separation layer (CSI), or - an area of ​​at least one insulating material (52).

4. Device according to one of claims 1 to 3, further comprising: - a doped semiconductor block, forming a first charge reservoir (DTI), the doped semiconductor block being arranged at a first end of the upper semiconductor bar (104) and of the first lower semiconductor bar (102), - another doped semiconductor block, forming a second charge reservoir (DT2), the other doped semiconductor block being arranged at a second end of the upper semiconductor bar (104) and of the lower semiconductor bar (102).

5. Device according to one of claims 1 to 4, in which a dielectric region (RD) is arranged between the first group of gates (GI1, GSI), and the second group of gates (GI2, GS2) and encapsulates the set of superimposed semiconductor bars (102, 104).

6. Device according to one of claims 1 to 5, in which the lower (GI2) and upper (GS2) grids of said second group of grids and / or of the first group (GI1, GSI) are coupled or capable of being coupled to a circuit (350) for measuring by reflectometry, said circuit (350) being in particular configured to: - emit an RF signal to the second lower grid or the second upper grid; - detect a variation in impedance following the reception of a signal reflected by said second semiconductor region of the lower semiconductor bar or by said second upper semiconductor region of the semiconductor bar following the emission of said RF signal.

7. Device according to one of claims 1 to 6, • wherein the lower semiconductor bar and the upper semiconductor bar have a width W1 less than a predetermined width, the second lower gate (GI2) and the second upper gate (GS2) being configured to control respectively, the chemical potential of the first quantum box (QD1) and the chemical potential of the second quantum box (QD2) or, • wherein the lower semiconductor bar and the upper semiconductor bar have a width W1 greater than a predetermined width, the second lower gate (GI2) and the second upper gate (GS2) being configured to control respectively, the chemical potential of a third quantum box (QD3) formed in said second region of the lower bar, the chemical potential of a fourth quantum dot (QD4) formed in said second region of the upper bar.

8. Device according to one of claims 1 to 7, in which the grids of said groups of grids (GI1, GI2) extend orthogonally to said superimposed semiconductor bars (102, 104) and are arranged against lateral zones of the bars (102, 104) and in which in a plane orthogonal to a main plane of the substrate and passing through said superimposed semiconductor bars (102, 104), the device does not comprise a bar control electrode.

9. Method for manufacturing a quantum device according to one of the preceding claims, comprising steps of: - producing on said substrate (10) a structure (16) formed from a stack of semiconductor rods comprising an alternation of rods (101, 103, 105) based on a first material (12), and rods (102, 104) based on a second material, the second material being semiconductor, then, - forming grid patterns (25) on either side of said structure (16), then, - selective removal of the rods (101, 103, 105) based on the first material (12).

10. Method according to claim 9, wherein the selective removal of the bars (102, 104) based on the first material (12) leads to freeing a space (55) between said grid patterns (25) and around the bars (102, 104) based on the second material (14), the method further comprising: a step of filling said space (55) using at least one dielectric material (58).

11. Method according to one of claims 10, further comprising, prior to the formation of the grid patterns (25) on either side of said structure (16), steps of: - partial etching of the bars (102, 104) based on the second material (14) by selective etching relative to the first material (12) so as to form recesses (17) on either side of lateral flanks of said structure (16), then - formation of dielectric plugs (19) in said recesses (17).

12. Method according to one of claims 9 to 11, further comprising, after formation of said structure (16) and prior to the selective removal of the bars (101, 103, 105) based on the first material (12), a formation of charge reservoirs (DTI, DT2) at ends of said structure (16), the formation of the charge reservoirs (DTI, DT2) comprising: - carrying out a partial selective etching of the first material (12) with respect to the second material (14) in order to create recesses (41) at the level of said ends of said stacking structure (16), - filling said recesses (41) with an insulating material in order to form insulating plugs (43) in said recesses, - carrying out an epitaxy of semiconductor material (48) from exposed ends of the bars (102, 104) based on the second material (14), while the bars (101, 103, 105) based on the first material (12) are protected by the insulating plugs (43).

13. Method according to one of claims 9 to 12, in which the grid patterns on either side of said structure are formed from a grid material (22), the method further comprising, after selective removal of the bars (101, 103, 105) based on the first material (12), steps of: - forming an insulating encapsulation (52) between and around the grid patterns (25), - partially removing said grid material (22) so as to retain a lower block (GI) of grid material and freeing cavities (64) above this lower block of grid material and surrounded by the encapsulation (52), - filling the cavities (64) with at least one insulating layer so as to form an insulation zone (ZI) on the lower block (GI) of grid material (22) then, - filling the cavities (64) with at least one layer of grid material, so as to form an upper block (GS) of grid material on the insulation zone (ZI).

14. The method of claim 13, wherein after forming the gate patterns (25) and before forming the encapsulation, the method further comprising steps of: - forming an insulating spacer distributed conformally over the gate patterns (25) and between the gate patterns (25) and arranged over a central area of ​​said stacking structure. 26

15. Method according to one of claims 13 or 14, further comprising steps of: - removing the insulating encapsulation (52) between the grid patterns or between the grid blocks, so as to free one or more spaces, - forming exchange grids in the space(s).

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