Photonic device comprising a layer of components arranged on a support substrate and method for preparing such a photonic device

Abstract

The invention relates to a photonic device (DP) comprising a hybrid waveguide capable of propagating an optical mode. The device comprises a layer of components (2) arranged via a first surface on a support substrate (1e) and comprising at least one ridge waveguide (2a) formed by a base flush with a second surface of the layer of components (2) and at least one ridge oriented toward the support substrate (1e). A dielectric layer (1b) is arranged on and in contact with the second surface of the layer of components (2). It is arranged so as to cover a peripheral contour (Zb) of the base of the ridge waveguide (2a) without extending over its central portion. A heterogeneous structure (4) is arranged in the central portion (Zc) of the base of the waveguide (2a). The heterogeneous structure (4) and the ridge waveguide (2a) together form the hybrid waveguide.

Description

Photonic device comprising a component layer arranged on a support substrate and method for preparing such a photonic device FIELD OF THE INVENTION

[0001] The present invention relates to a photonic device comprising a component layer disposed on a support substrate. It also relates to a method for preparing such a photonic device, the method comprising transferring the component layer onto the support substrate. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Photonic devices propagating an optical mode in a hybrid waveguide formed by assembling a heterogeneous structure (for example a structure with III-V semiconductor materials) on a silicon waveguide to form a laser-type or optical amplifier-type device are known from the state of the art.

[0003] Liang et al.'s paper "Hybrid silicon evanescent approach to optical interconnects." AppliedPhysicsA 95 (2009), 1045-1057 proposes etching a surface layer of a silicon base substrate to form an edge waveguide and directly bonding the heterogeneous structure to the edge of this waveguide. Before their direct contact, the materials may include a very thin surface oxide forming an interface between the silicon waveguide and the heterogeneous structure. Since the optical index of silicon is higher than that of the material forming the laser structure (generally based on InP or GaAs), the optical mode is mainly located in the silicon part of the hybrid waveguide, which is favorable for its propagation in the optical device.

[0004] This process requires transferring the laser structure directly onto the silicon waveguide, but it does not allow for the integration of other components in the photonic device other than the hybrid waveguide. The formation of other components on the base substrate (for example, a germanium photodetector, a silicon nitride waveguide, or metal lines forming buried contact structures) would require burying the silicon waveguide under layers of materials, which would no longer allow direct contact between the laser structure and the silicon waveguide.

[0005] Furthermore, the step of etching the surface layer of the base substrate intended to form the edge waveguide can lead to degradation of the surface state, which can make the step of bonding the heterogeneous structure more delicate. This etching step is in fact preceded by the deposition of an etching mask (made of silicon nitride, oxide or a resin) on the surface layer on the surface intended to form the edge of the waveguide, and this deposition is likely to contaminate the covered surface.

[0006] Document US7482184 discloses a method for preparing a photonic device which comprises forming a layer of photonic components in a starting substrate of the SOI type. This starting substrate is therefore formed from a base substrate, a buried dielectric layer, arranged on and in contact with the base substrate, and a surface layer, which may be made of monocrystalline silicon, arranged on and in contact with the buried dielectric layer. The photonic components of the layer of photonic components comprise at least one waveguide formed in the surface layer of the starting substrate, on and in contact with the buried dielectric layer. But it is also possible to form on and in this surface layer other photonic components, such as silicon nitride waveguides, photodetectors, and metal lines.These photonic components are then encapsulated by a covering material, typically silicon oxide.

[0007] In a next step, this state-of-the-art method comprises transferring the layer of photonic components onto a support substrate and removing the base substrate.

[0008] In practice, this removal can be achieved by grinding the base substrate followed by chemical etching of the residual part, for example using a chemical solution of TMAH. The buried dielectric layer forms an etch barrier layer.

[0009] This leads, at the end of the base substrate removal step, to exposing the buried dielectric layer.

[0010] Then, this method involves assembling a heterogeneous structure (for example, a gain structure made of III-V semiconductor materials) on and in contact with the buried dielectric layer and in line with the waveguide. The buried dielectric layer must be thin enough to allow optical coupling between the heterogeneous structure and the waveguide.

[0011] With this integration process, the dielectric layer must be sufficiently thick, for example of the order of 100 nm or 50 nm, so that it is not penetrated when the surface layer is structured by etching during waveguide formation. With this process, it is therefore difficult to have a thin dielectric between the silicon waveguide and the heterogeneous structure bonded to the waveguide.

[0012] Document FR3084174 proposes a similar integration method, proposing to assemble a heterogeneous structure on and in contact with a dielectric layer.

[0013] Document US9507089 proposes a method for preparing a photonic device by layer transfer similar to that which has just been presented. The elimination of the base substrate is followed by the complete removal of the buried dielectric layer. This is made possible by providing, during the preparation of the layer of photonic components on the initial substrate, a protective layer of silicon nitride arranged on the parts of the dielectric layer which are no longer covered by the surface layer after the structuring by etching of the waveguide. After the transfer of the layer of photonic components on the support substrate, the elimination of the base substrate and the dielectric layer, the silicon nitride layer and a rear face of the waveguide are exposed. Then a new dielectric layer is reformed to cover the silicon nitride layer and the waveguide.

[0014] However, it is understood that this approach, requiring the presence of the silicon nitride protective layer, the removal of the buried dielectric layer from the initial substrate and the formation of a new dielectric layer, is particularly complex. SUBJECT OF THE INVENTION

[0015] An aim of the invention is to remedy, at least in part, the problems which have just been presented. More particularly, an aim of the invention is to propose a photonic device comprising a hybrid waveguide for propagating an optical mode and a method for preparing this device which is both simple to implement and less sensitive to the risk caused by damage to the buried dielectric layer while allowing good dielectric coupling between the laser structure and the waveguide. BRIEF DESCRIPTION OF THE INVENTION

[0016] With a view to achieving one of these aims, the subject of the invention proposes a photonic device comprising a hybrid waveguide capable of propagating an optical mode comprising:a component layer arranged by a first surface on a support substrate, the component layer comprising, in a covering material, at least one edge waveguide formed of a base flush with a second surface of the component layer, opposite the first surface, and at least one edge oriented towards the support substrate;a dielectric layer arranged on and in contact with the second surface of the component layer, the dielectric layer being arranged to cover a peripheral contour of the base of the edge waveguide without however extending with its entire thickness over a central part of the base of the edge waveguide;a heterogeneous structure on the central part of the waveguide base, the heterogeneous structure and the edge waveguide forming, in combination, the hybrid waveguide.;

[0017] According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically feasible combination: the heterogeneous structure is arranged on and in contact with the central part of the base of the waveguide; the photonic device comprises a dielectric bonding layer arranged on the central part of the base of the waveguide, the heterogeneous structure being arranged on and in contact with the dielectric bonding layer; the heterogeneous structure is a gain structure formed of a first contact layer, an active region formed of a stack of layers of III-V semiconductor materials arranged on and in contact with the first contact layer and a second contact layer arranged on and in contact with the active region, and the photonic device is an amplifier or a laser;the heterogeneous structure also comprises, arranged between and in contact with the base of the waveguide and the first contact layer, an interlayer formed of an undoped semiconductor material; the first contact layer and the second contact layer comprise electrical contact pads; the heterogeneous structure comprises at least one amorphous confinement zone; the heterogeneous structure comprises a material having electro-optical properties, such as LiNbO3, BTO, or a stack of III-V materials, and the photonic device is an electro-optical modulator; the photonic device comprises at least one cavity formed in the base of the waveguide, the cavity being covered by the heterogeneous structure; the cavity has a bottom formed of at least one etching stop pattern. The photonic device comprises an encapsulation layer arranged on the component layer and on the heterogeneous structure;the photonic device comprises metal tracks arranged on the encapsulation layer, in electrical contact with the heterogeneous structure; the component layer comprises at least one buried contact structure; the photonic device further comprises metal vias passing through the encapsulation layer, the dielectric layer and a portion of the component layer to contact the buried contact structure; the edge waveguide is made of silicon and the dielectric layer is made of silicon dioxide.;

[0018] According to another aspect, the invention proposes the subject of the invention proposes a method for preparing a photonic device comprising a hybrid waveguide capable of propagating an optical mode, the method comprising the following steps:providing a starting substrate comprising a base substrate, a buried dielectric layer arranged on and in contact with the base substrate and a surface layer arranged on and in contact with the buried dielectric layer;forming a component layer in the starting substrate, the component layer comprising at least one ridged waveguide formed of a base on and in contact with the buried dielectric layer and at least one ridge overhanging the base, the component layer comprising a covering material encapsulating the at least one ridged waveguide;transferring the component layer onto a support substrate (1e) and removing the base substrate to expose the buried dielectric layer;selectively removing at least a thickness of the dielectric layer at a central portion of the edge waveguide while preserving the dielectric layer on a peripheral contour of the waveguide; forming a heterogeneous structure on the central portion of the base of the edge waveguide.;

[0019] The heterogeneous structure may comprise a stack of III-V semiconductor materials or an electro-optical material. Selective removal of the dielectric layer may result in exposing the central portion of the ridged waveguide. The method may comprise preparing the exposed surface of the central portion of the ridged waveguide base with an oxygen plasma and / or by depositing a dielectric bonding layer prior to the step of forming the heterogeneous structure.

[0020] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0021]

[0022] Figures 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h represent steps of a preparation method according to the invention;

[0023]

[0024] Figures 2a, 2b, 2c, 2d, 2e, 2f, 2g represent steps of another preparation method according to the invention;

[0025] The represents a photonic device in accordance with the invention;

[0026] Figures 4a, 4b, 4c, 4d illustrate an alternative embodiment of a photonic device according to the invention;

[0027] Figures 5a, 5b illustrate another alternative embodiment of a photonic device according to the invention;

[0028] Figures 6a, 6b illustrate yet another alternative embodiment of a photonic device according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] Figures 1h, 2g, 3 and 4c illustrate DP photonic devices according to the invention and comprising a hybrid waveguide capable of propagating an optical mode.

[0030] This photonic device DP comprises a support substrate 1e and a component layer 2 arranged on the support substrate 1e. The component layer 2 has a first surface arranged on the side of the support substrate 1e, and a second surface opposite the first surface, and therefore further from the support substrate 1e than the first surface.

[0031] The component layer comprises, in a covering material 2e, at least one edge waveguide 2a. The edge waveguide 2a is formed of a base flush with the second surface of the photonic component layer 2 and at least one edge oriented towards the support substrate 1e. The edge aims to promote the confinement of the optical mode in the silicon part of the hybrid waveguide. The edge waveguide 2a is advantageously formed of monocrystalline silicon, without this forming an essential characteristic of the photonic device DP which forms the subject of the present description. It can be structured to allow the formation of the resonance of an optical mode.

[0032] A dielectric layer 1b is arranged on and in contact with the second surface of the component layer 2a. The dielectric layer 1b is arranged to cover a peripheral contour Zb of the base of the waveguide 2a without however extending over a central part Zc of this base. The dielectric layer 1b is typically formed of a silicon oxide and may have a thickness of between a few tens of nanometers and several thousands of nanometers.

[0033] A heterogeneous structure 4 is assembled to the central part Zc of the base of the waveguide 2a, and therefore arranged on and in contact with this waveguide 2a or with a dielectric bonding layer (). The heterogeneous structure 4 and the waveguide 2a form, in combination, the hybrid waveguide of the optical device DP in which an optical mode can propagate.

[0034] By "heterogeneous structure" is meant a material or a stack of materials having a nature different from the material which constitutes the edge waveguide 2a.

[0035] It may thus be a gain structure, as shown in Figures 1h, 2g and 4c, formed from a stack of layers of III-V materials, for example based on InP or based on AsGa as is well known per se. With such a gain structure, the photonic device DP may be a laser or an optical amplifier. This gain structure 4 may in particular comprise a first contact layer 4n, made of N-type semiconductor material, arranged on the waveguide 2a, a 4W active region (wells or quantum dots) formed from a stack of layers of III-V materials arranged on and in contact with the first contact layer 4n and a second contact layer 4p, made of P-type semiconductor material, arranged on and in contact with the 4W active region.

[0036] It is also possible to provide in the gain structure 4, arranged between the waveguide 2a and the first contact layer 4n, an interlayer formed of an undoped semiconductor material.

[0037] Whether such an interlayer is present or not, the gain structure 4 comprises electrical contact pads 5, respectively in contact with the first contact layer 4n and the second contact layer 4p.

[0038] In the DP photonic device, the heterogeneous structure 4 is formed from a block of material having electro-optical properties, such as LiNbO3, BTO or a stack of III-V materials. With such a heterogeneous structure, the DP photonic device can be an electro-optical modulator. In this case, the heterogeneous structure 4 is surmounted by electrical contact pads S, G, S. The edge waveguide 2a can have two edges, each edge constituting a modulator arm.

[0039] The photonic device DP may comprise an encapsulation layer 6 arranged on the layer of photonic components 2 and on the heterogeneous structure 4. This encapsulation layer 6 may in particular be made of silicon dioxide. Metal tracks 8 may be arranged on the encapsulation layer 6, in electrical contact with the heterogeneous structure 4, in particular with the electrical contact pads 5 if this structure is provided with them.

[0040] The photonic device DP may comprise other photonic components than the stop waveguide 2a. Thus, in the embodiment shown in the, the photonic component layer comprises a silicon nitride waveguide 2b, a photodetector 2c, at least one buried contact structure 7 in the covering layer 2e in the form of metal tracks or vias. Metal vias passing through the encapsulation layer 6, the dielectric layer 1b and a portion of the component layer 2 make it possible to contact the buried contact structure 7.

[0041] In the photonic device DP shown in the, at least one cavity 20 (two cavities 20 in the example shown) formed in the base of the edge waveguide 2a is provided, the cavity 20 being covered by the heterogeneous structure 4. In order to facilitate its manufacture, the cavity 20 has a bottom formed by a pattern 9 for stopping etching, for example a pattern 9 made of a silicide or a metal, such as metallic TiN. The cavity(ies) may facilitate the assembly of the heterogeneous structure 4 on the edge waveguide 2a to absorb the gaseous species which may form during this assembly step, in particular when it is carried out by molecular bonding.

[0042] With reference to Figures 1a to 1h, an embodiment of a method for preparing a DP photonic device according to the invention is now presented.

[0043] In a first step shown in the, a starting substrate 1 is provided. This substrate, for example of the silicon-on-insulator type, is formed from a base substrate 1a, typically made of silicon and having a thickness of several hundred microns. A buried dielectric layer 1b, typically made of silicon oxide, is arranged on and in contact with the base substrate 1a. This layer may have a thickness of between a few tens of nanometers and several thousand nanometers.

[0044] The starting substrate 1 also comprises a surface layer 1c, generally semiconducting, arranged on and in contact with the buried dielectric layer 1b. This layer 1c can in particular be formed of monocrystalline silicon and have a thickness of between 50nm and 1000nm.

[0045] It is noted that the buried dielectric layer 1b, in particular when it is formed of silicon oxide, results from the oxidation, at high temperature, of the base substrate and / or of a donor substrate from which the surface layer was taken during the manufacture of the starting substrate. It therefore has a high density, higher than the density of a deposited dielectric layer. It is therefore distinguished from a covering layer (which will be described later), formed by deposition, even when these two layers are of the same nature, typically made of silicon oxide.

[0046] The buried dielectric layer 1b may be relatively thick, for example having a thickness greater than 20nm, or 50nm, 100nm, or even reaching one or more microns. The interfaces between the buried oxide layer 1b, the base substrate 1a on the one hand and the surface layer 1b on the other hand are very slightly rough, less than 1nm in peak-to-peak measurement (from the Anglo-Saxon expression "peak to valley").

[0047] During a second step of a method of this embodiment, illustrated in the, the starting substrate 1 is treated to form, in and on the surface layer 1c, components and in particular photonic components. The component layer 2 extends from a first exposed surface to a second surface, opposite the first surface, in contact with the buried dielectric layer 1b.

[0048] As is well known in itself, this treatment can include any type of conventional technological steps in the world of microelectronics: deposition, etching, photolithography, in order to define patterns making these components functional. By way of illustration, these conventional technological steps can be chained together to form, by etching the surface layer 1c, at least one edge waveguide 2a. As previously specified, this waveguide comprises a base resting on the buried dielectric layer 1b and a protruding edge on the base.

[0049] Selective deposition steps, for example of germanium, make it possible to form a photodetector 2c. Silicon nitride deposition steps make it possible to form an additional waveguide 2b. It is also possible, by way of illustration, to provide a modulator 2d. It is also possible to form metal tracks, at different levels, to conduct electrical signals. Multiple deposition steps, which can be followed by a polishing step, of a covering material 2e, for example silicon dioxide, make it possible to encapsulate the assembly and form a layer of components 2 resting on the base substrate 1a, via the buried dielectric layer 1b.

[0050] The covering material 2e of which the component layer 2 is partly made can be opened by etching, during the step of processing the starting substrate to form metal vias 2d, which can come into contact with the metal tracks 7, for example making it possible to make contacts on the active components of the component layer 2. For simplicity of expression, the tracks 7 and metal vias 2d arranged in the covering material 2e will be designated by "buried contact structure".

[0051] At the end of this processing step, and regardless of the components formed in and on the surface layer 1c, there is a layer of components 2 extending from the first to the second surface, these components being encapsulated in a covering material 2e. The components 2a, 2b, 2c, 2d, 7 of the layer 2 comprise at least one edge waveguide 2a formed in the surface layer 1c. It is noted that this waveguide 2a having been formed in the surface layer 1c, it rests via its base on, and is in contact with, the buried dielectric layer 1b, the base being flush with the second surface.

[0052] At the end of this processing step, it may be provided to polish the first, exposed surface of the layer of photonic components 2 in order to facilitate the following transfer step.

[0053] In a third step shown in the, the component layer 2 is transferred onto a support substrate 1e. This transfer can be carried out by any suitable technique. This transfer generally comprises the assembly of the component layer 2 carried by the base substrate 1a with this support substrate 1e via the first surface. This may for example be an assembly by molecular adhesion. This assembly can also be used to bring components formed in the support substrate into contact with metal tracks of the component layer 2, via surface contact pads, as is notably illustrated in the document by JA Theil, et al "Recent Developments in Fine Pitch Wafer-To-Wafer Hybrid Bonding with Copper Interconnect," 2019 International WaferLevelPackagingConference(IWLPC), San Jose, CA, USA, 2019, pp. 1-6.

[0054] Once the assembly is completed, the base substrate 1a is removed to expose the buried dielectric layer 1b. This removal can be carried out by grinding assisted by dry or wet etching, the buried dielectric layer 1b forming a barrier layer for this etching. By choosing an advantageously thick buried dielectric layer 1c, it is ensured that the step of removing the base substrate 1a does not lead to crossing or piercing this buried dielectric layer 1b. This preserves the quality of the underlying layers, in particular the component layer 2 and the photonic components it contains.

[0055] In a fourth step shown in Figures 1d and 1e, the dielectric layer 1b is selectively removed to expose a central portion Zc of the edge waveguide 2a, in particular to expose a central portion of the base of this waveguide 2a, while preserving the dielectric layer at its peripheral contour Zb. To achieve this, it is first possible to form, as shown in the, a mask layer 3 covering the buried dielectric layer 1b. The mask layer 3 may be made of a resin. A photolithography step makes it possible to form at least one opening in the mask layer 3, this opening being arranged at a central portion Zc of the waveguide 2a. During this step, care is taken to preserve a portion of the mask layer 3 covering the waveguide 2a, at its peripheral contour Zb.

[0056] The opening may have a rectangular shape overhanging the base of the edge waveguide 2a, the width of which is typically between 30 micrometers and 1 mm, and the length of a few millimeters, for example 2 mm or up to 2 mm. The peripheral contour Zb may have a width of the order of 10 micrometers, for example between 5 micrometers and 30 micrometers.

[0057] Once this opening has been made, the exposed part of the buried dielectric layer 1b can be removed by etching, for example wet etching. The etching solution is chosen to be selective with respect to the material making up the waveguide 2a. It may be a hydrofluoric acid (HF)-based solution in the case where the buried dielectric layer 1b is made of silicon oxide and the waveguide 2a is made of silicon. Since the peripheral contour of the waveguide Zb is covered by the mask layer 3, the buried dielectric layer 1b is preserved above this contour. This prevents the etching solution from damaging the buried dielectric layer 1b at the peripheral contour Zb of the waveguide. This also prevents this etching solution from infiltrating the sides of the waveguide 2a and damaging the covering layer 2e in its vicinity.The revealed surface of the waveguide 2a, at the central zone Zc, has a low roughness, identical or close to that present at the interface between the surface layer 1c and the buried dielectric layer 1b of the starting substrate 1. It has not been affected by the etching solution used during the removal of the base substrate 1a. It therefore has favorable characteristics, in particular in terms of roughness, cleanliness, and flatness for receiving, by assembly, a laser structure in a fifth step of a method according to the invention.

[0058] The state of the structure at the end of this step of selective elimination of the dielectric layer is shown. The mask layer 3 can be eliminated at the end of this step or in a later step.

[0059] In a fifth step of the method, a heterogeneous structure 4 is placed on and in contact with the central part Zc of the edge waveguide 2a, on the exposed surface of the base.

[0060] It is noted that it is possible to eliminate only a thickness of the dielectric layer at a central part of the edge waveguide, without revealing the surface of the waveguide 2a at the central zone Zc. The residual thickness of the dielectric layer 1b then forms a dielectric bonding layer, as will be explained in a later section of this description.

[0061] As previously specified, this heterogeneous structure 4 may for example be a gain structure of a laser or an optical amplifier or a structure formed from a material having electro-optical properties of a modulator.

[0062] In the example shown in Figures 1f to 1h, the heterogeneous structure is a 4-gain structure. This comprises, as is well known per se, a first 4n contact layer, made of N-type semiconductor material, arranged on the waveguide 2a, a 4W active region (well or quantum dot(s)) formed from a stack of layers of III-V materials arranged on and in contact with the first contact layer, a second 4p contact layer, made of P-type semiconductor material arranged on the 4W active region.

[0063] An interlayer formed of an undoped semiconductor material may be provided between and in contact with the waveguide 2a and the first contact layer 4n, to prevent the current injected into the stack from leaking into the silicon. This undoped layer may be formed of any suitable semiconductor material.

[0064] To enable its operation, the gain structure 4 comprises electrical contact pads 5, respectively in contact with the first contact layer 4n and the second contact layer 4b.

[0065] The fifth step of forming the gain structure 4 can be carried out using several approaches. In the approach shown in the, a stack 4' consisting of the second 4p contact layer, 4W active region, first 4n contact layer and, where appropriate, the interlayer, in the form of a vignette is first transferred onto the exposed surface of the waveguide 2a revealed during the previous step. This transfer can be carried out by assembly, for example by molecular adhesion of the vignette formed from the stack 4'. In a following step, this stack 4' is structured, for example by dry etching, to reveal a surface of the first 4n layer, using conventional techniques implementing photolithographic masking of the surfaces to be preserved from the structuring. Then two electrical contact pads 5 are produced, respectively in contact with the first and second 4p,4n contact layers.These pads 5 make it possible to circulate a current through the gain structure 4 and cause the generation / amplification of an optical mode MO, as is well known per se. It is noted that several pads 5 could be provided in contact with the first contact layer 4n, for example arranged on either side of the contact pad 5 in contact with the second contact layer 4p.

[0066] Advantageously, for reasons of optical amplification efficiency, the structuring is centered on the edge of the waveguide 2a. This centering is obtained during the photolithographic masking steps, which can be achieved with great precision. Since this centering can be obtained after the step of assembling the heterogeneous structure on the edge waveguide 2a, it is not necessary for this assembly itself to be carried out with great precision.

[0067] In certain embodiments, provision may be made to form in the heterogeneous structure 4, at least one implantation zone subsequently called the “amorphous confinement zone” I2. As can be seen in the, this amorphous confinement zone I2 may be arranged on either side of the heterogeneous structure 4, without extending entirely into the first contact layer 4n. The amorphous confinement zone(s) I2 may be obtained by selective ion implantation in the heterogeneous structure 4, by photolithographic masking.

[0068] In the next step of structuring the heterogeneous structure 4 shown in the, a surface of the first 4n layer is revealed. Then the electrical contact pads 5 are produced, in contact with the first and second 4p,4n contact layers. The amorphous confinement zone I2 is electrically much less conductive than the rest of the stack forming the gain structure 4. The current injected via the electrical contact pad 5 arranged on the second 4p contact layer therefore tends to be confined in the crystalline portion of the stack towards the electrical contact pads 5 arranged on the first 4n contact layer.

[0069] Advantageously, the positioning of the amorphous confinement zone I2 (or of the plurality of these zones) is carried out so as to center the crystalline part of the stack on the edge of the waveguide 2a, after having assembled the stack 4, by means of the photolithographic masking steps, which can be carried out with great precision. This centering can be obtained after the step of assembling the heterogeneous structure on the edge waveguide 2a, it is not necessary for this assembly itself to be carried out with great precision.

[0070] It is noted that the formation of an amorphous confinement zone I2 can be carried out on the heterogeneous structure 4 before its assembly on the component layer 2. As can be seen in the, this amorphous confinement zone I2 can be arranged by selective implantation on one side of the heterogeneous structure 4, before its assembly, and extend into the first contact layer 4n, in the active region 4W and, and in the second contact layer 4p. A surface portion of this second contact layer 4p is kept unimplanted.

[0071] In the next step of structuring the heterogeneous structure 4 shown in the, a surface of the first layer 4n is revealed. Then two electrical contact pads 5 are produced, respectively in contact with the first and second contact layers 4p,4n. The electrical contact pad 5 in contact with the second contact layer 4p is arranged at the right of the amorphous confinement zone. This second approach, however, requires a more precise assembly of the heterogeneous structure 4 to the waveguide 2a, because the centering of the current flow path on the edge can only be partially obtained during the structuring step.

[0072] Whatever the embodiment chosen to structure the heterogeneous structure 4, at the end of this sequence there is a gain structure 4, therefore equipped with its electrical contact pads 5, on and in contact with the waveguide 2a, as shown in the. Reference may be made to document WO2010100882A1 to obtain more details of the implementation of this first variant of this mode of implementation.

[0073] In an alternative to this variant, in which the 4-gain structure is finalized after the 4' stack has been transferred into the opening made in the buried dielectric layer 1c, it is possible to directly transfer the fully finalized 4-gain structure. This can be done, for example, using the microtransfer printing technique ("microtransfer printing" according to the Anglo-Saxon term in the field). A description of this technique and its use in the field of photonics can be found in the document by Camiel Op de Beeck, et al "Heterogeneous III-V on silicon nitride amplifiers and lasers via microtransfer printing," Optica 7, 386-393 (2020). In brief, and using this technique, a 4-gain structure, including the structured 4' stack and the electrical contacts 5, is entirely prepared on a temporary substrate.Using a handle, this gain 4 structure is removed from its temporary substrate, transferred and assembled on a final substrate, here on and in contact with the revealed surface of the waveguide base at edge 2a.

[0074] In contrast to the first approach, in this variant the electrical contacts 5 of the gain structure 4 are made, before its assembly on the central part of the waveguide.

[0075] The assembly can be carried out, for example, by molecular adhesion, just as in the first variant. It is noted that the receiving surface of the heterogeneous structure, the exposed surface of the waveguide base, having not received any treatment likely to degrade it, is particularly suitable for receiving the heterogeneous structure.

[0076] To facilitate this adhesion, and whatever the approach adopted, it is possible to prepare the exposed surface of the waveguide 2a which is intended to receive the gain structure 4. This preparation may comprise, by way of illustration, the exposure of this surface to a plasma, for example an oxygen plasma.

[0077] It is also possible, in all the approaches which have just been presented, to provide a dielectric bonding layer 1b' arranged at least on the central part Zc of the base of the waveguide 2a. This dielectric bonding layer 1b' can have a perfectly controlled thickness. This thickness can be less than that of the dielectric layer 1b. For example, this thickness can be less than 100nm, 50nm or 10nm. The formation of the dielectric bonding layer 1b' can be carried out by deposition at the end of the step of selective removal of the dielectric layer 1b in order to cover at least the central part Zc of the base of the waveguide 2a. This solution is shown in Figures 4a (just after the deposition of the dielectric bonding layer 1b') and 4b (after assembly of the heterogeneous structure 4 on and in contact with the dielectric bonding layer 1b').

[0078] The dielectric bonding layer 1b' may be of the same nature as that of the dielectric layer 1b, or of a different nature. It is typically a layer made of silicon dioxide. It is noted that this dielectric bonding layer 1b' which has been formed by deposition, and even when it is of the same nature as the dielectric layer 1b, is quite distinct from this dielectric layer 1b, obtained by oxidation as has been explained previously.

[0079] In a variant, the dielectric bonding layer may correspond to a remaining thickness of the dielectric layer 1b, on the central part Zc of the base of the waveguide 2a, when this portion of the dielectric layer 1b has not been entirely eliminated. The photonic device obtained according to this variant is shown in the. The thickness of the dielectric layer arranged on the central part Zc of the base of the waveguide 2a, which therefore constitutes the dielectric bonding layer, has in this case a thickness less than that of the dielectric layer 1b.

[0080] Returning to the general description of a method in accordance with the invention presented in figures 1a to 1h, we find on the state of the photonic device at the end of this step of forming the gain structure 4.

[0081] To finalize this photonic device, an encapsulation layer 6 can be deposited on the photonic component layer 2 and on the gain structure 4. Then electrical tracks 8 are produced on the encapsulation layer 6, these tracks being able to comprise metal vias 8' passing through the encapsulation layer 6 to a buried contact structure 7 in the covering layer 5 and to the electrical contacts 5 of the structure 4.

[0082] To obtain the electro-optical modulator DP shown in the, the fifth step comprises the transfer onto the exposed surface of the base of the edge waveguide 2a, of a block of material having electro-optical properties, for example LiNbO3, BTO or a stack of III-V materials. Just as in the previous case, electrical tracks 8 can be formed on an encapsulation layer 6, these tracks also forming electrical contact pads S,G,S on the heterogeneous structure 4 made of electro-optical material. It is noted that the edge waveguide 2a can have two edges in this case, each edge constituting a modulator arm.

[0083] Figures 2a to 2f illustrate a variant of the preparation method, which can be applied to any heterogeneous structure 4, in which at least one cavity 20 is formed in the base of the edge waveguide 2a to absorb degassing products resulting from the bonding of the heterogeneous structure to the base.

[0084] As shown in the, this method variant comprises the formation of at least one stop pattern 9 for etching on the base of the waveguide 2a during the step of forming the layer of photonic components. In this, and by way of illustration, a stop waveguide 2a has been defined, in the surface layer 1c of the starting substrate 1 and two stop patterns 9 in contact with the surface layer, on either side of the stop of the waveguide 2a. A stop pattern may in particular consist of a silicide or a metal, such as TiN.

[0085] The photonic component layer 2 is then transferred onto the support substrate 1e and the base substrate is removed to expose the buried dielectric layer 1b, just as in the first embodiment ().

[0086] At this stage, and as shown in the, a first mask layer 3a is placed on the buried dielectric layer 1b, this first mask layer 3a having openings at the right of the stop patterns 9 for etching. The successive localized etching of the buried dielectric layer 1b and the layer 1c is then carried out, for example by dry etching. The dry etching stops very precisely on the stop pattern 9. This removal can also be carried out by wet etching. In all cases, this etching is blocked by the stop pattern 9. The first mask layer 3a can then be eliminated.

[0087] The process can then be repeated as described previously, by placing a second mask layer 3b, this time to expose the central part Zc of the base of the waveguide at the stop 2a while masking its peripheral zone Zc. The second mask layer 3b is also open on the openings leading to the stop pattern 9.

[0088] It is noted that the flat bonding surface of the waveguide 2a has not been covered by any mask layer 3a, 3b. It therefore has favorable characteristics, particularly in terms of roughness, cleanliness, and flatness for receiving, by assembly, the heterogeneous structure. When a dielectric bonding layer 1b' has been previously formed, this relatively thin layer inherits the favorable characteristics of the flat surface of the waveguide 2a.

[0089] When, in the next step of forming the heterogeneous structure 4, this structure is assembled on the exposed face of the waveguide 2a, cavities 20 are formed, covered by the lower layer of the heterogeneous structure. This cavity 20 can be very useful for capturing the species, in particular gaseous species, which are formed or which are released at the assembly interface between the heterogeneous structure 4 and the waveguide 2a. This is particularly the case when this assembly is carried out by molecular adhesion.

[0090] To finalize the preparation of the photonic device DP, an encapsulation layer 6 can be deposited on the component layer 2 and on the heterogeneous structure 4. Then, after a possible planarization step, electrical tracks 8 are produced on the encapsulation layer 6, these tracks possibly comprising metal vias allowing electrical contacts to be made with the heterogeneous structure 4.

[0091] Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Photonic device (PD) comprising a hybrid waveguide capable of propagating an optical mode comprising:a component layer (2) arranged by a first surface on a support substrate (1e), the component layer (2) comprising, in a covering material (2e), at least one edge waveguide (2a) formed of a base flush with a second surface of the component layer (2), opposite the first surface, and at least one edge oriented towards the support substrate (1e);a dielectric layer (1b) arranged on and in contact with the second surface of the component layer (2), the dielectric layer being arranged to cover a peripheral contour (Zb) of the base of the edge waveguide (2a) without however extending with its entire thickness over a central part of the base of the edge waveguide (2a);a heterogeneous structure (4) on the central part (Zc) of the base of the waveguide (2a), the heterogeneous structure (4) and the edge waveguide (2a) forming, in combination, the hybrid waveguide.; Photonic device (PD) according to claim 1 wherein the heterogeneous structure (4) is arranged on and in contact with the central part (Zc) of the base of the waveguide (2a). Photonic device (PD) according to claim 1 comprising a dielectric bonding layer (1b') arranged on the central part (Zc) of the base of the waveguide (2a), the heterogeneous structure (4) being arranged on and in contact with the dielectric bonding layer (1b'). Photonic device (PD) according to one of the preceding claims in which the heterogeneous structure (4) is a gain structure formed of a first contact layer (4n), an active region (4W) formed of a stack of layers of III-V semiconductor materials arranged on and in contact with the first contact layer (4n) and a second contact layer (4p) arranged on and in contact with the active region (4W), and the photonic device (PD) is an amplifier or a laser. Photonic device (PD) according to the preceding claim in which the heterogeneous structure (4) also comprises, arranged between and in contact with the base of the waveguide (2a) and the first contact layer (4n), an interlayer formed of an undoped semiconductor material. Photonic device (PD) according to one of claims 4 and 5 in which the first contact layer (4n) and the second contact layer (4p) comprise electrical contact pads (5). Photonic device (PD) according to the preceding claim in which the heterogeneous structure (4) comprises at least one amorphous confinement zone (I2). Photonic device (PD) according to one of claims 1 to 3 in which the heterogeneous structure (4) comprises a material having electro-optical properties, such as LiNbO3, BTO, or a stack of III-V materials, and the photonic device (PD) is an electro-optical modulator. Photonic device (PD) according to one of the preceding claims comprising at least one cavity (20) formed in the base of the waveguide (2a), the cavity (20) being covered by the heterogeneous structure (4). Photonic device (DP) according to the preceding claim in which the cavity (20) has a bottom formed of at least one etching stop pattern (9). Photonic device (PD) according to one of the preceding claims comprising an encapsulation layer (6) arranged on the component layer (2) and on the heterogeneous structure (4). Photonic device (PD) according to the preceding claim comprising metal tracks (8) arranged on the encapsulation layer (6), in electrical contact with the heterogeneous structure (4). Photonic device (PD) according to one of the two preceding claims in which the component layer (2) comprises at least one buried contact structure (7,2d). Photonic device (PD) according to the preceding claim further comprising metal vias passing through the encapsulation layer (6), the dielectric layer (1b) and a portion of the component layer (2) for contacting the buried contact structure (7,2d). Photonic device (PD) according to one of the preceding claims in which the stop waveguide (2a) is made of silicon and the dielectric layer (1b) is made of silicon dioxide. A method for preparing a photonic device (PD) comprising a hybrid waveguide capable of propagating an optical mode, the method comprising the following steps:providing a starting substrate (1) comprising a base substrate (1a), a buried dielectric layer (1b) arranged on and in contact with the base substrate (1a) and a surface layer (1c) arranged on and in contact with the buried dielectric layer (1b);forming a component layer (2) in the starting substrate (1), the component layer comprising at least one ridged waveguide (2a) formed of a base on and in contact with the buried dielectric layer (1b) and at least one ridge overhanging the base, the component layer (2) comprising a covering material (2e) encapsulating the at least one ridged waveguide (2a);transferring the component layer (2) onto a support substrate (1e) and removing the base substrate (1a) to expose the dielectric layer buried (1b);selectively removing at least a thickness of the dielectric layer (1b) at a central part (Zc) of the edge waveguide (2a) while preserving the dielectric layer on a peripheral contour (Zb) of the waveguide (2a);forming a heterogeneous structure (4) on the central part of the base of the edge waveguide (2a).; Preparation method according to the preceding claim in which the heterogeneous structure (4) comprises a stack of III-V semiconductor materials or an electro-optical material. Preparation method according to one of the two preceding claims in which the selective elimination of the dielectric layer (1b) leads to exposing the central part (Zc) of the edge waveguide (2a). Preparation method according to one of claims 16 to 18 further comprising the preparation of the exposed surface of the central part (Zc) of the base of the edge waveguide (2a) by an oxygen plasma before the step of forming the heterogeneous structure (4) and / or by depositing a dielectric bonding layer (1b').

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