Method for manufacturing a paving donor substrate, involving an additive manufacturing technique

Abstract

The invention relates to a method for manufacturing a paving donor substrate comprising the following steps: a) the provision of an initial structure comprising a support substrate having a front face and a back face, and a plurality of paving stones in a first, monocrystalline material, arranged on the front face and spaced apart from each other, b) the formation of a complementary layer by an additive manufacturing technique, the complementary layer: - being arranged between the paving stones, in contact with the front face of the support substrate, - being composed of a material, called the second material, having a coefficient of thermal expansion matched to that of the first material, c) the application of a mechanical and / or mechano-chemical surface treatment to the complementary layer and to the paving stones, to obtain the paving donor substrate having a front face which has a flat and continuous surface, at the level of which the plurality of paving stones and the complementary layer are flush.No figure with the abbreviation.

Description

Title of the invention: Method for manufacturing a paving donor substrate, involving an additive manufacturing technique. FIELD OF THE INVENTION

[0001] The present invention relates to the field of microelectronics and semiconductors. In particular, the invention concerns a method for manufacturing a donor substrate comprising a useful layer in the form of tiles, a surface layer of said tiles being intended to be transferred onto a receiving substrate. The method according to the invention involves an additive manufacturing technique. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] In the fields of microelectronics, optics, or optoelectronics, it can be advantageous to transfer thin films (less than 1.5 µm) in the form of disjointed tiles (for example, in III-V material) onto a large substrate (for example, silicon). Specific components (on the tiled thin films) can thus be fabricated and potentially co-integrated with silicon components, while taking advantage of the equipment and substrate sizes available in the conventional microelectronics industry.

[0003] The Smart Cut™ process, a well-known thin-film transfer technique, can notably produce a composite structure comprising thin layers paved onto a receiving substrate, starting from a donor substrate that includes a useful layer in the form of pavers. As a reminder, the Smart Cut process is based on the formation of a fragile plane embedded in the paved useful layer of the donor substrate by implanting lightweight materials: this embedded fragile plane, together with the free surface of the paved useful layer, defines the surface layer to be transferred. This process then involves an assembly between the paved useful layer and the receiving substrate. Finally, a separation occurs along the embedded fragile plane to transfer the surface layer to the receiving substrate; the remaining donor substrate can be recovered, conditioned, and used to transfer a new surface layer.

[0004] The donor substrate, in such a case, therefore comprises a support substrate on which are arranged disjointed blocks, distributed on the surface of said support substrate according to the needs of the intended application for the final composite structure.

[0005] The fabrication of such a donor substrate (also called a pseudo-donor) is usually based on assembling the blocks of the useful layer onto the supporting substrate by direct bonding or adhesive. Each block typically has a thickness of between a few tens of micrometers and a few hundred micrometers, and lateral dimensions giving it a surface area of ​​between 1mm2 and 400mm2. Given their thickness, these pavers can be handled using "pick and place" techniques and assembled on the supporting substrate.

[0006] Since the pavers of the donor substrate may have uneven thicknesses and excellent surface flatness is required to obtain a high-quality assembly and subsequent transfer of the thin-layer paved surface, the surface preparation step of the useful layer is particularly critical. Given the discontinuity of this layer, mechanical or mechano-chemical thinning steps tend to alter, degrade, or damage the edges of the pavers, inevitably degrading the quality of the subsequent assembly. SUBJECT OF THE INVENTION

[0007] The present invention addresses this problem and proposes a method for manufacturing a donor substrate comprising a paved useful layer particularly suited for assembly onto a receiving substrate for the purpose of transferring a thin, paved surface layer. The method according to the invention implements an additive manufacturing step to form a layer complementary to the paved useful layer on the donor substrate, and to ensure material continuity between the pavers, thus enabling high-quality surface preparation. BRIEF DESCRIPTION OF THE INVENTION

[0008] The present invention relates to a method for manufacturing a paved donor substrate comprising the following steps:

[0009] a) the provision of an initial structure comprising a supporting substrate having a front face and a rear face, and a plurality of tiles made of a first, monocrystalline material, arranged on the front face and spaced apart from each other,

[0010] b) the formation of a complementary layer by an additive manufacturing technique, the complementary layer:

[0011] - being arranged between the paving stones, in contact with the front face of the supporting substrate,

[0012] - being composed of a material, called the second material, having a coefficient of thermal expansion matched to that of the first material,

[0013] c) the application of a mechanical and / or mechano-chemical surface treatment to the complementary layer and to the paving stones, to obtain the paving stone donor substrate having a front face with a flat and continuous surface, at the level of which the plurality of paving stones and the complementary layer are flush.

[0014] According to advantageous features of the invention, taken alone or in any feasible combination: • in step b), the additional layer is also formed on all or part of the paving stones; • the additional layer has a thickness greater than or equal to the average thickness of the paving stones; • The additive manufacturing technique implemented in step b) is based on : - the at least partial melting of a powder of the second material, in a nozzle heated by a laser beam or an electron beam, - the movement of the nozzle to deposit the fused powder on the substrate support, between the paving stones, and optionally on all or part of the paving stones, until the additional layer is formed; • Step b) is based on: - a sub-step of additive manufacturing of a stencil on a platform, the stencil having a surface identical to that of the supporting substrate and having openings located at the positions of the blocks of the initial structure, - a sub-step of assembly between the stencil and the initial structure, the stencil forming the complementary layer; • the support substrate is made of silicon; • the first single-crystal material forming the paving stones is chosen from among semiconductor materials, piezoelectric materials and electrical insulating materials; • the first single-crystal material used to make paving stones is indium phosphide; • the paving stones of the initial structure are spaced at a distance of between 100 mm and 10 mm, or even 10 cm; • the second material is of the same nature as the first material; • the second material is composite and includes a binder, the proportion of binder being less than 30%.

[0015] The invention also relates to the use of a paving donor substrate from a manufacturing process mentioned above, to transfer a surface layer of each paving stone onto a receiving substrate.

[0016] Advantageously, this use implements a thin-film transfer technique involving the following steps: - the formation of a fragile, buried plane, roughly parallel to a front face of the paved donor substrate, within the paving stones and the complementary layer,

[0017] - the assembly of the front face of the paved donor substrate onto the receiving substrate,

[0018] - the separation along the fragile buried plane, to form a composite structure including the receiving substrate and at least one thin layer from each paving stone transferred onto said receiving substrate.

[0019] Preferably, after separation, a remnant of the paved donor substrate is conditioned and then reused for a new thin film transfer onto a new recipient substrate. Brief description of the drawings

[0020] Other features and advantages of the invention will become apparent from the detailed description that follows, with reference to the accompanying figures in which:

[0021] [Fig. la]

[0022] [Fig.lb] Figures 1a and 1b show a paving donor substrate obtained by a manufacturing process according to the present invention;

[0023] [Fig.2a]

[0024] [Fig. 2b] Figures 2a and 2b present an initial structure provided in step a) of a manufacturing process according to the invention;

[0025] [Fig.3a]

[0026] [Fig. 3b] Figures 3a and 3b show examples of donor substrate intermediate obtained at the end of step b) of a manufacturing process according to the invention;

[0027] [Fig.4] Fig.4 presents a first embodiment of step b) of a process in accordance with the invention;

[0028] [Fig.5a]

[0029] [Fig.5b]

[0030] [Fig.5c]

[0031] [Fig.5d] Figures 5a, 5b, 5c and 5d show sub-steps of a second embodiment of step b) of a manufacturing process according to the present invention;

[0032] [Fig.6a]

[0033] [Fig.6b]

[0034] [Fig.6c]

[0035] [Fig.6d] Figures 6a, 6b, 6c and 6d show step c) of a manufacturing process according to the invention;

[0036] [Fig.7a]

[0037] [Fig.7b]

[0038] [Fig.7c]

[0039] [Fig.7d] Figures 7a, 7b, 7c and 7d show steps of using a paving donor substrate from a manufacturing process according to the invention.

[0040] The figures are schematic representations which, for the sake of readability, are not to scale. In particular, the layer thicknesses along the z-axis are not to scale with respect to the lateral dimensions along the x and y axes.

[0041] The same references in the figures or in the description may be used for elements of the same nature. DETAILED DESCRIPTION OF THE INVENTION

[0042] The invention relates to a method for manufacturing a 100 paving donor substrate as illustrated in figures 1a and 1b.

[0043] The manufacturing process includes a first step a) of providing an initial structure 10 comprising a support substrate 1 and a plurality of blocks 2 (Figures 2a and 2b). The support substrate 1 has a front face 1a and a rear face 1b and is preferably in the form of a wafer with a diameter of 200 mm, 300 mm or more. Its thickness is typically between 100 µm and 900 µm. Advantageously, the support substrate 1 is made of silicon, or another semiconductor material available in the form of a large-diameter wafer.

[0044] The blocks 2 are formed from a first, monocrystalline material, arranged on the front face and spaced apart. Typically, the blocks 2 are spaced at a distance of between 100 µm and 10 mm, or even up to 10 cm. Each block can have a thickness greater than or equal to 100 µm, for example between 300 µm and 600 µm, and dimensions ranging from 1 mm² up to 20 x 20 mm².

[0045] The first material is advantageously chosen from:

[0046] - semiconductor materials (such as a III-V compound, in particular nitride indium (InN), gallium nitride (GaN), aluminium nitride (AIN), indium arsenide (InAs), gallium arsenide (GaAs), aluminium arsenide (AlAs), indium phosphide (InP), gallium phosphide (GaP) or aluminium phosphide (A1P), or such as a material IV or IV-IV, including germanium or silicon carbide (SiC)),

[0047] - piezoelectric materials (such as lithium tantalate (LiTaO3), niobate lithium (LiNbO3), potassium-sodium niobate (KxNabxNbO3 or KNN), varyum titanate (BaTiO3), quartz, lead zirconate titanate (PZT), a lead-magnesium niobate-lead titanate compound (PMN-PT), zinc oxide (ZnO), aluminum nitride (AIN) or aluminum-scandium nitride (AIScN), and

[0048] - electrically insulating materials (such as diamond, strontium titanate, the yttria zirconia or sapphire).

[0049] This initial structure 10 can be produced using any technique known to those skilled in the art. Generally, the paving stones 2 are made from an initial substrate consisting of the first material, which has been cut by sawing, laser cutting, or other means. The thickness variation (TTV), at the scale of the initial substrate, can be several micrometers. The paving stones 2 may therefore exhibit these same thickness variations among themselves.

[0050] The tiles 2 are then assembled onto the support substrate 1. Their placement on said support substrate 1 can be carried out using pick-and-place equipment, widely used for handling vignettes or chips. The assembly is preferably based on direct bonding by molecular adhesion, not requiring the addition of intermediate adhesive layers. Surface treatments (cleaning, plasma activation, etc.) prior to assembly are recommended to obtain a good quality bonding interface providing significant mechanical strength.

[0051] The manufacturing process then includes a step b) corresponding to the formation of a complementary layer 20, on the front face of the initial structure 10, by an additive manufacturing technique (Figures 3a, 3b). The complementary layer 20 is at least disposed between the blocks 2, in contact with the front face of the support substrate 1. It can also be formed on all or part of the blocks 2.

[0052] The complementary layer 20 is composed of a material, called the second material, having a coefficient of thermal expansion matched to that of the first material. By "matched," it is meant that the difference between the coefficient of thermal expansion of the second material and that of the first material is less than or equal to + / -10%.

[0053] At the end of step b), an intermediate donor substrate 100' is obtained.

[0054] Advantageously, the first material and the second material are of the same nature; for example, for a first material in monocrystalline InP, the second material may be in polycrystalline or amorphous InP.

[0055] Advantageously, the support substrate 1 can also be chosen so as to have a coefficient of expansion close to that of the paving stone material. For example, the support substrate 1 can also be formed by the same additive manufacturing technique and with the same material (second material) as the complementary layer 20.

[0056] According to one embodiment, the second material is a composite and comprises a material whose coefficient of thermal expansion is close to that of the first material, and a binder. The proportion of binder is less than 30%, less than 20%, or even less than 10%, so as to minimize the difference between the coefficient of thermal expansion of the second composite material and that of the first material.

[0057] Preferably, the additional layer 20 also has a thickness greater than or equal to an average thickness of the paving stones 2, in order to limit as much as possible the discontinuities of material between the paving stones 2 and the additional layer 20, during the following step c) of the process.

[0058] According to a first embodiment, the additive manufacturing technique implemented in step b) is based on the at least partial melting of a powder of the second material, in a nozzle B heated by a laser beam or an electron beam ( [Fig.4]). The movement of nozzle B allows the fused powder 20' to be deposited on the support substrate 1, between the pavers 2, and optionally on all or part of the pavers 2, until the additional layer 20 is formed. Several passes of nozzle B over the same area may be required to achieve the desired thickness of the additional layer 20.

[0059] A CLAD type technique (“Direct Laser Additive Construction” according to Anglo-Saxon terminology) can in particular be implemented.

[0060] By way of example, if the second material constituting the powder is InP, a local temperature, generated by the laser or electron beam, between 650°C and 800°C, allows the powder grains to melt at least on the surface and consequently agglomerate into a complementary layer 20 as they cool. The temperature experienced by the initial structure 10 is well below this temperature, typically less than or equal to 100°C: this prevents any degradation of the adjacent blocks 2, the first material of which is, for example, single-crystal InP.

[0061] According to another example, the second material is a composite comprising InP and a binder (a polymer compatible with the operating temperatures): a local temperature, generated by the laser or electron beam, typically between 100°C and 800°C, can melt the binder, which ensures the agglomeration of the powder into a complementary layer 20. Here again, the temperature experienced by the initial structure 10 remains low (typically below 100°C), thus preventing its degradation. It should be noted that the use of a binder, even if its proportion is limited to 30%, 20%, or even 10%, implies a shrinkage of the complementary layer 20, which must be taken into account when defining the initial deposited thickness of the complementary layer.

[0062] Regardless of the specific examples of this first embodiment, it is important to ensure that the additional layer 20 adheres well to the front face of the supporting substrate 1. The presence of a binder in the second material promotes this adhesion. Alternatively, an initial structure 10 may be chosen that includes a surface layer on the supporting substrate 1, the nature of which is favorable to the adhesion of the additional layer 20.

[0063] Furthermore, to promote adhesion between the complementary layer 20 and the support substrate 1, texturing the front face la may be advantageous; this could be, for example, a level of roughness of the front face la greater than Inm RMS (on a 20x20qm2 scan in atomic force microscopy).

[0064] According to a second embodiment, step b) comprises a first substep of additive manufacturing of a 20” stencil on a platform. A DMLS (“direct metal laser sintering”) type 3D printing technique can in particular be implemented.

[0065] The stencil 20" has a surface identical to that of the support substrate 1 and includes openings 3 located at the positions of the blocks 2 of the initial structure 10 (Figures 5a, 5b). Step b) then comprises a second sub-step of assembly between the stencil 20" and the initial structure 10 ([Fig. 5c]), the stencil 20" then forming the complementary layer 20 ([Fig. 5d]).

[0066] Good flatness of the 20" stencil is important for obtaining a high-quality assembly, particularly when molecular bonding is considered (typically, a deformation of less than 100 µm and a maximum flatness variation of a few micrometers are expected). Note that any known type of assembly can be performed, provided that the mechanical and thermal resistance of the bond is compatible with the subsequent steps in the process and the intended use of the 100 paving stone donor substrate.

[0067] The process finally includes a step c) corresponding to the application of a mechanical (for example grinding) and / or mechano-chemical (for example polishing) surface treatment to the complementary layer 20 and the blocks 2 (Figures 6a, 6b, 6c).

[0068] Whether the complementary layer 20 is thinner, substantially equal to, or thicker than the average thickness of the pavers 2, step c) aims to planarize the front face 100'a of the intermediate donor substrate 100', to obtain the paver donor substrate 100 whose front face 100a has a flat and continuous surface, at which the plurality of pavers 2 and the complementary layer 20 are flush ([Fig. 6d]). By flat and continuous, we mean a surface free of relief (typically, less than 5 nm, less than 1 m, or even less than 0.5 nm of relief, particularly at the junctions between the pavers 2 and the complementary layer 20). The complementary layer 20 may optionally have a thickness substantially less than that of the pavers 2 after planarization, so as not to hinder the complete transfer of the surface layer of pavers originating from the pavers 2.

[0069] The material removal carried out in step c) can vary according to the configuration of the intermediate donor substrate 100', and according to the thickness of the complementary layer 20. Typically the removal is between Ipm and 200qm, preferably between 20qm and 60qm.

[0070] As mentioned previously, the paving stones 2 may exhibit variations in thickness between them, related to the TTV of the initial substrate from which they originate. Step c) rectifies these thickness variations and produces a flat surface compatible with thin-film transfer. Furthermore, the presence of the complementary layer 20 facilitates planarization because it ensures the continuity of the treated surface 100'a and consequently prevents corner rounding of the paving stone edges during the mechanical-chemical treatments.

[0071] Finally, the complementary layer 20 being preferentially composed mainly of a material of the same nature as the first material of the paving stones 2, surface treatments are facilitated and do not encounter problems of dual-material polishing, in particular with different abrasion rates.

[0072] According to the present invention, the donor substrate 100 can be used to transfer a surface layer of each paving stone 2 onto a receiving substrate 50. Preferably, a thin-film transfer technique involving the following steps is implemented. First, a buried brittle plane 4, substantially parallel to a front face 100a of the donor substrate 100, is formed in the paving stones 2 and in the complementary layer 20 ([Fig. 7a]). For this purpose, the implantation of light species such as hydrogen, helium, or a combination of these two species can be implemented. The next step consists of assembling the front face 100a of the donor substrate 100 onto the receiving substrate 50 ([Fig. 7b]). Preferably, this assembly is based on molecular adhesion, not requiring the presence of adhesive layers.As is well known, surface cleaning and other activation techniques can be implemented to improve the quality and mechanical strength of the bonding interface 5. Finally, a separation occurs along the buried weak plane 4, forming a composite structure comprising the receiving substrate 50 and at least one thin layer 2i from each paver 2, transferred onto said receiving substrate 50 ([Fig. 7c]). Depending on the nature of the second material of the complementary layer 20, a complementary thin layer 20i, from the complementary layer 20, can also be transferred onto the receiving substrate 50. In this case, a subsequent step consists of locally etching this complementary thin layer 20i, so as to retain only the pavered thin layer 2i on the receiving substrate 50 ([Fig. 7d]).

[0073] Polishing and cleaning sequences can be applied to restore a good surface condition to the paved thin layer 2i, before or after the removal of the complementary thin layer 20i (when present).

[0074] After the separation step, the remaining lOOi of the donor substrate 100 can be conditioned (mechanical rectification and / or mechano-chemical polishing and cleaning) and then reused for a new thin film transfer onto a new receiving substrate.

[0075] 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.

Claims

Demands

1. A method for manufacturing a paving donor substrate (100) comprising the following steps: a) providing an initial structure (10) comprising a support substrate (1) having a front face (la) and a back face (1b), and a plurality of paving stones (2) of a first, single-crystal material, arranged on the front face (la) and spaced apart from each other; b) forming a complementary layer (20) by an additive manufacturing technique, the complementary layer (20): - being disposed between the paving stones (2), in contact with the front face (la) of the support substrate (1), - being composed of a material, called the second material, having a coefficient of thermal expansion matched to that of the first material; c) applying a mechanical and / or mechano-chemical surface treatment to the complementary layer (20) and to the paving stones (2), to obtain the paving donor substrate (100) having a front face (100a) with a flat surface and continue,at which the plurality of paving stones (2) and the complementary layer (20) are exposed.

2. A manufacturing method according to claim 1, wherein, in step b), the additional layer (20) is also formed on all or part of the paving stones (2).

3. A manufacturing method according to any one of the preceding claims, wherein the additional layer (20) has a thickness greater than or equal to an average thickness of the paving stones (2).

4. A manufacturing method according to any one of the preceding claims, wherein the additive manufacturing technique implemented in step b) is based on: - at least partial melting of a powder of the second material, in a nozzle (B) heated by a laser beam or an electron beam, - moving the nozzle (B) to deposit the fused powder (20') on the support substrate, between the blocks (2), and optionally on all or part of the blocks (2), until the complementary layer (20) is formed.

5. A manufacturing method according to any one of claims 1 to 3, wherein step b) is based on: - a substep of additive manufacturing of a stencil (20”) on a platform, the stencil (20”) having a surface identical to that of the support substrate (1) and having openings located at the locations of the blocks (2) of the initial structure (10), - a substep of assembly between the stencil (20”) and the initial structure (10), the stencil (20”) forming the complementary layer (20).

6. A manufacturing method according to any one of the preceding claims, wherein the support substrate (1) is made of silicon.

7. A manufacturing method according to any one of the preceding claims, wherein the first single-crystal material forming the paving stones (2) is selected from semiconducting materials, piezoelectric materials and electrically insulating materials.

8. A manufacturing process according to any one of the preceding claims, wherein the first single-crystal material forming the paving stones (2) is indium phosphide (InP).

9. A manufacturing method according to any one of the preceding claims, wherein the blocks (2) of the initial structure (10) are spaced at a distance of between 100 mm and 10 mm, or even 10 cm.

10. A manufacturing method according to any one of the preceding claims, wherein the second material is of the same nature as the first material.

11. A manufacturing method according to any one of the preceding claims, wherein the second material is composite and comprises a binder, the proportion of binder being less than 30%.

12. Use of a paving donor substrate (100) from a manufacturing process according to claims 1 to 11, to transfer a surface layer of each paving stone (2) onto a receiving substrate (50).

13. Use of a paved donor substrate (100) according to the preceding claim, implementing a thin-film transfer technique involving the following steps: - the formation of a buried brittle plane (4), parallel to a front face (100a) of the paved donor substrate (100), in the pavers (2) and in the complementary layer (20), - the assembly of the front face (100a) of the paved donor substrate (100) onto the receiving substrate (50), - the separation along the buried brittle plane (4), to form a composite structure comprising the receiving substrate (50) and at least

14. a thin layer (2i) from each paving stone (2) transferred onto said receiving substrate (50). Use of a paved donor substrate (100) according to the preceding claim, wherein, after separation, a remainder (lOOi) of the paved donor substrate (100) is conditioned and then reused for a new thin film transfer onto a new receiving substrate.

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