Electro-optical device and method for producing electro-optical device

Abstract

The invention relates to a device (1) comprising a silicon-based substrate (10) stacked in a vertical direction (z); a nucleation layer (20) made of a nitride-based refractory material; a lithium niobate based portion (30) made in a mesa on the nucleation layer (20), referred to as an LNO portion bounded by a mask layer. The device (1) further comprises at least one electrode (51, 51b, 52) for applying an electric field to the LNO portion (30). The invention also relates to a method for producing such a device, comprising forming an LNO portion by local epitaxy. The method has optimized cost and / or compatibility compared to existing methods.

Description

Technical Field

[0001] The invention relates generally to an electro-optical component and to a method for producing a layer based on a material having the Pockels effect forming the core of the component. The invention relates more particularly to the production of an optical phase modulator. Background Art

[0002] These phase modulators can be used advantageously in "optical phased array" (OPA) type circuits, for example in the design of laser remote detection systems, called LIDAR (laser imaging detection and ranging) systems.

[0003] The principle of an optical phase modulator is usually based on the local modulation of the refractive index of the material in which the light wave propagates. For certain crystalline materials that do not have axial symmetry, this refractive index change can be advantageously obtained via the Pockels effect.

[0004] This is especially true of lithium niobate (LiNbO3) and tantalum niobate (LiTaO3). Their inherent properties make it possible in particular to consider the production of modulators operating at high frequencies, low optical losses (typically of the order of a few decibels at π phase shift) and low energy consumption. However, the synthesis of thin layers of these materials is complex and the requirements associated with their crystal quality are high. The thin layer of LiNbO3 or LiTaO3 must in particular have a high crystal quality and a controlled stoichiometry. It must also have a controlled crystal orientation depending on the architecture and position of the electrodes of the electro-optical element to be produced. Below, for the sake of brevity, only LiNbO3 is mentioned as an example. The properties of LiTaO3 and Li(Nb, Ta)O3 alloys are very close to those of LiNbO3. It will be appreciated that LiTaO3 or Li(Nb, Ta)O3 can directly replace LiNbO3.

[0005] Solutions have been developed that enable the synthesis of LiNbO3 in thin layers on sapphire substrates. This type of substrate is expensive and the applications associated with these solutions are still limited. The production of thin LiNbO3 layers on silicon-based substrates is a considerable challenge. This would enable consideration of a new generation of multifunctional systems including electro-optical, acoustic, microelectronic and / or quantum devices synergistically integrated on the same substrate. One solution consists in transferring a thin LiNbO3 layer from a donor substrate, typically a single-crystalline LiNbO3 substrate, to a receiver substrate, typically a silicon substrate with a surface oxide layer. This solution, which implements many technological steps, has a high cost. The achievable thin layer thickness range, which is typically greater than 200 nm and less than 1 μm, is also limited by the stresses of the transfer and thinning techniques. The thickness uniformity of the thin layers obtained by transfer is usually not sufficient for the target application. The standard deviation of the thickness of a 200 nm thin LiNbO3 layer obtained by transfer typically reaches about 50 nm. This type of transfer is further performed in a "solid plate" manner over the entire surface of the receiver substrate. Therefore, it is necessary to etch the transferred LiNbO3 layer in order to obtain a LiNbO3 layer portion locally on the receiver substrate. The etching of LiNbO3 is complex to control, especially to obtain a roughness compatible with optical applications. Problems may arise with lithium contamination of the production line during etching. It is also necessary to manage mechanical stresses related to the thermal expansion difference between silicon and LiNbO3 during the solid plate transfer. Therefore, it is difficult and expensive to form a localized LiNbO3 portion on the receiver substrate.

[0006] Therefore, there is a need to locally produce lithium niobate-based layers on silicon-based substrates, the crystal quality of which can meet the requirements of the target application while limiting the production costs. Summary of the invention

[0007] It is an object of the present invention to at least partially meet this need.

[0008] In particular, the object of the present invention is to propose a method for locally forming a lithium niobate layer portion on a silicon substrate, which method has optimized cost and / or compatibility compared to existing methods. Such a method is advantageously implemented to produce a device comprising a lithium niobate layer portion.

[0009] Another object of the present invention is to propose a device, typically an electro-optical device of the phase modulator type, comprising a lithium niobate layer portion.

[0010] Other objects, features and advantages of the present invention will become apparent upon studying the following description and accompanying drawings.It will be appreciated that other advantages may be included.

[0011] To achieve this goal, according to one embodiment, a method for producing a device is provided, the device including a lithium niobate or lithium tantalate layer portion, the method comprising the following steps:

[0012] -Providing a silicon-based substrate;

[0013] - forming a nucleation layer made of a nitride-based refractory material on a substrate;

[0014] - forming a mask layer on the nucleation layer, the mask layer comprising at least one opening exposing a portion of the nucleation layer;

[0015] - forming a lithium niobate-based or lithium tantalate-based portion, referred to as LNO portion, by epitaxy on a terrace on an exposed portion of the nucleation layer in at least one opening;

[0016] - Preferably two electrodes are formed, the two electrodes being configured to apply an electric field to the LNO portion.

[0017] Within the scope of the development of the present invention, the specifications of the nucleation layer have been established. The nucleation layer must preferably have the following properties:

[0018] - have a crystal structure and / or lattice parameters that are compatible with silicon-based substrates. This enables, in particular, epitaxial growth of a nucleation layer on the substrate.

[0019] -Having a crystal structure and / or lattice parameters close to or compatible with lithium niobate. This enables epitaxial growth of the LNO portion on the nucleation layer.

[0020] - preferably has a coefficient of thermal expansion close to that of lithium niobate. This makes it possible to limit the appearance of cracks caused by temperature variations during the formation of the LNO portion.

[0021] - Capable of preventing the diffusion of Li atoms, especially in Si or SiO2. This makes it possible to avoid stoichiometric losses of the LNO fraction.

[0022] One technical deviation from the prior art is that such a nucleation layer must necessarily be oxide-based in order to avoid stoichiometric losses of the LNO portion due to diffusion of oxygen from the LNO portion into the nucleation layer.

[0023] On the contrary, in order to meet these specifications, a nucleation layer made of a nitride-based refractory material is selected according to the present invention. For the sake of simplicity, this nucleation layer made of a nitride-based refractory material will be referred to as a refractory nitride-based nucleation layer below. Within the scope of the development of the present invention, it has indeed been observed that this refractory nitride-based nucleation layer enables the epitaxy of the LNO part completely unexpectedly under good conditions. Surprisingly, it has also been observed that this nucleation layer enables the diffusion of oxygen and lithium to the silicon-based substrate to be prevented. This allows the LNO part epitaxially grown on this nucleation layer to maintain the required stoichiometry.

[0024] In addition, the different crystal structures and lattice parameters of refractory nitrides (usually III-N nitrides) are fully compatible with those of lithium niobate and silicon. Therefore, this nucleation layer can be advantageously grown epitaxially on a silicon-based substrate, and then the epitaxy of the LNO part is achieved.

[0025] According to the invention, the epitaxy of LNO is carried out in a localized manner in at least one opening of the mask layer. This makes it possible to obtain only portions of the LNO layer. This makes it possible to limit the mechanical stresses caused by the difference in thermal expansion coefficients between lithium niobate and the nitride-based refractory material. The LNO portions are subjected to less mechanical stress than a "solid plate" layer of lithium niobate. After formation by epitaxy, the crystal quality of the LNO portions and their electro-optical properties are optimally preserved. Local growth also makes it possible to limit the presence of lithium niobate on the entire plate. This avoids etching of the lithium niobate, which is complicated to implement for LNO portions to obtain optical quality.

[0026] Epitaxy of LNO also enables better control of the thickness of the LNO portion. In particular, low thicknesses, for example less than or equal to 200 nm, can be obtained by epitaxy with good control of the thickness of the entire substrate. Layer transfer techniques cannot obtain such thicknesses over the entire substrate and / or cannot obtain such thicknesses with sufficient accuracy and reproducibility. The standard deviation of the thickness of a thin LNO layer of 200 nm obtained by transfer can reach about 50 nm. Such a thickness variation over the entire substrate is not consistent with optoelectronic target applications. In contrast, epitaxy of LNO advantageously enables a standard deviation of thickness less than 10 nm to be obtained for a 200 nm thick layer.

[0027] The present invention therefore proposes a solution that enables the synthesis of thin LNO layer portions directly on a silicon-based substrate by means of a refractory nitride-based nucleation layer, i.e. without a transfer step. Thanks to the refractory nitride-based nucleation layer, the LNO portion is stoichiometric and has a high crystalline quality. This method can also be directly integrated in production plants with CMOS technology standards (based on n-type and p-type complementary metal oxide semiconductor transistors).

[0028] According to another aspect of the present invention, a device is provided, which includes a silicon-based substrate stacked in a vertical direction z, a nucleation layer on the substrate, and a lithium niobate-based or lithium tantalate-based portion (referred to as an LNO portion) made in a table on the nucleation layer. The LNO portion borders a mask layer. The device also includes two electrodes configured to apply an electric field to the LNO portion.

[0029] Advantageously, the nucleation layer of the device is made of a nitride-based refractory material. The advantages described above apply mutatis mutandis. Such a device is further directly integrable in silicon technology. For example, it can be easily co-integrated with other microelectronic, optoelectronic or quantum devices. Preferably, the device is a phase modulator type electro-optical device. One aspect of the invention relates to a system comprising a plurality of devices on the same silicon-based substrate, each device comprising an LNO part according to the invention, for example, at least one electro-optical device and an electronic component, such as a superconductor detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The objects, goals, features and advantages of the present invention will best appear from the detailed description of embodiments of the present invention, which are illustrated by the following drawings, in which:

[0031] Figures 1 to 12 The steps of a method for producing a device according to one embodiment of the invention are shown in cross section.

[0032] Fig.13 The top view shows the Fig.12 Device of the embodiment shown.

[0033] Fig.14 A simulated distribution of the intensity of light propagating in a device according to an embodiment of the present invention is shown in cross section.

[0034] Fig.15 A variant of a device according to an embodiment of the invention is shown in cross section.

[0035] Fig.16 A further variant of a device according to an embodiment of the invention is shown in cross section.

[0036] Fig.17 A system according to one embodiment of the present invention is shown in cross section, the system comprising a co-integrated electro-optical device and a quantum device.

[0037] The accompanying drawings are provided as examples and do not limit the present invention. They constitute schematic diagrams intended to facilitate understanding of the principles of the present invention and are not necessarily in scale with actual applications. In particular, the thickness of different layers and parts and the size of patterns on the schematic diagrams do not represent actual conditions. DETAILED DESCRIPTION

[0038] Before starting to describe the embodiments of the present invention in detail, optional features will be described below, which can be optionally used in combination or alternatively:

[0039] According to one example, the LNO portion is lithium niobate LiNbO3 based. According to one example, the LNO portion is lithium tantalate LiTaO3 based. According to one example, the LNO portion is based on a Li(Nb, Ta)O3 alloy.

[0040] According to one example, the nitride refractory material of the nucleation layer is selected to have or form:

[0041] - Antioxidant properties,

[0042] -Hinders the diffusion of lithium.

[0043] This makes it possible to avoid diffusion of oxygen and lithium from the LNO portion to the nucleation layer. Therefore, the stoichiometry of the LNO portion is preserved.

[0044] According to one example, the nitride-based refractory material of the nucleation layer is selected to have a crystal structure compatible with the substrate and the LNO portion, for example a hexagonal structure. This makes it possible to limit the appearance of structural defects during the formation of the LNO portion by epitaxy. According to one example, the lattice parameter difference between the nitride-based refractory material and the LNO material is less than 2%. The lattice parameter difference can be determined in a subarray of a normal unit cell of the LNO material. For example, in the case of LiNbO3, the lattice parameter of the normal unit cell is However, in the plane (0001), the lattice parameters can be determined to be According to one example, if the nitride-based refractory material is a hexagonal or small unit cell array having a lattice parameter of For AlN, the lattice parameter difference between the LiNbO3 small unit cell and AlN is about 1.8%. Surprisingly, LiNbO3 epitaxy can therefore be performed on AlN. In order to align the AlN hexagonal array and the LiNbO3 small unit cell, a distortion of about 30° usually occurs between the LiNbO3 and AlN arrays in the plane (0001).

[0045] According to one example, the nitride-based refractory material is taken from III-N refractory nitrides based on group III elements, such as gallium nitride GaN, aluminum nitride AlN, and AlGaN alloys.

[0046] According to one example, the substrate is silicon-based, which is (111) oriented, the nucleation layer is aluminum nitride AlN-based, which is (0001) oriented, and the LNO portion is (0001) oriented.

[0047] According to one example, the LNO portion is in direct contact with the nucleation layer. In particular, there is no oxide interlayer between the nucleation layer and the LNO portion.

[0048] According to one example, the LNO portion is encapsulated by an aluminum-based encapsulation portion, such as aluminum nitride AlN-based or sapphire Al2O3-based. The aluminum-based encapsulation portion usually forms an encapsulation of the LNO portion together with a nucleation layer. This makes it possible to avoid diffusion of oxygen and / or lithium from the LNO portion to the upper layer. Therefore, the stoichiometry of the LNO portion is preserved. Compatibility with CMOS technology is preserved. The electro-optical properties of the LNO portion are preserved or even improved.

[0049] According to one example, a so-called upper electrode of the two electrodes is arranged above the LNO portion and a so-called lower electrode of the two electrodes is arranged below the LNO portion. This device structure is particularly suitable for oriented LNO portions (0001), the so-called "Z-cut".

[0050] According to one example, the device is configured to form an electro-optical device, such as an optical phase modulator. In particular, the phase modulation of the light wave propagating in the device is performed by applying an electric field to the LNO portion through the Pockels effect. The application of the electric field will cause a change in the refractive index of the LNO portion and a phase shift of the light wave.

[0051] According to one example, the LNO portion is clad by a silicon nitride SiN-based waveguide pattern configured to form a ridge waveguide together with the LNO portion.

[0052] According to one example, the LNO portion is coated by a niobium nitride NbN based structure, and the device forms a superconductor detector.

[0053] According to an example, the LNO portion has a thickness e3 between 50 nm and 500 nm, for example about 100 nm or 200 nm.

[0054] According to one example, the method further comprises: after the epitaxy of the LNO portion, at least partially removing the mask layer by retaining the LNO portion formed locally in at least one opening. This generally enables the deposition of LNO material on the mask layer to be removed outside the opening. This eliminates possible sources of contamination of other devices of the board where the device is located, including the lithium niobate layer portion. This limits the influence of the difference in thermal expansion coefficient with the silicon substrate in subsequent manufacturing steps.

[0055] According to one example, the removing is performed by chemical mechanical polishing.

[0056] According to an example, the method further includes: after the epitaxy of the LNO portion, forming an aluminum-based encapsulation portion on the LNO portion by epitaxy, such as an aluminum nitride AlN-based or a sapphire-based or an aluminum oxide Al2O3-based encapsulation portion.

[0057] According to one example, the method further comprises: after the epitaxy of the LNO portion, forming a waveguide pattern, the waveguide pattern being configured to form a ridge waveguide together with the LNO portion. According to one example, the waveguide pattern is based on silicon nitride SiN, or also TiO2, ZrO2, or Ta2O5.

[0058] According to one example, the formation of the nucleation layer and the formation of the LNO portion are performed by pulsed laser deposition, preferably without ventilation between the two steps. This makes it possible to avoid exposure of the surface of the nucleation layer to air. The nucleation layer is not contaminated with water and / or hydrocarbons. The growth of the LNO portion is optimized and the overall performance is improved. According to one example, the formation of the LNO portion and the formation of the encapsulation portion are performed continuously in the same reactor by pulsed laser deposition, without ventilation between the formations. This makes it possible to avoid exposure of the surface of the LNO portion to air. The LNO portion is not contaminated with water and / or hydrocarbons. This makes it possible to avoid intermediate surface cleaning steps, shorten the overall duration of the method and limit costs. The overall performance is improved.

[0059] According to one example, the formation of the nucleation layer is configured such that it has a thickness e2 less than or equal to 200 nm, preferably less than or equal to 50 nm. This makes it possible to limit the occurrence of structural defects during the formation of the nucleation layer by epitaxy.

[0060] According to one example, the formation of the LNO portion is configured such that the LNO portion has a thickness e3 between 50 nm and 500 nm, for example about 200 nm, after epitaxy. Such a thickness e3 corresponds to a thin LNO layer. Such a thickness e3 cannot be obtained by transferring and thinning a layer from a donor substrate different from a receiver substrate with good thickness control over the entire substrate.

[0061] According to one example, the method comprises: forming an upper electrode on the LNO portion and forming a lower electrode below the LNO portion. This enables in particular the production of a phase modulator type electro-optical device of a "Z-cut" structure.

[0062] Unless inconsistent, it is understood that all optional features and / or variations described above can be combined to form embodiments that do not necessarily need to be shown or described. Such embodiments are obviously not excluded from the present invention. Features of one aspect of the present invention, such as devices or methods, can be applied to another aspect of the present invention after necessary modifications.

[0063] It is explicitly pointed out that within the scope of the present invention, the terms "on", "coating", "covering", "underlying", "opposite to" and their equivalents do not necessarily mean "in contact with". Thus, for example, the deposition of a first layer on a second layer does not necessarily mean that the two layers are in direct contact with each other, but rather means that the first layer at least partially covers the second layer by being in direct contact with the second layer or being separated from it by at least one other layer or at least one other element.

[0064] Furthermore, a layer may consist of multiple sub-layers of the same material or of different materials.

[0065] By substrate, stack, layer "based on" material M or "M-based" layer is meant a substrate, stack, layer comprising only the material A or such material A and optionally other materials, such as alloying elements and / or doping elements. Thus, a silicon-based substrate refers, for example, to Si or doped Si, or a SiGe substrate. An AlN-based layer refers, for example, to AlN, a doped AlN-based layer or an AlN alloy (e.g., AlGaN). A silicon nitride SiN-based waveguide may, for example, comprise non-stoichiometric silicon nitride (SixNy) or stoichiometric silicon nitride (Si3N4).

[0066] Several examples of sequential steps of implementing the manufacturing method of the present invention are described below. Unless explicitly mentioned, the adjective "sequential" does not necessarily mean that the steps follow each other, even though this is generally preferred, intermediate steps may separate them.

[0067] Furthermore, the term "step" refers to a part of performing a method and may refer to a group of sub-steps.

[0068] Furthermore, the term "step" does not necessarily mean that the actions performed in a step are simultaneous or immediately consecutive. In particular, some actions of a first step may be followed by actions linked to a different step, which may then resume other actions of the first step. Thus, the term "step" does not necessarily refer to a single action, but rather to actions that are inseparable over time and in the order of the stages of a method.

[0069] In the drawings, a preferred orthogonal system is shown, which includes x, y, and z axes. When a single system is shown on the same set of figures, the system applies to all figures in the set.

[0070] In the present patent application, the thickness of a layer is taken in a direction perpendicular to the main extension plane of the layer. Thus, the thickness of a layer is usually in the z-direction. The relative terms "on", "enclosing", "under", "underlying", "interposed", "above", "below" refer to positions taken in the z-direction. This list of terms is not exhaustive. If necessary, other relative terms can be easily specified by reference to the accompanying drawings.

[0071] The terms "vertical", "vertically" refer to directions along the z-axis. The terms "horizontal", "horizontally", "lateral", "laterally" refer to directions in the xy plane. Unless explicitly mentioned, thickness, height and depth are measured along the z-axis.

[0072] An element being “vertically aligned with” or “on the “right side” of another element means that both elements are located on the same line perpendicular to a plane in which the lower or upper surface of the substrate mainly extends, i.e., on the same line oriented vertically in the figure.

[0073] Within the scope of the present invention, III-N nitrides are nitrides of elements which preferably belong to column IIIa (three valence electrons) of the periodic table. This column IIIa groups together earth elements such as boron, aluminum, gallium, indium, etc. The III-N nitrides considered in the present invention include in particular boron nitride BN, aluminum nitride AlN, gallium nitride GaN, indium nitride InN and alloys thereof (for example and in a non-limiting manner, AlGaN, GaInN).

[0074] Within the scope of the present invention, the waveguide is intended to ensure the propagation of light waves in the main propagation direction intercepted along the x-axis in the accompanying drawings. The light wave is preferably coherent, monochromatic and has a wavelength of λ. It preferably propagates according to a single optical propagation mode, typically the fundamental optical mode. Therefore, the waveguide can be configured to guide a single transverse electric (TE00) or transverse magnetic (TM00) fundamental mode of the light wave. Alternatively, the waveguide can be locally configured to be able to convert the TM mode into the TE mode (and into each other) during propagation. In addition to the fundamental mode, it can also have multiple secondary modes. If only the fundamental mode can propagate there, the waveguide is called single-mode. If it accepts at least two modes, it is identified as multi-mode.

[0075] In the examples described below, the LNO portion shown is lithium niobate LiNbO3 based. It will be appreciated that in these examples, LiTaO3 or Li(Nb, Ta)O3 can directly replace LiNbO3. The LNO portion protrudes from a nucleation layer located at the bottom. Relative to the nucleation layer, the LNO portion is presented in the form of a table or pad. The LNO portion is a finite entity. For example, this is not an abstract and arbitrary cut of a wider layer covering the entire board. The LNO portion is defined in particular by the cross-section of the opening of the mask layer.

[0076] X-ray diffraction analysis can be performed, for example in the configuration 2θ, or around and / or Ω rotations (phi scan and omega scan) to determine the crystal quality of the LNO layer and the nucleation and / or encapsulation layers and their epitaxial relationship.

[0077] Figures 1 to 12A first embodiment of an electro-optical device 1 according to the invention is shown.

[0078] like Figure 1 As shown, a substrate 10 is first provided. The substrate 10 may be a SOI (silicon on insulator) type substrate. Such a substrate 10 generally includes, in a stacked manner along the Z axis: a support layer 11, generally a so-called silicon "bulk" substrate), an insulating layer 12, generally a so-called "BOX" buried oxide layer, and a silicon-based semiconducting layer 13, such as a so-called topSi silicon layer. The insulating layer 12 generally has a thickness of about 2 μm. 12 The topSi layer 13 generally has a thickness of about 5 nm to 20 nm. 13 Preferably, the topSi layer 13 is made of silicon oriented along a (111) orientation. For example, depending on the desired structure of the device, other crystal orientations are possible for the silicon layer 13, in particular (001).

[0079] like Figure 2 As shown, the topSi layer 13 can be locally doped once or several times in order to locally have a silicon portion 13p having a doping difference with the rest of the layer 13. According to one example, all layers 13 are p-doped by implantation, then the layer 13 is masked at the portion 13p and a new doping is performed by implantation. Thus, a p+ doped layer 13+ and a p-doped portion 13p can be obtained. The p-doped portion 13p can form the lower electrode of an electro-optical device. Within the scope of optical applications, for example in order to form a phase modulator, it is generally preferred to adopt p-type doping in order to limit the optical losses in the device. For example, during a subsequent re-contact, a portion of the p+ doped layer 13+ can be configured to be in electrical contact with the portion 13p.

[0080] like Figure 3 As shown, a nucleation layer 20 is formed on the topSi layer 13 including the p-doped portion 13p. The nucleation layer 20 is preferably a III-N material base. It preferably has a hexagonal crystal structure. Such a III-N material structure can particularly realize the epitaxy of the nucleation layer 20 on silicon along the (001) and / or (111) orientation. This also enables the subsequent epitaxial growth of LNO material with different crystal orientations.

[0081] The nucleation layer 20 is, for example, based on aluminum nitride AlN. AlN can be deposited and / or epitaxially grown on silicon along a (111) orientation, and its deposition method is advantageously known and controlled. Aluminum nitride also has a lattice parameter close to that of lithium niobate. This is conducive to the epitaxial growth of lithium niobate to subsequently form the LNO portion. The thermal expansion coefficient of AlN is further between the thermal expansion coefficient of LiNbO3 and the thermal expansion coefficient of Si. This makes it possible to limit the occurrence of structural defects in the LNO portion during temperature changes associated with different deposition steps. AlN also has good oxidation resistance and good resistance to the LNO deposition method (tolerance to ionized material plasma and chemical precursors, enabling the synthesis of LNO materials). Boron nitride and gallium nitride have similar properties to the above-mentioned aluminum nitride. They can also be advantageously selected for the nucleation layer 20.

[0082] The nucleation layer 20 can be formed by physical or chemical deposition techniques, for example by pulsed laser deposition (PLD). Alternatively, it can also be formed by one of the following techniques: chemical vapor deposition (CVD), preferably metal organic chemical vapor deposition (MOCVD), PVD sputtering, plasma enhanced atomic layer deposition (PEALD).

[0083] The nucleation layer 20 is preferably monocrystalline. It has a preferred orientation. For the AlN nucleation layer 20 epitaxially grown on the topSi layer 13 (111) of silicon, the orientation can usually be selected along the growth plane (0001). The nucleation layer 20 is preferably stoichiometric. It has a thickness e2 of typically between 5nm and 20nm, for example about 10nm.

[0084] The use of a refractory nitride, in particular an AlN nucleation layer 20, advantageously enables heteroepitaxial growth of LiNbO3 on a silicon-based substrate 10. Epitaxy in particular enables obtaining a stoichiometric LiNbO3 layer which is preferably oriented and has a high crystalline quality. The thickness of the LiNbO3 layer obtained by epitaxy is further fully controlled. The LiNbO3 layer can be formed directly on substrates 10 of different sizes without an intermediate transfer step. This advantageously enables a reduction in the manufacturing costs of the LNO / AlN / Si layer stack.

[0085] like Figure 4 As shown, a mask layer 300 is then formed on the nucleation layer 20 and then structured. The mask layer 300 may generally include different layers 301, 302, 303 along the Z stack, for example, a SiO2-based layer 301, a SiN-based layer 302, and a SiO2-based layer 303. The SiN-based layer 302 inserted in the mask layer may generally be used as a stop layer, for example, in a subsequent chemical mechanical polishing (CMP) step. The SiO2-based layer 301 generally has a thickness of about 100 nm to 500 nm. 301The SiN-based layer 302 generally has a thickness of about 5 nm to 50 nm. 302 The SiO2-based layer 303 generally has a thickness of about 100 nm to 500 nm. 303 The thickness of layer 303 is 303 Preferably it is larger than the thickness provided for the LNO portion, for example twice as large.

[0086] The mask layer 300 is structured in a standard manner, for example by photolithography and etching, in order to form one or more openings 3a leading to the nucleation layer 20. The openings 3a typically have a lateral dimension I3 of a few micrometers, for example between 1 μm and 100 μm.

[0087] like Figure 5 As shown, a lithium niobate LiNbO3-based portion 30 (LNO) is then formed in the opening 3a on the exposed portion of the nucleation layer 20. The LNO portion 30 can be formed by a physical or chemical deposition technique, such as pulsed laser deposition PLD. It can alternatively be formed by one of the following techniques: chemical vapor deposition (CVD), preferably metal organic chemical vapor deposition (MOCVD), PVD sputtering, molecular beam epitaxy (MBE).

[0088] The LNO portion 30 is advantageously epitaxially grown on the nucleation layer 20. It is preferably single crystalline. It has a preferred orientation. An orientation along the growth plane (0001) can usually be chosen. This enables the Pockels effect within the LNO portion 30 to be maximized, with electrodes being placed below and above the LNO portion 30 along Z, respectively. Other orientations can be chosen depending on the desired device architecture and / or desired application.

[0089] The LNO portion 30 formed on the nucleation layer 20 is preferably stoichiometric, such as Li1Nb1O3. The atomic percentage of lithium is ideally close to the atomic percentage of niobium. According to one example, the atomic percentage of lithium and niobium is about 20%. The LNO portion 30 has a thickness e3 between 50nm and 500nm, for example, about 200nm. The thickness e3 of the LNO portion 30 can be selected according to the desired application.

[0090] After forming the LNO portion 30 in the opening 3a, an encapsulation portion 31, typically AlN based, is preferably formed by epitaxy on the LNO portion 30. The portion 31 has a thickness e of typically between 5 nm and 20 nm, for example about 10 nm. 31 The sum of the thicknesses of the portions 30, 31 is generally less than the thickness of the layer 301 located below the layer 302. 301 Thus, layer 302 remains above portions 30, 31 along z. This enables the use of layer 302 as a layer for detecting the end of polishing during subsequent CMP polishing.

[0091] Optionally, both the encapsulation part 31 and the LNO part 31 are produced in situ by PLD in the same growth reactor. Therefore, the growth of the encapsulation part 31 can be produced directly after the growth of the LNO part 30 is finished. This makes it possible to avoid ventilation of the LNO part 30 before the epitaxy of the encapsulation part 31. Therefore, the surface of the LNO part 30 remains clean. This avoids intermediate cleaning steps. The duration of the method is thus shortened. This also makes it possible to limit the occurrence of roughness during the formation of the encapsulation part 31. The surface state of the encapsulation part 31 is thus optimized.

[0092] Growth residues 30 r and 31 r may be deposited at the periphery of the opening 3 on the mask layer 300 during the epitaxy of the portions 30 , 31 in the opening 3 a .

[0093] like Figure 6 As shown, the opening 3 may be filled with a dielectric filling material 32, typically SiO 2. This enables planarization of the structure.

[0094] like Figure 7 As shown, after filling, chemical mechanical polishing CMP is performed to remove the growth residues 30r, 31r. The SiN-based layer 302 is advantageously used as a stop layer or as a layer for detecting the end of polishing. Polishing is usually stopped in layer 301 just after layer 302 is removed. After the CMP process, the portions 30, 31 defined by the layer portion 301 and covered by the material filling portion 32 remain.

[0095] like Figure 8 As shown, after polishing, a new opening 3b is formed above the portions 30, 31 to expose the surface 310 of the package portion 31. The lateral dimension l3 of the new opening 3b is usually smaller than or substantially equal to the lateral dimension of the opening 3a. The new opening 3b is usually centered on the portions 30, 31. The opening 3b can be made in a standard manner by photolithography and etching.

[0096] like Fig. 9 As shown, according to a preferred embodiment, a SiO2-based spacer layer 41 is first formed on the encapsulation part 31, and then layer 40 is formed. In this case, layer 40 is intended to be structured in the form of a waveguide pattern to guide the propagation of light along x in the device. Depending on the target application, for example, according to the wavelength of the light to be guided, and according to the material used, the thickness e4 of layer 40 is generally about 100nm to 800nm. Layer 40 can be, for example, SiN-based, TiO2-based, ZrO2-based, Ta2O5-based. Alternatively, the layer 40 can be amorphous silicon Si-a-based. The spacer layer 41 can be conformally deposited in the opening 3b. It generally has a thickness e4 of about 200nm. 41The spacer layer 41 makes it possible to control the optical coupling between the waveguide pattern and the LNO portion. This makes it possible to specifically limit the optical coupling loss when passing between an area including only the waveguide pattern (excluding the LNO portion) and a mixed area including both the LNO portion and the waveguide pattern.

[0097] like Fig.10 As shown, the layer 40 is structured in a standard manner by photolithography and etching to form a waveguide pattern 4. The waveguide pattern 4 typically has a lateral dimension l4 between 200 nm and 2000 nm along y, and a height e4 between 100 nm and 800 nm along z. In the example shown, the waveguide pattern 4 is configured to guide light to propagate along the x-direction in the device. It is also possible to propagate along the y-direction, or more generally in the xy plane, according to the design of the waveguide pattern 4 when the orientation of the LNO portion is a Z-cut. The waveguide pattern 4 can form a ridge waveguide with the LNO portion 30 located at the bottom layer. This typically enables the propagation of the TM optical mode in a phase modulation device based on a Z-cut LNO portion.

[0098] like Fig.11 As shown, after the fabrication of the waveguide pattern 4, encapsulation by a dielectric material 33, typically SiO2, is performed on and around the waveguide pattern 4. A CMP planarization step may be performed after filling by the dielectric material 33 to obtain a flat surface 330.

[0099] like Fig.12 As shown, after planarization, interconnections 50v in the form of through holes can be made to electrically connect the p-doped silicon portion 13p forming the lower electrode 51 of the device 1. These interconnections 50v generally pass through the layer 301 and the nucleation layer 20 and have ends in contact with the p+ doped topSi layer 13+. A contact level can then be produced on the front side of the device 1. This level generally includes a contact 50 connected to the through hole 50v and an upper electrode 52 arranged above the LNO portion 30. In this way, an electro-optical device 1 is formed. Advantageously, the device 1 includes an LNO portion 30 oriented (0001) on an oriented (111) silicon substrate. The LNO portion 30 is generally inserted between two layers AlN 20, 31 (0001). The device 1 also includes a lower electrode 51 located below the LNO portion 30 and an upper electrode 52 located above the LNO portion 30. According to one option, the device 1 includes a ridge waveguide pattern 4 covering the LNO portion 30. The electro-optical device 1 advantageously enables the phase of a light wave propagating along x in a waveguide formed by the LNO portion 30 and the ridge waveguide pattern 4 to be modulated by the Pockels effect by applying an electric field between the lower electrode 51 and the upper electrode 52 .

[0100] Fig.13 A top view of the electro-optical device 1 is shown. Section AA corresponds to Fig.12 The design of the coplanar contacts 50 and electrodes 52 can be produced according to rules known to those skilled in the art to minimize light propagation losses.

[0101] Fig.14 There are simulation results showing the distribution of light waves in the waveguide formed by the LNO portion 30 and the ridge waveguide 4 in the device 1. In this case, the light wave has a wavelength λ=1.55 μm. The thickness e of the topSi layer 13 is 13 =20nm. The thickness e2 of the AlN nucleation layer 20 is 20nm. The thickness e3 of the LNO portion 30 is 300nm. The thickness e4 of the AlN encapsulation layer 40 is 20nm. The height e4 of the waveguide pattern 4 is 200nm and the width I4 is 1200nm. The actual refractive index of the waveguide thus formed is 2.35. In this case, the coverage of the light wave on the LNO portion is 50%. Therefore, in this device, the phase of the light wave can be effectively modulated by modulating the refractive index of the LNO portion 30 through the Pockels effect. Therefore, an optical phase modulator including a LNO portion on silicon is advantageously produced. The phase modulator can be integrated into a Mach-Zehnder structure on silicon.

[0102] Fig.15 A variant of the electro-optical device 1 is shown in which the waveguide is completely formed by the LNO portion 30 inserted between the encapsulation portion 31 and the nucleation layer 20, without further protruding waveguides. This type of waveguide typically has a height e between 100 nm and 500 nm. 3’ and a width I3 along y between 500 nm and 2000 nm. This type of waveguide requires fewer manufacturing steps and is cheaper to produce.

[0103] Fig.16 Another variant of the electro-optical device 1 is shown, in which the lower electrode 51b is formed on the back side of the device, below the doped silicon-based support layer 11. In this case, the topSi layer 13 is undoped. This reduces the optical losses of the device 1.

[0104] Other applications can also be considered. Local epitaxy of LNO on silicon can be advantageously used to co-integrate different devices with different functionalities.

[0105] Fig.17A system according to the invention is shown, which comprises an electro-optical device 1 as described above and a niobium nitride NbN-based superconductor detector 2 located on the same silicon-based substrate 10. It is thus possible to form a second LNO portion 30b by epitaxy in a second opening of the mask layer and then to form an NbN structure 6 epitaxially on the LNO or NbN / AlN / LNO. This makes it possible to consider the synergistic integration of different devices 1, 2, which are partially formed by the same growth located in different openings. The LNO portion advantageously enables the epitaxial growth of transition metal nitride-based superconductor materials, such as NbN or TiN, or NbTiN or others. The LNO portion generally forms a nucleation layer for these superconductor materials. Their lattice parameters are close and their thermal expansion coefficient differences are small. The formation of the different layers and portions can advantageously be done sequentially by epitaxy. The overall cost of the method for manufacturing a system comprising an electro-optical device 1 and a superconductor detector 2 is reduced.

[0106] As can be clearly seen from the above, the present invention advantageously enables the formation of localized portions of a thin LNO layer with good crystal quality on a silicon-based substrate comprising a nucleation layer made of a nitride-based refractory material, typically a III-N material base. These localized LNO portions are advantageously directly integrated in electro-optical or quantum devices. Other applications can be considered. The present invention is not limited to the embodiments described above.

Claims

1. A device (1), comprising a silicon-based substrate (10) stacked in a so-called vertical direction (z); a nucleation layer (20) located on the substrate (10), the nucleation layer (20) being made of a nitride-based refractory material; a lithium niobate or lithium tantalate-based portion (30) in a terrace on the nucleation layer (20), referred to as an LNO portion, the LNO portion being defined by a mask layer, the device (1) further comprising two electrodes (51, 51b, 52), the two electrodes (51, 51b, 52) being configured to apply an electric field to the LNO portion (30).

2. The device (1) according to the preceding claim, wherein The nitride-based refractory material is selected from III-N refractory nitrides based on group III elements, such as gallium nitride GaN, aluminum nitride AlN and AlGaN alloys.

3. A device (1) according to any one of the preceding claims, wherein: The substrate (10) is silicon-based and oriented in a (111) direction, the nucleation layer (20) is aluminum nitride (AlN)-based and oriented in a (0001) direction, and the LNO portion (30) is oriented in the (0001) direction.

4. A device (1) according to any one of the preceding claims, wherein: The LNO part (30) is coated by an aluminum-based encapsulation part (31), such as aluminum nitride AlN-based or sapphire Al2O3-based.

5. A device (1) according to any one of the preceding claims, wherein A so-called upper electrode (52) of the two electrodes is arranged above the LNO portion (30), and a so-called lower electrode (51, 51b) of the two electrodes is arranged below the LNO portion (30).

6. A device (1) according to any one of the preceding claims, configured to form an electro-optical device, such as an optical phase modulator.

7. A device (1) according to any one of the preceding claims, wherein: The LNO portion (30) is covered by a waveguide pattern (4), and the waveguide pattern (4) is configured to form a ridge waveguide with the LNO portion (30).

8. The device (1) according to any one of claims 1 to 5, wherein: The LNO portion (30) is encapsulated by a structure (6) made of a transition metal nitride-based superconductor material, such as niobium nitride NbN, titanium nitride TiN or a NbTiN alloy, and the device forms a superconductor detector (2).

9. A system comprising at least one electro-optical device (1) according to any one of claims 6 to 7 and electronic components, such as a superconductor detector (2) according to claim 8, on the same silicon-based substrate (10).

10. A method for producing a device (1) according to any one of claims 1 to 8, comprising the following steps: - providing a silicon-based substrate (10); - forming a nucleation layer (20) made of a nitride-based refractory material on the substrate (10); - forming a mask layer (300) on the nucleation layer (20), the mask layer (300) comprising at least one opening (3a) exposing a portion of the nucleation layer (20); - forming by epitaxy a lithium niobate or lithium tantalate based portion (30), referred to as LNO portion, in the terrace on the exposed portion of the nucleation layer (20) in the at least one opening (3a); - forming two electrodes (51, 51b, 52), the two electrodes (51, 51b, 52) being configured to apply an electric field to the LNO portion (30).

11. The method according to the preceding claim, further comprising: After the epitaxy of the LNO portion (30), the mask layer (300) is at least partially removed while the LNO portion (30) locally formed in the at least one opening (3a) remains.

12. The method according to the preceding claim, wherein: The removal is performed by chemical mechanical polishing.

13. The method according to any one of claims 10 to 12, further comprising: After the epitaxy of the LNO portion (30), an aluminum-based encapsulation portion (31), such as an aluminum nitride AlN-based or a sapphire Al2O3-based, is formed on the LNO portion (30) by epitaxy.

14. The method according to any one of claims 10 to 13, further comprising: After the epitaxy of the LNO portion (30), a silicon nitride SiN-based waveguide pattern (4) is formed, wherein the silicon nitride SiN-based waveguide pattern (4) is configured to form a ridge waveguide together with the LNO portion (30).

15. The method according to any one of claims 10 to 14, wherein: The formation of the nucleation layer (20) and the formation of the LNO portion (30) are performed by pulsed laser deposition.

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