Method for preparing a photonic device comprising a plurality of hybrid waveguides capable of propagating an optical mode

Abstract

The invention relates to a method for preparing a photonic device. This method begins by placing a donor substrate (SD) by forming a sacrificial layer (SL) on a base substrate (SB). A surface stack (4e) is then established on this layer. Trenches (T) are cut into this stack down to the base substrate (SB) to define several vignettes (V). In parallel, a component layer (2) is prepared on a support substrate (1e), where primary waveguides (2a) are formed according to a predetermined arrangement. Transferring the isolated vignette onto this component layer involves precise alignment and assembly, followed by the selective removal of the sacrificial layer (SL), allowing the removal of the base substrate (SB). The transferred vignette is then processed to form heterogeneous structures (4), thus facilitating the propagation of an optical mode through the hybrid waveguides of the photonic device. Figure 1a

Description

Title of the invention: Method for preparing a photonic device comprising a plurality of hybrid waveguides capable of propagating an optical mode. FIELD OF THE INVENTION

[0001] The present invention relates to a photonic device comprising a layer of components arranged on a support substrate. It also relates to a method for preparing such a photonic device, this method comprising preparing a donor substrate of materials constituting the components and transferring these materials onto the support substrate. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] US patent 7482184 proposes forming a photonic device by transferring a III-V material vignette onto the back face of a component layer comprising a waveguide. This vignette is then processed by lithography and etching to create active IILV photonic components, for example, a light source (laser diode or micro-laser) or a detector. US patent 10884187 proposes, in a similar approach to transferring a IILV material vignette, to collectively form a plurality of active photonic components within a single vignette.

[0003] Typically, the image transfer process involves the formation of a surface stack comprising successively a p-doped layer, an active layer, and an n-doped layer, on a base substrate, these layers being based on III-V materials. The base substrate may be provided with an etching arrest layer disposed directly beneath the surface stack. The base substrate may have a thickness of between 200 micrometers and 650 micrometers, and the surface stack a thickness of a few micrometers, for example, between 1 and 5 micrometers. This substrate and the layers of the surface stack may be made of InP or InP-based materials. In this case, the arrest layer may be formed, for example, of InGaAs or InAlAs.The base substrate and the surface stack are then cut by sawing, for example into squares or rectangles where one side or length may have a dimension on the order of a mm, the surface stack placed on each cut portion then forming a vignette.

[0004] To implement the transfer operation mentioned in a previous paragraph, the vignettes are assembled on the back face of the component layer, and the base substrate supporting these vignettes is removed by wet etching. The etching solution is chosen to be selective with respect to the stop layer, which may itself being eliminated in a second etching step. Following this transfer operation, a plurality of active photonic components can be defined in each vignette by a sequence of lithography processes and etching of the surface stacks.

[0005] In detail, the transfer operation is described in the document by S. Menezo et al., "Advances on III-V on Silicon DBR and DFB Lasers for WDM Optical Interconnects and Associated Heterogeneous Integration 200mm-Wafer-Scale Technology", 2014 IEEE Compound Semiconductor Integrated Circuit Symposium (CSICS), La Jolla, CA, USA, 2014, pp. 1-6 or in "IILV / Si photonics by die-to-wafer bonding" by G. Roelkens, Materials today, Volume 10, Issues 7-8, Page 36-43.

[0006] This vignette approach is not entirely satisfactory, however, because: - during the separation of the base substrate and vignettes by sawing, the edges of these vignettes are altered. This alteration prevents intimate contact at the edge of the vignette with the component layer during their assembly in the transfer operation. The solutions used during the subsequent wet stages of the manufacturing process are then likely to seep into the interface and damage it; - the dissolution of the base substrate of the vignettes in the etching solution after the transfer operation does not allow its recycling; - the removal of the base substrate of the vignettes also generates particles and hinders the subsequent lithography / etching steps of the stacks.

[0007] Other approaches have been considered for transferring active III-V photonic components. 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 document by Camiel Op de Beeck, et al., "Heterogeneous IILV on Silicon nitride amplifiers and lasers via microtransfer printing," Optica 7, 386-393 (2020). In short, according to this technique, the photonic component is prepared on a temporary substrate. Using a stamp, this component is removed from its temporary substrate and transferred and assembled onto a target substrate, in this case, the front or back face of a component layer.

[0008] The document by J. O'Callaghan et al., "Comparison of InGaAs and InAlAs sacrificial layers for release of InP-based devices," Opt. Mater. Express 7, 4408-4414 (2017), reveals, however, that the assembly surface of a photonic component (which corresponds to the surface of the component detached from the temporary substrate) is The surface is particularly rough. This roughness makes assembly, especially molecular adhesion, and the transfer of the photonic component onto the component layer delicate. Furthermore, handling the component with the handle may require the use of a resin, which can generate polluting species that may further hinder molecular adhesion assembly. Moreover, this transfer step is not performed collectively, as it is carried out component by component, making the process of transferring multiple components lengthy and complex. SUBJECT OF THE INVENTION

[0009] One object of the invention is to remedy, at least in part, the problems just described. In particular, the invention aims to improve the step of assembling the vignette during its transfer. To this end, the invention seeks to overcome the problems associated with sawing the base substrate and the vignettes. It also seeks to avoid implementing the microtransfer printing technique. The invention also aims to avoid the complete removal, by etching, of the base substrate. BRIEF DESCRIPTION OF THE INVENTION

[0010] With a view to achieving one of these goals, the object of the invention proposes a method for preparing a photonic device comprising a plurality of hybrid waveguides capable of propagating an optical mode, each hybrid waveguide being formed of a primary waveguide at least partially overlaid by a heterogeneous structure, the method comprising the following steps: - a step of preparing a donor substrate comprising the formation, on and in contact with a base substrate, of a sacrificial layer, then the formation, on and in contact with the sacrificial layer, of a surface stack comprising successively, from the sacrificial layer, a p-doped layer, an active layer, an n-doped layer; - a step of defining a plurality of vignettes in the surface stacking, the definition step including the creation of trenches extending deep into the surface stacking down to the base substrate; - a step of singularizing the donor substrate to isolate at least one vignette; - a step of preparing a layer of components comprising the formation of a plurality of primary waveguides on a support substrate, the primary waveguides of the plurality of primary waveguides being distributed on the support substrate according to a predetermined arrangement; - a transfer step comprising a substep of alignment and assembly of the isolated vignette and the component layer aimed at placing the vignette and the plurality of primary waveguides opposite each other, and a substep of selective removal of the sacrificial layer to allow removal of the vignette's base substrate; - a step of forming a plurality of heterogeneous structures, the formation step including the processing of the vignette transferred onto the component layer to form a plurality of first metallic contacts and a plurality of second metallic contacts respectively in contact with the p-doped layer and the n-doped layer of the vignette.

[0011] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: - the creation of trenches during the step of defining a plurality of vignettes also includes the definition of a plurality of ribbons within the vignettes, the ribbons of the plurality of ribbons being disjoint and distributed according to the predetermined arrangement; - the substep of aligning and assembling the isolated vignette and the component layer is conducted in such a way as to place the plurality of ribbons and the plurality of primary waveguides opposite each other; - the step of forming a plurality of heterogeneous structures includes the definition of a plurality of ribbons within the vignette, the ribbons of the plurality of ribbons being disjoint and distributed according to the predetermined arrangement so as to reside opposite the plurality of primary waveguides; - the plurality of first metallic contacts and the plurality of second metallic contacts are respectively in contact with the p-doped layer and the n-doped layer of the ribbons of the plurality of ribbons; - the singularization step includes scanning the donor substrate with a laser beam; - the component layer has a superficial dielectric layer; - The component layer preparation step includes: • a sub-step of supplying a starting substrate comprising a temporary substrate, a buried dielectric layer disposed on and in contact with the temporary substrate and a surface layer disposed on and in contact with the buried dielectric layer; • a sub-step of forming the plurality of primary waveguides in the surface layer, the primary waveguides of the plurality of primary waveguides being arranged on and in contact with the buried dielectric layer; • a substep of depositing a covering material on the surface layer to bury the primary waveguides of the plurality of primary waveguides in the component layer; • a sub-step of assembling the component layer to the supporting substrate and removing the temporary substrate, the buried dielectric layer becoming the surface dielectric layer of the component layer; - the transfer step includes bringing the exposed face of the vignette into contact with the surface dielectric layer of the component layer; - the component layer preparation step includes the local removal of the surface dielectric layer at the central parts of the primary waveguides of the plurality of primary waveguides in order to expose these central parts; - the transfer step includes bringing the exposed face of the vignette into direct contact with the central parts of the primary waveguides of the plurality of primary waveguides; - the component layer preparation step includes the formation of spacing layers on and in contact with the central parts of the primary waveguides of the plurality of waveguides and in which the transfer step includes bringing the vignette into contact with the dielectric spacing layers; - the donor substrate preparation step includes the formation, on the doped n layer of the surface stack, of an intercalated layer consisting of an undoped semiconductor material or a dielectric layer; - the base substrate is InP, the sacrificial layer is InAlAs, the p-doped layer and the n-doped layer are InP and the active layer includes quantum wells; - the base substrate is made of AsGa, the sacrificial layer of AlGaAs, the p-doped layer and the n-doped layer are made of AsGa, and the active layer includes quantum dots. Brief description of the drawings

[0012] 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:

[0013] [Fig. la] [Fig.lb] [Fig.le][Fig. Id] Figures la, 1b, and le and Id each represent a photonic device which can be obtained using a preparation process according to the invention;

[0014] [Fig.2a] [Fig.2b] [Fig.2c][Fig.2d][Fig.2e] [Fig.2f] [Fig.2g] Figures 2a, 2b, 2c, 2d, 2e, 2f, 2g represent the steps in preparing a donor substrate according to different implementation methods;

[0015] [Fig.3a] [Fig.3b] [Fig.3c] [Fig.3d][Fig.3e] [Fig.3f]

[0016] Figures 3a, 3b, 3c, 3, 3e and 3f illustrate a step in preparing a layer of components;

[0017] [Fig.4a] [Fig.4b] [Fig.4c]

[0018] Figures 4a, 4b, 4c illustrate the steps of an integration sequence of the photonic device;

[0019] [Fig.5a] [Fig.5b]

[0020] Figures 5a and 5b represent the state of a photonic device during its integration employing a dielectric layer between a vignette and a component layer;

[0021] [Fig.6a] [Fig.6b]

[0022] Figures 6a and 6b represent the state of a photonic device during its integration without any dielectric layer between a vignette and a component layer;

[0023] [Fig.7a] [Fig.7b]

[0024] Figures 7a and 7b represent the state of a photonic device during its integration, a vignette being formed from a plurality of strips;

[0025] [Fig.8]

[0026] Fig. 8 illustrates a vignette with an alternative arrangement of ribbons. DETAILED DESCRIPTION OF THE INVENTION Photonic device

[0027] Figures 1a, 1b, and 1a and 1d each represent a DP photonic device that can be obtained using a preparation process according to the invention.

[0028] This device comprises a component layer 2 having a first surface resting on a support substrate 1, which may be made of silicon. The component layer 2 comprises, embedded in a covering material 2e, a plurality of waveguides 2a, called "primary waveguides," four primary waveguides 2a in the examples shown. These may be edge waveguides, as is the case in the examples shown, but this is not a necessary characteristic, and generally the primary waveguides 2a may be of any suitable nature. The primary waveguides 2a are typically made of silicon, Preferably monocrystalline, but may also be partially composed of crystalline silicon and amorphous and / or polycrystalline silicon. The covering material 2e may be made of silicon dioxide. Each primary waveguide 2a is flush with a second surface of the component layer 2, this second surface being opposite the first surface in contact with the supporting substrate le. A dielectric layer 1b, typically made of silicon dioxide, is disposed on and in contact with the second surface of the component layer 2.

[0029] The component layer 2 of the DP photonic device may include photonic components other than the primary waveguides 2a flush with its second surface. It may thus include one or a plurality of waveguides embedded in the covering material, for example, made of silicon nitride, one or a plurality of photodetectors, and contact structures embedded in the covering layer 2e in the form of metallic tracks or vias. In such a case, the DP photonic device may be equipped with through-vias that allow the contacts with the embedded contact structures to be transferred to the surface, at the level of metallic tracks.

[0030] The DP photonic device also includes, respectively arranged at the edges of the primary waveguides 2a of the plurality of primary waveguides, a plurality of heterogeneous structures 4. A "heterogeneous structure" is defined as a stack of materials having a different nature than the material constituting the primary waveguides 2a. A heterogeneous structure 4 and a waveguide 2a together form a hybrid waveguide of the DP photonic device in which an optical mode can propagate. The heterogeneous structures 4 can, in combination with the primary waveguides 2a they overlie, constitute optical amplifiers or laser emitters.

[0031] In the embodiment of [Fig.la], the heterogeneous structures 4 rest on, and are in contact with, the dielectric layer 1b.

[0032] In the embodiment of [Fig. 1b], the dielectric layer 1b has openings and does not extend above a central portion of the primary waveguides 2a. The heterogeneous structures 4 rest directly on, and are in contact with, the primary waveguides 2a. As illustrated in [Fig. 1b], a cavity 20 or a plurality of cavities 20 can be provided in at least some of the primary waveguides 2a, the cavity or cavities of a primary waveguide 2a being closed at least partially by a heterogeneous structure 4. The bottom of a cavity 20 can be defined by a stop pattern 9 which, during cavity formation, allows for selective etching of the material of the primary waveguide 2a, without penetrating the covering material 2e. This reason for stopping 9 may in particular consist of a silicide or a metal, such as TiN.

[0033] In the embodiments of [Fig. 1a] and [Fig. 1d], a gapping layer If is placed in the openings provided in the dielectric layer 1b at the center of the primary waveguides 2a. In some cases, this gapping layer If is of a thickness substantially equal to that of the dielectric layer 1b or of a thickness less than that of the dielectric layer 1b. It may be silicon oxide or silicon nitride deposited on the entire exposed surface of the component layer (including on the remaining parts of the dielectric layer 1b) or an undoped semiconductor material, for example InP or Al2O3 or AIN. It can also be predicted that the If gap layer is formed of a layer of silicon oxide or silicon nitride, in contact with the central part of the primary waveguide 2a and a layer of an undoped semiconductor material disposed on the silicon oxide layer.

[0034] The If gapping layer, when present, is at least disposed under the heterogeneous structure 4, in contact with this structure and with the exposed surface and the central part of the primary waveguides 2a. Depending on the embodiment chosen, the If gapping layer can completely cover the exposed central part of the primary waveguides 2a, in the openings provided in the dielectric layer, as shown in [Fig. i] or partially cover this central part, as shown in [Fig. i1].

[0035] The heterogeneous structures 4 are formed from a first n-doped layer, a 4W active layer formed from a stack of layers of III-V semiconductor materials arranged on and in contact with the n-doped layer, and a p-doped layer arranged on and in contact with the 4W active layer. By way of example, the p-doped layer and the n-doped layer may be made of InP, and the 4W active layer may include quantum wells. Alternatively, the p-doped layer and the n-doped layer may be made of GaAs, and the 4W active layer may include quantum dots. Preferably, the p-doped layer, the n-doped layer, and the 4W active layer are crystalline.

[0036] The heterogeneous structures 4 may comprise layers other than those presented above and illustrated in Figures 1a, 1b, 1c, and 1d. Thus, in all embodiments corresponding to these figures, and as already explained in relation to the embodiments of Figures 1a and 1d, an intercalated If layer formed of an unintentionally doped semiconductor material can be provided on the doped layer 4n of a heterogeneous structure, on the side of a primary waveguide. This unintentionally doped layer may be of the same nature as the doped layer 4n, i.e., InP or GaAs, to use the examples listed above. When such an intercalated If layer is present, it can constitute the gapping layer 1a shown in [Fig. 1d].

[0037] Regardless of how the heterogeneous structures 4 are based on the primary waveguides 2a, directly or indirectly, such a heterogeneous structure 4 generally takes the form of a ribbon with a lateral dimension (along the y-direction shown in Figures 1a, 1b, 1e, 1d) smaller than its longitudinal dimension (along the x-direction in Figures 1a, 1b, 1c, 1d). The general ribbon shape of a heterogeneous structure 4 can have a lateral dimension on the order of 5 micrometers at the active layer 4W, and is typically between 1 and 20 micrometers. Its longitudinal dimension can be on the order of 400 micrometers, and is typically between 100 and 4000 micrometers. Two adjacent heterogeneous structures 4 can be separated, in the lateral direction, by a spacing distance of the order of 150 micrometers, and more generally between 100 micrometers and 500 micrometers.

[0038] As can be clearly seen in the figures, the plurality of heterogeneous structures 4 comprises a plurality of first metallic contacts 5p and a plurality of second metallic contacts 5n respectively in contact with the exposed surfaces of the p-doped layers 4p and the n-doped layers 4n.

[0039] The DP photonic devices shown in Figures 1a, 1b, 1c, 1d comprise an encapsulation layer 6 disposed on the photonic component layer 2 and encapsulating the heterogeneous structures 4. This encapsulation layer 6 may, in particular, be made of silicon dioxide and / or silicon nitride. Metallic tracks 8 may be disposed on the encapsulation layer 6, in electrical contact with the heterogeneous structure 4, in particular with the first metallic contacts 5n and the second metallic contacts 5p, via a via penetrating the encapsulation layer 6. Other types of contact are naturally possible for electrically connecting the p-doped layer 4p and the n-doped layer 4n to metallic tracks 8.

[0040] The tracks 8, vias and metallic contacts 5n,5p allow a current to be conducted and circulated through the active layer 4W, in order to enable, by pumping, the optical emission or amplification mechanism. Optical modes can thus be propagated in, respectively, the hybrid waveguides, each hybrid waveguide being formed of a primary waveguide 2a and a heterogeneous structure 4.

[0041] We now present a method for implementing a preparation process according to the invention for the photonic devices just described. Preparation of a donor substrate

[0042] First, a preparation process according to the invention comprises the preparation of a donor substrate SD. This substrate serves to prepare the materials necessary for the fabrication of the heterogeneous structures 4 of the device DP photonics, by a layer transfer technique. The preparation step of the donor substrate SD, illustrated in [Fig. 2a], includes the formation, on and in contact with a base substrate SB, of a sacrificial layer SL, then the formation, on and in contact with the sacrificial layer, of a surface stack 4e comprising successively, from the sacrificial layer SL, a p-doped layer 4p, an active layer 4W, and an n-doped layer 4n. This preparation step can consist of successively depositing the sacrificial layer SL and the 4p, 4W, and 4n layers composing the surface stack onto the base substrate SB, using a conventional deposition technique (for example, MOCVD for "Metal-Organic Chemical Vapor Deposition," or MBE for "Molecular Beam Epitaxy").

[0043] Also shown in [Fig. 2a], in dashed lines, is an optional If gapping layer of the surface stack 4e, which may be present in an undoped semiconductor material. It may also be a silicon oxide or silicon nitride layer. This optional If gapping layer may be present in all embodiments of the photonic device preparation process described herein.

[0044] When the surface stacking 4e is InP-based, the base substrate SB can be a bulk InP substrate and the sacrificial layer SL can be made of or comprise InAlAs. When the surface stacking 4e is GaAs-based, the base substrate SB can be a bulk GaAs substrate and the sacrificial layer SL can be made of or comprise FAlGaAs.

[0045] In all cases, the sacrificial layer SL has a different nature from that of the base substrate SB and from that of the layers composing the surface stack 4e. This layer can then be selectively removed, by means of a selective etching solution as will be illustrated in a later section of this description, in order to detach the surface stack 4e from the base substrate SB. The etching solution can, for example, be a mixture based on ferric chloride (FeCl3) suitable for removing the sacrificial layer by etching when it is made of InAlAs, without affecting the base substrate SB or the surface stack 4e.

[0046] In a second step of a preparation process according to the invention, shown in top view in Figures 2b and 2e, a plurality of vignettes V are defined in the donor substrate SD by etching trenches T in the surface layer 4e, preferably by dry etching.

[0047] During this step, the donor substrate SD is therefore decomposed into vignettes V, here rectangular vignettes, whose length and width are typically between 1 mm and 2 mm, and more generally between 500 micrometers and 5 mm. In general, the vignettes V have a sufficient size to cover a plurality of waveguides 2a of the supporting substrate le, during a subsequent layer transfer operation.

[0048] Figures 2b and 2e show cutting paths d, arranged in the trenches T, allowing the vignettes V to be singled out in a later step of the process.

[0049] In the embodiment of [Fig. 2e], the creation of trenches T by etching is such that it also includes the definition of a plurality of disjoint strips M within the vignettes V. The strips M are distributed on each vignette V of the donor substrate SD according to a predetermined arrangement corresponding to the arrangement of the primary waveguides 2a on the supporting substrate le, which will allow, during a subsequent layer transfer operation, the strips M of a vignette V to be collectively transferred to the position of these waveguides 2a. Thus, trenches T can be provided between two strips M of the same vignette V, having a width between 50 micrometers and 500 micrometers, this trench width corresponding to the distance separating two adjacent primary waveguides 2a of the photonic device DP.

[0050] These ribbons can extend laterally, along the y direction, over a width of approximately 100 micrometers, and typically between 20 micrometers and 200 micrometers. Longitudinally, along the x direction shown in the figure, the ribbons M can extend over a length of approximately 100 micrometers to 1 mm, or even 4 mm, such as, for example, 700 micrometers.

[0051] As shown in the sections of Figures 2c, 2d (with reference to sections AA,BB of [Fig.2b]) and Figures 2f,2g (with reference to sections AA,BB of [Fig.2e]) the trenches T extend through the entire thickness of the surface stack 4e and the sacrificial layer, the bottom of the trench thus exposing the basic substrate SB.

[0052] The step of defining the plurality of vignettes V, and where applicable, the ribbons M, may include applying a mask to the surface stack 4e of the donor substrate SD shown in [Fig. 2a], the mask covering this stack 4e to define the shape of the vignettes V (and, where applicable, the ribbons M) and leaving exposed portions of the stack 4e between these patterns. The definition step may then include etching the exposed portions of the stack 4e, for example, a dry etch, to form the trenches T extending in depth, along the z-direction, into the base substrate SB.

[0053] In a subsequent singularization step, the donor substrate SD is cut along the cutting paths d to singularize the vignettes V. This step can advantageously be implemented by a stealth cutting technique (or "stealth dicking" in industry terminology) in which a laser beam is scanned along the cutting paths d, at the bottom of the trenches T, to focus it within the base substrate SB. The beam causes cracks to appear, extending between the upper and lower surfaces of the base substrate SB, along the cutting path. Then, forces are applied to the substrate SB, generating tensile stresses that lead to crack extension, thus separating the vignettes V from one another.

[0054] It is noted that this stealthy cutting is facilitated by the presence of deep trenches, penetrating into the base substrate SB. The cracks then develop in a single and homogeneous material, the extension of the cracks leading to the singularization of the vignettes V is not blocked by the presence of another material, for example that composing the sacrificial layer.

[0055] The presence of the trenches, regardless of the method used to cut the base substrate, ensures a clean and precise cut at the assembly face of the V-shaped vignettes, which is not possible with a more conventional cutting technique, as noted in the introduction to this application. Although the base substrate can be cut using any conceivable technique, the stealth laser cutting method is preferred, as it avoids or limits the generation of particles produced during conventional "mechanical" cutting.

[0056] At the end of these donor substrate preparation and singularization steps, we have at least one vignette V based on a portion of the base substrate (and generally a plurality of such vignettes V), this vignette V may or may not have a plurality of strips M separated by slices T and arranged according to the predetermined arrangement.

[0057] Preparation of the photonic component layer.

[0058] A method for preparing a DP photonic device also includes, before or after the step of preparing the donor substrate and the step of defining the plurality of motifs, a step of preparing the layer of component 2.

[0059] In general, this preparation step aims to form the plurality of primary waveguides 2a of the component layer 2 disposed on the support substrate le. The primary waveguides 2a extend over the support substrate to be covered by a vignette V and, where appropriate, are distributed over this support substrate le according to the same arrangement of the ribbons M on the surface of a vignette V when such ribbons have been properly defined in the donor substrate SD.

[0060] Generally speaking, the preparation step aims to collectively form numerous DP photonic devices on the same fabrication substrate, which naturally leads to the collective use of numerous vignettes V to complete their fabrication. For the sake of simplicity of illustration, the following are shown in the figures and we detail, in the continuation of this description, the preparation of a DP photonic device employing a single vignette V, it being understood that this description applies in the same way when a plurality of such devices or a plurality of vignettes are exploited collectively.

[0061] There are multiple ways to implement this preparation step, the simplest being to define on a substrate, for example silicon or silicon-on-insulator type, the primary waveguides 2a using the usual microelectronic techniques (deposition, etching, photolithography, oxidation...).

[0062] With reference to figures 3a to 3f, however, a preferred approach to implementing this step of preparing the layer of component 2 is set out.

[0063] In a first substep shown in [Fig. 3a], a starting substrate 1 is provided. This substrate, for example of the silicon-on-insulator type, is formed of a temporary substrate la, typically made of silicon and several hundred microns thick. A buried dielectric layer 1b, typically made of silicon oxide, is disposed on and in contact with the temporary substrate la.

[0064] 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.

[0065] 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 initial substrate. It therefore exhibits 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.

[0066] 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 temporary substrate la on the one hand, and the surface layer 1b on the other are very smooth, less than 1 m in peak-to-peak measurement.

[0067] In a second substep, illustrated in [Fig. 3b], the starting substrate 1 is treated to form, in and on the surface layer 1, a layer of photonic components 2 comprising, in particular, the plurality of primary waveguides 2a. This layer of components 2 extends from a first exposed surface to a second surface, opposite the first surface, in contact with the buried dielectric layer 1b. Conventional technological steps (deposition, etching, photolithography) can be chained together to form, by processing the surface layer of the starting substrate 1, the plurality of primary waveguides 2a and all the other photonic components that the component layer 2 can comprise. As already explained, the plurality of primary waveguides 2a is arranged on the temporary substrate in the same arrangement as that of the M motifs on the donor substrate.

[0068] Optionally, it may be provided that stopping patterns 9 are formed on at least some of the primary waveguides 2a, these patterns will allow controlled depth cavities to be formed in these primary waveguides, as will be illustrated in a later section of this description.

[0069] The treatments carried out in this substep include the deposition of a coating material 2e, for example silicon dioxide, in order to encapsulate the assembly and finalize the formation of the component layer 2 resting on the base substrate la, via the buried dielectric layer 1b. At the end of this treatment substep, the first exposed surface of the photonic component layer 2 may be polished to facilitate the subsequent transfer step.

[0070] Following this processing substep, 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 of layer 2 comprise at least a plurality of primary waveguides 2a formed in the surface layer 1 and arranged on a support substrate 1 according to the determined arrangement. It should be noted that these primary waveguides 2a, having been formed in the surface layer 1, rest on, and are in contact with, the buried dielectric layer 1b.

[0071] In a third substep shown in [Fig. 3c], the component layer 2 is transferred onto a support substrate. This transfer can be carried out by any suitable technique. This transfer generally involves assembling the component layer 2 carried by the temporary substrate with this support substrate via the first surface. This could, for example, be an assembly by molecular adhesion.

[0072] Once the assembly is complete, and in a fourth thinning substep, the temporary 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 1b, it is ensured that the step of removing the base substrate does not lead to penetration or perforation of this buried dielectric layer 1b. The quality of the layers is thus preserved. underlying, including component layer 2 and the photonic components it contains.

[0073] Once the temporary substrate is removed, the buried dielectric layer 1b is exposed and forms a superficial dielectric layer of the component layer 2. The component layer 2, equipped with the superficial dielectric layer 1b, transferred onto the supporting substrate is shown on a [Fig.3d].

[0074] According to the main approach to implementing the component layer preparation step, shown in [Fig.3d], the dielectric layer 1b is preserved to completely cover the component layer 2. It can be thinned, for example by polishing or chemically, without however removing it, even locally.

[0075] In a first embodiment of the component layer preparation step, shown in [Fig. 3e], this preparation step further includes a substep for the local and selective removal of the dielectric layer 1b. This substep aims to expose a central portion Zc of the primary waveguides 2a, while preserving the surface dielectric layer 1b at its peripheral contour Zb. The openings made in the surface dielectric layer 1b can be rectangular in shape and of sufficient size to accommodate a ribbon M, as will be made apparent later in this description. The width of a central area Zc is thus typically between 30 micrometers and 1 mm, and its length is a few millimeters, for example, 2 mm or up to 2 mm.The peripheral contour Zb can have a width on the order of 10 micrometers, for example, between 5 and 30 micrometers. Local and selective removal of the surface dielectric layer 1b can be achieved by etching, for example, using a wet HF-based solution, after the surface dielectric layer 1b has been coated with a resin that masks the areas to be preserved, in particular the peripheral contour Zb of the primary waveguides 2a. This prevents the etching solution from seeping around the sides of the primary waveguides 2a and damaging the surrounding coating layer 2e. The exposed surfaces of the primary waveguides 2a, in the central zone Zc, exhibit a low roughness, identical or close to that present at the interface between the surface layer 1e and the buried dielectric layer 1b of the original substrate 1.It was not affected by the etching solution used during the removal of the base substrate. It therefore exhibits favorable characteristics, particularly in terms of roughness, cleanliness, and flatness, for receiving, by assembly, an M-strip.

[0076] At this stage, optionally and during a complementary substep of the component layer preparation step, a cavity or a plurality of cavities 20 can be locally formed in at least some of the guides primary wave 2a, at the level of their exposed central Zc zones. This formation can be carried out at the stopping points 9 provided in the component layer 2, in contact with at least some of the waveguides, by selective etching. The cavities can facilitate the assembly of the component layer 2 with the ribbons M of a vignette M, by allowing the evacuation of gaseous species that may be released from the assembly interface.

[0077] Figure 3f illustrates a second embodiment of the component layer preparation step. This embodiment includes, after the substep of local and selective removal of the dielectric layer 1b in the first embodiment, a substep of depositing a spacer layer If onto the free face of the component layer. This spacer layer If is formed, in particular, on and in contact with the central portions Zc of the primary waveguides 2a. This deposition is therefore carried out in the openings provided in the surface dielectric layer 1b. The spacer layer If can facilitate the assembly of the component layer 2 with the strips M of a vignette. In this second embodiment, it can be formed from a dielectric such as silicon oxide or silicon nitride. It can have a thickness substantially equal to or less than that of the surface dielectric layer 1b. Finalization of the photonic device

[0078] Returning to the general description of the process for preparing the DP photonic device, we now present how a vignette V, where appropriate equipped with its ribbons M, and the layer of component 2 disposed on the support substrate le are exploited.

[0079] With reference to Figures 4a to 4c, a first integration sequence is presented using a vignette V without a ribbon M. In this case, a component layer obtained by the main approach to implementing the preparation step is used. According to this main approach, the dielectric layer 1b is preserved to completely cover the component layer 2.

[0080] During a transfer step, a vignette V from the donor substrate SD is assembled with the component layer 2 so that the vignette is positioned over the primary waveguides 2a. This alignment and assembly are shown in [Fig. 4a] when the component layer 2 is that shown in [Fig. 3d]. The assembly can be achieved by molecular adhesion of the exposed faces of the surface stack 4e with the exposed face of the component layer, here the buried dielectric layer 1b. This adhesion can be promoted by exposing at least one of these faces to a plasma, for example, an oxygen plasma.

[0081] It is possible to assemble during this transfer step a plurality of thumbnails V onto the component layer 2, particularly when such a layer is configured to allow the collective fabrication of a plurality of photonic devices, as is usually the case.

[0082] After this alignment and assembly substep, the sacrificial layer SL is selectively removed, for example using a solution for selectively etching this layer, as detailed in a previous section of this description. Removing the sacrificial layer allows the base substrate SB to be eliminated from the surface stack 4e forming the vignette. [Fig. 4b] illustrates the state of the structure after this removal.

[0083] In a subsequent step, a plurality of ribbons M are defined within the vignette V, for example by etching. This etching step (which may be identical or similar to that presented for the preparation of the donor substrate) leads to the formation of a plurality of disjoint ribbons distributed so as to reside respectively at the right of the plurality of primary waveguides 2a.

[0084] Figure 4c illustrates the state of the structure after the first integration sequence described above. It should be noted that this first integration sequence is perfectly compatible with a vignette in which the ribbons have been previously formed. These ribbons are arranged on the vignette V in the same predetermined arrangement in which the primary waveguides 2a are placed on the support substrate 2e, thus allowing them to be positioned precisely relative to one another. Such a configuration is shown in Figure 5a after assembly of a vignette V onto the dielectric layer 1b, and in Figure 5b after removal of the base substrate.

[0085] Figures 6a and 6b show another integration sequence using a vignette V equipped with a ribbon M. In this case, a component layer obtained according to the first embodiment of the preparation step is used. According to this first embodiment, the dielectric layer 1b was locally and selectively removed to expose a central portion Zc of the primary waveguides 2a. In this other integration sequence, the vignette V and the component layer 2 are aligned and assembled to bring the ribbons and primary waveguides into contact, respectively. Then, the base substrate SB supporting the vignettes can be detached as a block by selectively etching the sacrificial layer, as previously described.

[0086] Figures 7a and 7b present yet another integration sequence using a vignette V provided with a ribbon M. In this case, a component layer obtained by the second variant of the preparation step implementation is used, in which a gap layer If has been formed.

[0087] Regardless of the integration sequence chosen, the transfer step is followed by a step of forming heterogeneous structures 4 from the ribbons M. This step of forming heterogeneous structures includes the processing of the plurality of ribbons M arranged on the component layer 2, aimed at removing part of the p-doped 4p layer and part of the active 4W layer, this removal leading to the formation of a shoulder in the motif M, this shoulder freeing a surface of the n-doped layer. The heterogeneous structure formation step 4 also includes the formation, by deposition, of the plurality of first metal contacts and the plurality of second metal contacts respectively in contact with the p-doped 4p layers and the n-doped 4n layers.

[0088] Optionally, a substep of deposition of an encapsulation layer 6 and its possible planarization may be provided. In this case, metallic tracks 8 may also be formed on and within the encapsulation layer and brought into electrical contact with the heterogeneous structure 4, in particular with the first metallic contacts 5n and the second metallic contacts 5p, via penetrating vias.

[0089] Figures 1a, 1b, 1e and 1d show the DP photonic devices obtained at the end of the application of this step of formation of heterogeneous structures 4, including their encapsulation in the encapsulation layer 6, according to the different variants of the process of preparation of a DP photonic device which have just been described.

[0090] In all these variants, the problems arising from sawing the vignettes and removing the base substrate by dissolution, which were described in the introduction to this application, are avoided. In the proposed process, the vignettes V are singled out at predefined trenches T in the donor substrate, these trenches T passing through the sacrificial layer SL. Furthermore, the vignettes are transferred by bonding the doped layer n 4n or, where applicable, the gapping layer 2f, which have not undergone chemical etching and therefore do not exhibit excessive roughness. For these two reasons, the step of assembling the vignette V onto the component layer is of good quality, which is not the case in prior art approaches.

[0091] 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.

[0092] Thus, a vignette V can comprise any number of motifs M, arranged according to the predetermined arrangement as defined by the structure of the photonic device. [Fig. 8] shows vignettes V of substantially square shape, each vignette bearing 8 motifs arranged in two rows of 4 motifs.

Claims

1. Demands A method for preparing a photonic device (PD) comprising a plurality of hybrid waveguides capable of propagating an optical mode, each hybrid waveguide being formed of a primary waveguide (2a) at least partially overlain by a heterogeneous structure (4), the method comprising the following steps: - a step of preparing a donor substrate (SD) comprising the formation, on and in contact with a base substrate (SB), of a sacrificial layer (SL), then the formation, on and in contact with the sacrificial layer (SL), of a surface stack (4e) comprising successively, from the sacrificial layer (SL), a p-doped layer (4p), an active layer (4W), an n-doped layer (4n); - a step of defining a plurality of vignettes (V) in the surface stacking (4e), the definition step including the creation of trenches (T) extending in depth in the surface stacking (4e) down to the base substrate (SB); - a donor substrate singularization step (SD) to isolate at least one vignette (V); - a step of preparing a layer of components (2) comprising the formation of a plurality of primary waveguides (2a) on a support substrate (le), the primary waveguides of the plurality of primary waveguides (2a) being distributed on the support substrate (le) according to a predetermined arrangement; - a transfer step comprising a substep of alignment and assembly of the isolated vignette (V) and the component layer (2) aimed at placing opposite the vignette (V) and the plurality of primary waveguides (2a), and a substep of selective removal of the sacrificial layer (SL) to allow the removal of the base substrate (SB) of the vignette (V); - a step of forming a plurality of heterogeneous structures (4), the formation step including the processing of the vignette (V) transferred onto the layer of components (2) to form a plurality of first metallic contacts (5p) and a plurality of second metallic contacts (5n) respectively in contact with the p-doped layer (4p) and the n-doped layer (4n) of the vignette (V).

2. A preparation method according to the preceding claim in which the making of trenches (T) during the step of defining a plurality of vignettes (V) also includes the definition of a plurality of ribbons (M) within the vignettes (V), the ribbons (M) of the plurality of ribbons being disjoint and distributed according to the predetermined arrangement.

3. A preparation method according to the preceding claim in which the substep of alignment and assembly of the isolated vignette (V) and the component layer (2) is conducted so as to place opposite each other the plurality of ribbons (M) and the plurality of primary waveguides (2a).

4. A preparation method according to claim 1 wherein the step of forming a plurality of heterogeneous structures (4) comprises defining a plurality of ribbons (M) within the vignette (V), the ribbons (M) of the plurality of ribbons being disjoint and distributed according to the predetermined arrangement so as to reside opposite the plurality of primary waveguides (2a).

5. A preparation method according to any one of the preceding claims 2 to 4 wherein the plurality of first metallic contacts (5p) and the plurality of second metallic contacts (5n) are respectively in contact with the doped layer p (4p) and the doped layer n (4n) of the ribbons (M) of the plurality of ribbons.

6. A preparation method according to any one of the preceding claims, wherein the singularization step comprises scanning the donor substrate (SD) with a laser beam.

7. A preparation method according to any one of the preceding claims wherein the component layer (2) has a surface dielectric layer (1b).

8. A preparation method according to the preceding claim, wherein the preparation step of the component layer (2) comprises: - a substep of supplying a starting substrate (1) comprising a temporary substrate (1a), a layer - a buried dielectric layer (1b) disposed on and in contact with the temporary substrate (la) and a surface layer (le) disposed on and in contact with the buried dielectric layer (1b); - a substep of forming the plurality of primary waveguides (2a) in the surface layer (le), the primary waveguides (2a) of the plurality of primary waveguides being disposed on and in contact with the buried dielectric layer (1b), - a substep of depositing a covering material (2e) on the surface layer (le) to bury the primary waveguides (2a) of the plurality of primary waveguides in the component layer (2); - a substep of assembling the component layer (2) to the support substrate (le) and removing the temporary substrate (la), the buried dielectric layer becoming the surface dielectric layer (1b) of the component layer (2).

9. A preparation method according to one of the two preceding claims wherein the transfer step includes bringing the exposed face of the vignette (V) into contact with the surface dielectric layer (1e) of the component layer (2).

10. A preparation method according to any one of claims 7 and 8 wherein the preparation step of the component layer (2) comprises the local removal of the surface dielectric layer (1) at the center parts (Zc) of the primary waveguides (2a) of the plurality of primary waveguides in order to expose these center parts (Zc).

11. A preparation method according to the preceding claim in which the transfer step includes bringing the exposed face of the vignette (V) into direct contact with the central parts (Zc) of the primary waveguides (2a) of the plurality of primary waveguides.

12. A preparation method according to claim 11, wherein the preparation step of the component layer (2) comprises the formation of gapping layers (If) on and in contact with the central portions (Zc) of the primary waveguides (2a) of the plurality of waveguides, and wherein the transfer step comprises the contacting of the vignette (V) with the dielectric spacing layers (If).

13. A preparation method according to any one of the preceding claims, wherein the donor substrate (SD) preparation step comprises the formation, on the doped n (4n) layer of the surface stack, of an interlayer made of an undoped semiconductor material or a dielectric layer.

14. A preparation method according to any one of the preceding claims wherein the base substrate is InP, the sacrificial layer is InAlAs, the p-doped layer and the n-doped layer are InP and the active layer comprises quantum wells.

15. A preparation method according to any one of claims 1 to 13 wherein the base substrate is made of AsGa, the sacrificial layer of AlGaAs, the p-doped layer and the n-doped layer are made of AsGa, and the active layer comprises quantum dots.

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