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 (PD) comprising a hybrid waveguide capable of propagating an optical mode. The device comprises a layer of components (2) disposed by a first surface on a support substrate (1e) and comprising at least one edge waveguide (2a) formed of a base flush with a second surface of the component layer (2) and at least one edge oriented towards the support substrate (1e). A dielectric layer (1b) is disposed on and in contact with the second surface of the component layer (2). It is arranged to cover a peripheral contour (Zb) of the base of the edge waveguide (2a) without, however, extending over its central part. A heterogeneous structure (4) is disposed on and in contact with the central part (Zc) of the base of the waveguide (2a). The heterogeneous structure (4) and the edge waveguide (2a) together form the hybrid waveguide. Figure 1h

Description

Title of the invention: Photonic device comprising a layer of components disposed 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 layer of components disposed on a support substrate. It also relates to a method for preparing such a photonic device, the method comprising transferring the layer of components onto the support substrate. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Prior art is known of photonic devices propagating an optical mode in a hybrid waveguide formed by assembling a heterogeneous structure (for example a III-V semiconductor material structure) on a silicon waveguide to form a laser-type or optical amplifier-type device.

[0003] The document by Liang et al., "Hybrid Silicon evanescent approach to optical interconnects," Applied Physics A 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 layer 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 InP- or GaAs-based), the optical mode is predominantly located in the silicon portion of the hybrid waveguide, which is favorable to its propagation within the optical device.

[0004] This method, which requires transferring the laser structure directly onto the silicon waveguide, does not, however, allow the integration of any components other than the hybrid waveguide into the photonic device. Forming other components on the base substrate (for example, a germanium photodetector, a silicon nitride waveguide, or metal lines forming buried contact structures) would necessitate burying the silicon waveguide under layers of material, thus preventing direct contact between the laser structure and the silicon waveguide.

[0005] Furthermore, the step of etching the surface layer of the base substrate to form the edge waveguide can lead to degradation of its surface condition, which can make the step of bonding the heterogeneous structure more difficult. This step etching is in fact preceded by the deposition of an etching mask (in silicon nitride, oxide or 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] US patent 7482184 discloses a method for preparing a photonic device that includes forming a layer of photonic components in a SOI-type starting substrate. This starting substrate is thus formed of a base substrate, a buried dielectric layer disposed on and in contact with the base substrate, and a surface layer, which may be of single-crystal silicon, disposed on and in contact with the buried dielectric layer. The photonic components of the photonic component layer include at least one waveguide formed in the surface layer of the starting substrate, on and in contact with the buried dielectric layer. However, other photonic components, such as silicon nitride waveguides, photodetectors, and metal lines, may also be formed on and in this surface layer.These photonic components are then encapsulated by a coating material, typically silicon oxide.

[0007] In a subsequent step, this prior art process includes 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 portion, for example using a TMAH chemical solution. The buried dielectric layer forms a barrier to etching.

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

[0010] Next, 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 directly above the waveguide. The buried dielectric layer must be sufficiently thin to allow optical coupling between the heterogeneous structure and the waveguide.

[0011] With this integration method, the dielectric layer must have sufficient thickness, for example on the order of 100 nm or 50 nm, to prevent penetration during the etching of the surface layer during waveguide formation. Therefore, with this method, it is difficult to obtain a thin dielectric between the silicon waveguide and the heterogeneous structure bonded to the waveguide.

[0012] US patent 9507089 proposes a layer transfer method for preparing a photonic device similar to the one just described. The removal of the base substrate is followed by the complete removal of the buried dielectric layer. This is achieved by incorporating, during the preparation of the photonic component layer on the starting substrate, a protective silicon nitride layer over the portions of the dielectric layer that are no longer covered by the surface layer after the waveguide has been etched. After transferring the photonic component layer onto the substrate, and after removing the base substrate and the dielectric layer, the silicon nitride layer and one back face of the waveguide are exposed. A new dielectric layer is then formed over the silicon nitride layer and the waveguide.

[0013] It is understood, however, that this approach, requiring the presence of the silicon nitride protective layer, the removal of the buried dielectric layer from the starting substrate and the formation of a new dielectric layer, is particularly complex. SUBJECT OF THE INVENTION

[0014] One object of the invention is to remedy, at least in part, the problems just described. More particularly, one object of the invention is to provide a photonic device comprising a hybrid waveguide for propagating an optical mode and a method for preparing this device that 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

[0015] With a view to achieving one of these goals, the object 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 supporting 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 supporting substrate; - a dielectric layer disposed 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 over a central part of the base of the edge waveguide; - a heterogeneous structure on and in contact with the central part of the waveguide base, the heterogeneous structure and the edge waveguide forming, in combination, the hybrid waveguide.

[0016] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: - 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 includes, arranged between and in contact with the base of the waveguide and the first contact layer, an intercalated layer made of an undoped semiconductor material; - the first contact layer and the second contact layer have electrical contact pads; - the heterogeneous structure includes a material exhibiting 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 includes 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 by at least one stop pattern in the engraving. - The photonic device includes an encapsulation layer disposed on the component layer and on the heterogeneous structure; - the photonic device includes metallic tracks arranged on the encapsulation layer, in electrical contact with the heterogeneous structure; - the component layer includes at least one buried contact structure; - the photonic device further includes metallic vias passing through the encapsulation layer, the dielectric layer and part 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.

[0017] According to another aspect, 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: - provide a starting substrate comprising a base substrate, a buried dielectric layer disposed on and in contact with the base substrate and a surface layer arranged on and in contact with the buried dielectric layer; - form a component layer in the starting substrate, the component layer comprising at least one edge waveguide formed of a base on and in contact with the buried dielectric layer and at least one edge overhanging the base, the component layer comprising a covering material encapsulating at least one edge waveguide; - transfer the component layer onto a support substrate (the) and remove the base substrate to expose the buried dielectric layer; - selectively remove the dielectric layer to expose a central part of the waveguide to the edge while preserving the dielectric layer on a peripheral contour of the waveguide; - to form a heterogeneous structure on and in contact with the central part of the base of the edge waveguide.

[0018] The heterogeneous structure may comprise a stack of III-V semiconductor materials or an electro-optical material. The process may include preparing the exposed surface of the central portion of the waveguide base with an oxygen plasma before the heterogeneous structure formation step. Brief description of the drawings

[0019] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0020] [Fig.la] [Fig.lb] [Fig.lc] [Fig.ld] [Fig.le] [Fig.lf] [Fig.lg] [Fig.lh]

[0021] Figures la,lb,lc,ld,le,lf,lg,lh represent steps in a preparation process according to the invention;

[0022] [Fig.2a] [Fig.2b] [Fig.2c] [Fig.2d] [Fig.2e] [Fig.2f] [Fig.2g]

[0023] Figures 2a, 2b, 2c, 2d, 2e, 2f, 2g represent steps of another preparation process according to the invention;

[0024] [Fig.3] Fig.3 represents a photonic device according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] Figures Ih, 2g and 3 illustrate DP photonic devices according to the invention and comprising a hybrid waveguide capable of propagating an optical mode.

[0026] This DP photonic device comprises a support substrate le and a layer of components 2 disposed on the support substrate le. The layer of components 2 has a first surface disposed on the side of the support substrate le, and a second surface opposite the first surface, and therefore further away from the support substrate le than the first surface.

[0027] 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 substrate supporting the edge. The edge is intended to promote the confinement of the optical mode within the silicon portion of the hybrid waveguide. The edge waveguide 2a is advantageously formed of single-crystal silicon, although this is not an essential characteristic of the DP photonic device that is the subject of this description. It can be structured to allow the formation of an optical mode resonance.

[0028] A dielectric layer 1b is disposed 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 waveguide base 2a without, however, extending over a central portion Zc of this base. The dielectric layer 1b is typically formed of a silicon oxide and can have a thickness ranging from a few tens of nanometers to several thousand nanometers.

[0029] A heterogeneous structure 4 is assembled to the central part Zc of the base of the waveguide 2a, and thus disposed on and in contact with this waveguide 2a. The heterogeneous structure 4 and the waveguide 2a together form the hybrid waveguide of the optical device DP in which an optical mode can propagate.

[0030] By "heterogeneous structure" is meant a material or a stack of materials having a different nature from the material which constitutes the waveguide with edge 2a.

[0031] It can thus be a gain structure, as shown in Figures 1h and 2g, formed from a stack of layers of III-V materials, for example InP-based or GaAs-based, as is well known. With such a gain structure, the DP photonic device can be a laser or an optical amplifier. This gain structure 4 can in particular comprise a first contact layer 4n, of N-type semiconductor material, arranged on the waveguide 2a, an active region 4W (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, of P-type semiconductor material, arranged on and in contact with the active region 4W.

[0032] An intercalary layer made of an undoped semiconductor material can also be provided in the gain 4 structure, arranged between and in contact with the waveguide 2a and the first contact layer 4n.

[0033] Whether such an intercalated layer 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.

[0034] In the DP photonic device in [Fig. 3], the heterogeneous structure 4 is formed from a block of material exhibiting 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 waveguide with edge 2a can have two edges, each edge constituting a modulator arm.

[0035] The DP photonic device may include an encapsulation layer 6 disposed on the photonic component layer 2 and on the heterogeneous structure 4. This encapsulation layer 6 may, in particular, be made of silicon dioxide. Metallic tracks 8 may be disposed 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.

[0036] The DP photonic device may include photonic components other than the waveguide 2a. Thus, in the embodiment shown in [Fig. 1h], the photonic component layer comprises a silicon nitride waveguide 2b, a photodetector 2c, and at least one contact structure 7 embedded in the cover layer 2e in the form of metallic tracks or vias. Metallic vias passing through the encapsulation layer 6, the dielectric layer 1b, and part of the component layer 2 provide contact with the embedded contact structure 7.

[0037] In the DP photonic device shown in [Fig. 2g], at least one cavity 20 (two cavities 20 in the example shown) is provided in the base of the waveguide with edge 2a, the cavity 20 being covered by the heterogeneous structure 4. To facilitate its fabrication, the cavity 20 has a bottom formed by an etching stop motif 9, for example, a motif 9 made of a silicide or a metal, such as metallic TiN. The cavity or cavities can facilitate the assembly of the heterogeneous structure 4 onto the waveguide with edge 2a by absorbing the gaseous species that may form during this assembly step, particularly when it is carried out by molecular bonding.

[0038] With reference to figures 1a to 1h, we now present a method of implementing a process for preparing a DP photonic device according to the invention.

[0039] In a first step shown in [Fig. 1a], a starting substrate 1 is provided. This substrate, for example of the silicon-on-insulator type, consists of a base substrate 1a, typically made of silicon and several hundred microns thick. A buried dielectric layer 1b, typically made of silicon oxide, is placed on and in contact with the base substrate 1a. This layer can have a thickness ranging from a few tens of nanometers to several thousand nanometers.

[0040] The starting substrate 1 also includes a surface layer le, generally semiconducting, disposed on and in contact with the buried dielectric layer 1b. This layer le can in particular be formed of monocrystalline silicon and have a thickness of between 50nm and 1000nm.

[0041] It should be noted that the buried dielectric layer 1b, particularly when formed of silicon oxide, results from the high-temperature oxidation of the base substrate and / or a donor substrate from which the surface layer was taken during the fabrication of the starting substrate. It therefore has a high density, higher than the density of a deposited dielectric layer. It is thus distinct from a coating layer (which will be described later), formed by deposition, even when these two layers are of the same nature, typically silicon oxide.

[0042] The buried dielectric layer 1b can be relatively thick, for example, greater than 20 nm, or 50 nm, 100 nm, or even one or more microns. The interfaces between the buried oxide layer 1b, the base substrate on the one hand, and the surface layer 1b on the other are very smooth, less than 1 m in peak-to-peak measurement.

[0043] In a second step of a process in this embodiment, illustrated in [Fig. 1b], the starting substrate 1 is treated to form components, and in particular photonic components, in and on the surface layer 1e. 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.

[0044] As is well known, this process can include any type of conventional technological step in the world of microelectronics: deposition, etching, photolithography, in order to define patterns that make these components functional. By way of illustration, these conventional technological steps can be combined to form, by etching the surface layer 1, at least one waveguide with edge 2a. As previously stated, this waveguide comprises a base resting on the buried dielectric layer 1b and a protruding edge on the base.

[0045] Selective deposition steps, for example of germanium, allow the formation of a photodetector 2c. Silicon nitride deposition steps allow the formation of an additional waveguide 2b. A modulator 2d can also be provided, by way of illustration. Metallic tracks can also be formed at different levels to conduct electrical signals. Multiple deposition steps, which may be followed by a polishing step, of a coating material 2e, for example silicon dioxide, allow the assembly to be encapsulated and a layer of components 2 resting on the base substrate la, via the buried dielectric layer 1b.

[0046] The covering material 2e, of which the component layer 2 is partly made up, can be opened by etching during the processing step of the starting substrate to form metallic vias 2d, which can come into contact with the metallic tracks 7, allowing, for example, contact to be made on the active components of the component layer 2. For simplicity of expression, the tracks 7 and metallic vias 2d arranged in the covering material 2e will be designated as "buried contact structure".

[0047] Following this processing step, and regardless of the components formed in and on the surface layer 1, a layer of components 2 is obtained 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 layer 2 comprise at least one edge waveguide 2a formed in the surface layer 1. It should be noted that this waveguide 2a, having been formed in the surface layer 1, rests via its base on, and is in contact with, the buried dielectric layer 1b, the base being flush with the second surface.

[0048] At the end of this processing step, it is possible to polish the first exposed surface of the photonic component layer 2 in order to facilitate the next transfer step.

[0049] In a third step shown in [Fig. 1e], the component layer 2 is transferred onto a support substrate 1e. This transfer can be carried out by any suitable technique. This transfer generally involves bonding the component layer 2 carried by the base substrate 1e with this support substrate 1e via the first surface. This could be, for example, a molecular adhesion bond. This bonding can also be used to connect components formed in the support substrate with metallic tracks of the component layer 2, via surface contact pads, as illustrated in particular in the paper by JA Theil, et al., "Recent Developments in Fine Pitch Wafer-To-Wafer Hybrid Bonding with Copper Interconnect," 2019 International Wafer Level Packaging Conference (IWLPC), San Jose, CA, USA, 2019, pp. 1-6.

[0050] Once the assembly is complete, the base substrate is removed to expose the buried dielectric layer 1b. This removal can be carried out by dry or wet etching assisted grinding, the buried dielectric layer 1b forming a barrier to this etching. By choosing an advantageously thick buried dielectric layer, it is ensured that the step of removing the base substrate does not lead to penetrating or piercing this buried dielectric layer 1b. thus the quality of the underlying layers, in particular the component layer 2 and the photonic components it contains.

[0051] In a fourth step shown in Figures Id and Ie, the dielectric layer 1b is selectively removed to expose a central portion Zc of the waveguide with edge 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, a mask layer 3 can first be formed, as shown in [Fig. Id], covering the buried dielectric layer 1b. The mask layer 3 can 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 located 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.

[0052] The aperture may be rectangular in shape, overhanging the base of the waveguide with edge 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, for its part, have a width on the order of 10 micrometers, for example between 5 micrometers and 30 micrometers.

[0053] Once this opening is made, the exposed portion of the buried dielectric layer 1b can be removed by etching, for example by wet etching. The etching solution is chosen to be selective with respect to the material composing the waveguide 2a. It can 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 masking 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. It also prevents this etching solution from seeping around the sides of the waveguide 2a and damaging the covering layer 2e in its vicinity.The exposed surface of the waveguide 2a, at the central zone Zc, exhibits low roughness, identical or close to that present at the interface between the surface layer le and the buried dielectric layer 1b of the starting substrate 1. It was not affected by the etching solution used during the removal of the base substrate la. It therefore exhibits favorable characteristics, particularly in terms of roughness, cleanliness, and flatness, for receiving, by assembly, a laser structure in a fifth step of a process according to the invention.

[0054] Figure 11 shows the state of the structure after this step of selective removal of the dielectric layer. The mask layer 3 can be removed at the end of this step or in a subsequent step.

[0055] In a fifth step of the process, a heterogeneous structure 4 is placed on and in contact with the central part Zc of the waveguide with edge 2a, on the exposed surface of the base.

[0056] As previously stated, this heterogeneous structure 4 can, for example, be a gain structure of a laser or an optical amplifier or a structure formed of a material exhibiting electro-optical properties of a modulator.

[0057] In the example shown in Figures If to Ih, the heterogeneous structure is a gain 4 structure. This includes, as is well known in itself, a first contact layer 4n, of N-type semiconductor material, arranged on the waveguide 2a, an active region 4W (well or quantum point(s)) formed of a stack of layers of III-V materials arranged on and in contact with the first contact layer, a second contact layer 4p, of P-type semiconductor material arranged on the active region 4W.

[0058] An intercalated layer made of an undoped semiconductor material can be provided, positioned 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 can be made of any suitable semiconductor material.

[0059] To enable its operation, the gain structure 4 includes electrical contact pads 5, respectively in contact with the first contact layer 4n and the second contact layer 4b.

[0060] The fifth step in the formation of the gain structure 4 can be carried out according to several approaches. In the approach shown in [Fig. 1f], a stack 4' consisting of the second contact layer 4p, the active region 4W, the first contact layer 4n, and, where applicable, the intercalated layer, is first transferred onto the exposed surface of the waveguide 2a revealed in the previous step, in the form of a vignette. This transfer can be achieved by assembly, for example by molecular adhesion, of the vignette formed by the stack 4'. In a subsequent step, this stack 4' is structured, for example by dry etching, to reveal a surface of the first layer 4n. Then, two electrical contact pads 5 are created, respectively in contact with the first and second contact layers 4p,4n.These pads 5 allow a current to flow through the gain 4 structure and cause the generation / amplification of an optical mode, as is well known. At the end of this sequence, we have a gain 4 structure, equipped with its electrical contact pads 5, on and in contact. with waveguide 2a, as shown in [Fig. 1g]. Refer to document WO2010100882A1 for further details on this first variant of this implementation method.

[0061] As an alternative to this variant, in which the gain 4 structure is finalized after the stack 4' has been transferred into the opening in the buried dielectric layer, the fully finalized gain 4 structure can be transferred directly. This can be done, for example, using the microtransfer printing technique. A description of this technique and its use in photonics can be found in the paper 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 short, according to this technique, a gain 4 structure, including the structured stack 4' and the electrical contacts 5, is fully prepared on a temporary substrate.Using a handle, this gain 4 structure is taken from its temporary substrate, transferred and assembled onto a final substrate, here on and in contact with the revealed surface of the waveguide base at edge 2a.

[0062] 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.

[0063] The assembly can be carried out, for example, by molecular adhesion, just as in the first variant. It should be noted that the surface receiving the heterogeneous structure, the exposed surface of the waveguide base, having received no treatment likely to degrade it, is particularly well suited to receiving the heterogeneous structure.

[0064] To facilitate this adhesion, and regardless of 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 include, by way of illustration, the exposure of this surface to a plasma, for example an oxygen plasma.

[0065] Figure 1g shows the state of the photonic device at the end of this step of formation of the gain 4 structure.

[0066] 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 made on the encapsulation layer 6, these tracks being able to include metallic vias 8' passing through the encapsulation layer 6 to a contact structure buried 7 in the cover layer 5 and to the electrical contacts 5 of the structure 4.

[0067] To obtain the electro-optical DP modulator shown in [Fig. 3], the fifth step comprises transferring the waveguide base with edge onto the exposed surface 2a, of a block of material exhibiting electro-optical properties, for example LiNbO3, BTO, or a stack of III-V materials. As in the previous case, electrical tracks 8 can be formed on an encapsulation layer 6; these tracks also form electrical contact pads S, G, S on the heterogeneous structure 4 of electro-optical material. Note that the waveguide with edge 2a can in this case have two edges, each edge constituting a modulator arm.

[0068] Figures 2a to 2f illustrate a variant of the preparation process, which can be applied to any heterogeneous structure 4, in which at least one cavity 20 is formed in the base of the waveguide at edge 2a to absorb outgassing products resulting from the bonding of the heterogeneous structure to the base.

[0069] As shown in [Fig. 2a], this variant of the process includes the formation of at least one etching stop pattern 9 on the base of the waveguide 2a during the photonic component layer formation step. In [Fig. 2a], and by way of illustration, a waveguide with an edge 2a is defined in the surface layer 1 of the starting substrate 1, and two stop patterns 9 are in contact with the surface layer, on either side of the edge of the waveguide 2a. A stop pattern may, in particular, be made of a silicide or a metal, such as TiN.

[0070] The photonic component layer 2 is then transferred onto the support substrate le and the base substrate is removed to expose the buried dielectric layer 1b, just as in the first embodiment ([Fig.2b]).

[0071] At this stage, and as shown in [Fig. 2c], a first mask layer 3a is placed on the buried dielectric layer 1b. This first mask layer 3a has openings aligned with the etching stop patterns 9. The buried dielectric layer 1b and the layer 1e are then successively etched, for example by dry etching. The dry etching stops very precisely at the stop pattern 9. This removal can also be carried out by wet etching. In all cases, this etching is stopped by the stop pattern 9. The first mask layer 3a can then be removed.

[0072] The process can then be repeated as described above, by placing a second mask layer 3b, this time to expose the central part Zc of the waveguide base at stop 2a while masking its peripheral area Zc. The second mask layer 3b is also open at the openings leading to the stop pattern 9.

[0073] 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 the heterogeneous structure by assembly.

[0074] When, in the next step of forming the heterogeneous structure 4, this structure is assembled onto 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 species, particularly gaseous ones, that are formed or released at the assembly interface between the heterogeneous structure 4 and the waveguide 2a. This is especially true when this assembly is carried out by molecular adhesion.

[0075] To finalize the preparation of the DP photonic device, 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 made on the encapsulation layer 6, these tracks being able to include metallic vias allowing to make electrical contacts with the heterogeneous structure 4.

[0076] Of course the invention is not limited to the embodiments described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Demands

1. Photonic device (PD) comprising a hybrid waveguide capable of propagating an optical mode comprising: a component layer (2) disposed by a first surface on a support substrate (le), 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 to the first surface, and of at least one edge oriented towards the side of the support substrate (le); - a dielectric layer (1b) disposed 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 over a central part of the base of the edge waveguide (2a);- a heterogeneous structure (4) on and in contact with 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.;

2. Photonic device (PD) according to claim 1 wherein 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 disposed on and in contact with the first contact layer (4n) and a second contact layer (4p) disposed on and in contact with the active region (4W), and the photonic device (PD) is an amplifier or a laser.

3. Photonic device (PD) according to the preceding claim in which the heterogeneous structure (4) also comprises, disposed between and in contact with the base of the waveguide (2a) and the first contact layer (4n), an intercalated layer formed of an undoped semiconductor material.

4. Photonic device (PD) according to any one of claims 2 and 3 wherein the first contact layer (4n) and the second contact layer (4p) comprise electrical contact pads (5).

5. A photonic device (PD) according to claim 1, wherein the heterogeneous structure (4) comprises a material exhibiting electro-optical properties, such as LiNbO3, BTO, or a stack of III-V materials, and the photonic device (PD) is an electro-optical modulator.

6. Photonic device (PD) according to any 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).

7. Photonic device (PD) according to the preceding claim in which the cavity (20) has a bottom formed of at least one etching stop pattern (9).

8. Photonic device (PD) according to any one of the preceding claims comprising an encapsulation layer (6) disposed on the component layer (2) and on the heterogeneous structure (4).

9. Photonic device (PD) according to the preceding claim comprising metallic tracks (8) disposed on the encapsulation layer (6), in electrical contact with the heterogeneous structure (4).

10. Photonic device (PD) according to one of the two preceding claims wherein the component layer (2) comprises at least one buried contact structure (7,2d).

11. Photonic device (PD) according to the preceding claim further comprising metallic vias passing through the encapsulation layer (6), the dielectric layer (1b) and a portion of the component layer (2) to contact the buried contact structure (7,2d).

12. Photonic device (PD) according to any one of the preceding claims wherein the edge waveguide (2a) is made of silicon and the dielectric layer (1b) is made of silicon dioxide.

13. Method of 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 (la), a buried dielectric layer (1b) disposed on and in contact with the base substrate (la) and a surface layer (le) disposed on and in contact with the buried dielectric layer (1b); - form a component layer (2) in the starting substrate (1), the component layer comprising at least one edge waveguide (2a) formed of a base on and in contact with the buried dielectric layer (1b) and at least one edge overhanging the base, the component layer (2) comprising a covering material (2e) encapsulating the at least one edge waveguide (2a); - transfer the component layer (2) onto a support substrate (le) and remove the base substrate (la) to expose the buried dielectric layer (1b); - selectively remove the dielectric layer (1b) to expose a central part (Zc) of the edge waveguide (2a) while preserving the dielectric layer on a peripheral contour (Zb) of the waveguide (2a); - form a heterogeneous structure (4) on and in contact with the central part of the base of the edge waveguide (2a).

14. A 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.

15. A preparation method according to any one of claims 13 to 14 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 heterogeneous structure formation step (4).

Images