Method for manufacturing structure comprising layer acting as diffusion barrier for atomic species

Abstract

The invention relates to a method for manufacturing a structure (1) comprising a thin layer (4) bonded by means of a dielectric layer (3) to a support (2) comprising a charge trapping layer (2b) arranged on a surface of a base substrate (2a). The method includes applying a surface treatment to the exposed surface of the main face of the support and / or to the exposed surface of the main face of the donor substrate so as to form a layer thereon that acts as a diffusion barrier for certain atomic species. The surface treatment includes exposing the exposed surface to a plasma comprising oxygen, and then exposing the exposed surface to a plasma comprising nitrogen.

Description

Technical Field

[0001] The invention relates to a method for producing a structure comprising a thin layer transferred to a support provided with a charge-trapping layer. The invention is particularly useful in the fields of microelectronics, microsystems, photonics, etc. Background Art

[0002] Document WO2021008742 states that it is often advantageous to provide a charge trapping layer (more briefly referred to as "trapping layer" in the rest of this description) in a support of a structure formed by a thin layer transferred to the support via a dielectric layer. The manufacture of structures of this type is disclosed, for example, in documents FR2860341, FR2933233, FR2953640, US2015115480, US7268060 and US6544656. In particular, it can be used to shape electronic or electroacoustic components in the field of radio frequency (RF) signals.

[0003] The thin films, which are usually single crystals, can be semiconducting (eg, silicon) or insulating (eg, piezoelectric materials such as lithium tantalate or lithium niobate).

[0004] The above-mentioned document also discloses the fact that this type of structure is particularly sensitive to hydrogen, since this atomic species can diffuse and condense in the trapped layer, which tends to passivate the electrical defects comprised by this layer and thus degrade the RF performance of the structure. As described in the publication "White paper - RF SOI Characterisation" published by SOITEC in January 2015, the RF performance of the substrate can be characterized by second harmonic distortion measurements.

[0005] The Applicant has also observed that when the film contains lithium, this atomic species may also diffuse into the structure during its manufacturing steps, condense in the trapping layer and dope it. Like hydrogen, the presence of lithium in the trapping layer tends to degrade the RF performance of the structure.

[0006] In order to prevent RF performance degradation caused by the diffusion of atomic species (especially hydrogen) in a structure with a trapping layer, document WO2021008742 proposes integrating a diffusion barrier into the dielectric layer.

[0007] Purpose of the Invention

[0008] It is an object of the present invention to improve this prior art by proposing a particularly simple and effective method for incorporating diffusion barriers for certain atomic species, in particular hydrogen and / or lithium, in structures comprising charge-trapping layers. Summary of the invention

[0009] To achieve this object, the invention proposes a method for producing a structure comprising a thin layer transferred to a support by means of a dielectric layer, the support comprising a charge trapping layer superficially arranged on a base substrate, the method comprising the following steps:

[0010] - forming a dielectric layer on the exposed surface of the so-called "main" face of the support and / or on the exposed surface of the so-called "main" face of the donor substrate;

[0011] - applying a surface treatment to the exposed surface of the main face of the support and / or to the exposed surface of the main face of the donor substrate in order to form thereon a layer acting as a diffusion barrier for certain atomic species;

[0012] - assembling the support and the donor substrate by their respective main faces so as to form an intermediate structure;

[0013] At least a portion of the donor substrate is removed from the intermediate structure to form a thin layer.

[0014] A notable feature of the method is that the surface treatment applied to at least one of the exposed surfaces comprises:

[0015] - exposing the exposed surface to a plasma comprising oxygen to form a damaged thickness below the major surface, and then

[0016] - Exposing the exposed surface to a plasma comprising nitrogen to nitridate the damaged thickness.

[0017] Such surface treatments simply form a layer that acts as a diffusion barrier for certain atomic species, which is particularly effective for the diffusion of hydrogen and / or lithium. This therefore avoids providing a structure that degrades RF performance.

[0018] Other advantageous non-limiting features according to the invention (alone or in any technically feasible combination):

[0019] - the donor substrate comprises a single crystalline piezoelectric material;

[0020] - the donor substrate is a single crystal silicon substrate;

[0021] - The base substrate is a single crystal silicon substrate;

[0022] - the dielectric layer comprises silicon oxide;

[0023] - The trapping layer is made of polysilicon;

[0024] - the formation of the dielectric layer includes oxidation of the trapping layer;

[0025] - forming a dielectric layer before applying the surface treatment to the exposed surface of the main face of the support;

[0026] - a dielectric layer after applying a surface treatment to the exposed surface of the main face of the support;

[0027] - the silicon oxide dielectric layer is doped with nitrogen, preferably with a nitrogen / oxygen ratio of less than 0.5;

[0028] - forming the dielectric layer comprises forming at least a portion of the dielectric layer on a donor substrate;

[0029] - the application of the surface treatment comprises applying it to the exposed surface of the main face of the donor substrate;

[0030] - forming at least a portion of a dielectric layer on the donor substrate before applying the surface treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings, in which:

[0032] [ Figure 1 ] Figure 1 shows a structure according to the present invention;

[0033] [ Figure 2 ] Figure 2 A sequence of a method for manufacturing a structure according to the invention is shown;

[0034] [ Figure 3 ] Figure 3 The sub-steps involved in the surface treatment for forming the barrier layer in the method for producing the structure according to the invention are shown. DETAILED DESCRIPTION

[0035] In summary, and with reference to Figure 1 , the present description relates to a method for manufacturing a structure 1 comprising, in sequence, a thin layer of nanocrystals 4, a dielectric layer 3 and a support 2. The support 2 itself comprises a base substrate 2a provided with a charge trapping layer 2b. Preferably, the dielectric layer 3 is in contact with the trapping layer 2b and the thin layer 4. As explained in the introduction to the present application, such a structure 1 is particularly suitable for housing radio frequency (RF) components on or in the thin film 4.

[0036] In order to prevent certain atomic species from diffusing into the trapping layer 2b, the structure 1 comprises a barrier layer 5 arranged at Figure 1 In the dielectric layer 3 on the structure 1 shown. As will be explained in the rest of the disclosure, in addition to or instead of the barrier layer being arranged in the dielectric layer, the barrier layer can also be superficially arranged in or on the support 2 itself, or even on or in the thin layer 4 (on one side of the dielectric layer 3). The barrier layer has a thickness of about 5 nm, typically between 2 nm and 10 nm, and is nitrogen-rich.

[0037] The atomic species that is susceptible to diffusion towards the trapping layer 2b may in particular come from the thin layer 4. This may be lithium, for example, when the thin layer 4 is made of lithium tantalate or lithium niobate (or more generally any lithium-based material). By providing a barrier layer 5 capable of blocking the diffusion of lithium between the thin layer 4 and the trapping layer 2b, a degradation of the RF performance of the structure 1 is avoided.

[0038] Atomic species may also come from the dielectric layer 3. This is particularly the case when this layer is produced at least in part by deposition techniques involving moderate thermal treatments below 1000° C. These treatments do not allow certain species (such as hydrogen species) to diffuse out of the deposited layers, and these species may therefore diffuse towards the trapping layer 2 b during other steps in the manufacture of the structure 1. The presence of the barrier 5 again prevents the diffusion of these species towards the trapping layer 2 b and avoids RF performance degradation of the structure 1.

[0039] Typically, the structure 1 may be in the form of a circular wafer, which may be 100 mm, 150 mm, 200 mm, 300 mm or even 450 mm in diameter.

[0040] The base substrate 2a of the support 2 on which the capture layer 2b is located typically has a thickness of several hundred micrometers. Preferably, the base substrate 2a has a high resistivity of greater than 1000 ohm-cm, even more preferably greater than 2000 ohm-cm. The density of charges, holes or electrons that may move in the base substrate is thus limited. However, the present invention is not limited to base substrates 2a having such resistivities, and the present invention also provides RF performance advantages when the base substrate has a more compliant resistivity of the order of several hundred ohm-cm, for example less than 1000 ohm.cm, or less than 500 ohm.cm, or even less than 10 ohm.cm.

[0041] For reasons of availability and cost, the base substrate 2a preferably consists of single crystal silicon. For example, it can be a CZ silicon substrate with a low interstitial oxygen content between 6 ppm and 10 ppm, or in particular a FZ silicon substrate with a naturally very low interstitial oxygen content. It can also be a CZ silicon substrate with a large amount of interstitial oxygen (indicated by the expression "high Oi") greater than 26 ppm. The base substrate 2a can alternatively be formed of another material: for example, it can be sapphire, glass, quartz, silicon carbide, etc. In some cases, and in particular when the capture layer 2b is sufficiently thick, for example greater than 30 microns thick, the base substrate 2a can have a standard resistivity of less than 1 kohm.cm.

[0042] As documented in the literature forming the prior art, the trapping layer 2b can be very different in nature. Typically, it is a non-single crystalline layer with structural defects such as dislocations, grain boundaries, amorphous regions, interstices, inclusions, holes, etc. These structural defects form traps for charges that tend to circulate in the material, for example at incomplete or unresolved chemical bonds. This prevents conduction in the trapping layer, which therefore has a high resistivity.

[0043] Advantageously, and for simplicity of implementation, the trapping layer 2b is formed by a polysilicon layer. This layer can be formed by deposition on the base substrate 2a. In particular when it is formed on a resistive base substrate 2a, its thickness can be between 0.1 and 3 μm. However, other thicknesses below or above this range are fully conceivable, depending on the level of RF performance expected from the structure 1.

[0044] In order to preserve the polycrystalline quality of this layer during the thermal treatments that may be applied to the structure 1 , an amorphous layer, for example consisting of silicon dioxide, may advantageously be provided on the base substrate 2 a before depositing the trapping layer 2 b .

[0045] Alternatively, the trapping layer 2b can be formed by implanting a relatively heavy substance (such as argon) into the surface thickness of the base substrate 2a so as to form structural defects constituting electric traps therein. The layer 2b can also be formed by making the surface thickness of the base substrate 2a porous or by any other method capable of forming structural defects in the surface thickness of the base substrate 2a, wherein these structural defects are capable of trapping charges.

[0046] The dielectric layer 3 is preferably made of silicon oxide. Other chemical elements may also be doped therein in trace amounts or at higher concentrations. Specifically, the layer may be doped with nitrogen (to form a SiON layer), for example with a nitrogen / oxygen ratio of less than 0.5. In order to characterize the proportion of nitrogen in the layer, the measurement of its refractive index is used, which varies between 1.44 for SiO2 and 2.35 for Si3N4 (at a wavelength of 620 nm).

[0047] The thin layer 4 of the structure 1 may be of any suitable type. When the structure 1 is intended to receive an integrated semiconductor component, the thin layer 4 may therefore consist of single-crystal silicon, or of any other single-crystal semiconductor material, such as germanium, silicon germanium, silicon carbide. When the structure 1 is intended to receive a surface acoustic wave filter, the thin layer 4 may consist of a single-crystal piezoelectric and / or ferroelectric material, such as lithium tantalate or lithium niobate. The thin layer 4 may also comprise finished or semi-finished integrated components, which are formed on a donor substrate and transferred to the support 2 during the step of manufacturing the structure 1. Typically, the thickness of the thin layer may be between 10 nanometers and 10 micrometers.

[0048] As described in the prior art documents introduced in the introduction, the structure 1 can be manufactured in a variety of ways. Very generally, and with reference to Figure 2 , the structure 1 can be manufactured by a manufacturing method comprising the following steps:

[0049] - providing a support and a donor substrate;

[0050] - forming a dielectric layer on the exposed surface of the so-called "main" face of the support and / or on the exposed surface of the so-called "main" face of the donor substrate;

[0051] - applying a surface treatment to the exposed surface of the main face of the support and / or to the exposed surface of the main face of the donor substrate in order to form a barrier layer thereon;

[0052] - assembling the support and the donor substrate via their respective main faces to form an intermediate structure;

[0053] - Removing a portion of the donor substrate from the intermediate structure to form a thin layer 4 resting on a support by means of a dielectric layer.

[0054] The dielectric layer can be formed by deposition, for example using LPCVD (low pressure chemical vapor deposition) or PECVD (plasma enhanced chemical vapor deposition) techniques. HDP CVD (high density plasma chemical vapor deposition) techniques can also be used.

[0055] The silicon oxide dielectric layer 3 can be obtained by oxidation of the donor substrate (when the donor substrate is made of silicon) or by oxidation of the capture layer 2 (when this layer is also made of silicon). In this second case, the oxidation is followed by a step of polishing the oxidized surface to facilitate the subsequent assembly of the donor substrate and the support substrate 2.

[0056] The assembly step is advantageously carried out by molecular adhesion. As is well known, during the molecular adhesion method, the exposed surfaces of the support and donor substrate, which are completely clean, flat and smooth, are brought into close contact with each other to promote the formation of molecular bonds, for example of the van der Waals or covalent type. The two bodies are then assembled without the use of an adhesive. These bonds can be strengthened by applying a heat treatment to the intermediate structure.

[0057] The step of eliminating part of the donor substrate may be performed by chemical mechanical thinning of the substrate. Preferably, by applying Smart Cut TM The structure 1 is manufactured using a technique according to which the layer intended to form the thin layer 4 is defined by means of an embrittlement plane formed by implanting a light substance (generally hydrogen and / or helium) into a donor substrate. After the assembly step, the layer is removed from the donor substrate by fracture at the embrittlement plane and is thus transferred to the support 2.

[0058] The steps involved in the surface treatment during the manufacture of the structure 1 aimed at facilitating the formation of the barrier layer 5 in the structure will now be described in detail.

[0059] As we have seen, the surface treatment is applied to the exposed surface of a major face of the support and / or to the exposed surface of a major face of the donor substrate.

[0060] When a dielectric layer is previously formed on the main face of one of the two elements by deposition or by oxidation, the exposed surface to which the surface treatment is applied thus corresponds to the exposed surface of the dielectric layer. However, in very general terms, the surface treatment may be applied to one or both of the donor substrate and the support, whether or not they have a dielectric surface layer.

[0061] The exposed surface of the support and / or donor substrate may also be subjected to a surface treatment before the dielectric layer is deposited on the surface.

[0062] For the avoidance of doubt, it is therefore provided that the surface treatment leading to the formation of the barrier layer 5 may be applied to the donor substrate only, to the support only, or to both substrates. The formation of the dielectric layer may be performed before or after the application of the surface treatment.

[0063] Regardless of whether the surface treatment is performed on one or both of these substrates, it consists of 2 consecutive sub-steps, such as Figure 3 As shown. In a first sub-step, the exposed surface is exposed to a plasma comprising oxygen. This first sub-step results in the formation of a porous (or more generally) damaged layer of very small thickness (about 5 nm, typically between 2 nm and 10 nm) on the surface, or buried at a very shallow depth from the surface. The plasma to which the substrate surface is exposed in this first step can be an oxygen plasma, or an oxygen plasma in combination with sulfur hexafluoride (SF6) or with a gas having the general formula CxHyFz.

[0064] In a second sub-step following the first sub-step, the exposed surface of the treated substrate is exposed to a plasma comprising nitrogen. In the second sub-step, a large amount of nitrogen is introduced into the damaged layer formed in the first sub-step. The plasma to which the substrate surface is exposed in the second sub-step may consist of nitrogen.

[0065] These two steps do not have to be performed in situ, and the donor substrate or support may be exposed to the atmosphere between the first and second sub-steps.

[0066] The plasma exposure substep may include placing the associated substrate in a chamber of a plasma activation device, such as on a planar support disposed in the chamber, so that the main face is exposed to a plasma prepared by a source. An oxygen-based flow (first substep) or a nitrogen-based flow (second substep) is introduced into the plasma source of the device at a controlled flow rate, and a plasma of the gas is generated, for example, via a variable magnetic field or electric field. The plasma material is projected onto the exposed surface. These operations may be performed at atmospheric or subatmospheric pressures.

[0067] This series of sub-steps makes it very easy to create a relatively thin barrier of about 5 nanometers that is doped with a large amount of nitrogen, making it particularly effective. Specifically, the barrier is more effective at blocking the diffusion of certain atomic species than a barrier formed by exposure to a single nitrogen plasma alone.

[0068] Of course, the invention is not limited to the embodiments described and variant embodiments may be added thereto without departing from the scope of the invention as defined by the claims.

Claims

1. A method for producing a structure (1) comprising a thin layer (4) transferred via a dielectric layer (3) onto a support (2), the support comprising a charge trapping layer (2b) superficially arranged on a base substrate (2a), the method comprising the following steps: - forming a dielectric layer (3) on the exposed surface of the so-called "main" face of the support and / or on the exposed surface of the so-called "main" face of the donor substrate; - applying a surface treatment to the exposed surface of the main face of the support and / or to the exposed surface of the main face of the donor substrate in order to form thereon a layer acting as a diffusion barrier for certain atomic species; - assembling said support and said donor substrate by their respective main faces so as to form an intermediate structure; - removing at least a portion of the donor substrate from the intermediate structure to form the thin layer; The method is characterized in that the surface treatment applied to at least one of the exposed surfaces comprises: - exposing the exposed surface to a plasma comprising oxygen to form a damaged thickness below the major surface, and then - exposing the exposed surface to a plasma comprising nitrogen to nitridate the damaged thickness.

2. The manufacturing method according to the preceding claim, wherein the donor substrate comprises a single-crystalline piezoelectric material. The manufacturing method according to claim 1 , wherein the donor substrate is a single crystal silicon substrate.

4. The manufacturing method according to any of the preceding claims, wherein the base substrate (2a) is a single-crystal silicon substrate.

5. The manufacturing method according to any of the preceding claims, wherein the dielectric layer (3) comprises silicon oxide.

6. The manufacturing method according to any of the preceding claims, wherein the trapping layer (2b) is polysilicon.

7. Manufacturing method according to the preceding claim, wherein the formation of the dielectric layer (3) comprises oxidation of the trapping layer (2b).

8. Manufacturing method according to the preceding claim, wherein the dielectric layer (3) is formed before applying the surface treatment to the exposed surface of the main face of the support (2).

9. The manufacturing method according to claim 7, wherein the dielectric layer (3) is formed after applying the surface treatment to the exposed surface of the main face of the support (2).

10. The manufacturing method of claim 5, wherein the silicon oxide dielectric layer is doped with nitrogen, preferably with a nitrogen / oxygen ratio less than 0.

5.

11. The manufacturing method according to any of the preceding claims, wherein the forming of the dielectric layer (3) comprises forming at least a part of the dielectric layer on the donor substrate.

12. Manufacturing method according to the preceding claim, wherein the application of the surface treatment comprises applying it to the exposed surface of the main face of the donor substrate.

13. Manufacturing method according to the preceding claim, wherein at least a portion of the dielectric layer (3) is formed on the donor substrate before applying the surface treatment.

Images